Ionic nitriding of parts. Technological capabilities of ion nitriding in strengthening products made of structural and tool steels. Nitriding process technology

The temperature range of ion nitriding is wider than that of gas nitriding and is in the range of 400-600 0 C. Treatment at temperatures below 500 0 C is especially effective in strengthening products made from tool alloy steels for cold working, high-speed and maraging steels, because their performance properties are significantly increased while maintaining core hardness at the level of 55-60 HRC.

Parts and tools from almost all industries are subjected to hardening treatment using the IPA method (Fig. 1).

Rice. 1.

As a result, IPA can be improved the following characteristics products: wear resistance, fatigue endurance, anti-seize properties, heat resistance and corrosion resistance.

In comparison with widely used methods of strengthening chemical-thermal treatment steel parts, such as carburization, nitrocarburization, cyanidation and gas nitriding in furnaces, the IPA method has the following main advantages:

· higher surface hardness of nitrided parts;
· no deformation of parts after processing and high surface cleanliness;
· increasing the endurance limit and increasing the wear resistance of processed parts;
· more low temperature processing, due to which structural transformations do not occur in the steel;
· ability to process blind and through holes;
· maintaining the hardness of the nitrided layer after heating to 600-650 C;
· the possibility of obtaining layers of a given composition;
· ability to process products of unlimited sizes and shapes;
· no pollution environment;
· improving production standards;
· reduction in processing costs several times.

The advantages of IPA are also manifested in a significant reduction in basic production costs.

For example, compared to gas nitriding in furnaces, IPA provides:

· reduction of processing time by 2-5 times, both by reducing the heating and cooling time of the charge, and by reducing the isothermal holding time;
· reduction of fragility of the strengthened layer;
· reduction in the consumption of working gases by 20-100 times;
· reduction in energy consumption by 1.5-3 times;
· exclusion of the depassivation operation;
· reduction of deformation so as to eliminate finishing grinding;
· simplicity and reliability of screen protection against nitriding of non-hardening surfaces;
· improvement of sanitary and hygienic production conditions;
· full compliance of the technology with all modern environmental protection requirements.

Compared to hardening IPA processing allows:

· eliminate deformations;
· increase the service life of the nitrided surface by 2-5 times.

The use of IPA instead of carburization, nitrocarburization, gas or liquid nitriding, volumetric or high-frequency hardening allows you to save capital equipment and production space, reduce machine tools and transport costs, reduce the consumption of electricity and active gas media.

The principle of operation of the IPA is that in a discharged (p = 200-1000 Pa) nitrogen-containing gas environment between the cathode - parts - and the anode - the walls of the vacuum chamber - an anomalous glow discharge is excited, forming an active medium (ions, atoms, excited molecules), ensuring the formation of a nitrided layer consisting of an outer nitride zone and a diffusion zone located underneath it.

Technological factors influencing the efficiency of ion nitriding are process temperature, saturation duration, pressure, composition and flow rate of the working gas mixture.

Process temperature, the area of the charge involved in heat exchange and the efficiency of heat exchange with the wall (number of screens) determine the power required to maintain the discharge and ensure the desired temperature of the products. The choice of temperature depends on the degree of alloying of the steel being nitrided with nitride-forming elements: the higher the degree of alloying, the higher the temperature.

The processing temperature must be at least 10-20 0 C lower than the tempering temperature.

Process duration and temperature saturation determines the depth of the layer, the distribution of hardness along the depth and the thickness of the nitride zone.

Composition of the saturating medium depends on the degree of alloying of the steel being processed and the requirements for the hardness and depth of the nitrided layer.

Process pressure should be such that the discharge tightly “fits” the surface of the products and obtains a uniform nitrided layer. However, it should be borne in mind that the discharge at all stages of the process must be anomalous, i.e. the surface of all parts in the charge must be completely covered with glow, and the discharge current density must be greater than the normal density for a given pressure, taking into account the heating effect gas in the cathode region of the discharge.

With the advent of new-generation IPA installations, using composition-controlled mixtures of hydrogen, nitrogen and argon as a working medium, as well as “pulsating” rather than direct current plasma, the manufacturability of the ion nitriding process has increased significantly.

The use of combined heating (“hot” chamber walls) or enhanced thermal protection (triple heat shield), along with the ability to independently regulate the gas composition and pressure in the chamber, allows, when processing cutting tools, to avoid overheating of thin cutting edges during the heating of the charge, and to accurately regulate the saturation time and , respectively, and the depth of the layer, because Products can be heated in a nitrogen-free environment, for example, in an Ar+H 2 mixture.

Effective thermal insulation in the working chamber (triple heat shield) allows products to be processed with low specific energy consumption, which allows temperature differences inside the cage to be minimized during processing. This is evidenced by the distribution of microhardness along the depth of the nitrided layer for samples located in different places of the charge (Fig. 2).

Rice. 2.

a, c - gear weighing 10.1 kg, 51 pcs., st - 40X, module 4.5, exposure 16 hours, T = 530 0 C;

b, d - gear weighing 45 kg, 11 pcs., st - 38HN3MFA, module 3.25 (outer ring) and 7 mm (inner ring), exposure 16 hours, T = 555 0 C.

Cementation, nitrocarburization and high-frequency hardening are justified in the manufacture of heavily loaded parts (gears, axles, shafts, etc.) of low and medium precision that do not require subsequent grinding.

These types of heat treatment are not economically feasible in the manufacture of medium- and low-load high-precision parts, because With this treatment, significant warping is observed and subsequent grinding is required. Accordingly, when grinding it is necessary to remove a significant thickness of the hardened layer.

IPA can significantly reduce warping and deformation of parts while maintaining surface roughness within the range of Ra = 0.63...1.2 microns, which makes it possible to use IPA as a finishing treatment in the vast majority of cases.

In relation to the machine tool industry, ion nitriding of gears significantly reduces the noise characteristics of machine tools, thereby increasing their competitiveness in the market.

IPA is most effective when processing large-scale parts of the same type: gears, shafts, axles, toothed shafts, shaft-toothed gears, etc. Gears subjected to plasma nitriding have better stability sizes compared to cemented gears and can be used without additional processing. At the same time, the bearing capacity of the lateral surface and the strength of the tooth base, achieved with the help plasma nitriding, correspond to cemented gears (Table 1).

