Nitriding technologies are based on changing the surface structure of a metal product. This set of operations is required in order to endow the target object with protective characteristics. However, it is not only the physical qualities that increase the nitriding of steel at home, where there are no opportunities for more radical measures to endow the workpiece with improved characteristics.
General information about nitriding technology
The need for nitriding is due to the maintenance of characteristics that allow endowing products with high quality properties. The main share of nitriding techniques is performed in accordance with the requirements for thermal processing of parts. In particular, grinding technology is widespread, thanks to which specialists can more accurately adjust the parameters of the metal. In addition, it is allowed to protect areas that are not subject to nitriding. In this case, coating with thin layers of tin by means of a galvanic technique can be applied. Compared to deeper methods of structural improvement of the characteristics of the metal, nitriding is the saturation of the surface layer of steel, which affects the structure to a lesser extent.blanks. That is, the main qualities of metal elements related to internal characteristics are not taken into account in nitrided improvements.
Varieties of nitriding methods
Nitriding approaches may vary. Usually, two main methods are distinguished depending on the conditions of metal nitriding. These can be methods for improving surface wear resistance and hardness, as well as improving corrosion resistance. The first variant differs in that the structure is changed against the background of a temperature of about 500 °C. The reduction of nitriding is usually achieved during ion treatment, when glow discharge excitation is realized by means of anodes and cathodes. In the second option, alloyed steel is nitrided. This type of technology provides for heat treatment at 600-700 °C with a process duration of up to 10 hours. In such cases, processing can be combined with mechanical action and thermal finishing of materials, in accordance with exact requirements for the result.
Impact with plasma ions
This is a method of saturation of metals in a nitrogen-containing vacuum, in which electric glow charges are excited. The walls of the heating chamber can serve as anodes, while the directly processed workpieces act as the cathode. In order to simplify the control of the layered structure, a correction of the technological process is allowed. For example, the current density characteristics, the degree of vacuum, the nitrogen flow rate, the levels of addition of netprocess gas, etc. In some modifications, plasma nitriding of steel also provides for the connection of argon, methane and hydrogen. In part, this allows you to optimize the external characteristics of the steel, but the technical changes still differ from full-fledged alloying. The main difference is that deep structural changes and corrections are made not only on the outer coatings and shells of the product. Ionic processing may affect the overall deformation of the structure.
Gas nitriding
This method of saturation of metal products is carried out at a temperature level of about 400 °C. But there are also exceptions. For example, refractory and austenitic steels provide a higher level of heating - up to 1200 ° C. Dissociated ammonia acts as the main saturation medium. Structural deformation parameters can be controlled through the gas nitriding procedure, which involves different processing formats. The most popular modes are two-, three-stage formats, as well as a combination of dissociated ammonia. Modes that involve the use of air and hydrogen are less commonly used. Among the control parameters that determine steel nitriding by quality characteristics, one can single out the level of ammonia consumption, temperature, degree of dissociation, consumption of auxiliary process gases, etc.
Treatment with electrolyte solutions
Usually used application technologyanode heating. In fact, this is a kind of electrochemical-thermal high-speed processing of steel materials. This method is based on the principle of using a pulsed electric charge that passes along the surface of a workpiece placed in an electrolyte medium. Due to the combined effect of electricity charges on the surface of the metal and the chemical environment, a polishing effect is also achieved. With such processing, the target part can be considered as an anode with a supply of positive potential from an electric current. At the same time, the volume of the cathode should not be less than the volume of the anode. Here it is necessary to note some characteristics according to which ion nitriding of steels converges with electrolytes. In particular, experts note a variety of modes for the formation of electrical processes with anodes, which, among other things, depend on the connected electrolyte mixtures. This makes it possible to more accurately regulate the technical and operational qualities of metal blanks.
Catholic Nitriding
The working space in this case is formed by dissociated ammonia with the support of a temperature regime of about 200-400 °C. Depending on the initial qualities of the metal workpiece, the optimal saturation mode is selected, sufficient to correct the workpiece. This also applies to changes in the partial pressure of ammonia and hydrogen. The required level of ammonia dissociation is achieved by controlling the pressure and volumes of the gas supply. At the same time, in contrast to the classical methods of gassaturation, Catholic nitriding of steel provides for more gentle processing modes. Typically, this technology is implemented in a nitrogen-containing air environment with a glowing electric charge. The function of the anode is performed by the walls of the heating chamber, and the function of the cathode is performed by the product.
Structure deformation process
Practically all methods of saturation of the surfaces of metal blanks are based on the connection of temperature effects. Another thing is that electrical and gas methods for correcting characteristics can be additionally used, changing not only the external, but also the external structure of the material. Mainly, technologists seek to improve the strength properties of the target object and protection from external influences. For example, corrosion resistance is one of the main objectives of saturation, in which nitriding of steel is carried out. The structure of the metal after treatment with electrolytes and gaseous media is endowed with insulation that can withstand natural mechanical damage. Specific parameters for changing the structure are determined by the conditions for the future use of the workpiece.
Nitriding against the backdrop of alternative technologies
Along with the nitriding technique, the external structure of metal blanks can be changed by cyanidation and carburizing technologies. As for the first technology, it is more reminiscent of classical alloying. The difference of this process is the addition of carbon to the active mixtures. It has significant features and cementation. She alsoallows the use of carbon, but at elevated temperatures - about 950 ° C. The main purpose of such saturation is to achieve high operational hardness. At the same time, both carburizing and nitriding of steel are similar in that the internal structure can maintain a certain degree of toughness. In practice, such processing is used in industries where workpieces must withstand increased friction, mechanical fatigue, wear resistance and other qualities that ensure the durability of the material.
Benefits of nitriding
The main advantages of the technology include a variety of workpiece saturation modes and versatility of application. Surface treatment with a depth of about 0.2-0.8 mm also makes it possible to preserve the basic structure of the metal part. However, much depends on the organization of the process in which nitriding of steel and other alloys is performed. So, compared to alloying, the use of nitrogen treatment is less expensive and can be done even at home.
Disadvantages of nitriding
The method is focused on the external refinement of metal surfaces, which causes a limitation in terms of protective indicators. Unlike carbon treatment, for example, nitriding cannot correct the internal structure of the workpiece to relieve stress. Another disadvantage is the risk of negative impact even on the external protective properties of such a product. On the one hand, the steel nitriding process can improve corrosion resistance andmoisture protection, but on the other hand, it will also minimize the density of the structure and, accordingly, affect the strength properties.
Conclusion
Metal processing technologies involve a wide range of methods of mechanical and chemical action. Some of them are typical and are calculated for the standardized endowment of blanks with specific technical and physical methods. Others focus on specialized refinement. The second group includes nitriding of steel, which allows for the possibility of almost point refinement of the outer surface of the part. This method of modification makes it possible to simultaneously form a barrier against external negative influence, but at the same time not to change the basis of the material. In practice, parts and structures that are used in construction, mechanical engineering and instrument making are subjected to such operations. This is especially true for materials that are initially subjected to high loads. However, there are also strength indicators that cannot be achieved through nitriding. In such cases, alloying with deep full-format processing of the material structure is used. But it also has its drawbacks in the form of harmful technical impurities.
