Post-Welding Treatment for Q500NH Weathering Steel
For most applications, Q500NH does not require mandatory post-weld heat treatment (PWHT), but special considerations apply depending on usage conditions:
General Fabrication (Non-Critical Structures)
No PWHT needed if:
Preheat (100–150°C) was properly applied
Low-hydrogen electrodes were used (e.g., AWS E7018)
Welding heat input was controlled (<2 kJ/mm)
Critical Applications (High Stresses/Low Temperatures)
Stress Relief (Optional but Recommended):
550–600°C for 1–2 hours to reduce residual stresses
Especially for thick sections (>25 mm) or dynamic loads
Corrosion Performance Optimization
Patina Restoration:
After welding, the heat-affected zone (HAZ) loses its weathering resistance.
Natural repatination occurs over 6–12 months, or accelerate it with:
Weathering accelerants (e.g., dilute hydrogen peroxide spray)
Artificial aging (exposure to cyclic wet/dry conditions)
When PWHT Is Mandatory
If the welded structure will operate below -20°C (to restore impact toughness)
For pressure vessels or fatigue-loaded components (per EN 1993-1-10)
Key Recommendations:
Always remove slag and clean weld zones to prevent crevice corrosion.
For architectural applications, grind welds smooth to ensure uniform patina development.
In marine environments, consider applying weathering-resistant primers on weld seams.
