U.S. patent application number 12/376715 was filed with the patent office on 2010-07-29 for iron-based corrosion resistant wear resistant alloy and deposit welding material for obtaining the alloy.
This patent application is currently assigned to ING Shoji Co., Ltd.. Invention is credited to Hajime Kawatsu, Akira Shinnya.
Application Number | 20100189588 12/376715 |
Document ID | / |
Family ID | 39032674 |
Filed Date | 2010-07-29 |
United States Patent
Application |
20100189588 |
Kind Code |
A1 |
Kawatsu; Hajime ; et
al. |
July 29, 2010 |
IRON-BASED CORROSION RESISTANT WEAR RESISTANT ALLOY AND DEPOSIT
WELDING MATERIAL FOR OBTAINING THE ALLOY
Abstract
To provide a high-performance, inexpensive low C-high Si-high
Cr--B--Nb type iron-based corrosion-resistant and wear-resistant
alloy that is extremely superior in corrosion resistance and wear
resistance to 304 stainless steel, high-chromium cast iron and high
carbon-high chromium cast-iron-type materials, has a high
corrosion-resistant property that would never be obtained from a
high carbon-high chromium carbide precipitation-type iron-based
wear-resistant alloy and at the same time, a wear-resistant
property that is superior to these metals, and further hardly
causes brittle peeling that is inherent to high Si--containing
steel. This alloy contains, all percentages by weight, C: 0.5 to
2.5% by weight, Si: 2.5 to 4.5%, Mn: 0 to 10% or less, Cr: 15% to
31%, Ni: 0 to 16%, Cu: 7% or less, Mo: 10% or less, B: 0.5% to
3.5%, and 0.ltoreq.Nb+V.ltoreq.8%, and in this structure, within a
range of 15% Cr.ltoreq.Cr<27%,
(Si.times.B).ltoreq.2014/Cr.sup.2+0.083Cr+1.05 is satisfied, within
a range of 27%.ltoreq.Cr.ltoreq.31%, 1.25%.ltoreq.(Si.times.B) 6.0%
is satisfied, within a range of 15%.ltoreq.Cr<20%, (Si.times.B)
570/Cr.sup.2-0.066Cr+1.145 is satisfied, and within a range of
20%.ltoreq.Cr.ltoreq.31%, (Si.times.B).gtoreq.1.25 is
satisfied.
Inventors: |
Kawatsu; Hajime; (Osaka,
JP) ; Shinnya; Akira; (Osaka, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, L.L.P.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
ING Shoji Co., Ltd.
Osaka-shi
JP
|
Family ID: |
39032674 |
Appl. No.: |
12/376715 |
Filed: |
August 9, 2006 |
PCT Filed: |
August 9, 2006 |
PCT NO: |
PCT/JP2006/315732 |
371 Date: |
April 14, 2009 |
Current U.S.
Class: |
420/12 ; 420/10;
420/11; 420/34; 420/582; 420/60; 420/61; 420/62; 420/64;
420/70 |
Current CPC
Class: |
C22C 38/58 20130101;
C22C 38/42 20130101; C22C 38/48 20130101; C22C 38/44 20130101; C22C
38/54 20130101; C22C 38/56 20130101; C22C 37/08 20130101; C22C
37/10 20130101; B23K 35/3053 20130101; C22C 38/24 20130101; B23K
35/0266 20130101; C22C 38/34 20130101 |
Class at
Publication: |
420/12 ; 420/64;
420/70; 420/61; 420/60; 420/582; 420/10; 420/34; 420/11;
420/62 |
International
Class: |
C22C 38/36 20060101
C22C038/36; C22C 38/18 20060101 C22C038/18; C22C 38/00 20060101
C22C038/00; C22C 38/22 20060101 C22C038/22; C22C 30/00 20060101
C22C030/00; C22C 38/16 20060101 C22C038/16; C22C 30/02 20060101
C22C030/02; C22C 37/00 20060101 C22C037/00 |
Claims
1-3. (canceled)
4. An alloy comprising: all percentages by weight, C: 0.5 to 2.5%,
Si: 2.5 to 4.5%, Mn: 10% or less, Cr: 15% to 31%, Cu: 7% or less,
Mo: 10% or less, B: 0.5% to 3.5%, and 0.ltoreq.Nb+V.ltoreq.8%,
wherein (Si.times.B).ltoreq.2014/Cr.sup.2+0.083Cr+1.05 when
15%.ltoreq.Cr<27%, 1.25%.ltoreq.(Si.times.B).ltoreq.6.0% when
27%.ltoreq.Cr.ltoreq.31%,
(Si.times.B).gtoreq.570/Cr.sup.2-0.066Cr+1.145 when 15% Cr<20%,
and (Si.times.B).gtoreq.1.25 when 20%.ltoreq.Cr.ltoreq.31%.
5. The alloy according to claim 4, further comprising: one kind or
two or more kinds of Ni: 16% or less, Ti: 1.0% or less, Al: 3% or
less, rare earth metals: 0.5% or less in total, and N: 0.2% or
less.
6. The alloy according to claim 4, wherein a wear-resistant
property and a corrosion-resistant property are the same as, or
superior to cobalt-based alloys, stellites No. 1 and No. 6.
7. The alloy according to claim 4, in the form of clad welding
metal or cast steel.
8. The alloy according to claim 5, wherein a wear-resistant
property and a corrosion-resistant property are the same as, or
superior to cobalt-based alloys, stellites No. 1 and No. 6.
9. The alloy according to claim 5, in the form of clad welding
metal or cast steel.
Description
TECHNICAL FIELD
[0001] The present invention relates to a low carbon-high
silicon-boron-niobium-high chromium cast steel-type iron-based
alloy that is superior in corrosion resistance and wear resistance,
more specifically, to a high performance and inexpensive iron-based
corrosion-resistant and wear-resistant alloy that is overwhelmingly
superior in a corrosion-resistant property and wear-resistant
property in comparison with those of 304 stainless steel,
high-chromium cast iron, and high carbon-high chromium
cast-iron-type material, has a high corrosion-resistant property
that would never be obtained from a high carbon-high chromium
carbide precipitation-type iron-based wear-resistant alloy and at
the same time a wear-resistant property that is superior to that of
these metals, and further hardly generate brittle peeling that is
inherent to a high-Si content steel, and a clad (hard-surfacing)
welding material used for obtaining the same.
BACKGROUND ART
[0002] In recent years, refuse incinerating factories, car-shredder
fluidizing-layer incinerators, waste oil and waste fluid
incinerators and the like have been built and operated. In
heat-resistant and wear-resistant portions of these devices, high
chromium cast iron is used, and in the devices that are subjected
to high--temperature thermal oxidization, for example, SCH13 heat
resistant cast steel or the like is used. However, in a short
period of time after the start of these operations, those members
and devices are worn, burnt to be lost, and subjected to corrosive
loss by the treated matters and heat, and there have been strong
demands for prolonging the service life thereof.
[0003] With respect to the life-prolonging countermeasures for
these devices and members, repairing processes by clad welding are
mainly carried out on worn-out portions, and a high carbon-high
chromium cast iron-type clad welding material that is an iron-based
alloy has been mainly used as its welding material. The reasons for
this are because the iron-based alloy is inexpensive and it is
superior in a wear-resistant property and high-temperature
oxidation resistant property. However, these furnace devices and
peripheral devices are exposed to such as high-temperature
corrosive burning gases and acid dew-point corrosion that occurs
upon stopping the furnace, and at present, it becomes difficult to
deal with these conditions only by using simple high-temperature
oxidation resistant property and wear-resistant property.
[0004] That is, unless a superior corrosion-resistant property is
also provided, with a superior wear-resistant property possessed by
the high carbon-high chromium cast iron-type clad welding material
being maintained, it becomes difficult to prolong the service life
of these various devices. In particular, with respect to the
corrosion resistance, corrosion-resistant properties against
chlorine gas, hydrochloric acid, sulfuric acid, diluted sulfuric
acid and the like are required.
[0005] With respect to these application environments that call for
a corrosion-resistant property, an oxidation resistant property and
a high-temperature wear-resistant property, stellite that is a
cobalt-based alloy is particularly superior in comparison with the
iron-based clad welding material, and the application thereof as
the cladding material has been proposed. However, this alloy is
very expensive in comparison with the iron-based alloy, failing to
satisfy the cost-effectiveness balance. For this reason, there have
been strong demands for developments of an iron-based clad welding
material that is inexpensive and has the same performances
(Non-Patent Document 1).
[0006] Non-Patent Document 1: "Basics and Applications of Surface
Treatment Techniques" (Vol. 1) Textbook for 14.sup.th Practical
Welding Seminar, East Branch of Welding Society, Jun. 23 to 24,
1988
[0007] In addition to these, using expensive alloys having
rarity-value metal elements, such as nickel, cobalt and the like,
as simple disposable wear-resistant materials is very wasteful from
the viewpoint of the international trend of resource-saving
movements, and originally, these expensive alloys should be
effectively utilized as permanent materials having high value and
applications capable of recovering resources; thus, the present
inventors have always thought that inexpensive iron-based
wear-resistant alloys should be used for disposable applications
such as wear-resistant materials.
[0008] Then, at present, since the high carbon-high chromium
cast-iron-type clad welding material is inexpensive, this has been
continuously used in most cases as the iron-based wear-resistant
alloy; however, the corrosion-resistant property thereof is
extremely inferior to that of cobalt- and nickel-based materials,
and this is hardly called as a corrosion-resistant material. The
typical composition of the high carbon-high chromium cast-iron-type
clad welding material that has been mainly used conventionally is
"C: 3 to 6%, Cr: 16 to 36%, Mo: 0 to 3%, Fe: remaining
portion."
[0009] However, alloys belonging to this type are extremely
superior in wear resistance, and although these are iron-based
alloys, they are considerably superior in high-temperature
oxidation resistance because of the high chromium content, and have
been often used for high-temperature wearing applications at
600.degree. C. as well as at 600.degree. C. or more. One of typical
examples thereof is an alloy having the following chemical
components: "C: 5.2%, Cr: 32%, Si: 0.6%, Mn: 0.7%, Fe: remaining
portion."
[0010] This iron-based wear-resistant clad welding metal has a
superior wear-resistant property, that is, a wear test value of 5.0
to 10, if indicated by a wear coefficient, with that of SS400 mild
steel being set to 100, which is a wear-resistant property about 10
to 20 times higher than that of the mild steel. However, since this
has a carbon content that is extremely high, it can be said that
the corrosion resistance is not sufficient.
[0011] For this reason, the present inventors have tried to develop
an inexpensive iron-based alloy that has a wear-resistant property
that is the same as, or equivalent to that of this high carbon-high
chromium cast-iron-type clad welding alloy, a corrosion-resistant
property that is close to that possessed by cobalt alloys,
stellites No. 1 and No. 6, and exerts a corrosion-resistant
property that is the same as, or higher than that with respect to
certain kinds of corrosive media. Here, colmonoy No. 6 alloy has
been well known as a nickel-based alloy having a superior
wear-resistant property. The wear coefficient WR thereof is 5,
which is somewhat superior than WR=8 of stellite No. 1; however,
with respect to the sulfuric acid corrosion resistance, this is
inferior to that of the stellite alloy so that the target of the
present inventors is still placed on the cobalt-based stellite
alloy, and if the corrosion-resistant property of the iron-based
alloy becomes higher than that of the cobalt-based alloy, the
iron-based alloy has been determined as being superior to that of
the nickel-based alloy. The standard compositions of stellite No. 1
and No. 6 are shown below:
[0012] [Standard chemical components of cobalt-based alloy:
stellite No. 1]
"C: 2.1%, Si: 0.8%, Mn: 0.4%, Cr: 32.0%, Fe: 2.0%, W: 12.0, Ni:
1.7, Mo: 0.1, Co: remaining portion"
[0013] [Standard chemical components of cobalt-based alloy:
stellite No. 6]
"C: 1.2%, Si: 0.8%, Mn: 0.5%, Cr: 27%, Ni: 2.7%, W: 4.5%, Fe: 2.5%,
Mo: 0.1%, Co: remaining portion"
[0014] Upon reviewing alloy elements contained in these
cobalt-based alloys, it is found that large amounts of cobalt,
tungsten and the like are contained so that these alloys are
composed of very expensive elements. Therefore, since the
cobalt-based alloys are very expensive alloys, these do not become
profitable when applied to a device having a very wide cladding
area from the viewpoint of costs, and it is very difficult to
satisfy the cost-effectiveness.
[0015] For this reason, the use of this alloy is considered to be
limited only to applications in which a cladding process on a
portion having an extremely limited small area can exert a great
effect. These applications include various valve sheets, for
example, a tip of a needle valve, a pump rod, a pump sleeve, a cam
shaft and the like. Stellite No. 1 and No. 6 alloys are used for
applications calling for three factors as heat resistant,
corrosion-resistant and wear-resistant alloys simultaneously, and,
in particular, suitably used for applications having a temperature
of 600.degree. C. or more, and these are popular alloys in the
world. However, at present, these have also been continuously used
for applications at 600.degree. C. or less in many cases, so as to
carry out a cladding process in devices in which
corrosion-resistant and wear-resistant properties are required.
[0016] Using alloys containing expensive rare elements for even
applications at 600.degree. C. or less as simple wear-resistant
members is an anti-social practice from the viewpoints of wasteful
use of resources in the world and of exhaustion of resources in the
future as described earlier, and expensive rare elements should be
used for significant applications having high value, and should
also be used for applications capable of recovering resources.
[0017] Consequently, the present inventors have proposed a highly
wear-resistant "clad welding material and a clad member" that is an
inexpensive iron-based alloy and exerts a superior high-temperature
oxidation resistant property at a high temperature of 600.degree.
C. or more, as one of means for solving these problems and
achieving improvements as much as possible, and have granted a
patent thereof (Patent Document 1). This patented alloy exerts
performances superior to those of stellite No. 1, when cladded on a
device calling for a high-temperature wear-resistant property, an
oxidation resistant property and a corrosion-resistant property in
applications of 600.degree. C. or more, and makes it possible to
cut costs to a great degree.
Patent Document 1: U.S. Pat. No. 3,343,576
[0018] Typical practical examples include: cladding processes for a
scraping lifter of a rotary kiln to be used at an ambient
temperature of 800 to 900.degree. C., a falling inlet liner of a
clinker cooler to be used from 900 to 1000.degree. C., a
copper-resource recovering clinker grizzly bar used at 900.degree.
C. or more, a clinker transporting conveyer bucket of 800.degree.
C., a fluidizing bed furnace boiler tube, a wire of air blowing
nozzle and the like, and by many application achievements relaxing
to these cladding processes, the patented alloy has devoted to a
great reduction in costs by means of prolonged service life. A
typical composition of components and performances of this patented
cladding alloy are shown below:
[0019] [FREA-METAL chemical components (% by weight) of No. 55
alloy]
Fused metal composition "C: 1.3%, Si: 4.5%, Ni: 3.7%, Mn: 3.6%, Cr:
36%, Fe: remaining portion" Base material: SUS310S 9 mmt
Hardness: HV977
[0020] Wear coefficient: 4.2 First layer Cr analyzed value: 35%
Micro texture: .times.400 (photograph No. 1 in FIG. 2)
[0021] Moreover, a test piece No. 55 that was subjected to a
bending process (bending radius: 290 mmR) with its hardened metal
being placed inside thereof is shown by photograph No. 2 in FIG. 2.
Here, the alloy Nos. are those adopted in composition comparison
tests that will be described later (see FIG. 1).
[0022] The greatest feature of this patented alloy is that a high
Si-content was given to a high chromium iron-based alloy exceeding
30%. Here, Si is very inexpensive in comparison with expensive
elements such as V, W, Mo, Co, Ni and the like that give a
high-temperature resistant property and a heat resistant property,
and when obtained from silica by using a reducing process, it is
possible to utilize materials that inexhaustibly exist on the
earth. However, the greatest defect of the high Si-containing steel
is to make the alloy extremely brittle, and because of this defect,
a large amount of addition thereof to an iron-based wear-resistant
cladding metal has been avoided even at present. Nevertheless, the
present inventors have still been paying attention to
characteristics of Si, that is, the fact that it is an inexpensive
element that inexhaustibly exists on the earth, its
high-temperature oxidation resistant property and its property for
allowing chromium carbides to be formed into a needle-shape, and
such a high content as not to be used or to be avoided normally,
that is, 3.0 to 7.0%, was added thereto.
[0023] Incidentally, although a high Si-containing steel referred
to as "Silicolloy" has already been produced, this metal was an
alloy developed for use in wear-resistant purposes between metals,
and its carbon content was in a level of 1/100 so that the amount
of precipitation of carbides that give a wear-resistant property
was extremely small, failing to be practically used in severely
high-temperature grinding wear-resistant applications, as in the
case of the application of the patented alloy (Patent Document
2).
