1. What Is SMA490BP Steel?
SMA490BP is a low-alloy, atmospheric corrosion resisting structural steel specified in JIS G3114: Hot-rolled atmospheric corrosion resisting steels for welded structure. The SMA prefix denotes the weathering steel family, 490 indicates the nominal yield strength class, B indicates an intermediate corrosion-resistance alloying level, and P identifies a grade supplied without the mandatory Charpy impact test that applies to W-series grades. When exposed to the atmosphere under alternating wet and dry conditions, SMA490BP develops a dense, adherent oxide patina that protects the underlying steel, making it suitable for many applications in the bare, unpainted condition.
2. SMA490BP Chemical Composition (JIS G3114)
The composition limits below follow JIS G3114 for SMA490BP. Chromium and copper are the principal elements that provide the atmospheric corrosion resistance.
| Element | Limit (max %, unless shown as a range) |
|---|---|
| C | 0.18 |
| Si | 0.55 |
| Mn | 1.40 |
| P | 0.035 |
| S | 0.035 |
| Cu | 0.20–0.35 |
| Cr | 0.30–0.55 |
| Ni | not specified |
3. Mechanical Properties of SMA490BP
Minimum yield strength varies with thickness. Representative values from JIS G3114 for plates and sections are shown below.
| Thickness (mm) | Min Yield (MPa) | Tensile (MPa) | Min Elongation A% |
|---|---|---|---|
| ≤16 | 365 | 490–610 | 15 |
| 16–40 | 355 | 490–610 | 15 |
| 40–75 | 335 | 490–610 | 15 |
| 75–100 | 325 | 490–610 | 15 |
| 100–160 | 305 | 490–610 | 15 |
| 160–200 | 295 | 490–610 | 15 |
Note that the P-series grades do not carry the mandatory Charpy V-notch impact test requirement of the W-series grades; if impact toughness is critical, an SMA490CW equivalent or an agreed impact test supplement should be specified.
4. Available Sizes and Delivery Conditions
SMA490BP is produced as plate, sheet, bar, section steel and structural shapes. Plate sizes commonly range from 1 mm to 300 mm in thickness, 1000 mm to 3000 mm in width and 3000 mm to 12000 mm in length, subject to mill capability. Delivery conditions include hot rolled, cold rolled, as-rolled (AR), thermomechanical controlled processing (TMCP), normalized (N) and quenched and tempered (Q+T). Supplementary requirements such as ultrasonic examination, Z-direction testing (Z15/Z25/Z35), HIC testing, NDT, simulated post-weld heat treatment (PWHT), NACE MR0175 sour-service criteria and third-party inspection can be agreed with the supplier.
5. Typical Applications of SMA490BP
SMA490BP is widely used in air preheaters, economizers, railway carriages, container production, bridge building and general construction. The combination of 490 MPa-class strength and atmospheric corrosion resistance makes it a practical choice for outdoor welded structures designed to operate uncoated, where the maintenance cost of repainting carbon steel would be significant.
Frequently Asked Questions
What is the difference between SMA490BP and SMA490CW? SMA490CW is a W-series grade with Charpy impact testing specified and a richer composition (higher chromium plus nickel), while SMA490BP is a P-series grade without the mandatory impact test requirement and with a leaner chemistry.
What is the minimum yield strength of SMA490BP? The minimum yield strength is 365 MPa for thicknesses up to 16 mm and decreases in steps to 295 MPa for the 160–200 mm range; the tensile range is 490–610 MPa.
Does SMA490BP need to be painted? It is designed for bare use in atmospheric exposure. Painting is not required where wet-dry cycling allows the patina to form, but may be applied where aesthetics dictate or where the environment is unsuitable, such as permanent chloride exposure.
Can SMA490BP be welded? Yes, using standard arc welding processes with weathering-steel-compatible consumables and a qualified welding procedure specification. Low-hydrogen practice is recommended for thicker plates.
What delivery conditions are available? Hot rolled, cold rolled, AR, TMCP, normalized and quenched and tempered conditions can be supplied according to the application and the customer requirement.
