A.V. ARZAMASOV
MSTU im. N. E. Bauman
ISSN 0026-0819. "Metal science 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 actual problem

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

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 it is impossible to obtain a thickness the diffusion layer is more than 0.12 mm even during 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.

As a rule, after conventional nitriding, the corrosion resistance of the surface layers of austenitic steels deteriorates.

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

However, ion nitriding of austenitic steels according to previously developed regimes did not allow obtaining diffusion layers of large thickness even with long exposures.

Based on thermodynamic calculations and experimental studies, 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 a short time. Oxide films were removed from the surface of the parts during chemical-thermal treatment.

The standard austenitic steels 45Kh14N14V2M (EI69), 12Kh18N10T (EYa1T) were studied; 25Kh18N8V2 (EI946) and experimental high-nitrogen, developed by the Institute of Metal Science and Technology of Metals of the Bulgarian Academy of Sciences - type Kh14AG20N8F2M (0.46% N), Kh18AG11N7F (0.70% N), Kh18AG12F (0.88% N), Kh18AG20N7F (1, 09% N), X18AG20F (1.02% N), X18AG20F (2.00% N) .

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

Repeated repetition of experiments to study the distribution of nitrogen and chromium over the thickness of the diffusion layer revealed synchronous abrupt changes in their concentrations. In addition, as layered wear tests showed, 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
	C	N	Cr	Ni
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
* - rest Fe Notes: 1. Wear tests were carried out on a Skoda-Savin machine. 2. Relative wear resistance was determined by the ratio of the volumes of worn holes on the standard (steel sample with a hardness of 51 HRC) and the test sample ε = V ref / V arr (relative wear resistance of the core ε = 0.08).

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

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

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

Table 2.

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

In a new way technological process a batch of gears made of steel 45Kh14N14V2M was processed. Details matched technical requirements. Micro- and macrostructural analysis confirmed that the gears have a high-quality uniform diffusion layer 270 µm thick.

After long industrial testing There were no visible defects on the gears. Further control showed the conformity of the geometric dimensions of the gears technological requirements, as well as the absence of wear of 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 - by 2 times compared with similar parameters after conventional nitriding. In addition, labor intensity is reduced, the culture of production is increased and the environmental situation is improved.

Bibliography:
1. Progressive methods of chemical-thermal treatment / Ed. G. N. Dubinina, Ya. D. Kogan. M.: Mashinostroenie, 1979. 184 p.
2. Nitriding and carbonitriding / R. Chatterjee-Fischer, F. V. Eisell, R. Hoffman et al.: Per. with him. M.: Metallurgy, 1990. 280 p.
3. A. s. 1272740 USSR, MKI С23С8/36.
4. Bannykh OA, Blinov VM Dispersion-hardening non-magnetic vanadium-containing steels. M.: Nauka, 1980. 192 p.
5. Rashev TsV Production of alloyed steel. M.: Metallurgiya, 1981. 248 p.

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 the supply of 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 discharge in a hollow cathode); 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 the surface of the part 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 amount of machining is reduced by 30%, the number technological operations is reduced by 40%, cycle time is reduced by 50%.

Ion- plasma nitriding(IPA) IPA 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 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", Ufimskoe 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.

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Ionic nitriding.

Sometimes this process is called ionitration or nitriding in a glow discharge plasma. The essence of this method lies in the fact that a rarefied nitrogen-containing atmosphere is created in a sealed container. For this purpose, pure nitrogen, ammonia or a mixture of nitrogen and hydrogen can be used. Inside the container, nitrided parts are placed, which are connected to the negative pole of a constant voltage source. They play the role of a cathode. The wall of the container serves as the anode. A high voltage (500-1000 V) is switched on between the cathode and anode. Under these conditions, gas ionization occurs. The resulting positively charged nitrogen ions rush to the negative pole - the cathode. The electrical resistance of the gas medium near the cathode increases sharply, as a result of which almost all the voltage supplied between the anode and cathode falls on the resistance near the cathode, at a distance of several millimeters from it. This creates a very high tension. electric field near the cathode.

Nitrogen ions, entering this zone of high tension, are accelerated to high speeds and, colliding with the part (cathode), are introduced into its surface. In this case, the high kinetic energy that nitrogen ions had is converted into thermal energy. As a result, the part in a short time, approximately 15–30 min, is heated to a temperature of 470–580°C, at which nitrogen diffuses into the depth of the metal, i.e., the nitriding process takes place. In addition, when ions collide with the surface of the part, iron ions are knocked out from its surface. Due to this, the surface is cleaned of oxide films that prevent nitriding. This is especially important for the nitriding of corrosion-resistant steels, in which such a passivating film is very difficult to remove by conventional methods.

Ion nitriding has the following advantages over furnace nitriding:

1) reduction of the total duration of the process by 1.5-2 times;

2) the ability to control the process in order to obtain a nitrided layer with desired properties;

3) less deformation of parts due to uniform heating; 4) the possibility of nitriding corrosion-resistant steels and alloys without additional depassivating treatment.

Ion-plasma nitriding (IPA) is a method of chemical-thermal treatment of products made of steel and cast iron with large 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

The temperature range of ion nitriding is wider than that of gas nitriding and is within 400-600 0 С. 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 purity surfaces;
• 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 transportation costs, and reducing 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 a new generation of IPA plants, 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, makes 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 products can be heated 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.

