Key Welding Considerations for SPA-H Weathering Steel
Recommended processes: Shielded Metal Arc Welding (SMAW, stick welding), Gas Metal Arc Welding (GMAW, MIG welding), and Flux-Cored Arc Welding (FCAW) are the most widely used for SPA-H, as they provide good control over the weld pool and minimize oxidation.
Avoid for critical applications: Oxy-fuel welding is not recommended, as it can cause excessive grain growth in the heat-affected zone (HAZ) and reduce corrosion resistance.
The filler metal must match SPA-H's alloy composition (Cu, Cr, P) to ensure the weld joint forms the same protective patina as the base metal.
Recommended fillers: For SMAW, use E7018-W (weathering steel electrode); for GMAW/FCAW, use ER70S-W (solid wire) or E71T-W (flux-cored wire). These fillers contain the necessary copper and chromium to promote patina formation in the weld zone.
Avoid plain carbon steel fillers: Using standard carbon steel electrodes (e.g., E7018) will result in a weld joint with no weathering resistance, leading to rapid, uneven rusting at the weld.
Preheat: SPA-H has a low carbon content (≤0.12%), so preheating is only required for thick sections (≥25 mm) or in cold welding environments (≤5°C) to prevent hydrogen-induced cracking. A preheat temperature of 100–150°C is sufficient.
Post-weld treatment: No stress relief heat treatment is needed for most applications. For thick welds or critical structural joints, a light grind of the weld bead to a smooth finish can help promote uniform patina formation across the joint.
Remove mill scale, rust, oil, grease, and paint from the welding area (at least 20 mm on either side of the joint) using a wire brush, sandblasting, or grinding. Contaminants can cause porosity in the weld and disrupt patina formation later.
Avoid using chlorinated solvents for cleaning, as residual chlorine can cause corrosion in the weld zone.
The weld joint and heat-affected zone (HAZ) will form a patina slightly slower than the base metal, but with the correct filler metal, it will eventually develop a uniform reddish-brown finish that matches the rest of the steel.
For architectural applications where immediate aesthetic uniformity is required, the weld zone can be lightly sandblasted after welding to accelerate patina formation.
