Five Types of Cast Iron for Ease of Welding

Gray

• Gray iron is the most common kind of cast iron, the kind you find in skillets and similar household tools. Gray iron includes large flakes of graphite due to the casting process, which reduces ductility and makes it more brittle than other kinds of iron. Although it can be machined well and molds easily, gray iron doesn't heat and elongate the way you want iron to for welding. According to information at ESAB Cutting and Welding, it's a poor choice for welding projects as compared to steel but is better than most other kinds of iron.

Ductile

• Also called nodular or spheroidal graphite iron, ductile iron forms spheres of graphite during the casting process. Although it creates advantages for casting, the formations make welding ductile iron together challenging. According to an article at Ductile.org, welding ductile iron is easiest with an oxyacetyline torch using a process developed in the late 1960s.

Compacted Graphite

• Metallurgically, this type of cast iron splits the difference between gray and ductile irons. The graphite structures formed during casting are blunt flakes that interconnect for greater durability. However, information at FoundryGate.com lists this as a kind of cast iron suitable only for repair and finishing work. It won't work for joint welding.

Cast White

• Cast white, or malleable, iron is heat-treated at above 1,650 degrees Fahrenheit after being removed from its mold -- making the graphite form as irregular nodules throughout the iron. According to ESAB Cutting and Welding, you can't weld cast white iron, but you can heat it with a welding torch to the point that it actually changes to gray iron -- meaning you can fusion weld with it at the joints while keeping its durability on the unwelded sections of metal.

White

• White iron gets put through a rapid cooling process, which creates iron carbide instead of graphite during its production. This makes the metal brittle, but with high compression strength and durability under normal wear. Cogs and other machine parts that receive compression and wear often get cast with a surface of white iron. Even so, WeldingTechnologyMachines.info recommends against welding with white iron. The same properties that make it resist wear make it unsuitable for welding.