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Ionic nitriding of parts. Plasma nitriding - process and steps Protective pastes against ion plasma nitriding

Nitriding, during which the surface layer of a steel product is saturated with nitrogen, has been used in industrial scale recently. Such a processing method, proposed for use by Academician N.P. Chizhevsky, allows to improve many characteristics of products made of steel alloys.

The essence of technology

Nitriding of steel, when compared with such a popular method of processing this metal as carburizing, has a number of significant advantages. That is why this technology began to be used as the main way to improve the quality characteristics of steel.

During nitriding, the steel product is not subjected to significant thermal effects, while the hardness of its surface layer increases significantly. It is important that the dimensions of the nitrided parts do not change. This makes it possible to use this processing method for steel products that have already been hardened with high tempering and ground to the required geometric parameters. After nitriding, or nitriding as the process is often called, the steel can be immediately subjected to polishing or other finishing methods.

Nitriding of steel consists in the fact that the metal is subjected to heating in an environment characterized by a high content of ammonia. As a result of such treatment, the following changes occur with the surface layer of the metal saturated with nitrogen.

Due to the fact that the hardness of the surface layer of steel increases, the wear resistance of the part improves.
The fatigue strength of the product increases.
The surface of the product becomes resistant to corrosion. Such stability is maintained when steel comes into contact with water, moist air and steam-air medium.

The performance of nitriding makes it possible to obtain more stable indicators of steel hardness than when carburizing. Thus, the surface layer of a product that has been subjected to nitriding retains its hardness even when heated to a temperature of 550–600°C, while after cementation, the hardness of the surface layer may begin to decrease even when the product is heated above 225°C. The strength characteristics of the surface layer of steel after nitriding are 1.5–2 times higher than after hardening or carburizing.

How does the nitriding process proceed?

Metal parts are placed in a hermetically sealed muffle, which is then installed in a nitriding furnace. In the furnace, the muffle with the part is heated to a temperature, which is usually in the range of 500–600°C, and then kept for some time at this temperature regime.

In order to form the working medium inside the muffle necessary for the nitriding to proceed, ammonia is supplied to it under pressure. When heated, ammonia begins to decompose into constituent elements, this process is described by the following chemical formula:

2NH 3 → 6H + 2N.

Atomic nitrogen released during such a reaction begins to diffuse into the metal from which the workpiece is made, which leads to the formation of nitrides on its surface, which are characterized by high hardness. To fix the result and prevent the surface of the part from oxidizing, the muffle, together with the product and the ammonia that continues to remain in it, is slowly cooled together with the nitriding furnace.

The nitride layer formed on the metal surface during nitriding can have a thickness in the range of 0.3–0.6 mm. This is quite enough to give the product the required strength characteristics. Steel processed using this technology can not be subjected to any additional processing methods.

The processes occurring in the surface layer of a steel product during its nitriding are quite complex, but have already been well studied by specialists in the metallurgical industry. As a result of such processes, the following phases are formed in the structure of the treated metal:

solid solution Fe 3 N, characterized by a nitrogen content in the range of 8–11.2%;
a solid solution of Fe 4 N, which contains 5.7–6.1% nitrogen;
nitrogen solution formed in α-iron.

An additional α-phase in the metal structure is formed when the nitriding temperature begins to exceed 591°. At the moment when the degree of saturation of a given phase with nitrogen reaches its maximum, a new phase is formed in the metal structure. Eutectoid decomposition in the metal structure occurs when the degree of its saturation with nitrogen reaches a level of 2.35%.

Valves of high-tech internal combustion engines must undergo a nitriding process

Factors affecting nitrogenation

The main factors that affect nitriding are:

the temperature at which such a technological operation is performed;
gas pressure supplied to the muffle;
the duration of exposure of the part in the furnace.

The efficiency of such a process is also affected by the degree of ammonia dissociation, which, as a rule, is in the range of 15–45%. With an increase in the nitriding temperature, the hardness of the formed layer decreases, but the process of nitrogen diffusion into the metal structure accelerates. The decrease in the hardness of the surface layer of the metal during its nitriding occurs due to the coagulation of the nitrides of the alloying elements included in its composition.

