UNS N06625 at a glance
- UNS number
- N06625
- Common name
- Alloy 625 (trade name Inconel® 625)
- Werkstoff / EN
- 2.4856 / NiCr22Mo9Nb
- Alloy family
- Nickel-chromium-molybdenum-niobium, austenitic, solid-solution strengthened
- Forging standard
- ASTM B564 / ASME SB-564
- Bar standard
- ASTM B446 / AMS 5666
- Delivery condition
- Grade 1 annealed ≥871 °C, or Grade 2 solution annealed ≥1093 °C
- Service range
- −196 °C to about 982 °C (−320 °F to 1800 °F)
- Density
- 8.44 g/cm³ (0.305 lb/in³)
- Melting range
- 1290–1350 °C (2350–2460 °F)
- Sour service
- Listed in NACE MR0175 / ISO 15156-3 within the stated limits
- Certification
- EN 10204 3.1 standard, 3.2 third-party witnessed on request
- Forged by
- Jiangyin Jiangnan Metal Co., Ltd., Jiangyin, Jiangsu, China
What UNS N06625 is, and when to specify it
UNS N06625 is the Unified Numbering System designation for the nickel-base alloy usually called Alloy 625. Nickel holds the austenitic structure and chromium forms the passive oxide film. Molybdenum is what suppresses pitting and crevice attack in chlorides, and niobium stiffens the matrix while tying up carbon as niobium carbide, so the alloy can be welded and put into service without a stabilising heat treatment. None of this depends on precipitation hardening, so the material is supplied annealed.
Buyers normally specify it in place of a duplex or super-austenitic stainless steel because of the range of media it handles. It works in oxidising and reducing conditions, in seawater, in wet chlorine and in sour hydrocarbon service, and it is effectively immune to chloride stress-corrosion cracking. It is also strong. A Grade 1 forging has to reach 827 MPa (120 ksi) tensile, roughly 50% above annealed 316L.
Specify UNS N06625 when the part has to survive chlorides, when it must be welded and put into service without a stabilising heat treatment, or when the service temperature is above what a stainless steel will take. Use a cheaper grade when the medium is mild and the temperature moderate. The alloy costs several times more per kilogram than 316L and only pays back where the environment is aggressive.
Two points belong on the drawing. Long exposure between roughly 650 °C and 870 °C precipitates carbides and gamma double prime at the grain boundaries, which lowers ductility and toughness; where that band is unavoidable in service, use Grade 2 material and allow for it in the design. The alloy also work-hardens fast ahead of the cutting edge, so machining needs rigid tooling, positive feed and lower cutting speeds than stainless steel.
Chemical composition of UNS N06625
The limits below are the composition requirements for UNS N06625 in ASTM B564 / ASME SB-564, in weight percent. The four highlighted rows are the elements that define the grade. The rest are residual limits.
| Element | Minimum % | Maximum % | Role in the alloy |
|---|---|---|---|
| Nickel (Ni) | 58.00 | balance | Base element. Holds the austenitic structure and gives immunity to chloride stress-corrosion cracking |
| Chromium (Cr) | 20.00 | 23.00 | Forms the passive oxide film. Carries oxidation resistance and general corrosion resistance |
| Molybdenum (Mo) | 8.00 | 10.00 | Suppresses pitting and crevice corrosion in chlorides. Adds solid-solution strength |
| Niobium + Tantalum (Nb+Ta) | 3.15 | 4.15 | Stiffens the matrix and fixes carbon as NbC, preventing chromium-carbide sensitisation after welding |
| Iron (Fe) | — | 5.00 | Residual from melting stock. Kept low to protect corrosion performance |
| Carbon (C) | — | 0.10 | Held low. Excess carbon forms grain-boundary carbides on high-temperature exposure |
| Manganese (Mn) | — | 0.50 | Deoxidiser |
| Silicon (Si) | — | 0.50 | Deoxidiser. Restricted to protect hot workability |
| Aluminium (Al) | — | 0.40 | Residual limit. Deoxidiser during melting |
| Titanium (Ti) | — | 0.40 | Residual limit. Assists carbon and nitrogen control |
| Cobalt (Co) | — | 1.00 | Residual limit, determined when specified |
| Phosphorus (P) | — | 0.015 | Kept low for hot workability and weldability |
| Sulfur (S) | — | 0.015 | Kept low for hot workability and toughness |
Table compiled by Jiangyin Jiangnan Metal Co., Ltd. from ASTM B564. This is the specification window we forge to. Every heat is supplied with a ladle analysis on the mill certificate, and a product analysis on the finished forging can be added on request.
