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

INCOLOY Alloy 25-6MO / UNS N08926 / EN 1.4529 Forging Parts

• 🇺🇸 USAUNS N08926
ASTM B564
• 🇪🇺 Europe1.4529
X1NiCrMoCuN25-20-7
• 📜 Trade namesINCOLOY® 25-6MO
Cronifer® 1925 hMo
• Family6Mo super-austenitic
PREN ≈ 45
• ConditionSolution annealed
+ water quenched

Published: 12 May 2022 · Last updated: 17 August 2026 · Technically reviewed by the Jiangyin Jiangnan Metal Co., Ltd. Metallurgical Engineering Team

INCOLOY alloy 25-6MO is a 6 % molybdenum, nitrogen-enhanced, copper-bearing super-austenitic stainless steel designated UNS N08926 and EN 1.4529 (X1NiCrMoCuN25-20-7). Its nominal chemistry is 25 % nickel, 20 % chromium, 6.5 % molybdenum, 1 % copper and 0.20 % nitrogen with the balance iron, giving a pitting resistance equivalent number of about 45. That combination resists chloride pitting, crevice corrosion and chloride stress-corrosion cracking in seawater and other aggressive chloride media, while the copper addition adds resistance to sulfuric and phosphoric acid. It is the grade specified where 316L and 317L have run out of margin but a fully nickel-base alloy such as Inconel 625 or Hastelloy C-276 is not yet justified on cost.

Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, manufactures INCOLOY alloy 25-6MO 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 + VOD + ESR, solution annealed and water quenched, and supplied with EN 10204 3.1 certification as standard.

Trademark notice. INCOLOY® and INCONEL® 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. UR™ 926 is a trademark of Industeel / ArcelorMittal. 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 / X1NiCrMoCuN25-20-7 / alloy 926 / 6Mo super-austenitic stainless steel: the same generic chemistry, manufactured independently. We are not affiliated with, sponsored by, or endorsed by any of the trademark holders listed above.

Six engineering tools for UNS N08926 on this page

• 🧪 PREN & CPT CalculatorEnter a real heat analysis from your mill certificate → PREN, ranking band and how it compares with 316L, 904L, 254 SMO and super duplex.
• 🌊 Chloride Service CheckerChloride level, metal temperature and crevice condition → whether a 6Mo grade is the right answer or you need duplex or a nickel alloy.
• 🎯 Grade SelectorPick your medium (seawater, FGD, phosphoric, sulfuric, bleach, brine, sour gas) and get a recommended grade with the reasoning.
• 🔎 Designation LookupType N08926, 1.4529, 25-6MO, 926, Cronifer 1925 hMo, S31254, N08367 … and see exactly which grade the drawing means.
• ⚖️ Forging Weight CalculatorRing, disc, shaft, block or sleeve → net weight at 8.1 g/cm³ plus the rough forging weight to quote against.
• 📝 RFQ Text GeneratorBuilds a complete, unambiguous N08926 forging enquiry, including the heat-treatment and corrosion-test clauses most RFQs forget.

What is INCOLOY alloy 25-6MO (UNS N08926)?

INCOLOY alloy 25-6MO is a fully austenitic, iron-nickel-chromium alloy with 6 % molybdenum, deliberate nitrogen and about 1 % copper, developed to carry the corrosion resistance of the austenitic stainless family as far as it will go before a nickel-base alloy becomes necessary. It began as an uprating of alloy 904L (UNS N08904, EN 1.4539): molybdenum was raised from roughly 4.5 % to 6.5 %, and nitrogen was added at 0.15–0.25 %. Those two changes carry the pitting resistance equivalent number from about 34 to about 45, which is the threshold that opens up warm seawater and chlorinated service.

Three elements do the work, and knowing which does what makes the grade much easier to specify correctly:

• Molybdenum (6–7 %) is the primary defence against chloride pitting and crevice corrosion. It stabilises the passive film locally, inside a pit or crevice where the pH has already dropped and chloride has concentrated. This is the single most expensive element in the alloy and the reason the grade costs what it does.
• Nitrogen (0.15–0.25 %) does three jobs at once: it strengthens the austenite by solid solution, which is why the minimum yield strength is 295 MPa rather than the 205 MPa typical of 316L, and it slows down the precipitation of sigma and chi intermetallics that 6 % molybdenum would otherwise cause, and it contributes to pitting resistance with a weighting of 16 in the PREN formula, sixteen times the weighting of chromium.
• Copper (0.5–1.5 %) is the element that separates this grade from AL-6XN. It markedly improves resistance to sulfuric and phosphoric acid, particularly in the awkward mid-concentration range where reducing conditions dominate. If a specification calls for N08926 in an acid duty, the copper is usually the reason.

