JPH01275703A - Stainless steel powder for high-density sintering - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an austenitic stainless steel powder for powder metallurgy having good compressibility and sinterability.

(Prior Art) In recent years, a molten metal atomization method has been developed as a method for producing metal powder for powder metallurgy, and special steel powder has come to be mass-produced.

This type of special steel powder, that is, alloy steel powder, usually contains several types of alloying elements other than C in the iron base, and the alloy powder particles are hardened by the solid solution hardening effect of the alloying elements, so the alloy powder When the particles were sintered, they were generally less compressible than carbon steel powder and could not be made sufficiently dense.

For this reason, it is difficult to increase the density of stainless steel sintered bodies, which is a type of sintered body of special steel, so conventional stainless steel sintered bodies do not always have sufficient mechanical properties, corrosion resistance, and oxidation resistance. The current situation is that this has not been improved.

(Problems to be Solved by the Invention) Therefore, the problems to be solved by the present invention are as follows: 1. Stainless steel, which is a representative material with excellent mechanical properties and corrosion resistance, and is used for many purposes, can be made into a sintered body and highly The goal is to manufacture it with high density and exhibit the high toughness, corrosion resistance, etc. inherent to stainless steel.

Stainless steel powder containing alloying elements other than Fe, such as Ni, Cr, and Mo, has a problem in that it is hard and difficult to compress compared to iron powder, low alloy steel powder, and the like.

As a first solution to this problem, the above-mentioned Ni and Cr are added to the iron powder.
A conceivable method is to mix elemental powders such as , Mo, etc., compression mold them while taking advantage of the inherent good compressibility of iron powder, and then form a diffusion alloy during sintering. However, in the case of stainless steel, since it contains a large amount of Ni, Cr, etc. as its main constituent elements, it is difficult to form a sufficient diffusion alloy under normal sintering conditions, and it is easy to generate stable oxides, so it cannot be sintered and solidified in a clean manner. difficult to do.

The second solution is to increase the density during sintering, and this involves adding an auxiliary agent that promotes powder sintering, and the auxiliary agent has the inherent properties of stainless steel materials. Preferably something that does not impair the quality of the product.

The present inventors tried the above-mentioned second method and experimentally evaluated the effect of adding stainless steel powder or alloy powder similar thereto. As a result, it has been found that with austenitic stainless steel powder, that is, stainless steel powder containing Ni, adding a small amount of P facilitates densification during sintering and improves the mechanical properties of the sintered body.

An object of the present invention is to provide a stainless steel powder that has good compressibility and sinterability and is easily densified.

(Means for Solving the Problems) In order to achieve the above object, the stainless steel powder for high-density sintering of the present invention has an austenitic stainless steel powder containing Fe, Ni, and Cr as main components with an average particle size of 10 μm. It is characterized in that the following iron phosphorus fine powder is mixed in a phosphorus purity in a range of 0.3 to 1.5% by weight.

The austenitic stainless steel powder contains Fe, Ni
, Cr, and Mo are the main components. The austenitic stainless steel powder contains 4% Ni by weight.
As mentioned above, it is characterized by containing 12% or more of Cr. It is characterized by containing a total of 0.5% by weight or more of one or more solid solution strengthening elements in addition to the above-mentioned main components.

We targeted austenitic stainless steel powder (including those belonging to the α/γ two-layer region) because, when a melt of FezP, for example, diffuses into the stainless steel powder during sintering, N1- P-based low melting point substance (N
ia P, Nis Pa.

Ni
This is because the synergistic effect of the diffusion alloying action of the -P-based substance further promotes diffusion alloying of the entire material.

The reason why the average particle size of the iron phosphorus fine powder is set to 10 μm is that the average particle size of ordinary stainless steel powder for powder metallurgy is 50 μm or more, so the average particle size is less than one-fifth of that of this alloy powder. If iron phosphorus fine powder of 10 μm or less is mixed, the iron phosphorus fine powder will be incorporated in a uniformly dispersed form between the stainless steel powder particles as the mother alloy powder during sintering, and the original properties of the stainless steel powder will be impaired. This is because the compressibility of these mixed powders is improved without causing any damage.

The reason why fine iron phosphorus powder is added in the range of 0.3 to 1.5% by weight in terms of phosphorus purity is that fine iron phosphorus powder is mainly added to stainless steel powder.
When added in the form of e5P (eutectic temperature: 116°C), if the P content of these mixed powders is less than 0.3% by weight, the melt of (Fe, Ni) s P is sufficient during sintering. This is because densification by liquid phase sintering is hardly possible under normal sintering conditions. Furthermore, if the P content exceeds 1.5% by weight, the compressibility of the powder will decrease and the sintering promotion effect will be reduced, and P compounds will remain in the grain boundaries of the sintered body, and this P compound will cause sintering. This is because it is expected that the corrosion resistance of the compact will deteriorate and the mechanical properties, particularly the ductility and toughness, will be impaired.

The reason why Ni is set to 4% by weight or more is that the above-mentioned N1-P low melting point substance is melted during sintering, so that Fe s
This is because a synergistic effect of melting both P and N1-P-based substances occurs, and diffusion alloying of the entire material is promoted.

The reason why the Cr content is 12% or more is that when the Cr content is 12% or more, the stainless steel has further improved corrosion resistance.

Typical stainless steels containing Mo as one of the main elements include 304L, 316L, and 310L, among which 316L and the like contain MO as the main constituent element to enhance corrosion resistance.

The solid solution strengthening elements include Si, Mn, Cu, Ti,
There are Aβ, Nb, V, etc., and it is well known that these solid solution strengthening elements can be used in the low carbon region (C≦0.05%).

