Quick Answer
Quick Answer
JIS G3114 covers hot-rolled weathering steel plates, sheets, and sections with enhanced atmospheric corrosion resistance through copper, chromium, and nickel alloying. Three strength grades — SMA400, SMA490, and SMA570 — each with A, B, C, and/or W sub-grades, allow designers to balance strength, impact toughness, and surface weathering appearance. SMA490W is the closest Japanese equivalent to ASTM A588 Grade A (Corten) and EN S355W (EN 10025-5).
JIS G3114 (溶接構造用耐候性熱間圧延鋼材 — hot-rolled atmospheric corrosion resisting steel for welded structure) is the Japanese weathering steel standard. The alloying elements copper (Cu), chromium (Cr), and nickel (Ni) promote the formation of a stable, adherent rust patina (錆び — sabi) that acts as a protective barrier, slowing further corrosion at a rate approximately 4–8× slower than ordinary structural carbon steel in moderate industrial or marine atmospheres. JIS G3114 material is used unpainted on exposed bridges, buildings, and sculptures where the characteristic brown-orange weathered appearance is desired or where long maintenance-free service life is required.
JIS mill certificates for G3114 may be Japanese-only or bilingual — see [/standards/jis-mill-cert-guide].
Scope and Applicability
JIS G3114 applies to hot-rolled steel plates, flat bars, and sections used in welded structures. The standard is explicitly for welded use (溶接構造用), meaning all grades include carbon and CEV limits, similar to JIS G3106. Products covered include:
- Plates (厚板) in thicknesses from 6 mm to 100 mm
- Flat bars and strips
- Structural shapes (angles, channels) — subject to mill availability
Typical applications:
- Unpainted highway and railway bridges
- Architectural façades and sculptures requiring a weathered-steel aesthetic
- Retaining walls, noise barriers, and industrial structures in rural or suburban environments
- Situations where painting access is difficult or lifecycle painting costs are prohibitive
Important limitations: Weathering steel should not be used where standing water, wet-dry cycling with contaminated water, continuous immersion, or coastal salt spray are expected. In those environments, the protective patina does not form correctly and corrosion continues at a high rate.
JIS Grade Designation System
SMA grades combine:
- SMA = Steel for welded, Marine structure, Atmospheric corrosion resisting (溶接構造用耐候性鋼)
- Number = minimum tensile strength in MPa
- Suffix A / B / C = impact test sub-grade (A = no Charpy test; B = 27 J at 0 °C; C = 47 J at 0 °C)
- Suffix W = weathering grade with enhanced alloying (Cu + Cr + Ni) for maximum corrosion resistance
The W sub-grade has stricter alloying requirements (higher minimum Cu, Cr, Ni) than A/B/C sub-grades. For most true weathering-steel applications, the W sub-grade should be specified.
Grade Coverage
| Grade | Sub-grades Available | Min Tensile (MPa) | Impact Requirement |
|---|---|---|---|
| SMA400 | A, B, C, W | 400 | A: none; B: 27 J @ 0 °C; C: 47 J @ 0 °C; W: 27 J @ 0 °C |
| SMA490 | A, B, C, W | 490 | A: none; B: 27 J @ 0 °C; C: 47 J @ 0 °C; W: 27 J @ 0 °C |
| SMA570 | W only | 570 | 47 J @ −5 °C |
SMA570 is available only in the W sub-grade, reflecting that its high strength and weathering performance are both achieved through the same controlled alloying system.
Chemical Composition Requirements
All values are wt% maximum unless a range is stated. Ladle (heat) analysis.
