Alloy 706 (UNS N09706) Forgings: Rings, Discs, Shafts and Flanges
Alloy 706 (UNS N09706) is a nickel-iron-chromium precipitation-hardenable superalloy. The nominal chemistry is 41 % nickel, 16 % chromium, 2.9 % niobium plus tantalum and 1.75 % titanium, with iron as the balance, and it holds high strength from cryogenic temperatures up to about 650 °C (1200 °F). Alloy 706 is the leaner, molybdenum-free relative of Alloy 718. It segregates less during ingot solidification, so it can be cast as very large sound ingots and forged into the biggest gas-turbine discs and shafts made from any wrought superalloy. It also machines faster than Alloy 718 and resists post-weld strain-age cracking.
Jiangyin Jiangnan Metal Co., Ltd. is an independent open-die forging factory in Jiangyin, Jiangsu, China that manufactures Alloy 706 / UNS N09706 forgings to customer drawings: seamless rolled rings, turbine and compressor discs, stepped shafts, flanges, sleeves, bushings, tube sheets and round bars. We supply material solution-annealed or fully aged to either the three-step creep-optimised cycle or the two-step tensile-optimised cycle, with ultrasonic examination to ASTM A388, EN 10228-3 or SEP 1921 and EN 10204 3.1 certification as standard (3.2 third-party witness on request). Contact: sales@steelforgepieces.com · 0086-189-2135-9659.
- UNS
- N09706
- Density (aged)
- 8.08 g/cm³
- Max service
- ~650 °C
- Melting range
- 1338–1371 °C
- Aged UTS (typ.)
- 1170–1345 MPa
- Modulus
- 210 GPa
- Hot working
- 870–1150 °C
- Magnetic
- No μr ≈ 1.01
What Forged Products Are Available in Alloy 706 / UNS N09706?
Jiangyin Jiangnan Metal Co., Ltd. produces Alloy 706 forgings by three routes, chosen by geometry and section size. Open-die forging covers shafts, blocks, discs and stepped rounds. Seamless ring rolling produces Alloy 706 forged rings and contoured rolled rings, and is the usual route for turbine casings, spacer rings and flange blanks. Upset forging is used for short, large-cross-section discs and hubs where the grain flow must run radially. Near-net-shape profiling is used where the die geometry can take out 30 to 50 % of the rough machining stock. On a superalloy that saving is worth chasing harder than it would be on steel, because the billet cost per kilogram is several times higher.
- Seamless rolled rings
- Gas-turbine discs
- Compressor discs & spacers
- Forged shafts & spindles
- Turbine cases
- Forged flanges
- Forged sleeves & bushings
- Tube sheets
- Forged tubes & pipes
- Round bars & forging stock
- Valve stems, seats & bodies
- Fasteners & studs
- Nozzles
- Custom near-net forgings
What Is Alloy 706 (UNS N09706)?
Alloy 706 is a nickel-iron-chromium precipitation-hardenable superalloy, designated UNS N09706, developed as a more fabricable derivative of Alloy 718. Its nominal chemistry is 41 % Ni, 16 % Cr, 2.9 % Nb+Ta, 1.75 % Ti, balance Fe, and it is strengthened by ageing rather than by cold work or martensite transformation.
Strengthening comes from precipitates that form during ageing in the 595 to 760 °C range. γ″ (gamma double prime, Ni₃Nb), which is body-centred tetragonal, supplies most of the strength. γ′ (gamma prime, Ni₃(Ti,Al)), face-centred cubic, adds a second contribution and dominates when only the two-step cycle is used. A grain-boundary η phase (Ni₃Ti) forms during the 845 °C stabilisation step, and that is what gives the three-step cycle its better creep and stress-rupture life. None of these phases can be resolved by optical microscopy. Transmission electron microscopy is needed to see them.
Three properties keep Alloy 706 in production as a separate grade instead of it being displaced by Alloy 718.
1 · Very large sound ingots
Removing molybdenum and cutting niobium from about 5 % to 2.9 % sharply reduces the tendency to form freckles and other macro-segregation defects during vacuum arc remelting. Ingots and forgings far larger than are practical in Alloy 718 can be made with a structure clean enough to pass ultrasonic inspection. That is exactly the requirement a heavy-duty land-based gas-turbine wheel has to meet.
2 · Machinability
Alloy 706 accepts higher cutting speeds and gives longer tool life than Alloy 718 and most other age-hardenable superalloys, and can be cut in either the annealed or the aged condition. On a large disc with many hours of turning and drilling, that difference is a significant share of the finished part cost.
3 · Weldability
The precipitation reaction in Alloy 706 is deliberately sluggish. Residual welding stress relaxes before hardening begins, so the alloy resists post-weld strain-age cracking. That failure mode limits welded repair and fabrication in many γ′-strengthened alloys.
