Investigation on residual stress of EQ56 high strength steel butt weld.

In the welding process of high-strength steel (HSS), the intense temperature change in joints induces the formation of welding residual stress (WRS), which increases the fatigue crack growth rate. Developing an effective finite element (FE) model for accurately predicting the WRS distribution is critical to improve the quality of welded structures. Experimental tests and numerical simulations were carried out to investigate the WRS distribution of EQ56 HSS. The thermal expansion curves at various heating and cooling rates were measured through thermal simulation experiments for achieving the continuous cooling transformation (CCT) diagram of EQ56 HSS. Based on the CCT diagram, the thermo-metallurgical-mechanical (TMM) FE model was developed to consider the influence of solid-state phase transformation (SSPT) on distribution and magnitude of WRS for welded EQ56 HSS joints, as well as material hardening law. Comparison of predicted WRS distribution and experimental data shows that plastic hardening laws of materials significantly affect the precision of WRS distribution, and combined hardening law gives most reliable prediction. The FE model considering SSPT behavior provides more accurate estimation of WRS distribution than those without considering SSPT behavior. • Basic mechanical properties, thermophysical properties and thermal expansion curves of EQ56 HSS were determined. • Continuous cooling transformation curve of EQ56 HSS was obtained from the thermal expansion curves. • Thermo-metallurgical-mechanical FE models considering solid-state phase transition (SSPT) behavior were developed. • Effects of material hardening law and SSPT on welding residual stress distribution were investigated. [ABSTRACT FROM AUTHOR]