| In the paper, the welding method with hybrid heat source, rotated arc controling, welding parameters and performance detecting have been researched on the demand of the medium carbon heat treated steel with high intensity and high strength and stud welding with medium and large diameter. The stud welding method has been improved and the best welding parameter window has been obtained. The relationship of welding parameters and the quality of the welding joint has been acquired. Experiments show the strength coefficient of the welding joint is above 0.95.In order to prevent the welding defects, such as incomplete fusion, crack, molding defect in the none-symmetrical structure between the large diameter stud and the thick steel plate, the stud arc welding with induction heating and compound heating source has been adopted. In the experiments the stud diameter is 27mm and the thickness of the base metal are 45mm and 80mm. Results show the welding processing is stable and the appearance of the welding joint is good. The interface strength is above 350Mpa. The microstructure of the welding joint shows the heating and molting of the base matal and the stud is homogeneous and there is no existance of welding defects such as incomplete fusion, slag and crack. But in some joints there are some pores. The microstructure of the weld is Martensite and Bainite, and the microstructure HAZ of the high intensity and high strength steel is plate and lath Martensite. No crack is found in the welding joint.To solve the difficulty of melting asymmetry in welding hollow stud with medium and large diameter, the technology of rotating arc is applied to the hollow stud welding. The device with a rotated coil has been designed to weld the hollow stud with the diameter from 12mm to 20mm. The experiments of welding the hollow stud with the diameter of 16mm and 19mm show that the vertical magnetic field , which is added when the arc starts, forced the arc to rorate in 360 degree and the stud can been heated totally. Experiments show insufficient melting defect is eliminated and good welding joint can be obtained and the interface strength is above 400Mpa. Good welding paremater for hollow stud welding has been acquired.To solve the crack in welding the medium carbon heat treated steel with high intensity and high strength in large restriction, After analyzing many simulative experiments a conclusion can be made that the hardening tendency of the steel itself, the hydrogen content and distribution of the welding joint and the extent of restriction are the main factors for the forming of welding cold crack. Experiments show the crack extent is decreased by using the compound heating stud welding method. In fact, good stud welding joint with no cold crack has been obtained after many experiments. |
