Effects of Process Variables on HAZ in Submerged Arc Welds of Structural Steel Pipes

In submerged arc welding (SAW), selection of appropriate values of process variables is essential in order to control heat-affected zone (HAZ) dimensions and to get the required bead size and quality. Also, conditions must be selected that will ensure a predictable and reproducible weld bead, which is critical for obtaining high quality. In this investigation, mathematical models were developed to study the effects of process variables and heat input on various metallurgical aspects, namely, the widths of the HAZ, weld interface, grain growth and grain refinement regions of the HAZ. The color metallographic technique and response surface methodology were used for analysis. Direct and interaction effects of the process variables and heat input on the characteristics of the HAZ were presented in graphical forms. The study revealed that heat input and wire feed rate have a positive effect, but welding speed has a negative effect on all HAZ characteristics; secondly width of grain growth and grain refinement zones increased and weld interface decreased with an increase in arc voltage; and width of HAZ is maximum (about 2.2 mm) when wire-feed rate and welding speed are at their minimum limits.