U.S. patent application number 11/912829 was filed with the patent office on 2008-10-16 for powder-metallurgically produced, wear-resistant material.
This patent application is currently assigned to KOPPERN ENTWICKLUNGS GMBH & CO. KG. Invention is credited to Hans Berns, Andreas Packeisen, Werner Theisen.
Application Number | 20080253919 11/912829 |
Document ID | / |
Family ID | 36088287 |
Filed Date | 2008-10-16 |
United States Patent
Application |
20080253919 |
Kind Code |
A1 |
Theisen; Werner ; et
al. |
October 16, 2008 |
Powder-Metallurgically Produced, Wear-Resistant Material
Abstract
A wear-resistant material comprising an alloy that contains:
1.5-5.5 wt. % carbon, 0.1-2.0 wt. % silicon, max. 2.0 wt. %
manganese, 3.5-30.0 wt. % chromium, 0.3-10 wt. % molybdenum, 0-10
wt. % tungsten, 0.1-30 wt. % vanadium, 0-12 wt. % niobium, 0.1-12
wt. % titanium and 1.3-3.5 wt. % nickel, the remainder being
comprised of iron and production-related impurities, whereby the
carbon content fulfils the following condition: CAlloy [w
%]=S1+S2+S3 where S1=(Nb+2(Ti+V-0.9))/a, S2=(Mo+W/2+Cr-b)/5,
S3=c+(TH-900)0.0025, where 7<a<9, 6<b<8,
0.3<c<0.5 and 900.degree. C.<TH<1,220.degree. C. Also.
method for producing the wear-resistant material and to uses of the
material.
Inventors: |
Theisen; Werner; (Hattingen,
DE) ; Packeisen; Andreas; (Gladbeck, DE) ;
Berns; Hans; (Bochum, DE) |
Correspondence
Address: |
MARSHALL, GERSTEIN & BORUN LLP
233 S. WACKER DRIVE, SUITE 6300, SEARS TOWER
CHICAGO
IL
60606
US
|
Assignee: |
KOPPERN ENTWICKLUNGS GMBH & CO.
KG
Hattingen
DE
|
Family ID: |
36088287 |
Appl. No.: |
11/912829 |
Filed: |
May 2, 2006 |
PCT Filed: |
May 2, 2006 |
PCT NO: |
PCT/EP2006/004086 |
371 Date: |
June 3, 2008 |
Current U.S.
Class: |
420/12 ; 419/42;
420/585 |
Current CPC
Class: |
C22C 30/00 20130101;
C22C 38/56 20130101; C22C 38/52 20130101; B22F 3/02 20130101; B22F
9/08 20130101; B22F 3/20 20130101; B22F 3/17 20130101; B22F 3/02
20130101; B22F 3/04 20130101; B22F 3/15 20130101; Y10T 428/12
20150115; B22F 2998/10 20130101; B22F 3/10 20130101; B22F 2999/00
20130101; C22C 38/001 20130101; C22C 38/46 20130101; C22C 38/58
20130101; C22C 38/44 20130101; C22C 38/02 20130101; C22C 38/48
20130101; C22C 33/0257 20130101; C22C 38/34 20130101; B22F 2999/00
20130101; C22C 33/0285 20130101; B22F 2998/10 20130101; C22C 38/50
20130101 |
Class at
Publication: |
420/12 ; 420/585;
419/42 |
International
Class: |
C22C 38/36 20060101
C22C038/36; B22F 3/12 20060101 B22F003/12; B22F 3/15 20060101
B22F003/15 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 29, 2005 |
DE |
10 2005 202 081.8 |
Claims
1-32. (canceled)
33. Wear-resistant, powder-metallurgically produced material
comprising an alloy that contains: TABLE-US-00002 1.5-5.5 wt. %
carbon 0.1-2.0 wt. % silicon max. 2.0 wt. % manganese 3.5-30.0 wt.
