SM490YA
Hot-rolled weldable structural steel; 490 MPa tensile-strength class with enhanced yield strength · JIS G 3106:2024 — Rolled steels for welded structure
SM490YA is the higher-yield, A-quality member of the JIS G 3106 SM490 family. It combines 490–610 MPa tensile strength with a minimum yield point of 365 MPa at thicknesses up to 16 mm, falling to 325 MPa at 75–100 mm. It is intended for welded structures, but the A suffix is crucial: unlike SM490YB, the base grade carries no mandatory Charpy impact-energy requirement. Thickness, product form, delivery condition and any required toughness therefore need to be stated explicitly when ordering or approving a substitution.
- 490–610 MPa tensile strengthStrength class · Standard range for the normal thickness range through 100 mm.
- 365 MPa minimum at t ≤ 16 mmEnhanced yield strength · Higher than ordinary SM490A/B/C; the minimum decreases with increasing thickness.
- Generally up to 100 mmStandard thickness range · Plate thickness up to 150 mm may be available by purchaser–manufacturer agreement under the applicable provisions; do not apply the ≤100 mm requirements without
- No mandatory Charpy value for SM490YAImpact toughness · Use SM490YB or specify supplementary toughness requirements when notch toughness is design-critical.
- CEV ≤0.38% at t ≤50 mm; ≤0.40% at 50<t≤100 mmWeldability controls · Heat-analysis-based limits; Pcm limits are also defined.
- JIS G 3106:2024Current governing edition · Published February 20, 2024; it replaced the 2022 edition.
Overview
- Designation system
- Japanese Industrial Standards (JIS) grade designation
- Product forms
- Steel plate and sheet, Strip in coil and cut lengths from coil, Hot-rolled sections, Flats, Specially ordered hot-extruded sections under the applicable annex
- Condition
- Hot-rolled condition without a heat-treatment suffix, Normalized by agreement: SM490YAN, Tempered by agreement: SM490YAT, Quenched and tempered: SM490YAQ, Thermo-mechanically controlled by agreement: SM490YATMC, Other agreed heat treatment identified by an agreed suffix
- Density
- 7.85 g/cm³ (Representative density used for mass calculations; JIS G 3106 does not define density as an acceptance requirement.)
What the designation establishes
SM490YA is a structural steel designation defined by JIS G 3106, not a proprietary alloy name. “490” identifies the 490 MPa tensile-strength class. The “Y” variant has a higher specified yield point than SM490A, SM490B and SM490C at corresponding thicknesses. The final “A” denotes the quality variant without a specified Charpy absorbed-energy requirement; SM490YB has the same basic strength class but adds impact testing.
The designation alone does not completely define a purchase. Product form, dimensions, standard edition, heat-treatment suffix, inspection document and any project-specific toughness or testing requirements remain essential.
Product scope and thickness applicability
| Product form | Normal applicability for SM490YA | Important qualification |
|---|---|---|
| Plate/sheet and strip in coil | Thickness up to 100 mm | Plate thickness beyond 100 mm, up to the permitted agreed range, requires purchaser–manufacturer agreement and the applicable annex requirements. |
| Hot-rolled sections | Thickness at the test-piece location up to 100 mm | Section thickness is determined using the dimensional definitions in JIS G 3192. |
| Flats | Thickness up to 100 mm | Special tensile provisions apply to narrow flats. |
| Hot-extruded sections | At least 5 mm thick; leg length or height up to 250 mm | Specially ordered product under the normative annex and subject to agreement. Test-piece location may also require agreement. |
Dimensional tolerances are governed by the relevant JIS dimensional standard: JIS G 3192 for sections, JIS G 3193 for plate/sheet and strip, and JIS G 3194 for flats.
Mechanical properties are thickness-dependent. For sections, the controlling thickness is the thickness at the specified test-piece location, which may not be the nominal overall depth or flange width. Material over the normal 100 mm range must not be accepted simply by extrapolating the tabulated values for thinner product.
Chemical composition and weldability controls
| Element | Maximum, mass % |
|---|---|
| Carbon, C | 0.20 |
| Silicon, Si | 0.55 |
| Manganese, Mn | 1.65 |
| Phosphorus, P | 0.035 |
| Sulfur, S | 0.035 |
These are heat-analysis requirements, not target compositions. Other elements may be added when necessary and should be reported when intentionally added as required by the standard.
| Applicable thickness | Maximum carbon equivalent, CEV | Maximum weld-crack sensitivity composition, Pcm |
|---|---|---|
| t ≤ 50 mm | 0.38% | 0.24% |
| 50 < t ≤ 100 mm | 0.40% | 0.26% |
| t > 100 mm | By purchaser–manufacturer agreement | By purchaser–manufacturer agreement |
Values are calculated from heat analysis. The order and inspection certificate should make clear which weldability information is required and reported.
The composition envelope is designed for structural weldability, but compliance with a maximum CEV or Pcm is not a welding procedure. Required preheat, interpass temperature, heat input and hydrogen control still depend on the actual certificate chemistry, combined thickness, restraint, consumable hydrogen level, ambient conditions and applicable fabrication code. A numerical preheat temperature cannot be assigned safely from the grade name alone.
