Injection-Molded Sintered Alloy Steel Product

Now the invention is described in further detail with reference to non-limiting Examples.

A water-atomized fine powder (30 .mu.m in average particle diameter) of an Fe-Cr alloy containing 30% by weight of Cr (hereinafter Fe-30wt.%Cr alloy) as the mother alloy was mixed with carbonyl iron powder (5 .mu.m in average particle diameter) containing 0.9% by weight of carbon and natural graphite powder (22 .mu.m in average particle diameter) at ratios as shown in Table 1, and to the mixture was further added an organic binder to make a total of 10 kg. The resulting mixture was kneaded, and was injection-molded in a metal mold to obtain a test piece 10 mm in width, 10 mm in thickness, and 55 mm in length. Thus were obtained test pieces No.1 to No.7.

The molded test pieces were debindered in nitrogen atmosphere at 300 .degree. C., and subjected to sintering in a semicontinuous vacuum sintering furnance at 1250.degree. C. under vacuum of 5.times.10.sup.-2 Torr to obtain sound sinterings. The sinterings had a relative density ranging from 93% to 95%, depending on the composition.

Vickers hardness of the sintering was measured applying a load of 10 kg. The sinterings thereafter were subjected to oil-quenching and tempering. Quenching was carried out by oil-quenching a sintering maintained at 830 .degree. C. For 30 minutes. Tempering comprised air-cooling a sintering maintained at 170.degree. C. for 60 minutes. Vickers hardness under 10-kg load was then measured again on each of the heat-treated sintering.

Test piece No. 8 was then prepared in the same manner as described above, except for using a carbonyl iron powder (5 .mu.m in average particle diameter) containing 0.9 % by weight of carbon and carbonyl nickel powder (7 .mu.m in average particle diameter) at amounts shown in Table 1. Vickers hardness was also measured on this sintering having a relative density of 95%.

The measured hardness for the sintering and the heat-treated products are given in Table 1.

Table 1 reads that the as-sintered alloys according to the present invention have a low Hv of 260 or less. This signifies that the post workability of the alloys according to the present invention is quite comparable to that of the prior art alloy. Concerning the heat-treated alloys of the present invention, the hardness HV thereof exceeded 700, clearly indicating a superiority in hardenability.

A mechanically crushed fine powder (8 .mu.m in average particle diameter) of an Fe-Mn alloy containing 77% by weight of Mn (hereinafter Fe-77wt.%Mn alloy) as the mother alloy was mixed with carbonyl iron powder (5 .mu.m in average particle diameter) containing 0.05% or 0.9% by weight of carbon and natural graphite powder (22 .mu.m in average particle diameter) at ratios as shown in Table 1, and to the mixture was further added an organic binder to make a total of 10 kg. The resulting mixture was kneaded, and the kneaded product was injection-molded in a metal mold to obtain a test piece 10 mm in width, 10 mm in thickness, and 55 mm in length. Thus were obtained test pieces No. 9 to No. 15.

The molded test pieces were sintered in the same manner as in Example 1, to obtain sinterings having a relative density ranging from 92% to 95%, depending on the composition.

The hardness of the sinterings was measured in the same manner as in Example 1. Subsequent heat treatment and the hardness measurement on the heat-treated sinterings were carried out in accordance with the method described in Example 1.

The measured hardness for the sinterings and the heat-treated products are given in Table 2.

Table 2 reads that the as-sintered alloys according to the present invention have a low Hv of 270 or less. This signifies that the post workability of the alloys according to the present invention if quite comparable to that of the prior art alloy. Concerning the heat-treated alloys of the present invention, the hardness Hv thereof exceeds 700, clearly indicating superiority in hardenability.