Alloy 625 / UNS N06625 / 2.4856 Forging Parts: Rings, Flanges, Shafts and Discs

What Alloy 625 forged products are available?

Jiangyin Jiangnan Metal manufactures UNS N06625 components by three routes, chosen according to geometry and order size. Open-die forging covers shafts, blocks, discs and heavy tube sheets. Seamless ring rolling on our radial-axial mills produces Alloy 625 rings from 200 mm to 2500 mm outside diameter, which is the usual route for wellhead housings, valve flanges and pressure-retaining rings. Upset forging is used for short, large-section hubs and flange blanks.

Raw material dominates the cost of an Alloy 625 part far more than it does for steel, so near-net-shape forging is worth more here than on any steel grade. Cutting machining stock by 30 to 40 % on a 500 kg part removes a substantial amount from the order value. For bored shafts above roughly 100 mm bore we normally recommend a trepanned billet in place of a solid one.

• Seamless rolled rings (rectangular, contoured, T-section)
• Forged flanges (WN, SO, blind, spectacle, orifice)
• Forged shafts and spindles
• Forged discs and blanks
• Tube sheets and baffle plates
• Bushings and sleeves
• Valve bodies, bonnets, stems and seat rings
• Round, square and flat bars
• Forged pipe and hollow sections
• Nozzles and forged fittings
• Custom near-net forgings to drawing

What is Alloy 625 (UNS N06625)?

Alloy 625 is a nickel-chromium-molybdenum alloy with a niobium addition, strengthened by solid solution rather than by precipitation hardening. Its nominal composition is approximately 62 % nickel, 21.5 % chromium, 9 % molybdenum and 3.6 % niobium. Molybdenum and niobium atoms are substantially larger than nickel, so they distort the face-centred cubic lattice and impede dislocation movement throughout the matrix. The alloy therefore reaches roughly 827 MPa tensile strength straight out of the annealing furnace, with no ageing step and none of the solution-plus-double-age cycle that Alloy 718 requires.

That strengthening mechanism determines how the material behaves in service. There is no strengthening precipitate to over-age, so Alloy 625 does not soften progressively at moderate temperature in the way a precipitation-hardened grade does. The matrix is single-phase austenite, so the alloy is non-magnetic, stays tough at cryogenic temperatures, and welds without preheat or post-weld heat treatment. Alloy 625 is in fact used as a filler and weld-overlay material on other alloys about as often as it is used as a base material.

The high chromium content gives oxidation resistance to approximately 982 °C. The 9 % molybdenum gives resistance to chloride pitting and crevice attack. Together they produce a broad chemical resistance covering both oxidising and reducing media. The cost is the constraint: Alloy 625 runs roughly eight to twelve times the price of 316L per kilogram, so it is normally specified where nothing cheaper survives the duty. That means seawater, sour gas, flue-gas scrubbers, hot chlorides and hot acids.

What are the equivalent designations for Alloy 625?

Engineers searching under any of the names below are referring to the identical chemistry. Jiangyin Jiangnan Metal Co., Ltd. accepts purchase orders under all of them and issues a material test certificate listing every equivalent designation the heat satisfies.

What is the chemical composition of Alloy 625?

The limits below are those of ASTM B564 / B443 / B446 for UNS N06625, and are the values that appear on our material test certificates. Chromium provides the passive oxide film and high-temperature oxidation resistance. Molybdenum suppresses chloride pitting and crevice attack. Niobium supplies most of the solid-solution strengthening and ties up carbon as stable MC carbides, which reduces sensitisation. Iron is capped at 5 % because higher iron degrades both corrosion resistance and hot workability.

What is the difference between Alloy 625 Grade 1 and Grade 2?

This is the most consequential decision on an Alloy 625 purchase order, and the one most often left off drawings. ASTM B564 furnishes UNS N06625 in two grades of different heat-treated condition. They are not quality levels. They behave as different materials in service, with different grain sizes, different strengths and different temperature envelopes.

What are the mechanical properties of Alloy 625?

