Multiphase Microstructure Optimization to Enhance the Mechanical Properties of AISI M35 High‐Speed Steel

Abstract

It is crucial to conduct in‐depth research on the cryogenic‐treatment mechanism to promote the standardization and industrialization of cryogenic treatment in the high‐speed steel (HSS) industry. In this study, the microstructure and mechanical properties (microhardness and impact toughness) of AISI M35 HSS after deep‐cryogenic treatment (DCT) and conventional heat treatment (CHT) are investigated, and the microstructural characteristics at different stages of CHT and cryogenic treatment are studied. It is indicated in the results that DCT of the steel leads to the formation of fresh martensite from residual austenite, as well as the introduction of more dislocations due to plastic deformation. In addition, the deep‐cryogenic‐treated specimen that is tempered shows increased numbers of martensite blocks and secondary carbide precipitation. The carbides in the steel are mainly V‐rich (MC), W–Mo‐rich (M6C), and Cr‐rich (M23C6). The hardness of the deep‐cryogenic‐treated samples increases by approximately 50 HV1 because of the transformation of residual austenite and dislocation strengthening. Furthermore, specimens that are both deep‐cryogenic treated and tempered exhibit a 30% increase in impact toughness and a more uniform distribution in hardness, likely due to the more homogeneous precipitation of secondary carbides and refinement of martensite.