The high nickel content, 24–26 %, is what gives the alloy its resistance to chloride stress-corrosion cracking. Standard 300-series austenitics with 8–12 % nickel are vulnerable to chloride SCC above roughly 60 °C; at 25 % nickel the susceptibility is largely suppressed. This is why 6Mo grades appear on offshore firewater and seawater systems where a 316L component would crack in service rather than simply pit.

Two limitations follow directly from the same chemistry, and they cause most of the problems seen in the field:

• The alloy is not age hardenable and must never be aged. It is single-phase austenite with no hardening transformation. Strength comes from nitrogen in solution and from cold work, not from heat treatment. A heat cycle in the 600–1,000 °C range does not strengthen it. It precipitates sigma, chi and Laves phases along the grain boundaries, drops the impact toughness and strips molybdenum out of the surrounding matrix, which is where the corrosion resistance lived. Any drawing calling for "solution treatment and ageing" on UNS N08926 contains an error.
• Sustained service above roughly 400–425 °C is not advisable for the same reason. The grade is bought for aqueous corrosion service, not for high-temperature strength. Where a corrosion-resistant alloy is needed at 500 °C and above, the answer is Incoloy 800H/800HT, Inconel 625 or Inconel 617.

UNS N08926 forgings: supplier quick facts

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Jiangyin, Jiangsu Province, China, producing INCOLOY alloy 25-6MO (UNS N08926 / EN 1.4529) forged rings, seamless rolled rings, flanges, shafts, discs, tube sheets, sleeves, bushings and bars to customer drawings.

What forged products are available in 25-6MO?

Jiangyin Jiangnan Metal produces UNS N08926 through three routes, chosen by geometry and quantity. Open-die forging covers long 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 route for flange blanks, pressure-housing rings, valve seat rings and pump casings. Near-net-shape forging is used where a die profile can remove 30–50 % of the rough machining.

The economics of this grade push harder toward near-net-shape than they would on carbon or alloy steel. N08926 costs several times the price of 316L per kilogram, work-hardens under the tool and machines slowly, so every kilogram of chip is expensive twice over. On rings and discs it is normally worth spending an extra forging operation to avoid removing 40 % of the piece in the machine shop.

• 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
• Valve bodies, bonnets & seat rings
• Pump casings & impeller blanks
• Forged nozzles & manifolds
• Custom near-net-shape parts

What are the equivalent designations of 25-6MO / alloy 926?

This grade is bought under at least a dozen names, and two of the common ones belong to different UNS numbers. The table below separates the designations that are genuinely the same material from the neighbouring 6Mo grades that are often assumed to be interchangeable and are not. Jiangyin Jiangnan Metal Co., Ltd. accepts orders under any of the true equivalents, certifying to UNS N08926 / EN 1.4529 with the alternatives cross-listed on the certificate.

What is the chemical composition of UNS N08926?

The composition below follows the ASTM B564 / B625 limits for UNS N08926, which are the same limits EN 1.4529 works to within rounding. Every element in this alloy has a job, and the "why" column matters when a mill certificate comes back at the edge of a range.

Our melting practice. Jiangyin Jiangnan Metal Co., Ltd. melts UNS N08926 by EAF + VOD followed by ESR. Vacuum oxygen decarburisation is what makes the 0.020 % maximum carbon achievable while still holding 0.15–0.25 % nitrogen in solution. The two requirements pull in opposite directions and the VOD stage is where they are reconciled. Electroslag remelting then refines the inclusion population, which matters more on this grade than on most: every manganese sulfide inclusion left in the material is a pit waiting to start. Both the ladle analysis and the product analysis are reported on the EN 10204 certificate, together with the calculated PREN.

How corrosion resistant is 25-6MO?

UNS N08926 is specified for chloride service first and acid service second. Its strong suits are pitting and crevice corrosion in chloride media, chloride stress-corrosion cracking, and dilute-to-intermediate sulfuric and phosphoric acid. Its weak points are strongly reducing acids at high concentration and hydrofluoric acid, where a nickel-base alloy is required.

