Super Austenitic Stainless Steel · 6% Molybdenum · Nickel-Iron-Chromium-Molybdenum

NAS 255NM / UNS N08926 / EN 1.4529 Forging Parts

Published: 15 June 2016  |  Last updated: 21 August 2026  |  Technically reviewed by the Jiangyin Jiangnan Metal Co., Ltd. Metallurgical Engineering Team

NAS 255NM is a 6% molybdenum super austenitic stainless steel containing nominally 25% nickel, 20% chromium, 6.5% molybdenum, 1% copper and 0.2% nitrogen, balance iron. This chemistry is registered as UNS N08926 and standardised in Europe as EN 1.4529 (X1NiCrMoCu25-20-7). The high molybdenum and nitrogen give it a pitting resistance equivalent number (PREN) of roughly 45, so it resists pitting and crevice corrosion in warm chloride environments (seawater, flue gas desulfurisation scrubbers, bleach plants, brine evaporators) at a level approaching nickel alloys, for a fraction of their cost. The 25% nickel makes it highly resistant to chloride stress corrosion cracking, and the copper addition extends its usefulness into sulfuric and phosphoric acid service.

Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, manufactures NAS 255NM in forged form to customer drawings: seamless rolled rings to 2,500 mm outside diameter, forged discs to 1,800 mm diameter, shafts to 8 m length, bars from Ø25 mm to Ø500 mm, and single pieces to 8,000 kg. Material is melted by EAF + AOD/VOD + ESR, supplied solution annealed and water quenched, and certified to EN 10204 3.1 as standard.

Trademark notice. NAS® and NAS 255NM are designations of Nippon Yakin Kogyo Co., Ltd. Incoloy® and 25-6MO® are registered trademarks of the Special Metals Corporation group of companies. Cronifer® is a registered trademark of VDM Metals. 254 SMO® is a registered trademark of Outokumpu. AL-6XN® is a registered trademark of ATI Properties. Hastelloy® is a registered trademark of Haynes International, Inc. Material produced by those companies and sold under those brand names is theirs. Material produced by Jiangyin Jiangnan Metal Co., Ltd. is correctly described as UNS N08926 / EN 1.4529 / X1NiCrMoCu25-20-7, the same generic chemistry manufactured independently. We are not affiliated with, sponsored by, or endorsed by any of the trademark holders listed above.

What is NAS 255NM (UNS N08926)?

NAS 255NM is a super austenitic stainless steel: an austenitic grade alloyed far enough with molybdenum and nitrogen that it crosses out of the conventional stainless range and competes with nickel alloys on chloride corrosion. The dividing line the industry uses is roughly 6% molybdenum and a PREN above 40. NAS 255NM sits just over it, at 6.0–7.0% Mo and PREN 41–48.

Three alloying decisions explain everything the grade does:

• Molybdenum at 6–7% stabilises the passive film against chloride attack. This is the single largest contributor to pitting and crevice resistance, and it is why the grade costs roughly three times a 316L forging.
• Nitrogen at 0.15–0.25% does two jobs at once. It contributes to pitting resistance at 16 times the weight of chromium in the PREN formula, and it strengthens the austenite in solid solution, which is why the minimum proof strength is 296 MPa rather than the 170–220 MPa typical of 316L and 904L. Nitrogen also stabilises the austenite against sigma phase, partially offsetting the high molybdenum.
• Nickel at 24–26% holds the structure fully austenitic despite the high chromium and molybdenum, and pushes the alloy well clear of the 8–12% nickel window where austenitic stainless steels are most vulnerable to chloride stress corrosion cracking.

The 0.5–1.5% copper is a fourth, quieter addition. It does little for chloride pitting but markedly improves behaviour in reducing acids, particularly sulfuric and phosphoric. This is the main practical difference between NAS 255NM (UNS N08926) and AL-6XN (UNS N08367), which has near-identical Cr-Ni-Mo-N but no deliberate copper.