% chromium 0.3-10 wt. % molybdenum 0-10 wt. % tungsten 0.1-30 wt. %
vanadium 0-12 wt. % niobium 0.1-12 wt. % titanium 1.3-3.5 wt. %
nickel 1-6 wt. % cobalt 0.3-3.5 wt. % nitrogen
with the remainder being comprised of iron and production-related
impurities, wherein the carbon content fulfils the following
condition: CAlloy [w %]=S1+S2+S3 where: S1=(Nb+2(Ti+V-0.9))/a
S2=(Mo+W/2+Cr-b)/5 S3=c+(TH-900)0.0025 wherein 7<a<9
6<b<8 0.3<c<0.5 900.degree. C.<TH<1,220.degree.
C.
34. Wear-resistant material according to claim 32, wherein the
content of vanadium is less than 11.5 wt. %.
35. Wear-resistant material according to claim 32 wherein the alloy
comprises: TABLE-US-00003 2.0-2.5 wt. % carbon max. 1.0 wt. %
silicon max. 0.6 wt. % manganese 12.0-14.0 wt. % chromium 1.0-2.0
wt. % molybdenum 1.1-4.2 wt. % vanadium 2.0-3.5 wt. % nickel
1.0-6.0 wt. % cobalt 0.3-3.5 wt. % nitrogen.
36. Wear-resistant material according to claim 32, wherein the
nickel content is between 1.5 and 3.0 wt. %.
37. Wear-resistant material according to claim 32, wherein the
nickel content is between 1.3 and 2.0 wt. %.
38. Wear-resistant material according to claim 32, wherein the
nickel content is between 2.0 and 3.5 wt. %.
39. Wear-resistant material according to claim 32, wherein the
alloy additionally has 1-6 wt. % Co. CAlloy [w %]=S1+S2K+S3 is
fulfilled, wherein S2K=(Mo+W/2+Cr-b-12)/5 with 6<b<8 and
Cr>12.
40. Method for producing a wear-resistant material according to
claim 32, wherein a melt is produced, and then the melt is further
processed by means of one of the following steps: Atomization of
the melt into a powder; Spray compaction of the melt; and Casting
the melt into a semi-finished product, and processing the
semi-finished product for producing power chips.
41. Method according to claim 39, wherein the powder is compacted
into one of a semi-finished product or end product.
42. Method according to claim 40, wherein the compacting is
selected from the group comprising: cold isostatic pressing,
uniaxial pressing, extrusion, powder forging, hot isostatic
pressing, diffusion alloying, and sintering.
43. Method according to claim 39, wherein the powder is further
processed by means of thermal injection.
44. Method according to claim 40, wherein one of a semi-finished
product or an end product is heated to the hardening temperature
and subsequently one of quenched or cooled.
45. Method according to claim 43, wherein quenching is selected
from the group comprising: quenching in an oil bath, salt bath or
polymer bath, quenching in a fluidized bed or drizzle, and low and
high pressure gas quenching.
46. Method according to claim 43, wherein one of a semi-finished
product or end product is cooled from the hardening temperature by
one of the following steps: cooling in slightly moving air, cooling
in static air, oven cooling with a standard atmosphere or inert
gas, and cooling in an HIP system.
47. Method according to claim 43, wherein the cooling is continuous
and is interrupted by isothermal maintenance.
48. Method according to claim 43, wherein after the cooling from
the hardening temperature, performing the step of tempering in the
temperature range from 150-750.degree. C. one or more times.
49. The method of production of one of solid or hollow rolls, solid
or segmented rings which are arranged on solid or hollow roll
bodies, and thick-walled or compact components, comprising forming
the one of solid or hallow rolls, solid or segmented rings, and
thick-walled or compact components from the wear-resistant
materials of claim 32.
50. The method of claim 48 wherein the solid or segmented rings are
arranged on one of solid or hollow roll bodies by being shrunk
on.
51. Powder for the production of a wear-resistant material,
comprising: TABLE-US-00004 1.5-5.5 wt. % carbon 0.1-2.0 wt. %
silicon max. 2.0 wt. % manganese 3.5-30.0 wt. % chromium 0.3-10 wt.
