Does SUS304 material meet a drawing that calls for ASTM 304 or 303?

What does “SUS304” actually mean on a quote or mill certificate?

“SUS” is the JIS prefix for stainless steel, and SUS304 is a grade defined in a family of JIS product standards, one per product form. It names a chemistry and a set of properties inside a specific JIS standard, not a universal material.

The prefix is usually read as “steel use stainless”, and the number after it deliberately follows the old AISI series, which is why SUS304, SUS303, SUS316 and SUS430 look familiar to a US reader. What the name does not carry is the product form. In the JIS system the same grade name appears in separate standards for different forms: JIS G 4303 covers hot-worked stainless bars in round, square, hexagonal and flat sections, while other JIS standards in the G 43xx series cover cold-finished bar (JIS G 4318), hot-rolled plate, cold-rolled sheet and strip, wire rod and wire. A certificate that says “SUS304” without the standard number leaves open which of those documents, and which edition, the mill tested to.

The ASTM side works the same way. Grade 304 is defined for bars in ASTM A276/A276M, for plate and sheet in a different specification, and for pressure-vessel bar in ASTM A479. The “AISI 304” name that many drawings still use is historical: the American Iron and Steel Institute numbering survives as a grade name, but the requirements now live in ASTM and in the Unified Numbering System (UNS) number S30400. So the honest comparison is never “SUS304 versus AISI 304”; it is “JIS G 4303 SUS304 versus ASTM A276 304”, two product standards with their own limits, tests and conditions.

On quotes from suppliers in China and Southeast Asia, “SUS304” is also used loosely as a trade name for any 18-8 stainless. Chinese mills make bar to the national standard GB/T 1220, where the 304 type is named 06Cr19Ni10 and the 303 type Y12Cr18Ni9, yet the invoice may still say SUS304. That is not dishonest in itself, but it means the word on the quote is not evidence of which standard the bar was made to.

Does SUS304 material satisfy a drawing that calls for ASTM A276 304?

Not automatically. A bar whose certificate cites only JIS G 4303 SUS304 is very likely to fall inside the ASTM A276 chemistry for 304, but it has not been shown to, and the drawing requirement is met only when a document demonstrates conformance to the specification the drawing names.

The chemistry ranges for the main elements, carbon, chromium and nickel, are closely aligned between the two standards because both descend from the same grade. The differences sit at the edges: an element limited in one standard and not listed in the other, slightly different ranges for a secondary element, a different rounding or reporting convention. Nitrogen is the usual example, since ASTM stainless bar specifications typically set a nitrogen maximum for 304 that a JIS certificate may simply not report. A missing element is a finding, not a pass, as the mill test report guide explains.

The mechanical side differs more than the chemistry. ASTM A276 recognizes several conditions, including annealed and cold-worked conditions, and the tensile, yield and elongation minimums depend on condition and size; the general requirements for sampling and testing sit in ASTM A484/A484M, and the test methods in ASTM A370. A JIS certificate reports tests run to the JIS test methods, on the JIS condition, against JIS minimums. The numbers are usually close, but “usually close” is an engineering judgment, and that judgment belongs to the design authority, not to receiving inspection.

There are three acceptable ways to close the gap. The first and simplest is a multi-standard certificate: many mills test and document one heat against ASTM A276, ASTM A479, JIS G 4303 and EN 10088-3 at once, and a certificate listing all of them, with the heat number, satisfies a drawing that names any one. The second is a drawing or purchase order note that explicitly accepts JIS G 4303 SUS304 as an equivalent, ideally with a condition such as “chemistry to meet ASTM A276 limits”. The third is a written deviation after an engineer compares the certificate element by element with the ASTM table. What is not acceptable is silence, where the supplier assumes the names are interchangeable and the buyer assumes the certificate says ASTM.

If the part is for pressure-retaining service, the bar is often required to ASTM A479 or the ASME SA-479 version of it rather than A276, and JIS equivalence becomes a code question as well as an engineering one. Ask the code owner before accepting any substitution.

What should the certificate show when the bar was made to JIS?

It should show the heat number, the exact standard and edition, the grade, the product form and size, the condition, the full heat chemistry and the mechanical results the specification calls for (tensile for A276 bar, hardness for A582 free-machining bar), and it should say which standards the heat conforms to. If ASTM is on your drawing, ASTM should be on the certificate.

Read a JIS-based certificate the way you read any mill test report, with a few extra checks. Look for the standard number, not just “SUS304”; a certificate citing a sheet standard does not cover bar. Check the condition: JIS G 4303 covers hot-worked bar, and austenitic grades in it are normally supplied solution treated, while cold-finished bar comes under JIS G 4318 and may carry different properties. Check the strength units, because JIS certificates report in N/mm² (the same value in MPa) and a US drawing may state ksi. And check whether the document type is a mill-issued inspection certificate or a stockist’s summary; the EN 10204 3.1 vs 2.2 guide explains why that matters.

Watch for the cheap substitute. Some low-cost “stainless” bar sold under an 18-8 trade name is a 200-series grade that replaces part of the nickel with manganese and nitrogen. It looks the same, machines differently and corrodes sooner. A certificate with full chemistry exposes it immediately; a magnet does not. The 200-series grades are austenitic too, so they are essentially nonmagnetic when annealed, just like 304, while cold work can give 304 some magnetic response, as the association’s note on magnetic properties of austenitic stainless steels explains. If the stakes justify it, a positive material identification check by an independent lab on a sample from each heat is the usual way to close that risk.