304L steel (1.4307): properties, composition, equivalents

304L (1.4307, UNS S30403) is 304 with carbon capped at 0.030 %: the same 18/8 alloy, specified so that welds do not sensitise.

Last updated 3 October 2026

What is 304L?

304L is not a different alloy from 304. It is the same 18 % chromium, 8–10.5 % nickel austenitic stainless with carbon capped at 0.030 % instead of 0.08 %, and that single change is the entire specification.

The reason is welding. At ordinary carbon levels, the heat of welding holds the zone beside the weld in the 500–800 °C range long enough for chromium carbides to precipitate at the grain boundaries. Those carbides take their chromium from the metal immediately around them, leaving a depleted band that is no longer stainless — sensitisation, and the corrosion that follows it runs along the grain boundaries, invisibly, until the part falls apart. Below 0.030 % carbon there is not enough carbon for that to happen in normal welding times.

The cost is strength. 304L's proof stress runs 10 to 40 MPa below 304 depending on product form, and in a design governed by yield that is a real deduction. The cost is also availability in one direction only: because 304L satisfies a 304 specification on every count except the strength minimum, mills dual-certify most coil as 304/304L and the distinction disappears at the stockholder.

When to insist on it: welded section above roughly 6 mm, any welded assembly that will see a corrosive medium, and anything that cannot be solution-annealed after welding. When not to: thin sheet, unwelded parts, and designs where the extra proof stress of 304 is being used.

304L chemical composition

EN 10088-2:2014 for 1.4307 and ASTM A240 for S30403. The grades are dual-certified routinely; the EN limits on sulphur and nickel are the tighter pair, so EN material satisfies ASTM while the reverse needs checking on the certificate. Nothing else distinguishes 304L from 304 — there is no extra alloying, only less carbon.

304L mechanical properties

Values in the solution-annealed condition (+AT, 1000–1100 °C, rapidly cooled). The lower carbon costs roughly 10–40 MPa of proof stress against 304 depending on product form — the price paid for weld stability. Work-hardened strip conditions (+C700 and above) are available and are a different material for design purposes.

Impact toughness

304L requires a minimum Charpy V-notch energy of 60 J at -196 °C (typical, not a standard requirement). Austenitic structure: no ductile-to-brittle transition. 304L stays tough to cryogenic temperatures, and the low carbon makes it the preferred 18/8 grade for welded cryogenic vessels where 304 would risk sensitisation in the heat-affected zone.

304L equivalent grades

Identical = same composition and mechanical limits within rounding. Near = one limit differs (e.g. carbon max or impact temperature). Functional = interchangeable for most uses after an engineering check. Full cross-reference for 304L →

Old and superseded designations

Product forms and tolerance standards

Product forms: sheet, plate and coil (ASTM A240 / EN 10088-2), bar and section (A276 / EN 10088-3), welded and seamless pipe (A312 TP304L), tube for instrumentation and hygienic service (A269, A270), fittings, flanges and A2-class fasteners.

Dimensional tolerances: sheet and plate: ASTM A480 / EN ISO 9445; bar: ASTM A484 / EN 10278; pipe: ASTM A999 general requirements; surface finishes: 2B, BA, No. 4, No. 8 to ASTM A480 Table A1.1.

Key property values

304L yield strength

Rp0.2 ≥ 170 MPa (25 ksi) for plate under ASTM A240, ≥ 220 MPa for cold-rolled strip and ≥ 200 MPa for hot-rolled plate under EN 10088-2. Rp1.0, which EN 1993-1-4 uses for design, is ≥ 250 MPa for strip and ≥ 235 MPa for plate.

304L tensile strength

≥ 485 MPa (70 ksi) under ASTM A240; 520–700 MPa cold-rolled and 500–700 MPa hot-rolled under EN 10088-2. Elongation is 40–45 %, which is what makes the grade deep-drawable.

304L hardness

Annealed, ≤ 201 HB under ASTM A240 and ≤ 215 HB under EN. It cannot be hardened by heat treatment — only by cold work, which raises hardness to 300–400 HV and introduces a weak magnetic response.

Why the L exists: sensitisation

Between 500 and 800 °C, chromium combines with carbon to form Cr₂₃C₆ at the grain boundaries and strips those boundaries of chromium. The depleted band corrodes intergranularly in service and the failure is not visible from outside. Capping carbon at 0.030 % removes the mechanism; the alternative route is titanium stabilisation (321 / 1.4541).

304L against 304 on a certificate

Most mill coil is dual-certified 304/304L: it meets the low carbon of 304L and the strength minimum of 304 at the same time. Where a certificate names only 304, the carbon can legitimately be 0.08 % and the material is not 304L. Where it names only 304L, check the proof stress if the design used the 304 figure.

Corrosion resistance

PREN ≈ 18–19, identical to 304 — the carbon change does nothing for pitting resistance. Good against nitric and organic acids, food media and inland atmospheres; pits in warm chloride above roughly 200 ppm. Coastal facades, pool halls and de-icing salt require 316L or 1.4404.

Weldability

This is the grade's reason for existing, and it welds by all arc processes without preheat. Filler is ER308L / 19 9 L (EN ISO 14343) — the filler carries extra chromium and nickel to compensate for dilution, and its own carbon is already low. Interpass temperature should stay below about 150 °C to limit distortion, since austenitic stainless expands roughly 50 % more than carbon steel. Back-purge tube roots with argon. No post-weld heat treatment is required, and none should be applied casually: a stress-relief cycle through 500–800 °C would reintroduce exactly the problem the low carbon was bought to prevent. For heavy welded section in aggressive media, the next step is 1.4404 or 316L rather than a thicker 304L.

Machining, forming and heat treatment

Machinability index around 45 % of free-cutting steel, and marginally worse than 304 because the lower carbon makes the matrix gummier. The grade work-hardens rapidly, so the rules are the usual austenitic ones: sharp positive-rake tooling, heavy and uninterrupted feed, low surface speed and no dwelling — a tool that rubs instead of cutting hardens the surface and the next pass has to cut through it. Where a machined part needs no welding, 1.4305 (303) is the free-machining alternative at the cost of weldability and pitting resistance. Deep drawing, spinning and bending are excellent; spring-back is higher than carbon steel.

Typical applications

• Welded tanks, vessels and process piping in food, dairy, brewing and pharmaceutical plant
• Heavy-section welded fabrications that cannot be solution annealed afterwards
• Cryogenic vessels and lines, where austenite stays tough and the weld must stay stable
• Architectural handrails, cladding and street furniture inland
• Heat-exchanger shells and tube sheets in non-chloride service
• A2-class fasteners and welded wire products

304L compared with related grades

Frequently asked questions

Related grades

Verified against EN 10088-2:2014 · ASTM A240/A240M; EN 10088-2 — Stainless steels, Part 2: flat products (CEN); ASTM A240/A240M — Chromium and chromium-nickel stainless steel plate, sheet and strip; ASTM A312/A312M — Seamless and welded austenitic stainless steel pipe, for TP304L. Last checked: October 2026.