The trade-off you are buying

Everything that makes this alloy corrosion resistant also makes it harder to manufacture. High molybdenum narrows the hot-working window and raises flow stress, so forging is slower and takes more reheats than a standard austenitic. The same molybdenum makes the alloy strongly prone to sigma, chi and Laves phase precipitation between roughly 600 °C and 1000 °C, so every thermal cycle after the final forging blow (annealing, cooling, welding, any thought of stress relief) has to be planned around getting through that band quickly. And the work-hardening rate that comes with high nickel and nitrogen makes machining slow and tool-hungry.

None of these is a defect. They are the cost of the corrosion performance, and they are the reason a NAS 255NM forging should be bought from a shop that forges the grade regularly rather than from one treating it as a stainless steel with extra molybdenum.

NAS 255NM forgings: supplier quick facts

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Jiangyin, Jiangsu Province, China, producing NAS 255NM (UNS N08926 / EN 1.4529) forged rings, seamless rolled rings, flanges, shafts, discs, sleeves, bushings, tube sheets, valve bodies and bars to customer drawings.

What Forged Products Are Available in NAS 255NM?

Jiangyin Jiangnan Metal produces NAS 255NM through three routes, selected by geometry and quantity. Open-die forging covers shafts, blocks, tube sheets and large discs, wherever single-piece size matters more than repeatability. Seamless ring rolling produces rings from 200 mm to 2,500 mm outside diameter and is the normal choice for flange blanks, valve seat rings, pump wear rings and vessel nozzle reinforcement. Near-net-shape forging is used where the die profile removes 30–50% of the rough machining. The saving matters more on this grade than on most, because NAS 255NM is expensive per kilogram and slow to cut.

One route-selection point is specific to super austenitics. A rolled ring with continuous circumferential grain flow outperforms a ring machined from plate in exactly the applications this alloy is bought for. Machining across the through-thickness direction of a plate exposes any residual banding or inclusion stringers on the sealing face, and those are the sites where crevice corrosion initiates. For seawater flanges, valve seats and gasket faces, specify the forged route and prohibit machined-from-plate substitution on the drawing.

• Seamless rolled rings
• Forged rings
• Forged flanges
• Forged round bars
• Forged flat bars & blocks
• Forged discs & blanks
• Forged shafts & spindles
• Forged sleeves & bushings
• Forged tube sheets
• Forged tubes & hollows
• Forged valve bodies & bonnets
• Forged nozzles
• Forged pump casings
• Near-net-shape parts

What Are the Equivalent Designations of NAS 255NM?

Engineers arrive at this chemistry through at least a dozen names, depending on the standards body, the producer and the decade the drawing was written. Every designation in the table below refers to the same nominal 25Ni-20Cr-6.5Mo-Cu-N super austenitic chemistry. Jiangyin Jiangnan Metal Co., Ltd. accepts purchase orders under all of them, supplying material certified to UNS N08926 / EN 1.4529 with the equivalents cross-listed on the certificate.

What Is the Chemical Composition of NAS 255NM?

The composition below is the UNS N08926 / EN 1.4529 specification range, and is the range Jiangyin Jiangnan Metal Co., Ltd. melts to. Carbon is held to 0.020% maximum, a full order of magnitude below a standard 316, because chromium carbide precipitation at grain boundaries would sensitise the alloy and defeat the corrosion resistance. Sulfur is capped at 0.010% both for hot workability and because sulfide inclusions are classic pit-initiation sites.

Our melting practice. Jiangyin Jiangnan Metal Co., Ltd. melts NAS 255NM by EAF + AOD or VOD, followed by ESR (electroslag remelting). Argon-oxygen or vacuum-oxygen decarburisation is what makes the 0.020% carbon ceiling achievable while holding nitrogen at target; the two move in opposite directions and the refining step has to control both. ESR then refines the inclusion population and produces the directionally solidified ingot needed for a clean forging in a grade this segregation-prone. Full ladle and product analyses, plus the calculated PREN, are reported on the EN 10204 certificate.

What Is the PREN of NAS 255NM?

Using the standard formula PREN = %Cr + 3.3 × %Mo + 16 × %N, NAS 255NM has a pitting resistance equivalent number between 41 and 48 depending on where the heat falls within the specification, with a typical production value of about 45. The spread is wide because the specification bands themselves are wide, and it matters: a heat at the bottom of the Cr, Mo and N ranges lands near 41, while one aimed at the top reaches 48. If your service is marginal, this difference is the whole argument.

