CN111621722B

CN111621722B - Precipitation hardening stainless steel powder for powder metallurgy, compound, granulated powder, and precipitation hardening stainless steel sintered body

Info

Publication number: CN111621722B
Application number: CN202010125890.4A
Authority: CN
Inventors: 中村英文; 工藤纯一
Original assignee: Seiko Epson Corp
Current assignee: Seiko Epson Corp
Priority date: 2019-02-28
Filing date: 2020-02-27
Publication date: 2021-12-31
Anticipated expiration: 2040-02-27
Also published as: JP7263840B2; JP2020139203A; CN111621722A

Abstract

The invention provides a precipitation hardening stainless steel powder, a compound, a granulated powder and a precipitation hardening stainless steel sintered body for powder metallurgy. The precipitation hardening stainless steel powder for powder metallurgy is capable of suppressing deterioration of characteristics due to oxidation when being subjected to degreasing by an acid degreasing method, and is characterized in that Fe is a main component, Ni is contained in a proportion of 3.00 mass% or more and 5.00 mass% or less, Cr is contained in a proportion of 15.00 mass% or more and 17.50 mass% or less, Cu is contained in a proportion of 3.00 mass% or more and 5.00 mass% or less, Nb is contained in a proportion of 0.15 mass% or more and 0.45 mass% or less, Si is contained in a proportion of 0.30 mass% or more and 1.00 mass% or less, and Mn is contained in a proportion of 2.00 or more and 6.00 or less in terms of a mass ratio of Si/Mn of the Si content to the Mn content, and is subjected to degreasing by the acid degreasing method.

Description

Precipitation hardening stainless steel powder for powder metallurgy, compound, granulated powder, and precipitation hardening stainless steel sintered body

Technical Field

The present invention relates to a precipitation hardening stainless steel powder for powder metallurgy, a compound, a granulated powder, and a precipitation hardening stainless steel sintered body.

Background

In the powder metallurgy method, a composition obtained by including a metal powder and a binder is formed into a desired shape, an obtained molded body is degreased to obtain a degreased body, and the degreased body is fired to produce a sintered body. In the process of producing such a sintered body, the particles of the metal powder are subject to an atomic diffusion phenomenon, and the compact is gradually densified and sintered.

In such a powder metallurgy method, when the compact is degreased, the binder is thermally decomposed and removed by heating the compact. However, since the removal of the binder requires a long time for heating, there are problems that the production efficiency is lowered and the molded body is easily deformed during heating.

Thus, patent document 1 discloses that a molded body obtained by heating a metal material powder and a binder containing a polyoxymethylene resin in an acid-containing atmosphere is degreased. Thus, by performing the degreasing treatment under an acid-containing atmosphere, the binder can be effectively removed because the acid decomposes the binder. Therefore, the above-described problems can be reduced.

In the degreasing treatment described in patent document 1, for example, the molded body is heated in an atmosphere containing nitric acid to remove the binder contained in the molded body. However, the metal powder contained in the molded body is easily oxidized when the metal powder is contacted with nitric acid. Therefore, when the degreased body in which the metal powder is oxidized is baked in the subsequent baking step, there is a problem that the sinterability of the metal powder is lowered, or the corrosion resistance and the mirror surface property of the sintered body after sintering are lowered.

Patent document 1: japanese laid-open patent publication No. 4-247802

Disclosure of Invention

A precipitation hardening stainless steel powder for powder metallurgy according to an application example of the present invention is characterized in that,

the main component of the Fe is Fe,

ni is contained in a proportion of 3.00-5.00 mass%,

contains Cr in a proportion of 15.00-17.50 mass%,

cu is contained in a proportion of 3.00-5.00 mass%,

nb is contained in a proportion of 0.15 to 0.45 mass%,

si is contained in a proportion of 0.30 to 1.00 mass%,

mn is contained in a mass ratio of Si content to Mn content, Si/Mn being 2.00 or more and 6.00 or less,

for degreasing by an acid degreasing method.

Detailed Description

Embodiments of the precipitation hardening stainless steel powder, the composite, the granulated powder, and the precipitation hardening stainless steel sintered body for powder metallurgy according to the present invention will be described in detail below.

Precipitation hardening stainless steel powder for powder metallurgy

First, precipitation hardening stainless steel powder for powder metallurgy according to the embodiment will be described.

In the powder metallurgy technique, after a composition containing a metal powder and a binder is formed into a desired shape, a sintered body of the desired shape can be obtained by degreasing and baking. Such a powder metallurgy technique has an advantage in that a sintered body having a complicated and fine shape can be produced in a near-net shape, that is, a shape close to a final shape, as compared with other techniques.

In addition, the degreasing treatment is a treatment of decomposing by heating and removing the binder, and by performing this treatment under an acid-containing atmosphere, the binder can be effectively removed. Such a degreasing method is particularly called an acid degreasing method.

The precipitation hardening stainless steel powder for powder metallurgy according to the embodiment is a metal powder comprising: fe is a main component, Ni is contained at a ratio of 3.00-5.00 mass%, Cr is contained at a ratio of 15.00-17.50 mass%, Cu is contained at a ratio of 3.00-5.00 mass%, Nb is contained at a ratio of 0.15-0.45 mass%, Si is contained at a ratio of 0.30-1.00 mass%, and Mn is contained at a ratio of Si/Mn of 2.00-6.00 mass%. The precipitation hardening stainless steel powder for powder metallurgy is a metal powder to be degreased by an acid degreasing method.

According to the precipitation hardening stainless steel powder for powder metallurgy, even when the powder is subjected to degreasing by an acid degreasing method, deterioration of characteristics due to oxidation can be suppressed. That is, in the acid degreasing method, since the particles of each metal powder are exposed to the acid-containing atmosphere, the particles themselves are required to have good oxidation resistance, and in the precipitation-hardened stainless steel powder for powder metallurgy according to the embodiment, oxidation can be suppressed even in such a severe environment. Therefore, good sinterability can be ensured, and the quality of the sintered body can be improved. Further, since the sintered body to be produced is produced by a powder metallurgy method, dimensional accuracy is high, and secondary working or the amount of working can be suppressed. Further, the above effects are exhibited, and the advantage of performing degreasing treatment in a short time by an acid degreasing method is obtained, whereby a high-quality sintered body, particularly a sintered body excellent in heat resistance and surface properties, can be efficiently produced.

Hereinafter, the alloy composition of the precipitation hardening type stainless steel powder for powder metallurgy according to the embodiment will be described in more detail. In the following description, precipitation hardening stainless steel powder for powder metallurgy may be simply referred to as "metal powder".

