JPH10195502A - Stainless steel powder, stainless steel member and production of the stainless steel member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain stainless steel powder subjected to cold working to form into the raw material for a high strength and high toughness stainless steel member by subjecting the raw material powder of a stainless steel to mechanical milling for a specified time at an ordinary temp. SOLUTION: The raw material powder is suitably composed of 316L series austenitic stainless steel powder and contains 16 to 18% Cr, 12 to 15% Ni and 2 to 3% Mo. This powder is, e.g. charged to a device for milling such as an 'Attoritor(R)', a ball mill or the like and is subjected to cold working at an ordinary temp. for about several min. to several hundreds time. In this way, strains are given to the crystals of the raw material powder by intensive working, and after that, recrystallization occurs, but the average grain size of the crystals is extremely small of several tens to several hundreds nm. The stainless steel powder subjected to the cold working is subjected to heat treatment at 600 at 800 deg.C and is furthermore sintered at a temp. more than the heat treating temp. and also less than 1400 deg.C, by which a member having an ultrafine structure in which austenitic phases and sigma phases are uniformly mixed can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold-worked stainless steel powder by mechanical milling, a stainless steel member manufactured by using the cold-worked stainless steel powder, and a method of manufacturing the stainless steel member. It is.

[0002]

2. Description of the Related Art It is known that reducing the size of crystal grains of a material itself is effective in increasing the strength and toughness of a metal material such as stainless steel. Conventionally, as a processing method for achieving such crystal grain refinement, after subjecting austenitic stainless steel to cold rolling, a suitable heat treatment is applied thereto, or wire drawing is performed on the stainless steel. Is performed.

[0003]

As shown in FIG. 6, the conventional austenitic stainless steel processed by the above method has an average crystal grain size of several μm to several tens μm.
m and the crystal grains have not been sufficiently refined yet, and the sigma phase B mainly composed of Fe and Cr is unevenly dispersed between the austenite phase A, but the sigma phase B is hard and Because of brittleness, there was a problem that the desired high strength and high toughness were not sufficiently realized. In addition, since the working method is limited to cold rolling or drawing, there is a problem that the shape of the product is limited to a thin plate, a thin wire, or the like.

[0004]

According to the present invention, there is provided a cold-worked stainless steel powder which is a raw material for producing a high-strength, high-toughness stainless steel member by a powder processing method. An object of the present invention is to provide a stainless steel member manufactured using powder and a method for manufacturing the stainless steel member. Therefore, the cold-worked stainless steel powder of the first aspect is obtained by subjecting a raw material powder of stainless steel to mechanical milling at room temperature for several minutes to several hundred hours.

The average particle size of the crystals in the raw material powder is considerably large, for example, several μm to several tens μm, but the raw material powder is gradually strained by the cold working by the mechanical milling, and the original crystal is destroyed. It is being done. Thereafter, as time passes, recrystallization starts inside the powder, and the average particle diameter of the recrystallized crystal is several tens nm to several tens.
0 nm, which is extremely fine. Such cold-worked stainless steel powder can be used as a raw material for injection molding, extrusion molding and the like.

The cold-worked stainless steel powder according to claim 2 is the composition according to claim 1, wherein the raw material powder for the stainless steel is 16 to 18% Cr, 12 to 15% Ni, M
o2 to 3%. The composition of the above components is SUS316 of JIS (Japanese Industrial Standard).
Alternatively, it corresponds to the SUS316L standard.

A third aspect of the present invention is a stainless steel member having a fine structure in which an austenite phase and a sigma phase are uniformly mixed, and having an average crystal grain size of 1 μm or less.

[0008] The stainless steel member of the fourth aspect is the third aspect of the invention.
In the above structure, the stainless steel member is subjected to mechanical milling at room temperature for several minutes to several hundred hours on a raw material powder of stainless steel, and then to a heat treatment at 600 to 800 ° C., and further to the heat treatment temperature or more and 1400 ° C. or less. Characterized by being sintered at a temperature of

As described above, by subjecting the raw material powder to cold working by mechanical milling, the average particle diameter of the crystal inside the powder is made extremely fine of about several tens to several hundreds nm, and then the sigma phase formation temperature is reduced. Area 600
After performing heat treatment at a temperature of from about 800 ° C. to about 800 ° C., sintering can be performed to obtain a fine structure in which an austenite phase and a sigma phase are mixed. Here, since the stainless steel member is manufactured by the powder processing method, the stainless steel member can be arbitrarily made in a bulk shape in addition to the plate material or the fine wire.

