Stainless Grade Reference for Machined Parts
Eighteen grades, ordered by family. PREN is shown as a range from the specification limits as well as the typical midpoint, because a single number hides how much two heats of the same grade can differ.
Austenitic
Not magnetic when annealed, cannot be hardened by heat treatment, work hardens under a rubbing tool. Most machined stainless parts live here.
| Grade | UNS | EN | PREN typical | PREN from limits | Machinability | Weldable | Hardenable | Magnetic | Specified for |
|---|---|---|---|---|---|---|---|---|---|
| 303 | S30300 | 1.4305 | 18 | 17 to 19 | 78 | No | No | No | Dry indoor parts with threads and cross holes, fittings, bushings, shafts |
| 304 | S30400 | 1.4301 | 19 | 18 to 22 | 45 | Yes | No | No | General purpose, indoor and mild outdoor, food equipment away from chloride |
| 304L | S30403 | 1.4307 | 19 | 18 to 22 | 45 | Yes | No | No | Welded 304 parts and assemblies |
| 316 | S31600 | 1.4401 | 24 | 23 to 30 | 36 | With care | No | No | Chloride service where the part is not welded |
| 316L | S31603 | 1.4404 | 24 | 23 to 30 | 36 | Yes | No | No | Food, dairy, pharma, medical instruments, marine, chemical process |
| 316Ti | S31635 | 1.4571 | 24 | 23 to 30 | 36 | Yes | No | No | Sustained service above 400 C where the low carbon trick is not enough |
| 321 | S32100 | 1.4541 | 18 | 17 to 21 | 36 | Yes | No | No | Exhaust parts, furnace hardware, aerospace fittings |
| Nitronic 60 | S21800 | 1.3964 | 19 | 17 to 21 | 35 | Yes | No | No | Valve stems, sliding fits, threads that cycle, wear parts that cannot be lubricated |
| 904L | N08904 | 1.4539 | 35 | 32 to 41 | 33 | Yes | No | No | Sulphuric and phosphoric acid service, seawater |
- 303The sulphide stringers that make it cut well are where pitting starts. Keep it out of food contact, medical and marine parts.
- 304The default austenitic. Work hardens fast, so a rubbing tool makes the next pass harder than the last.
- 304LLow carbon so chromium carbide does not form at grain boundaries during welding. Specify it whenever the part is welded.
- 316Molybdenum buys chloride resistance. Use the L version if the part is welded.
- 316LThe grade medical and food buyers ask for by name, and the slowest of the common three to cut.
- 316TiTitanium grabs the carbon so chromium stays in solution. The carbides show as streaks on a polished surface, so avoid it on cosmetic parts.
- 321The stabilised version of 304, for hot service rather than for chloride.
- Nitronic 60Roughly the corrosion class of 304 with far better galling resistance. It machines worse than the rating suggests because it work hardens hard.
- 904LHigh nickel super austenitic. Similar chloride resistance to 2205 without the strength, and considerably more expensive.
Ferritic
Magnetic, low carbon, not hardenable by heat treatment. Cheaper and easier to cut than the austenitic grades, and weaker.
| Grade | UNS | EN | PREN typical | PREN from limits | Machinability | Weldable | Hardenable | Magnetic | Specified for |
|---|---|---|---|---|---|---|---|---|---|
| 430 | S43000 | 1.4016 | 17 | 16 to 18 | 55 | With care | No | Yes | Trim, appliance panels, indoor decorative parts |
- 430Cheap and magnetic. Does not work harden like the austenitic grades, so it cuts more easily, but it is not a structural choice.
Martensitic
Magnetic and hardenable like a carbon steel. You trade chromium, and therefore corrosion resistance, for the carbon that lets it harden.
| Grade | UNS | EN | PREN typical | PREN from limits | Machinability | Weldable | Hardenable | Magnetic | Specified for |
|---|---|---|---|---|---|---|---|---|---|
| 410 | S41000 | 1.4006 | 12 | 12 to 14 | 54 | With care | Yes | Yes | Valve parts, fasteners, pump shafts that stay dry |
| 416 | S41600 | 1.4005 | 13 | 12 to 14 | 85 | No | Yes | Yes | Dry indoor shafts, studs, screw machine parts |
| 420 | S42000 | 1.4021 | 13 | 12 to 14 | 45 | With care | Yes | Yes | Cutlery, moulds, surgical instruments that are dried between uses |
| 440C | S44004 | 1.4125 | 17 | 16 to 20 | 40 | No | Yes | Yes | Bearings, knife edges, wear parts, nozzles |
- 410Hardens by heat treatment to 35 to 45 HRC. Corrosion resistance is the weakest part of the bargain.
- 416The easiest stainless to cut and the least corrosion resistant. Passivate in citric, never nitric.
- 420Hardens to 48 to 52 HRC. Machine annealed, then harden, then grind the critical features.
- 440CReaches 58 to 60 HRC. Best corrosion resistance of the martensitic family and still well below 316L.
