ASTM A588, officially titled Standard Specification for High-Strength Low-Alloy Structural Steel, up to 50 ksi Minimum Yield Point, with Atmospheric Corrosion Resistance, is one of the most widely used weathering steel specifications for structural plate. It is often referred to as corten-type steel because, like the well-known trade name COR-TEN, it forms a protective rust-like surface that eliminates the need for additional coatings and reduces maintenance cost.
Designation and Coverage
A588 covers structural shapes, plates, and bars in Grades A, B, C, and K. The grades differ mainly in alloying approach: all of them rely on small additions of copper, chromium, nickel, and vanadium or other microalloys to achieve the required atmospheric corrosion index, which is specified as approximately two times that of plain carbon steel with copper. Grade selection is normally based on product form and thickness; for example, Grade K is commonly used for shapes and bars, while Grades A, B, and C cover plate production.
Mechanical Properties
For plate thickness up to 100 mm, ASTM A588 requires a minimum yield point of 345 MPa (50 ksi) and a minimum tensile strength of 485 MPa (70 ksi). For thickness over 100 mm up to 200 mm, the minimum yield point is 315 MPa (46 ksi). Minimum elongation is 21% for plate up to 19 mm and 18% for thicker sections. These values make A588 suitable for load-bearing structural members in bridges, buildings, and industrial frames.
Available Forms and Sizes
Hot-rolled A588 weathering steel plate is typically supplied in thicknesses from 2 mm to 300 mm, with 2-100 mm being the most common range for structural use; cold-rolled product is available in 0.5-2 mm. Widths range from 1000 mm to 3000 mm (1000-2200 mm usually used), and lengths from 1000 mm to 12000 mm. Plate is supplied hot-rolled, controlled-rolled, normalized, annealed, tempered, quenched, or with N+T and Q+T treatments as required by the application. Mill test certificates are provided with the goods, and third-party inspection (for example BV or SGS) is acceptable.
Related Weathering Steel Grades in Other Standards
Engineers frequently compare A588 with equivalent weathering grades in other standard systems. Under EN 10025-5 the common grades are S235J0W, S235J2W, S355J0W, S355J2W, S355K2W, S355J0WP, and S355J2WP. Under JIS G3114 the SMA400AW/BW/CW, SMA490AW/BW/CW, and SMA570W/P series apply, and under JIS G3125 the SPA-H and SPA-C grades. Chinese GB/T 4171 covers Q235NH, Q265GNH, Q295NH, Q295GNH, Q310GNH, Q355NH, Q355GNH, Q415NH, Q460NH, and higher grades. Although these grades behave in a similar way, they are not automatically interchangeable; strength, impact requirements, and thickness-dependent values must be checked against each standard.
Design and Fabrication Guidance
Weathering steel performs best in environments with regular wet-dry cycling and low chloride levels. Details should provide good drainage and avoid crevices that trap water. The steel can be welded with conventional processes and low-hydrogen consumables; preheat depends on thickness and restraint. During the first one to three years the developing patina sheds rust-coloured run-off, so downspouts and walkways near the structure should be planned accordingly. For bolted connections, use weathering-grade fasteners to avoid galvanic corrosion.
Frequently Asked Questions
Q1: What is the minimum yield strength of ASTM A588 plate?
A1: 345 MPa (50 ksi) for plate up to 100 mm thick; 315 MPa (46 ksi) for plate over 100 mm up to 200 mm.
Q2: Is ASTM A588 the same as A242?
A2: No, but they are related. A242 covers high-strength low-alloy steel with atmospheric corrosion resistance and allows a different set of grades and shapes; A588 is specifically limited to 50 ksi minimum yield point and is the more common choice for plate structures.
Q3: Does A588 steel require painting?
A3: In suitable atmospheric environments it can be left unpainted; the patina provides the corrosion protection. Painting is optional and should not be applied where bare weathering appearance is intended.
Q4: What thickness range is available for A588 plate?
A4: Hot-rolled plate is commonly available from 2 mm up to 300 mm, with 2-100 mm the usual range for structural applications; width and length depend on the mill.
Q5: Can A588 be used in coastal areas?
A5: With caution. High chloride exposure can prevent a stable patina; in severe marine splash zones, additional coating or a more corrosion-resistant material should be considered.
