Ion-plasma nitriding as one of the modern methods of surface hardening of materials. Ion-plasma hardening vacuum ion-plasma methods for hardening the surfaces of parts Ion-vacuum nitriding
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 ionic 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 of gear wheels by 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 Ionmet company provides services for the surface hardening of structural materials of various types of 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.
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Technological possibilities of ion nitriding in strengthening products from structural and tool steels
M. N. Bosyakov, S. V. Bondarenko, D. V. Zhuk, P. A. Matusevich
JV "Avicenna International", Republic of Belarus, Minsk,
st. Surganova, 2a, 220012, tel. +375 17 2355002
Ion-plasma nitriding (IPA) is a method of chemical-thermal treatment of steel and cast iron products with great technological capabilities, which makes it possible to obtain diffusion layers of the desired composition by using different 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 ion nitriding is wider than gas nitriding 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. Application of ion-plasma nitriding for hardening of 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 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; increasing the endurance limit and increasing the wear resistance of machined parts; lower processing temperature, due to which no structural transformations occur in the steel; the possibility of processing deaf and through holes; preservation of the hardness of the nitrided layer after heating to 600-650 С; 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.
- reduction of processing time by 2–5 times, both by reducing the heating and cooling time of the charge, and by reducing the isothermal holding time; reducing the fragility of the hardened layer; reduction in the consumption of working gases by 20–100 times; reduction of electricity 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 non-hardened surfaces; improvement of sanitary and hygienic conditions of production; full compliance of the technology with all modern requirements for environmental protection.
- exclude deformations; increase the service life of the nitrided surface by 2-5 times.
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Rice. 2. Distribution of microhardness over the depth of the nitrided layer for three samples located in different places of the cage.
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 ring)
and 7 mm (internal crown), exposure 16 hours, Т=555 0 С.
Ion nitriding is an effective method of hardening treatment of parts made of alloyed structural steels : gears, ring gears, gear shafts, shafts, spur, bevel and cylindrical gears, couplings, gear shafts of complex geometric configurations, etc. shafts, etc.) of low and medium accuracy, which 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 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
| Steel type | Type of processing | Bending endurance limit, MPa | Surface contact endurance limit, MPa | Tooth flank hardness, HV |
| alloyed | hardening | |||
| Improved (40X, 40XH, 40XFA, 40XH2MA, 40XMFA, 38XM, 38XH3MFA, 38X2H2MFA, 30X2NM, etc.) | Nitriding | |||
| Normalized | Plasma or induction hardening | |||
| Special nitrided (38HMYUA, 38H2MYUA, 35HYUA, 38HVFYUA, 30H3MF, etc.) | Nitriding | |||
| alloyed | Carburizing and Nitrocarburizing |
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Rice. 3. Distribution of microhardness over the depth of the nitrided layer for different steels
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 - g'- or e-layer; dynamic load - limited thickness of the nitride layer or no nitride layer at all; corrosion - e-layer.
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Rice. 4. Distribution of microhardness over the depth of the nitrided layer of steel 40Kh
1, 3, 5 - one-stage process;
2.4 - two-stage process by 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\u003d 15 hours, 5 - T \u003d 460 0 C, t = 16 hours
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Rice. 5. Spread of microhardness over the depth of the nitrided layer
for steel 40Kh (a) and 38KhNZMFA (b) for serial processes.
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 increases tool wear resistance and its 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.
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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 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 area and the mold filling process is less turbulent, which increases the life of the molds, and the casting is of higher quality.
Table 2.