What PREN does not tell you

PREN is a ranking index derived from laboratory pitting tests. It is genuinely useful for sorting alloys into tiers, and genuinely misleading if treated as a design limit. Three caveats apply:

1. Crevice corrosion resistance is always lower than pitting resistance. A gasketed flange face, a tube-to-tubesheet joint or a deposit under biofouling creates a local environment far more aggressive than the bulk fluid. Critical crevice temperature typically runs 15–20 °C below critical pitting temperature for the same alloy.
2. PREN ignores microstructure entirely. Two pieces with identical certificates behave very differently if one contains sigma phase from a slow quench. The formula assumes all the molybdenum is in solid solution, which is exactly what a correct solution anneal guarantees and a bad one destroys.
3. PREN says nothing about acids, sour service or SCC. It addresses chloride pitting only. Sulfuric acid behaviour is governed largely by copper content, stress corrosion cracking by nickel, and sour service by the full ISO 15156 environmental envelope.

How Corrosion Resistant Is NAS 255NM?

The alloy was designed as a replacement for 316L and 317L in exactly those services where they are pushed past their limit, and as a lower-cost alternative to nickel alloys and titanium where those are over-specified. The table below summarises behaviour by medium.

What Are the Mechanical Properties of NAS 255NM?

In the solution annealed condition NAS 255NM has a minimum tensile strength of 648 MPa (94 ksi), a minimum 0.2% proof strength of 296 MPa (43 ksi), minimum elongation of 35% and hardness not exceeding 86 HRB. Those minimums are well above than a conventional austenitic stainless. 316L requires only about 485 MPa tensile and 170 MPa proof, and the difference is the nitrogen, which strengthens the austenite in solid solution without any heat treatment.

Strength at temperature

Like all austenitic stainless steels, NAS 255NM loses proof strength steadily with temperature while retaining ductility. The values below are indicative for design screening; use the code allowables for actual pressure design.

What Are the Physical Properties of NAS 255NM?

How Is NAS 255NM Heat Treated?

NAS 255NM has exactly one heat treatment: solution annealing between 1100 °C and 1180 °C (2010–2155 °F), held roughly 30 minutes per 25 mm of section, followed by a rapid water quench. There is no ageing treatment, no hardening transformation, and no acceptable stress-relief cycle inside the precipitation range. Everything about the thermal processing of this grade exists to serve one goal: get all the molybdenum, chromium and nitrogen into solid solution, then get the part through the danger band fast enough that they stay there.

The 600–1000 °C danger band

Highly alloyed austenitics precipitate three families of intermetallic in this range: sigma (Fe-Cr-Mo), chi (Fe-Cr-Mo, richer in Mo) and Laves (Fe₂Mo). All three form preferentially at grain boundaries, all three are brittle, and all three pull molybdenum and chromium out of the surrounding matrix. The local depleted zone is what corrodes: a part that is 99% sound can pit at the boundary network within weeks in seawater.

Kinetics are fastest around 850–900 °C, where measurable sigma can appear in minutes in a 6% molybdenum grade. This is why:

• The quench from solution anneal must be water, not air, on anything but thin sections.
• Heavy sections need a quench arrangement that actually moves water. A large forging dropped into a still tank cools its core far more slowly than the surface, and the core is where sigma forms.
• Welding heat input must be kept low and interpass temperature below about 150 °C, so no part of the joint spends meaningful time in the band.
• Flame cutting, grinding and any local heating during fabrication need the same discipline.
• There is no such thing as a harmless "quick stress relief" on this grade.

NAS 255NM vs 254 SMO, AL-6XN, 904L, 2507 and Alloy 625

Materials selection in chloride service is a ladder, and the question is always which rung is the cheapest one that survives. The table below is the practical selection chart.

The comparison that matters most: the three 6Mo grades

254 SMO (S31254), NAS 255NM (N08926) and AL-6XN (N08367) sit within three PREN points of each other and are frequently treated as interchangeable. They are not, and the differences are worth knowing before you substitute.

