Influence of welding method on residual stress and metallography of a mild steel welded butt-joint plate

During welding process and cooling process after welding, residual stress will be generated and the microstructure of the weld joint will be changed inevitably, which will be harmful for mechanical performance of welded structures. Hence, it is necessary to study welding-induced residual stress and metallic phase transformation, so as to provide guidance for optimization of welding process. In this paper, three butt-joint plates were fabricated by using different welding methods including shielded metal arc welding (SMAW), gas metal arc welding (GMAW), and submerged arc welding (SAW). Secondly, welding residual stress was measured through blind-hole method. Thirdly, the microstructure of the welded joint was analyzed. Fourthly, thermal elastic-plastic finite element method (FEM) was used to numerically simulate the welding process. Finally, heat cycling curves of typical gauged points were extracted, the mechanism of how welding induces residual stress and phase transformation was analyzed from the perspective of cooling rate. Experimental and numerical results show that compared with longitudinal stress, the influence of welding method on transverse stress is more significant. When SMAW is used for welding process, the distribution of transverse residual stress is more uniform than that using GMAW and SAW. Under the three welding methods, the welded joints show similar metallographic compositions. However, the content and distribution of different metallographic compositions are quite different.