SM490YB
Higher-yield weldable structural steel · JIS G 3106:2024 — Rolled steels for welded structure
SM490YB is the higher-yield, impact-tested member of the JIS G 3106 490 MPa tensile-strength class. It combines a minimum yield strength of 365 MPa at thicknesses up to 16 mm, decreasing to 325 MPa above 75 mm through 100 mm, with a specified tensile range of 490–610 MPa and a longitudinal Charpy V-notch requirement of 27 J at 0 °C for products over 12 mm thick. Product form, thickness, delivery condition and test-piece applicability must remain attached to any property statement or purchase order.
- JIS G 3106:2024Current governing edition · The 2024 edition is the current JIS edition and replaced JIS G 3106:2022.
- 490–610 MPa tensile strengthStrength class · The number 490 identifies the lower limit of tensile strength, not yield strength.
- 365 MPa minimum yield at t ≤ 16 mmHigher-yield variant · The Y identifies the higher-yield version of the SM490 family; JIS G 3106 does not define it by a maximum yield ratio.
- 27 J minimum mean at 0 °CB-quality toughness · Longitudinal Charpy V-notch testing applies to covered products over 12 mm thick.
- Up to 100 mmNormal thickness scope · SM490YB plate may be supplied up to 150 mm by purchaser–manufacturer agreement under the standard's special provisions.
- Heat analysisChemistry basis · C ≤ 0.20%, Si ≤ 0.55%, Mn ≤ 1.65%, P ≤ 0.035% and S ≤ 0.035% for the normal thickness range.
Overview
- Designation system
- JIS grade designation
- Product forms
- Hot-rolled plate and sheet, Strip in coil and cut lengths, Hot-rolled sections, Flat steel, Hot-extruded sections subject to the applicable annex requirements, Deformed flats where the applicable annex requirements are met
- Condition
- Condition supplied without a heat-treatment suffix, Normalized by agreement (N), Tempered by agreement (T), Quenched and tempered (Q), Thermo-mechanically controlled by agreement (TMC), Other heat treatment identified by an agreed suffix
- Density
- 7850 kg/m³ (Representative engineering value for carbon and low-alloy structural steel; not a grade requirement of JIS G 3106.)
What the designation defines
SM490YB is a non-proprietary JIS structural-steel designation intended for welded structures such as bridges, ships, rolling stock, storage tanks, containers and comparable fabricated structures. It is not a single producer chemistry or heat-treatment recipe: conformance is established through the product-form, composition, mechanical-property, toughness, dimensional, inspection and identification requirements of JIS G 3106.
| Element | Practical meaning |
|---|---|
| SM | JIS family designation for rolled steels intended for welded structures. |
| 490 | Minimum tensile-strength class: 490 MPa. It does not indicate a 490 MPa yield strength. |
| Y | Higher-yield-strength variant relative to ordinary SM490A/B/C grades. |
| B | Impact-tested quality: 27 J minimum mean Charpy V-notch energy at 0 °C, subject to the standard's thickness and sampling rules. |
A Charpy test temperature is an acceptance-test condition, not by itself a minimum design or service temperature. Service-temperature suitability must be determined under the governing design code, detail category, stress state, section thickness and fabrication requirements.
Product scope, thickness and delivery condition
The normal applicable thickness for SM490YB plate/sheet, strip, sections and flats is 100 mm or less. For sections, the controlling thickness is the thickness at the prescribed test-piece location rather than necessarily the nominal overall section size. Plate up to 150 mm may be ordered by agreement, but the special composition and tensile-property provisions for the extended thickness range must then be applied; properties for ordinary ≤100 mm material should not simply be extrapolated.
