U.S. patent application number 13/137941 was filed with the patent office on 2012-04-26 for high hardness, high corrosion resistance and high wear resistance alloy.
This patent application is currently assigned to Toshiba Materials Co., Ltd.. Invention is credited to Tomohisa Arai, Nobuyoshi Jimbo, Takao Kusaka, Takashi Rokutanda.
Application Number | 20120097297 13/137941 |
Document ID | / |
Family ID | 36118819 |
Filed Date | 2012-04-26 |
United States Patent
Application |
20120097297 |
Kind Code |
A1 |
Rokutanda; Takashi ; et
al. |
April 26, 2012 |
High hardness, high corrosion resistance and high wear resistance
alloy
Abstract
There are provided a high hardness, high corrosion resistance
and high wear resistance alloy, wherein the alloy is an aging heat
treated Cr(chromium)-Al(aluminum)-Ni(nickel)-base alloy, the
proportion of a mixed phase of (.alpha. phase+.gamma.'
phase+.gamma. phase) precipitated at grain boundaries of .gamma.
phase grains in a metal structure in the cross section of the alloy
is not less than 95% in terms of area ratio, and the intensity
ratio as measured by X-ray diffractometry of the alloy is not less
than 50% and not more than 200% in terms of
I.alpha.(110)/[I.gamma.(200)+I.gamma.'(004)].times.100, and a
component comprising this alloy, a material for an alloy which can
form this alloy, and a process for producing this alloy. The
present invention can provide a Cr--Al--Ni-base alloy possessing
excellent corrosion resistance, hardness, wear resistance,
releasability, fatigue strength, and planishing property in a
molding face, a component comprising this alloy, a material for an
alloy which can form this alloy, and a process for producing this
alloy.
Inventors: |
Rokutanda; Takashi;
(Yokohama-shi, JP) ; Arai; Tomohisa;
(Yokohama-shi, JP) ; Kusaka; Takao; (Yokohama-shi,
JP) ; Jimbo; Nobuyoshi; (Odawara-shi, JP) |
Assignee: |
Toshiba Materials Co., Ltd.
Yokohama-shi
JP
Kabushiki Kaisha Toshiba
Tokyo
JP
|
Family ID: |
36118819 |
Appl. No.: |
13/137941 |
Filed: |
September 22, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11664275 |
Mar 30, 2007 |
8062441 |
|
|
PCT/JP05/17488 |
Sep 22, 2005 |
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13137941 |
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Current U.S.
Class: |
148/559 ;
148/405; 148/407; 148/410 |
Current CPC
Class: |
C22C 19/05 20130101;
C22C 19/052 20130101; C22C 19/058 20130101; C22F 1/10 20130101;
C22C 19/053 20130101; C22C 19/055 20130101 |
Class at
Publication: |
148/559 ;
148/405; 148/407; 148/410 |
International
Class: |
C21D 1/00 20060101
C21D001/00; C22C 28/00 20060101 C22C028/00; C22C 19/05 20060101
C22C019/05 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2004 |
JP |
2004-288964 |
Claims
1. A high hardness, high corrosion resistance and high wear
resistance alloy, wherein said alloy is an aging heat treated
Cr(chromium)-Al(aluminum)-Ni(nickel)-base alloy, the proportion of
a mixed phase of (.alpha. phase+.gamma.' phase+.gamma. phase)
precipitated at grain boundaries of .gamma. phase grains in a metal
structure in the cross section of the alloy is not less than 95% in
terms of area ratio, and the intensity ratio as measured by X-ray
diffractometry of the alloy is not less than 50% and not more than
200% in terms of
I.alpha.(110)/[I.gamma.(200)+I.gamma.'(004)].times.100.
2. The high hardness, high corrosion resistance and high wear
resistance alloy according to claim 1, which satisfies requirements
that: (i) the average grain diameter (D) of unaged .gamma. phase is
not more than 500 .mu.m; and (ii) the total length of the average
grain diameter (D) of unaged .gamma. phase and the average
precipitation width (W) of the mixed phase of (.alpha.
phase+.gamma.' phase+.gamma. phase) precipitated at the grain
boundaries is not more than 2 mm.
3. The high hardness, high corrosion resistance and high wear
resistance alloy according to claim 1, which comprises not less
than 25% by weight and not more than 60% by weight of Cr (chromium)
and not less than 1% by weight and not more than 10% by weight of
Al (aluminum) with the balance consisting of Ni (nickel), trace
elements and incidental impurities.
4. The high hardness, high corrosion resistance and high wear
resistance alloy according to claim 1, which comprises not less
than 30% by weight and not more than 45% by weight of Cr (chromium)
and not less than 2% by weight and not more than 6% by weight of Al
(aluminum) with the balance consisting of Ni (nickel), trace
elements and incidental impurities.
5. The high hardness, high corrosion resistance and high wear
resistance alloy according to claim 3 or 4, wherein a part of Cr
has been replaced with at least one element selected from Zr
(zirconium), Hf (hafnium), V (vanadium), Ta (tantalum), Mo
(molybdenum), W (tungsten), and Nb (niobium), provided that the
total amount of replacement of Zr, Hf, V, and Nb is not more than
1% by weight, the amount of replacement of Ta is not more than 2%
by weight, and the total amount of replacement of Mo and W is not
more than 10% by weight.
6. A high hardness, high corrosion resistance and high wear
resistance component formed of an alloy according to claim 1.
7. A material for a high hardness, high corrosion resistance and
high wear resistance alloy which can form an alloy according to
claim 1 by subjecting the material to aging heat treatment.
8. A material for a high hardness, high corrosion resistance and
high wear resistance alloy according to claim 7, wherein said
material is a solution treated material having such properties that
the intensity ratio as measured by X-ray diffractometry is not more
than 5% in terms of
I.gamma.'(110)/[I.gamma.'(110)+I.alpha.(110)+I.gamma.(200)+I.gamma.'(004)-
].times.100 and is not more than 5% in terms of
I.alpha.(110)/[I.gamma.'(110)+I.alpha.(110)+I.gamma.(200)+I.gamma.'(004)]-
.times.100, and the grain diameter is not more than 5 mm.
9.-11. (canceled)
12. A process for producing a high hardness, high corrosion
resistance and high wear resistance alloy, said process comprising
subjecting a material for an alloy according to claim 8 to
pretreatment heating prior to aging heat treatment, wherein the
material is heated to 400 to 700.degree. C. at a temperature rise
rate of not less than 100.degree. C./hr in the pretreatment
heating.