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

IPA is most effective when processing large-scale similar parts: gears, shafts, axles, toothed 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 minimum 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 performance characteristics tool 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.

Ion-plasma nitriding (IPA) is a modern hardening method of chemical-thermal treatment of products made of cast iron, carbon, alloyed and tool steels, titanium alloys, cermets, powder materials. The high efficiency of the technology is achieved by using different gaseous media that affect the formation of a diffusion layer of different composition, depending on the specific requirements for its depth and surface hardness.

Nitriding by the ion-plasma method is relevant for processing loaded parts operating in aggressive environments that are subject to friction and chemical corrosion, therefore it is widely used in the engineering industry, including machine tool building, auto and aviation industries, as well as in the oil and gas, fuel and energy and mining sectors, tool and high-precision production.

In the process of surface treatment by ion nitriding, the surface characteristics of metals and the operational reliability of critical parts of machines, engines, machine tools, hydraulics, precision mechanics and other products are improved: fatigue and contact strength, surface hardness and resistance to cracking increase, wear and tear resistance, heat and corrosion resistance.

Advantages of ion-plasma nitriding

The IPA technology has a number of undeniable advantages, the main of which is the stable quality of processing with a minimum spread of properties. The controlled process of diffusion saturation of the gas and heating provides a uniform coating of high quality, a given phase composition and structure.

• High surface hardness of nitrided parts.
• No deformation of parts after processing and high surface finish.
• Reducing the processing time of steels by 3-5 times, titanium alloys by 5-10 times.
• Increasing the exploitation of the nitrided surface by 2-5 times.
• Possibility of processing blind and through holes.

The low-temperature regime excludes structural transformations of steel, reduces the likelihood of fatigue failures and damages, and allows cooling at any rate without the risk of martensite. Treatment at temperatures below 500 °C is especially effective in hardening products made of tool alloyed, high-speed and maraging steels: their service properties increase without changing the core hardness (55-60 HRC).

The environmentally friendly method of ion-plasma nitriding prevents distortion and deformation of parts while maintaining the initial surface roughness within Ra = 0.63 ... 1.2 microns - that is why the IPA technology is effective as a finishing treatment.

Process technology

Installations for IPA operate in a rarefied atmosphere at a pressure of 0.5-10 mbar. An ionized gas mixture is fed into the chamber, which operates on the principle of a cathode-anode system. A glow pulsed discharge is formed between the workpiece being processed and the walls of the vacuum chamber. The active medium created under its influence, consisting of charged ions, atoms and molecules, forms a nitrided layer on the surface of the product.

The composition of the saturating medium, the temperature and duration of the process affect the depth of penetration of nitrides, causing a significant increase in the hardness of the surface layer of products.

Ionic nitriding of parts

Ion nitriding is widely used to harden machine parts, working tools and industrial equipment of unlimited sizes and shapes: gear rims, crankshafts and camshafts, bevel and cylindrical gears, extruders, couplings of complex geometric configuration, screws, cutting and drilling tool, mandrels, dies and punches for stamping, molds.

For a number of products (large diameter gears for heavy vehicles, excavators, etc.), IPA is the only way to obtain finished products With minimum percentage marriage.

Properties of products after hardening by IPA

hardening gear wheels ion nitriding increases the endurance limit of teeth during bending fatigue tests up to 930 MPa, significantly reduces the noise characteristics of machine tools and increases their competitiveness in the market.

Ion-plasma nitriding technology is widely used to harden the surface layer of molds used in injection molding: the nitrided layer prevents metal from sticking in the liquid jet supply zone, and the mold filling process becomes less turbulent, which increases the life of the molds, and ensures high quality casting.

Ion-plasma nitriding increases the wear resistance of stamping and cutting tools made of steel grades R6M5, R18, R6M5K5, R12F4K5 and others by a factor of 4 or more, with a simultaneous increase in cutting conditions. The nitrided surface of the tool, due to the reduced coefficient of friction, provides easier chip removal, and also prevents it from sticking to the cutting edges, which allows to increase the feed and cutting speed.

The company "Ionmet" provides services for surface hardening of structural materials various types parts and tools by ion-plasma nitriding - a correctly selected mode will allow you to achieve the required technical indicators hardness and depth of the nitrided layer, will provide high consumer properties of products.

• Hardening of the surface layer of fine and large-module gears, crankshafts and camshafts, guides, bushings, sleeves, screws, cylinders, molds, axles, etc.
• Increasing the resistance to cyclic and pulsating load of crankshafts and camshafts, tappets, valves, gears, etc.
• Improvement of wear resistance and corrosion resistance, reduction of metal sticking when casting molds, press and hammer dies, deep drawing punches, dies.

The nitriding process takes place in modern automated installations:

• table Ø 500 mm, height 480 mm;
• Table Ø 1000 mm, height 1400 mm.

To clarify the full range of products for hardening treatment, as well as the possibility of nitriding large-sized parts with complex geometry, please contact Ionmet specialists. For determining specifications nitriding and the beginning of cooperation, send us a drawing, specify the steel grade and approximate technology for manufacturing parts.