Quick Answer
Quick Answer
JIS G3106 covers hot-rolled steel plates, sheets, and sections for welded structural use. It specifies carbon limits, carbon equivalent (CEV) values, and Charpy impact requirements that JIS G3101 lacks, making SM grades the correct choice for welded bridges, buildings, and offshore structures. Key grades are SM400, SM490, SM520, and SM570, each with A, B, or C sub-grades indicating progressively stricter impact requirements.
JIS G3106 (溶接構造用圧延鋼材 — rolled steel for welded structure) was developed specifically for applications where weldability must be guaranteed by chemistry rather than assumed from mill practice. Compared to JIS G3101, every G3106 grade includes explicit carbon content limits and carbon equivalent (CEV) maxima, enabling reliable weld preheat calculation and reducing the risk of hydrogen-induced cracking. JIS mill certificates for G3106 material may be issued in Japanese only or bilingual Japanese/English depending on the mill and destination — see [/standards/jis-mill-cert-guide] for field-by-field reading guidance.
The "SM" designation derives from Steel for Marine structure (溶接構造用), reflecting the standard's origin in shipbuilding applications where weld integrity is safety-critical.
Scope and Applicability
JIS G3106 applies to hot-rolled steel in the following product forms intended for welded structures:
- Plates (厚板) and flat bars
- Strips and sheet (薄板 / 帯鋼)
- Shapes: H-sections, I-beams, channels, and angles
- Sheet piling (鋼矢板)
Typical applications include:
- Welded steel bridges and box girders
- Building structural frames (high-rise, industrial)
- Shipbuilding and offshore platforms
- Cranes, pressure-bearing frames, and machinery structures
For non-welded general structures where weldability assurance is not required, JIS G3101 (SS grades) may be sufficient.
JIS Grade Designation System
G3106 grades follow this naming convention:
- SM = Steel for welded (Marine) structure (溶接構造用)
- Number = minimum tensile strength in MPa
- Suffix A / B / C = impact test sub-grade (A = no impact test; B = 27 J at 0 °C; C = 47 J at 0 °C)
- Y suffix (SM490Y only) = higher yield strength variant
Examples:
- SM490B = welded structure steel, 490 MPa min tensile, 27 J Charpy at 0 °C
- SM490YA = higher yield SM490 variant, no Charpy requirement
- SM520C = 520 MPa min tensile, 47 J Charpy at 0 °C
Grade Coverage
| Grade | Sub-grades | Min Tensile (MPa) | Impact Requirement |
|---|---|---|---|
| SM400 | A, B, C | 400 | A: none; B: 27 J @ 0 °C; C: 47 J @ 0 °C |
| SM490 | A, B, C | 490 | A: none; B: 27 J @ 0 °C; C: 47 J @ 0 °C |
| SM490Y | A, B | 490 | A: none; B: 27 J @ 0 °C |
| SM520 | B, C | 520 | B: 27 J @ 0 °C; C: 47 J @ 0 °C |
| SM570 | — (single sub-grade) | 570 | 47 J @ −5 °C |
SM520 has no A sub-grade (impact testing is always required). SM570 has a single designation with the most stringent impact requirement.
Chemical Composition Requirements
All values are wt% maximum unless a range is stated. Ladle (heat) analysis applies; product analysis limits are slightly wider per the standard.
