Mechanisms of inclusion-induced pitting of stainless steels: A review

Pitting is a common type of localized corrosion in passive alloys that can cause rapid failure of material or equipment. In the case of stainless steels, non-metallic inclusions have been identified as the most susceptible sites for pitting, and have therefore garnered significant attention. This review critically examines the issue of how inclusions induce pitting, with a particular focus on three mechanisms: spontaneous dissolution of inclusions, active dissolution of Cr-depleted regions, and propagation of microcracks at the inclusion-matrix interface. While researchers have made significant strides in understanding these mechanisms over the past few decades, many gaps and controversies remain. Details such as the initial driving force of inclusion dissolution and factors affecting Cr-depleted regions require further study. Moreover, some old concepts and methods need to be revised to arrive at more credible conclusions. This review aims to delve deeply into these important issues and provide inspiration for future research.