| S355J2W+N weather-resistant steel has the advantages of high strength,strong atmospheric corrosion resistance and high impact toughness,which can further improve the welding quality and has important practical value and practical significance for improving the safe operation of high-speed trains.In the welding production process of bogie frame,some key welds can only be welded on one side and formed on both sides.In the process of bogie frame welding production,some key welds can only be welded on one side and formed on both sides.The penetration ability of conventional pulsed MAG welding is limited,and the root is often lack of fusion defects,and the welding residual stress is large;while the high-frequency pulse MAG welding arc penetration is strong,the melting pool effect is greater,increase the welding seam root meltwith,it is possible to solve the problem of poor fusion of the bottom welding root in the actual welding production of the bogie.In this paper,conventional pulsed MAG welding and high frequency pulsed MAG welding are used to compare welding process of 12 mm thick S355J2W+N weather-resistant steel;based on the results of weld appearance formation and non-destructive testing(UT),the welding process parameters of different joint conditions(groove angle,welding gap,etc.)are worked out.By studying the welding residual stress,macro morphology and microstructure,mechanical properties and the temperature field during the welding process,the welding temperature field was numerically simulated by ABAQUS finite element analysis software,and the optimal welding process parameters were obtained.The results are as follows1)Under the same joint conditions,the residual welding stress of the high-frequency pulse MAG welding joint was significantly reduced compared with conventional pulse MAG welding.With the decrease of groove angle,the welding residual stress value is lower.2)Well-formed weld,no cracks,porosity,slag and other welding defects,all to achieve single-sided welding double-sided forming.Compared with conventional pulse MAG welding,the organizational characteristics of high-frequency pulse MAG welding joints are more ideal,with more needle-like ferrite in the weld,no side lath ferrite in the fusion zone,less number of first co-dialysis of ferrite tissue,and less grain coarsening in the superheated zone.3)The hardness test shows that the lowest hardness value of the base material,the hardness value of the welded area is higher than the base material,the highest hardness value of the superheated area,the hardness value are less than 380 HV.4)The tensile test shows that the tensile strength of the joint conforms to the standard and the fracture locations are located in the base material;the bending test shows that there is no crack on the tensile surface when the bending specimen reaches 180°.The low temperature shock test of-40 shows that under the same joint conditions,high℃-frequency pulsed MAG welds have greater impact work in the weld and heat-affected zone than conventional pulsed MAG welds.As the groove angle decreases,the weld and impact work in the heat affected zone of the joint increases.5)The temperature-measuring point welding thermal cycle curve obtained by numerical simulation is very similar to the measured welding thermal cycle curve,and the overall trend is consistent.High-frequency pulse MAG welds have a higher peak temperature at the temperature measurement point,and the temperature measurement point cools faster when the cover is welded.6)Through the comprehensive analysis of welding residual stress,microtissue and mechanical properties of the joints,the optimal high-frequency pulse MAG welding process parameters are obtained as follows: groove angle of 30o,welding gap of "0" mm,backing welding current of 298 A,voltage of 31.2V,welding speed of 50cm/min,welding current of 240 A,voltage of 30 V and welding speed of 45cm/min. |
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