Data completeness: partial. Last verified 19 August 2026.
Designations
| Common name | Alloy 28 |
| UNS | N08028 |
| EN number | 1.4563 |
| Class | High-alloy austenitic stainless steel |
| Specified by | ASTM A240/A240M, EN 10088-2 |
Alloy 28 — sold as 725LN and as Sanicro 28 depending on who made it — is the high-chromium, copper-bearing austenitic built for hot phosphoric and sulphuric acid rather than for chlorides. At 25% chromium and only 2.1% molybdenum it reaches the same pitting ranking as 904L by the opposite route: chromium instead of molybdenum. Its proof strength minimum is the lowest of the high-alloy grades here, which tells you it was never a structural alloy.
Properties, with what each one rests on
| Property | Value | Unit | Condition | Evidence | Source | Retrieved |
|---|---|---|---|---|---|---|
| Proof strength Rp0.2, minimum (EN) | 250 | MPa | Quarto plate, 20 °C | E3 | EN 10088-2 via Outokumpu Ultra range datasheet — high-alloy austenitic stainless steels | 2026-08-20 |
| Tensile strength Rm, minimum | 540 | MPa | Quarto plate; datasheet gives a 540–740 range | E3 | EN 10088-2 via Outokumpu Ultra range datasheet — high-alloy austenitic stainless steels | 2026-08-20 |
| Elongation A, minimum | 40 | % | Quarto plate; A and A80 both 40 | E3 | EN 10088-2 via Outokumpu Ultra range datasheet — high-alloy austenitic stainless steels | 2026-08-20 |
| PREN | 34 | — | 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 | 195 | 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 |
| Corrosion rates in phosphoric and sulphuric acid | not established | — | — | — | isocorrosion data is the reason this alloy exists and it is not in the datasheet consulted | — |
| Cold rolled and hot rolled minima | not established | — | — | — | the datasheet consulted lists only Quarto plate for this grade | — |
| Composition limits | not established | — | — | — | ASTM A240 is paywalled; the datasheet gives typical values, which are not limits | — |
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). Plate; the datasheet consulted lists no other product form for this grade. The Rp1.0 cell on that row is blank, which is unusual in this table and is not explained.
PREN. 25% Cr, 2.1% Mo and 0.12% N give 33.9 in the datasheet’s own formula — the same 34 as 904L, which gets there on 19.8% Cr and 4.3% Mo. Two alloys with the same ranking number and different compositions do not behave the same way in the same medium, and this pair is the clearest example of that on the site.
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 Alloy 28 is usually chosen for
Wet-process phosphoric acid plants above all — evaporators, heat exchangers, agitators — and hot sulphuric acid duty where the copper addition does the work. High chromium handles the oxidising part of the attack and copper the reducing part, which is the combination that acid process streams present.
And what it is usually rejected for
Strength, chlorides and price. Its proof strength minimum is low even for an austenitic, so a pressure part in it is thick. The pitting ranking of 34 is short of seawater territory. And it competes with nickel alloys at a price close enough that the decision usually turns on corrosion rate data, which this page does not have.
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
- No corrosion rate data, which is the only reason to choose this alloy.
- Only plate minima are established here.
- Elevated temperature strength, fatigue and fracture toughness.
- Composition limits, not established.
- Whether the copper addition helps in your particular acid mixture. Composition alone does not answer it.
Generated from data/materials/alloy28.yaml. Regenerate rather than editing this file by hand — edits here are lost on the next build.