| Suffix | Condition | Procurement significance |
|---|---|---|
| None | Condition supplied without one of the listed treatment suffixes | Do not assume a specific rolling or heat-treatment route solely from the unsuffixed grade name; confirm the mill certificate when route matters. |
| N | Normalized by agreement | Ordered designation becomes SM490YBN. |
| T | Tempered by agreement | Treatment and resulting condition must be agreed. |
| Q | Quenched and tempered | Ordered designation becomes SM490YBQ. |
| TMC | Thermo-mechanically controlled by agreement | Ordered designation becomes SM490YBTMC; the standard provides agreed carbon-equivalent or PCM provisions for TMC plate. |
| Agreed symbol | Other agreed heat treatment | The suffix and treatment definition must be established between purchaser and manufacturer. |
Specified chemical composition
The following limits are heat-analysis requirements for SM490YB in its normal thickness range through 100 mm. JIS G 3106 permits other elements, including elements not listed in the basic composition table, to be added as necessary. Consequently, the complete certified analysis—not only the five listed elements—should be used for welding assessments and comparison with another specification.
| Element | Requirement, mass % | Technical relevance |
|---|---|---|
| Carbon, C | ≤ 0.20 | Principal basic control affecting strength, hardenability and weldability. |
| Silicon, Si | ≤ 0.55 | Deoxidation and strengthening contribution. |
| Manganese, Mn | ≤ 1.65 | Strength and hardenability contribution; the current limit must not be replaced by values taken from older JIS editions. |
| Phosphorus, P | ≤ 0.035 | Residual-element maximum. |
| Sulfur, S | ≤ 0.035 | Residual-element maximum; this limit does not constitute a through-thickness or lamellar-tearing performance guarantee. |
The basic SM490YB designation does not specify a universal through-thickness ductility class, ultrasonic quality class, maximum yield ratio, or corrosion-resistance enhancement. Any such requirement must be ordered separately under an applicable standard or agreed acceptance specification.
Mechanical-property requirements
| Product thickness t | Minimum yield point or proof stress | Tensile strength |
|---|---|---|
| t ≤ 16 mm | 365 MPa | 490–610 MPa |
| 16 < t ≤ 40 mm | 355 MPa | 490–610 MPa |
| 40 < t ≤ 75 mm | 335 MPa | 490–610 MPa |
| 75 < t ≤ 100 mm | 325 MPa | 490–610 MPa |
The thickness reduction in minimum yield strength is fundamental to the grade. A statement that SM490YB is simply a “365 MPa steel” is valid only for thicknesses through 16 mm. Tensile strength remains 490–610 MPa through the normal 100 mm range.
| Thickness range | JIS tensile test piece | Minimum elongation |
|---|---|---|
| t ≤ 5 mm | No. 5 | 19% |
| 5 < t ≤ 16 mm | No. 1A | 15% |
| 16 < t ≤ 50 mm | No. 1A | 19% |
| t > 40 mm where No. 4 applies | No. 4 | 21% |
Elongation values cannot be compared correctly without retaining the JIS test-piece type and product applicability. Small sections, narrow flats, hot-extruded sections and extended-thickness plate can invoke annex provisions that should be checked directly for the ordered form.
Charpy toughness requirement
| Parameter | SM490YB requirement |
|---|---|
| Applicability | Covered steel products over 12 mm thick |
| Test | Charpy V-notch according to JIS Z 2242 |
| Test temperature | 0 °C |
| Absorbed energy | Mean of three test pieces ≥ 27 J |
| Sampling direction | Longitudinal axis of test piece in the rolling direction |
| Notch orientation | Notch axis perpendicular to the rolled surface |
| Striker | 2 mm radius |
| Alternative temperature | A lower test temperature may be agreed between purchaser and manufacturer |
The B suffix is the principal distinction from SM490YA: SM490YB retains the higher-yield mechanical-property schedule while adding specified impact performance. For fracture-critical work, 27 J at 0 °C may be insufficient or may use a different specimen orientation from that required by the project. Required test temperature, energy, orientation, specimen size and any individual-value criterion should therefore be checked against the project specification rather than inferred from the grade name alone.
