SS400 steel: properties, composition, equivalents
SS400 is the Japanese general structural steel of JIS G3101: 245 MPa yield to 16 mm, 400–510 MPa tensile, with no impact requirement and almost no chemical specification.
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What is SS400?
SS400 is the default structural steel of Japanese production and one of the most frequently quoted grade names in Asian trade. The designation is read in two parts: SS is *steel structure* — rolled steel for general structure — and 400 is the minimum tensile strength in MPa. It is not a yield figure, which is the single commonest misreading of the name.
What makes SS400 unusual among structural grades is what JIS G3101 leaves out. The standard specifies phosphorus at 0.050 % and sulphur at 0.050 % and stops there: carbon, silicon and manganese are not controlled, there is no carbon equivalent limit, and no impact test is required at any temperature. Everything the standard guarantees is mechanical — 245 MPa yield to 16 mm, a 400–510 MPa tensile band, and elongation.
That is a deliberate design. SS400 exists for general fabrication where the load path is simple and the joint is not restrained, and Japanese practice moves to JIS G3106 SM400 — same strength, full chemistry, carbon equivalent and a graded Charpy test — the moment welding matters. Treating SS400 and SM400 as interchangeable is the mistake the two standards exist to prevent.
Against European practice, SS400 sits between S235JR and S275JR on strength and below both on specification. A substitution in either direction works on the numbers and should be checked on the certificate, because an SS400 plate can legitimately arrive with a carbon content that no S235JR plate would be allowed to carry.
SS400 chemical composition
| Element | Mass % | Note |
|---|---|---|
| C | — | not specified |
| Si | — | not specified |
| Mn | — | not specified |
| P | ≤ 0.05 | |
| S | ≤ 0.05 |
JIS G3101 controls only phosphorus and sulphur on SS400 — carbon, silicon and manganese are left to the mill. That is the defining feature of the grade and the reason it is a general structural steel rather than a weldable structural steel. Where composition matters, JIS G3106 SM400 is the grade to specify: same strength, full chemistry and a carbon equivalent limit.
SS400 mechanical properties
| Thickness / condition | Yield strength ReH / Rp0.2 MPa (ksi) | Tensile strength Rm MPa (ksi) | Elongation A % | Hardness |
|---|---|---|---|---|
| ≤ 16 mm | 245 (35.5) | 400–510 (58.0–74.0) | 17 | ≈ 120–140 HB (typical) |
| > 16 ≤ 40 mm | 235 (34.1) | 400–510 (58.0–74.0) | 21 | — |
| > 40 mm | 215 (31.2) | 400–510 (58.0–74.0) | 23 | — |
Yield point (not proof stress) by thickness; tensile band applies to all thicknesses. Elongation depends on the test piece as well as the thickness — JIS uses No. 1A, No. 5 and No. 4 pieces over different ranges, so a certificate can show different percentages for the same material. The 400 in the name is the tensile floor in MPa; it is not a yield figure.
Impact toughness
SS400 requires a minimum Charpy V-notch energy of J at °C (no requirement). JIS G3101 sets no Charpy requirement for SS400 at any temperature. A certificate that carries impact values is reporting a voluntary test, not conformity. Where toughness is part of the design, the JIS grade to specify is SM400A, B or C — the letter grades the impact test exactly as JR / J0 / J2 do in Europe.
SS400 equivalent grades
| Grade | System | Match | Why / differences |
|---|---|---|---|
| A36 | ASTM / ASME | Near | The closest single match: A36 is 250 MPa yield and 400–550 MPa tensile, and it too has no impact requirement for plate. A36 does cap carbon and manganese, which SS400 does not. |
| St37-2 | DIN (superseded German) | Near | JIS G3101 SS400: yield 245 MPa, Rm 400–510 MPa; often listed as St37 equivalent in Asian catalogues. |
| S235JR | EN (European) | Near | Yield 245 MPa against 235, tensile 400–510 against 360–510. SS400 is marginally stronger, but S235JR is tested to 27 J at +20 °C and specifies full chemistry with a carbon equivalent, which SS400 does not. |
| Q235 | GB/T (China) | Near | Q235B is the Chinese grade of the same tier — 235 MPa yield, 370–500 MPa tensile — but it carries a chemistry specification and a 27 J impact test at +20 °C. |
| St3sp | GOST (Russia/CIS) | Near | St3sp is 245 MPa yield to 20 mm and 370–480 MPa tensile with full chemistry; the strength tier matches, the specification depth does not. |
| E250 | IS (India) | Near | IS 2062 E250 is 250 MPa yield and 410 MPa minimum tensile — the same commodity structural tier, with a carbon equivalent limit that SS400 lacks. |
| S275JR | EN (European) | Functional | Yield 245 MPa, below S275; SM400 is closer on impact but also 245 MPa. |
Identical = same composition and mechanical limits within rounding. Near = one limit differs (e.g. carbon max or impact temperature). Functional = interchangeable for most uses after an engineering check. Full cross-reference for SS400 →
Old and superseded designations
| Old name | Standard | Note |
|---|---|---|
| SS41 | JIS G3101 (before 1995) | The number was the tensile floor in kgf/mm²: 41 kgf/mm² ≈ 400 MPa. Old Japanese drawings and second-hand machine plates still carry it. |
| SS34 / SS50 / SS55 | JIS G3101 (before 1995) | Renamed SS330, SS490 and SS540 in the same revision. |
Product forms and tolerance standards
Product forms: hot-rolled plate and sheet, sections: H beam (JIS G3192), channel, angle, flat bar, hot-rolled coil and strip, round and square bar, cold-formed and welded hollow sections certified separately to JIS G3466.