Patent Document 2: JP-A No. 54-81115
[0024] The deposited metal of a high Si-containing steel has a
characteristic of causing slice-shaped surface layer peeling on the
surface layer, with the result that, upon carrying out a bending
process thereon, there is a fear of scattering of slice-shaped
portions. When further pressed and bent strongly, the deposited
metal is fractured to drop off the base material. By viewing the
bending test piece No. 55 of the wear-resistant alloy, the typical
peeling state can be confirmed. Consequently, the patented alloy
has been mainly used in the form of a welding rod and a clad
welding wire that are hardly subjected to a bending process.
[0025] In this manner, the above-mentioned patented alloy has been
developed by adding Si hoghly, and the alloy is used for
high-temperature wear-resistant applications of 600.degree. C. or
more, and makes it possible to provide a high-temperature oxidation
resistant property as high as that of SUS310S in spite of the fact
that it is an iron-based alloy, and to remarkably improve the
high-temperature wear-resistant property and high-temperature
hardness by allowing a large amount of needle-shaped chromium
carbides that hardly drop off to be precipitated at high
temperatures. In particular, under a high-temperature condition
from 600 to 1000.degree. C., the alloy becomes rich in ductility in
comparison with a normal temperature state so that its brittleness
is alleviated, and further a large amount of Si was solid-deposited
on the matrix base in the deposited metal so that it contributes to
improvements of the high-temperature oxidation resistance of the
matrix, making it possible to endure even at a high temperature of
1000.degree. C.
[0026] In particular, a condition "Cr%.gtoreq.-1.6Si %+37Cr %",
which forms a base for constituting the patented alloy, is a
two-element correlation formula between Cr and Si that accelerates
a large amount of needle-shaped chromium carbide precipitation
required for ensuring a superior wear-resistant property at
600.degree. C. or more. Without satisfying this correlation
formula, a sufficient precipitation of needle-shaped chromium
carbides (Cr.sub.7C.sub.3) is not available, resulting in
degradation of the high-temperature wear resistance.
[0027] The natural characteristic of normal metal is such that,
within a high-temperature range of 600.degree. C. to 1000.degree.
C., the hardness of a metal matrix softens extremely so that wear
is easily accelerated; however, since needle-shaped carbides are
conjugated in the width direction while being entangled with one
another over the entire matrix like knitting fibers, selective wear
of soft matrix portions is prevented; thus, the above-mentioned
patent alloy technique is based upon the fact that by allowing a
large amount of high-hardness needle-shaped carbides to be
crystallized, high-temperature wear can be prevented. By viewing
the texture of this alloy, a precipitation of the remarkable
needle-shaped carbides can be confirmed (photograph No. 1 in FIG.
2).
[0028] However, the superior characteristic at high temperatures in
contrast becomes a serious defect in its brittleness at normal
temperature, and the extreme brittleness causes degradation of the
bending processability, and when a wear-resistant steel plate
cladded with the patented alloy is produced, the resulting product
can be only applied to linear items, and with respect to items
having a curvature, cladding processes need to be carried out by
using a welding wire or a hand welding rod, always resulting in
high production costs.
[0029] As described above, although the patented alloy can provide
performances that are almost equivalent to the stellite alloy, its
greatest defect is that the high Si-content easily causes
slice-shaped peeling on the surface layer of the deposited metal,
making it difficult, in particular, to produce a wear-resistant
steel plate having a large area. Moreover, upon carrying out a
join-welding process between clad steels formed by using the same
alloy, the hardened metal causes peeling when stretched by a
welding stress, making it very difficult to carry out the
join-welding process.
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0030] An object of the present invention is to provide a low
carbon-high chromium-high Si-boron-niobium-cast-iron-type
iron-based corrosion-resistant and wear-resistant alloy that can
alleviate brittleness which is a defect of a high Si-containing
steel, maintain an overwhelming corrosion-resistant performance in
comparison with that of a high chromium cast-iron-type cladding
alloy or 304 stainless steel, exerts performances that are the same
as, or higher than those of stellites No. 1 and No. 6 with respect
to some corrosive environments, and has a wear-resistant property
that is the same as, or higher than that of a high carbon-high
chromium cast-iron-type cladding alloy or stellites No. 1 and No.
6, and a clad welding material used for obtaining the same.
Means for Solving the Problems
[0031] In order to achieve the above-mentioned object, in order to
improve a sulfuric acid resistant property that is a weak point of
an iron-based alloy, the present inventors have tried to find an
alloy that is also superior in a hydrochloric acid resistant
property by appropriately combining a large amount of Cr and a
small amount of Si, Mo, Cu, Ni and the like and using as one model
a Worthite alloy (C<0.07%, Cr20%, Ni25%, Si3.5%, Mo3% and Cu2%)
that has been already developed, so as to develop an inexpensive
iron-based alloy having a corrosion-resistant property and a
wear-resistant property that are the same as, or superior to those
of stellites No. 1 and No. 6 that are expensive cobalt-based
alloys.
[0032] The Worthite alloy is a Cr--Ni--Si--Mo--Cu type stainless
steel developed by Worthington Pum Co., Ltd. in the United States,
and this is used for sulfuric acid corrosion-resistant applications
in chemical plants and boilers exclusively used for burning
petroleum. Although the Worthite alloy is used as one model from
the viewpoint of sulfuric acid corrosion prevention, the problem
with this alloy is that it contains much Ni, which is different
from the intention of the present inventors, and that this alloy
differs greatly from the attempt to save resources such as
rarity-value alloys, which is the original major premise. The
Worthite alloy is mainly used as a corrosion-resistant structural
material that requires strength, and utilized as, for example,
pumps or the like made of stainless cast steel. Therefore, it is
important that the metal itself has toughness; however, the alloy
becomes brittle because of its high Si-content, and it is assumed
that the alloy is designed to have a high Ni-content so as to
alleviate the brittleness. Of course, the high Ni-content mainly
aims to improve the corrosion-resistant property; however, this
causes low hardness, and makes it inferior in the wear-resistant
property as a wear-resistant hardened metal material, and the
resulting iron-based alloy is not applicable to a wear-resistant
alloy in which the present inventors aim to produce.
[0033] Since a cladding alloy to be developed by the present
inventors basically aims to simultaneously satisfy both of the
corrosion-resistant property and the wear-resistant property,
stainless steel is used as its base metal in many cases. For this
reason, since the Ni content is expected to increase by allowing
the deposited metal to pick up Ni from the stainless steel or the
like of the base metal, the present inventors set the Ni content
originally added to a welding material to 13% in the maximum level
so as to save resources. That is, with respect to the Ni content of
the developed alloy, it is normally set to 5% or less, and the
addition thereof is set to 13% in the maximum level only in a
limited occasion. On the other hand, concerning Si, the following
arrangement is made.
(1) Brittleness of High Si-Containing Steel
[0034] A high silicon steel plate is one of high Si-containing
steels of iron-based metal. One example of components thereof is
shown below:
[C: 0.12%, Si: 4.12%, Mn: 0.07%, S: 0.005%, Fe: remaining
portion]
[0035] The silicon steel plate is mainly used for transformers and
motor cores. When the Si content is increased, its magnetic
property is desirably made greater; however, the addition of Si of
5% or more causes the steel to become brittle, and further addition
of Si makes it difficult to carry out a rolling operation, and
causes a difficulty in producing a thin steel plate. Here, Si has
such a characteristic that, when only added to simple carbon steel,
the resulting steel becomes brittle. In the case where the same
amount of Si is added to a high chromium alloy containing much Cr,
the tendency of brittleness possessed by Si itself and highly hard
and brittle chromium carbides precipitated by the high chromium
alloy synergistically accelerate the brittleness of the alloy;
therefore, it becomes very difficult to provide ductility to a
developed alloy.
[0036] (2) Brittleness of High Si-Containing Steel and Effects of C
Exerted on Corrosion Resistance and Wear Resistance
[0037] In order to improve the ductility of deposited metal, that
is, to prevent the occurrence of peeling, and to improve the
corrosion resistance, first, the carbon content is proposed as one
of important component elements. A high carbon-high chromium
cast-iron-type clad welding material has a very high carbon
content, and is included within a cast iron range containing carbon
of 4.5 to 6.0%. As a result, a large amount of brittle chromium
carbides are precipitated to cause a reduction in Cr content
included in the matrix, resulting in extreme degradation of the
corrosion resistance. That is, the greatest reason for degradation
of the corrosion resistance of various high carbon-high chromium
cast-iron-type clad welding materials is in that, in order to
obtain a wear-resistant property, a large amount of carbon is
contained therein, and carbon is thus bonded with a carbide-forming
element having a strong affinity to carbon, that is, chromium,
tungsten, vanadium, titanium, niobium, or the like, so that, by
allowing a large amount of high-hardness carbides to be
precipitated in the metal matrix, the wear-resistant property is
ensured.
[0038] It is said that the chromium carbide has a high hardness in
a range of HV1650 to 2100, the niobium carbide has that of HV2400,
the titanium carbide has that of HV2800, the vanadium carbide has
that of HV2800 and the tungsten carbide has that in a range of
HV2400 to 3000. High chromium cast-iron-type alloys maintain a
superior wear-resistant property by these carbides that are
precipitated; however, in contrast, the corrosion-resistant
property of the deposited metal deteriorates extremely because of
the high carbon content.
[0039] In general, from an iron-carbon two-element state diagram,
it is said that, with the carbon content of 2.0 to 2.1% being set
as a border, those below the border are cast steels, while those
above the border are cast irons. Moreover, since it is determined
that the cast steel having a carbon content of 2.0% or less is
superior to the cast iron having a carbon content exceeding 2.0% in
its mechanical properties, in particular, in its toughness in the
metal matrix, the developed welding alloy has been designed so that
the carbon content of the first-layer deposited metal is set to 2%
or less. It was assumed that the low carbon content of course
contributes to improvements of corrosion resistance.
[0040] In the case where the carbon content of a welding material
is set to 3.0% or less, upon determining from the amount of
precipitation of carbides, a so-called hypo-eutectoid state is
exerted, and when one layer is cladded on a mild steel, a
sufficient carbide precipitation does not occur on the first
deposited metal due to melting-in of the mild steel, resulting in
serious degradation of the wear-resistant property. For example,
even in the case where a carbon content of 3.0% is given to the
welding material, upon cladding one layer on a mild steel or
stainless steel base material, the carbon content in the deposited
metal varies within a range of 1.8% to 2.1% although it depends on
the melt-in depth into the base metal (melt-in depth: about 30% to
40%). This content corresponds to near 2.0% of carbon content that
divides the cast steel and the cast iron from each other. Normally,
the carbon amount to be contained in a high carbon-high chromium
cast-iron-type welding material needs to be set to 4.5% or more so
that it is important to maintain a hyper-eutectoid state in which a
sufficient carbide can be precipitated even under influences of
dilution of mild steel from the first layer. That is, even upon
receipt of 30% of melting-in, the carbon content of the first layer
deposited metal needs to be set to about 3% or more so as to form a
hyper-eutectoid state.
[0041] Based upon above description, the upper limit value of the
carbon content of the first layer deposited metal of the developed
alloy was set to 2.0% or less that divides the cast steel and the
cast iron from each other as one target value. For another reason,
since the carbon content of stellite No. 1 alloy of the
cobalt-based alloy is C: 2.0%, and the criteria of the
corrosion-resistant performance of the developed welding material
is determined as the same as, or not less than the corrosion
resistance performance of stellite No. 1, the carbon content was
determined to virtually the same amount.
[0042] Table 1 shows comparisons of wear-resistant property
depending on differences in carbon contents. Here, alloys No. 41
and No. 42 are high Si-containing steels, and since these contain
neither Nb nor B, these are not included within the developed alloy
component range; however, since these are desirably used for
comparing the wear-resistant property depending on differences in
carbon amounts, they were listed.
TABLE-US-00001 TABLE 1 Effects of carbon content exerted on
wear-resistant property (% by weight) Wear Alloy C Si Ni Cr Mo Cu
Hardness coefficient 41 2.0 5.0 3.3 23 4.6 4.6 HV616 6.3 42 3.0 5.1
3.3 23 4.6 4.6 HV679 2.5
[0043] Alloy No. 41 and alloy No. 42 were produced by adjusting
them to have virtually the same chemical components except for the
carbon contents. Alloy No. 42, which had a higher carbon content,
provided a wear-resistant property that is about 2.5 time higher
than that of alloy No. 41. This is because, since alloy No. 42 has
a higher carbon content, the amount of precipitation of chromium
carbides increases so that the wear resistance is improved.
[0044] The carbon content is one of factors that cause great
adverse effects to the corrosion-resistant property; however, in
the case where the carbon content is reduced so as to improve the
corrosion-resistant property, the amount of precipitation of
carbides is reduced to cause serious degradation of the
wear-resistant property. Therefore, the present inventors have
revised component constitutions of a high carbon-high chromium cast
iron that allows a large amount of carbides to be precipitated by
its high carbon content, and can ensure the wear-resistant
property. That is, the target was to develop an alloy which, even
when it has an amount of carbon addition in a range of
0.5%.ltoreq.C.ltoreq.2.0 to 2.5%, can ensure a superior
wear-resistant property as well as a superior corrosion-resistant
property and sufficient toughness. There are various different
cladding methods with respect to the clad welding materials, and
the respective methods have different melting-in depths and
subsequently different dilution rates in the base material, the
maximum amount of addition of C was set to 2.5% or less.
(3) Effects of Cr Exerted on Brittleness and Wear-Resistant
Property of High Si-Containing Steel
[0045] Here, Cr is one of alloy elements that give greatest
influences to brittleness of a high Si-containing steel. The
chromium content of the first layer deposited metal that has been
actually cladded by using a welding material having a content of
chromium addition of 45% in the maximum, becomes about 23 to 34%
upon receipt of a base material dilution in a range of about 25% to
50%, in the case where the base material is a mild steel or an
esten steel. In the case of the amount of chromium addition of 25%,
the chromium content becomes about 15 to 19%. In the case where
SUS304 to 316 is used as a base material, on the assumption of the
use of a welding material of Cr: 35%, the chromium content in the
first layer deposited metal becomes about 26 to 31%. Although the
melting-in depth differs depending on the welding methods, the Cr
content of the first layer deposited metal is selected to be set to
about "15%.ltoreq.Cr.ltoreq.31%" on average.
[0046] The maximum amount of addition of 45% is used for providing
a hand welding rod having a base material dilution rate of 50% or
more, and when the base material is mild steel, the chromium
content of the first layer deposited metal becomes about 23%, and
is included in the above-mentioned range. In particular, in the
case of a wear-resistant steel plate, this is formed by using
one-layer cladding process, and the thickness of the deposited
metal becomes about 4 to 6 mm. With respect to the brittleness of
the deposited metal obtained by a clad welding material and a
wear-resistant steel plate, the behavior of the first layer
deposited metal is considered to be most important. Therefore, it
is necessary to properly design the range of the chromium content
in the first layer deposited metal. The reason for this is because
chromium is an element to be contained in a large amount in the
developed alloy in comparison with the other alloy elements, and
furthermore since this has great influences to the brittleness of
the deposited metal, the understanding of the degree of influences
of each of the other small-amount added alloys is most essentially
determined by the behavior of this element within a predetermined
range.
[0047] Incidentally, for the necessity of depositing a large amount
of needle-shaped chromium carbides so as to provide a superior
high-temperature wear-resistant property at temperatures higher
than 600.degree. C., it was very important that the above-mentioned
patented alloy satisfies a two-element correlation formula between
Cr and Si, "Cr.gtoreq.-1.6Si+37 (% by weight)". In the case where
the Cr content is 32% or more, with the Si content being 3% or
more, a large amount of needle-shaped chromium carbides are
precipitated to cause extreme brittleness and the subsequent
peeling on the surface of the hardened metal; this phenomenon has
been proved by No. 55 bending test piece (see photograph No. 2 in
FIG. 2).
[0048] On the contrary to the patented alloy, the developed alloy
is not an alloy formed by aiming in particular a high-temperature
wear-resistant property, but an alloy formed mainly by aiming to
ensure proper ductility of a brittle in high Si-containing steel as
well as to improve the corrosion-resistant property thereof by
using an iron-based alloy. Therefore, since it is not necessary to
satisfy the condition of "Cr.gtoreq.-1.6Si+37Cr %", the amounts of
addition of silicon and chromium that cause brittleness of the
deposited metal can be reduced in comparison with those of the
former; however, the reduction in the amounts of addition of Cr and
Si causes a reduction in the amount of precipitated chromium
carbides, with the result that the wear-resistant property is
lowered extremely although the ductility is recovered.
