Research On CMT Welding Of Rail Vehicle Stainless Steel

In recent years, the development of China's rail transit is very fast, and the demand of the car body is increased. Compared with common carbon steel and aluminum alloy body, the stainless steel car body has a great advantage. Traditional MIG / MAG welding of stainless steel car body has splash, overheating, and many other defects. In this paper, the use of heat input low, less spatter, strong ability to bypass the CMT welding technology of stainless steel railway vehicles welding process was studied. The experimental material is ER308 LSi welding wire, 301 L stainless steel.Through the single factor experimental study on CMT welding to research the influence welding speed, feeding wire speed, the arc length correction, thrust correction make on droplet transfer frequency, droplet size and weld penetration, weld width, depth width ratio, the influence of excess weld metal part of the area, the fusion area. By changing the gas flow and welding direction, the surface protection of the left welding is better than that of the right, and the wetting angle of the left welding is smaller than that of the right.The welding parameters were optimized by orthogonal test, and the microstructure and mechanical properties of the welded joint were analyzed. The optimization parameters 2mm thickness 301 L stainless steel plate docking: welding speed 95cm/min, wire feed rate 10.5m/min, butt gap 0.8mm, arc length correction-5%, push the amendment 0, dry elongation 12 mm. In the first, the ? ferrite is precipitated and solidified by the FA mode. The room temperature tissue is composed of ?austenite and a small amount of ? ferrite. The joint is composed of base metal, heat affected zone, the partially melted zone, weld columnar crystal, the fusion line between the parent material partially melted zone and weld columnar crystal, the part of heat affected zone near the part of the melting zone precipitated strip parallel ferrite would inhibit the growth of the regional grain in the heat affected zone. The microstructure hardness of base metal is highest, the heat affected zone is centered, the center of the welding joint is lowest, and the fusion line is similar to that of the base metal. The welding joint tensile strength reach 88% of the base metal for the 666 MPa, the elongation rate was 49% over the conventional minimum elongation rate of 301 L which is 40%, so the welding joint has good plasticity.By changing the amount of the butt joint gap and the wrong side, it is found that the CMT welding technology has strong adaptability to the gap and the wrong side. By contrast with MIG welding, we found that the CMT welding method to generate the splash rarely, grain size of the weld microstructure and weld heat affected zone than MIG welding income of small, CMT welding method is suitable for the process window can produce a large number of strip parallel ferrite, effectively inhibit the grains in the heat affected zone(HAZ) grew up.