Alloy 625,Inconel 625 Sheet,UNS N06625

Alloy 625,Inconel 625 Wire,UNS N06625

Introduction to Alloy 625 (Inconel 625 Wire, UNS N06625)

Alloy 625, commercially known as Inconel 625 and classified under UNS N06625, is a nickel-chromium-molybdenum-niobium (columbium) superalloy renowned for its exceptional corrosion resistance and high-temperature strength—all without the need for precipitation hardening. Unlike age-hardenable nickel alloys, its performance stems from a solid-solution strengthened austenitic microstructure, where molybdenum and niobium enhance both strength and resistance to localized corrosion. This alloy operates reliably across an extensive temperature range, from cryogenic conditions (-253°C/-423°F) up to 980°C/1800°F, making it a versatile choice for harsh environments. Inconel 625 wire, a key form of this alloy, is widely used in industries such as chemical processing, aerospace, marine engineering, and energy generation, where it delivers consistent performance in aggressive media (e.g., acids, seawater, sour gas) and extreme thermal conditions. Its excellent weldability and formability further expand its application scope, from precision components to structural supports.

1. Chemical Composition (Typical, wt%)

The chemical composition of UNS N06625 adheres to strict industry standards including ASTM B625 (for nickel-alloy wire), ASTM B443 (for nickel-alloy seamless tubes), and ASME SB625, ensuring consistent corrosion resistance, mechanical strength, and processability. The typical composition is as follows:

Element

Content Range (wt%)

Function

Nickel (Ni)

58.0 min.

Serves as the primary matrix element, stabilizing the austenitic structure and providing a foundation for corrosion resistance; enhances ductility at cryogenic temperatures.

Chromium (Cr)

20.0 - 23.0

Forms a dense, adherent chromium oxide (Cr₂O₃) layer on the surface, delivering superior oxidation resistance up to 980°C and resistance to pitting/crevice corrosion in chloride-containing environments.

Molybdenum (Mo)

8.0 - 10.0

A key solid-solution strengthener, significantly boosting high-temperature tensile and creep strength; enhances resistance to reducing acids (e.g., sulfuric acid) and localized corrosion.

Niobium (Nb) + Tantalum (Ta)

3.15 - 4.15

Acts as a dual-function element: strengthens the alloy via solid solution and forms carbides (NbC) that prevent intergranular corrosion; tantalum supplements niobium to further improve high-temperature stability.

Iron (Fe)

≤ 5.0

Improves hot workability and weldability (critical for wire production); controls alloy cost without compromising corrosion or strength properties.

Carbon (C)

≤ 0.10

Limited to prevent excessive carbide precipitation (which can reduce ductility); small amounts aid in forming niobium carbides for grain boundary strengthening.

Manganese (Mn)

≤ 0.50

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

Silicon (Si)

≤ 0.50

Controls oxide formation during hot processing; reduces molten alloy viscosity for casting, ensuring uniform chemistry in wire rods.

Phosphorus (P)

≤ 0.015

Strictly limited to avoid grain boundary embrittlement, especially in welded joints or components exposed to cyclic loading.

Sulfur (S)

≤ 0.010

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

Copper (Cu)

≤ 0.10

Controlled to avoid interference with the protective oxide layer and maintain resistance to sulfuric acid corrosion.

2. Physical Properties

Inconel 625 wire exhibits stable physical properties across its broad operating temperature range, with mechanical performance derived from solid-solution strengthening—eliminating the need for post-fabrication age hardening. Key properties (measured at room temperature unless specified otherwise) are:

Property

Value

Test Condition

Density

8.44 g/cm³

Room temperature (25°C)

Melting Point Range

1290 - 1350°C

-

Thermal Expansion Coefficient

12.8 × 10⁻⁶/°C

20 - 100°C; 16.3 × 10⁻⁶/°C (20 - 800°C)

Thermal Conductivity

11.8 W/(m·K)

100°C; 23.0 W/(m·K) (800°C)

Electrical Resistivity

1.38 × 10⁻⁶ Ω·m

Room temperature (25°C); 1.65 × 10⁻⁶ Ω·m (800°C)

Modulus of Elasticity

205 GPa

Room temperature (tensile); 150 GPa (800°C)

Poisson’s Ratio

0.30

Room temperature

Curie Temperature

≈ -196°C

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

Tensile Strength

≥ 827 MPa

Room temperature; ≥ 414 MPa (800°C)

Yield Strength (0.2% Offset)

≥ 414 MPa

Room temperature; ≥ 276 MPa (800°C)

Elongation

≥ 30%

Room temperature; ≥ 40% (-196°C, liquid nitrogen)

Hardness (Annealed)

≤ 248 HB

Room temperature

Creep Rupture Strength

140 MPa

1000 hours at 700°C; 48 MPa (1000 hours at 800°C)

3. Production Process of Inconel 625 Wire

The manufacturing of Inconel 625 wire focuses on preserving its solid-solution strengthened microstructure, ensuring corrosion resistance and dimensional accuracy. Unlike age-hardenable alloys, no post-drawing aging is required—simplifying processing while maintaining performance. Key steps include:

3.1 Raw Material Melting & Casting

Melting: High-purity raw materials (nickel, chromium, molybdenum, niobium, etc.) are melted via 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 molybdenum and niobium—critical for consistent solid-solution strengthening and corrosion resistance.

Casting: Molten alloy is cast into ingots (500 - 3000 kg) or blooms, which undergo homogenization annealing at 1150 - 1200°C for 8 - 12 hours. This step eliminates chemical segregation (especially of niobium) and refines the as-cast microstructure, preparing the material for hot working while preserving ductility.