Chloride pitting and crevice corrosion

With a PREN of about 45, the alloy resists pitting in natural seawater at ambient temperature and in chloride-bearing process streams well beyond where 316L fails. The relevant laboratory measures are the critical pitting temperature and the critical crevice temperature determined per ASTM G48. For 6 % molybdenum grades the critical pitting temperature in ASTM G48 Method A (6 % ferric chloride) is typically in the range 60–75 °C, and the critical crevice temperature typically 30–45 °C, both an order of magnitude better in service terms than 316L, which pits in G48 A at around 15–20 °C and crevice-corrodes below ambient.

Two practical points follow. First, crevice corrosion always governs, not pitting. The critical crevice temperature is 25–30 °C below the critical pitting temperature for the same alloy, so a gasketed joint, a bolted flange face, a tube-to-tubesheet gap or a marine-growth deposit sets the real limit on where the grade can be used. Second, chlorination and warm stagnant seawater are the failure conditions. Continuous chlorination above about 1 ppm residual, or stagnant seawater above roughly 30–35 °C in a crevice, moves 6Mo grades into marginal territory. Under those conditions a nickel-base alloy or a titanium alloy is the correct answer.

Chloride stress-corrosion cracking

This is where the 25 % nickel earns its cost. Austenitic stainless steels with 8–12 % nickel are susceptible to chloride SCC above roughly 60 °C, and the failures are fast, brittle and often occur under insulation or in trapped condensate. At 24–26 % nickel the alloy is, for practical purposes, resistant across the temperature range in which it is used. This, rather than pitting alone, is frequently the reason a specification jumps from 316L past 904L to a 6Mo grade.

Acids

25-6MO vs 254 SMO, AL-6XN, 904L, 2507 and Inconel 625

The 6Mo grades sit in a narrow band of the material-selection ladder, bracketed below by 904L and super duplex and above by the nickel-base alloys. The table below is the practical comparison: find the row that governs your duty and the choice usually follows.

The comparisons that actually come up

25-6MO vs 254 SMO. Chloride performance is close enough that either will do the same seawater job. The differences are commercial and code-related. N08926 carries a European Werkstoff number, 1.4529, which matters where a pressure-equipment approval or a European material certificate is required; S31254 does not have an equivalent standing in every EN scheme. N08926 also has more nickel and more copper, so it does better in mixed acid and reducing conditions. S31254 is often cheaper and more widely stocked in plate. On a purchase order the two are not interchangeable.

25-6MO vs AL-6XN. Nearly identical molybdenum and PREN. The material difference is copper: N08926 has 0.5–1.5 %, AL-6XN essentially none. For pure chloride duty they are equivalent; for sulfuric or phosphoric acid, or for chloride-contaminated acid, N08926 is the better choice. AL-6XN has no Werkstoff number, which limits its use in European pressure applications.

25-6MO vs 2507 super duplex. Similar PREN, very different mechanics. Super duplex has nearly twice the yield strength, so a pressure part can be thinner and lighter, and it is cheaper per kilogram. But it is limited to about 300 °C by 475 °C-range embrittlement, it is harder to weld correctly because ferrite/austenite balance must be controlled, and it does less well in acid. Choose duplex when strength and weight drive the design; choose 6Mo austenitic when fabrication simplicity, acid resistance or a wide temperature range drives it.

25-6MO vs Inconel 625. This is the upgrade decision. Move to Inconel 625 when the crevice temperature or the chlorination level puts 6Mo into the marginal band, when the service temperature goes above roughly 425 °C, or when hydrochloric acid or wet chlorine is present. Expect to pay two-and-a-half to three times as much per kilogram, so it is normally applied selectively: the crevice-critical seat ring in 625, the body in N08926.

What are the mechanical properties of N08926 forgings?

In the solution-annealed condition UNS N08926 must meet 650 MPa (94 ksi) tensile strength, 295 MPa (43 ksi) yield strength at 0.2 % offset and 35 % elongation. The yield strength is roughly 40 % above 316L, and that is entirely due to nitrogen in solid solution. There is no heat treatment that will raise it further.

What are the physical properties of alloy 926?

Data notes. Density, the expansion coefficients, modulus, conductivity and resistivity in this table are typical published values for the 1.4529 / N08926 chemistry and are suitable for design screening and weight calculation. The melting range is approximate. Where any physical property is contractually important, state it on the purchase order and Jiangyin Jiangnan Metal Co., Ltd. will report the measured result on the material certificate.

