THE DISTORTION OF BALL BEARING STEEL AFTER VARIOUS HEAT-TREATMENTS

Abstract

The distortion of the standard specimens, A and B type, made of ball-bearing steel was measured after various heat-treatments, such as conventional heat-treatment and interrupted quenching the so-called martempering or marquenching, and subzero-treatment.
The most of distortions on quenching were due to the thermal stress during the rapid cooling. By martempering, the thermal strains were eliminated excepting the unavoidable strains directly caused by austenite-martensite transformation. The distortion produced on quenching was reduced by subsequent tempering but increased by subzero-treatment, and in A type specimen whose shape was so complicated its tendency was less than in B type.
From these experimental results, it was indicated that hot-oil quenching and martempering were suitable for the heat-treatment of ball-bearing steel, and that the distortion after quench-temper-subzero-treatment was generally less than that after quench-subzero-treatment-temper.