Abstract: Using amicro-alloying cast iron electrode the relationship between preheat temperature and microstructure and properties of joint were investigated by backing welding with low-current and then continuous welding with high-current.The results showed that the micro-alloying cast iron electrode has strong graphitizing ability and the weld metal had a little chilling tendency.The applied welding process can effectively decrease the depth of fusion zone and suppress the precipitation of cementite in fusion zone at a great extent.Thus the welding with the micro-alloying cast iron electrode can be realize at ambient temperature.When the preheated temperature is less than 200℃, the homogeneous weld can be obtained which has the same microstructure and properties as base metal.With the increase of the preheat temperature, the graphite morphology in weld changes from spotted graphite to rosette graphite to flake graphite. The contents of graphite and ferrite increase, while the hardness of the weld decreases.If the preheated temperature reaches to 200℃, the microstructure of the weld consists of pearlite, ferrite, flaky graphite and rosette graphite, and the microstructure of fusion zone consists of pearlite, small shiver ferrite and undercooled graphite. The welded joint has excellent mechamical properties.