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Inconel 718 round bar

Inconel is a family of austenite nickel-chromium-based superalloys.[1] The name is a trademark of Special Metals Corporation, a wholly owned subsidiary of Precision Castparts Corp.[not verified in body]

Inconel alloys are oxidation and corrosion resistant materials well suited for service in extreme environments subjected to pressure and heat. When heated, Inconel forms a thick, stable, passivating oxide layer protecting the surface from further attack. Inconel retains strength over a wide temperature range, attractive for high temperature applications where aluminum and steel would succumb to creep as a result of thermally induced crystal vacancies. Inconel’s high temperature strength is developed by solid solution strengthening or precipitation strengthening, depending on the alloy.

Inconel alloys are typically used in high temperature applications. It is sometimes referred to in English as "Inco" (or occasionally[not verified in body] "Iconel"). Common trade names for Inconel Alloy 625 include: Inconel 625, Chronin 625, Altemp 625, Haynes 625, Nickelvac 625 and Nicrofer 6020.[2]


The Inconel family of alloys was first developed in the 1940s by research teams at Wiggin Alloys (Hereford, England), which has since been acquired by SMC,[3] in support of the development of the Whittle jet engine.[citation needed]


Different Inconels have widely varying compositions, but all are predominantly nickel, with chromium as the second element.

Inconel Element (% by mass)
Ni Cr Fe Mo Nb Co Mn Cu Al Ti Si C S P B
600 [4] 72.0 14.0-17.0 6.0-10.0 1.0 0.5 0.5 0.15 0.015
617 [5] 44.2-56.0 20.0-24.0 3.0 8.0-10.0 10.0-15.0 0.5 0.5 0.8-1.5 0.6 0.5 0.15 0.015 0.015 0.006
625 [6] 58.0 20.0-23.0 5.0 8.0-10.0 3.15-4.15 1.0 0.5 0.4 0.4 0.5 0.1 0.015 0.015
690 [7] 59.5 30 9.2 0.35 0.01 0.02 0.35 0.019 0.003
718 [8] 50.0-55.0 17.0-21.0 balance 2.8-3.3 4.75-5.5 1.0 0.35 0.2-0.8 0.65-1.15 0.3 0.35 0.08 0.015 0.015 0.006
X-750 [9] 70.0 14.0-17.0 5.0-9.0 0.7-1.2 1.0 1.0 0.5 0.4-1.0 2.25-2.75 0.5 0.08 0.01


Inconel alloys are oxidation- and corrosion-resistant materials well suited for service in extreme environments subjected to high pressure and kinetic energy. When heated, Inconel forms a thick and stable passivating oxide layer protecting the surface from further attack. Inconel retains strength over a wide temperature range, attractive for high-temperature applications where aluminium and steel would succumb to creep as a result of thermally induced crystal vacancies (see Arrhenius equation). Inconel's high temperature strength is developed by solid solution strengthening or precipitation strengthening, depending on the alloy. In age-hardening or precipitation-strengthening varieties, small amounts of niobium combine with nickel to form the intermetallic compound Ni3Nb or gamma prime (γ'). Gamma prime forms small cubic crystals that inhibit slip and creep effectively at elevated temperatures.[10] The formation of gamma-prime crystals increases over time, especially after three hours of a heat exposure of 850 °C, and continues to grow after 72 hours of exposure.[11]


Inconel is a difficult metal to shape and machine using traditional techniques due to rapid work hardening. After the first machining pass, work hardening tends to plastically deform either the workpiece or the tool on subsequent passes. For this reason, age-hardened Inconels such as 718 are machined using an aggressive but slow cut with a hard tool, minimizing the number of passes required. Alternatively, the majority of the machining can be performed with the workpiece in a solutionized form, with only the final steps being performed after age hardening.

