Last verified 19 August 2026.
The comparison
| Property | 316L | 317L | Evidence |
|---|---|---|---|
| Proof strength Rp0.2, minimum (EN) | 240 MPa | 220 MPa | E3 E3 |
| Tensile strength Rm, minimum | 530 MPa | 520 MPa | E3 E3 |
| Elongation, minimum | 40 % | 40 % | E3 E3 |
| PREN | 24 — | 28 — | E3 E3 |
| Modulus of elasticity | 200 GPa | 200 GPa | E3 E3 |
| Density | 8.0 g/cm³ | 8.0 g/cm³ | E3 E3 |
| Thermal conductivity | 15 W/(m·K) | 14 W/(m·K) | E3 E3 |
| Proof strength Rp0.2, minimum | 170 MPa | not established here | E3 / — |
Proof strength Rp0.2, minimum (EN) — different product forms — cold rolled coil and sheet against Quarto plate. The grades differ and so does what was tested, so the gap between these two numbers is not all material
Tensile strength Rm, minimum — different product forms — cold rolled coil and sheet against Quarto plate. The grades differ and so does what was tested, so the gap between these two numbers is not all material
Elongation, minimum — different product forms — cold rolled coil and sheet against Quarto plate. The grades differ and so does what was tested, so the gap between these two numbers is not all material
PREN — different documents — Outokumpu Supra range datasheet against Outokumpu Ultra range datasheet
Modulus of elasticity — different documents — Outokumpu Supra range datasheet against Outokumpu Ultra range datasheet
Density — different documents — Outokumpu Supra range datasheet against Outokumpu Ultra range datasheet
Thermal conductivity — different documents — Outokumpu Supra range datasheet against Outokumpu Ultra range datasheet
The trap on this comparison
Proof strength Rp0.2 is specified twice: 170 MPa (ASTM A240/A240M, plate, annealed, 20 °C) and 240 MPa (EN 10088-2, cold rolled coil and sheet, 20 °C) — 41% apart. Both correct. Which one governs is a question about your drawing and your product form, not about the material.
Where each side’s numbers come from
See 316L and 317L — each page lists every source, every demotion and every gap. Nothing on this page is derived from anything not on those two, and our coverage limits are stated separately.
Where a PREN appears above, read it as a ranking number rather than a qualification: what PREN can and cannot tell you.
When to choose which
316L. It is the default molybdenum-bearing austenitic, and the reasons are practical rather than exceptional. Single phase, so no phase balance to manage in welding. Forgiving heat input. Formable. Stocked by everyone in every product form. Every fabricator has qualified procedures for it. When a design is not strength-driven and the environment is not aggressive, 316L is chosen because choosing anything else has to be justified.
317L. Flue gas desulphurisation, pulp and paper bleaching, and process streams where 316L is pitting but the environment does not justify a six-molybdenum alloy. It is also specified where an existing 316L design is being uprated without redrawing it, because the mechanical minima on plate are identical and nothing structural has to change.
Against 316L: Two things. Strength: at the 170 MPa ASTM A240 plate minimum it is weak for a structural section, and a strength-driven part in 316L is thick. Chlorides: the molybdenum helps against pitting relative to 304, but 316L is marginal in warm chloride service, and the failure mode that usually appears is crevice corrosion at gaskets and joints, which PREN does not predict.
Against 317L: Availability and the size of the step. Four points of pitting ranking is a modest gain for a grade that many stockists do not hold in every form, and where the service is genuinely aggressive it is not enough. In practice the decision is usually between staying at 316L and jumping to a super-austenitic or a duplex, with 317L squeezed in between.
What this comparison does not cover
- Composition limits are not established, and they are what a purchase order actually specifies.
- Elevated and cryogenic temperature behaviour.
- Fatigue, fracture toughness and stress corrosion cracking.
- Welding procedure guidance, filler selection and post-weld treatment.
- Product forms other than plate, where minima differ.
- Whether 316L suits your application. No page can answer that.
- Only plate minima are established here; sheet and hot rolled are not.
- Critical pitting temperature, which is what separates this grade from 316L in service.
- Elevated temperature strength, fatigue and fracture toughness.
- Composition limits, not established.
- Crevice corrosion, which the pitting ranking number does not predict.
Generated from data/materials/316l.yaml and 317l.yaml.