AISI 316 and AISI 316L are two versions of the same steel. Their chromium, nickel and molybdenum ranges are exactly the same. The only difference is in carbon — and the letter “L” says precisely that: low carbon.
Why does carbon matter?
In AISI 316 carbon is max 0.08%, in AISI 316L max 0.03%. The difference looks small, but its consequence is large.
When stainless steel is welded, the zone next to the weld passes through the 450–850 °C range. At that temperature carbon combines with chromium and forms chromium carbides at the grain boundaries. Chromium tied up in carbides can no longer protect the surface; the grain boundaries become depleted in chromium and that zone becomes open to corrosion. This is called intergranular corrosion (sensitisation), and it can appear as a leak months after welding.
Because carbon is already very low in 316L, the amount of carbide that can form is negligible. That is why 316L is preferred for welded parts that cannot be solution annealed afterwards.
The price: some strength
Carbon also contributes to strength. According to our datasheets the tensile strength of 316 is 515 MPa and its yield strength 205 MPa, while in 316L those values are 485 MPa and 170 MPa. Elongation, hardness, density and the thermal properties are identical.
Comparison in numbers
| PROPERTY | AISI 316 | AISI 316L |
|---|---|---|
| Carbon (C) | max 0.08% | max 0.03% |
| Chromium (Cr) | 16.0 – 18.0% | 16.0 – 18.0% |
| Nickel (Ni) | 10.0 – 14.0% | 10.0 – 14.0% |
| Molybdenum (Mo) | 2.0 – 3.0% | 2.0 – 3.0% |
| Tensile strength Rm | 515 MPa | 485 MPa |
| Yield strength Rp0.2 | 205 MPa | 170 MPa |
| Elongation A50 | 40% | 40% |
| Hardness | max 217 HB | max 217 HB |
| UNS | S31600 | S31603 |
| W.Nr (DIN/EN) | 1.4401 | 1.4404 |
| AMS | 5648 (bar, forging) · 5524 (plate, sheet) · 5573 (tube) | 5653 (bar, forging) · 5507 (plate, sheet) |
Values are taken from our product datasheets; section thickness and the applied heat treatment regime change the result.
Which one, and when?
AISI 316 is preferred — parts that are not welded, or that can be solution annealed after welding: machined components, shafts, fasteners, forgings. Its strength is slightly higher.
AISI 316L is required — welded pipes and tanks, chemical and pharmaceutical pipework, food lines, welded structures in marine environments. If the specification calls out AMS 5653 or AMS 5507, the grade being asked for is 316L.
In practice the two are often supplied together on the same certificate (dual-certified material); such material satisfies both the 316 and the 316L requirement.
Neighbouring grades
For the molybdenum-free equivalents, see our AISI 304 – AISI 316 comparison. If stability after welding at high temperature is required, the titanium-stabilised AISI 316Ti and AISI 321 are alternatives.
Technical datasheets
AISI 316 — chemical composition, mechanical values, standard equivalents
AISI 316L — 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.