Effect of HAGBs for ultra-high strength stainless steel on pitting /microcrack initiation with synergy between strain and corrosion environment

In this work, the effect of high angle grain boundaries (HAGBs), including prior austenite grain boundaries (PAGB), packet grain boundaries (PGB) and block grain boundaries (BGB), on the priority of pitting and microcrack initiation for 10Cr13Co13Mo5Ni3W1VE ultra-high strength stainless steel (UHSS) has been clarified. PAGB had the highest carbide distribution coefficient and was the main location where pitting preferentially initiated for the UHSS in 3.5 wt.% NaCl solution without strain. It was shown that nano-carbides were the key factor of pitting initiation for the UHSS without strain. However, BGB was the key factor of pitting/microcrack initiation for the UHSS with strain, which was attributed to the high-density dislocations accumulated at BGB and then enhanced the local electrochemical activity of the UHSS surface. The change of the key factor for the pitting initiation in the UHSS was the result of the synergy between strain and corrosion environment. This study provides guidance for designing advanced UHSS with high service stability and safety.