Nickel Superalloy · Precipitation Hardening · Werkstoff 2.4668

NiCr19NbMo / 2.4668 / UNS N07718 / Alloy 718 Forging Parts

Published: 18 May 2016 · Last updated: 23 August 2026 · Technically reviewed by the Jiangyin Jiangnan Metal Co., Ltd. Metallurgical Engineering Team

What is NiCr19NbMo (UNS N07718)?

NiCr19NbMo is a precipitation-hardening nickel-chromium-iron superalloy that combines superalloy strength with something most superalloys do not have: it can be welded without cracking. That single property is why the grade accounts for a very large share of all superalloy tonnage produced worldwide, and why it appears on drawings from jet engines to subsea wellheads.

The alloy's strength comes from gamma double prime (γ″), a body-centred tetragonal Ni₃Nb precipitate that forms during ageing, assisted by a smaller amount of the more familiar gamma prime (γ′) Ni₃(Al,Ti). Niobium is the deliberate addition that makes this happen. At 4.75–5.5% it is the defining element of the grade, and it is why the alloy behaves so differently from the γ′-hardened superalloys such as Waspaloy and Nimonic 80A.

Two consequences follow from that choice of strengthening phase, and between them they explain nearly everything about how NiCr19NbMo is specified and processed.

• γ″ forms slowly, so the alloy is weldable. A γ′-hardened superalloy begins to harden while it is still cooling from welding temperature; the contraction strain that results tears the heat-affected zone apart, the failure known as strain-age cracking. NiCr19NbMo hardens sluggishly enough that a weldment can be cooled and then given a full post-weld solution and ageing treatment before appreciable precipitation occurs. Fabricated superalloy assemblies (engine casings, fabricated manifolds, welded rotor structures) became practical because of this.
• γ″ is metastable, so the ceiling is about 650 °C. Above roughly 650–680 °C the γ″ coarsens and transforms toward the equilibrium δ (delta) phase, the orthorhombic form of Ni₃Nb. Strength then falls away quickly. NiCr19NbMo is not a 800 °C alloy and no heat treatment will make it one; where the service temperature genuinely exceeds 650 °C, the honest answer is a different grade.

δ phase is not simply an enemy. A controlled quantity at the grain boundaries pins them during hot working, which is what delivers the fine, uniform grain size and the notch ductility that forgings are bought for. Too much δ ties up the niobium that should have formed γ″ and the part comes out weak. Managing that balance is the reason forging temperatures, finishing temperatures and solution temperatures for this grade are specified far more tightly than for ordinary alloy steel, and the reason a forging bought on price alone from an unqualified source can meet the chemistry certificate and still fail the mechanical test.

Chromium at 17–21% gives good oxidation and general corrosion resistance; molybdenum at 2.8–3.3% adds useful but modest pitting resistance. The alloy is not a corrosion alloy in the sense that Alloy 625 or Hastelloy C-276 are: its molybdenum level is roughly one third of theirs. It is a strength alloy that happens to have decent corrosion resistance, and specifying it where chloride pitting governs is one of the more expensive mistakes in the selection table further down this page.

NiCr19NbMo forgings: supplier quick facts

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging and ring-rolling factory in Jiangyin, Jiangsu Province, China, producing NiCr19NbMo (2.4668 / UNS N07718 / Alloy 718) forged rings, seamless rolled rings, flanges, shafts, discs, sleeves, bushings, tube sheets and bars to customer drawings.

What Forged Products Are Available in NiCr19NbMo?

Jiangyin Jiangnan Metal produces NiCr19NbMo through three routes, selected by geometry and quantity. Open-die forging covers long shafts, blocks, tube sheets and large discs, and is used 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, casing rings, seal rings and bearing races. Near-net-shape forging earns its tooling cost quickly on this grade, because NiCr19NbMo is expensive per kilogram and slow to machine. Removing 30–50% of the rough stock in the die is worth considerably more here than on a stainless steel part of the same shape.

One route-selection point is specific to superalloys. Grain flow and grain size are properties, not by-products. A rolled ring with continuous circumferential grain flow and a controlled ASTM 5–8 grain size carries hoop stress and resists fatigue crack initiation in a way that a ring machined from plate simply does not, even when both meet identical chemistry and tensile minimums. For rotating parts, pressure-containing parts and anything fatigue-critical, specify the forged route explicitly and prohibit machined-from-solid 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 gear blanks
• Valve bodies, stems & seat rings
• Forged nozzles & manifolds
• Custom near-net-shape parts

What Are the Equivalent Designations of NiCr19NbMo?

