In this investigation,hybrid laser/arc welding (HLAW) was employed to join 8-mm-thick high-strength quenched and tempered steel (HSQTS) plates in the butt-and T-joint configurations.The influences of welding parame ters,such as laser power,welding speed,stand-off distance (SD) between the arc of gas metal arc welding,and the laser heat source on the weld quality and mechanical properties of joints,were studied to obtain non-porous and crack-free fully-penetrated welds.The weld microstructure,crosssection,and mechanical properties were evaluated by an optical microscope,and microhardness and tensile tests.In addition,a finite element model was developed to investigate the thermal history and molten pool geometry of the HLAW process to join the HSQTS.The numerical study demonstrated that the SD had a paramount role in good synergy between the heat sources and the stability of the keyhole.For the butt-joint configuration,the results showed that,at a higher welding speed (35 mm/s) and optimum SD between the arc and laser,a fully-penetrated sound weld could be achieved.A non-porous weld in the T-joint configuration was obtained at a lower welding speed (10m/s).Microstructural evaluations indicated that the formation of residual austenite and the continuous network of martensitic structure along the grain boundary through the heat affected zone were the primary reasons of the softening behavior of this area.This was confirmed by the sharp hardness reduction and failure behavior of the tensile coupons in this area.