SM490A
Weldable hot-rolled structural carbon-manganese steel, 490 MPa tensile-strength class · JIS G 3106:2024 — Rolled steels for welded structure
SM490A is the basic, non-impact-tested quality in the JIS G 3106 SM490 family. It combines a specified tensile strength of 490–610 MPa with thickness-dependent minimum yield strength and chemistry intended for welded construction. Its principal limitation is the absence of a mandatory Charpy toughness guarantee; SM490B or SM490C, or a separately agreed impact requirement, should be considered where brittle-fracture resistance is design-critical.
- JIS G 3106:2024Current governing edition · Published on February 20, 2024 and listed by the Japanese Standards Association as active.
- 490–610 MPaTensile strength · Standard range for the normal product thickness range.
- 325 MPa at t ≤ 16 mm, decreasing to 275 MPa at 160 < t ≤ 200 mmMinimum yield strength · Design and purchasing must use the minimum applicable to the actual product thickness.
- No mandatory Charpy requirementNotch toughness · The suffix A must not be treated as equivalent to the impact-tested B or C qualities.
- Up to 200 mm for plate, sheet, strip and sections; up to 100 mm for flatsNormal dimensional scope · SM490A plate may be supplied up to 300 mm by agreement under the standard's special annex provisions.
- C ≤ 0.20% through 50 mm; C ≤ 0.22% over 50 through 200 mmWeldability control · Welding procedure decisions must also consider the actual heat analysis, carbon equivalent or Pcm, hydrogen, restraint and thickness.
Overview
- Designation system
- Japanese Industrial Standards (JIS)
- Product forms
- Plate and sheet, Strip in coil and cut lengths, Hot-rolled sections, Hot-rolled flats, Specially ordered hot-extruded sections, Deformed flats subject to the applicable annex requirements
- Condition
- No separately designated heat-treatment condition, Normalized by agreement: N, Tempered by agreement: T, Quenched and tempered: Q, Thermo-mechanically controlled by agreement: TMC, Other heat treatment by agreement
- Density
- 7850 kg/m³ (Typical engineering value for structural carbon steel; density is not a defining JIS G 3106 grade requirement.)
Definition and scope of the designation
JIS G 3106 covers highly weldable hot-rolled steels for welded structures such as bridges, ships, rolling stock, petroleum storage tanks and containers. In SM490A, “490” identifies the 490 MPa minimum tensile-strength class. The A quality is the basic SM490 quality and carries no standard Charpy absorbed-energy requirement.
SM490A is a product-standard designation, not merely a chemical composition. Compliance requires the applicable chemistry, tensile properties, product dimensions, tolerances, testing, inspection and marking provisions of JIS G 3106.
Product form, thickness and delivery condition
| Product form | Normal applicable thickness | Important qualification |
|---|---|---|
| Plate, sheet, strip in coil and hot-rolled sections | ≤ 200 mm | For sections, the governing thickness is the thickness at the tensile-test location as defined through JIS G 3192. |
| Hot-rolled flat | ≤ 100 mm | Narrow flats are subject to the special tensile provisions of Annex JB. |
| Plate by special agreement | ≤ 300 mm | The chemistry and tensile requirements in Annex JA apply; values for ordinary products must not simply be extrapolated. |
| Hot-extruded section | Annex-specific | Special shape, dimensions, test-piece location and manufacturing requirements apply by agreement. |
| Deformed flat | Annex-specific | Must be ordered and assessed under the dedicated requirements in Annex JD. |
Product availability from an individual mill may be narrower than the standard's dimensional scope.
The grade may be supplied without a separately identified heat-treatment suffix or with a specified condition. JIS suffixes include N for normalizing by agreement, T for tempering by agreement, Q for quenching and tempering, and TMC for thermo-mechanical control by agreement. Because processing route can affect toughness, weldability and behavior during subsequent heating, the ordered and certified condition should be recorded rather than inferred from the base designation.
Chemical composition and weldability controls
| Applicable thickness | C max. | Si max. | Mn max. | P max. | S max. |
|---|---|---|---|---|---|
| t ≤ 50 mm | 0.20% | 0.55% | 1.65% | 0.035% | 0.035% |
| 50 < t ≤ 200 mm | 0.22% | 0.55% | 1.65% | 0.035% | 0.035% |
These are heat-analysis requirements. Elements without stated limits, including microalloying or other alloying additions, may be used where permitted; added alloying elements are to be reported.
| Thickness | Ceq max. | Pcm max. |
|---|---|---|
| t ≤ 50 mm | 0.38% | 0.24% |
| 50 < t ≤ 100 mm | 0.40% | 0.26% |
| t > 100 mm | By agreement | By agreement |
The certificate should contain the alloying-element analyses needed to verify the applicable calculation.
The grade is intended for welded construction, but the designation alone does not establish that preheat is unnecessary. Welding controls must be selected from the actual material certificate and joint conditions, including thickness, restraint, consumable hydrogen level, heat input, ambient temperature and applicable fabrication code. Maximum permitted chemistry should not be used as a substitute for the heat-specific Ceq or Pcm when developing a welding procedure.
