Processes
Despite the naming the process is a modified form of
nitriding and not
carburizing. 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.[SUP]
[11][/SUP]
Salt bath ferritic nitrocarburizing
Salt bath ferritic nitrocarburizing is also known as
liquid ferritic nitrocarburizing or
liquid nitrocarburizing[SUP]
[12][/SUP] and is also known by the trademarked names
Tufftride[SUP]
[3][/SUP] and
Tenifer.[SUP]
[13][/SUP]
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 irons, and
cast irons to lower
friction and improve
wear and corrosion resistance.[SUP]
[14][/SUP][SUP]
[15][/SUP]
The process uses a salt bath of
alkali cyanate. 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. 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
nitrides and
carbides. 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.[SUP]
[14][/SUP]
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 salt bath at 400 °C (752 °F). 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.[SUP]
[16][/SUP]
Other trademarked processes are
Sursulf and
Tenoplus. Sursulf has a sulfur compound in the salt bath to create surface sulfides which creates
porosity in the workpiece surface. This porosity is used to contain lubrication. Tenoplus is a two-stage high-temperature process. The first stage occurs at 625 °C (1,157 °F), while the second stage occurs at 580 °C (1,076 °F).[SUP]
[17][/SUP]
Gaseous ferritic nitrocarburizing
Gaseous ferritic nitrocarburizing is also known as
controlled nitrocarburizing,
soft nitriding, and
vacuum nitrocarburizing or by the tradenames
Nitrotec,
Nitemper,
Deganit,
Triniding,
Corr-I-Dur,
Nitroc,
NITREG-C and
Nitrowear,
Nitroneg.[SUP]
[3][/SUP][SUP]
[18][/SUP] 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.[SUP]
[19][/SUP]
The parts are first cleaned, usually with a
vapor degreasing process, and then nitrocarburized around 570 °C (1,058 °F), 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 gas.[SUP]
[19][/SUP]
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.[SUP]
[20][/SUP][SUP]
[21][/SUP][SUP]
[22][/SUP][SUP]
[23][/SUP] 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 (420 °C (788 °F) to 580 °C (1,076 °F)) 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 420 °C (788 °F)) without the formation of chromium nitride precipitates and hence maintaining their corrosion resistance properties.[SUP]
[24][/SUP]
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 (Fe3O4), that greatly increases the corrosion resistance of the treated substrate while leaving an aesthetically attractive black color.[SUP]
[25][/SUP] Since the introduction of the
Glock pistol in 1982, this type of nitrocarburizing with postoxidation finish has become popular as a factory finish for military style handguns.
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,
gears,
dies,
hydraulic piston rods, and
powdered metal components.[SUP]
[26][/SUP]
Glock Ges.m.b.H., an
Austrian 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 0.05 mm (0.0020 in) thick and produces a 64
Rockwell C hardness rating via a 500 °C (932 °F) nitride bath.[SUP]
[27][/SUP] The final matte, non-glare finish meets or exceeds
stainless steel specifications, is 85% more corrosion resistant than a hard
chrome finish, and is 99.9% salt-water corrosion resistant.[SUP]
[28][/SUP] 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.[SUP]
[29][/SUP] Besides Glock several other pistol manufacturers, including
Smith & Wesson and
Springfield Armory, Inc., also use ferritic nitrocarburizing for finishing parts like barrels and slides but they call it Melonite finish.
Heckler & Koch 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 Plasox process.
Grandpower, a Slovakian firearms producer, also uses a
quench polish quench (QPQ) treatment to harden metal parts on its K100 pistols.[SUP]
[[/SUP]
