JPH0240735B2 - TETSUUTANSOGOKINSEIHINNIKAKUSANTANKABUTSUHIFUKUBUTSUOFUCHAKUSURUHOHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Application of the Invention The present invention relates to metallurgy, thermochemical processing of metals and alloys, and more particularly to iron-carbon alloy products.
- a method of depositing diffusion carbide coatings on carbon alloy articles.

In order to extend the durability and service life of mechanical and mechanical parts that are subjected to severe wear, these parts are diffusion saturated, thus creating a diffusion coating on the surfaces of those parts. This coating should be characterized by higher hardness and wear resistance than in the material of the product. These requirements are most fully met by carbide type diffusion coatings.

PRIOR ART One of the most common methods for depositing metal carbide coatings on various products, including those made from iron-carbon alloys, is to chemically deposit the carbide from the vapor phase (chemical vapor deposition). law). “Plansee” (Austria), “Berna AG” (Switzerland), “Concirc” (USA), Scientific Coatings Inc.
Coatings Inc. (USA), Troy (USA), PED Ltd.
Equipment for depositing carbide and other types of coatings, produced on a large scale by such companies as Co., Ltd. (UK), Coleshill (UK), “Sandvic” (Sweden), etc., includes a wide variety of By introducing modular equipment and increasing the active volume of the reaction vessel, a highly efficient process is ensured. Thus, by depositing a chromium carbide coating of the stoichiometric composition Cr ₂₃ C ₆ or Cr ₇ C ₃ or a mixture of these carbides on a steel tool, it is possible to use the tool at temperatures up to 950°C. , and the useful life of the tool is extended by 20 to 25 times. The carbide layer is
It is produced on the heated surface of the product due to the chemical interaction of chromium halides and methane. Place the product in the reaction vessel, apply vacuum, heat, and when the temperature rises to 850-1050℃, chromium halide,
A gaseous mixture of methane (CH ₄ ) and carrier gas is introduced into the reaction vessel.

A carbide layer with a thickness of up to 12 μm ensures high wear resistance. A carbide layer thickness of more than 12 μm is required in some cases for better working and tribological properties of the product, but this thickness is limited to the lower zone, i.e. just below the carbide layer. leads to decarburization of the layers of the base material that are present, which has an adverse effect on the properties. Moreover, in the above-mentioned process of depositing the carbide coating, the growth rate of the carbide layer generally does not exceed 2 μm/h, which increases the growth time.

The coating of chromium carbide Cr ₇ C ₃ is deposited at a fairly high rate and at low temperature by decomposition of bis-ethylbenzene vapor on the heated surface of the workpiece in vacuum. To prevent the formation of dendrites within the coating, the process is conducted under non-isothermal conditions (non-isothermal conditions).
-isothermic condition), i.e. in the first stage at 300-350°C for 10 minutes and then at 500-350°C for 50 minutes.
Performed at 600℃. working chamber
The pressure inside the chamber is 1.33Pa. The thickness of the chromium carbide layer deposited in this way is 340 μm, and this layer is characterized by high wear resistance and a micro hardness of 2500 NV. However, such coatings are subject to high specific loads, especially alternating loads.
loads) and significant tangential stresses. This is because this leads to delamination of the carbide layer due to the low adhesion strength at the interface with the base metal.

Chromium carbide coatings deposited at higher temperatures are of interest because of their significantly higher bond strength to the base metal. One of the prior art methods is to pre-treat the workpiece surfaces with a solution containing 5-20% _HNO3 and 10% fluoride and then coat these surfaces with a suspension based on chromium powder. It consists of This suspension combines a solution of an organic binder, e.g. an acrylic resin, with a solvent (e.g.
prepared from a solution in methylchloroform). Incidentally, the diffusion coating is applied by immersing the workpiece in a retort filled with the powder mixture and passing argon or hydrogen through it for 2 to 10 hours at 900-950°C. However, this technique is largely unproductive, labor-intensive, and
Also, the use of volatile organic compounds requires extra labor and environmental protection (US Pat. No. 4,347,267, IPC B05D 7/22, D05D
7/14, NPC 427/237, published August 31, 1982).