Precipitation hardening
Machined soft in Condition A, then aged to strength. Small distortion compared with through hardening, and the condition has to be on the drawing.
| Grade | UNS | EN | PREN typical | PREN from limits | Machinability | Weldable | Hardenable | Magnetic | Specified for |
|---|---|---|---|---|---|---|---|---|---|
| 17-4 PH | S17400 | 1.4542 | 16 | 15 to 18 | 50 | With care | Yes | Yes | Shafts, valve components, aerospace fittings, instrument parts needing 30 to 44 HRC |
| 15-5 PH | S15500 | 1.4545 | 15 | 14 to 16 | 48 | With care | Yes | Yes | The same jobs as 17-4 PH where transverse toughness matters |
- 17-4 PHMachine in Condition A then age. The condition is part of the specification, so H900, H1025, H1075 or H1150 has to be on the print.
- 15-5 PHLess delta ferrite than 17-4 PH, so better properties across the bar. Specified with the same H conditions.
Duplex
Roughly half austenitic and half ferritic. Around twice the strength of 316L and much better in chloride, at a real cost in the machine.
| Grade | UNS | EN | PREN typical | PREN from limits | Machinability | Weldable | Hardenable | Magnetic | Specified for |
|---|---|---|---|---|---|---|---|---|---|
| 2205 duplex | S32205 | 1.4462 | 35 | 34 to 38 | 30 | With care | No | Slightly | Seawater, brine, chemical process, pressure parts needing strength |
| 2507 super duplex | S32750 | 1.4410 | 43 | 38 to 48 | 20 | With care | No | Slightly | Hot seawater, desalination, offshore, aggressive chloride service |
- 2205 duplexAround twice the yield strength of 316L and far better against chloride stress corrosion cracking. Welding needs a qualified procedure.
- 2507 super duplexSpecify it only where 2205 has already been shown to pit. It is slow, hard on tooling and expensive.
Composition limits
Nominal limits from the common bar and plate specifications. These are what the PREN range above is calculated from. Balance is iron in every case.
| Grade | Chromium % | Nickel % | Molybdenum % | Nitrogen % | Carbon % | Other |
|---|---|---|---|---|---|---|
| 303 | 17 to 19 | 8 to 10 | none | none | 0.15 max | S 0.15 min |
| 304 | 18 to 20 | 8 to 10.5 | none | 0 to 0.1 | 0.08 max | none |
| 304L | 18 to 20 | 8 to 12 | none | 0 to 0.1 | 0.03 max | none |
| 316 | 16 to 18 | 10 to 14 | 2 to 3 | 0 to 0.1 | 0.08 max | none |
| 316L | 16 to 18 | 10 to 14 | 2 to 3 | 0 to 0.1 | 0.03 max | none |
| 316Ti | 16 to 18 | 10 to 14 | 2 to 3 | 0 to 0.1 | 0.08 max | Ti 5xC min |
| 321 | 17 to 19 | 9 to 12 | none | 0 to 0.1 | 0.08 max | Ti 5xC min |
| Nitronic 60 | 16 to 18 | 8 to 9 | none | 0.08 to 0.18 | 0.10 max | Si 3.5-4.5, Mn 7-9 |
| 904L | 19 to 23 | 23 to 28 | 4 to 5 | 0 to 0.1 | 0.02 max | Cu 1-2 |
| 430 | 16 to 18 | none | none | none | 0.12 max | none |
| 410 | 11.5 to 13.5 | 0 to 0.75 | none | none | 0.08-0.15 | none |
| 416 | 12 to 14 | none | none | none | 0.15 max | S 0.15 min |
| 420 | 12 to 14 | none | none | none | 0.15 min | none |
| 440C | 16 to 18 | none | 0 to 0.75 | none | 0.95-1.20 | none |
| 17-4 PH | 15 to 17.5 | 3 to 5 | none | none | 0.07 max | Cu 3-5, Nb |
| 15-5 PH | 14 to 15.5 | 3.5 to 5.5 | none | none | 0.07 max | Cu 2.5-4.5, Nb |
| 2205 duplex | 22 to 23 | 4.5 to 6.5 | 3 to 3.5 | 0.14 to 0.2 | 0.03 max | none |
| 2507 super duplex | 24 to 26 | 6 to 8 | 3 to 5 | 0.24 to 0.32 | 0.03 max | none |
How to read this table
PREN orders grades, it does not grade them. A PREN of 24 does not mean 316L survives a given chloride concentration. It means 316L resists pitting better than 304 at 19 and worse than 2205 at 35. Temperature, concentration, crevices and surface finish all move the real threshold.
Machinability is relative and approximate. 303 at 78 against 316L at 36 tells you 303 cuts roughly twice as fast on the same geometry. It does not tell you a cycle time. See work hardening for why the real gap on a difficult part is often wider than the ratings suggest.
The two columns pull against each other. That is the whole problem with specifying stainless. The grade that cuts easily is usually the one with the least chromium and molybdenum doing useful work, which is why 303 and 416 sit at the top for machinability and the bottom for corrosion. The grade selector walks that trade.
Write the environment, not just the grade. A sentence such as washed down daily with 2 percent caustic at 70 C lets a shop suggest a cheaper alloy that still survives. What to put in a stainless RFQ has the rest.