The Ar+CO

2

gas shielded welding method was used in the condition of non-preheating

and the low-alloy basic slag flux-cored wire was selected to weld Q620 steel under three heat inputs. The weldability and engineering usability of high strength and low alloy Q620 steel were studied by welding joint quality analysis

weld metal chemical composition analysis

microstructure observation and mechanical property test. The results show that Q620 steel has good weldability at room temperature

and the alloying elements in the weld zone are evenly distributed. When the welding heat input changes from low to high

the microstructure of the weld zone changes from ferrite +pearlite to bainite +martensite

and the strength and hardness of the weld zone decrease. With the increase of heat input

the impact fracture morphology of weld zone changes from ductile fracture to hybrid fracture mode of dimple and quasi-cleavage.