SM400
| Sub-grade | C max | Mn | Si max | P max | S max | CEV max |
|---|---|---|---|---|---|---|
| SM400A | 0.23 | — | — | 0.035 | 0.035 | — |
| SM400B | 0.20 | 0.60–1.40 | 0.35 | 0.035 | 0.035 | 0.36 |
| SM400C | 0.18 | 0.60–1.40 | 0.35 | 0.035 | 0.035 | 0.36 |
SM490
| Sub-grade | C max | Mn max | Si max | P max | S max | CEV max |
|---|---|---|---|---|---|---|
| SM490A | 0.20 | 1.60 | 0.55 | 0.035 | 0.035 | — |
| SM490B | 0.18 | 1.60 | 0.55 | 0.035 | 0.035 | 0.44 |
| SM490C | 0.18 | 1.60 | 0.55 | 0.035 | 0.035 | 0.44 |
SM490Y
| Sub-grade | C max | Mn max | Si max | P max | S max | CEV max |
|---|---|---|---|---|---|---|
| SM490YA | 0.20 | 1.60 | 0.55 | 0.035 | 0.035 | — |
| SM490YB | 0.20 | 1.60 | 0.55 | 0.035 | 0.035 | 0.44 |
SM520
| Sub-grade | C max | Mn max | Si max | P max | S max | CEV max |
|---|---|---|---|---|---|---|
| SM520B | 0.20 | 1.60 | 0.55 | 0.035 | 0.035 | 0.44 |
| SM520C | 0.20 | 1.60 | 0.55 | 0.035 | 0.035 | 0.44 |
SM570
| Grade | C max | Mn max | Si max | P max | S max | CEV max |
|---|---|---|---|---|---|---|
| SM570 | 0.18 | 1.70 | 0.55 | 0.035 | 0.035 | 0.44 |
Carbon Equivalent formula (JIS G3106): CEV = C + Mn/6 + (Si/24) + (Ni/40) + (Cr/5) + (Mo/4) + (V/14)
The CEV limit ensures consistent weld HAZ properties across heats and mills. C sub-grades have the same CEV limit as B sub-grades but also require the higher 47 J impact energy — the improved toughness is achieved through cleaner steelmaking (lower S, controlled inclusion morphology) rather than a lower CEV.
Mechanical Properties
SM400
| 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 |
SM490
| Thickness (mm) | Yield Strength min (MPa) | Tensile Strength (MPa) | Elongation min % |
|---|---|---|---|
| ≤ 16 | 325 | 490–610 | 22 |
| > 16, ≤ 40 | 315 | 490–610 | 22 |
| > 40, ≤ 75 | 295 | 490–610 | 22 |
| > 75, ≤ 100 | 295 | 490–610 | 21 |
SM490Y
| Thickness (mm) | Yield Strength min (MPa) | Tensile Strength (MPa) | Elongation min % |
|---|---|---|---|
| ≤ 16 | 365 | 490–610 | 19 |
| > 16, ≤ 40 | 355 | 490–610 | 19 |
| > 40, ≤ 75 | 335 | 490–610 | 19 |
| > 75, ≤ 100 | 325 | 490–610 | 19 |
SM520
| Thickness (mm) | Yield Strength min (MPa) | Tensile Strength (MPa) | Elongation min % |
|---|---|---|---|
| ≤ 16 | 365 | 520–640 | 19 |
| > 16, ≤ 40 | 355 | 520–640 | 19 |
| > 40, ≤ 75 | 335 | 520–640 | 19 |
| > 75, ≤ 100 | 325 | 520–640 | 19 |
SM570
| 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 test per JIS Z 2242. Specimen size: standard 10 × 10 × 55 mm where thickness permits; sub-size specimens used for thinner material with adjusted energy values.
| Grade / Sub-grade | Test Temperature | Min Average Energy (3 specimens) | Min Single Value |
|---|---|---|---|
| SM400A, SM490A, SM490YA | Not required | — | — |
| SM400B, SM490B, SM490YB, SM520B | 0 °C | 27 J | 21 J |
| SM400C, SM490C, SM520C | 0 °C | 47 J | 33 J |
| SM570 | −5 °C | 47 J | 33 J |
For SM570, the lower test temperature of −5 °C reflects its use in demanding applications where improved low-temperature toughness is needed. One specimen in a set of three may fall below the average minimum provided it does not fall below the single-value minimum.
JIS Mill Certificate Format
JIS G3106 mill certificates follow the same inspection-certificate-type framework as G3101 (3.1A, 3.1B, 3.1C, 3.2 — see [/standards/jis-mill-cert-guide]). For welded-structure grades, the certificate will additionally show:
- 炭素当量 (CEV) — carbon equivalent value for the heat
- 衝撃試験 (Impact test) — Charpy results for B and C sub-grades, including test temperature (試験温度) and absorbed energy (吸収エネルギー) in joules
- Sub-grade letter (e.g., SM490C, not just SM490)
Verify that the sub-grade on the certificate matches the sub-grade on the purchase order. A certificate showing SM490A would not satisfy a purchase order calling for SM490C, even though the tensile properties are identical — the impact test has not been performed.
