Finite element simulation of welding distortions in ultra -high strength steel S960 MC including comprehensive thermal and solid-state phase transformation models

The objective of this study is developing a thermo-metallurgical-mechanical finite element (FE) model in- corporating the effect of solid-state phase transformation (SSPT) to accurately simulate deformations for single bead -on -plate welding of an ultra -high strength carbon steel. Comprehensive phase transformation modeling including both diffusive and diffusionless (displacive) transformation kinetics, was performed and the effect of SSPT on welding -induced deformations was investigated. Modelling the heat source and thermal boundary conditions were accomplished in the ABAQUS user subroutines, the former based on the Goldak 's double el- lipsoidal heat source model. An ABAQUS user subroutine was developed in which kinetics of diffusive and diffusionless transformations based on Machnienko model and Koistinen-Marburger formula, respectively, were implemented. Modification of strains due to volumetric change as a result of SSPT was accomplished using an ABAQUS user -defined subroutine. A comparison between the temperature histories from thermal simulations (with isotropic as well as anisotropic conductivities) and measurement with thermocouples shows that much better verification with experiments can be obtained when anisotropic conductivity is applied. From the results of the mechanical simulations (with and without considering the effect of SSPT) and comparison with measured deformations, it is observable that more accurate prediction of welding -induced angular and bending distortions is possible when the effect of SSPT is incorporated for the material under investigation.