What is special about corten steel?
Weathering steel contains 0.25–0.55% copper, 0.40–0.80% chromium, up to 0.15% phosphorus and some nickel (S355J2WP: Cu 0.25–0.55, Cr 0.40–0.80, P 0.06–0.15). In alternating wet and dry cycles these elements make the rust layer dense and adherent instead of flaky, so after 18–36 months the patina seals the surface and the corrosion rate drops to 1–5 µm per year — a fifth to a tenth of plain S355. No paint, no maintenance, and an even orange-brown surface that architects specify for façades, screens, sculptures, planters, garden edging, bridges, chimneys and shipping-container-style structures. The yield strength is 355 MPa, the same as S355J2, so it is a structural steel, not just a cladding material.
Grades and equivalents
"WP" grades (higher phosphorus) weather faster and more evenly and are the choice for architecture in ≤ 12 mm; "W" grades are for welded structures and thick plate. All are supplied with EN 10204 3.1 showing Cu, Cr, Ni and P.
| Grade | Yield (MPa) | Tensile (MPa) | Impact | Thickness | Notes |
|---|---|---|---|---|---|
| S355J0WP | 355 | 470–630 | 27 J at 0 °C | ≤ 12 mm | High phosphorus; sheet, cladding, art |
| S355J2WP | 355 | 470–630 | 27 J at −20 °C | ≤ 12 mm | Stock grade; export standard |
| S355J2W | 355 | 470–630 | 27 J at −20 °C | ≤ 100 mm | Low P, weldable structural plate, bridges |
| S355K2W | 355 | 470–630 | 40 J at −20 °C | ≤ 100 mm | Heavy structural |
| ASTM A588 Gr. A/B | 345 | 485 min | — | ≤ 100 mm | US structural equivalent of S355J2W |
| ASTM A242 Type 1 | 345 | 480 min | — | ≤ 19 mm | Equivalent of S355J0WP |
| ASTM A606 Type 4 | 345 | 480 min | — | sheet | Cold- and hot-rolled sheet |
Grade pages
The two phosphorus-alloyed sheet grades of EN 10025-5 have their own pages with chemistry, patina timeline, exposure suitability, kg/m² and the month's band: S355J2WP corten sheet (−20 °C impact, the specified grade) and S355J0WP corten sheet (0 °C, the economical twin for cladding and landscaping).
Sizes, thickness and weight
| Thickness | kg/m² | 1 000 × 2 000 (kg) | 1 250 × 2 500 (kg) | 1 500 × 3 000 (kg) | Typical use |
|---|---|---|---|---|---|
| 1.0 mm | 7.9 | 16 | 25 | 35 | Cladding cassettes, screens, laser art |
| 1.5 mm | 11.8 | 24 | 37 | 53 | Façade panels, signage |
| 2.0 mm | 15.7 | 31 | 49 | 71 | Planters, edging, cladding |
| 3.0 mm | 23.6 | 47 | 74 | 106 | Planters, screens, fire pits, sculptures |
| 4.0 mm | 31.4 | 63 | 98 | 141 | Retaining edges, furniture, structures |
| 5.0 mm | 39.3 | 79 | 123 | 177 | Structural cladding, stairs |
| 6.0 mm | 47.1 | 94 | 147 | 212 | Structures, bridges (J2W) |
| 8.0 mm | 62.8 | 126 | 196 | 283 | Structures |
| 10 mm | 78.5 | 157 | 245 | 353 | Structures, columns |
Up to 40 mm (S355J2W) on mill order; widths 1 000 / 1 250 / 1 500 / 2 000 mm; coil 1.5–6 mm on request.
The weathering process — how long to rust and what it looks like
Pre-weathering: we blast the panels and cycle them through wet/dry treatment for 2–4 weeks so they arrive with a uniform orange-brown surface and much less run-off; a clear sealer can be applied for interiors. In permanently wet, marine-splash or de-icing-salt conditions weathering steel keeps corroding — design with drainage and avoid water traps.
| Time | Appearance | Notes |
|---|---|---|
| Delivery | Grey-black mill scale or blasted grey | Blasting (Sa 2½) gives the most even patina |
| 1–4 weeks | Orange, streaky | Run-off stains adjacent surfaces — protect concrete and glass |
| 3–6 months | Orange-brown, even | Surface still dusty to touch |
| 1–2 years | Dark brown, matt | Patina bonding; run-off decreases |
| 2–5 years | Stable chocolate / purple-brown | Corrosion rate 1–5 µm/yr; no more staining |
Is corten steel expensive? Price per ton
Weathering steel costs 2–2.5× plain S235/S355 sheet per ton because of the copper-chromium chemistry and small mill lots, but it saves the paint system (30–60 USD/m² over the building's life) and needs no maintenance. Indicative FOB Istanbul band from our weekly export list, S355J2WP 1–10 mm sheet, below; laser cutting, folding and pre-weathering are quoted per piece.
Bands from our weekly export list (September 2026), FOB Istanbul, full-container quantities, excluding freight and certificates. Firm price per project on RFQ within one working day.
Cutting, folding and fabrication
Laser cutting to 25 mm (clean edges, DXF patterns for perforated screens and signage), plasma to 80 mm, press-brake folding to 6 m (planters, cassettes, edging with return flanges), welding with matching E8018-W / ER80S-G consumables so the weld weathers the same colour. We supply cladding as flat panels or folded cassettes with hidden fixings, and planters and fire pits assembled.
