On the propagation of a single pit in stainless steel

Abstract

Single pits were produced on 10Cr and 12Cr stainless steels through an in-house experimental setup. The pitting propagation was investigated by confocal laser scanning microscope (CLSM), scanning electron microscope (SEM), electron diffraction spectroscopy (EDS), and electrochemical tests for simulating potentials inside and outside the pit in chloride solution. The results showed that the pit depth of 10Cr and 12Cr steel increased rapidly in the earlier stage, whereas the rate of increase declined significantly in later periods. The pit mouth diameter increases almost linearly with time. The pit cover and the metal salt film in the pit played important roles in pitting propagation. The cover served as a primary barrier to diffusion in the early stage of corrosion, and the pit bottom was under diffusion control. After a longer immersion time, the cover might collapse and disappear. A metal salt film formed at the pit bottom, and the pit bottom propagation was under diffusion control.