13. A process for producing a high hardness, high corrosion
resistance and high wear resistance alloy, said process comprising
subjecting a material for an alloy according to claim 8 to
pretreatment heating prior to aging heat treatment, wherein the
material is held in a temperature range of 400 to 500.degree. C.
for at least 0.5 hr in the pretreatment heating.
14. The process for producing a high hardness, high corrosion
resistance and high wear resistance alloy according to claim 12 or
13, wherein the aging heat treatment is carried out at 500 to
850.degree. C.
Description
TECHNICAL FIELD
[0001] The present invention is directed to a high hardness, high
corrosion resistance and high wear resistance alloy. More
specifically, the present invention is directed to a high hardness
and high corrosion resistance alloy, which is particularly suitable
for use under an environment in which corrosive materials such as
acids, alkalis, and salts are present, a component comprising this
alloy, a material for an alloy, which can form this alloy, and a
process for producing this alloy.
BACKGROUND ART
[0002] In compression molding a raw material such as powder or
granules into tablets of pharmaceuticals, quasi-drugs, cosmetics,
agricultural chemicals, feeds, foods or the like, a mold comprising
a combination of a mortar having through-holes corresponding to the
shape of tablets with a lower pestle and an upper pestle to be
inserted into the through-holes (mortar holes) has hitherto been
used. In a tablet molding machine using the above mold, a raw
material such as powder is filled into the mortar into which the
lower pestle has been inserted, and the raw material is compressed
by the upper pestle for molding into desired tablets.
[0003] As described, for example, in Japanese Patent Laid-Open No.
8540/1995, for example, iron-base alloys such as alloy tool steels,
for example, SKS2 and SKD11, or cemented carbide alloys composed
mainly of compounds of Mo (molybdenum), W (tungsten) and the like
have hitherto been adopted in molds used, for example, in tablet
molding machines.
[0004] Further, in order to improve corrosion resistance of molds
such as alloy tool steels, an attempt has also been made to coat
the surface with a chromium plating. However, satisfactory effect
cannot be attained due to the separation of the plating layer. The
chromium plating layer can have a given effect for an improvement,
for example, in surface hardness. Since, however, the chromium
plating layer per se is disadvantageously easily separated,
satisfactory and stable wear resistance improvement effects and the
like cannot be attained. This has led to a demand for an
improvement, for example, in corrosion resistance and wear
resistance while maintaining strength and hardness of the member
for a mold.
[0005] In order to solve the problem of wear resistance, Japanese
Patent Laid-Open No. 62595/2001 describes high hardness and high
corrosion resistance tablet molding pestle and mortar. This alloy
has high hardness and high corrosion resistance and, at the same
time, has releasability. Although this alloy can maintain good
releasability for approximately a few hours immediately after
tablet molding, a further improvement in releasability has been
desired for mass production purposes. Further, since this alloy has
a relatively low fatigue strength, an increase in strength has been
desired, and, in addition, the possession of a planishing property
of the molding face has also been desired.
[0006] On the other hand, applications in which corrosion
resistance is required include not only manufacturing equipment
such as the above-described mold for corrosive powder but also
processing equipment for chemicals, processing equipment for waste
liquids or waste sludge, combustion apparatuses, and their
peripheral components. Further, corrosion resistant steels such as
stainless steels have been used in applications where corrosion
resistance is mainly required, for example, molds for resin lenses
or engineering plastics or other resins, and components such as
cutting tools and direct acting bearings. Corrosion resistant
steels such as stainless steels, however, are unsatisfactory, for
example, in strength and hardness and, thus, cannot be used in
applications where hardness and wear resistance are particularly
required.
[0007] For example, Japanese Patent Laid-Open No. 18031/1988
describes a high corrosion resistance hot pressing mold comprising
20 to 50% by mass of Cr (chromium) and 1.5 to 9% by mass of Al
(aluminum) with the balance consisting essentially of Ni (nickel).
This hot pressing mold has such properties that it exhibits high
hardness against hot pressing under conditions of temperature 500
to 800.degree. C. and pressing pressure 500 to 2000 kg/cm.sup.2 (50
to 200 MPa) and has buckling resistance. Further, the mold has been
found to have corrosion resistance against Ni and Cr. So far as the
present inventors know, however, this mold component of an
Ni--Cr--Al-base alloy possesses excellent material hardness and
corrosion resistance, but on the other hand, the wear resistance is
not always satisfactory and, for some service conditions, wear
progresses in a sliding part of the component, disadvantageously
leading to shortened component service life.
[0008] Good planishing properties are required of molds for resin
lenses and resins such as the so-called "engineering plastics."
Since, however, the conventional steel product is an alloy which is
hardened by a relatively large precipitated carbide, pores are
formed due to falling of precipitated carbide particles during
polishing and, in addition, damage to the polished surface by
fallen particles, making it difficult to conduct planishing.
Further, in the conventional steel material, Ni plating or CrN
coating is carried out for releasability improvement purposes. The
conventional steel material, however, is disadvantageous in that
the releasability is not satisfactory, the releasability is
deteriorated depending upon surface roughness, and the
releasability varies depending upon wear.
[0009] In order to improve the wear resistance, Japanese Patent
Laid-Open No. 88431/2002 describes a member comprising a case
hardened layer provided on this Ni--Cr--Al-base alloy. A further
improvement in releasability, an improvement in fatigue strength,
and an improvement in planishing properties of the molding face
have been desired. In particular, molds for resin molding had a
serious problem involved in the production thereof associated with
releasability that the molding resin is likely to adhere to the
mold.
[0010] The realization of a homogeneous metal structure is desired
for improving the releasability, the fatigue strength, and the
planishing property of the molding face. That is, when an unaged
structure is present, in molding powder or the like, the powder is
cut into the unaged soft phase and the amount of the powder adhered
is gradually increased, resulting in deteriorated releasability.
Further, since the unaged soft layer is present, the fatigue
strength is lowered. Furthermore, there is a tendency that a
difference in hardness between the aging precipitated phase and the
unaged phase affects polishing and causes a difference in polishing
between the aging precipitated phase and the unaged phase, leading
to a tendency that planishing becomes difficult. As reported in
Materia Japan (a bulletin of The Japan Institute of Metals), Vol.