Engineers reach this grade through a dozen different names depending on which standards body, which producer and which decade the drawing came from. Every designation in the table below refers to the same nominal 52Ni-19Cr-19Fe-5Nb-3Mo chemistry. Jiangyin Jiangnan Metal Co., Ltd. accepts purchase orders under all of them and cross-lists the equivalents on the material certificate.

What Is the Chemical Composition of NiCr19NbMo?

The composition below is the specification range for material 2.4668 / UNS N07718 as supplied by Jiangyin Jiangnan Metal Co., Ltd. Read it as a set of deliberate choices rather than a list: niobium creates the strengthening phase, chromium buys oxidation resistance, molybdenum buys pitting resistance, and every impurity limit exists because that element does something specific and unwelcome during forging or ageing.

How Is NiCr19NbMo Heat Treated?

NiCr19NbMo arrives at the customer in one of two completely different states, and confusing them is the most expensive error on this grade. Solution treated material is soft, machinable and not yet strong. Solution treated and aged material has its full superalloy strength and is hard to machine. Which one you want depends entirely on whether you intend to age the part yourself after machining.

What Are the Mechanical Properties of NiCr19NbMo?

The table below is the reason engineers specify this alloy. Aged NiCr19NbMo is roughly three times stronger than 316 stainless steel and about two and a half times stronger than Alloy 625, while staying tough at cryogenic temperatures and usable at 650 °C.

Strength at Temperature and the 650 °C Ceiling

NiCr19NbMo holds most of its room-temperature strength to about 540 °C, loses a modest amount by 650 °C, and then falls away sharply. The curve is set by γ″ stability, not by oxidation, and this is why the alloy's practical ceiling is quoted as 650 °C (1,200 °F) for continuous service even though it does not visibly scale until much higher.

Time matters as much as temperature. A brief excursion to 700 °C does little; several thousand hours at 675 °C over-ages the microstructure permanently and the part never recovers its properties without a full re-solution and re-age. When assessing a service condition, ask what the metal temperature is for the life of the part, not at the design point. Where the answer is above 650 °C for extended periods, move to Waspaloy, Inconel 706 for large rotors, or a cast nickel superalloy.

What Are the Physical Properties of NiCr19NbMo?

Data notes. Density, melting range and modulus are well established for this chemistry and can be used directly. Values marked "typical" or "≈" vary with heat, section size and condition and should be treated as indicative for screening. Where any physical value is contractually important, state it on the purchase order and Jiangyin Jiangnan Metal Co., Ltd. will report the measured result on the material certificate.

Corrosion Resistance and Sour Service

NiCr19NbMo resists oxidation in air to roughly 980 °C, performs well in steam and in most oxidising acids, and is effectively immune to chloride stress-corrosion cracking, the failure mode that eliminates austenitic stainless steels from hot chloride service. What it does not have is the pitting and crevice resistance of a true corrosion alloy, because its molybdenum sits around 3% rather than the 9% of Alloy 625 or the 16% of Hastelloy C-276.

For H₂S-containing oil and gas service the alloy is accepted under NACE MR0175 / ISO 15156-3 in defined heat-treatment conditions, normally with hardness capped at 40 HRC. API Specification 6A718 takes this further and defines a dedicated version of the alloy for drilling and production equipment, with tightened chemistry, a specified high-temperature solution treatment and a single ageing treatment, producing 827–1,000 MPa (120–145 ksi) yield with the hardness controlled. Wellhead bodies, hangers, valve blocks, stems, subsea connectors and downhole tools are normally bought to API 6A718 rather than to any aerospace specification.

NiCr19NbMo vs Alloy 625, Inconel 706, A286, Waspaloy and X-750

Superalloys are chosen by the intersection of three things: the temperature, the environment, and how much strength you need. The table below is the practical selection chart for the grades Jiangyin Jiangnan Metal Co., Ltd. forges most often.

718 against 625 is the comparison that comes up most often, and it is usually asked the wrong way round. The question is not which alloy is "better", but which failure mode you are designing against. Alloy 625 will not yield in a corrosive duty because it has enough molybdenum to stay passive; NiCr19NbMo will not yield under load because it has γ″. Put 718 in a hot chloride crevice and it pits. Put 625 in a 1,000 MPa stress field and it deforms. Both are correct choices for their own problem and expensive mistakes for the other.

