Is Inconel rust proof?
Inconel alloys are among the most versatile metals. With their high performance and excellent characteristics, they are used in various industries.
They are a natural choice for the automotive, aerospace, marine, and oil and gas industries as they are specifically optimized to withstand some of the most demanding manufacturing conditions.
What exactly makes Inconel alloys so special? Here's everything you need to know about them.
How Inconel alloys are made
While the composition of Inconel alloys varies widely, they are all made with nickel and chromium as the primary elements. These specialty metals should not be confused with duplex stainless steel, austenitic stainless steel, or any other type of stainless steel alloy. Below is a brief overview of the different types of Inconel alloys and their respective compositions.
Inconel 600
This nickel-chromium alloy is highly resistant to many corrosive elements. It will not succumb to general oxidation or stress corrosion cracking caused by chloride ions, even under extreme temperature conditions.
Inconel 601
Inconel 601 contains nickel, chromium and aluminum. The addition of aluminum gives it excellent mechanical properties, even in high-temperature environments.
Inconel 625
Inconel 625 contains nickel, chromium, molybdenum and niobium. The reaction between molybdenum and niobium causes the alloy's matrix microstructure to harden, thereby increasing its overall tensile strength. This makes this nickel-based alloy extremely resistant to corrosive elements commonly found in harsh conditions.
Inconel 690
Unlike other metal alloys in the range, Inconel 690 is made from high chromium and nickel. The use of high chromium makes this special metal alloy variant highly resistant to the corrosive conditions of aqueous environments. Its high corrosion resistance also allows it to withstand the sulfurization that occurs in high-temperature environments.
Inconel 718
The structure and response of Inconel 718 is quite different from other metals in the series. This nickel-based superalloy is made from nickel and chromium with significant amounts of molybdenum, niobium and iron. It also contains trace amounts of aluminum and titanium. The combination of these alloying elements makes Inconel 718 very strong, flexible and resistant to post-weld cracking.
Applications of Inconel Alloy
Manufacturers and design engineers use Inconel alloys in a variety of industrial applications that require reliable and technically superior materials. The fact that they have excellent resistance to corrosion and high temperatures makes them very attractive.
These alloys are best reserved for use in environments that other materials cannot withstand. Outlined below are some of the leading industrial applications that rely on Inconel alloys.
Jet engine
aerospace industry
Jet engine components are constantly exposed to high pressure and temperature. Therefore, the materials used in its construction need to withstand these conditions while maintaining their strength and integrity.
Nickel-based superalloys are a natural choice for any high-temperature application. It is corrosion-resistant, resistant to creep deformation in high-stress environments, and has a low expansion rate even under high-temperature conditions. For example, Inconel 718 and 750 are used in the manufacture of turbine seals, fasteners and exhaust liners.
Automobile industry
A car engine is a precision mechanical component. It generates a lot of heat but still needs to be efficient, lightweight and reliable. Inconel 600, 601 and 625 have a wide range of applications including the construction of critical components in high performance vehicles. Additionally, it is frequently used in passive safety devices such as airbags, electrical switchgear, fuel pumps, sensors, ignition systems and exhaust connectors.
shipbuilding industry
Inconel alloys achieve high performance even under the most extreme conditions, such as those found in the shipbuilding industry. Nickel alloys can withstand the highly corrosive conditions of offshore processing plants that rely on seawater as a coolant.
Inconel 625 is widely used in subsea communications cable jackets, propulsion motors, propeller blades, wire ropes, and even downhole equipment.
Properties of Inconel Alloy
One of the most notable properties of Inconel alloy is its corrosion resistance. They also exhibit excellent resistance to oxidation, even compared to stainless steel, and can withstand high temperatures.
When exposed to high temperatures, Inconel forms a protective, passivating oxide layer on its surface to protect it from further damage. Not only is it resistant to heat, but it retains its strength under these conditions. In addition, Inconel is pressure resistant, making it ideal for extreme applications in various fields.
Sparks are produced when metal is cut
High Temperature Strength of Inconel Alloys
The strength of superalloys is improved by solid solution strengthening and precipitation strengthening or age hardening. The heat treatment used depends on the specific high temperature alloy.
These techniques combine nickel with varying amounts of niobium to form gamma bis (gamma). This intermetallic compound produces tiny cubic crystals that prevent creep deformation and slip at high temperatures.
The formation of these crystals increases over time, especially after exposing the alloy to temperatures of 1,560°F (850°C) and above for 3-72 hours. This thick passivating oxide layer allows the metal to remain exceptionally strong over a wide range of temperatures.
The following is an overview of the mechanical properties of Inconel 718 sheet after precipitation heat treatment.
Yield Strength in Annealed Condition (Minimum Offset 0.2%): 80,000 psi (550 MPa)
Ultimate tensile strength (minimum): 140,000 psi (965 MPa)
Elongation (minimum): 30 (% of 2 inches)
Coefficient of thermal expansion from 77°F to 1400°F: 8.9
Given the high strength of superalloys, there are some key machine considerations that must be taken into account when cutting them. Their high temperature resistance often adds extra heat to cutting tools, reducing their performance. Adding special heat-resistant blades or coatings to the machining process helps the machine hold up better during the cutting process.