Two tables matter here. The first shows what the standard guarantees, meaning the minimum values a certificate must report. The second shows what the alloy typically delivers at temperature, which is what a designer actually works with.

Note how little the alloy gives up between room temperature and 538 °C. Tensile strength falls by under 10 % across that whole range, and elongation actually rises. This flatness is characteristic of solid-solution strengthening and is the property that makes Alloy 625 useful for equipment holding pressure at temperature. Above roughly 650 °C the position changes and creep, not yield, governs the design. Short-term tensile data is then no longer the right basis for sizing a part.

Service temperature: where Alloy 625 is safe and where it embrittles

Alloy 625 has an unusually wide working range. It stays tough at cryogenic temperature and remains oxidation-resistant to nearly 1000 °C. That range is not uniform, though. There is a band in the middle of it where the alloy loses most of its room-temperature impact toughness. A designer who is unaware of that band can specify a part that passes every acceptance test at the mill and then fails years later during a shutdown, when a component that has been sitting at 700 °C cools to ambient and is struck.

Ranges are taken from the ASTM B444 / B564 caution on impact-strength loss after exposure between 1000 °F and 1400 °F, from the ASME BPVC requirement that N06625 pressure parts be solution annealed, and from published Special Metals data on the oxidation limit. Band widths on the chart are schematic and are not linear in temperature.

What happens in the embrittlement range

Between roughly 550 °C and 850 °C the supersaturated matrix begins to reject elements it is holding in solution. Three things precipitate, on different timescales.

• M₂₃C₆ and MC carbides form on grain boundaries within hours. These are the fastest and are the main cause of the early toughness loss.
• γ″ (gamma double-prime, Ni₃Nb, body-centred tetragonal), the same metastable phase that strengthens Alloy 718, precipitates over tens to hundreds of hours around 650 °C. It raises strength and lowers ductility.
• δ (delta, orthorhombic Ni₃Nb) forms over longer exposures, typically as grain-boundary plates. Delta phase is the stable end point and the most damaging to toughness.

None of this appears on a mill certificate, because it happens in service rather than at the mill. A Charpy test on as-supplied material says nothing about the condition of the part after 20,000 hours at 700 °C. Where that matters, the design must either use published aged-condition data or accept a substantially reduced toughness allowance.

What are the physical properties of Alloy 625?

How corrosion-resistant is Alloy 625?

Alloy 625 is one of the most broadly corrosion-resistant engineering alloys in commercial production. The nickel base resists reducing conditions and chloride stress-corrosion cracking. Chromium resists oxidising conditions. Molybdenum resists localised chloride attack. Few environments defeat all three at once. With a PREN of approximately 51 the alloy is effectively immune to pitting and crevice corrosion in ambient seawater, and its critical crevice corrosion temperature is far above that of any stainless grade.

Corrosion behaviour is environment-specific. The table gives typical published performance and is intended for screening only. For a defined process stream, consult iso-corrosion data or run a coupon test.

When should you choose Alloy 625 over 718, 825, C-276 or 316L?

Alloy 625 sits in a defined place in the corrosion-resistant alloy hierarchy. It is more capable than the super-austenitic stainless grades, cheaper and far more weldable than the Hastelloy family, and more corrosion-resistant but much weaker than Alloy 718. The comparison below covers the alloys it is most often traded against.

Typical published values for comparison purposes. Relative cost is indicative and moves with the nickel and molybdenum indices. Specific grades and conditions are covered by their own standards.

How is Alloy 625 forged, welded and machined?

Forging

Alloy 625 is forged from a maximum of 1180 °C, with the finishing temperature held above approximately 950 °C. Two characteristics dominate the practice. First, hot strength is very high. The alloy needs several times the press load of a carbon steel at the same temperature, which is why heavy Alloy 625 sections go on the 5000-tonne hydraulic press rather than under a hammer. Second, the useful working window is narrow, so the piece is reheated as often as necessary rather than worked all the way down in a single heat. Forging below about 950 °C risks cracking, and finishing too hot produces a coarse grain that will not meet a fine-grain requirement.

