✅ Furnaces for ion plasma nitriding

Ion plasma nitriding (IPA)

Ion plasma nitriding (IPA) is a modern strengthening method of chemical-thermal treatment of products made of cast iron, carbon, alloy and tool steels, titanium alloys, metal ceramics, and powder materials.
The high efficiency of the technology is achieved by using different gas media that influence the formation of a diffusion layer of various compositions, 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 subject to friction and chemical corrosion, therefore it is widely used in the mechanical engineering industry, including machine tool building, the automotive and aviation industries, as well as in the oil and gas, fuel and energy and mining sectors, instrumental 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 are increased, wear and tear resistance, heat and corrosion resistance.

Advantages of ion plasma nitriding

IPA technology has a number of undeniable advantages, the main one of which is stable processing quality with minimal variation in properties. The controlled process of diffusion gas saturation and heating ensures 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 cleanliness.
Reducing the processing time of steel by 3-5 times, titanium alloys by 5-10.
Increasing the service life of a nitrided surface by 2-5 times.
Possibility of processing blind and through holes.

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

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

Installations for IPA operate in a rarefied atmosphere at a pressure of 0.5-10 mbar. An ionized gas mixture is supplied to the chamber, which operates on the principle of a cathode-anode system. A glow pulse 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, 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.

Benefits of the PulsPlasma® process

Temperature distribution

The use of a chamber with electrically heated walls, along with an energy-saving effect, influences the temperature distribution throughout the setting of parts.

In order to avoid a significant increase in temperature in the cage when using a chamber with cold walls, in many cases the use of the entire volume is abandoned. Instead, cylindrical cages are formed in a cylindrical chamber. When using a hot wall installation, due to the lower energy input, nitriding of a complete charge is carried out using pulsating plasma without the risk of overheating in some areas. Nitriding of both densely packed charges and very large parts can be successfully implemented using units for the PulsPlasma® process.

Often PulsPlasma® installations are manufactured with a built-in automation system for chamber movement, in contrast to shaft and chamber furnaces.

The cage is installed directly on the supplied base using a cage device. The frame with parts can, if necessary, be pre-prepared and, complete with parts, installed in the installation.

In the case of particularly large, heavy tools or parts, it makes sense to abandon the bell-type principle in favor of a chamber-type installation. Such an installation for processing car body dies with a unit load of up to 40 tons is shown in the figure below. Using a crane, the part is loaded onto a cart, after which the cart with the part is placed into the installation chamber.

Gas consumption during the process

With PulsPlasma® - nitriding, depending on the specific application and the properties of the layer, they work with nitrogen-hydrogen-methane mixtures. The nitriding process does not produce unfriendly reaction products, so the used gases can be released into the environment without additional treatment. Plasma nitriding is carried out at low pressures, so the consumption of process gases is quite low. A chamber with dimensions of 1200x2000 mm consumes an average of 180 l/h of gas mixture. A gas nitriding installation with the same dimensions consumes from 6,000 to 10,000 l/h of ammonia and carbon-containing mixture. With classical carburization, the gas consumption is similarly high. Therefore, during gas nitriding and carburization, a large amount of flammable exhaust gas is formed, which is harmful to the environment and requires additional energy for its additional afterburning.

Flexible processing temperatures

On the basis of exciting the plasma of the nitriding process and dosing power thanks to the pulsating operating principle, it is possible to carry out PulsPlasma® - nitriding processes in a wide temperature range between 350 ºC and 600 º.

Parts susceptible to warping can be nitrided in this case under optimal conditions. Changes in the dimensions of parts due to the release of internal stresses at high processing temperatures are minimized.

The strength of the base metal of nitrided parts also remains unchanged, because The nitriding temperature is determined slightly lower than the tempering temperature during improvement (heat treatment process before nitriding). After nitriding, no additional heat treatment is required. Parts after PulsPlasma® nitriding can be immediately used for their intended purpose.

Steels with a high chromium content, which can be nitrided in molten salts with loss of corrosion resistance and by gas nitriding with high losses, are processed without problems with PulsPlasma® nitriding. In this case, immediately before saturation, depassivation of the surface is necessary by bombarding the surface with ions. Thanks to the choice of nitriding temperatures below 450 ºС and precise control of the composition of the gas mixture, it becomes possible to obtain a hard, wear-resistant layer on the surface of parts without loss of corrosion resistance.

Powder steel processing

Processing of powder parts using carburization, molten salt carbonitriding and gas nitriding, due to the limited conditions of these processes, leaves more or less pores in the powder material. When processing in plasma, only the outer surfaces covered by the glow discharge are actually processed. Due to low pressures (vacuum) and small amounts of gas, there is no danger of over-nitriding and over-curing during plasma nitriding. When carrying out the process, a sample is placed along with the parts, made of the same material as the parts in the cage, and subjected to the same treatment before nitriding.

Partial processing

There are no simpler surface hardening methods that allow partial treatment than PulsPlasma® - nitriding. Areas not subject to saturation are closed by simple mechanical means. Special protective putties, which must be removed after the process, are not required in this case. The protected surface is not affected in any way during the plasma nitriding process.