A286 deserves more consideration than it usually gets. It reaches about 655 MPa proof at roughly half the price of NiCr19NbMo, and for fasteners, non-rotating hardware and moderately loaded parts below 700 °C it is frequently the right answer. Where a design has specified 718 out of habit rather than analysis, A286 is the first substitution worth pricing.

How Do You Forge, Machine and Weld NiCr19NbMo?

Forging

NiCr19NbMo is one of the more demanding superalloys to forge, and the reason is the same δ phase that makes it useful. Ingot is homogenised at 1,090–1,175 °C to break up the niobium-rich Laves phase left by solidification. Skipping or shortening this step leaves segregation that no amount of later heat treatment will remove. Forging then starts at 1,040–1,120 °C with the finishing temperature held above roughly 955 °C for conventional practice.

Where a fine, uniform grain size (ASTM 8 or finer) is required for fatigue-critical rotating parts, the forging is finished sub-solvus at 900–955 °C, so-called δ-processing, so that δ particles at the grain boundaries pin them and prevent grain growth during the final blows. This is slower, needs more press capacity because the alloy is much stiffer at those temperatures, and is the reason a properly processed 718 forging costs what it does.

The alloy has a narrow hot-working window and cracks readily if worked too cold or if sulfur contamination is present. Reduction of at least 4:1 from the ingot is used to break down the as-cast structure. For seamless rolled rings, the pierced blank is expanded on a radial-axial mill so that grain flow follows the circumference, which is the structural reason a rolled NiCr19NbMo ring outperforms a ring machined from plate in fatigue, regardless of identical chemistry and tensile results.

Machining

NiCr19NbMo machines badly by design: it is strong, it work-hardens rapidly under a rubbing tool, and its low thermal conductivity concentrates every bit of cutting heat at the tool edge instead of carrying it away in the chip. The practical rules follow directly from those three facts.

• Decide when to age. Rough machining in the solution treated condition and ageing afterwards is far easier on tooling, but the part will move during ageing and must have stock left for finishing. Machining fully aged material avoids the distortion but costs three to five times the cycle time. For close-tolerance parts, rough solution treated → age → finish machine is the usual compromise.
• Speeds. Roughly 10–25 m/min with coated carbide in the aged condition, 20–35 m/min solution treated. Ceramic and whisker-reinforced inserts run much faster but need rigid, uninterrupted setups.
• Heavy positive feed, never a light one. A feed of 0.15–0.35 mm/rev keeps the edge under the work-hardened layer from the previous pass. Light feeds rub, harden the surface and destroy the next insert.
• Never dwell. A tool that stops feeding while still in contact glazes the surface and work-hardens a layer the following pass has to cut through.
• Rigid setups and flood coolant, at high pressure where the machine allows. Replace inserts on a schedule rather than running them to failure; a broken edge in this material usually takes the surface with it.

Welding

This is where NiCr19NbMo earns its position. It welds by GTAW, GMAW, electron beam, laser and plasma processes, normally with matching filler to AMS 5832, and it does so without the strain-age cracking that plagues γ′-hardened superalloys. Best practice is to weld in the solution treated condition and then apply a full post-weld solution treatment followed by the complete double age, which restores uniform γ″ across parent metal, heat-affected zone and weld.

Welding fully aged material is possible but leaves an over-aged, softened heat-affected zone that will not recover without re-solutioning. Interpass temperature should be kept low, joints must be clean and free of sulfur, lead and copper contamination, and heavy restraint should be avoided. Laves phase in the fusion zone of thick sections is the usual metallurgical concern and is controlled by heat input and by the post-weld solution treatment.

Where Is NiCr19NbMo Used?

Every application below relies on the same combination: very high strength that survives to 650 °C, in a component that usually has to be welded, machined or both.

NiCr19NbMo 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. NiCr19NbMo is produced on the same equipment as the rest of our nickel and superalloy range, with the tighter temperature control that this grade requires.

Standards, Testing and Certification

NiCr19NbMo orders at Jiangyin Jiangnan Metal Co., Ltd. are produced and certified against the specifications below. The chemistry specification is normally ASTM B637 or AMS 5662/5663; the inspection document is normally EN 10204 3.1; and for oil and gas work API 6A718 governs both heat treatment and hardness.

