U.S. patent application number 16/473496 was filed with the patent office on 2020-05-14 for casting and method for manufacturing casting.
The applicant listed for this patent is TOYO KOHAN CO., LTD.. Invention is credited to Hiroshi INAZAWA, Toshikazu OOGE, Hirofumi TASHIRO, Hiroki YANAGA.
Application Number | 20200147681 16/473496 |
Document ID | / |
Family ID | 62709488 |
Filed Date | 2020-05-14 |
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United States Patent
Application |
20200147681 |
Kind Code |
A1 |
YANAGA; Hiroki ; et
al. |
May 14, 2020 |
CASTING AND METHOD FOR MANUFACTURING CASTING
Abstract
The present invention provides a Ni--B--Si three-element-based
cast material containing a eutectic part of a solid phase mainly
composed of Ni and B and a solid phase mainly composed of Ni and
Si, wherein when a straight line is drawn in a surface or a cross
section of the eutectic part, the average number of interfaces
formed between the solid phase mainly composed of Ni and B and the
solid phase mainly composed of Ni and Si on the straight line is at
least 2.0 /.mu.m. The present invention also provides a cast
material comprising: hard phase particles mainly composed of a
boride; and a binder phase containing an alloy containing Ni, Si,
and B, wherein the average particle size of the hard phase
particles is 3 .mu.m or less, the average aspect ratio is 2.0 or
less, the contact ratio is 35% or less, and an intensity ratio
I.sub.A/I.sub.B is 1/10 or less, where I.sub.A is the intensity of
a peak derived from Ni.sub.31Si.sub.12 observed at a diffraction
angle 2.theta. within the range of 46.8.degree. to 47.8.degree.,
and I.sub.B is the intensity of a peak derived from Ni.sub.3Si
observed at a diffraction angle 2.theta. within the range of from
44.0.degree. to 45.0.degree., the intensities being determined by
X-ray diffraction measurement using CuK.alpha. radiation.
Inventors: |
YANAGA; Hiroki; (Yamaguchi,
JP) ; TASHIRO; Hirofumi; (Yamaguchi, JP) ;
INAZAWA; Hiroshi; (Yamaguchi, JP) ; OOGE;
Toshikazu; (Yamaguchi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TOYO KOHAN CO., LTD. |
Tokyo |
|
JP |
|
|
Family ID: |
62709488 |
Appl. No.: |
16/473496 |
Filed: |
December 26, 2017 |
PCT Filed: |
December 26, 2017 |
PCT NO: |
PCT/JP2017/046582 |
371 Date: |
June 25, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22F 1/00 20130101; B22D
27/04 20130101; C22C 1/1036 20130101; C22C 1/045 20130101; C22C
1/02 20130101; C22C 32/0073 20130101 |
International
Class: |
B22D 27/04 20060101
B22D027/04; C22C 32/00 20060101 C22C032/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 2016 |
JP |
2016-254171 |
Dec 27, 2016 |
JP |
2016-254179 |
Claims
1. A Ni--B--Si three-element-based cast material containing a
eutectic part comprising a solid phase mainly composed of Ni and B
and a solid phase mainly composed of Ni and Si, wherein when a
straight line is drawn in a surface or a cross section of the
eutectic part, the average number of interfaces formed between the
solid phase mainly composed of Ni and B and the solid phase mainly
composed of Ni and Si on the straight line is 2.0 /.mu.m or
more.
2. The cast material according to claim 1, wherein when two
perpendicular straight lines are drawn in the surface or the cross
section of the eutectic part, the average of the number of
interfaces on one of the two straight lines and the number of
interfaces on the other straight line is 2.0 /.mu.m or more.
3. A method for manufacturing the cast material according to claim
1, comprising steps of: melting a raw material for forming the cast
material, thereby providing a raw material melt; and cooling the
raw material melt, wherein the step of cooling the raw material
melt comprises continuously cooling the raw material melt at a
cooling rate of 100.degree. C./min or more over the temperature
range of a cooling start temperature to 400.degree. C.
4. The method for manufacturing the cast material according to
claim 3, wherein the raw material melt is cooled by pouring the raw
material melt into a mold having a temperature of room temperature
to 1100.degree. C.
5. A cast material comprising: hard phase particles mainly composed
of a boride; and a binder phase containing an alloy containing Ni,
Si, and B, wherein the average particle size of the hard phase
particles is 3 .mu.m or less, the average aspect ratio of the hard
phase particles is 2.0 or less, the contact ratio between the hard
phase particles is 35% or less, the binder phase contains Ni3Si and
Ni3B, and the cast material has an intensity ratio I.sub.A/I.sub.B
of 1/10 or less, where I.sub.A is the intensity of a peak derived
from Ni31 Si12 observed at a diffraction angle 2.theta. within the
range of 46.8.degree. to 47.8.degree., and I.sub.B is the intensity
of a peak derived from Ni3Si observed at a diffraction angle
2.theta. within the range of from 44.0.degree. to 45.0.degree., the
intensities being determined by X-ray diffraction measurement using
CuK.alpha. radiation.
6. The cast material according to claim 5, wherein the intensity
ratio I.sub.A/I.sub.B is 1/100 or less.
7. The cast material according to claim 5, wherein the hard phase
particles comprises at least one of multiple borides represented by
Mo2NiB2 and Mo2(Ni,Cr)B2.
8. The cast material according to claim 5, wherein the content of B
in the cast material is 1 to 6% by weight.
9. A method for manufacturing a cast material comprising hard phase
particles mainly composed of a boride and a binder phase containing
an alloy containing Ni, Si, and B, the method comprising: melting
mixed raw materials for forming the cast material, thereby
providing a melt mixture; continuously cooling the melt mixture at
a cooling rate of 100.degree. C./min or more over the temperature
range of the cooling start temperature to 400.degree. C., thereby
providing a sintered body; and subjecting the sintered body to a
heat treatment at a temperature of 700.degree. C. to 950.degree.
C.
10. The method for manufacturing a cast material according to claim
9, wherein the raw material melt is cooled by pouring the raw
material melt into a mold having a temperature of room temperature
to 1100.degree. C.
Description
TECHNICAL FIELD
[0001] The present invention relates to a cast material and a
method for manufacturing a cast material.
BACKGROUND ART
[0002] The severity of requirements for wear resistant materials
for use in various types of mechanical equipment and mechanical
devices has been increasing every year. In recent years, there is a
demand for wear resistant materials that have excellent properties
such as excellent corrosion resistance and excellent heat
resistance as well as high wear resistance.
[0003] As such wear resistant materials, cermet materials, which
are composite materials composed of ceramic and metal materials,
have been studied so far. Such cermet materials are known to be
producible by, for example, a powder metallurgy process that
includes: mixing a raw material powder; and firing the raw material
powder at a temperature not higher than the melting point thereof
while molding (e.g., press-molding) the raw material powder.
[0004] The powder metallurgy process can prevent excessive grain
growth of the raw material because the raw material is not melted.
As a result, it is possible to prevent the generation of shrinkage
cavities and dendrite structures (columnar crystals). The powder
metallurgy process, however, may leave voids in resulting cermet
materials, and therefore may result in an insufficient density.
[0005] In contrast, Patent Document 1 discloses a method for
manufacturing a cast material comprising a cermet containing Mo
(molybdenum), Ni (nickel), B (boron), and the like.
PRIOR ART DOCUMENT
Patent Document
[0006] [Patent Document 1] WO 2012/063879
SUMMARY OF INVENTION
Problems to be Solved by Invention
[0007] Unfortunately, although cast materials of cermets
manufactured by the casting method disclosed in Patent Document 1
have an increased density, dendrite structures tend to grow inside
the cast materials. Therefore, such cast materials manufactured by
the casting method disclosed in Patent Document 1 may readily break
from those dendrite structures grown therein. For this reason, it
has been difficult to use cast materials manufactured by the
casting method disclosed in Patent Document 1, in particular, in
applications where high bending strength is essential.
[0008] The objective of the present invention is to provide a cast
material having excellent corrosion resistance and excellent wear
resistance and having high hardness and high bending strength.
Means for Solving Problems
[0009] The present inventors have found that the objective can be
achieved by a Ni--B--Si three-element-based cast material
containing a eutectic part comprising a solid phase mainly composed
of Ni and B and a solid phase mainly composed of Ni and Si, wherein
the average number of interfaces formed between the solid phase
mainly composed of Ni and B and the solid phase mainly composed of
Ni and Si in a surface or a cross section of the eutectic part is
controlled within a predetermined range. The present invention has
thus been completed.
[0010] Specifically, the present invention provides a Ni--B--Si
three-element-based cast material containing a eutectic part
comprising a solid phase mainly composed of Ni and B and a solid
phase mainly composed of Ni and Si, wherein when a straight line is
drawn in a surface or a cross section of the eutectic part, the
average number of interfaces formed between the solid phase mainly
composed of Ni and B and the solid phase mainly composed of Ni and
Si on the straight line is 2.0 /.mu.m or more.
[0011] In the cast material of the present invention, when two
perpendicular straight lines are drawn in the surface or the cross
section of the eutectic part, the average of the number of
interfaces on one of the two straight lines and the number of
interfaces on the other straight line is preferably 2.0 /.mu.m or
more.
[0012] The present invention further provides a method for
manufacturing the cast material, the method comprising the steps
of: melting a raw material for forming the cast material, thereby
providing a raw material melt; and cooling the raw material melt,
wherein the step of cooling the raw material melt comprises
continuously cooling the raw material melt at a cooling rate of
100.degree. C./min or more over the temperature range of the
cooling start temperature to 400.degree. C.
[0013] In the manufacturing method of the present invention, the
raw material melt is preferably cooled by pouring the raw material
melt into a mold having a temperature of room temperature to
1100.degree. C.
[0014] The present inventors have further found that the objective
can also be achieved by a cast material comprising hard phase
particles mainly composed of a boride and a binder phase containing
an alloy containing Ni, Si, and B, wherein the average particle
size of the hard phase particles, the average aspect ratio of the
hard phase particles, and the contact ratio between the hard phase
particles are controlled within predetermined ranges, the binder
phase contains Ni.sub.3Si and Ni.sub.3B, and a proportion of a peak
derived from Ni.sub.3Si in the binder phase determined by X-ray
diffraction measurement is controlled within a predetermined range.
The present invention has thus been completed.
[0015] Specifically, the present invention provides a cast material
comprising hard phase particles mainly composed of a boride and a
binder phase containing an alloy containing Ni, Si, and B, wherein
the average particle size of the hard phase particles is 3 .mu.m or
less, the average aspect ratio of the hard phase particles is 2.0
or less, the contact ratio between the hard phase particles is 35%
or less, the binder phase contains Ni.sub.3Si and Ni.sub.3B, and
the cast material has an intensity ratio I.sub.A/I.sub.B of 1/10 or
less, where I.sub.A is the intensity of a peak derived from
Ni.sub.31Si.sub.12 observed at a diffraction angle 2.theta. within
the range of 46.8.degree. to 47.8.degree., and I.sub.B is the
intensity of a peak derived from Ni.sub.3Si observed at a
diffraction angle 2.theta. within the range of from 44.0.degree. to
45.0.degree., the intensities being determined by X-ray diffraction
measurement using CuK.alpha. radiation.
[0016] In the cast material of the present invention, the intensity
ratio I.sub.A/I.sub.B is preferably 1/100 or less.
[0017] In the cast material of the present invention, the hard
phase particles preferably comprise at least one of multiple
borides represented by Mo.sub.2NiB.sub.2 and
Mo.sub.2(Ni,Cr)B.sub.2.
[0018] In the cast material of the present invention, the content
of B in the cast material is preferably 1 to 6% by weight.
[0019] The present invention further provides a method for
manufacturing a cast material comprising hard phase particles
mainly composite of a boride and a binder phase containing an alloy
containing Ni, Si, and B, the method comprising the steps of:
melting a mixed raw material for forming the cast material, thereby
providing a melt mixture; continuously cooling the melt mixture at
a cooling rate of 100.degree. C./min or more over the temperature
range of the cooling start temperature to 400.degree. C., thereby
providing a sintered body; and subjecting the sintered body to a
heat treatment at a temperature of 700.degree. C. to 950.degree.
