SS400
General-purpose hot-rolled structural carbon steel · JIS G 3101:2024 — Rolled steels for general structure
SS400 is the 400 MPa tensile-strength class in JIS G 3101 for general structural hot-rolled products. It provides thickness-dependent yield strength, tensile strength, elongation and bendability, but controls only phosphorus and sulfur in its basic chemical specification and requires no Charpy impact toughness. It is therefore a broad general-purpose grade, not a chemistry-controlled or toughness-qualified welding grade.
- JIS G 3101:2024Current governing edition · Issued February 20, 2024 and active; it replaced the 2022 edition.
- 400–510 MPaTensile strength · The “400” in SS400 refers to the lower tensile-strength limit, not yield strength.
- 245 MPa at thickness ≤16 mmMinimum yield strength · Falls to 235 MPa above 16–40 mm, 215 MPa above 40–100 mm and 205 MPa above 100 mm.
- P ≤0.050%; S ≤0.050%Specified chemistry · No standard limits are stated for C, Si or Mn for SS400.
- Not specifiedImpact toughness · SS400 carries no Charpy test temperature or absorbed-energy requirement.
- JIS G 0415 certificate 3.1Default inspection document · Unless the purchase order specifies otherwise.
Overview
- Designation system
- Japanese Industrial Standard grade designation
- Product forms
- Hot-rolled plate and sheet, Hot-rolled strip in coil and cut lengths from strip, Hot-rolled sections, Flats and deformed flats, Hot-rolled bars and bar-in-coil, Specially ordered hot-extruded sections
- Condition
- Hot-rolled delivery, Heat-treated material where specifically manufactured or ordered; testing is grouped by heat-treatment condition, Hot-extruded sections and deformed flats by purchaser-manufacturer agreement under the applicable normative annex
- Density
- 7850 kg/m³ (Nominal carbon-steel value used for calculated mass. JIS G 3193 uses a basic plate mass of 7.85 kg per mm of thickness per square metre; this is not a grade-specific acceptance property.)
Definition and specification boundaries
JIS G 3101 covers hot-rolled steels used for general structures such as bridges, ships, vehicles and other structural work, together with certain hot-extruded sections. SS400 is one of the standard’s general structural grades. Its designation is strength-based: the number identifies the lower limit of the 400–510 MPa tensile-strength range.
SS400 is a product-standard designation, not a precise alloy composition. A certificate or drawing that says only “SS400” does not establish carbon content, carbon equivalent, impact toughness, through-thickness properties, ultrasonic quality, surface preparation or corrosion protection.
The 2024 edition is based on ISO 630-1:2021 and ISO 630-2:2021 but is classified as modified rather than identical. JIS retains its own tensile-strength-based grade designations and Japan-specific provisions, so an ISO grade should not be inferred solely from SS400.
Product form controls the applicable requirements
| Product form | Applicable requirement framework | Important qualification |
|---|---|---|
| Plate, sheet and strip | JIS G 3101 mechanical requirements; dimensions, mass and tolerances principally through JIS G 3193 | Strength and elongation depend on thickness and tensile-test specimen. |
| Hot-rolled sections | JIS G 3101 mechanical requirements; dimensions, mass and tolerances principally through JIS G 3192 | For yield strength, thickness is taken at the test-piece location. Small sections may fall under Annex JA. |
| Flats | JIS G 3101 with dimensional requirements principally through JIS G 3194 | Flats under 40 mm wide use the special mechanical-property provisions of Annex JA; deformed flats are addressed separately in Annex JC. |
| Bars and bar-in-coil | Separate bar mechanical-property table in JIS G 3101; dimensions and tolerances principally through JIS G 3191 | Yield is based on diameter or width across flats; elongation uses bar-specific test pieces. |
| Hot-extruded sections | Normative Annex JB | Specially ordered shapes are applied by agreement between purchaser and manufacturer. |
| Deformed flats | Normative Annex JC | Shape, dimensions and some test-piece provisions differ from ordinary flats and require agreement on the ordered product. |
Mechanical values from plate, bar and small-section tables must not be combined into one universal SS400 property set. The ordered form, controlling dimension and specimen type must be identified first.
Chemical composition: intentionally broad
| Element | JIS G 3101 limit, mass % | Interpretation |
|---|---|---|
| C | Not specified | Carbon content is not controlled by the SS400 grade requirement. |
| Si | Not specified | No silicon range or maximum is imposed. |
| Mn | Not specified | No manganese range or maximum is imposed. |
| P | ≤0.050 | Maximum heat-analysis value. |
| S | ≤0.050 | Maximum heat-analysis value. |
| Other elements | Not generally limited | Elements without stated limits may be added as necessary; added elements are to be reported on the inspection document. |
This sparse chemistry is the most important limitation of SS400. It allows producers considerable freedom to achieve the required mechanical properties, but it means weldability, hardenability, machinability and thermal-cutting response cannot be assessed reliably from the grade name alone. Typical mill chemistry must not be presented as a JIS requirement.
