Ionic plasma nitriding. Ion-plasma nitriding as one of the modern methods of surface hardening of materials Installation ion plasma nitriding ip

Industrial developed industries today give preference to chemical-thermal treatment, in particular, ion-plasma nitriding (hereinafter IPA), which favorably differs from an economic point of view from thermal technologies... Today, IPA is actively used in machine-building, shipbuilding and machine-tool building, in the agricultural and repair industry, for the production of installations in the power industry. Among the enterprises that actively use the technology of ion-plasma nitriding are such big names as the German concern Daimler Chrysler, the automobile giant BMW, the Swedish Volvo, the Belarusian plant of wheeled tractors, KamAZ and BelAZ. In addition, the advantages of the IPA were appreciated by the manufacturers of pressing tools: Skandex, Nughovens.

Process technology

Ion-plasma nitriding, used for working tools, machine parts, equipment for stamping and casting, provides saturation of the surface layer of the product with nitrogen or nitrogen-carbon mixture (depending on the material of the workpiece). Installations for IPA operate in a rarefied atmosphere at pressures up to 1000 Pa. A nitrogen-hydrogen mixture for processing cast iron and various steels or pure nitrogen as a working gas for working with titanium and its alloys is fed into the chamber, which operates on the principle of a cathode-anode system. The workpiece is the cathode, the chamber walls are the anode. Excitation of an anomalously glowing charge initiates the formation of plasma and, as a consequence, an active medium, which includes charged ions, atoms and molecules of the working mixture, which are in an excited state. Low pressure ensures uniform and complete glowing of the workpiece. Plasma temperature ranges from 400 to 950 degrees, depending on the working gas.

For ion-plasma nitriding, 2-3 times less electricity is required, and the surface quality of the processed product allows you to completely eliminate the stage of finishing grinding

The film formed on the surface consists of two layers: a lower diffusion layer and an upper nitride layer. The quality of the modified surface layer and economic efficiency the process as a whole depends on a number of factors, including the composition of the working gas, temperature and duration of the process.

Ensuring a stable temperature rests on the heat exchange processes occurring directly inside the chamber for the IPA. To reduce the intensity of metabolic processes with the walls of the chamber, special non-conductive heat shields are used. They can significantly save on power consumption. The temperature of the process, together with the duration, affect the penetration depth of nitrides, which causes changes in the graph of the depth distribution of hardness indicators. Temperatures below 500 degrees are the most optimal for nitriding cold worked alloy steels and martensitic materials, since the performance characteristics increase without changing the hardness of the core and thermal destruction of the internal structure.
The composition of the active medium affects the final hardness and size of the nitride zone and depends on the composition of the workpiece.

Results of using ion-plasma nitriding

Ion-plasma nitriding makes it possible to increase the wear resistance indicators with a simultaneous decrease in the tendency to fatigue violations of the metal structure. Obtaining the required surface properties is determined by the ratio of the depth and composition of the diffusion and nitride layers. Nitride layer based on chemical composition, it is customary to divide into two defining phases: "gamma" with a high percentage of Fe4N compounds and "ipsilon" with Fe2N Fe3N. - the phase is characterized by low plasticity of the surface layer with high rates resistance to various types of corrosion, the ε-phase gives a relatively plastic wear-resistant coating.

As for the diffusion layer, the adjacent developed nitride zone reduces the likelihood of intergranular corrosion, providing a roughness quality sufficient for active friction. Parts with such a ratio of layers are successfully used in mechanisms that work for wear. The elimination of the nitride layer prevents fracture with a constant change in the load force under conditions of sufficiently high pressure.

That. ion-plasma nitriding is used to optimize wear, heat and corrosion resistance with a change in fatigue endurance and roughness, which affects the likelihood of scuffing the surface layer.

Advantages of Plasma Nitriding

Ion-plasma nitriding in a well-established technical process gives a minimum spread of surface properties from part to part with a relatively low energy consumption, which makes IPA more attractive than traditional furnace gas nitriding, nitrocarburizing and cyanidation.