Where it stops
Temperature and corrosion are where it gives ground. With no molybdenum, Alloy 706 has less solid-solution strengthening and less resistance to reducing acids and pitting than Alloy 718. Above roughly 650 °C the precipitates coarsen and strength falls away.
What Are the Equivalent Designations for Alloy 706?
Engineers searching for any of the names below are referring to the same chemistry. Jiangyin Jiangnan Metal Co., Ltd. accepts purchase orders under all of them and issues a material certificate listing every designation the heat satisfies.
| Body / region | Designation | Notes |
|---|---|---|
| USA · UNS | N09706 | Generic Unified Numbering System designation, and the safest way to specify |
| USA · trade name | Inconel® 706 | Registered trademark of Special Metals Corporation. We do not sell under this name |
| USA · common usage | Alloy 706, ALLOY706, IN-706, IN706 | Generic industry shorthand used on drawings and RFQs |
| USA · SAE/AMS | AMS 5701, AMS 5702, AMS 5703 | Aerospace bars, forgings, rings and forging stock; differ in heat-treatment condition supplied |
| USA · ASTM | ASTM B637 | Precipitation-hardenable nickel alloy bars, forgings and forging stock for high-temperature service |
| USA · ASTM | ASTM B564 | Nickel alloy forgings, often cited for flanges and pressure parts |
| USA · ASME | ASME SB-637 | ASME Boiler & Pressure Vessel Code adoption of B637 |
| China · GB / YB | GH2706, GH4706, GH706 | Chinese superalloy designations; GH4706 is the form most used in current Chinese literature |
| Europe | No widely adopted EN grade name | Ordered against UNS N09706 or the AMS specifications. Some suppliers quote W.-Nr. 2.4615; confirm it against the mill certificate before relying on it |
What Is the Chemical Composition of Alloy 706?
Alloy 706 (UNS N09706) contains 39.0–44.0 % nickel plus cobalt, 14.5–17.5 % chromium, 2.50–3.30 % niobium plus tantalum and 1.50–2.00 % titanium, with iron as the balance. The limits below are per AMS 5701/5702/5703 and ASTM B637 and are the values we procure remelted billet against.
| Element | Min | Max | Role in the alloy |
|---|---|---|---|
| Nickel + Cobalt (Ni+Co) | 39.00 | 44.00 | Austenitic matrix; hosts the γ′ and γ″ precipitates |
| Chromium (Cr) | 14.50 | 17.50 | Oxidation and corrosion resistance |
| Iron (Fe) | Balance | Matrix; lowers cost and segregation vs a higher-nickel base | |
| Niobium + Tantalum (Nb+Ta) | 2.50 | 3.30 | Primary hardener, forms γ″ Ni₃Nb |
| Titanium (Ti) | 1.50 | 2.00 | Secondary hardener, forms γ′ and grain-boundary η Ni₃Ti |
| Aluminium (Al) | — | 0.40 | Contributes to γ′; deoxidiser |
| Cobalt (Co) | — | 1.00 | Incidental; counted within the Ni+Co range |
| Copper (Cu) | — | 0.30 | Residual |
| Manganese (Mn) | — | 0.35 | Deoxidiser |
| Silicon (Si) | — | 0.35 | Deoxidiser |
| Carbon (C) | — | 0.06 | Carbide former; kept low for toughness and weldability |
| Phosphorus (P) | — | 0.020 | Impurity |
| Sulfur (S) | — | 0.015 | Impurity, controlled for hot workability |
| Boron (B) | — | 0.006 | Grain-boundary strengthening; improves creep life |
What Are the Physical Properties of Alloy 706?
| Property | Metric | Imperial | Condition |
|---|---|---|---|
| Density | 8.08 g/cm³ | 0.2920 lb/in³ | Age-hardened |
| Density | 8.05 g/cm³ | 0.2910 lb/in³ | Annealed |
| Melting range | 1338–1371 °C | 2440–2500 °F | Solidus – liquidus |
| Modulus of elasticity (E) | 210 GPa | 30.4 × 10³ ksi | Room temperature |
| Poisson's ratio | 0.38 | 0.38 | Room temperature (per CarTech data) |
| Thermal conductivity | ≈ 12.5 W/m·K | 87 BTU·in/hr·ft²·°F | Room temperature |
| Specific heat | ≈ 444 J/kg·K | 0.106 Btu/lb·°F | Mean |
| Electrical resistivity | ≈ 0.98 µΩ·m | 592 Ω·cmil/ft | Room temperature |
| Mean CTE, 25–93 °C | 13.3 × 10⁻⁶/°C | 7.40 × 10⁻⁶/°F | 77–200 °F |
| Mean CTE, 25–316 °C | 15.2 × 10⁻⁶/°C | 8.42 × 10⁻⁶/°F | 77–600 °F |
| Mean CTE, 25–538 °C | 15.7 × 10⁻⁶/°C | 8.73 × 10⁻⁶/°F | 77–1000 °F |
| Mean CTE, 25–649 °C | 16.1 × 10⁻⁶/°C | 8.97 × 10⁻⁶/°F | 77–1200 °F |
| Magnetic permeability | ≈ 1.010 | at 200 Oe | Effectively non-magnetic |
| Curie temperature | < −73 °C | < −100 °F | Non-magnetic at all service temperatures |
| Dimensional change on ageing | ≈ 0.09 % contraction | ≈ 0.09 % | Allow for on close-tolerance parts |
What Are the Mechanical Properties of Alloy 706?
