Tempering kinetics of alloy steels as a function of quench rate and Ms temperature

Abstract

The effect of quench rate on the as-quenched hardness and carbide or carbon segregate particle size was studied for two alloy steels with Ms temperatures of 310 °C and 300 °C. The quench rate was varied from 681 to 93,000 °C per second. The hardness was studied using the Vickers hardness technique and the particle size was measured using the high-resolution, small-angle X-ray scattering technique. The as-quenched hardness and particle size were both found to decrease as the quench rate increased. Analysis of the data ruled out autotempering of the martensite as a likely basis for the observed quench rate effects. The effects of aging at room temperature (20 °C) on the hardness and particle size for these alloys were also studied. The hardness and particle size were both found to increase as the aging time increased. After 24 hours of aging, the effect of quench rate disappeared in that the hardness and particle size attained were each essentially independent of quench rate.