[0010] The stainless steel member according to the fifth aspect is the fourth aspect.
Wherein the raw material powder of the stainless steel is Cr
16-18%, Ni12-15%, Mo2-3%
It is characterized by including.

According to a sixth aspect of the present invention, the stainless steel material powder is subjected to mechanical milling at room temperature for several minutes to several hundred hours at a normal temperature, and then heat-treated at 600 to 800 ° C. (sigma phase formation temperature range). And sintering at a temperature not lower than the heat treatment temperature and not higher than 1400 ° C.

A method of manufacturing a stainless steel member according to claim 7 is characterized in that, in the method of claim 6, N ₂ gas or H ₂ gas is used as the sealing gas for the mechanical milling. The encapsulated N ₂ gas or H ₂ gas serves to make the powder hard and brittle, and to promote pulverization. During the heat treatment after the cold working, the N ₂ gas or the H ₂ gas is usually separated from the stainless steel.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. When a stainless steel member is manufactured by the powder processing method of the present invention, stainless steel powder having various component compositions can be used as a raw material powder. Preferably, JIS SUS316L (Cr
16-18%, Ni 12-15%, Mo2-3
%) Of austenitic stainless steel powder.

Then, the stainless steel powder is inserted into a milling device such as an attritor 1 or a ball mill as shown in FIG. 1 and subjected to cold working at room temperature for several minutes to several hundred hours. The attritor 1 is, for example,
A plurality of steel balls 4 are accommodated in a water-cooled container 3 having a cooling water circulation passage 2 formed in an outer peripheral portion thereof, and a stirring rod 5 extending in a horizontal direction is provided.
Is a device in which a vertical shaft 6 attached in a cross shape is rotatably disposed at the center of the water-cooled container 3. A stainless steel powder, Ar gas, N ₂
By rotating the shaft 6 with gas or H ₂ gas sealed, mechanical milling is performed on the stainless steel powder.

The above-mentioned stainless steel powder has a mean particle size of several tens μm to several hundreds μm at the stage of the raw material powder, and the average particle size of crystals in the powder is several tens μm.
Although being about μm, the crystal of the raw material powder is subjected to cold working by the attritor 1 so that the crystal is recrystallized after being subjected to strain by strong working. The average grain size of the crystals in the stainless steel powder that has been cold worked for a predetermined time and recrystallized becomes extremely small, several tens to several hundreds of nm.

The cold-processed stainless steel powder can be sold as it is as a raw material powder for injection molding or extrusion molding. Further, when sintering the cold-worked stainless steel powder to form a desired stainless steel member, the powder is stored in a predetermined container such as a mold, and the sigma phase generation temperature range of 600 to Around 800 ° C,
Preferably, heat treatment is performed at about 700 ° C. for a predetermined time (for example, about 2 hours) under a predetermined high pressure (for example, about 2000 atm).
At a temperature of about 400 ° C. or less, for example, about 800 ° C., for a predetermined time (for example, about 1 hour), at a predetermined high pressure (for example, 2 hours).
(Approximately 000 atm) for sintering.

The stainless steel member thus obtained has an ultrafine structure in which an austenite phase and a sigma phase are uniformly mixed, and has an average crystal grain size of 0.5 μm or less. That is, since mechanical milling has been performed on the stainless steel powder in advance, sintering is promoted by softening due to recrystallization of the cold-worked stainless steel powder and superplastic flow by ultra-fine crystal grains. In this case, since the grain growth is slow, an ultrafine grain structure is obtained.

The austenitic phase is rich in toughness, while the sigma phase is hard and brittle, but has high strength and high corrosion resistance. Becomes The sigma phase precipitates at the ultrafine austenite crystal grain boundaries, particularly at the triple point, and suppresses coarsening of the crystal grains.

Conventionally, it has been considered that the sigma phase is hard and brittle, so that the inclusion of the sigma phase in the structure of stainless steel is harmful. However, in the present invention, the crystal grain size is reduced and the austenite phase is reduced. By uniformly mixing the sigma phase with the sigma phase, the inventors succeeded in taking advantage of the advantages of the sigma phase such as higher strength and higher corrosion resistance than the disadvantages of the sigma phase.

