Inconel
Encyclopedia
Inconel is a registered trademark
of Special Metals Corporation
that refers to a family of austenitic nickel
-chromium
-based superalloy
s. Inconel alloys are typically used in high temperature applications. It is often referred to in English as "Inco" (or occasionally "Iconel"). Common trade names for Inconel include: Inconel 625, Chronin 625, Altemp 625, Haynes 625, Nickelvac 625 and Nicrofer 6020.
The Inconel family of alloys was first developed in the 1940s by research teams at the Wiggin Works in Hereford, England, in support of the development of the Whittle
jet engine.
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 (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.
. 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 using a screw machine. Holes with internal threads are made by welding
or brazing
threaded inserts made of stainless steel
. Cutting of plate is often done with a waterjet cutter. Internal threads can also be cut by single point method on lathe, or by threadmilling on a machining center. New whisker reinforced ceramic cutters are also used to machine nickel alloys. They remove material at a rate typically 8 times faster than carbide cutters. 718 Inconel can also be roll threaded after full aging by using induction heat to 1300 degrees F without increasing grain size.
and electron beam welding
.
New innovations in pulsed micro laser welding have also become more popular in recent years.
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 in nuclear pressurized water reactors, natural gas processing
with contaminants such as H2S and CO2, firearm
sound suppressor
blast baffles, and Formula One
and NASCAR
exhaust systems. Inconel is increasingly used in the boilers of waste incinerators
. The Joint European Torus
vessel is made in Inconel. Inconel 718 is commonly used for cryogenic storage tanks, downhole shafts and wellhead parts.
North American Aviation
constructed the skin of the X-15 rocket plane out of an Inconel alloy known as "Inconel X".
Rocketdyne
used Inconel X-750 for the thrust chamber of the F-1 rocket engine used in the first stage of the Saturn V Booster.
Inconel is also used for the lightweight Sport Exhaust of a recent supercar, the McLaren MP4-12C
.
Rolled Inconel was frequently used as the recording medium by engraving in black box
recorders on aircraft
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.
Trademark
A trademark, trade mark, or trade-mark is a distinctive sign or indicator used by an individual, business organization, or other legal entity to identify that the products or services to consumers with which the trademark appears originate from a unique source, and to distinguish its products or...
of Special Metals Corporation
Special Metals Corporation
Special Metals Corporation, headquartered in New Hartford, New York, U.S.A., with operations in Huntington, West Virginia; Dunkirk, New York; Burnaugh, Kentucky; Elkhart, Indiana and Hereford, England, is a supplier of refractory alloys....
that refers to a family of austenitic nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
-chromium
Chromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...
-based superalloy
Superalloy
A superalloy, or high-performance alloy, is an alloy that exhibits excellent mechanical strength and creep resistance at high temperatures, good surface stability, and corrosion and oxidation resistance. Superalloys typically have a matrix with an austenitic face-centered cubic crystal structure. ...
s. Inconel alloys are typically used in high temperature applications. It is often referred to in English as "Inco" (or occasionally "Iconel"). Common trade names for Inconel include: Inconel 625, Chronin 625, Altemp 625, Haynes 625, Nickelvac 625 and Nicrofer 6020.
The Inconel family of alloys was first developed in the 1940s by research teams at the Wiggin Works in Hereford, England, in support of the development of the Whittle
Frank Whittle
Air Commodore Sir Frank Whittle, OM, KBE, CB, FRS, Hon FRAeS was a British Royal Air Force engineer officer. He is credited with independently inventing the turbojet engine Air Commodore Sir Frank Whittle, OM, KBE, CB, FRS, Hon FRAeS (1 June 1907 – 9 August 1996) was a British Royal Air...
jet engine.
Composition
Different Inconels have widely varying compositions, but all are predominantly nickel, with chromium as the second element.| Inconel | Element (% by mass) | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Ni Nickel Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile... |
Cr Chromium Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable... |
Fe Iron Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust... |
Mo Molybdenum Molybdenum , is a Group 6 chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek , meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages, since its ores were confused with lead ores... |
Nb Niobium Niobium or columbium , is a chemical element with the symbol Nb and atomic number 41. It's a soft, grey, ductile transition metal, which is often found in the pyrochlore mineral, the main commercial source for niobium, and columbite... |
Co Cobalt Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal.... |
Mn Manganese Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals... |
Cu Copper Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish... |
Al Aluminium Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances.... |
Ti Titanium Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color.... |
Si Silicon Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table... |
C Carbon Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds... |
S Sulfur Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow... |
P Phosphorus Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks... |
B Boron Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the... |
|
| 600 | 72.0 | 14.0-17.0 | 6.0-10.0 | 1.0 | 0.5 | 0.5 | 0.15 | 0.015 | |||||||
| 617 | 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 | 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 | ||
| 718 | 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 | 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 | |||
Properties
Inconel alloys are oxidation and corrosionCorrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...
resistant materials well suited for service in extreme environments subjected to pressure and heat. When heated, Inconel forms a thick, stable, passivating
Passivation
Passivation is the process of making a material "passive", and thus less reactive with surrounding air, water, or other gases or liquids. The goal is to inhibit corrosion, whether for structural or cosmetic reasons. Passivation of metals is usually achieved by the deposition of a layer of oxide...
