JP7263840B2 - Precipitation hardening stainless steel powders, compounds, granulated powders and precipitation hardening stainless steel sintered bodies for powder metallurgy - Google Patents

Description

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.

In the powder metallurgy method, a composition containing a metal powder and a binder is formed into a desired shape, the resulting formed body is degreased to obtain a degreased body, and the degreased body is fired to obtain a sintered body. manufacture. In the process of manufacturing such a sintered body, an atomic diffusion phenomenon occurs between particles of the metal powder, thereby gradually densifying the compact and leading to sintering.

In such a powder metallurgy method, when the compact is degreased, the binder is thermally decomposed and removed by heating the compact. However, since removal of the binder requires heating for a long period of time, there are problems such as a decrease in production efficiency and a tendency for the molded body to deform during heating.

Therefore, Patent Document 1 discloses performing a degreasing treatment by heating a compact containing a metal material powder and a binder containing a polyoxymethylene resin in an acid-containing atmosphere. . By performing the degreasing treatment in an acid-containing atmosphere, the acid decomposes the binder, so that the binder can be efficiently removed. Therefore, the problems described above can be reduced.

JP-A-4-247802

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 compact contains metal powder, which is easily oxidized when it comes into contact with nitric acid. Therefore, when the degreased body in which the metal powder is oxidized is subsequently fired in the firing step, the sinterability of the metal powder is lowered, and the corrosion resistance and specularity of the sintered body after sintering are lowered. There is a problem of

A precipitation hardening stainless steel powder for powder metallurgy according to an application example of the present invention contains Fe as a main component,
Ni is contained at a ratio of 3.00% by mass or more and 5.00% by mass or less,
Cr is contained at a ratio of 15.00% by mass or more and 17.50% by mass or less,
Cu is contained at a ratio of 3.00% by mass or more and 5.00% by mass or less,
Nb is contained at a ratio of 0.15% by mass or more and 0.45% by mass or less,
Si is contained at a ratio of 0.30% by mass or more and 1.00% by mass or less,
Mn is contained at a ratio such that the mass ratio Si/Mn of the Si content to the Mn content is 2.00 or more and 6.00 or less,
It is characterized by being subjected to degreasing by an acid degreasing method.

Hereinafter, embodiments of the precipitation hardening stainless steel powder for powder metallurgy, the compound, the granulated powder and the precipitation hardening stainless steel sintered body of the present invention will be described in detail.

[Precipitation hardening stainless steel powder for powder metallurgy]
First, a precipitation hardening stainless steel powder for powder metallurgy according to an embodiment will be described.

In the powder metallurgy technique, a sintered body having a desired shape can be obtained by molding a composition containing a metal powder and a binder into a desired shape, followed by degreasing and firing. Such powder metallurgy technology has the advantage of being able to produce a sintered compact having a complicated and fine shape in a near-net shape, that is, a shape close to the final shape, as compared with other technologies.

The degreasing treatment is a treatment for decomposing and removing the binder by heating. By performing this treatment in an acid-containing atmosphere, the binder can be efficiently 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 contains Fe as a main component, Ni at a rate of 3.00 mass % or more and 5.00 mass % or less, and Cr at a content of 15.00 mass % or more. It contains 17.50% by mass or less, Cu is contained in a ratio of 3.00% by mass or more and 5.00% by mass or less, and Nb is contained in a ratio of 0.15% by mass or more and 0.45% by mass or less. contains Si at a rate of 0.30% by mass or more and 1.00% by mass or less, and the mass ratio Si/Mn of the Si content to the Mn content is 2.00 or more and 6.00 or less It is a metal powder containing Mn. Such a precipitation hardening stainless steel powder for powder metallurgy is a metal powder to be degreased by an acid degreasing method.

According to such a precipitation hardening stainless steel powder for powder metallurgy, even if it is subjected to degreasing by an acid degreasing method, deterioration of properties due to oxidation is suppressed. That is, in the acid degreasing method, each particle of the metal powder is exposed to an acid-containing atmosphere, so the particles themselves are required to have good oxidation resistance. , oxidation is suppressed even in such a severe environment. Therefore, good sinterability is ensured, and the quality of the sintered body can be improved. Moreover, since the sintered body to be manufactured is manufactured by a powder metallurgy method, it has high dimensional accuracy and can omit secondary processing or reduce the amount of processing. While exhibiting such effects, it is possible to receive the benefits of degreasing treatment in a short time by the acid degreasing method, and efficiently produce a high-quality sintered body, especially a sintered body having good heat resistance and surface properties. can be manufactured.

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

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

The Ni content in the metal powder is 3.00% by mass or more and 5.00% by mass or less, preferably 3.50% by mass or more and 4.70% by mass or less, and more preferably 3.80% by mass. % or more and 4.50 mass % or less. If the Ni content is below the above 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 above upper limit, the balance of the composition tends to be lost depending on the overall composition, which may deteriorate the corrosion resistance and surface properties of the produced sintered body.
The surface properties of the sintered body refer to properties such as specularity and smoothness.

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

The Cr content in the metal powder is 15.00% by mass or more and 17.50% by mass or less, preferably 15.20% by mass or more and 16.90% by mass or less, and more preferably 15.50% by mass. % or more and 16.70 mass % or less. If the Cr content is below the above lower limit, the sintered body to be produced may have insufficient corrosion resistance depending on the overall composition. On the other hand, if the Cr content exceeds the above upper limit, depending on the overall composition, the sinterability may be reduced, making it difficult to increase the density of the sintered body. may decrease.