• Nickel. NAS 255NM and AL-6XN carry 24–26% nickel; 254 SMO carries about 18%. That gives the first two a real margin in chloride stress corrosion cracking, and it is why they are formally classed as nickel alloys under some specifications (a UNS "N" number) while 254 SMO carries a stainless "S" number. On some projects that classification alone drives the choice.
• Copper. NAS 255NM has 0.5–1.5% Cu; AL-6XN has essentially none. In sulfuric and phosphoric acid the copper is worth having. In pure chloride service it makes little difference.
• Code and project acceptance. 254 SMO has the widest recognition in European pressure-equipment practice, AL-6XN in North American, and N08926 is well covered by both ASTM B564/B625/B649 and EN 1.4529. If a project specification names one, order that UNS number and do not substitute without written approval. Even though the metallurgy is nearly identical, an inspector will reject on the certificate.

How Do You Forge, Machine and Weld NAS 255NM?

Forging

NAS 255NM is hot worked from approximately 1,150–1,200 °C, with the finishing temperature held above 1,000 °C. That 1,000 °C floor is the single most important number in the process, and it is roughly 100 °C higher than the floor for a standard austenitic. Working below it does two things at once: the flow stress rises steeply and the piece can crack, and the deformation is happening inside the sigma-formation band, so the microstructure is being damaged even where the part survives.

Practical consequences on the shop floor:

• More reheats, smaller bites. The alloy takes roughly twice the forging load of 304 at the same temperature, and the usable window between the soak temperature and the 1,000 °C floor is narrow. Plan for frequent returns to the furnace rather than chasing the last few percent of reduction on a cooling piece.
• Do not overheat to compensate. Going above about 1,200 °C risks incipient melting at segregated interdendritic regions and coarsens the grain irreversibly.
• Reduction ratio of at least 4:1 from the ESR ingot to break down the as-cast structure and disperse the segregation this chemistry is prone to.
• Never air-cool a heavy section from forging heat and call it done. Every piece gets a full solution anneal and water quench after the final blow.
• Clean, neutral-to-slightly-reducing furnace atmosphere. Sulfur pick-up from fuel causes hot shortness at grain boundaries in high-nickel alloys.

Machining

Machining behaviour is the toughest of the common corrosion-resistant grades short of the nickel alloys: worse than 316L, comparable to or slightly worse than 904L. The alloy is gummy, work-hardens rapidly under a rubbing tool, has low thermal conductivity so heat stays at the cutting edge, and produces long stringy chips. Budget roughly 1.5 to 2 times the cycle time you would allow for 316L.

• Sharp, positive-rake coated carbide. Replace inserts at the first sign of edge rounding rather than running them out. A dull edge rubs, and rubbing work-hardens a layer the next pass has to cut through.
• Turning speeds of roughly 15–30 m/min with coated carbide; feed heavy and constant, 0.15–0.40 mm/rev.
• Never dwell. A tool that stops feeding while still in contact glazes the surface. This is the single most common cause of scrapped super austenitic parts.
• Rigid setups, minimum overhang, generous flood coolant delivered at the cut.
• Take a deep enough cut to get under the previously work-hardened layer. Light spring passes make things worse, not better.
• Drilling and tapping benefit from through-tool coolant and frequent peck retraction. Consider a slightly oversize tap drill on this grade.

Welding

Use an over-alloyed nickel-base filler, normally ERNiCrMo-3 (alloy 625) or ERNiCrMo-4 (C-276), not a matching filler. This is the rule that catches fabricators new to 6% molybdenum grades, and it is not optional.

The reason is solidification segregation. As a weld pool freezes, molybdenum partitions to the last liquid to solidify, leaving the dendrite cores depleted in molybdenum. In an as-welded matching deposit those depleted cores can sit 1.5–2% Mo below the nominal, which puts them below the pitting resistance of the parent plate. The weld then becomes the anode for the whole assembly and corrodes preferentially. Over-alloying the filler raises the depleted regions back to at least parent-metal resistance.

Where Is NAS 255NM Used?

Every application below shares one requirement: the part sits in warm, chloride-bearing or acidic fluid where a standard austenitic stainless would pit, and where a nickel alloy or titanium would work but cost two to five times as much.

