INCONEL® alloy 718

Alloy-718

Inconel 718 alloy is a precipitation hardening nickel-chromium-iron alloy containing niobium and molybdenum. It has high strength, good toughness and corrosion resistance in high and low temperature environments below 650°C. The state may be solution treated or precipitation hardened.

Inconel 718 Chemical composition

Alloy%NiCrFeMoNbCoCMnSiSCuAlTi
718Min.5017Balance2.84.750.20.7
Max.55213.35.510.080.350.350.010.30.81.15

Inconel 718 Physical properties

Density8.2 g/cm³
Melting point1260-1340 ℃

Inconel 718 Alloy minimum mechanical properties in the roomtemperature

AlloyTensile strength
Rm N/mm²
Yield strength
R P0. 2N/mm²
Elongation
A 5 %
Brinell hardnessHB
Solution treatment96555030≤363

718 Alloy Characteristic as below:

1.workability

2.High tensile strength,endurance strength,creep strength and rupture strength at 700℃.

3.High inoxidability at1000℃.
4.Steady mechanical performance in the low temperature.

5.Good welding performance.

Inconel 718 Metallurgical structure

718alloy is Austenitic structure, precipitation hardening generate “γ” made it excellent mechanical performance. G rain boundary generate “δ” made it the best plasticity in the heat treatment.

Inconel 718 Corrosion resistance

718 alloy with extremely resistance to stress corrosion cracking and pitting ability in high temperature or low temperature environments, especially the inoxidability in the high temperature.

Inconel 718 Application field:

The elevated temperature strength, excellent corrosion resistance and workability at 700℃ properties made it use in a wide range of high requirement environments.

1.Steam turbine

2.Liquid-fuel rocket

3.Cryogenic engineering

4.Acid environment

5.Nuclear engineering

Machining and Heat Treatingedit broadcast

Inconel 718 alloy is a difficult-to-machine material in the field of machining .

Warm up

The workpiece must be surface cleaned before and during heating to keep the surface clean. If the heating environment contains sulfur, phosphorus, lead or other low melting point metals, Inconel718 alloy will become brittle. Impurities originate from marked paint, chalk, lubricating oil, water, fuel, etc. The sulfur content of fuel should be low. For example, the impurity content of liquefied gas and natural gas should be less than 0.1%, the sulfur content of city gas should be less than 0.25g/m3, and the sulfur content of petroleum gas should be less than 0.5%.

The heated electric furnace should preferably have a relatively accurate temperature control ability, the furnace gas must be neutral or weakly alkaline, and the fluctuation of the furnace gas composition in oxidizing and reducing properties should be avoided.

Thermal processing

The suitable hot working temperature of Inconel718 alloy is 1120-900℃. The cooling method can be water quenching or other rapid cooling methods. After hot working, it should be annealed in time to ensure the best performance. During hot processing, the material should be heated to the upper limit of the processing temperature. In order to ensure the plasticity during processing, the final processing temperature when the deformation amount reaches 20% should not be lower than 960 °C.

Cold working

Cold working should be carried out after solution treatment . The work hardening rate of Inconel718 is greater than that of austenitic stainless steel , so the processing equipment should be adjusted accordingly, and there should be an intermediate annealing process during cold working.

Heat treatment

Different solution treatment and aging treatment processes will result in different material properties. Due to the low diffusion rate of the γ” phase, the best mechanical properties of Inconel718 alloy can be obtained by long-term aging treatment.

Polished

The oxides near the welds of Inconel718 workpieces are more difficult to remove than those of stainless steel. They need to be polished with a fine abrasive belt. Before pickling in a mixed acid of nitric acid and hydrofluoric acid , sandpaper should also be used to remove oxides or salt bath pretreatment. deal with.

Machining

Machining of Inconel718 needs to be carried out after solution treatment , taking into account the work hardening . Unlike austenitic stainless steel, Inconel718 is suitable for low surface cutting speeds .

Welding

The precipitation hardening Inconel 718 alloy is very suitable for welding and has no tendency to crack after welding. Weldability, ease of processing, and high strength are several advantages of this material.
Inconel718 is suitable for arc welding , plasma welding, etc. Before welding, the surface of the material should be clean, free of oil stains, chalk marks, etc., and the bright metal should be polished within 25mm around the weld .