% molybdenum 0-10 wt. % tungsten 0.1-30 wt. % vanadium 0-12 wt. %
niobium 0.1-12 wt. % titanium 1.3-3.5 wt. % nickel 1-6 wt. % cobalt
0.3-3.5 wt. % nitrogen
with the remainder being comprised of iron and production-related
impurities, wherein the carbon content fulfils the following
condition: CAlloy [w %]=S1+S2+S3 where: S1=(Nb+2(Ti+V-0.9))/a
S2=(Mo+W/2+Cr-b)/5 S3=c+(TH-900)0.0025 wherein 7<a<9
6<b<8 0.3<c<0.5 900.degree. C.<TH<1,220.degree.
C.
52. The method of production of a semi-finished product, comprising
forming a semi-finished product from the powder according to claim
50.
53. The method according to claim 51, where the semi-finished
product is produced by spray compaction.
54. The method of production of layer element of composite
components, comprising forming the powder according to claim 50, in
one of its powder form or as a semi-finished product, into a layer
element of composite components.
55. The method of production of hard material metal matrix
composite elements, comprising forming the power according to claim
50 into a matrix powder for hard material metal matrix composite
elements.
56. The wear-resistant material according to claim 33, wherein the
content of the vanadium is less than 9.5 wt. %.
57. The wear-resistant material according to claim 33, wherein the
content of the vanadium is less than 6.0 wt. %.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application claims the benefit of priority of
International Patent Application No. PCT/EP2006/004086 filed on May
2, 2006, which application claims priority of German Patent
Application No. 10 2005 020 081.8 filed Apr. 29, 2005. The entire
text of the priority application is incorporated herein by
reference in its entirety.
FIELD OF THE DISCLOSURE
[0002] The disclosure relates to a powder-metallurgically produced,
wear-resistant material from an alloy, as well as to a method for
producing the material, the use of said material and a powder
material.
BACKGROUND
[0003] Wear-resistant alloys on the basis of iron are widely used.
In this connection, the resistance to wear is achieved from the
hardness of the martensitic metal matrix and the content of hard
carbides, nitrides or borides of the elements chromium, tungsten,
molybdenum, vanadium, niobium or titanium. This group includes cold
work steel and high-speed tool steels, as well as white cast iron
and hardfacing alloys.
[0004] Powder-metallurgical steel alloys were developed when
striving for fine carbides, their homogenous distribution and high
contents, in order to improve the resistance to wear. The starting
powder of these materials is an alloyed powder that is created by
atomizing a melt. Normally powders of this type are filled into
thin sheet metal capsules that are compacted into a dense body
after the evacuation and seal welding in special autoclaves, using
the hot isostatic pressing (HIP) technique at a temperature below
the melting point and at an isostatic gas pressure of up to 2,000
bar. By means of subsequent hot working (forging or rolling), the
compacted capsules are reworked into semi-finished products of tool
steel that are available on the market in various dimensions.
Generally tools are produced from these semi-finished products,
whereby these tools obtain their service hardness by means of a
heat treatment known as hardening. The hardening consists of
austenitizing and cooling at such a speed that predominantly a hard
martensitic structure is formed. As the wall thickness of the
workpiece increases, the cooling speed needed for this is no longer
reached in the core and the high degree of hardness of the
martensite can be regulated only down to a certain depth in the
workpiece. This is called the effective hardening depth. In this
case, the core is not through-hardened.
[0005] A multitude of powder compositions for wear-resistant
materials are known, but these generally are not sufficient for
thick-walled composite parts as far as their through-hardening
characteristics are concerned. By way of example in this
connection, mention is made of a steel matrix hard material
composite material, disclosed in DE 3508982, as well as a
powder-metallurgically produced steel product with a high
vanadium-carbide content, as described in DE 2937724 and EP
0515018.
[0006] HIP technology can be used for more than just the production
of semi-finished products made of powder-metallurgically produced
steel; it is also suitable for applying a layer produced from
powder with a thickness in the mm to cm range onto an economical,
usually resistant steel substrate. This technology, known as HIP
cladding, is being more and more widely used for the production of
components that are subject to heavy wear and that are used in
processing technology and polymer processing. Some examples of
substances used in this case as wear-resistant layer substances are
atomized steel powder, to which hard material powder is
additionally added in some cases, with a view to a high level of
wear-resistance. In this way, today even workpieces with extremely
wear-resistant layers can be provided that greatly surpass, as far
as the life cycle is concerned, the conventional wearing components
not produced in the powder-metallurgical manner. New HIP systems
are being made for larger and larger components, which consequently
also have larger and larger wall thicknesses. This leads to the
development of the problem of insufficient hardening for the heat
treatment of the larger-walled composite parts after the HIP
step.
[0007] The objective of this heat treatment is the martensitic
through-hardening of the layer substance, which, in operation, is
largely consumed by wear and which consequently must be
through-hardened. Because of the high risk of cracks and
distortions in alloys containing hard material and the sudden
cooling in water or oil, these cooling media are ruled out,
particularly in the case of thick wall thicknesses, because of the
associated large thermal tensions. For this reason, there is a
demand for layer substances that can be converted to the martensite
phase that is needed for a high level of wear-resistance, even in
the case of the slow cooling of large composite components, e.g.,
in the air, vacuum ovens with nitrogen pressure<6 bar or in the
HIP system. The steel powders known today are not suitable for this
purpose, because they have been optimised for semi-finished
products and workpieces with smaller wall thicknesses.
SUMMARY OF DISCLOSURE
[0008] The object of the present disclosure is therefore to provide
alloys for the production of materials that allow for their matrix
to be converted into hard, wear-resistant martensite, even in the
event of very slow cooling.
[0009] This object is solved by means of a wear-resistant material
comprising an alloy that contains: 1.5-5.5 wt. % carbon, 0.1-2.0
wt. % silicon, max. 2.0 wt. % manganese, 3.5-30.0 wt. % chromium,
0.3-10 wt. % molybdenum, 0-10 wt. % tungsten, 0.1-30 wt. %
vanadium, 0-12 wt. % niobium, 0.1-12 wt. % titanium and 1.3-3.5 wt.
% nickel, the remainder being comprised of iron and
production-related impurities, whereby the carbon content fulfils
the following condition:
CAlloy [w %]=S1+S2+S3
[0010] where S1=(Nb+2(Ti+V-0.9))/a, S2=(Mo+W/2+Cr-b)/5,
S3=c+(TH-900)0.0025, where 7<a<9, 6<b<8,
0.3<c<0.5 and 900.degree. C.<TH<1,220.degree. C. In
this case, TH is the hardening temperature.
[0011] The alloy content in the metal matrix is decisive for
achieving the martensitic structure even in the event of slow
cooling. In principle, all alloy elements that are dissolved in the
metal matrix and that shift the "perlite notch" to the right in the
time-temperature transformation diagram (TTT diagram) shown in the
following have a favorable effect. In addition to carbon, this
includes the elements chromium, molybdenum and vanadium, but
particularly nickel, which is used in the alloys according to the
disclosure for this reason. Although the austenite-stabilizing
effect of nickel is known, it has not been used to any appreciable
degree in the PM alloys known until now. The regulation of a
desired nickel content in the metal matrix is relatively simple,
because nickel does not participate in the carbide formation
necessary for a high level of wear-resistance. Because of the
presence of the carbides deposited from the melt, the nickel
content is somewhat higher in the matrix than in the alloy. The
nickel content primarily acts in the metal matrix and increases the
austenite range as the content increases. It can be assumed that
the nickel content in the metal matrix per volume percent of
carbide lies above the content of nickel in the alloy by 0.025 wt
%. The austenite-stabilizing effect of the nickel makes it possible
to convert the alloys into the hard, wear-resistant martensite,
even in the case of very slow cooling.
[0012] Because in addition to the nickel content, the carbon is
particularly significant for the austenite stabilization, but
particularly due to the fact that this is bound in various carbide
types to various degrees, it must be related to the remaining alloy
elements with a view to the desired hardenability. In this process,
the C content calculated in the summands S1 and S2 stands for the
proportion of carbon that is indissolubly bound in the various
carbide types.
[0013] The summand S3 represents a portion of carbon that can be
dissolved, if there is sufficient molybdenum content in the alloy,
by means of the selection of the austenitizing temperature in the
metal matrix. As the hardening temperature increases, more
molybdenum-containing carbides are dissolved. As a result, the
austenite becomes richer in molybdenum and carbon, which expand the
austenite range and consequently increase the critical cooling
rate.
