Summary
NC15TnbA is the AFNOR designation for a precipitation-hardenable nickel-chromium superalloy containing a minimum of 70 % nickel and 14 to 17 % chromium, strengthened by titanium and aluminium additions that precipitate the gamma-prime phase during ageing. It is the same material as Inconel X-750, UNS N07750 and Werkstoff 2.4669. It carries the corrosion and oxidation resistance of Alloy 600 together with high tensile and creep-rupture strength, and it holds preload well over long periods at temperature. Service limit is approximately 700 °C (1300 °F). Typical uses are gas-turbine hardware, high-temperature springs and bolting, and nuclear reactor internals.
Jiangyin Jiangnan Metal Co., Ltd. forges NC15TnbA to customer drawings at its plant in Jiangyin, Jiangsu, China. Available shapes are listed in section 7.
- AFNOR
- NC15TnbA
- UNS / W.-Nr.
- N07750 / 2.4669
- Density
- 8.28 g/cm³
- UTS, aged
- ≥1103 MPa
- 0.2 % YS, aged
- ≥758 MPa
- Max service temp.
- ~700 °C
- Forging temp.
- 1040 °C
- Certification
- EN 10204 3.1 / 3.2
01What is NC15TnbA?
NC15TnbA is an age-hardening nickel-chromium alloy based on Alloy 600, with titanium, aluminium and niobium added. During ageing these additions precipitate a coherent gamma-prime (γ′) Ni3(Al,Ti) phase that pins dislocations and holds strength under sustained load. Useful tensile and creep-rupture strength is retained to about 700 °C. Lightly loaded parts remain serviceable to 980 °C. Toughness is maintained down to cryogenic temperatures.
The name follows the AFNOR convention: N for nickel, C15 for nominally 15 % chromium, TNbA for the titanium, niobium and aluminium additions. The designation appears mainly on French, EDF and European nuclear and turbine drawings. Buyers working from those drawings normally have to match it to Inconel X-750 or UNS N07750 before they can place an order.
Properties that drive the specification
| Property | Practical effect |
|---|---|
| Relaxation resistance | Loss of preload over long holds at temperature is small, which suits hot springs, spacer springs and heavily loaded fasteners. |
| Corrosion and oxidation resistance | The chromium level gives Alloy 600-class resistance in oxidising atmospheres and good resistance to chloride stress-corrosion cracking. |
| Wide usable temperature band | One heat-treat condition covers cryogenic through elevated-temperature service, which simplifies qualification. |
| Non-magnetic | Suitable for instrument hardware and reactor internals. |
Substitution warning. NC15TnbA and Inconel 718 are not interchangeable. Alloy 718 uses niobium-based γ″ strengthening and reaches higher room-temperature strength, but its strengthening phase coarsens faster under sustained load above 650 °C. NC15TnbA has no molybdenum and slightly less chromium, so it does not match 718 in reducing-acid service. Selection should be made on service temperature and environment as well as strength.
02Designation and standard equivalents
Most enquiries start with this cross-reference. All of the names below describe the same nickel-chromium superalloy. They differ only in the standards body that issued them.
| System / country | Designation | Notes |
|---|---|---|
| AFNOR, France | NC15TnbA (also written NC15TNbA) | The subject of this page |
| Trade name | Inconel X-750 / Alloy X-750 | Inconel is a Special Metals trademark. Alloy X-750 is the generic form. |
| UNS, USA | N07750 | The number to quote on ASTM and ASME orders |
| Werkstoff, Germany | 2.4669 | EN material number |
| EN / DIN name | NiCr15Fe7TiAl | Chemical-symbol name |
| ISO | NiCr15Fe7Ti2Al | |
| GB, China | GH4145 / GH145 | Chinese superalloy grade |
| JIS, Japan | NCF 750 | |
| BS, United Kingdom | HR 505 | |
| Equivalence is nominal. Trace-element limits, permitted melting routes and required heat-treat conditions vary between specifications. Confirm the governing document before substituting one designation for another. | ||
Product specifications for bar, forgings and rings
| Specification | Product form | Condition |
|---|---|---|
| ASTM B637 / ASME SB-637 | Bar, forgings, forging stock, rings | Precipitation-hardening nickel alloy for high-temperature service |
| AMS 5667 | Bar, rod, forgings, rings | Equalised and precipitation treated |
| AMS 5668 | Bar, rod, forgings, rings | Solution treated, stabilised and aged (triple treatment) |
| AMS 5669 | Bar, forgings | Annealed or solution treated only, for ageing after machining |
| AMS 5670 / 5671 / 5747 | Bar, rod, forgings | Solution treated plus furnace-cool precipitation treatments |
| AMS 5542 / AMS 5598 | Plate, sheet, strip | Precipitation treated |
| AMS 5698 / AMS 5699 | Wire, spring wire | |
| EN 10204 3.1 / 3.2 | All forms | Certification level, not a material specification |
03Chemical composition
Composition limits in weight percent, with nickel as the balance. These follow the ASTM B637 and AMS limits for UNS N07750.