The amount of labor required to deposit a diffused chromium carbide coating can be significantly reduced by heating the surface with a stream of HF. A saturated mixture containing chromium and halogen-containing compounds is sprinkled freely over the treated surface.
The equipment used for this process includes a water-cooled inductor and, if necessary, a separator made of non-metallic materials. This method is economical due to the localization of the heating surface and the possibility of recycling the material utilized for the application of the coating. At the same time, the carbide coating deposited in this way is non-uniform with respect to thickness, chemical composition and phase composition, since the heating of the workpiece by the HF flow does not take into account a uniform temperature distribution over the treated surface. It should be pointed out that (UK Patent Application No. 2109822, published 8 June 1983, IPC C23C 9/02).

It is noteworthy that all the above methods lead to decarburization of the lower zone, which reduces the permissible contact pressure to the reinforcement surface during subsequent working of the coated part. This is due to the diffusion of carbon contained in the iron-carbon alloy into the layer of deposited carbide-forming elements forming carbides.

In order to reduce or eliminate the decarburization effects of the lower zone as a whole, it is common to saturate the surface in two stages, i.e. by presaturating the surface layer with carbon or nitrogen and then by depositing carbide-forming elements. It has been implemented. Carbon or nitrogen introduced into the surface layer in the first stage forms carbides, nitrides or carbonitrides in the second stage,
Decarburization of the lower zone is thus prevented.

A method for applying a chromium carbide-based diffusion coating to the surface of steel products containing at least 0.2% carbon is patented in the United States.
At 450-650°C in an atmosphere of nitrogen-hydrogen mixture,
Perform preliminary fine nitriding to a depth of 100-350 μm for 5-40 hours.
1.5-2.5% nitrogen is generated within the nitrided layer. The second step of the method consists in gas chromizing (xpoMNpoBaHNN) at 850-1100°C for 5-30 hours; thick and characterized by high wear resistance. It should be noted that such a coating deposition process is very long, requires considerable power consumption, and cannot be considered a very efficient process (December 1980).
U.S. Patent No. 4242151, IPC C23C, issued March 30th
11/04, 11/16).

In a reducing atmosphere based on hydrogen, ferrochrome,
0.4−1.0% ammonium chloride and chromium (50
-75%) is known in the prior art. 0.35%
While processing steel products containing higher carbon content, 0.5-1.5% ammonium fluoride is added to the chromium plating mixture. The necessity of using a hydrogen atmosphere during heating reduces the economics of such a process and requires the provision of special fire and explosion precautions (French Patent Application No. 1/18 2439824, Cl. C23F 17/00, 1980 5
Published on March 23rd; French Patent No. 2483468, Cl.
C23C 9/00, released December 4, 1981).

A similar result was achieved in the first stage of the process by performing submerged nitridation in a molten nitrate medium at about 400-800°C for 12-150 hours, which significantly reduces process efficiency. (French Patent Application No. 2454471, Cl.C23C 11/04, 11/14, 1980
(Released on November 14th).

In the first stage of the process it is also possible to use carburizing, boronizing or sulfurizing; the chromium carbide coatings produced in this way have high wear resistance.

In some cases, a nitriding or carburizing step in a liquid or gaseous medium is performed after depositing a layer of carbide or nitride-forming elements on the treated surface. Carbide, nitride or carbonitride layers are also characterized by high wear resistance, but the adhesive strength of such coatings is substantially lower than in the case of previous coatings (East German Patent No. 2005730).
No., IPC C23F 17/00, published May 18, 1983).

However, a two-step process consisting of sequential operations such as saturation of the workpiece surface layer with carbon, nitrogen or boron and deposition of carbide- or nitride-forming elements, in either order, improves the overall economic and technical parameters of the process. As it worsens, it requires a very long period of time.

The rapid formation of carbide layers in steel products is also due to diffusion saturation in the antimony melt by alloying additive particles containing carbide-forming elements such as chromium.
It can be achieved again. Immerse the workpiece in the melt, 1090
℃ and hold for 5 hours. This involves the migration of atoms of the alloying elements to the workpiece surface and subsequent diffusion into the product material [Gene Wolfe Breakthrough in Diffuse Alloying].
diffusion alloying). “Plant Engineering” (USA), 1976, 30,
No. 25, p. 127-128]. In addition, this technical process is
From an economic point of view, it cannot be considered universal and promising.

