Best-Fit Fatigue Curves for Carbon and Low Alloy Steels, and Austenitic Stainless Steels Based on Material Properties and Loading Modes

Abstract The DFC and DFC2 subcommittees of the Japan Welding Engineering Society (JWES) have developed a novel approach to fatigue analysis. Parts of this analysis have been revised and incorporated into the JSME Environmental Fatigue Evaluation Method for Nuclear Power Plants, 2022 Edition (JSME S NF1-2022). The JSME code includes new best-fit fatigue curves for carbon and low-alloy steels, and austenitic stainless steels. These curves are derived from strain-controlled fatigue test data and utilize ultimate tensile strength as a parameter. Since components may generally be subjected to load-controlled mode, these best-fit fatigue curves are compared with load-controlled fatigue test data. The comparison reveals that even in the long fatigue life region, where the stress amplitude remains below the yield stress of material, the load-controlled fatigue test data deviate from the best-fit fatigue curves. To address this deviation, the best-fit fatigue curves are reconstructed using data from rotating bending fatigue tests and axial load-controlled fatigue tests. For the carbon and low-alloy steels, the best-fit fatigue curves are classified for two types of steels based on microstructure. For the austenitic stainless steels, the best-fit fatigue curves are classified based on loading mode: load-controlled and strain-controlled modes. Furthermore, the mean value and standard deviation of the best-fit fatigue curves are shown based on statistical analysis. These statistical parameters enable the calculation of design factors corresponding to target reliability levels.