[0014] The factors a, b and c were introduced because the carbide
formation functions with each of the elements Cr, Mo, V and W in a
certain bandwidth.
[0015] The dimensioning of the other elements mentioned, which
shift the "perlite notch" in the time-temperature transformation
diagram (TTT diagram) to the right, is very much more complex,
because on the one hand, one portion of these is hardened into
carbides that are deposited from the melt and that can no longer be
dissolved, and another portion is hardened into carbides that can
be dissolved again during the hardening.
[0016] The material according to the disclosure can be economically
hardened by known measures, whereby even thick-walled components
are through-hardened without increased costs.
[0017] Advantageously, the wear-resistant material can be made of
an alloy with the chemical composition: 1.5-5.5 wt. % carbon,
0.1-2.0 wt. % silicon, max. 2.0 wt. % manganese, 3.5-30.0 wt. %
chromium, 0.3-10 wt. % molybdenum, 0-10 wt. % tungsten, 0.1-30 wt.
% vanadium, 0-12 wt. % niobium, 0.1-12 wt. % titanium and 1.3-3.5
wt. % nickel, the remainder being comprised of iron and
production-related impurities, whereby the carbon content fulfils
the following condition:
CAlloy [w %]=S1+S2+S3
[0018] where S1=(Nb+2(Ti+V-0.9))/a,
S2=(Mo+W/2+Cr-b)/5,S3=c+(TH-900)0.0025, where 7<a<9,
6<b<8, 0.3<c<0.5 and 900.degree. C.<TH<1,2200 C.
In this case, TH is the hardening temperature. This alloy has
proven particularly satisfactory in practice.
[0019] According to a preferred embodiment, the proportion of
vanadium in the alloy of the wear-resistant material can be less
than 11.5 wt. %, preferably less than 9.5 wt. %, and particularly
preferably less than 6.0 wt. %. In this case, it is particularly
preferred if the volume content of the vanadium carbide in the
alloy amounts to less than 18.5 vol. %. Corresponding ranges have
proven particularly suitable in the implementation of the
disclosure.
[0020] According to another preferred embodiment, the alloy of the
wear-resistant material can comprise 2.0-2.5 wt. % carbon, max. 1.0
wt. % silicon, max. 0.6 wt. % manganese, 12.0-14.0 wt. % chromium,
1.0-2.0 wt. % molybdenum, 1.1-4.2 wt. % vanadium and 2.0-3.5 wt. %
nickel, the remainder being comprised of iron and unavoidable
impurities. This specific composition has proven particularly
satisfactory in practice.
[0021] The alloy can advantageously additionally have 1-6 wt. %
Co.
[0022] According to a further preferred embodiment, the alloy can
additionally have 0.3 to 3.5 wt. % N. In some applications, the
addition of nitrogen has proven advantageous.
[0023] The proportion of nickel can advantageously amount to
between 2.0 and 3.5%. In practice, a corresponding nickel content
has proven to be particularly suitable, particularly in quenching
the material with static air.
[0024] According to a further embodiment of the present disclosure,
the Ni content can lie between 1.3 and 2.0 %. An alloy with a
corresponding nickel content is particularly suitable for cooling
by means of gas<6 bar. For higher quenching pressures, a Ni
content of 1.0 to 1.3% is suitable.
[0025] The wear-resistant material can advantageously fulfill the
condition:
[0026] CAlloy [w %]=S1+S2K+S3, where S2K=(Mo+W/2+Cr-b-12)/5 with
6<b<8 and Cr>12. This condition can particularly be used
in the case that a corrosion-resistant alloy is desired. In this
case, there is a prerequisite that a minimum chromium content of
12% is dissolved in the metal matrix. In this case, for the summand
S2 of the above equation the summand S2K is used, which takes the
necessary chromium content into consideration.
