Alloy 718,Inconel 718 Fittings,UNS N07718

Alloy 718,Inconel 718 Wire,UNS N07718

Introduction to Alloy 718 (Inconel 718 Wire, UNS N07718)

Alloy 718, commercially known as Inconel 718 and classified under UNS N07718, is a versatile precipitation-hardening nickel-chromium-niobium-molybdenum superalloy. Renowned for its exceptional combination of high-temperature strength, excellent corrosion resistance, and superior weldability, it operates reliably across a broad temperature range—from cryogenic conditions (-269°C/-452°F) up to 650°C/1202°F. Its strength is primarily derived from the formation of gamma-double-prime (γ″, Ni₃Nb) and gamma-prime (γ′, Ni₃Al, Ti) precipitates during controlled age hardening, while its chromium and molybdenum content ensures robust resistance to oxidation, pitting, and crevice corrosion. Inconel 718 wire, a key form of this alloy, is widely used in industries requiring precision, durability, and performance under extreme conditions, such as aerospace, energy, and marine engineering. Unlike many high-temperature alloys, it maintains excellent ductility and machinability, making it suitable for both complex structural components and fine precision parts.

1. Chemical Composition (Typical, wt%)

The chemical composition of UNS N07718 adheres to strict industry standards including ASTM B625 (for nickel-alloy wire), ASTM B637 (for nickel-alloy bars), and ASME SB625, ensuring consistent precipitation-hardening behavior, weldability, and corrosion performance. The typical composition is as follows:

Element

Content Range (wt%)

Function

Nickel (Ni)

50.0 - 55.0

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

Chromium (Cr)

17.0 - 21.0

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

Iron (Fe)

Balance

Improves hot workability and weldability (critical for wire production and component fabrication); reduces alloy cost without compromising performance.

Niobium (Nb) + Tantalum (Ta)

4.75 - 5.50

Primary strengthening element—forms γ″ precipitates (Ni₃Nb), the main contributor to high tensile and creep strength; tantalum enhances high-temperature stability.

Molybdenum (Mo)

2.80 - 3.30

Enhances localized corrosion resistance (e.g., in sour gas or acidic media) and supplements high-temperature creep strength; improves weldability by reducing hot cracking risk.

Titanium (Ti)

0.65 - 1.15

Aids in γ′ precipitate formation (Ni₃Ti), complementing γ″ to optimize strength-ductility balance; controls grain growth during heat treatment.

Aluminum (Al)

0.20 - 0.80

Cooperates with titanium to refine γ′ precipitate size and distribution; supports the integrity of the protective oxide layer.

Carbon (C)

≤ 0.08

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

Manganese (Mn)

≤ 0.35

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

Silicon (Si)

≤ 0.35

Controls oxide formation during hot processing and reduces molten alloy viscosity for casting; limited to avoid excessive oxide inclusions.

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 welding) and reduce corrosion susceptibility.

Copper (Cu)

≤ 0.30

Controlled to avoid interference with γ″/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 components.

2. Physical Properties

Inconel 718 wire exhibits stable physical properties across its extensive 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

8.19 g/cm³

Room temperature (25°C)

Melting Point Range

1260 - 1320°C

-

Thermal Expansion Coefficient

12.2 × 10⁻⁶/°C

20 - 100°C; 15.4 × 10⁻⁶/°C (20 - 600°C)

Thermal Conductivity

11.4 W/(m·K)

100°C; 18.8 W/(m·K) (600°C)

Electrical Resistivity

1.29 × 10⁻⁶ Ω·m

Room temperature (25°C); 1.51 × 10⁻⁶ Ω·m (600°C)

Modulus of Elasticity

206 GPa

Room temperature (tensile); 167 GPa (600°C)

Poisson’s Ratio

0.30

Room temperature

Curie Temperature

≈ -196°C

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

Tensile Strength (After Aging)

≥ 1310 MPa

Room temperature; ≥ 965 MPa (600°C)

Yield Strength (0.2% Offset, After Aging)

≥ 1170 MPa

Room temperature; ≥ 860 MPa (600°C)

Elongation (After Aging)

≥ 15%

Room temperature

Hardness (After Aging)

38 - 44 HRC

Room temperature

Creep Rupture Strength

240 MPa

1000 hours at 600°C; 105 MPa (1000 hours at 650°C)

3. Production Process of Inconel 718 Wire

The manufacturing of Inconel 718 wire requires precise control of chemistry, heat treatment, and forming to optimize precipitation hardening, weldability, and dimensional accuracy. Key steps include:

3.1 Raw Material Melting & Casting

Melting: High-purity raw materials (nickel, chromium, niobium, molybdenum, etc.) are melted via vacuum induction melting (VIM) followed by vacuum arc remelting (VAR) or electron beam remelting (EBM). This dual/triple melting process eliminates gaseous impurities (O₂ < 20 ppm, N₂ < 40 ppm) and ensures uniform distribution of niobium, titanium, and boron—critical for consistent γ″/γ′ precipitate formation and grain boundary strength.

Casting: Molten alloy is cast into ingots (500 - 3000 kg) or blooms, which undergo homogenization annealing at 1100 - 1160°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.

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 prevent premature precipitate formation (which could reduce ductility during cold drawing).