Table 1. Characteristics of fatigue resistance of steels depending on methods of hardening gears

When strengthening treatment by ion nitriding of parts made of case-hardened, low- and medium-alloy steels (18KhGT, 20KhNZA, 20KhGNM, 25KhGT, 40Kh, 40KhN, 40KhFA, etc.), it is necessary to first improve the forgings - volumetric hardening and tempering to a hardness of 241-285 HB (for some steels - 269-302 HB), then mechanical processing and finally ion nitriding. To ensure minimal deformation of products before nitriding to relieve stress, it is recommended to carry out annealing in a protective gas atmosphere, and the annealing temperature should be higher than the nitriding temperature. Annealing should be carried out before precision machining.

The depth of the nitrided layer formed on these products made from steels 40Kh, 18KhGT, 25KhGT, 20Kh2N4A, etc. is 0.3-0.5 mm with a hardness of 500-800 HV depending on the steel grade (Figure 3).

For gears operating under heavier loads, the nitride layer should be 0.6-0.8 mm with a thin nitride zone or no nitride zone at all.

Rice. 3.

Optimization of the properties of the hardened layer is determined by the combination of the characteristics of the base material (core hardness) and the parameters of the nitrided layer. The nature of the load determines the depth of the diffusion layer, the type and thickness of the nitride layer:

· wear - "- or - layer;
· dynamic load - limited thickness of the nitride layer or no nitride layer at all;
· corrosion - layer.

Independent control of the flow rate of each component of the gas mixture, the pressure in the working chamber and the variation in process temperature make it possible to form layers of different depths and hardness (Fig. 4), thereby ensuring stable processing quality with minimal variation in properties from part to part and from charge to charge ( Fig. 5).

Rice. 4.

1, 3, 5 -one-step process;
2,4 - two-stage process according to N content 2 in the working mixture
1,2 - T=530 0 C, t=16 hours; 3 - T=560 0 C, t=16 hours;
4 - T=555 0 C, t=15 hours, 5 - T = 460 0 C, t = 16 hours

Rice. 5.

Ionic nitriding is widely known as one of effective methods increasing the wear resistance of cutting tools made from high speed steels brands R6M5, R18, R6M5K5, R12F4K5, etc.

Nitriding increases the wear resistance of the tool and its heat resistance. The nitrided surface of the tool, which has a reduced coefficient of friction and improved anti-friction properties, ensures easier removal of chips, and also prevents chips from sticking to the cutting edges and the formation of wear craters, which makes it possible to increase feed and cutting speed.

Optimal structure nitrided high-speed steel is high-nitrogen martensite that does not contain excess nitrides. This structure is ensured by saturating the tool surface with nitrogen at a temperature of 480-520 0 C during short-term nitriding (up to 1 hour). In this case, a strengthened layer with a depth of 20-40 microns is formed with a surface microhardness of 1000-1200 HV0.5 with a core hardness of 800-900 HV (Fig. 6), and the durability of the tool after ion nitriding increases 2-8 times depending on its type and type of material being processed.

Rice. 6.

The main advantage of ion nitriding of a tool is the possibility of obtaining only a diffusion-hardened layer, or a layer with monophase Fe 4 N nitride ("-phase) on the surface, in contrast to classical gas nitriding in ammonia, where the nitride layer consists of two phases - "+, which is a source of internal stresses at the interface and causes brittleness and peeling of the hardened layer during operation.

Ion nitriding is also one of the main methods for increasing durability stamping tools and injection molding equipment from steels 5KhNM, 4Kh5MFS, 3Kh2V8, 4Kh5V2FS, 4Kh4VMFS, 38Kh2MYuA, Kh12, Kh12M, Kh12F1.

As a result of ion nitriding, the following characteristics of products can be improved:

· Forging dies for hot stamping and molds for casting metals and alloys - increases wear resistance, reduces metal sticking.
· Molds for aluminum injection molding - the nitrided layer prevents metal from sticking in the liquid jet supply zone, and the mold filling process is less turbulent, which increases the service life of the molds, and the casting is more efficient High Quality.

Significantly improves ion nitriding and cold tool performance (T< 250 0 С) обработки - вытяжка, гибка, штамповка, прессование, резка, чеканка и прошивка.

The main requirements that ensure the high performance of such a tool are high compressive strength, wear resistance and cold resistance. shock load- achieved as a result of strengthening treatment using the ion nitriding method.

If high-chromium steel (12% chromium) is used for the tool, then the nitrided layer should only be diffusion; if low-alloy steels, then in addition to the diffusion layer there should be a g-layer - hard and plastic.

A feature of ion nitriding of high-chromium steels is that by choosing the process temperature, it is possible to maintain the hardness of the core of the product, determined by preliminary heat treatment, within a wide range (Table 2).

To obtain a wear-resistant surface layer while maintaining the viscous core of the die, it is necessary to first carry out hardening and tempering for secondary hardness, dimensional processing and then ion nitriding.

To eliminate or minimize deformations that occur during ion nitriding of a stamping tool, before final machining it is recommended to anneal in an inert gas environment at a temperature at least 20 C below the tempering temperature.

If necessary, polish nitrided working surfaces.

Table 2. Characteristics of alloy steels after ion plasma nitriding.

steel grade	Core hardness, HRC	Process temperature	Layer characteristics	Type of recommended connection layer
	Depth, mm	Pov. TV-set, HV 1	Connection layer thickness, µm
Hot working steels




Cold working steels

By varying the composition of the saturating medium, the temperature of the process and its duration, it is possible to form layers of different depths and hardness (Fig. 7,8).

punch weighing 237 kg
mold weighing 1060 kg.

Rice. 7. Examples of die tooling processing (a, b) and microhardness distribution along the depth of the nitrided layer (c, d).

Thus, as world experience shows, the use of ion nitriding technology for strengthening processing of products made of structural steels, as well as cutting and stamping tools, this technology is effective and relatively easy to implement, especially with the use of pulsating current plasma.

The durability of gas turbine engine parts is largely determined by the condition of their surface, and primarily by its wear resistance. One of the widespread methods of increasing the wear resistance of the surfaces of aircraft engine and aircraft parts is nitriding. Nitriding is applied to parts that mainly rely on friction during operation.

Nitriding is a process of diffusion saturation of the surface layers of steel products with nitrogen. Nitriding is carried out in order to increase the hardness and wear resistance of the surface layers of steel products, improve the resistance to fatigue and electrochemical corrosion of parts.