To speed up the nitriding process and increase its efficiency, a two-stage scheme of its implementation is used. The first stage of nitriding when using such a scheme is performed at a temperature not exceeding 525 °. This makes it possible to impart high hardness to the surface layer of the steel product. To perform the second stage of the procedure, the part is heated to a temperature of 600–620°C, while the depth of the nitrided layer reaches the required values, and the process itself is almost doubled. The hardness of the surface layer of a steel product processed using this technology is not lower than the similar parameter of products processed using a single-stage method.

Types of nitrided steels

Both carbonaceous and those characterized by a carbon content in the range of 0.3–0.5% can be processed using nitriding technology. The maximum effect when using such a technological operation can be achieved if steels are subjected to it, in chemical composition which include alloying elements that form solid and heat-resistant nitrides. Such elements, in particular, include molybdenum, aluminum, chromium and other metals with similar characteristics. Steels containing molybdenum are not subject to such a negative phenomenon as temper brittleness, which occurs when a steel product slowly cools. After nitriding steel of various grades acquire the following hardness:

Alloying elements in the chemical composition of the steel increase the hardness of the nitrided layer, but at the same time reduce its thickness. Such chemical elements as tungsten, molybdenum, chromium and nickel have the most active influence on the thickness of the nitrided layer.

Depending on the scope of the product that is subjected to the nitriding procedure, as well as on the conditions of its operation, it is recommended to use certain steel grades for such a technological operation. So, in accordance with the technological problem that needs to be solved, experts advise using products from the following steel grades for nitriding.

38X2MYUA

This is a steel that, after nitriding, has a high hardness of the outer surface. Aluminum contained in the chemical composition of such steel reduces the deformation resistance of the product, but at the same time contributes to an increase in the hardness and wear resistance of its outer surface. The exclusion of aluminum from the chemical composition of steel makes it possible to create products of a more complex configuration from it.

40X, 40HFA

These alloyed steels are used for the manufacture of parts used in the machine tool industry.

30H3M, 38HGM, 38HNMFA, 38HN3MA

These steels are used for the production of products that are subjected to frequent cyclic bending loads during their operation.

30X3MF1

Products are made from this steel alloy, the accuracy of geometrical parameters of which is subject to high requirements. To give higher hardness to parts made of this steel (these are mainly parts of fuel equipment), silicon can be added to its chemical composition.

Technological scheme of nitriding

To perform conventional gas nitriding, innovative plasma nitriding or ion nitriding, the workpiece is subjected to a series of process steps.

Preparatory heat treatment

Such processing consists in hardening the product and its high tempering. Hardening as part of this procedure is carried out at a temperature of about 940 °, while cooling the workpiece is carried out in oil or water. The subsequent tempering after quenching, which takes place at a temperature of 600–700 °, makes it possible to endow the metal being processed with a hardness at which it can be easily cut.

Mechanical restoration

This operation ends with its grinding, which allows to bring the geometric parameters of the part to the required values.

Protection of parts of the product that do not require nitriding

Such protection is carried out by applying a thin layer (not more than 0.015 mm) of tin or liquid glass. For this, electrolysis technology is used. The film of these materials, which is formed on the surface of the product, does not allow nitrogen to penetrate into its internal structure.

Performing the nitriding itself

The prepared product is subjected to processing in a gaseous environment.

Finishing

This stage is necessary in order to bring the geometric and mechanical characteristics of the product to the required values.

The degree of change in the geometric parameters of the part during nitriding, as mentioned above, is very small, and it depends on factors such as the thickness of the surface layer that is saturated with nitrogen; temperature regime of the procedure. Guaranteed practically complete absence deformation of the workpiece allows a more advanced technology - ion nitriding. By doing ionic plasma nitriding steel products are subjected to less thermal stress, due to which their deformation is minimized.

Unlike the innovative ion-plasma nitriding, traditional nitriding can be performed at temperatures up to 700°C. For this, a replaceable muffle or a muffle built into the heating furnace can be used. The use of a replaceable muffle, in which the workpieces are loaded in advance, before being installed in the furnace, can significantly speed up the nitriding process, but is not always an economically viable option (especially in cases where large-sized products are processed).