Two details on the analysis catch people out. Niobium and tantalum are specified as a combined figure, so a certificate reporting only Nb is acceptable provided the sum falls inside 3.15–4.15%. Cobalt is only determined when the purchase order asks for it, which matters for nuclear and some aerospace work where a cobalt cap applies.
Grade 1 vs Grade 2: which condition to order
ASTM B564 furnishes UNS N06625 in two grades. Both have the same chemistry and differ only in heat treatment. That one difference changes the grain size, the certified minimums and the temperature range the material suits. Ordering the wrong grade is the most common problem we see on Alloy 625 enquiries.
| Criterion | Grade 1 (annealed) | Grade 2 (solution annealed) |
|---|---|---|
| Heat treatment | ≥871 °C (1600 °F) | ≥1093 °C (2000 °F) |
| Optional stabilising anneal | Not applicable | ≥982 °C (1800 °F), raises resistance to sensitisation |
| Resulting grain size | Finer | Coarser |
| Tensile strength, min | 827 MPa / 120 ksi | 690 MPa / 100 ksi |
| Yield strength 0.2%, min | 414 MPa / 60 ksi | 276 MPa / 40 ksi |
| Governing property | Room-temperature strength, wet corrosion resistance | Creep and stress-rupture strength |
| Normal service band | Cryogenic to about 600 °C (1112 °F) | Above 600 °C, to about 982 °C (1800 °F) |
| Choose it when | Seawater, acid, sour or cryogenic service, and where the design needs the higher allowable stress at moderate temperature | Sustained load at high temperature, or where the code or specification calls for the solution-annealed condition |
The Grade 2 anneal temperature is higher than the Grade 1 anneal temperature, so Grade 1 stock can be converted to Grade 2 by an extra heat treatment. It does not work the other way round. If your specification is silent on the grade, state the service temperature on the enquiry and we will confirm the condition before the order is placed.
Mechanical properties of UNS N06625 forgings
Specified minimums to ASTM B564 / ASME SB-564
These are the room-temperature values a mill certificate has to meet. They are minimums, not typical values. For Grade 1 they step down above 100 mm (4 in) section thickness, because the heavier section cools more slowly through the anneal.
| Condition and section | Tensile, min | Yield 0.2%, min | Elongation, min |
|---|---|---|---|
| Grade 1, section ≤100 mm (4 in) | 827 MPa / 120 ksi | 414 MPa / 60 ksi | 30 % |
| Grade 1, section >100 mm (4 in) | 758 MPa / 110 ksi | 345 MPa / 50 ksi | 25 % |
| Grade 2, all sections | 690 MPa / 100 ksi | 276 MPa / 40 ksi | 30 % |
Typical as-delivered values
Annealed UNS N06625 forgings normally test above the specified minimums. The values below are representative of our production and vary with section size, forging reduction and cooling rate.
| Property | Typical range (metric) | Typical range (imperial) |
|---|---|---|
| Tensile strength | 827–1034 MPa | 120–150 ksi |
| Yield strength 0.2% offset | 414–655 MPa | 60–95 ksi |
| Elongation | 30–60 % | 30–60 % |
| Reduction of area | 40–60 % | 40–60 % |
| Hardness, annealed | 145–220 HBW | 145–220 HBW |
| Charpy V-notch, −196 °C | stays ductile | no ductile-to-brittle transition |
Typical values are for design screening only. The mill test certificate issued with each forging governs acceptance. Where a hardness cap applies, for example NACE MR0175 / ISO 15156-3 sour service, state it on the order so the heat treatment is set accordingly.
