Low-expansion superalloy forgings
Inconel 783 Forgings UNS R30783 · Alloy 783 · GH783 · AMS 5940
Inconel 783 is an oxidation-resistant, low thermal expansion nickel-cobalt-iron superalloy with aluminium, chromium and niobium additions, used for clearance-control parts in gas and steam turbines. Jiangyin Jiangnan Metal Co., Ltd. forges it into seamless rolled rings, discs, shafts, bars and turbine seal rings at its open-die plant in Jiangyin, Jiangsu, China.
- UNS
- R30783
- Billet spec
- AMS 5940
- Density
- 7.81g/cm³ · 0.282 lb/in³
- CTE @93 °C
- 10.08µm/m·°C · 5.60 µin/in·°F
- Tensile
- 1194MPa · 173 ksi
- Service temp
- 704°C max · 1300 °F
What is Inconel 783?
Inconel 783 (UNS R30783) is a three-phase, age-hardenable nickel-cobalt-iron superalloy of nominal composition Ni-34Co-26Fe-5.4Al-3Nb-3Cr. Ni3Al-type gamma prime and NiAl-type beta phases provide the strengthening. Its coefficient of thermal expansion runs about 20 % below Inconel 718 while oxidation resistance stays close to it.
Special Metals Corporation developed the alloy under U.S. Patent 5,478,417. It answers a conflict between two design requirements. Low-expansion alloys built on nickel, iron and cobalt need very little chromium, because chromium lowers the Curie temperature and pushes the expansion rate up across the working range. Cutting chromium, though, removes the usual oxidation defence and leaves the material open to stress-accelerated grain boundary oxidation (SAGBO). Alloy 783 works around this with a high aluminium content that forms a protective alumina scale and precipitates a beta aluminide phase alongside gamma prime. The alloy therefore holds close clearances without giving up surface stability.
Design advantages
- Dimensional stability under heat. Low CTE keeps seals, shrouds and casings at their running clearance through thermal cycles, which protects stage efficiency.
- Oxidation resistance demonstrated in cyclic testing at and beyond 704 °C (1300 °F), which is unusual for an alloy in this expansion class.
- SAGBO resistance comparable to Inconel 718 and well ahead of Incoloy 909.
- Density about 5 % below Inconel 718, which matters on rotating and flight hardware.
- Useful strength to about 704 °C (1300 °F) in the age-hardened condition.
The low-expansion advantage
Thermal expansion is the property this alloy was built around. The bars below compare mean coefficient of thermal expansion at the low end of the working range.
Coefficient of thermal expansion, relative
The Inconel 783 figure is measured at 93 °C (200 °F). The Inconel 718 bar is relative, based on the published statement by Special Metals that alloy 783 expands roughly 20 % less than alloy 718. Incoloy 909 expands less again, but its oxidation and SAGBO resistance are much weaker, and that gap is what alloy 783 was developed to close.
Low expansion in this alloy family is a magnetic effect. It holds while the material stays ferromagnetic and falls away above the Curie temperature. Chromium is restricted to 2.5–3.5 % for that reason. Expect Inconel 783 to be magnetic at room temperature.
Inconel 783 chemical composition
Inconel 783 contains 26–30 % nickel, 24–27 % iron, 5.0–6.0 % aluminium, 2.5–3.5 % chromium and 2.5–3.5 % niobium, with cobalt making up the balance at approximately 34 %.
| Element | Content (%) |
|---|---|
| Cobalt, Co | Balance (≈ 34) |
| Nickel, Ni | 26.0 – 30.0 |
| Iron, Fe | 24.0 – 27.0 |
| Aluminium, Al | 5.0 – 6.0 |
| Chromium, Cr | 2.5 – 3.5 |
| Niobium, Nb | 2.5 – 3.5 |
| Titanium, Ti | 0.10 – 0.40 |
| Boron, B | 0.003 – 0.012 |
| Copper, Cu | 0.50 max |
| Manganese, Mn | 0.50 max |
| Silicon, Si | 0.50 max |
| Carbon, C | 0.03 max |
| Phosphorus, P | 0.015 max |
| Sulfur, S | 0.005 max |
Chromium is deliberately low. In most Inconel grades chromium provides the oxidation defence; here that job passes to aluminium so the expansion coefficient can stay down. Certified heat analysis accompanies every forging on an EN 10204 3.1 material test report.
