Failure Mechanism‐Based Assessment of Damage Tolerance in Cr–Ni Alloy Steel: Synergistic Stress–Crack–Life Interaction and Carburization Influence

This research analyzes the very high cycle fatigue behavior of two kinds of Cr–Ni alloy steel, including a surface‐carburized variant, through fatigue tests under R = −1 and 0. The tested results reveal the effects of carburizing treatment and microstructure on failure mechanism. First, carburizing treatment cannot alter S – N characteristic of Cr–Ni alloy steel due to the fact that S – N curves are invariably characterized by single linear under R = −1 and bilinear under R = 0. Second, carburizing treatment and microstructure can impact the formation of fine granular area (FGA). Most notably, residual stresses would inhibit crack nucleation close to carburization layer, which can make internal crack nucleation much deeper. Furthermore, damage tolerance assessment (DTA) model and multiparametric Kitagawa–Takahashi diagram (K–T diagram), which can be widely applied on Cr–Ni alloy steel in different failure modes, are constructed according to the theory of stress concentration and statistic, synergistically considering the effect of carburization and stress–crack–life on failure mechanisms. DTA model significantly improves the accuracy of prediction for critical size, and multiparametric K–T diagram of internal failure with FGA not only contains a crack stagnation region corresponding to the formation of FGA but also makes the safety region more conservative. This research provides important theoretical support and practical guidance for engineering applications.