MODERN SURFACE TREATMENTS
NITRIDING | CARBURIZING | CARBONITRIDING
NITRIDING | CARBURIZING | CARBONITRIDING
Nitreg® is a modern heat treating 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.
Nitreg®-C is based on the proven Nitreg® potential-controlled nitriding technology, whose ability to control processes and produce the desired properties of the nitrided layer has revolutionized the whole concept and practice of nitriding. This was achieved mainly by introducing superior process control and providing excellent properties to the nitrided layer. Nitreg®-C has shorter process cycle times than Nitreg® for the same expected specifications and is carried out predominantly on carbon and low alloy materials.
Nitreg®-C is a nitrocarburizing process, which involves the diffusion of carbon and nitrogen into the steel surface simultaneously. The purpose of this treatment is to create a hardened superficial layer, enhancing wear and corrosion resistance, or improved fatigue resistance of treated steel or cast iron parts, without distortion of shape or dimensional changes. In order to maintain a proper concentration of nascent nitrogen and carbon at the surface of metal, Nitreg®-C technology utilizes the Nitriding and Carburizing Potentials (KN and KC) control concept.
It is often specified in industrial applications on the merit of its being an environmentally friendly but equivalent alternative to salt bath nitrocarburizing.
The advantage of a KN & KC 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, but also strongly depend on the relative level of porosity developed in the WL.
KN control is essential in producing the desired WL configuration.
Example of various porosity levels achieved through KN control
Potential-Controlled Nitriding of Stainless Steel
WHAT IS NITREG®-S?
Stainless steels respond to nitriding differently than other ferrous alloys, and there are also significant differences within the stainless group as well. The primary reason for this is that depending on the chemistry of the steel it will behave differently with respect to the kinetics of layer formation, and it is a rather difficult process to control. In other words, unless you know what you are doing you may end up with nothing, or too little, or too much case depth or white layer, or even damaged parts.
NITREG®-S is a process in which any stainless steel may be nitrided, with complete control over the formation of nitrided layers.
All types of stainless steel can be nitrided; martensitic, austenitic or PH materials inclusively.
Stainless steels have excellent corrosion resistance but possess relatively low strength and wear resistance. NANO-S™ can now expand their application range to include components that are subjected to intensive wear.
NANO-S™ is a surface hardening process that improves the wear and galling resistance of stainless steel components without affecting the inherent corrosion resistance. The process diffuses nitrogen and/or carbon into the surface of the steel, creating a new phase structure, the S-Phase, which provides extremely high hardness. Because NANO-S™ is a fully controlled process, there is no formation of chromium nitrides/carbides and consequently no loss of corrosion inhibiting properties. The treatment produces a hardened layer that is ductile and up to 25 μm deep (0.001”).
Achieved at low temperatures less than 932°F (500°C), NANO-S™ does not induce distortion, which eliminates final machining. Finished parts are uniformly hardened even inside small bores, tight grooves and at sharp edges.
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 with the Nitreg®-ONC process can easily pass well over 200 hours of salt-spray test per ASTM B117 before the first corrosion spot appears. Click here to view a comparison of metallurgical and corrosion test results obtained on three materials treated with the Nitreg®-ONC process.
Gas nitriding of titanium alloys
Titanium alloys, used mostly in the aerospace and defense industries, can also be successfully gas nitrided for increased wear resistance and to acheive 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.
Nitreg®-Ti Treated Communication Cable Connectors
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.
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:
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.
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:
The basic aspects or carburizing in general are described in the Conventional Carburizing section.
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.