Inconel 718: Properties And Applications

What are the characteristics of Inconel 718?

Alloy 718, often referred to as Inconel 718, is a high-strength, corrosion-resistant nickel chromium alloy supplied in the hot worked, solution annealed and age hardened condition. As with other types of Inconel, the JN Alloy owns the trademark for Incoloy Alloy 718. As a nickel-chromium alloy, Inconel 718 possesses acceptable corrosion resistance in a range of environments including sea water, hydrogen sulphide, CO2, elemental sulphur and chloride ions over various temperatures. It is resistant to sulphide stress cracking and is capable of passing the sulphide stress corrosion test in accordance with NACE TM 0177 Method C solution A.

Inconel 718 is an age-hardenable Nickel-Chromium-Columbium (Niobium)-Molybdenum alloy with high strength, corrosion-resistance, and good fabrication characteristics. Inconel 718 has high tensile, yield, and creep-rupture properties at high temperatures and can operate at cryogenic temperatures up to 1200°F (650°C). Developed in the early 1960's, Inconel 718 is still considered the material of choice for the majority of aircraft engine components with service temperatures below 1200°F (650°C). It combines corrosion resistance and high strength with outstanding weldability including resistance to postweld cracking. The alloy has excellent creep-rupture strength at temperatures to 1300°F (700°C).

The sluggish age-hardening response of Inconel 718 permits annealing and welding without spontaneous hardening during heating and cooling. This alloy has excellent weldability when compared to the nickel-base superalloys hardened by aluminum and titanium. This alloy has been used for jet engine and high-speed airframe parts such as wheels, buckets, spacers, and high temperature bolts and fasteners.

Chemical Composition of Inconel 718

Inconel 718 is a precipitation-hardenable nickel-chromium alloy also containing significant amounts of iron, niobium and molybdenum along with lesser amounts of aluminium and titanium. The addition of Nb, Ti, Al and Ni forms a series of precipitates during the controlled solution annealing and ageing process steps. This results in a significant increase in strength and hardness compared with alternative nickel alloys. These tensile and creep rupture properties are maintained from cryogenic to elevated temperatures. These properties make it suitable for applications between -250oC – 650oC. Typical chemical analysis of Inconel 718

Element	Percentage
Carbon	0.08 max
Manganese	0.35 max
Phosphorus	0.015 max
Sulfur	0.015 max
Silicon	0.35 max
Chromium	17-21
Nickel	50-55
Molybdenum	2.80-3.30
Columbium	4.75-5.50
Titanium	0.65-1.15
Aluminum	0.20-0.80
Cobalt	1.00 max
Boron	0.006 max
Copper	0.30 max
Tantalum	0.05 max
Iron	Balance

Physical Properties of Inconel 718

Heat Treatment

The following heat treatment of inconel 718 should be used to obtain the best combination of tensile properties and stress rupture properties: 1 hr 1750°F to 1800°F (954 to 982°C) air cool + 8hr 1325°F (718°C) cool 100°F /hr to 1150°F (56 °C/hr to 621°C), hold 8 hrs and air cool. To obtain the best room temperature and cryogenic tensile properties, the following heat treatment should be used: 1 to 2 hr 1950°F (1066°C), air cool + 8 hr 1325°F (718°C) cool 100°F/hr to 1150°F (56°C/hr to 621°C), hold 8 hr and air cool.

Hot Working

Hot-working is carried out using a 2050°F (1121°C) maximum furnace temperature. Hot-cold working in the range 1700/1850°F (927/1010°C) will improve the strength of the forging if the service temperature is below about 1100°F (593°C). Prolonged soaking at the forging temperature is not desirable. The material should be given uniform reductions to avoid the formation of duplex grain structures.

Machining

The alloy can be readily machined in either the annealed or the age-hardened condition. The age-hardened condition gives better chip action on chip breaker tools and produces a better finish. The annealed condition will give a slightly longer tool life.

Welding

Alloy 718 can be welded in either the annealed or the age condition. Welding in the aged condition will cause the formation of a softened heat-affected zone.

Uses of Inconel 718

Alloy 718 finds widespread utility owing to its outstanding mechanical properties, encompassing high tensile strength, resistance to creep, extended fatigue life, as well as impressive oxidation and corrosion resistance. This versatile alloy is integral in various applications, playing a pivotal role in the aerospace industry with uses ranging from landing gear components to automotive applications like exhaust manifolds.

WR.Nr 2.4668 Alloys also find a place in critical sectors such as medical devices, particularly in orthopedic surgery screws. Its adaptability extends to nuclear power plants, gas turbines, oil refineries, industrial valves, pressure vessels, heat exchangers, and fasteners like bolts and nuts. Notably, its exceptional heat resistance positions it as an ideal material for elevated temperature operations, making it indispensable for applications such as jet engines and combustion chambers in automobiles and motorcycles.

Inconel 718 is often used within the aviation and aerospace industries. Engineers are constantly looking to improve the reliability and efficiency of engines, not to mention their longevity. Superalloys, and in particular alloy 718, are selected for their balance between cost and performance. It’s imperative to use materials that can retain their strength and resistance to corrosion in the hottest sections of these engines. The materials used are under challenging conditions, with both mechanical and atmospheric stresses to consider.

Inconel 718 is ideal for use in these circumstances. For example, it has been used in jet engine and high-speed airframe parts, including wheels, fasteners, instrumentation parts, bolts, spacers and buckets. It is also used to engineer components for liquid-fuelled rockets, rings and casings, as well as various formed sheet metal parts for turbine engines, both aircraft and land-based.

Conclusion

Inconel 718 from JN Alloy is not just a material; it’s a commitment to excellence, durability, and performance. Elevate your projects with the reliability of our Inconel 718 – where quality meets innovation. Each supply comes with a Material Test Certificate (MTC) to ensure compliance with specified standards. Explore myriad industrial possibilities with us, your trusted Inconel 718 stockist and Inconel 718 suppliers. Contact us today for top-notch solutions that redefine quality and innovation in every aspect of Inconel 718.