Physical isolation barrier
The mature patina is a dense, firm oxide layer tightly bonded to the steel surface (not a loose rust layer), composed of stable iron oxides and alloy compounds (from Cu/Cr/Ni in ASTM A606). It physically blocks air, moisture, and mild atmospheric corrosive media from contacting the underlying base metal, fundamentally slowing down oxidation and corrosion.
Ultra-low corrosion rate
Once the patina matures (12–24 months outdoors), the corrosion rate of the underlying ASTM A606 steel drops to an extremely low level (≤0.03mm/year) in normal temperate environments-far lower than ordinary carbon steel, and the steel substrate will not experience significant thinning or damage even after decades of outdoor use.
Self-repairing protective ability
If the patina suffers minor scratches or wear (exposing a small area of bare steel), the alloy elements in the exposed ASTM A606 steel will react with air and moisture to rapidly form a new patina layer at the damaged site, automatically repairing the protective barrier and preventing further corrosion from spreading.
Stable protection in normal environments
In standard urban, garden, suburban and mild coastal areas (far from high salt spray), the patina's protective performance remains stable for life-no additional coatings or rust prevention treatments are needed to maintain its anti-corrosion effect. Only in harsh environments (high-salt coastal/heavy industrial acid mist areas) does it need a transparent sealer to enhance protection (not replace the patina's own function).