After the final operation the part is cooled in still air, then given the specified Grade 1 anneal or Grade 2 solution anneal. A forging reduction ratio of at least 4:1 is used to break down the cast structure and develop uniform properties. Because raw material cost dominates the price of an Alloy 625 part far more than it does for steel, near-net-shape forging and trepanned billets pay for themselves quickly on anything above a few hundred kilograms.

Welding

Alloy 625 is among the most weldable nickel alloys, to the point that the alloy is used as a filler metal and weld-overlay consumable for dissimilar joints and for cladding carbon steel. GTAW, GMAW, SMAW, plasma and submerged-arc processes are all used, normally with ERNiCrMo-3 filler wire to AWS A5.14. Neither preheat nor post-weld heat treatment is normally required, which is one of the practical advantages over Alloy 718.

Two things do need control. Heat input should be kept low and interpass temperature below roughly 100 °C, both to limit niobium segregation and Laves-phase formation in the weld metal and to avoid holding the heat-affected zone in the precipitation range. Joints must also be cleaned scrupulously, because sulphur, lead, phosphorus and any residue from marking crayons or cutting fluids cause hot cracking in nickel alloys. A slightly wider joint preparation than for steel helps, since the weld pool is sluggish and does not wet the sidewall as readily.

Machining

Alloy 625 is difficult to machine for two reasons that reinforce each other. It work-hardens rapidly ahead of the cutting edge, and its low thermal conductivity keeps heat in the cutting zone instead of carrying it away in the chip. The practical rules are those common to all nickel superalloys: low cutting speed, heavy positive feed, rigid setup, sharp tooling and flood coolant. Typical starting parameters for turning with coated carbide are 20 to 35 m/min at 0.15 to 0.30 mm/rev.

Above all, never dwell and never take a light spring pass over a previously cut surface. The tool will ride on the work-hardened layer, generate more heat, and harden it further. Each pass should cut below the layer left by the previous one. Ceramic tooling can run considerably faster but needs a rigid machine and continuous cuts. Where a part will need extensive finish machining, ordering it rough-machined from us is usually cheaper than shipping the stock and machining it locally.

Alloy 625 failure modes and how to design them out

Alloy 625 is a forgiving material, and most of the failures we and our customers have investigated trace back to a small number of causes. Nearly all of them are specification or fabrication decisions rather than material defects.

Alloy 625 production capability at Jiangyin Jiangnan Metal

Jiangyin Jiangnan Metal Co., Ltd. has operated as an open-die forging factory since 2008 at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, and exports to more than 40 countries. The plant employs approximately 460 people, including 9 senior engineers and 32 intermediate engineers, and is certified to ISO 9001:2015. Raw material, forging, heat treatment, machining, testing and inspection are all carried out in house, which is what makes single-source traceability from ingot to certificate possible.

Envelope figures are typical for UNS N06625 and differ from our carbon-steel capability, which extends to 6000 mm diameter and 15,000 kg. Confirm size and weight limits for a specific geometry at enquiry stage.

Alloy 625 process flow from ingot to certificate

1. Raw material and melting

   EAF with AOD or VOD refining plus ESR remelting as standard. VIM plus ESR is available where a premium melt route is specified for subsea or aerospace work. Every heat is traceable by heat number, and chemistry is verified by optical emission spectrometry before release to forging.

2. Forging or ring rolling

   Heated to a maximum of 1180 °C, finished above about 950 °C, reheated as often as required, reduction ratio of at least 4:1. Heavy sections on the 5000-tonne hydraulic press, rings on the radial-axial mills, cooled in still air.

3. Heat treatment

   Grade 1 annealed at 871 °C minimum or Grade 2 solution annealed at 1093 °C minimum, followed by rapid cooling. Furnace charts are recorded and issued with the certificate.

4. Rough machining

   Stock removed to expose the sub-surface for inspection and to bring the part close to final geometry before final NDT.

5. Non-destructive testing

   Ultrasonic testing to ASTM A388, EN 10228 or SEP 1921 as specified, plus liquid penetrant to ASTM E165. Magnetic particle testing does not apply, because Alloy 625 is non-magnetic.

