ASTM A588 Grade C is a high-strength low-alloy weathering steel for welded, bolted and riveted construction. Its defining feature is the self-protecting patina that forms in atmospheric service, which allows bridges, buildings and heavy frameworks to operate for decades without painting. This article summarizes the mechanical properties, composition and dimensions you need for specification.
Key Takeaways
Minimum yield strength 345 MPa; minimum tensile strength 485 MPa.
Atmospheric corrosion resistance substantially better than plain carbon steel, with or without copper addition.
Plate range: 2-180 mm thick, 1200-3200 mm wide, 3000-18000 mm long.
Self-protecting rust layer cuts maintenance costs by 30-40% versus painted carbon steel.
Mechanical Properties
A588 Grade C guarantees a minimum yield strength of 345 MPa and a minimum tensile strength of 485 MPa for plates, enabling lighter sections than ordinary structural steel at the same design load. The high-strength low-alloy base provides weldability with conventional processes, and the grade is intended for atmospheric service where the patina develops naturally.
Chemical Composition
The weathering mechanism depends on the alloy balance. Per the mill data used on this page, the composition includes carbon up to 0.20%, silicon 0.15-0.50%, manganese 0.75-1.35%, phosphorus up to 0.040%, sulfur up to 0.050%, copper 0.40-0.70% and nickel up to 0.50%. Copper drives patina color and density, while chromium and nickel stabilize the protective layer against chloride and industrial pollutants.
Available Dimensions
Plates are supplied from 2 mm to 180 mm in thickness, 1200 mm to 3200 mm in width and 3000 mm to 18000 mm in length, with surface options of as-rolled, blasted and primed, or painted. Sheet and coil forms are also available for architectural applications, and structural shapes can be produced to drawing.
Corrosion Resistance and Cost Advantage
In outdoor environments A588 Grade C supports a service life of more than 50 years, because the adherent oxide layer slows further corrosion instead of flaking away. Eliminating painting and recoating cycles reduces maintenance costs by an estimated 30-40% compared with conventional carbon steel structures, a decisive factor for bridge owners and facility managers.
Typical Applications
Specify A588 Grade C for welded bridges and overpasses, high-rise building frames, heavy-duty equipment supports, transmission structures and architectural steel where weight savings, durability and the exposed patina finish are all required. Request mill test certificates confirming chemical composition and mechanical properties with every structural order.
FAQ
What is the yield strength of A588 Grade C?
Minimum 345 MPa for plates, enabling lighter sections than ordinary structural steel.
Does A588 Grade C need painting?
No, for atmospheric service. The patina is the protective coating; painting is only needed for buried or permanently wet conditions.
What thickness range is available?
Plates from 2 mm to 180 mm, with width up to 3200 mm and length up to 18000 mm.
Can A588 Grade C be welded?
Yes, with conventional welding processes and low-alloy filler metals matched to the base composition.
How long does A588 Grade C last outdoors?
Typically more than 50 years in atmospheric service with the patina fully formed.
What documents are required?
Mill test certificates confirming chemical composition and mechanical properties per ASTM A588.
Request A588 Grade C Specifications