With respect to Ni

Ni (nickel) is an element that mainly imparts corrosion resistance and heat resistance to the sintered body to be produced. By using the metal powder containing Ni, corrosion resistance and heat resistance can be improved, and good oxidation resistance that can withstand degreasing by an acid degreasing method can be obtained, so that a sintered body having good corrosion resistance and surface properties even when produced by degreasing by an acid degreasing method can be obtained.

The Ni content in the metal powder is 3.00 mass% or more and 5.00 mass% or less, preferably 3.50 mass% or more and 4.70 mass% or less, and more preferably 3.80 mass% or more and 4.50 mass% or less. If the Ni content is less than the lower limit, the corrosion resistance and surface properties of the sintered body to be produced may not be sufficiently improved depending on the overall composition. On the other hand, if the Ni content exceeds the upper limit, the composition balance is likely to be lost depending on the entire composition, and the corrosion resistance and surface properties of the sintered body to be produced may be lowered.

The surface properties of the sintered body mean, for example, mirror surface properties, smoothness and the like.

With respect to Cr

Cr (chromium) is an element that mainly imparts corrosion resistance to the sintered body produced. By using the metal powder containing Cr, corrosion resistance can be improved, and good oxidation resistance that can withstand degreasing by an acid degreasing method can be obtained, so that a sintered body having good corrosion resistance even when produced by degreasing by an acid degreasing method can be obtained.

The content of Cr in the metal powder is 15.00 mass% or more and 17.50 mass% or less, preferably 15.20 mass% or more and 16.90 mass% or less, and more preferably 15.50 mass% or more and 16.70 mass% or less. If the Cr content is less than the lower limit, the corrosion resistance of the sintered body to be produced may be insufficient depending on the overall composition. On the other hand, if the Cr content exceeds the upper limit, the sinterability decreases depending on the overall composition, making it difficult to achieve a high density of the sintered body, and possibly leading to a decrease in the corrosion resistance and mechanical properties of the sintered body.

With respect to Cu

Cu (copper) is an element for precipitating an intermetallic compound in the sintered body to be produced to improve the mechanical properties of the sintered body.

The content of Cu in the metal powder is 3.00 mass% or more and 5.00 mass% or less, preferably 3.10 mass% or more and 4.50 mass% or less, and more preferably 3.20 mass% or more and 4.20 mass% or less. If the Cu content is less than the lower limit, precipitation of intermetallic compounds in the sintered body is limited, which may result in failure to sufficiently improve the mechanical properties of the sintered body. On the other hand, if the Cu content exceeds the upper limit, the intermetallic compound precipitates excessively, the density of the sintered body decreases, and the mechanical properties of the sintered body conversely decrease.

About Nb

Nb (niobium) is an element that precipitates in the produced sintered body to improve the mechanical properties of the sintered body.

The Nb content in the metal powder is 0.15 mass% or more and 0.45 mass% or less, preferably 0.20 mass% or more and 0.40 mass% or less, and more preferably 0.25 mass% or more and 0.35 mass% or less. If the content of Nb is less than the lower limit, precipitation of precipitates in the sintered body is restricted, which may result in failure to sufficiently improve the mechanical properties of the sintered body. On the other hand, if the Nb content exceeds the upper limit, precipitation of precipitates becomes excessive, the density of the sintered body decreases, and the mechanical properties of the sintered body conversely decrease.

With respect to Si

Si (silicon) is an element that mainly imparts corrosion resistance and high mechanical properties to the sintered body to be produced. By using the metal powder containing Si, corrosion resistance and mechanical characteristics can be improved, and good oxidation resistance that can withstand degreasing by an acid degreasing method can be obtained, so that a sintered body having good corrosion resistance even when produced by degreasing by an acid degreasing method can be obtained.

The content of Si in the metal powder is 0.30 mass% or more and 1.00 mass% or less, preferably 0.35 mass% or more and 0.95 mass% or less, and more preferably 0.40 mass% or more and 0.90 mass% or less. If the Si content is less than the lower limit, the corrosion resistance, surface properties, and mechanical properties of the sintered body to be produced may be deteriorated depending on the overall composition. On the other hand, if the Si content exceeds the upper limit, the composition balance is likely to be lost depending on the entire composition, and the corrosion resistance, surface properties, and mechanical properties of the sintered body to be produced may be deteriorated.

Regarding Mn

Mn (manganese) is an element that imparts corrosion resistance and high mechanical properties to the sintered body produced in the same manner as Si. By using the metal powder containing Mn, corrosion resistance and mechanical characteristics can be improved, and good oxidation resistance that can withstand degreasing by an acid degreasing method can be obtained, so that a sintered body having good corrosion resistance even when produced by degreasing by an acid degreasing method can be obtained.

The content of Mn in the metal powder is not particularly limited, but is preferably 0.05% by mass or more and 1.00% by mass or less, more preferably 0.07% by mass or more and 0.50% by mass or less, and further preferably 0.10% by mass or more and 0.40% by mass or less. If the Mn content is less than the lower limit, the corrosion resistance, surface texture, and mechanical properties of the produced sintered body may not be sufficiently improved depending on the overall composition, while if the Mn content exceeds the upper limit, the corrosion resistance, surface texture, and mechanical properties may be adversely reduced.

With respect to Si/Mn

When the mass ratio of the Si content to the Mn content is Si/Mn, Si/Mn determines how much the oxidation of the relatively easily oxidizable element Mn proceeds without impairing the composition balance of the metal powder as a whole. Specifically, for example, in degreasing by an acid degreasing method, by containing an appropriate amount of Si with respect to Mn in the metal powder, an oxide of Si, that is, silicon oxide is precipitated on the surface, thereby suppressing further oxidation. As a result, the corrosion resistance of the metal powder is not easily lowered even in an acid-containing atmosphere, and thereafter, when subjected to a firing step, the sintered density can be increased, and the obtained sintered body has excellent corrosion resistance and surface properties. That is, by optimizing Si/Mn, oxidation of Mn during degreasing by the acid degreasing method can be suppressed, and corrosion resistance and surface properties of the finally produced sintered body can be improved.

The Si/Mn ratio in the metal powder is 2.00 or more and 6.00 or less, preferably 2.50 or more and 5.00 or less, and more preferably 2.80 or more and 4.00 or less. If Si/Mn is less than the lower limit, the content of Si is relatively reduced compared to Mn, and therefore it is difficult to sufficiently suppress oxidation of Mn, which is relatively easily oxidized, by the oxide of Si. On the other hand, if Si/Mn exceeds the above upper limit, the Si content is relatively higher than Mn, and although oxidation is less likely, the composition balance is impaired, resulting in a decrease in corrosion resistance, surface properties, and mechanical properties of the sintered body.

