With a nitrogen content of a few percent, a nitride layer that is mostly cohesive (connecting layer) forms on the surface. The three traditional nitriding methods practiced on an industrial scale are: (a) salt bath (liquid) nitriding, where the source of nitrogen (and also carbon) is molten salt. NITREG® represents a family of potential-controlled gas nitriding technologies. If a carbon spending gas is added, the process is called gas nitrocarburising. h�bbd```b``f�S@$�&�dYfw��$��)�&5���,���6�� ������`�|n �q��Q��]@l�B ��g#�>�%�$���� �P
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google_ad_slot = "4743063532"; google_ad_client = "ca-pub-7057920448327527"; Because NANO-S™ is a fully controlled process, there is no formation of chromium nitrides/carbides and consequently no loss of corrosion inhibiting properties. A plasma nitrided part is usually ready for use. Comparison table - advantages and disadvantages of different nitriding methods. The schematic of a typical nitrided structure is given in Fig 3. 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. Nitriding and Metallurgical Behavior. The material of choice is generally a nitriding steel, alloyed steels with nitride-forming elements. Also, since only free cooling takes place, rather than rapid cooling or quenching, no subsequent transformation from austenite to martensite occurs. Since the deformability of the nitrided component not only depends on the thin, hard nitride layer but also on the chemical composition and structure of the base material, the following is true for all nitrided steels: The more homogenous and fine-grained the structure is, the better the nitriding result. Nitriding Effect - Properties of Nitrided Layers. 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® Advantage. Fig 1 Iron – nitrogen equilibrium diagram. So the process is not as old as, for example … As the temperature is further increased to the gamma prime (??) However, the various alloys have different characteristics with regard to surface conditions, the natural speed of diffusion and propensity to form nitrides. Most of these parameters can be controlled with relatively simple instrumentation and methods. For the nitriding process hydrogen gas is also added to keep the surface clear of oxides. The following are the properties of the nitrided steels. Click here to view a comparison of metallurgical and corrosion test results obtained on three materials treated with the Nitreg®-ONC process. The purpose of nitriding is to enrich the surface layer of a work piece with nitrogen in order to increase the hardness in the surface. Consequently, some users may have insurmountable difficulties, particularly if their methodology is primitive and/or their knowledge and experience inadequate. Proper understanding and application of the principles that tie nitriding potential (KN), temperature and time are the cornerstone of the Nitreg® technology. Other advantages of salt nitriding are quick processing time usually around 4 hours and simple operation. Through the ispatguru.com website I share my knowledge and experience gained through my association with the steel industry for over 54 years. It is also known as ion nitriding, plasma ion nitriding or glow-discharge nitriding. Generally speaking all ferrous alloys, including stainless steels, cast irons, and even titanium alloys, are capable of being nitrided. =t�V�h���&[Xu�A���3� I���i����3����x�UB k�� Z;� E�VX�qt"�� | BGC�HH��$�%-���h4��f*���]�z%Gc�9w�F���|1˝
��]�w�W3��-�Q7�������>?k����*j9��4��U>(���S{&Fy��˥0 �}�_����C_,����. For instance, at moderate temperatures (like 420 deg C), stainless steels can be nitrided without the formation of chromium nitride precipitates and hence maintaining their corrosion resistance properties. 416 0 obj
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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. The layer usually consists of two zones – the compound layer (white layer) which can be a cubic or hexagonal … This process permits the close control of the nitrided microstructure, allowing nitriding with or without compound layer formation. 3). This means that the molecular structure of the ferrite (bcc) does not change its configuration or grow into the face-centered cubic (fcc) lattice characteristic of austenite, as occurs in more conventional methods such as carburizing. 