An investigation of post-weld heat treatment for welded AISI 1007 steel using TIG-MIG hybrid welding technique

Abstract

The adoption of hybrid welding in manufacturing sectors that produce heavy-duty machinery is increasing. Manufacturing industries that produce heavy duty machinery are increasingly utilizing hybrid welding. This is as a result of several drawbacks of standalone welding processes, such as undercut formation, spatter formation and low weld metal toughness. TIG-MIG hybrid welding, a special, low-cost hybrid welding process incorporating the properties of both TIG and MIG welding processes, produces precise welds. While this hybrid technique combines the benefits and improvement in its quality, its efficiency can be enhanced. Therefore, the post weld heat treatment of the TIG-MIG hybrid welded joint is proposed. This research presents an investigation of post weld heat treatment on TIG-MIG hybrid welded AISI 1007 steel. The hybrid welding procedure was carried out on a 7 mm AISI 1007 steel plate. The butt joint configuration had a single V-notch groove. The hybridized TIG-MIG welded joint is subjected to Post-Weld Heat Treatment (PWHT) in both normalizing and annealing conditions at 850 °C. Tensile, microhardness and charpy impact test were employed to investigate the mechanical properties of the hybrid welded joint. The microstructural examination was achieved using Raman and SEM with EDS attachment. Findings show that post weld heat treatments, particularly normalizing and annealing, improve the uniformity and refinement of the grain structure in the as-weld TIG-MIG hybrid welded joints. However, unlike in the normalized condition, microstructural images of the annealed TIG-MIG interface confirm the presence of carbide precipitates. The as-welded condition exhibits higher strength, while heat-treated conditions enhance ductility and toughness. Selecting the optimal welding condition should depend on the balance of strength, ductility, and toughness required for the application.