Characteristics of alloyed steels after ion-plasma nitriding.
| steel grade | Heart hardnesseguilt | Process temperature 0 WITH | Layer characteristics | Type of recommended connection layer |
||
| Depth, mm | tv-st, HV 1 | Compound layer thickness, |
||||
| Steels for hot working |
||||||
| Steels for cold working |
||||||
And industrially developed productions 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, ship and machine tool building, agricultural and repair industries, for the production of energy industry installations. 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 advantage of IPA was 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, ensures the saturation of the surface layer of the product with nitrogen or a nitrogen-carbon mixture (depending on the material of the workpiece). IPA plants operate in a rarefied atmosphere at pressures up to 1000 Pa. The chamber, which operates on the principle of a cathode-anode system, is supplied with 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. The workpiece serves as the cathode, and the chamber walls serve as the anode. The excitation of an abnormally glowing charge initiates the formation of a plasma and, as a result, an active medium, which includes charged ions, atoms and molecules of the working mixture that are in an excited state. Low pressure provides a uniform and complete coating of the workpiece with a glow. The 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 quality of the surface of the treated product makes it possible to completely eliminate the stage of finishing grinding
The film formed on the surface consists of two layers: the lower diffusion layer and the 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, the temperature and the duration of the process.
Ensuring a stable temperature rests on the heat exchange processes occurring directly inside the IPA chamber. To reduce the intensity metabolic processes special non-conductive heat shields are used with the chamber walls. They allow significant savings in power consumption. The temperature of the process, coupled with the duration, affects the depth of penetration 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 performance is increased 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 the application of ion-plasma nitriding
Ion-plasma nitriding makes it possible to increase wear resistance indicators with a simultaneous decrease in the tendency to fatigue damage to 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, is usually divided into two defining phases: "gamma" with a high percentage of Fe4N compounds and "upsilon" with Fe2N Fe3N. -phase is characterized by low plasticity of the surface layer with high resistance values different types corrosion, the ε-phase gives a relatively ductile wear-resistant coating.
As for the diffusion layer, the adjacent developed nitride zone reduces the likelihood of intergranular corrosion, providing a roughness grade sufficient for active friction. Parts with such a ratio of layers are successfully used in wear mechanisms. The exclusion of the nitride layer makes it possible to prevent destruction 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 of the surface layer.
Advantages of ion plasma nitriding
Ion-plasma nitriding in a well-adjusted technical process provides a minimum spread of surface properties from part to part at a relatively low energy intensity, which makes IPA more attractive than traditional furnace gas nitriding, carbonitriding and cyanidation.
Ion-plasma nitriding eliminates workpiece deformation, and the structure of the nitrided layer remains unchanged even when the part is heated to 650 degrees, which, coupled with the possibility of fine adjustment of physical and mechanical properties, makes it possible to use IPA for solving a wide variety of problems. In addition, ion-plasma nitriding is excellent for processing steels of various grades, since working temperature process in the 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 damage and damage due to the high brittleness of the nitride phase.
To improve anti-corrosion performance and surface hardness by ion-plasma nitriding, workpieces of any shape and size with through and blind holes are suitable. Screen protection against nitriding is not a complex engineering solution, so the processing of individual sections of any shape is easy and simple.
Compared to other methods of hardening and increasing the intergranular resistance, IPA is characterized by a several times shorter duration of the process and a two-fold reduction in the consumption of working gas. That. ion-plasma nitriding requires 2-3 times less electricity, and the quality of the surface of the processed product makes it possible to completely eliminate the stage of finishing grinding. In addition, it is possible to reverse the nitriding process, for example before grinding.
Epilogue
Unfortunately, against the background of even neighboring countries, domestic manufacturers use nitriding by the ion-plasma method quite rarely, although the economic and physical and mechanical advantages are visible to the naked eye. The introduction of ion-plasma nitriding into production improves working conditions, increases productivity and reduces the cost of work, while the service life of the processed product increases by 5 times. As a rule, the issue of building technical processes using installations for IAS rests on the problem of the financial plan, although there are no subjectively real 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 creep up sharply. In addition, there are several companies in Russia and Belarus cooperating with foreign manufacturers of IPA equipment, which makes the purchase of such units more affordable and cheaper. Apparently, the main problem lies only in the banal decision-making, which, as a Russian tradition, will be born in our country for a long time and difficult.
Shortcut http://bibt.ru
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.
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