AISI 310 (310S) and AISI 314 are two austenitic stainless steels made for high-temperature service. Their chromium and nickel contents are identical. The difference between them lies in a single element: silicon.
Why add silicon?
What protects a steel at high temperature is the chromium oxide layer that forms on its surface. As the temperature rises, that layer eventually becomes inadequate and scaling begins. The 1.50 to 2.50 % silicon added to AISI 314 makes the oxide layer more resistant and pushes the scaling temperature upward.
The gain is concrete: to EN 10095 the continuous service temperature in dry air is 1050 °C for 310S and 1150 °C for 314. That roughly 100 °C difference is what the silicon buys.
The price: embrittlement
Silicon is not free. Outokumpu states that 1.4841 (314) has a high susceptibility to embrittlement during continuous operation in the 600–950 °C range. The German stainless steel information centre (ISER) writes that 1.4841 is more susceptible than 1.4845 (310S), and that 1.4845 itself can embrittle in the 600–900 °C band.
The practical consequence: if the temperature is steady and high, use 314; if there is heating and cooling cycling, use 310S. ISER notes that 310S is preferred under cyclic conditions because it forms a more adherent oxide scale.
Compared in figures
| PROPERTY | AISI 310S (1.4845) | AISI 314 (1.4841) |
|---|---|---|
| Carbon (C) | see the warning below | 0.20 % max |
| Silicon (Si) | 1.50 % max | 1.50 – 2.50 % |
| Manganese (Mn) | 2.00 % max | 2.00 % max |
| Sulphur (S) | — | 0.015 % max |
| Chromium (Cr) | 24.00 – 26.00 % | 24.00 – 26.00 % |
| Nickel (Ni) | 19.00 – 22.00 % | 19.00 – 22.00 % |
| Continuous service (EN 10095, dry air) | 1050 °C | 1150 °C |
| Suitability for cyclic heating | better | less suitable |
What to watch when ordering
310, 310S and 1.4845 are three different carbon ceilings.
ASTM Type 310 (S31000) allows carbon up to 0.25 %; ASTM 310S (S31008) up to 0.08 %; EN 1.4845 up to 0.10 %. So a bar certified to 1.4845 at 0.09 % carbon does not meet ASTM 310S. State clearly which one you want.
Likewise 1.4841 and UNS S31400 are not identical: EN 1.4841 limits silicon to 1.50–2.50 % while ASTM S31400 permits 1.50–3.00 %. A heat at 2.8 % silicon meets S31400 but fails 1.4841.
Two warnings
The intermittent temperature can be lower than the continuous one. In these two grades the scale spalls under thermal cycling, so the intermittent service limit is sometimes below the continuous one. Any source quoting a single “maximum temperature” without saying whether it is continuous or cyclic is therefore unusable.
Neither is a wet-corrosion steel. High nickel does not make these grades suitable for aqueous service; both are susceptible to intergranular corrosion. In carburising atmospheres, 310 and 314 should be replaced by nickel-base alloys.
Designations, standards and AMS equivalents
The same steel is called different things depending on which system you are speaking in. Most ordering and certification confusion starts here, so a short summary:
- AISI — the American Iron and Steel Institute’s grade naming (410, 316L and so on). It is the most widely used name in everyday use, but on its own it is not a purchasing specification: composition and mechanical requirements are defined in the ASTM standards.
- UNS — the Unified Numbering System operated jointly by ASTM and SAE (S41000 and so on). It is the number used for ordering and certification in North America, and it is more precise than the AISI name.
- W.Nr / EN — the European material number (1.4006 and so on) and EN name (X12Cr13 and so on). This is the governing designation in Europe. It is usually only an approximate equivalent of the AISI grade; carbon, sulphur or molybdenum limits frequently differ.
- AMS — SAE’s Aerospace Material Specifications. An AMS specification binds not only the composition but also the melting practice, the product form, the heat treatment condition and the inspection requirements. In aerospace and defence orders this is the designation that governs.
| DESIGNATION | AISI 310 | AISI 314 |
|---|---|---|
| AISI / trade name | AISI 310 | AISI 314 |
| EN material no. (W.Nr) | 1.4845 | 1.4841 |
| UNS number | S31000 | — |
| AMS specifications | AMS 5521 · AMS 5572 | AMS 5522 · AMS 5652 |
| Product page | AISI 310 technical page | AISI 314 technical page |
Two reminders. First: an AMS number is specific to a product form and condition. The same grade may have separate AMS specifications for bar, sheet and forgings, so establish which product form you need before calling up an AMS number.
Second: the AISI name, material number, UNS and AMS data in the table above are the designations shown on Defence Metal’s product pages. If you are working to a different edition of a standard or to a different product form, state the material number and the specification edition explicitly on your order.