Ion-plasma nitriding eliminates deformation of the workpiece, and the structure of the nitrided layer remains unchanged even when the part is heated to 650 degrees, which, together with the possibility of fine adjustment of the physical mechanical properties allows you to use the IPA for solving a wide variety of tasks. In addition, nitriding by the ion-plasma method is excellent for the treatment of steels of different grades, since the operating temperature of the process in a nitrogen-carbon mixture does not exceed 600 degrees, which excludes violations of the internal structure and, on the contrary, helps to reduce the likelihood of fatigue and damage due to high fragility of the nitride phase.

To increase anti-corrosion performance and surface hardness by ion-plasma nitriding, workpieces of any shape and size with through and blind holes are suitable. The screen nitriding protection is not a complex engineering solution, so the processing of individual areas of any shape is easy and simple.

Compared to other methods of hardening and increasing the intergranular resistance, IPA is distinguished by a several times shortened duration of the technical process and by two orders of magnitude reduced consumption of the working gas. That. for ion-plasma nitriding, 2-3 times less electricity is required, and the surface quality of the processed product makes it possible to completely exclude the stage of finishing grinding. In addition, it is possible to carry out a reverse nitriding process, for example before grinding.

Epilogue

Unfortunately, against the background of even the near abroad, domestic manufacturers use ion-plasma nitriding quite rarely, although the economic and physical and mechanical advantages are visible to the naked eye. The introduction of ion-plasma nitriding in production improves working conditions, increases productivity and reduces the cost of work, while the service life of the processed product increases 5 times. As a rule, the issue of building technological processes using installations for IPA rests on the problem financial plan, although there are no real subjective obstacles. Ion-plasma nitriding with a fairly simple equipment design performs several operations at once, the implementation of which by other methods is possible only in stages, when the cost and duration will rise sharply. In addition, there are several companies in Russia and Belarus that cooperate with foreign manufacturers of equipment for IPA, which makes the purchase of such installations more affordable and cheaper. Apparently, the main problem lies only in the banal decision-making, which, like the Russian tradition, will take a long time and difficult for us.

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Technological capabilities ion nitriding in the hardening of 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 required 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. The temperature range of ionic nitriding is wider than that of gas nitriding and is in the range of 400-600 ° C. Treatment at temperatures below 500 ° C is especially effective in hardening products made of tool alloy steels for cold working, high-speed and maraging steels, because their performance 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 processing by the IPA method (Fig. 1).

Rice. one. The use of ion-plasma nitriding for hardening various products

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 widely used methods of hardening chemical-thermal treatment of steel parts, such as carburizing, nitrocarburizing, cyanidation and gas nitriding in furnaces, the IPA method has the following main advantages:

environment

The advantages of IPA are also manifested in a significant reduction in basic production costs. So, for example, in comparison with gas nitriding in furnaces, IPA provides:

modern requirements

Compared to quenching IPA processing allows:

eliminate deformations; 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 HFC quenching allows you to save basic equipment and production areas, reduce machine and transport costs, and 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 medium between the cathode - parts - and the anode - the walls of the vacuum chamber - an anomalous glow discharge is excited, which forms an active medium (ions, atoms, excited molecules), providing the formation of a nitrided layer, consisting of an outer - nitride zone and a diffusion zone located under it. Technological factors affecting the efficiency of ion nitriding are process temperature, saturation time, pressure, composition and flow rate of the working gas mixture. Process temperature, the area of the cage 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 required temperature of the products. The choice of temperature depends on the degree of alloying of 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. Duration and temperature of the process saturations determine the depth of the layer, the distribution of hardness in depth and the thickness of the nitride zone. The composition of the saturating medium depends on the degree of alloying of the processed steel and the requirements for the hardness and depth of the nitrided layer. Process pressure should be such that a tight "fit" of the surface of the products by the discharge and obtaining a uniform nitrided layer is ensured. However, it should be borne in mind that the discharge at all stages of the process must be abnormal, 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 compositionally controlled mixtures of hydrogen, nitrogen and argon as a working medium, as well as “pulsed” rather than direct current plasma, the manufacturability of the ion nitriding process has significantly increased. 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, make it possible to avoid overheating of thin cutting edges during the heating of the charge when processing the cutting tool, to precisely regulate the saturation time a , respectively, and the depth of the layer, since heating of products can be done in a nitrogen-free environment, for example, in a mixture of Ar + H 2. Effective thermal insulation in the working chamber (triple heat shield) allows the processing of products with low specific energy consumption, thus minimizing temperature differences within the cage 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 cage (Fig. 2).