C.
[0020] In the manufacturing method of the present invention, the
melt mixture is preferably cooled by pouring the melt mixture into
a mold having a temperature of room temperature to 1100.degree.
C.
Effect of Invention
[0021] The present invention can provide a cast material having
excellent corrosion resistance and excellent wear resistance and
having high hardness and high bending strength.
BRIEF DESCRIPTION OF DRAWINGS
[0022] FIG. 1 shows secondary electron image photographs captured
after Ar etching of a cross section of the cast material of Example
1 using a field emission Auger microprobe (Auger).
[0023] FIG. 2 is a view for illustrating how to determine the
average number of interfaces in the eutectic part.
[0024] FIG. 3 shows secondary electron image photographs captured
after Ar etching of a cross section of the cast material of Example
2 using the field emission Auger microprobe (Auger).
[0025] FIG. 4 shows secondary electron image photographs captured
after Ar etching of a cross section of the cast material of
Comparative Example 1 using the field emission Auger microprobe
(Auger).
[0026] FIG. 5 shows secondary electron image photographs captured
after Ar etching of a cross section of the cast material of
Comparative Example 2 using the field emission Auger microprobe
(Auger).
[0027] FIG. 6 shows diffraction pattern graphs obtained by X-ray
diffraction measurement of the cast materials of Examples 1 and 2
using CuK.alpha. radiation.
[0028] FIG. 7 shows diffraction pattern graphs obtained by X-ray
diffraction measurement of the cast materials of Comparative
Examples 1 and 2 using CuK.alpha. radiation.
[0029] FIG. 8 is a view for illustrating how to evaluate the
corrosion resistance of a cast material.
[0030] FIG. 9 is a view for illustrating how to measure a
microstructure of the cast material of the second embodiment.
[0031] FIG. 10 shows graphs each showing one exemplary diffraction
pattern obtained by X-ray diffraction measurement of the cast
material of the second embodiment using CuK.alpha. radiation.
[0032] FIG. 11 shows views for illustrating how to measure the
contact ratio between the hard phase particles.
[0033] FIG. 12 shows graphs showing diffraction patterns obtained
by X-ray diffraction measurement of cast materials of examples and
comparative examples using CuK.alpha. radiation.
[0034] FIG. 13 are secondary electron image photographs captured
after Ar etching of cross sections of the cast materials of
examples and a comparative example using the field emission Auger
microprobe (Auger).
[0035] FIG. 14 shows reflection electron image photographs of cross
sections of the cast materials of examples and comparative examples
captured using a scanning electron microscope (SEM).
MODE(S) FOR CARRYING OUT THE INVENTION
First Embodiment
[0036] Hereinafter, a cast material of the first embodiment is
described.
[0037] The cast material of the present embodiment is a Ni--B--Si
three-element-based cast material which contains a eutectic part
comprising a solid phase mainly composed of Ni and B and a solid
phase mainly composed of Ni and Si, and is characterized in that
when a straight line is drawn in a surface or a cross section of
the eutectic part, the average number of interfaces formed between
the solid phase mainly composed of Ni and B and the solid phase
mainly composed of Ni and Si on the straight line is 2.0 /.mu.m or
more. When only one straight line is drawn in the surface or the
cross section of the eutectic part, the term "average number of
interfaces" means the number of interfaces per unit length (.mu.m)
of the straight line; when a plurality of straight lines is drawn
in the surface or the cross section of the eutectic part, the
average number of interfaces means the average of the numbers of
interfaces per unit length (.mu.m) determined for the straight
lines.
[0038] The cast material of the present embodiment contains a
eutectic part containing Ni, Si, and B, more specifically, a
eutectic part comprising a solid phase mainly composed of Ni and B
and a solid phase mainly composed of Ni and Si. The solid phase
mainly composed of Ni and B is mainly composed of Ni.sub.3B, and
may partially or entirely contain a Ni solid solution (a solid
solution of Ni and at least one element of B and Si). The solid
phase mainly composed of Ni and Si is mainly composed of
Ni.sub.3Si, and may partially or entirely contain a Ni solid
solution (a solid solution of Ni and at least one element of B and
Si). The composition of the solid phase mainly composed of Ni and B
and that of the solid phase mainly composed of Ni and Si can be
determined by X-ray diffraction measurement of the cast material.
The eutectic part of the cast material of the present embodiment
remarkably improves the hardness and the bending strength of the
cast material, and the cast material has remarkably improved
corrosion resistance compared to other cast materials such as those
mainly composed of an Fe-based alloy.
[0039] The cast material of the present embodiment can be obtained,
for example, by melting a raw material powder and the like for
forming the cast material to prepare a raw material melt, and then
cooling the raw material melt under predetermined conditions in the
manner described below. The obtained cast material may be further
subjected to a heat treatment, if necessary.
[0040] When a straight line is drawn in a surface or a cross
section of the eutectic part of the cast material of the present
embodiment, the average number of interfaces formed between the
solid phase mainly composed of Ni and B (hereinafter, also referred
to as "NiB phase") and the solid phase mainly composed of Ni and Si
(hereinafter, also referred to as "NiSi phase") is 2.0 /.mu.m or
more, preferably 2.5 /.mu.m or more, more preferably 3.0 /.mu.m or
more. When the average number of interfaces is within the above
range, crystals constituting the eutectic part have smaller
particle sizes, which contributes to a remarkable improvement in
bending strength of the resulting cast material. The upper limit of
the average number of interfaces is not particularly limited, but
is preferably 6.0 /.mu.m or less, more preferably 5.0 /.mu.m or
less.
[0041] A specific method for measuring the average number of
interfaces in the eutectic part in the present embodiment is
described with reference to FIGS. 1 and 2. FIG. 1 shows secondary
electron image photographs captured after Ar etching of a cross
section of a cast material of an example (described later) using a
field emission Auger microprobe (Auger). FIG. 1 shows the results
obtained by photographing two sites (View Field 1 and View Field 2)
in the cross section of the cast material at magnifications of
.times.3,000 and .times.10,000. FIG. 2 is an enlarged view of a
part of the higher magnification image (.times.10,000) of View
Field 1 shown in FIG. 1.
[0042] In the present embodiment, as shown in FIG. 2, a straight
line is drawn on the secondary electron image, and the average
number of interfaces between the solid phase (NiB phase) mainly
made of Ni and B and the solid phase (NiSi phase) mainly made of Ni
and Si on the straight line is determined. For example,
comparatively white portions (portions which look protruding)
correspond to the NiB phase, and comparatively black portions
(portions which look recessed) correspond to the NiSi phase in FIG.
2. The NiB phase and the NiSi phase in the secondary electron image
can be specified by measuring the cast material by Auger electron
spectroscopy (AES) to identify the elements, and specifying the NiB
phase and the NiSi phase based on the results thereof. For example,
the number of interfaces on the straight line y1 in FIG. 2 is 32,
and the number of interfaces on the straight line x1 is 23. The
numbers of interfaces on other straight lines are also shown in
FIG. 2. The secondary electron image of FIG. 2 has a size of 10
.mu.m (height).times.10 .mu.m (width). Accordingly, there are 32
interfaces on the 10 .mu.m-long section of the straight line y1
(3.2 interfaces /.mu.m of length), and there are 23 interfaces on
the 10 .mu.m-long section of the straight line x1 (2.3 interfaces
/.mu.m of length). On the straight lines y1 and x1, 55 interfaces
are present along the total length of 20 .mu.m. The average number
of interfaces per .mu.m of length based on the two straight lines
is 2.75 /.mu.m.
[0043] In the present embodiment, the average number of interfaces
in the eutectic part can be determined by determining the average
number of interfaces on at least one straight line in the surface
or the cross section of the cast material. A preferred method for
determining the average number of interfaces is to draw a plurality
of straight lines (for example, five straight lines) in the surface
or the cross section of the cast material, and calculate the
average of the numbers of interfaces per .mu.m of length of the
respective straight lines. In this case, it is particularly
preferred to draw two straight lines perpendicular to each other
like the straight lines y1 and x1 in FIG. 2, and determine the
average number of interfaces per .mu.m of length based on the
number of interfaces on one of the two perpendicular straight lines
and the number of interfaces on the other of the two perpendicular
straight lines. This method enables more accurate determination of
the average number of interfaces even when the NiB phase and the
NiSi phase are localized in the eutectic part. When the average
number of interfaces is determined based on such perpendicular
straight lines, it is also preferred to draw a plurality of
straight lines (for example, five straight lines) in one direction
(for example, the direction of the straight line y1) and a
plurality of straight lines (for example, five straight lines) in
the other direction (for example, the direction of the straight
line x1), and calculate the average number of interfaces per .mu.m
of length based on the numbers of interfaces on these straight
lines.
[0044] A conventionally known method for manufacturing a cast
material is to introduce a raw material powder into a mold and heat
the raw material powder in a heating furnace. Unfortunately, this
method may result in a cast material having insufficient bending
strength.
[0045] The present inventors have found that in conventional cast
materials, as a result of slow cooling in a mold after heating in a
heating furnace, crystals may grow to an excessively large particle
size, dendrite structures may grow therein, and consequently the
bending strength of the cast materials may be reduced. Based on
this finding, the present inventors have found that the bending
strength of a cast material can be remarkably improved by
controlling the state of crystals in a eutectic part in the cast
material.
[0046] In the present embodiment, any method for controlling the
average number of interfaces in the eutectic part can be used
without limitation. Examples thereof include a method including:
melting a raw material powder and the like for forming a cast
material to prepare a raw material melt; and cooling the raw
material melt under predetermined conditions, as described
below.
[0047] The cast material of the present embodiment may contain hard
phase particles mainly composed of a boride. When the cast material
contains such hard phase particles, the hard phase particles are
dispersed in a Ni-based alloy matrix including the above-described
eutectic part.
[0048] The boride constituting the hard phase particles is not
particularly limited, and examples thereof include MB-type,
MB.sub.2-type, M.sub.2B-type, M.sub.2B.sub.5-type, and M.sub.2M'
B.sub.2-type borides (where M and M' each represent at least one
metal of Ni, Co, Cr, Mo, Mn, Cu, W, Fe, and Si, and M' represents a
metal element different from M). Specific examples thereof may
include multiple borides such as CrB, MoB, Cr.sub.2B, Mo.sub.2B,
Mo.sub.2B.sub.5, Mo.sub.2FeB.sub.2, Mo.sub.2CrB.sub.2,
Mo.sub.2NiB.sub.2, and Mo(Ni,Cr)B.sub.2.
<Composition of Cast Material>
[0049] The composition of the cast material of the present
embodiment is not particularly limited, but preferably includes
0.01 to 0.06% by weight of C, 1 to 6% by weight of B, 3 to 10% by
weight of Si, and 0.05 to 1.5% by weight of Fe, with the remainder
being Ni.
[0050] B (boron) is an element for forming the NiB phase in the
above-described eutectic part. When the content of B therein is
within the above range, the wear resistance, the hardness, and the
bending strength of the cast material can be improved. The content
of B in the cast material is preferably 1 to 6% by weight, more
preferably 2 to 5% by weight.
[0051] C (carbon) improves the hardness and the bending strength of
the cast material when present in the form of a carbide in the cast
material. When it does not form a carbide, and is contained as an
inevitable impurity, the amount thereof is preferably 0.06% or
less, for example.
[0052] Ni (nickel) is an element for forming the above-described
eutectic part. When the content of Ni in the cast material is
within the above range, the corrosion resistance of the cast
material can be improved.
[0053] Si (silicon) is an element for forming the NiSi phase in the
above-described eutectic part, and acts to reduce the melting
temperature of the raw material for forming the cast material. When
the content of Si therein is appropriate, Si not only acts to
reduce the melting temperature but also prevents a reduction in the
bending strength of the cast material which is caused by excessive
silicides contained in the cast material.
[0054] Fe (iron) improves the hardness and the bending strength of
the cast material when it forms hard phase particles in the cast
material. When it does not form hard phase particles, and is
contained as an inevitable impurity, the amount thereof is
preferably 1.5% or less, for example.