Alloy 706 properties depend entirely on which ageing cycle is applied. The three-step cycle favours creep and stress-rupture life; the two-step cycle favours tensile strength. Both start from the same solution anneal.
| Condition | Tensile strength | 0.2 % yield | Elongation | Red. of area | Hardness |
|---|---|---|---|---|---|
| Solution annealed | 760–900 MPa (110–130 ksi) | 310–450 MPa (45–65 ksi) |
35–50 % | 45–60 % | ≈ 85–95 HRB |
| Three-step aged (creep / rupture optimised) |
1170–1240 MPa (170–180 ksi) | 930–1000 MPa (135–145 ksi) |
15–22 % | 25–40 % | ≈ 34–38 HRC |
| Two-step aged (tensile optimised) |
1275–1345 MPa (185–195 ksi) | 1030–1105 MPa (150–160 ksi) |
14–20 % | 22–35 % | ≈ 36–40 HRC |
| Three-step aged, tested at 650 °C | ≈ 1000 MPa (145 ksi) | ≈ 830 MPa (120 ksi) |
18–25 % | 30–45 % | — |
What Heat Treatment Is Used for Alloy 706 Forgings?
Both standard cycles begin with a solution anneal at 925–1010 °C (1700–1850 °F) followed by air cooling. The ageing sequence that follows decides whether the part is optimised for creep resistance or for tensile strength.
Cycle A — optimum creep & stress rupture
- Solution anneal 925–1010 °C, time to suit section, air cool
- Stabilise 845 °C (1550 °F) / 3 h, air cool
- Age 720 °C (1325 °F) / 8 h, furnace cool at 55 °C/h (100 °F/h)
- Hold 620 °C (1150 °F) / 8 h, air cool
The 845 °C stabilisation forms grain-boundary η phase. This is the cycle used for land-based gas-turbine discs and any part with a creep-life requirement.
Cycle B — optimum tensile strength
- Solution anneal 925–1010 °C, time to suit section, air cool
- Age 730 °C (1350 °F) / 8 h, furnace cool at 55 °C/h (100 °F/h)
- Hold 620 °C (1150 °F) / 8 h, air cool
The stabilisation step is omitted. Room-temperature tensile and yield strength rise roughly 8–10 % against Cycle A, at the cost of stress-rupture life.
How Is Alloy 706 Forged and Hot Worked?
Alloy 706 is hot worked between 870 °C and 1150 °C (1600–2100 °F). It has lower flow stress and better hot workability than most superalloys. Unlike Alloy 718, working in the lower part of the range is not required to develop properties.
| Operation | Temperature | Practice notes |
|---|---|---|
| Billet heating / start of forging | 1120–1150 °C (2050–2100 °F) | Soak time proportional to section; avoid overheating toward the 1338 °C solidus |
| Working range | 870–1150 °C (1600–2100 °F) | Broad window; multiple reheats acceptable |
| Finishing temperature | ≥ 950 °C typical | Lower finishing temperature refines grain but raises load and cracking risk |
| Ring rolling | 1050–1150 °C | Radial-axial rolling; reheat between passes on heavy sections |
| Post-forge cooling | Air cool | Then solution anneal and age. Do not rely on forging heat for properties |
| Solution anneal | 925–1010 °C (1700–1850 °F) | Air cool; time commensurate with thickness |
| Cold working | Room temperature | Behaves like 300-series stainless; softer than Alloy 718 in the annealed condition |
Forging reduction is planned to produce a fine, uniform grain size, because grain size controls ultrasonic inspectability as much as it controls mechanical properties. Coarse or duplex grain structure scatters the ultrasonic beam and raises the noise floor, which can make a sound disc impossible to certify to a tight UT class. On heavy Alloy 706 sections we plan the reduction sequence and reheat schedule around the UT acceptance class stated on the order, not only around the finished geometry.
