1. Core Requirement: Match Corrosion Resistance and Mechanical Properties
Weld metal composition: It should have copper content ≥0.2% (critical for patina formation), plus appropriate Cr (0.3–1.0%) and Ni (0.2–0.5%) to match the base metal's weathering performance.
Mechanical property matching: The weld metal's yield strength and tensile strength should be within ±10% of the base metal (e.g., for SPA-H steel, weld metal yield strength ≥335 MPa, tensile strength 490–610 MPa).
2. Mandatory Requirement: Use Low-Hydrogen Welding Materials
Shielded Metal Arc Welding (SMAW): Choose low-hydrogen electrodes (AWS classification E7018-G or E8018-G for high-strength weathering steel). These electrodes have a lime-based coating that reduces diffusible hydrogen content to ≤5 mL/100g (per AWS A5.5 standard).
Critical pre-use step: Bake the electrodes at 300–350°C for 1–2 hours to remove moisture, then store them in a heated electrode holder (100–150°C) during welding to prevent reabsorbing moisture.
Gas Metal Arc Welding (GMAW/MIG/MAG): Use solid wires with low hydrogen content, such as ER70S-G or ER80S-G (alloyed with Cu/Cr/Ni). Avoid wires with high moisture absorption or oily coatings.
Flux-Cored Arc Welding (FCAW): Select low-hydrogen flux-cored wires (e.g., E71T-8-G), and ensure the flux core is dry (no caking or moisture).
3. Shielding Gas Requirements for Gas Shielded Welding
Recommended gas mixture: 90–98% Argon + 2–10% CO₂ (MAG welding). This mixture balances arc stability, weld penetration, and corrosion resistance-pure argon is not recommended, as it may cause poor fusion and reduced weld strength.
High-purity gas requirement: The shielding gas must have a purity ≥99.99% to avoid contamination by oxygen, nitrogen, or moisture (which can cause porosity and reduce corrosion resistance).
Wind protection: For outdoor welding, use a windscreen to prevent shielding gas dissipation, especially when the wind speed exceeds 2 m/s (for MAG welding) or 0.5 m/s (for GTAW welding).
4. Special Requirements for Thick Plates and Low-Temperature Welding
For plates ≥20 mm thick: Use welding materials with higher toughness (e.g., electrodes with Charpy V-notch impact energy ≥27 J at -20°C) to avoid brittle fracture in the heat-affected zone (HAZ).
For welding in low-temperature environments (<5°C): Choose low-hydrogen materials with even lower diffusible hydrogen content (≤3 mL/100g) and increase preheating temperature to 150–200°C to slow HAZ cooling.
5. Avoid Using Ordinary Carbon Steel Welding Materials
Weld zones that rust faster than the base metal.
Uneven patina formation, damaging the component's appearance and service life.
