Alloy 706,Inconel 706 Rod,UNS N09706

Alloy 706,Inconel 706 Wire,UNS N09706

Introduction to Alloy 706 (Inconel 706 Wire, UNS N09706)

Alloy 706, commercially designated as Inconel 706 and classified under UNS N09706, is a precipitation-hardening nickel-iron-chromium superalloy engineered for an exceptional balance of high strength, excellent cryogenic toughness, and good corrosion resistance. Unlike many nickel-based superalloys that prioritize extreme high-temperature performance, Alloy 706 is optimized for service across a moderate temperature range—from cryogenic conditions (-253°C/-423°F) up to 540°C/1004°F—making it ideal for structural applications requiring both load-bearing capacity and low-temperature durability. Its strength is derived from the formation of gamma-prime (γ′, Ni₃Al, Ti) precipitates during controlled age hardening, while its chromium content ensures resistance to oxidation and pitting corrosion. Inconel 706 wire, a key form of this alloy, is widely used in industries such as aerospace, defense, and energy, where it contributes to critical components like fasteners, springs, and structural supports that operate in harsh, temperature-fluctuating environments.

1. Chemical Composition (Typical, wt%)

The chemical composition of UNS N09706 adheres to strict industry standards including ASTM B625 (for nickel-alloy wire) and ASME SB625, ensuring consistent precipitation-hardening behavior, mechanical performance, and corrosion resistance. The typical composition is as follows:

Element

Content Range (wt%)

Function

Nickel (Ni)

39.0 - 44.0

Serves as the primary matrix element, stabilizing the austenitic structure and enabling the formation of γ′ precipitates; enhances cryogenic toughness and resistance to reducing environments.

Iron (Fe)

Balance

Improves hot workability and weldability (critical for wire production); reduces alloy cost while maintaining strength and toughness—distinguishing it from iron-poor nickel superalloys.

Chromium (Cr)

14.0 - 17.0

Forms a dense chromium oxide (Cr₂O₃) protective layer, providing oxidation resistance up to 540°C and resistance to chloride-induced pitting/crevice corrosion in marine or chemical environments.

Titanium (Ti)

2.30 - 2.80

Key element for γ′ precipitate formation (Ni₃Ti), the primary contributor to high tensile and yield strength; controlled to avoid brittle intermetallic phases (e.g., TiC) that reduce toughness.

Aluminum (Al)

0.60 - 1.00

Cooperates with titanium to refine γ′ precipitate size and distribution, optimizing the strength-ductility balance; supports the integrity of the protective oxide layer.

Niobium (Nb)

1.70 - 2.30

Enhances grain boundary strength, improving creep resistance at 450 - 540°C; supplements γ′ hardening by forming small, secondary precipitates.

Carbon (C)

≤ 0.05

Minimized to prevent carbide precipitation at grain boundaries, which can cause intergranular cracking in cryogenic or cyclic thermal environments; small amounts aid in weld joint strength.

Manganese (Mn)

≤ 0.30

Aids in deoxidation during melting and improves cold workability for fine wire drawing; controlled to avoid brittleness at low temperatures.

Silicon (Si)

≤ 0.30

Controls oxide formation during hot processing; limited to avoid excessive oxide inclusions that reduce fatigue life.

Phosphorus (P)

≤ 0.015

Strictly limited to preserve cryogenic toughness, as phosphorus can embrittle grain boundaries at sub-zero temperatures.

Sulfur (S)

≤ 0.010

Minimized to prevent hot cracking during fabrication (essential for wire drawing) and reduce corrosion susceptibility in acidic media.

Copper (Cu)

≤ 0.20

Controlled to avoid interference with γ′ precipitate formation and maintain oxidation resistance.

Boron (B)

≤ 0.006

Trace element that strengthens grain boundaries, improving creep resistance and reducing intergranular cracking risk in welded or high-stress components.

2. Physical Properties

Inconel 706 wire exhibits stable physical properties across its operating temperature range, with mechanical performance optimized via age hardening—particularly for cryogenic toughness and mid-temperature strength. Key properties (measured at room temperature unless specified otherwise) are:

Property

Value

Test Condition

Density

8.03 g/cm³

Room temperature (25°C)

Melting Point Range

1330 - 1380°C

-

Thermal Expansion Coefficient

12.5 × 10⁻⁶/°C

20 - 100°C; 15.2 × 10⁻⁶/°C (20 - 500°C)

Thermal Conductivity

11.6 W/(m·K)

100°C; 18.1 W/(m·K) (500°C)

Electrical Resistivity

1.26 × 10⁻⁶ Ω·m

Room temperature (25°C); 1.48 × 10⁻⁶ Ω·m (500°C)

Modulus of Elasticity

201 GPa

Room temperature (tensile); 165 GPa (500°C)

Poisson’s Ratio

0.30

Room temperature

Curie Temperature

≈ -180°C

Below this temperature, weakly ferromagnetic (irrelevant for most application temperatures).

