AL-6XN (UNS N08367)
The 6 % Mo super austenitic in nickel-alloy classification — PREN about 43 at minimum chemistry (typically about 45) for seawater, brine and chlorinated water — with 95 ksi tensile in the annealed bar.
What AL-6XN is.
AL-6XN is a 24 percent nickel, 21 percent chromium, 6.5 percent molybdenum alloy with 0.2 percent nitrogen. Its pitting resistance equivalent number is about 43 at the B691 minimum chemistry and typically about 45, so it resists crevice corrosion in seawater and brines and chloride stress-corrosion cracking, and its higher nickel makes it more stable than the stainless 6-Mo grades in reducing conditions. Iron is the balance of the composition, so ASTM B691 classes it as an iron-nickel-chromium-molybdenum alloy under UNS N08367, though it is usually sold alongside the nickel alloys.
ASTM B691 covers the bar. We machine AL-6XN studs, bolts, nuts and components from certified B691 bar.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Nickel | Ni | 23.50 | 25.50 |
| Chromium | Cr | 20.00 | 22.00 |
| Molybdenum | Mo | 6.00 | 7.00 |
| Nitrogen | N | 0.18 | 0.25 |
| Copper | Cu | — | 0.75 |
| Manganese | Mn | — | 2.00 |
| Silicon | Si | — | 1.00 |
| Carbon | C | — | 0.030 |
| Phosphorus | P | — | 0.040 |
| Sulfur | S | — | 0.030 |
| Iron | Fe | balance | — |
Values per ASTM B691-18 Table 1 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Mechanical properties.
| Condition and size | Tensile strength, min (ksi) | Yield strength 0.2%, min (ksi) | Elongation, min (%) |
|---|---|---|---|
| Cold or hot finished, annealed — all sizes | 95 | 45 | 30 |
Values per ASTM B691-18 Table 2 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Specifications that apply.
How AL-6XN ships from Houston.
- Full-thread studs and stud bolts
- Hex and heavy hex bolts
- Socket head cap screws
- Hex nuts in the same alloy
- Threaded rod
- Machined components from certified bar
AL-6XN fasteners we make.
Every item is manufactured to your drawing or standard in AL-6XN, imperial or metric, with an EN 10204 3.1 certificate.
AL-6XN or 254 SMO?
Both are 6 percent molybdenum super austenitic alloys with nitrogen and near-identical pitting resistance. AL-6XN carries about 24 percent nickel against 18 for 254 SMO, which gives it a small edge in reducing acids and more margin against sigma-phase formation during welding of thick sections; 254 SMO adds copper for sulfuric acid. In bolting, 254 SMO has a defined A193 grade (B8MLCuN) while AL-6XN nuts appear in A194 as Grade 9C; either can be certified to the bar specification for studs. Most users treat them as interchangeable and buy on availability.
Testing, certification and marking
- Tensile and hardness tested per lot on the finished product
- Grade or alloy marking N08367 with heat number and manufacturer's identification on every piece
- EN 10204 3.1 material test report with heat number and chemistry; 3.2 witness available
ASTM A193 Grade B8MLCuN Class 1B (254 SMO, UNS S31254)
254 SMO bolting — a 6 % Mo super austenitic with PREN above 42 for seawater, chlorinated cooling water and flue-gas scrubbers where 316 pits.
ASTM A1082 bolting · ASTM A276 / A479 bar · ASTM A182 F53Super Duplex 2507 Stainless (UNS S32750)
25 Cr super duplex with a PREN above 40 — 116 ksi tensile and 80 ksi yield for the most aggressive seawater, sour and chloride bolting.
ASTM B473 barAlloy 20 (Carpenter 20Cb-3, UNS N08020)
The sulfuric-acid alloy — 3.5 % copper and 2.5 % molybdenum in a stabilised 35 % nickel base — for acid plants, pickling lines and pharmaceutical process equipment.