Required tensile properties
| Product thickness t | Minimum yield point or proof stress | Tensile strength |
|---|---|---|
| t ≤ 16 mm | 325 MPa | 490–610 MPa |
| 16 < t ≤ 40 mm | 315 MPa | 490–610 MPa |
| 40 < t ≤ 100 mm | 295 MPa | 490–610 MPa |
| 100 < t ≤ 160 mm | 285 MPa | 490–610 MPa |
| 160 < t ≤ 200 mm | 275 MPa | 490–610 MPa |
These values cover the ordinary dimensional range. Special plate over 200 mm is governed by Annex JA.
| Applicable thickness | JIS tensile test piece | Minimum elongation |
|---|---|---|
| t ≤ 5 mm | No. 5 | 22% |
| 5 < t ≤ 16 mm | No. 1A | 17% |
| 16 < t ≤ 50 mm | No. 1A | 21% |
| t > 40 mm | No. 4 | 23% |
The test-piece requirements are part of the property definition and are not interchangeable. For a No. 4 specimen from products over 100 mm thick, one percentage point is subtracted for each 25 mm thickness increment or fraction, with a maximum deduction of three points.
Sections with a leg length under 40 mm and flats under 40 mm wide are governed by Annex JB tensile requirements. Annex JB may also be applied in specified adjacent dimensional ranges; the main-table properties should therefore not be assumed for every small section or narrow flat.
Toughness and grade selection
SM490A has no mandatory Charpy V-notch absorbed-energy requirement. This does not mean that every heat has poor toughness; it means that compliance with SM490A does not certify a minimum notch toughness at any temperature. The grade should therefore not be selected solely from its tensile properties where low service temperature, high restraint, thick welded details, fatigue loading, impact loading or brittle-fracture consequences make toughness important.
| Grade | Tensile class | Standard Charpy requirement for products over 12 mm | Selection significance |
|---|---|---|---|
| SM490A | 490–610 MPa | None | Basic quality where a certified impact value is not required. |
| SM490B | 490–610 MPa | Mean of three longitudinal V-notch specimens: ≥ 27 J at 0 °C | Adds a defined toughness guarantee. |
| SM490C | 490–610 MPa | Mean of three longitudinal V-notch specimens: ≥ 47 J at 0 °C | Higher specified toughness than B quality. |
A lower test temperature or additional transverse testing may be agreed where required. Project specifications can be more restrictive than the base JIS grade.
Fabrication implications
SM490A can be fabricated by conventional structural-steel cutting, forming and welding processes, subject to qualified procedures. Thermal cutting edges and highly restrained welds deserve particular attention in thick material. Consumables are normally selected to satisfy the required joint strength and toughness under the governing welding code; JIS G 3106 does not itself prescribe a universal electrode or wire.
Cold-forming limits, bend radii, flame-straightening parameters, post-weld heat treatment and maximum heat input are not universally defined by the SM490A designation. These operations should be based on product thickness, certified delivery condition, mill recommendations where applicable, and the fabrication or design specification. Heating TMCP material without review may alter the properties developed by controlled rolling and cooling.
If through-thickness ductility or resistance to lamellar tearing is required, specify an appropriate through-thickness property and testing requirement. SM490A does not inherently guarantee a Z-direction reduction-of-area class.
Ordering, certification and acceptance
| Item | Why it matters |
|---|---|
| Full designation and edition | Specify SM490A to JIS G 3106:2024 unless the project requires another edition. |
| Product form and dimensions | Determines the applicable thickness range, tensile requirements and dimensional standard. |
| Delivery condition | Record N, T, Q, TMC or another agreed condition where required. |
| Impact toughness | SM490A provides none by default; specify test temperature, energy, orientation and sampling if needed, or select SM490B/C. |
| Weldability data | Require heat analysis and the applicable Ceq or Pcm information needed for welding-engineering review. |
| Dimensional tolerances | JIS G 3192 applies to sections, JIS G 3193 to plate, sheet and strip, and JIS G 3194 to flats, unless stricter tolerances are ordered. |
| Inspection document | State the required document type under JIS G 0415 and any project-specific traceability requirements. |
| Nondestructive examination | Ultrasonic or other internal-quality acceptance criteria require explicit agreement; they are not an automatic SM490A requirement. |
| Surface condition and repairs | Define any restrictions beyond the referenced dimensional and appearance standards. |
| Special plate over 200 mm | Confirm Annex JA chemistry, tensile properties, test arrangements and agreement with the manufacturer. |
Inspection should verify that the certificate matches the marked material, heat number, dimensions and delivery condition. Particular attention should be paid to the thickness-dependent yield requirement and to whether the product falls under the main tables or a special annex. A certificate showing only “SM490A” and nominal strength is insufficient for assessing welding procedure, toughness or substitution suitability.
Substitution and cross-standard comparison
There is no universal one-to-one ASTM, EN or GB replacement for SM490A. Grades such as ASTM A572 Grade 50 or EN 10025-2 S355 grades may occupy a broadly similar structural-strength range, but their thickness-dependent strengths, impact guarantees, chemical limits, carbon-equivalent rules, product scopes, test-piece conventions and certification requirements differ. Substitution should be assessed against the complete product specification and project design basis, not a commercial equivalence table.
Sources
- JIS G 3106:2024 — Rolled steels for welded structureJapanese Standards Association
- JIS G 3106:2024 English previewJapanese Standards Association
- Chapter 2 — Metallic Materials, Section 202: Rolled steels for welded structureTokyo Metropolitan Government, Bureau of Construction
- SM490A — JIS G 3106-2024 material dataH2ABC Material Database
- SM490A — JIS G 3106-2024 composition, mechanical properties and weldability indicesCaishuku Material Database
- JIS G 3106:2020 — Rolled steels for welded structureJapanese Standards Association reproduction
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