SMA400
| Sub-grade | C max | Si max | Mn max | P max | S max | Cu | Cr | Ni | Mo max | CEV max |
|---|---|---|---|---|---|---|---|---|---|---|
| SMA400A | 0.18 | 0.55 | 1.40 | 0.035 | 0.035 | — | — | — | — | — |
| SMA400B | 0.16 | 0.55 | 1.40 | 0.035 | 0.035 | — | — | — | — | 0.36 |
| SMA400C | 0.14 | 0.55 | 1.40 | 0.035 | 0.035 | — | — | — | — | 0.36 |
| SMA400W | 0.18 | 0.75 | 0.50–1.50 | 0.035 | 0.035 | 0.20–0.75 | 0.30–1.00 | ≤ 0.65 | 0.15 | 0.36 |
SMA490
| Sub-grade | C max | Si max | Mn max | P max | S max | Cu | Cr | Ni | Mo max | CEV max |
|---|---|---|---|---|---|---|---|---|---|---|
| SMA490A | 0.18 | 0.55 | 1.60 | 0.035 | 0.035 | — | — | — | — | — |
| SMA490B | 0.16 | 0.55 | 1.60 | 0.035 | 0.035 | — | — | — | — | 0.44 |
| SMA490C | 0.16 | 0.55 | 1.60 | 0.035 | 0.035 | — | — | — | — | 0.44 |
| SMA490W | 0.18 | 0.75 | 0.50–1.50 | 0.035 | 0.035 | 0.20–0.75 | 0.30–1.25 | ≤ 0.65 | 0.15 | 0.44 |
SMA570
| Sub-grade | C max | Si max | Mn max | P max | S max | Cu | Cr | Ni | Mo max | CEV max |
|---|---|---|---|---|---|---|---|---|---|---|
| SMA570W | 0.18 | 0.80 | 0.50–1.70 | 0.035 | 0.035 | 0.20–0.75 | 0.30–1.25 | ≤ 0.65 | 0.40 | 0.44 |
Key alloying notes:
- The A/B/C sub-grades contain no specified Cu, Cr, or Ni and are functionally plain carbon steel with the same chemistry as G3106 SM grades
- Only the W sub-grade includes the copper-chromium-nickel alloying package responsible for weathering performance
- For unpainted weathering applications, always specify the W sub-grade
- Phosphorus is also used in some weathering steel formulations for additional corrosion resistance; the G3114 P limit of 0.035% is a compromise between corrosion benefit and weld HAZ toughness
Mechanical Properties
SMA400
| Thickness (mm) | Yield Strength min (MPa) | Tensile Strength (MPa) | Elongation min % |
|---|---|---|---|
| ≤ 16 | 245 | 400–510 | 22 |
| > 16, ≤ 40 | 235 | 400–510 | 22 |
| > 40, ≤ 75 | 215 | 400–510 | 22 |
| > 75, ≤ 100 | 215 | 400–510 | 21 |
SMA490
| Thickness (mm) | Yield Strength min (MPa) | Tensile Strength (MPa) | Elongation min % |
|---|---|---|---|
| ≤ 16 | 325 | 490–610 | 19 |
| > 16, ≤ 40 | 315 | 490–610 | 19 |
| > 40, ≤ 75 | 295 | 490–610 | 19 |
| > 75, ≤ 100 | 295 | 490–610 | 18 |
SMA570
| Thickness (mm) | Yield Strength min (MPa) | Tensile Strength (MPa) | Elongation min % |
|---|---|---|---|
| ≤ 16 | 460 | 570–720 | 19 |
| > 16, ≤ 40 | 450 | 570–720 | 19 |
| > 40, ≤ 75 | 430 | 570–720 | 19 |
| > 75, ≤ 100 | 420 | 570–720 | 19 |
Elongation is measured on gauge length L₀ = 5.65√A₀.
Impact Test Requirements
Charpy V-notch per JIS Z 2242. Standard 10 × 10 × 55 mm specimen.
| Grade / Sub-grade | Test Temperature | Min Average Energy | Min Single Value |
|---|---|---|---|
| SMA400A, SMA490A | Not required | — | — |
| SMA400B, SMA490B, SMA400W, SMA490W | 0 °C | 27 J | 21 J |
| SMA400C, SMA490C | 0 °C | 47 J | 33 J |
| SMA570W | −5 °C | 47 J | 33 J |
Note that the W sub-grades are impact-tested at the B sub-grade energy level (27 J) for SMA400W and SMA490W. SMA570W requires the higher energy at −5 °C.