⚖️ Alloy 706 Forging Weight Calculator
Pick a shape and enter the dimensions to get net weight at the Alloy 706 aged density of 8.08 g/cm³. Use the result to fill in your enquiry.
Density used is 8.08 g/cm³ (aged). Annealed material is 8.05 g/cm³, a difference under 0.4 % that makes no practical difference to a quotation. The allowance figure estimates rough forging weight from finished weight and is a planning aid, not a quotation.
🔥 Alloy 706 Heat-Treatment Recipe Generator
Choose what the part has to survive and the tool writes out the full cycle, ready to hand to a heat-treatment shop.
Soak times use the usual 1 hour per 25 mm of ruling section for solution treatment, with a 1 hour minimum. Ageing hold times are fixed by the specification and do not scale with section. Validate on coupons cut from the same heat.
🔄 Alloy 706 or Alloy 718? — Selector
Answer four questions and the result explains which of the two grades the application points to, and why.
This is a screening aid. Final material selection belongs to the design authority for the equipment, which has to account for code requirements and qualification history.
Alloy 706 vs Alloy 718, Incoloy 901, Inconel X-750 and A286
| Property | Alloy 706 | Alloy 718 | Incoloy 901 | Inconel X-750 | A286 |
|---|---|---|---|---|---|
| UNS | N09706 | N07718 | N09901 | N07750 | S66286 |
| Base | Ni-Fe-Cr | Ni-Fe-Cr | Ni-Fe | Ni-Cr | Fe-Ni-Cr |
| Nickel | 39–44 % | 50–55 % | 40–45 % | ≥ 70 % | 24–27 % |
| Molybdenum | none | 2.8–3.3 % | 5.0–6.5 % | none | 1.0–1.5 % |
| Nb+Ta | 2.5–3.3 % | 4.75–5.5 % | none | 0.7–1.2 % | none |
| Main strengthener | γ″ + γ′ | γ″ | γ′ | γ′ | γ′ |
| Density | 8.08 g/cm³ | 8.19 g/cm³ | 8.23 g/cm³ | 8.28 g/cm³ | 7.94 g/cm³ |
| Typical aged UTS | 1170–1345 MPa | 1240–1400 MPa | 1100–1240 MPa | 1100–1275 MPa | 900–1050 MPa |
| Practical service limit | ≈ 650 °C | ≈ 650–700 °C | ≈ 600 °C | ≈ 815 °C | ≈ 700 °C |
| Max practical forging size | Largest of the group | Moderate | Moderate | Moderate | Moderate |
| Machinability | Best of the group | Difficult | Difficult | Difficult | Moderate |
| Strain-age crack resistance | Excellent | Good | Poor | Poor | Moderate |
| Sour / chloride service | Limited | Good | Moderate | Moderate | Limited |
| Best use | Very large gas-turbine discs, shafts and cases | Aerospace rotating parts, oilfield | Disc forgings to 600 °C | Springs, bolting, higher temperature | Lower-cost fasteners & discs |
As a rule of thumb, Alloy 706 suits parts that are large, carry heavy machining content or will be welded, with service at or below about 650 °C in a clean environment. Alloy 718 takes over where the last increment of strength matters, or where molybdenum is needed for sour or chloride service. Above 700 °C the choice moves to Inconel X-750 or Waspaloy.
How Corrosion-Resistant Is Alloy 706?
The 14.5–17.5 % chromium gives Alloy 706 good resistance to oxidation and to oxidising media, and the nickel content provides useful resistance in reducing conditions. Because there is no molybdenum, it is not a substitute for Alloy 718, Alloy 625 or Hastelloy in aggressive chloride or reducing-acid service.
| Environment | Rating | Comment |
|---|---|---|
| Humidity / atmospheric | Excellent | No practical limitation |
| Salt spray (NaCl) | Excellent | Suitable for marine atmospheric exposure |
| Sour oil & gas | Good | Shown superior to Cr-Mn-N austenitic stainless in laboratory pitting and SCC tests; qualify against the project's NACE MR0175 / ISO 15156 requirements before use |
| Sodium hydroxide | Good | — |
| Acetic acid | Good | — |
| Nitric acid | Moderate | Concentration and temperature dependent |
| Phosphoric acid | Moderate | Concentration and temperature dependent |
| Seawater (immersed) | Moderate | Not a full-immersion material; consider Alloy 625 or 725 |
| Sulfuric acid | Restricted | Not recommended |
Ratings are comparative screening values. Actual corrosion behaviour depends on temperature, concentration, pH, aeration, velocity, crevices, stress, surface finish and galvanic coupling. Run application testing before committing on a corrosion-governed design.
How Is Alloy 706 Machined and Welded?
