Last verified 19 August 2026.
The comparison
| Property | 17-4 PH | 316L | Evidence |
|---|---|---|---|
| Proof strength Rp0.2, typical | 850 MPa | 170 MPa | not comparable |
| Density | 7.8 g/cm³ | 8.0 g/cm³ | E3 E3 |
| Modulus of elasticity | 200 GPa | 200 GPa | E3 E3 |
| Thermal conductivity | 16 W/(m·K) | 15 W/(m·K) | E3 E3 |
| Proof strength Rp0.2, typical (bar) | 600 MPa | not established here | E3 / — |
| Tensile strength Rm, typical | 1100 MPa | not established here | E3 / — |
| Elongation A, typical | 22 % | not established here | E3 / — |
| Proof strength Rp0.2, minimum (EN) | not established here | 240 MPa | — / E3 |
| Tensile strength Rm, minimum | not established here | 530 MPa | — / E3 |
| Elongation, minimum | not established here | 40 % | — / E3 |
| PREN | not established here | 24 — | — / E3 |
Proof strength Rp0.2, typical — not compared: one side is measured and the other specified. Comparing across those is the trap this site exists to argue against.
Density — different documents — Outokumpu Dura range datasheet against Outokumpu Supra range datasheet
Modulus of elasticity — different documents — Outokumpu Dura range datasheet against Outokumpu Supra range datasheet
Thermal conductivity — different documents — Outokumpu Dura range datasheet against Outokumpu Supra 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 17-4 PH and 316L — 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
17-4 PH. Parts that need high strength, moderate corrosion resistance and dimensional stability through hardening. Pump and valve shafts, aerospace fittings, injection moulds, firearm and turbine components. It is machined soft and aged afterwards at a low enough temperature that the part barely moves, which is the property that distinguishes it from a quenched martensitic grade.
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.
Against 17-4 PH: Chlorides, temperature and toughness at the top of its range. Its corrosion resistance sits between 410 and 304, nowhere near 316L, and the shortest ageing treatments trade notch toughness and stress corrosion resistance for strength. Above roughly 300 °C the precipitates that give it strength begin to over-age, and no source consulted for this page covers that.
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.
What this comparison does not cover
- The heat treatment condition, which for this alloy is the difference between two grades’ worth of strength.
- No specified minima. Everything here is a mill typical value and cannot be used as a design allowable.
- No hardness values.
- No corrosion data, and the alloy is often chosen where 316L would be safer.
- Behaviour above roughly 300 °C, where the ageing that gives it strength starts to reverse. No source consulted here covers it.
- 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.
Generated from data/materials/17-4ph.yaml and 316l.yaml.