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Ferritic nitrocarburizing or FNC, also known by the proprietary names Tenifer, Tufftride and Melonite as well as ARCOR,Other trade names include Tuffride/ Tuffrider, QPQ, Sulfinuz, Sursulf, Meli 1, and Nitride, among others is a range of proprietary case hardening processes that diffuse
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
and
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...
into
ferrous In chemistry, the adjective Ferrous indicates a compound that contains iron(II), meaning iron in its +2 oxidation state, possibly as the divalent cation Fe2+. It is opposed to " ferric" or iron(III), meaning iron in its +3 oxidation state, suc ...
metals at sub-
critical temperature Critical or Critically may refer to: *Critical, or critical but stable, medical states **Critical, or intensive care medicine * Critical juncture, a discontinuous change studied in the social sciences. * Critical Software, a company specializing ...
s during a salt bath. Other methods of ferric nitrocarburizing include gaseous process such as Nitrotec and ion (plasma) ones. The processing temperature ranges from to , but usually occurs at . At this temperature steels and other ferrous alloys remain in the
ferritic A ferrite is a ceramic material made by mixing and firing large proportions of iron(III) oxide (Fe2O3, rust) blended with small proportions of one or more additional metallic elements, such as strontium, barium, manganese, nickel, and zinc. ...
phase region. This allows for better control of the dimensional stability that would not be present in case hardening processes that occur when the alloy is transitioned into the austenitic phase.. There are four main classes of ferritic nitrocarburizing: ''gaseous'', ''salt bath'', ''ion'' or ''plasma'', and ''fluidized-bed''.. The process is used to improve three main surface integrity aspects including scuffing resistance,
fatigue Fatigue describes a state of tiredness that does not resolve with rest or sleep. In general usage, fatigue is synonymous with extreme tiredness or exhaustion that normally follows prolonged physical or mental activity. When it does not resolve ...
properties, and
corrosion resistance Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engin ...
. It has the added advantage of inducing little shape distortion during the hardening process. This is because of the low processing temperature, which reduces thermal shocks and avoids
phase transition In chemistry, thermodynamics, and other related fields, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states ...
s in steel.


History

The first ferritic nitrocarburizing methods were done at low temperatures, around , in a liquid salt bath. The first company to successfully commercialize the process was the
Imperial Chemical Industries Imperial Chemical Industries (ICI) was a British chemical company. It was, for much of its history, the largest manufacturer in Britain. It was formed by the merger of four leading British chemical companies in 1926. Its headquarters were at ...
in
Great Britain Great Britain is an island in the North Atlantic Ocean off the northwest coast of continental Europe. With an area of , it is the largest of the British Isles, the largest European island and the ninth-largest island in the world. It ...
. ICI called their process "the cassel" due to the plant where it was developed or "Sulfinuz" treatment because it had sulfur in the salt bath. While the process was very successful with high-speed spindles and
cutting tool In the context of machining, a cutting tool or cutter is typically a hardened metal tool that is used to cut, shape, and remove material from a workpiece by means of machining tools as well as abrasive tools by way of shear deformation. The major ...
s, there were issues with cleaning the solution off because it was not very water
soluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubi ...
. Because of the cleaning issues the Joseph Lucas Limited company began experimenting with gaseous forms of ferritic nitrocarburizing in the late 1950s. The company applied for a patent by 1961. It produced a similar surface finish as the Sulfinuz process with the exception of the formation of sulfides. The atmosphere consisted of
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...
,
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
gases, and a small amount of other carbon-containing gases. This spurred the development of a more environmentally friendly salt bath process by the German company Degussa after acquiring ICI patents. Their process is the widely known as the Tufftride or Tenifer process. Following this the ion nitriding process was invented in the early 1980s. This process had faster cycle times, required less cleaning and preparation, formed deeper cases, and allowed for better control of the process.


Processes

Despite the naming the process is a modified form of nitriding and not
carburizing Carburising, carburizing (chiefly American English), or carburisation is a heat treatment process in which iron or steel absorbs carbon while the metal is heated in the presence of a carbon-bearing material, such as charcoal or carbon monoxide. ...
. The shared attributes of this class of this process is the introduction of nitrogen and carbon in the ferritic state of the material. The processes are broken up into four main classes: ''gaseous'', ''salt bath'', ''ion'' or ''plasma'', or ''fluidized-bed''. The trade name and patented processes may vary slightly from the general description, but they are all a form of ferritic nitrocarburizing.


