Study On The Welding Process Of Stainless Steel Sheet By Cold Metal Transfer (CMT)

Resistance spot welding process was used at lap weld of stainless steel rail vehicle body,but the end of slit should be sealed in order to achieve the seal ability of the entire vehiclebody. The traditional process was using Metal Active-gas Arc welding(referred as MAG),but welding seam have serious overheating, welding defects always be found. This paperfocused on process problems of stainless steel lap weld on railway vehicle body, Cold metaltransfer (referred as CMT) technology was proposed to replace MAG. CMT technology is amodified metal gas welding, compared with traditional MIG/MAG welding have a lowwelding heat input, no spatter, strong bypass capability.This paper studied CMT welding process optimization of stainless steel sheet, with adiameter Φ=1mmER308L stainless steel wire as filler material, and a thickness of1.5mmA304stainless steel sheet as base material. Microstructure and mechanical properties ofCMT welding joint was studied by optical microscopy, scanning electron microscopy(SEM)and universal tensile testing machine.CMT welding stainless steel sheet have a continuous and smooth weld seam, have nospatter particles and no obvious defects, and the entire joint welding deformation is small.Experiments showed that CMT stainless steel sheet lap weld seam get a good welding effect.CMT weld stainless steel joints, the weld area is mainly composed of black dendrites-ferriteand the white austenite. HAZ is narrow, coarse austenite have grain coarsening phenomenon.The hardness of stainless steel CMT welded joints is unevenly. The hardness of weld islower than the hardness of base metal, and the hardness of HAZ is the lowest. The tensiletest results showed that the tensile strength of CMT weld stainless steel joints was slightlylower than tensile strength of base material. The fracture mode was mainly HAZ fracturemode. The corrosion resistance experimental results showed that the corrosion rate ofstainless steel CMT welded joints is greater than that of base metal.With the increase of the wire feed speed, the weld seam becomes slightly wide on themacroscopic morphology, greater color range around weld seam. With weld depth, weldwidth gradually increasing, depth-width ratio tends to increase. The range of HAZ increasedsignificantly. With the increase of the arc length correction factor, the weld seam becomesslightly wide on the macroscopic morphology, greater color range around the weld seam.With weld depth, weld width gradually increasing, depth-width ratio tends to increase. The range of HAZ increased significantly. With the increase of the welding speed, the weld beambecomes slightly wide on the macroscopic morphology, smaller color range around the weld.With weld depth, weld width gradually decreasing, depth-width ratio tends to decrease. Therange of HAZ decreased significantly.CMT stainless steel welded joint fatigue experiments showed that the fatigue crackfracture zone including crack source, crack extend zone, and transient fault zone. Traces offatigue crack were found in crack extend zone, and dimples were found in transient faultzone. Experiments showed that stainless steel CMT welded joints has315.84MPa of fatiguestrength. The number is about50%of tensile strength of base material.Cold metal transfer welding technology (CMT) replace the traditional MAG weldingcan get superb performance welded joints of stainless steel. Through a lot of experimentalwork and theoretical analysis, and ultimately get the optimal parameters of stainless steelsheet CMT welding process: wire feed speed8m/min., arc length correction factor of5%,Welding speed is540mm/min.