SS400, S45C, SUS304, SPCC …. Issued by JSA. 2 grades and 2 standards are documented so far; each grade links to a full data sheet and a graded cross-reference to the other systems.
JIS designations begin with letters that identify what the steel is for, which makes them quicker to read than they first appear. SS is general structural (SS400), SM structural for welding (SM490), S..C is carbon steel for machine parts (S45C), SUS is stainless (SUS304), SUJ bearing steel (SUJ2), SKD die steel (SKD11), SPCC cold-rolled sheet, SPHC hot-rolled sheet.
Once the prefix is known the number usually gives the property: SS400 guarantees 400 MPa tensile, SM490 guarantees 490 MPa tensile, S45C carries 0.45 % carbon.
Tensile, not yield — a trap for EN users
This is the single most common misreading. SS400 is named for tensile strength, not yield. Its guaranteed yield is 245 MPa, close to S235, while the 400 in the name refers to a tensile minimum of 400 MPa.
Assuming SS400 is a 400 MPa yield steel because S355 is a 355 MPa yield steel overstates its capacity by well over half. The JIS structural series and the EN structural series use the same style of name for different properties.
Where JIS is stricter than the equivalent
JIS grades often carry tighter chemical limits than their nominal equivalents, particularly on phosphorus and sulphur, and Japanese mills commonly deliver above the specified minimum. That is why a JIS certificate frequently satisfies a European specification even when the standards do not formally cross-reference.
The reverse does not hold. An EN grade does not automatically satisfy a JIS specification, because the test methods and the product tolerances differ.
faq.h
What is SS400 steel?
A JIS general structural steel with a guaranteed tensile strength of 400 MPa and a yield of about 245 MPa. The number refers to tensile strength, not yield — a common source of confusion for users of EN designations.
Is SS400 equivalent to S235JR?
Approximately, on yield: SS400 guarantees about 245 MPa against 235 for S235JR. The impact requirements differ, so for a code-governed structure the specified standard should be followed rather than the equivalence.
What does SUS304 mean?
SUS is the JIS prefix for stainless steel, and 304 follows the AISI numbering. SUS304 is the Japanese designation for the same 18/8 austenitic grade as EN 1.4301 and UNS S30400.
What is S45C steel?
A JIS carbon steel for machine structural use with 0.45 % carbon — the same idea as EN C45 and AISI 1045. The S..C prefix marks the machine-structural carbon series.
What does SPCC mean?
JIS cold-rolled carbon steel sheet of commercial quality, broadly comparable to EN DC01. SPHC is the hot-rolled equivalent.