[0049] This phenomenon has been proved by experiments to be
discussed below. In the case where, by using the above-mentioned
patented alloy as its basic alloy, the amount of Cr addition that
gives greatest influences to the wear-resistant property was
reduced from 36% to about 20 to 25%, the toughness and
wear-resistant property of the resulting alloy were examined. The
examination of the toughness was carried out as follows: A
wear-resistant steel plate on which a layer of a test alloy with a
thickness of 5 mm was deposited on a SUS310S base material having a
size of 9 mm in thickness.times.100 mm in width.times.400 mm in
length was formed, and the toughness thereof was determined by
using bending tests of 200R and 290R. When even one portion of the
deposited metal was peeled or chipped in this bending test, this
state was determined as "poor in toughness". Based upon the
wear-resistant coefficient WR=15 or less possessed by stellite No.
6 as the standard, the wear coefficient WR was required to exceed
this level. Table 2 shows the alloy compositions and Table 3 shows
the results of the examination.
TABLE-US-00002 TABLE 2 FREA-METAL Modified Alloy (added % by
weight) Alloy C Si Mn Ni Cr Nb B 56 1.3 4.5 3.5 3.7 20 -- -- 57 1.3
4.5 3.6 3.7 20 0.6 1.0 58 1.3 4.5 3.6 3.7 20 0.6 2.0 69 1.3 4.5 3.6
3.7 20 8.0 -- 70 1.3 4.5 3.6 3.7 25 8.0 --
TABLE-US-00003 TABLE 3 Test Results Applied base Wear Alloy
material 200R 290R Hardness coefficient 56 310S .largecircle.
.largecircle. HV309 78 57 310S .largecircle. .largecircle. HV351 37
58 310S .largecircle. .largecircle. HV427 14 69 310S .largecircle.
.largecircle. HV335 17 70 310S .largecircle. .largecircle. HV362
15
[0050] In spite of a high added amount of Si, all the alloys were
acceptable (.largecircle.) in the bending performance, and the
reason for this is presumably because, since the Cr content was
small, the amount of precipitation of needle-shaped chromium
carbides was small so that bending ductility was improved; in
contrast, since the precipitation of carbides was small, the
wear-resistant property was greatly lowered.
[0051] This test indicated that Cr, that is, chromium carbides,
gives greatest influences to the toughness (bending ductility) and
wear-resistant property. With respect to the wear-resistant
property, two kinds of alloys No. 58 and No. 70 became narrowly
acceptable. In the case of a Cr added amount of 20% (content: about
21%) of No. 58 alloy as well as in the case of a Cr added amount of
25% (content: about 25%), even upon addition of the greatest amount
of Nb of 8%, the wear resistance WR exhibited the lowest value of
14 to 15 so that it was found that it was impossible to adjust the
wear-resistant property by adding Nb alone.
(4) Effects of Addition of B Exerted on Wear-Resistant Property and
Ductility of High Si-Containing Steel
[0052] In the case of FREA-METAL alloy (No. 55) in which, since Cr
and Si contents were great, a large amount of brittle needle-shaped
chromium carbides were precipitated in the matrix, peeling easily
occurred in the bending process (see photograph No. 2 in FIG. 2).
It is not possible to revise the characteristic that Si itself
causes brittleness of steels. However, with respect to the
developed alloy, although it has been found that the amount of
precipitated chromium carbides greatly causes brittleness of the
resulting alloy, the chromium carbides also tend to form a needle
shape as the Si content successively increases, and the shape of
the chromium carbides also accelerates the brittleness, and is
considered to form one of main causes that exert cracks and peeling
to lower the wear-resistant property.
[0053] In order to improve the bending ductility, it is important
to reduce a large amount of crystallization of brittle
needle-shaped chromium carbides. The wear-resistant property is
lowered correspondingly as the amount of the needle-shaped carbides
is reduced; therefore, by crystallizing finely miniaturized
compounds having high hardness, that is, dispersed and crystallized
spherical, island-shaped, network-shaped and indefinite shaped
compounds, so as to compensate for the lowering, the deposited
metal is prevented from becoming brittle, and this method is
considered to be the best means.
[0054] To provide a means for improving the wear-resistant property
without causing brittleness in high Si-containing steels, an
attempt was made to improve the wear-resistant property by
crystallizing a boride having extremely high hardness that gives no
adverse effects to the corrosion-resistant property, or by allowing
a niobium carbide that has a strong affinity with carbon and
crystallizes spherical miniaturized carbides so as to coexist
therewith. At the same time, it was expected that these two
elements would not give adverse effects to cause brittleness, and
the subsequent peeling and drops-off of the surface layer metal,
which is the greatest defect of the high Si-containing steel, and
would rather serve to suppress the brittleness.
[0055] In a chromium content in the deposited metal within a range
from 15%.ltoreq.Cr.ltoreq.31%, the wear-resistant property can be
improved by adding boron thereto; however, in the addition of boron
alone, for example, the addition of 0.5% did not improve the
wear-resistant property, while the addition of 4.0% caused the
deposited metal to become extremely hard, resulting in many cracks
developing in a right-angle direction relative to the welding bead.
The addition of B alone caused a narrowed range of the amount of
addition, making it very difficult to determine the degree of
ductility of the deposited metal. Upon comparison in wear-resistant
property between the low-B content steel and the high-B content
steel, although the high-B content steel exerted a superior
wear-resistant property, it also caused serious brittleness. The
effects of added amount of boron exerted on the wear-resistant
property and bending processability are shown in Table 4.
TABLE-US-00004 TABLE 4 Effects of added amount of boron exerted on
wear-resistant property and bending processability C Si Ni Cr Mo Nb
B Cu Hardness WR Low-B 1.5 3.5 3.3 23 4.6 4.0 0.5 4.6 602 9.2
High-B 0.5 3.6 3.3 24 4.6 0 4.0 4.5 744 2.0 Cr: content (first
layer fused metal)
[0056] Moreover, the high silicon content, which is the largest
characteristic of the developed alloy, serves as a very effective
factor to high-temperature oxidation resistance, sulfuric acid
corrosion resistance, hydrochloric acid corrosion resistance and
organic acid corrosion resistance; however, normally, the addition
of 3.5% or more to a normal iron-based alloy tends to cause serious
brittleness to the alloy, with the result that this has not been
used so much as an iron-based clad welding material, in spite of
its superior performance. When the added amount of Si in a high
Cr-content steel is increased, the chromium carbides are easily
formed into a needle shape, with the result that the deposited
metal tends to become brittle, and upon the addition of 5% of
silicon alone, surface layer peeling occurred on the deposited
metal, while the reduction thereof to 2.5% causes serious
degradation of the wear-resistant property. Therefore, the amount
of Si addition that features the developed alloy is essentially set
in a range from 2.5% in the minimum to 4.5% to 5.5% in the maximum,
and it was the absolute condition to eliminate brittleness within
this range of the added amount.
[0057] In the same manner as in B, the addition of Si alone also
caused a narrowed range of the amount of addition, making it very
difficult to evaluate the ductility and wear-resistant property of
the deposited metal. Therefore, the use of the product Si.times.B
(% by weight) was required as a method for evaluating B and Si with
the influences of both of them being included. Here, B crystallizes
borides to cause extremely high hardness, and it is considered that
the kinds, shapes and sizes of the borides and the amount of
crystallized borides give influences to the ductility of the steel.
In particular, in the case where the size was extremely small in
comparison with the size of needle-shaped chromium carbides, it was
assumed that factors that accelerate physical damages during the
bending process would be greatly reduced. It was also expected that
when the hardness of minute borides was extremely high, the
wear-resistant property of the deposited metal would be
improved.
[0058] Therefore, No. 10-C alloy that exerted superior results in
sulfuric acid resistance and hydrochloric acid resistance was taken
up, and carbides and borides to be crystallized in the alloy were
identified by using a SEM-EDX analyzer. Crystallized matters
included a Cr.sub.7C.sub.3 chromium carbide (about HV2100) and
three kinds of borides Cr.sub.2B (about HV1400), Mo.sub.2FeB.sub.2
(about HV2400) and NbB (about HV2250). All of these accounted for
30% of the total deposited metal. With respect to the shapes of
these crystallized matters, Cr.sub.7C.sub.3 had a petal shape or a
branch shape, and among borides, NbB had an indefinite shape,
Cr.sub.2B had a plate shape, and Mo.sub.2FeB.sub.2 had a net-work
shape (see photograph 1 in FIG. 3).
[0059] Since the carbon content of No. 10-C alloy was about 0.7% to
0.8% that was a low level, only the boride Cr.sub.7C.sub.3 was
crystallized with respect to carbides, and with respect to Nb, no
niobium carbides were produced. However, niobium borides (NbB) were
crystallized to cause high hardness equivalent to that of the
niobium carbides. Therefore, it was clarified that in the case
where the carbon content was small, Nb forms borides to contribute
to improve the wear-resistant property. It was clarified that
because of these crystallized borides, the superior wear-resistant
property was exerted even under a low carbon content.
[0060] Since, as the carbon content increases, more niobium
carbides are simultaneously crystallized so that they further
contribute to improve the wear-resistant property. By adding B and
Nb so as to coexist, the wear-resistant property was successfully
improved by their superior hardness, without causing degradation of
the bending ductility. Among various kinds of boride crystallized
matters, those that are assumed to cause brittleness of the alloy
by their shapes include chromium boride (Cr.sub.2B). Although these
have a plate-shaped texture, the shapes thereof are similar to
those of minute needle-shaped chromium carbides so that the
brittleness might be caused (see photograph 1 in FIG. 3). In an
actual bending test, No. 10-C alloy was easily bent and processed,
with no surface layer peeling caused by the bending process (see
photograph 2 in FIG. 3). Probably because of a difference of the
amount of produced crystals from that of the needle-shaped chromium
carbides, there was not so much influence given to the bending
processability. With respect to the hardness of borides, reference
was made to "Handbook of Metal Chemistry Thermal Processes (written
by G. V. Boricenork)."
(5) Correlation between Si.times.B and Cr content
[0061] The correlation between the product of added amounts
Si.times.B and Cr content can be considered as a correlation with
the amount of crystallized needle-shaped chromium carbides that
most greatly develop brittleness. When the Cr content is small, the
amount of crystallized Cr carbides is of course reduced so that the
tendency of brittleness is also reduced; however, in contrast, the
wear-resistant property is greatly lowered. In the case where the
amount of addition of Si alone is greatly increased, the tendency
of causing brittleness to the metal becomes stronger due to the
tendency of causing brittleness and the characteristic of forming
chromium carbides into a needle shape inherently possessed by Si;
therefore, examinations were carried out so as to find out what
degree the ductility and the wear-resistant property were improved
to by adding B so as to coexist, and how the appropriate alloy
composition range could be subsequently expanded.
[0062] In the case of a low Cr-content, the product Si.times.B was
set to 7.5 or more in a high level, and in the case of a high
Cr-content, the product Si.times.B was set to 1.55 to 6.4 in a low
level, so that the alloy composition range that would
simultaneously satisfy the ductility and wear-resistant property of
the alloy was examined. Tables 5 and 6 show the results of the
examinations.
TABLE-US-00005 TABLE 5 Si .times. B Alloy (% by weight) Alloy C Si
Mn Ni Cr Nb B 73 1.5 4.0 Cu4.6 20 3.0 74 1.5 3.5 Cu4.6 20 3.0 75
1.5 2.5 Cu4.6 28 3.0 76 1.5 3.1 Cu4.6 30 0.5 77 1.5 4.5 Cu4.6 30
0.5 78 1.5 3.2 Cu4.6 30 2.0 79 1.5 4.5 Cu4.6 30 1.0 80 1.5 3.5
Cu4.6 30 1.0
TABLE-US-00006 TABLE 6 Test Results Applied Wear Acceptance base Cr
Si .times. Hard- coef- or Alloy material 200R content B ness
ficient unsuitability 73 SS400 15% 12.0 HV686 5.0 Unsuitable 74
SS400 15% 10.5 HV726 6.3 Unsuitable 75 304 .largecircle. 26% 7.5
HV654 6.1 Acceptable 76 304 .largecircle. 27% 1.55 HV450 67.0
Unsuitable 77 304 .largecircle. 27% 2.25 HV460 17.0 Unsuitable 78
304 .largecircle. 27% 6.4 HV603 12.4 Acceptable 79 304
.largecircle. 27% 4.5 HV455 30.7 Unsuitable 80 304 .largecircle.
27% 3.5 HV457 19.4 Unsuitable
[0063] In the case of the upper limit value of 7.5 of Si.times.B,
although the wear-resistant property was ensured; however, the
further addition thereof failed to ensure the bending ductility,
while in the case of the lower limit value of 6.4 of Si.times.B,
although the bending ductility was ensured, the further reduction
thereof caused the wear-resistant property to be unsuitable, with
the result that upper and lower width of the adjusting range became
very narrow, with the upper limit value being set to 6.1 and the
lower limit value being set to 12.4 with respect to the wear
coefficient, failing to provide a superior wear-resistant property.
The alloy composition range that would simultaneously satisfy both
of superior ductility and wear-resistant property was obtained
within only a limited range having a narrow width. Thus, it was
difficult to obtain an alloy composition range having a wide width
that would simultaneously satisfy the ductility and the
wear-resistant property based upon only the correlation between the
product of Si.times.B and Cr.
(6) Effects of Added Nb
[0064] It is found that in particular, the lower limit value of
Si.times.B provides an excellent bending ductility, but in contrast
causes serious degradation of the wear-resistant property. The
addition of each of B and Nb alone is not so effective; however, it
is assumed that by adding these so as to coexist, the
wear-resistant property at the lower limit value would be greatly
improved. With this arrangement, it is considered that the alloy
composition range that satisfies both of the ductility and the
wear-resistant property can be greatly expanded.
[0065] Although Si.times.B of No. 35 alloy was 1.8, it became
possible to ensure a wear coefficient WR=9.3 by adding Nb=4.0% and
AL=2.0%. In the case of Si.times.B=3.5 of No. 33 alloy, a wear
coefficient WR=5.9 was obtained by adding Nb=4.0%. Since the lowest
reference value of the wear coefficient WR indicating the
wear-resistant property is 15, this range is sufficiently located
within the reference values so that it becomes possible to greatly
expand the alloy composition range that simultaneously satisfies
the ductility and wear-resistant property by adding Nb and B so as
to coexist.
[0066] In the product of Si.times.B, Nb is considered to be the
third effective element to improve the wear-resistant property, and
this can be selected within a very wide width of the added amount
thereof, that is, a range from 0 to 8.0% including no addition, so
that it is expected to easily adjust the wear-resistant property by
using this. It is a known fact that Nb is an element that form
carbides into a finely spherical shape, and since this has less
possibility to cause brittleness of the metal and niobium carbides
(about HV2400) and niobium borides (about HV2250) give high
hardness, the wear-resistant property can be improved.
[0067] In the case where a gray pig iron has a needle-shaped
graphite in its graphite shape, since the graphite causes
brittleness in the resulting cast product, a method is proposed in
which by adding Mg and Ca thereto, the graphite is formed into a
spherical shape so that the ductility equivalent to that of mild
steel is prepared; however, the addition of Nb exerts the same
effects as those of Mg and Ca with respect to carbides. In the case
where the carbon content of an alloy is set to a very low level,
such as, to 0.5%, produced crystals of carbides are greatly
reduced; however, by adding boron thereto so that niobium boride
(NbB) and chromium boride (Cr.sub.2B) are dispersed and
crystallized, the wear-resistant property is subsequently
improved.
[0068] In this manner, both of B and Nb form fine crystallized
matters to prevent brittleness of the present developed alloy, and
by exchanging brittle needle-shaped chromium carbides with both of
these, it becomes possible to recover the ductility of the steel,
and consequently to greatly improve the wear-resistant property by
their high hardness. As has been already proved by the experiments,
although the effect of the addition of Nb alone failed to provide a
sufficient wear-resistant property, it was possible to improve the
wear-resistant property by allowing B to be added so as to coexist
therewith.
[0069] The essential conditions of the developed alloy include the
product of Si.times.B and the addition of Nb to coexist, and
lacking either one of these makes it very difficult to ensure a
wide range of alloy compositions that sufficiently satisfy both of
the ductility and wear-resistant property.
[0070] It is greatly beneficial that the brittleness in the high
Si-containing steel, which was the biggest conventional defect of
the high Si-containing steel, can be alleviated by appropriately
combining three elements of Si, B and Nb, and it becomes possible
to effectively utilize Si that is inexpensive and gives a superior
wear-resistant property and a high-temperature oxidation resistant
property to a wear-resistant material for iron-based alloys, in the
future. With this arrangement, it is proposed to effectively
utilize Si in place of an expensive alloy element having a rarity
value, such as Co, Ni and the like, and since it is possible to
provide superior corrosion-resistant property against hydrochloric
acid and chlorine gas corrosions, the utilization thereof was
effectively expanded so as to be applied to hydrochloric acid
corrosion resistant and sulfuric acid corrosion resistant purposes
in industrial wastes, high-temperature burning furnaces, thermal
decomposing devices and fluidizing bed furnaces.
