JPH0657301A - Alloy steel powder for sintered material - Google Patents

Abstract

PURPOSE:To provide the alloy steel powder for a sintered material adequate for use in production of sintered parts which have high dimensional accuracy, high strength and high fatigue strength and being decreased in dimensional change and variation in strength. CONSTITUTION:While the raw material steel powder is previously alloyed with 0.1-2.0% Cr and/or 0.1-2.5% Mo, the raw material steel powder is alloyed with 0.5-5.05 Ni and/or 0.5-3.0% Cu by composite alloying; in addition, the geometrical standard deviation of the grain size distribution of the Ni powder is confined to <=1.8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alloy steel powder for a sintered material, which is suitable for production of various sintered parts which are required to have high dimensional accuracy, high strength and high fatigue characteristics. It is a thing.

[0002]

2. Description of the Related Art When manufacturing parts such as gears of automobile parts that require high strength and fatigue characteristics as well as high dimensional accuracy by powder metallurgy, alloying elements are added to improve strength and fatigue characteristics. Then, a carburizing process or a nitrifying process is further performed, followed by quenching and tempering.

In the case of a prealloyed steel powder, which is produced by dissolving alloy components in pure iron powder to form an alloyed steel powder, the dimensional accuracy of the sintered material after heat treatment is high, but the compressibility of the steel powder is impaired. In such a case, a high sintered density cannot be obtained, and as a result, improvement in strength and fatigue properties cannot be expected. Especially
Prealloying Ni reduces the compressibility.

In this respect, for example, in Japanese Examined Patent Publication (Kokoku) No. 45-9649, the above-mentioned problems are caused by diffusing and adhering alloying component powders such as Ni, Cu and Mo to pure iron powder (hereinafter referred to as a complex alloying method) We are trying to resolve However, although the composite alloy steel powder produced by the above method is excellent in compressibility, it is only partially alloyed by causing diffusion by heating after mixing different metal powders, so that the composition is completely Compared with the pre-alloying method, in which a uniform material can be obtained, the uniformity of the structure is poor, which causes variations in the dimensional accuracy of the product. As described above, in the above-described composite alloy steel powder, although the compressibility is high and the strength and fatigue characteristics of the sintered material can be improved, it is difficult to say that the dimensional accuracy is sufficient, and there is a problem in that the strength varies widely. Was left.

Further, the inventors previously proposed, in Japanese Patent Laid-Open No. 1-215904, a steel powder having high compressibility and high dimensional accuracy after heat treatment of a sintered material together with its manufacturing method. However, since this steel powder contains more than 5.0 wt% (hereinafter simply referred to as%) of Ni, it is not economically disadvantageous, but it is sufficient for the recent demands for strict dimensional accuracy and strength uniformity. I left a problem where I couldn't answer.

[0006]

SUMMARY OF THE INVENTION The present invention advantageously solves the above-mentioned problems. The sintered material has high dimensional accuracy after heat treatment, has good strength and fatigue characteristics, and has variations in strength. It is an object of the present invention to propose an alloy steel powder for a sintered material, which enables a small sintered material to be obtained economically as compared with conventional ones.

[0007]

[Means for Solving the Problems] As a result of intensive studies to achieve the above-mentioned object, the inventors have found that Cr and Mo are prealloyed, while Ni and Cu are complex alloyed, respectively. We have found that alloying is extremely effective in achieving the intended purpose. The present invention is based on the above findings.

That is, the present invention contains one or two selected from Cr: 0.1 to 2.0% and Mo: 0.1 to 2.5%, and the balance on the surface of a prealloyed steel powder consisting of Fe and unavoidable impurities. , Ni: 0.5 ~
An alloy steel powder in which 5.0% is partially diffused and adhered in the form of powder, and the geometric standard deviation of the particle size distribution of the above Ni powder is 1.8.
The alloy steel powder for a sintered material (first invention) is characterized in that:

The present invention also includes one or two selected from Cr: 0.1 to 2.0% and Mo: 0.1 to 2.5%, the balance being on the surface of a prealloyed steel powder consisting of Fe and inevitable impurities. , Ni: 0.5 ~
It is an alloy steel powder in which 5.0% and Cu: 0.5 to 3.0% are partially diffused and adhered in the form of powder, respectively, and the geometric standard deviation of the particle size distribution of the above Ni powder is 1.8 or less. 2 is an alloy steel powder for a sintered material (second invention).

