Alloy 725,Inconel 725 Foil，Shim,UNS N07725

Alloy 725,Inconel 725 Wire,UNS N07725

Introduction to Alloy 725 (Inconel 725 Wire, UNS N07725)

Alloy 725, commercially known as Inconel 725 and classified under UNS N07725, is a high-performance nickel-chromium-molybdenum-niobium alloy strengthened by age hardening. This superalloy is specifically engineered to deliver an exceptional balance of high tensile and yield strength, excellent corrosion resistance, and good toughness across a wide temperature range (from cryogenic conditions up to 450°C/842°F). Inconel 725 wire, a key form of this alloy, is highly sought after in industries where reliability in harsh, corrosive environments—such as offshore oil and gas, chemical processing, and marine engineering—is non-negotiable. Its unique combination of properties makes it suitable for manufacturing critical components that require both structural integrity and resistance to aggressive media like seawater, sour gases, and acidic solutions.

1. Chemical Composition (Typical, wt%)

The chemical composition of UNS N07725 is strictly controlled to ensure its superior mechanical and corrosion properties, complying with industry standards such as ASTM B625 (for nickel-alloy wire), ASTM B619 (for nickel-alloy rod and bar), and ASME SB625. The typical composition is as follows:

Element

Content Range (wt%)

Function

Nickel (Ni)

55.0 - 59.0

Serves as the primary matrix element, providing a stable austenitic structure; enhances corrosion resistance and supports the formation of strengthening precipitates.

Chromium (Cr)

19.0 - 22.5

Forms a dense, protective chromium oxide (Cr₂O₃) layer on the surface, delivering excellent resistance to oxidation, pitting, and crevice corrosion in chloride-containing environments.

Molybdenum (Mo)

7.0 - 9.0

Boosts resistance to localized corrosion (e.g., pitting and crevice corrosion) in harsh media like sulfuric acid and sour gas; also enhances high-temperature strength.

Niobium (Nb) + Tantalum (Ta)

2.75 - 4.00

Acts as the key strengthening element—forms gamma-double-prime (γ″, Ni₃Nb) precipitates during age hardening, significantly increasing tensile and yield strength without compromising ductility.

Iron (Fe)

1.0 - 3.0

Improves hot workability, facilitating the manufacturing of wire and other forms; helps control alloy cost while maintaining overall performance.

Titanium (Ti)

0.30 - 0.80

Aids in the formation of fine precipitates (alongside niobium), refining the microstructure and further enhancing strength; also contributes to corrosion resistance.

Aluminum (Al)

0.20 - 0.80

Works with titanium to stabilize precipitates, optimizing the age-hardening response and improving toughness; supports the integrity of the protective oxide layer.

Carbon (C)

≤ 0.03

Minimized to prevent the formation of carbides at grain boundaries, which can reduce corrosion resistance and cause intergranular cracking in corrosive environments.

Manganese (Mn)

≤ 0.30

Aids in deoxidation during melting, reducing the presence of gaseous impurities; improves cold workability for wire drawing.

Silicon (Si)

≤ 0.30

Controls oxide formation during hot processing; helps maintain the cleanliness of the alloy microstructure.

Phosphorus (P)

≤ 0.015

Strictly limited to avoid brittleness, especially in welded joints and components exposed to cyclic loading.

Sulfur (S)

≤ 0.010

Minimized to prevent hot cracking during fabrication (critical for wire drawing and forming) and reduce corrosion susceptibility in aggressive media.

Copper (Cu)

≤ 0.25

Controlled to avoid interference with the formation of strengthening precipitates and to prevent degradation of corrosion resistance.

2. Physical Properties

Inconel 725 wire exhibits consistent and reliable physical properties, making it suitable for a diverse range of applications, from deep-sea components to high-pressure industrial equipment. Key properties (measured at room temperature unless otherwise specified) are:

Property

Value

Test Condition

Density

8.24 g/cm³

Room temperature (25°C)

Melting Point Range

1320 - 1370°C

-

Thermal Expansion Coefficient

12.6 × 10⁻⁶/°C

20 - 100°C; 14.8 × 10⁻⁶/°C (20 - 400°C)

Thermal Conductivity

11.2 W/(m·K)

100°C; 18.5 W/(m·K) (400°C)

