Stress corrosion cracking behavior of a new kind of ultrahigh strength steel Cr12Ni4Mo2Co14 in acid environment

In recent years, the development of aerospace industry puts forward a higher requirement for the high strength, high toughness and good weldability of steel materials. Cr12Ni4Mo2Co14 steel is a new kind of ultrahigh strength steel, which is usually used as structure materials under complex stress/strain conditions. In this work, the stress corrosion cracking behavior of Cr12Ni4Mo2Co14 steel in acid environment was studied by slowstrain rate test (SSRT) and SEM. The results showed that the stress corrosion cracking (SCC) susceptibility of Cr12Ni4Mo2Co14 steel was enhanced by chlorine ions remarkably. The critical value of chlorine ion concentration was about 0.15%, above which, severe SCC occurred induced by chlorine ions, and the SCC cracks started from pits. The SCC mechanism of Cr12Ni4Mo2Co14 steel in acid solution containing chlorine ions can be clarified by "slide-film breaking" model. The hydrogen-charged samples of Cr12Ni4Mo2Co14 steel were sensitive to hydro-gen induced cracking, and second cracks occurred on the fracture surface. The critical value of hydrogen-charged current density is 10 mA/cm² for 30 min in solutions with pH=5, above which, the losses of strength and plasticity of Cr12Ni4Mo2Co14 steel reached to the maximum. The effects of chlorine ions and hydrogen had a complex interaction which cannot be added up directly.