How is 25-6MO forged and heat treated?

Hot forging

UNS N08926 is hot worked from approximately 1,150–1,200 °C, with the finishing temperature held above roughly 950 °C. The alloy has high hot strength, considerably higher than 316L at the same temperature, so it needs press capacity rather than speed, and the useful working window is narrow. Below about 950 °C the flow stress climbs steeply and the risk of edge cracking rises; above 1,200 °C incipient melting at segregated grain boundaries becomes a hazard. The correct response to a piece that has cooled out of range is to reheat, not to keep hitting it.

Forging reduction of at least 4:1 from the ingot is used to break down the as-cast dendritic structure. This is not simply a mechanical-property requirement on this grade: as-cast interdendritic segregation leaves molybdenum-lean regions, and those regions are where pitting starts. Adequate hot work plus a correct solution anneal is what homogenises them. For seamless rolled rings the pierced blank is expanded on a radial-axial mill so that grain flow follows the circumference.

Solution annealing: the step that determines corrosion resistance

Solution annealing followed by a rapid water quench is the only heat treatment applied to this grade. The purpose is to dissolve every intermetallic phase and every chromium carbide formed during forging and cooling, and then to get the piece through the precipitation range fast enough that none of them re-form.

1. MeltEAF + VOD + ESRC ≤ 0.020 %, N to 0.15–0.25 %
2. Homogenise & cog1,150–1,200 °C≥ 4:1 reduction from ingot
3. Forge / ring rollfinish > 950 °Creheat rather than work cold
4. Solution anneal1,100–1,200 °Csoak per section thickness
5. Water quenchrapid, no air coolthrough 1,000–600 °C fast
6. Rough machine2–5 mm stocksharp tools, flood coolant
7. TestUT · tensile · G48 / G28coupon from prolongation
8. Pickle & passivateremove all heat tintthen final machine & certify

How do you machine and weld UNS N08926?

Machining

Machining behaviour resembles 316L, only worse in every direction: the alloy work-hardens faster, is gummier, has lower thermal conductivity so heat stays at the cutting edge, and costs far more per kilogram of chip. The practical rules:

• Rigidity first. Heavy, rigid setups with minimal tool overhang. Chatter work-hardens the surface and the next pass has to cut through the hardened layer.
• Sharp, positive-rake carbide, replaced at the first sign of edge rounding rather than run to destruction.
• Turning speeds of roughly 15–35 m/min with coated carbide, with a heavy positive feed of 0.15–0.40 mm/rev. Slow and deep beats fast and light.
• Never dwell. A tool that stops feeding while still in contact glazes and work-hardens the surface.
• Flood coolant, generously. Chlorinated cutting fluids should be avoided or fully removed afterwards. Residual chloride on a 6Mo surface is exactly the contaminant the alloy was bought to resist.
• Leave 2–5 mm of stock after roughing. The finish pass should be a light, continuous cut in fully annealed material.

Welding

N08926 is readily welded by GTAW, GMAW, SMAW, PAW and SAW. No preheat is required and no post-weld heat treatment is normally required. One rule dominates all others:

• Keep heat input and interpass temperature low. Stringer beads, interpass below about 100 °C. Time spent in the 600–1,000 °C range is time spent precipitating intermetallics.
• Argon backing on root passes, and full removal of heat tint afterwards by pickling and passivation or by mechanical cleaning. Heat tint is chromium and molybdenum depleted and pits first.
• Clean before welding. Sulfur, lead, grease and marking-pen residues cause cracking in a high-nickel weld pool.
• Do not use carbon-steel tooling, brushes or grinding media anywhere near the joint. Embedded iron rusts and initiates pitting on an otherwise perfect surface.

Where is 25-6MO used?

Every application below rests on the same proposition: the fluid is aggressive enough to defeat 316L, and a fully nickel-base alloy would be over-specified.

25-6MO 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. UNS N08926 is produced on the same equipment used for our nickel-alloy and precipitation-hardening stainless ranges, with dedicated handling to keep carbon-steel contamination away from corrosion-resistant material.

Standards, testing and certification for N08926 forgings

UNS N08926 orders at Jiangyin Jiangnan Metal Co., Ltd. are produced and certified against the specifications below. For forgings the chemistry and heat-treatment specification is normally ASTM B564 or EN 1.4529, and the inspection document is normally EN 10204 3.1.

