Corrosion behaviours of low Mo Ni-(Co)-Cr-Mo alloys with various contents of Co in HF acid solution

Corrosion behaviours in hydrofluoric acid solution and mechanical performances of Ni-16Cr-11Mo-6Fe-2Cu and Ni-30Co-16Cr-11Mo-6Fe-2Cu alloys were investigated by using a variety of methods. No precipitate is observed in the present low Mo alloys, suggesting the excellent structural stability. Co leads to grain refinement and localized microstructure after hot rolling, resulting in significant enhancement in both hardness and tensile strength. Owing to the addition of Cu, all alloys with and without hot rolling show near weight loss rates after immersion. This is ascribed to the dominant passive film of Cu, which demonstrates the superior stability among the constitute elements of alloys.