| Element | Min | Max | Role |
|---|---|---|---|
| Nickel (Ni + Co) | 70.00 | bal. | Matrix |
| Chromium (Cr) | 14.00 | 17.00 | Oxidation and corrosion resistance |
| Iron (Fe) | 5.00 | 9.00 | Matrix, cost balance |
| Titanium (Ti) | 2.25 | 2.75 | Primary γ′ former |
| Aluminium (Al) | 0.40 | 1.00 | γ′ former |
| Niobium + tantalum (Nb+Ta) | 0.70 | 1.20 | Carbide and γ″ former |
| Manganese (Mn) | 1.00 | Residual | |
| Silicon (Si) | 0.50 | Residual | |
| Copper (Cu) | 0.50 | Residual | |
| Cobalt (Co) | 1.00 | Residual | |
| Carbon (C) | 0.08 | Grain-boundary carbides | |
| Sulphur (S) | 0.010 | Impurity, kept low for hot workability | |
| Phosphorus and other trace limits, where imposed, are set by the governing specification. Nuclear and aerospace orders frequently add tighter limits on S, P, Bi, Pb, Se and gas content. State these on the enquiry. | |||
Melting route
Cleanliness governs how the alloy behaves in a heavy forging, so the melting route forms part of the specification. Jiangyin Jiangnan Metal supplies NC15TnbA forgings from double or triple melted stock:
- EAF + AOD/VOD + ESR for valve, pump and pressure-equipment parts.
- VIM + ESR or VIM + VAR for aerospace, turbine and nuclear applications where gas content and inclusion ratings are controlled.
04Mechanical properties
Heat treatment sets the properties of NC15TnbA, not the grade name. The same chemistry can be delivered soft and machinable or fully hardened. The table below covers the common conditions for bar, ring and forged product.
| Condition | Tensile strength | 0.2 % yield | Elongation | Hardness |
|---|---|---|---|---|
| Equalised and aged AMS 5667 minima |
≥1103 MPa (160 ksi) |
≥758 MPa (110 ksi) |
≥20 % | 302–363 HBW |
| Solution, stabilise, age AMS 5668, typical |
1000–1100 MPa | 690–760 MPa | ≥20 % | 300–350 HBW |
| Solution treated only AMS 5669, typical |
790–900 MPa | 340–450 MPa | ≥30 % | ≤250 HBW |
| Values marked typical are for screening only. Acceptance is against the minima in the governing specification for the section size ordered. Heavier sections and transverse orientations run lower than longitudinal test bars. | ||||
Strength at temperature
Indicative tensile behaviour of equalised and aged material, for preliminary sizing.
