Numerical and experimental study on thermal-metallurgical-mechanical behavior of high-strength steel welded joint

The welding-induced residual stress is closely related to the mechanical properties of the welded joint, which can accelerate crack propagation and reduce the fatigue life of the welded joint. Therefore, a new composite heat source model based on the actual weld morphology was proposed to calculate the temperature field of highstrength steel single -pass full penetration laser welded joints. The solid-state phase transformation and precipitation hardening model were established based on the actual microstructure of welded joints for more accurately predict the residual stress. Four cases were designed to compare and analyze the influence mechanism of the interaction between solid-state phase transformation and precipitation hardening on the residual stress of welded joints. The solid-state phase transformation has a significant effect on the longitudinal and transverse stresses and stress evolution of welded joints. It increases the peak longitudinal compressive stress from - 140.6 MPa to - 755.1 MPa, with an increase of 529.52 %. Moreover, the longitudinal high stress gradient values generated at the junction of base metal and heat affected zone are as high as 860.9 MPa. Precipitation hardening behavior can weaken the peaks and high stress gradient values of transverse and longitudinal stresses. It can also make the longitudinal stress distribution of the fusion zone and the transverse stress distribution of the heat affected zone more homogeneous. In engineering applications, it was recommended that considering solid-state phase transformation in simulation calculation could accurately predict welding-induced residual stress without considering precipitation strengthening.