Process combination

Due to similar processes and almost identical equipment, it is possible to combine several surface treatment processes in a dedicated installation. To further improve the corrosion resistance of nitrided parts, by simply changing the process parameters and process gas, in addition to the PulsPlasma® - nitriding process, the PulsPlasma® - oxidation process can be obtained. The oxidation process promotes the formation of a layer of iron oxide Fe3O4 with a thickness of 1 to 3 microns on the nitrided binder layer.

Depending on the quality of the steel and the previous nitriding process, corrosion resistance can reach up to 200 hours in a DIN salt spray chamber. Another advantage of oxidation is the improvement of the antifriction properties of the treated surfaces so that, under certain lubrication conditions, friction pairs treated in this way can be restored.

Another field of application opens up thanks to the combination of PulsPlasma® - nitriding with plasma CVD and DLC (Diamond like Carbon) coating processes. Thanks to the previously formed nitrided layer, additional CVD coating allows you to obtain extreme values of hardness and wear resistance. As a result of such treatment, the durability of the cutting tool usually increases significantly.

Table 2 Overview of the main differences between gas nitriding and PulsPlasma® nitriding

Ionic nitriding of parts

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

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

Properties of products after hardening using the IPA method

Hardening of gears using the ion nitriding method increases the endurance limit of teeth during bending fatigue tests 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 service life of the molds and ensures high quality casting.

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

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

Strengthening the surface layer of fine- and coarse-module gears, crankshafts and camshafts, guides, bushings, sleeves, screws, cylinders, molds, axles, etc.
Increased resistance to cyclic and pulsating loads of crankshafts and camshafts, tappets, valves, gears, etc.
Increasing wear resistance and corrosion resistance, reducing metal adhesion when casting molds, press and hammer dies, punches for deep drawing, dies.

The nitriding process takes place in modern automated installations:

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

You can find out the full range of products for hardening treatment, as well as the possibility of nitriding large parts with complex geometry, from specialists. To determine the technical conditions for nitriding and begin cooperation, send us a drawing, indicate the steel grade and an approximate technology for manufacturing parts.

Increased wear and fatigue resistance, eliminating the need for final grinding, increasing the lifespan of plastic processing machine parts and improving the quality of plastic products

Increased wear resistance and corrosion resistance, reduced metal adhesion during casting

Increasing tool wear resistance and cutting performance, improving cutting properties

For more details contact us:

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620017, Ekaterinburg, st. Turbinnaya, 7, office. 401

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All information on the site is presented for informational purposes and under no circumstances constitutes a public offer. Detailed technical specifications are recorded in the relevant regulatory documents.

Cementation versus PulsPlasma - nitriding

From the listed data, it becomes clear that PulsPlasma® - nitriding is an alternative to classical methods of chemical-thermal surface hardening such as carburization, nitriding and carbonitriding in molten salts or gas nitriding.

Another aspect that has not yet been covered is the economic aspect. A practical example shows that it is advisable to reconsider the process of manufacturing parts in such a way as to abandon energy- and economically expensive carburizing in favor of PulsPlasma® nitriding.

It is necessary to take into account that such properties of the surface layer as surface hardness, wear resistance, and endurance limit after nitriding are similarly high, and in some cases even significantly better, than after carburization.

As for the small depths of the nitrided layer compared to the cemented layer, it should be noted that due to temperature deformations and changes in size after carburization, additional mechanical processing of the parts is necessary. This leads to a decrease in the thickness of the cemented layer. Strength requirements that will ensure high performance characteristics of parts can be achieved using nitriding thanks to the correct selection of the appropriate material.

The table shows, as an example, the option of using a part after PulsPlasma® nitriding instead of a cemented gear of a printing machine made of 15 CrNi 6 E steel. The steel for nitriding was first determined by calculation and confirmed by testing.

Table 3 Calculation of the strength of gears made of different materials after carburization and PulsPlasma nitriding

As a result of using nitriding instead of carburization, in addition to increasing the service life of the gear, an economic effect of up to 30% was achieved in the manufacture of the part.

Diagram 1 Comparison of the cost of manufacturing a part by carburizing and PulsPlasma® - nitriding

Ion nitriding units EVT 40, EVT 60, EVT 70, EVT 90, EVT 95

EVT installations are simple and reliable vacuum furnaces for performing a wide range of technological tasks for nitriding and nitrocarburizing of machine parts and tools.

The absence of massive thermal insulation ensures minimal inertia of the furnace. The use of a glow discharge as the only heating source ensures high operating efficiency (it is not the working volume that is heated, but only the part), especially when performing urgent work with a small number of parts.

Nitriding of steel

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

Equipment for nitriding [ edit | edit code]

To carry out gas nitriding, shaft, retort and chamber furnaces are mainly used. A dissociator is used to prepare the ammonia before entering the furnace.

To carry out catalytic gas nitriding, mainly shaft, retort and chamber furnaces are used, equipped with built-in catalysts and oxygen probes to determine the saturation capacity of the atmosphere.

To carry out ion-plasma nitriding processes, specialized installations are used, in which the products are heated due to cathode bombardment with ions and, in fact, saturation occurs.

For nitriding from electrolyte solutions, installations for electrochemical-thermal treatment are used.

