1. Select Appropriate Welding Materials
Match the corrosion resistance：Use welding consumables (electrodes, wires) designed for weathering steel, such as E71T-8-W2 (flux-cored wire) or E6013-W (electrode) in AWS standards, or equivalent grades in other standards (e.g., EN 16002). These contain alloying elements (Cu, Cr) to ensure the weld metal forms a protective patina similar to the base metal.
Avoid ordinary consumables：Do not use standard carbon steel welding materials (e.g., E6010, E7018) unless specified, as they will reduce the weld zone's corrosion resistance, leading to premature rusting.
2. Control Welding Parameters
Heat input：Excessive heat input (high current, slow travel speed) can cause:
Grain coarsening in the heat-affected zone (HAZ), reducing toughness.
Burn-off of alloying elements (especially P, Cr) in the weld, weakening corrosion resistance.
Recommended heat input: Generally 15–35 kJ/cm (adjust based on material thickness).
Interpass temperature：For thick plates (≥12mm), control interpass temperature below 250°C (or as specified by the welding procedure) to prevent HAZ embrittlement.
3. Pre-Welding Preparation
Clean the base metal：Remove oil, paint, rust, or oxide layers within 20–30mm of the weld joint using wire brushes, grinders, or chemical cleaning. Contaminants can cause porosity or reduce weld adhesion.
Avoid preheating (unless necessary)：SPA-H has good weldability at room temperature. Preheating (above 150°C) is only required for thick plates (>25mm) or in cold environments (<0°C) to prevent cold cracking. Over-preheating may degrade corrosion resistance.
4. Post-Welding Treatment
No mandatory heat treatment：Unlike high-strength steels, SPA-H typically does not require post-weld annealing or stress relief, as this can alter the patina-forming ability. Stress relief (if needed for thick sections) should be done at ≤620°C to avoid alloy element diffusion.
Surface treatment for corrosion resistance：
Remove welding spatter, slag, and oxides using grinding or wire brushing to ensure uniform patina formation across the weld and base metal.
For critical applications (e.g., coastal bridges), apply a weathering steel primer to the weld zone to accelerate patina development and prevent uneven corrosion.
5. Welding Methods
Suitable processes：SMAW (stick welding), GMAW (MIG), and FCAW (flux-cored arc welding) are preferred. Avoid oxy-fuel welding, as it produces excessive heat and may contaminate the weld.
Shielding gas：For GMAW, use Ar + 2–5% CO₂ shielding gas to reduce porosity and ensure good weld shape.
6. Avoid Welding Defects
Porosity：Common in SPA-H due to its P content. Ensure clean materials, proper shielding gas flow, and avoid moisture in fluxes/electrodes.
Cold cracking：Though rare, it may occur in thick sections or high-humidity environments. Use low-hydrogen welding consumables (storage in dry ovens) and control cooling rates.
Undercut or incomplete fusion：These create crevices where corrosion can initiate. Ensure proper torch angle and travel speed.
7. Patina Formation Consistency
The weld zone and base metal must form a uniform patina over time. Differences in alloy content or surface finish between them can cause "galvanic corrosion" (the less weather-resistant area corrodes faster).
After welding, if the weld surface is uneven or oxidized, lightly grind it to match the base metal's roughness, promoting uniform patina development.
