EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Although laser based powder bed fusion (LB-PBF) is a prominent additive manufacturing technique, the number of alloys that have been approved for the process remains limited. This is especially true for iron-based alloys such as low-alloy steels, where the high carbon contents of said alloys can promote cold cracking defects. In other carbon-containing iron-based alloys, preheating of the build plate has proven to be an effective mitigation strategy. However, the understanding of how build plate preheating affects LB-PBF of low-alloy steels remains limited. This study details the influence of build plate preheating (at 25˚C, 100˚C & 180˚C) on the printability of 4140, 4340 and 8620 low-alloy steels. Said study was carried out using pre-alloyed, gas atomized powder that was subsequently LB-PBF processed using an EOS M290 machine. The influence of build plate preheating on crack formation was characterized. Results indicate that increasing the volumetric energy density (VED) and/or the build plate preheating could effectively mitigate crack formation in alloys with carbon contents ≥0.4 wt.%. Increasing the preheating temperature also increased the VED range of crack-free specimens, as it lowered the minimum VED that was required to avoid cold cracking defects. Based on the obtained data, robust processing windows for all studied alloys could be established that produced high-density (>99.8%), crack-free components.