[0071] Assuming that a bending test is most simple and accurate as
a method for evaluating brittleness of an alloy, a bending process
was carried out to evaluate its ductility. The bending
processability and the wear-resistant property were collectively
summarized based upon the correlation between the chromium content
and the product of Si.times.B. As a result, with respect to the
tendency of the limit that causes neither peeling nor fractures in
a deposited metal, even bending tests have been carried out under a
fixed curvature, in the case of a low Cr content, the product of
Si.times.B becomes a high value, while in the case of a high Cr
content, the product of Si.times.B becomes a low value. The method
for evaluating the bending processability based upon the product of
Si.times.B makes it possible to greatly expand the evaluation range
in comparison with an evaluation method by the use of B or Si
alone, and consequently to determine performances more
accurately.
(7) Ductility Evaluation and Wear Resistance Evaluation by Bending
Process of Wear-Resistant Steel Plate
[0072] Supposing that the highest Si content of 4.5% is set, a
large amount of needle-shaped carbides are crystallized with the
chromium content of about 30% or more, from the expression of Cr
%.gtoreq.-1.6Si %+37, and since Cr becomes about 31% when Si=4%,
the range of the chromium content in the first layer deposited
metal is set to "15%.ltoreq.Cr-31%". Moreover, appropriate
component ranges of the main influential elements to be used for
obtaining deposited metal that has a superior bending
processability, that is, superior ductility, were specified as
follows:
[0073] 15%.ltoreq.Cr.ltoreq.31% (content in first layer deposited
metal)
[0074] 0.5%.ltoreq.C.ltoreq.2.0% (added amount)
[0075] 2.5%.ltoreq.Si.ltoreq.4.5% (added amount)
[0076] 0.ltoreq.Nb+V.ltoreq.8.0% (added amount)
[0077] 0.5%.ltoreq.B.ltoreq.3.5% (added amount)
[0078] Within these component specific ranges, an appropriate range
of Si.times.B giving influences to the bending processability was
found. The product of Si and B that would give superior bending
processability without causing brittleness to the matrix was in a
range of "1.25.ltoreq.Si.times.B.ltoreq.11.5." The schematic
tendency showed that in the case of a Low Cr content, the numeric
value of Si.times.B became higher, while in the case of a high
Cr-content, the numeric value of Si.times.B became lower. In
particular, as the numeric value of Si.times.B became lower, the
wear-resistant property tended to be lowered, and Nb was added so
as to compensate for the reduced wear-resistant property.
[0079] As the numeric value of Si.times.B became higher and higher,
the deposited metal tended to become more and more brittle, with
the result that the bending processability deteriorated; therefore,
in order to improve the bending processability, the numeric value
of Si.times.B had to be set to a low level. As the numeric value of
Si.times.B became lower, the ductility of the deposited metal was
improved so that the bending processability was subsequently
improved; however, in contrast, since the wear-resistant property
was lowered, Nb was added within a range of
0.ltoreq.Nb+V.ltoreq.8.0% so as to adjust the wear-resistant
property. In the case where the numeric value was high, that is,
for example, in the range of 4.0.ltoreq.Si.times.B.ltoreq.11.5%,
the amount of Nb addition was set within a range of 0.5 to 4%, that
is, a low level; in contrast, in the case where the numeric value
was low, for example, in the range of
4.0.gtoreq.Si.times.B.gtoreq.1.25%, the amount of Nb addition was
set within a range of 4 to 8%, that is, a high level so that the
wear-resistant property was improved.
[0080] The developed alloy aims at the improvement of the
corrosion-resistant property, and in the case where the chromium
content in the first layer deposited metal is set to 15 to 18%,
that is, to a low level, carbon and chromium are combined with each
other by welding heat to form a Cr.sub.23C.sub.6 carbide along the
crystal grain interface, and this carbide is precipitated along the
grain interface to cause a lack of Cr that is required for the
corrosion--resistant property, resulting in a possibility of grain
interface corrosion. By adding 0.5% or more of Nb thereto, Nb that
has a stronger affinity to carbon than Cr is allowed to bind with
carbon to exert an effect for suppressing the precipitation of
Cr.sub.23C.sub.6.
[0081] The addition of Ti.ltoreq.1.0% or less also aims at the same
effect as that of Nb, and since Ti exerts an extremely strong
affinity with oxygen so that, determining that more losses would be
generated during a high-temperature oxidizing reaction in the metal
than those generated by Nb, the amount of addition was set to
1%.
[0082] A method for evaluating the bending processability of
deposited metal is described as follows: A clad steel plate that
was cladded with deposited metal with a thickness of 5 to 6 mm as a
single cladded layer over the entire surface of each of steel
plates having a size of 9 mm in mass thickness.times.100 mm in
width.times.400 mm in length of SS400, SUS304 and SUS310S was
produced, and this was subjected to a bending process by a press
with the hardened metal placed on the inner side. A stellite No. 1
alloy, which was a target material, was cladded on SS400 with two
layers having a thickness of 5 mm, by a gas welding process. The
length of each sample piece was set to about 200 mm.
[0083] The bending curvature was set to about 200R, and the bending
ductility was evaluated in the following three-degree criteria: in
the case where no influences were caused on the hardened metal by
the bending and an appropriate bending performance was obtained
without causing any defects, this state was evaluated as
.largecircle., in the case where several surface-layer peeling and
extremely slight cracks occurred on the surface of the hardened
metal, this state was evaluated as .tangle-solidup., and in the
case where many surface-layer peeling and lamp-shaped cracks
occurred to cause poor toughness, this state was evaluated as . The
results are shown in Table
[0084] In FIG. 1, Si.times.B is plotted on the axis of ordinates
and the Cr content of the first layer deposited metal is plotted on
the axis of abscissas so that the relationship between these and
the ductility was indicated. A curve on the upper portion indicates
a fracture limit line of surface-layer face peeling and drops-off
occurred on the deposited metal during the bending process of the
clad steel plate with a curvature of 200R, and the upper side from
this line indicates that the bending process easily causes
fractures. The lower curve indicates a limit line where the
low-stress wear coefficient WR possessed by the deposited metal is
maintained at 15, and the lower portion below this indicates a
great reduction in the wear-resistant property with an increase in
the wear coefficient.
[0085] Within an appropriate component range surrounded by the
upper and lower limit lines, the bending processability of the
wear-resistant steel plate composed of one cladded layer can be
subjected to an R-bending process up to a radius of 200 mm with
respect to the curvature, and there are many alloys capable of
being subjected to a bending process with a minimum curvature lower
than this. The bending processability is the same as, or superior
to that of stellite No. 1, and a bending process performance that
is the same as, or superior to that of a high carbon-high chromium
cast iron alloy used for a wear-resistant steel plate is obtained.
Alloys that can be subjected to such a minimum R bending process
among high S-content steels have not been known from the past to
the present.
[0086] The next important characteristic is an improved
wear-resistant property at normal temperature. As has been
described earlier, since the carbon content that is the most
essential factor for improving the wear-resistant property is
greatly reduced in comparison with that of a high-chromium
cast-iron-type cladded alloy, the wear-resistant property is
lowered although the bending process performance and the
corrosion-resistant property are improved so that it becomes
important to ensure a sufficient wear-resistant property.
[0087] A method for determining and evaluating the wear-resistant
property was carried out by using an endless-belt grinder abrasion
tester. The wear coefficient of each of various alloys was
calculated by a ratio of the wear volume of SS400 and the wear
volume of an alloy to be compared, based upon that of mild steel
SS400 as a reference value.
[0088] The target wear-resistant property of the developed alloy
was a wear-resistant property obtained when stellite No. 1 alloy
was gas-welded, and the wear coefficient was WR=8. The cladding
method for the stellite alloy is normally carried out by a gas
welding in the case of a cladding process of a small object, while
in the case of a cladding process for a member having a large area,
an arc welding method is used for the cladding process. The arc
welding method has a higher welding efficiency in comparison with
the gas welding, and its cladding technique is easier than that of
the gas welding, and in recent years, welding technicians are well
skilled in the arc welding; however, the greatest defect in the
cladding process by the arc welding is that the melt-in depth in
the base material becomes greater to cause serious degradation of
the wear-resistant property.
[0089] In the case where stellite No. 1 is subjected to a cladding
process by the TIG method, the wear coefficient becomes 54, and
without carrying out cladding processes of two to three layers, a
wear-resistant property equivalent to that of the gas method is not
obtained. Moreover, the wear coefficient of high-chromium cast iron
is 14 to 17.5, and since the wear coefficient of a high carbon-high
chromium cast-iron-type welding rod is in a range of about 4 to 10,
the wear coefficient 14 of stellite No. 6 is set as a lowest target
value, with the true target value being set to WR=8 of the gas
welding of stellite No. 1. The appropriate range of the wear
coefficient WR of the developed alloy is set in a range of
1.ltoreq.WR.ltoreq.15.
(8) Evaluation on Bending Process Performance and Wear-Resistant
Property of Clad Welding Material
[0090] Evaluations on the bending process performance and
wear-resistant property of a welding material is basically matched
to the correlation formula of Si.times.B and Cr obtained in the
wear-resistant steel plate. Different points of cast steel from the
wear-resistant steel plate are that the dilution rate due to the
base material is different and that the bending process is not
particularly required. Therefore, a slightly larger amount of added
alloys is permissible in comparison with the production of the
wear-resistant steel plate.
[0091] With respect to the added component range in the welding
material, it is necessary to correct components obtained in a clad
steel plate since there are big variations depending on the clad
welding methods, the kinds of base materials and melting-in depths.
For example, in the case of a cladding operation of a hand welding
rod, a melting-in rate of about 50% is expected, that of about 35%
is expected in the MIG welding, that of about 45% is expected in
the TIG welding, that of about 35% is expected in a flux cored
wire, and that of 30 to 60% is expected in a submerged arc method.
In general, since the welding material is easily influenced by
considerably deep melting-in, a larger amount of addition is
required in comparison with the amount of addition upon producing a
clad steel plate. Here, it is assumed that in the case of a clad
steel plate, the melting-in depth is in a range from about 25 to
35%.
[0092] A different point of the clad welding material from the clad
steel plate is that the necessity of bending processes is very
small. Originally, since a cladding process is carried out on the
surface of an article formed into an original shape, it is not
necessary to carry out a bending process. However, in the case of
the clad welding, cladding processes are carried out in a manner so
as to laminate layers, such as a first layer, a second layer and on
the like, so that as the number of layers increases, effects from
the base material dilution are reduced and the resulting components
come to approximate to designed components. In general, a two-layer
cladding process is often carried out, and generally, the thickness
of the first layer is set to about 3 mm, and that of the second
layer is set to 5 to 6 mm. In the case where layers the number of
which is more than two are deposited, the amount of use of the
welding material increases, and the number of cladding processes is
also increased, resulting in high costs; therefore, a
generally-used method carries out two-layer cladding processes.
[0093] As a result of examinations on the respective alloy
components to be added to the welding material, the carbon content
is set to 0.5%.ltoreq.C.ltoreq.2.5%, the chromium content is set to
15%.ltoreq.Cr.ltoreq.45%, and 0.ltoreq.Ni.ltoreq.13%,
0.ltoreq.Mn.ltoreq.10% and 0.ltoreq.Nb+V.ltoreq.8% are set, while
Cu: 7% or less and Mo: 10% or less are set; thus, sufficient
performances can be maintained within these ranges, even when
subjected to melting-in effects.
[0094] Here, B, which gives great influences to the bending process
performances, was set from 0.5% to 4.5%, and Si was set from 2.5%
to 5.5%. In particular, the maximum added amount of Si, which gives
influences to the bending process performances, could be made 1.5%
less than that of U.S. Pat. No. 3,343,576. That is, since the
present developed alloy is not an alloy developed so as to be used
for high-temperature applications of 600.degree. C. or more, it is
not necessary to deposit needle-shaped carbides so that it becomes
possible to reduce the added amount of Si that directly relates to
the precipitation of needle-shaped carbides.
[0095] By appropriately combining four elements, Cr, Si, B and Nb,
it became possible to ensure a bending process performance
(ductility), the target wear-resistant property and
corrosion-resistant property at normal temperature in the present
developed alloy.
[0096] Table 7 shows the hardness and wear-resistant property of
each of various typical alloys so as to be compared with one
another. Each of SS400 and SUS310S stainless steels, high chromium
cast iron and sulfuric acid resistant steel plate was cut out from
a base material, and each of stellite No. 1 and stellite No. 6 was
cladded thereon by a two-layer gas welding method with a thickness
of 5 mm, and each of GL and UF was cladded thereon by a non-gas arc
method as two layers having a thickness of 5 mm.
[0097] The alloy of the wear-resistant steel plate was cladded by a
submerged arc method as one layer with a thickness of about 5 mm.
The base materials of cladded products were SS400, SUS304 and
SUS310S stainless steels, each having a thickness of 9 mm.
TABLE-US-00007 TABLE 7 Comparative table between hardness and
wear-resistant property of various typical alloys Main chemical
component % Applied base Wear Material by weight material Hardness
coefficient SS400 C--Mn--P < 0.050 Material HV160 100 S <
0.050, residual Fe SUS310S C < 0.08, Cr24 to 26, Material HV184
85.0 Ni19 to 22, residual Fe High-chromium C < 3, Cr26 to 30,
Material HV544 to 700 14 to cast iron residual Fe 17.5 Sulfuric
acid C0.04, Si0.1, Mn0.1, Material HV146 105 resistant Cu0.3,
residual Fe steel plate Stellite No. 1 C2.5, Cr32, Ni1.7, Cladding
HV838 8.0 W12, Fe2, residual Co material Gas method Stellite No. 6
C1.2, Cr27, Ni2.7 Cladding HV659 14.0 W4.6, Fe2.4, residual Co
material Gas method GL C5.3, Cr32, residual Fe Cladding HV766 6.0
material UF C5.8, Cr21, Mo6, W2.5, Cladding HV970 2.0 V1.2, Nb6,
residual Fe material
[0098] The present invention has been devised based upon the
above-mentioned findings, and the iron-based corrosion-resistant
and wear-resistant clad welding material contains, all percentages
by weight, C: 0.5 to 2.5%, Si: 2.5 to 5.5%, Mn: 0 to 10% or less,
Cr: 15% to 45%, Ni: 0 to 13%, Cu: 7% or less, Mo: 10% or less, B:
0.5% to 4.5%, and 0.ltoreq.Nb+V.ltoreq.8%, with remaining portions
being composed of iron and incidental impurities.
[0099] In addition to these components, the clad welding material
can include one kind or two or more kinds of Ti: 1.0% or less, Al:
3% or less, rare earth metals: 0.5% or less in total, and N: 0.2%
or less.
[0100] The welding material is provided as a coated arc welding
rod, a flux cored complex wire, a metallic powder or a cast
rod.
[0101] Moreover, the iron-based corrosion-resistant and
wear-resistant alloy of the present invention is a low carbon-high
silicon-high chromium--boron-niobium-type iron-based
corrosion-resistant and wear-resistant alloy that contains, all
percentages by weight, C: 0.5 to 2.5% by weight, Si: 2.5 to 4.5%,
Mn: 0 to 10% or less, Cr: 15% to 31%, Ni: 0 to 16%, Cu: 7% or less,
Mo: 10% or less, B: 0.5% to 3.5%, and 0.ltoreq.Nb+V.ltoreq.8%, and
in this arrangement, within a range of 15%.ltoreq.Cr<27%,
(Si.times.B) 2014/Cr.sup.2+0.083Cr+1.05 is satisfied, within a
range of 27%.ltoreq.Cr.ltoreq.31%,
1.25%.ltoreq.(Si.times.B).ltoreq.6.0% is satisfied, within a range
of 15%.ltoreq.Cr<20%,
(Si.times.B).gtoreq.570/Cr.sup.2-0.066Cr+1.145 is satisfied, and
within a range of 20%.ltoreq.Cr.ltoreq.31%,
(Si.times.B).gtoreq.1.25 is satisfied.
[0102] In addition to these components, the alloy can include one
kind or two or more kinds of Ti: 1.0% or less, Al: 3% or less, rare
earth metals: 0.5% or less in total, and N: 0.2% or less.
[0103] This iron-based corrosion-resistant and wear-resistant alloy
is more specifically a clad welding metal or cast steel that has a
wear-resistant property and a corrosion-resistant property that are
the same as, or superior to those of cobalt-based alloys, stellites
No. 1 and No. 6 that are.
