| Ferritic stainless steel(FSS)had good corrosion resistance and economy,and was widely used in machinery manufacturing,commodities,housing construction,home appliances and automobile manufacturing industries.However,there were some problems of grain coarsening and low production efficiency in welding FSS by traditional arc welding method,which reduced the service performance of components.In this study,during the cold metal transfer(CMT)welding of AISI430 FSS with ER308 L welding wire as the filler metal,the grain refinement of weld metal and the improvement of production efficiency were realized through the research on the strong and weak specifications and the ultrasonic vibration assisted welding,which provided the theoretical foundation for the CMT welding manufacturing of FSS.Firstly,by adjusting the wire feeding speed to change the welding heat input,the CMT welding parameter range of AISI430 FSS was determined,and the well-formed welding joint was obtained.Secondly,the microstructure,mechanical properties and corrosion resistance of welded joints obtained under different welding heat input conditions were tested,and the influence rule of welding heat input on microstructure,mechanical properties and corrosion resistance of welded joints was studied.After that,by taking the welding heat input corresponding to the optimal welding parameter as the benchmark,the matching of wire feeding speed and welding speed was adjusted to ensure the constant heat input,so as to realize the strong,medium and weak specification welding.The influence of different welding specifications on the microstructure and comprehensive performance of the welded joint was studied.Finally,the ultrasonic vibration was introduced into strong specification welding,and the mechanism of ultrasonic vibration on grain refinement and element distribution uniformity of weld metal was studied.According to the above research,it was found that the solidification process of weld metal followed the FA solidification mode of L(1)L+F(1)L+F+(F+A)(1)F+A.Therefore,the weld metal consisted of ferrite and austenite.The heat affected zone(HAZ)was divided into coarse and fine grain zones.The coarse grain zone consisted of coarse ferrite grains,a lot of intergranular martensite and intragranular carbides,while the fine grain zone consisted of fine ferrite grains and a little of intergranular martensite.The micro-hardness of weld metal and HAZ was significantly higher than that of base metal,and the micro-hardness of weld metal of weak specification welding was significantly lower than that of medium and strong specification welding about40 HV.In addition,the tensile fracture of all samples was located at base metal,with many dimples evenly distributed at the fracture.The corrosion resistance of welded joints increased with the increase of heat input.The corrosion resistance of the welded joint obtained by the weak,medium and strong specifications welding increased first and then decreased.It was found that the introduction of ultrasonic vibration could significantly refine the primary ferrite grains formed in the solidification process of weld metal,and then affected the subsequent solid phase transformation process,and finally reduced the ferrite content in weld metal by about 45%.In addition,the introduction of ultrasonic vibration can reduce the segregation of chromium elements and improve the distribution uniformity of alloying elements in weld metal.At the same time,the ultrasonic vibration increased the width of the element transition zone between the weld metal and the HAZ by about 8?m,thus reducing the mismatch between the weld metal and the base metal.Based on the above effects brought by ultrasonic vibration,the corrosion resistance of weld metal was obviously improved under the condition of strong specification. |
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