Tensile Strength (After Aging)

≥ 1240 MPa

Room temperature; ≥ 895 MPa (500°C)

Yield Strength (0.2% Offset, After Aging)

≥ 1035 MPa

Room temperature; ≥ 795 MPa (500°C)

Elongation (After Aging)

≥ 16%

Room temperature; ≥ 20% (-196°C, liquid nitrogen)

Hardness (After Aging)

36 - 42 HRC

Room temperature

Impact Toughness (Charpy V-Notch)

≥ 60 J

-196°C (cryogenic); ≥ 80 J (room temperature)

3. Production Process of Inconel 706 Wire

The manufacturing of Inconel 706 wire requires precise control of chemistry, heat treatment, and forming to optimize precipitation hardening, cryogenic toughness, and dimensional accuracy. Key steps include:

3.1 Raw Material Melting & Casting

Melting: High-purity raw materials (nickel, iron, chromium, titanium, etc.) are melted via vacuum induction melting (VIM) followed by vacuum arc remelting (VAR). This dual-melting process eliminates gaseous impurities (O₂ < 25 ppm, N₂ < 45 ppm) and ensures uniform distribution of titanium, aluminum, and niobium—critical for consistent γ′ precipitate formation and cryogenic toughness.

Casting: Molten alloy is cast into ingots (500 - 2500 kg) or blooms, which undergo homogenization annealing at 1100 - 1150°C for 8 - 10 hours. This step eliminates chemical segregation (especially of titanium and niobium) and refines the as-cast microstructure, preparing the material for hot working while preserving low-temperature ductility.

3.2 Hot Working & Wire Rod Production

Hot Rolling: Ingots/blooms are hot-rolled at 1000 - 1100°C into wire rods (diameter: 8 - 20 mm). Hot rolling breaks down coarse grains and improves workability; rods are air-cooled to room temperature to prevent premature precipitate formation— which could reduce ductility during cold drawing and compromise cryogenic toughness.

Descaling: Hot-rolled rods undergo shot blasting (to remove loose oxide scale) followed by acid pickling (nitric-hydrofluoric acid solution) to eliminate residual oxide layers. This step is critical for preventing surface defects (e.g., pits, cracks) that could act as stress concentrators in high-stress or cryogenic applications.

3.3 Cold Drawing (Wire Formation)

Multi-Pass Cold Drawing: Wire rods are cold-drawn through diamond dies in 5 - 9 passes to achieve the desired diameter (typically 0.15 mm - 10 mm). Each pass reduces diameter by 15 - 20%, with intermediate solution annealing (950 - 1000°C for 30 - 45 minutes, water-quenched) between passes. This annealing step dissolves existing precipitates, relieves work hardening, and restores ductility—preventing wire breakage and ensuring uniform mechanical properties.

Dimensional Control: Tension, die alignment, and drawing speed are precisely regulated to maintain tight diameter tolerance (±0.02 mm for precision wire) and roundness (≤0.01 mm). For cryogenic or aerospace applications, laser diameter monitoring is used to ensure consistency, as dimensional variations can affect component performance under stress.

3.4 Age Hardening (Strength & Toughness Optimization)

Age hardening is the core step to activate γ′ precipitates while preserving cryogenic toughness. The process follows a standardized two-stage cycle (per ASTM B625):

Solution Annealing: Heating the wire to 980 - 1020°C for 1 - 2 hours, followed by rapid water quenching. This step ensures a uniform austenitic microstructure and dissolves all precipitates, setting the stage for controlled γ′ formation.

Aging (Final): Heating to 700 - 730°C for 16 - 20 hours, followed by air cooling. This step promotes the growth of fine, evenly distributed γ′ precipitates (5 - 8 nm) — optimizing strength without sacrificing ductility. Unlike some superalloys, no intermediate cooling step is needed, simplifying processing while maintaining cryogenic toughness.

Note: For ultra-fine wire (diameter < 0.5 mm), aging time is reduced to 12 - 16 hours to avoid excessive hardening, which could compromise flexibility for applications like springs or sensor wires.

3.5 Surface Finishing & Quality Inspection

Surface Treatment:

Pickling: Post-aging pickling in nitric-hydrofluoric acid to remove oxide scales and enhance corrosion resistance—critical for marine or chemical applications.

Passivation: Optional nitric acid passivation to strengthen the protective oxide layer, reducing the risk of pitting corrosion in chloride-rich environments.

