The main objective of nitriding is to increase the hardness of the component’s surface by enriching it with nitrogen. Of the three traditional methods Nitrex does not employ salt bath techniques due to their environmental and safety risks. Plasma nitriding is described later in this section and traditional gas nitriding is gradually being phased out thanks to the development of the Nitreg® family of processes.

General principles of the various nitriding methods and an explanation of potential-controlled techniques are described in more detail in an extension of this page, accessible by clicking here. This will open a separate viewing window and you will be able to return back here by simply closing it.

Nitreg® is a modern process, capable of meeting the metallurgical requirements of all nitriding specifications that may have been originally written for salt bath, plasma or traditional gas nitriding. The ability to control the concentration of nitrogen in the surface allows the user to control the growth of the compound layer virtually independently from developing a desirable diffusion zone. This approach facilitates not only meeting any specification requirements but it also makes it possible to improve on them by allowing tighter tolerances to be satisfied, particularly with regard to the thickness and properties of the compound layer.

Summary of Benefits:

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Its objective is to reliably produce a nitrided case with typically increased WL content and a particular nitrided phase configuration in the WL.

Nitreg®–C is a controlled version of ferritic nitrocarburizing. It allows for precise Kn control during the process. The additions of carbon bearing gases to the nitriding atmosphere help to increase the relative content of the epsilon phase.

The advantage of a Kn controlled technology is best evidenced when increased wear and/or corrosion resistance is sought. Such properties of the nitrided case are not only influenced by the thickness and relative phase composition of the WL. They also strongly depend on the relative level of porosity developed in the WL.

The Kn control is essential in producing the desired WL configuration

Example of various porosity levels achieved through Kn control are shown below.

Depending on the type of steel, parts treated in the Nitreg®-ONC process can easily pass well over 200 hours of salt-spray test per ASTM B117 before the first corrosion spot appears. Fig. 2 shows a comparison of metallurgical and corrosion test results obtained on three materials treated by the Nitreg®-ONC process.

Benefits:

Improved corrosion resistance

Attractive black surface finish

Inherent wear resistance

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The rules applying to nitriding of stainless steel or refractory alloys are no different than those for the other groups of steels, with one exception.

The exception is the proprietary de-passivation stage that allows for a removal of oxides of alloying elements such as Cr, Ni and others which, if not removed, will effectively block the nitriding process. The same way they block the rust formation on the stainless steel surface.

All types of stainless steel can be nitrided. The martensitic, austenitic or PH materials inclusive.

Example of a nitrided stainless steel part.

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Nitreg®-Ti: Potential-Controlled Nitriding of Titanium Alloys

Titanium alloys, used mostly in the aerospace and defense industries can also be successfully gas nitrided leading to an increased wear resistance and providing an attractive golden finish.

The technology is not widely known since the applications involved are also very specific. For best results consult with our engineers who will advise you on certain unique aspects of the manufacturing sequence of operations.

Example of a nitrided titanium alloy part.

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As an alternative to gas nitriding, nitriding plasma (ion) nitriding process has been developed to overcome the shortcomings of the earlier traditional uncontrolled gas nitriding processes and to offer certain operational advantages that gas nitriding does not have.

Plasma is essentially a gas nitriding treatment in which the method of delivering nitrogen atoms to the surface of nitrided components is quite different from the standard gas nitriding processes. It occurs at a very low pressure and under high voltage.

From the metallurgical, tribological and mechanical properties standpoint the properties of nitrided case obtained with Nitreg® and well controlled plasma technology are comparable.

Plasma offers certain distinct advantages such as:

• The ease of masking the component surface where nitriding is to be avoided.
   
• Ability to nitride low density powder metallurgy parts

Ask us for an advice about which nitriding method is better suited to your situation.

If your drawing calls for "ion" or "plasma" nitriding we are at your service.

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Vacuum Carburizing

Vacuum carburizing is a state-of-the-art thermal process where carburizing is effected under very low pressures. First the parts are heated in vacuum to above the transformation temperature of the alloy. Then they are exposed to carbon-carrying gas, or gas mixtures, under partial pressure. Nitrex has developed a revolutionary process called "Pulse- Pressure", a method quickly becoming the industry standard.

Relative to conventional carburizing, the main advantages of the method are:

• repeatable results to within ±0.001" (±25µm),
   
• significantly reduced size changes and distortion,
   
• improved fatigue strength,
   
• better control of the surface layer chemistry,
   
• the process is environmentally friendly.
   

The basic aspects or carburizing in general are described in the Conventional Carburizing section.

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Vacuum Carbonitriding

It is a thermal process of simultaneously diffusing both carbon and nitrogen into ferrous alloys under partial pressure. This leads to an extremely hard and wear resistant surface. Vacuum carbonitriding is a significant improvement over conventional gas carbonitriding. The process contains all of the inherent benefits of vacuum carburizing, but also has the additional benefit of precise computer control of surface ammonia content. Furthermore, this process does not require any additional refractory burn-outs so not only is the end product of higher quality, but it is often less expensive than with competing conventional gas processes.

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Corr-Check®: Corrosion Protective Treatment

•  Easy and safe treatment,
•  Non-sticky surface when the surface has dried off,
•  Significant enhancement of corrosion resistance.

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