What's the Difference Between Grade 304 and 304L Stainless Steel?

1. The Only Real Difference: Carbon

Grade 304 and grade 304L are austenitic stainless steels with nearly identical compositions. The only significant difference is the maximum carbon content: 0.08% for grade 304 and 0.03% for grade 304L. The L in 304L stands for low carbon, and this single difference governs most of the practical decisions between the two grades.

2. Chemical Composition (ASTM A240)

The table below compares the specified limits of both grades per ASTM A240. Iron makes up the balance.

Element (wt %)	Grade 304 (UNS S30400)	Grade 304L (UNS S30403)
Carbon (C)	0.08 max	0.03 max
Chromium (Cr)	18.00-20.00	18.00-20.00
Nickel (Ni)	8.00-10.50	8.00-10.50
Manganese (Mn)	2.00 max	2.00 max
Silicon (Si)	0.75 max	0.75 max
Phosphorus (P)	0.045 max	0.045 max
Sulfur (S)	0.030 max	0.030 max
Nitrogen (N)	0.10 max	0.10 max

3. Mechanical Properties (Annealed)

In the annealed condition, ASTM A240 requires the following minimum values for plate, sheet and strip. The low-carbon grade has slightly lower minimum strengths, but the difference is small and rarely governs design.

Property (annealed, min)	Grade 304	Grade 304L
Tensile strength	515 MPa	485 MPa
Yield strength (0.2 % offset)	205 MPa	170 MPa
Elongation in 50 mm	40 %	40 %

The density of both grades is the same, about 7.9 g/cm3, and their physical and thermal properties are essentially identical.

4. Why Choose the Lower-Carbon Grade?

The reason to specify 304L is welding. When 304 is heated in the range of about 425-900 C, for example in the heat-affected zone of a weld, chromium carbides can precipitate at grain boundaries, depleting the adjacent metal of chromium and leaving it susceptible to intergranular corrosion. With a maximum carbon content of 0.03%, 304L largely eliminates this risk, so welded 304L components can be used in the as-welded condition even in corrosive environments, without post-weld annealing. This is particularly important for thick sections, which cool slowly through the sensitizing range after welding.

5. Practical Selection Guidance

For general fabrication with no welding, or welded service in mild environments, grade 304 is sufficient and slightly stronger.

For welded structures that will contact corrosive media, for thick sections, or where post-weld heat treatment is impractical, specify 304L.

Where maximum resistance to chlorides and acids is required, consider molybdenum-bearing grades such as 316/316L instead of 304/304L.

Both grades are acceptable for food-contact and architectural applications; selection is usually driven by cost and weldability.

Frequently Asked Questions

Is 304L stronger than 304? No. Per ASTM A240, 304L has slightly lower minimum tensile and yield strengths than 304 because of its lower carbon content. In practice the difference is small and rarely affects design.

What does the L in 304L stand for? L stands for low carbon. The maximum carbon content is limited to 0.03%, compared with 0.08% for grade 304.

Why is 304L better for welding? The low carbon content prevents chromium carbide precipitation at grain boundaries in the weld heat-affected zone, which avoids intergranular corrosion and allows as-welded service in corrosive media.

Is 304L more expensive than 304? The price difference is small. Because the alloying elements are nearly identical, 304L is only slightly more costly, and the difference is often offset by eliminating post-weld annealing.

Can 304 and 304L be used interchangeably? For many applications, yes. Where welding and corrosive service are involved, 304L is the safer choice. Where slightly higher minimum strength is needed and welding is not critical, 304 is acceptable.