<Cast Material Manufacturing Method>
[0055] Next, the method for manufacturing the cast material of the
present embodiment is described.
[0056] First, a raw material powder for forming the cast material
of the present embodiment is prepared. The raw material powder is
prepared in a desired compositional ratio of contained elements for
forming the cast material. The raw material powder may be in the
powder form, or may contain aggregates (bulk form) of powder.
[0057] Next, if necessary, in order to micronize the prepared raw
material powder into a predetermined particle size, agents such as
a binder and an organic solvent are added to the raw material
powder, and the resulting mixture is mixed and pulverized using a
pulverizer (e.g., a ball mill).
[0058] The binder is added to improve moldability during molding
and prevent oxidation of the powder. The binder is not particularly
limited, and known binders can be used. Examples thereof include
paraffin. The amount of the binder to be added is not particularly
limited, but is preferably 3 to 6 parts by weight relative to 100
parts by weight of the raw material powder. The organic solvent is
not particularly limited, and low-boiling-point solvents such as
acetone can be used. The pulverization-mixing time is not
particularly limited, but is typically 15 to 30 hours.
[0059] Next, the above-described raw material powder is melted to
prepare a raw material melt, and impurities such as gas and oxides
are then removed if necessary. In this process, the melting
temperature can be determined according to the raw material used,
and is preferably 1100.degree. C. to 1300.degree. C., more
preferably 1200.degree. C. to 1250.degree. C.
[0060] Subsequently, the raw material melt thus prepared can be
casted into a cast material by pouring the raw material melt into a
cast material mold such as a mold of a desired shape, and then
cooling the raw material melt.
[0061] In the present embodiment, the step of cooling the raw
material melt includes continuously cooling the raw material melt
at a cooling rate of 100.degree. C./min or more over the
temperature range of the cooling start temperature to 400.degree.
C. In the present embodiment, the expression "includes continuously
cooling the raw material melt at a cooling rate of 100.degree.
C./min or more" means that the cooling rate is continuously
controlled to 100.degree. C./min or more for a certain period of
time. The cooling step preferably includes cooling at a cooling
rate of 100.degree. C./min or more for 1 minute or more, more
preferably 5 minutes or more. For example, a case where the cooling
rate instantaneously reaches 100.degree. C./min or more (for
example, a case where the cooling rate reaches 100.degree. C./min
or more for 1 second or less) is not included. Although it is
sufficient that the step of cooling the raw material melt includes
continuously cooling the raw material melt at a cooling rate of
100.degree. C./min or more over the temperature range of the
cooling start temperature to 400.degree. C., the cooling rate is
preferably 200.degree. C./min or more, more preferably 400.degree.
C./min or more. When the raw material melt is cooled under the
above conditions, the average number of interfaces between the NiB
phase and the NiSi phase in the eutectic part can be controlled
within the above range.
[0062] In the present embodiment, any method for cooling the raw
material melt under the above conditions can be used without
limitation. Examples thereof include a method including pouring the
raw material melt into a mold preferably at room temperature to
110.degree. C., more preferably 300.degree. C. to 1100.degree. C.,
and cooling the raw material melt. The room temperature is, for
example, 1.degree. C. to 30.degree. C.
[0063] Any casting method can be used without limitation, but
casting methods such as mold casting, lost-wax casting, continuous
casting, and centrifugal casting are preferably used because these
methods enables formation of cast materials having complicated
shapes and formation of thick-walled cast materials.
[0064] In the present embodiment, the cast material cooled under
the above conditions may be further subjected to a heat treatment.
The heat treatment can reduce a variation in the bending strength
of the entire cast material obtained, and thereby can further
stabilize the quality of the cast material. The reason for this is
not clearly understood, but it is assumed that crystals including
Ni.sub.3B and Ni.sub.3Si which constitute the eutectic part are
further stabilized because, for example, the heat treatment
promotes the diffusion of atoms in the eutectic part in the cast
material in such a manner as to eliminate a disturbed arrangement
of atoms in the eutectic part (for example, when Si is contained in
the NiB phase, the heat treatment causes Si in the NiB phase to
diffuse, thereby reducing the content of Si in the NiB phase).
[0065] The temperature for the heat treatment of the cast material
is preferably 700.degree. C. to 950.degree. C., more preferably
750.degree. C. to 900.degree. C., further preferably 800.degree. C.
to 850.degree. C. When the temperature for the heat treatment is
within the above range, a disturbed arrangement of atoms in the
eutectic part can be eliminated, the variation in the bending
strength of the entire cast material obtained can be reduced, and
the quality of the cast material can be further stabilized. Too
high a temperature in the heat treatment, specifically a
temperature higher than 1,000.degree. C. melts the cast material
and deforms the cast material.
[0066] The treatment time for the heat treatment of the cast
material is preferably 0.17 to 3 hours, more preferably 0.33 to 2
hours, further preferably 0.5 to 1.5 hours. When the treatment time
for the heat treatment is within the above range, a disturbed
arrangement of atoms in the eutectic part can be eliminated, the
variation in the bending strength of the entire cast material
obtained can be reduced, and the quality of the cast material can
be further stabilized.
[0067] The cast material of the present invention is manufactured
as described above.
[0068] The cast material of the present embodiment is a Ni--B--Si
three-element-based cast material containing a eutectic part
comprising a solid phase mainly composed of Ni and B and a solid
phase mainly composed of Ni and Si, wherein when a straight line is
drawn in a surface or a cross section of the eutectic part, the
average number of interfaces formed between the solid phase mainly
composed of Ni and B and the solid phase mainly composed of Ni and
Si on the straight line is 2.0 /.mu.m or more. Because of this
structure, the cast material of the present embodiment has
excellent corrosion resistance and excellent wear resistance, and
has high hardness and high bending strength.
[0069] The cast material of the present embodiment can be suitably
used as a wear resistant material that can exhibit excellent
durability even in environments under a high load (e.g., rolls,
cylinders, bearings, industrial pump components, and the like)
because it has excellent corrosion resistance and excellent wear
resistance, and has high hardness and high bending strength.
Second Embodiment
[0070] Hereinafter, a cast material of the second embodiment is
described.
[0071] The cast material of the present embodiment is a cast
material comprising hard phase particles mainly composed of a
boride and a binder phase containing an alloy containing Ni, Si,
and B, wherein the average particle size of the hard phase
particles is 3 .mu.m or less, the average aspect ratio of the hard
phase particles is 2.0 or less, the contact ratio between the hard
phase particles is 35% or less, the binder phase contains
Ni.sub.3Si and Ni.sub.3B, and the cast material has an intensity
ratio I.sub.A/I.sub.B of 1/10 or less, where I.sub.A is the
intensity of a peak derived from Ni.sub.31Si.sub.12 observed at a
diffraction angle 2.theta. within the range of 46.8.degree. to
47.8.degree., and I.sub.B is the intensity of a peak derived from
Ni.sub.3Si observed at a diffraction angle 2.theta. within the
range of from 44.0.degree. to 45.0.degree., the intensities being
determined by X-ray diffraction measurement using CuK.alpha.
radiation.
<Hard Phase Particles>
[0072] The hard phase particles constituting the cast material of
the present embodiment mainly contain a boride, and contribute to
the hardness and the wear resistance of the cast material. In the
cast material of the present embodiment, the hard phase particles
are dispersed in a binder phase matrix described below.
[0073] The boride constituting the hard phase particles is not
particularly limited, and examples thereof include MB-type,
MB.sub.2-type, M.sub.2B-type, M.sub.2B.sub.5-type, and M.sub.2M'
B.sub.2-type borides (where M and M' each represent at least one
metal of Ni, Co, Cr, Mo, Mn, Cu, W, Fe, and Si, and M' represents a
metal element different from M). Specific examples of thereof may
include multiple borides such as CrB, MoB, Cr.sub.2B, Mo.sub.2B,
M.sub.2B.sub.5, Mo.sub.2FeB.sub.2, Mo.sub.2CrB.sub.2,
Mo.sub.2NiB.sub.2, and Mo.sub.2(Ni,Cr)B.sub.2.
[0074] The content of the hard phase particles in the cast material
of the present embodiment is preferably 10 to 50 vol %, more
preferably 20 to 45 vol %. A method that can be used to control the
content of the hard phase particles in the cast material is to
adjust the content of B in the cast material. When the content of
the hard phase particles is within the above range, the cast
material of the present embodiment has well-balanced mechanical
strengths such as corrosion resistance, wear resistance, hardness,
and bending strength. Additionally, when the content of the hard
phase particles is within the above range, an excessive increase in
the contact ratio between the hard phase particles can be
prevented, preventing a reduction in the bending strength of the
cast material which is caused by aggregation of hard phase
particles. Moreover, when the content of the hard phase particles
is within the above range, the temperature required to melt the raw
materials of the hard phase particles can be reduced. This leads to
a reduction in heat energy necessary for melting, and provides an
advantage in cost.
<Binder Phase>
[0075] The binder phase in the cast material of the present
embodiment contains an alloy containing Ni, Si, and B, and forms a
matrix for connecting the hard phase particles. Among other alloys
containing Ni, Si, and B, the binder phase in the cast material of
the present embodiment contains Ni.sub.3Si and Ni.sub.3B. In the
cast material of the present embodiment, the presence of Ni.sub.3Si
and Ni.sub.3B in the binder phase remarkably improves the hardness
and the bending strength of the cast material, and improves the
corrosion resistance of the resulting cast material compared to a
case where the binder phase contains an alloy mainly composed of an
Fe-based alloy or the like.
[0076] Additionally, the binder phase in the cast material of the
present embodiment is controlled such that the content of
Ni.sub.3Si in the binder phase determined by X-ray diffraction
measurement is within a predetermined range. Specifically, when
measured with an X-ray diffraction measurement device using
CuK.alpha. radiation, the cast material of the present embodiment
has an intensity ratio I.sub.A/I.sub.B of 1/10 or less, preferably
1/100 or less, more preferably 1/300 or less. The intensity ratio
I.sub.A/I.sub.B is the ratio of the intensity I.sub.A of a peak
derived from Ni.sub.31Si, observed at a diffraction angle 26 within
the range of 46.8.degree. to 47.8.degree. to the intensity I.sub.B
of a peak derived from Ni.sub.3Si and observed at a diffraction
angle 2.theta. within the range of from 44.0.degree. to
45.0.degree.. When the intensity ratio I.sub.A/I.sub.B is 1/10 or
less, the bending strength of the resulting cast material can be
remarkably improved.
[0077] A conventionally known method for manufacturing a cast
material is to place a raw material powder containing Mo, Ni, and B
into a mold, and heat the raw material powder in a furnace. This
method, however, may provide a cast material containing hard phase
particles having a too large average particle size, a too large
aspect ratio, and a too large contact ratio because the cast
material is slowly cooled in the mold. Unfortunately, the hardness
and the bending strength of the cast material may be
insufficient.
[0078] In contrast, the present inventors have found that when a
cast material is manufactured by melting a mixed raw material
powder containing Mo, Ni, and B to prepare a melt mixture, pouring
the melt mixture into a mold, and cooling the melt mixture while
controlling the cooling rate within a predetermined range higher
than that of the conventional method, the average particle size of
the hard phase particles, the average aspect ratio of the hard
phase particles, and the contact ratio between the hard phase
particles of the obtained cast material can be controlled within
the respective ratios described above, and as a result, the
hardness and the bending strength of the cast material can be
remarkably improved.
