What is the difference between Corten A and Corten B?
The useful differences are in the specified chemistry, product forms, available dimensions and acceptance requirements. Both names refer to weathering steels, but a buyer needs more than a rust-coloured finish to identify the right material. Begin with the grade on the drawing, the producer's data and the inspection documents required for the order.
For a concrete example, SSAB's hot-rolled COR-TEN® A reference lists phosphorus at 0.07–0.15%, compared with a maximum of 0.035% for its COR-TEN® B. Both cited data sheets list 345 MPa minimum yield strength and 485 MPa minimum tensile strength. Thus, the letter B does not by itself mean a universally higher strength.
Side-by-side buying comparison
| Buying question | Corten A | Corten B |
|---|---|---|
| Which specification? | Identify the producer specification, product form and required test values. | Identify the producer specification, product form and required test values. |
| Reference chemistry difference | Higher phosphorus range in the cited SSAB A data. | Lower phosphorus limit in the cited SSAB B data. |
| Typical inquiry focus | Architectural panels, sheet and landscape details; verify project suitability. | Plate components and engineered outdoor steelwork; verify project suitability. |
| What size is available? | Ask for thickness, width, length and quantity against the actual offer. | Ask for thickness, width, length and quantity against the actual offer. |
| Can another grade replace it? | Only after checking all project requirements and gaining acceptance. | Only after checking all project requirements and gaining acceptance. |
| Does the name guarantee a finish? | No; define surface treatment, exposure and appearance acceptance. | No; define surface treatment, exposure and appearance acceptance. |
This table is a purchasing guide. It does not establish a universal division between architectural and structural use, certify supplied material or approve either grade for a particular structure.
Choose around the application
For façades, the specification also needs flatness, bends, joints, fixing design, drainage and an appearance sample. For landscape work, consider soil contact, retained moisture, edges and staining around the installation. For bridges, follow the engineer's required material standard, toughness and inspection provisions.
Discuss persistent wetness, salt and sheltered water traps before accepting unpainted steel. The development of patina depends on the location and detail, so selecting A or B alone cannot promise a particular colour or service life. Read the patina guide for the appearance considerations.
Do not use a simple equivalence shortcut
A242, A588, S355J2W and S355J2WP are specifications or grade designations with their own requirements. A supplier's comparison table is a starting point for discussion, not evidence that a plate meets another standard. Ask for the actual offered designation, standard edition, chemistry, mechanical properties, thickness, delivery condition and testing.
If the design says ASTM A588, keep that requirement in the inquiry. If branded COR-TEN® is required, state the producer and traceability requirement explicitly. A generic Corten A or B inquiry does not establish mill origin.
Compare quotations on the same basis
Send both suppliers the same dimensions, quantities, tolerances, inspection, finish and destination. Separate raw plate from cut blanks or finished panels. An offer with lower material cost may include less processing or a different freight scope. Use the Corten steel price guide to compare the full order cost.
Frequently asked questions
Which grade is better, Corten A or Corten B?
The better choice is the one accepted by the project specification for its application, dimensions, processing and exposure. There is no universal winner.
Do the two grades look different after weathering?
Appearance depends strongly on exposure, surface condition and detailing. Colour alone cannot reliably identify A or B or verify a grade.
Can I switch from A to B without changing the drawing?
Treat it as a material substitution. Review the offered specification and obtain the required project approval before ordering.
What should I send if I am not sure which grade I need?
Send the drawing or specification, application, dimensions, quantities, site conditions and document requirements. Identify the undecided items so the quotation can make the proposed material clear.
Related products and buying guides
- Corten A steel plate, Corten B steel plate and ASTM A588 weathering steel plate
- Corten A vs Corten B: compare before ordering
- Corten steel price guide: prepare a comparable quote
- Material certificate checklist and RFQ checklist
Request a project quotation
Send SHANDONG DAZHI your grade, thickness × width × length, quantity, finish, inspection requirements and destination. Include drawings for cut parts. Your quotation will confirm the proposed material, availability, processing scope, price and delivery schedule.
SSAB COR-TEN® A hot-rolled and COR-TEN® B product data, reviewed 20 September 2026. Numerical examples are specific to those data sheets. COR-TEN® is a registered trademark.