Influence of strain-hardening models and slopes on the predicted residual stresses in structural steel S235 weldments

Abstract

The objective of this research is to systematically understand how strain-hardening models and phase- and temperature-dependent strain-hardening slopes affect the computed residual stresses in single-pass welded joints made of the widely used structural steel S235. Both experimental methods and numerical simulation have been utilized for investigation. The results reveal that the material plasticity model has a massive effect on the predicted welding residual stresses (WRS). The calculated magnitude of WRS in the base metal (BM) adjacent to the weld zone inside the plate is largest when the isotropic hardening model is used, while it is smallest applying the kinematic hardening model. The comparison of predictions with measurements shows that the isotropic hardening model can predict WRS more accurately for S235 steel. The change in the temperature-dependent strain-hardening slopes of the generated phases (austenite and bainite in this case) have practically no impact on the predicted WRS. The calculated longitudinal residual stress (LRS) amount in BM nearby the weld zone is highly sensitive to the applied strain-hardening slopes of the initial microstructure (ferrite here), while that of transverse residual stress (TRS) is not. In contrast to the strain-hardening slopes of the initial microstructure at elevated temperatures, that at room temperature plays a crucial role in the simulated LRS. In this study, guidance is provided on how the phase- and temperature-dependent strain-hardening slopes of a specific steel can be determined economically and reliably in numerical welding simulation.