(Cu)
Cu (copper) is an element that precipitates an intermetallic compound in the manufactured sintered body and enhances the mechanical properties of the sintered body.

The content of Cu in the metal powder is 3.00% by mass or more and 5.00% by mass or less, preferably 3.10% by mass or more and 4.50% by mass or less, and more preferably 3.20% by 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 restricted, so there is a possibility that the mechanical properties of the sintered body cannot be sufficiently improved. On the other hand, if the Cu content exceeds the upper limit, the intermetallic compound is excessively precipitated, the density of the sintered body is lowered, and the mechanical properties of the sintered body are rather lowered.

(Nb)
Nb (niobium) is an element that causes precipitates to form in the sintered body to be manufactured and enhances the mechanical properties of the sintered body.

The content of Nb in the metal powder is 0.15% by mass or more and 0.45% by mass or less, preferably 0.20% by mass or more and 0.40% by mass or less, and more preferably 0.25% by mass. % or more and 0.35 mass % or less. If the Nb content is below the above lower limit, precipitation of precipitates in the sintered body is restricted, so there is a possibility that the mechanical properties of the sintered body cannot be sufficiently improved. On the other hand, if the Nb content exceeds the above upper limit, excessive precipitates are formed, the density of the sintered body is lowered, and the mechanical properties of the sintered body are rather lowered.

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

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

(Mn)
Mn (manganese), like Si, is an element that imparts corrosion resistance and high mechanical properties to the produced sintered body. By using a metal powder containing Mn, corrosion resistance and mechanical properties are improved, and good oxidation resistance that can withstand degreasing by an acid degreasing method can be obtained. A sintered body having good corrosion resistance can also be obtained.

Although the content of Mn in the metal powder is not particularly limited, it is preferably 0.05% by mass or more and 1.00% by mass or less, and more preferably 0.07% by mass or more and 0.50% by mass or less. , more preferably 0.10% by mass or more and 0.40% by mass or less. If the Mn content is below the above lower limit, depending on the overall composition, the corrosion resistance, surface properties, and mechanical properties of the sintered body to be produced may not be sufficiently improved. If the upper limit is exceeded, the corrosion resistance, surface properties, and mechanical properties may rather deteriorate.

(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 Mn, an element that is relatively easily oxidized, progresses without impairing the compositional balance of the entire metal powder. or not. Specifically, for example, in degreasing by an acid degreasing method, since an appropriate amount of Si is contained relative to Mn in the metal powder, an oxide of Si, that is, silicon oxide is precipitated on the surface. Oxidation is suppressed. As a result, even in an acid-containing atmosphere, the corrosion resistance of the metal powder is less likely to decrease, and when it is subsequently subjected to the firing process, the sintered density is improved, and the obtained sintered body has high corrosion resistance. and excellent surface properties. That is, by optimizing the Si/Mn ratio, oxidation of Mn during degreasing by an acid degreasing method can be suppressed, and the corrosion resistance and surface properties of the finally produced sintered body can be improved.

Si/Mn 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 above lower limit, the content of Si is relatively small compared to Mn, so it becomes difficult to sufficiently suppress the oxidation of Mn, which is relatively easily oxidized, with Si oxide. On the other hand, when Si/Mn exceeds the above upper limit, the content of Si is relatively large compared to Mn, so although it becomes difficult to oxidize, the composition balance is impaired, so the corrosion resistance and surface properties of the sintered body , the mechanical properties deteriorate.

(Fe)
Fe (iron) is the element with the highest content rate among the elements contained in the precipitation hardening stainless steel powder for powder metallurgy according to the embodiment, that is, the main component, and has a great influence on the properties of the produced sintered body. effect. The Fe content is not particularly limited, but is preferably 50% by mass or more, more preferably 60% by mass or more.

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

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

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

Mo (molybdenum) is an element that enhances the corrosion resistance of the manufactured sintered body.
Although the content of Mo in the metal powder is not particularly limited, it is preferably 1.00% by mass or less, and more preferably 0.01% by mass or more and 0.50% by mass or less. By setting the Mo content within the above range, the corrosion resistance of the sintered body can be further enhanced without causing a significant decrease in the density of the sintered body to be produced.

W (tungsten) is an element that enhances the heat resistance of the manufactured sintered body.
Although the content of W in the metal powder is not particularly limited, it is preferably 1.00% by mass or less, and more preferably 0.01% by mass or more and 0.50% by mass or less. By setting the W content within the above range, the heat resistance of the sintered body can be further enhanced without causing a significant decrease in the density of the sintered body to be manufactured.

N (nitrogen) is an element that enhances mechanical properties such as yield strength of the manufactured sintered body.
The content of N in the metal powder is not particularly limited, but is preferably 1.00% by mass or less, more preferably 0.001% by mass or more and 0.50% by mass or less, and 0.05% by mass. More preferably, the content is 0.30% by mass or less. By setting the N content within the above range, mechanical properties such as yield strength of the sintered body can be further enhanced without causing a significant decrease in the density of the manufactured sintered body.

In order to produce the metal powder to which N is added, for example, a method using a nitrided raw material, a method of introducing nitrogen gas into the molten metal, a method of subjecting the produced metal powder to a nitriding treatment, and the like are used. be done.

