1. Root Causes of Welding Cracking in Weathering Steel
Cold cracking (delayed cracking): The main risk factor. Residual hydrogen from moisture in welding materials (electrodes, flux) or rust/oil on the steel surface penetrates the weld zone. Combined with high residual stress from welding and the hardenable microstructure (martensite) in the heat-affected zone (HAZ), hydrogen-induced cracking may occur within hours to days after welding.
Lamellar tearing: Common in thick weathering steel plates. Non-metallic inclusions (e.g., sulfides, silicates) in the steel are elongated during rolling, forming weak planes. When welding thick plates, high tensile stress perpendicular to the rolling direction can cause tearing along these weak planes.
Hot cracking: Rare in weathering steel. It may occur only if the weld pool has excessive sulfur or phosphorus, or if the welding speed is too fast, leading to solidification shrinkage stress in the weld seam.
2. Key Preventive Measures to Avoid Welding Cracking
Pre-welding preparation:
Clean the welding area (20–30 mm on both sides of the joint) to remove rust, oil, moisture, and paint using a wire brush or grinder-this reduces hydrogen sources.
Dry welding electrodes (e.g., low-hydrogen electrodes E7018-G) at 300–350°C for 1–2 hours before use to eliminate moisture.
Preheat thick plates (≥16 mm) to 100–150°C; this slows cooling speed, reduces HAZ hardness, and promotes hydrogen diffusion.
Welding process control:
Use low-heat-input welding methods (e.g., shielded metal arc welding, gas metal arc welding) with moderate welding speed to avoid overheating the HAZ.
Adopt multi-layer, multi-pass welding to distribute heat evenly and reduce residual stress; avoid continuous welding of long seams.
Post-weld treatment:
Perform stress relief annealing (heat to 550–650°C, hold for 1–2 hours per 25 mm thickness, then cool slowly) for thick plates or high-stress components (e.g., welded weathering steel signs, planters). This eliminates residual stress and reduces hydrogen trapping.
Conduct a post-weld hydrogen bake-out (heat to 200–250°C for 2–4 hours) for components sensitive to cold cracking to accelerate hydrogen escape.
3. Weldability of Common Weathering Steel Grades
SPA-H (JIS standard): Low carbon content (≤0.12%), no preheating required for plates ≤12 mm; preheating recommended for thicker plates.
A588 (ASTM standard): Designed for welding, with low cracking tendency when proper procedures are followed.
Q235NH (Chinese standard): Similar weldability to SPA-H, suitable for most conventional welding methods.
