Which Welding Rod for Cast Iron Repair
Cast iron contains 2-4% carbon, roughly 10 times more than steel. This high carbon content makes it extremely brittle and prone to cracking during and after welding. The correct rod, proper preheat, and slow cooling are all required for a successful repair. Standard mild steel rods alone are not ideal for cast iron.
Recommended Electrodes
E7018
Acceptable for non-critical cast iron repairs where the weld will be under compression, not tension. Low-hydrogen deposit reduces cracking risk compared to other mild steel rods. Use lowest practical amperage and short beads.
E6013
For very minor cosmetic cast iron tack welds only. Light penetration means less dilution into the casting. Not recommended for any load-bearing repair.
Technique Tips
Preheat the entire casting to 300-500F before welding. Use short beads no longer than 1 inch. Peen each bead while still red to relieve stress. Let each bead cool until you can touch it before welding the next. Allow the casting to cool slowly by wrapping in an insulating blanket or burying in dry sand. Drill a small hole at each end of any crack to prevent propagation before welding. For best results, use a dedicated nickel cast iron rod (ENi-CI or ENiFe-CI) which are purpose-built for this application.
Common Mistakes to Avoid
Welding cast iron cold. Without preheat, thermal shock creates new cracks faster than you can repair old ones. Using E6011 or E6010, which deposit high-carbon diluted weld metal that is even more brittle than the casting. Running long continuous beads that overheat the surrounding area. Quenching or rapid cooling after welding, which guarantees cracking.
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