304 Stainless Across Standards: 1.4301, SUS304, 06Cr19Ni10 and S30400

The same steel, four passports

System	Grade	UNS
AISI / ASTM	304	S30400
EN	1.4301 (X5CrNi18-10)	—
JIS	SUS304	—
GB	06Cr19Ni10	—

All four describe an austenitic stainless of roughly 18% chromium, 8–10% nickel and low carbon, and for most service they are used interchangeably. But certificates are written against a specific standard, and the windows are not identical.

Where the windows differ

• Carbon: ASTM permits up to 0.08% for 304; EN 1.4301 caps carbon at 0.07%. A heat at 0.075% C is legal 304 and not legal 1.4301.
• Chromium: the ASTM, JIS and GB windows start at 18.0% (18.0–20.0%); the EN window starts lower, at 17.5% (17.5–19.5%). A heat at 17.8% Cr passes EN and fails the other three.
• Nickel limits and minor-element rules also differ slightly by standard, and product standards for plate, bar and tube add their own permitted variations on top of the grade chemistry.

Substitution therefore has to be checked element by element against the target standard, heat by heat. The check is one-directional in each case: a heat that passes says nothing about the next heat from the same mill.

The 304 / 304L / 1.4307 trap

• 304L (UNS S30403, SUS304L, GB 022Cr19Ni10, EN 1.4307 / X2CrNi18-9) caps carbon at 0.03%, which is what protects welded fabrications against sensitization.
• 1.4301 is not 304L. A 1.4301 heat at 0.06% C is perfectly in grade — and cannot be re-certified as 304L or 1.4307.
• The reverse direction is the well-known exception: dual-certified 304/304L is common and legitimate when a low-carbon heat also meets the higher strength minima of straight 304. It must be ordered and certified as dual — it is not automatic for every 304L heat.
• Close siblings that are not interchangeable: 304H (S30409, carbon 0.04–0.10%, specified for creep strength at temperature), 1.4306 (X2CrNi19-11, a low-carbon variant with a higher nickel range), and the nitrogen-strengthened 304N / 1.4311 family.

Strength minima differ as well. Under ASTM A240, straight 304 carries a minimum yield strength of 205 MPa against 170 MPa for 304L — the reason dual certification requires the heat to be tested up to the straight-grade values rather than merely having low carbon. Anyone designing to minimum properties should read the grade actually certified, not the family name.

Practical rules

1. Put the governing standard on the purchase order, not just "304".
2. For welded pressure or process service, default to the L grade unless the design specifies otherwise.
3. Read the heat analysis on the mill certificate against the ordered standard window. Equivalence tables — including the one at the top of this guide — are starting points for that check, not approvals.