Polishing: For high-precision applications (e.g., aerospace fasteners, medical devices), the wire is polished to a smooth surface finish (Ra ≤ 0.2 μm) using abrasive belts or electrochemical polishing, minimizing stress concentrations.

Quality Control:

Chemical Analysis: Optical emission spectroscopy (OES) to verify titanium, aluminum, and niobium content—critical for γ′ formation and cryogenic performance.

Mechanical Testing: Tensile testing (strength/elongation at room and cryogenic temperatures), impact testing (Charpy V-notch at -196°C), hardness testing (HRC), and fatigue testing (for cyclic-loading components like springs).

Corrosion Testing: Salt spray testing (ASTM B117) and crevice corrosion testing (ASTM G48) to validate resistance to harsh environments.

Non-Destructive Testing: Eddy current testing (for surface defects like cracks or pits) and ultrasonic testing (for internal flaws)—essential for high-stress applications like aerospace structural components.

Dimensional Inspection: Laser measurement to confirm diameter, straightness (≤0.1 mm/m), and length accuracy. For coil wire, payout tension testing ensures consistent unwinding during fabrication.

4. Product Applications

Inconel 706 wire’s unique combination of high strength, cryogenic toughness, and corrosion resistance makes it indispensable in industries requiring reliable performance across moderate-to-low temperature ranges:

4.1 Aerospace & Defense

Aircraft Structural Components: Fine wire (0.2 - 1.5 mm) for high-strength fasteners (rivets, bolts) in fuselages and wings—resists cyclic stress and maintains strength at high altitudes (where temperatures can drop to -50°C).

Spacecraft & Launch Vehicles: Wire for cryogenic fuel line supports and valve springs—maintains toughness at -196°C (liquid oxygen) and -253°C (liquid hydrogen) without brittle fracture, critical for rocket propulsion systems.

Military Equipment: Wire for armor plating fasteners and missile guidance system components—balances strength with impact resistance, even in extreme temperature fluctuations (e.g., desert to arctic environments).

4.2 Energy Generation

Nuclear Power: Wire for control rod drives and reactor vessel fasteners—resists corrosion from borated water, maintains strength at 300 - 400°C (reactor operating temperatures), and exhibits low neutron absorption.

Cryogenic Energy Storage: Wire for structural supports in liquid natural gas (LNG) storage tanks—withstands -162°C (LNG boiling point) without embrittlement, ensuring tank integrity during long-term storage.

Wind Energy: Wire for offshore wind turbine generator components (e.g., rotor shaft springs)—resists marine atmospheric corrosion and maintains strength in temperature cycles (-20°C to 50°C).

4.3 Marine Engineering

Offshore Platforms: Wire for mooring line tensioners and subsea structural fasteners—resists seawater corrosion (3.5% NaCl) and maintains toughness in cold ocean depths (-10°C to 20°C).

Naval Vessels: Wire for hull fasteners and propulsion system components—outperforms stainless steel in saltwater, reducing maintenance costs and extending service life in harsh marine environments.

4.4 Industrial Machinery & Medical Devices

High-Stress Machinery: Wire for springs in heavy-duty pumps and valves—maintains elasticity under high load and temperature fluctuations (0°C to 500°C), suitable for chemical processing or oil & gas equipment.

Medical Devices: Ultra-fine wire (0.05 - 0.2 mm) for surgical instruments and implantable devices (e.g., orthopedic screws)—biocompatible (ISO 10993), resists bodily fluid corrosion, and maintains strength at body temperature (37°C).

Conclusion

Alloy 706 (Inconel 706 Wire, UNS N09706) is a high-performance precipitation-hardening superalloy wire, distinguished by its exceptional balance of strength, cryogenic toughness, and corrosion resistance. Its optimized chemistry and manufacturing process make it a preferred choice for critical applications in aerospace, defense, and energy—where reliability across moderate-to-low temperature ranges is non-negotiable. Whether used in rocket fuel systems, nuclear reactors, or offshore platforms, Inconel 706 wire delivers consistent performance under stress and temperature extremes. For custom requirements—such as ultra-precision wire (down to 0.01 mm diameter), specialized surface finishes (e.g., electropolishing), or tailored aging cycles for specific strength-toughness balances—manufacturers offer customized solutions to meet unique application challenges.

Packing of Standard Packing:

 Typical bulk packaging includes palletized plastic 5 gallon/25 kg. pails, fiber and steel drums to 1 ton super sacks in full container (FCL) or truck load (T/L) quantities. Research and sample quantities and hygroscopic, oxidizing or other air sensitive materials may be packaged under argon or vacuum. Solutions are packaged in polypropylene, plastic or glass jars up to palletized 771 gallon liquid totes Special package is available on request.