Rice. 2. Distribution of microhardness along the depth of the nitrided layer for three samples located in different places of the cage.

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

b, d - gear wheel weighing 45 kg, 11 pcs., st - 38XH3MFA, module 3.25 (outer rim)

and 7 mm (inner crown), exposure 16 hours, Т = 555 0 С.

Ionic nitriding is an effective method of hardening processing of parts made of alloyed structural steels: gears, gear rims, gear shafts, shafts, spur, bevel and cylindrical gears, couplings, gear shafts of complex geometric configuration, etc. shafts, etc.) of low and medium accuracy, which do not require subsequent grinding. These types of heat treatment are economically inexpedient 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 allows to significantly reduce warpage and deformation of parts while maintaining surface roughness in the range of Ra = 0.63 ... 1.2 microns, which allows in the overwhelming majority of cases to use IPA as a finishing treatment. With regard to machine tool construction, ion nitriding of gear wheels significantly reduces the noise characteristics of machine tools, thereby increasing their competitiveness in the market. IPA is most effective when processing large-scale similar parts: gears, shafts, axles, gear shafts, gear shafts, etc. Gears subjected to plasma nitriding have better dimensional stability compared to case-hardened gears and can be used without additional processing. In this case, the bearing capacity of the lateral surface and the strength of the tooth base, achieved by plasma nitriding, correspond to cemented gears (Table 1).

Table 1

Fatigue resistance characteristics of steels depending on the methods of hardening of gear wheels

Steel type	Treatment type	Flexural fatigue limit, MPa	Surface contact endurance limit, MPa	Side surface hardness of teeth, HV
Alloyed	Hardening
Improvable (40X, 40XH, 40XFA, 40XH2MA, 40XMFA, 38XM, 38XN3MFA, 38X2N2MFA, 30X2NM, etc.)	Nitriding
Normalized	Plasma or induction hardening
Special nitrided (38HMYUA, 38H2MYUA, 35HYUA, 38HVFYUA, 30H3MF, etc.)	Nitriding
Alloyed	Cementation and nitrocarburizing

When hardening treatment by ion nitriding of parts made of case-hardened, low- and medium-alloyed steels (18KhGT, 20KhNZA, 20KhGNM, 25KhGT, 40Kh, 40KhN, 40KhFA, etc.), it is necessary at the beginning to improve the forgings - volume quenching and tempering to a hardness of 241-285 HB (for some steels - 269-302 HB), then mechanical treatment and finally ion nitriding. To ensure minimal deformation of products before nitriding for stress relief, 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 done prior to precision machining. The depth of the nitrided layer formed on the specified products made of steels 40X, 18XGT, 25XGT, 20X2H4A, etc. is 0.3-0.5 mm at a hardness of 500-800 HV, depending on the steel grade (Fig. 3). For gears operating under heavier loads, the nitrided layer should be 0.6-0.8 mm with a thin nitride zone or no zone at all.

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

Optimization of the properties of the hardened layer is determined by the combination of 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 - 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 of the components of the gas mixture, pressure in the working chamber and variation in the process temperature allow the formation of layers of different depths and hardness (Fig. 4), thereby ensuring a stable processing quality with a minimum spread of 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 40X

1, 3, 5 - one-stage process;

2.4 - two-stage process in terms of 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 С, t = 16 hours

Rice. 5. The spread of microhardness along the depth of the nitrided layer

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

Ionic nitriding is widely known as one of the effective methods increasing the wear resistance of the cutting tool made of high speed steels grades P6M5, P18, P6M5K5, 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 antifriction properties, provides easier chip evacuation, and also prevents chip sticking and formation of wear holes, which makes it possible to increase feed and cutting speed. Optimal structure nitrided high speed steel is a highly nitrogenous martensite that does not contain excess nitrides. The specified structure is provided by saturation of the tool surface with nitrogen at a temperature of 480-520 0 С during short-term nitriding (up to 1 hour). In this case, a hardened 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 by 2-8 times, depending on its type and type of processed material.

