What Corten B Steel Plate Is
Corten B steel plate is a weathering steel alloy containing controlled additions of copper, chromium, nickel and other elements that give it far better atmospheric corrosion resistance than plain carbon steel. Exposed to the weather, the surface develops a dense, protective rust-like layer, and that layer both produces the characteristic warm brown appearance and blocks further corrosion of the plate underneath. Corten B is the higher-strength, lower-phosphorus member of the weathering steel family: it is stronger and easier to weld than the phosphorus-bearing Corten A, so thicker plate and heavy welded fabrication are its natural territory. It is widely used in architecture, construction, bridges and other outdoor structures, where it removes the need for protective coatings and cuts long-term maintenance.
Key Features
Weather resistance: a stable surface oxide forms outdoors and limits further atmospheric attack.
High strength: minimum 345 N/mm2 yield and 485 N/mm2 tensile strength are maintained as the surface weathers.
Low maintenance: the self-protecting layer means no repainting and lower whole-life cost.
Aesthetic value: the natural rusted tone suits architectural facades, sculpture and landscaping.
Versatility: used for bridges, facades, cladding, containers, outdoor sculpture and general structural work.
Long service life: structures remain sound for decades when detailing allows the surface to dry.
Standards and Equivalent Grades
Corten B is specified around the world through several national systems, and equivalent grades allow the same performance to be sourced from different regions.
| System | Designation | Note |
|---|---|---|
| United States | ASTM A588 / A588M, also ASME SA588 | High-strength low-alloy structural steel with improved atmospheric corrosion resistance; ASTM A588 Grade B is the grade most often equated with Corten B |
| Europe | EN 10025-5:2004 S355J0W and S355J2W | The European weathering grades that correspond to Cor-Ten B; the BS 4360 WR 50 B designation of the older British system has been withdrawn and is now covered by the EN 10025 series |
| Japan | JIS G3125 SPA-H | The Japanese weathering grade used in the same family of applications |
Because the grades come from different systems, the chemistry and mechanical requirements are not identical, and a purchase specification should state the standard, grade and thickness range rather than a trade name alone.
Typical Specifications
| Item | Range |
|---|---|
| Standard grade | ASTM A588 / ASME SA588, EN 10025-5 weathering grades |
| Width | 1500 - 3200 mm |
| Length | 6000 - 12000 mm |
| Thickness | 2 - 460 mm |
| Hot rolled plate size | Thickness 3 - 150 mm, width 900 - 4100 mm, length 3000 - 18000 mm |
Chemical Composition
| Grade | C | Si | Mn | P | S | Cr | Ni | Cu | Al | V |
|---|---|---|---|---|---|---|---|---|---|---|
| Corten B | 0.19 max | 0.30 - 0.65 | 0.80 - 1.25 | 0.035 max | 0.030 max | 0.40 - 0.65 | 0.40 max | 0.25 - 0.40 | 0.020 - 0.06 | 0.02 - 0.10 |
Compared with Corten A, the manganese level is higher, phosphorus is capped at 0.035 %, and vanadium is added; that combination raises strength and weldability while retaining the corrosion chemistry. Copper remains the element that governs the formation of the protective rust layer, and the trace elements listed above are the ones that distinguish a genuine weathering grade from an ordinary structural plate.
Mechanical Properties
| Grade | Yield strength ReL, min | Tensile strength Rm, min | Elongation A50, min |
|---|---|---|---|
| Corten B | 345 N/mm2 | 485 N/mm2 | 19 % |
Under ASTM A588 the plate is required to reach at least 345 MPa yield strength and 485 MPa tensile strength, with a minimum tensile range extending up to about 630 MPa in the European EN 10025-5 grades and a minimum elongation of 19 - 22 % depending on the standard and thickness. Typical Charpy V-notch impact results reach at least 27 J at minus 20 degrees Celsius, so the plate keeps useful toughness in cold service. Actual values vary with thickness and rolling practice and are confirmed on the mill certificate.
Frequently Asked Questions
Q: What is the difference between Corten A and Corten B?
Corten A carries a deliberate phosphorus addition that strengthens the patina and is supplied mainly as sheet and strip; Corten B has a higher manganese content with phosphorus capped at 0.035 % and vanadium added, giving higher strength and better weldability for plate and heavy welded structures.
Q: Which ASTM grade is equivalent to Corten B?
ASTM A588 Grade B, also published as ASME SA588, is the grade most often used interchangeably with Corten B.
Q: Does Corten B need to be painted?
No. It is designed for bare exposure and forms its own protective layer; coating is used only where the steel stays permanently wet, is embedded, or faces heavy chloride exposure.
Q: What are the mechanical values?
Minimum yield strength 345 N/mm2, minimum tensile strength 485 N/mm2 and minimum elongation of 19 % in 50 mm gauge length for the tabulated European values, with ASTM requirements at 21 % and typical Charpy impact energy of at least 27 J at minus 20 degrees Celsius.
Q: What sizes are available?
Thickness from 2 mm to 460 mm, width 1500 - 3200 mm and length 6000 - 12000 mm as standard, with hot rolled plate supplied from 3 mm to 150 mm thick and up to 4100 mm wide and 18000 mm long.
Q: Can Corten B plate be welded and cut normally?
Yes. It is welded with low-hydrogen consumables of matching strength using standard structural procedures, and cut by flame, plasma, laser or shear; removing slag and spatter afterwards keeps the weld area weathering evenly with the plate.
