The one difference that matters: molybdenum
Both 304L and 316L are low-carbon austenitic stainless steels with a maximum carbon content of 0.03%. That low carbon is what the "L" means, and it governs weldability, not corrosion in service. The corrosion story is written by a single alloying element: molybdenum.
316L contains 2-3% molybdenum. 304L contains essentially none. Molybdenum stabilizes the passive film against chloride attack, which is why 316L resists pitting and crevice corrosion in environments where 304L breaks down. If you remember nothing else about this comparison, remember that you are paying for the molybdenum, and you should match it to the actual chloride risk of the service.
| Attribute | 304L | 316L |
|---|---|---|
| Family | Austenitic stainless | Austenitic stainless |
| Carbon (max) | 0.03% | 0.03% |
| Molybdenum | None (nominal) | 2-3% |
| PREN (approx.) | ~18 | ~24 |
| Chloride pitting resistance | Lower | Higher |
| Chloride-SCC | Susceptible | Susceptible |
| Relative cost | Lower | Higher |
What PREN tells you
PREN, the pitting resistance equivalent number, puts a single figure on how well a grade resists chloride pitting. On the orderable ladder it runs 304 (~18) < 316 (~24) < 904L (~34). 304L sits near the bottom and 316L a clear step above it, and that gap is almost entirely the molybdenum talking. For a full explanation of how the number is built and how to read it against your service, see our guide on PREN and pitting resistance and the deeper note on pitting corrosion.
Chloride, crevice, and stress-corrosion cracking
Pitting is the mechanism most buyers are trying to avoid when they weigh 304L against 316L. Chlorides from seawater, brackish water, de-icing salt, coastal air, or process brine attack the passive film locally, and the higher PREN of 316L buys you a wider safe window. The same molybdenum advantage carries into crevice corrosion under gaskets, deposits, and lap joints, where the local chemistry is harsher than the bulk environment.
One honest caveat: both grades are austenitic, so both remain susceptible to chloride stress-corrosion cracking under tensile stress in hot chloride service. 316L raises the pitting threshold but does not make the problem disappear. When hot concentrated chlorides are in play, the real answer is often a super-austenitic or duplex grade rather than either of these two. See how the step up looks in 904L vs 316L.
Why both are "L" grades: carbon and welding
The 0.03% carbon ceiling on both grades exists to prevent sensitization. When standard-carbon stainless is held in the 425-815 °C range, typically in the heat-affected zone of a weld, chromium carbides precipitate at the grain boundaries and strip the adjacent metal of the chromium it needs to stay passive. The result is intergranular corrosion, also called weld decay. Low carbon starves that reaction, so L grades keep their corrosion resistance through welding without a mandatory post-weld solution anneal. Our guide on how to prevent sensitization covers the mechanism and the alternatives.
The filler follows the base metal. Weld 304L with its matched procedure described in how to weld 304L, and weld 316L with ER316L to retain molybdenum across the joint, as covered in how to weld 316L. Using a 304-type filler on 316L would throw away the molybdenum advantage exactly where corrosion starts.
Cost and when to upgrade
316L costs more than 304L, and the premium is driven by its nickel and molybdenum content. The practical rule is simple:
- Stay with 304L for dry indoor service, general fabrication, architectural work away from the coast, and food and dairy equipment that is not exposed to standing chlorides.
- Upgrade to 316L for marine and coastal duty, chloride-bearing process streams, pharmaceutical and hygienic systems cleaned with chlorinated agents, and anywhere crevices will trap salts.
- Go beyond both to 904L or duplex when chlorides are hot and concentrated and 316L's PREN is no longer enough.
The most common and most expensive error is defaulting to 304L for chloride-adjacent or coastal duty where it pits. Confirm the actual service chlorides before choosing, because stepping up one grade is far cheaper than a failed part and a shutdown. Our stainless grade selector and the how to select a stainless grade guide walk through the decision; the broader context on alloying elements explains what each addition buys you.
Standards and available forms
Both grades are supplied to ASTM A240 and the ASME equivalent SA-240 for plate, sheet, strip, and coil. Nandini Steel holds both grades ex-stock across forms for immediate dispatch, with an EN 10204 3.1 or 3.2 mill test certificate on every order.
| Form | 304L | 316L |
|---|---|---|
| Plate | 304L plate | 316L plate |
| Sheet | 304L sheet | 316L sheet |
| Coil | 304L coil | 316L coil |
If you are also weighing the standard-carbon versions, compare 304 vs 304L and 316 vs 316L to see what the low-carbon choice changes within each grade.
Frequently asked questions
Is 316L always better than 304L?
What is the real difference between 304L and 316L?
Does 304L resist saltwater?
Do 304L and 316L need post-weld heat treatment?
How much more does 316L cost than 304L?
Request a quote
Tell us the grade, form, dimensions, and quantity and the Nandini Steel team will confirm ex-stock availability and live pricing, with an EN 10204 3.1 or 3.2 mill test certificate on every order. Email reachus@nandinisteel.com, call +91 22 43404600, or message WhatsApp +91 99202 09184.