Physical properties of UNS N06625
| Property | Metric | Imperial |
|---|---|---|
| Density | 8.44 g/cm³ | 0.305 lb/in³ |
| Melting range | 1290–1350 °C | 2350–2460 °F |
| Modulus of elasticity | 207.5 GPa | 30.1 × 10⁶ psi |
| Specific heat, 20 °C | 410 J/kg·K | 0.098 Btu/lb·°F |
| Thermal conductivity, 20 °C | 9.8 W/m·K | 68 Btu·in/ft²·h·°F |
| Mean expansion, 20–100 °C | 12.8 µm/m·K | 7.1 × 10⁻⁶ in/in·°F |
| Electrical resistivity | 1.29 µΩ·m | 129 µΩ·cm |
| Magnetic permeability | about 1.0006 | essentially non-magnetic |
| Curie temperature | below −196 °C | below −320 °F |
Low thermal conductivity combined with high strength is what makes the alloy hard to machine. Heat stays at the cutting edge instead of leaving with the chip. Use rigid setups, sharp carbide tooling, positive rake and plenty of coolant, and do not let the tool dwell in the cut, which work-hardens the surface.
Corrosion performance and sour service
The pitting resistance equivalent number, calculated as Cr + 3.3 × Mo, comes out between about 47 and 56 across the composition window. Super duplex stainless steel sits near 40 and 316L near 24. That is why UNS N06625 gets specified for seawater-cooled equipment, for hydrochloric and sulfuric acid duty and for wet chlorine handling.
| Environment | Behaviour |
|---|---|
| Seawater and brine | Resists pitting and crevice attack. Used for splash-zone and subsea hardware, including stagnant conditions where stainless steels fail |
| Chloride stress-corrosion cracking | Effectively immune, from the high nickel content |
| Sour service (H₂S) | Listed in NACE MR0175 / ISO 15156-3 for solid-solution nickel alloys, within the environmental and hardness limits tabulated there |
| Oxidising acids | Good resistance from chromium. Nitric acid service is well established |
| Reducing acids | Molybdenum gives useful resistance in hydrochloric, sulfuric and phosphoric acid at moderate concentration and temperature |
| Organic acids and salts | Resistant, including acetic, formic and mixed process streams |
| Oxidation in air | Protective chromia scale to about 982 °C (1800 °F) |
| Intergranular attack after welding | Niobium fixes carbon as NbC, so a stabilising heat treatment is not normally required |
Corrosion data is comparative guidance, not a design allowance. Rates depend on concentration, temperature, aeration, velocity and contaminants. For a specific duty, qualify the material against your own service conditions or an applicable corrosion table before committing to the design.
UNS N06625 equivalent designations
| System | Designation |
|---|---|
| UNS (USA) | N06625 |
| Werkstoff Nr. (Germany) | 2.4856 |
| EN / DIN name | NiCr22Mo9Nb |
| AFNOR (France) | NC22DNb |
| BS (UK) | NA 21 |
| JIS (Japan) | NCF 625 |
| GB (China) | GH3625 / NS3306 |
| Aerospace | AMS 5666 (bar, forgings, rings), AMS 5837, AMS 5599 (sheet, strip, plate) |
| Trade names | Inconel® 625, Nicrofer® 6020 hMo, Haynes® 625, Chronin® 625, Altemp® 625, Nickelvac® 625 |
Do not confuse 2.4856 with 2.4816. 2.4856 is alloy 625 (UNS N06625). 2.4816 is alloy 600 (UNS N06600), a nickel-chromium alloy with no molybdenum and no niobium, and a completely different corrosion envelope. Where a drawing shows 2.4816 but the specification text describes molybdenum-bearing material, query it before the order is placed.
Where a code case, design registration or pressure-equipment approval is involved, order to the UNS number rather than to a trade name, and confirm the equivalence against the mill certificate. A trade name identifies a specification. Material carrying those names is made by the trademark holders themselves.