[0079] The present inventors have also found that although the
hardness and the bending strength of the cast material can be
remarkably improved by controlling the cooling rate within a higher
range than that of the conventional method, the bending strength of
the cast material may be reduced depending on the morphology of
crystals composed of Mo, Ni, B, and the like contained in the cast
material. Specifically, the present inventors have found that when
crystals including a stable phase Ni.sub.3Si, a metastable phase
Ni.sub.31Si.sub.12, and the like are present in the cast material,
and when the content ratio of Ni.sub.31Si.sub.12 to Ni.sub.3Si is
too high (an excessive amount of the metastable phase
Ni.sub.31Si.sub.12 is crystallized), high internal strain energy is
generated due to the metastable phase Ni.sub.31Si.sub.1, and as a
result, the cast material may have reduced bending strength, and
may readily break. In contrast, the present inventors have found
that the bending strength of the resulting cast material can be
remarkably improved by controlling the content ratio of
Ni.sub.31Si.sub.12 to Ni.sub.3Si in the cast material,
specifically, controlling the intensity ratio I.sub.A/I.sub.B
(where I.sub.A is the intensity of a peak derived from
Ni.sub.31Si.sub.12 observed at a diffraction angle 2.theta. within
the range of 46.8.degree. to 47.8.degree., and I.sub.B is the
intensity of a peak derived from Ni.sub.3Si observed at a
diffraction angle 2.theta. within the range of from 44.0.degree. to
45.0.degree., the intensities being determined by X-ray diffraction
measurement using CuK.alpha. radiation) within the above range.
Based on this finding, the present inventors have completed the
present invention.
[0080] In the present embodiment, any method for controlling the
intensity ratio I.sub.A/I.sub.B of the cast material within the
above range can be used without limitation, and examples thereof
include a method including melting a raw material powder and the
like for forming the cast material to prepare a melt mixture,
cooling the melt mixture under predetermined conditions, and
subjecting the cast material to a heat treatment at a temperature
of 700.degree. C. to 950.degree. C., as described later.
[0081] FIGS. 10(A) and 10(B) show examples of diffraction patterns
actually obtained by X-ray diffraction measurement of cast
materials using CuK.alpha. radiation. Specifically, the cast
materials were prepared by heating and hardening a raw material
powder for forming a cast material using a vacuum furnace at
1160.degree. C. for 30 minutes to prepare an ingot, melting the
ingot by heating to 1200.degree. C. in air using an air atmosphere
furnace to prepare a melt mixture, pouring the melt mixture into a
mold at room temperature, and air cooling the melt mixture to room
temperature. One cast material was subjected to the heat treatment
at 800.degree. C. for 1 hour, and the measurement results thereof
are shown in FIG. 10(A). The measurement results of the other cast
material not subjected to the heat treatment are shown in FIG.
10(B).
[0082] FIGS. 10(A) and 10(B) show that the cast material of FIG.
10(B), which was not subjected to the heat treatment, had a
relatively small ratio of the intensity I.sub.Q, which is the
intensity of the peak derived from the stable phase Ni.sub.3Si
(2.theta.=46.8.degree. to 47.8.degree.), to the intensity I.sub.A,
which is the intensity of the peak derived from the metastable
phase Ni.sub.31Si.sub.12 (2.theta.=46.8.degree. to 47.8.degree.).
Namely, the results show that the content of the stable phase
Ni.sub.3Si is relatively low, and the content of the metastable
phase Ni.sub.31Si.sub.12 is relatively high.
[0083] In contrast, in the cast material of FIG. 10(A), which was
subjected to the heat treatment, the heat treatment at 800.degree.
C. for 1 hour caused a phase transition from the metastable phase
(Ni.sub.31Si.sub.12) to the stable phase (Ni.sub.3Si), so that the
intensity I.sub.B of the peak derived from the stable phase
Ni.sub.3Si (2.theta.=44.0 to 45.0) became large relative to the
intensity I.sub.A of the peak derived from the metastable phase
Ni.sub.31Si.sub.12 (2.theta.=46.8 to 47.8). Namely, the results
show that the content of the stable phase Ni.sub.3Si is relatively
high, and the content of the metastable phase Ni.sub.31Si.sub.12 is
relatively low.
[0084] In the present embodiment, the bending strength of the
obtained cast material can be remarkably improved by controlling,
within the above range, the intensity ratio I.sub.A/I.sub.B of the
intensity I.sub.A of a peak derived from Ni.sub.31Si.sub.12 to the
intensity I.sub.B of a peak derived from Ni.sub.3Si, the
intensities being determined by X-ray diffraction measurement using
CuK.alpha. radiation.
[0085] In the present embodiment, the intensity ratio
I.sub.A/I.sub.B based on X-ray diffraction measurement using
CuK.alpha. radiation can be determined, for example, as follows.
First, the cast material is subjected to X-ray diffraction
measurement under the conditions: X-ray source: Cu, 40 kV, 200 mA,
emission slit: 2.degree., scattering slit: 1.degree., and receiving
slit: 0.3 mm. Based on the data obtained by the X-ray diffraction
measurement, a peak derived from Ni.sub.31Si.sub.12 observed at a
diffraction angle 2.theta. within the range of 46.8.degree. to
47.8.degree. and a peak derived from Ni.sub.3Si observed at a
diffraction angle 2.theta. within the range of 44.0.degree. to
45.0.degree. are determined. The intensities I.sub.A and I.sub.B of
these peaks from which background is removed are determined (where
I.sub.A is the intensity of the peak observed at a diffraction
angle 2.theta. within the range of 46.8.degree. to 47.8.degree.,
and I.sub.B is the intensity of the peak observed at a diffraction
angle 2.theta. within the range of 44.0.degree. to 45.0.degree.),
and the ratio therebetween is calculated to determine the intensity
ratio I.sub.A/I.sub.B. Another peak derived from Ni.sub.3Si also
appears at a 2.theta. of about 35.6.degree. to 36.6.degree. in
addition to the peak in the diffraction angle 2.theta. range of
46.8.degree. to 47.8.degree.. However, the peak at a 2.theta. of
about 35.6.degree. to 36.6.degree. has a relatively small
intensity. Therefore, in the present embodiment, the peak in the
diffraction angle 2.theta. range of 46.8.degree. to 47.8.degree. is
detected as a peak derived from Ni.sub.3Si.
[0086] Among the above-described features of the hard phase
particles and the binder phase constituting the cast material of
the present embodiment, it is particularly preferable that the
binder phase contain Ni.sub.3Si and Ni.sub.3B, and the hard phase
particles comprise at least one of multiple borides represented by
Mo.sub.2NiB.sub.2 and Mo.sub.2(Ni,Cr)B.sub.2.
<Microstructure of Cast Material>
[0087] In the cast material of the present embodiment, the average
particle size of the hard phase particles, the average aspect ratio
of the hard phase particles, and the contact ratio between the hard
phase particles are controlled within predetermined ranges
described later, and the binder phase contains Ni.sub.3Si and
Ni.sub.3B. According to the present embodiment, by controlling
these properties within the predetermined ranges described later,
it is possible to provide a cast material having excellent
corrosion resistance and excellent wear resistance and having high
hardness and high bending strength.
[0088] In the cast material of the present embodiment, the average
particle size of the hard phase particles is 3 .mu.m or less,
preferably 2.8 .mu.m or less, more preferably 2.5 .mu.m or less.
When the average particle size of the hard phase particles is
controlled within the above range, the resulting cast material has
sufficient hardness and bending strength. When the average particle
size of the hard phase particles is too large, the cast material,
unfortunately, may break from the hard phase particles, and may
have remarkably reduced bending strength. The lower limit of the
average particle size of the hard phase particles is not
particularly limited, but is preferably 0.5 .mu.m. In order to
control the average particle size of the hard phase particles to
less than 0.5 .mu.m, the cooling rate should be remarkably high.
Such a rate may not be achieved by typical techniques such as water
cooling. Therefore, even if attempted to achieve this rate, the
manufacturing cost will be increased.
[0089] The average particle size of the hard phase particles can be
determined, for example, by calculating the equivalent circle
diameters of hard phase particles, and calculating the average of
the calculated equivalent circle diameters. Specifically, a
reflection electron image of a cross section of the cast material
is captured using a scanning electron microscope (SEM), and the
average particle size of the hard phase particles is calculated
using the captured reflection electron image based on Fullaman's
formula (equation (1) shown below).
d.sub.m=(4/.pi.).times.(N.sub.L/N.sub.S) (1)
In the equation (1), do is the average particle size of the hard
phase particles. n is the ratio of the circumference of a circle.
N.sub.L is the number of hard phase particles hit by an arbitrary
straight line on a cross section of the structure (the number of
hard phase particles touched or crossed by a straight line
arbitrarily drawn) per unit length of the arbitrary straight line.
Specifically, N.sub.L is determined by dividing the number of
particles hit by an arbitrary straight line having a length L in a
cross section of the structure by the length L of the arbitrary
straight line. N.sub.S represents the number of hard phase
particles included in an arbitrary unit area, and is a value
obtained by dividing the number of particles included in an
arbitrary measurement region S having a measurement area by the
arbitrary measurement region S. In this case, the straight line L
should be long enough to cross a number of hard phase particles
sufficient for measurement of the average particle size, and the
length thereof is preferably 20 .mu.m or more, and may be 100
.mu.m, for example. The measurement region S should be large enough
to include a number of hard phase particles sufficient for
measurement of the average particle size, and is preferably 20
.mu.m or more in length and 20 .mu.m or more in width.
[0090] The average aspect ratio, that is, the average ratio (major
diameter/minor diameter) of the major diameter to the minor
diameter of the hard phase particles of the cast material according
to the present embodiment is 2.0 or less, preferably 1.9 or less,
more preferably 1.8 or less. When the average aspect ratio of the
hard phase particles is within the above range, the bending
strength of the cast material can be remarkably improved. When the
average aspect ratio of the hard phase particles is too large due
to growth of dendrite structures (columnar crystals) of the hard
phase particles, for example, the cast material has reduced bending
strength in the dendrite structures, and may readily break.
[0091] The average aspect ratio of the hard phase particles can be
determined, for example, in accordance with JIS R1670 as follows.
First, the cast material is cut, and a reflection electron image of
the cut surface is captured using a scanning electron microscope
(SEM). Then, a predetermined number of hard phase particles are
randomly selected from the measurement region S (a region having a
length of 20 .mu.m or more and a width of 20 .mu.m or more) in the
same manner as when the average particles size is measured, and
each particle is measured for the length (major diameter) of the
longest part and the length (minor diameter) of the longest part
extending in the direction perpendicular to the major diameter. The
ratio of the major diameter to the minor diameter can be determined
from the measured major diameter and minor diameter as the aspect
ratio of the hard phase particle. In the present embodiment, the
aspect ratio is determined for a predetermined number of hard phase
particles (for example, 10 or more particles), and the average
thereof can be determined as the average aspect ratio of the hard
phase particles.
[0092] The contact ratio (contiguity) between the hard phase
particles of the cast material of the present embodiment is 35% or
less, preferably 30% or less, more preferably 25% or less. The
contact ratio between the hard phase particles is a measure of the
dispersibility of the hard phase particles. A lower contact ratio
corresponds to higher dispersibility, and provides improved
strength. When the contact ratio between the hard phase particles
is too high, the hard phase particles may contact each other to
form bulk aggregates, and the hard phase particles may bond to each
other, resulting in growth of particles. Unfortunately, as a
result, the cast material may break from a portion with grown
particles, and may have reduced bending strength.
[0093] The contact ratio between the hard phase particles can be
determined, for example, as follows. First, a reflection electron
image of the surface of the cast material is captured using a
scanning electron microscope. As shown in FIG. 9, a measurement
line L having a predetermined length is arbitrarily drawn on the
reflection electron image in the same manner as when the average
particle size is measured, and the interfaces between hard phases
on the line L are observed. FIG. 9 is a view for illustrating how
to measure the microstructure of the cast material of the present
embodiment. Specifically, the interfaces between hard phase
particles are observed. An interface between hard phase particles
in contact with each other is referred to as a hard phase-hard
phase interface I.sub.HH, and an interfaces between a hard phase
particle and the binder phase in contact with each other is
referred to as a hard phase-binder phase interface I.sub.HB. These
interfaces are counted. The term "hard phase particle" refers to a
particle which is composed of a boride, and is generated and grows
during heating of a raw material containing Mo, Ni, Cr, B and the
like, as described later. When grown particles are in contact with
each other, these particles do not form a single integrated
particle, but are present as separate particles in contact with
each other. A method for extracting the contours of the hard phase
particles and the interfaces between hard phase particles in
contact with each other is described with reference to FIG. 11(A),
which is one exemplary reflection electron image obtained by
imaging the surface of the cast material using a scanning electron
microscope (SEM). In the reflection electron image shown in FIG.
