The best and most widely recommended welding rod for welding cast iron to mild steel is a nickel-based rod, specifically the Nickel-Iron type (also called ENiFe-CI, 55% Nickel electrode).
Recommended Welding Rod:
ENiFe-CI (Nickel-Iron Electrode)
- Common Trade Names:
- Lincoln Electric ENiFe-CI (55% Nickel)
- Harris NI-55
- Hobart 770509 Nickel-55
- Washington Alloy NI-55
- Composition: Approximately 55% nickel, balanced with iron and minimal trace elements.
- Properties and Benefits:
- Offers excellent ductility and strength.
- Good weldability with minimal preheat requirements.
- Reduced risk of cracking because of its flexible weld metal.
- Handles thermal expansion differences between materials effectively.
Why ENiFe-CI Over Other Electrodes?
- Flexibility and Crack Resistance:
Nickel-based electrodes have excellent ductility, which helps prevent cracking when welding cast iron due to the brittle nature of cast iron. - Thermal Expansion Compatibility:
Cast iron and mild steel have different expansion and contraction rates. Nickel-Iron electrodes help manage these differences without cracking, providing greater reliability and durability in the joint. - Easy to Use:
Provides easier welding characteristics, less sensitive to minor fluctuations and imperfections, and less need for extensive pre/post-heat treatments.
Alternative Electrodes (Less Ideal, but Viable):
- Nickel 99 (Pure Nickel, ENi-CI): Good ductility, but slightly softer and not as strong as ENiFe-CI. Best used for repairs of pure cast iron rather than dissimilar welds.
- Mild Steel Electrodes like E7018 or E6013: Cheaper option, but higher risk of cracking and potentially weaker joints due to thermal expansion issues. Mostly suitable for simpler, non-critical joints with proper pre-heat and slow cooling conditions.
Recommended Procedures and Tips:
- Clean the Surface Thoroughly: Remove all contaminants, grease, surface impurities, and rust from both parts.
- Preheat (if practical): Mild preheat (200-400°F or 100-200°C) of cast iron often reduces cracking risk.
- Use Short Weld Passes (Stitch Welding): Keep the area cool; shorter weld beads with pauses or peening in between passes benefit crack prevention.
- Allow Controlled Cooling: Cooling slowly down helps relieve internal stresses, minimizing cracking likelihood.
Conclusion:
The best general choice as a welding rod for joining cast iron to mild steel is a nickel-based electrode—specifically the Nickel-Iron (ENiFe-CI, Nickel-55) type—for best quality, strength, and crack prevention.