Data completeness: partial. Last verified 19 August 2026.
Designations
| Common name | 321 |
| UNS | S32100 |
| EN number | 1.4541 |
| Class | Austenitic stainless steel |
| Specified by | ASTM A240/A240M, EN 10088-2 |
321 is 304 stabilised with titanium. It is the grade that survives in the sensitisation range rather than merely passing through it, which is why it turns up in exhausts, expansion joints and anything welded that then gets hot and stays hot. Its close relative 347 does the same job with niobium instead. Neither has molybdenum, so neither is a chloride alloy.
Properties, with what each one rests on
| Property | Value | Unit | Condition | Evidence | Source | Retrieved |
|---|---|---|---|---|---|---|
| Proof strength Rp0.2, minimum (EN) | 220 | MPa | cold rolled coil and sheet, 20 °C | E3 | EN 10088-2 via Outokumpu Core range datasheet — standard austenitic and ferritic stainless steels | 2026-08-20 |
| Tensile strength Rm, minimum | 520 | MPa | cold rolled; datasheet gives a 520–720 range | E3 | EN 10088-2 via Outokumpu Core range datasheet — standard austenitic and ferritic stainless steels | 2026-08-20 |
| Elongation A, minimum | 40 | % | cold rolled; A and A80 both 40 | E3 | EN 10088-2 via Outokumpu Core range datasheet — standard austenitic and ferritic stainless steels | 2026-08-20 |
| PREN | 17 | — | from typical composition, not from a heat | E3 | Outokumpu Core range datasheet — standard austenitic and ferritic stainless steels | 2026-08-20 |
| Density | 7.9 | g/cm³ | 20 °C | E3 | Outokumpu Core range datasheet — standard austenitic and ferritic stainless steels | 2026-08-20 |
| Modulus of elasticity | 200 | GPa | 20 °C | E3 | Outokumpu Core range datasheet — standard austenitic and ferritic stainless steels | 2026-08-20 |
| Thermal conductivity | 15 | W/(m·K) | 20 °C | E3 | Outokumpu Core range datasheet — standard austenitic and ferritic stainless steels | 2026-08-20 |
| Elevated temperature strength | not established | — | — | — | the Core datasheet carries no elevated temperature table; the sister Therma datasheet covers 321H, which is a different carbon range | — |
| Titanium content and the Ti:C ratio required for stabilisation | not established | — | — | — | set by the standard, which is paywalled | — |
| 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
PREN. 17.3% Cr, no molybdenum, no nitrogen in the datasheet’s own formula gives 17.3, printed as 17. The lowest number in the austenitic part of that table, and one point below 304 — because stabilising with titanium costs a little chromium.
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 321 is usually chosen for
Welded assemblies that then run hot. Titanium stabilisation holds through the range where unstabilised austenitics precipitate chromium carbides, so the grade keeps its corrosion resistance after hours at temperature rather than only after minutes. Automotive and industrial exhausts, bellows, heat exchanger shrouds and flue ducting are the recurring uses.
And what it is usually rejected for
Chlorides and surface finish. No molybdenum means it ranks below 316L on pitting, and titanium carbonitrides make a poor polished surface, so it is the wrong grade for architectural and hygienic work. It is also the wrong grade when the service is cold and welded, where 304L does the same job cheaper and with a cleaner surface.
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.
Compare
What this page does not cover
- No elevated temperature values, which is the service most 321 is bought for.
- The titanium content and the stabilisation ratio are not established here.
- The ASTM plate minima are not established here.
- Fatigue, creep, fracture toughness and chloride stress corrosion cracking.
- The distinction between 321 and 321H, which is a carbon range set by the standard and not carried on this page.
Generated from data/materials/321.yaml. Regenerate rather than editing this file by hand — edits here are lost on the next build.