6. Mechanical and metallurgical testing

   Tensile testing to ASTM E8 on the 300 kN universal machine, Charpy V-notch to ASTM E23, hardness, grain size to ASTM E112 and metallography where specified.

7. Final inspection, certification and packing

   Dimensional inspection, marking with heat number and grade, and issue of the EN 10204 3.1 certificate, or 3.2 with third-party witness, listing all equivalent designations satisfied.

Equipment used for Alloy 625 work

Standards, testing and certification for Alloy 625 forgings

For UNS N06625 forgings the governing specification is ASTM B564 / ASME SB-564. European projects usually specify W.Nr. 2.4856 / NiCr22Mo9Nb with VdTÜV-Wb 499 for pressure equipment. Aerospace work uses AMS 5666 for annealed material or AMS 5837 for solution annealed. Offshore work adds NORSOK M-630 MDS N-01, and any H₂S-containing service adds NACE MR0175 / ISO 15156-3.

• ASTM B564
• ASME SB-564
• ASTM B443
• ASTM B446
• ASTM B444
• ASTM B366
• AMS 5666
• AMS 5837
• W.Nr. 2.4856
• NiCr22Mo9Nb
• VdTÜV-Wb 499
• NACE MR0175 / ISO 15156-3
• NORSOK M-630 MDS N-01
• JIS NCF 625
• GB NS3306 / GH3625
• EN 10204 3.1
• EN 10204 3.2
• ISO 9001:2015

Testing performed

Certification

EN 10204 3.1 mill test certificates are issued as standard. EN 10204 3.2 certificates witnessed by a client-nominated third party such as Lloyd's Register, DNV, Bureau Veritas, ABS, TÜV or an inspector of your choosing are available on request and are quoted per order. Every certificate states the heat number, melting route, heat-treatment condition and grade, full chemical analysis, mechanical results, NDT results, and each equivalent designation the heat satisfies, so that a single document supports ASTM, EN and JIS callouts at the same time.

How to specify an Alloy 625 forging order

Alloy 625 carries one decision that most grades do not, which is Grade 1 or Grade 2, and one that is easy to forget, which is the cobalt limit for nuclear work. The seven steps below make both explicit and remove most of the ambiguity that causes requotes.

1. State the designation

   Write UNS N06625 / ASTM B564, or W.Nr. 2.4856 / NiCr22Mo9Nb for European projects, or AMS 5666 / 5837 for aerospace. Avoid ordering against a trademarked brand name alone, since that implies material from one specific producer.

2. Choose the grade

   Grade 1 annealed for service to 593 °C. Grade 2 solution annealed above 593 °C, and for all ASME BPVC pressure parts. If the order is silent, Grade 1 is supplied.

3. Supply the drawing

   2D drawing or 3D model with critical dimensions, machining allowance, tolerances, surface roughness and any grain-flow requirement. State whether you want as-forged, rough-machined or finish-machined.

4. Define the melting route

   EAF plus AOD or VOD plus ESR is our standard. State if VIM plus ESR or a restricted cobalt content is required, as subsea, aerospace and nuclear projects frequently do.

5. Define NDT and acceptance

   Ultrasonic testing to ASTM A388, EN 10228 or SEP 1921 with the acceptance class, plus liquid penetrant to ASTM E165 where required. Add grain size to ASTM E112 and ASTM G28 corrosion testing if the service warrants it.

6. Specify certification and compliance

   EN 10204 3.1 or 3.2, and add NACE MR0175 / ISO 15156-3 or NORSOK M-630 MDS N-01 compliance statements where the service requires them.

7. Give quantity, delivery and terms

   Quantity, target date, Incoterms and destination port. Send it to sales@steelforgepieces.com or use the RFQ generator below.

The eight most common Alloy 625 ordering mistakes

Drawing callout template for Alloy 625

Copying the block below into a drawing's material callout removes most ordering ambiguity. Adjust the grade, NDT class and certification level to suit the application.

