Research On Welding Performance Of Homogeneous Cast Iron Electrode

It has significant social and economic benefits of welding repair on the defective casting,due to the complexity of the foundry process and various casting defects which are inevitably generated during the forming process.Cast iron has poor weld-ability,because of the high carbon,silicon,sulfur and phosphorus,the low strength,and the large brittleness.The white cast iron and cracks are two major problems in cast iron welding.The tendency of white cast iron and cracks in the welding zone can be reduced using the micro-alloyed homogeneous cast iron electrodes with cast iron core and strong graphitized coating.However,there is problem of the present micro-alloying homogeneous cast iron electrode poor in weld forming performance,mainly reflected in the rough weld surface,indentation,etc,and have slight porosity tendency in welded surface,which are caused by excess coating temperature,basicity alkalinity and surface tension of the slag.In order to satisfy the development of cast iron welding and achieve high-quality and high-efficiency welding,this paper uses orthogonal test design methods to optimize the present coating composition,under consideration of the relative welding performance and by analyzing the influence rules of coating compositions on the properties of slag.And the effects of coating composition on the microstructure and properties in welding zone are studied.The results showed that:The principal factor affecting the melting point of the slag is the content of marble and barium carbonate.Melting point of coating will be increased when increasing the content of marble,as well as increasing the content of barium carbonate will reduce the melting point of the slag.The marble content is also the most important affecting factor of the basicity and surface tension of the slag.As the increasing of marble,the basicity and surface tension of slag are tend to be enhanced.The orthogonal test is used to obtain the two optimized coating composition.Based on several test index such as coating melting point,slag basicity and surface tension.the composition as follows:1st,marble22,fluorite13,white clay6,barium carbonatel6,rutile10,margin are feldspar,mud graphite,squama graphite,ferrosilicon and aluminum powder,with the component ratio is 3:8:12:8:2.2nd,marble22,fluorite15,white clay4,barium carbonatel8,rutile8,margin are feldspar,graphite,ferrosilicon and aluminum powder,with fixed proportion.The arc stability,slag detachability and splashing of the corresponding optimized electrode has a significant improvement compared with the present electrodes.However,hydrogen holes occur in the weld because of the reduction of fluorite,which resulting in the dehydrogenation of weld are decreased.The latter weld surfaces are smooth and uniform,and welds have regular shape,without any porosity,indentation,cracks with the increase of fluorspar.Therefore,the latter electrode has the optimum welding performance.The capability of graphitization in weld zone of optimized electrode are enhanced,and the content of ferrite is increased,as well as the hardness of weld zone is decreased,due to the reduction of marble,the addition of rutile,and the elevated transition of C and Si form coating.Under the conditions of the welding electricity is 210A and the preheating temperature is 300?,optimized electrodes are used to weld HT250 iron casting,and no white cast iron in the weld zone.The microstructures of the weld and the fusion zone are ferrite and pearlite.The solid phase transformation do not occur in the HAZ,and the matrix structure is still pearlite with a small amount of ferrite.The fusion zones have the highest hardness,which is HB212;the weld zones have lower hardness,which is HB193,all above the welding zone have little diversity with the base metal,machining properties is accessible.