Q355NH is a general-purpose weathering steel that relies on forming a stable patina for corrosion protection. Its performance changes significantly at low, normal, and high temperatures, so targeted improvement methods are needed.
1. At normal temperature (10–35°C)
This is the optimal environment for patina formation.Improvement measures:
Ensure sufficient wet‑dry cycles (rain + sun) to promote dense patina.
Keep surface clean, free of oil, dust, and cement stains.
Use surface pretreatment (sandblasting, shot blasting) for more uniform patina.
Avoid long‑term contact with water, soil, or wood.
For critical parts, use weathering‑matched welding materials to maintain overall corrosion resistance.
Effect: Patina stabilizes quickly, and long‑term atmospheric corrosion resistance is excellent.
2. At low temperature (below 0°C, winter / cold regions)
Low temperature slows or stops patina formation; snowmelt, deicing salt, and freeze–thaw cycles accelerate corrosion.Improvement measures:
Prevent deicing salt (chloride) contact - it destroys patina.
Keep surface dry during freezing periods.
Apply epoxy primer + polyurethane topcoat if used in coastal or salted road areas.
Use Q355NHD or Q355NHE (better low‑temperature toughness + more stable patina) instead if possible.
Ensure good drainage to avoid water accumulation and freezing on the surface.
Effect: Reduces pitting corrosion and patina damage caused by low temperature and salt.
3. At high temperature & strong sun (above 40°C, summer / hot dry areas)
High temperature accelerates surface oxidation but tends to form loose rust instead of stable patina.Improvement measures:
Avoid long‑term dryness - properly spray water periodically to form wet‑dry cycles.
Prevent excessive dust accumulation, which traps moisture.
For outdoor structures, avoid one‑side long‑term exposure to intense heat radiation.
If used near heat sources, add heat insulation or protective coating to reduce temperature difference corrosion.
Effect: Promotes compact patina instead of powdery rust.
4. In high humidity / rainy / tropical temperature environment
High humidity + high temperature easily causes continuous rusting; patina cannot stabilize.Improvement measures:
Strengthen ventilation to avoid long‑term wet conditions.
Use accelerated patina treatment to quickly form a protective layer.
Apply transparent anti‑rust sealer to reduce rain erosion.
Optimize structure for drainage, no gaps or slots that hold water.
Effect: Prevents excessive rust runoff and local perforation corrosion.
5. Universal methods to improve corrosion resistance of Q355NH
Choose higher‑grade weathering steel (Q355GNH, Q345GNH, SPA‑H) for harsh environments.
Use professional anti‑corrosion coating in non‑atmospheric environments (buried, immersed, soil contact).
Control surface quality during fabrication: no deep scratches, no oil contamination, uniform roughness.
Use matching weathering welding materials to avoid weld corrosion.
