Understanding the passive behaviour of low-chromium high-strength Hybrid steel in corrosive environments

We investigated the unique passive behaviour of Hybrid steel in de-aerated sulfuric acid and aqueous sodium chloride solutions through corrosion tests, surface analysis, and thermochemical modelling. Electrochemical measurements confirmed that Hybrid steel possesses stainless steel characteristics, including passivity, breakdown, and pitting, akin to low-alloyed stainless steel. Synchrotron hard X-ray photoelectron spectroscopy revealed a dynamically protective nanoscale passive film composed of Fe, Cr, Ni, and Al oxides, contributing to its stainless nature. The presence of Al and Ni enhances Cr’s role in forming a spontaneously passive and protective surface, resulting in exceptional corrosion resistance in acidic and chloride-containing solutions. Hybrid steel’s surface oxides remain robust even beyond the Cr(III)-to-Cr(VI) redox potential, distinguishing it from other stainless steels. This work demonstrates the potential for designing sustainable stainless steel with high-strength properties without requiring the conventional Cr threshold concentration of 10.5 per cent.