AL-6XN Forgings UNS N08367, forged to ASTM A182 Grade F62. Melted, forged, heat treated and tested in one works.

AL-6XN is a trade name, not a specification. The alloy itself is UNS N08367, and when it is bought as a forging the governing document is normally ASTM A182 / A182M Grade F62. The two names describe the same steel.

Composition and property limits for N08367 differ between the plate, pipe, bar and forging specifications. Confirm specification, edition and product form on the purchase order.

Not the same as F44

The most common mix-up on enquiries for this alloy is with ASTM A182 Grade F44, which is UNS S31254, sold as 254 SMO. Both are 6 % molybdenum nitrogen-alloyed super-austenitic stainless steels and both land in similar service, but they are different alloys with different certificates, and the gap is in the nickel.

The extra six points of nickel in AL-6XN is what buys the margin against chloride stress-corrosion cracking. F44 answers with a tighter carbon limit and a deliberate copper addition. If a drawing calls out AL-6XN and the purchase order says F44, we stop and ask before cutting steel. Our A182 F44 page covers that grade on its own terms.

ASTM A182 / A182M requirements for grade identification symbol F62, UNS N08367, weight per cent.

Nitrogen has a floor here as well as a ceiling, which is unusual on a stainless data sheet and easy to read past. It is not a residual to be tolerated, it is an alloying addition that has to be hit, and it is the reason this alloy is stronger than 316L. Nitrogen appears on every certificate we issue.

Melting route

The grade runs through the electric arc furnace, is refined in a ladle furnace and is decarburised under vacuum, which is the route that delivers the 0.030 % maximum carbon and the tight nitrogen band at the same time. Protective-atmosphere electroslag remelting is available where an order calls for it. Maximum heat size is 60 tonnes.

A182 permits stainless grades to be melted by electric furnace with optional separate degassing and refining, by vacuum furnace, or by either route followed by vacuum or electroslag consumable remelting, so both of our routes meet the specification. Enough discard is taken to keep the material free of injurious piping and undue segregation.

Project specifications often set a minimum pitting resistance equivalent number for 6 % molybdenum grades. Two things are worth settling before the order, because both change the answer.

The first is the formula. The common form is PREN = %Cr + 3.3 × %Mo + 16 × %N, but the nitrogen coefficient differs between published versions, so name the formula on the purchase order rather than assuming ours matches yours. Taking the minimum grade limits of 20.0 % chromium, 6.00 % molybdenum and 0.18 % nitrogen, that formula gives about 42.7. On a typical analysis of 21 % chromium, 6.3 % molybdenum and 0.22 % nitrogen it comes out at about 45.3. Supplier literature for this alloy quotes both 44 and 45, which is why we show a range rather than a single figure, and one published comparison credits it with better pitting resistance than 254 SMO on PREN.

The second is the threshold being applied. A frequently cited rule of thumb puts the minimum for seawater pitting resistance near 32, while one published guide sets the working threshold for dependable seawater service at ambient to moderate temperatures above 40. AL-6XN clears both. We report the full heat analysis so PREN can be calculated by whichever formula and threshold your specification names.

Acceptance minima at room temperature for ASTM A182 F62, solution treated and quenched. These are not typical values, and the distinction matters at design review.

Typical tensile properties at temperature

Producer literature credits UNS N08367 with ASME allowable stresses substantially above 316L and more than double those of copper-nickel alloys, with ASME coverage to 800 °F. Published figures in that comparison range from 40 % to 75 % higher than 316L depending on the source and temperature, so treat them as reference rather than as design input and state the values a design depends on at enquiry stage.

ASTM A182 calls for one tension test per heat on austenitic grades. Specimens are removed only after all heat treatment is finished, and test blanks get about the same amount of working as the finished forging and are heat treated with it.

Physical property figures vary slightly between published mill data sheets. Where a value is contractual it should be taken from the purchase specification.

The alloy was developed as a seawater-resistant material and has more than twenty-five years of service behind it in that duty.

Critical crevice corrosion temperature measured to ASTM G48 Method B.

Beyond chlorides, the grade handles hot low-pH process streams that strip 316L. Tomato juice at pasteurising temperature near 100 °C is the standard illustration, and it is the reason the alloy turns up in food processing as well as in seawater plant. The high nickel content is what gives it practical immunity to stress-corrosion cracking in sodium chloride environments.

Against duplex and super duplex

Buyers routinely weigh this alloy against duplex 2205 and super duplex 2507. Producer data positions UNS N08367 above conventional duplex stainless steels on strength and corrosion resistance and below nickel-base alloys on cost. In practice the PREN figures for super duplex land close to this grade, so the decision usually turns on something else: AL-6XN stays fully austenitic, which means non-magnetic, tough at low temperature, and no ferrite phase balance to control through a heavy section. Super duplex still wins on yield strength per unit weight. Decide against the actual chloride level, temperature and design code rather than on PREN alone, and if sour service governs instead, say so at enquiry, because NACE MR0175 and ISO 15156 add hardness and heat treatment constraints on top of A182.