3.2 Hot Working & Wire Rod Production

Hot Rolling: Ingots/blooms are hot-rolled at 1050 - 1150°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 maintain the solid-solution microstructure—avoiding premature carbide precipitation.

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 compromise corrosion resistance in aggressive environments.

3.3 Cold Drawing (Wire Formation)

Multi-Pass Cold Drawing: Wire rods are cold-drawn through diamond dies in 6 - 10 passes to achieve the desired diameter (typically 0.1 mm - 10 mm). Each pass reduces diameter by 12 - 20%, with intermediate annealing (980 - 1050°C for 30 - 60 minutes, water-quenched) between passes. This annealing step relieves work hardening, restores ductility (preventing wire breakage), and maintains the solid-solution microstructure—critical for consistent corrosion performance.

Dimensional Control: Tension, die alignment, and drawing speed are precisely regulated to maintain tight diameter tolerance (±0.015 mm for precision wire) and roundness (≤0.008 mm). For applications like aerospace sensors or medical devices, laser diameter monitoring ensures consistency, as dimensional variations can affect component functionality.

3.4 Surface Finishing & Quality Inspection

Surface Treatment:

Pickling: Post-drawing pickling in nitric-hydrofluoric acid to remove oxide scales and enhance the protective chromium oxide layer—critical for marine or chemical applications.

Passivation: Optional nitric acid passivation to further strengthen the oxide layer, reducing the risk of pitting corrosion in chloride-rich environments (e.g., seawater, brines).

Polishing: For high-precision applications (e.g., pharmaceutical equipment, aerospace fasteners), the wire is polished to a smooth surface finish (Ra ≤ 0.15 μm) using abrasive belts or electrochemical polishing, minimizing contamination risks and stress concentrations.

Quality Control:

Chemical Analysis: Optical emission spectroscopy (OES) and inductively coupled plasma mass spectrometry (ICP-MS) to verify molybdenum and niobium content—critical for solid-solution strengthening and corrosion resistance.

Mechanical Testing: Tensile testing (strength/elongation at room and high temperatures), hardness testing (HB), and fatigue testing (for cyclic-loading components like springs).

Corrosion Testing: Salt spray testing (ASTM B117), crevice corrosion testing (ASTM G48), and intergranular corrosion testing (ASTM A262 Practice C) 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 oil & gas downhole tools.

Dimensional Inspection: Laser measurement to confirm diameter, straightness (≤0.08 mm/m), and length accuracy. For coil wire, payout tension testing ensures consistent unwinding during fabrication.

4. Product Applications

Inconel 625 wire’s unique combination of exceptional corrosion resistance, high-temperature strength, and formability makes it indispensable in industries requiring reliability in harsh environments:

4.1 Chemical & Petrochemical Industry

Acid Processing Equipment: Fine wire (0.2 - 1.0 mm) for manufacturing wire mesh filters and sensor probes in sulfuric acid (H₂SO₄), hydrochloric acid (HCl), and phosphoric acid (H₃PO₄) production—resists both oxidizing and reducing acids.

Downhole Tools: Wire for electrical conductors and thermocouple sheaths in sour gas wells—withstands H₂S and chloride-induced corrosion at temperatures up to 800°C, ensuring long-term tool functionality.

Pump & Valve Components: Small-diameter wire for springs in chemical pumps and valves—maintains elasticity in aggressive media (e.g., organic solvents, molten salts) without degradation.

4.2 Aerospace & Defense

Aircraft Engines: Wire for turbine engine exhaust systems and combustion chamber liners—resists high-temperature oxidation (up to 980°C) and thermal cycling, reducing maintenance frequency.

Spacecraft Components: Wire for cryogenic fuel line supports and satellite structural parts—maintains ductility at -196°C (liquid oxygen) and resists space radiation, ensuring mission reliability.

Military Equipment: Wire for armor plating fasteners and missile guidance system components—balances strength with corrosion resistance, even in extreme environments (e.g., desert sand, saltwater spray).

4.3 Marine Engineering

Offshore Platforms: Wire for mooring line tensioners, subsea electrical cables, and riser components—resists seawater corrosion (3.5% NaCl) and biofouling, even in deep-sea environments (up to 3000 meters depth).

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

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

4.4 Energy Generation

Nuclear Power: Wire for control rod drives and reactor auxiliary system components—low neutron absorption, resistance to borated water corrosion, and stability under radiation.

Concentrated Solar Power (CSP): Wire for heat absorber tubes and molten salt transport systems—withstands 600 - 800°C molten salt corrosion and cyclic thermal stress.

Fossil Fuel Power Plants: Wire for flue gas desulfurization (FGD) system components—resists acidic flue gas corrosion, ensuring compliance with emissions regulations.

4.5 Pharmaceutical & Medical Industries

Pharmaceutical Manufacturing: Sanitary wire for mixing blades and filtration systems in drug production—complies with FDA standards (21 CFR Part 177) for food/drug contact and resists cleaning agents (e.g., sodium hydroxide, nitric acid).

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

Conclusion

Alloy 625 (Inconel 625 Wire, UNS N06625) is a premier solid-solution strengthened superalloy wire, distinguished by its exceptional corrosion resistance, high-temperature strength, and versatility. Its ability to perform reliably without age hardening simplifies manufacturing, while its broad temperature range and chemical tolerance make it a go-to material for critical applications in chemical processing, aerospace, and marine engineering. Whether used in acid reactors, aircraft engines, or deep-sea equipment, Inconel 625 wire delivers consistent performance under extreme conditions. For custom requirements—such as ultra-precision wire (down to 0.01 mm diameter), specialized surface finishes (e.g., electropolishing), or large-diameter wire (up to 15 mm) for structural components—manufacturers offer tailored 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 762 gallon liquid totes Special package is available on request.