(V) Hardening of Selective Laser Melted M2 Steel

Selective laser melting (SLM) is one of the additive manufacturing techniques can be used to make the near-net-shape metal parts. M2 is a high speed steel used in cutting tools, which is due to the high hardness of this steel. Conventionally, the hardening heat treatment process, including quenching and tempering, is conducted to achieve the high hardness for M2 wrought parts. It is debated if the hardening is needed for additively manufactured M2 parts. In the present work, M2 steel part is fabricated by SLM. It is found the hardness of as-fabricated M2 SLM parts is much lower than the hardened M2 wrought parts. The characterization was conducted including X-ray diffraction (XRD), optical microscopy, Scanning Electron Microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS) to investigate the microstructure evolution of as-fabricated, quenched, and tempered M2 SLM part. The M2 wrought part was heat treated simultaneously with the SLM part for comparison. It was found that after the heat treatment the hardness of M2 SLM part is increased and comparable to the wrought part. Both quenched and tempered M2 SLM and wrought parts have the same microstructure while the carbides size in wrought part is larger than that in SLM part.