11(A), white regions each correspond to the hard phase (boride),
and grey regions each correspond to the binder phase. In such a
reflection electron image, the contour of each hard phase can be
detected, as shown in FIG. 11(B), by detecting the boundaries
between the white regions and the grey regions based on the
difference in brightness therebetween. Recesses (portions having an
inner angle of 1800 or more) of the detected contour of the hard
phase are detected, and a straight line which connects a pair of
facing recesses is extracted as the interface between hard phase
particles in contact with each other. Specifically, as shown in
FIG. 11(C), which is an enlarged view of the encircled area in FIG.
11(B), pairs of facing recesses are connected by straight lines,
and the line segments (line segments indicated by a, b, c and d in
FIG. 11(C)) can be defined as interfaces where hard phase particles
are in contact with each other.
[0094] In the present embodiment, the contact ratio Cont (unit: %)
between the hard phase particles can be calculated in accordance
with the following equation (2) based on the number N(I.sub.H) of
hard phase-hard phase interfaces I.sub.HH per unit length of L1 and
the number N(I.sub.HB) of hard phase-binder phase interfaces
I.sub.HB per unit length of L1.
Cont=2N(I.sub.HH)/[2N(I.sub.HH+N(I.sub.HB)].times.100 (2)
[0095] When the contact ratio between the hard phase particles is
calculated in the manner described above, it is preferable to
repeat the following operation five times, and calculate the
contact ratio between the hard phase particles based on the results
of the five-time measurement: the operation comprising drawing
another measurement line L different from the above line on the SEM
photograph such that the line L runs a different part from the part
through which the above line runs; and counting hard phase-hard
phase interfaces I.sub.HH and hard phase-binder phase interfaces
I.sub.HB in the same manner as above.
[0096] In the present embodiment, any method for controlling the
average particle size of the hard phase particles, the average
aspect ratio of the hard phase particles, and the contact ratio of
the hard phase particles within the above ranges can be used
without limitation. Examples thereof include a method including
melting a raw material powder and the like for forming the cast
material to prepare a melt mixture, and then cooling the melt
mixture under predetermined conditions, as described later.
[0097] The contact ratio between the hard phase particles can also
be controlled by adjusting the compositional ratio of the cast
material within a predetermine range.
[0098] The binder phase of the cast material of the present
embodiment contains Ni.sub.3Si and Ni.sub.3B, as described above.
Since the binder phase contains Ni.sub.3Si and Ni.sub.3B, in
particular, the stable phase Ni.sub.3Si, the bending strength of
the cast material can be remarkably improved. The formation of
crystals of the metastable phase Ni.sub.31Si.sub.12 in the binder
phase increases the internal strain energy in the cast material. As
a result, the cast material may have reduced bending strength, and
may readily break.
[0099] In addition, the cast material of the present embodiment has
an intensity ratio I.sub.A/I.sub.B of 1/10 or less, where I.sub.A
is the intensity of a peak derived from Ni.sub.31Si.sub.12 observed
at a diffraction angle 2.theta. within the range of 46.8.degree. to
47.8.degree., and I.sub.B is the intensity of a peak derived from
Ni.sub.3Si observed at a diffraction angle 2.theta. within the
range of from 44.0.degree. to 45.0.degree., the intensities being
determined by X-ray diffraction measurement using CuK.alpha.
radiation. When the intensity ratio I.sub.A/I.sub.B is within the
above range, that is, the ratio of the content of the stable phase
Ni.sub.3Si to the content of the metastable phase
Ni.sub.31Si.sub.12 is relatively high, the bending strength of the
resulting cast material can be remarkably improved.
<Composition of Cast Material>
[0100] The composition of the cast material of the present
embodiment is not particularly limited. When the binder phase
comprises a Ni-based alloy mainly composed of Ni, the composition
is preferably composed of 1 to 6% by weight of B, 0 to 5% by weight
of Si, 0 to 20% by weight of Cr, and 5 to 40% by weight of Mo, with
the remainder being Ni.
[0101] B (boron) is an element which forms a boride, which in turn
forms hard phase particles. When the content of B is within the
above range, the content of the hard phase particles in the cast
material can be controlled adequately. As a result, the wear
resistance of the cast material can be improved. In addition, when
the content of B is within the above range, the contact ratio
between the hard phase particles can be controlled within the above
range, improving the hardness and the bending strength of the cast
material. The content of B in the cast material is preferably 1 to
6% by weight, more preferably 2 to 5% by weight.
[0102] Ni is an element which can be incorporated in the hard phase
particles when a Ni-based alloy is used for the binder phase of the
cast material, and is also an element for forming the binder phase.
Ni acts to improve the corrosion resistance of the cast
material.
[0103] Si is an element for forming the binder phase of the cast
material, and acts to reduce the melting temperature of the raw
material for forming the cast material. When the content of Si is
adequate, it is possible not only to reduce the melting temperature
but also to prevent a reduction in the bending strength of the cast
material which is caused by excessive silicides contained in the
cast material.
[0104] Cr is an element which can be incorporated in the hard phase
particles, and also can be incorporated in the binder phase. Cr
acts to improve the corrosion resistance, the wear resistance, the
high-temperature characteristics, the hardness and the bending
strength of the cast material. When the content of Cr is adequate,
the content of the hard phase particles in the cast material is
controlled within the above range, resulting in improved bending
strength of the cast material.
[0105] Mo is an element which can be incorporated in the hard phase
particles, and also can be incorporated in the binder phase. Mo
acts to improve the corrosion resistance of the cast material.
Specifically, a portion of Mo is present as a solid solution in the
binder phase, thereby improving the corrosion resistance of the
cast material. When the content of Mo is adequate, the wear
resistance and the corrosion resistance of the cast material can be
improved.
<Cast Material Manufacturing Method>
[0106] Next, the method for manufacturing the cast material of the
present embodiment is described.
[0107] First, a raw material powder for forming the cast material
of the present embodiment is prepared. The raw material powder is
prepared in a desired compositional ratio of the elements for
forming the cast material. The raw material powder may be in the
form of powder or may contain aggregates (bulk form) of powder. In
the present embodiment, in the raw material powder, the hard phase
particles mainly composed of a boride may be preliminarily
contained. Alternatively, in the raw material powder, the hard
phase particles may not be contained, and boron and carbon in the
raw material powder may form the hard phase particles mainly
composed of a boride in the cast material in the process of
manufacture of the cast material using the raw material powder. It
is preferred that the hard phase particles mainly composed of a
boride be preliminarily contained in the raw material powder. The
boride contained in the raw material powder is preferably at least
one of multiple borides represented by Mo.sub.2NiB.sub.2 and
Mo.sub.2(Ni,Cr)B.sub.2, particularly preferably
Mo.sub.2(Ni,Cr)B.sub.2. When the boride contains Cr in the form of
Mo.sub.2(Ni,Cr)B.sub.2, for example, the boride tends to have a
tetragonal crystalline structure. Because of this structure, the
boride prevents the growth of the boride crystals into a larger
size, and further improves the characteristics of the resulting
cast material compared to Cr-free borides which tend to have an
orthorhombic crystalline structure.
[0108] Next, a binder, an organic solvent, and the like are added
to the prepared raw material powder to micronize the raw material
powder into a predetermined particle size if necessary, and the
mixture is mixed and pulverized using a pulverized such as a ball
mill.
[0109] The binder is added to improve the moldability during
molding and prevent oxidation of the powder. The binder is not
particularly limited, and known binders can be used. Examples
thereof include paraffin. The amount of the binder to be added is
preferably 3 to 6 parts by weight relative to 100 parts by weight
of the raw material powder. The organic solvent is not particularly
limited, and low-boiling-point solvents such as acetone can be
used. The pulverizing/mixing time is not particularly limited, and
can be selected such that hard phase particle having an average
particle size within the above range are formed in the resulting
cast material. The pulverizing/mixing time is typically 15 to 30
hours.
[0110] Next, the raw material powder is melted into a melt mixture,
and impurities such as gas and oxides are removed from the melt
mixture if necessary. In this process, the melting temperature is
determined according to the materials used, and is preferably
1100.degree. C. to 1300.degree. C., more preferably 1200.degree. C.
to 1250.degree. C.
[0111] Next, the melt mixture obtained as described above can be
casted into a cast material by pouring the melt mixture into a cast
material mold such as a mold of desired shape, and then cooling the
melt mixture.
[0112] In the present embodiment, the step of cooling the melt
mixture includes continuously cooling the melt mixture at a cooling
rate of 100.degree. C./min or more over the temperature range of
the cooling start temperature to 400.degree. C. In the present
embodiment, the expression "includes continuously cooling the melt
mixture at a cooling rate of 100.degree. C./min or more" means that
the cooling rate is continuously controlled to 100.degree. C./min
or more for a certain period of time. The cooling step preferably
includes cooling at a cooling rate of 100.degree. C./min or more
for 1 minute or more, more preferably 5 minutes or more. For
example, a case where the cooling rate instantaneously reaches
100.degree. C./min or more (for example, a case where the cooling
rate reaches 100.degree. C./min or more for 1 second or less) is
not included. Although it is sufficient that the step of cooling
the melt mixture includes continuously cooling the melt mixture at
a cooling rate of 100.degree. C./min or more over the temperature
range of the cooling start temperature to 400.degree. C., the
cooling rate is preferably 200.degree. C./min or more, more
preferably 400.degree. C./min or more. When the melt mixture is
cooled under the above conditions, the average particle size of the
hard phase particles, the average aspect ratio of the hard phase
particles, and the contact ratio between the hard phase particles
of the resulting cast material can be controlled within the above
ranges.
[0113] In the present embodiment, any method for cooling the melt
mixture can be used without limitation, and an example thereof is
to pour the melt mixture into a mold preferably having a
temperature of room temperature to 1100.degree. C., more preferably
300.degree. C. to 1100.degree. C., and cool the melt mixture. The
room temperature is, for example, 1.degree. C. to 30.degree. C.
[0114] Any casting method can be used without limitation, but
casting methods such as mold casting, lost-wax casting, continuous
casting, and centrifugal casting are preferably used because these
methods enables formation of cast materials having complicated
shapes and formation of thick-walled cast materials.
[0115] In the present embodiment, the cast material obtained by
cooling under the above conditions is then subjected to a heat
treatment at a temperature of 700.degree. C. to 950.degree. C. The
heat treatment under such a condition causes a phase transition
from the metastable phase (Ni.sub.31Si.sub.12) to the stable phase
(Ni.sub.3Si), thereby remarkably improving the bending strength of
the cast material.
[0116] The temperature for the heat treatment of the cast material
is 700.degree. C. to 950.degree. C., as described above, and is
preferably 750.degree. C. to 900.degree. C., more preferably
800.degree. C. to 850.degree. C. When the temperature for the heat
treatment is within the above range, the phase transition from the
metastable phase (Ni.sub.31Si.sub.12) to the stable phase
(Ni.sub.3Si) successfully occurs, thereby resulting in improved
bending strength of the cast material. When the temperature for the
heat treatment is too high, specifically higher than 950.degree.
C., the metastable phase (Ni.sub.31Si.sub.12) is generated again.
At a temperature of higher than 1,000.degree. C., the cast material
may melt and deform.
[0117] In the present embodiment, the temperature for the heat
treatment of the cast material is 700.degree. C. to 950.degree. C.,
as described above, but preferably satisfies the following
expression (1) in order to more successfully cause the phase
transition from the metastable phase (Ni.sub.31Si.sub.12) to the
stable phase (Ni.sub.3Si) in the cast material, and therefore to
further improve the bending strength of the cast material.
-85.324x+966.13.ltoreq.y.ltoreq.-85.324x+1216.1 (1)
(In the expression (1), x is the content (unit: % by weight) of B
in the cast material, and y is the temperature for the heat
treatment.)
[0118] In the present embodiment, the temperature for the heat
treatment of the cast material more preferably satisfies the
following expression (2).