With respect to Fe

Fe (iron) is an element having the highest content rate among the elements contained in the precipitation-hardened stainless steel powder for powder metallurgy according to the embodiment, i.e., a main component, and has a large influence on the characteristics of the sintered body to be produced. The content of Fe is not particularly limited, but is preferably 50 mass% or more, and more preferably 60 mass% or more.

With respect to other elements

The precipitation hardening stainless steel powder for powder metallurgy may contain at least one of C, Mo, W, N, S and P, if necessary, in addition to the above elements.

C (carbon) is an element that causes solid solution hardening as an interstitial element or precipitation hardening by precipitates containing C or another element in the produced sintered body. By using the metal powder containing C, a sintered body having high mechanical characteristics can be obtained.

The content of C in the metal powder is 0.07 mass% or less, preferably 0.01 mass% or more and 0.05 mass% or less. If the content of C exceeds the upper limit, the composition balance is likely to be lost depending on the entire composition, and the mechanical properties of the sintered body to be produced may be deteriorated.

Mo (molybdenum) is an element that enhances the corrosion resistance of the produced sintered body.

The content of Mo in the metal powder is not particularly limited, but is preferably 1.00 mass% or less, and more preferably 0.01 mass% or more and 0.50 mass% or less. By setting the content of Mo within the above range, the corrosion resistance of the sintered body can be further enhanced without causing a large decrease in the density of the produced sintered body.

W (tungsten) is an element that enhances the heat resistance of the sintered body produced.

The content of W in the metal powder is not particularly limited, but is preferably 1.00 mass% or less, and more preferably 0.01 mass% or more and 0.50 mass% or less. By setting the content of W within the above range, the heat resistance of the sintered body can be further enhanced without causing a large decrease in the density of the sintered body produced.

N (nitrogen) is an element that improves mechanical properties such as the durability of the sintered body to be produced.

The content of N in the metal powder is not particularly limited, but is preferably 1.00 mass% or less, more preferably 0.001 mass% or more and 0.50 mass% or less, and further preferably 0.05 mass% or more and 0.30 mass% or less. By setting the content of N within the above range, mechanical properties such as the durability of the sintered body can be further improved without causing a significant decrease in the density of the sintered body to be produced.

In order to produce the metal powder to which N is added, for example, a method of using a nitriding raw material, a method of introducing nitrogen gas into molten metal, a method of subjecting the produced metal powder to nitriding treatment, or the like is employed.

S (sulfur) is an element that improves the machinability of the sintered body produced.

The content of S in the metal powder is not particularly limited, but is preferably 0.50 mass% or less, and more preferably 0.001 mass% or more and 0.30 mass% or less. By setting the S content within the above range, the machinability of the produced sintered body can be further improved without causing a significant decrease in the density of the produced sintered body.

P (phosphorus) is an element that causes solid solution hardening as an interstitial element or precipitation hardening by precipitates formed by combination with other elements with respect to the sintered body to be produced. By using the metal powder containing P, a sintered body having high mechanical characteristics can be obtained.

The content of P in the metal powder is 0.50% by mass or less, preferably 0.001% by mass or more and 0.35% by mass or less, and more preferably 0.005% by mass or more and 0.30% by mass or less. If the content of P is less than the lower limit, the mechanical properties of the sintered body may not be sufficiently improved depending on the overall composition even if P is added. On the other hand, if the content of P exceeds the upper limit, the composition balance is likely to be lost depending on the overall composition, and the mechanical properties of the sintered body produced from the composition may be degraded.

On the other hand, O (oxygen) may be intentionally added or inevitably mixed, and the content thereof is preferably 0.01 mass% or more and 0.70 mass% or less, more preferably 0.08 mass% or more and 0.60 mass% or less, and further preferably 0.15 mass% or more and 0.50 mass% or less. By controlling the amount of oxygen in the metal powder within this range, silicon oxide is precipitated on the particle surface of the metal powder, and oxidation of elements such as Mn and Cr can be suppressed. As a result, the corrosion resistance and surface properties of the finally produced sintered body can be improved.

If the content of O is less than the lower limit, the amount of precipitated silicon oxide is reduced, and oxidation of elements such as Mn and Cr may be promoted. In this case, the corrosion resistance, surface properties, and mechanical properties of the sintered body to be produced may be deteriorated. On the other hand, if the content of O exceeds the upper limit, oxides of Mn and Cr are generated in addition to silicon oxide in the production of the metal powder. Therefore, it is difficult to increase the density of the sintered body to be produced, and the corrosion resistance, surface properties, and mechanical properties are liable to be lowered.

When the mass ratio of the O content to the Si content is O/Si, by optimizing the O/Si, an appropriate amount of Si is precipitated as an oxide, and a part of Si may be dissolved as a solid. The O/Si is preferably 0.10 or more and 0.90 or less, more preferably 0.20 or more and 0.80 or less, and further preferably 0.30 or more and 0.70 or less. By setting the O/Si ratio within such a range, oxidation of Mn and Cr in degreasing by the acid degreasing method can be suppressed, and corrosion resistance and surface properties of the finally produced sintered body can be improved.

If the O/Si ratio is lower than the lower limit, the amount of O is insufficient relative to the amount of Si, and the amount of precipitated silicon oxide is reduced, and a sufficient effect may not be obtained. On the other hand, if O/Si exceeds the upper limit value, the amount of O becomes excessive relative to the amount of Si, so that oxidation of Mn, Cr, and the like may be promoted.

When the Si content is s [% by mass ], the Mn content is m [% by mass ], and the Cr content is c [% by mass ], the metal powder preferably satisfies s/{ m (c/10) } of 0.15 or more and 0.50 or less, more preferably 0.20 or more and 0.48 or less, and still more preferably 0.22 or more and 0.45 or less. In such a metal powder, the precipitation of oxides of Mn and Cr is realized, and the oxidation resistance is improved by the precipitation of silicon oxide. As a result, the sinterability is ensured, a high-density sintered body is obtained, and the corrosion resistance and surface properties of the obtained sintered body can be improved.

Further, if s/{ m (c/10) } is lower than the lower limit value, the amount of Si is insufficient relative to the amounts of Mn and Cr, so that oxides of Mn and Cr may be more easily generated than the precipitation of silicon oxide. On the other hand, if s/{ m (c/10) } exceeds the upper limit value, the amount of Si becomes excessive relative to the amounts of Mn and Cr, possibly resulting in a decrease in the corrosion resistance of the sintered body.

In addition to the above elements, H, Be, B, Al, Co, As, Sn, Se, Zr, Y, Ti, Hf, Ta, Te, Pb, etc. may Be added to the precipitation hardening stainless steel powder for powder metallurgy in order to improve the characteristics of the sintered body. In this case, the content of these elements is not particularly limited, and may be set to such an extent that the characteristics of the sintered body are not impaired, and each is preferably less than 0.1 mass%, and the total is preferably less than 0.2 mass%. In addition, these elements may be inevitably included.

