ASTM A588 Grade B is a high-strength low-alloy weathering steel, often called Corten-type steel, that is known for its atmospheric corrosion resistance and high strength. It is commonly used in bridges, buildings, and heavy equipment. The alloying elements, including chromium, nickel, and copper, allow the steel to form a protective rust-like patina in weather cycles, which reduces the need for painting and maintenance over the life of the structure.
What Makes A588 Grade B a Weathering Steel
When A588 Grade B is exposed to alternating wet and dry cycles, its surface develops a dense, adherent oxide layer called a patina. This patina acts as a barrier that slows further corrosion, giving the material roughly four to six times better atmospheric corrosion resistance than plain carbon steel. The patina forms only under suitable exposure conditions with regular wet-dry cycling, so the steel performs best in open structures where moisture can drain and dry naturally.
Chemical Composition
The chemical composition of A588 Grade B is controlled to develop the weathering behavior. Carbon is limited to 0.19 percent, manganese is 0.80 to 1.25 percent, chromium is 0.40 to 0.65 percent, silicon is 0.30 to 0.65 percent, and copper is 0.25 to 0.40 percent. Phosphorus is limited to about 0.05 percent, sulfur to 0.040 percent, nitrogen to 0.010 percent, and nickel to about 0.05 percent. The copper and chromium are the key elements for the protective patina.
Mechanical Properties by Thickness
For thickness up to 100 mm, A588 Grade B provides a minimum yield strength of 340 MPa and a minimum tensile strength of 480 MPa. For thickness from about 100 to 127 mm, the minimum yield strength is 320 MPa and the tensile strength is 460 MPa, and for 127 to 203 mm the values are 290 MPa yield and 430 MPa tensile. The grade also guarantees a minimum yield point of 50 ksi, 345 MPa, for plates up to about 100 mm in common specification practice, with elongation typically above 20 percent.
Welding and Fabrication
A588 Grade B is weldable with standard processes such as SMAW, GMAW, and SAW, using low-hydrogen practice. For general structural welding, low-hydrogen electrodes such as E7018 are suitable, and for applications where the weld must match the weathering performance of the base metal, weathering-type filler metals in the E70xx-W series should be used. The steel can be cut, drilled, and formed by conventional methods, and edge preparation for welding should follow normal practice for HSLA steels.
Typical Applications
Bridges, transmission towers, and wind turbine towers exposed to the atmosphere
Buildings and structures where durability and low maintenance are required
Mining equipment, excavators, loaders, bulldozers, and cranes
Architectural elements where the natural patina finish is desired
General construction and heavy equipment components in harsh environments
Frequently Asked Questions
What is A588 Grade B steel used for? It is used for exposed structural applications such as bridges, buildings, and transmission towers where weathering properties provide a protective patina and reduce painting needs.
What is the yield strength of A588 Grade B? The minimum yield strength is 340 to 345 MPa for plates up to about 100 mm, decreasing for thicker plates.
How does Grade B differ from Grade A of A588? The grades differ mainly in chemical composition, with slightly different alloy limits, while achieving similar weathering performance.
Is A588 Grade B weldable? Yes, it is weldable with standard processes using low-hydrogen practice; weathering-type filler metals are used to match corrosion resistance.
How good is the corrosion resistance of A588 Grade B? It offers atmospheric corrosion resistance roughly four to six times better than plain carbon steel when the patina can form and dry properly.
Can A588 Grade B be used in coastal areas? It can be used, but performance is reduced in severe salt-rich coastal environments, where protective coating is usually recommended.