Novel high nitrogen austenitic stainless steels: From high-throughput screening to experimental validation and properties relationship

Abstract

The quest for affordable and price-stable alternatives for nickel as the main austenitizing alloying element is pushing the stainless steel industries to develop new types of Ni-lean austenitic stainless steels. This work focuses on the challenges of designing austenitic stainless steels with appreciable nitrogen content using computational methods, which can still be produced at 1 atm N2 pressure and thermomechanically processed without excessive cracking or N2 degassing. CALPHAD-based computational tools enabled the identification of promising alloys by high-throughput screening from more than 2000 candidates based on predefined criteria considering composition (Ni-poor, N-rich), phase stability (austenite), degassing (far from N2 loss from liquid or solid phase), cost (Ni-lean), and pitting resistance equivalent number (PREN > AISI 201 stainless steel). The resulting alloys exhibited an austenitic microstructure with dispersed micrometric and nanometric aluminum nitrides (AlN) precipitates. Even with the occurrence of appreciable AIN precipitates, hot rolling was performed without cracking, resulting in equiaxed austenitic grains. The mechanical properties of the developed alloys exceeded those of AISI 201 stainless steel in terms of hardness, yield strength, and ultimate tensile strength, with values of 304 HV, 534 MPa, and 953 MPa, respectively, yet with considerable ductility (∼40% elongation). Even in the presence of AlN that pick up some of the nitrogen from solid solution, the corrosion resistance of the developed alloy was superior to the AISI 201 stainless steel. This research provides valuable insights for developing and processing high-nitrogen austenitic stainless steels to compete with 201 and 304 stainless steels in terms of mechanical properties and corrosion resistance.