Three-dimensional finite element modelling of welding residual stresses of medium carbon steel pipes with consideration of solid-state austenite-martensite transformation and post-weld heat treatment

In the present work, three-dimensional finite element modelling is presented to simulate welding of the medium carbon steel pipes by considering both the solid-state austenite-martensite transformation and the post-weld heat treatment. Thermo-elasto-plastic and metallurgical analyses are carried out by developing two user-defined subroutines: one for applying the heat flux and the another one for considering phase transformation effects on welding residual stresses. The applied heat flux is simulated by a double ellipsoid model. Furthermore, the effects of volumetric change due to the solid-state austenite-martensite transformation are taken into account. The results obtained have revealed that volumetric change owing to the solid-state austenite-martensite transformation has a significant effect on the magnitude and distribution of welding residual stresses. The main contribution of the present work is providing helpful knowledge about welding residual stresses evolution after and before the post-weld heat treatment by considering the solid-state austenite-martensite transformation. In addition to reference to the time-temperature-transformation diagram, this study can result in safe selection of post-weld heat treatment parameters, which not only prevents sensitization to stress corrosion cracking and intergranular corrosion but also provides enough and more importantly controlled relaxation of welding residual stresses.