Furthermore, the precipitation hardening stainless steel powder for powder metallurgy may contain inevitable impurities. As the impurities, all elements other than the above elements can be cited. The respective mixing ratios of these impurities are smaller than the respective contents of Fe, Ni, Cr, Cu, Nb, Si, and Mn. In addition, the mixing ratios of these impurities are preferably less than 0.03 mass%, respectively, and the mixing ratios of the impurities are preferably less than 0.30 mass% in total. In addition, if the content of these impurities is within the above range, the above effects may not be inhibited, and therefore, the impurities may be intentionally added.

Analytical method

The composition ratio of the precipitation hardening stainless steel powder for powder metallurgy according to the embodiment can be determined by, for example, JIS G1257: iron and steel atomic absorption spectrometry specified in 2000, JIS G1258: iron and steel-ICP emission spectrometry specified in 2007, JIS G1253: iron and steel-spark discharge emission spectrometry specified in 2002, JIS G1256: 1997, iron and steel-X-ray fluorescence analysis method, and weight/titration/absorptiometry methods defined in JIS G1211 to G1237. Specifically, examples of the spark discharge emission spectroscopic analyzer include a solid-state emission spectroscopic analyzer manufactured by spectra corporation, model: SPECTROLA, type: LAVMB08A, or an ICP apparatus manufactured by Nippon Kabushiki Kaisha, CIROS120 type.

JIS G1211 to G1237 are as follows.

JIS G1211: 2011 method for determining iron and steel-carbon

JIS G1212: 1997 iron and steel-silicon quantitative method

JIS G1213: 2001 method for quantifying manganese in iron and steel

JIS G1214: 1998 iron and steel-phosphorus quantitative method

JIS G1215: 2010 iron and steel-sulfur quantitative method

JIS G1216: 1997 iron and steel-nickel quantitative method

JIS G1217: 2005 iron and Steel-chromium quantitative method

JIS G1218: 1999 iron and steel-molybdenum quantitative method

JIS G1219: 1997 iron and steel-copper quantitative method

JIS G1220: 1994 iron and steel-tungsten quantitative method

JIS G1221: 1998 iron and steel-vanadium quantitative method

JIS G1222: 1999 iron and Steel-cobalt quantitative method

JIS G1223: 1997 iron and steel-titanium quantitative method

JIS G1224: 2001 method for quantifying aluminum in iron and steel

JIS G1225: 2006 iron and steel-arsenic quantitative method

JIS G1226: 1994 iron and steel-tin quantitative method

JIS G1227: 1999 method for determining boron in iron and steel

JIS G1228: 2006 iron and steel-nitrogen quantitative method

JIS G1229: 1994 steel-lead quantification method

JIS G1232: method for quantifying zirconium in 1980 steel

JIS G1233: 1994 steel-selenium quantitative method

JIS G1234: method for quantifying tellurium in 1981 steel

JIS G1235: 1981 method for quantifying antimony in iron and steel

JIS G1236: 1992 method for quantifying tantalum in steel

JIS G1237: 1997 iron and steel-niobium quantitative method

In addition, when C (carbon) and S (sulfur) are specified, in particular, JIS G1211: 2011 combustion-infrared absorption method for an oxygen flow combustion high frequency induction heating furnace. Specifically, a carbon/sulfur analyzer manufactured by LECO, CS-200, may be mentioned.

Further, when N (nitrogen) and O (oxygen) are specified, in particular, JIS G1228: method for determining nitrogen content in iron and steel, as defined in 2006, JIS Z2613: 2006, the method for determining oxygen in a metal material. Specifically, an oxygen/nitrogen analyzer manufactured by LECO, TC-300/EF-300, is exemplified.

Further, the martensite-type crystal structure can be precipitated by subjecting the sintered body produced using the precipitation hardening stainless steel powder for powder metallurgy according to the embodiment to various heat treatments. The martensite type crystal structure imparts high hardness to the sintered body. Therefore, the precipitation hardening stainless steel powder for powder metallurgy according to the embodiment can produce a sintered body having high hardness and high mechanical strength.

Further, whether or not the sintered body has a martensite-type crystal structure can be determined by, for example, an X-ray diffraction method.

The average particle size of the precipitation hardening stainless steel powder for powder metallurgy according to the embodiment is preferably 0.50 μm or more and 50.00 μm or less, more preferably 1.00 μm or more and 30.00 μm or less, and further preferably 2.00 μm or more and 10.00 μm or less. By using the precipitation hardening stainless steel powder for powder metallurgy having such a particle diameter, since the number of pores remaining in the sintered body is extremely small, a sintered body having a high density and excellent mechanical properties can be produced.

In addition, in the cumulative particle size distribution on a mass basis obtained by the laser diffraction method, the particle size at which the cumulative amount is 50% from the smaller diameter side is determined as the average particle size of the precipitation-hardening stainless steel powder for powder metallurgy.

In addition, if the average particle diameter of the precipitation hardening stainless steel powder for powder metallurgy is less than the lower limit, moldability may be lowered and the sintered density may be lowered when forming a shape which is difficult to mold, and if it exceeds the upper limit, the sintered density may be lowered because gaps between particles become large at the time of molding.

The maximum particle size of the precipitation hardening stainless steel powder for powder metallurgy is not particularly limited as long as the average particle size is within the above range, and is preferably 200 μm or less, and more preferably 150 μm or less. By controlling the maximum particle diameter of the precipitation hardening stainless steel powder for powder metallurgy within the above range, the particle size distribution of the precipitation hardening stainless steel powder for powder metallurgy can be narrowed, and the sintered body can be further densified.

The maximum particle size is a particle size at which the cumulative amount of particles in the cumulative particle size distribution on a mass basis obtained by the laser diffraction method is 99.9% from the smaller diameter side.

When the short diameter and the long diameter of the particles of the precipitation hardening stainless steel powder for powder metallurgy are S [ mu ] m and L [ mu ] m, the average value of the aspect ratio defined by S/L is preferably from about 0.4 to 1, and more preferably from about 0.7 to 1. Since the precipitation hardening stainless steel powder for powder metallurgy having such an aspect ratio has a shape relatively close to a spherical shape, the filling ratio at the time of molding can be improved. As a result, the sintered body can be further densified.

Further, the long diameter refers to the maximum length obtainable by the particle in a projection image, and the short diameter refers to the maximum length obtainable in a direction perpendicular to the long diameter. In addition, the average value of the aspect ratio values measured for 100 or more particles was obtained as the average value of the aspect ratio.

Method for producing sintered body

Next, a method for producing a sintered body using the precipitation hardening stainless steel powder for powder metallurgy will be described.