Mechanical, physical and thermal properties
Values below are for the age-hardened condition at room temperature unless stated otherwise.
| Property | Metric | Imperial |
|---|---|---|
| Tensile strength | 1194 MPa | 173 ksi |
| Yield strength (0.2 % offset) | 779 MPa | 113 ksi |
| Elongation at break | 24 % | 24 % |
| Elastic modulus | 177.3 GPa | 25,720 ksi |
| Poisson’s ratio | 0.31 | 0.31 |
| Property | Metric | Imperial |
|---|---|---|
| Density | 7.81 g/cm³ | 0.282 lb/in³ |
| Melting range | 1336 – 1407 °C | 2437 – 2565 °F |
| Property | Metric | Imperial |
|---|---|---|
| Coefficient of thermal expansion (at 93 °C / 200 °F) | 10.08 µm/m·°C | 5.60 µin/in·°F |
| Thermal conductivity (at 21 °C / 70 °F) | 10.1 W/m·°C | 70 BTU·in/hr·ft²·°F |
Published values are typical and intended for design guidance. Acceptance properties for a given forging depend on the applicable specification, section size and heat treatment, and are reported on the certified test report issued with the order.
Forging and heat treatment of Inconel 783
Inconel 783 is hot worked between 927 °C and 1121 °C (1700–2050 °F). The standard heat treatment runs in three stages: solution anneal at 1121 °C for 1 hour, beta age at 845 °C for 4 hours, then age harden at 718 °C for 8 hours with a controlled furnace cool to 621 °C for a further 8 hours.
| Stage | Temperature | Time and cooling |
|---|---|---|
| Hot working range | 927 – 1121 °C 1700 – 2050 °F | Reheat as required to stay in range |
| Solution anneal | 1121 °C / 2050 °F | 1 hour, air cool |
| Beta age | 845 °C / 1550 °F | 4 hours, air cool to room temperature |
| Age harden, stage 1 | 718 °C / 1325 °F | 8 hours, then furnace cool at 55 °C (100 °F) per hour |
| Age harden, stage 2 | 621 °C / 1150 °F | 8 hours, air cool |
Forging notes
- The working window is narrow. Finishing below 927 °C risks cracking, and long soaks near 1121 °C coarsen the grain. Reheat between operations instead of pushing a heat.
- Beta aging is not optional. Skipping the 845 °C stage costs the beta aluminide precipitation that carries the SAGBO resistance.
- The furnace cool between aging stages runs at a specified rate. Cooling faster changes the gamma prime distribution and the strength that comes with it.
- Allow for movement during the long aging cycle. Rough machine before final age where the geometry permits.
Applications and forged product forms
Inconel 783 is used for containment and clearance-control hardware in aircraft gas turbines, and for bolting and static parts in steam turbines, where a low expansion rate keeps assemblies dimensionally predictable through thermal cycling.
Seamless rolled rings
Turbine seal rings, compressor casings, shroud rings and spacer rings, the highest-volume Inconel 783 form.
Discs, blocks and plates
Forged discs and blanks for turbine wheels, blisks and impellers; sawn blocks and forged plate for machined structures.
Round, square and flat bars
Machining stock, turbine blade and vane blanks, and forged flats for brackets and mounting hardware.
Hollow bars, sleeves and bushings
Trepanned hollows, cylinders, barrels, casings, hubs and housings, cutting machining time on tubular parts.
Valve spindles and stems
Gas and steam turbine valve spindles, stems and long shafts where straightness must survive thermal cycling.
Near-net custom forgings
Stepped shafts, flanges and shaped forgings produced to drawing, lowering the buy-to-fly ratio on expensive alloy.
Inconel 783 forgings from Jiangyin Jiangnan Metal
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, producing Inconel 783 (UNS R30783) seamless rolled rings, discs, bars, hollow sections and custom forged parts to customer drawing and specification, with certified material test reports to EN 10204 3.1.
Jiangyin lies in the Yangtze River Delta forging cluster, about two hours from the ports of Shanghai and Zhangjiagang, which keeps export lead times short for buyers in Europe, North America and the Middle East. Jiangyin Jiangnan Metal works from customer drawings and specifications rather than a fixed catalogue, and takes prototype and qualification quantities alongside production runs.
