Microstructure and mechanical properties of HSLA thick plates welded by novel double-sided gas metal arc welding

In this paper, a novel double-sided gas metal arc welding procedure was developed to weld 50 mm thick, low-alloy high-tensile steel. The good weld joint without visible flaws can be obtained. The microstructure and mechanical properties were investigated in detail. The results show that the base metal metallographic microstructure mainly consists of tempering lath martensite and a small amount of granular bainite. The fusion zone is mainly composed of acicular ferrite and lath martensite while the microstructure of the welded bead is composed of acicular ferrite and a small amount of granular bainite. The average hardness value of the welded bead (384.9 HV) is higher than the base metal (282.2 HV), but lower than the heat-affected zone. The average tensile strength of the welded specimens (862.73 MPa) reaches 98.04 % of the base metal (880 MPa). No crack produced when the samples have been bended to 180° and the welding joints all have better plastic property. The impact absorbing energies in FL + 2 mm and FL + 5 mm are higher than those in WC and FL. The fracture modes of WC and FL are cleavage fracture and those of FL + 2 mm and FL + 5 mm are ductile fracture. Consequently, the double-sided GMAW is a high-efficiency welding method without back chipping which has certain advantages and possibility in welding thick plates.