Data completeness: partial. Last verified 19 August 2026.
Designations
| Common name | 317LMN |
| UNS | S31726 |
| EN number | 1.4439 |
| Class | Austenitic stainless steel |
| Specified by | ASTM A240/A240M, EN 10088-2 |
317LMN is 317L with nitrogen added and molybdenum pushed up to about four percent. The nitrogen does two jobs at once — it lifts the pitting ranking by more than two points and it raises the proof strength minimum by a third over 317L on the same product form. It sits in the gap between the ordinary molybdenum austenitics and the six-molybdenum super-austenitics, and that gap is narrow enough that the choice usually comes down to price and stock.
Properties, with what each one rests on
| Property | Value | Unit | Condition | Evidence | Source | Retrieved |
|---|---|---|---|---|---|---|
| Proof strength Rp0.2, minimum (EN) | 290 | MPa | cold rolled coil and sheet, 20 °C | E3 | EN 10088-2 via Outokumpu Ultra range datasheet — high-alloy austenitic stainless steels | 2026-08-20 |
| Tensile strength Rm, minimum | 580 | MPa | cold rolled; datasheet gives a 580–780 range | E3 | EN 10088-2 via Outokumpu Ultra range datasheet — high-alloy austenitic stainless steels | 2026-08-20 |
| Elongation A, minimum | 35 | % | cold rolled; A and A80 both 35 | E3 | EN 10088-2 via Outokumpu Ultra range datasheet — high-alloy austenitic stainless steels | 2026-08-20 |
| PREN | 33 | — | from typical composition, not from a heat | E3 | Outokumpu Ultra range datasheet — high-alloy austenitic stainless steels | 2026-08-20 |
| Density | 8.0 | g/cm³ | 20 °C | E3 | Outokumpu Ultra range datasheet — high-alloy austenitic stainless steels | 2026-08-20 |
| Modulus of elasticity | 200 | GPa | 20 °C | E3 | Outokumpu Ultra range datasheet — high-alloy austenitic stainless steels | 2026-08-20 |
| Thermal conductivity | 14 | W/(m·K) | 20 °C | E3 | Outokumpu Ultra range datasheet — high-alloy austenitic stainless steels | 2026-08-20 |
| Critical pitting temperature | not established | — | — | — | not in the datasheet consulted, and in this alloy band it is what separates candidates | — |
| Composition limits | not established | — | — | — | ASTM A240 is paywalled; the datasheet gives typical values, which are not limits | — |
| Sigma phase formation and the limits it puts on heat input | not established | — | — | — | at four percent molybdenum this matters in welding and the datasheet consulted does not cover it | — |
7 sourced values, 3 gaps named. Publishing the gaps is more useful than filling them from an aggregator that does not say where its numbers came from. The routes to filling them are the standard itself, a mill datasheet, or a mill certificate for your actual heat — which supersedes both at E5.
Where the numbers come from
Proof strength Rp0.2, minimum (EN). Quarto plate for the same grade is 270 MPa. Comparing this against the 317L page here means comparing cold rolled against plate, because the datasheet lists no cold rolled row for 317L — a product form difference sitting on top of the grade difference.
PREN. 17.3% Cr, 4.1% Mo and 0.14% N give 33.1 in the datasheet’s own formula. Five points above 317L, one below 904L, and ten below 254 SMO — the middle of a range where the ranking number stops discriminating usefully and service data has to take over.
Why we do not just copy an aggregator. Because then this page would be a worse copy of MatWeb with no way for you to tell which rows to trust, and the one thing we have that MatWeb does not is the evidence column. Our coverage and its limits.
What 317LMN is usually chosen for
Flue gas desulphurisation absorbers, pulp bleaching and chemical process equipment where 316L and 317L are pitting but a six-molybdenum alloy cannot be justified. The nitrogen strengthening is a genuine bonus rather than a side effect: at the same wall thickness the vessel takes more pressure, so the uprating is not purely a corrosion decision.
And what it is usually rejected for
Stock and the size of the gap it fills. Few distributors hold it in every form, and the band between 317L and 254 SMO is narrow enough that many projects step straight over it. High molybdenum also makes it prone to sigma phase, so welding needs controlled heat input and procedure qualification, which erodes the saving against a super-austenitic.
The number to be more careful with than any of the above is the difference between a specified minimum and a typical value — a floor the standard guarantees, versus what a supplier’s production usually does. The full version, and the most expensive routine mistake in material data.
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What this page does not cover
- Critical pitting temperature is not established here, and the pitting ranking number is a poor substitute in this band.
- Only cold rolled minima are carried; plate figures differ and are named in the notes rather than tabulated.
- Elevated temperature strength, fatigue and fracture toughness.
- Composition limits, not established.
- Welding heat input limits and sigma phase risk.
Generated from data/materials/317lmn.yaml. Regenerate rather than editing this file by hand — edits here are lost on the next build.