Rice. 6. The structure of the nitrided layer of steel R6M5 (a) and the distribution of microhardness over the depth of the layer (b).

The main advantage of ion nitriding of the tool is the possibility of obtaining only a diffusion hardened layer, or a layer with monophase nitride Fe 4 N ('-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. Ionic nitriding is also one of the main methods of increasing durability stamping tools and molding equipment from steels 5ХНМ, 4Х5МФС, 3Х2В8, 4Х5В2ФС, 4Х4ВМФС, 38Х2МЮА, Х12, Х12М, Х12Ф1. As a result of ionic nitriding, the following product characteristics can be improved:

Forging dies for hot stamping and molds for casting metals and alloys - increased wear resistance, reduced metal adhesion. Injection Molds for Aluminum - 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 results in a higher quality casting. Significantly improves ion nitriding and tool performance for cold (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			Recommended compound layer type
steel grade	Hardness of heartseguilt,	Process temperature 0 WITH	Depth mm	tv-st, HV 1	Connecting layer thickness,	Recommended compound layer type
Hot work steels




Steel for cold working

A.V. ARZAMASOV
MSTU them. N. E. Bauman
ISSN 0026-0819. "Metallurgy and heat treatment of metals", No. 1. 1991

Development of new production processes ion nitriding in order to increase the wear resistance of the surface of parts made of austenitic steels is an urgent task

Austenitic steels are difficult to nitrogen, since their surface oxide films prevent nitrogen saturation and the nitrogen diffusion coefficient in austenite is lower than in ferrite. In this regard, in order to remove oxide films during conventional nitriding, pretreatment of the steel surface or the use of depassivators is necessary.

The usual nitriding of most austenitic steels is carried out in ammonia at 560-600 ° C for 48-60 hours. However, these modes do not allow obtaining diffusion layers with a thickness of more than 0.12-0.15 mm, and on steel 45Kh14N14V2M (EI69) it is impossible to obtain a thickness the diffusion layer is more than 0.12 mm even with nitriding for 100 hours. An increase in the nitriding temperature in the furnace above 700 ° C leads to a more complete dissociation of ammonia and, as a result, to a decrease in the activity of the process.

Typically, after conventional nitriding, the corrosion resistance of the surface layers of austenitic steels deteriorates.

Ionic nitriding of austenitic steels increases the diffusion coefficient of nitrogen and does not require the use of depassivating agents. This reduces the duration of the process and improves the quality of the resulting nitrided layers.

However, ion nitriding of austenitic steels according to the previously developed modes did not allow obtaining thick diffusion layers even with long holding times.

Based on thermodynamic calculations and experimental research a mode of ion nitriding of parts made of austenitic steels was developed, which makes it possible to obtain high-quality deep wear-resistant non-magnetic corrosion-resistant diffusion layers in a relatively short time. Oxide films were removed from the surface of the parts during the process of chemical-thermal treatment.

Investigated standard austenitic steels 45Kh14N14V2M (EI69), 12Kh18N10T (EYA1T); 25Х18Н8В2 (ЭИ946) and experimental high-nitrogenous ones, developed by the Institute of Metallurgy and Metal Technology of the Bulgarian Academy of Sciences - types Х14АГ20Н8Ф2М (0.46% N), Х18АГ11Н7Ф (0.70% N), Х18АГ12Ф (0.88% N), Х18АГ20Н7Ф (1, 09% N), Kh18AG20F (1.02% N), Kh18AG20F (2.00% N).