-85.324x+1016.1.ltoreq.y.ltoreq.-85.324x+1166.1 (2)
(In the expression (2), x is the content (unit: % by weight) of B
in the cast material, and y is the temperature for the heat
treatment.)
[0119] The treatment time for the heat treatment of the cast
material is not particularly limited, and is preferably 0.17 to 3
hours, more preferably 0.33 to 2 hours, further preferably 0.5 to
1.5 hours. When the treatment time for the heat treatment is within
the above range, the phase transition from the metastable phase
(Ni.sub.31Si.sub.12) to the stable phase (Ni.sub.3Si) more
successfully occurs in the cast material, thereby further improving
the bending strength of the cast material.
[0120] The cast material of the present embodiment is manufactured
as described above.
[0121] The cast material of the present embodiment contains the
hard phase particles mainly composed of a boride and the binder
phase containing an alloy containing Ni.sub.3Si and Ni.sub.3B. The
average particle size of the hard phase particles is controlled to
3 .mu.m or less. The average aspect ratio of the hard phase
particles is controlled to 2.0 or less. The contract ratio between
the hard phase particles is 35% or less. The cast material has an
intensity ratio I.sub.A/I.sub.B controlled to 1/10 or less, where
I.sub.A is the intensity of a peak derived from Ni.sub.31Si.sub.1
observed at a diffraction angle 2.theta. within the range of
46.8.degree. to 47.8.degree., and I.sub.B is the intensity of a
peak derived from Ni.sub.3Si observed at a diffraction angle
2.theta. within the range of 44.0.degree. to 45.0.degree., the
intensities being determined by X-ray diffraction measurement using
CuK.alpha. radiation. Due to these features, the cast material of
the present embodiment has excellent corrosion resistance and
excellent wear resistance, and has high hardness and high bending
strength.
[0122] Since the cast material of the present embodiment has
excellent corrosion resistance and excellent wear resistance, and
has high hardness and high bending strength, the cast material can
be suitably used as a wear resistant material that can exhibit
excellent durability even in environments under a high load (e.g.,
rolls, cylinders, bearings, industrial pump components, and the
like).
EXAMPLES
[0123] Hereinafter, the present invention is described in more
detail by way of examples, but the present invention is not limited
to these examples.
[0124] The definition and the evaluation method for each
characteristic are described as follows.
<Average Number of Interfaces between NiB Phase and NiSi Phase
in Eutectic Part>
[0125] Two secondary electron images were captured at two sites in
a cross section of a cast material using a field emission Auger
microprobe (Auger) after Ar etching. Five straight lines in one
direction and five straight lines perpendicular to the former lines
were drawn on each of the captured secondary electron images in the
manner described above. The number of interfaces between the NiB
phase and the NiSi phase on the ten straight lines was determined.
Next, the average per .mu.m of length (unit: number of interfaces
/.mu.m) was calculated from the sum of the numbers of interfaces on
the ten straight lines.
<Hardness>
[0126] The cast material was measured for hardness (Rockwell C
scale hardness).
<Bending Strength>
[0127] The cast material was cut into a test piece having a size of
4 mm.times.8 mm.times.24 am. The obtained test piece was measured
for bending strength (unit: MPa) in accordance with JIS B4104
(three-point bending flexural test).
<Intensity Ratio I.sub.A/I.sub.Q>
[0128] The cast material was subjected to X-ray diffraction
measurement using an X-ray diffraction device (RINT2500/PC,
available from Rigaku Corporation) under the conditions: X-ray
source: CuK.alpha., 40 kV, 200 mA, emission slit: 2.degree.,
scattering slit: 1.degree., receiving slit: 0.3 m, and measurement
range: 30.degree.<2.theta.<60.degree.. From a diffraction
pattern obtained by the X-ray diffraction measurement, the
intensity I.sub.A of a peak derived from Ni.sub.31Si.sub.12
observed at a diffraction angle 2.theta. within the range of
46.8.degree. to 47.8.degree. and the intensity I.sub.B of a peak
derived from Ni.sub.1Si observed at a diffraction angle 2.theta.
within the range of 44.0.degree. to 45.0.degree. were calculated,
and the ratio I.sub.A/I.sub.B of these intensities were
calculated.
<Average Particle Size of Hard Phase Particle, Average Aspect
Ratio of Hard Phase Particle, Contact Ratio Between Hard Phase
Particles>
[0129] A reflection electron image of a cross section of the cast
material was captured using a scanning electron microscope (SEM),
and the average particle size of the hard phase particles, the
average aspect ratio of the hard phase particles, and the contract
ratio between the hard phase particles were determined in the
manner described above.
Example 1
[0130] First, a Ni-based self-fluxing alloy (melting point:
985.degree. C., composition: 0.02% by weight of C, 2.27% by weight
of B, 7.03% by weight of Si, and 0.11% by weight of Fe, with the
remainder being Ni) was prepared as a raw material powder. The raw
material powder was then placed in a crucible, and was heated and
hardened using a vacuum furnace at 1160.degree. C. for 30 minutes
to prepare an ingot. The ingot was melted by heating to
1200.degree. C. in air using an air atmosphere furnace to prepare a
raw material melt. The obtained raw material melt at 1200.degree.
C. was poured into a mold at room temperature, and was then air
cooled to roam temperature. Thus, a cast material was obtained by
air casting. In this process, when measured 2 minutes after being
taking out from the furnace, the melt mixture had a temperature of
400.degree. C. Namely, the melt mixture was cooled from
1200.degree. C. to 400.degree. C. in 2 minutes after being taken
out from the air atmosphere furnace, and the cooling rate of the
melt mixture was 400.degree. C./min. This result shows that the
melt mixture was continuously cooled at a cooling rate of about
400.degree. C./min over the range of 1200.degree. C. to 400.degree.
C.
[0131] Subsequently, the average number of interfaces between the
NiB phase and the NiSi phase in the eutectic part of the obtained
cast material was determined in the manner described above. The
results are shown in Table 1.
[0132] FIGS. 1 and 2 show secondary electron images captured in two
view fields to determine the average number of interfaces (the
images were captured at two sites in a cross section of the cast
material, one of the images is referred to as View Field 1, and the
other is referred to as View Field 2). The secondary electron
images shown in FIG. 1 have magnifications of .times.3,000 and
.times.10,000, respectively. The secondary electron image at
.times.10,000 was used to determine the number of interfaces (the
same applies to FIGS. 3 to 5 described below). In View Field 1, the
NiB phase is present in a grain-like form. In View Field 2, the
NiSi phase extends in a net-like form.
[0133] The cast material of Example 1 was subjected to X-ray
diffraction measurement using an X-ray diffraction apparatus (RINT
2500/PC, available from Rigaku Corporation) under the conditions:
X-ray source: CuK, 40 kV, 200 mA, emission slit: 2.degree.,
scattering slit: 1.degree., receiving slit: 0.3 am, and measurement
range: 20.degree.<2.theta.<80.degree.. The measurement
results are shown in FIG. 6(A). In FIG. 6(A), a circle and a square
indicate the peaks derived from Ni.sub.3Si and the peaks derived
from Ni.sub.3B respectively (the same applies to FIGS. 6(B), 7(A)
and 7(B)).
Example 2
[0134] A cast material was manufactured in the same manner as in
Example 1, and the obtained cast material was subjected to a heat
treatment at 800.degree. C. for 1 hour. The heat-treated cast
material was evaluated in the same manner as above. The results are
shown in Table 1. FIG. 3 shows two secondary electron images (View
Field 1 and View Field 2) captured to determine the average number
of interfaces. The NiB phase is present in a grain-like form in
View Field 1 of FIG. 3, and the NiSi phase extends in a net-like
form in View Field 2. The cast material of Example 2 was further
subjected to X-ray diffraction measurement in the same manner as in
Example 1. The measurement results are shown in FIG. 6(B).
Comparative Example 1
[0135] A cast material was obtained by placing the raw material
powder used in Example 1 in a crucible, melting the raw material
powder in vacuo at 1200.degree. C. for 30 minutes using a vacuum
furnace, and cooling the melt in an Ar atmosphere in the furnace.
The obtained cast material was evaluated in the same manner as
above, and the results are shown in Table 1. FIG. 4 shows two
secondary electron images (View Field 1 and View Field 2) captured
to determine the average number of interfaces. The NiB phase is
present in a grain-like form in the View Field 1 of FIG. 4, and the
NiSi phase extends in a net-like form in the View Field 2. The cast
material of Comparative Example 1 was further subjected to X-ray
diffraction measurement in the same manner as in Example 1. The
measurement results are shown in FIG. 7(A).
Comparative Example 2
[0136] A cast material was manufactured in the same manner as in
Comparative Example 1, and the obtained cast material was subjected
to a heat treatment at 800.degree. C. for 1 hour. The heat-treated
cast material was evaluated in the same manner as above, and the
results are shown in Table 1. FIG. 5 shows two secondary electron
images (View Field 1 and View Field 2) captured to determine the
average number of interfaces. In the View Field 1 of FIG. 5, the
NiB phase is present in a grain-like form, and in the View Field 2,
the NiSi phase extends a net-like form. The cast material of
Comparative Example 2 was further subjected to X-ray diffraction
measurement in the same manner as in Example 1. The results are
shown in FIG. 7(B).
TABLE-US-00001 TABLE 1 Average number of interfaces Heat (number of
interfaces/.mu.m) treament Straight line in y1 Straight line in x1
Manu- Temper- direction direction facturing ature Time View View
View View method (.degree. C.) (hr) Field 1 Field 2 Field 1 Field 2
Average Example 1 Air N/A 4.3 2.7 2.4 2.9 3.1 Example 2 casting 800
1 2.4 2.5 2.5 2.5 2.5 Comparative Vacuum N/A 1.2 1.5 0.7 0.5 1.0
Example 1 casting Comparative 800 1 0.7 0.6 0.4 0.6 0.6 Example
2
[0137] Subsequently, the cast materials of Examples 1 and 2 and
Comparative Example 1 were measured for hardness and bending
strength in the manners described above. The results are shown in
Table 2
TABLE-US-00002 TABLE 2 Average number of interfaces (number of
interfaces/.mu.m) Physical Straight line in y1 Straight line in x1
properties direction direction Bending View View View View strength
Hardness Field 1 Field 2 Field 1 Field 2 Average (MPa) (HRC)
Example 1 4.3 2.7 2.4 2.9 3.1 2370 61 Example 2 2.4 2.5 2.5 2.5 2.5
2400 61 Comparative Example 1 1.2 1.5 0.7 0.5 1.0 800 58
[0138] The cast material of Example 1 was further evaluated for
corrosion resistance in the following manner. Specifically, the
cast material was cut into a test piece having a size of
10.0.times.7.5.times.3.5 nm, and the prepared test piece was
weighed. The test piece was then placed in a centrifuge tube
together with a test solution (a 10 wt % sulfuric acid aqueous
solution, a 10 wt % hydrochloric acid aqueous solution, or a 10 wt
% phosphoric acid aqueous solution). The centrifuge tube was
immersed in water controlled at 40.degree. C., and was held therein
for 10 hours. The test piece was then taken out, and was weighed
again to determine the reduction in weight (unit: % by weight). A
smaller reduction in weight can be determined as better corrosion
resistance. In addition to the cast material of Example 1, an alloy
tool steel material SKD11 (HRC60) (Reference Example 1) and a
stainless steel material SUS304 (Reference Example 2) were also
evaluated for corrosion resistance. The results are shown in Table
3.
[0139] The cast material of Example 1 was further evaluated for
wear resistance in the following manner. Specifically, the cast
material was cut into a plate-like test piece having a size of
25.times.50.times.5 mm and a ring-like test piece having a diameter
of 31 mm and a thickness of 3 mm. The obtained plate-like test
piece and ring-like test piece each were tested with an Okoshi-type
wear tester to measure the reduction in the volume (unit: mm.sup.2)
of the test piece. Thus, a sliding wear test was performed. The
sliding wear test was performed under the following conditions:
finial load: 19.5 kgf; sliding distance: 200 m; and sliding speed:
0.20 m/s, 0.45 m/s, and 0.9 m/s. A smaller wear amount (a smaller
reduction in volume) can be determined as better wear resistance.
