US 5,427,600 A · Low alloy sintered steel and method of preparing the same

Abstract

A low alloy sintered steel contains at least 0.15 percent by weight and less than 0.8 percent by weight of carbon. Its matrix is formed by a tempered martensite containing prior austenite crystal grains of not more than 15 .mu.m in mean grain size. Pores and nonmetallic inclusions contained in the matrix are not more than 50 .mu.m in maximum diameter, and the density of the low alloy sintered steel is at least 96 percent of theoretical density. A raw material powder for forming the low alloy sintered steel includes iron alloy powder which is prepared by an atomizing process, and is treated with a dry mill in an inert gas atmosphere or in the atmospheric air. Thus, dislocations are introduced into the raw material powder, and nonmetallic inclusions contained in the raw material powder are pulverized to be not more than 50 .mu.m in maximum diameter. Not only static characteristics but also dynamic characteristics, such as fatigue strength, of the low alloy sintered steel are improved.

Claims17

Dependent claims

A low alloy sintered steel containing at least 0.15 percent by weight and less than 0.8 percent by weight of carbon and having a matrix of a tempered martensite containing prior austenite crystal grains of not more than 15 .mu.m in mean grain size, said matrix containing pores and nonmetallic inclusions of not more than 50 .mu.m in maximum diameter, and having a density of at least 96 percent of theoretical density.

A method of preparing a low alloy sintered steel, comprising the following steps:

treating a raw material powder containing at least one of atomized iron powder and atomized iron alloy powder and containing nonmetallic inclusions in a treatment atmosphere containing one of an inert gas and atmospheric air with a dry mill for introducing dislocations into said raw material powder and pulverizing said nonmetallic inclusions to a maximum diameter of not more than 50 .mu.m;
annealing said treated raw material powder for softening said treated raw material powder;
adding and mixing carbon powder with said annealed raw material powder to obtain a mixed powder with a carbon content of at least 0.15 percent by weight and less than 0.8 percent by weight in the final composition;
cold-forming said mixed powder to obtain a compact;
densifying said compact to a density of at least 96 percent of theoretical density by one of sintering and hot plastic working;
and
heat treating said densified compact to obtain a low alloy sintered steel having a matrix of a tempered martensite.

4 more elements

Dependencies are inferred from the claim text.

Low alloy sintered steel and method of preparing the same

Life of this patent

Low alloy sintered steel and method of preparing the same

Life of this patent

Abstract

Claims17