SS 304 and SS 316 are the two most widely ordered austenitic stainless steel round bars. They look identical and share similar strength, but one small difference in composition decides where each performs best.
| Property | SS 304 / 304L | SS 316 / 316L |
|---|---|---|
| UNS number | S30400 / S30403 | S31600 / S31603 |
| Chromium | 18.0–20.0% | 16.0–18.0% |
| Nickel | 8.0–10.5% (304L up to 12.0%) | 10.0–14.0% |
| Molybdenum | None | 2.0–3.0% |
| Min tensile, ASTM A276 annealed | 515 MPa (304L: 485 MPa) | 515 MPa (316L: 485 MPa) |
| Min yield, ASTM A276 annealed | 205 MPa (304L: 170 MPa) | 205 MPa (316L: 170 MPa) |
| Chloride / pitting resistance | Moderate (PREN about 19) | Good (PREN about 24–25) |
| Relative cost | Lower | Higher |
SS 316 contains 2–3% molybdenum, which SS 304 does not. Molybdenum improves resistance to pitting and crevice corrosion in chloride environments such as seawater, coastal air, de-icing salts and many chemical process streams. SS 316 also carries slightly more nickel, which helps in some acids.
Minimum specified strength in ASTM A276 annealed bar is the same for both grades, so you choose between them on corrosion environment and cost, not on strength.
SS 304 is the economical choice for food-processing equipment, indoor architectural parts, general engineering shafts and fasteners, and any application where chlorides are absent or very low. It is also the easier of the two to source in a wide range of sizes.
Choose SS 316 for marine and coastal installations, chemical and pharmaceutical equipment, and pump and valve shafts handling mild chlorides. If your environment is more aggressive than 316 can handle, such as warm seawater or high-chloride process streams, step up to duplex 2205, super duplex or 254 SMO instead.
304L and 316L limit carbon to 0.03% maximum. This reduces carbide precipitation during welding, which protects against intergranular corrosion in welded sections. Many mills dual-certify bars as 304/304L or 316/316L, which is why our listings are shown that way.
The two grades are visually identical, and both are essentially non-magnetic when annealed. A positive material identification (PMI) test, or the heat-specific EN 10204 3.1 mill test certificate, confirms the molybdenum content. Always match the heat number on the bar marking to the certificate.
