Data completeness: partial. Last verified 19 August 2026.
Designations
| Common name | 304L |
| UNS | S30403 |
| EN number | 1.4307 |
| Class | Austenitic stainless steel |
| Specified by | ASTM A240/A240M, EN 10088-2 |
304L is 304 with the carbon held down, and the reason to specify it is welding: below roughly 0.03% C there is not enough carbon left to form chromium carbides at the grain boundaries as the weld cools, so the heat-affected zone keeps the chromium that makes it stainless. You pay for that in strength. On the same EN 10088-2 cold rolled row, 304L sits 10 MPa below 304 in proof strength and 20 MPa below it in tensile — a real difference on a thin section, and one that a drawing calling for “304/304L dual certified” quietly resolves in favour of the lower pair.
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 520–700 range | E3 | EN 10088-2 via Outokumpu Core range datasheet — standard austenitic and ferritic stainless steels | 2026-08-20 |
| Elongation A, minimum | 45 | % | cold rolled; A and A80 both 45 | E3 | EN 10088-2 via Outokumpu Core range datasheet — standard austenitic and ferritic stainless steels | 2026-08-20 |
| PREN | 18 | — | 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 |
| Proof strength Rp0.2, minimum (ASTM plate) | not established | — | — | — | ASTM A240 is paywalled and no secondary source was checked for this grade | — |
| Composition limits | not established | — | — | — | ASTM A240 is paywalled; the datasheet gives typical values, which are not limits | — |
| Carbon maximum | not established | — | — | — | the 0.03% figure is the grade’s defining limit and belongs to the standard, which was not opened | — |
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). The datasheet table is headed “values according to EN 10088-2:2014” and names the product form per row: C is cold rolled coil and sheet. Hot rolled and Quarto plate rows for the neighbouring 1.4306 sit 20 MPa lower, so the form matters more than the grade suffix here.
PREN. The datasheet states its formula, PRE = %Cr + 3.3 × %Mo + 16 × %N, and its typical composition, 18.1% Cr with no molybdenum and no nitrogen. Those reproduce the printed 18 exactly, so this row is arithmetic we can repeat rather than a number we copied. It stays at E3 because the composition behind it is a typical value, not a heat analysis.
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 304L is usually chosen for
Welded fabrication that has to stay corrosion resistant at the weld. That is the whole argument. Everything else about it — price, availability, formability, the fact that every shop already knows how to handle it — is inherited from 304. If a part is welded and will see moisture, specifying 304L costs almost nothing and removes a failure mode that is invisible until it is not.
And what it is usually rejected for
Two reasons, in order of how often they bite. Strength: the EN cold rolled minima are the lowest in the austenitic family, and a strength-driven section in 304L is heavy. Chlorides: with no molybdenum it is no better than 304, and coastal air, de-icing salt and process water all find that out. For welded service in chlorides the honest step up is 316L, not 304L.
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
304L vs 316l · 304L vs 321 · 304L vs 304
What this page does not cover
- The ASTM plate minima are not established here, and they are the figures most North American projects need.
- The 0.03% carbon maximum that defines the grade is not sourced on this page.
- Elevated and cryogenic temperature behaviour, and the creep range.
- Fatigue, fracture toughness and chloride stress corrosion cracking.
- Sensitisation behaviour after long exposure in the 450–850 °C range, which the low carbon delays rather than prevents. Not sourced here; the standard and the mill datasheet are the routes.
- Whether 304L suits your application. No page can answer that.
Generated from data/materials/304l.yaml. Regenerate rather than editing this file by hand — edits here are lost on the next build.