Mechanical requirements for plate, sheet, strip, ordinary flats and sections
| Controlling thickness t | Minimum, MPa |
|---|---|
| t ≤16 mm | 245 |
| 16 < t ≤40 mm | 235 |
| 40 < t ≤100 mm | 215 |
| t >100 mm | 205 |
Unless otherwise specified, upper yield point is used where pronounced; otherwise 0.2% proof strength is used. For sections, t is the thickness at the test-piece location.
| Tensile strength (MPa) | All applicable thicknesses |
|---|---|
| Tensile strength | 400–510 |
The tensile-strength range does not remove the thickness dependence of yield strength.
| Product thickness t | JIS tensile specimen | Minimum elongation |
|---|---|---|
| t ≤5 mm | No. 5 | 21% |
| 5 < t ≤16 mm | No. 1A | 17% |
| 16 < t ≤50 mm | No. 1A | 21% |
| t >40 mm | No. 4 | 23% |
The overlap above 40 through 50 mm reflects the applicable specimen alternatives. For No. 4 specimens from plate or sheet over 90 mm thick, one percentage point is deducted for each additional 25 mm or fraction thereof, with a maximum deduction of three points.
| Bending angle | Minimum inside radius | Standard bend specimen | Acceptance basis |
|---|---|---|---|
| 180° | 1.5 × product thickness | No. 1 | No cracking on the outside of the bent portion |
The manufacturer may omit the production bend test unless the purchaser requires it, but the product must still satisfy the specified bendability.
The specified bend test is an acceptance test, not an unrestricted shop-forming rule. Actual minimum bend radius also depends on bend orientation, edge condition, tooling, plate thickness, local chemistry and forming method.
Mechanical requirements for bars
| Diameter or width across flats d | Minimum yield or proof strength | Tensile strength |
|---|---|---|
| d ≤16 mm | 245 MPa | 400–510 MPa |
| 16 < d ≤40 mm | 235 MPa | 400–510 MPa |
| 40 < d ≤100 mm | 215 MPa | 400–510 MPa |
| d >100 mm | 205 MPa | 400–510 MPa |
| Bar size | Tensile specimen | Minimum elongation | Bend requirement |
|---|---|---|---|
| d ≤25 mm | No. 2 | 20% | 180° around an inside radius of 1.5d; No. 2 bend specimen |
| d >25 mm | No. 14A | 22% | 180° around an inside radius of 1.5d; No. 2 bend specimen |
For non-round bars, d represents side length or width across flats as applicable.
Testing, inspection and certification
Heat analysis is performed under JIS G 0320 and the general delivery and inspection provisions of JIS G 0404. Tensile testing is conducted at room temperature under JIS Z 2241, while bend testing follows JIS Z 2248. Mechanical-test material is sampled in accordance with JIS G 0416; for plate, strip and flat products the test-piece centre is normally located one-quarter of the width from the edge or as close as practicable.
| Product | Basic lot grouping | Number of specimens |
|---|---|---|
| Plate, sheet and ordinary flat | Same heat; maximum thickness no more than twice the minimum thickness in the lot | One; two when lot mass exceeds 50 t. A plate over 50 t is tested individually. |
| Strip and cut lengths from strip | Same heat and rolled to the same thickness | One; two when lot mass exceeds 50 t. |
| Sections | Same heat and same sectional profile; maximum thickness no more than twice the minimum | One; two when lot mass exceeds 50 t. |
| Bars | Same heat and same sectional profile; maximum diameter or width no more than twice the minimum | One; two when lot mass exceeds 50 t. |
| Heat-treated products | Otherwise applicable product grouping, additionally separated by heat-treatment condition | As required for each heat-treatment lot. |
Unless the order states otherwise, the manufacturer submits an inspection certificate 3.1 under JIS G 0415. Product marking normally includes the grade, heat or inspection number, dimensions, bundle quantity or mass where applicable, and the manufacturer’s name or identifying mark. Agreed omissions are permitted only where product identification remains possible.
Fabrication and service implications
SS400 is commonly fabricated by welding, but JIS G 3101 does not guarantee a maximum carbon content, carbon equivalent or weld-cracking parameter. The grade name alone is therefore insufficient for selecting preheat, heat input, consumables or hydrogen controls. For consequential welding, obtain the full heat analysis, calculate the carbon-equivalent measure required by the governing welding procedure, consider restraint and thickness, and qualify the procedure under the applicable fabrication code. Where assured weldability is a fundamental design requirement, a JIS G 3106 SM grade is generally the more appropriate specification family.