In addition to the cast material of Example 1, the alloy tool steel
material SKD11 (HRC60) (Reference Example 1) was also evaluated for
corrosion resistance. The results are shown in Table 3.
TABLE-US-00003 TABLE 3 Corrosion resistance (% by weight) 10 wt %
10 wt % 10 wt % Wear resistance (mm.sup.2) sulfuric acid
hydrochrolic phosphoric Sliding Sliding Sliding aqueous acid
aqueous acid aqueous speed speed speed solution solusion solution
0.20 m/s 0.45 m/s 0.9 m/s Example 1 0.015 0.032 0.015 0.310 0.172
0.138 Reference Example 9.822 3.702 3.106 0.591 0.310 1.286 1
(SKD11) Reference Example 0.059 0.157 0.000 -- -- -- 2 (SUS304)
[0140] Tables 1 and 2 show that the cast materials of Examples 1
and 2, whose average number of interfaces between the NiB phase and
the NiSi phase in the eutectic part was 2.0 /.mu.m or more, had
high hardness and high bending strength. In particular, the bending
strength thereof was remarkably high.
[0141] Table 3 show that the cast material of Example 1 was
excellent in corrosion resistance and wear resistance compared to
the cast materials of Reference Examples 1 and 2.
[0142] As shown in FIGS. 6 (A) and 6(B), it is presumed that in
Example 2 (FIG. 6(B)) in which the cast material was subjected to
the heat treatment, the diffusion of atoms in the eutectic part was
promoted by the heat treatment, thereby eliminating a disturbed
arrangement of atoms in the eutectic part. This leads to further
stabilization of crystals of Ni.sub.3B, Ni.sub.3Si, and the like in
the eutectic part and a reduced variation in the bending strength
of the entire cast material compared to the cast material of
Example 1 (FIG. 6(A)) which was not subjected to the heat
treatment.
[0143] On the other hand, Tables 1 and 2 show that the cast
material of the Comparative Example 1, whose average number of
interfaces between the NiB phase and the NiSi phase in the eutectic
part was less than 2.0 /.mu.m, had a smaller bending strength.
Likewise, the cast material of Comparative Example 2 is presumed to
also have a smaller bending strength because its average number of
interfaces between the NiB phase and the NiSi phase in the eutectic
part was also less than 2.0 /.mu.m.
Example 3
[0144] A powder mixture was obtained by dry mixing 5% by weight of
a Mo.sub.2NiB.sub.2-type multiple boride (composed of 8.1% by
weight of B, 71.8% by weight of Mo, and 14.6% by weight of Cr with
the remainder being Ni) and 95% by weight of a Ni-based
self-fluxing alloy (composed of 0.06% by weight or less of C, 2.3%
by weight of B, 7.1% by weight of Si, and 1.5% by weight or less of
Fe with the remainder being Ni). Subsequently, the obtained powder
mixture was heated and hardened in vacuo using a vacuum furnace at
1160.degree. C. for 30 minutes to prepare an ingot. The ingot was
then melted by heating to 1200.degree. C. in air using an air
atmosphere furnace to prepare a raw material melt. The obtained raw
material melt at 1200.degree. C. was poured into a mold at room
temperature, and was air cooled to room temperature in air. As a
result, a cast material containing the Mo.sub.2NiB.sub.2-type
multiple boride as a hard phase was obtained by air cast material.
In this process, when measured 2 minutes after being taking out
from the furnace, the melt mixture had a temperature of 400.degree.
C. Namely, the melt mixture was cooled from 1200.degree. C. to
400.degree. C. in 2 minutes after being taken out from the air
atmosphere furnace, and the cooling rate of the melt mixture was
400.degree. C./min. This result shows that the melt mixture was
continuously cooled at a cooling rate of about 400.degree. C./min
over the range of 1200.degree. C. to 400.degree. C.
[0145] Subsequently, the obtained cast material was subjected to a
heat treatment at 750.degree. C. for 1 hour.
[0146] The heat-treated cast material was measured for the
intensity ratio I.sub.A/I.sub.B, the hardness, and the bending
strength in the manners described above. The results are shown in
Table 4.
[0147] In Table 4, when the intensity ratio I.sub.A/I.sub.B was
1/75 or less, it was determined that the binder phase was
substantially free from Ni.sub.31Si.sub.12, and thus had a
composition composed of "Ni solid solution, Ni.sub.3Si, and
Ni.sub.3B". On the other hand, when the intensity ratio
I.sub.A/I.sub.B was more than 1/75, it was determined that the
binder phase contained Ni.sub.31Si.sub.12, and thus had a
composition composed of "Ni solid solution, Ni.sub.3Si, Ni.sub.3B,
and Ni.sub.31Si.sub.12".
Examples 4 to 7
[0148] Cast materials were manufactured and evaluated in the same
manner as in Example 3 except that the condition of the heat
treatment for the cast material (the temperature for the heat
treatment) was changed as shown in Table 4. The results are shown
in Table 4.
Comparative Examples 3 to 5
[0149] Cast materials were manufactured and evaluated in the same
manner as in Example 3 except that the condition of the heat
treatment for the cast material (the temperature for the heat
treatment) was changed as shown in Table 4. In Comparative Example
3, the heat treatment was not performed. The results are shown in
Table 4.
[0150] Another cast material was manufactured in the same manner as
in Example 3 except that the heat treatment for the cast material
was performed at 1000.degree. C. for 1 hour (the temperature for
the heat treatment was changed). Unfortunately, this cast material
was melted and deformed during the heat treatment.
TABLE-US-00004 TABLE 4 Physical Amount of Heat treatment
Composition properties Mo.sub.2NiB Manu- Temper- Intensity Bending
Hard- added facturing ature Hour Hard ratio strength ness (% by
weight) method (.degree. C.) (hr) phase Binder phase
I.sub.A/I.sub.B (MPa) (HRC) Example 3 5 Air 750 1 Mo.sub.2NiB.sub.2
Ni solid solution, Ni.sub.3Si, 1/12.6 1064 63.5 casting Ni.sub.3B,
Ni Si Example 4 800 Mo.sub.2NiB.sub.2 Ni solid solution,
Ni.sub.3Si, 1/181.6 1344 62.6 Ni.sub.3B Example 5 850
Mo.sub.2NiB.sub.2 Ni solid solution, Ni.sub.3Si, 1/101.4 1348 62.0
Ni.sub.3B Example 6 900 Mo.sub.2NiB.sub.2 Ni solid solution,
Ni.sub.3Si, 1/2273.9 1389 60.9 Ni.sub.3B Example 7 950
Mo.sub.2NiB.sub.2 Ni solid solution, Ni.sub.3Si, 1/1238.8 1447 60.2
Ni.sub.3B Comparative N/A Mo.sub.2NiB.sub.2 Ni solid solution,
Ni.sub.3Si, 1/2.3 882 63.4 Example 3 Ni.sub.3B, Ni.sub.31Si.sub.12
Comparative 400 1 Mo.sub.2NiB.sub.2 Ni solid solution, Ni.sub.3Si,
1/0.4 873 61.1 Example 4 Ni.sub.3B, Ni.sub.31Si.sub.12 Comparative
600 Mo.sub.2NiB.sub.2 Ni solid solution, Ni.sub.3Si, 1/1.9 803 62.3
Example 5 Ni.sub.3B, Ni.sub.31Si.sub.12 indicates data missing or
illegible when filed
Example 8
[0151] A cast material was manufactured and evaluated in the same
manner as in Example 3 except that the powder mixture used was
obtained by dry mixing 10% by weight of an Mo.sub.2NiB.sub.2
multiple boride (composed of 8.1% by weight of B, 71.8% by weight
of Mb, and 14.6% by weight of Cr, with the remainder being Ni) and
90% by weight of a Ni-based self-fluxing alloy (composed of 0.06%
by weight or less of C, 2.3% by weight of B, 7.1% by weight of Si,
and 1.5% by weight or less of Fe, with the remainder being Ni). The
obtained cast material was subjected to a heat treatment at
700.degree. C. for 1 hour, and was then evaluated in the same
manner as above. The results are shown in Table 5.
Examples 9 to 12
[0152] Cast materials were manufactured and evaluated in the same
manner as in Example 8 except that the condition of the heat
treatment for the cast material (the temperature for the heat
treatment) was changed as shown in Table 5. The results are shown
in Table 5.
Comparative Examples 6 to 8
[0153] Cast materials were manufactured and evaluated in the same
manner as in Example 8 except that the condition of the heat
treatment for the cast material (the temperature for the heat
treatment) was changed as shown in Table 5. In Comparative Example
6, the heat treatment was not performed. The results are shown in
Table 5.
[0154] Another cast material was manufactured in the same manner as
in Example 8 except that the heat treatment for the cast material
was performed at 1000.degree. C. for 1 hour (the temperature for
the heat treatment was changed). Unfortunately, this cast material
was melted and deformed during the heat treatment.
TABLE-US-00005 TABLE 5 Physical Amount of Heat treatment
Composition properties Mo.sub.2NiB.sub.2 Manu- Temper- Intensity
Bending Hard- added facturing ature Hour Hard ratio strength ness
(% by weight) method (.degree. C.) (hr) phase Binder phase
I.sub.A/I.sub.B (MPa) (HRC) Example 8 10 Air 700 1
Mo.sub.2NiB.sub.2 Ni solid solution, Ni.sub.3Si, 1/13.2 1004 62.7
casting Ni.sub.3B, Ni Si Example 9 800 Mo.sub.2NiB.sub.2 Ni solid
solution, Ni.sub.3Si, 1/124.4 1323 63.7 Ni.sub.3B Example 10 850
Mo.sub.2NiB.sub.2 Ni solid solution, Ni.sub.3Si, 1/738.6 1663 63.4
Ni.sub.3B Example 11 900 Mo.sub.2NiB.sub.2 Ni solid solution,
Ni.sub.3Si, 0 1680 61.4 Ni.sub.3B Example 12 950 Mo.sub.2NiB.sub.2
Ni solid solution, Ni.sub.3Si, 1/465.6 1621 61.3 Ni.sub.3B
Comparative N/A Mo.sub.2NiB.sub.2 Ni solid solution, 1/1.8 824 63.3
Example 6 Ni.sub.3B, Ni.sub.31Si.sub.12 Comparative 400 1
Mo.sub.2NiB.sub.2 Ni solid solution, 1/1.4 625 62.0 Example 7
Ni.sub.3B, Ni.sub.31Si.sub.12 Comparative 500 Mo.sub.2NiB.sub.2 Ni
solid solution, 1/1.6 726 61.8 Example 8 Ni.sub.3B,
Ni.sub.31Si.sub.12 indicates data missing or illegible when
filed
Example 13
[0155] A cast material was manufactured and evaluated in the same
manner as in Example 8 except that the powder mixture used was
obtained by dry mixing 15% by weight of an Mo.sub.2NiB.sub.2
multiple boride (composed of 8.1% by weight of B, 71.8% by weight
of Mo, and 14.6% by weight of Cr, with the remainder being Ni) and
85% by weight of a Ni-based self-fluxing alloy (composed of 0.06%
by weight or less of C, 2.3% by weight of B, 7.1% by weight of Si,
and 1.5% by weight or less of Fe, with the remainder being Ni). The
results are shown in Table 6. A diffraction pattern obtained by
X-ray diffraction measurement is shown in FIG. 12.
[0156] A cross section of the cast material of Example 13 was
further subjected to Ar etching using a field emission Auger
microprobe (Auger), and a secondary electron image thereof was
captured. The secondary image is shown in FIG. 13(A). In the
secondary electron image of FIG. 13(A), the states of crystals in
the cast material predicted from the results of measurement by
Auger electron spectroscopy (AES) are shown. The results confirm
that in Example 13, Mo.sub.2NiB.sub.2 constituting a hard phase and
Ni.sub.3Si and Ni.sub.31Si.sub.12 constituting a binder phase were
present.
