Study of the aging treatment on selective laser melted maraging 300 steel

The aim of this work was to evaluate the effects of aging treatments, in terms of microstructure and micro-hardness, on 18 Ni 300 Maraging steel samples processed by Selective Laser Melting (SLM) and to compare them with those of the same material made by casting. Optimized process parameters were used to build SLM parts in order to obtain almost full density (above 99%). For aging treatments, following the principles of the Design of Experiments, a full factorial plan with 4 levels of temperature and 6 levels of time was used. Before aging, the microstructure consisted of many overlapping fused/resolidified zones with a dendritic solidification morphology and epitaxial growth of the grains. After aging, the fused/resolidified zones disappeared and the hardening of the material was mainly governed by the mechanism of precipitation. The maximum value of hardness, on selective laser melted samples, was obtained, for a treatment temperature of 480 °C for 10 h: whereas, at the same temperature and after 10 h, on casting sample, it stabilized at 640 HV. Compared to samples produced by casting, SLM samples showed a lower increment in micro hardness at the aging temperature of 440 °C, while for 510 °C and 560 °C, trends were similar.