If you work with European fastener specifications, you've seen the EN material numbers — 1.4301, 1.4401, 1.4462 — and you know they map to familiar AISI grades like 304 and 316. But the relationship between the EN material designation system, the ISO 3506 property classes (A2-70, A4-80, etc.), and the actual mechanical and corrosion properties of each grade is where things get slippery.
This reference sheet is designed to be RFQ-ready, QA-document-ready, and supplier-spec-ready. Keep it handy for every stainless steel fastener inquiry that crosses your desk.
How the Systems Connect
European stainless steel grades are identified by two parallel systems:
Material number (Werkstoffnummer) — a 5-digit code like 1.4301 that uniquely identifies a specific chemistry. This is the most precise identifier and the one you should specify on formal documents.
EN material name — a systematic name like X5CrNi18-10 that encodes the alloy composition in the name itself. The digits after each element tell you the approximate percentage: 18% chromium, 10% nickel.
These map to AISI/ASTM equivalents (304, 316, etc.) for cross-referencing with US specifications, and to ISO 3506 property classes (A2-70, A4-80) which describe both corrosion resistance (A2 = 304-type, A4 = 316-type) and strength (70 = 700 MPa minimum tensile).
The table below brings all four systems together in one place, along with the practical data you need for material selection.
The Complete Reference Table
| EN Name | Mat. No. | AISI / ASTM | ISO 3506 | Type | Tensile (MPa) | Magnetic | Weldability | Typical Use |
|---|---|---|---|---|---|---|---|---|
| X5CrNi18-10 | 1.4301 | 304 | A2-70 / A2-80 | Austenitic | 500–700 | Slight (cold-worked) | Excellent | General fasteners, kitchen, process equipment |
| X2CrNi18-9 | 1.4307 | 304L | A2-70 | Austenitic | 480–700 | Slight | Excellent | Welded parts, piping, tanks |
| X6CrNiMo17-12-2 | 1.4401 | 316 | A4-70 / A4-80 | Austenitic | 500–800 | Slight | Excellent | Marine, chemical, chloride environments |
| X2CrNiMo17-12-2 | 1.4404 | 316L | A4-70 | Austenitic | 480–700 | Slight | Excellent | Welded assemblies, food & pharma |
| X2CrNiMoN22-5-3 | 1.4462 | Duplex 2205 | — | Duplex | 700–900 | Partial | Good | Offshore, bridges, pressure vessels |
| X2CrNiMoCuWN25-7-4 | 1.4501 | Super Duplex 2507 | — | Duplex | 800–1000 | Partial | Good | Subsea, desalination, chemical |
| X6Cr17 | 1.4016 | 430 | F1-60 | Ferritic | 400–600 | Yes | Moderate | Decorative trim, appliances |
| X12Cr13 | 1.4006 | 410 | C1-110 / C1-120 | Martensitic | 700–1100 | Yes | Poor | Screws, turbine blades, shafts |
| X20Cr13 | 1.4021 | 420A | C3-110 | Martensitic | 800–1100 | Yes | Poor | Cutlery, valves |
| X46Cr13 | 1.4034 | 420C | C4-120 | Martensitic | 950–1200 | Yes | Poor | Blades, bearings, surgical tools |
| X5CrNiCuNb16-4 | 1.4542 | 17-4 PH / 630 | — | PH | 900–1200 | Yes | Good | Aerospace, high-strength fasteners |
| X1NiCrMoCu25-20-5 | 1.4539 | 904L | — | Super Austenitic | 500–750 | No | Good | Chemical tanks, seawater piping |
Quick-Reference by Microstructural Family
Austenitic (A2, A4)
The default choice for stainless fasteners. Non-magnetic in the annealed condition (though cold working — like thread rolling — can induce slight magnetism). Excellent corrosion resistance, excellent formability, good weldability.
- A2 grades (1.4301/304, 1.4307/304L): General-purpose. Use for dry interiors, mild atmospheres, and food-contact surfaces. Avoid in chloride-heavy or marine environments.
