Post-Heating Processes E7018

Base Metal Matching and Preheating/Post-Heating Processes

Base Metal Suitability
E7018 electrodes are primarily used for welding low-alloy high-strength steels (e.g., Q345, Q390, ASTM A572 Gr.50), as their weld strength (≥482MPa) matches these materials.

Not recommended for thin low-carbon steel (thickness ＜3mm): Risk of burn-through or poor fusion due to current control issues. E6013 (acidic electrodes) are more suitable for thin low-carbon steel.

When welding higher-strength steels (e.g., Q460, ASTM A514), verify if weld strength meets design requirements; perform a Welding Procedure Qualification Record (PQR) if necessary.

Preheating Requirements
Preheating is critical for preventing cold cracks. Determine preheating temperature based on base metal thickness, carbon equivalent (CE), and ambient temperature:

For base metal thickness ＞12mm, ambient temperature ＜0℃, or CE ＞0.45%, preheating temperature is recommended at 80~150℃.

For thick plates (＞25mm) or high-constraint structures (e.g., pipe circumferential seams), increase preheating to 150~200℃.

Preheat uniformly (using flame or electric heating) to ensure the groove and 100mm on both sides reach the target temperature, verified with a thermometer.

Post-Heating and Hydrogen Relief
For structures under dynamic loads, low-temperature conditions, or high constraint, post-weld hydrogen relief is required:

Process: Heat to 250~350℃, hold for 1~2 hours (increase holding time by 1 hour for every additional 25mm thickness), then cool slowly to room temperature.

Purpose: Accelerate hydrogen diffusion from the weld and heat-affected zone (HAZ) to avoid delayed cracks (low risk for low-hydrogen electrodes but critical under high constraint).

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