Mechanical-property requirements
| Nominal 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 |
For sections, thickness means thickness at the test-piece location. Requirements beyond 100 mm must be taken from the agreed thick-plate provisions rather than this table.
| Product thickness | Test piece | Minimum elongation |
|---|---|---|
| t ≤ 5 mm | JIS No. 5 | 19% |
| 5 < t ≤ 16 mm | JIS No. 1A | 15% |
| 16 < t ≤ 50 mm | JIS No. 1A | 19% |
| 40 < t ≤ 100 mm | JIS No. 4 | 21% |
The thickness ranges overlap because different specimen geometries apply. Elongation values must not be compared or transferred without retaining the specified specimen type and gauge geometry.
The principal distinction from ordinary SM490A/B/C is yield strength rather than tensile strength: all remain within the 490–610 MPa tensile band, while SM490YA provides substantially higher minimum yield values. This distinction matters for design resistance, forming loads, residual-stress behavior and substitution reviews.
Toughness limitation of the A quality
JIS G 3106 does not assign a mandatory Charpy absorbed energy to SM490YA. A compliant SM490YA certificate can therefore contain no impact-test result, even for material thicker than 12 mm. The grade must not be treated as having demonstrated notch toughness at 0 °C or any lower service temperature solely because it is intended for welded structures.
| Grade | Minimum yield at t ≤16 mm | Standard Charpy requirement for t >12 mm | Practical distinction |
|---|---|---|---|
| SM490YA | 365 MPa | None | Higher-yield A quality. |
| SM490YB | 365 MPa | 27 J average at 0 °C, longitudinal V-notch | Higher-yield grade with specified impact toughness. |
| SM490B | 325 MPa | 27 J average at 0 °C, longitudinal V-notch | Lower-yield SM490 grade with B-level toughness. |
| SM490C | 325 MPa | 47 J average at 0 °C, longitudinal V-notch | Lower-yield SM490 grade with higher specified absorbed energy. |
Charpy requirements apply under the thickness and test provisions of JIS G 3106. Project specifications may impose different temperatures, orientations or energy values.
For bridges, fatigue-sensitive details, dynamically loaded structures, cold-service equipment or fracture-critical components, specify the required Charpy temperature, energy, orientation, specimen size and sampling location rather than relying on SM490YA alone.
Delivery condition and metallurgical route
JIS G 3106 permits normalizing, tempering, quenching and tempering, thermo-mechanical control and other agreed heat treatments. The appropriate suffix is appended to the grade when such treatment applies. Consequently, two products marked SM490YA and SM490YATMC may satisfy the same basic strength table while having different manufacturing histories, microstructures and responses to subsequent thermal processing.
| Suffix | Condition represented | Procurement implication |
|---|---|---|
| None | No separately identified heat-treatment condition in the designation | Do not assume normalized or TMCP supply. |
| N | Normalized by agreement | Condition forms part of the ordered designation. |
| T | Tempered by agreement | Confirm the producer's complete processing route. |
| Q | Quenched and tempered | Heat treatment is explicitly identified. |
| TMC | Thermo-mechanically controlled by agreement | Review heat-input and post-fabrication thermal-treatment restrictions with the producer. |
Any producer-specific rolling or cooling practice that is not represented by a standard suffix should be confirmed through the order and inspection documentation.
Stress relieving, hot forming or other fabrication heat treatment can alter the properties created by controlled rolling or quenching and tempering. Where such operations are planned, compatibility with the actual delivery condition should be established rather than inferred from the generic SM490YA designation.
Specification, purchasing and inspection
| Item | Why it matters |
|---|---|
| Complete designation and standard edition | Specify SM490YA to JIS G 3106:2024 and include any condition suffix. |
| Product form and dimensions | Strength, sampling and dimensional tolerances depend on form and thickness. |
| Required delivery condition | Plain, N, T, Q and TMC conditions are not interchangeable descriptions. |
| Impact toughness, if needed | The base YA grade has no standard Charpy guarantee. |
| CEV or Pcm reporting | Needed for welding-engineering review; require the relevant alloy analyses used in the calculation. |
| Inspection document | State the required document type and project certification expectations. |
| Additional testing | Ultrasonic testing, through-thickness properties, low-temperature Charpy testing and restricted chemistry are not automatically created by the grade designation. |
| Surface and dimensional requirements | Invoke the applicable JIS product-dimensional standard and any tighter project tolerances. |
Certificate review should verify the exact grade and suffix, heat number, product dimensions, heat analysis, calculated weldability index where required, yield and tensile results, elongation specimen, and any separately ordered tests. For sections, confirm that the reported tensile result corresponds to the applicable test location and thickness.
A mill result exceeding a property not required by the grade—such as an incidental Charpy value—does not convert SM490YA into SM490YB or create a continuing guarantee for later orders.
Substitution and cross-standard comparison
SM490YA has no universal one-to-one ASTM or EN substitute. Materials in the S355 or nominal 50 ksi yield-strength families may appear similar in selected thicknesses, but their tensile ranges, toughness classes, chemistry limits, weldability indices, permissible product forms, delivery conditions and certification rules differ. Substitution should compare the complete governing product specification and project requirements, not only nominal yield strength.
Within JIS G 3106, SM490YB is the closest related designation when the same higher-yield level is required together with a standard 0 °C impact guarantee. SM490A, B and C are not strength-equivalent alternatives because their specified minimum yield point is lower at corresponding thicknesses.
Sources
- JIS G 3106:2024 — Rolled steels for welded structureJapanese Standards Association
- JIS G 3106:2024 English previewJapanese Standards Association
- Structural Shapes — Chemical Composition and Mechanical PropertiesNippon Steel Corporation
- Major Building Materials CatalogJFE Steel Corporation
- Steel Product SpecificationsChina Steel Corporation
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