Inconel 718 UNS N07718

Introduction to Inconel 718

Inconel 718 is a high-performance nickel-chromium-based superalloy renowned for its exceptional strength, corrosion resistance, and ability to withstand extreme temperatures. Developed in the 1960s，Inconel 718 has become one of the most widely used superalloys in industries such as aerospace, oil and gas, nuclear engineering, and chemical processing.

Composition and Properties

Inconel 718 is primarily composed of nickel (50-55%) and chromium (17-21%), with significant additions of niobium (4.75-5.5%), molybdenum (2.8-3.3%), and smaller amounts of titanium, aluminum, and iron. The alloy also contains trace elements such as carbon, manganese, and silicon. The combination of these elements gives Inconel 718 its remarkable mechanical properties, including high tensile strength, excellent fatigue resistance, and outstanding creep resistance at elevated temperatures.

One of the key features of Inconel 718 is its ability to maintain strength and stability at temperatures up to 700°C (1292°F). This makes it particularly suitable for applications in high-temperature environments, such as gas turbine engines and rocket motors. Additionally, the alloy exhibits excellent resistance to oxidation and corrosion, even in harsh chemical environments, making it ideal for use in chemical processing and offshore oil and gas applications.

Heat Treatment and Fabrication

Inconel 718 can be heat treated to enhance its mechanical properties. The most common heat treatment process involves solution annealing followed by aging. Solution annealing is typically performed at temperatures around 955-1010°C (1750-1850°F), followed by rapid cooling. Aging is then carried out at 720°C (1325°F) for 8 hours, followed by furnace cooling to 620°C (1150°F) and holding for a total aging time of 18 hours. This process precipitates gamma prime (γ') and gamma double prime (γ'') phases, which significantly increase the alloy's strength.

Fabrication of Inconel 718 can be challenging due to its high strength and work-hardening rate. However, it can be machined, welded, and formed using appropriate techniques. Welding, in particular, requires careful control of heat input to avoid cracking and to maintain the alloy's corrosion resistance.

Applications

Inconel 718 is widely used in the aerospace industry for components such as turbine blades, discs, and engine casings. Its ability to withstand high temperatures and stresses makes it indispensable in jet engines and rocket propulsion systems. In the oil and gas industry, Inconel 718 is used for downhole tools, wellhead components, and valves, where it provides excellent resistance to sour gas environments.

The alloy is also employed in nuclear reactors, where its resistance to radiation-induced embrittlement and corrosion is critical. In the chemical processing industry, Inconel 718 is used for reactors, heat exchangers, and piping systems that handle aggressive chemicals.

Conclusion

Inconel 718 is a versatile and highly reliable superalloy that has become a cornerstone material in many high-performance applications. Its unique combination of strength, corrosion resistance, and high-temperature stability ensures its continued use in some of the most demanding environments across various industries. As technology advances and the need for materials that can withstand extreme conditions grows, Inconel 718 will remain a critical material in engineering and manufacturing.

Chemistry

Tensile Data

D- Forging quality is furnished to chemical requirements and surface inspection only. No mechanical properties required.

Specifications

Machining

Machinability Ratings