Inconel 718 is an age-hardenable superalloy designed to resist a wide range of severely corrosive environments, including pitting corrosion.
This nickel-chromium alloy also displays exceptionally high yield, tensile, and creep-rupture properties at high temperatures.
The combination of high-temperature strength with good fabricability and corrosion resistance makes Inconel 718 particularly useful for manufacturing purposes.
Its age-hardenability allows it to be heat treated to high strengths that cannot be achieved with other alloys.
This post will delve into further detail about this amazing alloy, including a comprehensive description of how it is made, as well as some of its primary properties and applications.
Inconel Alloy 718 is a high-strength, corrosion-resistant nickel-chromium alloy used in applications where high strength, good weldability, and corrosion resistance are required.
The alloy has excellent creep and rupture strength at temperatures up to 1300°F (704°C).
Its unique composition results in a set of properties that make it an ideal material to use in many hostile environments.
Inconel 718 is mostly composed of nickel and chromium, but also contains many other additional elements such as molybdenum, iron, columbium, and ruthenium.
Its chemical composition is as follows:
As you can see from the list above, Inconel 718 has various elements in its total composition.
In terms of its usefulness for making custom metal parts, its high levels of iron, molybdenum, niobium, and cobalt are of particular interest.
This is because they make it a suitable material for both high-temperature and cryogenic environments.
Moreover, the metallurgical stability of Inconel 718, which helps it resist both internal and external decomposition, is largely due to its chemical structure.
Inconel 718 can be produced through two sets of heat treatments: annealing and precipitation hardening.
Heat treatments are used to change the microstructure of an alloy, which in turn can change its mechanical properties.
The overall purpose of any kind of heat treatment on an alloy is to improve its chemical, functional, and mechanical properties.
The main goal of annealing is to increase the ductility of a material and reduce its hardness, thus making it more workable.
With annealing, the material is heated to a temperature higher than its recrystallization temperature, which is then maintained for an appropriate amount of time, before the material is allowed to cool to formation.
The temperature at which Inconel 718 is annealed is usually between 1700-1850°F (926 – 1010°C). The heating is rapidly followed by water cooling and sometimes air cooling if needed.
Inconel 718 is usually annealed when it needs to be softened for cold work.
Precipitation hardening, (also known as age hardening, or particle hardening) is used to increase the hardness of metals.
The process involves precipitating small particles of a harder metal within the metal’s grain structure.
Through this process, alloys are strengthened by providing additional support to the grain boundaries, which ultimately boosts the overall strength of the material.
This process can also make Inconel 718 easier to work with, as when its hardness increases, it becomes easier to shape.
Both annealing and precipitation hardening can be used to improve Inconel 718’s natural properties, depending on what outcome is needed.
When the material needs to be softened, then annealing is the heat treatment of choice, and when the material needs to be hardened and strengthened, then precipitation hardening is ideal.
The chemical composition of Inconel 718, combined with the heat treatments discussed in the last section, gives it an outstanding combination of properties that have made it an ideal material for manufacturing components that must operate in corrosive environments and high temperatures.
Below is a list of the most outstanding ones:
Out of the properties listed above, the three most sought-after ones are its strength, corrosion resistance, and temperature resistance.
The most important strength of Inconel 718 lies in its ability to resist stress corrosion cracking and creep.
Its high-nickel content gives it good resistance to stress corrosion cracking and its creep resistance makes it an ideal material for high-temperature applications.
Inconel 718 may not be the strongest alloy in the Inconel family, but the addition of molybdenum and niobium gives it a higher strength level than many of the other Inconel alloys.
This superalloy also exhibits excellent corrosion resistance in a wide range of aggressive media.
For instance, Inconel 718 is resistant to both reducing and oxidizing acids.
Its corrosion resistance is primarily due to the formation of a dense and tenacious oxide film on its surface that protects the underlying metal from a corrosive attack.
Additionally, Inconel 718 is resistant to both high and low temperatures.
It can be used at temperatures ranging from -423°F to 1300°F (-252°C to 704°C).
The alloy’s resistance to both hot and cryogenic temperatures along with its high strength-to-weight ratio, and resistance to corrosion makes it perfect for use in high-stress environments where temperature fluctuations and corrosive agents are the norm.
Inconel 718 is often used in the aerospace industry for the manufacture of parts that are subject to high temperatures and stress. It is also used in the chemical processing industry for components and systems that need to withstand corrosive chemicals.
Aside from aeronautics and chemical processing, Inconel 718 is also commonly used in the following industries:
Within these industries, its most popular applications include the following:
Inconel 718 is also utilized for 3D printing because of its outstanding strength, corrosion resistance, and machinability.
It is an ideal material for 3D printing metal parts, as it offers a high degree of accuracy and repeatability.
Yet another application of this versatile alloy is its use in die casting.
Die casting is a manufacturing process that helps create metal parts by injecting molten metal under high pressure into a mold.
Inconel 718 can be used to produce die and die holders, since it tends to resist deformation under intense heat much longer than other alloys.
Its excellent mechanical and weldability properties have made it a popular manufacturing material within the chemical, aerospace, oil and gas, power generation, and automotive industries.
Inconel 718 is an ideal choice for many applications that must operate and function in harsh environments—its high strength, corrosion resistance, temperature resistance, and oxidation resistance make it durable, reliable, and functional in high and low-temperature environments as well as in highly corrosive settings.
The alloy is also easy to weld and fabricate, making it a versatile material for many industries that need a tough and strong material for their metal parts.
If your project requires a material that can withstand high temperatures and harsh environments, then Inconel 718 could be the right material for the job.