The method for manufacturing the sintered body comprises the following steps: [A] a composition preparation step of preparing a composition for producing a sintered body; [B] a molding step for producing a molded body; [C] a degreasing step for performing a degreasing treatment; and [ D ] a burning step of burning. The respective steps are explained in order below.

[A] Process for producing composition

First, precipitation hardening stainless steel powder for powder metallurgy and a binder are prepared and kneaded by a kneader to obtain a kneaded product, that is, the composite according to the embodiment. The kneaded product contains the precipitation-hardening stainless steel powder for powder metallurgy and a binder that binds particles of the precipitation-hardening stainless steel powder for powder metallurgy to each other. According to this kneaded material, a sintered body in which deterioration of characteristics due to oxidation is suppressed, specifically, a sintered body having excellent corrosion resistance and surface properties can be produced.

In the kneaded mixture, precipitation hardening stainless steel powder for powder metallurgy was uniformly dispersed.

Precipitation hardening stainless steel powder for powder metallurgy is produced by various powder-making methods such as an atomization method such as a water atomization method, a gas atomization method, and a high-speed rotating water atomization method, a reduction method, a carbonyl method, and a pulverization method.

Among these, precipitation hardening stainless steel powder for powder metallurgy is preferably produced by an atomization method, and more preferably produced by a water atomization method or a high-speed rotating water atomization method. The atomization method is a method of manufacturing metal powder by making a molten metal collide with a liquid or gas injected at a high speed to micronize the molten metal and cooling it. By producing the precipitation hardening stainless steel powder for powder metallurgy by such atomization method, an extremely fine powder can be efficiently produced. In addition, the particle shape of the obtained powder is close to spherical due to the action of surface tension. Therefore, a high filling rate can be obtained when molding. That is, a powder capable of producing a high-density sintered body can be obtained.

When the atomization method is a water atomization method, the water pressure of the spray to the molten metal is not particularly limited, but is preferably about 75MPa to 120MPa, and more preferably about 90MPa to 120 MPa.

The temperature of the atomized water is not particularly limited, and is preferably about 1 ℃ to 20 ℃.

Further, the atomized water is generally ejected in a conical shape having an apex on a dropping path of the molten metal and an outer diameter gradually decreasing downward. In this case, the vertex angle θ of the cone formed by the atomized water is preferably about 10 ° or more and 40 ° or less, and more preferably about 15 ° or more and 35 ° or less. Thus, the precipitation hardening stainless steel powder for powder metallurgy having the above composition can be reliably produced.

In addition, according to the water atomization method, particularly the high-speed rotating water stream atomization method, the molten metal can be cooled particularly rapidly. Thus, high quality powders can be obtained in a wide range of alloy compositions.

The cooling rate in cooling the molten metal in the atomization method is preferably 1 × 104 ℃/s or more, and more preferably 1 × 105 ℃/s or more. By such rapid cooling, a uniform precipitation hardening stainless steel powder for powder metallurgy can be obtained. As a result, a high-quality sintered body can be obtained.

The precipitation-hardened stainless steel powder for powder metallurgy thus obtained may be classified as necessary. Examples of the classification method include dry classification such as sieve classification, inertia classification, and centrifugal classification, and wet classification such as sedimentation classification.

On the other hand, as the binder, a resin which can be decomposed in a short time by functioning as a catalyst in an acid-containing atmosphere in an acid degreasing method described later is used. Examples of the resin include polyether-based resins, aliphatic carbonate-based resins, and polylactic acid-based resins, and one or two or more of these resins may be used in combination.

Among them, examples of the polyether resin include: and aromatic polyether resins such as polyacetal resins, linear polyether resins such as polyethylene oxide resins, polyether ketone resins, polyether ether resins, polyether nitrile resins, polyether sulfone resins, and polythioether sulfone resins.

Examples of the aliphatic carbonate-based resin include a resin mainly composed of an alkylene glycol polycarbonate such as ethylene glycol polycarbonate, propylene glycol polycarbonate, butylene glycol polycarbonate, hexylene glycol polycarbonate, and decylene glycol polycarbonate, or a derivative thereof.

Examples of the polylactic acid resin include: lactic acid homopolymers such as poly-L-lactic acid resins, poly-D-lactic acid resins and poly-L/D-lactic acid resins, and in addition, aliphatic hydroxycarboxylic acids such as glycolic acid and hydroxybutyl carboxylic acid, aliphatic lactones such as glycolide, butyrolactone and caprolactone, aliphatic diols such as ethylene glycol, propylene glycol, butylene glycol and hexylene glycol, polyalkylene ethers such as polyethylene glycol, polypropylene glycol, polybutylene ether, diethylene glycol, triethylene glycol and ethylene/propylene glycol, aliphatic polycarbonates such as polybutylene carbonate, polyhexanecarbonate and polyoctanecarbonate, copolymer resins of aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid and decanedicarboxylic acid, and the like with lactic acid, and the like can be cited.

In addition, in addition to the resin which can decompose the acid-containing atmosphere as a catalyst as described above, the binder may be exemplified by: polyolefins such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymers, acrylic resins such as polymethyl methacrylate and polybutyl methacrylate, styrene resins such as polystyrene, various resins such as polyvinyl chloride, polyvinylidene chloride, polyamide, polyethylene terephthalate, and polyesters such as polybutylene terephthalate, polyethers, polyvinyl alcohol, polyvinylpyrrolidone, and copolymers thereof, and various organic binders such as various waxes, paraffins, higher fatty acids, higher alcohols, higher fatty acid esters, and higher fatty acid amides, and one or a mixture of two or more of these resins may be used.

The content of the binder is preferably about 2 to 20 mass%, more preferably about 5 to 15 mass%, of the whole kneaded material. By controlling the content of the binder within the above range, a molded article can be formed with good moldability, and the density can be increased to particularly improve the stability of the molded article shape and the like. In addition, this can optimize the difference in size between the molded body and the degreased body, that is, the so-called shrinkage rate, and prevent the reduction in dimensional accuracy of the finally obtained sintered body. That is, a sintered body with high density and high dimensional accuracy can be obtained.

Further, a plasticizer may be added to the kneaded mixture as needed. Examples of the plasticizer include phthalate esters, adipate esters, trimellitate esters, and sebacate esters, and one of them or two or more of them may be used in combination.

Further, in the kneaded mixture, various additives such as a lubricant, an antioxidant, a degreasing accelerator, and a surfactant, as well as other metal powder, ceramic powder, and the like may be added as necessary in addition to the precipitation hardening stainless steel powder for powder metallurgy, the binder, and the plasticizer.

