Unexpected enhancement of hot corrosion resistance of V-containing high-Mn nickel-saving austenitic heat-resistant steel in molten Na₂SO₄ at 1173 K

The infiuence of V addition on the hot corrosion behaviour of a high-Mn nickel-saving austenitic (HMA) heat-resistant steel is investigated. Advanced high-resolution microscopy techniques are performed to examine the corrosion behaviours and mechanisms of V-containing and V-free HMA steels in the molten Na₂SO₄ at 1173 K in air. It reveals that V addition unexpectedly improves the hot corrosion resistance of this steel against molten Na₂SO₄. It suggests that the rapid formation of a dense corrosion scale acts as a barrier to suppress the initial internal sulphidation. Furthermore, the subsequently generated inner mixed (Cr, Mn, V)-rich corrosion layer can effectively impede the outward diffusion of Cr and Mn from the matrix and the ingress of oxygen and sulphur. A critical role of V in enhancing the resistance against sodium sulphate-induced hot corrosion environment is established, challenging the conventional view that V-alloying exacerbates hot corrosion performance of heat-resistant alloys in molten salts.