NAS 255NM Production Capability at Jiangyin Jiangnan Metal

Jiangyin Jiangnan Metal Co., Ltd. operates an open-die forging and ring-rolling plant in Jiangyin, Jiangsu Province, China, employing approximately 460 people including 9 senior engineers and 32 intermediate engineers. NAS 255NM is produced alongside the rest of our super austenitic and nickel-alloy range (254 SMO, AL-6XN, 904L, 654 SMO, Alloy 20, Inconel 625 and Hastelloy C-276) on equipment qualified for high-molybdenum grades.

Standards, Testing and Certification

NAS 255NM orders at Jiangyin Jiangnan Metal Co., Ltd. are produced and certified against the specifications below. For forgings, the chemistry and product specification is normally ASTM B564 / ASME SB-564 or EN 10088-3, and the inspection-document type is normally EN 10204 3.1.

• UNS N08926
• EN 1.4529
• X1NiCrMoCu25-20-7
• ASTM B564 / ASME SB-564
• ASTM B649
• ASTM B625
• ASTM B677
• ASTM B462
• EN 10088-3
• EN 10028-7
• EN 10204 3.1
• EN 10204 3.2
• EN 10228-3 (UT)
• SEP 1921 (UT)
• ASTM A388 (UT)
• EN ISO 3452 (PT)
• ASTM G48 Method A (CPT)
• ASTM A262 Practice E
• ASTM G28
• NACE MR0175 / ISO 15156-3
• ASME BPVC Section VIII
• ASME B31.3
• ISO 9001:2015

What appears on the certificate

• Heat number, with full ladle and product chemical analysis
• Calculated PREN from the product analysis
• Melting route (EAF + AOD/VOD + ESR)
• Mechanical test results (tensile, 0.2% and 1.0% proof, elongation, hardness) on coupons from the delivered heat
• Solution annealing record: temperature, hold time, quench medium and the time-temperature chart
• Ultrasonic examination report to the ordered standard and acceptance class
• Liquid penetrant examination report where machined surfaces are involved
• Corrosion test results on request: ASTM G48 Method A critical pitting temperature, ASTM A262 Practice E or ASTM G28 intergranular attack
• Dimensional inspection report
• Cross-listed equivalent designations (NAS 255NM / UNS N08926 / EN 1.4529 / X1NiCrMoCu25-20-7)
• Statement of NACE MR0175 / ISO 15156-3 compliance where ordered

Quality gates and non-conformance handling

Every NAS 255NM order passes six mandatory hold points at which production cannot continue without QA sign-off: raw-material chemistry and PREN verification, forging temperature compliance (including the 1,000 °C finishing floor), post-forging ultrasonic examination, solution anneal chart and quench record approval, mechanical and corrosion test acceptance, and final NDE plus dimensional inspection. Customer-witnessed hold points can be added at no charge. Any out-of-specification finding raises a formal non-conformance report within 24 hours, with root-cause analysis inside five working days and the proposed disposition sent to the customer before any rework is carried out.

How to Specify a NAS 255NM Forging Order

NAS 255NM carries two specification decisions that most grades do not: the delivery condition has to be stated and protected, and the corrosion requirement has to be written down. Chemistry alone does not guarantee either. The steps below remove the ambiguity that causes most disputes on this grade.