External threads are machined using a lathe to "single-point" the threads or by rolling the threads in the solution treated condition (for hardenable alloys) using a screw machine. Inconel 718 can also be roll-threaded after full aging by using induction heat to 1300 °F without increasing the grain size.[citation needed] Holes with internal threads are made by threadmilling. Internal threads can also be formed using a sinker EDM (electrical discharge machining).[citation needed]

Cutting of a plate is often done with a waterjet cutter. New whisker-reinforced ceramic cutters are also used to machine nickel alloys. They remove material at a rate typically eight times faster than carbide cutters. Apart from these methods, Inconel parts can also be manufactured by selective laser melting.


Welding of some Inconel alloys (especially the gamma prime precipitation hardened family, e.g. Waspalloy and X-750) can be difficult due to cracking and microstructural segregation of alloying elements in the heat-affected zone. However, several alloys such as 625 and 718 have been designed to overcome these problems. The most common welding methods are gas tungsten arc welding and electron beam welding.[12]

Innovations in pulsed micro laser welding have also become more popular in recent years for specific applications.


Inconel is often encountered in extreme environments. It is common in gas turbine blades, seals, and combustors, as well as turbocharger rotors and seals, electric submersible well pump motor shafts, high temperature fasteners, chemical processing and pressure vessels, heat exchanger tubing, steam generators and core components in nuclear pressurized water reactors,[13] natural gas processing with contaminants such as H2S and CO2, firearm sound suppressor blast baffles, and Formula One, NASCAR and APR, LLC exhaust systems.[14][15] It is also used in the turbo system of the 3rd generation Mazda RX7, and the exhaust systems of high powered rotary engined Norton motorcycles where exhaust temperatures reach more than 1,000 degrees C.[16] Inconel is increasingly used in the boilers of waste incinerators.[17] The Joint European Torus and DIII-D (fusion reactor) tokamaks vacuum vessels are made in Inconel.[18] Inconel 718 is commonly used for cryogenic storage tanks, downhole shafts and wellhead parts.[19]

Several applications of inconel in aerospace include:

Tesla Motors is now using Inconel, in place of steel, to upgrade the main battery pack contactor in its Model S so that it remains springy under the heat of heavy current. Tesla claims that this allows upgraded vehicles to safely increase the max pack output from 1300 to 1500 Amps, allowing for an increase in power output (acceleration) Tesla refers to as "Ludicrous Mode."[29][23]

Rolled Inconel was frequently used as the recording medium by engraving in black box recorders on aircraft.[30]

Alternatives to the use of Inconel in chemical applications such as scrubbers, columns, reactors, and pipes are Hastelloy, perfluoroalkoxy (PFA) lined carbon steel or fiber reinforced plastic.

The exhaust valves on NHRA Top Fuel and Funny Car drag racing engines are made of Inconel.[citation needed] Iconel is also used in the manufacture of exhaust valves in high performance aftermarket turbo and Supercharged Mazda Miata engine builds (see Flying Miata INC).

Inconel alloys[edit]

Alloys of inconel include:

  • Inconel 600: Solid solution strengthened
  • Inconel 625: Acid resistant, good weldability. The LCF version is typically used in bellows.
  • Inconel 690: Low cobalt content for nuclear applications, and low resistivity[31]
  • Inconel 713C: Precipitaion hardenable nickel-chromium base cast alloy[32]
  • Inconel 718: Gamma double prime strengthened with good weldability[33]
  • Inconel 751: Increased aluminium content for improved rupture strength in the 1600 °F range[34]
  • Inconel 792: Increased aluminium content for improved high temperature corrosion properties, used especially in gas turbines
  • Inconel 939: Gamma prime strengthened to increase weldability

In age hardening or precipitation strengthening varieties, alloying additions of aluminum and titanium combine with nickel to form the intermetallic compound Ni3(Ti,Al) or gamma prime (γ’). Gamma prime forms small cubic crystals that inhibit slip and creep effectively at elevated temperatures.