Working environment types

For nitriding can be used Various types working environments. The most common of these is a gas medium consisting of 50% ammonia and 50% propane or ammonia and endogas, taken in the same proportions. The nitriding process in such an environment is carried out at a temperature of 570 °. In this case, the product is exposed to the gas environment for 3 hours. The nitrided layer created by using such a working medium has a small thickness, but high strength and wear resistance.

Recently, the method of ion-plasma nitriding, which is performed in a nitrogen-containing discharged medium, has been widely used.

Ion-plasma nitriding - a look "from the inside"

A distinctive feature of ion-plasma nitriding, which is also called glow discharge treatment, is that the workpiece and the muffle are connected to a source electric current, while the product acts as a negatively charged electrode, and the muffle - as a positively charged one. As a result, a flow of ions is formed between the part and the muffle - a kind of plasma consisting of N 2 or NH 3, due to which both the heating of the treated surface and its saturation occur necessary quantity nitrogen.

In addition to traditional and ion-plasma nitriding, the process of saturation of the steel surface with nitrogen can be performed in a liquid medium. As a working medium, which has a heating temperature of about 570 °, in such cases, a melt of cyanide salts is used. The time of nitriding carried out in a liquid working medium can be from 30 to 180 minutes.

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 gaseous media, i.e. the diffusion saturation process is controllable and can be optimized depending on the specific requirements for layer depth and surface hardness. plasma nitriding microhardness alloyed

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

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

Rice. 1.

As a result of IPA, the following characteristics of products can be improved: wear resistance, fatigue endurance, extreme pressure properties, heat resistance and corrosion resistance.

In comparison with the widely used methods of hardening chemical-thermal treatment of steel parts, such as carburizing, carbonitriding, 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 finish;
increase in endurance limit and increase in wear resistance of machined parts;
lower processing temperature, due to which structural transformations do not occur in the steel;
Possibility of processing deaf 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 possibility of processing products of unlimited sizes and shapes;
no pollution environment;
Improving the culture of production;
Reducing the cost of processing several times.

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

So, for example, in comparison with gas nitriding in furnaces, IPA provides:

· Reducing the duration of treatment by 2-5 times, both by reducing the time of heating and cooling of the charge, and by reducing the time of isothermal exposure;
· reduction of brittleness of the hardened layer;
· Reducing the consumption of working gases by 20-100 times;
· reduction of power consumption by 1.5-3 times;
exclusion of the depassivation operation;
reduction of deformation so as to exclude finishing grinding;
· simplicity and reliability of screen protection against nitriding of unhardened surfaces;
· improvement of sanitary and hygienic conditions of production;
Full compliance of the technology with all modern requirements for environmental protection.

Compared to hardening IPA processing allows:

Avoid deformities
· to increase the service life of the nitrided surface by 2-5 times.

The use of IPA instead of carburizing, nitrocarburizing, gas or liquid nitriding, volumetric or high-frequency hardening allows saving the main equipment and production areas, reducing machine and transport costs, 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 gaseous medium between the cathode - parts - and the anode - the walls of the vacuum chamber - an abnormal glow discharge is excited, forming an active medium (ions, atoms, excited molecules), providing the formation of a nitrided layer, consisting of an external - nitride zone and a diffusion zone located under it.

Technological factors affecting the efficiency of ion nitriding are the process temperature, duration of saturation, pressure, composition and consumption 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 provide 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 should be at least 10-20 0 С lower than the tempering temperature.

Process duration and temperature saturations determine the depth of the layer, the distribution of hardness over depth, and the thickness of the nitride zone.

The composition of the saturating medium depends on the degree of alloying of the treated steel and the requirements for hardness and depth of the nitrided layer.

Process pressure should be such as to ensure a tight "fit" by the discharge of the surface of the products and obtain 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 luminescence, 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 units, which use compositionally 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” walls of the chamber) or enhanced thermal protection (triple heat shield), along with the ability to independently adjust the gas composition and pressure in the chamber, make it possible to avoid overheating of thin cutting edges during the heating of the charge during processing of the cutting tool, to precisely control the saturation time and , respectively, and the depth of the layer, because it is possible to heat up products in a nitrogen-free environment, for example, in a mixture of Ar+H 2 .