Ion plasma nitriding (IPA) is a method of chemical-thermal treatment of steel and cast iron products with great technological capabilities, which makes it possible to obtain diffusion layers of the desired composition by using different gas media, i.e. The diffusion saturation process is controllable and can be optimized depending on the specific requirements for layer depth and surface hardness. plasma nitriding microhardness alloyed

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

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

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

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

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

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

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

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

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

Compared to hardening, IPA processing allows :

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

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

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

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

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

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

The duration and temperature of the saturation process determine the depth of the layer, the distribution of hardness along the depth and the thickness of the nitride zone.

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

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

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

The use of combined heating (“hot” chamber walls) or enhanced thermal protection (triple heat shield), along with the ability to independently regulate the gas composition and pressure in the chamber, allows, when processing cutting tools, to avoid overheating of thin cutting edges during the heating of the charge, and to accurately regulate the saturation time and , respectively, and the depth of the layer, because Products can be heated in a nitrogen-free environment, for example, in a mixture of Ar+H2.

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

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

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

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b, d – gear weighing 45 kg, 11 pcs., st – 38ХН3МФА, module 3.25 (outer ring) and 7 mm (inner ring), exposure 16 hours, T=555 0 C.

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

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

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

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

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

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

Table 1. Fatigue resistance characteristics of steels depending on the methods of hardening gears

Bending endurance limit, MPa

Surface contact endurance limit, MPa

Purpose of nitriding

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

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

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

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

Nitriding process technology

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

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

Ion-vacuum nitriding workshop

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

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

Steel nitriding modes

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

PulsPlasma - nitriding

The first application of plasma nitriding appeared in the 30s and 40s of the last century. Later, in the 60-70s, this method developed to an industrial scale. The first plasma nitriding installations had cold chamber walls and operated with direct current. Plasma nitriding received a further impetus in the development in the mid-80s with the advent of the so-called. pulsating method. In this case, plasma excitation is achieved by means of a pulsating direct voltage. Electric arcing is avoided by permanent voltage interruption. It is also necessary to separate the supplied plasma power and heating of the parts to the processing temperature. DC installations with the need to cool the chamber walls to remove excess thermal energy (installations with cold walls) are gradually losing their relevance. Hot wall units with separate heating of the chamber walls are the standard in plasma nitriding today.

During the classical processes of nitriding and carbonitriding in molten salts and gases, dissociation of nitrogen-containing components occurs and the formation of a nitrided layer due to a thermochemical process under conditions of atmospheric pressure or slight excess pressure. For the decomposition of nitrogen-containing components, activation of the process and formation of nitrides, thermal reaction energy is required. To maintain the nitriding process, there is a minimum temperature at which the saturation process does not yet occur or proceeds very slowly, which is not economically profitable. The required process temperatures are given in Table 1.

In contrast to the processes mentioned above, PulsPlasma® nitriding requires the energy of an excited gas (glow discharge plasma) to activate the necessary reaction for the formation of a binding layer (BL) and the dissociation of nitrogen molecules into atoms.

Nitrided parts, formed into a charge, are placed in a heated vacuum chamber. After pumping to operating pressure (50 to 400 Pa), a pulsating voltage of more than a hundred volts is applied between the charge (cathode) and the chamber wall (anode), so that the gas in the chamber is ionized and becomes electrically conductive. Depending on the magnitude of the applied voltage, a glow discharge is ignited between the workpieces and the chamber wall, which, depending on the pressure, temperature and gas, is characterized by a certain glow. Active nitrogen atoms in the mixture of processing gases can form a chemical compound with the iron atoms of the nitrided steel. In addition, nitrogen atoms diffuse deep into the steel depending on temperature and time.

For PulsPlasma® - nitriding or carbonitriding, mixtures of nitrogen and hydrogen and gases with carbon additives, such as methane, are used. During the nitriding process, nitrogen atoms are deposited on the surface of the workpiece with the formation of iron nitride FexNy - a binding layer of SS. Depending on the duration of the saturation process and temperature, nitrogen atoms penetrate deep into the boundary zone and form a diffusion layer (DL). This nitrogen can be located either in the crystal lattice of iron or contained in the form of compounds. The layers formed using the PulsPlasma® process generally have a similar structure to layers obtained by other nitriding methods. The SS is located, depending on the material and process parameters, in the region of about 1 – 20 µm. The thickness of the diffusion zone, which characterizes the thickness of the strengthened layer, can be up to 0.6 mm under standard nitriding conditions.

Nitriding to a depth of more than 0.6 mm, for example, for highly loaded gearbox parts, is possible if a suitable material is selected.

Metals and alloys subjected to nitriding

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

Microstructure of steels after nitriding

Nitrogen is added when using the following steel grades:

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

Main types of nitriding

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

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

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

Main types of nitriding [edit | edit code ]

Nitriding in salt baths [edit | edit code ]

Immersion and exposure of parts in a solution of molten salts at a temperature of 530-650 degrees Celsius (does not affect the structural change of the material).

The resulting surface structure has:

Layer thickness: 0.01-0.5 mm;
Surface hardness – 400–1200 HV
Reducing the friction coefficient by 1.5-5 times;
Layer fragility - absent;
Increased scuffing resistance, including stainless steels;
Increased fatigue strength by 1.5–2 times;
There is practically no warping or movement of long parts.
Corrosion resistance can reach 800 hours in salt spray.

