Cold Metal Transfer Surfacing Of Water-walls Of Boiler

ER-310 austenitic stainless steel was deposited on Q235 steel substrate using cold metal transfer(CMT)welding process to solve the problem of thinning and even tube bursting of boiler water wall caused by erosion and corrosion at elevated temperature.The welding process was systematically studied,and the microstructures and mechanical properties of the overlay were analyzed.The main results were summarized as follows:(1)With optimized parameters for CMT surfacing,welding current 118 A,welding voltage 14.2V,welding speed 2.4mm/s,swing width 12 mm,swing speed 26mm/s,and amount of overlap 7mm,sound 310 stainless steel overlay could be formed.There were no macroscopic defects such as pores or cracks in the overlay,and the thickness of the overlay was about 3mm.(2)There were no pores,cracks,incomplete fusion and other defects in the overlay.The microstructures of the overlay were austenite,consisted of equiaxed fine crystalline region nearing surface,columnar crystal area nearing the fusion zone and mixed crystal region in the middle.The essential elements in the overlay were Fe,Cr and Ni.And content of them in the overlay was far different from that on the bonding interface.The dilution rate of CMT overlay was 8.78%.The hardness of CMT overlay was from 190 HV to 200 HV.Bend specimen qualified by penetration test could be bent to 180° without cracking,and the overlay had good ductility.The overlay also had good corrosion resistance.(3)Compared with the optimized MIG surfacing process,CMT surfacing process had a series of advantages such as low heat input,small deformation,low dilution rate,good plastic property and high corrosion resistance(4)CMT surfacing process was applied to Q235 steel plate and 20 G boiler tube.The bonding strength between the overlay and the substrate was over 400 MPa.