During nitriding, nitrogen forms a number of phases with iron: nitrogenous ferrite - a solid solution of nitrogen in -iron, nitrogenous austenite - a solid solution of nitrogen in -iron, intermediate ` -phase Fe4N, -phase Fe2N, etc. However, iron nitrides have insufficient strength, hardness, high fragility compared to chromium nitrides CrN, Cr2N, molybdenum MoN, aluminum AlN and some other alloying elements. Therefore, alloy steels containing the indicated elements are subjected to nitriding: 45Х14Н14В2М, 1Х12Н2ВМФ, 15Х16К5Н2МВФАБ-Ш and other steels that are used for the manufacture of bushings, rods, valve seats, various bodies, etc.

The method of nitriding in dissociated ammonia using furnace heating, widely used in industry, has such serious disadvantages as the long duration of the process, the difficulty of saturating easily passivated high-alloy steels with nitrogen, the formation of a brittle phase on the surface of parts, and their significant unstable deformations. Grinding, which is the main operation when processing nitrided surfaces, is a long and labor-intensive process.

The ion nitriding process is carried out in a vacuum working chamber, in which the parts are the cathode, and the grounded chamber body is the anode. At low pressure in a nitrogen-containing atmosphere, the application of an electrical potential between the parts and the chamber body causes ionization of the gas. As a result of bombardment with ions, the parts are heated to the required temperature, and the surface, saturated with nitrogen, is strengthened.

Typically, nitriding is carried out at temperatures below 600C, when preferential diffusion of nitrogen occurs. The rate of diffusion transfer of nitrogen depends on temperature, concentration gradient, composition and structure of the base material and other factors. Diffusion of nitrogen atoms occurs along vacancies, dislocations and other defects in the crystal structure. As a result of diffusion, the nitrogen concentration in the surface layer changes in depth.

The greatest acceleration of the nitriding process is achieved in a glow discharge plasma, when a glow discharge is excited in a rarefied atmosphere between the part (cathode) and the anode. Gas ions bombard the surface of the cathode and heat it to a temperature of 470-580C. Positively charged nitrogen ions under the influence of energy electrostatic field move at a certain speed perpendicular to the surface of the part, and the energy of the nitrogen ion obtained in the glow discharge plasma at a potential difference of 800 V is approximately 3000 times higher than the energy of the nitrogen atom during furnace nitriding in dissociated ammonia. Nitrogen ions heat the surface of the part and also sputter iron atoms from the surface (cathode sputtering). Iron atoms combine with nitrogen in the glow discharge plasma and form iron nitride, which is deposited on the surface of the part in a thin layer. Subsequently, bombardment of the FeN layer with nitrogen ions is accompanied by the formation of lower nitrides FeNFe3NFe4N and a solid solution of nitrogen in -iron Fe(N). Nitrogen formed during the decomposition of lower nitride diffuses deep into the material of the part, and iron is again sprayed into the plasma.

In contrast to furnace heating, during ion nitriding (in a glow discharge plasma), the parts are heated using plasma energy, consumed in proportion to the mass of the charge. In this case, stoves with massive masonry are not required.

Nitriding of easily passivated high-chromium stainless steels necessarily requires the addition of hydrogen to the gaseous environment. To obtain high-quality diffusion layers without an -phase on the surface during ion nitriding of steels of various classes, it is advisable to carry out the stage of cathode sputtering in hydrogen at a pressure of about 13 Pa and a voltage of about 1000 V, and the saturation stage in a mixture (3-5%) of hydrogen and (95 -97%) nitrogen at a pressure of 133-1330 Pa. A gas environment of this composition ensures uniform thickness of diffusion layers on parts placed in the cage throughout the volume of the working chamber. An increase in the pressure of the mixture at the second stage (nitriding) promotes an increase in the depth of the diffusion layer.

It has been established that the duration of the ion nitriding process is approximately half that of furnace nitriding using the current serial technology. The dependence of the depth of the diffusion layer on the duration of saturation during ion nitriding, as well as during furnace nitriding, has a parabolic character. The effect of ion nitriding temperature on the layer depth has a dependence close to exponential.

During conventional nitriding in dissociated ammonia, the maximum hardness for most steels is located at some distance from the surface, and the surface layer, which is a brittle phase, is usually ground off. As a result of ion nitriding, the surface has maximum hardness. The diameters of nitrided parts of the “shaft” type change, as a rule, by 30-40 microns, which often falls within the tolerance range. Therefore, taking into account the high quality of the surface after ion nitriding and maintaining cleanliness, it is possible not to process it, or to limit it to polishing or light lapping.

Using ion nitriding at the base plant, it was possible to achieve high efficiency in increasing the durability of cutting tools and hot forming dies in the manufacture of parts made of difficult-to-cut heat-resistant nickel, titanium and stainless steels.

The practice of introducing and using the process of ion nitriding of parts in industry has shown the feasibility of widespread introduction of this process into mass production. The ion nitriding process allows:

Increase the service life of nitrided parts;

Provide hardening of parts for which the use of other hardening methods is difficult or impossible;

Reduce the labor intensity of manufacturing by eliminating the operation of electroplating;

In some cases, avoid grinding after nitriding;

Reduce the duration of the nitriding cycle by more than 2 times;

Improve occupational health.

A special feature of the production of aircraft engines is a wide variety of steel grades, including those strengthened by nitriding. The development of the technological process of ion nitriding was preceded by a deep analysis of achievements in this area of foreign and domestic research.

Strengthening by ion nitriding was studied on structural steels of pearlitic, austenitic, martensitic, transition classes, maraging steels of the following materials: 38Х2МУА, 30Х3ВА, 38ХА, 40ХА, 13Х11Н2В2МФ (EI961), 45Х14Н14В2М (ЭИ69), 25Х18Н8 B2, 40Х10С2М, 14Х10С2М, 14Х17Н2, 15Х15К5Н2МВФАБ -Sh (EP866), 30Kh2NVA, 16Kh3NVFAB-Sh, (DI39, VKS-5), N18K9M5T (MS200), etc. The objective of the research is the development of technological processes for the purpose of converting furnace nitriding of parts to ion, new technological processes for ion nitriding of parts instead of carburization , as well as previously not strengthened by chemical-thermal treatment.

For parts subject to wear at low contact pressures under corrosion conditions, it is necessary to obtain a diffusion layer with a developed nitride zone, on which the running-in of rubbing surfaces and corrosion resistance depend.

For parts operating under cyclic loads under wear conditions with increased contact loads, one must strive to obtain a layer with a large zone of internal nitriding.

Varying the layer structure allows one to obtain various combinations of layer and core. This is confirmed by numerous examples of nitriding for various groups of parts.