Compared to other technologies (gas and plasma nitriding), nitriding in salt baths has a smaller depth of the nitrided layer, but has better performance in terms of corrosion resistance and surface roughness. The main advantage is the ability to quickly achieve the required characteristics, thereby reducing processing time and cost.

Gas nitriding [ edit | edit code ]

Saturation of the metal surface is carried out at temperatures from 400 °C (for some steels) to 1200 °C (austenitic steels and refractory metals). The saturation medium is dissociated ammonia. To control the structure and mechanical properties of the layer during gas nitriding of steels, the following is used:

two- and three-stage saturation temperature regimes
dilution of dissociated ammonia:

air
less often hydrogen

The process control parameters are:

degree of ammonia dissociation
ammonia consumption
temperature
costs of additional process gases (if applicable).

Catalytic gas nitriding [edit | edit code ]

This is the latest modification of gas nitriding technology. The medium for saturation is ammonia, dissociated at a temperature of 400-600 degrees Celsius on a catalyst in the working space of the furnace. To control the structure and mechanical properties of the layer during catalytic gas nitriding of steels, a change in the saturation potential is used. In general, lower temperatures are used than for gas nitriding.

Ion plasma nitriding [edit | edit code ]

Technology of saturating metal products in a nitrogen-containing vacuum (approximately 0.01 atm), in which a glowing electric discharge is excited. The anode is the walls of the heating chamber, and the cathode is the workpiece. To control the structure of the layer and the mechanical properties of the layer, the following is used (at different stages of the process):

change in current density
change in nitrogen consumption
change in vacuum degree
Additives to nitrogen from highly pure process gases:

hydrogen
argon
methane

Nitriding from electrolyte solutions [edit | edit code ]

The use of the anodic effect for diffusion saturation of the treated surface with nitrogen in multicomponent electrolyte solutions, one of the types of high-speed electrochemical-thermal treatment ( anodic electrolytic heating

) small-sized products. When applying a constant voltage in the range from 150 to 300 V, the anode part is heated to temperatures of 450–1050 °C. Achieving such temperatures is ensured by a continuous and stable vapor-gas shell separating the anode from the electrolyte. To ensure nitriding, in addition to the electrically conductive component, donor substances, usually nitrates, are introduced into the electrolyte.

Catalytic gas nitriding

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

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

Steel nitriding process

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

Properties of nitrided metal surfaces

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

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

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

Steel nitriding: purpose, technology and process types

Nitriding, during which the surface layer of a steel product is saturated with nitrogen, began to be used on an industrial scale relatively recently. This processing method, proposed for use by Academician N.P. Chizhevsky, allows you to improve many characteristics of products made from steel alloys.

Ion-vacuum nitriding workshop

The essence of technology

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

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

Scheme of a glow discharge nitriding installation

Nitriding of steel involves heating the metal in an environment characterized by a high ammonia content. As a result of this treatment, the following changes occur with the surface layer of the metal, saturated with nitrogen.

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

Microstructure of a high-quality nitrided layer of steel grade 38Х2МУА

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

Surface heat treatment

Ion plasma nitriding (IPA) is a type of chemical-thermal treatment of machine parts, tools, stamping and casting equipment, ensuring diffusion saturation of the surface layer of steel and cast iron with nitrogen or nitrogen-carbon in a nitrogen-hydrogen plasma at a temperature of 450-600 ° C, and also titanium and 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 environment discharged to 200-000 Pa between the cathode on which the workpieces are located and the anode, which serves as the walls of the vacuum chamber, an anomalous 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 and a diffusion zone located underneath it.

By varying the composition of the saturating gas, pressure, temperature and holding time, it is possible to obtain layers of a given structure and phase composition, ensuring strictly regulated properties of steels, cast irons, titanium and alloys. Optimization of the properties of the hardened surface 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 a y-phase (Fe4N) or an e-phase (Fe2-3N). The e-nitride layer is corrosion-resistant, and the y-layer is wear-resistant and relatively ductile. At the same time, depending on the purposes of processing, as a result of ion plasma nitriding it is possible to obtain:

diffusion layer with a developed nitride zone, providing high corrosion resistance and wearability of rubbing surfaces - for parts subject to wear
diffusion layer without nitride zone - for cutting and stamping tools and parts operating under alternating loads under wear conditions at high pressures

The company carries out maintenance and technical maintenance operations according to the technological route for manufacturing customer parts.

For enterprises concerned about the ecology of production, it is important to know that the ion nitriding method is highly environmentally friendly. High-quality ion nitriding cannot be carried out without the appropriate equipment - our specialists will provide you with all the necessary information.

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

wear resistance,
fatigue endurance,
anti-scuff properties,
heat resistance,
corrosion resistance.

The main advantage of the method is the stable quality of processing with minimal variation in properties from part to part and from charge to charge. In comparison with widely used methods of strengthening chemical-thermal treatment of steel parts, such as carburization, nitrocarburization, cyanidation and gas nitriding in furnaces, the ion plasma nitriding method has the following main advantages:

higher surface hardness of nitrided parts,
no deformation of parts after processing,
increasing the endurance limit and increasing the wear resistance of processed parts,
lower processing temperature, due to which structural transformations do not occur in the steel,
possibility of processing blind and through holes,
maintaining the hardness of the nitrided layer after heating to 600 - 650°C,
the possibility of obtaining layers of a given composition.