MATERIAL:      UNS N06625 / ASTM B564
               (also satisfies ASME SB-564, W.Nr. 2.4856,
                NiCr22Mo9Nb, AMS 5666, JIS NCF 625, GB NS3306)

CONDITION:     GRADE 1, annealed 871 C min, rapid cool
               // or GRADE 2, solution annealed 1093 C min, rapid cool
               // Grade 2 mandatory above 593 C and for ASME BPVC pressure parts

MELT ROUTE:    EAF + AOD/VOD + ESR
               // specify VIM + ESR for subsea / aerospace
               // specify Co max 0.10 % for nuclear service

MECHANICAL:    Grade 1 - UTS min 827 MPa, YS0.2 min 414 MPa, El min 30 %
               Grade 2 - UTS min 690 MPa, YS0.2 min 276 MPa, El min 30 %

HARDNESS:      35 HRC max, verified after final machining
               // mandatory for NACE MR0175 / ISO 15156-3 service

GRAIN SIZE:    Per ASTM E112, report on certificate
               // specify a limit for Grade 2 / high-temperature service

NDE:           UT per ASTM A388 (or EN 10228 / SEP 1921), class ___
               PT per ASTM E165
               MT NOT APPLICABLE, material is non-magnetic

CORROSION:     ASTM G28 method A  // chemical process
               ASTM G48           // seawater / offshore

CERTIFICATION: EN 10204 3.1 mill certificate
               // or EN 10204 3.2 with third-party witness
               // add NACE MR0175 / ISO 15156-3 compliance statement
               // add NORSOK M-630 MDS N-01 where applicable

MARKING:       Heat number, grade, specification, drawing number
               Low-stress stamp or vibro-etch on non-functional surface
               NO sulphur-bearing marking crayons

Where is Alloy 625 used?

Alloy 625 is specified where a cheaper alloy has already failed, or where the cost of failure is far greater than the cost of the material. Six sectors account for most of what we forge in this grade.

Representative project scenarios

The following are representative of the work we do in this grade. Specific project data and customer references are available under confidentiality agreement on request.

Glossary

Alloy 625

Generic name for the nickel-chromium-molybdenum-niobium solid-solution alloy designated UNS N06625.

UNS N06625

Unified Numbering System designation, the unambiguous generic identifier to use on purchase orders.

W.Nr. 2.4856 / NiCr22Mo9Nb

German material number and EN chemical name for the same alloy.

Inconel® 625

Registered trademark of Special Metals Corporation for their production of this chemistry. Generic equivalents are UNS N06625, ASTM B564 and 2.4856.

Grade 1 (annealed)

ASTM B564 condition, annealed at 871 °C minimum. Higher room-temperature strength, normal service to 593 °C.

Grade 2 (solution annealed)

ASTM B564 condition, solution annealed at 1093 °C minimum. Coarser grain and better creep resistance. Required above 593 °C and for ASME BPVC pressure parts.

Solid-solution strengthening

Strengthening by dissolved alloying atoms, here molybdenum and niobium, distorting the lattice and impeding dislocation movement. No ageing treatment is involved.

γ″ (gamma double-prime)

Metastable body-centred-tetragonal Ni₃Nb precipitate. Used deliberately to strengthen Alloy 718. In Alloy 625 it forms unintentionally during hot service and reduces ductility.

δ (delta) phase

Stable orthorhombic Ni₃Nb, usually as grain-boundary plates. The end point of prolonged exposure in the precipitation range and the most damaging to toughness.

M₂₃C₆ carbide

Chromium-rich grain-boundary carbide that precipitates within hours in the 538 to 760 °C range, causing the initial loss of impact toughness.

PREN

Pitting Resistance Equivalent Number, Cr + 3.3 Mo + 16 N. Approximately 51 for Alloy 625, against about 25 for 316L.

ESR

Electroslag Remelting, a secondary refining process that improves cleanliness and solidification structure.

VIM

Vacuum Induction Melting, premium primary melting used where the tightest cleanliness and gas content are required.

