What Is SA588 Grade B Steel?
SA588 Grade B is a weathering resistant steel plate defined in ASME SA588, equivalent to ASTM A588. It is highly resistant to atmospheric corrosion because of its alloy design: copper, chromium, nickel and vanadium promote a dense, adherent rust layer that protects the substrate. The grade is widely used in air preheaters, economisers, railway carriages, containers, bridge building and construction.
Chemical Composition
Table 1 lists the commonly quoted composition limits for SA588 Grade B (heat analysis).
| Element (max, %) | SA588 Grade B |
|---|---|
| Carbon (C) | 0.20 |
| Manganese (Mn) | 0.75 – 1.35 |
| Phosphorus (P) | 0.04 |
| Sulfur (S) | 0.05 |
| Silicon (Si) | 0.15 – 0.50 |
| Copper (Cu) | 0.20 – 0.40 |
| Nickel (Ni) | 0.50 |
| Chromium (Cr) | 0.40 – 0.70 |
| Vanadium (V) | 0.01 – 0.10 |
Mechanical Properties
SA588 Grade B guarantees a minimum yield strength of 345 MPa (50 ksi) and a minimum tensile strength of 485 MPa (70 ksi) for plate up to 100 mm thick, with elongation requirements per ASTM A588 (21% minimum on a 2-inch gauge for the common thickness range). The exact values for each thickness class are confirmed on the mill test certificate.
| Property | Value |
|---|---|
| Minimum yield strength (t ≤ 100 mm) | 345 MPa (50 ksi) |
| Minimum tensile strength | 485 MPa (70 ksi) |
| Elongation | Per ASTM A588 thickness and gauge length |
Weathering Behaviour and Corrosion Resistance
The atmospheric corrosion resistance of SA588 Grade B is substantially better than that of carbon steels such as A36 and A572-50, with or without copper addition, when properly exposed to the atmosphere. The steel is suitable for many applications in the unpainted condition, where the stable patina forms over time and reduces maintenance. In continuously wet, chloride-rich or sheltered environments, the corrosion assessment should be performed for the specific site conditions.
Fabrication and Surface Treatment
SA588 Grade B can be welded with standard processes for structural weathering steel, with consumables selected so that the weld zone provides corrosion behaviour close to the parent plate. Common surface treatments include shot blasting and painting or coating; for uncoated service, the surface should be clean and free of grease so that the patina develops evenly.
Typical Applications
Bridges and structural steelwork
Railway carriages and containers
Air preheaters and economisers
Building construction and facades
Outdoor equipment in industrial atmospheres
Frequently Asked Questions
Which standard applies to SA588 Grade B?
ASME SA588/SA588M, equivalent to ASTM A588/A588M, for high-strength low-alloy structural steel with improved atmospheric corrosion resistance.
What is the yield strength of SA588 Grade B?
Minimum 345 MPa (50 ksi) for plate up to 100 mm thick.
Does SA588 Grade B need painting?
It is designed for unpainted service in suitable atmospheres; painting or coating can be applied where required by the design.
Can SA588 Grade B be welded?
Yes, with standard procedures for weathering steel; consumables should be selected to keep the corrosion behaviour of the weld zone close to the base metal.
What forms are available?
Plate, sheet, bar and section steel are commonly supplied; typical plate ranges cover thicknesses from 2 mm to 450 mm, widths from 1000 mm to 4200 mm and lengths from 3000 mm to 18000 mm.
How does it compare with carbon steels like A36?
SA588 Grade B offers substantially better atmospheric corrosion resistance than A36 or A572-50, allowing uncoated service in many outdoor applications.