[0027] According to a further preferred embodiment, the
wear-resistant material can be produced by means of a method
whereby first a melt is produced and the melt is further processed
by means of one of the following methods: atomization of the melt
into a powder or spray compaction of the melt. The material
according to the disclosure can therefore be produced by means of
various methods, and so allows, firstly, the manufacture of powders
and, secondly, by the use of spray compaction, the production of a
very wide range of semi-finished products, as well as end
products.
[0028] Another preferred embodiment comprises a production method
in which first a melt is formed and then this melt is cast into a
semi-finished product, whereby the semi-finished product is further
processed for creating chips and/or powder.
[0029] The powder can advantageously be compacted into a
semi-finished product or end product under high pressure and/or
increased temperature. A number of possible compaction methods
again present themselves here, with cold isostatic pressing,
uniaxial pressing, extrusion, powder forging, hot isostatic
pressing, diffusion alloying and sintering being named as examples.
In practice, it is consequently possible to select a suitable
method without limitation in order to produce an end product.
[0030] The powder can also advantageously be further processed by
means of thermal injection.
[0031] According to an additional preferred embodiment, the
semi-finished product or an end product can be heated to the
hardening temperature and subsequently quenched. In this case, a
method for quenching can be chosen from the group comprising:
quenching in an oil bath, salt bath or polymer bath, quenching in a
fluidized bed or drizzle and low and high pressure gas
quenching.
[0032] According to an additional preferred embodiment, the
semi-finished product or an end product can be heated to the
hardening temperature and subsequently cooled. Included among the
preferred methods for cooling in this case are cooling in slightly
moving air, cooling in static air, oven cooling in a standard
atmosphere or inert gas and cooling in an HIP system.
[0033] The quenching or cooling in this connection primarily serves
the purposes of hardening.
[0034] The cooling can advantageously be interrupted by an
isothermal maintenance stage (interrupted hardening).
[0035] Preferably, following the cooling from the hardening
temperature, tempering in the temperature range 150-750.degree. C.
can be performed one or more times, in order to achieve a desired
combination of characteristics with respect to hardness and
toughness.
[0036] According to a preferred utilization, the material according
to the disclosure is used as a powder. In the form of a powder, the
material can be converted into a desired semi-finished product form
or end form by means of a multitude of various methods. This also
includes use in the form of a layer element of composite
components, particularly also as a matrix powder for hard material
metal matrix composites.
[0037] One application area is the utilization of the
wear-resistant material for the production of solid and hollow
rolls. Some of the uses of corresponding rolls are for the purpose
of crush-ing, briquetting and compacting natural, chemical or
mineral feedstocks, particularly cement clinker, ore and stone.
Furthermore, corresponding rolls can also be used for the purpose
of the movement and transport of products that promote wear,
particularly of metallic rolled and forged products.
[0038] A further application area is the use of the wear-resistant
material for producing rings which are arranged on solid or hollow
roll bodies. In this case, only an outer layer is made of the
wear-resistant material, not the entire roll. Corresponding rolls
can be deployed in the same scope of functions mentioned above.
[0039] Solid or segmented rings made of the wear-resistant material
can be advantageously arranged on solid or hollow rolls by means of
shrinking them on. This is a proven method in practice for placing
the rings.
[0040] The wear-resistant material can advantageously be used for
producing thick-walled or compact components. Corresponding
components can, for example, be used in the area of wear protection
in extraction and processing, as well as in the transport of
natural, chemical or mineral goods, as well as metallic goods,
polymer goods and ceramic goods.
[0041] According to a further preferred embodiment, the disclosure
relates to a powder for the production of a wear-resistant material
comprising: 1.5-5.5 wt. % carbon, 0.1-2.0 wt. % silicon, max. 2.0
wt. % manganese, 3.5-30.0 wt. % chromium, 0.3-10 wt. % molybdenum,
0-10 wt. % tungsten, 0.1-30 wt. % vanadium, 0-12 wt. % niobium,
0.1-12 wt. % titanium and 1.3-3.5 wt. % nickel, the remainder being
comprised of iron and production-related impurities, whereby the
carbon content fulfils the following condition:
CAlloy [w %]=S1+S2+S3
[0042] where: S1=(Nb+2(Ti+V-0.9))/a, S2=(Mo+W/2+Cr-b)/5,
S3=c+(TH-900)0.0025, where 7<a<9, 6<b<8,
0.3<c<0.5 and 900.degree. C.<TH<1,220.degree. C.