22, No. 4, p. 323, in the precipitated phase of this alloy system
after aging treatment, a .gamma.' phase is composite precipitated
in a thin layer form at boundaries between the layered a phase and
.gamma. matrix phase to form a characteristic three-layer structure
of .alpha., .gamma.', and .gamma. parent phases. In this
conventional production process of this alloy, even after aging
heat treatment at a proper temperature of 650.degree. C. to
800.degree. C., a certain level of an unaged .gamma. phase stays,
and, thus, a complete three-phase (.alpha., .gamma.', and .gamma.)
structure cannot be realized.
[0011] Accordingly, in order to improve the releasability, fatigue
strength, and the planishing property of the molding face, a
reduction in unaged phase and homogeneous refinement have been
desired. Further, stable precipitation of three phases (.alpha.,
.gamma.', and .gamma.) in the aged structure has also been desired.
[0012] Patent document 1: Japanese Patent Laid-Open No. 62595/2001
[0013] Patent document 2: Japanese Patent Laid-Open No. 18031/1988
[0014] Patent document 3: Japanese Patent Laid-Open No. 88431/2002
[0015] Non-patent document 1: Materia Japan (a bulletin of The
Japan Institute of Metals), Vol. 22, No. 4, p. 323
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0016] The present invention has been made with a view to solving
the above problems of the prior art, and an object of the present
invention is to provide an alloy for a mold for resin molding that
has improved releasability, fatigue strength, and planishing
property of the molding face while maintaining strength required of
the mold for press molding of powder, plastics or the like and
corrosion resistance against corrosive materials such as acidic
powder, and to provide a mold component for a mold for resin
molding.
Means for Solving the Problems
[0017] The above object can be attained as follows.
[0018] According to the present invention, there is provided a high
hardness, high corrosion resistance and high wear resistance alloy,
wherein said alloy is a Cr(chromium)-Al(aluminum)-Ni(nickel)-base
alloy, the proportion of a mixed phase of (.alpha. phase+.gamma.'
phase+.gamma. phase) precipitated at grain boundaries of .gamma.
phase grains in a metal structure in the cross section of the alloy
is not less than 95% in terms of area ratio, and the intensity
ratio as measured by X-ray diffractometry of the alloy is not less
than 50% and not more than 200% in terms of
I.alpha.(110)/[I.gamma.(200)+I.gamma.'(004)].times.100.
[0019] In a preferred embodiment of the present invention, the high
hardness, high corrosion resistance and high wear resistance alloy
according to the present invention satisfies requirements that:
[0020] (i) the average grain diameter (D) of unaged .gamma. phase
is not more than 500 .mu.m; and
[0021] (ii) the total length of the average grain diameter (D) of
unaged .gamma. phase and the average precipitation width (W) of the
mixed phase of (.alpha. phase+.gamma.' phase+.gamma. phase)
precipitated at the grain boundaries is not more than 2 mm.
[0022] In a preferred embodiment of the present invention, the high
hardness, high corrosion resistance and high wear resistance alloy
according to the present invention comprises not less than 25% by
weight and not more than 60% by weight of Cr (chromium) and not
less than 1% by weight and not more than 10% by weight of Al
(aluminum) with the balance consisting of Ni (nickel), trace
elements and incidental impurities.
[0023] In a further preferred embodiment of the present invention,
the high hardness, high corrosion resistance and high wear
resistance alloy according to the present invention comprises not
less than 30% by weight and not more than 45% by weight of Cr
(chromium) and not less than 2% by weight and not more than 6% by
weight of Al (aluminum) with the balance consisting of Ni (nickel),
trace elements and incidental impurities.
[0024] In a preferred embodiment of the present invention, in the
high hardness, high corrosion resistance and high wear resistance
alloy according to the present invention, a part of Cr has been
replaced with at least one element selected from Zr (zirconium), Hf
(hafnium), V (vanadium), Ta (tantalum), Mo (molybdenum), W
(tungsten), and Nb (niobium), provided that the total amount of
replacement of Zr, Hf, V, and Nb is not more than 1% by weight, the
amount of replacement of Ta is not more than 2% by weight, and the
total amount of replacement of Mo and W is not more than 10% by
weight.
[0025] Further, according to the present invention, there is
provided a high hardness, high corrosion resistance and high wear
resistance component formed of the above alloy according to the
present invention.
[0026] Furthermore, according to the present invention, there is
provided a material for a high hardness, high corrosion resistance
and high wear resistance alloy which can form an alloy according to
the present invention by subjecting the material to aging heat
treatment.
[0027] Furthermore, according to the present invention, there is
provided a material for a high hardness, high corrosion resistance
and high wear resistance alloy according to the present invention,
wherein said material is a solution treated material having such
properties that the intensity ratio as measured by X-ray
diffractometry is not more than 5% in terms of
I.gamma.'(110)/[I.gamma.'(110)+I.alpha.(110)+I.gamma.(200)+I.gamma.'(004)-
].times.100 and is not more than 5% in terms of
I.alpha.(110)/[I.gamma.(110)+I.alpha.(110)+I.gamma.(200)+I.gamma.'(004)].-
times.100, and the grain diameter is not more than 5 mm.
[0028] Furthermore, according to a present invention, there is
provided a process for producing a high hardness, high corrosion
resistance and high wear resistance alloy, said process comprising
subjecting the above material for an alloy according to the present
invention to aging heat treatment.
[0029] In a preferred embodiment of the present invention, in the
process for producing a high hardness, high corrosion resistance
and high wear resistance alloy according to the present invention,
the aging heat treatment is carried out at 500 to 850.degree.
C.
[0030] In a preferred embodiment of the present invention, in the
process for producing a high hardness, high corrosion resistance
and high wear resistance alloy according to the present invention,
prior to the aging heat treatment, said material is subjected to
(i) pretreatment heating in which the material is heated to 400 to
700.degree. C. at a temperature rise rate of not less than
100.degree. C./hr and not more than 500.degree. C./hr and (ii)
pretreatment heating in which the material is held in a temperature
range of 400 to 500.degree. C. for at least 0.5 hr.
Effect of the Invention
[0031] The present invention can provide a high hardness, high
corrosion resistance and high wear resistance alloy that has
excellent corrosion resistance, hardness, and wear resistance and,
at the same time, has releasability, fatigue strength, and
planishing property of the molding face.