The kneading conditions vary depending on various conditions such as the metal composition and particle size of the precipitation-hardening stainless steel powder for powder metallurgy to be used, the composition of the binder, and the amount of the binder to be blended, and may be, for example, a kneading temperature: about 50 ℃ or higher and 200 ℃ or lower, and a kneading time: about 15 minutes or more and 210 minutes or less.

Further, the kneaded product is formed into pellets as needed. The particle diameter of the particles is, for example, about 1mm or more and 15mm or less.

In addition, according to the molding method described later, the granulated powder according to the embodiment may be used instead of the kneaded product. These kneaded materials, granulated powders, and the like are examples of compositions to be used in a molding step described later.

The granulated powder is formed by granulating precipitation hardening stainless steel powder for powder metallurgy, and bonding a plurality of metal particles to each other with a binder. That is, the granulated powder is formed by granulating the precipitation hardening stainless steel powder for powder metallurgy. According to the granulated powder, a sintered body in which deterioration of characteristics due to oxidation is suppressed, specifically, a sintered body having excellent corrosion resistance and surface properties can be produced.

Examples of the binder used for producing the granulated powder include the above-mentioned binders.

The content of the binder is preferably about 0.2 mass% to 10 mass%, more preferably about 0.3 mass% to 5.0 mass%, of the entire granulated powder. By controlling the content of the binder within the above range, it is possible to suppress the generation of significantly large particles or the large amount of remaining metal particles that have not been granulated, and to efficiently form granulated powder. Further, since moldability is improved, stability of the shape of the molded article can be particularly improved. Further, by controlling the content of the binder within the above range, the difference in size between the molded body and the degreased body, that is, the so-called shrinkage ratio, can be optimized, and the reduction in dimensional accuracy of the finally obtained sintered body can be prevented.

Further, various additives such as a plasticizer, a lubricant, an antioxidant, a degreasing accelerator, and a surfactant, and other metal powder, ceramic powder, and the like may be added to the granulated powder as necessary.

On the other hand, examples of the granulation treatment include a spray drying method, a rolling granulation method, a fluidized bed granulation method, a rolling fluidized granulation method, and the like.

In the granulation treatment, a solvent for dissolving the binder may be used as necessary. Examples of the solvent include: water, an inorganic solvent such as carbon tetrachloride, an organic solvent such as a ketone solvent, an alcohol solvent, an ether solvent, a cellosolve solvent, an aliphatic hydrocarbon solvent, an aromatic heterocyclic compound solvent, an amide solvent, a halogen compound solvent, an ester solvent, an amine solvent, a nitrile solvent, a nitro solvent, or an aldehyde solvent, and one or a mixture of two or more selected from these solvents can be used.

The average particle size of the granulated powder is not particularly limited, but is preferably about 10 μm or more and 200 μm or less, more preferably about 20 μm or more and 100 μm or less, and still more preferably about 25 μm or more and 60 μm or less. The granulated powder having such a particle size has good fluidity and can reflect the shape of the mold more faithfully.

In addition, in the cumulative particle size distribution on a mass basis obtained by the laser diffraction method, the particle size at which the cumulative amount is 50% from the small diameter side is obtained as the average particle size.

[B] Shaping step

Next, the kneaded product or granulated powder is molded to produce a molded body having the same shape as the target sintered body.

Examples of the molding method include a powder compaction method, a metal powder injection molding method, and an extrusion molding method.

The molding conditions in the case of the powder compaction method vary depending on various conditions such as the composition and particle size of the precipitation hardening stainless steel powder for powder metallurgy used, the composition of the binder, and the amount of the binder added, and the molding pressure is preferably about 200MPa to 1000 MPa.

The molding conditions in the metal powder injection molding method vary depending on various conditions, but the material temperature is preferably about 80 ℃ to 210 ℃ inclusive, and the injection pressure is preferably about 50MPa to 500MPa inclusive.

The molding conditions in the extrusion molding method vary depending on various conditions, but the material temperature is preferably about 80 ℃ to 210 ℃ inclusive, and the extrusion pressure is preferably about 50MPa to 500MPa inclusive.

The molded body thus obtained is in a state in which the binder is uniformly distributed in the gaps between the plurality of particles of the precipitation hardening stainless steel powder for powder metallurgy.

The shape and size of the molded article to be produced are determined in consideration of the shrinkage of the molded article in the subsequent degreasing step and the subsequent baking step.

[C] Degreasing step

Subsequently, the obtained molded body was subjected to degreasing treatment to obtain a degreased body. Specifically, the binder is removed from the molded body by heating the molded body to decompose the binder, and degreasing treatment is performed.

In the degreasing treatment, an acid degreasing method in which the molded body is heated in an acid-containing atmosphere is used. The acid degreasing method is a method of heating a molded body in an acid-containing atmosphere to degrease the molded body by the catalytic action of an acid. According to the acid degreasing method, the binder can be decomposed in a short time even at a low temperature, and therefore, the degreasing treatment can be effectively performed even for a molded body having a large volume.

The acid-containing atmosphere refers to an atmosphere containing an acid capable of decomposing the binder. Examples of the acid include nitric acid, oxalic acid, ozone, and the like, and one of them or two or more of them may be used in combination. Further, a mixed gas obtained by mixing these acids with another gas may be used. An example of the mixed gas is fuming nitric acid. Further, the atmospheric pressure may be atmospheric pressure, reduced pressure, or increased pressure.

The heating conditions for the molded article vary slightly depending on the composition and amount of the binder and the type of the acid-containing atmosphere, but the temperature is preferably about 100 ℃ to 750 ℃ and 0.1 hour to 20 hours, more preferably about 150 ℃ to 600 ℃ and 0.5 hour to 15 hours. Thereby, the molded body can be degreased in a short time even at a relatively low temperature. In addition, sintering or oxidation of the molded body can be suppressed.

In addition, such a degreasing step may be performed by dividing the degreasing step into a plurality of steps under different degreasing conditions, so that the binder in the molded body is more rapidly decomposed and removed without remaining in the molded body.

Further, the degreased body may be subjected to machining such as cutting, polishing, or dicing, as necessary. Since the degreased body has low hardness and high plasticity, the shape collapse of the degreased body can be prevented and the mechanical processing can be easily performed. By such machining, a sintered body with high dimensional accuracy can be obtained easily in the end.

[D] Firing procedure

And (C) firing the degreased body obtained in the step [ C ] in a firing furnace to obtain a sintered body.

By this sintering, the precipitation hardening stainless steel powder for powder metallurgy is diffused at the interface between the particles, and sintering is achieved. At this time, the degreased body is rapidly sintered by the above mechanism. As a result, a compact and high-density sintered body can be obtained.

