1. Key Differences in Weather Resistance
| Comparison Dimension | Hot-Rolled Weathering Steel Plates | Cold-Rolled Weathering Steel Plates |
|---|---|---|
| Surface Texture & Patina Nucleation | Rough surface with natural mill scale (a thin iron oxide layer formed during hot rolling). The rough texture provides abundant nucleation sites for patina formation, allowing a dense, protective patina to form quickly and evenly in outdoor environments. | Smooth, clean surface (no mill scale-removed during pickling before cold rolling). The smooth texture reduces nucleation sites, slowing down the initial patina formation rate; the patina layer may be thinner and less uniform in the early stage. |
| Patina Maturation Speed | Fast: Natural patina matures (reaches optimal protective thickness of 0.08–0.15 mm) in 6–12 months in humid environments. | Slow: Natural patina maturation takes 12–24 months in the same environment; the initial rust layer is more prone to unevenness (light spots or thin areas). |
| Long-Term Corrosion Resistance | Consistent: Once the patina matures, its corrosion resistance is equivalent to cold-rolled plates-the core alloy elements ensure the patina's density and adhesion. | Consistent: After full patina maturation, the protective effect matches hot-rolled plates; the smooth surface does not affect long-term performance. |
| Susceptibility to Early Corrosion | Low: The mill scale acts as a "precursor" to patina, reducing the risk of localized pitting in the early stage. | Slightly higher: The smooth surface is more likely to trap moisture in small crevices (e.g., from processing scratches), leading to minor localized rust before patina matures. |
2. Root Causes of the Difference
Surface Roughness: Hot-rolled plates have a rough, uneven surface that promotes the formation of a continuous patina layer; cold-rolled plates' smooth surface delays patina nucleation.
Residual Stress: Cold rolling introduces residual tensile stress in the steel's microstructure (from room-temperature plastic deformation). This stress can accelerate minor localized corrosion in the early stage, though it does not affect the mature patina's protective ability.
3. Measures to Eliminate the Weather Resistance Gap
Artificial Patina Acceleration: Apply a patina accelerator after sandblasting (to create a rough surface). This shortens the maturation period to 2–4 weeks, achieving a uniform, dense patina quickly.
Stress Relief Annealing: Heat cold-rolled plates to 200–300°C and hold for 1–2 hours to eliminate residual stress, reducing the risk of early localized corrosion.
Post-Patina Sealing: Apply a transparent breathable fluorocarbon sealant after patina maturation-this locks in the protective layer and ensures long-term weather resistance consistency between the two types of plates.
4. Application Recommendations Based on Weather Resistance
Outdoor structural/decorative applications (no pre-treatment): Choose hot-rolled plates-they form protective patina faster and have lower early corrosion risk.
Precision thin-gauge applications (e.g., decorative nameplates, lightweight panels): Choose cold-rolled plates-pair them with artificial patina acceleration to compensate for slower natural maturation.
