Material selection
Stainless 304 vs 316L
Same density, same general shape of alloy, and the same machine shop can cut both. The choice almost never comes down to strength. It comes down to one element, molybdenum, and whether the part will ever see chlorides. The numbers below are the same published values used on each material's own page, set side by side.
| Stainless 304 | Stainless 316L | |
|---|---|---|
| Density | 8.00 g/cm³ | 8.00 g/cm³ |
| Tensile strength | 515 MPa | 485 MPa |
| Yield strength | 205 MPa | 170 MPa |
| Elongation | 40 % | 40 % |
| Hardness | 201 HB max | 217 HB max |
| Melting range | 1400–1450 °C | 1375–1400 °C |
| Relative cost | Medium | High |
Published values for standard grades at 23 °C unless stated, taken from each material's own datasheet page. Confirm against the supplier datasheet for the grade you specify.
What Stainless 304 is
304 is an austenitic chromium-nickel stainless and the most used stainless grade worldwide. The chromium forms a passive oxide film that reforms on its own if scratched, which is what gives the alloy its corrosion resistance without a coating. It is very ductile, deep draws well, and welds without special procedure, but it work hardens aggressively, which is what makes it slow and expensive to machine.
What Stainless 316L is
316L is 304's chemistry with 2–3 % molybdenum added, which sharply improves resistance to chlorides: seawater, saline, de-icing salt, and many process chemicals that pit 304 over time. The L designation means low carbon, which prevents chromium carbide forming at grain boundaries during welding. It is the standard stainless for surgical instruments, implants, and pharmaceutical process equipment, and it machines almost identically to 304, only slightly harder.
Stainless 304 against Stainless 316L
| Stainless 304 | Stainless 316L | |
|---|---|---|
| Weight | 8.00 g/cm³, identical to 316L | 8.00 g/cm³, identical to 304, weight is never the deciding factor between these two |
| Strength | Higher tensile at 515 MPa and higher yield at 205 MPa | Slightly lower on both, 485 MPa tensile and 170 MPa yield, though still comfortably enough for the vast majority of machined parts |
| Corrosion resistance | Passive chromium oxide film handles most indoor and general outdoor exposure without a coating | Molybdenum addition resists pitting and crevice corrosion in chlorides where 304 will eventually pit: seawater, saline spray, de-icing salt, many process chemicals |
| Machinability | Work hardens aggressively with dwelling in the cut; already slow next to aluminum or mild steel | Machines almost identically to 304, only marginally harder and slower on the same rigid, sharp-tool setup |
| Weldability | Welds readily; use 304L on welded assemblies to avoid carbide precipitation at the joint | Welds with 316L filler and a back-purge to protect the root pass; the low-carbon grade avoids the same carbide problem by default |
| Relative cost | Medium, and the default choice unless the service environment says otherwise | High, the molybdenum addition typically prices 316L 20 to 40 percent above 304 for the same stock size |
Which one, for which part
- Marine hardware, coastal outdoor equipment, or anything exposed to de-icing salt or saline spray favours 316L; 304 will pit in continuous chloride exposure regardless of how well it is finished.
- Surgical instruments, implantable components, and pharmaceutical or biotech process equipment is 316L's case outright: it is the industry-standard stainless for patient-contact and process-wetted parts, with ASTM F138 the usual bar-stock spec for implants.
- Food, beverage, architectural, and general indoor hygienic equipment with no chloride exposure is answered by 304 at a real cost saving, since the extra corrosion margin from molybdenum goes unused.
- Chemical processing components handling acids, chlorides, or aggressive cleaning agents favours 316L; check the specific chemical against a corrosion resistance table rather than assuming, since some acids favour 304 or a duplex grade instead.
- Cost-sensitive brackets, fixtures, and enclosures made in volume where the environment is dry or mild favour 304; paying the 316L premium here buys corrosion resistance the part will never be tested on.
Our status
Trumould machines and forms both stainless 304 and 316L in-house across CNC machining and sheet metal fabrication; neither runs through injection molding or 3D printing here. Send the part, its service environment, and target volume, and the quote states which of the two is recommended and why, not just a price for whichever one you asked about first.
Specifying this part?
Send your CAD and target volumes. We come back with a price, a lead time, and any material or design notes that would reduce either.