See also[edit]


  1. ^ "High-Performance Alloys". Special Metals Corporation. Retrieved 2010-04-26. 
  2. ^ "Special Alloys: Inconel 625". Retrieved 2010-04-26. 
  3. ^ "Special Metals Corporation: History". Retrieved 2012-05-18. 
  4. ^ INCONEL alloy 600, Special Metals Corporation
  5. ^, High Temp Metals
  6. ^ INCONEL alloy 625, Special Metals Corporation
  7. ^ Stress Corrosion Cracking of Alloy 600 and Alloy 690 in Hydrogen/Steam at 380C. G. Sui, J. Titchmarsh, G. Heys, J. Congleton. Corrosion Science, Vol 39, No. 3, pp 565-587, 1997
  8. ^ INCONEL alloy 718, Special Metals Corporation
  9. ^ INCONEL alloy X-750, Special Metals Corporation
  10. ^ [1],
  11. ^ [2], University of Cambridge: Dissemination of IT for the Promotion of Materials Science (DoITPoMS).
  12. ^ Joining (PDF), retrieved 2009-10-09 .
  13. ^ Inconel alloy 625, Specials Metals, 2015
  14. ^ Power Generation, Special Metals Corporation.
  15. ^ Chemical Processing, Special Metals Corporation.
  16. ^ Motorcycle Trader.Norton Rotary Revival.Cathcart.Dec 2007.
  17. ^ Inconell - state-of-the-art corrosion protection by Babcock & Wilcox Vølund, 2003
  18. ^ The Inconel JET vessel in use since 1983. A simple, sturdy structure.
  19. ^ Inconel Alloy, Inconel 718.
  20. ^ Robert S. Houston, Richard P. Hallion, and Ronald G. Boston, EDITOR'S INTRODUCTION, "Transiting from Air to Space: The North American X-15", The Hypersonic Revolution: Case Studies in the History of Hypersonic Technology, Air Force History and Museums Program, 1998.
  21. ^ Anthony Young, "The Saturn V Booster: Powering Apollo into History", Springer-Verlag, 2009.
  22. ^ "SpaceX Falcon 9". Space Launch Report. Retrieved 2013-08-13. 
  23. ^ a b "Elon Musk’s recent “Ludicrous” announcement hints at more synergy between Tesla and SpaceX - Electrek". Electrek. Archived from the original on 12 September 2015. 
  24. ^ Norris, Guy (2014-05-30). "SpaceX Unveils ‘Step Change’ Dragon ‘V2’". Aviation Week. Retrieved 2014-05-30. 
  25. ^ Kramer, Miriam (2014-05-30). "SpaceX Unveils Dragon V2 Spaceship, a Manned Space Taxi for Astronauts — Meet Dragon V2: SpaceX's Manned Space Taxi for Astronaut Trips". Retrieved 2014-05-30. 
  26. ^ Bergin, Chris (2014-05-30). "SpaceX lifts the lid on the Dragon V2 crew spacecraft". Retrieved 2015-03-06. 
  27. ^ Foust, Jeff (2014-05-30). "SpaceX unveils its "21st century spaceship"". NewSpace Journal. Retrieved 2015-03-06. 
  28. ^ "SpaceX Launches 3D-Printed Part to Space, Creates Printed Engine Chamber for Crewed Spaceflight". SpaceX. Retrieved 2015-03-06. Compared with a traditionally cast part, a printed [part] has superior strength, ductility, and fracture resistance, with a lower variability in materials properties. ... The chamber is regeneratively cooled and printed in Inconel, a high performance superalloy. Printing the chamber resulted in an order of magnitude reduction in lead-time compared with traditional machining – the path from the initial concept to the first hotfire was just over three months. During the hotfire test, ... the SuperDraco engine was fired in both a launch escape profile and a landing burn profile, successfully throttling between 20% and 100% thrust levels. To date the chamber has been fired more than 80 times, with more than 300 seconds of hot fire. 
  29. ^, Tesla Motors
  30. ^
  31. ^ INCONEL alloy 690, NDT Resource Center
  32. ^ [3]
  33. ^ DMLS in Aluminum, Inconel or Titanium - Is it worth it?
  34. ^ INCONEL alloy 751, Special Metals Corporation