Investigation of the High-Temperature Low-Cycle fatigue failure characteristics of P91 steel weld joints and their fatigue strength reduction factors under various load control regimes

Low cycle fatigue tests are conducted on the base metal, weld metal, a welded joint under the condition that the strain control region is the joint (WJWJ) and a welded joint under the condition that the strain control region is the base metal (WJBM) of P91 steel at 500celcius using different total strain ranges. The cyclic stress response is highest for the weld metal, followed by the base metal, and is relatively similar for WJWJ and WJBM. At 2.0 % total strain range conditions, the materials generally exhibit non-Masing behavior and dynamic strain hardening aging. At all total strain ranges, WJWJ failed in the heat-affected zone, and WJBM broke in the base metal. For the difference in fatigue life between base metal and welded joints, the fatigue strength reduction factor of P91 steel welded joints at 500 degrees C is given as a suggested value. The fatigue behavior of P91 steel welded joints is verified based on a hybrid hardening model and a modified damage model. This study presents a theoretical framework for analyzing the fatigue strength reduction factors of weldments and comparatively analyzes the effects of different geometrical features.