S (sulfur) is an element that enhances the machinability of the produced sintered body.
Although the content of S in the metal powder is not particularly limited, it is preferably 0.50% by mass or less, and more preferably 0.001% by mass or more and 0.30% by mass or less. By setting the content of S within the above range, the machinability of the produced sintered body can be further enhanced 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 in the sintered body to be produced, or causes precipitation hardening by means of precipitates formed by combining with other elements. By using a metal powder containing P, a sintered body having high mechanical properties 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, more preferably 0.005% by mass or more and 0.30% by mass. % or less. If the P content is below the above lower limit, the addition of P may not sufficiently improve the mechanical properties of the sintered body, depending on the overall composition. On the other hand, if the P content exceeds the above upper limit, the balance of the composition is likely to be lost depending on the overall composition, which may deteriorate the mechanical properties of the sintered body to be produced.

On the other hand, O (oxygen) may also be intentionally added or unavoidably mixed, but its content is preferably 0.01% by mass or more and 0.70% by mass or less. It is more preferably 08% by mass or more and 0.60% by mass or less, and more preferably 0.15% by mass or more and 0.50% by mass or less. By keeping the oxygen content in the metal powder within this range, silicon oxide precipitates on the particle surface of the metal powder, so that 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 O content is less than the lower limit, the amount of silicon oxide precipitated is reduced, so that elements such as Mn and Cr may be oxidized. In this case, the corrosion resistance, surface properties, and mechanical properties of the produced sintered body may deteriorate. On the other hand, if the content of O exceeds the above upper limit, oxides of Mn and Cr will be produced in addition to silicon oxide at the time of production of the metal powder. For this reason, it becomes difficult to increase the density of the sintered body to be manufactured, and there is a risk that the corrosion resistance, surface properties, and mechanical properties will be lowered accordingly.

When the mass ratio of the O content to the Si content is O/Si, by optimizing O/Si, a moderate amount of Si precipitates as an oxide, while some Si forms a solid solution. can do. 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 still more preferably 0.30 or more and 0.70 or less. By setting O/Si in such a range, it is possible to suppress the oxidation of Mn and Cr during degreasing by the acid degreasing method, and to improve the corrosion resistance and surface properties of the finally produced sintered body. can.

If O/Si is less than the above lower limit, the amount of O is insufficient with respect to the amount of Si, so the amount of silicon oxide precipitated is reduced, and a sufficient effect may not be obtained. On the other hand, if the O/Si ratio exceeds the upper limit, the amount of O becomes excessive with respect to the amount of Si, so there is a risk that oxidation of Mn, Cr, and the like will progress.

Further, when the Si content is s [mass%], the Mn content is m [mass%], and the Cr content is c [mass%], the metal powder is s/{m(c /10)} is preferably 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, oxidation resistance is improved by precipitation of silicon oxide while suppressing precipitation of oxides of Mn and Cr. As a result, sinterability is ensured, a high-density sintered body can be obtained, and corrosion resistance and surface properties of the obtained sintered body can be improved.

If s/{m(c/10)} is below the lower limit, the amount of Si is insufficient with respect to the amount of Mn or Cr. is likely to be generated more easily. On the other hand, if s/{m(c/10)} exceeds the above upper limit, the amount of Si becomes excessive with respect to the amount of Mn and Cr, which may reduce the corrosion resistance of the sintered body.

Precipitation hardening stainless steel powder for powder metallurgy contains H, Be, B, Al, Co, As, Sn, Se, Zr, Y, Ti, and Hf, in addition to the elements described above, in order to enhance the properties of the sintered body. , Ta, Te, Pb and the like may be added. In that case, the content of these elements is not particularly limited, but is set to a degree that does not impair the characteristics of the sintered body described above, and each is preferably less than 0.1% by mass, and the total is 0.2% by mass. preferably less than. Note that these elements may inevitably be included.

Furthermore, the precipitation hardening stainless steel powder for powder metallurgy may contain unavoidable impurities. Impurities include all elements other than those mentioned above. The mixing ratio of each of these impurities should be less than the respective content of Fe, Ni, Cr, Cu, Nb, Si and Mn. In particular, the mixing ratio of these impurities is preferably less than 0.03% by mass, and the total mixing ratio of impurities is preferably less than 0.30% by mass. It should be noted that these impurities may be added intentionally since the aforementioned effects are not impaired as long as the content is within the above range.

(analysis method)
The composition ratio of the precipitation hardening stainless steel powder for powder metallurgy according to the embodiment is, for example, iron and steel specified in JIS G 1257: 2000 - atomic absorption spectrometry, iron and steel specified in JIS G 1258: 2007 - ICP emission spectrometry, iron and steel specified in JIS G 1253:2002 - spark discharge emission spectrometry, iron and steel specified in JIS G 1256: 1997 - fluorescent X-ray analysis, JIS G 1211 ~ It can be specified by weight, titration, spectrophotometry, etc. specified in G1237. Specifically, for example, SPECTRO's solid-state emission spectrometer, model: SPECTROLAB, type: LAVMB08A, which is a spark discharge emission spectrometer, and Rigaku's ICP device, CIROS120 type, can be used.