Efficient thermal insulation in the working chamber (triple heat shield) allows the processing of products with low specific energy consumption, which allows minimizing temperature differences within the load during processing. This is evidenced by the distribution of microhardness over 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 pieces, st - 40X, module 4.5, exposure 16 hours, T = 530 0 C;

b, d - gear weighing 45 kg, 11 pcs., st - 38KhN3MFA, module 3.25 (outer crown) and 7 mm (inner crown), exposure 16 hours, T = 555 0 C.

Ion nitriding is an effective method of hardening treatment of parts made of alloy structural steels: gears, gear rims, gear shafts, shafts, spur, bevel and cylindrical gears, couplings, gear shafts of complex geometric configuration, etc.

Carburizing, nitrocarburizing and high-frequency hardening justify themselves in the manufacture of heavily loaded parts (gear wheels, axles, shafts, etc.) of low and medium accuracy that do not require subsequent grinding.

These types of heat treatment are not economically feasible in the manufacture of medium- and low-loaded high-precision parts, because with this treatment, significant warpage 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 warpage and deformation of parts while maintaining surface roughness within Ra = 0.63 ... 1.2 µm, which allows in the vast majority of cases to use IPA as a finishing treatment.

Applied to machine tools, ion nitriding gear wheels significantly reduces the noise characteristics of machines, thereby increasing their competitiveness in the market.

IPA is most effective when machining large-scale similar parts: gears, shafts, axles, gear shafts, shaft-toothed gears, etc. Plasma nitrided gears have better dimensional stability compared to carburized 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 case-hardened gears (Table 1).

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

During hardening treatment by ion nitriding of parts made of carburized, low- and medium-alloy steels (18KhGT, 20KhNZA, 20KhGNM, 25KhGT, 40Kh, 40KhN, 40KhFA, etc.), it is necessary to improve forgings at the beginning - volumetric hardening and tempering to a hardness of 241-285 HB (for some steels - 269-302 HB), then machining and, finally, ion nitriding. In order to ensure minimal deformation of products before stress relief nitriding, 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 of steels 40Kh, 18KhGT, 25KhGT, 20Kh2N4A, etc., is 0.3-0.5 mm with a hardness of 500-800 HV, depending on the steel grade (Fig. 3).

For gears operating under conditions of heavier loads, the nitrided layer should be at the level of 0.6-0.8 mm with a thin nitride zone or without it at all.

Rice. 3.

The optimization of the properties of the hardened layer is determined by the combination of the characteristics of the base material (hardness of the core) 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 - - a layer.

Independent control of the flow rate of each of the components of the gas mixture, the pressure in the working chamber and the variation in the temperature of the process make it possible to form layers of various depths and hardness (Fig. 4), thereby ensuring a stable quality of processing with a minimum spread of 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 by 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.

Ion nitriding is widely known as one of the effective methods increase the wear resistance of cutting tools made of high speed steels grades R6M5, R18, R6M5K5, R12F4K5, etc.

Nitriding improves tool wear resistance and heat resistance. The nitrided surface of the tool, which has a reduced coefficient of friction and improved anti-friction properties, provides easier chip removal, and also prevents chips from sticking to the cutting edges and the formation of wear holes, which makes it possible to increase the 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 saturation of 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 hardened layer with a depth of 20–40 μm 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 by 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 phase boundary 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 - wear resistance increases, metal sticking decreases.
· Aluminum Die Casting Molds - The nitrided layer prevents metal from sticking in the liquid jet zone, and the mold filling process is less turbulent, which increases the life of the molds, and the casting is of higher quality.

Significantly improves ion nitriding and tool performance for cold (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 - high compressive strength, wear resistance and resistance to cold shock loading - are achieved as a result of hardening treatment by ion nitriding.

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

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 in a wide range, which is set by the preliminary heat treatment(Table 2).

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

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

If necessary, apply polishing of nitrided working surfaces.

Table 2. Characteristics of alloyed steels after ion-plasma nitriding.

steel grade	Core hardness, HRC	Process temperature	Layer characteristics	Type of recommended connection layer
	Depth, mm	Pov. TV-st, HV 1	Connection layer thickness, µm
Steels for hot working




Steels for cold working

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 distribution of microhardness over the depth of the nitrided layer (c, d).

