Alloy 722,Inconel 722 Strip,UNS N07722

Alloy 722,Inconel 722 Wire,UNS N07722

Introduction to Alloy 722 (Inconel 722 Wire, UNS N07722)

Alloy 722, commercially designated as Inconel 722 and classified under UNS N07722, is a precipitation-hardening nickel-chromium superalloy engineered for exceptional mechanical performance and corrosion resistance in moderate-to-high temperature environments (up to 650°C/1202°F). Its strength is derived from the formation of fine gamma-prime (γ′, Ni₃Al, Ti) precipitates during controlled age hardening, while its chromium-rich matrix delivers robust resistance to oxidation, pitting, and crevice corrosion. Inconel 722 wire— a critical form of this alloy— is widely utilized in industries requiring lightweight, high-strength components that withstand cyclic thermal stress and aggressive media, such as aerospace propulsion systems, gas turbines, and advanced chemical processing equipment. Unlike conventional nickel alloys, it balances high yield strength with sufficient ductility, making it suitable for both structural and precision applications.

1. Chemical Composition (Typical, wt%)

The chemical composition of UNS N07722 adheres to strict industry standards including ASTM B625 (for nickel-alloy wire) and ASME SB625, ensuring consistent precipitation-hardening behavior and corrosion performance. The typical composition is as follows:

Element

Content Range (wt%)

Function

Nickel (Ni)

68.0 - 72.0

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

Chromium (Cr)

15.0 - 17.0

Forms a dense chromium oxide (Cr₂O₃) protective layer, providing oxidation resistance up to 650°C and resistance to chloride-induced pitting.

Iron (Fe)

5.0 - 7.0

Improves hot workability (critical for wire rod production) and reduces alloy cost without compromising high-temperature strength.

Titanium (Ti)

2.0 - 2.5

Key element for γ′ precipitate nucleation (Ni₃Ti), directly enhancing tensile and creep strength; controlled to avoid brittle intermetallic phases.

Aluminum (Al)

1.0 - 1.5

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

Molybdenum (Mo)

2.0 - 3.0

Enhances localized corrosion resistance (e.g., in sour gas or acidic media) and supplements high-temperature creep strength.

Carbon (C)

≤ 0.08

Minimized to prevent carbide precipitation at grain boundaries, which can cause intergranular cracking in corrosive or cyclic thermal environments.

Manganese (Mn)

≤ 0.5

Aids in deoxidation during melting and improves cold workability for fine wire drawing.

Silicon (Si)

≤ 0.5

Controls oxide formation during hot processing and reduces molten alloy viscosity for casting.

Phosphorus (P)

≤ 0.015

Strictly limited to avoid brittleness, especially in welded joints or components under cyclic loading.

Sulfur (S)

≤ 0.010

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

Copper (Cu)

≤ 0.25

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

2. Physical Properties

Inconel 722 wire exhibits stable physical properties across its operating temperature range, with mechanical performance optimized via age hardening. Key properties (measured at room temperature unless specified otherwise) are:

Property

Value

Test Condition

Density

8.20 g/cm³

Room temperature (25°C)

Melting Point Range

1360 - 1400°C

-

Thermal Expansion Coefficient

12.5 × 10⁻⁶/°C

20 - 100°C; 15.6 × 10⁻⁶/°C (20 - 600°C)

Thermal Conductivity

11.3 W/(m·K)

100°C; 19.2 W/(m·K) (600°C)

Electrical Resistivity

1.25 × 10⁻⁶ Ω·m

Room temperature (25°C); 1.50 × 10⁻⁶ Ω·m (600°C)

Modulus of Elasticity

203 GPa

Room temperature (tensile); 168 GPa (600°C)

Poisson’s Ratio

0.30

Room temperature

Curie Temperature

≈ -190°C

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

Tensile Strength (After Aging)

≥ 1050 MPa

Room temperature; ≥ 800 MPa (600°C)

Yield Strength (0.2% Offset, After Aging)

≥ 900 MPa

Room temperature; ≥ 700 MPa (600°C)

Elongation (After Aging)

≥ 18%

Room temperature

Hardness (After Aging)

29 - 35 HRC

Room temperature

Creep Rupture Strength

180 MPa

1000 hours at 600°C

3. Production Process of Inconel 722 Wire

The manufacturing of Inconel 722 wire requires precise control of chemistry, heat treatment, and forming to optimize precipitation hardening and ensure dimensional accuracy. Key steps include:

3.1 Raw Material Melting & Casting

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

Casting: Molten alloy is cast into ingots (500 - 2000 kg) or blooms, which undergo homogenization annealing at 1120 - 1180°C for 6 - 8 hours. This step eliminates chemical segregation and refines the as-cast microstructure, preparing the material for hot working.

3.2 Hot Working & Wire Rod Production

Hot Rolling: Ingots/blooms are hot-rolled at 1050 - 1150°C into wire rods (diameter: 8 - 18 mm). Hot rolling breaks down coarse grains and improves workability; rods are air-cooled to room temperature to prevent premature precipitate formation.

Descaling: Hot-rolled rods undergo shot blasting or acid pickling to remove surface oxide scales, which could cause defects during cold drawing.

3.3 Cold Drawing (Wire Formation)

Multi-Pass Cold Drawing: Wire rods are cold-drawn through diamond dies in 5 - 8 passes to achieve the desired diameter (typically 0.15 mm - 8 mm). Each pass reduces diameter by 15 - 20%, with intermediate solution annealing (980 - 1030°C for 30 - 45 minutes, water-quenched) between passes. This annealing step dissolves existing precipitates and restores ductility, preventing wire breakage during drawing.

