STRESS RELAXATION CRACKING IN 347H AUSTENITIC STEEL WELDMENTS UNDER VARIOUS HEAT TREATMENTS: EXPERIMENTS AND MODELING

347H austenitic stainless steel exhibits exceptional creep and corrosion resistance, rendering it an exemplary candidate for pipeline materials, particularly in mid- to high-temperature working conditions. However, due to constraints in component dimensions, welding has been chosen as the preferred method for joining pipeline systems extensively employed in nuclear power plants, fossil fuel plants, and petrochemical companies. The welding process entails the accumulation of residual stress during the cooling stage, along with the introduction of microstructure evolution. Moreover, the residual stress field and microstructure continuously evolve under service conditions, thereby intensifying the susceptibility of crack initiation and propagation. The initial residual stress attains its maximum value but subsequently undergoes relaxation, while the microstructure gradient and uneven distribution of residual stress give rise to stress concentration, ultimately promoting premature failure, known as stress relaxation cracking (SRC).

Prior investigations pertaining to the SRC issue have typically separated simulation and experimentation, leading to unreliable predictions. Concurrently, the lack of appropriate methods to integrate material thermo-mechanical properties into simulation models exacerbates the inaccuracies in predicting failure as the service time increases. Additionally, SRC tests necessitate the application of external loads to accelerate the testing process, thereby introducing additional uncertainties into the experiments and widening the disparity between simulation predictions and the actual failure time. Therefore, this report introduces a methodology that combines both simulation and experimentation to forecast the lifespan of 347H weldments, whereby the simulation model and experimental measurements can mutually corroborate each other.