Welding Cast Iron Polarity. When using a steel electrode the contraction of the steel weld metal the carbon picked up from the cast iron by the weld metal and the hardness of the weld metal caused by rapid cooling must be considered. They also claim that preheating of the area to be repaired was not necessary though experiences have varied here.
Polarity and settings for welding cast iron You should keep the welder settings at the lowest amperage possible to conduct the weld. Both higher than the cast iron base material. It would first depend on the exact electrode involved and there are many available.
The repairs may be made in the foundry where the castings are produced or may be made to repair casting defects that are discovered after the part is.
The mix of nickel and iron has a lower coefficient of thermal expansion which lowers welding stresses and makes it less prone to cracking. As far as I know you can use either AC or DC polarity to complete the weld of course the final polarity settings depend on the electrode being used. As a result it produces a stronger and more durable weld. To maintain a nice weld use the MIG welder to maintain the lowest feed rate and the lowest current.