Price list

Ionic nitriding

№	Installation	Cage weight (kg)	Temperature nominal (°C)	Furnace working space (Diameter x Height, mm)
1.	NAIC	2000	650	1050 x 1750
2.	OKB	2000	650	850 x 3850
3.	NSHV	2000	650	1780 x 2000
4.	NGV	50	650	600 x 600

Anti-corrosion nitriding

№	Installation	Cage weight (kg)	Temperature nominal (°C)	Furnace working space (Diameter x Height, mm)
1.	NAIC	2000	650	1050 x 1750
2.	OKB	2000	650	850 x 3850
3.	NSHV	2000	650	1780 x 2000
4.	NGV	50	650	600 x 600

Chemical-Thermal Carburization

№	Installation	Cage weight (kg)	Temperature nominal (°C)	Furnace working space (Diameter x Height, mm)
1.	EVT 25	600	1000	800 x 1500

Oxycarbonation

№	Installation	Cage weight (kg)	Temperature nominal (°C)	Furnace working space (Diameter x Height, mm)
1.	NAIC	2000	650	1050 x 1750
2.	OKB	2000	650	850 x 3850
3.	NSHV	2000	650	1780 x 2000
4.	NGV	50	650	600 x 600

Maintenance in vacuum (0.1 mmHg)

№	Installation	Cage weight (kg)	Temperature nominal (°C)	Furnace working space (Diameter x Height, mm)
1.	EVT 25	600	1000	800 x 1500

How does the nitriding process proceed?

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

Vacuum heat treatment furnace with gas nitriding system

To create the working environment inside the muffle necessary for nitriding to take place, ammonia is supplied to it under pressure. When heated, ammonia begins to decompose into its constituent elements; this process is described by the following chemical formula:

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

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

Classification of nitriding processes

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

Fe3N solid solution, characterized by a nitrogen content in the range of 8–11.2%;
Fe4N solid solution, which contains 5.7–6.1% nitrogen;
a nitrogen solution formed in α-iron.

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

Review of nitriding methods

Nitriding methods are often distinguished by the aggregate state of nitrogen in the initial state:

— liquid: Carbonitriding (cyanidation) in molten salts

- gaseous: Gas nitriding and carbonitriding

— ionized gas: nitriding and carbonitriding in glow discharge plasma

Table 1 - Overview of nitriding methods

The named nitriding methods, however, have their own advantages and disadvantages, which should be taken into account when choosing nitriding as an alternative to carburizing, depending on the required parameters of the part and the properties achieved during the nitriding process.

The molten salt nitriding process is very flexible due to its short process time. This method is most beneficial in cases where the first priority is to increase the wear and corrosion resistance of the surfaces being treated. However, some more and less significant disadvantages of this process limit the use of this method, especially for large parts:

— High costs for cleaning after nitriding

— High costs for recovery and removal of salt and cleaning solution

— High energy consumption when operating the bath, which limits the size of the bath

— Processing temperature is highly limited

— Partial nitriding is difficult to implement

Gas nitriding and carbonitriding are more versatile nitriding processes that have undergone intensive development over the past 10 years in terms of technology, equipment and control systems. These two methods are very good alternatives to cementation. Particularly when machining large tools and gears, nitriding has economic advantages over carburization due to the significant reduction in processing temperature and the absence of further processing.

Despite the high technological level of these gas nitriding methods, there are several points that limit the applicability of these methods from technical, economic and environmental points of view:

— High gas consumption

— Use of flammable gases, which requires special protection measures

— There is no possibility of depassivation of the surface of parts during the nitriding process

— Nitriding of stainless steels is not possible

— High costs for applying and removing special products to protect non-nitrided surfaces

Factors influencing nitridation

The main factors that influence nitriding are:

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

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

The influence of temperature and alloying elements on the formation of a nitrided layer

To speed up the nitriding process and increase its efficiency, a two-stage scheme is used. The first stage of nitriding when using this scheme is performed at a temperature not exceeding 525°. This makes it possible to impart high hardness to the surface layer of the steel product. To perform the second stage of the procedure, the part is heated to a temperature of 600–620°, while the depth of the nitrided layer reaches the required values, and the process itself is almost doubled. The hardness of the surface layer of a steel product processed using this technology is no lower than a similar parameter for products processed using a single-stage method.

Introduction

To increase the wear resistance of highly loaded interacting surfaces of tools and gearbox parts made of steel, the process of carburization followed by hardening is most often used to this day. Depending on the method of carburization and the operational characteristics of the part, the designer determines not only the material, but also such values as surface hardness and carburization depth. This means that the gears of gearboxes, for example for highly loaded drives of wind power plants, must be carburized before hardening at temperatures above 900 ºC for quite a long time in order to achieve a depth of the hardened layer of about 1..2 mm. Hardening after carburization leads to a change in the structure of the processed material and, as a consequence, to a change in weight and shape. After hardening, the parts must be additionally tempered to reduce internal stresses and obtain the required structure. To achieve the required surface quality and weight of parts after heat treatment, additional mechanical processing is necessary.

