Possibility of Mn substitution of Ni through evaluation of mechanical properties and corrosion resistance in superaustenitic stainless steel weld metal

In this study, the evaluation of the mechanical and corrosion properties of Ni, Mn and the possibility of Mn substitution of Ni in superaustenitic stainless steel weld metal were researched. Axial tensile, polarization, and critical pitting temperature (CPT) tests were performed with variation of Ni and Mn to evaluate the mechanical and corrosion properties for the gas tungsten arc welding (GTAW)-fabricated weld metals. As a result, the weld metals mainly consisted of γ-dendrite and sigma (σ) phases at interdendritic boundaries, and a fraction of the sigma phases decreased due to the increase of both the Ni and Mn content at these boundaries. The Mo content in the sigma phase increased with Ni, resulting in aggravation of the Mo depletion zone. On the other hand, Mn prevented the Mo clustering in the sigma phase. The tensile test indicated that elongation and toughness were clearly improved by the decrease of only the sigma phase fraction regardless of difference in the Ni and Mn. From the results, reduction of the sigma phase induced variation of the fracture behavior from brittle to ductile. The polarization test showed that an amount of the sigma phase induced degradation of pitting potential (Epit), while Ecorr, icorr, and Epass varied as relatively uniform, despite of changes of the Ni and Mn content. Likewise, CPT values were found to be inversely related to the sigma phase fraction with variation of the Ni and Mn content.