The structure of diffusion layers on steels was studied using metallographic, X-ray diffraction, and X-ray microanalysis. It was found that the structural criterion of high wear resistance of nitrided austenitic steels is the presence of CrN-type nitrides in the diffusion layer. Analysis of the concentration curves of chemical elements obtained using microanalyzers ISM-35 CF, Cameca MS-46, Camebax 23-APR-85 showed that, compared to other heavy elements, chromium is most abruptly distributed over the layer thickness. The distribution of chromium in the core of the samples is uniform.

Repeated repetition of experiments to study the distribution of nitrogen and chromium over the thickness of the diffusion layer revealed synchronous jump-like changes in their concentrations. In addition, as shown by layer-by-layer wear tests, the microzone of the diffusion layer with the maximum content of nitrogen and chromium has the highest wear resistance (Table 1).

Table 1.

h, micron	Content of chemical elements,%				ε
h, micron	C	N	Cr	Ni	ε
20	0,70	10,0	19,0	11,0	9,5
40	0,85	12,0	25,0	8,0	10,7
45	0,88	15,0	25,0	8,0	11,2
50	0,92	10,0	25,0	8,0	11,0
70	0,90	0	14,0	12,0	1,7
* - the rest is Fe Notes: 1. Wear tests were carried out on a Skoda-Savin machine. 2. The relative wear resistance was determined by the ratio of the volumes of the wiped holes on the standard (steel sample with a hardness of 51 HRC) and the test sample ε = V et / V sample (relative wear resistance of the core ε = 0.08).

Further investigation of the structure of nitrided austenitic steels using X-ray microanalysis made it possible to establish that in microzones of diffusion layers with an increased content of nitrogen and chromium, a reduced concentration of carbon, nickel and iron is observed (Table 1).

Comparative analysis of the microstructure of the layer and core of nitrided steel 45Kh14N14V2M, taken in characteristic chromium K α-radiation, showed that the diffusion layer contains more clusters of "white dots" - chromium compounds than in the core.

Layer-by-layer measurements of the magnetic permeability using an F 1.067 magnetoscope and determination of the ferrite phase content on an MF-10I ferritometer showed that the developed method of ion nitriding of parts made of austenitic steels promotes the production of non-magnetic diffusion layers (Table 2).

Table 2.

It was also found that nitrided steels 45Kh14N14V2M and type Kh14AG20N8F2M have satisfactory corrosion resistance.

In a new way technological process a batch of gears made of steel 45Х14Н14В2М was processed. The parts were in accordance with the technical requirements. Micro- and macrostructural analysis confirmed the presence of a high-quality uniform diffusion layer with a thickness of 270 microns in the gears.

After lengthy industrial tests, no visible defects were found on the gears. Further control showed that the geometrical dimensions of the gears corresponded to the technological requirements, as well as the absence of wear on the working surfaces of the parts, which was confirmed by microstructural analysis.

Conclusion. The developed mode of ion nitriding of parts made of austenitic steels makes it possible to reduce the duration of the process by more than 5 times, while the layer thickness increases by 3 times, and the wear resistance of the layer is 2 times compared with similar parameters after conventional nitriding. In addition, labor intensity is reduced, the culture of production is increased and the ecological situation is improved.

Bibliography:
1. Progressive methods of chemical thermal treatment / Ed. G.N.Dubinin, Ya.D. Kogan. M .: Mashinostroenie, 1979.184 p.
2. Nitriding and carbonitriding / R. Chatterjee-Fisher, F.V. Eisell, R. Hoffman et al.: Per. with him. Moscow: Metallurgy, 1990.280 p.
3. A. s. 1272740 USSR, MKI S23S8 / 36.
4. Bannykh OA, Blinov VM Dispersion-hardening non-magnetic vanadium-containing steels. Moscow: Nauka, 1980.192 p.
5. Rashev Ts.V. Production of alloy steel. Moscow: Metallurgy, 1981.248 p.

