High-pressure quenching effect on martensitic transformation characteristics and mechanical properties of low-alloy medium-carbon steel

Abstract

In this study, the effect of high-pressure quenching at 2, 3 GPa on the martensitic transformation characteristics and mechanical properties of 40Cr steel was examined using EBSD, Mössbaue, and TEM. The results reveal that the microstructure following high-pressure quenching is a mixture of lath martensite and plate martensite, with plate martensite content increasing steadily as pressure is increased. Plate martensite exhibits distinct characteristics in the 2 GPa-sample, either crossing the prior austenite grain (PAG) or growing from the grain boundary into the interior. In 3 GPa-sample, the lath and plate martensite are distributed in clusters, with the majority of adjacent laths exhibiting {112} <111> twinning orientation relationship (OR). The number of variants was decreased from 24 for conventional quenching to 15 and the PAG size was refined to 15 μm. The percentage of M2 martensite increased from 67.71% at atmospheric pressure to 72.59% at 3 GPa, resulting in a decrease in the solid solution C content, which appears to incorporate with Cr to form fine, dispersed Cr23C6 particles. The hardness of the 3 GPa sample (807 HV) enhanced by 40%, and the compressive yield strength reached 3.5 GPa, which was three times that of conventional quenching.