When developing technological processes, comprehensive systematic studies were carried out on the influence of the main technological factors on the quality and operational characteristics of the diffusion layer during ion nitriding in order to optimize their parameters.

The high hydrogen content in the mixture, including that corresponding to the composition with complete dissociation of ammonia, promotes the formation of nitride phases on the nitrided surface in the form of a monolayer up to the - phase (Fe2N). In addition, a mixture of nitrogen with a high hydrogen content both in the mixer cylinder, where the mixture is prepared, and in the working chamber through certain time begins to influence the depth of the nitrided layer, as well as its unevenness on parts throughout the volume of the charge. Hydrogen in a gaseous environment during ion nitriding plays the role of a reducing agent for oxides on the surface being hardened, which prevent direct contact and interaction of nitrogen with the metal.

Regular grade steels are nitrided in pure nitrogen without hydrogen additives. However, nitrided layers are not always uniform in depth.

As a result of studies of the influence of pressure in the working chamber on the quality of the nitrided layer, it can be recommended to carry out the first stage (cathode sputtering) in hydrogen at a pressure of about 13 Pa and at a voltage of about 1000 V. Increasing the pressure of the mixture of the second stage (nitriding) promotes an increase in the depth of the diffusion layer, and Ionic nitriding should be carried out at a pressure of 133-1330 Pa.

The quality of diffusion layers is affected by temperature and process duration. The figure shows the influence of these factors on the layer depth of some steels that differ in composition and are typical representatives of various classes.

It has been established that the duration of the ion nitriding process is approximately half that of furnace nitriding using the current serial technology.

The distribution of microhardness along the depth of the nitrided layer is an important performance characteristic. During conventional nitriding in dissociated ammonia, the maximum hardness for most steels is located at some distance from the surface, and the surface layer, which is a brittle phase, is usually ground off. As a result of ion nitriding of all steels, the surface has maximum hardness. Therefore, taking into account the high quality of the surface after ion nitriding and maintaining cleanliness, it can be left untreated or limited to polishing or light lapping.

After ion nitriding, all steels have no -phase on the surface. The absence of the -phase on the surface during ion nitriding is probably due to the barrier effect of oxides that reduce the nitrogen content directly on the metal, cathode sputtering and the lower stability of the -phase in vacuum and in glow discharge plasma.

One of the main performance characteristics of many aircraft engine and aircraft parts is wear resistance.

The wear resistance study was carried out both from the surface of nitrided samples and after grinding to a depth of 0.03-0.06 mm.

Ion nitriding of parts in mass production Mainly three types of parts are subjected. These are parts subjected to conventional nitriding in dissociated ammonia, cemented parts with small and medium loads of work on the product, and parts with significant wear that are not subjected to hardening by chemical-thermal treatment due to the impossibility of subsequent refinement by grinding due to the complex geometric shape.

A long duration of isothermal exposure, reaching 50 hours, with a large range of nitrided parts, often disrupts the rhythm of production. Another significant disadvantage of serial technology is the high labor intensity in the manufacture of parts associated with the application and removal of galvanic coatings used to protect against nitriding. Grinding of nitrided parts, especially complex configurations, is sometimes accompanied by uneven defects, which are practically not detected by control and only appear during operation on a production engine as a result of premature wear of the defective layer. When grinding parts, especially from such complex alloy steel as 15Kh16K5N2MVFAB, cracks sometimes formed on sharp edges due to relaxation of residual stresses, as well as in the places of transition from the cylindrical surface to the end surface immediately after nitriding.

It is advisable to subject finally manufactured parts to hardening by ion nitriding. This is due to the fact that after ion nitriding, the surface itself or layers close to it have the maximum hardness and wear resistance, while after conventional nitriding, layers located at some distance from the surface are more efficient.

To take into account the allowance for “swelling” during manufacturing, the effect of ion nitriding on changes in the dimensions of parts was studied. The studies were carried out on typical representatives of parts. Statistics on the distribution of parts based on size changes were established. Shaft-type parts have an increase in diameter after ion nitriding. For bushings and spheres, the outer diameter increases and the inner diameter decreases. For most nitrided parts, the diameter has changed by 30 - 40 microns.

Some parts are nitrided after finishing machining, and dimensional deviations were within the tolerance range. Thus, during the manufacturing process of parts, the labor-intensive operation of grinding the nitrided surface was eliminated. This circumstance makes it possible to expand the range of hardened parts where mechanical processing after hardening is difficult or impossible (for example, curved parts such as a bandage).

Equipment has been developed and manufactured to protect non-nitrided surfaces. When ion nitriding of parts, in contrast to furnace nitriding, the protection of surfaces that are not subject to nitriding is the most technologically advanced. Nickel plating and tinning, used to protect non-nitrided surfaces during furnace nitriding, are labor-intensive operations and do not always provide required quality protection. In addition, after nitriding, it is often necessary to remove these coatings by chemical or mechanical means.

When ion nitriding, protection of non-nitriding surfaces is carried out using metal screens that are in close contact with the surface not subject to nitriding (gap no more than 0.2 mm). This surface is not exposed to the glow charge and is thus reliably protected from nitriding. When nitriding parts, protection against nitriding was repeatedly used using screens of various surfaces, such as planes, internal and external cylindrical surfaces, threaded surfaces, etc. Practice has shown the reliability and convenience of this method of protection. Devices for these purposes can be used repeatedly. The surfaces of parts that are not subject to nitriding can be finally treated.

The ion nitriding process allows:

increase the service life of nitrided parts;

provide hardening of parts for which the use of other hardening methods is difficult or impossible;

reduce the labor intensity of manufacturing by eliminating electroplating operations;

in some cases, refuse grinding after nitriding;

reduce the duration of the nitriding cycle by more than half;

improve occupational hygiene.

Three different types of nitriding are currently used in industry: to obtain high hardness of the surface layer, anti-corrosion ionic and “soft” nitriding, etc.

To obtain high hardness of parts made of structural steels, the process is carried out at temperatures from 500 to 520C for up to 90 hours. The degree of ammonia dissociation is regulated by its supply and ranges from 15 to 60%. In a single-stage nitriding mode, the process is carried out at a constant temperature (500520C), and then it is raised to 560570C. At low temperatures, this first leads to the formation of a thin layer well saturated with nitrogen with finely dispersed nitrides, and then, with increasing temperature, the diffusion rate increases and the time to obtain the required thickness of the nitrided layer is reduced. A two-stage nitriding cycle reduces the time of the process of saturating steel with nitrogen by 22.5 times.

