Thermo-mechanical processing and heat treatments can be tailored to emphasize properties particularly desired for a given application. The work piece should be reheated if any part cools below 1650F before the desired amount of reduction has been achieved. In order to minimize creep notch sensitivity, the metal should be worked uniformly with gradually decreasing temperature and with relatively light finishing reductions (20 to 25 percent for open-die work and 10 percent for closed-die work) in the 1750 to 1650F range. Heating above 2050F is undesirable because of the danger of severe grain coarsening. Inconel 718 is recommended at a hot-work range of 2050F maximum to 1650F minimum. Forgingĭo to its good strength at elevated temperatures, Inco 718 has relatively high resistance to hot working. This heat treatment involves solution annealing above the delta solvus temperature, as follows: Solution heat treat at 1950F, one-half to one hour, AC or faster duplex precipitation heat treat at 1400F. It is used for optimum ductility and low temperature toughness in heavy sections, although it can also produce notch brittleness in creep rupture and is not recommended for applications operating above 1000F. A second heat treat procedure involves slightly higher solutioning and aging temperatures. Standard heat treatment for most specifications includes a solution heat treatment in the range of 1750F to 1800F, followed by a duplex precipitation heat treatment of 1325F/8 hours with a ~100F/hour cool down to 1150F, and holding an additional 8 hours at 1150F, for a total precipitation heat treat time of 18 hours, then AC. The second lower temperature aging treatment promotes additional fine precipitate for improved tensile strength and creep rupture life. The first aging treatment coarsens this precipitate as well as forming additional precipitate. The heat treatments generally involve a high temperature anneal for solutioning of these second phases followed by one or two lower temperature aging treatments to re-precipitate the strengthening phases in the desired distributions.Some strengthening precipitate generally forms on cooling from the solution annealing temperature. Heat treatment schedules for wrought Inconel 718 are based primarily on considerations of solution and re-precipitation reactions of the gamma-prime and gamma-double-prime phases for strengthening and of delta phase for grain size control. It also has good sea water corrosion resistance and it is attractive for marine applications. Inconel 718 possesses excellent corrosion and oxidation resistance. Formingįorming for IN 718 is good in the solution annealed condition.
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A full post-weld solution anneal and precipitation heat treatment is often applied to obtain optimum properties in weldments. The precipitation hardened alloy is also weldable, but weld joints are relatively soft and weak until heat treated.
Welding is generally carried out on solution annealed material, and appropriate post-weld heat treatment is employed to develop the desired properties. Parent metal weld filler is typically used. Inconel 718 has good weldability, particularly in conjunction with gas-tungsten-arc (GTA), plasma-arc, and electron-beam welding. The use of annealed material provides easier machining and longer tool life, but machining of the age-hardened alloy results in better chip action on chipbreaker tools and slightly better surface finish. Nevertheless, with proper selection of tool materials, speeds, feeds, and coolants, it can be machined in either the annealed or age-hardened condition. Like other nickel-base superalloys, the machinability of Inconel 718 is inferior to that of most steels including stainless steels. Inco 718 has a machining ability rating of 14. Modulus of Elasticity: 29 msi in STA conditionĬoefficient of Expansion: 7.9 x10-6 in/in/F RT-800F. Inconel 718 Additional Information: Physical Propertiesĭensity: 0.296 lbs per cubic inch in the solution annealed condition and 0.297 lbs per cubic inch in the solution and precipitation heat treated condition.
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