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

, , students;

, Art. teacher

Improving the quality of metal and its mechanical properties is the main way to increase the durability of parts and one of the main sources of savings in steels and alloys. Improving the quality and durability of products is carried out through a rational choice of materials and methods of hardening while achieving high technical and economic efficiency. There are many different methods surface hardening- hardening by high-frequency currents, plastic deformation, chemical heat treatment (CHT), laser and ion-plasma treatment.

Traditionally used in industry, the process of gas nitriding, as one of the types of CTO, is the process of diffusion saturation of the surface layer of steel with nitrogen. Nitriding with great effect can be used 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 indisputable advantages, such as: the relative simplicity of the process, the possibility of using universal equipment and devices for stacking parts, the possibility of nitriding parts of any size and shape. At the same time, gas nitriding also has a number of disadvantages: a long process duration (20-30 hours) even with nitriding for 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; the application of various electroplating coatings (copper plating, tinning, nickel plating, etc.) requires the organization of a special production.

One of the directions of intensification of production 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, providing diffusion saturation of the surface layer of steel and cast iron with nitrogen (nitrogen and carbon) in nitrogen-hydrogen plasma at a temperature
400-600 ° C, titanium and titanium alloys at a temperature of 800-950 ° C in nitrogen-containing plasma. This process is now widespread in all economically developed countries: USA, Germany, Switzerland, Japan, England, France.

In many cases, ionic nitriding is more expedient than gas nitriding. Among the advantages of IPA in a glow discharge plasma are the following: the ability to control the saturation process, which provides a high quality coating, a given phase composition and structure; ensuring absolutely the same activity of the gaseous medium on the entire surface of the part covered by the glow discharge, this ultimately ensures the obtaining of a nitrided layer uniform in thickness; reducing the labor intensity of local protection of surfaces that are not subject to nitriding, which is performed by metal screens; a sharp reduction in the duration of nitriding of parts (2-2.5 times); reduction of deformation of parts. The use of IPA instead of carburizing, nitrocarburizing, gas or liquid nitriding, volumetric or HFC quenching allows you to save basic equipment and production areas, reduce machine and transport costs, and reduce the consumption of electricity and active gas 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 initiated. Nitriding is carried out with an abnormal glow discharge, at a high voltage of the order of W. Modern installations ensure the stability of the glow discharge at the border of its transition to normal and arc. The principle of operation of arc suppression devices is based on a short-term shutdown of the installation when a volt arc ignites.

Nitriding increases the corrosion resistance of parts made of carbon and low-alloy steels. Parts nitrided to increase surface strength and wear resistance, at the same time acquire properties against corrosion in steam, in tap water, in alkali solutions, in crude oil, gasoline, and a polluted atmosphere. Ionic nitriding significantly increases the hardness of parts, which is due to highly dispersed precipitates of nitrides, the amount and dispersion of which affects the achieved hardness. The fatigue limit is increased by nitriding. This is explained, firstly, by an increase in the strength of the surface, and secondly, by the appearance of residual compressive stresses in it.

The advantages of ionic nitriding are most fully realized in large-scale and mass production, in the strengthening of large batches of the same type of 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 ionic nitriding has technical, economic and social benefits.

20.01.2008

Ionic plasma nitriding (IPA) - This is a type of chemical-thermal treatment of machine parts, tools, stamping and casting equipment, providing 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 temperature 800-950 ° C in nitrogen plasma.

The essence of ion-plasma nitriding is that in a nitrogen-containing gas medium discharged to 200-000 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.

By varying the composition of the saturating gas, pressure, temperature, holding time, layers of a given structure with the required phase composition can be obtained, providing strictly regulated properties of steels, cast irons, titanium or its alloys. Optimization of the properties of the surface to be hardened is ensured by the necessary combination of nitride and diffusion layers, which grow into the base material. Depending on the chemical composition, the nitride layer is either the y-phase (Fe4N) or the e-phase (Fe2-3N). The e-nitride layer is corrosion-resistant and the y-layer is wear-resistant but relatively ductile.

