GRADE PROFILE
444 — S44400 / X2CrMoTi18-2
444 is a stabilised ferritic at 18% chromium with 1.75 to 2.50% molybdenum. Its PREN of 25 is comparable to a 316L, without a gram of nickel. That is the whole logic of the grade — and its immunity to chloride stress corrosion cracking is the corollary.
- Ferritic
- PREN 23–28
- Cost index 100
When to choose it
On heat exchanger and condenser tube in fresh and domestic hot water, hot water cylinders and networks, solar thermal and heating. The use case that belongs to 444 is the one where chloride stress corrosion cracking disqualifies 304L and 316L: a chlorinated domestic hot water cylinder is exactly that context, and an austenitic cracks there where a ferritic does not.
It is also the grade to consider where the nickel price is decisive in the costing.
When not to choose it
In cryogenic or low-temperature service. Ferritics have a ductile-to-brittle transition that austenitics do not: below a certain temperature, fracture becomes brittle. That is the family's hard limit.
In seawater: a PREN of 25 is that of a 316L, not a duplex.
On heavy welded sections without precautions, because of grain growth in the heat-affected zone.
In severe forming, ductility being lower than that of an austenitic.
And by confusing it with 430: molybdenum and stabilisation are what separate the two.
Composition
| Element | % |
|---|---|
| C | ≤ 0.025 |
| Mn | ≤ 1 |
| P | ≤ 0.04 |
| S | ≤ 0.03 |
| Si | ≤ 1 |
| Ni | ≤ 1 |
| Cr | 17.5–19.5 |
| Mo | 1.75–2.5 |
| N | ≤ 0.035 |
| TiCb | Ti + Cb = 0,20 + 4 × (C + N) minimum, et 0,80 % maximum |
Mechanical properties
| Standard | Form | Rm (MPa) | Rp0.2 (MPa) | A (%) | Hardness |
|---|---|---|---|---|---|
| ASTM A268/A268M−10, tableau 3 | tube soudé et sans soudure, paroi 8 mm | ≥ 415 | ≥ 275 | ≥ 20 | ≤ 217 HBW · ≤ 95 HRB |
Designations and standards
| Reference | Designation |
|---|---|
| EN (numeric) | 1.4521 |
| EN (symbolic) | X2CrMoTi18-2 |
| ASTM / AISI | 444 / 18Cr-2Mo |
| UNS | S44400 |
| JIS | — |
| AFNOR | — |
Tube product standards :
- ASTM A268/A268M
- ASME SA268
- EN 10088-2 (produits plats)
Availability
Available in welded and seamless tube to ASTM A268. Structured dimensional data for this grade is not yet documented in our reference set: send us your sizes. EN 10204 3.1 material certificates supplied with the goods.
Related grades
- 316L (1.4404) — the equivalent PREN in austenitic, more ductile but susceptible to stress corrosion cracking.
- 430 (S43000) — the ferritic without molybdenum, not to be confused.
- 2304 (S32304) — the duplex answering the same cracking problem, with far higher mechanical strength.
My grade isn't listed → · PREN calculator → · Compare grades →
Frequently asked questions
- Can 444 replace a 316L?
- On pitting in fresh or moderately chlorinated water, yes, at equivalent PREN. On stress corrosion cracking, it does better. However, it is less ductile, harder to form, and unusable at low temperature. The replacement makes sense on heat exchangers and cylinders, not everywhere.
- Why does a ferritic not crack under stress?
- Because chloride stress corrosion cracking is specific to austenitic structure. Ferritics are practically immune, which is the main reason to choose a 444 on a chlorinated hot water circuit.
- Is it magnetic?
- Yes, like all ferritics. That has no bearing on service, but it may affect nearby instruments or inspection methods.