304L Stainless Steel: Weld-Friendly Low-Carbon Variant of 304

What Makes 304L Different from 304

Type 304L is the low-carbon variant of Type 304. The only meaningful difference in specification is carbon: 304L limits carbon to 0.03%, while 304 allows up to 0.08%. During welding or service in the temperature range of about 450–850°C, carbon can combine with chromium at grain boundaries to form chromium carbides. This leaves the neighboring steel depleted in chromium and vulnerable to intergranular corrosion, a condition known as sensitization. By capping carbon at 0.03%, 304L keeps this reaction at a level that is harmless for most corrosive services.

Chemical Composition per ASTM A240

Element wt%	Type 304 UNS S30400	Type 304L UNS S30403
Carbon	≤ 0.08	≤ 0.030
Silicon	≤ 0.75	≤ 0.75
Manganese	≤ 2.00	≤ 2.00
Phosphorus	≤ 0.045	≤ 0.045
Sulfur	≤ 0.030	≤ 0.030
Chromium	18.0 – 20.0	18.0 – 20.0
Nickel	8.0 – 10.5	8.0 – 12.0

Mechanical Properties

Property	Type 304	Type 304L
Tensile strength	≥ 515 MPa	≥ 485 MPa
Yield strength	≥ 205 MPa	≥ 170 MPa
Elongation	≥ 40%	≥ 40%
Hardness	≤ 201 HB	≤ 201 HB

304L retains excellent toughness at low temperature and is used in cryogenic equipment down to −196°C. At the other end of the range, it can be used for intermittent service up to about 870°C, though oxidation resistance rather than strength becomes the limiting factor.

Welding Behavior

304L is the standard choice when heavy sections are welded and the assembly will not receive post-weld heat treatment. The low carbon content keeps the heat-affected zone free of harmful chromium carbide networks, so the welded joint retains its corrosion resistance in most media. For matching welds, low-carbon filler such as ER308L is normally used. If the application is a highly oxidizing service, a post-weld solution anneal may still be required by the design code, but for typical chemical, food and architectural service no heat treatment is necessary.

304 vs 304L: Selection Guidance

For sheet-metal products, consumer goods and architectural trim that are not heavily welded, 304 is economical and sufficient.

For welded tanks, vessels and piping carrying corrosive aqueous media, 304L is the safer choice, especially in sections thicker than about 6 mm.

For seawater or chloride-rich service, neither 304 nor 304L is suitable; a molybdenum-bearing grade such as 316L should be used.

304L costs slightly more than 304 because of the tighter carbon control.

Frequently Asked Questions

Q1: Should I choose 304 or 304L?
A1: Choose 304L when the component is welded, thick, or exposed to corrosive media where sensitization matters; choose 304 for non-welded, general-purpose applications where cost is the priority.

Q2: Does 304L need post-weld heat treatment?
A2: Not normally. The low carbon content prevents sensitization during welding, so the assembly can be used without solution annealing in most services.

Q3: Can 304L be used in seawater?
A3: No. 304L has no molybdenum and can suffer pitting and crevice corrosion in chloride-rich environments; use 316L or a higher-alloy grade instead.

Q4: Is 304L weaker than 304?
A4: The specified minimum tensile and yield strengths of 304L are slightly lower, but in practice the difference is small and rarely affects design for most applications.

Q5: Why does 304L allow nickel up to 12%?
A5: The wider nickel range in the UNS S30403 specification gives producers flexibility while keeping the austenitic structure stable.

Q6: What is the EN designation of 304L?
A6: EN 1.4306, and the JIS designation is SUS304L.