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
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
would succumb to creep as a result of thermally-induced crystal vacancies (see Arrhenius equation
Arrhenius equation
The Arrhenius equation is a simple, but remarkably accurate, formula for the temperature dependence of the reaction rate constant, and therefore, rate of a chemical reaction. The equation was first proposed by the Dutch chemist J. H. van 't Hoff in 1884; five years later in 1889, the Swedish...
). Inconel's high temperature strength is developed by solid solution
Solid solution
A solid solution is a solid-state solution of one or more solutes in a solvent. Such a mixture is considered a solution rather than a compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the mixture remains in a single homogeneous phase...
strengthening or precipitation strengthening
Precipitation strengthening
Precipitation hardening, also called age hardening, is a heat treatment technique used to increase the yield strength of malleable materials, including most structural alloys of aluminium, magnesium, nickel and titanium, and some stainless steels...
, depending on the alloy. In age hardening or precipitation strengthening varieties, small amounts of niobium
Niobium
Niobium or columbium , is a chemical element with the symbol Nb and atomic number 41. It's a soft, grey, ductile transition metal, which is often found in the pyrochlore mineral, the main commercial source for niobium, and columbite...
combine with nickel to form the intermetallic compound Ni3Nb or gamma prime (γ'). Gamma prime forms small cubic crystals that inhibit slip and creep
Creep (deformation)
In materials science, creep is the tendency of a solid material to slowly move or deform permanently under the influence of stresses. It occurs as a result of long term exposure to high levels of stress that are below the yield strength of the material....
effectively at elevated temperatures.
Machining
Inconel is a difficult metal to shape and machine using traditional techniques due to rapid work hardeningWork hardening
Work hardening, also known as strain hardening or cold working, is the strengthening of a metal by plastic deformation. This strengthening occurs because of dislocation movements within the crystal structure of the material. Any material with a reasonably high melting point such as metals and...
. 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
Screw thread
A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread...
are machined using a lathe
Lathe
A lathe is a machine tool which rotates the workpiece on its axis to perform various operations such as cutting, sanding, knurling, drilling, or deformation with tools that are applied to the workpiece to create an object which has symmetry about an axis of rotation.Lathes are used in woodturning,...
to "single point" the threads, or by rolling the threads using a screw machine. Holes with internal threads are made by welding
Welding
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...
or brazing
Brazing
Brazing is a metal-joining process whereby a filler metal is heated above and distributed between two or more close-fitting parts by capillary action. The filler metal is brought slightly above its melting temperature while protected by a suitable atmosphere, usually a flux...
threaded inserts made of stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....
. Cutting of plate is often done with a waterjet cutter. Internal threads can also be cut by single point method on lathe, or by threadmilling on a machining center. New whisker reinforced ceramic cutters are also used to machine nickel alloys. They remove material at a rate typically 8 times faster than carbide cutters. 718 Inconel can also be roll threaded after full aging by using induction heat to 1300 degrees F without increasing grain size.
Joining
Welding inconel alloys is difficult due to cracking and microstructural segregation of alloying elements in the heat affected zone. However, several alloys have been designed to overcome these problems. The most common welding methods are gas tungsten arc weldingGas tungsten arc welding
Gas tungsten arc welding , also known as tungsten inert gas welding, is an arc welding process that uses a nonconsumable tungsten electrode to produce the weld...
and electron beam welding
Electron beam welding
Electron beam welding is a fusion welding process in which a beam of high-velocity electrons is applied to the materials being joined. The workpieces melt as the kinetic energy of the electrons is transformed into heat upon impact, and the filler metal, if used, also melts to form part of the weld...
.
New innovations in pulsed micro laser welding have also become more popular in recent years.
