Guide
304 vs 316 stainless: which one the fabricated part needs
304 and 316 look the same on the shelf and the shop forms and welds them the same way. The difference is molybdenum, which 316 has and 304 does not, and which buys resistance to chlorides. Salt, bleach, many cleaning chemicals and coastal air attack 304 by pitting; 316 holds up. Most industrial enclosures, guards and brackets are 304. Food, pharma, marine and wash-down parts are usually 316, and the drawing should say which and why.
Send a drawingUpdated October 8, 2026
What the two alloys are
304 is the general-purpose austenitic stainless: about 18 percent chromium and 8 percent nickel. It is non-magnetic as sheet, forms well, welds well and polishes well. The L grade, 304L, has less carbon so it welds without losing corrosion resistance at the weld; most sheet today is dual certified 304/304L.
316 adds 2 to 3 percent molybdenum. That is what resists pitting in chlorides. 316L is the low-carbon version for welded work and is the usual spec for sanitary and marine fabrication. 316 costs more per pound and the price moves with nickel and molybdenum.
Where 304 is right
- Indoor equipment, enclosures, guards, brackets and frames in a dry or occasionally damp plant.
- Parts that are washed with water and mild detergents without bleach.
- Cosmetic panels where a brushed or mirror finish is the point; 304 polishes well.
- Any part where the environment does not include chlorides and the budget is a factor.
Where 316 earns its cost
- Food and beverage, pharma and chemical wash-down with chlorinated cleaners or CIP chemistry.
- Marine and coastal installations, pool and spa equipment, de-iced roads.
- Parts in contact with salt water, brine or seawater spray.
- Where the customer's spec or the sanitary standard names 316L.
Fabrication differences
Both alloys pick up iron from the shop if they share tools with carbon steel, which shows later as rust spots on a stainless part. A shop that does sanitary work keeps stainless tooling separate and passivates after fabrication; if your part needs that, write "passivate per ASTM A967" and ask on the request whether the shop segregates stainless.
| 304 / 304L | 316 / 316L | |
|---|---|---|
| Forming | Good, work hardens | Good, work hardens slightly more |
| Welding | 308L filler | 316L filler |
| Passivation | ASTM A967, same process | ASTM A967, same process |
| Finish | 2B mill, #4 brushed, #8 mirror | Same finishes available |
| Magnetism | Slight after forming | Slight after forming |
| Cost | Base | Higher, moves with nickel and molybdenum |
What to put on the drawing
- Alloy and condition: 304/304L 2B, or 316L #4 brushed, not just "stainless".
- Grain direction on a brushed cosmetic face, so the shop nests it that way.
- Weld finish: as welded, ground flush, or polished to match, and whether welds are continuous (sanitary) or stitched.
- Passivation if the part sees chemicals or is sanitary.
Questions buyers ask
- Will a shop substitute 304 for 316?
- Only if you allow it, and the quote says so. If the drawing says 316L, the shop quotes 316L. If you are not sure the part needs 316, say what it is exposed to and ask; the quote can offer both.
- Why did my 304 part rust?
- Usually iron contamination from carbon steel tooling or grinding dust, or chlorides from a cleaner. Passivation removes the free iron; the chloride problem is an alloy choice.
- Is 316 harder to form?
- Marginally. For sheet metal brackets, enclosures and welded frames a shop that forms 304 forms 316 the same way.
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