Influence of temperature- and phase-dependent yield strength on residual stresses in ultra-high strength steel S960 weldments

The temperature- and phase-dependent yield strength plays a decisive role in the precise prediction of residual stresses in structural steel weldments. Since it is very expensive and time-consuming to directly measure the yield strength of a given steel by experimental method, numerical simulation has commonly been performed using the available yield strength of the same steel grades in scientific literature and material database or using the evaluated data based on the empirical formulations in standards/codes for the given steel. Nevertheless, the yield strengths of the same steel grades are usually different mainly due to the disparity in chemical composition and grain size. Furthermore, there are considerable differences in the yield strength at elevated temperatures obtained from the predictive functions for the given steel. Therefore, it is necessary to clarify the influence of the variation in temperature- and phase-dependent yield strength obtained from different methods on the predicted welding residual stresses in numerical simulation. In this study, numerical sensitivity analyses have been conducted to clarify the effect of yield strength on the predicted residual stresses in ultra-high strength steel S960 weldments. Furthermore, tensile tests and welding experiments were carried out for comparison and validation. Based on the current work, the effect of temperature- and phase-dependent yield strength on the calculated welding residual stresses is clarified. Besides, the reliability of the proposed functions to evaluate yield strength based on the tensile test results mainly from mild steels and conventional high strength steels is assessed for the recently developed ultra-high strength steel S960. Finally, guidance on how to economically determine the reliable temperature- and phase-dependent yield strength for S960 steel in numerical welding simulation is provided.