Influence of heat treatment on wear behavior and impact toughness of AISI M4 coated by laser melting deposition

This study focuses on post-deposition heat treatment for possible hardfacing of cold press dies using M4 high-speed tool steel. For the experimental investigations, using the direct energy deposition (DED) process, powdered AISI M4 (a high-speed tool steel) is deposited on a substrate of AISI D2 (a general-use die steel). Since the post-deposition heat treatment may change the metallurgical characteristics of the deposits, the effect of post-deposition heat treatment on the mechanical behavior was investigated by observing the microstructure evolution, hardness, wear behavior, and Charpy impact tests of the specimens with different post-deposition heat treatments. The experimental results showed that post-deposition quenching and tempering led to a reduction in hardness, which was attributed to the relieved residual stress, tempered martensite, and removal of carbon from the martensite during tempering. The M4-deposited specimen without post-deposition heat treatment and the tempered M4-deposited specimen had the better wear resistance, compared to the quenched-tempered M4-deposited specimen with fine carbides. Nevertheless, the toughness increased significantly in the quenched and tempered specimen. The results presented in this paper provide guidelines for practical hardfacing applications that use high-alloy tool steel powders to achieve highly improved die and mold performances in terms of wear resistance and toughness.