[0104] The functions of the respective elements forming the
material of the present invention and the alloy of the present
invention are explained below:
C: 0.5 to 2.5% (material), 0.5 to 2.0% (alloy)
[0105] In the case of 0.5% or less of the amount of C, the amount
of precipitation of chromium carbides contributing to the
wear-resistant property is lowered. In the case of 3% or more of
the amount of C, (Cr, Fe).sub.7C.sub.3-type carbides are
precipitated as needle-shaped carbides formed into roughened grains
to cause peeling and brittleness of the cladding metal, resulting
in degradation of the processability. In the case of the
wear-resistant steel plate, since bending processability is
required, the carbon content contained in the deposited metal is
preferably set to 2% or less. Determining from the iron-carbon
state diagram, the content 2% or less forms a transition point
where cast iron is converted to cast steel so that the cast steel
becomes richer than the cast iron in its ductility. The clad
welding is influenced by melting-in to the base material metal, and
even when 2.5% of C is added to the alloy material, the carbon
content of the first layer deposited metal is lowered to about 1.5
to 1.9% upon receipt of a base material dilution of 25 to 40%.
Therefore, the amount of carbon to be added to the alloy is set to
2.5% or less even in the maximum.
[0106] Moreover, the amount of carbon contained in the deposited
metal gives influences to the corrosion-resistant property, and the
addition thereof in a range of 0.5% to 3.0% does not cause much
influences to corrosion relating to a 10% hydrochloric acid
solution; however, the addition thereof exceeding 2.0% causes an
abrupt reduction in the corrosion-resistant property against
corrosion caused by a 10% sulfuric acid solution. Although the
amount thereof in a range from 0.5% to 1.5% does not cause any
change in the corrosive weight reduction, an abrupt change occurs
when the amount thereof becomes 2.0%.
[0107] In particular, with respect to a desirable amount of the
carbon addition, the lower limit is preferably set to 0.5% or more,
and determining from the sulfuric acid corrosion-resistant
property, the upper limit is preferably set to 2.0% or less, and is
more preferably set to 2.5% or less even in the maximum, when taken
into consideration effects of the melting-in depths derived from
various kinds of welding methods.
Si: 2.5 to 5.5 (material), 2.5% to 4.5% (alloy)
[0108] Here, Si has a function for preventing oxidation of the
steel. The amount of Si addition of 2.5% or more increases an
oxidation resistance, and the amount of Si addition alone of 5% or
more effectively prevents oxidation in a temperature range up to
1100.degree. C. From the viewpoint of corrosion-resistant property,
Si is effective to the hydrochloric acid corrosion-resistant
property and sulfuric acid corrosion-resistant property, and the
real merit is exerted when it coexists with Cr, Mo and Cu.
[0109] However, a high Si-content causes brittleness of the steel,
and a large amount of addition thereof makes the steel vulnerable
to surface layer peeling, and, in particular, gives adverse effects
to the bending processability of a wear-resistant steel plate;
therefore, the minimum amount of addition was set to 2.5%. The
amount less than this causes degradation of the wear-resistant
property and corrosion-resistant property, and simultaneously gives
adverse effects to the hydrochloric acid corrosion resistance.
[0110] Here, Si exceeding 4.5% causes serious brittleness to the
steel and the subsequent degradation of ductility of the steel,
with the result that slice-shaped peeling occur on the surface
layer face, with cladded portions remaining thereon. Moreover, this
gives adverse effects to the bending processability so that this
value is set as the upper limit value of the maximum amount of
addition. Furthermore, when Si exceeds 4.5%, with the Cr content
being 30% or more, a large amount of needle-shaped chromium
carbides are precipitated to cause brittleness. In particular, with
respect to the amount of Si addition, the lower limit is preferably
set to 2.5% or more, and determining from the sulfuric acid
corrosion-resistant property, the upper limit is preferably set to
5.5% or less even in the maximum, when taken into consideration
effects of the melting-in depths derived from various kinds of
welding methods, and in particular, the upper limit is more
preferably set to 4.5% or less.
[0111] As the Si content is increased with the Cr content being
made constant, the resulting hardened metal becomes brittle in
proportion thereto. Therefore, the Si content is made as low as
possible within the essential range of 2.5%.ltoreq.Si.ltoreq.4.5%
so as to prevent brittleness. Since the wear-resistant property is
lowered in response to the reduction of Si, the lowered
wear-resistant property is recovered by adding B, Nb, V and the
like thereto so as to coexist. In this case, the shapes of borides,
niobium and vanadium carbides need to be formed into a spherical
shape, in the same manner as in spherical graphite grains of
ductile cast iron, so as to physically improve the fracture
toughness of the alloy, and this arrangement forms the best means
for ensuring the ductility of the high Si-containing steel.
Cr: 15% to 45% (material), 15% to 31% (alloy)
[0112] Generally speaking, Cr is very effective to suppress
oxidation of the steel, and contributes to improvements of
high-temperature oxidation resistant property. Here, Cr combines
with carbon to deposit various kinds of chromium carbides to
provide high hardness so that the wear-resistant property of the
steel is improved. However, in order to improve the wear-resistant
property, carbon needs to be combined with Cr to form chromium
carbides, and for this reason, a large amount of carbon should be
added. However, in the case of the amount of carbon addition of
less than 3%, the first layer deposited metal is made to have a
carbon content of about 2% when subjected to the base material
dilution, with the result that a sufficient precipitation of
carbides is not expected to cause degradation of the wear-resistant
property; in contrast, the corrosion resistant property is
improved. In order to improve the corrosion-resistant property of
an iron-based alloy that is the main objective of the present
invention, the precipitation of a large amount of carbides is
suppressed so that the carbides are allowed to remain in the
matrix.
[0113] The corrosion-resistant property is improved by increasing
the amount of Cr, while the wear-resistant property is improved by
adding thereto B, Nb and Si that give no adverse effects to the
corrosion-resistant property, so that the amount of addition of C
is suppressed to 2.5% or less. Moreover, with respect to the alloy
of the present invention, one of the major objectives of the claims
of the present invention is to provide ductility to the high
Si-containing steel, and the Cr content gives great influences to
the ductility of the high Si-containing steel. The correlation
between the Cr content and the product of Si and B has been already
explained in detail.
[0114] Since the clad welding process is carried out on a different
kind of base metal, it is subjected to dilution from the base
material metal. In the present invention, the chromium content of
the first layer deposited metal obtained by receiving the base
material dilution is set to 15% as the minimum value, while it is
also set to 31% as the maximum value. Therefore, since different
dilution rates are caused by base metals depending on various kinds
of different cladding methods, the minimum rate of addition is set
to 15%, and the maximum rate of addition is set to 45%.
[0115] In the case of a high Cr-content of 25% or more, brittle
needle-shaped carbides tend to be precipitated depending on
combinations with S, and in the case where the alloy is subjected
to impact wear due to the application thereof, and calls for
ductility, a low Cr-content steel in which needle-shaped carbides
are hardly precipitated is selected so that, for example, a 15%
chromium steel is desirably used. With respect to desirable Cr
values, the lower limit is set to 15% or more, and the upper limit
is set to 31% or less.
Mn: 0 to 10% (material, alloy)
[0116] Mn and Ni accelerate austenitizing to increase its
stability. The austenite-forming capability of Mn is about half
that of Ni. Mn has an effect for stabilizing the processability of
a clad welding operation. Since the alloy of the present invention
has a high Si-content as its basic composition, ferrites are
contained therein, and in order to maintain the austenite texture,
Mn is added thereto in place of Ni because Ni is expensive. In
particular, a desirable amount of Mn addition is set from 0% to 8%
or less as its upper limit.
Ni: 0 to 13% (material) 0 to 16% (alloy)
[0117] Determining from the purpose of the present invention, a
high amount of Ni addition is not desirable from the viewpoint of
consumption of a rarity-value alloy, and 0% is preferable.
Therefore, Ni is unavoidably used only when the addition thereof is
required for maintaining the wear-resistant property and bending
process ductility. In the case of the Cr content from 23.5% or more
to 31% or less, when the Ni content increases by 3 to 6%, the
bending ductility is improved or the tendency of surface layer face
peeling is reduced so that an effect for improving the Si.times.B
value by 3 points is confirmed. The alloy of the present invention
is applied to refuse burning facilities in many cases, and a high
Ni-content is desirable so as to effectively improve a chlorine gas
corrosion-resistant property. This is also effective for preventing
carburization at high temperatures, and also has an effect for
preventing peeling of a passive-state coat film of Cr in the
application vulnerable to a thermal shock; therefore, a high
Ni-content is desirably applied for use at high temperatures.
[0118] Basically, the alloy texture of the present invention easily
forms a ferrite+austenite mixed texture, and by the use of a joined
addition of Mn and Ni, the texture can be converted into an
austenite texture. For example, in the case where, upon carrying
out a hardened cladding process on an austenite stainless steel
heavily constrained, the present device is subjected to a thermal
shock due to serious temperature changes, a stress tends to appear
on a welding fusion line due to a difference in linear expansion
coefficients from the base material austenite stainless steel to
cause a possibility of peeling when a large amount of ferrites are
contained in the hardened cladding metal. In this case, by adding
Ni thereto, the hardened metal can be changed into an austenite
simple-substance texture so as to be adjusted to the same texture
as that of the base material. For this reason, the maximum amount
of Ni addition is preferably set to 13% or less. If the addition
should be insufficient, Mn may be added so as to be adjusted.
Nb+V: 0% or more, 8% or less (material, alloy)
[0119] Nb has an effect for finely spherizing carbides so that a
physical texture that is hardly subjected to fractures and
brittleness is formed. As has beer described earlier, this exerts
the same effects and functions on carbide shapes as those exerted
by Ca and Mg so as to spherize graphite in the same manner as in
graphite shapes that give influences to the ductility of gray pig
iron and ductile cast iron, as described earlier. Moreover, the
greatest purpose of the addition is that the niobium carbides
themselves have high hardness, that is, about HV2400. In the case
of a low carbon content, for example, C=0.7%, within a range where
no NbC (niobium carbides) is crystallized, high-hardness NbB
(niobium boride, Hv2250) is crystallized in place thereof so that
it becomes possible to prevent degradation of the wear-resistant
property.
[0120] Here, V forms fine carbides, and its forming capability is
located between those of Cr and Mo, and this carbide reaction
provides a tempering resistance and improvements of secondary
hardening by the tempering so that the high-temperature wear
resistance can be improved. Moreover, the resistance against cracks
is improved by softening deformation and heat checking caused by a
temperature rise.
[0121] In the case of such a high Si.times.B value as to cause
peeling and drops-off in the deposited metal in the correlation
formula of Cr content and Si.times.B, that is, in a limited state
where no bending ductility is available, it is not necessarily
required to add these elements. The addition further accelerates
brittleness of the deposited metal. From the viewpoint of
preventing grain interface corrosicn of a 15% low-chromium content
steel, the addition of at least Nb+V.gtoreq.0.5% is preferably
carried out. Therefore, the amount of addition is set to 0% or
more, preferably, to 0.5% or more. However, since the addition of
8% or more in the total saturates the effect thereof, and causes a
possibility of causing brittleness of the cladding metal, the
maximum amount of addition is set to 8% in the total.
B: 0.5% to 4.5% (material, 0.5% to 3.5% (alloy)
[0122] Some of borides to be crystallized in the alloy component
range of the present invention have such shapes as not to
accelerate brittleness of the alloy, and, for example,
Mo.sub.2FeB.sub.2 has a network shape, NbB has an indefinite shape,
and Cr.sub.2B has a plate shape. The respective micro hardnesses
are HV2400, HV2250 and HV1400, which are very hard. Here, Cr.sub.2B
is crystallized with a plate shape, and the resulting crystallized
matters include bigger ones in comparison with needle-shaped
chromium carbides; however, the number of them is small, and most
of them have short lengths and are discontinuous, and although they
have problems with shapes, they cause less possibility of making
the matrix physically brittle as long as they are not continuously
crystallized. This is proved by the fact that, even after a 200R
bending process has been carried out, the resulting hardened metal
is very normal without having even small pieces of peeling. In
order to obtain these effects, the amount of B addition is set from
0.5% in the minimum amount of addition to 3.5% in the maximum
amount of addition, and when taken into consideration effects of
the melting-in depths derived from various kinds of welding
methods, the maximum amount of addition is set to 4.5% or less with
respect to the welding material.
Ti: 1.0% or less (material, alloy)
[0123] Titanium carbides also provide extremely high hardness;
however, titanium impairs welding operability, failing to finish
the bead surface flatly. Therefore, in the same manner as in Nb,
the amount of addition thereof is set to 1% or less in the maximum,
from the viewpoint of preventing grain interface corrosion of a 15%
low-chromium content steel. Al: 3% or less, N: 0.2%, rare earth
metals, such as Ce and Y: 0.5% in the total amount of one kind or
two or more kinds
[0124] The alloy of the present invention may be used for
applications ranging from normal temperature to a high temperature
of 600.degree. C. or more, and needs to be provided with a
high-temperature oxidation resistant property. These elements can
be selectively added so as to mainly improve the oxidation
resistant property at high temperatures. For example, Al improves
the oxidation resistant property at high temperatures, and exerts
its effects in particular in the application atmosphere including
much sulfur gas. In this case, the amount of Ni is preferably made
smaller, while the amount of Al is preferably made greater. When Al
exceeds 3%, an alumina coat film is generated on the cladding
metal, with the result that slag is easily included to impair the
welding operability. In order to obtain the effects stably, the
amount of addition is preferably set to 0.5% or more to 3% or
less.
Mo: 10% or less (material, alloy)
[0125] Mo exerts remarkable effects to sulfuric acid corrosion
resistance and hydrochloric acid corrosion resistance when added so
as to coexist with Cr, Cu and Si, and the resulting
corrosion-resistant property is the same as, or more than that of
stellites No. 1 and No. 6. that are cobalt-based alloys. However,
at present, Mo has become a very expensive alloy, and since an
increase of the amount of addition causes an extreme rise of the
production unit price of the alloy of the present invention, the
minimum amount of addition is set to 0%, and the maximum amount of
addition is set to 10%. In particular, since the amount of addition
of 8% provides a sulfuric acid resistant property that exceeds the
resistant property of the stellite, the further addition causes an
excessive addition so that the maximum amount of addition is set to
10% or less, with the maximum amount of addition being more
preferably set to 8%.
Cu: 7% or less (material, alloy)
[0126] Cu improves the sulfuric acid resistant property and
hydrochloric acid resistant property. In the case where, in a
refuse incinerator, a burning process is suspended, highly
corrosive acid dew-point solutions, such as sulfuric acid and
hydrochloric acid solutions, are generated, and with respect to
these, the addition of Mo alone is not so effective, a composite
addition with Cu is effectively carried out. Moreover, the
composite addition miniaturizes the micro texture, thereby allowing
fine needle-shaped carbides to be easily precipitated in a high
Cr-content and high Si-content state so that the high-temperature
wear-resistant property is improved.
[0127] With respect to the base material metal, irrespective of the
kinds thereof, in particular, for example, easily weldable steels,
such as mild steel, weather-resistant steel plates, sulfuric acid
resistant steel, sea-water resistant steel, various stainless
steels, Mn--Cr austenite steel, nickel alloy steel, chromium alloy
steel and the like, may be used, and from the viewpoints of
suppressing dilution and of ensuring the corrosion-resistant
property and high-temperature oxidation resistant property, those
containing Cr in a range of 9 to 35% and Ni in a range of 0 to 25%
are preferably used.
EFFECTS OF THE INVENTION
[0128] The iron-based corrosion-resistant and wear-resistant metal
is an epoch-making alloy which, although produced as an inexpensive
iron-based alloy, endures sulfuric acid corrosion and hydrochloric
acid corrosion as an alternative metal for expensive cobalt-based
alloy and nickel-based alloy, also has a wear-resistant property
that is the same as, or superior to that of these alloys, and is
applicable as various welding materials, wear-resistant steel
plates and cast steel.
[0129] From the world-wide viewpoint, at present, enormous amounts
of expensive rarity-value alloys, such as cobalt and nickel, have
been consumed as alloys for use as simply wear-resistant clad
welding materials for production facilities, and worn and lost,
dispersion-consumed, and discarded without being recovered in all
over the world. In the future-oriented standpoint, the current
wasteful consumptions of these rarity-value alloys will lead to
lack of resources in the next generations sooner or later, and from
now, effective utilizations of rare alloys and improvements of the
resource-recovering efficiency have to be taken into consideration.
Therefore, from the standpoint of effective utilizations of
resources, the present inventors have proposed the utilization of
silicon that has enormous amounts of deposits on the earth and is
inexpensive since 26 years ago, and have continuously studied its
application to clad welding materials as one of effective
utilizations thereof.
