Welding Cast Iron to Mild Steel, with Stick Electrode

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:

1. Clean the Surface Thoroughly: Remove all contaminants, grease, surface impurities, and rust from both parts.
2. Preheat (if practical): Mild preheat (200-400°F or 100-200°C) of cast iron often reduces cracking risk.
3. Use Short Weld Passes (Stitch Welding): Keep the area cool; shorter weld beads with pauses or peening in between passes benefit crack prevention.
4. 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.