- A4 grades (1.4401/316, 1.4404/316L): Molybdenum-bearing for chloride resistance. The go-to for coastal, marine, chemical, and pharmaceutical applications. The "L" variants (304L, 316L) have lower carbon for better weldability — specify these for welded assemblies.
ISO 3506 strength classes: A2-70 and A4-70 (700 MPa) are standard. A2-80 and A4-80 (800 MPa) are available in smaller diameters through additional cold working.
Ferritic (F1)
Magnetic, low cost, moderate corrosion resistance. Not hardenable by heat treatment. The only ferritic grade in common fastener use is 1.4016 (430 / F1-60), typically for decorative fasteners and interior architectural trim where stainless appearance matters but chlorides are not present.
Weakness: Poor weldability compared to austenitics, and significantly lower toughness.
Martensitic (C1, C3, C4)
The hardenable stainless steels. Magnetic, and capable of reaching high strength through heat treatment. The trade-off is drastically reduced corrosion resistance compared to austenitics — the chromium content is lower and the carbon is tied up in carbides rather than contributing to the passive layer.
- C1 (1.4006 / 410): Standard martensitic for self-tapping screws, turbine blades, and pump shafts. Strength range 700–1100 MPa.
- C3 (1.4021 / 420A): Higher carbon, slightly better hardness. Used for valve components and cutlery-grade fasteners.
- C4 (1.4034 / 420C): The highest carbon of the common martensitics. Used for blades, bearings, and surgical instruments. Can reach 1200 MPa.
WARNING: Martensitics must be heat treated to develop their strength. As-supplied (annealed) material is soft and unsuitable for load-bearing fasteners. Always verify the condition — and never specify martensitics for welded applications.
Duplex and Super Duplex
The premium choice for demanding environments. Duplex grades have a mixed austenitic-ferritic microstructure that delivers roughly twice the yield strength of 316 with superior stress corrosion cracking resistance.
- 1.4462 (Duplex 2205): 700–900 MPa tensile. The standard duplex for offshore structural bolting, bridge hardware, and pressure vessel fasteners.
- 1.4501 (Super Duplex 2507): 800–1000 MPa tensile. For subsea, deep-well, and high-chloride environments where even 316 would fail prematurely.
Caveat: Duplex grades are partially magnetic and require more care in machining and cold forming than standard austenitics.
Precipitation Hardening (PH)
The aerospace-grade solution. 1.4542 (17-4 PH / 630) achieves its strength through a low-temperature aging treatment that precipitates copper-rich particles within the martensitic matrix — no quenching required. Tensile strengths of 900–1200 MPa with good corrosion resistance make it the material of choice for high-strength aircraft fasteners, valve stems, and chemical processing hardware.
Practical Guidance for Fastener Selection
For standard bolts, screws, and nuts in dry or mildly corrosive environments: Specify A2-70 (1.4301 / 304). It is the most economical, most available, and most formable option.
For marine, coastal, chemical, or any chloride-containing environment: Step up to A4-70 or A4-80 (1.4401 / 316 or 1.4404 / 316L). The molybdenum content is not optional — it is the difference between a fastener that lasts decades and one that pits within a season.
For self-tapping screws and thread-forming fasteners requiring high hardness: Consider martensitic C1-110 (1.4006 / 410) — but only if the environment is mild and the parts will not be welded.
For offshore, subsea, or pressure-containing bolting: Duplex 1.4462 or Super Duplex 1.4501. The higher initial cost is justified by service life in conditions that would destroy A4 fasteners.
For aerospace or extreme-strength requirements: Precipitation hardening 1.4542 (17-4 PH). When you need 1000+ MPa in a stainless fastener, this is the standard answer.
A Note on Material Certification
When specifying stainless steel fasteners for critical applications — and especially when deviating from standard A2 or A4 — always request material certification to EN 10204 Type 3.1. This provides traceability from the mill through the fastener manufacturer, with documented chemical analysis and mechanical properties. The 3.1 certificate is the only reliable way to verify that the material number on the drawing matches the material in the part — and that the grade you paid for is the grade you received.