JIS G 1211 to G 1237 are as follows.
JIS G 1211:2011 Iron and steel - Determination of carbon JIS G 1212:1997 Iron and steel - Determination of silicon JIS G 1213:2001 Determination of manganese in iron and steel JIS G 1214:1998 Iron and steel - Determination of phosphorus JIS G 1215:2010 Iron and steel - Determination of sulfur JIS G 1216:1997 Iron and steel - Determination of nickel JIS G 1217:2005 Iron and steel - Determination of chromium JIS G 1218:1999 Iron and steel - Determination of molybdenum JIS G 1219: 1997 Iron and steel - Copper determination method JIS G 1220: 1994 Iron and steel - Tungsten determination method JIS G 1221: 1998 Iron and steel - Vanadium determination method JIS G 1222: 1999 Iron and steel - Cobalt determination method JIS G 1223: 1997 Iron and steel - Determination of titanium JIS G 1224:2001 Determination of aluminum in iron and steel JIS G 1225:2006 Iron and steel - Determination of arsenic JIS G 1226:1994 Iron and steel - Determination of tin JIS G 1227:1999 Method for determining boron in iron and steel JIS G 1228:2006 Iron and steel-Method for determining nitrogen JIS G 1229:1994 Steel-Method for determining lead JIS G 1232:1980 Method for determining zirconium in steel JIS G 1233:1994 Steel-Selenium Determination method JIS G 1234:1981 Method for determination of tellurium in steel JIS G 1235:1981 Method for determination of antimony in iron and steel JIS G 1236:1992 Method for determination of tantalum in steel JIS G 1237:1997 Method for determination of niobium in iron and steel

In addition, when specifying C (carbon) and S (sulfur), the oxygen flow combustion high-frequency induction heating furnace combustion-infrared absorption method specified in JIS G 1211:2011 is also used. A specific example is CS-200, a carbon/sulfur analyzer manufactured by LECO.

Furthermore, when specifying N (nitrogen) and O (oxygen), in particular, the nitrogen determination method for iron and steel specified in JIS G 1228: 2006, and the oxygen determination method for metal materials specified in JIS Z 2613: 2006. is also used. Specifically, an oxygen/nitrogen analyzer TC-300/EF-300 manufactured by LECO is exemplified.

In addition, the sintered body manufactured using the precipitation hardening stainless steel powder for powder metallurgy according to the embodiment can be subjected to various heat treatments to precipitate a martensitic crystal structure. . The martensitic 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.

Whether or not the sintered body has a martensitic crystal structure can be determined, for example, by an X-ray diffraction method.

In addition, the average particle diameter 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, More preferably, it is 2.00 μm or more and 10.00 μm or less. By using the precipitation hardening stainless steel powder for powder metallurgy with such a particle size, the number of pores remaining in the sintered body is extremely reduced, so that a sintered body with high density and excellent mechanical properties can be produced. be able to.

The average particle size of the precipitation hardening stainless steel powder for powder metallurgy is obtained as the particle size when the cumulative amount is 50% from the small diameter side in the cumulative particle size distribution based on mass obtained by the laser diffraction method. .

Further, if the average particle size of the precipitation hardening stainless steel powder for powder metallurgy is less than the above lower limit, there is a risk that the moldability will decrease when forming a shape that is difficult to mold, and the sintered density will decrease. If the upper limit is exceeded, the sintered density may decrease because the gaps between particles become large during 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. By controlling the maximum particle size 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 compact can have a higher density. can be improved.

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

Further, when the short diameter of the particles of the precipitation hardening stainless steel powder for powder metallurgy is S [μm] and the long diameter is L [μm], the average value of the aspect ratio defined by S/L is 0.4. It is preferably about 1 or more, and more preferably about 0.7 or more and 1 or less. Precipitation hardening stainless steel powder for powder metallurgy having such an aspect ratio has a shape relatively close to a sphere, so that the packing rate is increased when molded. As a result, the density of the sintered body can be further increased.

The major axis is the maximum length that can be taken in the projected image of the particle, and the minor axis is the maximum length that can be taken in the direction orthogonal to the major axis. Also, the average value of the aspect ratio is obtained as the average value of the aspect ratio values measured for 100 or more particles.

[Manufacturing method of sintered body]
Next, a method for producing a sintered body using such a precipitation hardening stainless steel powder for powder metallurgy will be described.

The method for producing a sintered body includes [A] a composition preparation step of preparing a composition for producing a sintered body, [B] a molding step of producing a molded body, and [C] a degreasing step of performing a degreasing treatment. and [D] a firing step of performing firing. Each step will be described below in sequence.

[A] Composition Preparing Step 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 compound according to the embodiment. The kneaded material contains the aforementioned precipitation hardening stainless steel powder for powder metallurgy and a binder for binding particles of the precipitation hardening stainless steel powder for powder metallurgy. With such a kneaded product, it is possible to produce a sintered body in which deterioration of properties due to oxidation is suppressed, specifically a sintered body with good corrosion resistance and surface properties.

In this kneaded product, precipitation hardening stainless steel powder for powder metallurgy is uniformly dispersed.
Precipitation hardening stainless steel powder for powder metallurgy is produced by atomization methods such as water atomization method, gas atomization method and high-speed rotating water jet atomization method, reduction method, carbonyl method, pulverization method and the like.

Among them, the precipitation hardening stainless steel powder for powder metallurgy is preferably produced by the atomization method, more preferably by the water atomization method or the high-speed rotating water stream atomization method. The atomization method is a method of producing a metal powder by colliding molten metal with liquid or gas jetted at high speed to pulverize and cool the molten metal. By producing the precipitation hardening stainless steel powder for powder metallurgy by such an atomizing method, extremely fine powder can be efficiently produced. Also, the particle shape of the obtained powder becomes nearly spherical due to the action of surface tension. Therefore, when molded, a product with a high filling rate can be obtained. That is, it is possible to obtain a powder capable of producing a high-density sintered body.

When the water atomization method is used as the atomization method, the pressure of the water injected toward the molten metal is not particularly limited, but is preferably about 75 MPa or more and 120 MPa or less, more preferably about 90 MPa or more and 120 MPa or less. It is said that

The temperature of the atomizing water is also not particularly limited, but is preferably about 1° C. or higher and 20° C. or lower.