| Test temperature | Tensile strength | 0.2 % yield |
|---|---|---|
| 20 °C | ~1170 MPa | ~810 MPa |
| 540 °C | ~1070 MPa | ~730 MPa |
| 650 °C | ~1000 MPa | ~720 MPa |
| 760 °C | ~740 MPa | ~650 MPa |
| 870 °C | ~400 MPa | ~340 MPa |
| Above roughly 700 °C the γ′ precipitate begins to over-age and much of the precipitation-hardening benefit is progressively lost. For sustained load above that point, design against creep-rupture data rather than short-term tensile values. | ||
05Physical properties
| Property | Metric | Imperial |
|---|---|---|
| Density | 8.28 g/cm³ | 0.299 lb/in³ |
| Melting range | 1393–1427 °C | 2540–2600 °F |
| Modulus of elasticity | 214 GPa | 31.0 ×10⁶ psi |
| Thermal expansion (20–100 °C) | 12.6 µm/m·K | 7.0 µin/in·°F |
| Thermal conductivity | 12.0 W/m·K | 83 Btu·in/h·ft²·°F |
| Specific heat | 431 J/kg·K | 0.103 Btu/lb·°F |
| Electrical resistivity | 1.22 µΩ·m | 733 Ω·circ mil/ft |
| Magnetic response | Non-magnetic in the annealed and aged conditions | |
06Forging practice and heat treatment
NC15TnbA is difficult to move hot. Below roughly 980 °C it resists deformation and can split, so heavy reduction is carried out around 1040 °C and the piece is returned to the furnace whenever it drops to that limit. Finishing passes in the 870–980 °C band refine grain size. Enough hot work has to go into the part for the subsequent ageing treatment to develop full properties.
Heat-treatment routes
| Route | Cycle | Application |
|---|---|---|
| Equalise and age AMS 5667 |
885 °C/24 h, air cool, then 704 °C/20 h, air cool | General high strength and notch-rupture ductility for service to about 590 °C |
| Triple treatment AMS 5668 |
1149 °C solution, then 843 °C/24 h AC, then 704 °C/20 h AC | Maximum creep, rupture and relaxation strength above 590 °C, used for hot springs and turbine hardware |
| Solution and furnace-cool age AMS 5670 |
982 °C solution, then 732 °C/8 h, furnace cool to 621 °C, hold to 18 h total, AC | Higher tensile properties with a shorter cycle, for service to about 590 °C |
| Solution only AMS 5669 |
Solution treat, air cool, no ageing | Parts with heavy machining to follow. Age harden after final machining. |
| Surfaces must be clean before heat treatment. Particles of aluminium or copper left on the part alloy rapidly at temperature and locally destroy corrosion resistance and mechanical properties. | ||
Machining and welding
Machining. Machinability is rated at roughly 15 % of free-machining steel. Rough machine in the solution-treated condition where the design allows. Use rigid setups, positive sharp geometry, heavy constant feed and generous coolant. Avoid dwelling, since the alloy work-hardens quickly.
Welding. The alloy is weldable, but the aluminium and titanium content makes it sensitive to strain-age cracking. Weld in the solution-treated condition, keep restraint to a minimum, apply intermediate stress-relief anneals on heavy sections, and age after welding. Alloy 718 filler is a common choice.
07NC15TnbA forged products
Jiangyin Jiangnan Metal Co., Ltd. forges NC15TnbA to drawing. Open-die forging is used for solid and stepped shapes, ring rolling where a seamless circumferential grain flow is required. Every item below is made to order and single pieces are accepted.
- Seamless rolled ringsOD 200–3000 mm
- Forged flangesWN, SO, BL, SW, LJ, orifice
- Forged shafts & step shaftsto 6000 mm long
- Forged round barsØ20–800 mm
- Forged discs & disksto 2000 mm dia.
- Forged sleeves & bushingshollow forged, bored
- Forged tube sheetsto drawing
- Forged hollow bars & tubestrepanned or mandrel forged
- Forged blocks & blanksrectangular, stepped
- Valve bodies & bonnetsball, gate, globe, check
- Valve stems & seat ringsbar or near-net forged
- Forged nozzles & couplingsset-in, set-on
- Gear & pinion blanksrough-turned to drawing
| Item | Standard offering |
|---|---|
| Minimum order | 1 piece. Prototypes and single spares accepted. |
| Surface condition | As-forged, shot blasted, rough machined, or machined to finished drawing |
| Machining allowance | Per drawing, or standard forging tolerance to the applicable class |
| Marking | Heat number, grade, specification and purchase order number, hard stamped or vibro-etched |
| Documentation | Material test certificate to EN 10204 3.1 (3.2 on request), UT report, dimensional report, heat-treatment chart |
| Typical lead time | 25 to 45 days from drawing approval, subject to raw material availability |
| Packing | Fumigation-free plywood cases or steel pallets, marked for sea or air freight |
08Applications by industry
Common end uses for NC15TnbA forgings and the shapes usually specified.