The stainless steel members manufactured by the above method include, for example, decorative materials for measuring instruments such as watches, various tools,
Nuclear materials. As described above, in the present invention, since the powder processing method is used, not only conventional plate materials and thin wires but also stainless steel products of various shapes can be produced. Further, the stainless steel member may be a final product, but the stainless steel member is used as an intermediate product such as a plate material, and further processed such as bending to obtain a final product such as a can. It may be. In that case, the stainless steel plate material produced by the method of the present invention has a fine structure, and can be easily deformed by superplastic working.

[0021]

Next, a specific embodiment will be described. JIS SUS316L stainless steel powder (Cr 17.6%, Ni 12.3%, Mo 2.3%, C
0.01%, Si 0.49%, Mn 0.84%, P0.
01%, the balance Fe) was produced by PREP (plasma rotating electrode method). The average particle size of the powder is about 200μ
m. This raw material powder was subjected to mechanical milling for up to 400 hours in an Ar atmosphere using a planetary ball mill having a SUS316L stainless steel vessel with air cooling blades and a SUS304 stainless steel ball. The temperature of the outer wall of the container during the milling process is about 10 ° C. higher than room temperature.

FIG. 2 shows the relationship between the milling time and the hardness of the powder (Vickers hardness Hv). Further, FIG. 8 shows the hardness of the annealed material before processing (CW. 0%) and the hardness of the annealed material of 98%.
% Cold-rolled (CW 98%) hardness is also shown. As is clear from FIG. 2, after the start of powder milling,
After about 10 hours, the hardness became almost the same as that of a 98% cold-rolled material. Thereafter, the hardness increased with milling until about 200 hours, but after 200 hours, the powder gradually softened.

In the first half of the milling, the strain increases due to the strong working, but in the second half of the milling, the above-mentioned strain is recovered, and as the recrystallization progresses as finer crystals than before the milling, it becomes softer. Seem. Note that FIG.
Shows the structure of the powder subjected to mechanical milling for 400 hours, and this figure was made based on a micrograph.

The powder that has been subjected to mechanical milling for 200 hours is subjected to HIP at 490 MPa at 800 ° C. for 3 hours.
The sintered body was processed and subjected to a structure observation and a tensile test. FIG. 4 shows the structure after the HIP treatment, which was also made based on a micrograph. As shown in FIG. 4, the sigma phase indicated by hatching is uniformly dispersed in the austenite phase.

As shown in FIG. 4, the sintered body of this embodiment has a yield strength of 78.7 kg / mm ² and a tensile strength of 123.3 kg / m.
m ² and growth were 37.4%. On the other hand, the yield strength of the comparative material, which is an annealed SUS316L stainless steel having the same component composition as the above example, is 23.4 kg.
/ Mm ² , tensile strength 93.5 kg / mm ² , growth 8
It was 4.6%.

As is evident from the above results, the sintered body of this example has significantly improved both the yield strength and the tensile strength as compared with the comparative material. On the other hand, the growth is inferior to that of the comparative material. However, in such a stainless steel material, it is usually sufficient if the growth is about 20%.
If the value is 7.4%, there is no problem.

FIG. 5 shows the relationship between tensile strength and spread of various stainless steel materials. Curve C is a ferritic SUS43
0, curve D is austenitic SUS304, curve E
Is austenitic SUS301, and point F is SUS316L in the present embodiment. Further, a straight line G indicated by a virtual line is an ideal curve of the relationship between the tensile strength and the spread, and in the present embodiment, the straight line G is located near the ideal curve G.

[0028]

As described above, the cold-worked stainless steel powder of the present invention is subjected to mechanical milling at a normal temperature for several minutes to several hundred hours on the raw material powder of stainless steel, whereby a high strain is applied to the powder. The stainless steel member having high strength, high toughness, and high corrosion resistance by using such cold-worked stainless steel powder as a raw material for injection molding, extrusion molding, etc. Can be manufactured.

The cold-worked stainless steel powder of claim 2 is the same as that of claim 1, wherein the raw material powder of the stainless steel is 16 to 18% of Cr, 12 to 15% of Ni,
o2 to 3%, and stainless steel having such a composition is particularly preferable in order to obtain the above-described good properties such as high strength, high toughness, and high corrosion resistance.

The stainless steel member according to claim 3 has a fine structure in which an austenite phase and a sigma phase are uniformly mixed, and has an average crystal grain size of 1 μm or less, preferably 0.5 μm or less.
m, the stainless steel member has high strength, high toughness, and high corrosion resistance.