At the same time, using ion-plasma nitriding, it is possible to obtain:

diffusion layer with a developed nitride zone, which provides high resistance to corrosion and wear-in of rubbing surfaces - for parts that are subject to wear

diffusion layer without nitride zone - for cutting, stamping tools or parts operating at high pressures with alternating loads.

Ion plasma nitriding can improve the following product characteristics:

wear resistance

fatigue endurance

anti-seize properties

heat resistance

corrosion resistance

The main advantage of the method is consistent processing quality with minimal variation in properties from detail to detail, from cage to cage. In comparison with widely used methods of hardening chemical-thermal treatment of steel parts, such as carburizing, nitrocarburizing, cyanidizing, gas nitriding, the method of ion-plasma nitriding has the following main advantages:

higher surface hardness of nitrided parts

no deformation of parts after processing

increasing the endurance limit with increasing wear resistance of machined parts

lower process temperature, due to which there are no structural changes in the workpieces

the ability to process blind and through holes

preservation of the hardness of the nitrided layer after heating to 600 - 650 ° С

the ability to obtain layers of a given composition

the ability to process products of unlimited sizes of any shape

no environmental pollution

improving production culture

reducing the cost of processing several times

The advantages of ion-plasma nitriding are manifested in a significant reduction in basic production costs. For example, in comparison with gas nitriding, IPA provides:

reduction of the processing time from 2 to 5 times, both by reducing the heating-cooling time of the charge, and by reducing the isothermal holding time

reduction of the consumption of working gases (20 - 100 times)

reduction of energy consumption (1.5 - 3 times)

reduction of deformation enough to exclude finishing sanding

improvement of sanitary and hygienic conditions of production

full compliance of the technology with all modern requirements for environmental protection

In comparison with hardening, treatment by the method of ion-plasma nitriding allows:

eliminate deformations

increase the service life of the nitrided surface (2-5 times)

The use of ion-plasma nitriding instead of carburizing, nitrocarburizing, gas or liquid nitriding, volumetric or HFC quenching allows:

save basic equipment and production space

reduce machine costs, transport costs

to reduce the consumption of electricity, active gas media.

The main consumers of equipment for ion-plasma nitriding are automobile, tractor, aviation, shipbuilding, ship repair, machine-tool / machine-tool plants, factories for the production of agricultural machinery, pumping and compressor equipment, gears, bearings, aluminum profiles, power plants ...

The method of ion-plasma nitriding is one of the most dynamically developing areas of chemical thermal treatment in industrially developed countries. The IPA method has found wide application in the automotive industry. It is successfully used by the world's leading auto / engine manufacturers: Daimler Chrysler (Mercedes), Audi, Volkswagen, Voith, Volvo.
For example, the following products are processed by this method:

nozzles for passenger cars, automatic drive carrier plates, dies, punches, dies, molds (Daimler Chrysler)

springs for injection system (Opel)

crankshafts (Audi)

camshafts (Volkswagen)

crankshafts for 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.)

There is a positive experience in industrial use this method CIS countries: Belarus - MZKT, MAZ, BelAZ; Russia - AvtoVAZ, KamAZ, MMPP Salyut, Ufa Engine-Building Association (UMPO).
The IPA method is used to process:

gears (MZKT)

gears and other parts (MAZ)

gears of large (more than 800 mm) diameter (BelAZ)

intake and exhaust valves (AvtoVAZ)

crankshafts (KamAZ)

As the world experience in the application of ion-plasma nitriding technology shows, economic effect from its implementation is provided mainly by reducing the consumption of electricity, working gases, reducing the labor intensity of manufacturing products due to a significant reduction in the volume of grinding work, improving product quality.

With regard to cutting and punching tools, the economic effect is ensured by reducing its consumption due to an increase of 4 or more times in its wear resistance with a simultaneous increase in cutting conditions.

For some products, ion-plasma nitriding is the only way to obtain finished product with a minimum percentage of defects.

In addition, the IPA process ensures complete environmental safety.

Ion-plasma nitriding can be used in production instead of liquid or gas nitriding, carburizing, nitrocarburizing, high-frequency current hardening.

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