Machining
Improved machinability is one of the main commercial arguments for Alloy 706 over Alloy 718: higher cutting speeds and longer tool life are achievable, and the alloy can be cut in either the annealed or the aged condition. It still work-hardens, so the usual superalloy discipline applies: rigid setups, sharp positive-rake carbide, constant feed with no dwelling in the cut, generous through-tool coolant, and climb milling where the machine allows. Because ageing contracts the part by about 0.09 %, close-tolerance features are finished after ageing or compensated in the program.
Welding
Alloy 706 welds well and uses the same procedures as Alloy 718, normally GTAW or GMAW with matching or Alloy 718-type filler. Its delayed hardening response is the main advantage: residual stress from welding relaxes before precipitation begins, so the heat-affected zone resists strain-age cracking. Weld in the solution-annealed condition wherever the sequence allows, then solution treat and age the completed assembly so that weld metal, HAZ and parent metal all finish in the same condition.
Where Is Alloy 706 Used?
⚡ Land-based gas turbines
The dominant application. Turbine wheels, compressor discs, spacers, shafts and casings in heavy-duty industrial gas turbines, including parts too large to make soundly in Alloy 718. Supplied three-step aged for creep life.
✈ Aero engines
Turbine discs, shafts, cases, diffuser cases, engine mounts and fasteners, ordered against AMS 5701 / 5702 / 5703 with the associated cleanliness and NDT requirements.
🛢 Oil, gas and drilling
A candidate where strength and corrosion resistance must combine with non-magnetic behaviour: drill collars, stabilisers and MWD/LWD housings. Laboratory testing has shown it to outperform Cr-Mn-N austenitic stainless steels where pitting and stress-corrosion cracking are the concern.
🔩 High-strength fasteners & rings
Studs, bolting, seal rings and retaining rings where 650 °C-class strength is needed and the machining volume makes Alloy 718 uneconomic.
🏭 Pressure and process equipment
Forged flanges, tube sheets, sleeves, bushings, nozzles and valve components ordered against ASTM B564 or ASTM B637 for elevated-temperature service.
❄ Cryogenic service
Strength is retained down to cryogenic temperatures with no ductile-to-brittle transition, making the alloy usable for low-temperature structural and rotating parts.
Alloy 706 Forging Capability at Jiangyin Jiangnan Metal
Jiangyin Jiangnan Metal Co., Ltd. operates an open-die forging plant at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, employing around 460 people including 9 senior and 32 intermediate engineers. The plant produces forgings across a factory envelope of 80–6000 mm diameter, 100–12000 mm length and 10–15000 kg single-piece weight. For Alloy 706 specifically, the practical envelope is set by remelted billet supply and press capacity and is confirmed against your drawing at enquiry stage.
| Stage | Equipment | Capability |
|---|---|---|
| Forging — hammers | Open-die forging hammers | 1 t · 3 t · 5 t · 6 t · 9 t |
| Forging — press | Hydraulic free-forging press | 4500–5000 t |
| Ring rolling | Radial-axial seamless ring mills | 3 m and 6 m |
| Melting route (billet) | EAF + VOD + ESR; VIM + ESR + VAR for aerospace-grade material | Specified per order |
| Heat treatment | Solution and ageing furnaces with chart recording | Cycle A and Cycle B |
| Volumetric NDT | Ultrasonic examination | ASTM A388 · EN 10228-3 · SEP 1921 |
| Surface NDT | Magnetic particle and liquid penetrant lines | PT used for Alloy 706 (non-magnetic) |
| Mechanical lab | Universal testing machine, impact tester, hardness testers | Tensile, Charpy, HB/HRC |
| Metallurgical lab | Metallographic microscope, spectrometer | Grain size, microstructure, chemistry |
| Machining | CNC turning, boring, milling | Rough or finish machined to drawing |
Alloy 706 is non-magnetic, so magnetic particle inspection does not apply and surface NDT is by liquid penetrant. This catches out specifications copied across from a steel drawing.
Which Standards and Inspection Apply to Alloy 706 Forgings?
| Category | Standard | Covers |
|---|---|---|
| Material — aerospace | AMS 5701 / 5702 / 5703 | Bars, forgings, rings and forging stock; differ by supplied heat-treatment condition |
| Material — general | ASTM B637 / ASME SB-637 | Precipitation-hardenable nickel alloy bars, forgings and forging stock, high-temperature service |
| Material — forgings | ASTM B564 | Nickel alloy forgings, frequently cited for flanges and pressure parts |
| Ultrasonic testing | ASTM A388 · EN 10228-3 · SEP 1921 | Volumetric examination of forgings; state the acceptance class |
| Liquid penetrant | ASTM E165 / E1417 | Surface examination, the applicable method for this non-magnetic alloy |
| Tensile testing | ASTM E8 / E21 | Room and elevated temperature |
| Stress rupture | ASTM E139 | Creep and rupture testing where the design demands it |
| Grain size | ASTM E112 | Reported on the certificate, and drives UT inspectability |
| Certification | EN 10204 3.1 / 3.2 | 3.1 as standard; 3.2 witnessed by Lloyd's, DNV, BV, ABS, TÜV or your own inspector |
| Quality system | ISO 9001:2015 | Factory quality management system |
How Do You Specify an Alloy 706 Forging Order?
