Effect of Cr content on microstructural evolution, general corrosion and stress corrosion cracking of 42CrMo high-strength steel in simulated marine environment

The effect of Cr content on the microstructural evolution, general corrosion and stress corrosion cracking (SCC) behaviors of 42CrMo high-strength steel in simulated marine environment was investigated in this study. The results show that increasing the Cr content reduces the size of Cr-rich carbides while increasing their number density. Higher Cr content facilitates the progressive precipitation of intragranular M₇C₃ and intergranular M₂₃C₆ carbides. Although elevated Cr content can improve the mechanical properties and general corrosion resistance of 42CrMo high-strength steel, it simultaneously increases the SCC susceptibility in simulated marine environment. The enhanced corrosion resistance is primarily attributed to the formation of a continuous Cr-enriched passive film, coupled with corrosion products dominated by α-FeOOH. Together, they form a more compact and protective layer. However, the refined and densely distributed Cr-rich carbides act as reversible hydrogen traps with limited binding energy. This leads to localized hydrogen accumulation in the regions of stress concentration under tensile loading, which weakens the grain boundary cohesion and shifts the SCC fracture mode from ductile-dominated fracture at lower Cr content to hydrogen embrittlement-driven intergranular cracking at higher Cr content.