Weldability and fabrication implications
JIS G 3106 is specifically directed at weldable structural steels, and the basic carbon limit is compatible with that purpose. Nevertheless, the grade name alone does not determine preheat, interpass temperature, heat input, hydrogen control, consumable classification or post-weld heat treatment. Those decisions depend on the complete heat analysis, calculated carbon equivalent or PCM, thickness, joint restraint, welding process, consumable hydrogen level, ambient conditions and applicable welding code.
Cold forming, hot forming, flame straightening and stress-relief operations can change properties locally or globally, especially when the delivered steel is normalized, quenched and tempered, or thermo-mechanically controlled. Fabrication procedures should preserve the certified condition or be qualified to demonstrate that required strength and toughness remain available after processing.
Ordering and inspection essentials
| Item | What to state or verify |
|---|---|
| Standard and edition | JIS G 3106:2024 and grade SM490YB. |
| Product form and dimensions | Plate, sheet, strip, section, flat, hot-extruded section or other covered form; nominal thickness and applicable dimensional standard. |
| Delivery condition | Unsuffixed grade or the required N, T, Q, TMC or other agreed suffix. |
| Extended thickness | For plate over 100 mm through 150 mm, explicitly invoke the purchaser–manufacturer agreement and applicable annex requirements. |
| Toughness | Confirm whether the standard 27 J at 0 °C longitudinal test is sufficient; state any lower temperature, higher energy or transverse testing requirement. |
| Weldability data | Request full heat analysis and, where needed, reported Ceq or PCM. Do not calculate from only C, Si and Mn if other alloy additions are present. |
| Nondestructive testing | Specify ultrasonic or other NDT method, sampling and acceptance class separately; the base grade does not automatically include a plate UT quality class. |
| Inspection document | Specify the required inspection document under JIS G 0415 and ensure heat number, grade and condition remain traceable. |
| Dimensions and tolerances | Apply the relevant standard: JIS G 3192 for sections, JIS G 3193 for plate/sheet/strip, or JIS G 3194 for flat steel. |
| Additional requirements | State through-thickness properties, surface class, repair restrictions, weldability limits or project-specific testing where required. |
Acceptance testing is lot-based and depends on product form, heat, thickness grouping and heat-treatment grouping. Impact testing normally uses three specimens from a sample representing the maximum thickness in the applicable lot. Material certificates should therefore be checked for traceability to the supplied pieces and for the correct product form, thickness, test direction, test temperature and delivery condition—not merely for the printed grade designation.
Grade selection and substitution
SM490YB should not be substituted solely by matching a nominal 355 MPa yield-strength class or a 490 MPa tensile-strength class. A valid substitution review must compare the governing product specification, thickness-dependent strength, Charpy temperature and orientation, chemistry and weldability controls, delivery condition, dimensional tolerances, testing frequency, certification and any project-specific approvals.
| Grade | Relationship to SM490YB | Important distinction |
|---|---|---|
| SM490YA | Same higher-yield schedule and 490–610 MPa tensile range | YA does not carry the SM490YB standard Charpy requirement. |
| SM490B | Same tensile range and 27 J at 0 °C impact class | Lower minimum yield strength: 325 MPa at t ≤ 16 mm rather than 365 MPa. |
| SM490C | Same tensile range with higher specified impact energy | 47 J at 0 °C, but uses the lower ordinary SM490 yield schedule. |
| SM520B | Same nominal yield schedule and 27 J at 0 °C impact class | Higher tensile range of 520–640 MPa and a separate grade chemistry/property definition. |
Sources
- JIS G 3106:2024 — Rolled steels for welded structureJapanese Standards Association
- JIS G 3106:2024 English previewJapanese Standards Association
- Tokyo Metropolitan Government Materials Specification — Rolled steels for welded structuresTokyo Metropolitan Government
- Manufacturing standards — JIS G 3106 rolled steels for welded structureNippon Steel Structural Shapes Corporation
- Steel Plates Product CatalogueNippon Steel Corporation
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