When improving the nitriding process, the following important tasks must be solved:

creation of a controlled process that ensures obtaining a given gas composition, structure and depth of the diffusion layer;

intensification of the process of formation of the nitrided layer.

Two fundamentally new methods of direct control of the nitriding process have been developed, one of them allows one to evaluate the nitrogen potential of the furnace atmosphere by its ionic composition (ionic dissociamers), and on the other, it opens up the possibility of direct analysis of the kinetics of the formation of diffusion coatings during the nitriding process (eddy current analyzers). Nitrogen potential is monitored using an ionization sensor with feedback with a mixing system.

For nitriding, qualitatively new installations with program controlled technological process. Intensification of the nitriding process can be achieved by increasing the saturation temperature, regulating the activity of the atmosphere, changing its composition, as well as the use of magnetic fields and various types electrical discharges (spark, corona, glow).

During chemical-thermal treatment, the depth of the saturated layer in some cases is greater than required, in others it is less than required, sometimes warping and deformation occur, the saturated layer cracks, etc. Characteristics of defects in chemical-thermal treatment, the main reasons for its occurrence, and measures to eliminate defects are given in the table.

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Technological capabilities of ion nitriding in strengthening products made of structural and tool steels

M. N. Bosyakov, S. V. Bondarenko, D. V. Zhuk, P. A. Matusevich

JV "Avicenna International", Republic of Belarus, Minsk,

St. Surganova, 2a, 220012, tel. +375 17 2355002

Ion plasma nitriding (IPA) is a method of chemical-thermal treatment of steel and cast iron products with great technological capabilities, which makes it possible to obtain diffusion layers of the desired composition by using different gas media, i.e. The diffusion saturation process is controllable and can be optimized depending on the specific requirements for layer depth and surface hardness. The temperature range of ion nitriding is wider than that of gas nitriding and is in the range of 400-600 0 C. Treatment at temperatures below 500 0 C is especially effective in strengthening products made from tool alloy steels for cold working, high-speed and maraging steels, because their performance properties are significantly increased while maintaining core hardness at the level of 55-60 HRC. Parts and tools from almost all industries are subjected to hardening treatment using the IPA method (Fig. 1).

Rice. 1. Application of ion plasma nitriding to strengthen various products

As a result of IPA, the following product characteristics can be improved: wear resistance, fatigue endurance, anti-scuff properties, heat resistance and corrosion resistance. In comparison with widely used methods of strengthening chemical-thermal treatment of steel parts, such as carburization, nitrocarburization, cyanidation and gas nitriding in furnaces, the IPA method has the following main advantages:

higher surface hardness of nitrided parts; no deformation of parts after processing and high surface cleanliness; increasing the endurance limit and increasing the wear resistance of processed parts; lower processing temperature, due to which structural transformations do not occur in the steel; possibility of processing blind and through holes; maintaining the hardness of the nitrided layer after heating to 600-650 °C; the possibility of obtaining layers of a given composition; the ability to process products of unlimited sizes and shapes; no environmental pollution; improving production standards; reduction in processing costs several times. The advantages of IPA are also manifested in a significant reduction in basic production costs. For example, compared to gas nitriding in furnaces, IPA provides:

reduction of processing time by 2–5 times, both by reducing the heating and cooling time of the charge, and by reducing the isothermal holding time; reducing the fragility of the strengthened layer; reduction of working gas consumption by 20–100 times; reduction in energy consumption by 1.5-3 times; exclusion of the depassivation operation; reduction of deformation so much as to eliminate finishing grinding; simplicity and reliability of screen protection against nitriding of non-hardening surfaces; improvement of sanitary and hygienic production conditions; full compliance of the technology with all modern environmental protection requirements.Compared to hardening IPA processing allows:

eliminate deformations; increase the service life of the nitrided surface by 2-5 times. The use of IPA instead of carburization, nitrocarburization, gas or liquid nitriding, volumetric or high-frequency hardening allows you to save capital equipment and production space, reduce machine tool and transportation costs, and reduce the consumption of electricity and active gaseous media. The principle of operation of the IPA is that in a discharged (p = 200-1000 Pa) nitrogen-containing gas environment between the cathode - parts - and the anode - the walls of the vacuum chamber - an anomalous glow discharge is excited, forming an active medium (ions, atoms, excited molecules), ensuring the formation of a nitrided layer consisting of an outer nitride zone and a diffusion zone located underneath it. Technological factors influencing the efficiency of ion nitriding are process temperature, saturation duration, pressure, composition and flow rate of the working gas mixture. Process temperature, the area of the charge involved in heat exchange and the efficiency of heat exchange with the wall (the number of screens) determine the power required to maintain the discharge and ensure the desired temperature of the products. The choice of temperature depends on the degree of alloying of the nitrided steel with nitride-forming elements: the higher the degree of alloying, the higher the temperature. The processing temperature must be at least 10-20 0 C lower than the tempering temperature. Process duration and temperature saturation determines the depth of the layer, the distribution of hardness along the depth and the thickness of the nitride zone. Composition of the saturating medium depends on the degree of alloying of the steel being processed and the requirements for the hardness and depth of the nitrided layer. Process pressure should be such that the discharge tightly “fits” the surface of the products and obtains a uniform nitrided layer. However, it should be borne in mind that the discharge at all stages of the process must be anomalous, i.e. the surface of all parts in the charge must be completely covered with glow, and the discharge current density must be greater than the normal density for a given pressure, taking into account the heating effect gas in the cathode region of the discharge. With the advent of new-generation IPA installations, using composition-controlled mixtures of hydrogen, nitrogen and argon as a working medium, as well as “pulsating” rather than direct current plasma, the manufacturability of the ion nitriding process has increased significantly. The use of combined heating (“hot” chamber walls) or enhanced thermal protection (triple heat shield), along with the ability to independently regulate the gas composition and pressure in the chamber, allows, when processing cutting tools, to avoid overheating of thin cutting edges during the heating of the charge, and to accurately regulate the saturation time and , respectively, and the depth of the layer, because Products can be heated in a nitrogen-free environment, for example, in an Ar+H 2 mixture. Effective thermal insulation in the working chamber (triple heat shield) allows products to be processed with low specific energy consumption, which allows temperature differences inside the cage to be minimized during processing. This is evidenced by the distribution of microhardness along the depth of the nitrided layer for samples located in different places of the charge (Fig. 2).

