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Modern Surface Treatments


    Nitreg®-C Potential-Controlled Gas Nitrocarburizing (FNC process)

    ONC® In-process Post-Nitriding/Nitrocarburizing Oxidation

     

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    Nitreg®: Potential-Controlled Nitriding


     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.
     

    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:

    control of the thickness of the compound (white) layer and its properties

    elimination of closed nitride networks within the diffusion zone

    control of case depth

    control of surface hardness

    no distortion

    family of derivative and related processes.

     

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    Nitreg®-C: Potential-Controlled Nitrocarburizing


    A shorter cycle time of the Nitreg® process carried out predominantly on carbon and low alloy materials.

    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.

    Benefits:

    Increased wear/corrosion resistance on selected alloys

    No distortion

    No brittleness

    Excellent process reliability

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    ONC®: In-process Post-Nitriding/Nitrocarburizing Oxidation


    When resistance to atmospheric corrosion and an attractive black finish are the predominant requirements, ONC® is the appropriate process.

    Its objective is to transform the very top portion of the WL obtained with either Nitreg® or Nitreg®-C technologies into a complex spinel type structure consisting mostly of Fe3O4 type of iron oxide.

    Such a post-nitriding oxidation treatment has a net effect of enhancing the corrosion resistance of an already nitrided component. This integrated process (i.e. Nitreg® + ONC® or Nitreg®-C + ONC®) simultaneously enhances corrosion and wear resistance of steel, while giving the surface an attractive dark or black appearance, expressly desired by many customers.

    ONC®, applied in combination with the Nitreg® potential-controlled nitriding process or the Nitreg®-C potential-controlled nitrocarburizing process, is a clean technology that in many instances can replace chrome plating and salt bath nitriding with their inherent problems of pollution and cost.

    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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    Nitreg®-S: Potential-Controlled Nitriding of Stainless Steel


    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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    Nano-STM: Potential-Controlled Nitriding of Stainless Steel


    NANO-STM is a surface hardening process that improves the wear and galling resistance of stainless steel components without affecting the inherent corrosion resistance.

    Benefits:

    Attains excellent wear resistance

    Improves fatigue strength

    Retains intrinsic corrosion properties

    Prevents galling

    Does not alter chemical composition of alloy

    Has no effect on the steel’s non-magnetic nature

    No change in the color, shape or size

    Uniformly hardened even small bores, tight grooves and sharp edges

    Green technology, no waste pollution

    Treatable Materials:

    Austenitic Stainless Steels

    Martensitic Stainless Steels

    A286

    Custom 465

    Duplex Stainless Steel

    Hastelloy C22 and C276

    Inconel 625 and 718

    Inquire about other materials

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    Nitreg®-Ti: 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.

     

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    Blac-Tride® Post-Nitriding/Nitrocarburizing Oxidation


    Blac-Tride® is a proprietary Nitrex Metal post-oxidation treatment performed after the Nitreg® nitriding process and Nitreg®-C nitrocarburizing process for simultaneous improvement of wear properties and corrosion resistance. The flat black color of Blac-Tride® provides a uniform, aesthetically pleasing appearance while maintaining the mechanical and tribological properties of the nitrided or nitrocarburized component.
    Blac-Tride® is available exclusively to clients of our heat treating services and is used for products across a wide range of markets from brake discs, shafts, screws, firearm components to sporting goods.

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    Plasma (Ion) Nitriding


     

    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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