• UNS N07718
• W.Nr. 2.4668
• AMS 5662
• AMS 5663
• AMS 5664
• AMS 5832 (filler)
• ASTM B637
• ASME SB-637
• API 6A718
• NACE MR0175 / ISO 15156-3
• VdTÜV 485
• GH4169
• EN 10204 3.1
• EN 10204 3.2
• EN 10228-3 (UT)
• SEP 1921 (UT)
• ASTM A388 (UT)
• ASTM E112 (grain size)
• ISO 9001:2015

What appears on the certificate

• Heat number, melting route and full ladle plus product chemical analysis
• Complete heat-treatment records: solution temperature, soak time, cooling method, both ageing steps, the controlled furnace-cool rate, and the furnace charts
• Mechanical test results (tensile, 0.2% proof, elongation, reduction of area, hardness) on coupons from the delivered heat, tested in the delivered condition
• Grain size to ASTM E112 and, where specified, δ phase assessment
• Ultrasonic examination report to the ordered standard and acceptance class
• Hardness survey against the API 6A718 or NACE MR0175 limit where sour service is specified
• Dimensional inspection report
• Cross-listed equivalent designations (NiCr19NbMo / 2.4668 / UNS N07718 / Alloy 718 / GH4169)

Quality gates and non-conformance handling

Every NiCr19NbMo order passes six mandatory hold points at which production cannot continue without QA sign-off: raw-material chemistry verification, forging temperature compliance, post-forging ultrasonic examination, heat-treatment chart approval, mechanical and hardness 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 NiCr19NbMo Forging Order

NiCr19NbMo carries one specification decision that most grades do not: the delivery condition changes the strength of the part by a factor of roughly two, and the grade name alone does not communicate it. The eight steps below remove the ambiguity that causes most disputes on this alloy.

Recommended drawing callout

Top 10 Mistakes When Ordering NiCr19NbMo Forgings

1. Writing "Alloy 718" and nothing else. The mill cannot tell whether you want soft, machinable material or fully aged 1,034 MPa material. Always add the specification and the delivery condition.
2. Ordering aerospace-aged material for sour service. AMS 5663 ageing lands at 38–44 HRC; NACE MR0175 normally caps N07718 at 40 HRC. Specify API 6A718 for H₂S duty instead.
3. Assuming the alloy is good above 650 °C. γ″ over-ages and transforms toward δ. No heat treatment recovers it. Above 650 °C continuous, evaluate Waspaloy or a cast grade.
4. Substituting 718 for 625 to "upgrade" corrosion resistance. It has roughly a third of the molybdenum. In chlorides it will pit where 625 would not.
5. Accepting a single-step ageing treatment. The controlled 56 °C/h furnace cool between 718 °C and 621 °C is what produces the correct γ″ distribution. Ask for the furnace chart.
6. Leaving grain size unspecified on fatigue-critical parts. Chemistry and tensile results can be identical across ASTM 3 and ASTM 8 material while fatigue life differs by a large factor. Specify ASTM E112 grain size and require it on the certificate.
7. Accepting parts machined from plate in place of forgings. Grain flow is a property. For rings under hoop stress, a rolled ring and a machined disc are not equivalent.
8. Not specifying the melting route. ESR is standard here; aerospace work usually requires VIM + VAR. If your specification demands double vacuum, say so at RFQ stage; it changes price and lead time materially.
9. Machining fully aged material without allowing for it. Cycle times run three to five times those of solution treated stock. Where tolerances permit, rough machine soft, age, then finish.
10. Welding aged material and skipping the re-solution treatment. The heat-affected zone stays over-aged and soft. Weld solution treated, then solution treat and double age the assembly.

Glossary

NiCr19NbMo

European short designation for the age-hardenable nickel-chromium-iron superalloy of material number 2.4668, equivalent to UNS N07718 and generically called Alloy 718.

Gamma double prime (γ″)

Body-centred tetragonal Ni₃Nb precipitate, the principal strengthening phase in this alloy. Its slow formation is what makes the grade weldable.

Gamma prime (γ′)

Face-centred cubic Ni₃(Al,Ti) precipitate. A secondary strengthener here, but the primary one in Waspaloy, Nimonic and X-750.

Delta (δ) phase

Equilibrium orthorhombic Ni₃Nb. Useful in controlled amounts for grain-size control during forging; harmful in excess because it consumes the niobium needed for γ″.

Laves phase

A brittle intermetallic that forms in niobium-rich interdendritic regions during solidification. Removed by homogenisation before forging; a common defect in poorly processed material.

Strain-age cracking

Cracking in the heat-affected zone of a weld caused by precipitation hardening occurring during cooling. The failure mode that NiCr19NbMo largely avoids.

