Design and Characterization of Super Austenitic Stainless Steel Stabilized with Niobium Produced by Induction Melting at Open Atmosphere

Abstract

In this work, a Super Austenitic Stainless Steel is designed supported by Thermo-Calc modeling and produced at open atmosphere induction furnace, based on 254SMO (UNSS31254). The technological challenge of this work is to prevent the sensitization of the alloy, due to its high C content (0.072%). The chemical composition includes 0.25%Nb and 2.2%Mn to stabilize the alloy and improve mechanical properties. Furthermore, two different types of solution annealing are performed in order to study the effect of the precipitates on the corrosion resistance (HD-1120 C and HD-1180 C). As main results, the microstructure of sample HD-1180 C shows an Austenitic matrix and, Nb-MX and Z-phase as secondary phases; whereas, sample HD-1120 C presents coarse Mo-rich particles formed during solidification. The designed alloy SASS-NbMn (HD-1120 C and HD-1180 C) shows slightly better mechanical properties than alloy 254SMO. In addition, the corrosion behavior of SASS-NbMn is studied by cyclic polarization in 1M NaCl solution.Sample HD-1120 C shows poor pitting resistance due the presence of Morich particles generating Mo-depleted zones. However, Sample HD-1180 C shows outstanding pitting resistance, even better than 254SMO. These promising results open the possibility to develop a new field of stabilized SASS, with comparable mechanical and corrosion properties, and lower cost than commercial SASS.