Inconel is a registered trademark of Special Metals Corporation for a family of austenitic nickel-chromium-based superalloys.[1]

Inconel 718 round bar

Inconel alloys are oxidation-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 hardening, depending on the alloy.[2][3]

Inconel alloys are typically used in high temperature applications. Common trade names for

  • Inconel Alloy 625 include: Inconel 625, Chronin 625, Altemp 625, Haynes 625, Nickelvac 625 and Nicrofer 6020.[4]
  • Inconel Alloy 600 include: NA14, N06600, BS3076, 2.4816, NiCr15Fe (FR), NiCr15Fe (EU) and NiCr15Fe8 (DE).
  • Inconel 718 include: Nicrofer 5219, Superimphy 718, Haynes 718, Pyromet 718, Supermet 718, and Udimet 718.[5]


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 Special Metals Corporation[6]) in support of the development of the Whittle jet engine.[7]

Specific data

Alloy Solidus (°C) Liquidus (°C)
Inconel 600[8] 1354 1413
Inconel 617[9] 1332 1377
Inconel 625[10] 1290 1350
Inconel 690[11] 1343 1377
Inconel 718[12] 1260 1336
Inconel X-750[13] 1390 1430


Inconel alloys vary widely in their compositions, but all are predominantly nickel, with chromium as the second element.

Inconel Element, proportion by mass (%)
Ni Cr Fe Mo Nb & Ta Co Mn Cu Al Ti Si C S P B
600[14] ≥72.0[lower-alpha 1] 14.0–17.0 6.0–10.0 N/A ≤1.0 ≤0.5 ≤0.5 ≤0.15 ≤0.015
617[15] 44.2–61.0 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 0.05–0.15 ≤0.015 ≤0.015 ≤0.006
625[16] ≥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[17] ≥58 27–31 7–11 ≤0.50 ≤0.50 ≤0.50 ≤0.05 ≤0.015
Nuclear grade 690[17] ≥58 28–31 7–11 ≤0.10 ≤0.50 ≤0.50 ≤0.50 ≤0.04 ≤0.015
718[2] 50.0–55.0 17.0–21.0 Balance 2.8–3.3 4.75–5.5 ≤1.0 ≤0.35 ≤0.3 0.2–0.8 0.65–1.15 ≤0.35 ≤0.08 ≤0.015 ≤0.015 ≤0.006
X-750[18] ≥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
  1. Includes cobalt


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 double prime (γ″). Gamma prime forms small cubic crystals that inhibit slip and creep effectively at elevated temperatures. 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.[19]


Inconel is a difficult metal to shape and to machine using traditional cold forming 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 1,300 °F (700 °C) without increasing the grain size. Holes with internal threads are made by threadmilling. Internal threads can also be formed using a sinker electrical discharge machining (EDM).

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 cemented carbide cutters. Apart from these methods, Inconel parts can also be manufactured by selective laser melting.

More often than machining, water-jet or laser, grinding is a preferred and economical method for forming nickel alloy components to shape and finish. Due to the hardness of the abrasives used, the grinding wheels are not as affected by the material work hardening and remain sharp and durable.


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.[20]


Astra rocket engine

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,[21] natural gas processing with contaminants such as H2S and CO2, firearm sound suppressor blast baffles, and Formula One, NASCAR, NHRA, and APR, LLC exhaust systems.[22][23] It is also used in the turbo system of the 3rd generation Mazda RX7, and the exhaust systems of high powered Wankel engined Norton motorcycles where exhaust temperatures reach more than 1,000 °C.[24] Inconel is increasingly used in the boilers of waste incinerators.[25] The Joint European Torus and DIII-D tokamaks' vacuum vessels are made of Inconel.[26] Inconel 718 is commonly used for cryogenic storage tanks, downhole shafts and wellhead parts.[27]

Several applications of inconel in aerospace include:

Inconel is also used in the automotive industry:

  • Tesla uses Inconel in place of steel in the main battery pack contactor of its Model S so that it remains springy under the heat of heavy current. Tesla claims that this allows these upgraded vehicles to safely increase the maximum pack output from 1300 to 1500 amperes, allowing for an increase in power output (acceleration) Tesla refers to as "Ludicrous Mode".[32][39]
  • Ford Motor Company is using Inconel to make the turbine wheel in the turbocharger of its EcoBlue diesel engines introduced in 2016.[40]
  • The exhaust valves on NHRA Top Fuel and Funny Car drag racing engines are made of Inconel. Inconel is also used in the manufacture of exhaust valves in high performance aftermarket turbo and Supercharged Mazda Miata engine builds (see Flyin' Miata).
  • BMW has since used Inconel in the exhaust manifold of its high performance luxury car, the BMW M5 E34 with the iconic S38 engine, withstanding higher temperatures and reducing backpressure.
  • Jaguar Cars has fit, in their Jaguar F-Type SVR high performance sports car, a new lightweight Inconel titanium exhaust system as standard which withstands higher peak temperatures, reduces backpressure and eliminates 16 kg (35 lb) of mass from the vehicle.[41]

Rolled Inconel was frequently used as the recording medium by engraving in black box recorders on aircraft.[42]

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.