JIS Mill Certificate Format
JIS G3114 mill certificates follow the standard JIS inspection certificate framework (3.1A, 3.1B, 3.1C, 3.2 — see [/standards/jis-mill-cert-guide]). For W sub-grades, the certificate must show the alloying elements Cu, Cr, and Ni in the chemical composition section, confirming that the weathering alloy package is present. Key fields to verify:
- Sub-grade suffix must be clearly stated (e.g., SMA490W, not just SMA490)
- Cu, Cr, Ni values reported for W grades — confirm they fall within the specified ranges
- CEV reported for B, C, and W sub-grades
- For W grades, the certificate may also note "耐候性" (weathering/atmospheric corrosion resistance) as a characteristic
Cross-Standard Equivalents
| JIS G3114 | ASTM | EN 10025-5 | BS 7668 | GB/T 4171 |
|---|---|---|---|---|
| SMA400W | A588 Gr.A (approx) | S235W (approx) | WR 235 (approx) | Q235NH (approx) |
| SMA490W | A588 Gr.A / A242 (approx) | S355W (approx) | WR 355 (approx) | Q355NH (approx) |
| SMA570W | A709 HPS 70W (approx) | S460W (approx) | — | Q460NH (approx) |
All equivalences are approximate. ASTM A588 Gr.A has different Cu/Cr/Ni ranges and a minimum yield of 345 MPa (50 ksi). EN S355W (EN 10025-5) tests Charpy at −20 °C versus SMA490W's 0 °C. Formal compliance with any of these standards requires separately certified material.
MTC Verification Checklist
When verifying a JIS G3114 mill test certificate:
- Standard confirmed as JIS G3114 (not G3106)
- Grade and sub-grade (e.g., SMA490W) exactly match purchase order
- Heat number (熱番号) traceable to physical markings
- For W sub-grades: Cu, Cr, Ni reported and within specified ranges
- Carbon reported and within limit for the grade/sub-grade
- CEV reported for B, C, and W sub-grades — confirm ≤ limit
- P ≤ 0.035%, S ≤ 0.035%
- Yield strength meets thickness-appropriate minimum
- Tensile strength falls within the specified range
- Elongation meets minimum
- For B, C, W sub-grades: Charpy results at correct temperature with sufficient energy
- Certificate type matches contract requirement
- Mill authorized-inspector signature/stamp present
Frequently Asked Questions
What is the difference between SMA490B and SMA490W?
Both grades have the same tensile strength range (490–610 MPa) and identical CEV limits (0.44 max). The critical difference is chemistry and corrosion performance: SMA490B contains no specified copper, chromium, or nickel, making it essentially a carbon-manganese steel with the same weathering performance as ordinary structural steel. SMA490W contains 0.20–0.75% Cu, 0.30–1.25% Cr, and up to 0.65% Ni, which produce the stable patina responsible for atmospheric corrosion resistance. For unpainted weathering applications, SMA490W is mandatory. SMA490B is used in painted structures where the carbon content and CEV limits are needed but weathering performance is irrelevant.
Is SMA490W the same as ASTM A588 Grade A (Corten)?
They are the closest Japanese-to-American equivalents for unpainted weathering steel. Both achieve atmospheric corrosion resistance through Cu-Cr-Ni alloying and have comparable tensile strength ranges. Key differences: ASTM A588 Gr.A has a minimum yield of 345 MPa (50 ksi) for plates up to 100 mm, while SMA490W achieves 325 MPa minimum at the same thickness. A588 does not require Charpy impact testing unless supplementary requirements are invoked; SMA490W includes a 27 J at 0 °C Charpy requirement as standard. For formal ASTM compliance, A588-certified material must be obtained.
Can SMA490W be used in coastal marine environments?
Not without additional protection. The weathering patina on SMA490W and similar atmospheric corrosion resisting steels forms effectively only in environments with moderate pollution, alternating wet-dry cycles, and moderate humidity. In environments with airborne chloride concentrations above approximately 0.05 mg/m²/day (typical within about 1 km of an open coastline), the patina does not stabilize and the steel corrodes at rates comparable to ordinary carbon steel. In such environments, paint, coating, or stainless cladding must be used.
How long does it take for the weathering patina to stabilize?
Under typical moderate-climate conditions with adequate wet-dry cycling, the stable protective patina develops over 2–5 years. During this initial period, rust runoff (brownish streaking on adjacent surfaces) is expected and should be accounted for in the design. The final patina color ranges from deep brown to purple-grey depending on the local atmosphere. In very clean or dry atmospheres, full patina stabilization may take longer.
Does JIS G3114 cover the same thickness range as JIS G3106?
Yes. Both standards cover plates up to 100 mm thickness in the standard thickness ranges. G3114 mechanical properties are specified for the same thickness bands (≤16, >16–40, >40–75, >75–100 mm). For plates thicker than 100 mm in weathering steel, special order arrangements with individual mills are required.
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