Abstract: In this paper,three effects of carbon on the quality of pure nickel electrode for welding cast iron were investigated:1) the effect on the hot-cracking susceptibility;2) the effect on the porosity formation,and 3) the effect on the contraction stress of the weld metal.The optimum carbon content of the weld metal was determined.Any carbon content higher or lower than the optimum value will result in reduced hot-cracking resistance.The porosity formation and contraction stress docrease with the increase of carbon content.The reasons for being so were discussed.