The creep-fatigue fracture behavior of heat-resistant steel welded joint under different tensile and compressive holding

Abstract

The stress-controlled creep-fatigue test was conducted to investigate the damage mechanism for the CrMoV steel welded joint by introducing tensile holding and tensile-compressive holding respectively. It was found that the final fracture mode changed from creep void-induced fracture inside the over-tempered zone (OTZ) to fatigue crack-induced fracture in the fine-grain heat-affected zone (FGHAZ) as the stress amplitude decreased to 250 MPa and compressive holding of 180 s was introduced. Simulation results based on the local miniature tensile test indicated that the strain mainly concentrated inside the OTZ because of the low strength, while the stress concentrated on the surface of the FGHAZ and inside the OTZ due to the constraint of high-strength weld metal (WM) on the radial deformation. The distribution of strain and stress demonstrated the competitive failure between OTZ and FGHAZ with different modes of damage. The crack initiation on the surface of FGHAZ was promoted in the oxide due to compressive holding, then the sharpened tip of cracks induced sufficient propagation during numerous cycles under low stress amplitude, resulting in the fracture of fatigue crack-induced mode.