Effects of Cu-alloying in minute quantities on the corrosion-induced mechanical degradation behaviors of medium C-based ultrahigh-strength steel in aqueous environments

Abstract This study examined the applicability of Cu-alloying in minute quantities to medium C-based ultrahigh-strength automotive steel with a tensile strength of more than 2000 MPa to improve the resistance to mechanical degradation caused by aqueous corrosion. Cu-alloying of this steel favored the precipitation of fine-(Ti,Mo)C particles, leading to a smaller prior-γ grain size (PAGS) and inter-lath size, resulting in higher tensile strain. In addition, Cu-alloyed steel showed the surface inhibiting characteristics in a neutral aqueous condition based on higher corrosion resistance (i.e., larger polarization resistance and less weight loss). The smaller particle size of corrosion scale (CuxFe3-xO4), more uniform surface roughness, and smaller PAGS can be the major mechanistic reasons for suppressing the reduction in the mechanical properties of Cu-alloyed ultrahigh-strength steel in the corrosive environment.