[0032] The alloy according to the present invention can be utilized
in various applications by taking advantage of such excellent
properties, for example, is usable in the field of pharmaceuticals
and resin molding in which, even after use for a long period of
time in a corrosive environment under high temperature and high
pressure conditions, the level of deformation and wear should be
low and the releasability should also be excellent.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1A diagram showing the relationship between the area
ratio of a mixed phase of (.alpha. phase+.gamma.' phase+.gamma.
phase) in an alloy and the releasability.
[0034] FIG. 2A diagram showing the relationship between the area
ratio of a mixed phase of (.alpha. phase+.gamma.' phase+.gamma.
phase) in an alloy and the fatigue strength.
[0035] FIG. 3A diagram showing the relationship between the area
ratio of a mixed phase of (.alpha. phase+.gamma.' phase+.gamma.
phase) in an alloy and the planishing property.
[0036] FIG. 4A diagram showing the relationship between the
intensity ratio for an alloy as measured by X-ray diffractometry
and the releasability.
[0037] FIG. 5A diagram showing the relationship between the
intensity ratio for an alloy as measured by X-ray diffractometry
and the fatigue strength.
[0038] FIG. 6A diagram showing the relationship between the
intensity ratio for an alloy as measured by X-ray diffractometry
and the planishing property.
[0039] FIG. 7A typical view of a metal structure in a cross section
of a high hardness, high corrosion resistance and high wear
resistance alloy according to the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0040] The mode for carrying out the invention will be
described.
[0041] <High Hardness, High Corrosion Resistance and High Wear
Resistance Alloy>
[0042] It is generally observed that, in a solution treated
Cr--Al--Ni-base alloy, as aging heat treatment progresses, a mixed
phase of (.alpha. phase+.gamma.' phase+.gamma. phase) [that is, a
mixed phase composed of a phase, .gamma.' phase, and .gamma. phase]
is precipitated at boundaries of .gamma. phase grains and, at the
same time, the unaged phase part is gradually reduced.
[0043] The high hardness, high corrosion resistance and high wear
resistance alloy according to the present invention is a
Cr(chromium)-Al(aluminum)-Ni(nickel)-base alloy subjected to such
aging heat treatment, wherein the proportion of a mixed phase of
(.alpha. phase+.gamma.' phase+phase) precipitated at grain
boundaries of .gamma. phase grains in a metal structure in the
cross section of the alloy is not less than 95% in terms of area
ratio, and the intensity ratio as measured by X-ray diffractometry
of the alloy is not less than 50% and not more than 200% in terms
of I.alpha.(110)/[I.gamma.(200)+I.gamma.'(004)].times.100.
[0044] In the present invention, the proportion of the mixed phase
of (.alpha. phase+.gamma.' phase+.gamma. phase) is not less than
95%, preferably not less than 98%, particularly preferably 100%, in
terms of area ratio. When the proportion of the mixed phase of
(.alpha. phase+.gamma.' phase+.gamma. phase) is less than 95% in
terms of area ratio, the homogeneity of the structure is lowered
and, thus, the object of the present invention cannot be attained.
It is needless to say that the high hardness, high corrosion
resistance and high wear resistance alloy according to the present
invention embraces an alloy consisting essentially of a mixed phase
of (.alpha. phase+.gamma.' phase+.gamma. phase) (that is, an alloy
in which the proportion of the mixed phase of (.alpha.
phase+.gamma.' phase+.gamma. phase) is 100% in terms of area
ratio).
[0045] In the high hardness, high corrosion resistance and high
wear resistance alloy according to the present invention, the
intensity ratio for the alloy as measured by X-ray diffractometry
is not less than 50% and not more than 200%, preferably not less
than 70% and not more than 200%, particularly preferably not less
than 100% and not more than 200%, in terms of
I.alpha.(110)/[I.gamma.(200)+I.gamma.'(004)].times.100. When the
intensity ratio is outside the above-defined range, the object of
the present invention cannot be attained.
[0046] In this connection, it should be noted that .gamma.(111) or
.gamma.'(112) peak as a main peak was excluded, because the peak is
located near an .alpha.(110) peak and thus cannot be separated and
cannot be subjected to determination of the intensity ratio without
difficulties, or is likely to cause errors.
[0047] Among the high hardness, high corrosion resistance and high
wear resistance alloys according to the present invention specified
above, those satisfying the following requirements (i) and (ii) are
particularly preferred:
(i) the average grain diameter (D) of unaged .gamma. phase is not
more than 500 .mu.m; and (ii) the total length of the average grain
diameter (D) of unaged .gamma. phase and the average precipitation
width (W) of the mixed phase of (.alpha. phase+.gamma.'
phase+.gamma. phase) precipitated at the grain boundaries is not
more than 2 mm.
[0048] In requirement (i), the expression "the average grain
diameter (D) of the unaged .gamma. phase" means "the average value
of the maximum grain diameter of unaged .gamma. phase grains
surrounded by a mixed phase of (.alpha. phase+.gamma.'
phase+.gamma. phase) in metal crystal grains." Incidentally, when
the presence of "unaged .gamma. phase" is not substantially
observed, the "average grain diameter (D) of the unaged .gamma.
phase" is "0 .mu.m."
[0049] In requirement (ii), the expression "the average
precipitation width (W) of a mixed phase of (.alpha. phase+.gamma.'
phase+.gamma. phase) precipitated at grain boundaries" means "the
average value of the shortest distance between an unaged .gamma.
phase grain present in one metal crystal grain and another unaged
.gamma. phase grain present in another metal crystal grain adjacent
to this metal crystal grain." When the presence of the "unaged
.gamma. phase" is not substantially observed, for convenience, it
is regarded that an unaged .gamma. phase is present in the position
of the center of gravity in the crystal grain.
[0050] Accordingly, in such a case, the "average value" of the
distance between the positions of the center of gravity in adjacent
metal crystals is regarded as the average precipitation width (W)
of the mixed phase of (.alpha. phase
[0051] +.gamma.' phase+.gamma. phase) precipitated at the grain
boundaries.
[0052] The total length of the average grain diameter (D) of the
unaged .gamma. phase and the average precipitation width (W) of the
mixed phase of (.alpha. phase+.gamma.' phase+.gamma. phase)
precipitated at the grain boundaries (hereinafter often referred to
herein as "D+W") is not more than 2 mm, preferably not more than 1
mm. When the total length of the average grain diameter (D) and the
average precipitation width (W) (that is, "D+W") exceeds 2 mm, the
unaged part is likely to stay and, thus, the object of the present
invention cannot be attained. The above value of "D+W" determined
from a number of samples large enough to be statistically reliable
(that is, a satisfactory number of crystal grains) is substantially
equal to the value of the average diameter of the crystal grains.
