Chemical Composition of EN 1.4401 Stainless Steel (316)

EN 1.4401 stainless steel, known under the European designation X5CrNiMo17-12-2, is the direct European equivalent of AISI 316. It owes its position as the workhorse molybdenum-bearing austenitic grade to a balance of chromium, nickel and molybdenum that holds up in chemical processing, marine service, pharmaceutical production and food contact equipment. This article sets out the specified chemical composition to EN 10088-1, the equivalent grades in other standards, the role of each element and the mechanical values normally required at purchase.

What the EN 1.4401 Designation Covers

EN 1.4401 is defined in EN 10088-1, the European list of stainless steels, and is supplied as sheet, plate, strip, bar, tube and forgings under EN 10088-2, EN 10088-3 and the relevant product standards. The X5CrNiMo17-12-2 designation encodes the essential chemistry: approximately 17% chromium, 12% nickel and a molybdenum addition in the 2% range. The grade is austenitic at room temperature, non-magnetic in the annealed condition and hardenable only by cold work.

Chemical Composition of 1.4401 Stainless Steel

Element	Symbol	Content (wt.%)
Carbon	C	≤ 0.07
Silicon	Si	≤ 1.00
Manganese	Mn	≤ 2.00
Phosphorus	P	≤ 0.045
Sulphur	S	≤ 0.015
Chromium	Cr	16.5 - 18.5
Nickel	Ni	10.0 - 13.0
Molybdenum	Mo	2.00 - 2.50
Nitrogen	N	≤ 0.10
Iron	Fe	Balance

Values are the EN 10088-1 specification ranges for the grade. National and product specifications may narrow the ranges further, and mill certificates should always be checked against the standard called up on the purchase order, whether that is EN 10088-2 for flat products, EN 10088-3 for bar and sections, or ASTM A240 and ASTM A276 for the American equivalents.

Equivalent Grades in Other Standards

Standard system	Grade designation
EN / DIN	1.4401 / X5CrNiMo17-12-2
AISI / ASTM	316
UNS	S31600
JIS	SUS316
GB/T 20878	06Cr17Ni12Mo2

Equivalence is approximate. EN 1.4401 and ASTM 316 share the same intended chemistry, but their permissible ranges and mechanical requirements are not identical. For pressure equipment and safety-related components, the material certificate must reference the standard that the design code actually permits.

What Each Element Contributes

Carbon: raises strength but consumes chromium as carbide when the material is held in the 425 - 815 °C range, which is why the limit is kept at 0.07% in this grade.

Chromium: forms and maintains the chromium oxide passive film, and is the primary contributor to general corrosion resistance.

Nickel: stabilises the austenitic structure, improves toughness and helps resist reducing acids.

Molybdenum: the key addition for pitting and crevice corrosion resistance in chloride-bearing environments.

Nitrogen: increases strength and adds to pitting resistance while retarding carbide precipitation.

Manganese: partly substitutes for nickel and improves hot ductility with a low cost penalty.

Silicon: acts as a deoxidiser in melting and improves resistance to oxidising media at high temperature.

Phosphorus and sulphur: residual elements kept low because both impair weldability and hot workability.

The balance between the austenite formers (nickel, carbon, nitrogen, manganese) and the ferrite formers (chromium, molybdenum, silicon) determines whether the structure stays fully austenitic after processing. Molybdenum is a strong ferrite former, which is why the nickel range in 1.4401 sits above that of plain 18-8 grades such as 1.4301.

Mechanical Properties and PREN

Property	Typical requirement	Reference
Tensile strength, Rm	≥ 515 MPa	ASTM A240, grade 316
0.2% proof strength, Rp0.2	≥ 205 MPa	ASTM A240, grade 316
Elongation in 50 mm	≥ 40%	ASTM A240, grade 316
Hardness	≤ 95 HRB	ASTM A240, grade 316

The pitting resistance equivalent number, calculated as PREN = Cr + 3.3 Mo + 16 N, lands at about 24 to 25 for a mid-range heat. A typical analysis of 17.0% Cr, 2.2% Mo and 0.05% N gives 25.1. That places 1.4401 clearly above 304 and its molybdenum-free relatives, but below duplex grades and super austenitic grades such as 1.4539, which reach the mid-thirties.

Processing and Fabrication Notes

Annealing: solution anneal in the 1010 - 1120 °C range followed by rapid cooling to dissolve carbides and remove cold work.

Hot forming: work in the 1150 - 900 °C band and finish above 900 °C, then anneal to restore corrosion resistance.

Cold forming: readily drawn, bent and spun, with work hardening requiring intermediate anneals on severe reductions.

Welding: good weldability by all common arc processes; if heavy welded sections must resist intergranular attack, the low-carbon 1.4404 variant is usually selected instead.

Machining: gummy and prone to work hardening, so use sharp tooling with generous feeds and continuous cuts.

Where 1.4401 Is Used

Heat exchangers, pressure vessels and process piping

Food and beverage processing equipment

Pharmaceutical and cosmetic manufacturing lines

Marine fasteners and structural parts in atmospheric service

Architectural and sanitary components exposed to humidity

Frequently Asked Questions

Q: Is EN 1.4401 the same as 316 stainless steel?
They are the intended equivalents: EN 1.4401 is the European designation and 316 is the AISI or ASTM designation with UNS number S31600. Individual ranges and mechanical guarantees can differ between the two standards.

Q: What is the difference between 1.4401 and 1.4404?
Carbon content. 1.4401 permits up to 0.07% carbon, while 1.4404, the 316L equivalent, is limited to 0.030%. The lower carbon level in 1.4404 reduces the risk of chromium carbide precipitation in welded zones.

Q: Why is molybdenum added to 316 stainless steel?
Molybdenum markedly improves resistance to pitting and crevice corrosion in chloride environments such as seawater splash zones, chloride-bearing process streams and de-icing salts.

Q: What heat treatment does 1.4401 require?
Solution annealing between 1010 and 1120 °C followed by rapid cooling. The grade cannot be hardened by heat treatment; strength is obtained only by cold working.

Q: Can 1.4401 be used in seawater?
Only with care. It suits flowing, aerated seawater in low-velocity systems, but stagnant conditions or deposits promote crevice attack. For critical marine duty, higher-alloyed grades such as 1.4539 are preferred.

Q: How is the composition verified at delivery?
By the mill test certificate under EN 10204 type 3.1 together with incoming positive material identification. The certificate should list heat analysis for all specified elements in the table above.