An alternative to carburization is surface hardening using the nitriding method. In this case, we are talking about a thermochemical diffusion process to enrich the surface layer of parts with nitrogen. In this case, nitrogen interacts with the base metal and alloying elements, forming chemical compounds. As a result of nitriding, a nitrided layer appears in the surface zone of the part with an outer region (the so-called binding layer SS) and an internal diffusion region (the so-called diffusion zone 3D). Due to the hardness of the nitrided layer and the stresses arising in it, wear resistance, corrosion resistance and resistance to long-term loads increase, regardless of the strength characteristics of the part. At the same time, a significant advantage of nitriding compared to carburizing is that the diffusion of nitrogen into steel requires temperatures equivalent to tempering temperatures for tempering and tool steels. Structural transformations and associated warping, changes in size and strength during nitriding are significantly lower. In addition, after nitriding, as a rule, no additional processing is required.

Types of Nitrided Steels

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

Hardness of steels after nitriding

Alloying elements found in the chemical composition of steel increase the hardness of the nitrided layer, but at the same time reduce its thickness. The thickness of the nitrided layer is most actively influenced by chemical elements such as tungsten, molybdenum, chromium and nickel.

Depending on the scope of application of the product that is subjected to the nitriding procedure, as well as on its operating conditions, it is recommended to use certain grades of steel to carry out such a technological operation. So, in accordance with the technological problem that needs to be solved, experts advise using products made from the following steel grades for nitriding. 38Х2МУА

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

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

30Х3М, 38ХГМ, 38ХНММА, 38ХН3МА

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

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

Characteristics of some steels after nitriding

20.01.2008
Ion plasma nitriding (IPA)- This is a type of chemical-thermal treatment of machine parts, tools, stamping and casting equipment, ensuring diffusion saturation of the surface layer of steel (cast iron) with nitrogen or nitrogen and carbon in a 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 environment 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 anomalous 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 underneath it.

By varying the composition of the saturating gas, pressure, temperature, and holding time, it is possible to obtain layers of a given structure with the required phase composition, ensuring strictly regulated properties of steels, cast irons, titanium or its alloys. Optimization of the properties of the hardened surface 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 a y-phase (Fe4N) or an e-phase (Fe2-3N). The e-nitride layer is corrosion-resistant, while the y-nitride layer is wear-resistant but relatively ductile.

At the same time, with the help of ion plasma nitriding it is possible to obtain:

diffusion layer with a developed nitride zone, providing high corrosion resistance and wearability of rubbing surfaces - for parts subject to wear
diffusion layer without a nitride zone - for cutting, stamping tools or parts operating at high pressures with alternating loads.

Ion plasma nitriding can improve the following characteristics of products:

wear resistance
fatigue endurance
anti-scuff properties
heat resistance
corrosion resistance

The main advantage of the method is the stable quality of processing with minimal variation in properties from part to part, from charge to charge. In comparison with widely used methods of strengthening chemical-thermal treatment of steel parts, such as carburization, nitrocarburization, cyanidation, gas nitriding, the ion plasma nitriding method 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 processed parts
lower process temperature, due to which there are no structural changes in the processed parts
possibility of processing blind and through holes
maintaining the hardness of the nitrided layer after heating to 600 - 650 °C
possibility of obtaining layers of a given composition
possibility of processing products of unlimited sizes of any shape
no pollution
improving production standards
reduction in processing costs several times

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

reduction of processing time from 2 to 5 times, both by reducing the heating and cooling time of the charge, and by reducing the isothermal holding time
reduction in the consumption of working gases (20 - 100 times)
reduction in energy consumption (1.5 - 3 times)
Reduces deformation enough to eliminate finishing sanding
improvement of sanitary and hygienic production conditions
full compliance of the technology with all modern environmental protection requirements

Compared to hardening, treatment by 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 carburization, nitrocarburization, gas or liquid nitriding, volumetric or high-frequency hardening allows:

save capital equipment and production space
reduce machine costs, transport costs
reduce the consumption of electricity and active gas media.

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

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

injectors for passenger cars, automatic drive support 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 positive experience in the industrial use of this method in the 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)
large (over 800 mm) diameter gears (BelAZ)
intake and exhaust valves (AvtoVAZ)
crankshafts (KAMAZ)

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

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

For some products, ion plasma nitriding is the only way to obtain a 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, carburization, nitrocarburization, and high-frequency hardening.

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Technological scheme of nitriding

To perform traditional gas nitriding, innovative plasma nitriding or ion nitriding, the workpiece is subjected to a series of technological operations.

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

Heat treatment modes before nitriding

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

Protection of areas of the product that do not require nitriding

Such protection is carried out by applying a thin layer (no more than 0.015 mm) of tin or liquid glass. Electrolysis technology is used for this. A film of these materials that forms on the surface of the product does not allow nitrogen to penetrate into its internal structure.

Carrying out the nitriding itself

The prepared product is processed in a gas environment.

Recommended steel nitriding modes

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

The degree of change in the geometric parameters of the part when performing nitriding, as mentioned above, is very insignificant, and it depends on factors such as the thickness of the surface layer that is saturated with nitrogen; temperature regime of the procedure. A more advanced technology – ion nitriding – can guarantee the almost complete absence of deformation of the processed product. When performing ion plasma nitriding, steel products are exposed to less thermal influence, due to which their deformation is minimized.