Furthermore, the atomized water is often sprayed in a conical shape having a peak on the molten metal drop path and an outer diameter gradually decreasing downward. In this case, the apex angle θ of the cone formed by the atomized water is preferably about 10° or more and 40° or less, more preferably about 15° or more and 35° or less. As a result, the precipitation hardening stainless steel powder for powder metallurgy having the composition described above can be reliably produced.

Further, the water atomization method, particularly the high-speed rotating water stream atomization method, can cool the molten metal particularly quickly. Therefore, high-quality powder can be obtained in a wide range of alloy compositions.

Further, the cooling rate when cooling the molten metal in the atomizing method is preferably 1×10 ⁴ ° C./s or more, more preferably 1×10 ⁵ ° C./s or more. Such rapid cooling results in a homogeneous precipitation hardening stainless steel powder for powder metallurgy. As a result, a high-quality sintered body can be obtained.

The precipitation hardening stainless steel powder for powder metallurgy thus obtained may be classified as necessary. Classification methods include, for example, sieving classification, inertial classification, dry classification such as centrifugal classification, and wet classification such as sedimentation classification.

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

Among these, polyether-based resins include, for example, polyacetal-based resins, linear polyether-based resins such as polyethylene oxide-based resins, polyetherketone-based resins, polyetherether-based resins, polyethernitrile-based resins, poly Aromatic polyether-based resins such as ethersulfone-based resins and polythioethersulfone-based resins are included.

Examples of the aliphatic carbonate-based resin include alkanediol polycarbonate such as ethanediol polycarbonate, propanediol polycarbonate, butanediol polycarbonate, hexanediol polycarbonate, and decanediol polycarbonate, or those containing derivatives thereof as a main component. .

Examples of polylactic acid-based resins include lactic acid homopolymers such as poly-L-lactic acid resin, poly-D-lactic acid resin, and poly-L/D-lactic acid resin, as well as glycolic acid and hydroxybutylcarboxylic acid. aliphatic hydroxycarboxylic acids such as glycolide, butyrolactone, aliphatic lactones such as caprolactone, aliphatic diols such as ethylene glycol, propylene glycol, butanediol, hexanediol, polyethylene glycol, polypropylene glycol, polybutylene ether, diethylene glycol, polyalkylene ethers such as triethylene glycol, ethylene/propylene glycol; aliphatic polycarbonates such as polybutylene carbonate, polyhexane carbonate, polyoctane carbonate; succinic acid, adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid; and copolymer resins of lactic acid and aliphatic dicarboxylic acids.

In addition to the above-described resins that can be decomposed using an acid-containing atmosphere as a catalyst, the binder may also include polyolefins such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymer, and acrylics such as polymethyl methacrylate and polybutyl methacrylate. resins, styrene resins such as polystyrene, polyesters such as polyvinyl chloride, polyvinylidene chloride, polyamide, polyethylene terephthalate, polybutylene terephthalate, polyether, polyvinyl alcohol, polyvinylpyrrolidone, or copolymers thereof, Various organic binders such as various waxes, paraffins, higher fatty acids, higher alcohols, higher fatty acid esters, and higher fatty acid amides can be mentioned, and one or more of these can be used in combination.

The binder content is preferably about 2% by mass or more and 20% by mass or less, more preferably about 5% by mass or more and 15% by mass or less, of the entire kneaded product. When the content of the binder is within the above range, it is possible to form a molded article with good moldability, increase the density, and improve the stability of the shape of the molded article. In addition, this makes it possible to optimize the difference in size between the molded body and the degreased body, that is, the so-called shrinkage rate, and prevent deterioration in the dimensional accuracy of the finally obtained sintered body. That is, a sintered body with high density and high dimensional accuracy can be obtained.

In addition, a plasticizer may be added to the kneaded product, if necessary. Examples of the plasticizer include phthalates, adipates, trimellitates, sebacates and the like, and one or more of these may be used in combination.

Furthermore, in addition to the precipitation hardening stainless steel powder for powder metallurgy, the binder, and the plasticizer, the kneaded product contains various additives such as lubricants, antioxidants, degreasing accelerators, surfactants, and other additives. Metal powder, ceramic powder, etc. can be added as needed.

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 used, the composition of the binder, and the amount of these ingredients. C. to 200.degree. C., kneading time: about 15 minutes to 210 minutes.

Moreover, the kneaded material is pelletized as needed. The grain size of the pellets is, for example, about 1 mm or more and 15 mm or less.

The granulated powder according to the embodiment may be used instead of the kneaded material depending on the molding method described below. These kneaded products, granulated powders, and the like are examples of compositions to be subjected to the molding step described below.

Such a granulated powder is obtained by subjecting a precipitation hardening stainless steel powder for powder metallurgy to a granulation treatment to bind a plurality of metal particles together with a binder. That is, the granulated powder is obtained by granulating the aforementioned precipitation hardening stainless steel powder for powder metallurgy. According to such a granulated powder, it is possible to produce a sintered body in which the deterioration of properties due to oxidation is suppressed, specifically a sintered body with good corrosion resistance and surface properties.

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

The content of the binder is preferably about 0.2% by mass or more and 10% by mass or less, more preferably about 0.3% by mass or more and 5.0% by mass or less, based on the entire granulated powder. When the content of the binder is within the above range, the granulated powder can be efficiently produced while suppressing the granulation of extremely large particles and the remaining large amount of metal particles that have not been granulated. can be formed. In addition, since the moldability is improved, the stability of the shape of the molded product can be made particularly excellent. In addition, by setting the content of the binder within the above range, the difference in size between the molded body and the degreased body, the so-called shrinkage ratio, is optimized, thereby preventing deterioration in the dimensional accuracy of the finally obtained sintered body. can do.

