Microstructural evolution and mechanical performance after precipitation hardening of PH 13-8Mo martensitic stainless steel fabricated by wire arc additive manufacturing

In the present study, wire arc additive manufactured precipitation hardening (PH) 13-8Mo martensitic stainless steel was subjected to various solution and aging treatments to eliminate the columnar structure, non-equilibrium phases (e.g., 6-ferrite), inhomogeneous microstructure, and anisotropic ductility, detected in the as-printed part. The microstructural characterizations showed that 1050 degrees C was the optimum solutionizing temperature to remove the columnar grain structure and deleterious 6-ferrite phases, leading to a fully martensitic microstructure with a slightly higher hardness as compared to the as-printed part. The subsequent aging treatment at 450 and 500 degrees C led to the formation of nanometric and coherent f-NiAl precipitates inside the martensite laths, resulting in a substantial microhardness and tensile strength improvement. Higher temperature aging at 550 and 600 degrees C caused the formation of other secondary phases, i.e., Cr-rich carbides and reverted austenite, respectively, contributing to enhanced ductility at the expense of reduced tensile strength of the material. The implemented post-printing heat treatment was found to be efficient in suppressing the observed anisotropic ductility in the as-printed part, primarily dictated by the texture weakening that occurred during solution treatment.