Homogenization of microstructure and mechanical properties of wire arc additive manufactured martensitic stainless steel through optimization of post-process heat treatment

Abstract

A single-bead multilayer martensitic stainless steel thin wall was fabricated using the wire arc additive manufacturing (WAAM) process. After the WAAM process, the tempering heat treatment was carried out to homogenize the microstructure distribution in the wire arc additive manufactured (WAAMed) part. To optimize the tempering temperature, the as-WAAMed samples were subjected to varying tempering temperatures of 300, 500, 600, and 700 °C for 2 h. The heterogeneous structure within the as-WAAMed part was hardly eliminated by the low tempering temperatures of 300 and 500 °C. On the other hand, the inhomogeneous hardness profiles were significantly homogenized by the tempering temperature of 600 and 700 °C. Tempering at 600 °C removed the heterogeneous structure, resulting in the effective homogenization of the significantly heterogeneous hardness profile and microstructure distribution in the as-WAAMed part. Tempering at 700 °C led to the lower hardness than that at 600 °C.The anisotropic tensile properties of the as-WAAMed part were also eliminated after tempering at 600 °C. The significant differences in the toughness of the different layers of the as-WAAMed part were effectively reduced by proper tempering. The slight decrease in toughness of the post-process heat-treated sample from the bottom to the top of the thin wall was mainly caused by the increase in the martensitic block size inherited from the prior austenite grain structure. This study suggests that tempering at 600 °C for 2 h is an effective post-process heat treatment to homogenize the microstructure and mechanical properties of as-WAAMed 2Cr13 martensitic stainless steel.