A study on the quality of two-wire tandem submerged arc welds under iso-heat input conditions

The influence of the leading and trailing arc welding current on two-wire tandem submerged (SAW-T) arc weld quality was studied at a iso-heat input of 2.5 kJ/mm. The weld quality includes weld bead dimensions, cooling time from 800 to 500 °C in the weld pool, weld bead ferrite phase fraction, and micro-hardness. The cooling time was calculated from the temperature distribution predicted using the numerical model. For a constant heat input, the weld penetration significantly reduced with decreasing leading arc current at a low level of trailing arc current while the final weld penetration was less sensitive to the leading arc current at higher trailing arc current. Significant variation of the average weld pool cooling time from 800 to 500 °C was not observed with increasing leading arc current from 700 to 1000 A at a constant trailing arc current and heat input of 1000 A and 2.5 kJ/mm. However, minimum weld pool cooling time was observed at higher currents. An increase of the leading or trailing arc current at a constant heat input yielded a minor rise of the weld pool acicular ferrite phase volume fraction and decreased the amount of allotriomorphic ferrite phase, leading to a small improvement in the weld bead micro-hardness. In the present study, the welds produced at a leading and trailing arc current of 1000 A and welding speed of 26.80 mm/s displayed better quality weld beads with high productivity.