The standardized 180° bendability requirement demonstrates a basic level of ductility, but forming performance can vary because chemistry and microstructure are only loosely constrained. Heavy bending, small radii, bending parallel to the rolling direction, flame-cut edges and thick sections deserve procedure trials or product-specific confirmation.
SS400 is normally processed using conventional carbon-steel sawing, shearing, drilling, machining and thermal-cutting methods. However, the broad permitted chemistry means cutting response, tool life and heat-affected-zone hardness can vary between heats and suppliers. Production settings should be based on the actual certificate and process trials rather than an assumed fixed carbon content.
No Charpy impact test is required for SS400. Compliance with tensile and bend requirements does not establish fracture toughness or suitability for low-temperature, dynamically loaded, fatigue-sensitive or impact-critical service. Such applications require a material standard and grade with the necessary toughness qualification, or additional purchaser-specified testing accepted by the responsible engineer.
SS400 is an unalloyed structural steel without a corrosion-resistance requirement. Coating, galvanizing, painting, corrosion allowance and surface preparation must be specified according to the exposure and fabrication process. A request for SS400 alone does not define mill scale removal, blast-cleaning grade, primer, coating system or final appearance.
Ordering and receiving checklist
| Item | Recommended specification detail | Why it matters |
|---|---|---|
| Standard and edition | JIS G 3101:2024 | Prevents use of an obsolete edition or a supplier’s generic interpretation. |
| Grade and product form | SS400 plus plate, sheet, strip, section, flat or bar | Selects the applicable mechanical table and dimensional standard. |
| Dimensions | Thickness or diameter, width, length and section designation | Strength requirements and tolerances are dimension-dependent. |
| Section classification | For sections, include the JIS G 3192 steel grade and relevant series where required | These are mandatory ordering inputs under JIS G 3101 for applicable sections. |
| Inspection document | JIS G 0415 certificate 3.1 unless another document is required | Defines traceability and reported inspection results. |
| Full heat analysis | Explicitly require C, Si, Mn and other elements needed for welding calculations | The basic SS400 chemistry table does not require these limits. |
| Bend testing | State whether an actual bend test is required | The standard permits the manufacturer to omit the test unless the purchaser specifies it. |
| Additional quality requirements | Impact testing, ultrasonic examination, through-thickness properties, surface class, flatness class or special tolerances as applicable | None should be assumed from SS400 alone. |
| Delivery and processing condition | Heat treatment, pickling, shot blasting, priming, coating or galvanizing where required | These are not universally defined by the grade designation. |
| Identification and traceability | Heat-number transfer rules for cut parts | Maintains linkage between received certificates and fabricated components. |
At receipt, verify that the certificate, markings and dimensions refer to the same heat and product form. Confirm the thickness-dependent yield requirement rather than checking only the prominent 400–510 MPa tensile range.
Selection and substitution boundaries
SS400 should not be replaced solely by matching a nominal strength class. A valid substitution review compares the complete product standards: form and dimensional range, chemistry, yield strength by thickness, tensile range, elongation specimen, bendability, toughness, manufacturing route, inspection, certification and project-code recognition.
| Engineering need | More relevant specification family | Reason |
|---|---|---|
| Controlled weldability or welded structural service | JIS G 3106 SM grades | Provides chemistry and weldability controls; B and C grades also introduce specified impact toughness. |
| Building structures requiring controlled structural behavior | JIS G 3136 SN grades | Building-specific requirements include tighter chemistry and, depending on grade, toughness, yield-ratio or through-thickness provisions. |
| Pressure-retaining service | Applicable boiler, pressure-vessel or pressure-piping material standard | SS400 is a general structural grade and does not provide pressure-purpose qualification. |
| Low-temperature or impact-critical service | A grade with a specified Charpy test temperature and absorbed energy | SS400 has no impact-toughness guarantee. |
| Precisely controlled machining or heat-treatment response | A chemistry-defined machine-structural steel | SS400 does not define a narrow carbon or alloy composition. |
Sources
- JIS G 3101:2024 — Rolled steels for general structureJapanese Standards Association
- JIS G 3101:2024 official previewJapanese Standards Association
- JIS G 3106:2024 — Rolled steels for welded structure, official previewJapanese Standards Association
- JIS G 3136:2022 — Rolled steels for building structureJapanese Standards Association
- JIS G 3193:2025 — Dimensions, shape, mass and permissible variations of hot rolled steel plates, sheets and stripsJapanese Standards Association
- Hot-Rolled Products Specifications, including JIS G 3101:2024China Steel Corporation
- Bars and Wire Rod Specifications, including JIS G 3101:2024China Steel Corporation
- JIS bars — G 3101 Rolled steel for general structuresKobe Steel, Ltd.
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