How To Use Cast Iron Welding Rods？

Cast iron welding electrodes, due to their high carbon content, uneven microstructure, low strength, and extremely poor plasticity, are materials with poor weldability, making them highly prone to cracking during welding. The extremely rapid cooling rate after welding easily leads to the formation of white cast iron, causing difficulties in machining. To achieve satisfactory results in welding and repairing cast iron, it is essential to adhere to the principle of "30% material, 70% process," meaning that not only is the selection of welding electrodes crucial, but also the adoption of appropriate welding methods is paramount.

The following welding processes are recommended for reference when welding and repairing cast iron:
 

• Workpiece cleaning: Thoroughly remove oil, rust, moisture, and other impurities from the welding area; for cast iron parts used in high-temperature or steam environments for extended periods, also remove the surface carbon-depleted layer and oxide layer.
• Beveling and crack arresting holes: Prepare U-shaped or V-shaped bevels according to the defect shape, and drill crack arresting holes at both ends of the crack to prevent crack propagation.
• Preheating: For thick or large workpieces or applications with high requirements, preheat to 300–600℃ (the specific temperature depends on the size of the workpiece) to reduce welding stress.

• Drying: Before use, the welding electrodes should be baked at approximately 150℃ for 1–2 hours to remove moisture from the coating.
• Selection: Commonly used cast iron welding electrodes include Z308 (pure nickel) and Z508 (nickel-copper), selected according to the composition of the base metal and strength requirements; for general non-load-bearing parts, the lower-priced 506 welding electrode can also be used.

• Current and Polarity: Use DC positive (DC+) or AC/DC dual-purpose; the current should be low, for example, 90–100A for φ3.2mm electrodes and 130–160A for φ4mm electrodes.
• Arc and Electrode Movement: Maintain a short arc and narrow weld bead; each weld bead should not exceed 50mm in length, and the electrode oscillation amplitude should not exceed 1.5 times the electrode diameter.
• Segmented Welding: Long welds should use skip welding, back-and-forth welding, or symmetrical welding to avoid heat concentration.

• Hammering: Immediately after each pass, lightly tap the weld with a small hammer until the weld ripples disappear to release stress.
• Interpass Temperature: Wait for the weld temperature to drop below 60℃ before welding the next pass.
• Cut-off: Fill the crater to prevent cracking at the cut-off point.

• Heating and slow cooling: After welding, heat the area around the weld within 200mm to 300–350℃ and hold for 30 minutes. Then cover with asbestos powder and cool slowly.
• Machining: If machining is required, it is recommended to anneal or shot peening the surface after welding to improve machinability.

• Wear a protective mask and gloves to prevent arc burns and metal spatter.
• Ensure good ventilation and avoid inhaling welding fumes.