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

Punch weighing more than 230 kg, subjected to nitriding treatment

Ion plasma nitriding

Author:

Alexander Gushcha, specially for www.EquipNet.ru Photos from the sites vdm-plant.ru, metall43.ru

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

Process technology

Ion plasma nitriding, used for working tools, machine parts, stamping and casting equipment, ensures the saturation of the surface layer of the product with nitrogen or a nitrogen-carbon mixture (depending on the material of the workpiece). Installations for IPA operate in a rarefied atmosphere at pressures up to 1000 Pa. The chamber, operating 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. 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 that are in an excited state. Low pressure ensures uniform and complete coverage of the workpiece with glow. The plasma temperature ranges from 400 to 950 degrees depending on the working gas.

Ion plasma nitriding requires 2-3 times less electricity, and the quality of the surface of the processed product allows us to completely eliminate the finishing grinding stage

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

Ensuring a stable temperature depends on the heat exchange processes occurring directly inside the IPA chamber. To reduce the intensity of exchange processes with the walls of the chamber, special, non-heat-conducting screens are used. They allow significant savings on 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 most optimal for nitriding cold-worked alloy steels and martensitic materials, since performance increases without changing core hardness or 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 wear resistance while simultaneously reducing the tendency to fatigue damage to the metal structure. Obtaining the necessary surface properties is determined by the ratio of the depth and composition of the diffusion and nitride layers. The nitride layer, based on its chemical composition, is usually divided into two defining phases: “gamma” with a high percentage of Fe4N compounds and “upsilon” with Fe2N Fe3N. The -phase is characterized by low plasticity of the surface layer with high resistance to various types of corrosion, the ε-phase provides a relatively plastic wear-resistant coating.

As for the diffusion layer, the adjacent developed nitride zone reduces the likelihood of the formation of intercrystalline corrosion, providing a roughness quality sufficient for active friction. Parts with this layer ratio are successfully used in wear-resistant mechanisms. The exclusion of the nitride layer makes it possible to prevent destruction when the load force constantly changes under conditions of sufficiently high pressure.

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

Advantages of ion plasma nitriding

Ion plasma nitriding in a well-functioning technical process gives a minimal variation in surface properties from part to part with a relatively low energy intensity, which makes IPA more attractive than traditional furnace gas nitriding, nitrocarburizing and cyanidation.

Ion plasma nitriding eliminates the deformation of the workpiece, 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, allows the use of IPA to solve a wide variety of problems. In addition, nitriding by the ion-plasma method is excellent for processing steels of various grades, since the operating temperature of the process in the nitrogen-carbon mixture does not exceed 600 degrees, which eliminates damage to the internal structure and, even vice versa, helps reduce the likelihood of fatigue failures and damage due to high fragility of the nitride phase.

To increase anti-corrosion properties and surface hardness using the ion-plasma nitriding method, workpieces of any shape and size with through and blind holes are suitable. Screen protection against nitriding is not a complex engineering solution, so processing individual sections of any shape is easy and simple.

Compared to other methods of strengthening and increasing intergranular resistance, IPA is distinguished by a several-fold reduction in the duration of the technical process and a reduction in the consumption of working gas by two orders of magnitude. That. Ion plasma nitriding requires 2-3 times less electricity, and the quality of the surface of the processed product allows us to completely eliminate the finishing grinding stage. In addition, it is possible to carry out the reverse process of nitriding, for example before grinding.

Epilogue

Unfortunately, even compared to 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 5 times. As a rule, the issue of constructing technical processes using installations for IPA comes up against 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 only possible in stages, when the cost and duration 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 accessible and cheaper. Apparently, the main problem lies only in the banal decision-making, which, like the Russian tradition, will take a long and difficult time to come up with us.

Types of working environments

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

Recently, the method of ion-plasma nitriding, performed in a nitrogen-containing rarefied environment, has become widespread.

Ion plasma nitriding – a view from the inside

A distinctive feature of ion plasma nitriding, which is also called glow discharge processing, is that the workpiece and the muffle are connected to an electric current source, with the product acting as a negatively charged electrode, and the muffle as a positively charged one. As a result, a flow of ions is formed between the part and the muffle - a kind of plasma consisting of N2 or NH3, due to which the surface being treated is heated and it is saturated with the required amount of nitrogen.

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

Ion plasma nitriding

Currently, the use of IPA technology has become widespread, as it allows saving capital equipment and production space, reducing machine tools and transportation costs, and reducing the consumption of electricity and active gas media. The IPA method has the following main advantages:

¾ higher surface hardness;

¾ no deformation after processing and high surface cleanliness;

¾ increasing the endurance limit and increasing the wear resistance of the processed part;

¾ lower processing temperature, due to which structural transformations do not occur in the steel;

¾ maintaining the hardness of the nitrided layer after heating to 600...650°C;

¾ the possibility of obtaining layers of a given composition;

¾ the ability to process products of unlimited sizes and shapes;

¾ no environmental pollution;

¾ improving production standards;

reduction in processing costs several times.

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

Figure 2 shows a diagram of an installation for ion plasma nitriding.

