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Types of Nitriding

Index to types of nitrocarburizing methods

	Nitriding and Nitrocarburizing
	Nitempering
	Controlled Nitrocarburizing
	Soft Nitriding
	Triniding
	Nitroc Process
	Vacuum Nitrocarburizing
	Nitrotec Process
	Austenite Nitrocarburizing

Nitriding and Nitrocarburizing

With the use of external heating or submerged-combustion heating, the atmospheres used in conventional furnaces can also be used.  Some of the advantages of FNC treatments include:

• Reduced cycle times
• Faster recovery rates
• Rapid changes of atmosphere compositions

Its primary disadvantage is the volume of reactive gas needed to fluidize the bed.  To improve operating efficiencies and reduce cost it is necessary to increase the depth of the bed which increases its volume and reduce the required gas flow.  The TherMaLLifeÒ process meets this efficiency at a depth of 48 inches.

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Other Types

Nitempering

Usually carried out in sealed quench furnaces, uses an inlet atmosphere consisting of 50% ammonia and 50% endothermic gas.  Tempering temperatures 1060 degrees F.  Treatment times between 1-3 hours.  Quenching by oil or cooling with recirculating protective gases.  Nitemper has been in use since the early 90's.  Mostly done in Germany, Sweden, USA, Japan, and the United Kingdom.

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Controlled Nitrocarburizing

This type of nitriding overcomes some of the limitations of Nitempering by introducing infrared monitoring and a control system.  Controlled nitrocarburizing can take account not only of variable loads and materials but can also provide reproducible component growth characteristics.  The treatment involves processing in an atmosphere with a predetermined nitriding and carburizing potential and controlling the nitrocarburizing potential within the furnace by infrared gas analysis of the ammonia content.  This is a limitation of Nitempering which is overcome by this method of nitrocarburizing.

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Soft Nitriding

Original studies of the use of ammonia/propane nitrocarburizing mixtures have been extended to ammonia/methane mixtures, including the influence of oxygen additions on the rate of nitrocarburizing.  Data details on relative proportions of gases and structure and composition of the compound layer have not, however, been published or are publicly available.  A low degree of porosity within the compound layer has been reported, together with the probable presence of free oxides.  This process is available under license and has been patented in Romania.  It is regularly used on various sewing machine parts.

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Triniding

This form of ferritic nitrocarburizing does not indicate a presence of any carbon-bearing gases in the processing atmosphere in technical literature published by Lincoln, of Surface Combustion, Inc.  Lincoln reported that Triniding, which is carried out at the standard temperatures involves treating the components in an inert nitrogen-base exothermic carrier gas together with controlled low percentages of ammonia for up to 4 hours.

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Nitroc Process

Introduced in Germany, this treatment is based on the use of exothermic gas and ammonia.  Unlike Triniding, this process uses unpurified gas as the carburizing agent which is claimed to have a sufficiently high inherent oxygen potential to enhance the formation of the carbonitride.  The level of ammonia used is approximately 50% of the inlet exothermic gas-flow rate.

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Vacuum Nitrocarburizing Process

Here we have two basic approaches to sub-atmospheric pressure thermochemical processing.  One is known as the "glow-discharge" method.  This type of "ion nitriding", which is being used increasingly as an alternative to conventional gas nitriding in ammonia atmospheres, was the first thermochemical treatment to use the glow-discharge technique.  This process is an alternative to conventional gas nitiding in ammonia atmospheres.

The other approach involves the use of hot or cold wall vacuum furnaces.  Nitrocarburizing in a vacuum furnace as first reported by Dawes, Tranter, and Reynoldson in 1973.

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Nitrotec Process

In the mid 90's, this Nitrotec (Lucas patent) process was introduced.  It is a further derivative of all the above processes and is designed primarily to improve corrosion resistance.

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Austenite Nitrocarburizing

The process is primarily performed in a salt and commonly know as Noskuff, a trademark of Dgussa-Metz Metallurgical Corp.  This process has since been modified to operate in atmosphere furnaces.

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Source: R.W. Reynoldson
"Heat Treatment in Fluidized Bed Furnaces"