1.4404 vs S31603: Two Designations for the Same 316L Stainless Steel

Two Designations, One Material: 316L

Engineers and buyers sourcing 316L stainless steel regularly encounter two designations that appear to name different materials: EN 1.4404 and UNS S31603. They are in fact the same alloy. 1.4404 is the material number assigned in the European standard EN 10088-1, where the steel name is X2CrNiMo17-12-2. S31603 is the Unified Numbering System (UNS) designation used by ASTM and ASME standards, including ASTM A240 for plate, sheet, and strip, ASTM A312 and A269 for pipe and tube, and ASME SA240 for pressure-vessel applications. The difference is one of naming convention and regional code, not of metallurgy.

Where Each Designation Comes From

EN 1.4404: defined in EN 10088-1 (general stainless steel grade standard) and delivered under EN 10088-2 (sheet/strip) or EN 10088-3 (bar). Steel name X2CrNiMo17-12-2.

UNS S31603: defined in ASTM A240, A312, A269, A276, and related ASME SA specifications. Common commercial name: 316L.

Equivalent national designations: JIS SUS316L (JIS G4303/G4304) and GB 022Cr17Ni12Mo2 (GB/T 20878) in China.

Chemical Composition Comparison

Element (% by mass)	EN 1.4404 (EN 10088-1)	UNS S31603 (ASTM A240)
C	0.030 max	0.030 max
Cr	16.5-18.5	16.0-18.0
Ni	10.0-13.0	10.0-14.0
Mo	2.00-2.50	2.00-3.00
Mn	2.00 max	2.00 max
Si	1.00 max	0.75 max
P	0.045 max	0.045 max
S	0.015 max	0.030 max
N	0.11 max	0.10 max

The carbon limit, the property that defines the L (low-carbon) grade, is identical at 0.030% max in both systems. Chromium, nickel, and molybdenum ranges overlap almost completely; the small differences in silicon and sulfur limits reflect regional practice and do not change corrosion or mechanical behavior in practice.

Mechanical Properties

Property	ASTM A240 (plate)	EN 10088-2 (cold-rolled sheet, typical)
Tensile strength	485 MPa min	530-680 MPa
Yield strength	170 MPa min	240 MPa min (Rp0.2)
Elongation	40% min	40% min

Both systems specify a ductile, weldable austenitic material. The low carbon content prevents chromium-carbide precipitation at grain boundaries during welding, which is why 316L is the default choice for welded process equipment in chloride-bearing service.

Are 1.4404 and S31603 Interchangeable?

Yes for most engineering applications: the two designations describe the same alloy, and material supplied to either standard will meet the other's typical requirements. The qualification matters in code-governed work. Pressure vessels, piping systems, and heat exchangers are designed to a specific edition of ASME, EN, or other codes, and inspection bodies require material certificates that reference the governing standard. A buyer in a European project should request EN 10204 3.1 certificates for 1.4404; a buyer in an ASTM project should request certificates referencing S31603. Mixing standards without engineering review can cause documentation failures at inspection.

Applications of 316L (1.4404 / S31603)

Marine hardware and coastal architectural components

Pharmaceutical, food, and beverage processing equipment

Chemical storage tanks, piping, and evaporators

Heat exchangers and condensers

Welded structures in chloride-bearing environments where sensitization must be avoided

FAQ

Is 1.4404 the same as 316L?

Yes. 1.4404 is the EN material number for 316L, with the steel name X2CrNiMo17-12-2. The same alloy is called UNS S31603, JIS SUS316L, and GB 022Cr17Ni12Mo2.

What does the L in 316L mean?

L stands for low carbon. The maximum carbon content is 0.030%, compared with 0.08% for standard 316. The lower carbon limit prevents chromium-carbide precipitation during welding, preserving corrosion resistance in the heat-affected zone.

Can I use S31603 material when the drawing specifies 1.4404?

Chemically and mechanically yes, but the delivered material certificate must reference the standard required by the project code. Confirm with the design or inspection authority before substituting across EN and ASTM documentation systems.

What is the difference between 1.4401 and 1.4404?

1.4401 (X5CrNiMo17-12-2) is the EN equivalent of standard 316 with 0.07% max carbon, while 1.4404 is the low-carbon 316L with 0.030% max carbon. 1.4404 is preferred for welded applications; 1.4401 is used where higher room-temperature strength is needed and welding is limited.

Which mechanical values should I use for design?

Use the values from the standard that governs your project. For ASME pressure-vessel design, use ASME SA240 allowable stresses; for European design, use EN 10028-7 for pressure plates. Typical minimums are 485 MPa tensile and 170 MPa yield per ASTM A240 for plate.