Hard special nickel 718 alloy has good plasticity, ductility, fatigue properties, creep properties, and tensile strength, so it is widely used in various fields. The typical applications are liquid rockets, columns, protective sleeves, and a variety of aircraft on the molding sheet metal parts, gas turbine engines on the ground, cryogenic storage tanks, as well as fasteners and instrument parts.
Workpieces must be surface cleaned before and during heating. If the heating environment contains sulfur, phosphorus, lead, or other low melting point metals, Inconel 718 alloy will become brittle. Impurities come from marking paints, chalk, lubricants, water, fuels, and so on.
The sulfur content of fuels should be low, for example, it should be less than 0.1% in liquefied petroleum gas and natural gas, less than 0.25g/m3 in city gas, and less than 0.5% in petroleum gas.
The electric furnace should have the function of precise temperature control. The furnace gas must be neutral or weakly alkaline. The fluctuation between oxidizing and reducing of the furnace gas composition is not allowed.
5.2 Hot working on Inconel 718
The hot working temperature of Inconel 718 alloy is 1120-900 ℃. Cooling can be water quenching or other rapid cooling methods, annealing needs to be done promptly after hot working to ensure the best performance.
The material should be heated to the upper limit of the processing temperature during hot working, to ensure plasticity during processing. The final processing temperature should not be lower than 960℃ when the deformation reaches 20%.
5.3 Inconel 718 Cold working
Cold working should be carried out after solution treatment. The work hardening rate of Inconel 718 is greater than austenitic stainless steel, so the processing equipment should be adjusted accordingly, and there should be an intermediate annealing process during the cold working.
5.4 Inconel 718 Heat Treatment
Different solution treatment and aging processes result in different material properties. Due to the low diffusion rate of the γ" phase, the best mechanical properties of Inconel 718 alloy can be obtained by prolonged aging.
5.5 Inconel 718 Sanding
It requires fine abrasive belt sanding because oxides around welds of Inconel 718 workpieces are more difficult to remove than in stainless steel.
The removal of oxides with sandpaper or salt bath pretreatment is also needed before pickling in a mixture of nitric and hydrofluoric acids.
5.6 Inconel 718 Machining
Machining of Inconel 718 needs to be carried out after solution treatment. Inconel 718 is suitable for low cutting speeds because of its work-hardening properties of the material.
ᆞTurning
Inconel 718 turning processing
The main processing difficulties of nickel-based alloys are large plastic deformation, high cutting force, high cutting temperature, severe hardening, and severe tool wear, making it difficult to ensure surface quality and accuracy.
So, people usually use new high-performance cutting tool materials, suitable cutting fluid, and appropriate heat treatment processes to improve the cutting processability of the material. It also requires suitable cutting parameters to optimize cutting, to achieve a high machining speed of Inconel 718.
Burrs may appear on the machined surface during dry machining Inconel 718. Adjusting the feed amount to change the direction of chip flow and the shape of the chip, can reduce the generation of burrs.
5.7 Inconel 718 Welding
Precipitation-hardened Inconel 718 alloy is well suited for welding. There is no tendency to crack after welding.
Inconel718 is suitable for arc welding, plasma welding, and so on.
ᆞNotice:
Before welding, the surface of the material should be clean, with no oil, and no chalk marks, and the weld should be polished to reveal bright metal within a range of 25mm around the weld.
Inconel 718 is recommended welding material:
ᆞGTAW/GMAW
ᆞNicrofer S 5219
ᆞW.-Nr. 2.4667
ᆞSG-NiCr19NbMoTi
ᆞAWS A 5.14 ERNiFeCr-2
ᆞBS 2901 Part 5: NA 51
