EN 1.4401 (SUS316): EU Standard Stainless Steel Overview

EN 1.4401, designated X5CrNiMo17-12-2 in EN 10088, is the European standard molybdenum-bearing austenitic stainless steel, equivalent to JIS SUS316 and ASTM UNS S31600. The addition of 2.00-2.50% molybdenum to the 17-12 chromium-nickel base markedly improves resistance to pitting and crevice corrosion in chloride environments and to attack by reducing acids, which is why 1.4401 is a standard material for chemical, marine and food processing equipment.

Chemical composition (EN 10088-2, wt%)

	0.07 max
	1.00 max
	2.00 max
	0.045 max
	0.015 max
	0.11 max
	16.50 - 18.50
	10.00 - 13.00
	2.00 - 2.50

For solution-annealed products, typical guaranteed mechanical properties of 1.4401 are a tensile strength of 520-670 MPa, a 0.2% proof strength of 220 MPa min and an elongation of 40% min. For the JIS designation SUS316, JIS G4304 specifies a tensile strength of 520 MPa min, a yield strength of 205 MPa min and an elongation of 40% min for plate.

	520 MPa (JIS) / 520-670 MPa (EN)
0.2% proof strength	205 MPa (JIS) / 220 MPa (EN)
	40%

The molybdenum addition gives 1.4401 significantly better pitting resistance than 304 in chloride-bearing media, and good resistance to dilute sulfuric acid, phosphoric acid, acetic acid and organic media. It remains susceptible to pitting in warm stagnant seawater and to stress corrosion cracking in hot chloride solutions, and it is not suitable for concentrated hydrochloric or sulfuric acid service at elevated temperature.

1.4401 is formed, machined and welded using standard austenitic practice. Welding with matching or low-carbon filler (such as 1.4404 / ER316L type consumables) is recommended, followed by pickling and passivation to restore the passive film. Stainless steel tooling should be used exclusively to avoid iron contamination of the surface.

Typical applications include chemical and petrochemical vessels and piping, pulp and paper equipment, food and beverage processing lines, pharmaceutical and biotech plant, marine and offshore components, heat exchangers, valves, flanges, tanks and architectural elements.

Q1: What is the difference between EN 1.4401 and EN 1.4404? A1: 1.4404 (X2CrNiMo17-12-2) is the low-carbon variant with 0.030% carbon max, preferred for welded construction; 1.4401 is the standard-carbon grade.

Q2: Is 1.4401 the same as SUS316? A2: Yes, SUS316 (JIS G4303/G4304) and UNS S31600 are the equivalent designations of the same 17-12-2 molybdenum grade.

Q3: Can 1.4401 be used in seawater? A3: It has good resistance in marine atmospheres and mild chloride service, but for warm or stagnant seawater, higher-alloyed grades such as 6% molybdenum super-austenitic or duplex stainless steels should be evaluated.

Q4: What heat treatment is applied? A4: Products are supplied solution annealed, typically at 1020-1120℃C followed by rapid cooling, to restore the corrosion-resistant austenitic structure.

Q5: What is the maximum service temperature? A5: Continuous service up to about 870℃C is possible in oxidizing atmospheres; for aqueous chloride service the temperature and chloride concentration must be limited to avoid localized attack.