Impact toughness influence law and weldability analysis of 800 MPa grade steel for photovoltaic brackets

Through welding thermal simulation experiments, the welding thermal cycle process of the coarse grain heat affected zone (CGHAZ) of 800 MPa grade steel for photovoltaic brackets under different cooling rates was simulated. The microstructure of the thermal simulation sample was observed under an optical microscope (OM), and the influence of cooling rate on the microstructure of CGHAZ was analyzed. The influence of cooling rate on the toughness of CGHAZ was analyzed by impact test of the thermal simulation sample and scanning electron microscope (SEM). The results show that with the increase in cooling rate, the microstructure of CGHAZ gradually changes from granular bainite (GB) and proeutectoid ferrite (PF) existing at the grain boundary to GB and a small amount of lamellar bainite (LB) and finally to all LB. Moreover, with the increase in cooling rate, the impact toughness gradually improves, and the average impact absorption energy at −20 ℃ increases gradually from 14.33 J to 58 J. The impact fracture morphology gradually changes from a typical brittle fracture morphology to a toughness and cleavage mixed fracture and finally becomes a clear ductile fracture. In addition, by considering the high strength of 800 MPa grade steel for photovoltaic brackets, its weldability is indirectly evaluated by the carbon equivalent and the Granville diagram, and its cold crack tendency is evaluated by the cold crack sensitivity index. The analysis results show that its weldability is good, and the cold crack tendency during welding is low.