1. What Is SMA490AP Steel?
SMA490AP is a hot-rolled atmospheric corrosion resisting structural steel specified in JIS G3114. The SMA prefix identifies the weathering steel family for welded structures, 490 indicates the nominal minimum yield strength class, and the suffix P distinguishes grades supplied without the Charpy impact test requirement that applies to the W-series grades. Like other corten-type steels, SMA490AP develops a stable oxide patina when exposed to alternating wet and dry atmospheric conditions, which protects the base material and reduces the need for maintenance painting.
2. SMA490AP Chemical Composition (JIS G3114)
The composition limits below are as stated in JIS G3114 for SMA490AP. The chromium and copper additions are the key elements responsible for 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 SMA490AP
Yield strength, tensile strength and elongation requirements vary with plate thickness. The values below follow JIS G3114 for plates and sections.
| 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 |
4. Available Sizes and Delivery Conditions
SMA490AP is commonly supplied as plate, sheet, bar and structural sections. Plate is available in thicknesses from 6 mm to 300 mm, widths from 1500 mm to 4050 mm and lengths from 3000 mm to 15000 mm, depending on the mill. Delivery conditions include hot rolled, cold rolled, as-rolled (AR), controlled rolling, normalized (N), thermomechanical controlled processing (TMCP) and quenched and tempered (Q/T), selected according to the application and the customer request.
5. Typical Applications of SMA490AP
The combination of 490 MPa-class yield strength and atmospheric corrosion resistance makes SMA490AP suitable for vehicles, bridges, transmission towers, containers and similar outdoor welded structures. It is often selected where higher load capacity is needed without increasing section weight, and where the structure is designed to operate in the bare, uncoated condition.
Frequently Asked Questions
What is the difference between SMA490AP and SMA490CW? Both are 490 MPa-class weathering steels in JIS G3114. SMA490CW is a W-grade with Charpy impact testing specified and higher chromium plus a nickel addition, while SMA490AP is a P-grade supplied without the mandatory impact test and with a leaner composition.
Does SMA490AP require painting? The grade is designed for uncoated use in atmospheric environments where wet-dry cycling is present. Painting may be applied for aesthetic reasons or where the environment is not suitable for patina formation, such as continuous chloride exposure.
Can SMA490AP be welded? Yes. SMA490AP welds with standard arc welding processes using weathering-steel-compatible consumables. A qualified welding procedure specification and low-hydrogen practice for thicker sections are recommended.
What is the minimum yield strength of SMA490AP? The minimum yield strength is 365 MPa for thicknesses up to 16 mm, decreasing to 295 MPa for the 160–200 mm thickness range, with a tensile range of 490–610 MPa throughout.
In which product forms is SMA490AP available? It can be produced as plate, sheet, bar and section steel, including structural shapes, allowing the same grade to be used for both flat products and rolled sections.