(Function) When the stainless steel powder for high-density sintering is used, fine iron phosphorus powder with a small particle size is mixed with the stainless steel powder in the form of Fe3P, so that the stainless steel powder is not absorbed during compression molding. The iron phosphorus becomes a melt during sintering, and the alloying elements are uniformly diffused through liquid phase sintering, making it possible to increase the density of the sintered body without sacrificing its original good properties and compressibility.

(Example) Examples of the present invention will be described.

0.8% by weight of Fe5P fine powder of various particle sizes was mixed into stainless steel powder (-100 mesh, average particle size 68 μm) produced by water spraying, and a lubricant was further added.
A green compact was produced by compression molding at a pressure of 8 tons/cm''. At this time, a mold specified in JSPM Standard 1-64 was used.

The relationship between the density of the obtained green compact and the compacting pressure is shown in FIG. 1, and the relationship between the Rattler value and the compacting pressure is shown in FIG. 2.

As is clear from Figures 1 and 2, when Fe5P powder is mixed with stainless steel powder (304L), Fe5P powder
It can be seen that when the average particle size of P exceeds 10 μm, the green density of the stainless steel powder decreases and the compressibility is impaired, and the Rattler value also increases, resulting in a decrease in the formability, that is, the strength of the green compact.

Three types of stainless steel powder (-10
0 mesh, average particle size of about 70 μm) was used. The compositions of these stainless steel powders are shown in Table 1.

(Margins below) Fe5 with an average particle size of 3.6 μm was added to the stainless steel powders shown in Test Example 1, Test Example 2, and Comparative Example 3, respectively.
Mix P fine powder and add lubricant to produce 4-8 tons/c
A green compact was produced by compression molding at a pressure of 1.5 m.The green compact was vacuum sintered at 1200°C for 1 hour above the melting point of Fe3P, and the density of the sintered body was measured.

The relationship between the green density of the obtained green compact and the compacting pressure and the relationship between the sintered density of the sintered compact and the compacting pressure are shown in FIGS. 3 to 5.

Fig. 3 shows Test Example 1, Fig. 4 shows Test Example 2, and Fig. 5 shows Comparative Example 3. This shows the state in which the sintered density changes.

As shown in Figures 3 to 5, compared to ferritic stainless steel powder (Figure 5), austenitic stainless steel powder (Figures 3 and 4) is more effective due to the stress relaxation effect of the original Ni. It can be seen that the compacted powder density is high and the compressibility is good.

Next, as shown in Figs. 3 and 4, when the austenitic stainless steel 304L and 316L powders (Test Examples 1 and 2) increase their phosphorus content in the form of Fe5P to 0.8% by weight, Sintered density increases rapidly compared to green powder density. On the other hand, in the case of ferrite-based 41OL powder (Comparative Example 3), the sintered density when 0.8% by weight of Fe5P is added as a phosphorus pure content is not much higher than the sintered density of 41OL powder without Fe3P added. There is no difference, and the addition of P in this case has little effect on improving sinterability.

From this, austenitic stainless steel powder has better compressibility and F e y compared to ferritic stainless steel powder.
Since liquid phase sintering is promoted by adding a predetermined amount of P,
It is estimated that the sintered density will increase rapidly. Furthermore, when the phosphorus content is increased to 1.2% by weight, it becomes 304L and 316L.
The powder sintered bodies (Test Example 1, Test Example 2) have dramatically higher density,
be converted into

In this case, as a feature of liquid phase sintering, the dependence of sintered density on pressure is small, and high density can be achieved even if the compacting pressure during sintering is not very high.

(Effects of the Invention) As explained above, in the present invention, since a small amount of fine iron phosphorus powder with a small particle size is mixed into the austenitic stainless steel powder, the original good compressibility of the stainless steel powder is not impaired, and the Since it becomes easier to create a diffusion atmosphere during sintering, this has the effect of increasing the density of the sintered body by synergistically improving both compressibility and sinterability.

[Brief explanation of the drawing]

Fig. 1 is a graph showing how the relationship between compaction pressure and green density changes depending on the average particle size of the iron phosphorus fine powder of the example of the present invention, and Fig. 2 is a graph showing how the relationship between the compacting pressure and green density changes depending on the average particle size of the iron phosphorus fine powder of the example of the present invention. A graph showing how the relationship between Rattler value and molding pressure changes depending on the average particle size, FIGS. 3 and 4 are graphs showing the relationship between molding pressure and density in test examples of the present invention, FIG. 5 is a graph showing the relationship between molding pressure and density in a comparative example. Molding pressure (Totamopo) Fig. 1 34567B Sword support shape I5 force (Door c0 child) Fig. 2 □ P = 0 61°---0.5°l. 11------i, s °m Figure 3-P=O'/. Fig. 4 -1,561° Fig. 5

Claims (4)

[Claims] (1) Fine iron phosphorus powder with an average particle size of 10 μm or less is mixed with austenitic stainless steel powder whose main components are Fe, Ni, and Cr in a range of 0.3 to 1.5% by weight of pure phosphorus. Stainless steel powder for high-density sintering. (2) The austenitic stainless steel powder contains Fe
The stainless steel powder for high-density sintering according to claim 1, characterized in that the main components are Ni, Cr, and Mo. (3) The stainless steel powder for high-density sintering according to claim 1 or 2, wherein the austenitic stainless steel powder contains 4% or more Ni and 12% or more Cr by weight. (4) The stainless steel for high-density sintering according to claim 1, 2 or 3, characterized in that it contains one or more solid solution strengthening elements in addition to the main component in a total of 0.5% by weight or more. steel powder.