Recommended drawing callout

Top 10 Mistakes When Ordering NAS 255NM Forgings

1. Specifying an ageing or stress-relief treatment. The grade has no ageing response. Any hold in the 600–1000 °C band precipitates sigma and chi phase, embrittles the part and permanently reduces corrosion resistance. This error appears on legacy datasheets and gets copied into purchase orders.
2. Accepting a slow cool from the solution anneal. On a heavy forging the core cools far more slowly than the surface. Require a water quench, an agitated tank, and the time-temperature chart with the certificate.
3. Ordering matching filler metal for welds. Molybdenum segregation leaves as-welded matching deposits below parent-metal pitting resistance. Specify ERNiCrMo-3 or ERNiCrMo-4 in the fabrication documents, not just in the welder's head.
4. Treating the three 6Mo grades as interchangeable. N08926, S31254 and N08367 are metallurgically close but are separate UNS numbers with different code acceptance. If the project specification names one, an inspector will reject the others on the certificate regardless of PREN.
5. Ordering the chemistry but not the PREN. "NAS 255NM" legitimately covers heats from PREN 41 to 48. If your service is marginal, put a minimum PREN on the order.
6. Assuming the alloy is immune to chloride stress corrosion cracking. It is highly resistant, not immune. Hot concentrated chlorides with tensile stress and oxygen can still crack it.
7. Ignoring crevices. The alloy almost never fails by general corrosion. It fails under gaskets, in tube-to-tubesheet joints and under deposits. Crevice corrosion resistance runs 15–20 °C below pitting resistance.
8. Leaving heat tint on after welding or hot forming. Heat tint is a chromium-depleted oxide and a preferred pitting site. Specify pickling and passivation, and specify that brushing alone is not acceptable.
9. Specifying magnetic particle inspection. The alloy is non-magnetic, so MPI will not work. Specify liquid penetrant examination instead. This appears on more drawings than it should.
10. Using it in hot hydrochloric acid or heavily chlorinated hot seawater. Both are outside the envelope. Move to alloy C-276, C-22 or a super duplex solution and accept the cost, rather than buying the wrong material twice.

Glossary

NAS 255NM

Nippon Yakin Kogyo's designation for the 6% molybdenum super austenitic stainless steel registered as UNS N08926 and standardised in Europe as EN 1.4529. Nominally 25% Ni, 20% Cr, 6.5% Mo, 1% Cu, 0.2% N, balance iron.

Super austenitic stainless steel

A fully austenitic stainless steel with roughly 6% or more molybdenum and a deliberate nitrogen addition, giving a PREN above 40. The class sits between conventional austenitics such as 316L and nickel-base alloys such as 625.

PREN

Pitting Resistance Equivalent Number, calculated as %Cr + 3.3 × %Mo + 16 × %N. A ranking index for chloride pitting resistance, not a design limit.

CPT

Critical Pitting Temperature. The lowest temperature at which stable pitting occurs in a defined test solution, most commonly measured to ASTM G48 Method A in 6% ferric chloride.

CCT

Critical Crevice Temperature. The equivalent threshold for crevice attack, measured with an artificial crevice former. Typically falls 15–20 °C below the CPT of the same alloy, which is why crevices govern real service.

Sigma phase

A hard, brittle Fe-Cr-Mo intermetallic that precipitates at grain boundaries when highly alloyed stainless steels are held between roughly 600 °C and 1000 °C. It embrittles the alloy and strips molybdenum and chromium from the adjacent matrix, creating a depleted zone that corrodes preferentially.

Chi phase

A related Fe-Cr-Mo intermetallic, richer in molybdenum than sigma, that often precipitates first in 6% Mo grades and has the same practical consequences.

Laves phase

An Fe₂Mo-type intermetallic, another product of the same 600–1000 °C exposure band.

Solution annealing

Heating an austenitic alloy high enough to dissolve carbides and intermetallic phases (1100–1180 °C for NAS 255NM), then quenching fast enough to hold everything in solid solution at room temperature. The only correct final heat treatment for this grade.

Sensitisation

Precipitation of chromium carbides at grain boundaries, leaving chromium-depleted zones that corrode intergranularly. The 0.020% maximum carbon in NAS 255NM is what keeps it out of reach in normal fabrication.

Over-alloyed filler metal

A welding consumable richer in molybdenum and nickel than the parent metal, typically ERNiCrMo-3 (alloy 625) or ERNiCrMo-4 (C-276), used so that the segregated as-welded deposit is still at least as corrosion resistant as the base material.

Heat tint

The coloured oxide left on stainless surfaces by welding or hot work. It is chromium-depleted and is a preferred pitting site, so it must be removed by pickling or mechanical removal followed by passivation, not simply brushed.

Chloride stress corrosion cracking (Cl-SCC)

Cracking of a stressed austenitic alloy in hot chloride solution. Susceptibility peaks around 8–12% nickel, which is why the 24–26% nickel of NAS 255NM gives it a large margin over 304 and 316L.

ESR

Electroslag remelting. A secondary melting process that refines inclusion content and produces a directionally solidified ingot suited to forging segregation-prone chemistries.

AOD / VOD

Argon-oxygen decarburisation and vacuum-oxygen decarburisation. Secondary refining steps that bring carbon down to the 0.020% ceiling while holding nitrogen on aim.