Salt bath ferritic nitrocarburizing

Salt bath ferritic nitrocarburizing is also known as liquid ferritic nitrocarburizing or liquid nitrocarburizing. and is also known by the trademarked names Tufftride and Tenifer. The simplest form of this process is encompassed by the trademarked Melonite process, also known as Meli 1. It is most commonly used on steels,
sintered Clinker nodules produced by sintering Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction. Sintering happens as part of a manufacturing ...
irons, and
cast iron Cast iron is a class of iron– carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impuri ...
s to lower
friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative lateral motion of ...
and improve
wear Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical (e.g., erosion) or chemical (e.g., corrosion). The study of wear and related processes is referred to as tribology. Wear in ...
and corrosion resistance.. The process uses a salt bath of
alkali In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a ...
cyanate Cyanate is an anion with the structural formula , usually written . It also refers to any salt containing it, such as ammonium cyanate. It is an isomer of the much less stable fulminate anion .William R. Martin and David W. Ball (2019): "Sma ...
. This is contained in a steel pot that has an aeration system. The cyanate thermally reacts with the surface of the workpiece to form alkali
carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...
. The bath is then treated to convert the carbonate back to a cyanate. The surface formed from the reaction has a compound layer and a diffusion layer. The compound layer consists of iron, nitrogen, and oxygen, is abrasion resistant, and stable at elevated temperatures. The diffusion layer contains
nitride In chemistry, a nitride is an inorganic compound of nitrogen. The "nitride" anion, N3- ion, is very elusive but compounds of nitride are numerous, although rarely naturally occuring. Some nitrides have a find applications, such as wear-resistant ...
s and
carbide In chemistry, a carbide usually describes a compound composed of carbon and a metal. In metallurgy, carbiding or carburizing is the process for producing carbide coatings on a metal piece. Interstitial / Metallic carbides The carbides of t ...
s. The surface hardness ranges from 800 to 1500 HV depending on the steel grade. This also inversely affects the depth of the case; i.e. a high carbon steel will form a hard, but shallow case. A similar process is the trademarked Nu-Tride process, also known incorrectly as the Kolene process (which is actually the company's name), which includes a preheat and an intermediate quench cycle. The intermediate quench is an
oxidizing Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...
salt bath at . This quench is held for 5 to 20 minutes before final quenching to room temperature. This is done to minimize distortion and to destroy any lingering cyanates or cyanides left on the workpiece. Other trademarked processes are Sursulf and Tenoplus. Sursulf has a sulfur compound in the salt bath to create surface sulfides which creates
porosity Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measur ...
in the workpiece surface. This porosity is used to contain lubrication. Tenoplus is a two-stage high-temperature process. The first stage occurs at , while the second stage occurs at .


Gaseous ferritic nitrocarburizing

Gaseous ferritic nitrocarburizing is also known as controlled nitrocarburizing, soft nitriding, and vacuum nitrocarburizing or by the tradenames UltraOx, Nitrotec, Nitemper, Deganit, Triniding, Corr-I-Dur, Nitroc, NITREG-C, Nitrowear, and Nitroneg. The process works to achieve the same result as the salt bath process, except gaseous mixtures are used to diffuse the nitrogen and carbon into the workpiece.. The parts are first cleaned, usually with a
vapor degreasing Vapor degreasing is a surface finishing process. It involves solvents in vapor form to cleanse the workpiece in preparation for further finishing operations. Process The acting principle behind the vapor degreaser process is that the solvents will ...
process, and then nitrocarburized around , with a process time that ranges from one to four hours. The actual gas mixtures are proprietary, but they usually contain ammonia and an
endothermic In thermochemistry, an endothermic process () is any thermodynamic process with an increase in the enthalpy (or internal energy ) of the system.Oxtoby, D. W; Gillis, H.P., Butler, L. J. (2015).''Principle of Modern Chemistry'', Brooks Cole. ...
gas.


Plasma-assisted ferritic nitrocarburizing

Plasma-assisted ferritic nitrocarburizing is also known as ion nitriding, plasma ion nitriding or glow-discharge nitriding. The process works to achieve the same result as the salt bath and gaseous process, except the reactivity of the media is not due to the temperature but to the gas ionized state. In this technique intense electric fields are used to generate ionized molecules of the gas around the surface to diffuse the nitrogen and carbon into the workpiece. Such highly active gas with ionized molecules is called plasma, naming the technique. The gas used for plasma nitriding is usually pure nitrogen, since no spontaneous decomposition is needed (as is the case of gaseous ferritic nitrocarburizing with ammonia). Due to the relatively low temperature range ( to ) generally applied during plasma-assisted ferritic nitrocarburizing and gentle cooling in the furnace, the distortion of workpieces can be minimized. Stainless steel workpieces can be processed at moderate temperatures (like ) without the formation of chromium nitride precipitates and hence maintaining their corrosion resistance properties.