NACE MR0175 / ISO 15156

The standard governing materials for H₂S-containing oil and gas service. UNS N06625 is listed as an acceptable solid-solution nickel CRA at 35 HRC maximum.

NORSOK M-630

Norwegian offshore material data sheets. MDS N-01 covers UNS N06625 forged components.

EN 10204 3.1 / 3.2

Inspection document types. 3.1 is certified by the manufacturer's independent inspection department. 3.2 is countersigned by a third party or the purchaser's representative.

ERNiCrMo-3

AWS A5.14 classification for matching Alloy 625 bare filler wire.

Trepanned billet

A billet with the centre bored out before forging, used to avoid machining away, and paying for, the core of a hollow part.

Technical references

Chemistry, mechanical property, heat-treatment and corrosion data on this page are taken from the published standards and engineering references listed below. Test results on our material test certificates are independent and traceable to calibrated equipment.

1. ASTM B564 / B564M, Standard Specification for Nickel Alloy Forgings, ASTM International, West Conshohocken, PA.
2. ASTM B443 / B443M, Standard Specification for Nickel-Chromium-Molybdenum-Columbium Alloy and Nickel-Chromium-Molybdenum-Silicon Alloy Plate, Sheet, and Strip, ASTM International.
3. ASTM B446 / B446M, Standard Specification for Nickel-Chromium-Molybdenum-Columbium Alloy Rod, Bar, and Wire, ASTM International.
4. ASTM B444, Standard Specification for Nickel-Chromium-Molybdenum-Columbium Alloys Pipe and Tube, ASTM International.
5. ASME Boiler and Pressure Vessel Code, Section II Part B (SB-564, SB-443, SB-444, SB-446) and Section II Part D, latest edition, ASME.
6. AMS 5666, Nickel Alloy, Corrosion and Heat-Resistant, Bars, Forgings, and Rings, 62Ni-21.5Cr-9.0Mo-3.65Cb, Annealed, SAE International.
7. AMS 5837, Nickel Alloy, Corrosion and Heat-Resistant, Bars, Wire, Forgings, and Rings, Solution Heat Treated, SAE International.
8. 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, ISO.
9. NORSOK M-630, Material data sheets and element data sheets for piping, MDS N-01 (UNS N06625), Standards Norway.
10. VdTÜV-Werkstoffblatt 499, NiCr22Mo9Nb (2.4856), VdTÜV, Germany.
11. EN 10204, Metallic products. Types of inspection documents, CEN, Brussels.
12. EN 10228-3, Non-destructive testing of steel forgings, CEN, and SEP 1921, Stahl-Eisen-Prüfblatt, Germany.
13. ASTM A388 / A388M, Standard Practice for Ultrasonic Examination of Steel Forgings, ASTM International.
14. ASTM E165 / E165M, Standard Practice for Liquid Penetrant Testing for General Industry, ASTM International.
15. ASTM E112, Standard Test Methods for Determining Average Grain Size, ASTM International.
16. ASTM G28, Standard Test Methods for Detecting Susceptibility to Intergranular Corrosion in Wrought, Nickel-Rich, Chromium-Bearing Alloys, ASTM International.
17. ASTM G48, Standard Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys, ASTM International.
18. AWS A5.14 / SFA-5.14, Specification for Nickel and Nickel-Alloy Bare Welding Electrodes and Rods, American Welding Society.
19. ASM Handbook, Volume 1: Properties and Selection: Irons, Steels, and High-Performance Alloys, ASM International, Materials Park, OH.
20. ASM Specialty Handbook: Heat-Resistant Materials, J.R. Davis (ed.), ASM International.
21. Special Metals Corporation, INCONEL alloy 625 technical publication (SMC-063), Huntington, WV.
22. API Specification 6A, Specification for Wellhead and Tree Equipment, and API 6ACRA, Age-Hardened Nickel-Based Alloys for Oil and Gas Drilling and Production Equipment, American Petroleum Institute.

Standards cited are the most current revisions known at the date of the last page review. For procurement, always reference the revision in force at the contract date. Trademarks are the property of their respective owners.