Annealed Type 304L, 304 and 302 are closely related austenitic stainless steels. Each has its own AMS specification and its own chemistry and strength limits, but those limits overlap. A single heat of material that falls inside all three sets of limits can be certified to all three alloys at once. That is what “triple certified” means, and it is how our annealed 304L / 304 / 302 is stocked.
The chemistry overlap
The biggest difference between the three alloys is carbon. Type 302 allows up to 0.15% carbon, Type 304 allows up to 0.08%, and Type 304L — the “L” stands for low carbon — allows only 0.030%. Their chromium and nickel ranges differ slightly as well.
Material made to 304L’s low carbon limit, with chromium and nickel kept inside the ranges all three alloys share, meets the chemistry of all three.
Chemical Requirements — Type 302, 304 & 304L (weight %)
| Element | 302UNS S30200 | 304UNS S30400 | 304LUNS S30403 | Triple-CertifiedOverlap Range |
|---|---|---|---|---|
| Covering specs | AMS 5516 A240 · A666 | AMS 5513 A240 · A666 | AMS 5511 A240 · A666 | Meets all |
| Carbon (C) | 0.15 max | 0.08 max | 0.030 max | 0.030 max |
| Manganese (Mn) | 2.00 max | 2.00 max | 2.00 max | 2.00 max |
| Silicon (Si) | 0.75 max | 0.75 max | 0.75 max | 0.75 max |
| Phosphorus (P) | 0.045 max | 0.045 max | 0.045 max | 0.045 max |
| Sulfur (S) | 0.030 max | 0.030 max | 0.030 max | 0.030 max |
| Chromium (Cr) | 17.0–19.0 | 18.0–20.0 | 18.0–20.0 | 18.0–19.0 |
| Nickel (Ni) | 8.0–10.0 | 8.0–10.5 | 8.0–12.0 | 8.0–10.0 |
| Nitrogen (N) | 0.10 max | 0.10 max | 0.10 max | 0.10 max |
| Iron (Fe) | Balance | Balance | Balance | Balance |
The mechanical overlap
The minimum strength requirements differ too. The “L” (low carbon) grade has slightly lower minimums, so triple-certified material has to meet the higher 302 and 304 values.
Mechanical Requirements — Annealed (minimum)
| Property | 302 | 304 | 304L | Triple-CertifiedMust Meet |
|---|---|---|---|---|
| Tensile strength, psi | 75,000 | 75,000 | 70,000 | 75,000 |
| Yield strength, psi | 30,000 | 30,000 | 25,000 | 30,000 |
| Elongation in 2″ | 40% | 40% | 40% | 40% |
The specifications
Because the material meets every requirement, it can be certified to each alloy’s specification:
- AMS 5511 — 304L
- AMS 5513 — 304
- AMS 5516 — 302
- ASTM A240 and ASTM A666
- UNS S30403, S30400 and S30200
What it means on your paperwork
A purchase order that calls out 304L, 304 or 302 in the annealed condition can be filled from the same triple-certified material, and the test report and certificate of conformance show the alloys and specifications it meets.
Triple certification applies to our annealed material. Our cold-rolled tempers (Quarter, Half and Full Hard) are dual certified to 302 / 304 — see Why are our tempered 302 / 304 dual certified?
This article is educational information only. Always order to the current revision of the governing specification.