Inconel alloys

Alloys of inconel include:

  • Inconel 188: Readily fabricated for commercial gas turbine and aerospace applications.
  • Inconel 230: Alloy 230 Plate & Sheet mainly used by the power, aerospace, chemical processing and industrial heating industries.
  • Inconel 600: Solid solution strengthened
  • Inconel 601:
  • Inconel 617: Solid solution strengthened (nickel-chromium-cobalt-molybdenum), high-temperature strength, corrosion and oxidation resistant, high workability and weldability.[43] Incorporated in ASME Boiler and Pressure Vessel Code for high temperature nuclear applications such as molten salt reactors c. April, 2020.[44]
  • 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[45]
  • Inconel 713C: Precipitation hardenable nickel-chromium base cast alloy[3]
  • Inconel 718: Gamma double prime strengthened with good weldability[46]
  • Inconel X-750: Commonly used for gas turbine components, including blades, seals and rotors.
  • Inconel 751: Increased aluminium content for improved rupture strength in the 1600 °F range[47]
  • Inconel 792: Increased aluminium content for improved high temperature corrosion resistant properties, used especially in gas turbines
  • Inconel 907
  • Inconel 909
  • Inconel 706
  • Inconel 939: Gamma prime strengthened to increase weldability.
  • Inconel 925: Inconel 925 is a nonstabilized austenitic stainless steel with low carbon content.[48]

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

See also


  1. "High-Performance Alloys". Special Metals Corporation. Archived from the original on 2012-12-08. Retrieved 2010-04-26.
  2. INCONEL alloy 718, Special Metals Corporation
  3. "Archived copy". Archived from the original on 2015-09-02. Retrieved 2015-09-16.CS1 maint: archived copy as title (link)
  4. "Special Alloys: Inconel 625". Archived from the original on 2009-06-05. Retrieved 2010-04-26.
  5. "Alloy 600 Inconel 600". Retrieved 2018-06-30.
  6. "Special Metals Corporation: History". Archived from the original on April 21, 2008. Retrieved 2012-05-18.
  7. Jones, T.L. "Frank Whittle's W2B Turbojet: United Kingdom versus United States Development". Aircraft Engine Historical Society, Inc. Archived from the original on 30 March 2016. Retrieved 27 March 2016.
  14. INCONEL alloy 600, Special Metals Corporation
  15., High Temp Metals
  16. INCONEL alloy 625, Special Metals Corporation
  17. Inconel alloy 690, Special Metals Corporation
  18. INCONEL alloy X-750, Special Metals Corporation
  19. "DoITPoMS - Full Record".
  20. Joining (PDF), retrieved 2009-10-09.
  21. "Inconel alloy 625, Specials Metals, 2015" (PDF). Archived from the original (PDF) on 2009-02-26.
  22. Power Generation Archived 2012-09-14 at, Special Metals Corporation.
  23. Chemical Processing Archived 2013-02-02 at, Special Metals Corporation.
  24. Motorcycle Trader.Norton Rotary Revival.Cathcart.Dec 2007.
  25. Inconell – state-of-the-art corrosion protection Archived 2008-11-15 at the Wayback Machine by Babcock & Wilcox Vølund, 2003
  26. The Inconel JET vessel in use since 1983 Archived 2010-02-27 at the Wayback Machine. A simple, sturdy structure.
  27. Inconel Alloy, Inconel 718.
  28. 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.
  29. Anthony Young, "The Saturn V Booster: Powering Apollo into History", Springer-Verlag, 2009.
  31. "SpaceX Falcon 9". Space Launch Report. Retrieved 2013-08-13.
  32. "Elon Musk's recent "Ludicrous" announcement hints at more synergy between Tesla and SpaceX - Electrek". Electrek. Archived from the original on 12 September 2015.
  33. Norris, Guy (2014-05-30). "SpaceX Unveils 'Step Change' Dragon 'V2'". Aviation Week. Retrieved 2014-05-30.
  34. 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.
  35. Bergin, Chris (2014-05-30). "SpaceX lifts the lid on the Dragon V2 crew spacecraft". Retrieved 2015-03-06.
  36. Foust, Jeff (2014-05-30). "SpaceX unveils its "21st century spaceship"". NewSpace Journal. Retrieved 2015-03-06.
  37. "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.
  38. SpaceX Casting Raptor Engine Parts from Supersteel Alloys Feb 2019
  39. "Three Dog Day".
  40. "New Ford EcoBlue turbodiesel engine debuts amid diesel woes". April 26, 2016.
  41. "Jaguar Introduces Ultra-High Performance F-TYPE SVR Ahead Of Geneva Debut".
  42. Barrett, Brian. "The Secret Sauce of an Airplane's Black Box".
  43. "Inconel alloy 617" (PDF). Retrieved 28 March 2019.
  44. "COMMERCIAL ALLOY QUALIFIED FOR NEW USE, EXPANDING NUCLEAR OPERATING TEMPERATURE". U.S. Department of Energy Idaho National Laboratory. April 28, 2020.
  45. INCONEL alloy 690 Archived 2013-11-12 at the Wayback Machine, NDT Resource Center
  46. "DMLS in Aluminum, Inconel or Titanium - Is it worth it? - Blog".
  47. INCONEL alloy 751, Special Metals Corporation
  48. Vishal Kumar Jaiswal "Experimental Investigation of Process Parameters on Inconel 925 for EDM Process by using Taguchi Method." International Journal for Scientific Research and Development 6.5 (2018): 277-282. , IJSRD
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