Furthermore, various additives such as plasticizers, lubricants, antioxidants, degreasing accelerators, surfactants, other metal powders, ceramic powders, etc. are added to the granulated powder as necessary. good too.

On the other hand, examples of granulation include spray drying, tumbling granulation, fluidized bed granulation, and tumbling fluidized granulation.

In addition, in the granulation process, a solvent that dissolves the binder is used as necessary. Such solvents include, for example, water, inorganic solvents such as carbon tetrachloride, ketone solvents, alcohol solvents, ether solvents, cellosolve solvents, aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, aromatic organic solvents such as group heterocyclic compound solvents, amide solvents, halogen compound solvents, ester solvents, amine solvents, nitrile solvents, nitro solvents, aldehyde solvents, etc., and selected from these One or a mixture of two or more is used.

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

The average particle size is determined as the particle size at which the cumulative amount is 50% from the smaller diameter side in the cumulative particle size distribution on a mass basis obtained by laser diffraction.

[B] Molding step Next, the kneaded material or the granulated powder is molded to produce a molded body having the same shape as the desired sintered body.

The molding method includes, for example, a compaction molding method, a metal powder injection molding method, an extrusion molding method, and the like.

Of these, the molding conditions for 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 these ingredients. It is preferably about 200 MPa or more and 1000 MPa or less.

Molding conditions for metal powder injection molding vary depending on various conditions, but preferably the material temperature is about 80° C. or higher and 210° C. or lower, and the injection pressure is about 50 MPa or higher and 500 MPa or lower.

Molding conditions in the case of extrusion molding vary depending on various conditions, but preferably the material temperature is about 80° C. or higher and 210° C. or lower, and the extrusion pressure is about 50 MPa or higher and 500 MPa or lower.

In the molded body thus obtained, the binder is uniformly distributed between the plurality of particles of the precipitation hardening stainless steel powder for powder metallurgy.

The shape and dimensions of the molded body to be produced are determined by taking into consideration the amount of shrinkage of the molded body in the subsequent degreasing process and firing process.

[C] Degreasing Step Next, the obtained compact is subjected to a degreasing treatment to obtain a degreased body. Specifically, the molded body is heated to decompose the binder, thereby removing the binder from the molded body and performing a degreasing treatment.

In this degreasing treatment, an acid degreasing method is used in which the compact is heated in an acid-containing atmosphere. The acid degreasing method is a method of heating a compact in an acid-containing atmosphere and degreasing it using the catalytic action of an acid. According to the acid degreasing method, the binder can be decomposed in a short period of time even at a low temperature, so that even a compact having a large volume can be efficiently degreased.

The acid-containing atmosphere means an atmosphere containing an acid capable of decomposing the binder. Such acids include, for example, nitric acid, oxalic acid, ozone and the like, and one or more of these can be used in combination. A mixed gas in which these acids are mixed with other gases may also be used. An example of a mixed gas is fuming nitric acid. The atmospheric pressure may be atmospheric pressure, reduced pressure, or increased pressure.

The heating conditions for the molded body slightly differ depending on the composition and amount of the binder and the type of acid-containing atmosphere, but it is preferable that the temperature is 100 ° C. or higher and 750 ° C. or lower x 0.1 hour or higher and 20 hours or lower, and 150 ° C. or higher. More preferably, the time is 600° C. or less×0.5 hours or more and 15 hours or less. As a result, the compact can be degreased in a short time even at a relatively low temperature. In addition, sintering or oxidation of the compact can be suppressed.

Incidentally, such a degreasing step may be performed in a plurality of steps with different degreasing conditions so that the binder in the molded body can be decomposed and removed more quickly and without remaining in the molded body. good.

Further, if necessary, the degreased body may be subjected to machining such as cutting, polishing, and cutting. Since the degreased body has relatively low hardness and relatively high plasticity, it can be easily machined while preventing the shape of the degreased body from collapsing. According to such machining, it is possible to easily obtain a final sintered body with high dimensional accuracy.

[D] Firing Step The degreased body obtained in the step [C] is fired in a firing furnace to obtain a sintered body.

Due to this sintering, the precipitation hardening stainless steel powder for powder metallurgy causes diffusion at the interfaces between the particles, leading to sintering. At this time, the degreased body is quickly sintered by the mechanism described above. As a result, a dense and dense sintered body is obtained as a whole.

The firing temperature varies depending on the composition, particle size, etc. of the precipitation hardening stainless steel powder for powder metallurgy used in the production of the compact and degreased body. Also, the temperature is preferably about 1050° C. or higher and 1260° C. or lower.

Also, the firing time is 0.2 hours or more and 7 hours or less, preferably 1 hour or more and 6 hours or less.

In the firing process, the sintering temperature and the firing atmosphere, which will be described later, may be changed during the firing process.

By setting the sintering conditions within such a range, the entire degreased body can be sufficiently sintered while preventing oversintering and enlargement of the crystal structure due to excessive sintering. As a result, a sintered body having a high density and particularly excellent mechanical properties can be obtained.

Moreover, the sintered body thus manufactured may be subjected to additional treatment as necessary. Additional treatments include, for example, solution treatment, age hardening treatment, double aging treatment, sub-zero treatment, tempering treatment, hot working treatment, cold working treatment, etc., one or two of these. The above are used in combination.

