What Is the Difference Between 304 and 304L Stainless Steel?

The One-Number Difference That Matters: Carbon Content

304 and 304L look identical, cost almost the same, and share the same chromium and nickel base, but they are specified differently in one key element. Type 304 allows carbon up to 0.08%, while Type 304L limits carbon to 0.03%. The L stands for low carbon. This single difference controls how the steel behaves when it is welded or held in the temperature range of about 450–850°C.

Chemical Composition Comparison 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

Because carbon is a strengthening element in austenitic stainless steel, the specified minimum tensile and yield strengths of 304L are slightly lower than those of 304. In most real applications the difference is small, and design codes usually treat the two grades as interchangeable for strength purposes when using the lower 304L values.

Why Low Carbon Prevents Sensitization

When austenitic stainless steel is heated in the range of about 450–850°C, carbon diffuses to grain boundaries and reacts with chromium to form chromium carbides. The region next to the grain boundary becomes depleted in chromium, and this chromium-depleted zone can corrode preferentially, a failure mode called intergranular corrosion or sensitization. Welding inevitably passes the heat-affected zone through this temperature range. With 304L, the low carbon content means very little chromium carbide can form, so the welded joint keeps its corrosion resistance without post-weld heat treatment. This is the reason 304L dominates in welded tanks, vessels and piping for chemical, food and pharmaceutical service.

Cost, Availability and Selection Guidance

304 is more common in consumer products and architecture, including tableware, kitchen equipment, railings and cladding, where welding is limited and cost matters. 304L is preferred in engineering applications: storage tanks, reactors, pipework, brewery and dairy equipment, and any welded assembly that cannot be solution-annealed after welding. 304L costs slightly more than 304 because the tighter carbon control adds a small production premium, and in many markets 304L is actually the standard stocked grade, so availability is rarely an issue.

No heavy welding and ambient service: 304 is economical and sufficient.

Welded sections thicker than about 6 mm: choose 304L.

Severe chloride environments: move up to 316L rather than relying on either grade.

Existing drawings specifying 304 can generally be supplied as 304L if the strength requirements are checked.

Frequently Asked Questions

Q1: Which is more commonly used, 304 or 304L?
A1: 304 has a higher share in civilian fields such as tableware and building materials because of its lower cost, while 304L dominates professional fields such as chemical engineering and energy where welded corrosion resistance is required.

Q2: What are the mechanical differences between 304 and 304L?
A2: The tensile and yield strengths of 304L are slightly lower than those of 304, about 485 MPa versus 515 MPa tensile and 170 MPa versus 205 MPa yield, while elongation and hardness are similar.

Q3: How can I distinguish 304 from 304L?
A3: Check the product label and material certificate, or have the chemical composition tested; the carbon content is the decisive element.

Q4: Is 304L more expensive than 304?
A4: Yes, usually slightly, because the lower carbon limit requires tighter production control.

Q5: What does the L in 304L mean?
A5: L stands for low carbon: the carbon content is limited to 0.03%, compared with 0.08% for standard 304.

Q6: Can 304L replace 304?
A6: In most applications yes, if the slightly lower specified strength is acceptable; 304L is the safer choice for welded and corrosive service.