| Industry | Components | Reason for selection |
|---|---|---|
| Gas turbines & aero engines | Casing rings, seal rings, bolting, blade retention hardware, thrust reverser and hot-air ducting parts | Creep-rupture strength and preload retention at temperature |
| Nuclear power | Reactor internals, spacer springs, fuel assembly hold-down springs, bolting, seal components | Relaxation resistance and resistance to chloride SCC in high-purity water |
| Oil, gas & subsea | Valve bodies, stems, seat rings, wellhead and Christmas-tree components, deepwater production hardware | Strength combined with corrosion resistance in sour and marine service |
| Pressure equipment | Flanges, tube sheets, forged nozzles, shell and tube heat-exchanger parts, air receivers | Elevated-temperature strength with code-acceptable material |
| Rotating equipment | Shafts, spindles, discs, sleeves, gear and pinion blanks, compressor hardware | Fatigue strength and dimensional stability at temperature |
| Chemical process | Pump shafts, plunger-pump parts, column and tower internals, preheater hardware, crystalliser components | Oxidation resistance with high strength |
| Springs & fasteners | Hot springs, Belleville washers, high-temperature studs and nuts | Minimal load loss over long holds at temperature |
| Tooling | Extrusion dies, forming tools, heat-treating fixtures, hot test-machine grips | Hot hardness and thermal fatigue resistance |
09Testing, inspection and certification
Test scope is agreed on the order. The list below covers what Jiangyin Jiangnan Metal Co., Ltd. routinely performs on NC15TnbA forgings.
| Test | Standard | Notes |
|---|---|---|
| Chemical analysis | Spectrometer or wet analysis | Ladle analysis, product analysis on request |
| Ultrasonic testing | EN 10228-3, SEP 1921, ASTM A388 | Acceptance class stated on the order |
| Liquid penetrant | ASTM E165, EN ISO 3452 | Surface indications on machined faces |
| Tensile test | ASTM E8/E8M, EN ISO 6892-1 | Room and elevated temperature |
| Impact test | ASTM E23, EN ISO 148-1 | Where required by the specification |
| Hardness | ASTM E10 / E18 | Brinell or Rockwell as specified |
| Stress-rupture test | ASTM E139 | Required by some AMS conditions |
| Grain size & microstructure | ASTM E112 | On request |
| Intergranular corrosion | ASTM G28, ASTM A262 as applicable | On request |
| Dimensional inspection | Drawing, or ASME B16.5 for flanges | Report issued with the shipment |
| Certification | EN 10204 3.1 standard, 3.2 on request | Third-party witness by TUV, BV, SGS, DNV or Lloyd’s Register |
10How to request a quotation
Send the items below to sales@steelforgepieces.com. A priced offer normally follows within one working day. A drawing or sketch is enough to open the enquiry.
- Shape and size. Drawing, sketch or plain dimensions covering OD, ID, thickness and length, and whether the price is for as-forged or machined.
- Grade and specification. NC15TnbA, or the equivalent you work to: Inconel X-750, UNS N07750, 2.4669, GH4145. State the governing document, for example ASTM B637 or AMS 5667.
- Heat-treat condition. Equalised and aged, triple treated, or solution treated only. This drives both properties and price.
- Quantity and delivery date, including whether repeat orders are expected.
- Testing and certification. UT class, EN 10204 3.1 or 3.2, any third-party witness, any customer-specific approval.
- Service conditions. Temperature, pressure and medium. Optional, but it allows a material mismatch to be flagged before the order is placed.
11Frequently asked questions
What is NC15TnbA?