Electrical Resistivity

1.31 × 10⁻⁶ Ω·m

Room temperature (25°C); 1.52 × 10⁻⁶ Ω·m (400°C)

Modulus of Elasticity

205 GPa

Room temperature (tensile); 180 GPa (400°C)

Poisson’s Ratio

0.30

Room temperature

Curie Temperature

≈ -196°C

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

Tensile Strength (After Aging)

≥ 1100 MPa

Room temperature; ≥ 850 MPa (400°C)

Yield Strength (0.2% Offset, After Aging)

≥ 950 MPa

Room temperature; ≥ 750 MPa (400°C)

Elongation (After Aging)

≥ 15%

Room temperature

Hardness (After Aging)

32 - 38 HRC

Room temperature

3. Production Process of Inconel 725 Wire

The manufacturing of Inconel 725 wire requires precise control of chemistry, heat treatment, and forming processes to ensure optimal strength, corrosion resistance, and dimensional accuracy. Key steps include:

3.1 Raw Material Melting & Casting

Melting: High-purity raw materials (nickel, chromium, molybdenum, niobium, etc.) are melted using vacuum induction melting (VIM) followed by vacuum arc remelting (VAR). This dual-melting process eliminates gaseous impurities (O₂ < 20 ppm, N₂ < 40 ppm) and ensures uniform distribution of alloying elements—particularly niobium, which is critical for the formation of strengthening precipitates.

Casting: The molten alloy is cast into ingots (typically 500 - 2000 kg) or blooms. These cast forms undergo homogenization annealing at 1100 - 1150°C for 8 - 10 hours to eliminate chemical segregation and refine the microstructure, preparing the material for subsequent hot working.

3.2 Hot Working & Wire Rod Production

Hot Rolling: Ingots or blooms are hot-rolled at 1000 - 1100°C into wire rods with a diameter of 8 - 18 mm. This process breaks down the coarse as-cast microstructure and improves the material’s workability. Hot-rolled rods are air-cooled to room temperature to prevent premature precipitation of strengthening phases.

Descaling: After hot rolling, rods undergo descaling (via 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: Hot-rolled rods are cold-drawn through diamond dies in multiple passes to achieve the desired wire diameter (typically 0.1 mm - 10 mm for industrial applications). Each drawing pass reduces the diameter by 10 - 20%, with intermediate solution annealing performed between passes to relieve work hardening. Solution annealing is conducted at 950 - 1000°C for 30 - 60 minutes, followed by rapid water quenching to dissolve any existing precipitates and restore ductility.

Dimensional Control: During cold drawing, precise tension and die alignment are maintained to ensure tight diameter tolerances (±0.02 mm for precision wire) and roundness (≤0.01 mm), which are critical for applications like spring manufacturing and electrical components.

3.4 Age Hardening (Key Strength-Enhancing Step)

The final critical step in Inconel 725 wire production is age hardening, which activates the formation of γ″ precipitates to achieve maximum strength. The process follows a specific two-step cycle:

First Aging Stage: Heating the wire to 700 - 730°C for 8 - 10 hours, followed by air cooling. This step initiates the nucleation of fine γ″ precipitates.

Second Aging Stage: Reheating the wire to 620 - 650°C for 12 - 16 hours, then air cooling. This step promotes the growth and uniform distribution of γ″ precipitates, resulting in the alloy’s characteristic high strength and toughness.

Note: For ultra-fine wire (diameter < 0.5 mm), aging times are slightly reduced (by 2 - 3 hours) to avoid excessive hardening, which could compromise flexibility.

3.5 Surface Finishing & Quality Inspection

Surface Treatment: After age hardening, the wire undergoes surface finishing to remove any residual oxides or contaminants. This includes:

Pickling: Immersion in a nitric-hydrofluoric acid solution to dissolve surface scales and improve corrosion resistance.

Passivation: Optional chromate treatment to enhance the protective oxide layer, further boosting resistance to pitting and crevice corrosion.

Polishing: For precision applications (e.g., medical devices), the wire is polished to achieve a smooth surface finish (Ra ≤ 0.2 μm).

Quality Control: Rigorous testing is performed to ensure compliance with industry standards:

Chemical Analysis: Optical emission spectroscopy (OES) to verify the composition of key elements (niobium, molybdenum, chromium) within specified ranges.