Figure 2 - Installation diagram for ion-plasma nitriding (1 - part, 2 - vacuum container, 3 - power supply unit, 4 - temperature control device, 5 - gas comb, 6 - vacuum - pump)

In the rarefied space between the cathode (part) and the anode (vacuum container), a glow discharge is excited in a gas environment containing nitrogen atoms and ions. Ammonia from cylinders, a mixture of nitrogen and hydrogen, or nitrogen thoroughly purified from oxygen are used as a saturating atmosphere. When a glow discharge is excited, a stream of positively charged nitrogen ions rushes to the surface of the part. When ions hit the cathode, heat is released, due to which the surface of the part is heated. Low pressure ensures uniform and complete coverage of the part with glow. The operating pressure in the furnace chamber is 1…10 mm Hg. The plasma temperature ranges from 400 to 950°C. The film formed on the surface consists of two layers: lower diffusion and upper nitride.

Ensuring a stable temperature depends on the heat exchange processes occurring directly inside the IPA chamber. To reduce the intensity of exchange processes with the walls of the chamber, special, non-heat-conducting screens are used. They allow significant savings on 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. In this case, temperatures below 500 degrees are the most optimal for nitriding alloy steels since performance characteristics increase without changing the hardness of the core and thermal destruction of the internal structure. As a result, the adjacent developed nitride zone in the diffusion layer reduces the likelihood of the formation of intercrystalline corrosion, providing a roughness quality sufficient for active friction. With this ratio of layers, the gear will be successfully used in mechanisms subject to wear.

By varying the gas saturation composition, pressure, temperature and holding time, it is possible to obtain layers of a given structure and phase composition, ensuring strictly regulated properties of steels and its alloys.

The use of IPA in the proposed technological process is as follows. To improve the mechanical properties of the material, the part is subjected to IPA before finishing, ensuring surface protection due to an allowance, the value of which is greater than the maximum thickness of the nitrided layer. As a result of heat treatment, the surface hardness of the teeth should be in the range of 64...72 HRC with a nitrided layer depth of 1.1...1.3 mm.

After ion plasma nitriding (IPA) hardening of gears, the endurance limit of teeth during bending fatigue tests reaches 930 MPa. The contact fatigue strength after IPA is higher, and the wear resistance of the diffusion ion-plasma nitrided layer is 2...4 times higher than the wear resistance of the cemented layer.

The ion plasma nitriding installation consists of a working chamber, a control cabinet, an pumping system, a water cooling system, connecting cables and lines (Fig. 3).

Figure 3 — Installation of ion-plasma nitriding EVT 40

The working chamber consists of a fixed base. At the base of the chamber there is an exhaust pipe, a power supply, a thermocouple input, a gas inlet and fittings for the cooling system. The cathode is mounted on supports having dielectric inserts.

Control of the operation of the installation and monitoring of the progress of the processing process is carried out automatically according to a given program using a specialized controller and a personal computer built into the control cabinet.

All stages of installation (vacuuming the chamber, heating the charge, holding and cooling) are automated. The transition from one process step to another is carried out either after a specified time interval has elapsed (during the holding period), or upon reaching a certain specified value of a certain parameter - temperature or pressure (during the heating of the charge).

During the technological process, the installation monitors the following parameters, which are displayed on the display in the form of a graphical process protocol:

¾ working pressure;

¾ temperature;

¾ consumption of three working gases;

¾ voltage and discharge current.

Upon completion of the process, the total consumption of each component of the gas mixture and the consumption of electricity spent on the formation of the discharge during the processing process are determined.

¾ higher surface hardness;

¾ no deformation after processing and high surface cleanliness;

¾ increasing the endurance limit and increasing the wear resistance of the processed part;

¾ lower processing temperature, due to which structural transformations do not occur in the steel;

¾ maintaining the hardness of the nitrided layer after heating to 600...650°C;

¾ the possibility of obtaining layers of a given composition;

¾ the ability to process products of unlimited sizes and shapes;

¾ no environmental pollution;

¾ improving production standards;

reduction in processing costs several times.

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

Figure 2 shows a diagram of an installation for ion plasma nitriding.

Figure 2 - Installation diagram for ion-plasma nitriding (1 - part, 2 - vacuum container, 3 - power supply unit, 4 - temperature control device, 5 - gas comb, 6 - vacuum - pump)

Ensuring a stable temperature depends on the heat exchange processes occurring directly inside the IPA chamber. To reduce the intensity of exchange processes with the walls of the chamber, special, non-heat-conducting screens are used. They allow significant savings on 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. In this case, temperatures below 500 degrees are the most optimal for nitriding alloy steels since performance characteristics increase without changing the hardness of the core and thermal destruction of the internal structure. As a result, the adjacent developed nitride zone in the diffusion layer reduces the likelihood of the formation of intercrystalline corrosion, providing a roughness quality sufficient for active friction. With this ratio of layers, the gear will be successfully used in mechanisms subject to wear.

The ion plasma nitriding installation consists of a working chamber, a control cabinet, an pumping system, a water cooling system, connecting cables and lines (Fig. 3).

Figure 3 — Installation of ion-plasma nitriding EVT 40

During the technological process, the installation monitors the following parameters, which are displayed on the display in the form of a graphical process protocol:

¾ working pressure;

¾ temperature;

¾ consumption of three working gases;

¾ voltage and discharge current.