Effect of microstructure on local corrosion behavior of ultra-high strength stainless steel 10Cr13Co13Mo5Ni3W1VE

10Cr13Co13Mo5Ni3W1VE (S280) martensitic ultra-high-strength stainless steel under aging at 200, 400, and 500 ℃ was used as the research object. Through XRD, TEM, EBSD and other test methods, combined with electrochemical test methods and X-ray photoelectron spectroscopy (XPS) tests, the microstructure evolution of S280 and the structural composition and corrosion resistance of the passivation film were analyzed. The relationship between the stability characteristics of the passivation film and the microstructure of the material was studied.The results show that S280 steel aged at 500 ℃ has fine and dispersed precipitates with rich Cr and Mo elements distributed in martensite laths. As the aging temperature increases, there is no obvious precipitation of retained austenite and reverse transformed austenite.At the potential (0.1-0.85 V) of forming a passivation film, the S280 passivation film is a p-type semiconductor in a pH=8.5 borate buffer solution, having a double-layer film structure.The outer layer is composed of loose and porous Fe/Cr hydroxide, and the inner layer is composed of dense Cr/Fe oxide whose composition is mainly Cr2O3.The electrochemical impedance test combined with Mott-Schottky analysis proves that S280 steel aged at 200 ℃ has the best corrosion resistance. Its corrosion resistance is affected by the grain boundary characteristics and the element segregation caused by the precipitated phase.