Evaluation of Bearing Steels Produced by Powder Metallurgy Process

Abstract

A variety of steel powders for bearing applications, such as high-speed tool steel, M50 and 440C steels, etc., prepared through vacuum induction melting (VIM) and inert gas atomizer were canned and consolidated by hot extrusion to bars for specimens used in this experiment. The carbide sizes of the extruded materials through powder metallurgy (P/M) route were extremely fine as compared to ingot metallurgy (I/M) materials. Nonmetallic inclusions were finely dispersed and the materials were rated to have good cleanliness per ASTM E 45-85 (Method A), Practice for Determining the Inclusion Content of Steel. It is found that lower hardening temperature for P/M materials, with finer carbides that dissolve to the matrix rapidly, can produce hardness comparable to one of I/M materials quenched from a standard temperature. P/M materials, in addition, show significantly better impact values and bending fracture strength than I/M materials due to finer carbides and inclusions. The rolling contact fatigue test results of M50 steel revealed that fatigue life of P/M materials is comparable to the highest class of life obtained in the same grade of I/M materials. Also, flaking leading to extremely short life, which is sometimes encountered in I/M materials, did not occur in P/M materials.