Examples 14 to 18
[0157] Cast materials were manufactured and evaluated in the same
manner as in Example 13 except that the condition of the heat
treatment for the cast material (the temperature for the heat
treatment) was changed as shown in Table 6. The results are shown
in Table 6. Diffraction patterns obtained by X-ray diffraction
measurement in Examples 15 and 17 are shown in FIG. 12.
[0158] A cross section of the cast material of Example 15 was
further subjected to Ar etching using a field emission Auger
microprobe (Auger), and a secondary electron image thereof was
captured. The secondary image is shown in FIG. 13(B). In the
secondary electron image of FIG. 13(B), the states of crystals in
the cast material predicted from the result of measurement by Auger
electron spectroscopy (AES) are shown. The result confirms that in
Example 15, Mo.sub.2NiB.sub.2 constituting a hard phase and
Ni.sub.3Si and Ni.sub.3B constituting a binder phase were
present.
Comparative Examples 9 to 12
[0159] Cast materials were manufactured and evaluated in the same
manner as in Example 13 except that the condition of the heat
treatment for the cast material (the temperature for the heat
treatment) was changed as shown in Table 6. In Comparative Example
9, the heat treatment was not performed. The results are shown in
Table 6. Diffraction patterns obtained by X-ray diffraction
measurement in Comparative Examples 9 and 12 are shown in FIG.
12.
[0160] Another cast material was manufactured in the same manner as
in Example 13 except that the heat treatment for the cast material
was performed at 1000.degree. C. for 1 hour (the temperature for
the heat treatment was changed). Unfortunately, this cast material
was melted and deformed during the heat treatment.
[0161] A cross section of the cast material of Comparative Example
9 was further subjected to Ar etching using a field emission Auger
microprobe (Auger), and a secondary electron image thereof was
captured. In the secondary electron image of FIG. 13(C), the states
of crystals in the cast material predicted from the result of
measurement by Auger electron spectroscopy (AES) are shown. The
result confirms that in Comparative Example 9, Mo.sub.2NiB.sub.2
constituting a hard phase and Ni.sub.3Si and Ni.sub.31Si.sub.12
constituting a binder phase were present.
Comparative Example 13
[0162] A powder mixture obtained in the same manner as in Example
13 was placed in a crucible, and was melted in vacuo using a vacuum
furnace at 1200.degree. C. for 30 minutes. The melt was cooled in
an Ar atmosphere in a furnace (furnace-cooled). Thus, a cast
material was obtained. The time needed to cool the internal
temperature of the furnace to 400.degree. C. from the start of
cooling (introduction of Ar gas) was 68 minutes. Namely, the melt
mixture was cooled from 1200.degree. C. to 400.degree. C. in 68
minutes, and the cooling rate was 13.degree. C./min. The obtained
cast material was then evaluated in the same manner as above. The
results are shown in Table 6.
Comparative Example 14
[0163] A cast material was manufactured in the same manner as in
Comparative Example 13. The obtained cast material was subjected to
a heat treatment at 800.degree. C. for 1 hour, and was then
evaluated in the same manner as above. The results are shown in
Table 6.
TABLE-US-00006 TABLE 6 Physical Amount of Heat treatment
Composition properties Mo.sub.2NiB.sub.2 Manu- Temper- Intensity
Bending Hard- added facturing ature Hour Hard ratio strength ness
(% by weight) method (.degree. C.) (hr) phase Binder phase
I.sub.A/I.sub.B (MPa) (HRC) Example 13 15 Air 700 1
Mo.sub.2NiB.sub.2 Ni solid solution, Ni.sub.3Si, 1/10.1 1014 65.4
casting Ni.sub.3B, Ni.sub.31Si.sub.12 Example 14 750
Mo.sub.2NiB.sub.2 Ni solid solution, Ni.sub.3Si, 1/154.5 1190 64.9
Ni.sub.3B Example 15 800 Mo.sub.2NiB.sub.2 Ni solid solution,
Ni.sub.3Si, 1/119.1 1563 64.5 Ni.sub.3B Example 16 850
Mo.sub.2NiB.sub.2 Ni solid solution, Ni.sub.3Si, 1/363.3 1704 64.3
Ni.sub.3B Example 17 900 Mo.sub.2NiB.sub.2 Ni solid solution,
Ni.sub.3Si, 0 1734 62.9 Ni.sub.3B Example 18 950 Mo.sub.2NiB.sub.2
Ni solid solution, Ni.sub.3Si, 1/12.6 1155 63.3 Ni.sub.3B,
Ni.sub.31Si.sub.12 Comparative N/A Mo.sub.2NiB.sub.2 Ni solid
solution, 1/0.4 838 64.2 Example 9 Ni.sub.3B, Ni.sub.31Si.sub.12
Comparative 400 1 Mo.sub.2NiB.sub.2 Ni solid solution, 1/1.3 661
64.7 Example 10 Ni.sub.3B, Ni.sub.31Si.sub.12 Comparative 500
Mo.sub.2NiB.sub.2 Ni solid solution, 1/1.2 840 64.2 Example 11
Ni.sub.3B, Ni.sub.31Si.sub.12 Comparative 600 Mo.sub.2NiB.sub.2 Ni
solid solution, Ni.sub.3Si, 1/0.8 891 65.4 Example 12 Ni.sub.3B,
Ni.sub.31Si.sub.12 Comparative Vacuum N/A Mo.sub.2NiB.sub.2 Ni
solid solution, Ni.sub.3Si, 1/6.2 598 63.3 Example 13 melting
Ni.sub.3B, Ni.sub.31Si.sub.12 Comparative 800 1 Mo.sub.2NiB.sub.2
Ni solid solution, Ni.sub.3Si, 1/3.9 701 63.0 Example 14 Ni.sub.3B,
Ni.sub.31Si.sub.12
[0164] As shown in Tables 4 to 6, the cast materials having an
intensity ratio I.sub.A/I.sub.B of 1/10 or less had a high bending
strength (Examples 3 to 18). Namely, the cast materials of Examples
3 to 18 had high bending strength and high hardness in addition to
excellent corrosion resistance and excellent wear resistance, which
are characteristics of cast materials containing hard phase
particles mainly composed of a boride and a binder phase containing
an alloy mainly composed of Ni.
[0165] FIG. 12 confirms that in the cast materials subjected to the
heat treatment, higher temperatures further promoted the phase
transition from the metastable phase (Ni.sub.31Si.sub.12) to the
stable phase (Ni.sub.3Si), increasing the content of the stable
phase Ni.sub.3Si. In particular, it is confirmed that the content
of the stable phase Ni.sub.3Si was remarkably increased by
controlling the temperature for the heat treatment to 700.degree.
C. or higher.
[0166] On the other hand, as shown in Tables 4 to 6, the cast
materials having an intensity ratio I.sub.A/I.sub.B of more than
1/10 resulted in a low bending strength (Comparative Examples 3 to
14).
[0167] The cast materials of Examples 4, 9 and 15 and Comparative
Examples 3, 6 and 9 were measured for the average particle size of
the hard phase particles, the average aspect ratio of the hard
phase particles, and the contact ratio between the hard phase
particles in the manners described above. The results are shown in
Table 7. Reflection electron images captured for measurement using
a scanning electron microscopy (SEM) are shown in FIG. 14.
[0168] The cast materials of Example 15 and Comparative Example 9
were further evaluated for corrosion resistance in the following
manner. Specifically, each cast material was cut into a test piece
having a size of 10.0.times.7.5.times.3.5 mm, and was weighed. The
test piece was then placed in a centrifuge tube together with a
test solution (a 10 wt % sulfuric acid aqueous solution, a 10 wt %
hydrochloric acid aqueous solution, or a 10 wt % phosphoric acid
aqueous solution). The centrifuge tube was immersed in water
controlled at 40.degree. C., and was held therein for 10 hours. The
test piece was then taken out, and was weighed again to determine
the reduction in weight (unit: % by weight). A smaller reduction in
weight can be determined as better corrosion resistance. In
addition to the cast materials of Example 15 and Comparative
Example 9, the alloy tool steel material SKD11 (HRC60) (Reference
Example 1) and the stainless steel material SUS 304 (Reference
Example 2) were also evaluated for corrosion resistance. The
results are shown in Table 8.
[0169] Additionally, the cast materials of Example 15 and
Comparative Example 9 were further evaluated for wear resistance in
the following manner. Specifically, each cast material was cut into
a plate-like test piece having a size of 25.times.50.times.5 mm and
a ring-like test piece having a diameter of 31 mm and a thickness
of 3 am. The obtained plate-like test piece and ring-like test
piece each were tested with an Okoshi-type wear tester to measure
the reduction in the volume (unit: mm.sup.2) of the test piece.
Thus, a sliding wear test was performed. The sliding wear test was
performed under the following conditions: finial load: 19.5 kgf;
sliding distance 200 m; and sliding speed: 0.445 m/s and 0.9 m/s. A
smaller wear amount (a smaller reduction in volume) can be
determined as better wear resistance. In addition to the cast
materials of Example 15 and Comparative Example 9, the alloy tool
steel material SKD11 (HRC60) (Reference Example 1) was also
evaluated for corrosion resistance. The results are shown in Table
8.
TABLE-US-00007 TABLE 7 Amount of Heat treatment Composition Hard
phase particle Mo.sub.2NiB.sub.2 Manu- Temper- Intensity Average
Contact added facturing ature Hour Hard ratio particle size Aspect
ratio (% by weight) method (.degree. C.) (hr) phase Binder phase
I.sub.A/I.sub.B (.mu.m) ratio (%) Example 4 5 Air 800 1
Mo.sub.2NiB.sub.2 Ni solid solution, Ni.sub.3Si, 1/181.6 2.05 1.6
13 casting Ni.sub.3B Example 9 10 800 Mo.sub.2NiB.sub.2 Ni solid
solution, Ni.sub.3Si, 1/124.4 2.55 1.8 24 Ni.sub.3B Example 15 15
800 Mo.sub.2NiB.sub.2 Ni solid solution, Ni.sub.3Si, 1/119.1 2.27
1.4 31 Ni.sub.3B Comparative 5 N/A Mo.sub.2NiB.sub.2 Ni solid
solution, Ni.sub.3Si, 1/2.3 2.67 1.6 9 Example 3 Ni.sub.3B,
Ni.sub.31Si.sub.12 Comparative 10 N/A Mo.sub.2NiB.sub.2 Ni solid
solution, Ni.sub.3B, 1/1.8 2.73 1.6 13 Example 6 Ni.sub.31Si.sub.12
Comparative 15 N/A Mo.sub.2NiB.sub.2 Ni solid solution, Ni.sub.3B,
1/0.4 2.20 1.6 27 Example 9 Ni.sub.31Si.sub.12
TABLE-US-00008 TABLE 8 Corrosion resistance (% by weight) Hard
phase particle 10 wt. % 10 wt. % 10 wt. % Wear Average sulfuric
hydrochrolic phosphoric resistance(mm.sup.5) Composition particle
Contact acid acid acid Sliding Sliding Intensity size Aspect ratio
aqueous aqueous aqueous speed speed ratio I.sub.A/I.sub.B (.mu.m)
ratio (%) solution solusion solution 0.445 m/s 0.5 m/s Example 15
1/119.1 2.27 1.4 31 0.070 0.065 0.052 0.156 0.220 Comparative 1/0.4
2.20 1.6 27 0.218 0.066 0.184 0.230 0.292 Example 9 Reference
Example 1 (SKD11) 9.822 3.702 3.106 0.310 1.286 Reference Example 2
(SUS304) 0.059 0.157 0.000 -- --
[0170] As shown in Tables 7 and 8, the cast material of Example 15,
which had an average particle size of the hard phase particles of 3
.mu.m or less, an average aspect ratio of the hard phase particles
of 2.0 or less, a contact ratio between the hard phase particles of
35% or less, and an intensity ratio I.sub.A/I.sub.B of 1/10 or
less, had corrosion resistance and wear resistance equivalent to or
higher than those of the cast material of Comparative Example 9 and
the materials of Reference Examples 1 and 2.
* * * * *