Last verified 19 August 2026.
The comparison
| Property | 4565 | 654 SMO | Evidence |
|---|---|---|---|
| Proof strength Rp0.2, minimum (EN) | 420 MPa | 430 MPa | E3 E3 |
| Tensile strength Rm, minimum | 800 MPa | 750 MPa | E3 E3 |
| Elongation A, minimum | 30 % | 40 % | E3 E3 |
| PREN | 46 — | 56 — | E3 E3 |
| Density | 8.0 g/cm³ | 8.0 g/cm³ | E3 E3 |
| Modulus of elasticity | 190 GPa | 190 GPa | E3 E3 |
| Thermal conductivity | 12 W/(m·K) | 11 W/(m·K) | E3 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 A, 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
Where each side’s numbers come from
See 4565 and 654 SMO — 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
4565. Pressure-bearing seawater and brine equipment where a duplex would be the obvious answer but cannot be used — because the part runs too hot for a duplex, because it must stay austenitic for toughness at low temperature, or because non-magnetic behaviour is required. Umbilicals, seawater pumps and high-pressure process vessels.
654 SMO. Hot, aerated seawater and the harshest bleaching and scrubbing duties, where 254 SMO and super duplex both have a service record of crevice attack. The usual comparison at this level is not against another stainless but against a nickel alloy or titanium, and 654 SMO wins on fabricability and on the fact that it is still a steel.
Against 4565: Cost and formability. It is among the most expensive alloys in the range, and the same nitrogen that gives it strength makes it work harden hard, so forming and machining need more power, more tool wear and more intermediate annealing than an ordinary austenitic. It is also a specialist product with long lead times.
Against 654 SMO: Price and everything that follows from it. Seven percent molybdenum and 22% nickel make it one of the most expensive alloys in any stainless catalogue, welding needs an overmatching nickel-base filler, and lead times are long because almost nobody stocks it. Every project that can be solved one grade down is solved one grade down.
What this comparison does not cover
- Critical pitting and crevice temperatures are not established here.
- Work hardening and forming behaviour, which is where the grade costs money in the shop.
- Weld metal properties and filler selection.
- Elevated temperature strength, fatigue and fracture toughness.
- Composition limits, not established.
- Only plate minima are established here.
- Critical pitting and crevice temperatures, which are the whole basis for choosing this alloy.
- Corrosion rate data in the services it is bought for.
- Welding practice, filler selection and the properties of the resulting weld metal.
Generated from data/materials/4565.yaml and 654smo.yaml.