The sintering temperature varies depending on the composition, particle size, and the like of the precipitation hardening stainless steel powder for powder metallurgy used for producing the compact and the degreased body, and is, for example, approximately 980 ℃ to 1330 ℃. Further, it is preferably about 1050 ℃ to 1260 ℃.

The baking time is set to 0.2 hours or more and 7 hours or less, and preferably about 1 hour or more and 6 hours or less.

In the firing step, the firing temperature and firing atmosphere described later may be changed halfway.

By setting the firing conditions within such a range, it is possible to prevent overburning due to excessive sintering and thus enlargement of the crystal structure, and to sufficiently sinter the entire degreased body. As a result, a sintered body having a high density and particularly excellent mechanical characteristics can be obtained.

The sintered body thus produced may be subjected to additional treatment as needed. Examples of the additional treatment include solutionizing treatment, age hardening treatment, secondary aging treatment, cryogenic treatment, tempering treatment, hot working treatment, cold working treatment, and the like, and one or two or more of them are used in combination.

Further, as a specific example of the above-described additional processing, the following processing can be cited: the method comprises performing a solutionizing treatment in which cooling is performed from a temperature of 1000 ℃ to 1250 ℃ for a time of 30 minutes to 120 minutes, and then performing an age hardening treatment in which cooling is performed from a temperature of 600 ℃ to 800 ℃ for a time of 6 hours to 48 hours.

The sintered body of precipitation hardening stainless steel produced as described above, that is, the sintered body obtained by sintering precipitation hardening stainless steel powder for powder metallurgy, contains Fe as a main component, Ni in a proportion of 3.00 mass% or more and 5.00 mass% or less, Cr in a proportion of 15.00 mass% or more and 17.50 mass% or less, Cu in a proportion of 3.00 mass% or more and 5.00 mass% or less, Nb in a proportion of 0.15 mass% or more and 0.45 mass% or less, Si in a proportion of 0.30 mass% or more and 1.00 mass% or less, and Si/Mn which is a mass ratio of the Si content to the Mn content is 2.00 or more and 6.00 or less.

According to such a sintered body, when subjected to degreasing by an acid degreasing method, deterioration of characteristics due to oxidation can be suppressed. As a result, a sintered body excellent in corrosion resistance and surface properties can be obtained. In the following description, the precipitation hardening stainless steel sintered body may be simply referred to as a sintered body.

In addition, the precipitation hardening stainless steel sintered body according to the embodiment preferably has precipitates containing silicon oxide precipitated on the surface thereof. By including a sufficient amount of Si in the precipitation hardening stainless steel powder for powder metallurgy used for producing a sintered body and by having silicon oxide present on the particle surface, oxidation of elements relatively easily oxidized such as Mn and Cr is suppressed, and along with this, the precipitates are precipitated. Therefore, the precipitation hardening stainless steel sintered body containing precipitates of silicon oxide suppresses deterioration of characteristics due to oxidation, and has excellent corrosion resistance and surface properties.

The amount of precipitates in the sintered body is not particularly limited, and when the surface of the sintered body is observed by an electron microscope and a region having a total content of Si and O of 50 mass% or more is defined as a precipitate, one or more precipitates are preferably observed in a range of 50 μm square, and more preferably three or more precipitates are observed. Such a sintered body has particularly excellent corrosion resistance and surface properties.

The content of Si and O can be measured by energy dispersive X-ray spectroscopy (EDX), for example.

The precipitation hardening stainless steel sintered body can be used as a material constituting all or a part of decorative articles such as automobile parts, bicycle parts, railway vehicle parts, ship parts, airplane parts, space transportation machine (e.g., rocket) parts, electronic equipment parts such as personal computer parts, mobile phone terminal parts, tablet terminal parts, wearable terminal parts, electric equipment parts such as refrigerator, washing machine, air conditioner, machine parts such as machine tools and semiconductor manufacturing equipment, plant equipment parts such as nuclear power plant, thermal power plant, hydroelectric power plant, oil refinery, chemical combination plant, and clock parts, tableware, jewelry, and spectacle frames, for example.

The precipitation hardening stainless steel powder, the composite, the granulated powder, and the precipitation hardening stainless steel sintered body for powder metallurgy according to the present invention have been described above based on preferred embodiments, but the present invention is not limited thereto. For example, any additives may be added to the composite and granulated powder.

Examples

Next, examples of the present invention will be explained.

1. Production of sintered body

Sample No.1

[1] First, precipitation hardening stainless steel powder for powder metallurgy having a composition shown in table 1, which was produced by a water atomization method, was prepared.

Further, the composition of the metal powder shown in table 1 was determined and quantified by inductively coupled high-frequency plasma emission spectrometry and an ICP apparatus CIROS120 model manufactured by shiko corporation. Further, C was determined and quantified by using a carbon/sulfur analyzer CS-200 manufactured by LECO. Further, O was determined and quantified by using an oxygen/nitrogen analyzer TC-300/EF-300 manufactured by LECO.

[2] Then, the mass ratio of 89: 11 the metal powder and the organic binder were weighed and mixed to obtain a mixed raw material. Further, in the organic binder, a polyacetal resin containing 2.5 mass% of butanediol and polyethylene were used in a mass ratio of 50: 6 a resin obtained by mixing.

[3] Subsequently, the mixed raw materials were kneaded by a kneader to obtain a composite.

[4] Next, the composite was molded by an injection molding machine under the molding conditions shown below to produce a molded body.

Molding conditions

Material temperature: 180 deg.C

Injection pressure: 11MPa (110 kgf/cm)²)

[5] Next, the molded body obtained was subjected to a heat treatment under the below-described degreasing conditions to obtain a degreased body.

Conditions of degreasing

Degreasing temperature: 400 deg.C

Degreasing time: 1 hour (holding time at degreasing temperature)

Degreasing atmosphere: a mixed gas atmosphere of nitrogen and nitric acid, the concentration of nitric acid being 2% by volume

[6] Next, the degreased body obtained was baked under the baking conditions shown below. Thereby, a sintered body was obtained. Further, the sintered body had a cylindrical shape with a diameter of 10mm and a thickness of 5 mm.

Burning condition

The sintering temperature is as follows: 1300 ℃ C

And (3) baking time: 3 hours (holding time at the temperature of sintering)

Sintering atmosphere: argon atmosphere

[7] Next, the obtained sintered body was subjected to solutionizing treatment and age hardening treatment in this order under the conditions shown below.

Solutionizing treatment conditions

Heating temperature: 1120 deg.C

Heating time: 30 minutes

The cooling method comprises the following steps: cooling with water

Age hardening treatment conditions

Heating temperature: 700 deg.C

Heating time: 24 hours

The cooling method comprises the following steps: cooling with water

Sample Nos. 2 to 25

Sintered bodies were obtained in the same manner as in sample No.1, except that the composition and the like of the precipitation hardening stainless steel powder for powder metallurgy were changed as shown in table 1. Further, in the production of some sintered bodies, metal powder produced by a gas atomization method is used. In this case, "gas" is noted in the remarks column of table 1.