Dimensional Control: Tension and die alignment are precisely regulated to maintain diameter tolerance (±0.02 mm for precision wire) and roundness (≤0.01 mm)— critical for applications like spring manufacturing or aerospace fasteners.

3.4 Age Hardening (Strength Optimization)

Age hardening is the core step to activate γ′ precipitates and achieve target strength. The process follows a two-stage cycle:

Stabilization Annealing: Heating the wire to 800 - 830°C for 2 - 4 hours, followed by air cooling. This step controls grain growth and initiates uniform γ′ nucleation.

Final Aging: Reheating to 620 - 650°C for 16 - 20 hours, then air cooling. This promotes the growth of fine, evenly distributed γ′ precipitates (5 - 10 nm), maximizing strength while preserving ductility.

Note: For ultra-fine wire (diameter < 0.5 mm), aging time is reduced to 12 - 16 hours to avoid excessive hardening and maintain flexibility.

3.5 Surface Finishing & Quality Inspection

Surface Treatment:

Pickling: Immersion in nitric-hydrofluoric acid to remove post-aging oxide scales and enhance corrosion resistance.

Passivation: Optional chromate treatment to strengthen the protective oxide layer, ideal for marine or chemical applications.

Polishing: For precision uses (e.g., medical devices), wire is polished to Ra ≤ 0.2 μm to ensure surface smoothness.

Quality Control:

Chemical Analysis: Optical emission spectroscopy (OES) to verify titanium, aluminum, and molybdenum content within standard ranges.

Mechanical Testing: Tensile testing (strength/elongation), hardness testing (HRC), and fatigue testing (for cyclic-loading components like springs).

Corrosion Testing: Salt spray testing (ASTM B117) and crevice corrosion testing (3.5% NaCl solution) to validate 耐蚀性.

Non-Destructive Testing: Eddy current testing for surface defects (cracks, pits) and ultrasonic testing for internal flaws.

Dimensional Inspection: Laser measurement to confirm diameter, straightness (≤0.1 mm/m), and roundness.

4. Product Applications

Inconel 722 wire’s combination of high-temperature strength, corrosion resistance, and processability makes it indispensable in demanding industries:

4.1 Aerospace & Defense

Propulsion Systems: Fine wire (0.2 - 1.0 mm) for aircraft engine turbine blade fasteners, compressor springs, and fuel injector components— withstands 600 - 650°C and cyclic thermal stress.

Missile & Satellite Components: Wire for guidance system actuators and satellite structural supports— balances lightweight properties with resistance to space radiation and thermal cycling (-150°C to 600°C).

Aerospace Fasteners: Cold-drawn wire for high-strength rivets and bolts in fuselages— resists atmospheric corrosion and maintains strength at high altitudes.

4.2 Energy Generation

Gas Turbines: Wire for turbine rotor springs and heat exchanger tubes in combined-cycle power plants— resists 550 - 650°C flue gas corrosion and creep deformation.

Nuclear Power: Thermocouple sheaths and control rod wires for pressurized water reactors (PWRs)— low neutron absorption and resistance to borated water corrosion.

Renewable Energy: Wire for concentrated solar power (CSP) heat absorber components— withstands 600 - 650°C molten salt corrosion.

4.3 Chemical & Petrochemical Industry

High-Temperature Reactors: Wire mesh filters and agitator springs for polymer production reactors— resists 500 - 600°C and aggressive monomers (e.g., ethylene).

Sour Gas Processing: Wire for downhole sensor cables and valve stems in sour gas wells— withstands H₂S and chloride corrosion at 400 - 500°C.

Pharmaceutical Manufacturing: Sanitary wire for drug production equipment (e.g., mixer blades)— complies with FDA standards and resists cleaning agents (sodium hydroxide, nitric acid).

4.4 Marine Engineering

Offshore Platforms: Wire for mooring line tensioners and subsea valve springs— resists seawater corrosion and biofouling in deep-sea environments (up to 2000 meters).

Naval Vessels: Wire for propulsion system components and hull fasteners— outperforms stainless steel in saltwater, reducing maintenance costs.

4.5 Medical Devices

Surgical Instruments: Ultra-fine wire (0.05 - 0.2 mm) for laparoscopic tools and orthopedic implant springs— biocompatible, resists bodily fluid corrosion, and provides sufficient strength for load-bearing applications.

Diagnostic Equipment: Wire for catheter sensors— flexible yet strong, enabling precise movement within the human body.

4.6 Industrial Machinery

High-Temperature Furnaces: Wire for heating element supports and thermocouple protection tubes— operates at 600 - 650°C in air or inert gas.

Automotive (High-Performance): Wire for exhaust system springs and turbocharger components— resists 550 - 600°C exhaust gas corrosion and thermal cycling.

Conclusion

Alloy 722 (Inconel 722 Wire, UNS N07722) is a high-performance precipitation-hardening superalloy wire, distinguished by its exceptional mid-to-high temperature strength, corrosion resistance, and versatility. Its strict manufacturing controls— particularly for age hardening and impurity reduction— ensure reliability in critical applications like aerospace propulsion and energy generation. Whether used in turbine components, subsea equipment, or medical devices, Inconel 722 wire delivers consistent performance under extreme conditions. For custom requirements— such as ultra-precision wire (down to 0.05 mm diameter), specialized surface finishes, or tailored aging cycles— 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 805 gallon liquid totes Special package is available on request.