[0010]

In the present invention, among alloy components, Cr and Mo are prealloyed, while Ni and Cu are composite alloyed.
Hereinafter, the reason and the reason why the composition range of each element is limited to the above range will be described. Cr: 0.1-2.0% Cr is an element useful for improving the strength and fatigue properties of sintered materials, and by pre-alloying it, in particular, reduces the oxygen activity and suppresses the formation of oxides. Therefore, in the present invention, alloying is intended by prealloying. here
When the Cr content is less than 0.1%, these effects are small. On the other hand, when it exceeds 2.0%, the compressibility is lowered and the strength and fatigue properties are lowered by the Cr precipitates.
The content is set to be in the range of%.

Mo: 0.1-2.5% Mo is an alloying element that improves the strength of the sintered material, and at least 0.1% is required to improve the strength, while 2.5%
If added in excess of 0.1%, the compressibility will decrease, the density of the sintered material cannot be increased, and the strength and fatigue properties will decrease.
The content should be within the range of up to 2.5%. Further, within the above range, the compressibility is not greatly impaired, and the diffusion into the iron powder is fast, so alloying is performed by prealloying.

The method of adding Ni: 0.5 to 5.0% Ni is a major feature of the present invention. Ni is
It is an element that improves the strength and toughness of the sintered material, but if pre-alloyed, the compressibility is significantly deteriorated, and the strength and fatigue properties are reduced. In this respect, since the above problems do not occur in complex alloying, in the present invention, alloying is performed by complex alloying. In order to suitably perform the composite alloying here,
After mixing the Ni powder with the prealloyed steel powder, diffusion annealing may be performed in hydrogen at 750 to 1050 ° C, followed by crushing and classification. Note that
Ni should be added in an amount of 0.5% or more to improve the strength and toughness of the sintered material. On the other hand, if added in excess of 5.0%, austenite is excessively generated, which lowers the strength and fatigue properties. It was limited to the range of 0.5-5.0%.

Cu: 0.5-3.0% Cu effectively contributes to the improvement of sinterability and, in turn, the strength and fatigue properties of the sintered material.
It is necessary to add 0.5%. On the other hand, if added over 3.0%, the strength and fatigue properties will be deteriorated, so the addition was made within the range of 0.5 to 3.0%. Note that since pre-alloying impairs the compressibility of Cu, it was decided to add Cu for complex alloying.

By the way, Ni is an extremely useful element for improving the strength and toughness of the sintered material as described above, but even in the case of complex alloying, the geometric standard deviation of the particle size distribution of Ni powder is If the value exceeds 1.8, the dimensional accuracy decreases during heat treatment and the tensile strength of the sintered material increases, so it is important to keep the geometric standard deviation of the particle size distribution of the Ni powder to 1.8 or less. . Here, the geometric standard deviation is defined by the following equation: Geometric standard deviation = d _84.1 / d ₅₀ , where d _84.1 and d ₅₀ are the cumulative frequency distributions of the powder particle size at 84.1% and 50%, respectively. Means particle size.

In FIG. 1, (a) Cr: 1.0% and Mo: 0.3%
Steel powder that is pre-alloyed with Ni: 2.0% and (b) Cr: 1.0% and Mo: 1.0% is pre-alloyed, and Ni: 1.0% and Cu: 1.0% is a composite alloy. Graphite 0.2% and zinc stearate 1% were added to each of the converted steel powders, molded at a pressure of 7 t / cm ² and sintered at 1250 ° C for 60 min, then at 910 ° C for 120 min, carbon potential 0.8.
% Of the Ni powder particle size distribution on the variation in tensile strength of each sintered material obtained by carburizing in 80% oil immediately after carburizing at 80% and then tempering at 180 ° C for 45 min. The result of having investigated about the influence of geometric standard deviation is shown. As is clear from the figure, in all the steel types, when the geometric standard deviation of the grain size distribution exceeds 1.8, the variation in tensile strength becomes large.

