Corten Steel (Weathering Steel): Properties & Applications Guide
Corten steel (also called weathering steel) is a group of steel alloys that develop a stable rust-like patina when exposed to weather. The name ‘Corten’ comes from its two key properties: CORrosion resistance and TENsile strength. Originally developed by US Steel in the 1930s, it eliminates the need for painting while providing an attractive, self-protecting surface.
What Is Corten Steel?
Corten steel (also called weathering steel) is a group of steel alloys that develop a stable rust-like patina when exposed to weather. The name ‘Corten’ comes from its two key properties: CORrosion resistance and TENsile strength. Originally developed by US Steel in the 1930s, it eliminates the need for painting while providing an attractive, self-protecting surface.
How the Protective Patina Works
Unlike regular steel that rusts through, weathering steel forms a dense, protective oxide layer (patina) on its surface. This patina develops through wet-dry cycling and acts as a barrier against further atmospheric corrosion. The alloying elements — copper (0.25-0.55%), chromium (0.40-0.65%), phosphorus (0.04-0.12%), and nickel (0.25-0.40%) — accelerate patina formation and stabilize it.
Key Grades & Standards
ASTM A588 Gr.A/B (yield 345 MPa) is the most common structural weathering steel. ASTM A242 Types 1 & 2 (yield 250-345 MPa depending on thickness) is used for lighter structural applications. ASTM A606 Types 4 & 5 (yield 345 MPa) is used for sheet and strip products. European equivalent: EN 10025 S355J0WP/S355J2WP. These grades offer 4-8× better atmospheric corrosion resistance than carbon steel.
Patina Development Timeline
The patina development process takes 18-36 months in typical outdoor conditions: Year 1: steel surface turns from metallic to dark brown/black with active rusting. Year 2: patina stabilizes to a warm orange-brown, corrosion rate drops significantly. Year 3+: fully stabilized deep brown patina, minimal further color change. The patina development is accelerated by acid rain and slowed by constant moisture or salt spray.
Design Considerations & Limitations
Weathering steel requires specific design considerations: avoid water traps (ensure drainage), maintain ventilation behind panels, keep away from saltwater environments (chlorides break down the patina), and account for runoff staining on adjacent materials (concrete, glass). It should not be used in: marine splash zones, heavily polluted industrial atmospheres with high sulfur, or environments with constant moisture exposure.
Weathering Steel Supply from CoreMetal
CoreMetal supplies weathering steel plates, sheets, and structural sections in ASTM A588, A242, and A606 grades. Available in thickness 1.5-50mm, width up to 2500mm, length up to 12000mm. We also supply Corten steel for architectural facade, bridge, and sculpture applications. Contact Tracy at tracy@coremetalsteel.com for weathering steel specifications and pricing.
About Xi’an Coremetal Steel Co., Ltd.
CoreMetal is a leading Chinese steel supplier specializing in carbon steel, stainless steel, galvanized products, aluminum, and specialty alloys. With ISO 9001 certification and export experience to 60+ countries, we provide competitive pricing and reliable delivery for projects of all sizes. Contact Tracy at tracy@coremetalsteel.com or +86 18291910632 for inquiries.