Microstructure And Hardness Of Cast Iron Homogeneous Welded Zone With Cobalt And Nickel Alloyed

In this paper,aiming at the two major problems of chill structure and crack in the homogeneous welding zone of cast iron,the graphitizing elements Co and Ni were directly added into the cast iron welding core to prepare alloyed cast iron homogeneous welding rod.The welding repair tests of gray iron and ductile iron were carried out to analyze the influence of Co,Ni element content and welding process parameters on the microstructure and performance of the weld zone.The research results show that:The microstructure of common cast iron welding core is mainly composed of pearlite,ferrite and graphite,in which the ferrite content is 18%,and the hardness of welding core is HB195.Ni can promote the precipitation of graphite in the welding core and the formation of ferrite.When the Ni content is 0.2%,the ferrite content is 23%and the hardness is reduced to HB170.In the welding core containing 0.2%Ni,with the addition of Co,as the Co content in the welding core increases from 0 to 2.8%,the graphitization effect of Co promotes the ferrite content in the core to increase from 23%to 35%.The solid solution strengthening of Co strengthened the ferrite phase in the weld core.Under the action of Co,the hardness of the solder decreased first and then increased.When the C.o content is 1.6%,the minimum hardness is HB138.The alloyed cast iron homogeneous welding rod with 0.2%Ni and 1.0%Co was used to weld HT250,under the conditions of welding current I=230A,preheating temperature T0=200??300? and air cooling after welding.The obtained weld microstructure consist of ferrite,pearlite and flake graphite,with ferrite content of 36%?45%and weld hardness of HB228?HB240.The microstructure of the fusion zone is composed of pearlite and a small amount of intermittently distributed ledeburite,and the hardness is HB257-HB280.The alloyed cast iron homogeneous electrode containing 0.2%Ni and 1.6%Co was used to weld QT450-10 under the conditions of welding current I=210A,preheating temperature T0=250??500? and air cooling after welding.The obtained weld microstructure consists of ferrite,pearlite and spherical graphite,with ferrite content of 46%-58%and weld hardness of HB235?HB275.There is no chill structure in the fusion zone,and the microstructure is composed of pearlite and ferrite,and the hardness is HB275-HB321.Homogeneous welding of gray iron and nodular iron can be realized by using the developed Co and Ni alloyed cast iron homogeneous welding rod,and the homogeneous welding zone of cast iron with no chill structure and crack,and the microstructure and hardness match the base metal.