A preliminary investigation on selective laser melting of M2 high speed steel

Selective Laser Melting (SLM) is an Additive Manufacturing (AM) technique that is able to process both metallic and ceramic materials in powder form. The main attraction of SLM is the ability to produce near fully dense functional parts with high geometrical complexity. Parts can be fabricated with features and designs conventional manufacturing methods cannot achieve. In this study, the feasibility of processing M2 High Speed Steel (HSS) with the SLM technique is investigated. The main focus is on understanding the material properties to facilitate the optimization of process parameters in order to produce parts with good quality and high density. Laser powers of 90 W and 105 W were used with scan speeds ranging from 100 mm/s to 850 mm/s. Preliminary results show that parts exhibit warpage, cracking and partial separation from the base plate. In addition, the degree of cracking and base plate separation is more pronounced at lower scan speeds. While residual stresses mainly accounted for the problems occurred in this study, in depth microstructural analysis might also explain the cracking at lower scan speeds. It was found that the microstructure was different for parts produced at different scan speeds, providing some insights on suitable processing parameters for the family of tool steels. In an attempt to reduce residual stresses, lower thermal gradient was achieved by preheating of the base plate to 180 o C. Indeed, cracking, warpage and base plate separation were greatly reduced upon close visual inspection. It was also found that the chances of parts separating from the base plate were lower for AISI 1085 steel than for M2 HSS base plates. In conclusion, this study showed that SLM of M2 HSS is feasible with preheating conditions.