1. Thin Gauges (1.6–6 mm): Excellent Weldability
No mandatory preheating needed, thanks to low heat retention and a small heat-affected zone (HAZ).
Recommended processes: GMAW/MIG and FCAW (for fast, precise heat control to avoid burn-through); SMAW is usable with skilled operation.
Only minimal surface prep is required; no post-weld heat treatment needed (weld distortion is the main concern).
2. Medium Gauges (6–25 mm): Good Weldability
Preheating is optional (80–120°C) only for cold conditions (≤5°C) or tight joint fit-ups, to prevent hydrogen-induced cracking (HIC).
Recommended processes: SMAW, GMAW, and FCAW are all suitable (GMAW/FCAW for productivity, SMAW for on-site welding).
Light weld bead grinding may improve patina uniformity; no stress relief treatment required.
3. Thick Gauges (25–100 mm): Reduced Weldability (Strict Controls Needed)
Mandatory preheating (100–150°C for 25–50 mm; 150–200°C for >50 mm) to slow cooling, avoid brittle microstructures, and reduce HIC risk.
Recommended process: SMAW (ideal for multi-pass welding and heat control); oxy-fuel welding is avoided.
Critical structural joints may need stress relief heat treatment (550–650°C); weld/HAZ grinding is required for patina uniformity and stress reduction.
4. Universal Welding Rules for All Thicknesses
Always use weathering steel-matched fillers (e.g., E7018-W, ER70S-W) to preserve corrosion resistance in welds.
Thoroughly clean the weld zone (20 mm on each side) to remove contaminants and prevent porosity.
Control heat input: low heat for thin gauges (prevent burn-through) and controlled multi-pass heat for thick gauges (manage cooling rates).
