Abstract
The large heat input of submerged arc welding (SAW) usually leads to coarse grains, reducing the mechanical properties of weldments. In this work, double-pulsed (DP) current waveform modulation technology was innovatively applied in SAW. The SAW experiments with/without DP current were performed to investigate the comprehensive effect of low frequency on the welding process stability, weld formation, microstructure and mechanical properties of the Q235 weldments. The results demonstrated that DP current significantly improved welding stability, and high-quality weldments with slight undercuts and spatters, without welding collapse, cracks or hump were obtained by DP-SAW. The low frequency had a significant effect on the spacing between each fish scale pattern. In addition, the microstructure of weld metal mainly consisted of proeutectoid ferrite, acicular ferrite, fine-grained ferrite and slight pearlite, while the microstructure of the heat-affected zone consisted of proeutectoid ferrite and widmanstatten. The stirring action of DP-SAW on the molten pool refined the weld microstructure, which improved the mechanical properties of weldments. With the optimal low frequency of 4 Hz, the microhardness, tensile strength and impact toughness of DP weldment were 188.2 HV, 537.9 MPa and 81.1 J/cm2 respectively, which were enhanced by 11.1%, 8.1% and 9.8% compared with that of SP weldment respectively. The obtained results provide a new idea for improving the weld quality of submerged arc welding.