Thus, as world experience shows, the use of ion nitriding technology for hardening treatment of structural steel products, 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 parts of gas turbine engines is largely determined by the state of their surface, and primarily by its wear resistance. Nitriding is one of the widely used methods for increasing the wear resistance of surfaces of aircraft engines and aircraft parts. Nitriding is applied to parts that, during operation, mainly work on friction.

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 fatigue resistance and electrochemical corrosion of parts.

During nitriding, nitrogen forms a number of phases with iron: nitrous ferrite - a solid solution of nitrogen in -iron, nitrous austenite - a solid solution of nitrogen in -iron, intermediate `-phase Fe4N, -phase Fe2N, etc. However, iron nitrides have insufficient strength, hardness, high brittleness compared to chromium nitrides CrN, Cr2N, molybdenum MoN, aluminum AlN and some other alloying elements. Therefore, alloyed steels containing the indicated elements are subjected to nitriding: 45Kh14N14V2M, 1Kh12N2VMF, 15Kh16K5N2MVFAB-Sh and other steels that are used for the manufacture of bushings, stems, valve seats, various bodies, etc.

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

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

Usually, nitriding is carried out at temperatures below 600C, when the predominant diffusion of nitrogen occurs. The diffusion transfer rate 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 with depth.

The greatest acceleration of the nitriding process is achieved in the glow discharge plasma, when a glow discharge is excited in a rarefied atmosphere between the workpiece (cathode) and the anode. Gas ions bombard the cathode surface and heat it up to a temperature of 470-580C. Positively charged nitrogen ions under the action of the energy of the electrostatic field move at a certain speed along the 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 to form iron nitride, which is deposited on the surface of the part. thin layer. Subsequently, the 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). The nitrogen formed during the decay of the lower nitride diffuses into the depth of the material of the part, and the iron is again sprayed into the plasma.

In contrast to furnace heating, during ion nitriding (in glow discharge plasma), the parts are heated due to the plasma energy consumed in proportion to the mass of the charge. This does not require stoves with massive masonry.

Nitriding of easily passivating high-chromium stainless steels necessarily requires the addition of hydrogen to the gaseous medium. To obtain high-quality diffusion layers without a -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. The gaseous medium of such a composition ensures the uniformity of the thickness of the diffusion layers on the parts placed in the charge over the volume of the working chamber. Increasing the pressure of the mixture in 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 about half that of furnace nitriding, according to 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 influence of the ion nitriding temperature on the layer depth has a dependence close to the exponent.

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 α-phase, is usually ground off. As a result of ion nitriding, the surface has the maximum hardness. The diameters of nitrided parts of the “shaft” type vary, as a rule, by 30-40 microns, which often falls within the tolerance field. Therefore, taking into account the high quality of the surface after ion nitriding and the preservation of cleanliness, it can be left untreated, or limited to polishing or light lapping.

With the help of ion nitriding at the base plant, it was possible to achieve high efficiency in increasing the durability of cutting tools and hot deformation dies in the manufacture of parts from difficult-to-machine 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 the 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 applying electroplating;

In some cases, refuse grinding after nitriding;

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

Improve occupational health.

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

Structural steels of pearlitic, austenitic, martensitic, transitional classes, maraging steels of the following materials were subjected to the study of hardening by ion nitriding: V2, 40X10X2M, 14X10X2M, 14X17N2, 15X15K5N2MVFAB -Sh (EP866), 30Kh2NVA, 16Kh3NVFAB-Sh, (DI39, VKS-5), N18K9M5T (MS200) and others. The task of research is the development of technological processes with the aim of transferring furnace nitriding of parts to ionic, new technological processes of ionic nitriding of parts instead of carburizing , as well as previously not hardened by chemical-thermal treatment.

For parts that work for 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, it is necessary to strive to obtain a layer with a large internal nitriding zone.

Variation of the layer structure makes it possible to obtain various combinations of the layer and the core. This is confirmed by numerous examples of nitriding for various groups of parts.

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

A high hydrogen content in the mixture, including that corresponding to the composition at 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, after a certain time, begins to affect the depth of the nitrided layer, as well as its unevenness on the parts over the volume of the charge. Hydrogen in a gaseous medium during ion nitriding plays the role of a reducing agent of oxides on the hardened surface, which prevent direct contact and interaction of nitrogen with the metal.

