Uncovering the influence of Mo and N on the hot-corrosion resistance of super austenitic stainless steels in a chloride-containing oxidizing environment

The corrosion behavior of two super austenitic stainless steels (SASSs) 4Mo0.06 N and 6Mo0.18 N at 800 ℃ in a chloride-containing oxidizing environment was meticulously examined. The results indicated that higher Mo and N contents in 6Mo0.18 N facilitate the formation of Laves, σ phase and Cr₂N, concomitantly, the volatile Mo-oxides weaken the protectiveness of oxides scales and enhance the diffusion of chlorine, thereby exacerbating corrosion. Here, we elucidate that the addition of more Mo and N results in an increase of secondary phase particles in 6Mo0.18 N as well as chlorine-induced grain boundaries deterioration, causing an obvious internal corrosion. Instead, the distinctly enhanced corrosion resistance in 4Mo0.06 N is attributed to the formation of continuous Ni-Mo rich metallic phases at the oxide/matrix interfaces so as to reduce the diffusion of ions, which effectively diminishes the inner corrosion. These findings provide a great guiding significance in optimizing high-performance alloy designs for their potential applications.