TABLE 1

In table 1, of the precipitation hardening stainless steel powder and sintered body for powder metallurgy of each sample No. the ones corresponding to the present invention are referred to as "examples", and the ones not corresponding to the present invention are referred to as "comparative examples".

Each sintered body contains a small amount of impurities, and the description thereof in table 1 is omitted.

2. Evaluation of sintered body

2.1 evaluation of Corrosion resistance

First, according to JIS G0591: 2012, the degree of corrosion was measured on the sintered body of each sample No. shown in table 1. Further, as the sulfuric acid, boiling 5 mass% sulfuric acid was used.

Next, with respect to the degree of corrosion of the sintered body of each sample No.20, the degree of corrosion (unit: g/m) to be measured with respect to the sintered body of sample No.20 was calculated²H) is set to 1. Then, the calculated relative value is evaluated based on the following evaluation criteria.

Evaluation criterion of degree of corrosion

A: the relative value of the corrosion degree of the sintered body is less than 0.50

B: the relative value of the corrosion degree of the sintered body is 0.50 or more and less than 0.75

C: the relative value of the corrosion degree of the sintered body is more than 0.75 and less than 1.00

D: the relative value of the corrosion degree of the sintered body is more than 1.00 and less than 1.25

E: the relative value of the corrosion degree of the sintered body is more than 1.25 and less than 1.50

F: the relative value of the degree of corrosion of the sintered body was 1.50

The above evaluation results are shown in table 2.

2.2 evaluation of specularity

Next, the sintered body of sample No. shown in Table 1 was subjected to barrel polishing treatment.

Next, according to JIS Z8741: 1997, the specular gloss of the sintered body was measured. The incident angle of light with respect to the sintered body surface was 60 °, and as a reference surface for calculating the specular glossiness, glass having a specular glossiness of 90 and a refractive index of 1.500 was used. Then, the measured specular gloss was evaluated according to the following evaluation criteria.

Evaluation criteria for specular gloss

A: the surface has very high mirror surface glossiness of more than 200

B: the surface has high specularity, and the specular gloss is 150 or more and less than 200

C: the surface has high specularity, and the specular gloss is more than 100 and less than 150

D: the surface has low specularity, and the specular gloss is 60 or more and less than 100

E: the surface has low specularity, and the specular gloss is more than 30 and less than 60

F: the surface has low specularity and the specular gloss is less than 30

The above evaluation results are shown in table 2.

2.3 evaluation of tensile Strength

Next, according to JIS Z2241: 2011, tensile strength was measured for each sintered body of sample nos. shown in table 1.

Then, the measured tensile strength was evaluated according to the following evaluation criteria.

Evaluation criteria for tensile Strength

A: the sintered body has a tensile strength of 1130MPa or more

B: the sintered body has a tensile strength of 1080MPa or more and less than 1130MPa

C: the sintered body has a tensile strength of 1030MPa or more and less than 1080MPa

D: the sintered body has a tensile strength of 980MPa or more and less than 1030MPa

E: the tensile strength of the sintered body is 930MPa or more and less than 980MPa

F: the tensile strength of the sintered body is less than 930MPa

The above evaluation results are shown in table 2.

TABLE 2

As is clear from table 2, although the sintered bodies of the examples were produced by degreasing by the acid degreasing method, both corrosion resistance and mirror surface property were good.

However, the sintered bodies of the comparative examples were insufficient in corrosion resistance and mirror surface property. Specifically, when the content of Si or the Si/Mn ratio deviates from a predetermined range, it is confirmed that both the corrosion resistance and the mirror surface property are reduced.

Further, the surface of the sintered body of each sample No. was observed by an electron microscope, and when the number of precipitates existing in a square range of 50 μm was counted, it was confirmed that one or more precipitates were observed in any of the examples.

Further, when the molding method was changed from the injection molding method to the compression molding method, and the same sintered body as described above was produced and evaluated, it was confirmed that the same tendency as the above evaluation result was exhibited.

Claims

1. A precipitation hardening stainless steel powder for powder metallurgy, characterized in that,

the content of Fe is 50% by mass or more,

ni is contained in a proportion of 3.00-5.00 mass%,

contains Cr in a proportion of 15.00-17.50 mass%,

cu is contained in a proportion of 3.00-5.00 mass%,

nb is contained in a proportion of 0.15 to 0.45 mass%,

si is contained in a proportion of 0.30 to 1.00 mass%,

mn is contained in a mass ratio of Si content to Mn content, Si/Mn, of 2.00 or more and 2.80 or less or 5.10 or more and 6.00 or less,

for degreasing by an acid degreasing method.

2. The precipitation hardening stainless steel powder for powder metallurgy according to claim 1,

the mass ratio of the O content to the Si content, O/Si, is 0.10 to 0.90.

3. The precipitation hardening stainless steel powder for powder metallurgy according to claim 1 or 2,

when the Si content is s, the Mn content is m, and the Cr content is c, s/{ m + (c/10) } is 0.15 or more and 0.50 or less.

4. The precipitation hardening stainless steel powder for powder metallurgy according to claim 1,

the content of O is 0.01 to 0.70 mass%.

5. The precipitation hardening stainless steel powder for powder metallurgy according to claim 1,

the average particle diameter is 0.50 to 50.00. mu.m.

6. A composite, characterized in that,

comprises the following steps:

the precipitation hardening stainless steel powder for powder metallurgy according to any one of claims 1 to 5; and

and a binder for binding the particles of the precipitation hardening stainless steel powder for powder metallurgy to each other.

7. A granulated powder characterized by containing, as a main component,

the precipitation hardening stainless steel powder for powder metallurgy according to any one of claims 1 to 5 is granulated.

8. A precipitation hardening stainless steel sintered body characterized in that,

the precipitation hardening stainless steel powder for powder metallurgy according to any one of claims 1 to 5 is sintered.

9. A precipitation hardening stainless steel sintered body characterized in that,

the content of Fe is 50% by mass or more,

ni is contained in a proportion of 3.00-5.00 mass%,

contains Cr in a proportion of 15.00-17.50 mass%,

cu is contained in a proportion of 3.00-5.00 mass%,

nb is contained in a proportion of 0.15 to 0.45 mass%,

si is contained in a proportion of 0.30 to 1.00 mass%,

the mass ratio of Si content to Mn content, Si/Mn, is 2.00 or more and 2.80 or less or 5.10 or more and 6.00 or less, and Mn is contained,

precipitates containing silicon oxide are precipitated on the surface.