A Comprehensive Guide to Nickel-Based Superalloys: Inconel 718 (Alloy 718/UNS N07718)
Inconel 718 is also called "Alloy 718" and is named UNS N07718 or W.Nr.2.4668 (Chinese brand name: GH4169). It is an age-hardening Ni-Cr-Fe-based superalloy containing large amounts of iron, niobium and molybdenum, and small amounts of aluminum and titanium. Titanium and niobium are added to overcome the problem of strain age cracking during welding and repair. Inconel 718 combines corrosion resistance and high strength with excellent weldability, including post-weld cracking resistance. The alloy has excellent creep rupture strength at temperatures up to 1300 °F [700 °C].
Inconel 718 alloy precipitates through the body-centered tetragonal γ' phase and the FCC γ' phase, and has good comprehensive properties in the temperature range of -253°C to 700°C. The yield strength below 650℃ ranks first among deformed high-temperature alloys. It has good fatigue resistance, radiation resistance, oxidation resistance and corrosion resistance, and has good cutting processability, weldability and long-term structural stability. Parts with complex shapes can be manufactured and have been widely used in the aerospace, nuclear energy and petroleum industries within the above temperature range.
Properties of Inconel 718 (Alloy 718/UNS N06718)
Inconel718 precipitation hardening molybdenum alloy contains niobium and nickel-chromium alloy. It has high strength and good toughness at 700℃, and has good corrosion resistance in high and low temperature environments. Delivery condition can be solution treated or precipitation hardened.
Easy to process;
It has high tensile strength, fatigue strength, creep strength and fracture strength at 700℃;
Oxidation resistance at 1000℃;
Chemically stable at low temperatures;
It is characterized by good welding performance.
Alloy 718 has excellent resistance to stress corrosion cracking and pitting corrosion in both high and low temperature environments. Alloy 718 has particularly outstanding oxidation resistance at high temperatures.
Corrosion resistance of Inconel 718 (Alloy 718/UNS N06718)
The chemical composition of alloys can be divided into three categories: standard composition, high-quality composition and high-purity composition. High-quality ingredients can reduce carbon and increase niobium on the basis of standard ingredients, thereby reducing the amount of niobium carbide, reducing fatigue sources, increasing the number of strengthening phases, and improving fatigue resistance and material strength. At the same time, the content of harmful impurities and gases is reduced. High-purity ingredients are based on high-quality standards to reduce the content of sulfur and harmful impurities and improve the purity and comprehensive performance of materials.
The boron content of Inconel 718 alloy for nuclear energy needs to be controlled (other elements remain unchanged), and the specific content is determined by negotiation between both parties. When ω(b)≤0.002%, it is different from the Inconel 718 alloy used in the aerospace industry, and the alloy grade is Inconel 718A.