• ASTM B564 / ASME SB-564 (forgings)
• ASTM B625 (plate, sheet, strip)
• ASTM B649 (bar & wire)
• ASTM B677 (seamless pipe & tube)
• ASTM B673 / B674 (welded pipe & tube)
• ASTM B366 (fittings)
• UNS N08926
• EN 1.4529 / X1NiCrMoCuN25-20-7
• EN 10088-3 (bars & rods)
• EN 10204 3.1 / 3.2
• EN 10228-4 (UT, austenitic)
• ASTM A388 (UT)
• SEP 1921 (UT)
• ASTM E165 / EN ISO 3452 (PT)
• ASTM E112 (grain size)
• ASTM G48 A / E (pitting & crevice)
• ASTM G28 A (intergranular attack)
• ISO 15156-3 (sour service, conditional)
• ISO 9001:2015

What appears on the certificate

• Heat number, with full ladle analysis and product analysis
• Calculated PREN from the product analysis, reported as standard on every N08926 certificate
• Melting route (EAF + VOD + ESR)
• Mechanical test results (tensile, 0.2 % yield, elongation, hardness, impact where ordered) on coupons cut from a prolongation of the delivered piece
• Solution-annealing record: temperature, soak time, furnace chart reference, transfer time to quench and quench medium
• Ultrasonic examination report to the ordered standard, acceptance class and probe/frequency detail
• Dye penetrant report on machined surfaces where ordered
• Grain size to ASTM E112 and intermetallic-phase check where ordered
• Corrosion test results (ASTM G48 Method A or E, ASTM G28 Method A) where ordered
• Dimensional inspection report
• Pickling and passivation confirmation
• Cross-listed equivalent designations: UNS N08926 / EN 1.4529 / X1NiCrMoCuN25-20-7 / ASTM B564

Quality gates

Every N08926 order passes seven mandatory hold points at which production cannot continue without QA sign-off: incoming chemistry and PREN verification, forging temperature compliance, post-forging ultrasonic examination, solution-anneal chart and quench-transfer approval, mechanical and corrosion test acceptance, surface condition after pickling and passivation, 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 is sent to the customer before any rework is carried out.

How to specify a 25-6MO forging order

This grade carries two specification decisions that most alloys do not: the heat-treated condition must be stated as solution annealed and quenched with no ageing, and the corrosion acceptance criteria have to be named explicitly, because chemistry alone does not prove that the quench was fast enough. The eight steps below remove the ambiguity that causes most disputes.

1. Name the grade genericallyUNS N08926 / 1.4529not a brand name alone
2. State the specificationASTM B564 for forgingsB625 / B649 / B677 for other forms
3. Send the drawingdims · tolerances · finishplus required grain-flow direction
4. Specify the conditionsolution annealed + water quenchednever ageing
5. Specify corrosion testsG48 A/E · G28 Aand a minimum PREN if the duty is marginal
6. Define NDEUT to EN 10228-4 or A388PT not MT, the alloy is non-magnetic
7. Specify certificationEN 10204 3.1 or 3.2name the third party for 3.2
8. State quantity & deliverypieces · date · port · Incotermsand heat-number marking

Recommended drawing callout

Top 10 mistakes when ordering 25-6MO forgings

1. Specifying "solution treatment and ageing". N08926 is not age hardenable. Ageing precipitates sigma and chi phases and destroys the corrosion resistance the alloy was bought for. This error appears surprisingly often on drawings copied from a precipitation-hardening grade.
2. Accepting air cooling on a heavy section. The quench rate through 1,000–600 °C is what preserves corrosion resistance. On thick forgings, only a water quench will do it, and the mechanical test will not reveal the failure. Only a G28 or G48 test will.
3. Substituting 254 SMO or AL-6XN without written approval. The parts will probably perform, but the certificate will not match the drawing and the non-conformance surfaces at the worst possible moment, during final documentation review.
4. Ordering the grade but not a minimum PREN. A legitimate heat can calculate anywhere from 42 to 48. In a marginal chloride duty that range spans pass and fail.
5. Leaving heat tint on welded or hot-worked surfaces. The most common cause of premature pitting on 6Mo equipment in the field. Specify pickling and passivation explicitly.
6. Specifying magnetic particle examination. The alloy is non-magnetic, so MT is physically impossible. Inspection plans copied from carbon-steel templates carry this error through to the ITP and it is caught at inspection, delaying release.
7. Quoting EN 10228-3 for ultrasonic testing. Part 3 covers ferritic and martensitic forgings; Part 4 covers austenitic. Wrong probe frequency and wrong acceptance criteria on coarse austenitic grain leads either to false rejections or to missed indications.
8. Ignoring crevice geometry in the material choice. The critical crevice temperature is 25–30 °C below the critical pitting temperature. A design decision to use a gasketed joint can invalidate the alloy selection made on pitting data.
9. Allowing carbon-steel contamination in the shop. Carbon-steel slings, brushes, grinding discs and layout tables embed iron particles that rust and initiate pitting on an otherwise perfect surface.
10. Using a matching-composition weld filler. Molybdenum segregation leaves the weld metal anodic to the parent metal. Specify ERNiCrMo-3 or ERNiCrMo-4 in the weld procedure.

