Parametric Study of Submerged Arc Welding on Mild Steel

Abstract

The use of arc welding for fabrication, repair, hard facing and erection has resulted in increase in productivity and quality. Quality of welding largely depends on the bead the characteristics, penetration, mechanical properties, HAZ dimensions and microstructures of weld metal and HAZ. The micro structural sub zones in the heat-affected zone of a weld are spheroidised zone, partially transformed zone, grain refined zone and grain-coarsened zone. Welding parameters has a direct effect on the microstructure and the bead characteristics of a base metal. The typical microstructure formed in the HAZ of mild steel consists of grain boundary ferrite, Widmanstaten ferrite, pearlite, banite, acicular ferrite and martensite depending upon the cooling rate below critical temperature. In submerged arc welding (SAW), selecting appropriate values for process variables is essential in order to control heat-affected zone dimensions and 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. Present study was conducted to observe the bead geometry and microstructures of weld zone and heat affected zone of submerged arc welding. The experiments were performed on 13 mm thick mild steel plate and single pass submerged arc weld was carried out by varying welding parameters, metallurgical tests where performed using inverted binocular optical metallurgical microscope fitted with digital camera which is connected to a computer. The effects of welding variables on bead geometry and microstructure of weld metal and heat affected zone were experimentally studied using suitable wire flux combination and finally the results were analyzed.