Corten Weathering Steel

Plain English is a quick buyer's guide. Engineer view adds the full property tables, composition and design-for-laser figures.

Overview

Corten is a low-alloy weathering steel: small additions of copper, chromium and nickel (and phosphorus in the WP type) make the surface rust form a tight, stable patina that seals the steel beneath it. Left exposed, it weathers from bare grey to a warm orange-brown over weeks to months, and that patina then slows further corrosion — so unlike ordinary mild steel it needs no paint or galvanising outdoors. It carries the same 355 MPa minimum yield as structural S355, so it is strong as well as decorative. It is the default choice for architectural and landscape work — screens, planters, cladding and signage — where a rusted look and low maintenance are wanted. Where staining of adjacent surfaces or constant wetting is a problem, choose painted or galvanised steel, or stainless, instead.

Best for

Architectural screens, gates and cladding
Garden planters, edging and landscape features
Signage, house numbers and lettering
Fire pits and decorative outdoor structures
Sculpture and feature panels

Less ideal for

Constant-wet, marine or de-iced surroundings
Anywhere patina runoff would stain stonework
Indoor or hidden parts (patina never develops)
Food-contact or hygienic use (use stainless)

Properties

BS EN 10025-5:2019

Physical

Density	7.85	g/cm³
Melting point	~1500	°C
Thermal expansion	12	×10⁻⁶/K
Modulus of elasticity	210	GPa
Thermal conductivity	~52	W/m·K
Electrical resistivity	~0.20	µΩ·m

Mechanical

Yield strength (ReH)	355 min	MPa
Tensile strength (Rm)	470–630	MPa
Elongation A	20 min	%
Impact (Charpy, J0/J2)	27 min	J

S355J0WP / S355J2W, ≤16 mm (typical; figures vary with thickness)

Chemical Composition

BS EN 10025-5 · S355J0WP (1.8945), ladle analysis

Fe Cr Mn Si Cu Ni P C S N

Element		% present
Iron	Fe	Balance
Chromium	Cr	0.30 – 1.25
Manganese	Mn	0.20 – 1.00
Silicon	Si	0.0 – 0.75
Copper	Cu	0.25 – 0.55
Nickel	Ni	0.0 – 0.65
Phosphorus	P	0.06 – 0.15
Carbon	C	0.0 – 0.12
Sulphur	S	0.0 – 0.035
Nitrogen	N	0.0 – 0.009

Formability & Fabrication

Corten cold-forms much like ordinary S355 structural steel: it bends and folds well at sensible radii, with a little more springback than mild steel. It welds readily by MIG and MMA — for fully exposed work use a weathering-grade filler so the weld develops a matching patina, otherwise the joint stays bright while the parent steel rusts down. Machinability is fair, and the surface mill scale should be removed where an even patina is wanted.

Cold working

Good

Bending

Good

Gas welding

Fair

Arc / MIG / MMA

Good

Resistance weld

Good

Brazing

Fair

Soldering

Poor

Machinability

Fair

Recommended filler: a weathering-steel consumable (such as a Cr–Ni–Cu type to EN ISO 14341 / 18276) on exposed work so the weld patinas to match the parent metal; a standard low-carbon filler is fine only where the joint is hidden or will be coated.

Corrosion Resistance

Corten's whole purpose is corrosion behaviour: in ordinary wet-and-dry outdoor cycles the alloying elements make the rust layer dense and adherent, so it self-arrests and protects the steel without paint. That depends on the surface being able to dry out between wettings — in constantly damp, enclosed, marine or salt-laden settings the patina never stabilises and the steel keeps corroding like ordinary mild steel. The orange runoff in the early years can also stain anything it drains onto.

Environment	Suitability
Atmospheric / outdoor (drying)	Excellent
Rural / mild industrial air	Excellent
Sheltered / occasional damp	Good
Coastal / chloride-laden air	Fair
Constant-wet / enclosed	Poor
Salt-water / marine immersion	Avoid

Typical Applications

Architectural screens & cladding Garden planters & edging Signage & house numbers Fire pits & outdoor features Sculpture & feature panels Landscape walls & gabion faces Fences, gates & railings Bridge & structural fascias

Need a part in Corten Weathering Steel? Build it to your exact size for an instant price — or browse our ready-made laser-cut parts.

Build your part → Browse products

Laser Cutting & Ordering

at Metal Parts Direct

Thicknesses we cut

1.5 mm2 mm3 mm4 mm5 mm6 mm8 mm10 mm12 mm

Cut tolerance

±0.25 mm up to 20 mm, ±0.5 mm above

Max part size

1000 × 1000 mm

Max part weight

No maximum

Estimated delivery if ordered today

Friday 28th August 2026 – Monday 31st August 2026

UK-made Laser cut to your spec No minimum order Material certs on request

Design-for-laser quick reference

These are the exact minimums the Part Builder enforces as you design, relative to sheet thickness — so your part and your quote never disagree.

Feature	Minimum
Min hole / bore Ø	0.7 × thickness (min 1 mm)
Min slot / opening width	0.7 × thickness (min 1 mm)
Min web / wall between cuts	0.7 × thickness (min 1 mm)
Min cut-to-edge distance	0.7 × thickness (min 1 mm)

Frequently Asked Questions

Will the orange rust stain my paving or wall?

It can, especially in the first year or two while the patina is settling. Rain washes loose rust off the surface and the orange runoff can stain porous stone, render, concrete and decking below the part. Allow for drainage and a drip gap, keep it clear of light-coloured masonry, or pre-weather the piece before installing so the worst of the bleed has passed.

Do I need to paint or treat Corten?

No — that is the point of it. Left exposed outdoors it forms its own protective patina and needs no paint or galvanising. You can speed up or even the colour with a weathering accelerator, or lock the look with a breathable sealer, but neither is required for the steel to protect itself.

How long does the patina take to develop?

It is gradual. The steel starts bare grey, goes through a patchy yellow-orange over a few weeks, and settles to an even deep brown over several months to a year or more, depending on how wet-and-dry the location is. Repeated wetting and drying drives the process, so a fully sheltered part will weather slowly or unevenly.

Is Corten as strong as ordinary structural steel?

Yes. S355J0WP / S355J2W carry the same 355 MPa minimum yield as standard S355 structural steel, so you get the decorative weathering finish without giving up strength.

Can I use Corten by the sea?

It is best avoided in marine and salt-laden settings. Chlorides stop the patina stabilising, so the steel keeps corroding rather than self-protecting. Near the coast, or anywhere de-icing salt is used, choose painted, galvanised or stainless steel instead.

Will my laser-cut part arrive already rusted?

Usually not — sheet is typically supplied as bare or lightly oxidised steel and the patina develops once the part is outdoors. Expect some surface mill scale and handling marks; the weathering process evens these out as the patina forms.

Equivalents

Also designated

S355J0WP (1.8945) S355J2W+N (1.8965) COR-TEN A COR-TEN B ASTM A588 ASTM A242

Cross-references are indicative and may not be exact equivalents — confirm against the certificate for critical work.

Build your part in Corten Weathering Steel

Pick a shape, set the size, choose Corten Weathering Steel — and get an instant price. Laser-cut to your spec and shipped, with no minimum order.

Build in Corten → Browse products

This data is indicative and provided in good faith from recognised EN standards and industry references. It is not a substitute for the full specification or material certificate; mechanical properties in particular vary with temper, form and dimension. Material supplied will conform to the relevant applicable standards but may differ from these figures. No liability is accepted for actions taken in reliance on this guide. Confirm critical values against the certificate for your delivery.