NC15TnbA is the AFNOR designation for a precipitation-hardenable nickel-chromium superalloy containing a minimum of 70 % nickel, 14 to 17 % chromium, 5 to 9 % iron, plus titanium and aluminium additions that form the strengthening gamma-prime phase. It is the same material as Inconel X-750, UNS N07750 and Werkstoff 2.4669. It is used where high strength, relaxation resistance and oxidation resistance are required up to approximately 700 °C (1300 °F).
Is NC15TnbA the same as Inconel X-750?
Yes. They describe the same alloy under different national systems. NC15TnbA is AFNOR, Inconel X-750 is the Special Metals trade name, UNS N07750 is the North American number, 2.4669 and NiCr15Fe7TiAl are German, GH4145 is the Chinese GB grade, NCF 750 is Japanese JIS.
When ordering, state the governing specification and the heat-treat condition, for example ASTM B637 UNS N07750, AMS 5667 condition. The designation on its own does not fix the mechanical properties.
Who manufactures NC15TnbA forged rings and flanges?
Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, manufactures NC15TnbA seamless rolled rings, forged flanges, shafts, discs, sleeves, bushings and tube sheets to customer drawings. Enquiries go to sales@steelforgepieces.com or +86 189 2135 9659.
What is the chemical composition of NC15TnbA?
In weight percent: carbon 0.08 max, manganese 1.00 max, silicon 0.50 max, sulphur 0.010 max, chromium 14.0 to 17.0, nickel 70.0 min, iron 5.0 to 9.0, titanium 2.25 to 2.75, aluminium 0.40 to 1.00, niobium plus tantalum 0.70 to 1.20, copper 0.50 max, cobalt 1.00 max. Full limits are in Table 4. Confirm against your purchase specification, because AMS, ASTM B637 and EN documents differ slightly on trace elements.
What are the mechanical properties of NC15TnbA?
In the equalised and aged condition to AMS 5667 the minima are 1103 MPa (160 ksi) tensile strength, 758 MPa (110 ksi) 0.2 % yield strength, 20 % elongation and 302 to 363 HBW hardness. Triple heat treated material to AMS 5668 typically gives 1000 to 1100 MPa tensile and 690 to 760 MPa yield. Solution treated material to AMS 5669 typically gives 790 to 900 MPa tensile, 340 to 450 MPa yield and 30 % or more elongation. Full tables are in section 4. Acceptance is against the minima in the governing specification for the section size ordered.
What are the physical properties of NC15TnbA?
Density is 8.28 g/cm³ (0.299 lb/in³). Melting range is 1393–1427 °C. Modulus of elasticity is approximately 214 GPa. Coefficient of thermal expansion between 20 and 100 °C is 12.6 µm/m·K. Thermal conductivity is 12.0 W/m·K, specific heat 431 J/kg·K and electrical resistivity 1.22 µΩ·m. The alloy is non-magnetic in the annealed and aged conditions. See section 5.
What heat treatment is used for NC15TnbA forgings?
Three routes are in common use. For service below about 590 °C, equalise at 885 °C for 24 h, air cool, then age at 704 °C for 20 h (AMS 5667). For maximum creep and relaxation strength above that, solution treat at 1149 °C, stabilise at 843 °C for 24 h, then age at 704 °C for 20 h (AMS 5668). Parts facing heavy machining are supplied solution treated only and aged afterwards. Full cycles are in Table 8.
What forged shapes can be produced in NC15TnbA?
Seamless rolled rings, forged flanges, shafts and step shafts, round bars, discs and disks, hollow bars, sleeves, bushings, tube sheets, forged nozzles, valve bodies, valve stems, seat rings, blocks and forged blanks to drawing. Ring rolling is used where a seamless circumferential grain flow is required. Open-die forging covers the remaining shapes.
How is NC15TnbA forged?
Heavy reduction is carried out at about 1040 °C. Below roughly 980 °C the alloy becomes stiff and prone to splitting, so the piece is reheated whenever it cools to that level. Finishing passes in the 870–980 °C range refine grain size. Sufficient hot work must be put into the part for ageing to develop full properties.
Which standards cover NC15TnbA forgings?