The stainless steel member according to the fourth aspect is the third aspect.
In the above structure, the stainless steel member is subjected to mechanical milling at room temperature for several minutes to several hundred hours on the raw material powder of stainless steel, and then to a heat treatment at 600 to 800 ° C. (sigma phase generation temperature range). The sintering is performed at a temperature not lower than the heat treatment temperature and not higher than 1400 ° C. As described above, the powder that has been subjected to cold working by mechanical milling is heat-treated in the sigma phase generation temperature range, thereby sintering. The subsequent stainless steel member has an ultrafine structure in which the austenite phase and the sigma phase are uniformly mixed, and has high strength, high toughness, and high corrosion resistance.

The stainless steel member may be a final product itself. For example, by using a plate material of the above stainless steel member and subjecting it to a bending process or the like,
A final product may be obtained. Also in this case, the plate made of the stainless steel member can be easily formed by superplastic working.

The stainless steel member according to the fifth aspect is the fourth aspect.
Wherein the raw material powder of the stainless steel is Cr
16-18%, Ni12-15%, Mo2-3%
Such a component configuration is particularly preferable for imparting high strength, high toughness, and high corrosion resistance to the stainless steel member.

According to a sixth aspect of the present invention, there is provided a method for manufacturing a stainless steel member, wherein the raw material powder of stainless steel is subjected to mechanical milling at room temperature for several minutes to several hundred hours, and then heat-treated at 600 to 800 ° C. (sigma phase generation temperature range). And further sintering at a temperature not lower than the heat treatment temperature and not higher than 1400 ° C., the stainless steel member after sintering has an ultrafine structure in which the austenite phase and the sigma phase are uniformly mixed. , Such stainless steel members have high strength, high toughness,
Good characteristics such as high corrosion resistance are exhibited.

According to a seventh aspect of the present invention, in the method of the sixth aspect, since N ₂ gas or H ₂ gas is used as the sealing gas for the mechanical milling, oxidation is prevented by these gases. While promoting the pulverization of the powder, as well as N ₂ gas and H
_{The two} gases have a cost advantage that they are less expensive than the conventionally used Ar gas or the like. In addition, during mechanical milling, N ₂ and H ₂ are dissolved in stainless steel components,
Normally, N ₂ and H ₂ separate from the stainless steel during the subsequent heat treatment.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an attritor used in the method of the present invention.

FIG. 2 is a graph showing the relationship between the milling time and the hardness of the powder in an example of the present invention.

FIG. 3 is an explanatory view showing the structure of a powder subjected to mechanical milling according to the above embodiment.

FIG. 4 shows that HIP is applied to the powder subjected to the mechanical milling.
Explanatory drawing which shows the structure of the stainless steel which processed and was made into the sintered compact.

FIG. 5 is a graph showing the relationship between tensile strength and spread of various stainless steel materials.

FIG. 6 is an explanatory view showing the structure of a conventional austenitic stainless steel.

[Explanation of symbols]

 1 Attritor (device for milling)

Claims (7)

[Claims] A cold-processed stainless steel powder obtained by subjecting a raw material powder of stainless steel to mechanical milling at room temperature for several minutes to several hundred hours. 2. The stainless steel raw material powder is Cr1
The cold-worked stainless steel powder according to claim 1, comprising 6 to 18%, 12 to 15% Ni, and 2 to 3% Mo. 3. A stainless steel member made of stainless steel having a fine structure in which an austenite phase and a sigma phase are uniformly mixed and having an average crystal grain size of 1 μm or less. 4. The stainless steel member is subjected to mechanical milling at room temperature for several minutes to several hundred hours on a raw material powder of stainless steel, and then to a heat treatment at 600 to 800 ° C. The stainless steel member according to claim 3, wherein the member is sintered at the following temperature. 5. The stainless steel material powder is Cr1
The stainless steel member according to claim 4, comprising 6 to 18%, 12 to 15% Ni, and 2 to 3% Mo. 6. After subjecting the raw material powder of stainless steel to mechanical milling at room temperature for several minutes to several hundred hours,
A method for producing a stainless steel member, comprising: performing a heat treatment at a temperature of from 00 to 800 ° C .; 7. The method for producing a stainless steel member according to claim 6, wherein an N ₂ gas or an H ₂ gas is used as a sealing gas for said mechanical milling.