Study on High-Temperature Fatigue Properties and Notch Sensitivity of Haynes 230 Alloy TIG-Welded Joints

This study investigates the high-temperature high-cycle fatigue behavior of TIG-welded Haynes 230 alloy using smooth and notched specimens (Kt=3) at 850–950°C. Both elevated temperature and notch effect significantly degrade fatigue performance. As temperature increases, thermally activated crack initiation and propagation accelerate, shifting the S–N curves downward. Notched specimens exhibit substantially shorter fatigue lives due to stress concentration-induced multi-source crack initiation, dispersed propagation zones, and fragmented sudden fracture zones. The alloy shows low notch sensitivity across the test temperature range, with the lowest value at 900°C. A unified fatigue life prediction model is established using a temperature correction factor σ_a^corr 〖= σ〗_a×exp[P×(1/T_ref -1/T)], demonstrating high fitting accuracy. M-G curves of notched specimens shift downward and leftward, revealing the aggravating effect of the notch on creep–fatigue interaction. Fractographic analysis shows that with increasing temperature, smooth specimens exhibit expanded sudden fracture zones and degraded striations, while notched specimens display multi-source initiation and a composite morphology of striations with fine dimples, consistent with macroscopic mechanical behavior. This study provides a theoretical basis for the fatigue-resistant design and life assessment of high-temperature structural components.