These seven steps remove most of the ambiguity that otherwise turns into a non-conformance after the forging has already been made.
- State the generic designation. Write UNS N09706 / Alloy 706 plus the governing specification (AMS 5703, ASTM B637 or ASTM B564). Ordering against the Inconel® trademark alone can only be filled by the trademark holder.
- Choose the heat-treatment condition. Solution-annealed, three-step aged for creep and stress rupture, or two-step aged for maximum tensile strength. Say whether the part ships aged, or annealed for you to age after machining.
- Send the drawing. 2D or 3D, with machining allowance, tolerances, surface finish and any grain-flow requirement marked.
- Define the melting route. VIM+ESR, VIM+VAR or triple melt, plus any macro-cleanliness or segregation acceptance criteria. This is the single biggest cost driver on superalloy forgings.
- Define NDT. Ultrasonic acceptance to ASTM A388, EN 10228-3 or SEP 1921, including the class, plus liquid penetrant requirements. Do not specify MT, because the alloy is non-magnetic.
- Specify testing and certification. Room-temperature and elevated-temperature tensile, stress rupture if required, grain size, hardness, test orientation and location, and EN 10204 3.1 or 3.2.
- Give quantity, delivery terms and destination. Quantity, required date, Incoterms and destination port, so lead time and freight can be confirmed with the price.
Drawing callout template
| MATERIAL | UNS N09706 (Alloy 706) per ASTM B637 / AMS 5703 |
|---|---|
| MELT ROUTE | VIM + ESR minimum (VIM + VAR if specified) |
| CONDITION | Solution 980 °C/AC + 845 °C/3 h/AC + 720 °C/8 h/FC 55 °C/h → 620 °C/8 h/AC |
| GRAIN SIZE | ASTM E112 No. 5 or finer, uniform, reported on MTC |
| NDE | UT per EN 10228-3 class 3 (or ASTM A388) · PT per ASTM E165. MT not applicable, alloy is non-magnetic |
| TESTING | Tensile at RT and 650 °C; hardness; stress rupture if specified. Tangential specimens from prolongation |
| CERTIFICATION | EN 10204 3.1 (3.2 with third-party witness if required) |
| MARKING | Heat number, condition, drawing number, low-stress stamp on non-functional surface |
Common Alloy 706 Specification Mistakes
Specifying magnetic particle inspection
Alloy 706 is austenitic and non-magnetic (μr ≈ 1.01), so MT cannot work. The requirement usually arrives copied from a steel forging drawing. Fix: specify liquid penetrant to ASTM E165 or E1417 instead.
Ordering "Inconel 706" on the purchase order
Inconel® is a Special Metals Corporation trademark. A PO demanding it can strictly only be filled with their material. Fix: order UNS N09706 / Alloy 706 per ASTM B637 or the applicable AMS specification, and note the trade name in brackets for reference only.
Asking for a UT class without considering grain size
A tight ultrasonic acceptance class on a heavy superalloy section is a forging and heat-treatment requirement, not only an inspection one. Coarse or duplex grains scatter the beam and raise the noise floor. Fix: state the UT class and the required grain size at RFQ stage so the reduction sequence can be planned around it.
Choosing the wrong ageing cycle for the duty
The two-step cycle gives higher tensile numbers on a certificate, which looks better on paper, but the three-step cycle is what delivers stress-rupture life in a turbine disc. Fix: decide from the governing design property, not the headline tensile figure.
Assuming Alloy 706 substitutes for Alloy 718 in sour service
Finish machining tight tolerances before ageing
Ageing contracts the part about 0.09 %. On a 600 mm bore that is roughly 0.5 mm, far outside a fitted tolerance. Fix: rough machine, age, then finish machine; or compensate in the program.
Leaving the melting route unstated
"Alloy 706 bar" without a melt route can mean anything from single-melt to triple-melt material, with a large price and cleanliness difference. Fix: state VIM+ESR, VIM+VAR or triple melt explicitly on the enquiry.
Glossary
- UNS N09706
- Unified Numbering System designation for the nickel-iron-chromium precipitation-hardenable superalloy known as Alloy 706.