[0130] At that time, an SLCE alloy having added amounts of alloy
elements of C: 5.2%, Si: 12.3% and Cr: 20% (wear coefficient WR=7,
average hardness HV=730) was developed, and a wear-resistant steel
plate was produced. Many of this were supplied to copper refining
factories, paper-manufacturing companies and cement companies, and
were also exported to a paper-manufacturing company in Sweden.
Although this alloy is strong against hydrochloric acid corrosion
and sulfuric acid corrosion, and considerable evaluations were
obtained; however, the alloy was poor in processability in a
bending process or the like, and had a very brittle
characteristic.
[0131] When Si was added to metal as an alloy, brittleness that was
inherent to Si was caused, in particular, in an inexpensive
iron-based alloy, making it very difficult to practically apply
this as a welding material. In particular, this was characterized
by the fact that innumerable cracks were caused in the thickness
direction of the deposited metal. Because of its brittleness,
slice-shaped peeling occur on the surface layer face of the clad
welding metal and lump-shaped drops-off are generated from the base
metal as the content thereof increases. Moreover, in the case of a
wear-resistant steel plate, even upon applying a pressure by using
a press or the like in a distortion removing process, peeling and
drops-off occur, thereby limiting the application thereof to
restricted usages. In the case where applied as a clad welding wire
and a welding rod, even upon application of a slight impact to the
cladded matter, peeling and drops-off occurred in the hardened clad
welding metal.
[0132] After having studied for long years, the present inventors
have given up the idea of applying Si alone, and succeeded in
revising its brittleness by adding elements such as B, Nb and V so
as to coexist therewith; thus, the present invention has been
completed. In this method, although it is not possible to prevent
Si from causing brittleness to an iron-based alloy, by using the
characteristic that, when Si increases, Si forms chromium carbides
in a high chromium-content steel into a needle-shape, niobium that
forms niobium carbides that are miniaturized into spherical shapes
or boron that allows plate-shaped borides having a net-work shape,
an indefinite shape or a plate shape to be crystallized are added
in order to suppress the amount of precipitation of needle-shaped
carbides and also to compensate for the reduced portion; thus, the
brittleness is suppressed and the wear-resistant property is
improved. In particular, Nb is a very effective alloy element as an
alloy that expands the adjusting range of the wear-resistant
property so as to adjust the wear-resistant property.
BEST MODE FOR CARRYING OUT THE INVENTION
[0133] The following description will discuss embodiments of the
present invention.
[0134] Tables 8 to 10 show compositions of deposited metals of
various kinds of wear-resistant steel plates that were produced so
as to obtain a correlation formula between Si.times.B and Cr.
TABLE-US-00008 TABLE 8 Added chemical components (% by weight) to
fused metals of wear-resistant steel plates TP. C Si Ni Cr Mo Nb B
Cu 1 1.5 4.0 3.3 20.0 4.5 2.0 3.0 4.6 2 1.5 3.5 3.3 20.0 4.5 2.0
3.0 4.6 3 1.5 3.5 3.3 20.0 4.5 2.0 2.3 4.6 4 1.5 3.5 3.3 20.0 4.5
3.0 1.6 4.6 5-C 1.5 2.5 3.3 13.0 4.5 4.0 1.0 4.6 6, 19 0.7 2.6 3.3
25.0 4.7 0.5 2.5 4.6 7, 20 0.7 2.5 3.3 27.0 4.6 3.0 1.7 4.5 8 2.5
2.6 3.3 25.0 4.6 6.0 1.0 4.6 9, 22 1.5 3.5 10.0 25.0 4.6 4.0 0.5
4.6 10 0.7 3.6 3.3 27.0 4.6 0.5 2.4 4.5 11 1.4 5.0 3.3 29.0 4.4 0.5
1.7 4.6 12 0.5 4.0 3.6 29.0 4.6 0.5 1.7 4.6 13 1.5 3.5 3.3 30.0 4.6
4.0 0.5 4.6 14 3.0 4.1 3.3 32.0 0 6.0 1.8 3.5 15 0.7 3.7 3.3 26.0
4.6 4.0 1.7 4.5 16 2.0 3.1 3.3 32.0 0 6.0 1.8 3.5 17 1.5 3.6 3.3
31.0 4.6 4.0 1.0 4.6 18 1.5 2.6 3.3 25.0 4.6 0.5 3.0 4.6 18-1 1.5
2.6 0 27.5 4.6 0.5 3.0 4.6 19-1 0.7 2.6 0 27.5 4.6 0.5 2.5 4.6 21
1.5 2.5 0 27.0 4.5 8.1 1.0 4.6 23 1.5 3.5 0 31.0 4.5 2.0 2.4 4.6 24
1.5 2.5 3.3 28.0 4.5 4.0 0.5 4.6 25 1.5 3.5 0 32.0 4.5 2.0 2.3 4.6
26 2.5 3.1 3.3 25.0 0 6.0 1.5 3.5 27 1.5 2.5 3.3 32.0 4.6 4.0 1.0
4.6
TABLE-US-00009 TABLE 9 28 1.5 3.5 3.3 24.0 4.6 6.0 0.5 4.6 Mn8 29
1.5 3.5 3.3 25.0 8.1 6.0 0.5 4.6 30 1.5 3.5 3.3 25.0 4.6 6.0 0.5
6.0 31 2.0 3.5 0 29.0 0 0.5 2.1 4.6 31-1 2.0 3.5 0 31.5 0 0.5 2.1
4.6 32 2.0 3.5 0 29.0 0 2.0 1.6 4.6 32-1 2.0 3.5 0 31.5 0 2.0 1.6
4.6 33 2.0 3.5 0 29.0 0 4.0 1.0 4.6 34 2.0 3.5 0 33.0 0 2.0 1.6 3.5
35AL 1.5 3.5 AL2 23.0 0 4.0 0.5 4.6 36 1.5 4.0 0 25.0 4.5 0.5 2.5
4.6 37 3.0 4.0 0 23.0 0 0.5 2.1 3.5 38 2.0 4.0 0 29.0 0 0.5 2.1 4.6
39 5.5 4.0 0 22.0 0 6.0 0 3.3 40 3.0 4.0 3.3 32.0 0 0.5 1.7 4.6 41
2.0 5.0 3.3 30.0 4.6 0 0 4.6 42 3.0 5.1 3.3 30.0 4.6 0 0 4.6 43 3.0
4.0 0 30.0 0 3.1 1.6 3.5 44 3.0 4.0 0 34.0 0 3.1 1.6 3.5 45 1.5 4.0
9 25.0 4.5 0.5 2.5 4.6 46 1.5 3.5 6 24.0 4.5 0.5 3.0 4.5 47 2.5 3.0
8 25.0 0 0.5 3.0 4.5 48 0.7 3.5 3.3 30.0 4.6 V2.0 1.7 4.6 49 1.5
3.5 3.3 31.0 4.6 V4.0 0.5 4.6 50 0.7 2.5 3.3 27.0 4.6 V2.0 1.7 4.6
51 0.5 4.0 3.3 30.0 0 0 0 4.7 52 1.5 4.0 3.3 30.0 0 0 0 4.7 53 2.5
4.0 3.3 30.0 0 0 0 4.7 54 3.0 4.0 3.3 30.0 Mn4 0 0 4.7 55 1.5 4.0
3.7 36.0 Mn4 0 0 0 56 1.3 4.5 3.7 20.0 Mn3.5 0 0 0 57 1.3 4.5 3.7
20.0 Mn3.6 0.6 1.0 0 58 1.3 4.5 3.7 20.0 Mn3.6 0.5 2.0 0
TABLE-US-00010 TABLE 10 59 1.5 3.5 0 20.0 4.6 V8.0 0.5 4.6 60 1.5
3.5 0 20.0 4.6 V6.0 0.5 4.6 61 0.7 2.5 0 20.0 4.6 V6.0 1.7 4.6 62
2.0 2.6 3.3 25.0 4.6 6.0 1.0 4.6 63 2.0 4.0 3.3 31.0 0 6.0 1.8 4.6
64 2.0 3.2 3.3 25.0 0 6.0 1.5 3.5 65 2.0 4.1 0 24.0 0 0.5 2.1 3.5
66 1.5 2.5 3.3 13.0 4.5 4.0 3.5 4.6 67 1.5 2.5 3.3 18.0 4.5 0.5 3.5
4.6 68 1.5 2.5 3.3 20.0 4.5 0.5 3.0 4.6 69 1.3 4.5 3.7 20.0 Mn3.6
8.0 0 0 70 1.3 4.5 3.7 25.0 Mn3.6 8.0 0 0 71 2.0 4.1 3.3 30.0 0 0 0
4.7 72 1.5 2.5 3.3 26.0 4.5 0.5 2.7 4.6
[0135] The bending processability of each of these wear-resistant
steel plates was examined. The content of Cr contained in the first
layer deposited metal was calculated with a base-material dilution
ratio being set to 25%. As described earlier, the evaluation of the
bending processability of the deposited metal was carried out by
using the following method in which a clad steel plate that was
cladded with deposited metal with a thickness of 5 to 6 mm with a
single cladded layer over the entire surface of each of steel
plates having a size of 9 mm in mass thickness.times.100 mm in
width.times.400 mm in length of SS400, SUS400, SUS304 and SUS310S
was produced, and this was subjected to a bending process by a
press with the hardened metal placed on the inner side. A stellite
No. 1 alloy, which was a target material, was cladded on SS400 with
two layers having a thickness of 5 mm, by a gas welding process.
The length of each sample piece was set to about 200 mm.
[0136] The bending curvature was set to about 200R, and the
flextural ductility was evaluated in the following three-degree
criteria: in the case where no influences were caused on the
hardened metal by the bending and an appropriate bending
performance was obtained without causing any defects, this state
was evaluated as .largecircle., in the case where several
surface-layer peeling and extremely slight cracks occurred on the
surface of the hardened metal, this state was evaluated as , and in
the case where many surface-layer peeling and lamp-shaped cracks
occurred to cause poor toughness, this state was evaluated as . The
results are shown in the following Tables.
TABLE-US-00011 TABLE 11 Influences of Si .times. B to bending
processability of wear-resistant steel plate Amount of Cr contained
in the first-layer fused metal (not the amount of addition, with a
base material dilution ratio being set to 25%) Si .times. B round
off to the nearest Hard- whole Bending Base ness TP C Si Cr Nb
number ductility material HV WR 1 1.5 4.0 15.0 2.0 12 SS 806 2.2 2
1.5 3.5 15.0 2.0 10.5 .largecircle. SS 758 4.0 3 1.5 3.5 15.0 2.0
8.1 .largecircle. SS 746 9.6 4 1.5 3.5 15.0 3.0 5.6 .largecircle.
SS 618 9.1 5-C 1.5 2.5 16.0 4.0 2.5 .largecircle. 310 360 15.0 6
0.7 2.6 19.0 0.5 6.5 .largecircle. SS 615 5.6 7 0.7 2.5 20.0 3.0
4.3 .largecircle. SS 533 11.0 8 2.5 2.6 19.0 6.0 2.6 .largecircle.
SS 680 4.0 9 1.5 3.5 19.0 4.0 1.8 .largecircle. SS 404 11.0 10 0.7
3.6 20.0 0.5 8.6 SS 655 3.3 10-C 27.0 .largecircle. 310 595 4.1 11
1.4 5.0 22.0 0.5 8.5 SS 818 2.0 12 0.5 4.0 22.0 0.5 7.0
.largecircle. SS 563 7.4 13 1.5 3.5 23.0 4.0 1.8 .largecircle. SS
744 9.0 14 3.0 4.1 24.0 6.0 7.4 SS 712 2.0 14-C 30.0 310 747 2.3 15
0.7 3.7 24.0 4.0 6.3 304 662 5.0
TABLE-US-00012 TABLE 12 16 2.0 3.1 24.0 6.0 5.6 .largecircle. SS
624 4.0 16-C 30.0 .tangle-solidup. 310 622 4.8 17 1.5 3.6 23.0 4.0
3.6 .tangle-solidup. SS 780 3.3 17-C 30.0 .largecircle. 310 18 1.5
2.6 25.0 0.5 7.8 .largecircle. 310 482 4.5 18-1 1.5 2.6 25.0 0.5
7.8 304 -- -- 19 0.7 2.6 25.0 0.5 6.5 .largecircle. 310 501 4.1
19-1 0.7 2.6 25.0 0.5 6.5 .tangle-solidup. 304 -- 5.6 20 0.7 2.5
25.0 3.0 4.3 .largecircle. 310 405 12.6 21 1.5 2.5 25.0 8.1 2.5
.largecircle. 304 547 11.0 22 1.5 3.5 25.0 4.0 1.8 .largecircle.
310 358 11.3 23 1.5 3.5 30.0 2.0 8.4 .largecircle. 310 658 3.6 24
1.5 2.5 27.0 4.0 1.3 .largecircle. 310 402 14.0 25 1.5 3.5 30.0 2.0
8.1 .tangle-solidup. 310 665 6.3 26 2.5 3.1 23.0 6.0 4.7
.largecircle. 304 666 3.9 27 1.5 2.5 30.0 4.0 2.5 .largecircle. 310
596 8.7 28 1.5 3.5 23.0 6.0 1.8 .largecircle. 304 483 8.0 29 1.5
3.5 23.0 6.0 1.8 .largecircle. 304 621 9.3 30 1.5 3.5 23.0 6.0 1.8
.largecircle. 304 512 10.0
TABLE-US-00013 TABLE 13 Bending Base TP No C Si Cr Nb Si .times. B
ductility material Hardness WR 31 2.0 3.5 28.0 0.5 7.4
.largecircle. 310 587 4.9 31-1 2.0 3.5 28.0 0.5 7.4 304 -- -- 32
2.0 3.5 28.0 2.0 5.6 .largecircle. 310 551 3.8 32-1 2.0 3.5 28.0
2.0 5.6 .largecircle. 304 -- -- 33 2.0 3.5 28.0 4.0 3.5
.largecircle. 310 504 5.9 34 2.0 3.5 31.0 2.0 5.6 .largecircle. 310
560 5.3 35 1.5 3.5 22.0 4.0 1.8 .largecircle. 304 528 9.3 AL2. 0 36
1.5 4.0 19 0.5 10.0 SS 696 4.0 37 3.0 4.0 24 0.5 8.4 .largecircle.
310 558 5.3 38 2.0 4.0 28 0.5 8.4 .largecircle. 310 699 2.8
.circle-w/dot.39 5.4 4.0 16.0 6.4 0 SS 852 2.0 Base material 310
for use in corrosion test 310 862 2.7 Cr = 23%, SS: bending test 40
3.0 4.0 24.0 0.5 6.8 SS 814 2.4 41 2.0 5.0 23.0 0 0
.tangle-solidup. SS 616 6.3 42 3.0 5.0 23.0 0 0 SS 679 2.5 43 3.0
4.0 27.0 3.0 6.0 304 706 3.0 44 3.0 4.0 30.0 3.0 6.0 304 739
3.0
TABLE-US-00014 TABLE 14 45 1.5 4.0 19.0 0.5 10.0 SS 713 1.8 46 1.5
3.5 22.0 0.5 10.5 304 608 6.7 47 2.5 3.0 23.0 0.5 9.0 304 622 2.8
48 0.7 3.5 23.0 V2.0 6.0 .tangle-solidup. SS 488 16.0 49 1.5 3.5
24.0 V4.0 1.8 .largecircle. SS 569 19.0 50 0.7 2.5 20.0 V2.0 4.3
.largecircle. SS 589 7.4 51 0.5 4.0 27.0 0 0 .largecircle. 304 362
99.0 52 1.5 4.0 27.0 0 0 .largecircle. 304 385 31.0 53 2.5 4.0 27.0
0 0 .largecircle. 304 563 5.8 54 3.0 4.0 27.0 0 0 .largecircle. 304
597 4.1 55 1.5 4.0 36.0 0 0 310 977 4.2 56 1.3 4.5 20.0 0 0
.largecircle. 310 309 77.8 57 1.3 4.5 20.0 0.6 4.5 .largecircle.
310 351 37.3 58 1.3 4.5 20.0 0.6 9.0 .largecircle. 310 427 13.5 59
1.5 3.5 20.0 V8.0 1.8 .largecircle. 310 479 18.7 60 1.5 3.5 20.0
V6.0 1.8 .largecircle. 310 415 22.4 61 0.7 2.5 20.0 V6.0 4.3
.largecircle. 310 368 14.6 62 2.0 2.6 19.0 6.0 2.6 .largecircle. SS
624 6.5
TABLE-US-00015 TABLE 15 63 2.0 4.0 24.0 6.0 7.2 SS 640 3.3 63-1 2.0
4.0 30.0 6.0 7.2 310 649 3.6 64 2.0 3.2 23.0 6.0 4.8 .largecircle.
