Inconel 718 Alloy

General Characteristics of Inconel 718 Alloy

This is a nickel-based precipitation-hardening alloy designed for very high yield strength, tensile strength and creep rupture properties at temperatures up to 1300ºF (705ºC.) The alloy has excellent weldability.

Chemical Analysis
C Carbon
0.08 max
Mn Manganese
0.35 max
P and S Phosphorus and Sulfur
0.015 maxx
Si Silicon
0.35 max
Ni(+Co) Nickel Colbalt
50.0/55.0
Cr Chromium
17/21
Co Cobalt
1.00 max
Cu Copper
0.15 max/td>
Al Aluminium
0.35/0.80
Mo Molybdenum
2.80/3.30
Ti Titanium
0.65/1.15
Cb + Ta Columbium + Tantalum
4.75/5.50
B Boron
0.001/0.006

Applications

The alloy is used in jet engine and high-speed airframe parts such as wheels, buckets and spacers, and high-temperature bolts and fasteners. The alloy is also used in the oil and gas drilling and production industries due to its high strength and resistance to chlorides, stress corrosion and sulfide stress cracking. Within these industries the alloy has been used for valves, pump shafts and wellhead components.

Forging

Alloy 718 should be forged from a maximum furnace temperature of 2050ºF (1120ºC) and should not be soaked for an overly long time at this temperature. Uniform reductions during forging will prevent the formation of a duplex grain structure. Working in the range 1700/1850ºF (925/1010ºC) will improve the forging’s strength if its subsequent service temperature is below 1100ºF (595ºC.)

Heat treatment

Heat treatments may be adjusted to give required properties. For the best combination of tensile and stress rupture properties, the following quite complex cycle is recommended :
1 hr at 1750/1800ºF (955/980ºC) and air cool, then 8 hrs at 1325ºF (720ºC) and cool at 100ºF/hr (56ºC/hr) to 1150ºF (620ºC), hold for 8 hrs and air cool.
For the best room temperature and cryogenic tensile properties, the cycle is :

1-2hrs at 1950ºF (1065ºC) and air cool, then 8 hrs at 1325ºF (720ºC) and cool at 100ºF/hr (56ºC/hr) to 1150ºF (620ºC), hold for 8 hrs and air cool.

Machinability

The alloy may be readily machined in either the annealed or age-hardened conditions. The age-hardened condition gives a better surface finish, the annealed condition a longer tool life.

Weldability

The alloy may be welded in either the aged or annealed conditions. Welding an age-hardened material will result in the formation of a softened heat-affected zone

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