Applicable standards by product form
| Product form | ASTM | ASME |
|---|---|---|
| Forgings and forged fittings | B564 | SB-564 |
| Rod, bar and wire | B446 | SB-446 |
| Plate, sheet and strip | B443 | SB-443 |
| Seamless pipe and tube | B444 | SB-444 |
| Welded pipe | B705 | SB-705 |
| Welded tube | B704 | SB-704 |
| Wrought fittings | B366 | SB-366 |
Dimensional standards are separate from material standards. Flanges are ordered to ASME B16.5 up to NPS 24, ASME B16.47 Series A or B above NPS 24, or EN 1092-1. Forged fittings follow ASME B16.11 or MSS SP-79 / SP-83 / SP-95. Sour service is governed by NACE MR0175 / ISO 15156-3, and upstream oil and gas work often adds API 6A CRA requirements. State the dimensional standard, the material standard and any supplementary requirement separately on the purchase order.
UNS N06625 forgings we produce
Every item below is forged to the customer's drawing or dimensional sketch. Open-die work needs no dies, so there is no tooling charge and no minimum piece quantity, and one-off or prototype orders are economic.
Size and weight capability
| Product form | Dimensional range | Unit weight |
|---|---|---|
| Seamless rolled rings | OD 200–3,000 mm, height to 800 mm | 20–8,000 kg |
| Round bars | Ø80–800 mm, length to 6,000 mm | 20–6,000 kg |
| Discs and tube sheets | Ø200–2,500 mm, thickness to 600 mm | 30–10,000 kg |
| Shafts, sleeves and blocks | to 6,000 mm long | to 10,000 kg |
Equipment: 1 t, 3 t, 5 t and 9 t open-die forging hammers, a 5,000 t hydraulic press, and 3 m and 6 m ring-rolling mills. Machining allowance is normally 6–20 mm per surface depending on section size unless the drawing states otherwise. Finish-machined parts to print are also supplied.
How UNS N06625 forgings are made
- Melting
UNS N06625 stock is melted by EAF + AOD/VOD, with ESR or VIM + ESR + VAR remelting where the specification or the service calls for better cleanliness and less segregation. Aerospace and subsea work normally requires a remelted route.
- Ingot and billet verification
Heat chemistry is checked by spectrometer against the ASTM B564 limits, including the combined Nb + Ta window, before any material is heated. Heat number traceability starts here and follows the part to despatch.
- Heating and open-die forging
Forged from a start temperature not exceeding about 1180 °C, finishing above roughly 950 °C, with reheats as required. Reduction is controlled to close ingot porosity and develop a wrought grain flow that follows the part contour. Rings are ring-rolled seamless.
- Heat treatment
Grade 1: anneal at 871 °C (1600 °F) minimum. Grade 2: solution anneal at 1093 °C (2000 °F) minimum, with an optional stabilising anneal at 982 °C (1800 °F) to raise resistance to sensitisation. Cooling is rapid in both cases. Alloy 625 is not age-hardened for corrosion service.
- Rough or finish machining
Turned, bored, drilled and faced to the drawing with the agreed machining allowance, or finish machined to final dimensions.
- Non-destructive testing
Ultrasonic examination to EN 10228-3, SEP 1921, ASTM A388 or the nominated class, plus liquid penetrant examination and dimensional inspection as required.
- Certification and despatch
EN 10204 3.1 mill certificate as standard, 3.2 with third-party witness on request. Hard stamped with heat number, preserved and packed for sea or air freight.
Where UNS N06625 forgings are used
| Industry | Components forged in UNS N06625 |
|---|---|
| Offshore oil and gas | Subsea wellhead and Christmas tree components, hubs, connectors, seal rings, valve blocks and bodies, forged nozzles for deepwater production systems |
| Chemical processing | Reactor and column flanges, forged nozzles, agitator shafts, pump shafts and casings, crystalliser components, acid plant hardware |
| Pressure vessels and heat exchangers | Forged tube sheets, shell flanges, girth rings, blind covers, forged pipe sections and headers |
| Valves and flow control | Bodies, bonnets, gate and plug blanks, seat rings, stems for ball, gate, globe, check and plug valves |
| Marine and seawater systems | Pump and propulsion shafts, sleeves, bushings, seawater-cooled exchanger hardware, splash-zone fittings |
| Power generation | Gas turbine ducting and casing rings, flue gas desulfurisation hardware, waste-to-energy boiler components |
| Aerospace | Engine casing rings, ducting, bellows and exhaust hardware forged to AMS 5666 |
| Pharmaceutical and pulp & paper | Digester and bleach plant hardware, process module flanges, mixer and agitator components |
In most of these cases the part sees chlorides, an acid or a temperature that rules out stainless steel, and it has to be welded into an assembly without a post-weld solution treatment. Where high temperature is the only requirement and corrosion is not an issue, a cheaper grade such as Alloy 800HT is usually the better buy.