Uses
Inconel is often encountered in extreme environments. It is common in gas turbineGas turbine
A gas turbine, also called a combustion turbine, is a type of internal combustion engine. It has an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in-between....
blades, seals, and combustors, as well as turbocharger
Turbocharger
A turbocharger, or turbo , from the Greek "τύρβη" is a centrifugal compressor powered by a turbine that is driven by an engine's exhaust gases. Its benefit lies with the compressor increasing the mass of air entering the engine , thereby resulting in greater performance...
rotors and seals, electric submersible well pump motor shafts, high temperature fasteners, chemical processing and pressure vessels, heat exchanger
Heat exchanger
A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact...
tubing, steam generators in nuclear pressurized water reactors, natural gas processing
Natural gas processing
Natural-gas processing is a complex industrial process designed to clean raw natural gas by separating impurities and various non-methane hydrocarbons and fluids to produce what is known as pipeline quality dry natural gas.-Background:...
with contaminants such as H2S and CO2, firearm
Firearm
A firearm is a weapon that launches one, or many, projectile at high velocity through confined burning of a propellant. This subsonic burning process is technically known as deflagration, as opposed to supersonic combustion known as a detonation. In older firearms, the propellant was typically...
sound suppressor
Suppressor
A suppressor, sound suppressor, sound moderator, or silencer, is a device attached to or part of the barrel of a firearm which reduces the amount of noise and flash generated by firing the weapon....
blast baffles, and Formula One
Formula One racing
A Formula One race or Grand Prix is a sporting event which takes place over three days , with a series of practice and qualifying sessions prior to a race on Sunday....
and NASCAR
NASCAR
The National Association for Stock Car Auto Racing is a family-owned and -operated business venture that sanctions and governs multiple auto racing sports events. It was founded by Bill France Sr. in 1947–48. As of 2009, the CEO for the company is Brian France, grandson of the late Bill France Sr...
exhaust systems. Inconel is increasingly used in the boilers of waste incinerators
Incineration
Incineration is a waste treatment process that involves the combustion of organic substances contained in waste materials. Incineration and other high temperature waste treatment systems are described as "thermal treatment". Incineration of waste materials converts the waste into ash, flue gas, and...
. The Joint European Torus
Joint European Torus
JET, the Joint European Torus, is the largest magnetic confinement plasma physics experiment worldwide currently in operation. Its main purpose is to open the way to future nuclear fusion experimental tokamak reactors such as ITER and :DEMO....
vessel is made in Inconel. Inconel 718 is commonly used for cryogenic storage tanks, downhole shafts and wellhead parts.
North American Aviation
North American Aviation
North American Aviation was a major US aerospace manufacturer, responsible for a number of historic aircraft, including the T-6 Texan trainer, the P-51 Mustang fighter, the B-25 Mitchell bomber, the F-86 Sabre jet fighter, the X-15 rocket plane, and the XB-70, as well as Apollo Command and Service...
constructed the skin of the X-15 rocket plane out of an Inconel alloy known as "Inconel X".
Rocketdyne
Rocketdyne
Rocketdyne was a Rocket engine design and production company headquartered in Canoga Park, California, United States. The company was related to North American Aviation for most of its history. NAA merged with Rockwell International, which was then bought by Boeing in December, 1996...
used Inconel X-750 for the thrust chamber of the F-1 rocket engine used in the first stage of the Saturn V Booster.
Inconel is also used for the lightweight Sport Exhaust of a recent supercar, the McLaren MP4-12C
McLaren MP4-12C
The McLaren MP4-12C is a sports car designed and manufactured by McLaren Automotive. It is the first production car wholly designed and built by McLaren since the McLaren F1. The car's final design was unveiled on 8 September 2009, and it is set to be launched in 2011...
.
Rolled Inconel was frequently used as the recording medium by engraving in black box
Flight recorder
A flight recorder is an electronic recording device placed in an aircraft for the purpose of facilitating the investigation of an aircraft accident or incident. For this reason, flight recorders are required to be capable of surviving the conditions likely to be encountered in a severe aircraft...
recorders on aircraft
Alternatives to the use of Inconel in chemical applications such as scrubbers, columns, reactors, and pipes are Hastelloy
Hastelloy
Hastelloy is the registered trademark name of Haynes International, Inc. The trademark is applied as the prefix name of a range of twenty two different highly corrosion-resistant metal alloys loosely grouped by the metallurgical industry under the material term “superalloys” or “high-performance...
, perfluoroalkoxy
Perfluoroalkoxy
Perfluoroalkoxy or PFA is a type of fluoropolymer with properties similar to polytetrafluoroethylene . It differs from the PTFE resins in that it is melt-processable using conventional injection molding and screw extrusion techniques....
(PFA) lined carbon steel or fiber reinforced plastic.
Inconel alloys
- Inconel 600: Solid solution strengthened
- Inconel 625: Acid resistant, good weldability
- Inconel 690: Low cobalt content for nuclear applications, and low resistivity
- Inconel 718: Gamma double prime strengthened with good weldability
- Inconel 751: Increased aluminum content for improved rupture strength in the 1600°F range
- Inconel 792: Increased aluminum content for improved high temperature corrosion properties, used especially in gas turbines
- Inconel 939: Gamma prime strengthened with good weldability