Descaling: Hot-rolled rods undergo shot blasting (to remove loose scale) followed by acid pickling (nitric-hydrofluoric acid solution) to eliminate residual oxide layers—critical for preventing surface defects in the final wire.

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 solution annealing (950 - 1000°C for 30 - 60 minutes, water-quenched) between passes. This annealing step dissolves existing precipitates, relieves work hardening, and restores ductility—preventing wire breakage during drawing.

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 fasteners or medical devices, laser diameter monitoring is used to ensure consistency.

3.4 Age Hardening (Strength Optimization)

Age hardening is the core step to activate γ″ and γ′ precipitates and achieve target strength. The process follows a standardized three-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.

First Aging (Intermediate): Heating to 715 - 745°C for 8 hours, then furnace cooling to 600 - 630°C at a rate of 55 - 85°C/hour. This step initiates the formation of fine γ″ precipitates.

Second Aging (Final): Holding at 600 - 630°C for 8 hours, followed by air cooling. This step promotes the growth of γ″ (primary strengthener) and γ′ (secondary strengthener), resulting in the alloy’s characteristic high strength and toughness.

Note: For ultra-fine wire (diameter < 0.5 mm), aging times are reduced by 2 - 3 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.

Passivation: Optional chromate or nitric acid passivation to strengthen the protective oxide layer—ideal for marine or chemical applications exposed to saltwater or aggressive media.

Polishing: For high-precision applications (e.g., medical instruments, aerospace sensors), the wire is polished to a smooth surface finish (Ra ≤ 0.15 μm) using abrasive belts or electrochemical polishing.

Quality Control:

Chemical Analysis: Optical emission spectroscopy (OES) and inductively coupled plasma mass spectrometry (ICP-MS) to verify niobium, molybdenum, and boron content—critical for precipitation hardening and weldability.

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

Corrosion Testing: Salt spray testing (ASTM B117), crevice corrosion testing (ASTM G48), and intergranular corrosion testing (ASTM A262 Practice E) to validate resistance to harsh environments.

Non-Destructive Testing: Eddy current testing (for surface defects like cracks or pits), ultrasonic testing (for internal flaws), and magnetic particle testing (for ferromagnetic inclusions—rare in Inconel 718 but checked for critical applications).

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

4. Product Applications

Inconel 718 wire’s unique combination of high strength, corrosion resistance, weldability, and temperature versatility makes it indispensable in demanding industries:

4.1 Aerospace & Defense

Aircraft Engines: Fine wire (0.2 - 1.5 mm) for turbine blade fasteners, compressor rotor springs, and fuel injector components—withstands 600 - 650°C and cyclic thermal stress. Its weldability allows for on-site repair of engine parts.

Spacecraft Components: Wire for satellite structural supports, rocket nozzle actuators, and cryogenic fuel line fasteners—maintains strength at -269°C (liquid helium temperatures) and resists space radiation.

Aerospace Fasteners: Cold-drawn wire for high-strength rivets, bolts, and nuts in fuselages and wings—resists atmospheric corrosion (e.g., from humidity or pollutants) and maintains integrity at high altitudes.

4.2 Energy Generation

Gas Turbines: Wire for turbine rotor blades, stator vanes, and heat exchanger tubes in combined-cycle power plants—resists 550 - 650°C flue gas corrosion and creep deformation. Its weldability simplifies turbine assembly.

Nuclear Power: Wire for control rod drives, coolant circulation pipes, and steam generator components—low neutron absorption, resistance to borated water corrosion, and stability under radiation.

Renewable Energy: Wire for concentrated solar power (CSP) heat absorber tubes and wind turbine generator coils—withstands 600 - 650°C molten salt corrosion (CSP) and marine atmospheric corrosion (offshore wind).

4.3 Chemical & Petrochemical Industry

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

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

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

4.4 Marine Engineering

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

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

4.5 Medical Devices

Surgical Instruments: Ultra-fine wire (0.05 - 0.2 mm) for laparoscopic tools, orthopedic implant screws, and dental braces—biocompatible (ISO 10993), resists bodily fluid corrosion (e.g., saliva, blood), and provides sufficient strength for load-bearing applications.

Diagnostic Equipment: Wire for catheter sensors and MRI-compatible components—non-magnetic (above curie temperature) and stable under sterilization (autoclaving at 134°C).

4.6 Industrial Machinery

High-Temperature Furnaces: Wire for heating element supports, thermocouple sheaths, and furnace door springs—operates at 600 - 650°C in air or inert gas (e.g., argon).

Automotive (High-Performance): Wire for turbocharger components, exhaust system springs, and electric vehicle (EV) battery connectors—resists 550 - 600°C exhaust gas corrosion and maintains conductivity in EV systems.

Conclusion

Alloy 718 (Inconel 718 Wire, UNS N07718) is a premier precipitation-hardening superalloy wire, distinguished by its unmatched balance of high-temperature strength, corrosion resistance, weldability, and versatility. Its strict manufacturing controls—from dual melting to precision age hardening—ensure reliability in critical applications across aerospace, energy, and medical industries. Whether used in aircraft turbines, nuclear reactors, or surgical tools, Inconel 718 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 tailored aging cycles for specific strength needs—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 792 gallon liquid totes Special package is available on request.