Nitriding of steel at home: structure, technology and description

Nitriding technologies are based on changes in the surface structure of a metal product. This complex of operations is required to provide the target with protective characteristics. However, not only physical qualities increase the nitriding of steel in the home, where there is no room for more radical measures to give the workpiece better characteristics.

General information about nitriding technology

The need for nitriding is due to the maintenance of characteristics that allow the products to be given high-quality properties. The main share of nitriding techniques is performed in accordance with the requirements for thermal methods of processing parts. In particular, the technology of grinding 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 can be applied by galvanic technique. Compared with deeper methods of structural improvement of metal characteristics, nitriding is the saturation of the surface layer of steel, which has a lesser effect on the structure of the blanks. That is, the basic qualities of metal elements associated with internal characteristics are not taken into account in nitrided improvements.

Varieties of nitriding methods

Approaches to nitriding may vary. Two main methods are usually distinguished, depending on the conditions for nitriding the metal. This can be methods to increase surface wear and hardness, as well as improve corrosion resistance. The first variant is characterized in that the structure is changed against a background of a temperature of about 500 ° C. Reduction of nitriding is usually achieved by ion treatment, when anode discharge and cathode discharge are excited. In the second variant, doped nitriding of steel is produced. The technology of this type provides a temperature treatment at 600-700 ° C with a process duration of up to 10 hours. In such cases, the treatment can be combined with mechanical action and thermal refinement of materials, in accordance with exact requirements, to the result.

Exposure to plasma ions

This is the method of saturation of metals in a nitrogen-containing vacuum, in which electric glowing charges are excited. The walls of the heating chamber can serve as anodes, and the directly processed blanks act as the cathode. In order to simplify the control of the layer structure, it is possible to correct the technological process. For example, the current density, the degree of vacuum, the nitrogen consumption, the levels of addition of pure process gas, etc. can vary. In some modifications, the plasma nitriding of steel also involves the connection of argon, methane and hydrogen. This in part allows us to optimize the external characteristics of the steel, but the technical changes still differ from the full alloying. The main difference lies in the fact that deep structural changes and corrections are made not only by external coatings and shells of the product. Ionic treatment can affect the complete deformation of the structure.

Gas nitridation

This method of saturation of metal products is performed at a temperature level of 400 ° C. But there are also exceptions. For example, refractory and austenitic steels provide for a higher level of heating - up to 1200 ° C. As the main saturation medium, dissociated ammonia appears. The parameters of structural deformation can be controlled by means of the gas nitriding procedure, which assumes different processing formats. The most popular modes are two-, three-stage formats, as well as a combination of dissociated ammonia. Regimes that involve the use of air and hydrogen are used less often. Among the control parameters that determine the nitriding of steel by qualitative characteristics, one can distinguish the level of ammonia consumption, temperature, dissociation, the consumption of auxiliary process gases, etc.

Treatment with solutions of electrolytes

As a rule, the technology of using anodic heating is used. In fact, this is a kind of electrochemical-thermal processing of steel materials. This method is based on the principle of the use of a pulsed electric charge, which passes along the surface of the billet located in an electrolyte medium. Due to the combined effect of electric charges on the metal surface and the chemical environment, the polishing effect is also achieved. With this treatment, the target part can be considered as an anode with a positive potential from the electric current. At the same time, the cathode volume should not be less than the anode volume. Here it is necessary to note some characteristics by which ionic 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 plug-in electrolyte mixtures. This makes it possible to more accurately regulate the technical and operational qualities of metal blanks.

Catholic Nitration

The working space in this case is formed by dissociated ammonia with the support of a temperature regime of the order of 200-400 ° C. Depending on the initial quality of the metal workpiece, the optimum saturation regime is selected, which is sufficient to correct the workpiece. This also applies to changes in the partial pressure of ammonia and hydrogen. The necessary level of dissociation of ammonia is achieved by controlling the pressure and volume of gas supply. In this case, in contrast to the classical methods of gas saturation, the catholic nitriding of steel provides for more gentle processing regimes. Usually, this technology is realized in a nitrogen-containing air environment with a glowing electric charge. The anode function is performed by the walls of the heating chamber, and the cathode by the product.

The process of deformation of the structure

Practical all methods of saturating the surfaces of metal blanks are based on connecting the temperature effect. Another thing is that in addition, electrical and gas correction techniques can be used that change not only the external but also the external structure of the material. Mainly, technologists are trying to improve the strength properties of the target object and protect them from external influences. For example, resistance to corrosion is one of the main problems of saturation, within which nitriding of steel is performed. The structure of the metal after treatment with electrolytes and gas media is endowed with insulation that is able to resist and mechanical natural disruptions. Specific parameters for changing the structure are determined by the conditions for future use of the workpiece.

Nitriding against the background of alternative technologies

Along with the method of nitriding, the external structure of metal preforms can be changed by technologies of cyanidation and cementation. As for the first technology, it is more like classical alloying. The difference between this process is the addition of carbon to the active mixture. Has significant features and carburizing. It also allows the use of carbon, but at elevated temperatures - about 950 ° C. The main goal of such saturation is to achieve high operational hardness. In this case both carburizing and nitriding become similar in that the internal structure can retain a certain degree of viscosity. In practice, this treatment is used in industries where blanks 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 the diversity of saturation regimes and the universality of applications. Surface treatment with a depth of about 0.2-0.8 mm makes it possible to also maintain the basic structure of the metal part. However, much depends on the organization of the process, within which nitriding of steel and other alloys is performed. So, in comparison with alloying, the use of nitrogen treatment requires less expenditure and is allowed even at home.

Disadvantages of nitriding

The method is focused on external refinement of metal surfaces, which causes a limitation on protective parameters. Unlike carbon processing, for example, nitriding is not able to correct the internal structure of the workpiece in order 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 process of nitriding the steel can increase the corrosion resistance and moisture resistance, but on the other hand it will also minimize the density of the structure and, accordingly, affect the strength properties.

Conclusion

The technology of metal processing involves a wide range of methods of mechanical and chemical impact. Some of them are typical and are calculated on the standardized allocation of blanks in concrete technical and physical ways. Others are focused on specialized refinement. The second group includes nitriding of steel, which allows for the possibility of an almost point-like refinement of the external surface of the part. This method of modification allows simultaneously to form a barrier against external negative influence, but at the same time not to change the basis of the material. In practice, such operations are subjected to parts and structures that are used in construction, machinery and instrumentation. This is especially true for materials that are initially subjected to high loads. However, there are also indicators of strength, which can not be achieved through nitriding. In such cases, doping with deep full-format processing of the material structure is applied. But it also has its drawbacks in the form of harmful technical impurities.