Mechanical Properties of Laser-Powder Bed Fusion Processed Fe-15Cr-6Ni-6Mn Multi-phase Steel at Room and Cryogenic Temperatures

Abstract

Although additive manufacturing with 3XX austenitic stainless steel has been widely established owing to its high strength, good corrosion resistance and weldability, the substitution of Mn for Ni is required to overcome the price increment of stainless steels due to the high demand for Ni. In this study, the mechanical properties of a laser-powder bed fusion processed Fe-15Cr-6Ni-6Mn alloy were investigated. Because appropriate processing parameters (e.g., laser power and laser scan speed) for this alloy have not yet been established, the optimized processing parameters were obtained using a response surface method. Based on the processing optimization, the present additively manufactured Fe-15Cr-6Ni-66Mn alloy achieved 800 MPa tensile strength and 40% elongation, which can be compared to recent additively manufactured 3XX stainless steels. In addition, the low stacking fault energy of the Fe-15Cr-6Ni-6Mn alloy induces a subsequent ?-austenite ? e-martensite ? a'-martensite phase transformation, which provides an extra-strain-hardening capability in the middle of plastic deformation stage. Meanwhile, in a cryogenic temperature, accelerated martensitic transformation occurs due to the reduced stacking fault energy at a low temperature that degrades ductility after tensile test. The results show that the substitution of Ni with Mn is a good solution for the development of low-cost stainless steel, but additional chemical content tuning required to overcome ductility degradation at a cryogenic environment.