Steels of the usual class are nitrided in pure nitrogen without the addition of hydrogen. However, nitrided layers are not always uniform in depth.

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

The quality of the diffusion layers is affected by the temperature and duration of the process. 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 about half that of furnace nitriding using the current serial technology.

The distribution of microhardness over 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 α-phase, is usually ground off. As a result of ion nitriding of all steels, the surface has the 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, which reduce the nitrogen content directly on the metal, cathode sputtering, and the lower stability of the -phase in vacuum and glow discharge plasma.

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

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

Ionic nitriding of parts in serial production subjected mainly to three kinds of parts. These are parts subjected to conventional nitriding in dissociated ammonia, cemented parts with light and medium work loads 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.

The long duration of isothermal exposure, reaching 50 hours, with a significant 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 of a complex configuration, is sometimes accompanied by uneven defects, which are practically not detected by control and manifest themselves only during operation on a serial engine as a result of premature wear of the defective layer. When grinding parts, especially from such a complex alloy steel as 15Kh16K5N2MVFAB, cracks sometimes formed on sharp edges due to the relaxation of residual stresses, as well as at the transition points from a cylindrical surface to an end surface immediately after nitriding.

It is advisable to subject the finished parts to hardening by ion nitriding. This is due to the fact that the maximum hardness and wear resistance after ion nitriding is possessed directly by the surface or layers closely adjacent to it, while after conventional nitriding, layers located at some distance from the surface are more efficient.

To take into account the allowance for "swelling" in the manufacture, the effect of ion nitriding on the change in the dimensions of parts was investigated. The studies were carried out on typical representatives of parts. The statistics of the distribution of parts by size change was established. Parts of the shaft type 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 fit into the tolerance field. Thus, in the process of manufacturing parts, the laborious operation of grinding a nitrided surface was excluded. This circumstance makes it possible to expand the range of parts to be hardened, where machining after their hardening is difficult or impossible (for example, bent parts such as a bandage).

Tooling was designed and manufactured to protect non-nitrided surfaces. During 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 tin plating, 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.

During ion nitriding, non-nitriding surfaces are protected by metal screens that are in close contact with the surface that is not subject to nitriding (the gap is not 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 with the help of 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. Surfaces of parts that are not subject to nitriding can be finished.

The ion nitriding process allows:

increase the service life of nitrided parts;

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

reduce the complexity of manufacturing by eliminating operations for applying electroplating;

in some cases, abandon grinding after nitriding;

reduce the duration of the nitriding cycle by more than two times;

improve occupational health.

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

To obtain high hardness of parts from structural steels, the process is carried out at a temperature of 500 to 520C for up to 90 hours. The degree of dissociation of ammonia 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. This leads at a low temperature to the formation at first of a thin layer well saturated with nitrogen with finely dispersed nitrides, and then, with an increase in 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 steel saturation with nitrogen by 22.5 times.

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

creation of a controlled process that provides 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 estimate the nitrogen potential of the furnace atmosphere by its ionic composition (ionic dissociamers), and on the other hand, it opens up the possibility of direct analysis of the kinetics of the formation of diffusion coatings during the nitriding process (eddy current analyzers). The nitrogen potential is monitored by an ionization sensor with feedback with mixing system.

For nitriding, qualitatively new installations with program management technological process. The 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 using magnetic fields and various kinds electrical discharges (spark, corona, glow).

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

In our company for favorable price you can order ion-plasma nitriding in Nizhny Novgorod. This is one of the varieties of chemical heat treatment. This technology is usually used for processing products and parts made of cast iron, steel and other metals and alloys. The use of ion-plasma nitriding is relevant if it is required:

increase the strength of the metal;

increase the wear resistance of the product;

minimize the likelihood of metals sticking to the mold surface during the casting process;

improve anti-seize properties, etc.

The installations we use were developed by our company specialists, so we know exactly how this type of processing is carried out. We are true professionals in this field of activity.

Benefits of cooperation with us

Our company has more than 17 years of experience in the production of vacuum coating systems and the provision of related services. Therefore, we can offer our clients the following conditions:

Professional consulting assistance on any issues and at any stage of cooperation with us.

