The Droplet Transfer And Welding Process Research In Triple-wire GMAW Of High Strength Steel Q960E For Construction Machinery

As the construction machinery continues to develop in the direction of large-scale and lightweight,a new generation of construction machinery steel Q960 E has been rapidly developing with its good comprehensive mechanical performance.To ensure the welding performance of Q960 E and to improve the welding efficiency is the problem to be solved.In this paper,the Q960 E high-strength steel was welded by triple-wire gas metal arc welding,the arc interference was reduced by the pulse phase control,and the stable droplet transfer mode was explored.The combination of thermal simulation and test was used to study the effect of process parameters on the microstructures and properties of the welded joints.The results show that the interference between the arcs can be reduced and the arc stability can be improved by changing the phase angle in the triple-wire welding process.When the phase angle is 0°,three welding wires burn at the same time,the arcs interfere with each other and an abnormal voltage appears;when the phase angle is 180°,the trialing wire and two leading wires burn alternately and the mutual arc interference is serious;when the phase angle is 120°,three welding wires burn in turn,the interference between the arcs is minimal and the arc stability is improved.In addition,there is a stable transition form of one droplet per pulse when the preset current and voltage ratio is appropriate.The SHCCT curve of the coarse-grained region of Q960 E heat-affected zone was conducted by welding thermal simulation technique,which can provide the basis for establishing reasonable welding process.The results show that the phase transformation microstructure of coarse grain region of Q960 E mainly includes lath martensite,lath bainite and granular bainite.When the cooling rate is less than 2℃/s,the microstructure of the coarse grain zone is granular bainite.When the cooling rate is between 5 ~ 10℃/s,the structure of coarse grain zone is composed of lath bainite.When the cooling rate is 10 ~ 30℃/s,the coarse grain zone consists of lath bainite and lath martensite.When the cooling rate is more than 50℃/s,the microstructure of coarse grained zone is lath martensite.The study of Q960 E triple-wire GMAW welding process shows that when the preheating temperature is 100~120℃,the welding heat input is 1.26-1.56kJ/mm and the groove angle is 60°,the microstructure of the weld zone is mainly acicular ferrite and coarse grain heat affected zone is composed of lath martensite and lath bainite.The welded joints have good mechanical properties with its tensile strength reaching85% of the base metal and the impact toughness reaching up to 62 J.