Abstract: Based on SYSWELD software,a “thermo-metallurgical-mechanical” coupling computational approach with consideration of solid-state phase transformation is established to simulate temperature field, fraction of phase and welding residual stress in a multi-layer and multi-pass butt-welded joint of wear-resistant NM500 steel. Meanwhile, microstructure, hardness and surface residual stress distribution of the joint were observed by optical microscope, measured by micro-hardness tester and by hole-drilling method,respectively, and the measured data are compared with the corresponding simulation results. The results show that the simulated melting zone above the melting point of the NM500 steel butt-welded joint is in a good agreement with the actual melting zone, and this proves that the numerical simulation method reproduced the actual welding heat input for the butt-welded joint. For NM500 steel butt-welded joint, the peak value of longitudinal residual stress located the base metal adjacent to the heat-affected zone, and its value is about 1 600 MPa, which is similar to the yield strength of base metal at room temperature. The transverse residual stress distributed in the thickness direction in the shape of “tension-compression – tension”. In general, the magnitude and distribution of longitudinal and transverse residual stresses obtained by numerical simulation are in good agreement with the experimental measurements, which verified the effectiveness of the “thermo-metallurgical-mechanical” coupling computational method. Based on the numerical simulation results, the formation mechanism of welding residual stress in NM500 steel multi-layer multi-pass butt-welded joint is also investigated.

Key words: wear-resistant steel, weld, solid-state transformation, residual stress, numerical simulation