All work is carried out by our qualified specialists in compliance with all international norms and rules.

Our regular customers and partners - large enterprises automotive, space, aviation, chemical industries.

Long-term cooperation with leading Russian and foreign research institutes and enterprises allows us to constantly improve the quality of the services provided.

Ion-plasma hardening Vacuum ion-plasma methods for hardening the surfaces of parts include the following processes: generation (formation) of a corpuscular flow of matter; its activation, acceleration and focusing; ; condensation and penetration into the surface of parts (substrates). Generation: corpuscular flow of matter is possible by its evaporation (sublimation) and spraying. Evaporation: the transition of the condensed phase into vapor is carried out as a result of supplying thermal energy to the evaporated substance. Solids usually melt when heated and then turn into a gaseous state. Some substances pass into the gaseous state bypassing liquid phase. This process is called sublimation. .

Using the methods of vacuum ion-plasma technology, it is possible to perform: 1) modification of surface layers: ion-diffusion saturation; (ionic nitriding, carburizing, boriding, etc.); ion (plasma) etching (cleaning); ion implantation (implementation); glow discharge annealing; CTO in the environment of non-self-sustained discharge; 2) coating: glow discharge polymerization; ion deposition (triode sputtering system, diode sputtering system, using hollow cathode discharge); electric arc evaporation; ion-cluster method; cathode sputtering (dc, high frequency); chemical deposition in glow discharge plasma.

Advantages of vacuum ion-plasma hardening methods high adhesion of the coating to the substrate; uniformity of coating in thickness over a large area; variation of the coating composition in a wide range, within one technological cycle; obtaining high purity of the coating surface; ecological cleanliness production cycle.

Ion sputtering Ion sputters are divided into two groups: plasmonic sputters, in which the target is in a gas-discharge plasma created by a glow, arc, and high-frequency discharge. Sputtering occurs as a result of the bombardment of the target with ions extracted from the plasma; autonomous sources without focusing and with focusing of ion beams bombarding the target.

Principal spray system 1 - chamber; 2 - substrate holder; 3 - details (substrates); 4 - target; 5 - cathode; 6 - screen; 7 - supply of working gas; 8 - power supply; 9 - pumping out.

CTO in a glow discharge environment Glow discharge diffusion plants are used for nitriding, carburizing, siliconization and other types of CTO from the gas phase. The depth of the diffusion layer reaches several millimeters with uniform saturation of the entire surface of the product. The process is carried out at a reduced pressure of 10 -1 - 10 -3 Pa, which ensures the existence of a glow discharge. Advantages of using a glow discharge: high energy efficiency (consumption only for gas ionization and heating of the part); reducing the duration of the process, due to rapid heating to saturation temperature; increase in the activity of the gaseous medium and the surface layer; the possibility of obtaining coatings from refractory metals, alloys and chemical compounds. Disadvantages of the process: low pressure in the chamber (10 -1 Pa), low productivity, batch operation, impossibility of processing long products (for example, pipes), significant power consumption, high cost of installations.

Ion-diffusion saturation Advantages over conventional gas nitriding: cycle time reduction by 3-5 times; reduction of deformation of parts by 3-5 times; the possibility of carrying out controlled nitriding processes to obtain layers with a given composition and structure; the possibility of reducing the temperature of the nitriding process to 350 -400 0 С, which makes it possible to avoid softening of the core materials of the products; reducing the fragility of the layer and increasing its performance characteristics; ease of protection of individual sections of parts from nitriding; elimination of the danger of furnace explosion; reduction in unit costs electrical energy 1.5-2 times and working gas 30-50 times; improvement of working conditions for thermal workers. Disadvantages: the impossibility of accelerating the process by increasing the density of the ion flux, because as a result of overheating of the parts, the surface hardness decreases; intensification of the process of ion nitriding; applying a magnetic field to increase current density and reduce gas pressure; by creating a part surface of a given defectiveness (preliminary plastic deformation, heat treatment).