Accordingly, in such a case, the value of "average diameter of
crystal grains" can be utilized as the value of "D+W."
[0053] In the present invention, the above-described "average grain
diameter (D)," "average precipitation width (W)," and "D+W" are
those determined by observing any desired sectional plane of a high
hardness, high corrosion resistance and high wear resistance alloy
according to the present invention under an optical microscope,
designating 20 crystal grains in total as a sample, measuring the
grain diameter and the precipitation width for the selected crystal
grains, and determining the average of the measurements to
determine D and W and determining D+W based these averages.
[0054] In one preferred embodiment of the present invention, the
high hardness, high corrosion resistance and high wear resistance
alloy according to the present invention comprises not less than
25% by weight and not more than 60% by weight of Cr (chromium) and
not less than 1% by weight and not more than 10% by weight of Al
(aluminum) with the balance consisting of Ni (nickel), trace
elements and incidental impurities. In one further preferred
embodiment, the high hardness, high corrosion resistance and high
wear resistance alloy according to the present invention comprises
not less than 30% by weight and not more than 45% by weight of Cr
(chromium) and not less than 2% by weight and not more than 6% by
weight of Al (aluminum) with the balance consisting of Ni (nickel),
trace elements and incidental impurities.
[0055] In a preferred high hardness, high corrosion resistance and
high wear resistance alloy according to the present invention, Cr
is an element indispensable for ensuring corrosion resistance and
workability, and the content of Cr is preferably not less than 25%
by weight and not more than 60% by weight.
[0056] In a preferred high hardness, high corrosion resistance and
high wear resistance alloy according to the present invention, Al
is an alloying element that mainly acts on the hardness of the
alloy. When the Al content falls within the above-defined range, a
necessary level of hardness can be provided.
[0057] In a preferred high hardness, high corrosion resistance and
high wear resistance alloy according to the present invention, Ni
is an alloying element that mainly acts on the corrosion resistance
and workability of the alloy and is present as one of balance
elements, that is, elements other than Cr and Al, in the high
hardness, high corrosion resistance and high wear resistance alloy
according to the present invention.
[0058] In a preferred high hardness, high corrosion resistance and
high wear resistance alloy according to the present invention, a
part of Cr is replaced with at least one element selected from Zr
(zirconium), Hf (hafnium), V (vanadium), Ta (tantalum), Mo
(molybdenum), W (tungsten), and Nb (niobium), provided that the
total amount of replacement of Zr, Hf, V, and Nb is not more than
1% by weight, the amount of replacement of Ta is not more than 2%
by weight, and the total amount of replacement of Mo and W is not
more than 10% by weight. The replacement of a part of Cr with one
or at least two elements of Zr (zirconium), Hf (hafnium), V
(vanadium), Ta (tantalum), Mo (molybdenum), W (tungsten), and Nb
(niobium) can further improve the hardness of the alloy.
[0059] Further, in a preferred high hardness, high corrosion
resistance and high wear resistance alloy according to the present
invention, a part of Al may be replaced with Ti, provided that the
total amount of replacement of Ti (titanium) is preferably not more
than 1% by weight. This is effective in regulating the hardness of
the alloy.
[0060] The high hardness, high corrosion resistance and high wear
resistance alloy according to the present invention may optionally
contain Mg (magnesium). A high hardness, high corrosion resistance
and high wear resistance alloy having an Mg content of not more
than 0.25% by weight is one preferred embodiment of the present
invention.
[0061] In the high hardness, high corrosion resistance and high
wear resistance alloy according to the present invention, other
trace elements and incidental impurities which may be intentionally
or unavoidably mixed in the alloy, include, for example, C
(carbon), Mn (manganese), P (phosphorous), O (oxygen), S (sulfur),
Cu (copper), and Si (silicon). The total amount of these elements
is preferably not more than 0.3% by weight.
[0062] Unlike the conventional Cr--Al--Ni-base alloy or steel
product, the high hardness, high corrosion resistance and high wear
resistance alloy according to the present invention is free from
the formation of the pores by falling of precipitated carbide
particles during polishing and damage to polished face by the
fallen particles and thus can be evenly polished, whereby a
specular surface can be provided in a short time. Further, three
phases of .alpha., .gamma.', and .gamma. in the aged structure are
stably precipitated. Therefore, a local battery of .alpha.,
.gamma.', and .gamma. phases is formed, and the interfacial energy
of solid/gas interface is larger than solid/solid interface and
solid/liquid interface, and the releasability is improved. Further,
regardless of the surface roughness, the releasability is good, and
a wear-derived variation in releasability is not significant.
[0063] Thus, the present invention can provide a high hardness,
high corrosion resistance and high wear resistance alloy possessing
corrosion resistance, hardness, wear resistance, releasability,
fatigue strength and planishing property.
[0064] <High Hardness, High Corrosion Resistance and High Wear
Resistance Component>
[0065] The high hardness, high corrosion resistance and high wear
resistance component according to the present invention is formed
of the above high hardness, high corrosion resistance and high wear
resistance alloy. The term "component" as used herein refers to not
only the so-called "parts," which are incorporated, for example, in
machines and apparatuses to function as one constituent part of
machines, apparatuses and the like but also to articles which are
used solely without combining with other parts or the like.
[0066] As described above, the alloy according to the present
invention possesses excellent corrosion resistance, hardness and
wear resistance and, at the same time, possesses releasability,
fatigue strength, and planishing property of the molding face.
Accordingly, the high hardness, high corrosion resistance and high
wear resistance component according to the present invention is
particularly suitable for various applications where such various
properties are required. For example, the high hardness, high
corrosion resistance and high wear resistance component according
to the present invention is particularly suitable in components for
molding devices for compressing a raw material such as powder or
granules, for example, highly corrosive powder such as acidic
powder and alkaline powder, into tablets of pharmaceuticals,
quasi-drugs, cosmetics, agricultural chemicals, feeds, foods or the
like, for example, a mortar having through-holes corresponding to
the shape of tablets and a lower pestle and an upper pestle to be
inserted into the through-holes (mortar holes).
