Effect of short-term annealing on the microstructure and tensile behaviour of high-strength Ni-free Cr-Mn-(C+N) austenitic stainless steel processed by PBF-LB/M

High-interstitial austenitic stainless steels offer several advantages over conventional Cr–Ni grades, including a stable austenitic microstructure with superior strength while avoiding critical nickel resources. Additive manufacturing can further enhance strength and reduce component weight, however, suitable post-processing heat treatments are required to relieve residual stresses and improve ductility without eliminating the beneficial substructure introduced by the process. In this study, Powder Bed Fusion Laser Beam/Metal samples of a Cr–Mn–(C+N) austenitic stainless steel were produced and subjected to different annealing treatments: conventional solution annealing at 1150 °C for 30 min and two short-term treatments at 1100 °C for 3 min and 1200 °C for 1 min. The short-term treatments were performed at the limits of the calculated single-phase austenite stability range for the alloy composition to assess the feasibility and effects of rapid annealing. Heat-treatment times were selected to achieve comparable microstructural states. As-built and heat-treated samples were characterized using OES, SEM, EBSD, XRD, and tensile testing. Conventional solution annealing resulted in stress relief, recovery and incomplete recrystallization, leading to significant grain growth, increased ductility, and reduced strength. In contrast, short-term annealing maintained a stable austenitic microstructure and promoted stress relief and recovery with minimal recrystallization, causing only slight grain growth, a marked reduction in dislocation density, and minor strength decrease. While the 1200 °C/1 min treatment increased ductility similarly to conventional annealing, the 1100 °C/3 min condition produced enhanced strain hardening with ductility comparable to the as-built state. These results enable development of tailored, efficient heat treatments for Ni-free austenitic steels produced by additive manufacturing.