Weathering Steel: A Complete Guide to Corten Common Grades

Weathering steel is a group of low-alloy structural steels that develop a stable, protective patina layer when exposed to the atmosphere. This dense oxide film prevents further corrosion, eliminates the need for painting, and extends service life significantly. Corten is the most well-known trade name for weathering steel, widely used in construction, bridges, shipping containers, and architectural facades.

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Product Details

What Is Corten Steel

Corten steel is designed to resist atmospheric corrosion without coating. Its alloying elements — including copper, chromium, nickel, phosphorus and silicon — form a tight, self-repairing oxide layer over time.

It is available in two main types: Cor-Ten A and Cor-Ten B, each serving different thickness and application ranges.

Comparison: Corten A vs Corten B

Property	Cor-Ten A (ASTM A242)	Cor-Ten B (ASTM A588)
Typical thickness	Up to 1/2″ (12.7 mm) thick	Over 1/2″ (12.7 mm) thick
Key characteristic	Higher phosphorus content	Higher strength & weldability
Main standard	ASTM A242	ASTM A588
Typical use	Thin plates, general structures	Heavy plates, structural components

Typical Mechanical Properties (Reference)

Grade	Tensile Strength (MPa)	Yield Strength (MPa)	Elongation
Corten A (A242)	≥ 435	≥ 310	≥ 20%
Corten B (A588)	≥ 485	≥ 345	≥ 18%
S355J2WP (EN)	≥ 490	≥ 355	≥ 21%

How Weathering Steel Works

Under natural outdoor exposure, the steel surface goes through repeated wet-dry cycles.

Alloy elements form a dense, adherent patina
This layer blocks moisture, oxygen and corrosive ions
Corrosion rate slows down dramatically
No painting or frequent maintenance required

Advantages of Weathering Steel

Self-protective patina, no coating needed
Long service life (up to 120 years in proper environment)
Lower lifecycle cost and less maintenance
Good strength, toughness and formability
Unique industrial aesthetic appearance
Eco-friendly, no paint VOCs or repainting waste

Main Applications

Bridges, highway guardrails and steel structures
Shipping containers and transport equipment
Building facades, sculptures and landscape design
Transmission towers, mining trucks and rail wagons
Outdoor industrial facilities and coastal infrastructure

Conclusion

Corten and equivalent weathering steels provide excellent corrosion resistance, reliable mechanical performance and low maintenance cost. Whether under ASTM or EN standards, they are widely recognized as a cost-effective, durable solution for long-term outdoor and structural projects worldwide.