- Laser-cut perforated screens and signage to DXF
- Folded cladding cassettes 1.5–3 mm, hidden-fix
- Planters, edging, retaining panels 3–6 mm, welded corners
- Pre-weathering (2–4 weeks) and clear sealer for interiors
- Bolted structures with weathering-grade fasteners (A325 Type 3)
Design details that matter
Let water run off — no horizontal ledges or pockets; ventilate the back of cladding; keep the steel 100 mm above soil or use a gravel strip; protect adjacent concrete, stone and glass from run-off for the first two years; use stainless or weathering-grade bolts, never zinc-plated; expect 0.5–1 mm section loss over 50 years in the design. Weathering steel is not for permanently wet or marine-splash zones.
Corten vs painted steel vs galvanized vs stainless
| Weathering (corten) | Painted S235 | Galvanized | Stainless 316 | |
|---|---|---|---|---|
| Maintenance | None after patina | Repaint every 8–15 yr | None 20–30 yr | None |
| Look | Rust patina, evolving | Any RAL | Zinc grey | Bright / brushed |
| Marine / wet | Not suitable | Good with system | Good | Best |
| Material cost per ton | 2.0–2.5 | 1.0 + paint | 1.3 | 4.5–5.5 |
| Run-off staining | Yes, first 2 years | No | No | No |
Export and packing
Sheets in packs of 1–3 t on skids, interleaved paper for laser-cut parts, wrapped; pre-weathered panels crated. HS code 7225.40 (alloy flat-rolled, other) or 7208 depending on chemistry declaration.
| Term | Detail |
|---|---|
| MOQ | 2 t; 1 × 20' (≈20 t) for best freight; mixed with other products |
| Incoterms | FOB Istanbul · CIF / CFR Gulf · DAP EU, Balkans, UK, Caucasus |
| Lead time | Stock 5–10 working days; laser/folding +5–7; pre-weathering +3–4 weeks |
| Packing | Packs 1–3 t on skids, paper interleaving, wrapped; crates for finished panels |
| Container / truck | 20' ≈ 20 t · 40' HC ≈ 24 t · truck 22–24 t |
| Documents | Invoice, packing list, EN 10204 3.1 with Cu/Cr/Ni/P, certificate of origin; CE, SASO on request |
| Payment | 30% advance, balance against B/L copy; L/C at sight via London office |
Certificates
EN 10204 3.1 with full chemistry including Cu, Cr, Ni, P (the proof it is weathering steel), certificate of origin; CE per EN 10025-5; SASO/SONCAP on request.
How to order
Send thickness, sheet sizes or DXF files, quantity, finish (mill / blasted / pre-weathered) and port. Reply within one working day with price per ton and per piece, nesting, weight and lead time; stock sheets ship in 5–10 working days.
Standards
- EN 10025-5 (structural steels with improved atmospheric corrosion resistance)
- ASTM A588 / A588M Grade A/B
- ASTM A242
- ASTM A606 Type 4 (sheet)
- EN 10029 / EN 10051 (tolerances)
Grades
Grade data sheets (chemistry, mechanicals, equivalents) are on our reference site: S355J2 (base structural) · S355J2W (Corten B)
Frequently asked questions
What is special about corten steel?
Its copper-chromium-phosphorus chemistry forms a dense rust patina that protects the steel instead of flaking off, so after 2–5 years corrosion nearly stops and no paint is needed. It keeps the 355 MPa strength of structural steel.
Is corten steel expensive?
About 2–2.5× the price of plain S235/S355 sheet per ton (see the band above), but with no paint system and no maintenance it is usually cheaper over 20 years for façades, screens and landscape work.
Is corten steel just rusted steel?
No. Plain steel rust is porous and keeps eating the metal; weathering steel rust is dense, adherent and self-sealing because of the alloying elements. The 3.1 certificate shows the copper and chromium content that makes the difference.
What are the disadvantages of corten steel?
Rust run-off stains concrete, stone and glass in the first 1–2 years; it keeps corroding in permanently wet, marine-splash or de-icing-salt conditions; it is 2–2.5× the cost of plain steel; welds need matching consumables; and the colour evolves for years.
How long does corten take to rust?
Orange within 1–4 weeks outdoors, even brown in 3–6 months, stable dark patina in 2–5 years depending on climate. Pre-weathering before delivery gives a uniform orange-brown from day one.
Which grade should I order — S355J2WP or S355J2W?
S355J2WP (high phosphorus, ≤ 12 mm) for cladding, screens, planters and sculptures — faster, more even patina. S355J2W for welded load-bearing structures, thick plate and bridges. ASTM A588 = S355J2W, A242 = S355J0WP.
Can you laser-cut and fold corten?
Yes — laser to 25 mm and plasma to 80 mm to your DXF, press-brake folding to 6 m, welded planters and cassettes, pre-weathering and clear sealing, all in Dilovası.
Can corten be used near the sea?
Not within the splash zone or where salt spray keeps it wet — the patina never stabilises. Beyond about 2 km from the coast with good drainage it performs; otherwise choose galvanized or stainless.