Bar, forgings, forging stock and rings are covered by ASTM B637 and ASME SB-637. The SAE AMS specifications are AMS 5667 (equalised and precipitation treated), AMS 5668 (solution treated, stabilised and aged), AMS 5669 (annealed or solution treated only), and AMS 5670, 5671 and 5747 (solution treated plus furnace-cool precipitation treatments). Plate, sheet and strip are covered by AMS 5542 and AMS 5598, wire by AMS 5698 and AMS 5699. EN 10204 3.1 and 3.2 are certification levels rather than material specifications. Full list in Table 3.
Can NC15TnbA be replaced by Inconel 718?
Not as a drop-in substitution. Inconel 718 has higher room-temperature strength and contains molybdenum for better resistance in reducing environments. Its γ″ strengthening phase is less stable under sustained load above about 650 °C, where NC15TnbA has the better relaxation resistance. Spring and bolting applications generally depend on that property. Any substitution requires engineering approval.
What certification is supplied with NC15TnbA forgings?
Material test certificates to EN 10204 3.1 as standard, and EN 10204 3.2 witnessed by a third party such as TUV, BV, SGS, DNV or Lloyd’s Register on request. Ultrasonic testing is performed to EN 10228-3, SEP 1921 or ASTM A388 at the acceptance class stated on the order.
Do you accept single-piece and prototype orders?
Yes. There is no minimum order quantity on NC15TnbA forgings. Single spares and prototypes are quoted the same way as production batches. Send a drawing or dimensions to sales@steelforgepieces.com.
12Related nickel alloy forgings
Grades most often compared with or specified alongside NC15TnbA:
Forged shapes across every grade: forging pieces, forged valve stems and the full product range.
SUPPLIERAbout the manufacturer
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Jiangyin, Jiangsu Province, China. The plant produces forged rings, seamless rolled rings, flanges, shafts, discs, sleeves, bushings and tube sheets in carbon steel, alloy steel, tool steel, stainless steel and nickel-based superalloys, including NC15TnbA / Inconel X-750 (UNS N07750). Work is made to customer drawings and supplied worldwide with EN 10204 3.1 or 3.2 certification.
This datasheet is maintained by the company’s engineering and sales team. Property values are compiled from published specifications for UNS N07750 and are given for guidance. Acceptance is always against the specification named on the purchase order.
- Company
- Jiangyin Jiangnan Metal Co., Ltd.
- Address
- No.1 Chengxiqiao Road,
Zhouzhuang Town, Jiangyin City,
Jiangsu Province 214423, China - Telephone
- +86 189 2135 9659
- Website
- steelforgepieces.com
- Business
- Open-die forging & ring rolling
Document control
Document: NC15TnbA (Inconel X-750 / UNS N07750) Forgings, Composition, Properties and Product Range.
Issued by: Jiangyin Jiangnan Metal Co., Ltd., Jiangyin, Jiangsu, China.
First issued 18 June 2015. Revision date 22 August 2026.
Reference: https://www.steelforgepieces.com/Nickel-Alloy/NC15TnbA.html
Reviewed 22 August 2026 by the engineering team at Jiangyin Jiangnan Metal Co., Ltd. Reuse of the tables is permitted with attribution and a link to this page.
13Sources and further reading
Property data on this page is compiled from the following public specifications and producer datasheets for UNS N07750 and W.-Nr. 2.4669:
- ASTM B637 / ASME SB-637, precipitation-hardening and cold-worked nickel alloy bars, forgings and forging stock for high-temperature service.
- SAE AMS 5667, 5668, 5669, 5670, 5671 and 5747, Alloy X-750 bar, rod, forgings and rings in the respective heat-treated conditions.
- EN 10204, metallic products, types of inspection documents.
- EN 10228-3, SEP 1921 and ASTM A388, ultrasonic testing of forgings.
- Producer datasheets for Alloy X-750 published by Special Metals, VDM Metals and Carpenter Technology.
Inconel® is a registered trademark of Special Metals Corporation, used here only to identify the equivalent alloy. Jiangyin Jiangnan Metal Co., Ltd. is not affiliated with, endorsed by, or a licensee of Special Metals Corporation.