Next, FIG. 2 shows the results of an examination of the effect of the geometric standard deviation of the Ni powder particle size distribution on the variation in dimensional changes during carburizing, quenching and tempering of the respective sintered materials obtained as described above. Show. As is clear from the figure, in all the steel types, when the geometric standard deviation of the grain size distribution exceeds 1.8, the variation in dimensional change becomes large.

By shaping and sintering the alloy steel powder as described above, the dimensional accuracy of the sintered material after heat treatment can be improved, and the strength and fatigue of the obtained sintered / heat treated material can be improved. The characteristics are extremely good. Incidentally, the term “molding and sintering” as used herein generally means a method for manufacturing powder metallurgical parts, for example, after compression molding under a pressure of 4 to 8 t / cm ² , N ₂ , AX, RX at 1100 to 1300 ° C. Sintering in gas or vacuum is preferred. If necessary, graphite may be added prior to molding for the purpose of improving strength, and the amount is preferably 0.05 to 0.4%.

[0018]

[Example] To alloy steel powder having the chemical composition shown in Table 1, 0.1% of graphite and 1% of zinc stearate as a lubricant were added.
After mixing, compression molding at a pressure of 7 t / cm ² , sintering at 1250 ° C for 60 min in N ₂ gas, then at 910 ° C for 30 mi.
n, Carbon potential: Carburized at 0.8%, immediately quenched in oil at 80 ° C, and then tempered at 180 ° C for 45 min. The fatigue strength and tensile strength (n = 30) of the thus obtained sintered / heat-treated material were examined by the Mori type 6 spherical pressure fatigue test. Outer diameter: 60 mm, inner diameter: 20
With respect to a ring-shaped test piece having a height of 5.5 mm and a height of 5.5 mm, the standard deviation of the variation in the dimensional change between the sintered material and the tempered material was obtained as shown in FIG. In this experiment, alloy steel powder was prepared by mixing a predetermined amount of carbonyl Ni powder (average particle size: 16 μm, geometric standard deviation: 1.6) and Cu powder (metal copper powder) with prealloyed steel powder, and then in hydrogen. 900 ° C, 60 min
It was obtained by crushing and classifying after diffusion annealing. The survey results are also shown in Table 1.

[0019]

[Table 1]

As is clear from the table, according to the present invention, by pre-alloying Cr and Mo while making a composite alloy of Ni and Cu, it is possible to obtain a sintered body having excellent strength, fatigue characteristics and dimensional accuracy. The material could be obtained.

[0021]

The alloy steel powder of the present invention is excellent not only in strength and fatigue properties after sintering and heat treatment, but also can maintain extremely high dimensional accuracy and reduce variations in strength and dimensional change. For example, it is very effective as a raw material steel powder for a sintered part, which requires high dimensional accuracy as well as high strength and high fatigue strength such as a cam gear of an automobile.

[Brief description of drawings]

FIG. 1 is a graph showing the effect of the geometric standard deviation of the Ni powder particle size distribution on the variation in tensile strength of sintered materials.

FIG. 2 is a graph showing the effect of the geometric standard deviation of the Ni powder particle size distribution on the variation in dimensional change of the sintered material.

FIG. 3 is an explanatory diagram of a dimensional accuracy measurement procedure.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshiaki Maeda 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Chiba Steel Works (72) Inventor Eiji Hattani, Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Chiba Steel Works, Ltd.

Claims (2)

[Claims] 1. A pre-alloyed steel powder containing one or two selected from Cr: 0.1 to 2.0 wt% and Mo: 0.1 to 2.5 wt%, the balance being Fe and inevitable impurities on the surface of the powder. Ni: 0.5 ~
It is an alloy steel powder in which 5.0 wt% is partially diffused and adhered in the form of powder, and the geometric standard deviation of the particle size distribution of the above Ni powder is
Alloy steel powder for sintered materials, characterized by being 1.8 or less. 2. A surface of a prealloyed steel powder comprising one or two selected from Cr: 0.1 to 2.0 wt% and Mo: 0.1 to 2.5 wt%, the balance being Fe and inevitable impurities, Ni: 0.5 ~
5.0 wt% and Cu: 0.5 to 3.0 wt% are alloy steel powders partially diffused and adhered in the form of powder, and the geometric standard deviation of the particle size distribution of the above Ni powder is 1.8 or less. Alloy steel powder for characteristic sintering materials.