Solution treatment

Heating to 954–1,010 °C (or 1,021–1,052 °C for creep-optimised practice) to dissolve precipitates into the austenitic matrix before ageing.

Double ageing

The two-step precipitation treatment: 718 °C for 8 hours, controlled furnace cool at 56 °C/h to 621 °C, hold to 18 hours total, air cool.

ESR

Electroslag remelting. Secondary melting that refines inclusion content and gives a directionally solidified ingot suited to superalloy forging.

VIM + VAR

Vacuum induction melting followed by vacuum arc remelting. This is the double-vacuum route required by most aerospace specifications.

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.

EN 10204 3.1 / 3.2

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

API 6A718

API specification for Alloy 718 in drilling and production equipment, with heat treatment and hardness controlled for sour service.

Frequently Asked Questions: NiCr19NbMo / 2.4668 / UNS N07718

Technical References

Chemistry, heat-treatment, mechanical and physical 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. AMS 5662, Nickel Alloy, Corrosion and Heat Resistant, Bars, Forgings and Rings, 52.5Ni-19Cr-3.0Mo-5.1Cb-0.90Ti-0.50Al-18Fe, Solution Heat Treated, Precipitation Hardenable, SAE International.
2. AMS 5663, Nickel Alloy, Corrosion and Heat Resistant, Bars, Forgings and Rings, Solution and Precipitation Heat Treated, SAE International.
3. AMS 5664, Nickel Alloy, Corrosion and Heat Resistant, Bars, Forgings and Rings, 1,900 °F Solution and Precipitation Heat Treated, SAE International.
4. AMS 5832, Nickel Alloy, Corrosion and Heat Resistant, Welding Wire, SAE International.
5. ASTM B637, Standard Specification for Precipitation-Hardening and Cold Worked Nickel Alloy Bars, Forgings, and Forging Stock for Moderate or High Temperature Service, ASTM International.
6. ASME SB-637, Specification for Precipitation-Hardening Nickel Alloy Bars, Forgings, and Forging Stock, ASME Boiler and Pressure Vessel Code, Section II Part B.
7. API Specification 6A718, Nickel Base Alloy 718 for Oil and Gas Drilling and Production Equipment, American Petroleum Institute.
8. ANSI/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.
9. EN 10204:2004, Metallic products - Types of inspection documents, CEN, Brussels.
10. EN 10228-3, Non-destructive testing of steel forgings, Part 3: Ultrasonic testing of ferritic or martensitic steel forgings, CEN.
11. SEP 1921, Ultrasonic testing of steel forgings, Stahl-Eisen-Prüfblatt.
12. ASTM A388, Standard Practice for Ultrasonic Examination of Steel Forgings, ASTM International.
13. ASTM E112, Standard Test Methods for Determining Average Grain Size, ASTM International.
14. ASTM E140, Standard Hardness Conversion Tables for Metals, ASTM International.
15. VdTÜV Werkstoffblatt 485, Nickel-Chrom-Eisen-Legierung NiCr19NbMo (2.4668), Verband der TÜV e.V.
16. ASM Handbook, Volume 4E: Heat Treating of Nonferrous Alloys, ASM International; sections on precipitation-hardening nickel alloys.
17. ASM Specialty Handbook: Nickel, Cobalt and Their Alloys, J.R. Davis (ed.), ASM International.
18. Donachie, M.J. and Donachie, S.J., Superalloys: A Technical Guide, 2nd edition, ASM International.
19. Reed, R.C., The Superalloys: Fundamentals and Applications, Cambridge University Press.
20. Proceedings of the International Symposium on Superalloys 718, 625, 706 and Derivatives, TMS; the standing reference series on γ″ and δ phase behaviour in this alloy family.

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

• 2.4668
• Inconel 625
• 2.4816 / Inconel 600
• Inconel 706
• Inconel 725
• Inconel X-750
• Waspaloy
• Incoloy 925
• Incoloy 945
• A286
• 17-4PH
• PH13-8Mo
• Seamless rolled rings
• Forged & rolled rings
• Forged disks
• Forged tubes
• Forged spindles
• Open die forgings

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). NiCr19NbMo / 2.4668 / UNS N07718 / Alloy 718 Forging Parts: Technical Datasheet and Manufacturing Guide. Jiangyin, Jiangsu, China. Retrieved from https://www.steelforgepieces.com/Nickel-Alloy/NiCr19NbMo.html. Last updated 23 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