Simulation of transient heat transfer and phase transformation in laser beam welding for low alloy steel and studying its influences on the welding residual stresses

Abstract

The welding process causes high local heat input on the material, which leads to microstructural changes in the base material, followed by the development of residual stresses in the welded components. This has a significant impact on the performance of the welding joint. Therefore, it is crucial to effectively predict the effect of temperature, metallurgical and structural changes on the component, which can be achieved by numerical simulation.The main goal of this work is to mathematically investigate the influence of thermo-metallurgical phase transformations on the welding residual stresses which was induced by laser beam welding in low alloy steel (S235JR). In this study, two separate numerical simulation models were analyzed using the software Abaqus CAE. One numerical model describes the thermo-mechanical behavior and the other describes the thermo-metallurgical-mechanical behavior of the system which was realized using UEXPAN user subroutine. In this user subroutine, the kinematics of phase transformation was computed using the modified Johnson-Mehl-Avrami and Kolomogorov while considering a nucleation and growth process that controls the dissolution of the initial microstructure. The generation of martensitic transformation has been accounted by the Koistinen-Marburger equation. In the next step, the phase transformation subroutine has been integrated with a structural model along with a special temperature step function to realize the effect of thermal strain and the strain caused by phase transformation on the welding residual stresses. The computed residual stresses of both the models were compared with the experimentally measured residual stresses using the hole drilling method. These results show that the inclusion of phase transformations has a significant effect on the residual stresses of the welded component.