Nickel Alloy Inconel 718 Specification, Composition and Density

-- A Guide to Its Properties and Standards

Explore Inconel 718, a high-strength nickel alloy. This guide covers its key specifications, chemical composition, density, and uses in aerospace and oil & gas.

Inconel 718 is a high-performance precipitation-hardening nickel-chromium-iron alloy that maintains excellent strength, corrosion resistance, and good machinability at temperatures up to 700°C (1300°F). Understanding its key technical specifications, chemical composition, and density is crucial for proper material selection and application in harsh industrial environments such as aerospace and oil and gas.

Nickel Alloy Inconel 718  Chemical Composition

The typical elemental composition of Inconel 718 is: Nickel (Ni) 50-55%, Chromium (Cr) 17-21%, and Iron (Fe) balance. Unlike other nickel-based alloys, 718 alloys achieve age hardening through the addition of approximately 5% niobium (Nb) and appropriate amounts of titanium (Ti) and aluminum (Al). During heat treatment, niobium, titanium, and aluminum form dispersed γ'' (Ni3Nb) and γ' (Ni3(Al,Ti)) phases, which are the fundamental reason for its ultra-high strength. The addition of molybdenum (Mo) further enhances its resistance to pitting corrosion and its corrosion resistance in reducing environments.

Key Technical Specifications and Standards

To ensure the stability and reliability of material properties, the production and supply of Inconel 718 typically follow a series of international standards. These standards specify stringent requirements for chemical composition, heat treatment processes, mechanical properties, and non-destructive testing. In the oil and gas and other industrial sectors, ASTM B637 details the technical requirements for precipitation-hardened nickel alloy bars, forgings, and blanks. In the aerospace field, AMS 5662 (bars and forgings) and AMS 5663 (solution-treated and aging-treated bars and forgings) are widely used standards.

Density and Key Physical Properties

Inconel 718 typically has a density of approximately 8.19 g/cm³ (0.296 lb/in³), a crucial reference for structural design and weight calculations. In addition to its high strength, this alloy exhibits excellent fatigue resistance and weldability. Compared to some other difficult-to-weld nickel-based superalloys, it is less prone to cracking after welding, facilitating the manufacture of complex structural components. Furthermore, it demonstrates excellent resistance to creep rupture, making it ideal for manufacturing gas turbine disks, blades, and fasteners.

Typical Applications

Inconel 718 is widely used in critical components requiring high-temperature strength and corrosion resistance. Typical applications include: engine components for liquid-fueled rockets; combustion chambers, turbine disks, and blades for aero-engines and industrial gas turbines; downhole tools, valves, and wellhead equipment in the oil and gas industry; and high-strength fasteners and structural components in nuclear reactors and chemical equipment.