AC cold arc welding process with AWS E Ni-CI and NiFe-CI is sometimes used to repair damaged cast iron parts in diesel engine room. But if some difference in hardness on welding zones, repaired parts would be cracked in a short. To overcome this default. this study is performed on varying preheating temperature of welding parts, selecting welding rod etc. Experimental results showed that difference in hardness on welding zones at $200^{circ}C$ was less than $100^{circ}C$ and less low current than high current. From this study we could conclude that repair welding at $200^{circ}C$ preheating and low current as possible as welding in damaged cast iron parts was a little difference in hardness on welding zones.