Ion carburizing unit EVT

Ionic cementation Ion cementation creates a high carbon concentration gradient in the boundary layer. The growth rate of the carburized layer of material is 0.4…0.6 mm/h, which is 3…5 times higher than for other carburizing methods. The duration of ion cementation to obtain a layer with a thickness of 1 ... 1.2 mm is reduced to 2 ... 3 hours. Due to the low consumption of gases, electricity and short processing times production costs decrease by 4 ... 5 times. The technological advantages of ion carburizing include high uniformity of carburization, the absence of external and internal oxidation, and a decrease in warping of parts. The volume of machining is reduced by 30%, the number of technological operations is reduced by 40%, the duration of the processing cycle is reduced by 50%.

Ion-plasma nitriding (IPA) IPA is a type of chemical-thermal treatment of machine parts, tools, die and casting equipment, which provides diffusion saturation of the surface layer of steel (cast iron) with nitrogen or nitrogen and carbon in nitrogen-hydrogen plasma at a temperature of 450 - 600 ° C , as well as titanium or titanium alloys at a temperature of 800 - 950 ° C in nitrogen plasma. The essence of ion-plasma nitriding is that in a nitrogen-containing gas medium discharged to 200–1000 Pa between the cathode, on which the workpieces are located, and the anode, the role of which is played by the walls of the vacuum chamber, an abnormal glow discharge is excited, forming an active medium (ions, atoms, excited molecules). This ensures the formation of a nitrided layer on the surface of the product, consisting of an outer nitride zone with a diffusion zone located under it.

Microstructure of the nitrided layer of tool steel 4 X 5 MFS a b Microstructures of steels U 8 (a) and 20 X 13 (b) after ion-plasma nitriding

Installation UA-63 -950/3400 with variable geometry of the working chamber (height 1.7 or 3.4 m)

Application of the method of ion-plasma nitriding by this method the following products are processed: nozzles for cars, automatic drive carrier plates, dies, punches, dies, molds (Daimler Chrysler); springs for the injection system (Opel); crankshafts (Audi); distribution (cam) shafts (Volkswagen); crankshafts for the compressor (Atlas, USA and Wabco, Germany); gears for BMW (Handl, Germany); bus gears (Voith); hardening of pressing tools in the production of aluminum products (Nughovens, Scandex, John Davis, etc.). Have a positive experience industrial use this method CIS countries: Belarus - MZKT, MAZ, Bel. AZ; Russia - Auto. VAZ, Kam. AZ, MMPP "Salyut", Ufimskoye engine-building association(UMPO). The IPA method processes: gears (MZKT); gears and other parts (MAZ); gears of large (more than 800 mm) diameter (Bel. AZ); intake and exhaust valves (Avto. VAZ); crankshafts (Kam. AZ).

Metallization of products according to type 1 is carried out for decorative purposes, to increase hardness and wear resistance, to protect against corrosion. Due to the weak adhesion of the coating to the substrate, this type of metallization is not advisable for parts operating under high loads and temperatures. The technology of metallization according to types 1 and 2 a provides for the application of a layer of a substance on the surface of a cold or heated to relatively low temperatures product. These types of metallization include: electrolytic (electroplating); chemical; gas-flame processes for obtaining coatings (sputtering); coating by cladding (mechano-thermal); diffusion, immersion in molten metals. Metallization technology according to type 2 b provides for diffusion saturation of the surface of parts heated to high temperatures with metal elements, as a result of which an alloy is formed in the diffusion zone of the element (Diffusion metallization). In this case, the geometry and dimensions of the metallized part practically do not change.

Ion-plasma metallization Ion-plasma metallization has a number of significant advantages over other types of metallization. The high plasma temperature and neutral environment make it possible to obtain coatings with greater structural uniformity, lower oxidizability, higher cohesive and adhesive properties, wear resistance, etc. compared to these properties of other types of metallization. Using this metallization method, various refractory materials can be sputtered: tungsten, molybdenum, titanium, etc., hard alloys, as well as oxides of aluminum, chromium, magnesium, etc. Coating can be carried out by spraying both wire and powder. The actual metallization consists of three processes: melting of the solid metal of the wire or powder (during ion-plasma metallization), spraying of the molten metal, and formation of a coating. Spray materials can be any refractory metals in the form of wire or powder, but medium-carbon to alloyed wires of the Np-40, Np-ZOHGSA, Np-ZKh 13 types, etc. can also be used. high wear resistance and corrosion resistance.