- γ″ (gamma double prime)
- Body-centred-tetragonal Ni₃Nb precipitate that provides most of the strengthening in Alloy 706 and Alloy 718.
- γ′ (gamma prime)
- Face-centred-cubic Ni₃(Ti,Al) precipitate; the secondary strengthener in Alloy 706 and the dominant one after the two-step cycle.
- η (eta) phase
- Hexagonal Ni₃Ti phase precipitated at grain boundaries during the 845 °C stabilisation step, improving stress-rupture behaviour.
- Strain-age cracking
- Heat-affected-zone cracking caused by precipitation hardening occurring while welding residual stress is still present. Alloy 706 resists it because hardening is delayed.
- ESR — electroslag remelting
- Secondary melting route that refines the structure and reduces segregation and inclusion content in a superalloy ingot.
- VAR — vacuum arc remelting
- Secondary melting under vacuum, used for the cleanest aerospace-grade superalloy billet.
- Freckles
- Channel-type macro-segregation defects that form during remelting of heavily alloyed ingots. Alloy 706's leaner chemistry makes them far less likely, which is why larger ingots are feasible.
- Ruling section
- The thickest section that governs soak time and cooling rate during heat treatment.
- EN 10204 3.1 / 3.2
- Inspection certificate issued by the manufacturer's independent inspection department (3.1), or additionally witnessed by a third party or the customer (3.2).
- Prolongation
- Integral extension of a forging, heat treated with the part, from which test specimens are cut so tests represent the delivered part.
Frequently Asked Questions — Alloy 706 / UNS N09706
What is Alloy 706?
Alloy 706 (UNS N09706) is a nickel-iron-chromium precipitation-hardenable superalloy containing nominally 41 % nickel, 16 % chromium, 2.9 % niobium plus tantalum and 1.75 % titanium, with iron as the balance. It is strengthened by γ′ and γ″ precipitates during ageing and retains high strength from cryogenic temperatures up to about 650 °C (1200 °F). Compared with Alloy 718 it contains no molybdenum and less niobium, which lowers segregation, allows much larger sound ingots and forgings, and makes it significantly easier to machine.
Are Alloy 706, Inconel 706, UNS N09706 and GH2706 the same material?
Yes, they describe the same chemistry. UNS N09706 is the generic designation; AMS 5701, 5702 and 5703 are the SAE aerospace specifications; GH2706, GH4706 and GH706 are the Chinese designations; Inconel 706 is a trade name. Inconel® is a registered trademark of Special Metals Corporation, so material produced by Jiangyin Jiangnan Metal Co., Ltd. is correctly described as Alloy 706 / UNS N09706, not by the trademark.
What is the chemical composition of Alloy 706?
Nickel + cobalt 39.0–44.0 %, chromium 14.5–17.5 %, niobium + tantalum 2.50–3.30 %, titanium 1.50–2.00 %, aluminium 0.40 % max, cobalt 1.0 % max, copper 0.30 % max, manganese 0.35 % max, silicon 0.35 % max, carbon 0.06 % max, phosphorus 0.020 % max, sulfur 0.015 % max, boron 0.006 % max, iron balance.
What is the density of Alloy 706?
8.08 g/cm³ (0.292 lb/in³) age-hardened, and 8.05 g/cm³ (0.291 lb/in³) annealed.
What is the difference between Alloy 706 and Alloy 718?
Alloy 706 has no molybdenum and about 2.9 % Nb+Ta; Alloy 718 has roughly 3 % Mo and 5 % Nb. The leaner chemistry of Alloy 706 reduces macro-segregation during solidification, so much larger ingots and turbine-disc forgings can be produced with a structure sound enough to pass ultrasonic inspection. Alloy 706 is also easier to machine and more resistant to post-weld strain-age cracking. Alloy 718 has higher strength at temperature and better corrosion resistance from the molybdenum. Alloy 706 wins on very large land-based gas-turbine discs and shafts; Alloy 718 wins where maximum strength or sour-service corrosion resistance governs.
What is the heat treatment for Alloy 706 forgings?
Both cycles start with a solution anneal at 925–1010 °C (1700–1850 °F), air cool. For creep and stress rupture (three-step): 845 °C / 3 h / air cool, then 720 °C / 8 h, furnace cool at 55 °C per hour to 620 °C, hold 8 h, air cool. For maximum tensile strength (two-step): 730 °C / 8 h, furnace cool at 55 °C per hour to 620 °C, hold 8 h, air cool. Contraction during ageing is about 0.09 %.
What is the maximum service temperature of Alloy 706?
Alloy 706 retains high strength from cryogenic temperatures to approximately 650 °C (1200 °F), and precipitation-hardened material holds useful strength to about 705 °C (1300 °F). Above that the precipitates coarsen and strength falls away, so Alloy 718, Waspaloy or Inconel X-750 becomes the better choice.