Mechanical Testing: Tensile testing (to confirm strength and elongation), hardness testing (HRC measurement), and fatigue testing (for components like springs).

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

Non-Destructive Testing: Eddy current testing to detect surface defects (e.g., cracks, pits) and ultrasonic testing to check for internal imperfections.

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

4. Product Applications

Inconel 725 wire’s unique combination of high strength, excellent corrosion resistance, and good processability makes it a preferred material for critical applications across multiple industries:

4.1 Oil & Gas Industry

Offshore Drilling Components: Used to manufacture wire ropes for subsea wellhead systems, control cables for offshore platforms, and springs for downhole tools (resists corrosion from seawater, sour gases like H₂S, and brines).

Sour Gas Wells: Thermocouple sheaths and electrical conductors for downhole logging tools—withstands high pressure (up to 15,000 psi) and corrosive environments (H₂S + chloride ions) without degradation.

Pipeline Maintenance: Welding filler wire for repairing or joining corrosion-resistant pipelines (matches the base metal’s strength and corrosion resistance, ensuring leak-free performance).

4.2 Chemical & Pharmaceutical Industry

Chemical Processing Equipment: Precision wire mesh for filtration in sulfuric acid and hydrochloric acid production plants (resists aggressive acids and high temperatures up to 400°C).

Pharmaceutical Manufacturing: Sanitary wire for sensor probes and heating elements in drug production equipment (complies with FDA standards for food and drug contact, and resists cleaning agents like sodium hydroxide).

Pump & Valve Components: Small-diameter wire for springs in chemical pumps and valves (maintains elasticity and strength in corrosive media like organic solvents and oxidizing acids).

4.3 Marine Engineering

Subsea Components: Wire for mooring lines of underwater drones and remote-operated vehicles (ROVs)—resists seawater corrosion and biofouling, ensuring long-term reliability in deep-sea environments (up to 3000 meters depth).

Marine Hardware: Fastener wires for ship hulls and offshore structures (outperforms stainless steel in saltwater, reducing maintenance costs and extending service life).

Coastal Power Plants: Wire for heat exchanger tubes and condenser components (resists corrosion from seawater used for cooling, preventing tube leaks and downtime).

4.4 Aerospace & Defense

Aerospace Fasteners: Fine wire for manufacturing high-strength fasteners (e.g., rivets, bolts) in aircraft engines and fuselages (combines lightweight properties with resistance to jet fuel and atmospheric corrosion).

Missile Systems: Wire for guidance system components and actuator springs (maintains strength and dimensional stability under extreme temperature fluctuations, from -50°C to 400°C).

Satellite Components: Electrical conductors for satellite power systems (resists corrosion in the vacuum of space and thermal cycling between sunlight and shadow).

4.5 Medical Devices

Surgical Instruments: Ultra-fine wire (0.05 - 0.2 mm diameter) for laparoscopic tools and orthopedic implants (biocompatible, resists corrosion from bodily fluids, and provides sufficient strength for load-bearing applications).

Diagnostic Equipment: Wire for catheter sensors and endoscope components (flexible yet strong, enabling precise movement within the human body).

4.6 Other Applications

Nuclear Power: Wire for control rod drives and auxiliary system components (resists corrosion from reactor coolants and has low neutron absorption, ensuring safety and reliability).

Automotive: High-performance springs for exhaust systems of luxury and racing vehicles (resists high temperatures and exhaust gas corrosion, extending spring life).

Conclusion

Alloy 725 (Inconel 725 Wire, UNS N07725) is a premier age-hardening nickel-based superalloy wire that excels in demanding environments requiring both high strength and superior corrosion resistance. Its carefully controlled chemical composition, advanced production processes (including precise cold drawing and age hardening), and versatile properties make it an indispensable material for critical applications in oil & gas, chemical processing, marine engineering, and aerospace. Whether used in subsea wellheads, pharmaceutical equipment, or aerospace fasteners, Inconel 725 wire delivers consistent performance and long service life. For custom requirements—such as ultra-precision wire diameters (down to 0.01 mm), specialized surface finishes, or tailored age-hardening cycles to meet specific strength needs—manufacturers can provide customized solutions to align with 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 823 gallon liquid totes Special package is available on request.