This study focuses on the relationship between thermal history, microstructure, and hardness of different composition gradients obtained from 316L-Si stainless steel (austenitic) and 9Cr-1Mo steel (martensitic) powders using the Direct Energy Deposition – LASER Based (DED-LB) process. The process is monitored using an infrared thermal camera, which tracks the cooling of each deposited metal layer. Thus, it can be observed that each printed layer has an in-situ tempering effect on the previous layers due to the accumulation of heat during printing. The chemical gradient imposed by the projected powders influences the crystallography with the change from a Face-Centered Cubic (FCC) phase to a Body-Centered Cubic (BCC) phase or vice versa. The presence of ferrite or martensite in BCC zones depends on the thermal and chemical composition, which modifies the martensitic start (Ms)temperature. This study provides an understanding of the atypical hardness profile observed, which, in reverse, could itself be a good initial indicator of the phases obtained.

Keywords: DED-LB-p, chemically gradient steel, thermal history, phase transformation