以板厚为5 mm的1600 MPa级超高强钢为研究对象，采用熔化极惰性气体保护焊(MIG)焊接方法和ER307Si焊丝制备了单道对接接头，分别利用盲孔法和显微硬度仪测量残余应力和接头硬度分布。基于接头热影响区和软化区的硬度测量结果，以SYSWELD软件为平台，开发了考虑超高强钢固态相变和软化效应以及焊缝金属加工硬化和退火软化的“热-冶金-力学”多场耦合的有限元计算方法。采用该方法模拟了超高强钢单道对接接头的温度场及残余应力，并与实验结果进行了比较。基于数值模拟结果探讨了固态相变和软化效应对焊接残余应力的影响机制。数值模拟结果表明，固态相变对纵向残余应力的大小和分布有显著影响；对横向残余应力的大小和分布有一定程度的影响。软化效应对纵向残余应力的峰值有较显著的影响，对横向残余应力几乎没有影响。将数值模拟结果与实验结果比较可知，在同时考虑固态相变和软化效应的情况下，平板对接接头的焊接残余应力计算结果与实验测量结果最为吻合。

In recent years, ultra-high strength steel (UHSS) has been widely utilized in engineering structures, mining machinery, and military equipment. However, UHSS is prone to brittle fracture and fatigue failure due to high strength and relatively low plasticity. Moreover, residual stress induced by welding process affects both brittle fracture and fatigue failure. In this work, a single-pass butt-welded joint was fabricated by metal inert-gas welding. The base metal was 1600 MPa grade UHSS with a 5 mm thickness, and the filler metal was ER307Si. The distributions of welding residual stress and hardness of the butt-welded joint were measured using the hole drilling method and a microhardness tester, respectively. Based on measured values of hardness in the heat-affected zone (HAZ) and softening zone (SZ), SYSWELD software was used to develop an advanced computational approach with consideration of “thermal-metallurgical-mechanical” coupling behaviors. In addition to the strain hardening and annealing effects of weld metal, the established computational model accounted for both the solid-state phase transformation (SSPT) of HAZ and softening effect of SZ. The temperature field and residual stress distribution of the UHSS single-pass butt-welded joint were simulated. Furthermore, the simulated results were compared with the corresponding measured data. The simulation results revealed the effect of SSPT and softening on welding residual stress. The numerical results indicated that SSPT has a strong influence on both the magnitude and distribution of the longitudinal residual stress; however, it has a limited effect on transverse residual stress. Meanwhile, the softening effect drastically affects the peak values of the longitudinal residual stress, while it hardly influences transverse residual stress. When both SSPT and softening effects are simultaneously considered in the numerical model, the computed results of welding residual stress are in good agreement with the experimental measurements.