In addition, as a specific example of the above-mentioned additional treatment, after performing a solution treatment of cooling from a temperature of 1000 ° C. or higher and 1250 ° C. or lower for 30 minutes or more and 120 minutes or less, A treatment that performs an age hardening treatment that cools for a time of 1 hour or more and 48 hours or less is exemplified.

The precipitation hardening stainless steel sintered body produced as described above, that is, the sintered body obtained by sintering the precipitation hardening stainless steel powder for powder metallurgy has Fe as the main component and Ni is 3.00. % by mass or more and 5.00% by mass or less, Cr is contained in a proportion of 15.00% by mass or more and 17.50% by mass or less, and Cu is contained in a proportion of 3.00% by mass or more and 5.00% by mass or less. Nb is contained at a ratio of 0.15% by mass or more and 0.45% by mass or less, Si is contained at a ratio of 0.30% by mass or more and 1.00% by mass or less, relative to the Mn content The Si content mass ratio Si/Mn 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 properties due to oxidation can be suppressed. As a result, a sintered body having excellent corrosion resistance and surface properties can be obtained. In the following description, the precipitation hardened stainless steel sintered body may be simply referred to as the sintered body.

In addition, it is preferable that the precipitation hardening stainless steel sintered body according to the embodiment has a precipitate containing silicon oxide deposited on its surface. These precipitates are formed by Mn and Cr, which are relatively easily oxidized, are prevented from being oxidized. Therefore, the precipitation hardened stainless steel sintered body in which precipitates containing silicon oxide are deposited is suppressed from deteriorating in properties due to oxidation, and has excellent corrosion resistance and surface properties.

The amount of precipitates in the sintered body is not particularly limited, but when the surface of the sintered body is observed with an electron microscope and the region where the total content of Si and O is 50% by mass or more is defined as precipitates, It is preferable that one or more, more preferably three or more, of such precipitates are found within the range of 50 μm square. 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.

Precipitation hardened stainless steel sintered bodies are used in transportation equipment parts such as automobile parts, bicycle parts, railroad vehicle parts, ship parts, aircraft parts, and parts for space transport vehicles (such as rockets). , parts for personal computers, parts for mobile phone terminals, parts for tablet terminals, parts for wearable terminals, parts for electrical equipment such as refrigerators, washing machines, air conditioners, machine tools, and semiconductor manufacturing equipment. machine parts, plant parts such as nuclear power plants, thermal power plants, hydroelectric power plants, oil refineries, chemical complexes, watch parts, metal tableware, jewelry, ornaments such as eyeglass frames, or It can be used as a material constituting a part.

The precipitation hardening stainless steel powder for powder metallurgy, the compound, the granulated powder, and the precipitation hardening stainless steel sintered body of the present invention have been described above based on preferred embodiments, but the present invention is limited to these. not a thing For example, optional additives may be added to compounds and granulated powders.

Next, examples of the present invention will be described.
1. Production of sintered body (Sample No. 1)
[1] First, a precipitation hardening stainless steel powder for powder metallurgy having the composition shown in Table 1 and produced by the water atomization method was prepared.

The composition of the metal powder shown in Table 1 was identified and quantified using an inductively coupled high-frequency plasma emission spectrometry method and an ICP device CIROS120 manufactured by Rigaku Corporation. For identification and quantification of C, a carbon/sulfur analyzer CS-200 manufactured by LECO was used. Furthermore, for the identification and quantification of O, an oxygen/nitrogen analyzer TC-300/EF-300 manufactured by LECO was used.

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

[3] Next, this mixed raw material was kneaded with a kneader to obtain a compound.
[4] Next, this compound was molded by an injection molding machine under the molding conditions shown below to produce a molded body.

<Molding conditions>
・Material temperature: 180℃
・Injection pressure: 11 MPa (110 kgf/cm ² )

[5] Next, the obtained compact was subjected to heat treatment under the following degreasing conditions to obtain a degreased body.

<Degreasing conditions>
・Degreasing temperature: 400°C
・Degreasing time: 1 hour (holding time at degreasing temperature)
・Degreasing atmosphere: mixed gas atmosphere of nitrogen and nitric acid, the concentration of nitric acid is 2% by volume

[6] Next, the obtained degreased body was fired under the following firing conditions. A sintered body was thus obtained. The shape of the sintered body was a cylinder with a diameter of 10 mm and a thickness of 5 mm.

<Baking conditions>
・Firing temperature: 1300°C
・Baking time: 3 hours (holding time at baking temperature)
・Firing atmosphere: Argon atmosphere

[7] Next, the obtained sintered body was sequentially subjected to solution treatment and age hardening treatment under the following conditions.

<Solution treatment conditions>
・Heating temperature: 1120℃
・Heating time: 30 minutes ・Cooling method: Water cooling

<Age hardening treatment conditions>
・Heating temperature: 700℃
・Heating time: 24 hours ・Cooling method: Water cooling

(Sample Nos. 2 to 25)
Except for changing the composition of the precipitation hardening stainless steel powder for powder metallurgy as shown in Table 1, sample Nos. A sintered body was obtained in the same manner as in case 1. Metal powder produced by the gas atomization method was used in the production of some sintered bodies. For applicable items, "gas" is written in the remarks column of Table 1.

In addition, in Table 1, each sample No. Among precipitation hardening stainless steel powders and sintered bodies for powder metallurgy, those corresponding to the present invention are referred to as "Examples" and those not corresponding to the present invention are referred to as "Comparative Examples."
In addition, each sintered body contained a small amount of impurities, but their description in Table 1 was omitted.

