Thickness–heat input coupling in submerged arc welding and gas metal arc welding of DH36 steel: From microstructure evolution to joint-level tensile performance

This study investigates the combined influence of the welding process and plate thickness on the mechanical and microstructural behavior of DH36 shipbuilding steel joints produced by submerged arc welding (SAW) and gas metal arc welding. DH36 steel plates with thicknesses of 6, 8, and 10 mm were welded under different heat input conditions using industrial multi-pass welding procedures. Optical microscopy, radiographic inspection, hardness measurements, and transverse tensile testing were employed to evaluate weld integrity and joint-level mechanical performance. The results indicate that increasing plate thickness resulted in increased heat input and broader thermal influence zones for both welding processes. Gas metal arc welding joints exhibited relatively higher weld metal hardness values, reaching approximately 96 HRB in the 10 mm condition, whereas submerged arc welding joints showed more stable hardness distributions associated with ferritic weld metal structures. Tensile testing performed on selected representative joints showed ultimate tensile strengths of approximately 527 MPa for G10 and 537 MPa for S10 conditions, while the S8 condition exhibited lower tensile performance. Optical microstructural observations suggested finer ferritic features in gas metal arc welding weld regions and relatively coarser ferritic morphologies in submerged arc welding joints under higher heat input conditions. The findings demonstrate that both submerged arc welding and gas metal arc welding processes produced defect-free joints, while the 8 mm submerged arc welding condition approached the practical limit of the investigated processing window, revealing the critical influence of thickness–heat input coupling on joint mechanical performance. This highlights the critical necessity of precise heat-input scaling and process selection when joining different plate thicknesses of DH36 steel.