Glossary

Super-austenitic stainless steel

An austenitic stainless steel alloyed far beyond the standard 300 series, typically 6 % molybdenum, high nickel and deliberate nitrogen, to resist chloride pitting and crevice corrosion. UNS N08926, S31254 and N08367 are the common members.

UNS N08926

Unified Numbering System designation for the 25Ni-20Cr-6.5Mo-Cu-N super-austenitic chemistry sold under trade names including INCOLOY alloy 25-6MO and Cronifer 1925 hMo. The generic, brand-free name to use on purchase orders.

EN 1.4529

European Werkstoff number for the same chemistry, with the descriptive steel name X1NiCrMoCuN25-20-7. Its existence is one practical reason to choose this grade over AL-6XN in European pressure applications.

PREN

Pitting Resistance Equivalent Number, normally calculated as %Cr + 3.3 × %Mo + 16 × %N. A ranking index for resistance to chloride pitting, not a design limit. Approximately 45 for N08926.

CPT (critical pitting temperature)

The lowest temperature at which pitting initiates in a defined test solution, usually per ASTM G48. Typically 60–75 °C for 6Mo grades in Method A.

CCT (critical crevice temperature)

The equivalent threshold for crevice corrosion, always 25–30 °C lower than the CPT for the same alloy. In real equipment the CCT normally governs, because gaskets, bolted joints and deposits all create crevices.

Chloride stress-corrosion cracking

Brittle cracking of an austenitic stainless steel under tensile stress in a hot chloride environment. Standard 300-series grades are susceptible above roughly 60 °C; the 24–26 % nickel in N08926 largely suppresses it.

Sigma, chi and Laves phases

Hard, brittle intermetallic compounds that precipitate at grain boundaries in high-molybdenum alloys held between roughly 600 °C and 1,000 °C. They embrittle the material and strip molybdenum from the surrounding matrix, locally destroying corrosion resistance. Avoiding them is why the quench matters.

Solution annealing

Heating to 1,100–1,200 °C to dissolve carbides and intermetallics into solid solution, followed by rapid cooling to hold them there. The only heat treatment applied to this grade.

Heat tint

The coloured oxide film formed on stainless surfaces by welding or hot working. It is chromium and molybdenum depleted and pits preferentially, so it must be removed by pickling and passivation or mechanically.

ASTM G48

Standard test methods for pitting and crevice corrosion resistance using ferric chloride solution. Method A is a pitting immersion test; Method E determines the critical pitting temperature.

ASTM G28 Method A

Boiling ferric sulfate / sulfuric acid test for detecting intergranular attack in nickel-rich chromium-bearing alloys. The practical way to prove that a solution anneal and quench were performed correctly.

ESR (electroslag remelting)

A secondary melting process that refines the inclusion population and produces a directionally solidified ingot. On this grade it matters because manganese sulfide inclusions are preferential pit initiation sites.

VOD (vacuum oxygen decarburisation)

A secondary refining step that lowers carbon while retaining nitrogen in solution, the two competing requirements of this chemistry.

EN 10204 3.1 / 3.2

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

EN 10228-4

The part of the European forging ultrasonic-testing standard that covers austenitic and austenitic-ferritic stainless steel forgings. Part 3, which is more often quoted, applies to ferritic and martensitic forgings and is the wrong reference for this grade.

Seamless rolled ring

A ring made by piercing a forged billet and expanding it on a radial-axial ring mill, giving continuous circumferential grain flow, no exposed end grain at the bore and no through-thickness plate segregation.

