Phase-field simulations of intergranular stress corrosion cracking in Fe-Cr-Ni alloy incorporating σ phase precipitation

σ phase is a common precipitate in Fe-Cr-Ni alloy, which may significantly influence intergranular stress corrosion cracking (IGSCC). This influence stems primarily from the compositional segregation and elastic mismatch induced by σ phase precipitation, which complicates the IGSCC process. Taking FeCr24Ni20 (at. %) as the model alloy, this study developed a phase-field model framework to elucidate the mechanism of σ phase on IGSCC, and validated its accuracy through experimental results. Analysis of the corrosion crack propagation path and stress distribution revealed that Cr segregation is the key factor governing whether the σ phase inhibits or promotes IGSCC. Without Cr segregation, the σ phase’s low susceptibility to corrosion and elastic mismatch disrupt stress symmetry at the corrosion crack tip, causing intergranular corrosion crack path deflection and consequently retarding propagation. Conversely, the Cr-depletion zones resulting from σ phase precipitation significantly increase the corrosion susceptibility of the adjacent matrix. The overlap of the crack-tip stress concentration zone with the Cr-depletion zone can effectively counteract the σ phase’s crack deflection effect, thereby sustaining continuous intergranular corrosion cracking. This mechanistic understanding suggests that targeted mitigation of elemental redistribution through composition optimization could effectively counteract the detrimental effects of σ phase precipitation.