1. What Is SMA400CW Corten Steel?
SMA400CW is an atmospheric corrosion resisting structural steel, commonly referred to as corten steel, specified in JIS G3114: Hot-rolled atmospheric corrosion resisting steels for welded structure. The grade is designed for welded assemblies that remain exposed to the weather without protective painting. When the steel surface cycles between wet and dry conditions, the alloying elements, chromium, copper and nickel, promote the formation of a dense, adherent oxide layer that slows further corrosion. In practice, this allows the steel to be left uncoated in many architectural and industrial applications, with maintenance intervals far longer than those of ordinary carbon steel.
2. SMA400CW Chemical Composition (JIS G3114)
The composition limits below follow JIS G3114. Among the SMA400 A/B/C series, the C grades carry the highest chromium range and a nickel addition, which supports the corrosion performance.
| Element | Limit (max %, unless shown as a range) |
|---|---|
| C | 0.18 |
| Si | 0.15–0.65 |
| Mn | 1.25 |
| P | 0.035 |
| S | 0.035 |
| Cr | 0.45–0.75 |
| Cu | 0.30–0.50 |
| Ni | 0.05–0.30 |
3. SMA400CW Mechanical Properties
JIS G3114 sets minimum yield strengths that decrease with plate thickness. Representative values for plates up to 100 mm are shown below.
| Thickness (mm) | Min Yield (MPa) | Tensile (MPa) |
|---|---|---|
| ≤16 | 245 | 400–540 |
| 16–40 | 235 | 400–540 |
| 40–75 | 215 | 400–540 |
| 75–100 | 215 | 400–540 |
Grades ending in W are supplied with Charpy V-notch impact testing per JIS G3114; for SMA400CW the standard impact requirement is 27 J minimum at 0 °C.
4. Plate Sizes and Delivery Conditions
SMA400CW plate is produced in a practical range of 3–200 mm thickness, 1000–4100 mm width and 1000–12000 mm length, subject to mill capability. Common delivery conditions include hot rolled (as-rolled), controlled rolling, normalized (N), quenched and tempered (QT), and cold rolled for thin sheet. Additional options such as ultrasonic examination, Z-direction testing (Z15/Z25/Z35), Charpy V-notch impact testing, simulated post-weld heat treatment (PWHT), NACE MR0175 sour-service criteria and third-party inspection can be specified on request.
5. Typical Applications of SMA400CW
Because it welds like conventional structural steel yet survives atmospheric exposure with minimal coating, SMA400CW is widely used in air preheaters, economizers, railway carriages, container production, bridge building and general construction. It is a common choice where structural members are left exposed, or where industrial atmospheres would shorten the service life of painted carbon steel.
Frequently Asked Questions
What does the CW suffix in SMA400CW mean? In JIS G3114, W indicates a grade intended for welded structures with Charpy impact testing specified, while C indicates the highest atmospheric-corrosion alloying level of the SMA400 A/B/C series, with increased chromium and a nickel addition.
Does SMA400CW need to be painted? Not necessarily. The grade forms a protective patina through natural wet-dry cycling, which is the basis for its use in bare (unpainted) applications. Painting is still an option where aesthetics, splash zones or chloride exposure require additional protection.
Can SMA400CW be welded like ordinary carbon steel? It can be welded with standard processes such as MMA, MIG/MAG and SAW using consumables suitable for weathering steel. Low-hydrogen practice is recommended for thicker plates, and a qualified welding procedure specification should always be followed.
How long does the patina take to form? In a typical outdoor environment with regular wet-dry cycles, a stable patina usually develops within one to three years. The process needs alternating wetting and drying; permanently damp or chloride-rich environments should be avoided.
What is the difference between SMA400CW and SMA400AW? Both belong to the SMA400 strength class under JIS G3114. The C grade carries more chromium (0.45–0.75%) plus nickel (0.05–0.30%), giving higher atmospheric corrosion resistance than the A grade; the yield strength requirements are the same.
What thickness range is available for SMA400CW plate? Plates are typically available from 3 mm to 200 mm thick, with widths from 1000 mm to 4100 mm and lengths from 1000 mm to 12000 mm, depending on the producing mill.