After hot working, forgings are cooled below 1000 °F [538 °C] before heat treatment starts. Where the temperature straight after hot working has not dropped below the minimum solution annealing temperature, A182 also allows austenitic grades such as this one to be rapid quenched individually from the forging heat.

Two cautions govern the practice. Do not anneal below the specified minimum, and do not slow cool, because slow cooling reduces corrosion resistance. The solution temperature also sits uncomfortably close to a melting range that starts at 2410 °F, so furnace uniformity and soak time have to be held tightly rather than approximately. That single fact is the strongest argument for buying this grade from a shop that runs it regularly. Three high-temperature car-bottom furnaces cover the solution temperature the grade needs, and two 15 m well-type furnaces allow long shafts to be quenched vertically.

Hot working

Forge and upset within the normal hot working range for the grade, bringing the billet up to heat slowly and evenly. The alloy is stiff at temperature and a chilled corner or a cold centre is where cracking starts. Every hot worked part is solution treated and quenched afterwards to restore corrosion resistance.

Hardening

The grade does not respond to hardening heat treatment. Higher strength comes from cold reduction only, and the work hardening rate makes that heavy going. Material that has taken heavy cold work is annealed and water quenched before service.

Machining

Machining is slow and should be quoted as such. The alloy is ductile in the solution-annealed condition but work hardens fast, needs more power at the tool than plain carbon steel, and throws stringy tough chips. As a starting point only, around 70 sfm for turning and milling and 50 sfm for drilling, with a rigid setup, positive feed and plenty of coolant. Keep tool overhang short, and keep the feed heavy enough that the edge cuts under the previous pass instead of rubbing on the hardened skin it has just made. All cutting fluid comes off before annealing, welding or corrosive service.

Welding

Use an overmatching filler carrying about 9 % molybdenum. A matching filler leaves the weld metal short of molybdenum relative to the parent material, and the weld then corrodes first. ERNiCrMo-3 filler wire of the alloy 625 type and ENiCrMo-3 covered electrodes are the normal choices. Open the root gap enough that the bead is mostly filler rather than diluted parent metal, and avoid feather-edge preparations. Keep heat input and interpass temperature down. Clean with stainless or non-metallic tools only, because iron picked up from a carbon steel wire brush will seed pits in chloride service.

All made to drawing: seamless rolled rings and forged rings, weld neck, blind and slip-on flange blanks, round bars and billets, forged discs and disc blanks, hollow forgings, sleeves and bushings, shafts, spindles and eccentric shafts, tube sheets, nozzles, valve bodies, valve stems, seat rings and valve blocks, and tube and pipe blanks bored from solid.

Producer literature lists flue-gas desulphurisation scrubbers, reverse osmosis, distillation columns, offshore oil and gas, and heat exchangers among the established uses for this alloy, backed by more than twenty-five years of seawater service.

Regular end uses for our forgings in this grade: seawater, firewater and subsea pipework with risers, manifolds, pressure vessels, valves and heat exchangers; desalination plant including high-pressure reverse osmosis trains and seawater piping; flue-gas desulphurisation and other pollution-control equipment in power generation; pulp and paper digesters, liquor tanks, bleaching washers, vats, press rolls and paper machines; chemical and pharmaceutical reaction vessels; tall oil distillation columns and packing; salt dryers; mining, metallurgical and marine equipment including transformer cases; food processing and medical sterilisation plant; and corrosion-resistant components in power transmission, gearboxes, turbines and gas compressors.

The works holds CCS, BV, DNV, LR and NK classification society approvals and runs its own laboratory.

ASTM A182 provides for intergranular attack testing to ASTM A262 practices on austenitic stainless steels where a purchaser specifies it as a supplementary requirement, so name it on the order rather than assuming it. Certificates are issued to EN 10204 3.1, or to EN 10204 3.2 witnessed by BV, DNV, LR, SGS, TUV or your own inspector. Supporting records cover heat treatment charts, NDT reports, dimensional reports and PMI results. Traceability runs from the melt number through forging, heat treatment and machining to shipment.

State the test scope with the enquiry rather than after the order, because it moves both the price and the delivery date.

If this alloy is not the right answer for the duty, these are the grades most often compared with it. Tell us the medium, the temperature and the chloride level and we will suggest candidates.

• ASTM A182 F62, specification page
• A182 F44
• A182 F51, duplex 2205
• A182 F53, super duplex
• A182 F61
• 904L
• Sanicro 28
• Nitronic 50
• Incoloy 825
• Incoloy 926
• Alloy 31
• Hastelloy C-276
• Seamless rolled rings
• Forged discs
• Forged bars

Composition, property and heat treatment values are quoted from ASTM A182 / A182M for grade identification symbol F62, UNS N08367, together with published mill data for this alloy. Where published sources differ, ranges are shown. Order against the current edition of the specification. Data is given for engineering reference and is not a warranty for any particular application. AL-6XN is a registered trademark of Allegheny Ludlum Corporation; Jiangyin Jiangnan Metal Co., Ltd. is not affiliated with or licensed by the trademark owner and names it here for identification only. Reviewed 2 October 2026. A plain text version of this data sheet is also available.