Cross-Standard Equivalents
| JIS G3106 | ASTM | EN 10025-2 | GB/T 1591 | IS 2062 |
|---|---|---|---|---|
| SM400A/B | A36 (approx) | S235JR / S235J0 (approx) | Q235B (approx) | E250B (approx) |
| SM490A/B | A572 Gr.50 (approx) | S355JR / S355J0 (approx) | Q345B/C (approx) | E350B (approx) |
| SM490C | A572 Gr.50 + CVN (approx) | S355J2 (approx) | Q345D (approx) | E350C (approx) |
| SM520B/C | A572 Gr.60 (approx) | S355K2 / S420 (approx) | Q390C/D (approx) | — |
| SM570 | A633 Gr.E / A572 Gr.65 (approx) | S460M/ML (approx) | Q460C/D (approx) | — |
All equivalences are approximate. CEV limits, impact temperatures, and product-form coverage differ between standards.
MTC Verification Checklist
When verifying a JIS G3106 mill test certificate:
- Standard is confirmed as JIS G3106 (not G3101 or another standard)
- Grade and sub-grade (e.g., SM490C) exactly match purchase order
- Heat number (熱番号) is traceable to physical markings
- Carbon (C) reported and within the limit for the grade/sub-grade
- CEV calculated or reported (for B and C sub-grades) — confirm ≤ specified limit
- P ≤ 0.035% and S ≤ 0.035%
- Yield strength meets thickness-appropriate minimum
- Tensile strength falls within the specified range
- Elongation meets the minimum
- For B and C sub-grades: Charpy results shown at correct test temperature
- Charpy average energy meets or exceeds the minimum (27 J or 47 J as applicable)
- No single Charpy specimen below the single-value minimum
- Certificate type (3.1B, 3.2, etc.) matches contract requirement
- Mill authorized-inspector signature and stamp present
Frequently Asked Questions
What is the difference between SM490A and SM490B and SM490C?
All three have the same tensile strength range (490–610 MPa) and minimum yield strength, and identical chemical composition limits. The only differences are in the Charpy impact testing requirement. SM490A has no Charpy requirement. SM490B requires a minimum average of 27 J at 0 °C. SM490C requires 47 J at 0 °C. For welded structures exposed to low temperatures or dynamic loading, SM490C provides the highest assurance of ductile fracture resistance. Sub-grade A is typically used for non-critical members.
Why is SM490Y a separate designation from SM490?
SM490Y (the Y stands for 降伏 — yield) is a higher yield strength variant of SM490. While SM490 has a minimum yield of 325 MPa (for t ≤ 16 mm), SM490Y achieves 365 MPa minimum at the same thickness range. The tensile strength range is identical. SM490Y is used where designers need extra yield strength margin without stepping up to SM520's higher tensile requirement. It is available only in A and B sub-grades, not C.
Is SM490 the same as ASTM A572 Grade 50?
They are approximate equivalents for tensile and yield strength purposes, but not directly interchangeable. SM490 has a minimum tensile of 490 MPa (71 ksi) versus A572 Gr.50's 450 MPa (65 ksi) minimum, so SM490 is actually slightly stronger. The chemical composition profiles also differ: A572 controls carbon, manganese, phosphorus, and sulfur, while SM490 additionally limits CEV. For projects requiring formal compliance with A572 Gr.50, separately certified material must be obtained.
Does JIS G3106 require through-thickness (Z-grade) testing?
No. JIS G3106 does not include through-thickness tensile testing (the "Z25" or "Z35" designation in EN 10164). If through-thickness ductility is required — for example in heavily restrained welded joints prone to lamellar tearing — through-thickness properties must be specified as a supplementary requirement on the purchase order, and the mill must confirm it can supply to those requirements.
How do JIS G3106 grades compare to EN S355 grades?
SM490B/C is the closest Japanese counterpart to EN S355J0/J2. Both have minimum yield strengths around 355 MPa for thin sections and minimum tensile strengths around 490–510 MPa. The primary difference is in the Charpy sub-zero temperature requirements: EN S355J2 tests at −20 °C while SM490C tests at 0 °C. For projects designed to EN 1993 (Eurocode 3) in moderate climates, SM490C may be accepted by engineering agreement, but formal compliance requires EN-certified material.
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