Inconel 718 (2.4668 / UNS N07718) — AMS 5596 / AMS 5663 Nickel Alloy

​‌​​‌​

Inconel 718 (UNS N07718): A Nickel Super Alloy Strengthened by Age Hardening​‌​​‌​

Technical Description

Inconel 718 is a nickel-based super alloy whose strength has been increased by age hardening. The typical composition of the alloy is 50-55% nickel, 17-21% chromium, 4.75-5.5% niobium + tantalum, 2.8-3.3% molybdenum, 0.65-1.15% titanium, 0.2-0.8% aluminium and up to 18.5% iron. This distinctive composition provides high temperature strength and excellent fatigue resistance.​‌​​‌​

The most characteristic property of Inconel 718 is that it is suitable for precipitation hardening. With heat treatment, gamma prime and gamma double prime precipitates (γ’ – Ni₃(Al,Ti) and γ” – Ni₃Nb) are formed and its mechanical strength is significantly increased. Thanks to this property it exhibits high yield strength and creep resistance at temperatures up to 700 °C.

The alloy has good weldability properties; in this respect it differs from other nickel alloys that show a tendency to cracking after welding (for example Inconel 625). The tensile strength of Inconel 718 is approximately 1240 MPa, and its yield strength is at a level of 1030 MPa.​‌​​‌​

​‌​​‌​

Inconel 718 Relevant Standards

Inconel 718 appears in many standards for various industrial and aerospace applications. These standards are summarised below:​‌​​‌​

• ASTM B637 – Bar, wire, forged parts
• AMS 5662 – Bar, forging, ring (not precipitation hardened)​‌​​‌​
• AMS 5663 – Bar, forging, ring (precipitation hardened)
• AMS 5596 / AMS 5597 – Sheet and plate products​‌​​‌​
• AMS 5832 – Welding wire
• ASTM B670 – Plate and sheet​‌​​‌​
• API 6A CRA – Its suitability for oil and gas applications

Compliance with these standards plays a determining role in purchasing processes in both the aerospace and the petrochemical sectors.​‌​​‌​

Inconel 718 Trade Names and Equivalents

• Inconel® 718 – Registered name of Special Metals Corporation​‌​​‌​
• Alloy 718 – Common trade name
• UNS N07718 / Werkstoff Nr. 2.4668 – International material designations​‌​​‌​
• NC19FeNb – Its equivalent in the EN norms
• NiCr19Fe19Nb5Mo3 – Chemical composition designation​‌​​‌​

Inconel 718 Application Areas

The high temperature, fatigue and corrosion resistance properties of Inconel 718 make it indispensable in a very wide variety of critical engineering applications. Its principal areas of use are given below:​‌​​‌​

• • Aerospace Industry — Gas turbine engine parts*Exhaust systems
    *Compressor discs
    *Jet engine blades
    *Landing gear components
    *Aircraft fasteners
  • Oil and Natural Gas Industry*Well equipment operating under high pressure and temperature
    *Downhole safety valves
    *Pump shafts and compressor parts
    *Long-life use in sour gas environments thanks to NACE MR0175 compliance​‌​​‌​

• • Nuclear Industry*Heat exchangers operating at high temperature
    *Pressurised reactor covers
    *Radiation resistant fasteners​‌​​‌​
  • Automotive and Motorsport*Turbocharger components
    *Performance exhaust systems
  ​‌​​‌​

• • Chemical and Process Industry*Agitator shafts operating in acidic environments,
    *Reactor components
    *Pressure vessels
  ​‌​​‌​

Inconel 718 Advantages

• High Strength Through Age Hardening: Thanks to the intermetallic phases precipitated after heat treatment, it offers superior mechanical strength up to 700 °C.​‌​​‌​
• Extraordinary Fatigue Resistance: It provides a long service life under repeated loads in aircraft and engine systems.
• Weldability: Unlike other nickel alloys, it is resistant to weld cracks. This property provides a great advantage in terms of structural integrity.​‌​​‌​
• Corrosion and Oxidation Resistance: Thanks to its resistance to oxidative degradation even at high temperature, it is used with confidence in heavy industry applications.
• Microstructural stability: It is resistant to structural problems such as grain growth or phase separation after heat treatment.​‌​​‌​

Inconel 718 Disadvantages

• Limited Machinability: High tool wear is seen during machining, especially in the cold condition. CNC tool paths and cutting speeds need to be selected very carefully.​‌​​‌​
• Cost: The high nickel, niobium and molybdenum content makes Inconel 718 expensive compared with other alloys. For this reason it is preferred only in critical engineering applications.
• Heat Treatment Requirement: In order to reach high mechanical properties, the solution and ageing operations must always be applied correctly.​‌​​‌​
• Upper Limit on Creep Resistance: At temperatures above 700 °C, alloys more durable against creep deformation (for example Inconel 625 or Rene 41) may be preferred.

Purchasing and Engineering Notes​‌​​‌​

When selecting Inconel 718, the part geometry, the operating temperature and the target strength level should always be taken into account. The AMS 5662 and AMS 5663 specifications are preferred especially in aerospace part production, while the ASTM B637 standard is generally suitable for the oil, natural gas and process industry.

Conclusion and Industrial Evaluation​‌​​‌​

Inconel 718 is an industrial super material able to meet a large number of engineering needs at the same time — such as load carrying capacity, fatigue strength and oxidative resistance — in systems operating under high temperature.

It stands out as a long-life and maintenance-free solution in many sectors, from aerospace engines to oil wells and from nuclear reactors to high performance automotive systems. Although it has some limitations in terms of machinability and cost, the high performance it offers overshadows these disadvantages in most applications.​‌​​‌​

#Inconel718
#Alloy718
#UNSN07718
#2.4668
#NiCr19Fe19Nb5Mo3
#AMS5596
#AMS5662
#AMS5597
#AMS5589
#AMS5590
#ASTMB637
#ASTMB670

​‌​​‌​

​‌​​‌​