2. 2. Evaluation of Sintered Body 2.1 Evaluation of Corrosion Resistance The degree of corrosion of the sintered body was measured according to the sulfuric acid corrosion test method for stainless steel specified in JIS G 0591:2012. Boiled 5% by mass sulfuric acid was used as the sulfuric acid.

Then, each sample no. Regarding the corrosion rate of the sintered body of sample No. A relative value was calculated when the degree of corrosion (unit: g/m ² /h) measured for 20 sintered bodies was set to 1. Then, the calculated relative value was evaluated in light of the following evaluation criteria.

<Evaluation Criteria for Corrosion Degree>
A: The relative value of the corrosion rate of the sintered body is less than 0.50 B: The relative value of the corrosion rate of the sintered body is 0.50 or more and less than 0.75 C: The relative value of the corrosion rate of the sintered body The value is 0.75 or more and less than 1.00 D: The relative value of the corrosion rate of the sintered body is 1.00 or more and less than 1.25 E: The relative value of the corrosion rate of the sintered body is 1.25 or more Less than 1.50 F: The relative value of the degree of corrosion of the sintered body is 1.50 or more Table 2 shows the above evaluation results.

2.2 Evaluation of specularity The sintered body of was subjected to barrel polishing.

Next, the specular glossiness of the sintered body was measured according to the specular glossiness measuring method specified in JIS Z 8741:1997. The incident angle of light on the surface of the sintered body was 60°, and glass with a specular gloss of 90 and a refractive index of 1.500 was used as a reference surface for calculating the specular gloss. Then, the measured specular gloss was evaluated according to the following evaluation criteria.

<Evaluation Criteria for Specular Glossiness>
A: Very high surface specularity, specular glossiness of 200 or more B: High specularity of the surface, specular glossiness of 150 or more and less than 200 C: Slightly high surface specularity, specular glossiness degree is 100 or more and less than 150 D: The surface has a slightly low specularity and the specular gloss is 60 or more and less than 100 E: The surface has a slightly low specularity and the specular gloss is 30 or more and less than 60 F: The specularity of the surface is low and the specular glossiness is less than 30. Table 2 shows the above evaluation results.

2.3 Evaluation of Tensile Strength Next, each sample No. shown in Table 1 was tested. The tensile strength of the sintered body was measured according to the metal material tensile test method specified in JIS Z 2241:2011.
Then, the measured tensile strength was evaluated according to the following evaluation criteria.

<Evaluation Criteria for Tensile Strength>
A: Tensile strength of sintered body is 1130 MPa or more B: Tensile strength of sintered body is 1080 MPa or more and less than 1130 MPa C: Tensile strength of sintered body is 1030 MPa or more and less than 1080 MPa D: Sintered The tensile strength of the body is 980 MPa or more and less than 1030 MPa E: The tensile strength of the sintered body is 930 MPa or more and less than 980 MPa F: The tensile strength of the sintered body is less than 930 MPa Table 2 shows the above evaluation results. show

As is clear from Table 2, the sintered bodies of Examples had both good corrosion resistance and specularity, although they were produced through degreasing by an acid degreasing method.

On the other hand, the sintered bodies of the comparative examples were insufficient in corrosion resistance and specularity. Specifically, when the Si content rate or the Si/Mn ratio is out of the predetermined range, both the corrosion resistance and specularity are found to be degraded.

Each sample No. When the surface of the sintered body was observed with an electron microscope and the number of precipitates existing within a 50 μm square area was counted, one or more precipitates were found in all examples.

Further, when the molding method was changed from the injection molding method to the compression molding method, a sintered body similar to the above was produced and evaluated, and the same tendency as the above evaluation results was observed.

Claims (8)

Fe is the main component,
Ni is contained at a ratio of 3.00% by mass or more and 5.00% by mass or less,
Cr is contained at a ratio of 15.00% by mass or more and 17.50% by mass or less,
Cu is contained at a ratio of 3.00% by mass or more and 5.00% by mass or less,
Nb is contained at a ratio of 0.15% by mass or more and 0.45% by mass or less,
Si is contained at a ratio of 0.30% by mass or more and 1.00% by mass or less,
Mn is contained at a ratio such that the mass ratio Si/Mn of the Si content to the Mn content is 2.00 or more and 6.00 or less,
A precipitation hardening stainless steel powder for powder metallurgy, characterized by being subjected to degreasing by an acid degreasing method. 2. The precipitation hardening stainless steel powder for powder metallurgy according to claim 1, wherein the mass ratio O/Si of the O content to the Si content is 0.10 or more and 0.90 or less. Where s is the content of Si, m is the content of Mn, and c is the content of Cr, s/{m+(c/10)} is 0.15 or more and 0.50 or less. Precipitation hardening stainless steel powder for powder metallurgy according to . The precipitation hardening stainless steel powder for powder metallurgy according to any one of claims 1 to 3, wherein the O content is 0.01% by mass or more and 0.70% by mass or less. The precipitation hardening stainless steel powder for powder metallurgy according to any one of claims 1 to 4, having an average particle size of 0.50 µm or more and 50.00 µm or less. A precipitation hardening stainless steel powder for powder metallurgy according to any one of claims 1 to 5, and a binder for binding particles of the precipitation hardening stainless steel powder for powder metallurgy. compound to A granulated powder obtained by granulating the precipitation hardening stainless steel powder for powder metallurgy according to any one of claims 1 to 5. A precipitation hardening stainless steel sintered body obtained by sintering the precipitation hardening stainless steel powder for powder metallurgy according to any one of claims 1 to 5.