The Welding Performance Of High Nickel Nodular Iron Homogeneous Electrode

The weldability of cast iron is relatively bad.The welding effect of cast iron is determined in large part by welding materials.The existing cast iron electrodes can not meet welding of high-performance cast iron demand,due to weld metal bad crack resistance,the colors glow such as the nickel base materials or high energy consumption and cost such as homogeneous cast iron.This paper,according to the principle of both promoting graphitization and expanding the austenite phase during welding metallurgic process,a new type high nickel ductile iron homogeneous welding electrode was designed.The effect of Ni contents on microstructure of welding rod core was investigated.The influence rules of coated components on the physical performance of slag were studied with the orthogonalizing experimental method.coated components of high nickel ductile iron homogeneous welding electrode were optimized by assessment of welding processing property and the effect rules of welding process on welding structure and joint properties were investigated.The results show that:This experiment adopts the CaO-CaF2-SiO2 type basic covering slag series,the slag series has big transition coefficient of alloy elements and process performance good advantage.Fluorite and marble have a significant impact on the melting point of the slag and decrease with increasing of Fluorite and marble.With increasing 75#FeSi,the basicity of the slag is decreased.With increase of marble,the basicity of the slag increases.The surface tension of the slag mainly depends on 75#FeSi and BaCO3.with increasing of 75#FeSi and BaCO3,The surface tension of the slag increased as well.With performance as an index,the best formulation(marble25%,Fluorite18%,BaCO328%,75#FeSi8%,clay graphite 6%,squama graphite 11%,85#MnFe 1.6%,aluminum powder 1.6%,and nodularizer 0.8%)is given by orthogonal experiment.The stability changes for the better and no redness phenomenon of the high nickel ductile iron homogeneous welding electrodas by self-developed.The appearance of weld is better.The spatter rate was about 4.9%?8.1%and the slag detachability was about 98%.The welding process of high nickel iron welding electrode is good.With increasing Ni content from WNi =30%to WNi = 35%in the cores,on the one hand,the nodularity and precipitation of graphite in weld metal increases obviously,the number of nodular graphite also increases and distributas homogeneously,nevertheless,the intercrystalline carbides decreases.The morphology on the fusion zone was congruent to welding seam,and the width of fusion zone was decreased.On the other hand,the hardness in weld joint is a little lower than base metal,the tensile strength increases and up to 387MPa.Adopting WNi = 35%high ni ductile iron core pressures with the optimal coating formula preparation of high ni ductile iron welding electrode,welding technology parameter is chosen I= 200A.At room temperature,graphite nodules distribute homogeneously and the number of it was 124 per square millimeter in the welding area.The graphite spheroidization was about 88.3%or more and the precipitation of graphite was 8.7%.The microstructure of the high nickel ductile iron homogeneous weld is composed of austenite and a little intergranular carbide.This hardness ranges from 189 to 236 Brinell.Welding joint has excellent whole processing property.By using the high nickel ductile iron homogeneous welding electrod,At room temperature,the microstructure of the high nickel ductile iron homogeneous weld is composed of fine columnar austenite dendrite,spheroidal graphite and a little intergranular carbide.With the increase of welding current,the morphology of columnar dentrite in the weld tends to be coarsening,the graphite nodularity increases,the graphite morphology becomes more spherical and the number of intergranular carbides increases,therefor the strength and hardness of the joint approaches properties of the base metal.When the welding current is constant,with the increase of preheat temperature,the graphite morphology becomes worse,the amount of carbides precipitated increases,so the tensile strength of the joint decreases and the hardness increases.Along with the large welding current technology at room temperature,the microstructure and mechanical properties of the weld could be controlled effectively and the high quantity homogeneous weld with excellent machining property can be obtained.