[0067] Further, the high hardness, high corrosion resistance and
high wear resistance component according to the present invention
is particularly suitable as components for resin production
machines or apparatuses, for example, for resin molding machines.
For example, the high hardness, high corrosion resistance and high
wear resistance component according to the present invention is
particularly suitable as components for machines for molding of
resins, for example, (i) general-purpose resins, for example,
polyethylenes, polyvinyl chlorides, polystyrenes, and ABS resins,
and (ii) engineering plastics, for example, polyamides,
polycarbonates, modified polyethylene ethers, polyphenylene
sulfides, polyamideimides, polyetherimides, and polyimides. The
high hardness, high corrosion resistance and high wear resistance
component according to the present invention, even when used for a
long period of time in a corrosive environment under high
temperature and high pressure conditions in producing high
functional resins, is less likely to undergo deformation or wear
and has excellent releasability.
[0068] <Material for High Hardness, High Corrosion Resistance
and High Wear Resistance Alloy>
[0069] The present invention also relates to a material for an
alloy that can form the above high hardness, high corrosion
resistance and high wear resistance alloy by subjecting the
material to aging heat treatment.
[0070] A specific example of a preferred material for an alloy is a
solution treated material having such properties that the intensity
ratio as measured by X-ray diffractometry is not more than 5% in
terms of
I.gamma.'(110)/[I.gamma.'(110)+I.alpha.(110)+I.gamma.(200)+I.gamma.'(004)-
].times.100 and is not more than 5% in terms of
I.alpha.(110)/[I.gamma.'(110)+I.alpha.(110)+I.gamma.(200)+I.gamma.'(004)]-
.times.100, and the grain diameter is not more than 5 mm.
[0071] The material for an alloy according to the present invention
is more preferably such that (i) the intensity ratio as measured by
X-ray diffractometry is not more than 1% in terms of
I.gamma.'(110)/[I.gamma.'(110)+I.alpha.(110)+I.gamma.(200)+I.gamma.'(004)-
].times.100, (ii) the intensity ratio as measured by X-ray
diffractometry is not more than 1% in terms of
I.alpha.(110)/[I.gamma.'(110)+I.alpha.(110)+I.gamma.(200)+I.gamma.'(004)]-
.times.100, and (iii) the crystal grain diameter is not more than 2
mm.
[0072] The material for an alloy according to the present invention
is preferably produced, for example, by forming an ingot of a
Cr--Al--Ni-base alloy by a melting process, subjecting the ingot to
hot working and cold working, optionally working the material into
a suitable shape, and then subjecting the material to solid
solution treatment in such a manner that the material is subjected
to solid solution heat treatment in an argon or nitrogen atmosphere
or under the atmospheric pressure at a suitable temperature for a
suitable time (preferably at a temperature of 1000 to 1300.degree.
C. for 30 to 120 min) and is then immersed in an oil for
quenching.
[0073] The aging heat treatment will be described later.
[0074] <Production Process of High Hardness, High Corrosion
Resistance and High Wear Resistance Alloy>
[0075] The process for producing a high hardness, high corrosion
resistance and high wear resistance alloy according to the present
invention is characterized by subjecting the above material for an
alloy to aging heat treatment.
[0076] The aging heat treatment adopted in the present invention is
preferably carried out at 500 to 850.degree. C., particularly at
600 to 750.degree. C., for 1 to 8 hr, particularly for 3 to 5
hr.
[0077] In the present invention, before the aging heat treatment of
the material for an alloy, the material is preferably subjected to
suitable pretreatment heating. In the present invention, upon the
pretreatment heating, in the aging heat treatment, the metal
structure can be more homogeneously precipitated. Further, the
metal structure precipitation speed can be optimized, and, at the
same time, the occurrence of cracks in the interior of the alloy
material can be prevented.
[0078] Preferred methods of pretreatment heating before the aging
heat treatment include (i) a method in which the material is heated
to a temperature of 400 to 700.degree. C. at a temperature rise
rate of not less than 100.degree. C./hr and not more than
500.degree. C./hr, preferably not less than 100.degree. C./hr and
not more than 400.degree. C./hr, and (ii) a method in which the
material is kept at a temperature range of 400 to 500.degree. C.
for at least 0.5 hr. When the temperature rise rate in the method
(i) is lower than 100.degree. C./hr, the property requirements can
be satisfied. In this case, however, the necessary treatment time
is excessively long and, thus, a temperature rise rate of lower
than 100.degree. C./hr is unfavorable from the viewpoint of
production. When the temperature rise rate exceeds 500.degree.
C./hr, the level of heterogenization of the temperature
distribution and the level of volume shrinkage caused by
precipitation are excessively high, often leading to cracking. When
the holding time in the method (ii) is less than 0.5 hr, the effect
of this pretreatment heating is unsatisfactory. The upper limit of
the holding time is preferably 5 hr. Even when the heat treatment
is carried out for longer than 5 hr, the effect is saturated.
[0079] The material for an alloy according to the present invention
(the metal crystal in this material for an alloy being composed
mainly of an .alpha. phase), when subjected to this aging heat
treatment, preferably subjected to the above aging heat treatment
after the above pretreatment heating, causes precipitation of a
mixed phase of (.alpha. phase+.gamma.' phase+.gamma. phase) to
produce the high hardness, high corrosion resistance and high wear
resistance alloy according to the present invention. That is, full
precipitation of fine crystals of micron size by this aging heat
treatment results in the production of an alloy according to the
present invention possessing excellent corrosion resistance,
hardness, wear resistance, releasability, fatigue strength and
planishing property of the molding face.
EXAMPLES
Example 1
[0080] A Cr--Al--Ni-base alloy was melted by a vacuum melting
method and was casted. This Cr--Al--Ni-base alloy comprised 38.2%
by weight of Cr (chromium), 3.78% by weight of Al (aluminum), and
0.012% by weight of Mg (magnesium) with the balance consisting of
Ni (nickel) (hereinafter referred to as "alloy A").
[0081] The alloy A thus obtained was forged to prepare a round bar
having a size of 30 mm in diameter.times.1000 mm in length. This
round bar was subjected to solution treatment in a vacuum heat
treatment furnace of which the atmosphere had been brought to an
argon atmosphere, at a temperature of 1200.degree. C. for 2 hr. The
round bar was then immersed in an oil and was subjected to solution
treatment and was cut into a size of 30 mm in diameter.times.10 mm
in length with a water cooled cuter or a wire cutter.