Frequently asked questions: INCOLOY 25-6MO / UNS N08926

Technical references

Chemistry, mechanical, physical 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 B625, Standard Specification for UNS N08925, UNS N08031, UNS N08932, UNS N08926, UNS N08354, UNS N08830 Plate, Sheet, and Strip, ASTM International.
3. ASTM B649, Standard Specification for Ni-Fe-Cr-Mo-Cu Low-Carbon Alloys Bar and Wire, ASTM International.
4. ASTM B677, Standard Specification for UNS N08904, UNS N08925, UNS N08926, UNS N08932 Seamless Pipe and Tube, ASTM International.
5. ASTM B673 / B674, Welded pipe and welded tube specifications for the same alloy group, ASTM International.
6. ASTM B366, Standard Specification for Factory-Made Wrought Nickel and Nickel Alloy Fittings, ASTM International.
7. EN 10088-3, Stainless steels — Technical delivery conditions for semi-finished products, bars, rods, wire, sections and bright products, CEN, Brussels.
8. EN 10204:2004, Metallic products — Types of inspection documents, CEN, Brussels.
9. EN 10228-4, Non-destructive testing of steel forgings — Part 4: Ultrasonic testing of austenitic and austenitic-ferritic stainless steel forgings, CEN, Brussels.
10. ASTM A388, Standard Practice for Ultrasonic Examination of Steel Forgings, ASTM International.
11. SEP 1921, Ultrasonic testing of steel forgings, Stahl-Eisen-Prüfblatt, Verein Deutscher Eisenhüttenleute.
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 G28, Standard Test Methods for Detecting Susceptibility to Intergranular Attack in Wrought, Nickel-Rich, Chromium-Bearing Alloys, ASTM International.
14. ASTM E112, Standard Test Methods for Determining Average Grain Size, ASTM International.
15. ASTM E165 / EN ISO 3452-1, Liquid penetrant examination.
16. ISO 15156-3 / NACE MR0175, 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, ISO / AMPP.
17. ASME Boiler and Pressure Vessel Code, Section II Part B (SB-564, SB-625, SB-677) and Section VIII allowable stress tables for UNS N08926.
18. ASM Specialty Handbook: Stainless Steels, J.R. Davis (ed.), ASM International: chapters on super-austenitic grades and intermetallic precipitation.
19. ASM Handbook, Volume 13B: Corrosion: Materials, ASM International: chloride pitting, crevice corrosion and CPT/CCT data for 6Mo alloys.
20. Industeel / ArcelorMittal, published technical data sheet for UR™ 926 (1.4529 / N08926): physical property values.
21. Sedriks, A.J., Corrosion of Stainless Steels, Wiley: PREN methodology and its limitations.

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

• Incoloy 926Same UNS N08926 chemistry, other trade name
• Incoloy 825N08825 · acid and chloride, lower Mo
• Incoloy 925N09925 · age-hardenable, higher strength
• Incoloy 945N09945 · sour service, high strength
• Inconel 625N06625 · the upgrade beyond 6Mo limits
• Inconel 725N07725 · age-hardened 625 chemistry
• Hastelloy C-276N10276 · wet chlorine, HCl, mixed acids
• Hastelloy C-22N06022 · oxidising plus reducing acids
• Alloy 59N06059 · highest-purity Ni-Cr-Mo
• Monel 400N04400 · hydrofluoric acid, seawater
• Incoloy 800HN08810 · high-temperature service
• Inconel 600N06600 · general-purpose Ni-Cr
• Forged & rolled rings200 – 2,500 mm OD, all grades
• Forged disksTo 1,800 mm diameter
• Forged tubes & hollowsTrepanned heavy-wall sections
• Open die forgingsTo 8,000 kg single piece

Cite this page

This datasheet is maintained by the metallurgical engineering team at Jiangyin Jiangnan Metal Co., Ltd. and is free to quote, reference or link to. If you use the data in a specification, report or article, please attribute it as follows.

Jiangyin Jiangnan Metal Co., Ltd. (2026). INCOLOY Alloy 25-6MO / UNS N08926 / EN 1.4529 Forging Parts: Technical Datasheet and Manufacturing Guide. Jiangyin, Jiangsu, China. Retrieved from https://www.steelforgepieces.com/Nickel-Alloy/INCOLOY-ALLOY-25-6MO.html. Last updated 17 August 2026.

Source of record: Jiangyin Jiangnan Metal Co., Ltd., open-die forging factory, No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China · +86-189-2135-9659 · sales@steelforgepieces.com · www.steelforgepieces.com