[0043] According to a further preferred embodiment, the disclosure
relates to a powder for the production of a wear-resistant material
with the following chemical composition: 1.5-5.5 wt. % carbon,
0.1-2.0 wt. % silicon, max. 2.0 wt. % manganese, 3.5-30.0 wt. %
chromium, 0.3-10 wt. % molybdenum, 0-10 wt. % tungsten, 0.1-30 wt.
% vanadium, 0-12 wt. % nio-bium, 0.1-12 wt. % titanium and 1.3-3.5
wt. % nickel, the remainder being comprised of iron and
production-related impurities, whereby the carbon content fulfils
the following condition:
CAlloy [w %]=S1+S2+S3
[0044] where: S1=(Nb+2(Ti+V-0.9))/a, S2=(Mo+W/2+Cr-b)/5,
S3=c+(TH-900)0.0025, where 7<a<9, 6<b<8,
0.3<c<0.5 and 900.degree. C.<TH<1,2200 C. A
corresponding composition has proven particularly satisfactory in
practice.
[0045] The powder can advantageously be used as a semi-finished
product. One result of this is to make it possible for a buyer to
convert the semi-finished product into the desired end form.
[0046] A further application area is the use of the powder in
powder form or as a semi-finished product as a layer substance or
layer element of composite components.
[0047] Another further application area is the use of the powder as
a matrix powder for hard material metal matrix composite elements.
Corresponding hard material metal matrix composite elements are
particularly suitable for the production of semi-finished products
and composite components.
BRIEF DESCRIPTION OF THE DRAWINGS
[0048] A preferred embodiment of the present disclosure is
explained in the following using a drawing, but this is not
intended to restrict the scope of the disclosure.
[0049] Shown are:
[0050] FIG. 1a and FIG. 1b: Time-temperature transformation diagram
(TTT diagram) of an alloy according to the disclosure (PM1) as well
as a commercially available PM steel;
[0051] FIG. 2: Hardness tempering temperatures of an alloy
according to the disclosure (PM1) as well as a commercially
available PM steel (X230CrVMo13-4);
[0052] FIG. 3a: The structure of a commercially available PM steel
(X230CrVMo13-4);
[0053] FIG. 3b: A micrograph of an alloy according to the
disclosure (PM).
DETAILED DESCRIPTION
[0054] The heat treatment characteristic of hardenable steels and
alloys is generally evaluated on the basis of time-temperature
transformation diagrams (TTT diagrams). The TTT diagram shown in
FIG. 1 serves to compare an alloy according to the disclosure with
a commercially available powder metallurgical steel with the
composition X230CrVMo13-4 (material no. 1.2380). Because the
martensite formation for the mentioned material group is
indispensable, the cooling from the hardening temperature (in this
case, 1,050.degree. C.) must take place so quickly that the ferrite
and perlite soft structure phases are avoided in the layer
substance. For this reason, the cooling rate deserves increased
attention, which is described in heat treatment technology by the
cooling time from 800.degree. C. to 500.degree. C. The cooling
parameter .lamda., which is noted as a numerical value for several
cooling curves in FIG. 1, is formed by dividing the cooling time
(in seconds) by 100.
[0055] From the TTT diagram for the steel X230CrVMo13-4 shown in
FIG. 1a, it can be seen that the high level of hardness needed for
a high level of wear resistance can only be reached in a component
in areas in which the cooling parameter .lamda.<9. For example,
cooling with .lamda.=55 provides a hardness of only 345 HV30, but
such a hardness level is completely inadequate for applications as
a tool. Because X is greater in the interior of thick-walled
components than at the edge, and it additionally depends on the
cooling medium, the through-hardening characteristic of steel is
often described with the example of a cylindrical body. The heat
transfer upon quenching in various media (air, oil, water) is known
for this simple geometry, so that .lamda. values can be given for
the interior of the cylinders. With .lamda.=9 as the limiting value
for the critical cooling rate for powder-metallurgical steel
X230CrVMo13-4, this steel can be through-hardened under the basic
conditions given in the following Table 1. The table does not
contain any information on water quenching, because this method
does not come into consideration technically because of the
expected hardening cracks resulting from cooling that is too
brusque.
