Materials
How to weld cast iron
Quick answer
To weld cast iron: use stick with nickel (ENiFe) rods, low and slow with preheat, filler matched to the parent metal (ENiFe-CI (nickel-iron) rods; plain steel rods crack), and prepare properly — grind the casting skin off, drill small stopper holes at crack ends. The key adjustment vs mild steel: low current for the rod size, many small passes.
Process and filler
Process: stick with nickel (ENiFe) rods, low and slow with preheat. Filler: ENiFe-CI (nickel-iron) rods; plain steel rods crack. Preheat 100–250°C, short staggered beads, peen each pass, cool slowly under a blanket — rushing it cracks the job
Preparation
Grind the casting skin off, drill small stopper holes at crack ends. Fit-up matters more than most beginners expect: a gap you can see daylight through is a gap the filler has to fill, at the cost of heat control.
Amps and approach
Set current by thickness as you would for steel, then apply the adjustment: low current for the rod size, many small passes. Run test coupons first — every cast iron joint tells you loudly when the parameters are wrong.