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Physical Composition
Approximately half of Inconel 718 is made of nickel, including some cobalt, ranging between 50 percent and 55 percent of the material's composition. Chromium content is between 17 percent and 21 percent for a random sampling. Niobium plus tantalum is around 5 percent, while molybdenum is about 3 percent. Small contributions (less than 1 percent each) also come from titanium, aluminum, carbon, manganese, copper, silicon, phosphorous, sulfur and boron.
Physical Property Constants
The density of Rockwell's Inconel 718 alloy is 0.296 lbs. per cubic inch. It will begin melting around 2,300 degrees Fahrenheit, or 1,260 degrees Celsius. Further, the specific heat is 0.104 British Thermal Units per lb. at 70 degrees Fahrenheit. Lastly, its permeability in a magnetic field of 200 oersted at 70 degrees Fahrenheit is 1.001.
Modulus and Thermal
Thomas Young's modulus of elasticity at cold temperatures, between -308 and 500 degrees Fahrenheit, ranges between 31.3 and 28.0 thousand ksi. At the hottest temperature tested, 2,000 degrees, it can drop as low as 14.3 thousand ksi. At 1,000 degrees, thermal conductivity is 135 BTU-h-(degrees Fahrenheit)-inches per square foot, and its electrical resistivity is 728 ohm-circ-mil per foot.
Welding
Rockwell provides Inconel filler metal 718 as solder. It has a very similar chemical composition to the original metal, except for about half the chromium content. Inconel 718 welds well using the gas tungsten-arc process. After welding and age hardening, joint efficiencies are close to unity, meaning the the welded joint is nearly as strong as the original alloy itself.