Postoxidation black oxide

An additional step can be added to the nitrocarburizing process called postoxidation. When properly performed, postoxidation creates a layer of
black oxide Black oxide or blackening is a conversion coating for ferrous materials, stainless steel, copper and copper based alloys, zinc, powdered metals, and silver solder. It is used to add mild corrosion resistance, for appearance, and to minimize li ...
(Fe3O4), that greatly increases the corrosion resistance of the treated substrate while leaving an aesthetically attractive black color. Since the introduction of the
Glock Glock is a brand of polymer- framed, short recoil-operated, locked-breech semi-automatic pistols designed and produced by Austrian manufacturer Glock Ges.m.b.H. The firearm entered Austrian military and police service by 1982 after it was ...
pistol in 1982, this type of nitrocarburizing with postoxidation finish has become popular as a factory finish for military style handguns. This combination of nitrocarburizing and oxidizing is sometimes called "nitrox", but this word also has another meaning.


Uses

These processes are most commonly used on low-carbon, low-alloy steels, however they are also used on medium and high-carbon steels. Common applications include spindles, cams,
gear A gear is a rotating circular machine part having cut teeth or, in the case of a cogwheel or gearwheel, inserted teeth (called ''cogs''), which mesh with another (compatible) toothed part to transmit (convert) torque and speed. The basic ...
s,
dies Dies may refer to: * Dies (deity), the Roman counterpart of the Greek goddess Hemera, the personification of day, daughter of Nox (Night) and Erebus (Darkness). * Albert Christoph Dies (1755–1822), German painter, composer, and biographer * Jos ...
, hydraulic piston rods, and
powdered metal Powder metallurgy (PM) is a term covering a wide range of ways in which materials or components are made from metal powders. PM processes can reduce or eliminate the need for subtractive processes in manufacturing, lowering material losses and ...
components. Glock Ges.m.b.H., an
Austria Austria, , bar, Östareich officially the Republic of Austria, is a country in the southern part of Central Europe, lying in the Eastern Alps. It is a federation of nine states, one of which is the capital, Vienna, the most populous ...
n firearms manufacturer, utilized the Tenifer process until 2010, to protect the barrels and slides of the pistols they manufacture. The finish on a Glock pistol is the third and final hardening process. It is thick and produces a 64 Rockwell C hardness rating via a nitride bath. The final matte, non-glare finish meets or exceeds
stainless steel Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's r ...
specifications, is 85% more corrosion resistant than a hard chrome finish, and is 99.9% salt-water corrosion resistant. After the Tenifer process, a black Parkerized finish is applied and the slide is protected even if the finish were to wear off. In 2010 Glock switched to a gaseous ferritic nitrocarburizing process. Besides Glock other pistol and other firearms manufacturers, including
Smith & Wesson Smith & Wesson Brands, Inc. (S&W) is an American firearm manufacturer headquartered in Springfield, Massachusetts, United States. Smith & Wesson was founded by Horace Smith and Daniel B. Wesson as the "Smith & Wesson Revolver Company" in 1856 ...
and
Springfield Armory, Inc. Springfield Armory, Inc., is an American commercial firearms manufacturer and importer based in Geneseo, Illinois. Founded in 1974 by Bob Reese and family, the company produces rifles such as the M1A and imports handguns such as the XD seri ...
, also use ferritic nitrocarburizing for finishing parts like barrels and slides but they call it Melonite finish.
Heckler & Koch Heckler & Koch GmbH (HK; ) is a German defense manufacturing company that manufactures handguns, rifles, submachine guns, and grenade launchers. The company is located in Oberndorf am Neckar in the German state of Baden-Württemberg, and also ...
use a nitrocarburizing process they refer to as Hostile Environment. Pistol manufacturer Caracal International L.L.C. uses ferritic nitrocarburizing for finishing parts such as barrels and slides with the plasma-based post oxidation process (PlasOx). Grandpower, a Slovakian firearms producer, also uses a
quench polish quench Quench polish quench (QPQ) is a specialized type of nitrocarburizing case hardening that increases corrosion resistance. It is sometimes known by the brand name of Tufftride, Tenifer or Melonite. Three steps are involved: nitrocarburize ("quench"), ...
(QPQ) treatment to harden metal parts on its K100 pistols.


References


Bibliography

* * * *


External links


Tufftride-/QPQ-process: technical information: What is Tufftride?
{{DEFAULTSORT:Ferritic Nitrocarburizing Metal heat treatments