304 vs 316 stainless steel is the most common material question we get, and the answer isn’t “316 is better”. It’s more corrosion resistant and it costs more, and picking it by default wastes money on parts that never needed it. This guide covers the practical difference, what welding changes, and when both alloys are the wrong answer.
Need stainless welded or fabricated? Weld Creations TIG welds 304, 316 and the L grades in Glendora, California. See stainless steel welding or request a quote.
The difference in one line
316 has molybdenum. 304 doesn’t.
| 304 / 304L | 316 / 316L | |
|---|---|---|
| Chromium | ~18% | ~16–18% |
| Nickel | ~8–10% | ~10–14% |
| Molybdenum | none | ~2–3% |
| Chloride resistance | Moderate | Much better |
| Relative cost | Baseline | Meaningfully higher |
| Weldability | Excellent | Excellent |
Chromium gives both alloys the passive oxide layer that makes stainless “stainless”. Molybdenum is what resists pitting and crevice corrosion from chlorides: salt, bleach, brine, seawater, many cleaning chemicals and plenty of food products.
When 304 is the right call
- Dry product contact, such as powders, tablets, capsules and grain
- Equipment frames, stands, guards, enclosures and structure
- Indoor equipment that isn’t exposed to chlorides or aggressive cleaners
- Most architectural and general fabrication
Using 304 where it’s appropriate frees budget for the parts that genuinely need 316.
When to specify 316
- Salty, acidic or high-chloride products, including brines, sauces, dairy washdowns and seafood
- Aggressive cleaning chemicals, especially chlorinated sanitizers
- Pharmaceutical product contact, where 316L is the default
- Marine and coastal exposure
- Anywhere a pit means a contamination risk, not just a cosmetic blemish
In a single machine, mixing is normal and sensible: 316L for product-contact surfaces, 304 for the frame and guards. See food grade fabrication and pharmaceutical equipment fabrication.
What welding changes: specify the L grades
This is the part that gets missed on drawings.
When stainless is held in roughly the 800–1,500°F range, as it is next to a weld, carbon can combine with chromium and form chromium carbides at the grain boundaries. That leaves those boundaries short of chromium and vulnerable to corrosion. It’s called sensitization, and it shows up as corrosion in a band parallel to the weld.
304L and 316L have lower carbon, which largely prevents it. For welded parts in corrosive or product-contact service, specify the L grade. The strength difference is small and rarely matters for fabricated equipment.
Welding also needs the right filler, typically 308L for 304/304L and 316L for 316/316L, and an argon back purge on full-penetration joints so the root doesn’t oxidize. For the detail, see stainless steel welding.
What the grades cost you in practice
Price moves with the nickel and molybdenum market, so treat any ratio as a snapshot rather than a rule. What stays true:
- 316 costs meaningfully more per pound than 304, and the gap widens when nickel prices rise.
- On a fabricated part, material is often not the dominant cost. Cutting, forming, welding, finishing and inspection can outweigh it, so upgrading a small product-contact part to 316L may add far less to the finished price than the raw-material difference suggests.
- Availability matters too. 304 is stocked more widely in more shapes, so an unusual section in 316 can carry a longer lead time.
The sensible approach is to specify 316L where the service demands it and 304 everywhere else, rather than applying one grade to the whole assembly.
Two myths worth clearing up
“316 can’t rust.” It can. Rust spots on new stainless are usually free iron embedded in the surface from carbon-steel tools or grinding media, not the alloy failing. The fix is proper tooling discipline and passivation, not a more expensive alloy.
“Magnetic means it isn’t real stainless.” Annealed 304 and 316 are essentially non-magnetic, but forming, bending and machining can make them slightly magnetic. That’s normal.
When neither is enough
If you’re replacing 316 parts regularly, the alloy is the problem. Next steps up:
- 2205 duplex: high strength, strong chloride resistance, resists stress corrosion cracking
- 6% molybdenum superaustenitics (AL-6XN, 254 SMO): seawater, brine and bleach
- Hastelloy C-276 or C-22: severe chemistry and reducing acids. See Hastelloy vs stainless.
Specifying it on the drawing
- Name the grade including the L, for example “316L” rather than “316 stainless”.
- Call out which parts are product contact, so the right alloy goes in the right place.
- State the surface finish for product-contact surfaces.
- Say whether passivation is required, and to which standard. See passivation vs electropolishing.
- Describe the service conditions if you’re unsure of the grade. Chemistry, temperature and cleaning regime tell us more than a guessed alloy.
Send a drawing and the service conditions, and we’ll confirm the grade and filler before anything gets welded. See our capabilities.