Rice. 2. Microhardness distribution along the depth of the nitrided layer for three samples located in different places of the charge.

a, c – gear weighing 10.1 kg, 51 pcs., st – 40X, module 4.5, exposure 16 hours, T = 530 0 C;

b, d – gear weighing 45 kg, 11 pcs., st – 38HN3MFA, module 3.25 (outer ring)

and 7 mm (inner crown), exposure 16 hours, T=555 0 C.

Ion nitriding is an effective method of strengthening treatment of parts made of alloyed structural steels: gears, ring gears, shaft-toothed gears, shafts, spur, bevel and cylindrical gears, couplings, shaft-gears of complex geometric configuration, etc. Cementation, nitrocarburization and high-frequency hardening are justified in the manufacture of heavily loaded parts (gears, axles, shafts, etc.) of low and medium precision, which do not require subsequent grinding. These types of heat treatment are not economically feasible in the manufacture of medium- and low-load high-precision parts, because With this treatment, significant warping is observed and subsequent grinding is required. Accordingly, when grinding it is necessary to remove a significant thickness of the hardened layer. IPA can significantly reduce warping and deformation of parts while maintaining surface roughness within the range of Ra = 0.63...1.2 microns, which makes it possible to use IPA as a finishing treatment in the vast majority of cases. In relation to the machine tool industry, ion nitriding of gears significantly reduces the noise characteristics of machine tools, thereby increasing their competitiveness in the market. IPA is most effective when processing large-scale parts of the same type: gears, shafts, axles, toothed shafts, shaft-toothed gears, etc. Gears subjected to plasma nitriding have better dimensional stability compared to cemented gears and can be used without additional processing. At the same time, the bearing capacity of the side surface and the strength of the tooth base, achieved using plasma nitriding, correspond to cemented gears (Table 1).

Table 1

Characteristics of fatigue resistance of steels depending on methods of hardening gears

Steel type	Type of processing	Bending endurance limit, MPa	Surface contact endurance limit, MPa	Hardness of the side surface of the teeth, HV
Alloyed	Hardening
Improved (40Х, 40ХН, 40ХФА, 40ХН2МА, 40ХМFA, 38ХМ, 38ХН3МФА, 38Х2Н2ММА, 30Х2НМ, etc.)	Nitriding
Normalized	Plasma or induction hardening
Special nitrided (38ХМУА, 38Х2МУА, 35ХУА, 38ХВФУА, 30Х3МФ, etc.)	Nitriding
Alloyed	Cementation and nitrocarburization

When strengthening treatment by ion nitriding of parts made of case-hardening, low- and medium-alloy steels (18KhGT, 20KhNZA, 20KhGNM, 25KhGT, 40Kh, 40KhN, 40KhFA, etc.), it is necessary to first improve the forgings - volumetric hardening and tempering to a hardness of 241-285 HB (for some steels - 269-302 HB), then mechanical processing and finally ion nitriding. To ensure minimal deformation of products before nitriding to relieve stress, it is recommended to carry out annealing in a protective gas atmosphere, and the annealing temperature should be higher than the nitriding temperature. Annealing should be carried out before precision machining. The depth of the nitrided layer formed on these products made from steels 40Kh, 18KhGT, 25KhGT, 20Kh2N4A, etc. is 0.3-0.5 mm with a hardness of 500-800 HV depending on the steel grade (Figure 3). For gears operating under heavier loads, the nitride layer should be 0.6-0.8 mm with a thin nitride zone or no nitride zone at all.

Rice. 3. Distribution of microhardness along the depth of the nitrided layer for different steels

wear – g’- or e-layer; dynamic load – limited thickness of the nitride layer or no nitride layer at all; corrosion – e-layer. Independent control of the flow rate of each component of the gas mixture, the pressure in the working chamber and the variation in process temperature make it possible to form layers of different depths and hardness (Fig. 4), thereby ensuring stable processing quality with minimal variation in properties from part to part and from charge to charge ( Fig. 5).

Rice. 4. Distribution of microhardness along the depth of the nitrided layer of steel 40Х

1, 3, 5 – one-stage process;

2.4 – two-stage process in contentN 2 in the working mixture

1,2 – T=530 0 C, t=16 hours; 3 –T=560 0 C, t=16 hours;

4 – T=555 0 C, t=15 hours, 5 – T = 460 0 C, t = 16 hours

Rice. 5. Dispersion of microhardness along the depth of the nitrided layer

for steel 40X (a) and 38KhNZMFA (b) for serial processes.

Ion nitriding is widely known as one of the effective methods for increasing the wear resistance of cutting tools made from high speed steels grades R6M5, R18, R6M5K5, R12F4K5, etc. Nitriding increases the wear resistance of the tool and its heat resistance. The nitrided surface of the tool, which has a reduced coefficient of friction and improved anti-friction properties, ensures easier removal of chips, and also prevents chips from sticking to the cutting edges and the formation of wear craters, which makes it possible to increase feed and cutting speed. The optimal structure of nitrided high-speed steel is high-nitrogen martensite, which does not contain excess nitrides. This structure is ensured by saturating the tool surface with nitrogen at a temperature of 480-520 0 C during short-term nitriding (up to 1 hour). In this case, a strengthened layer with a depth of 20-40 microns is formed with a surface microhardness of 1000-1200 HV0.5 with a core hardness of 800-900 HV (Fig. 6), and the tool life after ion nitriding increases 2–8 times depending on its type and type of material being processed.

Rice. 6. Structure of the nitrided layer of steel R6M5 (a) and distribution of microhardness along the depth of the layer (b).

The main advantage of ion nitriding of a tool is the possibility of obtaining only a diffusion-hardened layer, or a layer with monophase Fe 4 N nitride ('-phase) on the surface, in contrast to classical gas nitriding in ammonia, where the nitride layer consists of two phases - '+ , which is a source of internal stresses at the interface and causes brittleness and peeling of the hardened layer during operation. Ion nitriding is also one of the main methods for increasing durability stamping tools and injection molding equipment from steels 5KhNM, 4Kh5MFS, 3Kh2V8, 4Kh5V2FS, 4Kh4VMFS, 38Kh2MYuA, Kh12, Kh12M, Kh12F1. As a result of ion nitriding, the following characteristics of products can be improved:

Forging dies for hot stamping and molds for casting metals and alloys - increases wear resistance, reduces metal sticking. Molds for aluminum injection molding - the nitriding layer prevents metal from sticking in the liquid jet feed zone, and the mold filling process is less turbulent, which increases the service life of the molds, and the casting is of higher quality. Significantly improves ion nitriding and cold tool performance (T< 250 0 С) обработки – вытяжка, гибка, штамповка, прессование, резка, чеканка и прошивка. Основные требования, обеспечивающие высокую работоспособность такого инструмента – высокая прочность при сжатии, износостойкость и сопротивление холодной ударной нагрузке – достигаются в результате упрочняющей обработки методом ионного азотирования. Если для инструмента используется высокохромистая сталь (12% хрома), то азотированный слой должен быть только диффузионным, если низколегированные стали – то дополнительно к диффузионному слою должен быть γ-слой – твердый и пластичный. Особенностью ионного азотирования высокохромистых сталей является то, что выбирая температуру процесса можно в широких пределах сохранять твердость сердцевины изделия, задаваемую предварительной термической обработкой (табл. 2). Для получения износостойкого поверхностного слоя при сохранении вязкой сердцевины штампа необходимо проводить вначале закалку с отпуском на вторичную твердость, размерную обработку и затем ионное азотирование. Для исключения или сведения к минимуму деформаций, возникающих при ионном азотировании штампового инструмента, перед окончательной механической обработкой рекомендуется проводить отжиг в среде инертного газа при температуре как минимум на 20 С ниже температуры отпуска. При необходимости применяют полировку азотированных рабочих поверхностей.

Table 2.

Characteristics of alloy steels after ion plasma nitriding.

steel grade	Hardness of Heartseguilt,	Process temperature 0 WITH	Layer characteristics			Type of recommended connection layer
steel grade	Hardness of Heartseguilt,	Process temperature 0 WITH	Depth, mm	TV, H.V. 1	Connection layer thickness,	Type of recommended connection layer
Hot working steels




Cold working steels

Improving the properties of a metal can occur by changing it chemical composition. An example is the nitriding of steel - relatively new technology saturation of the surface layer with nitrogen, which began to be used in industrial scale about a century ago. The technology under consideration was proposed to improve certain qualities of products made from steel. Let's take a closer look at how steel is saturated with nitrogen.

Purpose of nitriding

Many people compare the process of cementing and nitriding because both are designed to significantly improve the performance of a part. The technology of introducing nitrogen has several advantages over carburization, among which there is no need to increase the temperature of the workpiece to the values at which the atomic lattice is attached. It is also noted that the technology of introducing nitrogen practically does not change the linear dimensions of the workpieces, due to which it can be used after finishing processing. On many production lines, parts that have been hardened and ground are subjected to nitriding and are almost ready for production, but some qualities need to be improved.

The purpose of nitriding is associated with a change in the basic performance qualities during the heating of the part in an environment characterized by a high concentration of ammonia. Due to this effect, the surface layer is saturated with nitrogen, and the part acquires the following performance qualities:

The wear resistance of the surface is significantly increased due to the increased hardness index.
The endurance value and resistance to increased fatigue of the metal structure are improved.
In many industries, the use of nitriding is associated with the need to impart anti-corrosion resistance, which is maintained upon contact with water, steam or air with high humidity.

The above information determines that the results of nitriding are more significant than carburization. The advantages and disadvantages of the process largely depend on the technology chosen. In most cases, the transferred performance qualities are maintained even when the workpiece is heated to a temperature of 600 degrees Celsius; in the case of cementation, the surface layer loses hardness and strength after heating to 225 degrees Celsius.

Nitriding process technology

In many ways, the process of steel nitriding is superior to other methods that involve changing the chemical composition of the metal. The nitriding technology for steel parts has the following features:

In most cases, the procedure is performed at a temperature of about 600 degrees Celsius. The part is placed in a sealed iron muffle furnace, which is placed in the furnace.
When considering nitriding modes, temperature and holding time should be taken into account. For different steels, these indicators will differ significantly. The choice also depends on what performance qualities need to be achieved.
Ammonia is supplied from a cylinder into the created metal container. High temperatures cause ammonia to begin to decompose, causing nitrogen molecules to be released.
Nitrogen molecules penetrate the metal due to the process of diffusion. Due to this, nitrides are actively formed on the surface, which are characterized by increased resistance to mechanical stress.
The chemical-thermal treatment procedure in this case does not involve sudden cooling. As a rule, the nitriding furnace is cooled along with the ammonia flow and the part, due to which the surface does not oxidize. Therefore, the technology under consideration is suitable for changing the properties of parts that have already undergone finishing processing.

The classic process of obtaining the required product with nitriding involves several stages:

Preparatory heat treatment, which consists of hardening and tempering. Due to the rearrangement of the atomic lattice under a given regime, the structure becomes more viscous and strength increases. Cooling can take place in water or oil, or another medium - it all depends on how high quality the product should be.
Next, mechanical processing is performed to give the desired shape and size.
In some cases, there is a need to protect certain parts of the product. Protection is carried out by applying liquid glass or tin in a layer about 0.015 mm thick. Due to this, a protective film is formed on the surface.
Steel nitriding is carried out using one of the most suitable methods.
Finishing work is underway machining, removing the protective layer.

The resulting layer after nitriding, which is represented by nitride, ranges from 0.3 to 0.6 mm, which eliminates the need for a hardening procedure. As previously noted, nitriding has been carried out relatively recently, but the process of transforming the surface layer of the metal has already been almost completely studied, which has significantly increased the efficiency of the technology used.

Metals and alloys subjected to nitriding

There are certain requirements that apply to metals before carrying out the procedure in question. Typically, attention is paid to carbon concentration. The types of steels suitable for nitriding are very different, the main condition is a carbon fraction of 0.3-0.5%. Better results are achieved when using alloyed alloys, since additional impurities contribute to the formation of additional solid nitrites. Example chemical treatment metal we call the saturation of the surface layer of alloys, which contain impurities in the form of aluminum, chromium and others. The alloys under consideration are usually called nitralloys.

Nitrogen is added when using the following steel grades:

If the part will be subject to significant mechanical impact during operation, then choose grade 38Х2МУА. It contains aluminum, which causes a decrease in deformation resistance.
In the machine tool industry, the most widely used steels are 40X and 40HFA.
In the manufacture of shafts that are often subjected to bending loads, grades 38ХГМ and 30ХЗМ are used.
If during production you need to get high accuracy linear dimensions, for example, when creating parts for fuel units, then steel grade 30ХЗМФ1 is used. In order to significantly increase the strength of the surface and its hardness, alloying with silicon is first carried out.

When choosing the most suitable grade of steel, the main thing is to comply with the condition associated with the percentage of carbon, and also take into account the concentration of impurities, which also have a significant impact on the performance properties of the metal.

