Experimental and numerical study of thermal field and weld bead characteristics in submerged arc welded plate

Submerged arc welding experiments were performed on mild steel plates, and thermal field, characteristic of heat affected zone, weld bead geometry and microstructure of heat affected and fusion zones were studied. Macrostructural examination in the transverse and frontal plane establishes that the weldpool dimensions have similarity to the oval shape heat source. A computational process model of the welding process is presented that solves three-dimensional fluid flow and heat transfer considering an oval shape moving volumetric heat source. The computational model considers melting and solidification phase change in the workpiece, natural and Marangoni convection in the meltpool, and convective and radiative heat losses from the welded plate. The parameters of three-dimensional oval heat source are estimated using the experimentally measured weldpool dimensions. Decent agreement is realized between the predicted and the measured thermal field, heat affected zone width and weld bead geometry. The comparison suggested the utility of the oval shape heat source model for predicting the transient temperature distribution, heat affected zone width and weld bead geometry on the welded plate in submerged arc welding process. Microstructural examinations on samples reveal prominent grain growth in the heat affected zone, and fine and equiaxed grains in the fusion zone.