Metal Additive Manufacturing Conference 2019

Laser powder bed fusion (LPBF) is an additive manufacturing process employed in many industries, for example for aerospace, automotive and medical applications. In these sectors, nickel-, aluminum- and titanium-based alloys are mainly used. In contrast, the mechanical engineering industry is interested in tool steels for many of their applications. Current research is often limited to hot work tool steel with up to 0.5 % carbon content using LPBF. However, many applications need more wear-resistant steel alloys with higher hardness, both of which can be achieved with a higher carbon content, like in high-speed steels. Since these steels are susceptible to cracking, preheating temperature needs to be applied during LPBF processing. In a previous study, we applied a preheating temperature of 500 °C for HS 6-5-3-8 (also called ASP2030) with 1.3 % carbon content. We were able to manufacture dense (ρ > 99.9 %) and crack-free parts from HS 6-5-3-8 with a hardness > 62 HRC (as built) by LPBF. In this study, we investigate the influence of preheating temperatures up to 600 °C on hardness and microstructure as a function of part height for HS 6-5-3-8. The analysis of different part height is necessary because state-of-the-art preheating systems induce heat only into the base plate. Consequently, parts are subject to temperature gradients and different heat treatment effects apply depending on part height during the LPBF process. The microstructure was studied by light optical microscopy (LOM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD).