JIS SS400 Steel: Equivalent Grades and What They Mean

SS400 is the structural grade much of Asia quotes by default, and it is the grade most often misread. The 400 in the name is a minimum tensile strength, not a yield strength, so an SS400 certificate cannot be compared line by line with a Q235B or an S355JR certificate that is named after its yield. This page sets out what JIS G3101 actually guarantees, which grades buyers normally accept as equivalents, and the four points at which substitution stops being safe.

How to read the designation

SS400 comes from JIS G3101, the Japanese standard for rolled steel for general structure. The letters and the number each carry a meaning that a buyer needs before comparing it with anything else:

• SS — steel for general structure. Not a pressure grade, not a boiler grade, not a shipbuilding grade; a general structural grade.
• 400 — the lower limit of the tensile strength range, not the yield strength. This is the single most common source of confusion in Far East enquiries.

European and Chinese structural grades work the other way round. S235 under EN 10025-2 and Q235 under GB/T 700 are both named for a minimum yield of 235, and A36 under ASTM A36 is named for a minimum yield of 36 ksi. A buyer who reads “SS400” as a sibling of “S400” will expect a far stronger steel than the standard delivers, and a buyer who reads it as weaker than Q235 will over-specify.

What JIS G3101 specifies, and what it leaves to the mill

The standard fixes a tensile range, a minimum yield, a minimum elongation, and caps on phosphorus and sulphur. It does not set limits on carbon, silicon or manganese for SS400, which is why two SS400 certificates from two mills can look quite different in composition while both being fully compliant.

There is no impact toughness requirement in the SS400 specification. That single omission is what rules SS400 out of cold-climate and dynamic-load work, and it is the first thing an inspector looks for when a substitution is proposed on a project that has an impact requirement written into the specification.

The equivalence table buyers actually use

The grades below are the ones normally offered against an SS400 enquiry. They occupy the same mechanical role, which is what “equivalent” means in a commercial conversation — it does not mean the certificates are interchangeable.

For the Chinese side of the same family — Q195, Q235B and Q355B, with the GB, ASTM, EN and JIS columns side by side — see Q235B vs A36 vs S235JR, and for how the Q-series is constructed see Chinese steel grades explained.

Four questions that decide whether substitution is safe

Whether A36 or S235JR may be delivered in place of SS400 is not a metallurgical argument in the first instance. It is a documentary one, and then a service one. Four questions settle almost every case:

1. What standard does the contract name? If the specification says ASTM A36, an SS400 certificate is not an A36 certificate, and an inspector is entitled to reject the substitution on that ground alone. Substitution needs written approval before shipment, not a discussion at destination.
2. Is there an impact or low-temperature requirement? SS400 carries no toughness requirement. Where the design temperature or the service demands impact testing, the grade must be one that specifies it.
3. Is the item pressure-retaining or safety-critical? SS400 is a general structural grade. Pipe, vessel and boiler work belongs to standards written for that duty, with their own inspection regime.
4. Is the joint welded and dynamically loaded? Composition is not specified for SS400, so weldability varies between mills. For cyclically loaded welded work, specify a grade with guaranteed composition and toughness rather than accept whatever the mill ran.

SS400 is not SM400

The two designations are one letter apart and are routinely confused in enquiries. SM400 belongs to JIS G3106, the standard for rolled steel for welded structure, and it carries guaranteed weldability and notch toughness that SS400 does not. On a welded fabrication — a bridge, a crane girder, a dynamically loaded frame — the difference is the whole point of the specification.

The practical instruction is simple: if the drawing says SS400 but the application is a welded structure with fatigue or low-temperature exposure, raise the question before the order is placed. Accepting SS400 because it is what the mill had in stock is how a compliant delivery becomes a non-compliant structure.

Markets where SS400 is not the accepted grade

SS400 dominates Japan, Korea, Taiwan and much of South East Asia, and it travels well through those supply chains. It is not what every market asks for. Indian projects normally specify IS 2062, and Australian and New Zealand projects normally specify AS/NZS 3678; in both cases the certificate must be issued to the named standard, and an SS400 certificate will not be accepted as a substitute however close the mechanical properties look. Projects in the Gulf and in Africa frequently follow the ASTM or the EN route instead.

The commercial consequence is that the destination decides the standard, and the standard decides which mill can quote. Sending an SS400 enquiry to a mill that only rolls to ASTM wastes a week; naming the destination standard in the first message is the cheapest acceleration available.

What to put on the purchase order

A purchase order that says “SS400” and nothing else leaves the mill free to choose the product form, the delivery condition and the documentation. Six items close that gap:

1. The standard and its edition — JIS G3101, not simply “SS400”.
2. Product form and dimensions: plate, sheet, equal angle, channel, beam or flat bar, with the size range.
3. Delivery condition: as-rolled, pickled, or with a specified surface treatment.
4. Certificate type: an EN 10204 3.1 mill test certificate, or the specific document the project requires.
5. Any additional requirement the standard does not carry — composition limits, impact testing, ultrasonic inspection, dimensional tolerance class.
6. Marking, bundling and sea-worthiness, including how the bundles are strapped and protected for the voyage.

A well-written enquiry with those six items gets comparable offers from every mill that can roll the grade. See the steel plate and equal angle ranges, or how certificates and inspection are handled on an order.

Related reading

• Q235B vs A36 vs S235JR
• Chinese steel grades explained
• EN 10025 S235JR, S275JR and S355JR
• Steel plate range
• Equal angle steel
• Sections and profiles

Frequently asked questions

What is SS400 steel?

A general structural steel under JIS G3101, the Japanese standard for rolled steel for general structure. The 400 refers to the lower limit of its tensile strength range, not to a yield strength.

What is the equivalent of SS400?

The usual cross-references are ASTM A36, EN 10025-2 S235JR, DIN 17100 St37-2 and ISO 630 Fe360. They share a mechanical role, but each is a separate certificate and substitution needs the buyer’s written approval.

Does the 400 in SS400 mean yield strength?

No. It is a tensile strength figure. S235 and Q235 are named from minimum yield, which is why the numbers are not comparable across those designation systems.

Is SS400 the same as Q235B?

They fill the same role in general structures but belong to different standards. A Q235B mill certificate is not an SS400 certificate, and the two differ in specified composition and yield.

Can SS400 be welded?

Generally yes, but JIS G3101 does not set carbon, silicon or manganese limits for SS400, so weldability varies between mills. For welded structures with fatigue or toughness requirements, specify a grade that guarantees composition and impact properties.

Can SS400 be used at low temperature?

Not on the strength of the SS400 specification, which carries no impact toughness requirement. Cold-climate service needs a grade with a defined impact test temperature and energy.

Buying SS400 to a project standard? Send the standard and edition, the product form and size range, the quantity and the destination port. Browse the sections and profiles range, the steel plate range, or request a quotation.