Testing, inspection and certification
- Chemical analysis. Spectrometric heat analysis against ASTM B564 limits, and product analysis on the finished forging on request.
- Mechanical testing. Room-temperature tensile, yield and elongation per ASTM B564. Elevated-temperature tensile, stress rupture and Charpy V-notch impact testing to your specification.
- Hardness. Brinell or Rockwell, including verification against a specified sour-service cap.
- Ultrasonic testing. EN 10228-3, SEP 1921 class C/D/E, ASTM A388 or your nominated class.
- Surface NDT. Liquid penetrant examination per ASTM E165 / ASME Section V Article 6.
- Intergranular corrosion. ASTM G28 method A, or ASTM A262 practice as agreed.
- Positive material identification. PMI on each piece, guarding against grade mix-ups between nickel alloys of similar appearance.
- Grain size. Determined per ASTM E112 where the specification requires it.
- Certification. EN 10204 3.1 as standard. EN 10204 3.2 witnessed by TÜV, BV, LR, SGS or DNV on request. Full heat traceability and hard stamping.
Frequently asked questions about UNS N06625
Is UNS N06625 the same as Inconel 625?
Yes. UNS N06625 is the Unified Numbering System designation for the alloy sold under the trade name Inconel® 625. The same material is also called Alloy 625, W.Nr. 2.4856, NiCr22Mo9Nb, NCF 625 and NC22DNb. Inconel is a registered trademark of Special Metals Corporation. When ordering from a producer other than the trademark holder, specify UNS N06625 with ASTM B564 so the requirement is unambiguous.
What is the Werkstoff number for UNS N06625?
UNS N06625 is W.Nr. 2.4856, EN name NiCr22Mo9Nb. It is often confused with 2.4816, which is Alloy 600 (UNS N06600), a nickel-chromium alloy with no molybdenum or niobium. If a drawing shows 2.4816 where alloy 625 is intended, query it before ordering.
What is the difference between Grade 1 and Grade 2 UNS N06625?
The difference is the anneal temperature, which changes the grain size and therefore the strength. Grade 1 is annealed at 871 °C (1600 °F) minimum and must reach 827 MPa (120 ksi) tensile and 414 MPa (60 ksi) yield for sections up to 100 mm. Grade 2 is solution annealed at 1093 °C (2000 °F) minimum, which coarsens the grain and lowers the room-temperature minimums to 690 MPa (100 ksi) tensile and 276 MPa (40 ksi) yield, while improving creep and stress-rupture strength.
Specify Grade 1 for wet corrosion service below about 600 °C, and Grade 2 above it. Grade 1 material can be converted to Grade 2 by a further heat treatment. The reverse is not possible.
What standard covers UNS N06625 forgings?
ASTM B564, and its ASME equivalent SB-564, is the specification for UNS N06625 forgings and forged fittings. Round bar is covered by ASTM B446 and AMS 5666, plate, sheet and strip by ASTM B443, and seamless pipe and tube by ASTM B444. Flange dimensions follow ASME B16.5, ASME B16.47 or EN 1092-1 as specified on the order.
What is the maximum service temperature of UNS N06625?
The alloy can be used from cryogenic temperature up to about 982 °C (1800 °F), where oxidation resistance sets the practical ceiling. For sustained load above about 600 °C (1112 °F), specify Grade 2 solution-annealed material, because long exposure between roughly 650 °C and 870 °C precipitates carbides and gamma double prime, reducing ductility.
For pressure-retaining parts the governing limit is the allowable stress table in ASME BPVC Section II Part D and the applicable construction code, not the oxidation limit.
Can UNS N06625 be used in sour service?