304 511 12.3 65 2.0 4.1 24.0 0.5 8.6 .largecircle. 310 506 8.8 66
1.5 2.5 16.0 4.0 8.8 .largecircle. 310 583 2.4 67 1.5 2.5 18.0 0.5
8.8 .largecircle. 304 618 4.0 68 1.5 2.5 19.5 0.5 7.6 .largecircle.
304 627 4.8 69 1.3 4.5 21.0 8.0 0 .largecircle. 310 335 17.3 70 1.3
4.5 25.0 8.0 0 .largecircle. 310 362 15.0 71 2.0 4.1 27.0 0 0
.largecircle. 304 407 35.6 72 1.5 2.5 19.5 0.5 6.8 .largecircle.
304 716 6.1
(1) Correlation Between Si.times.B and Cr
[0137] These results are arranged and shown in FIG. 1. In spite of
the fact that the amount of carbon addition was extremely reduced
to 0.5 to 2.0% within an appropriate range in the correlation graph
relating to the product of Si.times.B and Cr content, each of
alloys of No. 2, No. 6, No. 10-C, No. 15, No. 16, 16-C, No. 23, No.
26, No. 32, No. 32-1, No. 33, No. 34, No. 38, No. 66, No. 67, No.
68 and No. 72 had a wear coefficient in a range of 3 to 6, which
indicated that there were many alloys that could ensure a
wear-resistant property that was about two times or more higher
than that of stellite No. 1 and No. 6.
[0138] It is an epoch-making discovery that an wear-resistant
property that is higher than that of high carbon-high chromium
cast-iron-type cladding alloy GL (WR=6), and at present, an
iron-based high-temperature wear-resistant clad welding alloy UR
(WR=2) has been recognized in the world as an alloy having the
highest wear-resistant property; however, alloys N. 6 and No. 38
ensure a wear-resistant property as high as the wear-resistant
property thereof.
[0139] In a tendency of the upper limit curve, within the content
of Cr between about 15% to about 27%, the numeric value of
Si.times.B dropped from about 11.5 to 6, and the numeric value was
saturated at about 6, between Cr=27% or more and Cr=31%. When
Si.times.B exceeds this limit value, the bending performance is
extremely lowered to cause peeling and drops-off in the deposited
metal itself, resulting in serious degradation in the
ductility.
[0140] As the numeric value of Si.times.B became higher, the wear
resistance was improved, and in contrast, as the numeric value of
Si.times.B became lower, the bending performance became better,
while the wear resistance was lowered greatly. In order to improve
the wear resistance, Nb was added thereto.
(2) Effects of Addition of Nb
[0141] With respect to No. 6 alloy having a Cr content of 19%, a
wear coefficient of WR=5.6 was obtained with Si.times.B=6.5 and an
amount of Nb addition of 0.5%, and with respect to No. 62 alloy
with the same Cr content, a wear coefficient of WR=6.5 was obtained
with Si.times.B=2.6 and an amount of Nb addition of 6.0%; thus,
virtually the same wear resistance was obtained. In the case where
Si.times.B became a low value of 2.6, the wear coefficient was
lowered to about 9 to 15; however, upon addition of 6% of Nb, the
wear coefficient could be recovered up to 6.5.
[0142] Thus, Nb exerted capability of positively improving the wear
resistance. In the case where the numeric value of Si.times.B was
set within 1.25 to 4.5, the wear coefficient WR tended to be
lowered to 8 to 15, that is, a seriously poor level, regardless of
the Cr content; however, in contrast, the bending performance was
improved. In order to improve the wear resistance within this
range, the improvement can be obtained by increasing or reducing
the amount of Nb addition within a range of 4 to 8%. In the case
where the numeric value of Si.times.B became 4.5 or more to 11.5 or
less, by adjusting the amount of Nb addition within 0.5 to 4%, the
wear resistance was improved without lowering the bending
ductility, and in the case where the numeric value of Si.times.B
became 4.5 or less, by selecting the amount thereof within a range
from 4 to 8%, the wear resistance was improved without lowering the
bending ductility.
[0143] The bending ductility of No. 10 is ; however, since the
product of Si.times.B is as high as 8.6, the bending ductility can
be changed to .largecircle., by reducing this to about 7. With
respect to No. 17 alloy as well, by reducing the amount of Nb
addition from 4% to 1 to 2%, the bending ductility can be changed
from to .largecircle.. It is found that by adjusting the amount of
Nb addition, as well as by adjusting Si.times.B, within a range
surrounded by the upper and lower limit curves, good bending
ductility and superior wear resistance can be obtained.
(2) Effects of V Serving as a Substitution Element for Nb
[0144] Normally, it has been said that V and Nb exhibit the same
effects as spherical carbide-forming elements; therefore, the
effects of V are examined. In order to examine a difference of
effects given by Nb and V to the wear resistance, a group of Nb
alloys and a group of V alloys are compared with each other. The
group of Nb-added alloys are shown in Table 16, while the group of
V-added alloys are shown in Table 17.
TABLE-US-00016 TABLE 16 Nb-added alloy (Cr: content in the first
layer) Bending Base Alloy C Si Cr Nb Si .times. B ductility
material Hardness WR 7 0.7 2.5 20 3 4.3 .largecircle. SS 533 11.0 9
1.5 3.5 19 4 1.8 .largecircle. SS 404 11.0 20 0.7 2.5 25 3 4.3
.largecircle. 310 405 12.6 29 1.5 3.5 23 6 1.8 .largecircle. 304
621 9.3
TABLE-US-00017 TABLE 17 V-added alloy (Cr: content in the first
layer) Bending Base Alloy C Si Cr Nb Si .times. B ductility
material Hardness WR 48 0.7 3.5 23 2 6.0 .tangle-solidup. SS 488
16.0 49 1.5 3.5 24 4 1.8 .largecircle. SS 589 19.0 50 0.7 2.5 20 2
4.3 .largecircle. SS 589 7.4 59 1.5 3.5 20 8 1.8 .largecircle. 310
479 19.0 60 1.5 3.5 20 6 1.8 .largecircle. 310 415 22.0 61 0.7 2.5
20 6 4.3 .largecircle. 310 368 15.0
[0145] When Nb alloy No. 7 and V alloy No. 50 were compared with
each other, the base material of SS400 was used in both of the
alloys, and Si.times.B=4.3, with the same amounts of addition of C,
Cr and Si being used, and Nb=3% and V=2%. The wear coefficient WR
was 11.0 for the Nb alloy, and 7.4 for the V alloy so that the
V-added alloy was superior in wear resistance to a certain
degree.
[0146] When Nb alloy No. 9 and V alloy No. 49 were compared with
each other. The amounts of the added alloys were all the same, and
the same base material of SS400 was used. When the same amount of
addition was used, that is, Nb=4% and V=4%, and the former had a
wear coefficient WR=11.0 and the latter had a wear coefficient
WR=19.0; thus, there was a difference between the two values.
[0147] In the case of Si.times.B=4.3, V made it possible to improve
the wear resistance better than Nb in spite of the fact that the
amount of V addition was somewhat smaller than that of Nb. In the
case of Si.times.B=1.8, Nb made it possible to improve the wear
resistance overwhelmingly when the amounts of addition were the
same.
[0148] Based upon the comparison tests, it is found that in the
case of Si.times.B=1.8 that is a low level, the addition of Nb is
more effective, while in the case of Si.times.B=4.3 that is a high
level, the addition of V is more effective to improve the wear
resistance even when the amount of V addition is smaller than the
amount of Nb addition. That is, V contributes to improve the wear
resistance in the same manner as in Nb. With respect to the bending
ductility also, the amount of V addition was limited to a maximum
level of 8% in the same manner as in Nb. Moreover, Nb and V may be
added so as to coexist, and the total amount of additions of the
two materials is preferably set to 8% or less.
(3) Effects of Kinds of Base Materials Given to Wear Resistance
[0149] In the case where the content of Cr was in a range from 25%
or more to 31% or less, more of SUS310S base material was used;
however, in the case of 25% or less, since base materials of mild
steel and 304 stainless steel were commonly used and subjected to a
cladding process, it was feared that the differences in the base
materials might cause variations in the wear resistance. The reason
for this is because, with respect to the numeric values of wear
coefficients WR indicating wear resistance, the numeric values
obtained between the stainless steel base material and the mild
steel base material were compared with each other in a mixed
mariner. Although originally, the test should be carried out by
using the same base material, it cannot help but to use this method
because, since the content of chromium in the deposited metal needs
to be varied from 15% to 31%, the adjustment of the content of
chromium in the deposited metal is carried out by utilizing the
melting-in of the base material.
[0150] Table 18 shows effects of kinds of base materials that are
given to wear resistance. Here, No. 6 alloy and No. 19 alloy had
the same amounts of added components, and the kind of the base
material of the former was SS400 and that of the latter was
SUS310S. In the same manner, with respect to No. 7 alloy and No. 20
alloy, that of the former was SS400, and that of the latter was
SUS310S. With respect to No. 9 alloy and No. 22 alloy, that of
former was SS400, and that of the latter was 310S.
TABLE-US-00018 TABLE 18 Effects of differences of base materials
given to wear resistance Kind of base Wear Kind of alloy material
Hardness resistance WR No. 6 SS400 HV615 5.6 No. 19 SUS310S HV501
4.1 No. 7 SS400 HV533 11.0 No. 20 SUS310S HV405 12.6 No. 9 SS400
HV404 11.0 No. 22 SUS310S HV358 11.3
[0151] The factor that was influenced by the differences of the
base materials was the hardness value, and hardly any influences
were given to the wear resistance. Since these differences in wear
coefficient were included within the scope of claims, no problems
were raised. Therefore, it is determined that the wear coefficients
of SS400 and SUS310S may be regarded as the same.
(4) Relationship Between Ni Content and Bending Ductility
[0152] Table 19 shows the relationship between Ni content and
bending processability of deposited metal.
TABLE-US-00019 TABLE 19 Relationship between nickel content of
disposed metal and bending processability Ni content of Difference
Alloy Ni added Base disposed in average Bending number amount
material metal value ductility No. 18 3.3% 310 7.5% to 5.7%
.largecircle. 8.3% No. 18-1 0.0% 304 2.0% to .tangle-solidup. 2.4%
No. 19 3.3% 310 7.5% to 5.7% .largecircle. 8.3% No. 19-1 0.0% 304
2.0% to .tangle-solidup. 2.4% No. 31 0.0% 310 5.0% to 33%
.largecircle. 6.0% No. 31-1 0.0% 304 2.0% to 2.4%
[0153] In the case of Cr content from 23 to 24%, stainless steel
base materials SS400 and SUS304 were used, and in the case of Cr
content of 25% or more, stainless steel SUS310S was used. In the
case of using SS400 mild steel base material, the range of the Ni
content is set about 0.0 to 10%, in the case of using SUS304 base
material, it is set about 2.0 to 12%, and in the case of SUS310
base material, it is set about 5.0 to 16%.
[0154] In the case of Cr content from 23.5% or more to 31% or less,
when the Ni content is increased by about 3 to 6%, the bending
ductility tends to be improved by about 3 points in the Si.times.B
value; however, alloys causing cracks also exist in a mixed manner,
and in a range surrounded by this area, combinations of various
elements should be examined carefully, and alloy structures should
be made carefully. In the case of Cr content of 23.5% or less, the
deposited metal causes fractures even when the Ni content becomes 7
to 8%, failing to obtain a fracture-preventive effect by the Ni
addition.
(5) Correlation Formula Between Si.times.B and Cr Content
[0155] 1) Upper limit curve under which peeling and drops-off of
hardened metal are caused
[0156] 15% Cr 27%
Si.times.B.ltoreq.2014/Cr.sup.2+0.083Cr+1.05 (1)
[0157] 27%.ltoreq.Cr.ltoreq.31%
1.25%.ltoreq.Si.times.B.ltoreq.6.0% (2)
2) Lower limit curve that can keep The wear resistance WR of
hardened metal at the lowest value of 15
[0158] 15%.ltoreq.Cr.ltoreq.20.0%
Si.times.B=570/Cr.sup.2-0.066Cr+1.145 (3)
[0159] 20% Cr 31%
Si.times.B.gtoreq.1.25 (4)
3) In the case where the Ni content of the deposited metal is
increased by 3 to 6%, with respect to the upper limit curve
relating to peeling and drops-off, formula (I) is parallel-shifted
upward by a portion corresponding to Si.times.B=3 points, in the
range from 23.5%.ltoreq.Cr.ltoreq.31% so that the range that hardly
causes cracks is expanded.
(6) Evaluation of Corrosion-Resistant Property of Clad Welding
Material
[0160] As described earlier, the corrosion-resistant property of
the alloy of the present invention has been developed for achieving
that of Worthite alloy as its target.
[0161] The chemical components thereof are explained as follows:
C<0.07%, Cr20%, Ni25%, Si3.5%, Mo3.0%, Cu2.0%
[0162] In addition to these, DIN8556, E20.25.5LCuR26 may be used as
welding materials. The typical chemical components are explained as
follows: C0.025%, Mn2%, Si0.4%, Cr21%, Ni25%, Mo5%, Cu1.8%, Nb0.1%,
No. 08%
[0163] Both of the alloys, which have a high Ni content and are
structural materials having a corrosion-resistant property, are not
used as wear-resistant metals. The latter is a welding material;
however, since it has a low Si content, that is, Si=0.4%, with an
extremely low carbon content, it cannot be used as a wear-resistant
metal. Therefore, the present inventors have set a carbon content
required for the wear-resistant metal in a range of 0.5% or more to
2.0% or less. Moreover, since the development of a Si-containing
alloy is a main objective of the present developed alloy, the SL
content is set in a range of 2.5%.ltoreq.Si.ltoreq.5.5%. Moreover,
in order to improve the wear-resistant property, Nb and V, which
are carbide-forming elements, are added thereto, and B, which forms
a boride that gives high hardness, is also added so as to
co-exist.
[0164] An alloy-designing process was carried out so as to modify
two kinds of corrosion-resistant alloys into a wear-resistant
alloy, and also so as not to impair corrosion-resistant properties
that the two kinds of the alloys originally had. Since DIN8556
welding rods are cladded on mild steel and low alloy steel and used
as joining materials and corrosion-resistant materials for plants
in phosphate, sulfate, acetate, salt and sea water environments;
however, these are not wear-resistant materials, and used for a
cladding operation on mechanical structural members.
[0165] Alloys, which have a corrosion-resistant property that is
superior to that of stellite No. 1 and stellite No. 6 alloys in the
range of the graph capable of ensuring proper bending ductility and
abrasion-resistant property, are invented. Comparison tests for
corrosion-resistant property were carried out on these alloys. In
the corrosion tests, the amount of corrosive reduction of each of
these, when immersed into each of a 10% sulfuric acid aqueous
solution, a 5% ferrous chloride aqueous solution, a 10%
hydrochloric acid aqueous solution and a 48% caustic soda aqueous
solution for 480 hours continuously, was measured, and based upon
the resulting differences, the superiority and inferiority of the
corrosion-resistant property were compared.
[0166] With respect to SS400 mild steel, SUS310S and SUS304
stainless steels, high-chromium cast iron, and sulfuric acid
resistant steel, cut pieces were obtained from a plate member of
each of these so that test pieces were prepared. All the other
materials were cladding materials, and cladded on SUS310S steel
with a thickness of 5 mm so that test pieces were prepared. The
cladding test pieces were subjected to a corrosive reduction
including the base material SUS310S, and using the hardened metal
obtained by sampling the hardened metal itself for the corrosion
test made it impossible to compare the samples with each other
because many cracks occurred in some of alloys; therefore, on the
assumption of an actual machine plant, a corrosion test including
the base material was carried out.
[0167] The size of the test piece was set to 50.times.50 mm, with
its thickness being set to 9 mm. The thickness of the hardened
metal was about 5 mm, and the base material face was ground based
upon the hardened metal face so that a thickness of 9 mm was
maintained. The entire surface area of the test piece was 68
cm.sup.2. The corrosive reduction per unit area was supposed to be
indicated; however, since a different kind of metal SUS310S was
included in the base metals, the total corrosive reduction measured
values, as they are, are displayed so as to be compared.
[0168] The reason that SUS310S is selected as one of the base
metals is because a large amount of chromium can be transferred to
the deposited metal as a melting-in portion from the base metal.
