Study on Residual Stress of Multi-layer and Multi-pass Butt-welded Joint for Ultra-high Strength Wear-resistant Steel NM500
Based on SYS WELD 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.
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