Yes, within limits. UNS N06625 is listed in NACE MR0175 / ISO 15156-3 as a solid-solution nickel alloy for sour service, subject to the environmental limits and the maximum hardness stated there for the relevant material type and equipment class. Order the material solution annealed and unaged, state the H₂S partial pressure, chloride content, pH and temperature on the enquiry, and require NACE MR0175 / ISO 15156-3 compliance on the mill certificate.
Why does UNS N06625 resist pitting and crevice corrosion?
The combination of 20–23% chromium with 8–10% molybdenum gives a pitting resistance equivalent number (Cr + 3.3 × Mo) of roughly 47 to 56. Super duplex stainless steel sits near 40. The high nickel base also makes the alloy effectively immune to chloride stress-corrosion cracking. Niobium ties up carbon as niobium carbide, so the alloy resists sensitisation at grain boundaries after welding without a stabilising heat treatment.
Can UNS N06625 be welded?
Yes. The alloy is readily welded by GTAW, GMAW, SMAW and submerged arc, normally with a matching ERNiCrMo-3 filler. Because niobium fixes carbon, a post-weld solution treatment is not usually required for corrosion service. Keep heat input and interpass temperature controlled, clean thoroughly between passes, and avoid holding the weld region in the 650–870 °C band.
What size UNS N06625 forgings can you supply?
Jiangyin Jiangnan Metal Co., Ltd. forges UNS N06625 as seamless rolled rings from 200 to 3,000 mm outside diameter, round bars from 80 to 800 mm diameter and up to 6,000 mm long, discs and tube sheets to 2,500 mm diameter, and shafts and sleeves to 6,000 mm long, with single-piece weights from 10 kg upward. All work is open die, so there is no tooling charge and no minimum piece quantity. Confirm the exact envelope for your part when you send the drawing.
What certificate is supplied with UNS N06625 forgings?
Every forging ships with an EN 10204 3.1 mill test certificate as standard, listing heat number, ladle analysis, room-temperature mechanical results, heat treatment record and NDT results. EN 10204 3.2 certification witnessed by TÜV, BV, LR, SGS or DNV is available on request at the time of order, as are PMI reports, ASTM G28 method A intergranular corrosion testing and NACE MR0175 / ISO 15156-3 compliance statements.
How long does a UNS N06625 forging take to produce?
Lead time depends on whether the grade is in raw stock and on the size of the forging. Simple rings and discs from stock material typically run 25–40 days. Parts needing a new melt, ESR or VAR remelting, heavy machining or third-party witnessed inspection take longer. Send the drawing and we will confirm a firm date with the quotation.
Who supplies open-die forged UNS N06625 parts in China?
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. It forges UNS N06625 (Alloy 625) and other nickel alloys, stainless steels, tool steels, alloy steels and carbon steels into seamless rolled rings, flanges, bars, discs, shafts, sleeves and tube sheets to customer drawings, and exports worldwide. Enquiries: sales@steelforgepieces.com or +86 189 2135 9659.
Request a quotation for UNS N06625 forgings
Send a drawing, a sketch, or just the dimensions and quantity. We quote open-die forgings in UNS N06625 with no tooling charge and no piece minimum.
Useful details if you have them: grade and standard (UNS N06625 / ASTM B564), Grade 1 or Grade 2, product form, dimensions with machining allowance, quantity, NDT class, certificate type (EN 10204 3.1 or 3.2), any sour-service or hardness requirement, and the required delivery date.
Send your drawing, get a price
Quotations are normally returned within 24 hours on working days. English and Chinese enquiries both welcome.
Email your drawing for a quote- Company
- Jiangyin Jiangnan Metal Co., Ltd.
- Business
- Open-die forging factory
- Address
- No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
- Telephone / WhatsApp
- +86 189 2135 9659
- Website
- www.steelforgepieces.com
Citing this page
Jiangyin Jiangnan Metal Co., Ltd. (2026). UNS N06625 Forgings: Alloy 625 Rings, Flanges and Bars to ASTM B564. Jiangyin, Jiangsu, China. https://www.steelforgepieces.com/Nickel-Alloy/UNS-N06625.html