[0056] The mode of operation of the alloy according to the
disclosure and particularly the addition of nickel and molybdenum
can be described using the TTT diagram in FIG. 1b, which was
determined for an alloy variant PM1 with 12.5% Cr, 3% Ni, 1.5% V,
2% Mo, 2.5% C and 0.2% Ti, with the remainder iron
(X250CrNiVMo13-3-2-2). Compared to the conventional nickel-free
steel X230CrVMo13-4, the perlite field is shifted far to the right
on the logarithmically depicted time axis due to the addition of
nickel and molybdenum, and the beginning of the martensitic
transformation (martensite start temperature) is shifted downwards.
The addition of nickel and molybdenum, in conjunction with a high
hardening temperature, leads to an increase in the residual
austenite, because the martensite finish temperature is pressed
further down below room temperature.
[0057] This results in advantages with regard to the heat treatment
that have not yet been achieved with conventional
powder-metallurgical alloys. The hardness values assigned to the
cooling curves confirm that the soft, perlitic structure, for
example, at .lamda.=55, can be avoided with the alloy shown here by
way of example. FIG. 1b shows a macro-hardness between 763 and 814
HV30 for such cooling of the alloy PM1, in comparison to the
hardness of the conventional powder-metallurgical steel of only 345
HV30. Therefore, considerably larger layer or wall thicknesses can
also be through-hardened in air, without it being necessary to call
on brusque quenching means (Table 1). The vacuum hardening with
compressed gas quenching frequently used today can be replaced with
the considerably more economical and also safe cooling in static
air.
[0058] Furthermore, when the HIP technology is used, the alloys
according to the disclosure open up the possibility of
martensitically hardening even thick-walled components with the
normally existing slow cooling from the HIP temperature (.lamda.
approximately 130) (see FIG. 1b). By means of this measure, the
process of the subsequent, expensive vacuum hardening can be
completely spared. Because in many HIP systems, the cooling can
also take place under pressure, isostatic pressure can additionally
be used against the risk of cracks, which increases with the
hard-phase content.
[0059] Steels that are alloyed with chromium, vanadium and
molybdenum and that have sufficient C content can be secondarily
hardened by tempering above 500.degree. C. This allows the
transformation of the remaining residual austenite by repeated
tempering in the range of the secondary hardness maximum.
[0060] In this connection, FIG. 2 shows hardness tempering curves
for the PM steel X230CrVMo13-4 and for a variant PM1 alloyed
according to claim 1. While the commercially available
powder-metallurgical steel was hardened in oil with .lamda.>9
because of the desired quick cooling, the steel PM1 according to
the disclosure was cooled with a value of approximately 80 for
.lamda.. Although the hardness after quenching is somewhat less in
the alloy according to the disclosure than in the conventional
comparison steel due to the high residual austenite content, the
same hardness is reached as in the conventional steel by means of
repeated tempering in the range of the secondary hardness maximum
and the residual austenite transformation and special carbide
precipitation associated with this.
[0061] Because nickel does not participate in the carbide formation
and is completely dissolved in the metal matrix, the structure of
the conventional Ni-free steel X230CrVMo13-4 and the alloy
according to the disclosure are similar with respect to the carbide
type, size and volume content. FIG. 3 depicts corresponding
structures of the corresponding commercially available steel and
the alloy according to the disclosure.
TABLE-US-00001 TABLE 1 Maximum through-hardenable diameter of
cylindrical bodies, in mm, with cooling in air and oil for a
commercially obtainable PM steel and an alloy variant according to
the disclosure for selected cooling parameters .lamda.. Cooling
Designation Alloy parameter .lamda. Air Oil 1.2380 X230CrVMo13-4 9
65 320 PM1 X250CrNiVMo13-3-2-2 55 300 900 1.2380 X230CrVMo13-4 9 65
320 PM1 X250CrNiVMo13-3-2-2 55 300 900
* * * * *