[0082] Next, this material was introduced into a vacuum furnace,
and the atmosphere in the vacuum furnace was subjected to
degassing. The material was then subjected to aging heat treatment
in an argon atmosphere at a temperature of 850.degree. C. for 5 hr
and was subsequently cooled in an Ar gas over a period of one hr so
that the material was cooled to around a temperature of 150.degree.
C. Thereafter, the material was taken out of the vacuum furnace to
produce a high hardness, high corrosion resistance and high wear
resistance alloy according to the present invention. It was
confirmed that, in this alloy, no unaged .gamma. phase was observed
and, thus, the proportion of the (.alpha. phase+.gamma.'
phase+.gamma. phase) mixed phase was 100% in terms of area ratio.
The intensity ratio was measured by X-ray diffractometry in the
same manner as described above and was found to be not more than
162% in terms of
I.alpha.(110)/[I.gamma.(200)+I.gamma.'(004)].times.100.
[0083] Upon aging heat treatment, the surface of this material
became somewhat cloudy. The material, however, could easily be
planished by finish planishing with a polisher.
Examples 2 to 8 and Comparative Examples 1 to 4
[0084] High hardness, high corrosion resistance and high wear
resistance alloys (Examples 2 to 8) according to the present
invention and comparative alloys (Comparative Examples 1 to 4) were
produced and were evaluated in the same manner as in Example 1,
except that the aging heat treatment temperature was varied as
shown in Table 1.
[0085] The results were as shown in Table 1.
[0086] Each parameter in Table 1 was measured as follows. The
intensity ratio as measured by X-ray diffractometry was determined
by applying X-ray (CuKa line) to the surface of each alloy and
measuring each peak ratio.
[0087] The powder adherence was determined as follows. A citric
acid hydrate powder was spread between two alloy samples of the
upper sample and the lower sample (30 mm in diameter.times.10 mm in
length), and a load of 490 MPa was applied from the top of the
assembly. Thereafter, the upper sample was removed, and the area
ratio (%) of the powder adhered when the test was carried out with
the powder adherence face of the upper sample and the lower sample
being placed in the lower position, was determined.
[0088] The resin moldability was determined by preparing a mold
from an alloy sample, molding the resin using this mold, repeating
this work 10000 times, and determined the percentage defective of
the molded resins (resin molded products).
[0089] The fatigue strength was determined by carrying out a
tensile compression fatigue test (repetition frequency not more
than 40 Hz) to determine a fatigue strength (MPa) necessary for
breaking the sample at 6.times.10.sup.6 cycles. For example, a
fatigue strength of 780 MPa means that the sample breaks when the
sample is rotarily hammered by 6.times.10.sup.6 times at 780
MPa.
[0090] The planishing property was determined by measuring the
proportion of defects present on the surface of the sample after
planishing to a surface roughness Ra level of not more than 1
.mu.m. In this case, the measurement conforms to the cleanness d
(%) specified in attached document 1 in JIS G 0555. Specifically,
the measurement was carried out under conditions of d60.times.400
(number of fields 60 and magnification 400 times).
TABLE-US-00001 TABLE 1 Releasability Alloy Solution heat Aging
Aging Area ratio of X-ray intensity Powder Resin Fatigue Planishing
compo- treatment temp., time, precipitated D, D + W, ratio of
adherence*.sup.2, moldability*.sup.3, strength*.sup.4,
property*.sup.5, nent temp., .degree. C. .degree. C. H layer, %
.mu.m .mu.m alloy*.sup.1, % % % MPa % Ex. 1 A 1200 850 5 100 0 --
162 2.0 0.01 780 0.065 Ex. 2 A 1200 800 5 100 0 -- 172 2.3 0.02 750
0.045 Ex. 3 A 1200 750 5 100 0 -- 150 0.9 0.01 660 0.008 Ex. 4 A
1200 700 5 100 0 -- 143 1.9 0.01 510 0.021 Ex. 5 A 1200 650 5 100 0
-- 117 0.7 0.02 410 0.015 Ex. 6 A 1200 600 5 99 100 1050 128 1.7
0.03 360 0.023 Ex. 7 A 1200 550 5 97 120 1080 70 2.2 0.01 320 0.043
Ex. 8 A 1200 500 5 96 200 1110 55 3.4 0.05 290 0.058 Comp. A 1200
450 5 73 520 1120 12 7.8 0.15 170 0.105 Ex. 1 Comp. A 1200 400 5 35
850 1100 3 11.6 0.20 150 0.155 Ex. 2 Comp. A 1200 350 5 15 990 1130
0 15.4 0.22 180 0.222 Ex. 3 Comp. A 1200 300 5 12 1020 1100 0 16.2
0.20 200 0.243 Ex. 4 X-ray intensity ratio of alloy*.sup.1:
I.alpha.(110)/[I.gamma.(200) + I.gamma.'(004)] .times. 100 Powder
adherence*.sup.2: Adherence amount//compressed powder amount (%)
(citric acid used) in compression test Resin moldability*.sup.3:
Percentage defective of resin molding (%) (10000-time test) Fatigue
strength*.sup.4: Strength at cycles to failure 6 .times. 19.sup.6
Planishing property*.sup.5: Cleanness d (%) specified in JIS G
0555
Examples 9 to 11 and Comparative Examples 5 to 9
[0091] High hardness, high corrosion resistance and high wear
resistance alloys (Examples 9 to 11) according to the present
invention and comparative alloys (Comparative Examples 5 to 9) were
produced and were evaluated in the same manner as in Example 1,
except that a Cr--Al--Ni-base alloy comprising 38.1% by weight of
Cr, 3.79% by weight of Al, and 0.001% by weight of Mg with the
balance consisting of Ni (hereinafter referred to as "alloy B") was
used instead of "alloy A" and the conditions were changed as shown
in Table 2. The results were as shown in Table 2.
TABLE-US-00002 TABLE 2 Releasability Alloy Solution heat Aging
Aging Area ratio of X-ray intensity Powder Resin Fatigue Planishing
compo- treatment temp., time, precipitated D, D + W, ratio of
adherence, moldability, strength, property, nent temp., .degree. C.
.degree. C. H layer, % .mu.m .mu.m alloy, % % % MPa % Ex. 9 B 1200
850 5 100 0 -- 155 2.3 0.02 720 0.032 Ex. 10 B 1200 800 5 100 0 --
132 2.0 0.05 610 0.017 Ex. 11 B 1200 750 5 98 110 1080 96 2.5 0.06
390 0.025 Comp. B 1200 700 5 76 520 1100 42 8.5 0.23 190 0.124 Ex.