With this arrangement, the amount of addition of Cr to the
deposited metal can be easily adjusted. The amount of chromium
content in SUS304 is as small as 18%, and the amount of chromium
content in SUS310S is 25% so that this allows a large amount of
chromium to be obtained from the base material metal. Moreover,
SUS310S is also superior in corrosion-resistant property. By the
effect of the melting-in portion, the Cr content of the single
cladded-layer deposited metal becomes the same as, or higher than
the added component, with Cr being picked up from the SUS310S base
material metal. The melting-in rate of the base material was set to
25%.
[0169] In the correlation drawing between Si.times.B and Cr content
in the first layer deposited metal, alloys, located in the
surrounded area, were properly selected, and corrosion tests were
carried out thereon. Those alloys that were subjected to the
corrosion tests were surrounded by .largecircle. so as to be easily
recognized. Upon using in a high temperature range of 800.degree.
C., heat resistant stainless steel base materials, such as SUS310
and SUS3105, are selected, and plate members to be used as heat
resistant materials used from the proximity of room temperature to
800.degree. C., stainless steels, such as SUS304 and SUS316, are
mainly used. Therefore, determining from the amount of addition of
chromium, the Cr content of the first layer deposited metal is
assumed to be in a range from about 23 to 30%. In the case where
the Cr content less than this level, mild steel or esten steel is
selected as the base material and the chromium content tends to be
lowered in most cases. In the case where the corrosion-resistant
property is required, at least stainless steel is adopted as the
base material metal, and steels, such as 304, 316 and 316L, are
mainly used. Therefore, the corrosion tests were carried out mainly
centered on the Cr content in a range of about 23 to 30%; however,
16% chromium steel was also examined since examinations on
low-chromium steels were partially required.
[0170] The values close to the upper limit value of the amount of
addition of each of alloy components, such as Ni, Mn, Mo and Cu,
were selected in the alloys of the present invention, that is, No.
5 alloy was selected in the case of a low Cr content of 16%, Nos.
10 and 17 alloys were selected in the case of Cr contents of 27%
and 30% with valuable Mo contained therein, Nos. 16, 14 and 39
alloys were selected in the case of varying Cr contents of 2%, 3%
and 5.4% with no Mo contained therein, No. 22 alloy was selected in
the case of a 10% Ni content, No. 28 alloy was selected in the case
of a 8% Mn content, No. 29 alloy was selected in the case of a 8%
Mo content, and No. 30 alloy was selected in the case of a 6% Cu
content, and differences in corrosion were examined. The results of
the examination are collectively shown in Tables 20 to 22.
TABLE-US-00020 TABLE 20 Various alloy chemical components used for
corrosion resistance comparisons Deposited chemical components (Cr,
Ni: Content, Others: Amounts of addition) Charac- TP C Si Mo Cr Ni
B Nb Cu Si .times. B teristics 5-C 1.5 2.5 4.5 16 7.5 1.0 4.0 4.6
2.5 Low chromium 10-C 0.7 3.6 4.6 27 7.5 2.4 0.5 4.5 8.6 with Mo
17-C 1.5 3.6 4.6 30 7.5 1.0 4.0 4.6 3.6 with Mo 16-C 2.0 3.1 0 30
7.5 1.8 6.0 3.5 5.6 without Mo 14-C 3.0 4.1 0 30 7.5 1.8 6.0 3.5
7.4 without Mo No. 39 5.4 4.0 0 23 5.0 0 6.0 3.3 0 without Mo 22-C
1.5 3.5 4.6 25 12.5 0.5 4.0 4.6 1.8 High Ni 28-C 1.5 3.5 4.6 24 7.5
0.5 6.0 4.6 1.8 High Mn Mn8 29-C 1.5 3.5 8.1 25 7.5 0.5 6.0 4.6 1.8
High Mo 30-C 1.5 3.5 4.6 25 7.5 0.5 6.0 6.0 1.8 High Cu
TABLE-US-00021 TABLE 21 Results of comparison tests for
corrosion-resistant property of various alloys 5% ferrous 10%
sulfuric chloride Material Kind of steels acid solution solution
SS400 Mild steel 62.2 g 5.27 g SUS304 Stainless 9.6 g 0.105 g steel
SUS310S Stainless 0.1 g 0.01 g steel Sulfuric acid Esten-1 steel
127.2 g 4.16 g resistant steel plate High chromium Wear-resistant
138.9 g 26.3 g cast iron cast iron GL Clad welding 48.3 g 8.37 g
rod UF Clad welding 17.4 g 4.93 g rod Stellite No. 1 Clad welding
0.64 g 0.09 g bare rod Stellite No. 6 Clad welding 0.58 g 0.02 g
bare rod No. 5-C alloy Low Cr 0.17 g 0.116 g No. 10-C alloy with Mo
0.56 g 0.037 g No. 17-C alloy with Mo 0.55 g 0.210 g No. 16-C alloy
without Mo 2.60 g 0.363 g No. 14-C alloy without Mo 2.80 g 1.404 g
No. 39 alloy without Mo 20.00 g 6.400 g No. 22-C alloy High Ni 0.03
g 0.155 g No. 28-C alloy High Mn 0.06 g 1.486 g No. 29-C alloy High
Mo 0.03 g 0.034 g No. 30-C alloy High Cu 0.04 g 0.068 g
TABLE-US-00022 TABLE 22 Corrosion test against 10% hydrochloric
acid aqueous solution and 48% caustic soda aqueous solution 48%
caustic 10% hydrochloric acid soda aqueous Material solution
solution SS400 28.00 g 0.0210 g SUS304 2.84 g 0.0008 g SUS310S 0.11
g 0.0006 g Sulfuric acid 2.42 g 0.0183 g resistant steel plate High
chromium 101.39 g 0.0110 g cast iron GL 32.58 g 0.0110 g UF 25.54 g
0.0040 g Stellite No. 1 0.11 g increased weight Stellite No. 6 0.14
g increased weight No. 10-C alloy with Mo 0.075 g 0.0023 g No. 17-C
alloy with Mo 1.151 g 0.0130 g No. 16-C alloy without Mo 1.080 g
0.0090 g No. 14-C alloy without Mo 0.277 g 0.0194 g No. 39 alloy
without Mo 0.435 g 0.0210 g
[0171] Since SUS310S was used as all the base materials for the
corrosion tests, Cr was picked up from the base material so that
the Cr content was increased. For example, in No. 10 alloy, the Cr
content was 20% in the bending ductility test in the graph;
however, in the corrosion test piece, the content was increased to
Cr=27%. Here, since Cr and Ni were of course picked up from the
SUS310S base material, the contents of Cr and Ni of the deposited
metal were increased. With respect to corrosion test numbers,
following the numbered numeric value, C was put by taking the first
letter C of "Corrosion". Therefore, all the alloys relating to the
corrosion tests were indicated as alloys-C.
(7) Concerning 10% Sulfuric Acid Corrosion (Relating to
Alloys-C)
[0172] Comparisons of corrosive reductions caused by immersing them
in a 10% sulfuric acid solution for 480 hours showed that No. 5,
No. 22, No. 28, No. 29 and No. 30 alloys exerted a very good
corrosion-resistant property in comparison with that of stellites
No. 1 and No. 6. The wear coefficient WR indicating the wear
resistance was in a range of 8 to 10, which was the same level of
the wear resistance as that of stellite No. 1. Here, No. 10 and No.
17 alloys exerted the same level of the corrosion-resistant
property as that of stellite, and the wear resistance thereof was
the highest among the alloys of the present invention, with a wear
coefficient WR of 3.3.
[0173] It was remarkable that these iron-based alloys exerted
superior results in comparison with those of stellite alloys that
are cobalt-based alloys; therefore, in order to confirm the
reliability of the results, a 40% sulfuric acid solution
corresponding to a concentration exerting a severe corrosive
property was selected, and this solution was heated to a range from
50 to 70.degree. C. so that by immersing test pieces into this
solution continuously four hours, the resulting amounts of
corrosive reductions were compared with one another. Since it was
difficult to carry out corrosion tests again over 480 hours,
accelerating tests for a short period of time were carried out as
simple confirming tests. Table 23 shows the results of the
tests.
TABLE-US-00023 TABLE 23 Results of 40% sulfuric acid solution-50 to
70.degree. C. accelerating corrosion tests (Test time: 4 H) Various
alloy Feature of alloy Corrosive reduction Stellite No. 1 C = 2.5%,
1.946 g cobalt-based alloy Stellite No. 6 C = 1.2%, 1.667 g
cobalt-based alloy No. 5-C Low Cr steel 1.304 g No. 22-C 12.5% high
Ni added 1.768 g steel No. 28-C 8% high Mn added 1.687 g steel No.
29-C 8% high Mo added 1.679 g steel No. 30-C 6% high Cu added 2.331
g steel
[0174] In the accelerating tests also, the corrosion-resistant
property against sulfuric acid that was the same as, or higher than
those of stellites No. 1 and No. 6 was exerted. In particular, No.
5 alloy was very good, and although No. 30 alloy was slightly
inferior to stellite, there was no big difference, and considered
to be equivalent thereto.
[0175] Next, the effects of the carbon content exerted on corrosion
resistance against sulfuric acid were examined. Tables 24 and 25
show the results of the examination.
TABLE-US-00024 TABLE 24 Effects of carbon content exerted on
corrosion resistance against sulfuric acid Alloy No. C Si Cr Ni Mo
Cu B 12-C 0.5 4.0 29 3.6 4.6 4.6 1.7 10-C 0.7 3.6 27 3.3 4.6 4.5
2.4 17-C 1.5 3.6 31 3.3 4.6 4.6 1.0 A 2.0 3.0 30 3.3 4.6 4.6 0 B
2.5 5.1 30 3.3 4.6 4.6 0 C 3.0 5.2 30 3.3 4.6 4.6 0
TABLE-US-00025 TABLE 25 Comparison of immersion tests for 480 hours
Amount of 10% carbon 10% sulfuric hydrochloric TP No addition acid
solution acid solution 12-C 0.50 0.5925 0.0941 10-C 0.74 0.5608
0.0744 17-C 1.5 0.5515 1.1507 A 2.0 0.8425 0.4529 B 2.5 1.4840
0.1062 C 3.0 1.3470 0.1058
[0176] In a range of carbon content from 0.5%.ltoreq.C.ltoreq.3.0%,
the correlation to the corrosion resistance showed that the
sulfuric acid corrosion was easily influenced by the carbon
content, and in the case of 2% or more, the corrosion resistance
against sulfuric acid tended to deteriorate. It is determined that
boron gives no influences to sulfuric acid corrosion. Therefore,
with respect to applications vulnerable to sulfuric acid corrosion,
the amount of carbon addition should be set to 2% or less.
[0177] With respect to sulfuric acid corrosion, conventionally,
iron-based wear-resistant metals are considered to be inapplicable;
however, an iron-based alloy, which is a corrosion-resistant and
wear-resistant material, is superior to stellites No. 1 and No. 6
containing 50 to 65% of expensive cobalt, and has the same as, or
higher than that of No. 1 in wear resistance, has been invented.
From the world-wide point of view, consuming the stellite alloy
containing a large amount of cobalt having a rarity value for a
simple wear-resistant purpose and for purposes incapable of
recovering resources is wasteful use of effective resources;
therefore, the alloy of the present invention should be used as an
alternative metal for these from now on.
(8) Concerning Hydrochloric Acid Corrosion
[0178] With respect to hydrochloric acid corrosion, No. 29 alloy,
No. 10 alloy and No. 30 alloy were superior to the stellite alloy,
and in particular, in the corrosion-resistant tests against 10%
hydrochloric acid solution, No. 10 alloy was superior to stellites
No. 1 and No. 6, and it is important to use No. 10 alloy for the
purpose of corrosion resistance against hydrochloric acid.
[0179] The effects of the carbon content exerted on corrosion
resistance against hydrochloric acid were examined. With respect to
the corrosion resistance against hydrochloric acid, only the
numeric value of No. 17 alloy exhibited a corrosive reduction about
10 times as high as those of the other alloys; however, no big
differences were seen on the other alloys, with no effects being
caused on the deposited metal by the carbon content. Certainly,
stellite No. 1 had a tendency of being stronger in the corrosion
resistance against hydrochloric acid than stellite No. 6 having a
smaller carbon content, and different from the sulfuric acid
corrosion, the corrosion resistance against hydrochloric acid is
not affected by the amount of carbon addition.
[0180] In order to obtain the corrosion resistance as high as that
of the stellite, an addition of expensive Mo is required. However,
in recent years, a unit price of Mo alloy has abnormally risen,
with the result that the addition of a large amount of this causes
serious effects to the alloy cost, and might reduce the merit of
using an inexpensive iron-based alloy. Consequently, the present
inventors try not to find a corrosion-resistant property as high as
the stellite, but to simultaneously invent an alloy that is
superior in the corrosion-resistant property in comparison with
mutually the same iron-based alloys. Those alloys are No. 16 and
No. 14 alloys.
[0181] In comparison with high chromium cast iron produced by iron
cast, No. 16 alloy exhibited a corrosion-resistant property about
54 times higher with respect to 10% sulfuric acid solution, about
72 times higher with respect to 5% ferrous chloride solution, and
about 94 times higher with respect to 10% hydrochloric acid
solution. Here, No. 14 alloy exhibited virtually the same tendency.
In comparison with high carbon-high chromium cast-iron-type welding
alloy GL, No. 16 alloy exhibited a superior corrosion-resistant
property about 19 times higher with respect to 10% sulfuric acid
solution, and about 23 times higher with respect to 5% ferrous
chloride solution; thus, it has a superior corrosion-resistant
property in comparison with conventionally used high-chromium
cast-iron-type alloys, and is proved to be sufficiently applicable
to corrosion-resistant and wear-resistant purposes as the
iron-based alloy.
EXAMPLES
[0182] The following description will discuss examples, and in
comparison with comparative examples, the effects of the present
invention will be clarified. In recent years, along with the price
hike of petroleum, import costs of coals have risen in association
therewith, and our country, which is lacking resources, is at
present worried about fuel price hikes. In particular, in coal
thermal plants, iron works and cement factories where enormous
amounts of coals are used, the amount of use of expensive good
coals is reduced, while the use of mixed coals with inexpensive
coarse coals is increased. Among the coarse coals, coals having a
great amount of sulfur content are present, and when these are
stacked in stock yards outside, they get wet in rain, and have an
increase in their moisture content, with the result that sulfur
components contained in the coal come to react with water to
produce diluted sulfuric acid.
[0183] In one example, a troughing conveyer is used in processes to
introduce coals into a crusher, and since the bottom plate liner
thereof is conventionally subjected to wear, a wear-resistant steel
plate cladded with a high-carbon-high chromium cast-iron-type alloy
has been used for this purpose. The chemical component thereof is a
GL alloy that has been described before. Here, since the start of
using mixed coals having a large amount of sulfur content, the
service life thereof, which has been long since it has been
subjected to simple wear, is shortened to only about 2.5 months due
to corrosion caused by diluted sulfuric acid. When the developed
alloy of the present invention was used as the bottom plate liner,
neither corrosion nor wear has occurred therein, even after a lapse
of one year, and the bottom plate liner has been continuously
used.
[0184] In order to prove deterioration of high Si-containing steel,
bead photographs were taken after the above-mentioned bending
process. As a typical example, No. 55 alloy exhibited deterioration
that was a defect of high Si-content, with the result that peeling
were generated over the entire bead surface that had been pressed
down by a press. However, in the case of No. 10-C alloy
corresponding to the alloy of the present invention, its toughness
was proved in a bending process with 200R.
[0185] With respect to the amount of precipitation of chromium
carbide depending on differences in chromium content, No. 5
(Cr=16%) low-chromium content steel and No. 10-C (Cr=27%)
high-chromium content steel were compared with each other in their
micro textures. As shown in Photograph 1 of FIG. 3 and FIG. 4, in
the 10-C high-chromium content alloy, plate-shaped crystals of
coarse bulky chromium borate (Cr.sub.2B) were produced, while no
crystals were seen in No. 5 alloy. Therefore, a low-chromium steel
may be used for applications subjected to heavy impact wear, while
a high-chromium steel may be used for applications subjected to
only light impact wear.
BRIEF DESCRIPTIONS OF THE DRAWINGS
[0186] FIG. 1 is a graph that shows effects of Si.times.B amount
and Cr amount exerted on bending processability.
[0187] FIG. 2 includes photographs relating to alloy evaluations,
and photograph 1 is a microscopic photograph showing a
needle-shaped texture of a conventional alloy, and photograph 2 is
a photograph of a sample cross section indicating bent cracks of
the conventional alloy.
[0188] FIG. 3 includes photographs, and photograph 1 is a
microscopic photograph showing a texture of alloy No. 10-C of the
present invention, and photograph 2 is a photograph taken after a
bent-crack test.
[0189] FIG. 4 is a microscopic photograph showing a texture of
alloy No. 5 of the present invention.
* * * * *