Main types of nitriding

There are several technologies used to carry out nitriding of steel. Let's take the following list as an example:

Ammonia-propane environment. Gas nitriding has become very widespread today. In this case, the mixture is represented by a combination of ammonia and propane, which are taken in a ratio of 1 to 1. As practice shows, gas nitriding when using such a medium requires heating to a temperature of 570 degrees Celsius and holding for 3 hours. The resulting layer of nitrides is characterized by a small thickness, but at the same time the wear resistance and hardness are much higher than when using classical technology. Nitriding of steel parts in this case makes it possible to increase the hardness of the metal surface to 600-1100 HV.
Glow discharge is a technique that also involves the use of a nitrogen-containing environment. Its peculiarity lies in the connection of the nitrided parts to the cathode; the muffle acts as a positive charge. By connecting the cathode, it is possible to speed up the process several times.
The liquid medium is used a little less frequently, but is also highly effective. An example is a technology that involves the use of a molten cyanide layer. Heating is carried out to a temperature of 600 degrees, the holding period is from 30 minutes to 3 hours.

In industry, the gas medium has become most widespread due to the ability to process large batches at once.

Catalytic gas nitriding

This type of chemical treatment involves creating a special atmosphere in the stove. Dissociated ammonia is pre-treated on a special catalytic element, which significantly increases the number of ionized radicals. Features of the technology include the following points:

Preliminary preparation of ammonia makes it possible to increase the proportion of solid solution diffusion, which reduces the proportion of reaction chemical processes during the transition of the active substance from the environment to iron.
Provides for the use of special equipment that provides the most favorable conditions for chemical processing.

This method has been used for several decades and allows changing the properties of not only metals, but also titanium alloys. The high costs of installing equipment and preparing the environment determine the applicability of the technology to the production of critical parts that must have precise dimensions and increased wear resistance.

Properties of nitrided metal surfaces

Quite important is the question of what hardness of the nitrided layer is achieved. When considering hardness, the type of steel being processed is taken into account:

Carbon steel can have a hardness in the range of 200-250HV.
Alloy alloys after nitriding acquire a hardness in the range of 600-800HV.
Nitralloins, which contain aluminum, chromium and other metals, can achieve a hardness of up to 1200HV.

Other properties of steel also change. For example, the corrosion resistance of steel increases, making it possible to use it in aggressive environments. The process of introducing nitrogen itself does not lead to the appearance of defects, since heating is carried out to a temperature that does not change the atomic lattice.

ION-PLASMA NITRIDING AS ONE OF THE MODERN METHODS FOR SURFACE HARDENING OF MATERIALS

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Improving the quality of metal and its mechanical properties– this is the main way to increase the durability of parts and one of the main sources of saving steel and alloys. The quality and durability of products are improved through a rational choice of materials and hardening methods while achieving high technical and economic efficiency. There are many different methods of surface hardening - current hardening high frequency, plastic deformation, chemical thermal treatment (CHT), laser and ion plasma treatment.

The gas nitriding process, traditionally used in industry, as one of the types of chemical treatment, is the process of diffusion saturation of the surface layer of steel with nitrogen. Nitriding can be used to great effect to improve wear resistance, hardness, fatigue strength, corrosion and cavitation resistance various materials(structural steels, heat-resistant steels and alloys, non-magnetic steels, etc.), has a number of undeniable advantages, such as: relative simplicity of the process, the ability to use universal equipment and devices for laying parts, the ability to nitriding parts of any size and shape. At the same time, gas nitriding also has a number of disadvantages: the long process duration (20-30 hours) even when nitriding to small layer thicknesses (0.2-0.3 mm); the process is difficult to automate; local protection of surfaces that are not subject to nitriding is difficult; application of various galvanic coatings (copper plating, tinning, nickel plating, etc.) requires the organization of special production.

One of the areas of production intensification is the development and implementation of industrial enterprises new promising processes and technologies that improve the quality of products, reduce labor costs for their production, increase labor productivity and improve sanitary and hygienic conditions in production.

Such a progressive technology is ion plasma nitriding (IPA) - a type of chemical-thermal treatment of machine parts, tools, stamping and casting equipment, ensuring diffusion saturation of the surface layer of steel and cast iron with nitrogen (nitrogen and carbon) in a nitrogen-hydrogen plasma at a temperature
400-600ºС, titanium and titanium alloys at a temperature of 800-950 ºС in nitrogen-containing plasma. This process is now widespread in all economic developed countries: USA, Germany, Switzerland, Japan, England, France.

In many cases, ion nitriding is more appropriate than gas nitriding. The advantages of IPA in glow discharge plasma include the following: the ability to control the saturation process, which ensures the production of a high-quality coating with a given phase composition and structure; ensuring absolutely identical activity of the gaseous medium over the entire surface of the part covered by the glow discharge, this ultimately ensures the production of a nitrided layer of uniform thickness; reducing the labor intensity of local protection of surfaces that are not subject to nitriding, which is carried out with metal screens; a sharp reduction in the duration of nitriding of parts (2-2.5 times); reduction of parts deformation. The use of IPA instead of carburization, nitrocarburization, gas or liquid nitriding, volumetric or high-frequency hardening allows you to save capital equipment and production space, reduce machine tool and transportation costs, and reduce the consumption of electricity and active gaseous media.

The essence of the ion nitriding process is as follows. In a closed evacuated space between the part (cathode) and the furnace casing (anode), a glow discharge is excited. Nitriding is carried out with an anomalous glow discharge, at a high voltage of the order of W. Modern installations ensure the stability of a glow discharge at the boundary of its transition to normal and arc. The principle of operation of arc extinguishing devices is based on a short-term shutdown of the installation when a voltaic arc ignites.

Nitriding increases the corrosion resistance of parts made of carbon and low-alloy steels. Parts that are nitrided to increase surface strength and wear resistance simultaneously acquire properties against corrosion in steam, tap water, alkali solutions, crude oil, gasoline, and polluted atmospheres. Ion nitriding significantly increases the hardness of parts, which is due to highly dispersed nitride precipitation, the quantity and dispersion of which affects the achieved hardness. Nitriding increases the fatigue limit. This is explained, firstly, by an increase in the strength of the surface, and secondly, by the occurrence of residual compressive stresses in it.

The advantages of ion nitriding are most fully realized in large-scale and mass production, when strengthening large batches of similar parts. By varying the gas composition, pressure, temperature and holding time, layers of a given structure and phase composition can be obtained. The use of ion nitriding provides technical, economic and social effects.