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. It is almost unavoidable that this layer displays a certain degree of porosity. Today plasma nitriding is carried out on virtually all steels and cast irons. The microstructure of nitrided iron is shown in Fig 2. This also helps the thermal stability of the plasma unit, since the heat added by the plasma is already present during the warm up and hence once the process temperature is reached the actual nitriding begins with minor heating changes. Such a post-nitriding oxidation treatment has a net effect of enhancing the corrosion resistance of an already nitrided component. Along with the nitride forming alloy elements, nitrides form and disperse sub microscopically in the matrix. Nitrides form around seed points on the surface of the component (grain boundaries and nodes at which several grains meet). Since nitrogen lowers the gamma / alpha transformation temperature of iron down to 590 deg C, the nitriding temperatures are generally below this temperature. However, the increased surface hardness also leads to a higher risk of cracking during mechanical stressing. 1). 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. 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. The higher surface hardness, which is caused by the additional alloy elements, results in a lower tendency to adhere to a wear partner and in increased abrasion resistance. Enter your e-mail address and your password. In plasma nitriding processes nitrogen gas is usually the nitrogen carrying gas. The latter has a fundamental influence on the resultant properties of the surface. (c) plasma nitriding where molecular nitrogen (N2) is split into ions in an electromagnetic field. Recent developments have led to a process that can be accurately controlled. The nitride hardening process integrates into the bulk material, allowing the portion of metal below the surface layer to remain soft. Usually steels are beneficially treated with plasma nitriding. NANO-S. is a surface hardening process that improves the wear and galling resistance of stainless steel components without affecting the inherent corrosion resistance. Above 1.0 %, aluminum has no effect on the resultant nitriding hardness. Frictional wear caused by metal to metal contact is significantly reduced with NANO-STM, In-process Post-Nitriding/Nitrocarburizing Oxidation, Related technologies: NITREG® | NITREG®-C | NITREG®-S | NANO-S™. Aluminum has a strong affinity for nitrogen, forming very hard aluminum nitrides that are quite stable in amounts up to 1.0 % aluminum. We use cookies to optimise this website and continuously update it according to your needs. The gas used for plasma nitriding is usually pure nitrogen, since no spontaneous decomposition is needed. Create your account. In conclusion, 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, Related technologies: NITREG® | NITREG®-S | NANO-S™ | ONC®. Underneath the white layer we have a diffusion case or diffusion zone. In plasma nitriding, the reactivity of the nitriding media is not due to the temperature but to the gas ionized state. Materials: 17-4PH, 13-8Mo, 15-5PH and 416, Surface Hardening Process For Stainless Steel, Related technologies: NITREG® | NITREG®-C | NITREG®-S | ONC®. hUmO9�+�x�g{�.UHI It is often specified in industrial applications on the merit of its being an environmentally friendly but equivalent alternative to salt bath nitrocarburizing. The transition from the hardness of the diffusion zone to the core hardness of the base material is fluid, which, unlike surface layers, reduces the risk of chipping during mechanical stressing. The depth of nitriding hardness may reach 500 ?m with maximum hardness levels of > 1000 HV. This is due to a recombination to molecular nitrogen in energetically suitable spots, such as grain boundaries, in the connecting layer. satyendra; August 28, 2014; 0 Comments ; carburizing, heat treatment, nitriding, Wear resistance, zz, Nitriding Process and Nitriding Steels According to DIN EN 10052:1994-01, nitriding is defined as the thermo-chemical treatment of a work piece in order to enrich the surface layer with nitrogen. 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. The greater the carbon content, there is higher potential for the ?phase to form. As the tempering temperature increases, the amount of Cr and Mo carbides increases as well. Not only the performance of steel parts is enhanced, but working life spans also increase, and so do the strain limit and the fatigue strength of the steels being treated. The one on the right is a product of a Nitreg® process where, in spite of the same hardness, cracks have not formed. However, 1 % aluminum results in a higher increase in hardness than 3 % chromium, and it is independent upon the carbon content of the steel since aluminum does not form carbides and is therefore fully available for nitride formation. The disadvantages of gas nitriding process are (i) reaction kinetics heavily influenced by surface condition, (ii) surface activation is sometimes needed to treat steels with high chromium content, and (iii) ammonia is used as nitriding medium which is though not toxic but can be harmful when inhaled in large quantities.