Discovery of a novel low-cost medium-entropy stainless steel with exceptional mechanical behavior over a wide temperature range

Abstract

Over 100 years, stainless steels have been extensively used as engineering materials in many areas1-4. However, the strength-ductility trade-off1,3 and insufficient elevated-temperature strength largely hinder their processing and applications. Here, we report a novel Co-free Fe47Cr16Ni26Ti6Al5 medium-entropy stainless steel (MESS) strengthened by high-density coherent L12 nanoprecipitates (NPs). We use a thermodynamic approach to pursuing a large volume fraction of stable L12 NPs in the coarse-grained face-centered-cubic (FCC)-structured matrix of the MESS, which is then readily fabricated through conventional casting and thermomechanical-treatment techniques. The MESS exhibits a high ultimate tensile strength of 1.35 gigapascals (GPa) and a great total elongation of 36% at room temperature (RT), evading the strength-ductility trade-off dilemma in conventional stainless steels. The high strength is mainly due to the chemical- ordering strengthening of high-density coherent L12 NPs. The ductile L12 NPs cooperative with the dynamic refinement of the deformation substructures endow the MESS with an excellent work-hardening ability and a large uniform ductility. Furthermore, the MESS maintains a high yield strength of ~ 0.8 GPa at 700 oC, which is better than many Fe-based superalloys and stainless steels, even comparable to some Ni-based superalloys. The steady-state creep rates at 750 oC are at least two orders of magnitude lower than those of conventional Ni-based superalloys and heat-resistant steels. The excellent creep resistance is achieved via the strong interactions between sliding dislocations and stable L12 NPs at elevated temperatures, which effectively impedes the dislocation movement. The present study has huge potential for designing cost-effective engineering MESSs with excellent mechanical performance for practical applications.