5 Comp. B 1200 650 5 68 590 1030 34 10.3 0.27 180 0.203 Ex. 6 Comp.
B 1200 600 5 63 610 1000 38 14.2 0.62 190 0.135 Ex. 7 Comp. B 1200
550 5 56 720 1050 27 13.7 0.53 180 0.168 Ex. 8 Comp. B 1200 500 5
44 790 1100 36 14.5 0.68 210 0.208 Ex. 9
Examples 12 to 14 and Comparative Examples 10 to 14
[0092] High hardness, high corrosion resistance and high wear
resistance alloys (Examples 12 to 14) according to the present
invention and comparative alloys (Comparative Examples 10 to 14)
were produced and were evaluated in the same manner as in Example
1, except that the solution treatment temperature and the aging
heat treatment temperature were varied as shown in Table 3.
[0093] The results were as shown in Table 3.
TABLE-US-00003 TABLE 3 Releasability Alloy Solution heat Aging
Aging Area ratio of X-ray intensity Powder Resin Fatigue Planishing
compo- treatment temp., time, precipitate D, D + W, ratio of
adherence, moldability, strength, property, nent temp., .degree. C.
.degree. C. H layer, % .mu.m .mu.m alloy*.sup.3, % % % MPa % Ex. 12
A 1300 850 5 100 0 -- 179 2.4 0.02 760 0.018 Ex. 13 A 1300 800 5 98
210 1890 134 3.8 0.03 670 0.021 Ex. 14 A 1300 750 5 96 320 1960 88
3.1 0.06 450 0.036 Comp. A 1300 700 5 80 720 2110 45 9.3 0.43 200
0.142 Ex. 10 Comp. A 1300 650 5 62 1140 2040 34 12.6 0.46 180 0.293
Ex. 11 Comp. A 1300 600 5 44 1480 2080 27 22.1 0.52 190 0.224 Ex.
12 Comp. A 1300 550 5 37 1660 2160 38 18.3 0.63 170 0.241 Ex. 13
Comp. A 1300 500 5 34 1710 2090 31 20.1 0.48 190 0.261 Ex. 14
Examples 15 to 30
[0094] High hardness, high corrosion resistance and high wear
resistance alloys (Examples 15 to 30) according to the present
invention were produced using the same alloy component as in
Example 1 and were evaluated in the same manner as in Example 1,
except that, prior to the aging heat treatment, pretreatment
heating shown in Table 4 or 5 was carried out. The results were as
shown in Tables 4 and 5.
TABLE-US-00004 TABLE 4 Releaseability Solution Heating Area X-ray
Pow- Resin Plan- Alloy heat Aging Aging as pretreatment (i) ratio
of intensity der ad- mold- Fatigue ishing compo- treatment temp.,
time, Temp., Temp. rise rate, precipitate D, D + W, ratio of
herence, ability, strength, property, nent temp., .degree. C.
.degree. C. H .degree. C. .degree. C./H layer, % .mu.m .mu.m alloy,
% % % MPa % Ex. 15 A 1200 850 5 600 400 100 0 -- 162 2.0 0.01 780
0.065 Ex. 16 A 1200 800 5 600 300 100 0 -- 172 2.3 0.02 750 0.045
Ex. 17 A 1200 750 5 600 300 100 0 -- 150 0.9 0.01 660 0.008 Ex. 18
A 1200 700 5 600 300 100 0 -- 143 1.9 0.01 510 0.021 Ex. 19 A 1200
650 5 600 300 100 0 -- 117 0.7 0.02 410 0.015 Ex. 20 A 1200 600 5
600 300 99 100 1050 128 1.7 0.03 360 0.023 Ex. 21 A 1200 550 5 550
200 97 120 1080 70 2.2 0.01 320 0.043 Ex. 22 A 1200 500 5 500 200
96 200 1110 55 3.4 0.05 290 0.058
TABLE-US-00005 TABLE 5 Releasability Solution Heating Area X-ray
Pow- Resin Plan- Alloy heat Aging Aging as pretreatment (ii) ratio
of intensity der ad- mold- Fatigue ishing compo- treatment temp.,
time, Temp., Temp. holding precipitate D, D + W ratio of herence,
ability, strength, property, nent temp., .degree. C. .degree. C. H
.degree. C. time, H layer, % .mu.m .mu.m alloy, % % % MPa % Ex. 23
A 1200 850 5 500 0.5 100 0 -- 172 1.8 0.02 780 0.062 Ex. 24 A 1200
800 5 500 0.5 100 0 -- 170 2.1 0.01 740 0.042 Ex. 25 A 1200 750 5
500 1.0 100 0 -- 155 1.2 0.01 660 0.009 Ex. 26 A 1200 700 5 500 1.0
100 0 -- 145 1.5 0.02 520 0.020 Ex. 27 A 1200 650 5 500 0.5 100 0
-- 142 1.0 0.02 420 0.016 Ex. 28 A 1200 600 5 500 0.5 100 90 1050
135 1.8 0.02 350 0.022 Ex. 29 A 1200 550 5 450 0.5 98 100 1070 72
2.1 0.02 310 0.041 Ex. 30 A 1200 500 5 400 0.5 98 180 1110 60 3.1
0.04 290 0.054
[0095] Based on data obtained in Examples 1 to 14 and Comparative
Examples 1 to 10,
[0096] (i) the relationship between the area ratio of (.alpha.
phase+.gamma.' phase+.gamma. phase) mixed phase and the
releasability, fatigue strength, and planishing property was
determined (FIGS. 1 to 3), and
[0097] (ii) the relationship between the X-ray intensity and the
releasability, fatigue strength, and planishing property was
determined (FIG. 4 to FIG. 6).
[0098] As can be seen from data shown in Tables 1 to 5 and FIGS. 1
to 6, corrosion resistant alloys having excellent releasability,
fatigue strength, and planishing property could be obtained when
the proportion of a mixed phase of (.alpha. phase+.gamma.'
phase+.gamma. phase) is not less than 95% in terms of area ratio,
and the intensity ratio as measured by X-ray diffractometry is not
less than 50% and not more than 200% in terms of
I.alpha.(110)/[I.gamma.(200)+I.gamma.'(004)].times.100.
* * * * *