Effect of Deep Cryogenic Time on the Microstructure and Mechanical Property of Cr-Mn-Si High-Strength Alloy Steel

Abstract

Cr-Mn-Si alloyed high-strength steel was subjected to deep cryogenic treatment after quenching and tempering (Q-T), and the microstructure and property evolution of the alloy steel after deep cryogenic treatment were studied. The tensile strength increased by about 30 MPa, the yield strength decreased by about 10 MPa, and the grains of alloy steel were refined, indicating that the strength and toughness of the alloy steel can be relatively improved via the deep cryogenic treatment (−120 °C × 1 h); the secondary carbides precipitated inside the martensitic matrix were uniformly distributed; and the average size was also significantly reduced, presenting a more uniform microstructure than that of the Q-T samples. Furthermore, the dislocation density of alloy steel also evolved during the deep cryogenic treatment, with the highest dislocation density after the 2 h treatment, thus providing a dislocation-strengthening effect. Therefore, the overall properties of the alloyed steel could be comprehensively improved by the deep cryogenic treatment after Q-T.