Inconel 718
Designated as UNS N07718 or W.Nr. 2.4668, Inconel 718, also known as “Alloy 718”, is a precipitation-hardenable nickel-chromium alloy containing significant amount of iron, niobium, and molybdenum along with lesser amounts of aluminum and titanium. The titanium and niobium are added to overcome strain-age cracking problems during welding and weld repair. Inconel Alloy 718 combines corrosion resistance and high strength with outstanding weldability, including resistance to postweld cracking. The alloy has excellent creep-rupture strength at temperatures up to 1300°F[700°C]. The Inconel 718 is fabricated for gas turbines, rocket motors, spacecraft, nuclear reactors, pumps and other piping tools. Most commonly, it is used for fasteners and springs.
Inconel 718 fasteners: hexagonal bolts with nuts.
1. Chemical Composition Requirements
Element | Content, % |
Nickel (plus Cobalt) | 50.00-55.00 |
Chromium | 17.00-21.00 |
Iron | Balance |
Niobium (plus Tantalum) | 4.75-5.50 |
Molybdenum | 2.80-3.30 |
Titanium | 0.65-1.15 |
Aluminum | 0.20-0.80 |
Cobalt | ≤1.00 |
Carbon | ≤0.08 |
Manganese | ≤0.35 |
Silicon | ≤0.35 |
Phosphorus | ≤0.015 |
Sulfur | ≤0.015 |
Boron | ≤0.006 |
Copper | ≤0.30 |
2. Physical Properties
Inconel 718 springs used in a trunnion mounted ball valve.
Density, lb/in3 | Melting Range | Specific Heat at 70°F, Btu/lb °F | Curie Temperature, °F(°C) | Permeability at 200 oersted and 70°F |
Annealed | Annealed and Aged | °F | °C | at 21°C, J/kg °C) | Annealed Material | Annealed and Aged Material | Annealed Material | Annealed and Aged Material |
0.296 | 0.297 | 2300-2437 | 1260-1336 | 0.104(435) | <-320(<-196) | -170(-112) | 1.0013 | 1.0011 |
3. Product Forms and Related Standards of Inconel 718
Products form | Standard |
Rod, bar and wire | ASTM B166 |
Plate, sheet and strip | ASTM B168, B906 |
Seamless pipe and tube | ASTM B167, B829 |
Billet and bar for reforging | ASTM B472 |
Forging | ASTM B564 |
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