Supply scope for Inconel 783
- Forms: seamless rolled rings, discs, blocks, plates, round bars, square and flat bars, hollow bars, sleeves, bushings, shafts, spindles, stems, and custom open-die shapes.
- Specification: forging billet to SAE AMS 5940, or to the customer’s own material and process specification.
- Documentation: EN 10204 3.1 material test report with heat analysis, mechanical test results and heat treatment record.
- Testing: chemical analysis, tensile and hardness testing, ultrasonic inspection and dimensional report available on request.
- Condition: supplied as-forged, rough machined, solution treated, or fully heat treated to the standard three-stage cycle.
Requesting a quotation
Send a drawing or a description of the part, the quantity, the specification you need it certified to, and the delivery condition. A quotation with lead time normally follows within one working day.
Frequently asked questions about Inconel 783
What is the UNS number for Inconel 783?
The UNS number for Inconel 783 is R30783. The alloy is also referred to as Alloy 783, Nickel Alloy 783 and, in Chinese standards, GH783 or GH6783. All of these designations refer to the same nickel-cobalt-iron low-expansion superalloy.
What specification covers Inconel 783 forging billet?
SAE AMS 5940 covers Inconel 783 forging billet. Special Metals supplies the alloy as forging billet to AMS 5940, together with rod and bar for machining, extruded section and wire rod. Many aerospace buyers also impose their own company material specification on top of AMS 5940, and Jiangyin Jiangnan Metal can forge and certify to either.
Inconel 783 or Inconel 718: which should I specify?
Choose based on which failure mode you are designing against.
Specify Inconel 783 when dimensional stability is the constraint, such as seal rings, shrouds, casings and clearance-control hardware. Its coefficient of thermal expansion is around 20 % lower than Inconel 718 and its density is about 5 % lower.
Specify Inconel 718 when you need maximum absolute strength at temperature and expansion is not the governing concern. Inconel 718 is also far more widely stocked and generally cheaper per kilogram.
The two alloys have comparable SAGBO resistance, so that is not usually the deciding factor between them.
What is the maximum service temperature of Inconel 783?
Inconel 783 retains much of its strength up to approximately 704 °C (1300 °F) in the age-hardened condition, and cyclic testing has demonstrated oxidation resistance at and beyond that temperature. Above this range the alloy loses the strength advantage that justifies its cost.
Why does Inconel 783 have such low chromium?
Chromium lowers the Curie temperature of nickel-iron-cobalt alloys, and because the low expansion behaviour of this family is a magnetic effect, a lower Curie temperature means the expansion rate rises across a wider temperature range. Chromium is therefore held to 2.5–3.5 % to preserve low expansion. Oxidation protection comes instead from the high aluminium content, which forms a protective alumina scale and precipitates the beta aluminide phase that resists stress-accelerated grain boundary oxidation.
Is Inconel 783 magnetic?
Yes. Inconel 783 is ferromagnetic at room temperature. This is inherent to how the alloy works, since the low thermal expansion of nickel-iron-cobalt alloys depends on the material remaining ferromagnetic, and expansion increases once the Curie temperature is exceeded. Plan magnetic-particle inspection and any magnetic-sensitive assembly accordingly.
What temperature range is used to forge Inconel 783?
Inconel 783 is hot worked between 927 °C and 1121 °C (1700–2050 °F). The window is narrow, so reheating between forging operations is normal practice.
Can Inconel 783 be welded?
Yes. Inconel 783 can be joined using standard nickel-alloy welding practice, with a post-weld heat treatment applied where the specification requires it. Because the alloy relies on a precisely controlled three-stage aging cycle for its properties, any welding on a finished forging should be agreed with the design authority and followed by the appropriate re-heat-treatment.
Who supplies Inconel 783 forgings in China?
Jiangyin Jiangnan Metal Co., Ltd. supplies Inconel 783 (UNS R30783) open-die forgings from its factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. Product forms include seamless rolled rings, discs, bars, hollow sections, turbine seal rings and custom forged parts made to drawing. Enquiries: sales@steelforgepieces.com or +86 189 2135 9659.
What is the minimum order quantity for Inconel 783 forgings?
Jiangyin Jiangnan Metal accepts single-piece prototype and qualification orders as well as production quantities. Inconel 783 is normally forged to order from billet rather than pulled from stock, so the practical constraint is billet availability and heat size rather than a fixed piece count. Send the drawing and the quantity together and both can be confirmed in the quotation.