Studying properties of SLM fabricated parts and relating properties of SLM parts to heat treated metals

Abstract

M2 High Speed Steel (HSS) parts are produced with an Additive Manufacturing (AM) technique, Selective Laser Melting (SLM). M2 HSS are valued for its high hardness and resistance to wear. In this work, the microhardness tests with a 100 g load were carried out on green SLM M2 HSS samples. On average, microhardness values are evaluated to be between 700 HV to 870 HV. In addition, microstructures were also found to be non homogenous. Two different microstructural regions were identified resulting in two different hardness values which were consistent. Hence, heat treatment processes were carried out for two reasons. First, to achieve good microstructural homogeneity and secondly, to increase the hardness. A modified hardening heat treatment derived conventionally for M2 HSS was applied in vacuum atmosphere, the observed microstructure is homogeneous and the sample hardness increased by 15 % to 800 HV after a double tempering and decreased by 1% to 700 HV after triple tempering. Single, double and triple tempering were done on green samples and hardnesses of 820 HV, 880 HV and 860 HV were evaluated respectively. However, homogeneous microstructure was not observed this time. This report concludes that conventional hardening heat treatment processes may not be suitable for SLM M2 HSS parts and a hardening heat treatment with double tempering is necessary to optimize microstructural homogeneity and microhardness.