EN 10204 3.1 / 3.2

Inspection document types. 3.1 is a mill certificate issued by the manufacturer's own independent inspection department; 3.2 is countersigned by an independent third party nominated by the purchaser.

Seamless rolled ring

A ring produced by piercing a forged billet and expanding it on a radial-axial ring mill, giving continuous circumferential grain flow and better integrity on sealing faces than a ring machined from plate.

Frequently Asked Questions: NAS 255NM / UNS N08926

Technical References

Chemistry, corrosion, physical-property and heat-treatment data on this page are drawn from the published standards and engineering references below. Test results reported on our material certificates are independent and traceable to calibrated laboratory equipment.

1. ASTM B564, Standard Specification for Nickel Alloy Forgings, ASTM International, West Conshohocken, PA.
2. ASTM B649, Standard Specification for Ni-Fe-Cr-Mo-Cu-N Low-Carbon Alloys Bar and Wire, ASTM International.
3. ASTM B625, Standard Specification for UNS N08925, UNS N08354, UNS N08926 and related alloy Plate, Sheet and Strip, ASTM International.
4. ASTM B677, Standard Specification for Seamless Pipe and Tube, and ASTM B673 / B674 / B676 for welded product, ASTM International.
5. ASTM B462, Standard Specification for Forged or Rolled Alloy Pipe Flanges, Forged Fittings, and Valves and Parts, ASTM International.
6. EN 10088-3, Stainless steels — Technical delivery conditions for semi-finished products, bars, rods, wire, sections and bright products, CEN, Brussels.
7. EN 10028-7, Flat products made of steels for pressure purposes — Part 7: Stainless steels, CEN.
8. EN 10204:2004, Metallic products — Types of inspection documents, CEN, Brussels.
9. EN 10228-3, Non-destructive testing of steel forgings — Part 3: Ultrasonic testing, CEN.
10. SEP 1921, Ultrasonic testing of steel forgings, Stahl-Eisen-Prüfblatt.
11. ASTM A388, Standard Practice for Ultrasonic Examination of Steel Forgings, ASTM International.
12. ASTM G48, Standard Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride Solution, ASTM International.
13. ASTM G150, Standard Test Method for Electrochemical Critical Pitting Temperature Testing of Stainless Steels and Related Alloys, ASTM International.
14. ASTM A262, Standard Practices for Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels, ASTM International.
15. ASTM G28, Standard Test Methods for Detecting Susceptibility to Intergranular Corrosion in Wrought, Nickel-Rich, Chromium-Bearing Alloys, ASTM International.
16. NACE MR0175 / ISO 15156-3, Petroleum and natural gas industries — Materials for use in H₂S-containing environments in oil and gas production — Part 3: Cracking-resistant CRAs and other alloys.
17. ASME Boiler and Pressure Vessel Code, Section II Part B and Section VIII Division 1; ASME B31.3 Process Piping, The American Society of Mechanical Engineers.
18. ASM Handbook, Volume 13B: Corrosion: Materials, ASM International, sections on austenitic and highly alloyed stainless steels.
19. ASM Specialty Handbook: Stainless Steels, J.R. Davis (ed.), ASM International.
20. Sedriks, A.J., Corrosion of Stainless Steels, 2nd edition, Wiley-Interscience. Standard reference for PREN, pitting and crevice behaviour.
21. Nippon Yakin Kogyo Co., Ltd., published product data for NAS 255NM (UNS N08926 equivalent).
22. ISO 9001:2015, Quality management systems — Requirements.

Standards cited are the revisions known to us at the time of the last page review. For procurement, always reference the revision in force at the contract date. All trademarks referenced belong to their respective owners.

Related Grades and Forged Products

• 254 SMO / S31254
• AL-6XN / N08367
• 904L / N08904
• 654 SMO / S32654
• Alloy 20 / N08020
• Incoloy 926
• Incoloy 825
• Inconel 625
• Hastelloy C-276
• Hastelloy C-22
• Incoloy 800HT
• Incoloy 800H
• Forged & rolled rings
• Forged disks
• Forged tubes
• Forged spindles
• Forged nozzles
• Open die forgings