Study On Arc Behavior And He Microstructure And Properties Of Weld Joints In Magnetic Field

The shape and the working area of the welding arc on base metal were changed by the magnetic field applied in welding process on the one hand, on the other hand,can stir the weld metal, which lead to the inhibiting the forming of dendrite,the refining grain size and the improving of the properties of the welding joints.The movement forms of the welding arc in transverse deflection magnetic field and transverse rotating magnetic field were studied in the first part of the paper. In this part, the effects of both transverse deflection magnetic field and transverse rotating magnetic field on welding arc’s deflection amplitude and shape were mainly discussed. The study showed that the arc’s deflection amplitude increased with the increase of the magnetic field strength under the condition of transverse DC deflection magnetic field. The working area of the welding arc on the base metal was stretched at the side of deflection, and the shape mainly like a combination of semi-circle and semi-ellipse. Besides, the stability of the arc decreased. The arc’s deflection amplitude increased with the increase of the magnetic field strength within a certain range of magnetic field strength under the condition of transverse AC deflection magnetic field, and the working area of the welding arc on base metal was stretched at two sides of deflection, and the shape just like a flat ellipse. When magnetic field frequency was between 600 and 900, the arc swing left and right. When magnetic field frequency was between 900 and 1500, the deflection and rotation were not obvious,and the arc was much stable. When magnetic field frequency was beyond 1500, the increasing Lorenz force of the charged particles decreased the stability of the arc and increased the trend of arc blowout. The arc was rotating and the condition of transverse rotating magnetic field. When the strength of the magnetic field was relatively small, the arc working area on the base metal was two concentric circles, the smaller one is the heating overlap area, which had more heat. When the strength of the magnetic field increased to a certain value,the arc working area became nearly a normal circle, and themeasure of the area is bigger. When the strength of the magnetic field beyond this value,the arc working area was a ring, and welding line could not form at this moment. The changing of the stability of the arc with the change of magnetic field frequency was similar with the condition of transverse AC deflection magnetic field.Technological test with transverse rotating magnetic field was studied in the second part. In this part, the microstructure and technical properties of the weld joints were studied.The study showed that magnetic field can improve the formation of the weld line. The weld with magnetic field got more shallow and wider molten pool and decreased the phenomenon of prominent middle section on the weld and thus eased the stress concentration of weld line. Transverse rotating magnetic field in the welding process can refine the grain size of weld metal and HAZ area by decreasing the content and the size of lath martensite and granular ferrite. The result is the improvement of properties of weld joints. The welding joints got under the condition of transverse rotating magnetic field have higher hardness and toughness and less defects.