AISI 304 and AISI 304L are two versions of the most widely used stainless steel in the world. Their chromium and nickel ranges are exactly the same; the difference is only in carbon. The letter “L” stands for low carbon.
What does the carbon difference do?
In AISI 304 carbon is max 0.07%, in AISI 304L max 0.03%. That difference shows itself during welding.
As the zone beside the weld bead passes through the 450–850 °C range, carbon combines with chromium and forms chromium carbides at the grain boundaries. The chromium content falls in that zone and the protective oxide layer on the surface weakens. The result is intergranular corrosion: a deterioration that begins right beside the weld line and is hard to see with the naked eye.
Because carbon is already very low in 304L, that mechanism is practically switched off. This is why 304L is used for welded parts that cannot be solution annealed afterwards.
What is given up in return?
Since carbon contributes to strength, the yield strength of 304L is slightly lower: according to our datasheets the yield strength is min 190 MPa in 304 and min 175 MPa in 304L. Tensile strength (500–700 MPa), elongation (min 45%), hardness (max 215 HB) and all thermal properties are identical.
Comparison in numbers
| PROPERTY | AISI 304 | AISI 304L |
|---|---|---|
| Carbon (C) | max 0.07% | max 0.03% |
| Chromium (Cr) | 17.50 – 19.50% | 17.50 – 19.50% |
| Nickel (Ni) | 8.00 – 10.50% | 8.00 – 10.50% |
| Manganese (Mn) | max 2.0% | max 2.0% |
| Sulphur (S) | max 0.03% | max 0.02% |
| Tensile strength Rm | 500 – 700 MPa | 500 – 700 MPa |
| Yield strength Rp0.2 | min 190 MPa | min 175 MPa |
| Elongation A50 | min 45% | min 45% |
| Hardness | max 215 HB | max 215 HB |
| UNS | S30400 | S30403 |
| W.Nr (DIN/EN) | 1.4301 | 1.4307 |
| AMS | 5511 · 5513 · 5560 · 5565 · 5639 · 5647 | 5511 · 5513 · 5560 · 5565 · 5639 · 5647 |
| ASTM | A276 · A479 · A484 | A276 · A479 · A484 |
Values are taken from our product datasheets; section thickness and the applied heat treatment regime change the result.
Which one, and when?
AISI 304 is preferred — machined components, shafts, fasteners, and parts that are not welded or that can be solution annealed after welding.
AISI 304L is required — welded tanks, pipes, food and chemical lines, structures welded on site. In thick-section welds, 304L is very nearly the standard choice.
In practice the material is often supplied as dual certified to both grades; such material satisfies the 304 and the 304L requirement at once.
The molybdenum-bearing equivalents
Where chloride-bearing environments are involved, the 316 family is used instead of the 304 family; we covered the difference in our AISI 304 – AISI 316 comparison, and the 316 / 316L distinction in this article.
Technical datasheets
AISI 304 — chemical composition, mechanical values, standard equivalents
AISI 304L — chemical composition, mechanical values, standard equivalents
Both grades are supplied to order in round bar, flat bar, plate, sheet, pipe and forged forms. Contact us for a quotation.