On the Optimization of Microstructure and Mechanical Properties of CrWMn Tool Steel by Deep Cryogenic Treatment

The authors explore here the influence of cryogenic treatment on the microstructure and mechanical properties of CrWMn tool steel. Compared to the normal quenching and tempering process, the tensile strength, toughness, and hardness is enhanced after quenching-cryogenic-tempering treatment. The result is attributed to the high number density of precipitated ultra-fine small granular carbide (SGC), the transformation of retained austenite, and the refinement of the martensite. Two types of retained austenite (filmy and blocky) would transform at low temperature or during the tempering process. Results of tempering curves indirectly prove that a part of SGCs precipitates during the deep cryogenic treatment. The wear resistance is improved and the friction coefficient is decreased by adding cryogenic treatment. The excellent wear resistance after cryogenic treatment is ascribed to the enhancement of hardness and low friction coefficient. The extra precipitation of small granular carbides induced by cryogenic treatment contributes to the wear resistance.