Effect of Subzero Treatment on the Hardness and Magnetic Properties of High Carbon-High Chromium Steel

Abstract

High carbon-high chromium steel containing 1.3%C, 0.4%Mn, 6%Cr, 0.4%W is used as cold dies and magnet for various uses. The authors studied the effect of the quenching temperature on the expansion of steel subjected to subzero treatment and the change of hardness and magnetic properties due to normalizing and quenching, the effect of subzero treatment, and also the behavior of the retained austenite. The results of this experiment are as follows:—(1) The re-begin temperature of transformation shifts higher as the quenching temperature rises in the range of 800∼1000°, but the inverse is true as the normalizing temperature of more than 1100°. (2) The retained austenite after quenching changes to martensite by subzero treatment at −72°, and the magnetic saturation and the residual magnetism increase but the coercive force decreases. (3) The more of the retaind austenite decomposes to martensite as the subzero treating temperature is lower. (4) The hardness of steel increases to Rc 50∼55 by the subzero treatment after normalizing at 1150° including no quenching, but the retained austenite scarcely decomposes even at −183°.