What forging temperature is used for Alloy 706?
Hot working runs from 870 °C to 1150 °C (1600–2100 °F), with billet heating typically 1120–1150 °C and finishing above about 950 °C. Alloy 706 has lower flow stress and better hot workability than most superalloys, so working in the lower part of the range is not required to develop properties. Reduction is planned to give a fine, uniform grain size for ultrasonic inspectability.
Is Alloy 706 magnetic?
No. Alloy 706 is austenitic and effectively non-magnetic, with a relative permeability of about 1.01 at 200 Oe and a Curie temperature below −73 °C. That makes it a candidate for non-magnetic drill collars and MWD/LWD housings, and it also means magnetic particle inspection cannot be used on it.
Can Alloy 706 be welded?
Yes, with the same procedures as Alloy 718. Its delayed hardening response gives excellent resistance to post-weld strain-age cracking, which is a major reason it is chosen for large fabricated turbine structures. Weld in the solution-annealed condition, then solution treat and age the assembly.
Which standards apply to Alloy 706 forgings?
AMS 5701, AMS 5702 and AMS 5703 for aerospace bars, forgings and rings; ASTM B637 / ASME SB-637 for precipitation-hardenable nickel alloy bars, forgings and forging stock; and ASTM B564 for nickel alloy forgings. Ultrasonic acceptance is usually to ASTM A388, EN 10228-3 or SEP 1921, with certification to EN 10204 3.1 or 3.2.
Who manufactures Alloy 706 forgings in China?
Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, manufactures Alloy 706 (UNS N09706) forged rings, seamless rolled rings, discs, shafts, flanges, sleeves, bushings and tube sheets to customer drawings. Enquiries: sales@steelforgepieces.com, telephone 0086-189-2135-9659.
What sizes of Alloy 706 forgings can be produced?
The factory envelope is 80–6000 mm diameter, 100–12000 mm length and 10–15000 kg single-piece weight, using 1–9 t forging hammers, a 4500–5000 t hydraulic press and 3 m and 6 m ring mills. For Alloy 706 the practical envelope is set by remelted billet supply and is confirmed against your drawing at enquiry stage.
What is the lead time for Alloy 706 forgings?
It depends on remelted billet availability, part weight, heat-treatment cycle and certification level. Superalloy billet procurement, not forging, is usually the critical path. Confirmed lead time is quoted with the price, normally within 24 hours of receiving a drawing or dimensioned enquiry.
Technical References
- 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, West Conshohocken, PA.
- ASTM B564, Standard Specification for Nickel Alloy Forgings, ASTM International.
- SAE AMS 5701, AMS 5702, AMS 5703, Alloy Bars, Forgings and Rings, 41Ni–16Cr–2.9Cb–1.75Ti, SAE International.
- Carpenter Technology Corporation, CarTech® 706 Alloy technical datasheet (UNS N09706).
- Special Metals Corporation, INCONEL® alloy 706 publication.
- H. L. Eiselstein, "Properties of a Fabricable, High Strength Alloy", Metals Engineering Quarterly, November 1971, pp. 20–25.
- J. H. Moll, G. N. Maniar and D. R. Muzyka, "Heat Treatment of 706 Alloy for Optimum 1200 °F Stress-Rupture Properties", Metallurgical Transactions, Vol. 2, 1971, pp. 2153–2160.
- J. H. Moll, G. N. Maniar and D. R. Muzyka, "The Microstructure of 706, a New Fe–Ni-Base Superalloy", Metallurgical Transactions, Vol. 2, 1971, pp. 2143–2151.
- ASM Handbook, Volume 1: Properties and Selection: Irons, Steels, and High-Performance Alloys, ASM International.
- ASM Handbook, Volume 14A: Metalworking: Bulk Forming, ASM International.
- EN 10228-3, Non-destructive testing of steel forgings — Ultrasonic testing of ferritic or martensitic steel forgings, CEN. (Applied by analogy where specified on superalloy orders.)
- ASTM A388, Standard Practice for Ultrasonic Examination of Steel Forgings, ASTM International.
- ASTM E112, Standard Test Methods for Determining Average Grain Size, ASTM International.
- EN 10204:2004, Metallic products — Types of inspection documents, CEN.
- NACE MR0175 / ISO 15156, Materials for use in H₂S-containing environments in oil and gas production, ISO.
Standards cited are the revisions current at the date of the last page review. Reference the revision in force at your contract date. Property values on this page are typical published data for guidance; contractual values are those on the material certificate for your heat.
Request a Quote — Alloy 706 / UNS N09706 Forgings
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