Process, design and quality of submerged arc welding

Abstract

Welding is one of the few final manufacturing processes in which the material being worked exists simultaneously at various places in two phases, liquid and solid. This together with the large temperature range and high rates of change of temperature gives rise to the potential for great variability in metallurgical structure of the joint and its physical homogeneity. In modern fabrication industry, the relationship between process variables and weld bead parameters need to be well understood so as to produce quality welds. Because of its high reliability, deep penetration, smooth finish and high productivity, Submerged Arc Welding (SAW) has become a natural choice in industries especially for welding of pipes. In this present study, possibilities of improving the weld quality by modifying the existing welding process parameters used in a local pipe manufacturing industry are investigated. Mechanical properties including the metallurgical properties of the weld metal and heat affected zone are compared. Thirteen test runs are performed under selection of different process variables which include arc current, arc voltage and weld speed. Mechanical properties of the weldment are tested which include Bend test, charpy impact test, tensile test, Vickers hardness test, bead size measurement including microstructure and chemical composition. Results indicated that there is a scope of enhancing the weld quality by modifying the existing process parameters. An increase in arc current and a little decrease in weld speed by keeping arc voltage values constant at existing level can improve weld quality characteristics. The HAZ hardness prediction model is also validated and is found to be satisfactory.