Dimensional tolerances: plate and sheet: JIS G3193; sections: JIS G3192; bar: JIS G3191; hot-rolled coil: JIS G3193.
Key property values
SS400 yield strength
245 MPa minimum up to 16 mm, 235 MPa from 16 to 40 mm and 215 MPa above 40 mm. JIS specifies a yield *point* rather than a 0.2 % proof stress, which is appropriate for a low-carbon steel with a defined yield plateau but is not strictly the same quantity as the European Rₑₕ.
SS400 tensile strength
400–510 MPa across all thicknesses. The band is narrower than the European S235JR band of 360–510 MPa and sits 40 MPa higher at the floor, which is why SS400 material normally satisfies an S235JR tensile requirement without difficulty.
SS400 chemical composition
Only P ≤ 0.050 % and S ≤ 0.050 % are specified. Typical mill analysis runs 0.15–0.20 % C, 0.30–0.60 % Mn and low silicon, but none of that is guaranteed. A buyer who needs a composition should ask for the ladle analysis before accepting the heat, not after.
SS400 and SM400
SM400 (JIS G3106) is the weldable equivalent: identical strength, but with carbon, silicon, manganese, phosphorus and sulphur all limited, a carbon equivalent ceiling, and a Charpy test graded A (none), B (27 J at 0 °C) and C (47 J at 0 °C). Japanese structural codes call up SM grades for welded work; SS400 is for general and lightly loaded fabrication.
SS400 against S235JR on a certificate
Three checks decide whether the substitution holds. Impact: if the design needs 27 J at +20 °C, SS400 does not guarantee it. Carbon equivalent: S235JR caps CEV at 0.35–0.40 depending on thickness; SS400 sets none. Thickness: above 40 mm the SS400 yield drops to 215 MPa, below the S235JR floor of 215 MPa at 80–100 mm — the two ladders do not step at the same points.
The SS grade ladder
SS330 (330–430 MPa tensile, 205 MPa yield), SS400, SS490 (490–610 MPa, 285 MPa yield), SS540 and SS590. The numbers are all tensile minimums in MPa. SS540 and SS590 are not intended for welding at all — the standard says so explicitly.
Weldability
SS400 is welded routinely by all arc processes, and in thin sections with simple joints it causes no trouble. The risk is structural rather than metallurgical: because the standard limits neither carbon nor the carbon equivalent, two heats of conforming SS400 can behave very differently in a restrained thick joint. A welding procedure qualified on one heat is not evidence for the next. Where the joint is thick, restrained or fatigue-loaded, specify SM400B or SM400C instead, or order SS400 with a maximum carbon equivalent agreed as a supplementary requirement. Consumables are the ordinary mild-steel classes — E4316 / E7016 or ER70S-6 equivalents.
Machining, forming and heat treatment
Machinability is good and comparable with other low-carbon structural steels, but it is not consistent between heats for the same reason the weldability is not: the carbon and manganese are whatever the mill ran. Cold forming and bending are acceptable in thin sections; there is no yield ceiling, so spring-back varies. For press work and deep drawing the correct Japanese specification is JIS G3131 SPHC, SPHD or SPHE, not SS400.
Typical applications
- General building steelwork and light structural frames in Japanese and export construction
- Machine frames, bases, guards and non-critical weldments
- Platforms, walkways, stairs and handrails
- Plate for hoppers, chutes, tanks and covers with no pressure duty
- Sections and coil exported against an S235JR or A36 requirement
- Shipbuilding ancillary structure (hull steel is classification-society grade, not SS400)
SS400 compared with related grades
Frequently asked questions
What is SS400 steel?
SS400 is the Japanese general structural steel of JIS G3101, with a 400–510 MPa tensile band and a 245 MPa minimum yield up to 16 mm. The standard controls only phosphorus and sulphur and requires no impact test, which makes it a mechanical specification rather than a metallurgical one.
Is SS400 the same as S235JR?
They are close on strength and not equivalent on specification. SS400 is 245 MPa yield against 235 and has a higher tensile floor, but S235JR guarantees 27 J at +20 °C, full chemistry and a carbon equivalent limit, none of which SS400 provides.
Is SS400 the same as A36?
It is the closest single match. A36 is 250 MPa yield and 400–550 MPa tensile, and like SS400 it carries no plate impact requirement. A36 does specify carbon and manganese, so it is the better-defined of the two.
Does the 400 in SS400 mean yield strength?
No — it is the minimum tensile strength in MPa. The yield is 245 MPa up to 16 mm. The confusion is common because European grades such as S235 and S355 are named after their yield instead.
What is the difference between SS400 and SM400?
SM400 (JIS G3106) has the same strength but adds a full chemical specification, a carbon equivalent limit and a graded Charpy test. Japanese design codes call up SM grades for welded structure and leave SS400 for general fabrication.
What was SS41?
The same grade under the pre-1995 designation, when the number was the tensile floor in kgf/mm²: 41 kgf/mm² is about 400 MPa. SS41 and SS400 describe the same material.
Can SS400 be used for pressure vessels?
No. It has no impact requirement, no carbon equivalent limit and no elevated-temperature properties. Japanese pressure-vessel plate is JIS G3115 SPV or JIS G3103 SB; the European counterparts are the EN 10028 P-grades.
Related grades
Verified against JIS G3101:2020; JIS G3101 — Rolled steels for general structure (JISC); JIS G3106 — Rolled steels for welded structure, for the SM400 comparison. Last checked: September 2026.