1. Pre-Welding Preparation
(1) Material Cleaning
Remove mill scale, rust, oil, and moisture using grinding, brushing, or degreasing solvents.
Avoid chlorinated cleaners (risk of cracking).
(2) Joint Design & Edge Preparation
Use V-groove, U-groove, or bevel joints for thick plates (>6 mm).
Maintain a root gap of 2–4 mm for proper penetration.
(3) Preheating (If Required)
Preheat to 100–150°C for:
Thick sections (>20 mm).
Ambient temperatures below 5°C (41°F).
High restraint conditions.
No preheating needed for thin plates (<12 mm) in mild climates.
2. Welding Methods & Consumables
(1) Recommended Processes
| Welding Method | Best For | Notes |
|---|---|---|
| Shielded Metal Arc Welding (SMAW/MMAW) | Field welding, repairs | Use low-hydrogen electrodes |
| Gas Metal Arc Welding (GMAW/MIG) | High productivity, thin plates | Requires shielding gas (Ar + CO₂ mix) |
| Flux-Cored Arc Welding (FCAW) | Thick plates, outdoor welding | Self-shielded or gas-shielded options |
| Tungsten Inert Gas (GTAW/TIG) | Precision welding, root passes | Best for thin sheets & critical joints |
(2) Filler Metal Selection
Match weathering properties (use filler with Cu, Cr, Ni for corrosion resistance):
AWS A5.1 E7018 (SMAW) – Low-hydrogen, general-purpose.
AWS A5.18 ER70S-6 (GMAW) – For MIG welding.
AWS A5.20 E71T-1 (FCAW) – For flux-cored welding.
Special weathering fillers (e.g., S355J0W-type wires for EN standards).
3. Welding Parameters
| Process | Current (A) | Voltage (V) | Travel Speed | Shielding Gas (If Applicable) |
|---|---|---|---|---|
| SMAW | 90–140 (3.2 mm) | 22–28 V DC+ | Medium | N/A |
| GMAW | 150–220 (1.2 mm) | 22–28 | Fast | 75% Ar + 25% CO₂ |
| FCAW | 180–250 (1.2 mm) | 24–30 | Medium | CO₂ or self-shielded |
| GTAW | 80–150 (2.4 mm) | 10–15 | Slow | 100% Argon |
4. Post-Welding Treatments
(1) Slow Cooling
Allow the weld to cool naturally (avoid rapid quenching).
For thick sections (>25 mm), use post-heating (200–250°C) to reduce residual stress.
(2) Stress Relief (If Needed)
Heat to 550–600°C for 1 hour per 25 mm thickness (for critical applications).
(3) Surface Finishing for Corrosion Resistance
Grind weld seams smooth to promote even patina formation.
Avoid paint or coatings unless necessary (weathering steel relies on rust layer).
5. Common Welding Defects & Prevention
| Defect | Cause | Solution |
|---|---|---|
| Hydrogen Cracking | Moisture in electrodes, fast cooling | Use low-H electrodes, preheat, slow cooling |
| Porosity | Contaminated base metal, improper gas shielding | Clean joints, check gas flow |
| Lamellar Tearing | High restraint, poor joint design | Use buttering layers, reduce stress |
| Reduced Corrosion Resistance | Wrong filler metal | Use weathering-compatible consumables |