A production method for diffusion carbide coatings developed in Japan [“Toyota-Diffusion”]
] combines sufficiently high production capacity with suitability for production. Anhydrous borax (Na ₂ B ₄ O ₇ ),
The work piece is placed into a crucible filled with _a melt _of boric anhydride, boron oxide ( _B2O3 ) or _the compound _K2B4O7 . Depending on the desired composition of the carbide coating, the borax melt is mixed with an amount of 1-60% of these alloying carbide-forming elements in the form of finely divided compounds. The content of carbide-forming compounds should be at least 30% borax content. The function of carbide-forming elements may be performed by chromium and the metals of group Va of Mendeleev's periodic law, namely vanadium, niobium and tantalum. Compounds of these elements may be used in the form of ferroalloys or oxides (US Pat. No. 4,158,578, IPCC 23C 9/10, 1979).
(Published June 19, 2013), Forms of Chromium or Its Alloys as Oxides and Pure Metals in a Mass Relationship of Boron and Oxides Within 7-40% (U.S. Pat.
No. 4230751, IPC C23C 9/16, C25D 3/66,
Published October 28, 1980; U.S. Patent No. 4,202,705;
IPC C23C 9/10, published May 13, 1980). This process is carried out at 850-1100℃.
It is done within 1-20 hours. The coatings produced in this way have high abrasion resistance, but
This method requires a subsequent dressing of the workpiece surface; moreover, the surface of such a product after application of the coating is necessarily oxidized and often has the required surface roughness. additional machining is required to impart this to the product.

Problems to be Solved by the Invention It is an object of the present invention to provide a method for depositing, precipitating, depositing, etc. a diffusion carbide coating on an iron-carbon alloy product, which improves the physico-mechanical properties of the coating. In particular, the object is to provide a method for improving the hardness and abrasion resistance, thereby increasing the service life of the product.

Means for Solving the Problems The above problems are solved by: - charging a powder mixture containing solid components, i.e. carbide-forming elements, carbon-bearing compounds, activators, inert fillers, into a container; - heating the products to the carburizing temperature of their surfaces; - carrying out carburization of the product surfaces; - removing the carburized products so that their product surfaces are saturated with carbide-forming elements; in a method for depositing a diffusion carbide coating on an iron-carbon alloy product, comprising diffusion saturating the product surface with carbide-forming elements at temperatures ranging from -950 to 1100°C; According to the invention: - carburization of the workpiece surface takes place within a period selected from 0.6 to 1.2 hours at a temperature in the range 560-720°C; - heating the carburized product to the temperature of diffusion saturation; At a temperature selected from the range of 950 to 1100℃,
be carried out at a rate varying from 0.8 to 2.4 degrees per second (°/s); - diffusion saturation of the workpiece surface by carbide-forming elements;
occurs within a period of 1.2 to 1.8 hours at a temperature of 950 to 1100°C; - after diffusion saturation of the workpiece surface with carbide-forming elements, the workpiece is heated at a rate of 300 - 2.4°/s;
- applying a diffusion carbide coating onto an iron-carbon alloy product characterized in that the above operations are repeated at least once, starting with heating the product to the carburizing temperature; solved by providing a method for attaching.

The above operation is repeated up to seven times in order to deposit a diffused carbide coating which gives the product maximum surface hardness and abrasion resistance.

DETAILED DESCRIPTION OF THE INVENTION A detailed description of a method for depositing a diffusion carbide coating on an iron-carbon alloy article is provided below.

The deposition of diffusion carbide coatings on iron-carbon alloy products is based on contact deposition from the gas phase within a powder mixture consisting of carburization of the product surface and subsequent diffusion saturation with carbide-forming elements. The powder mixture in this method consists of the following solid components:
It should contain carbide-forming elements, carbon-containing compounds, activators and inert fillers. The carbide-forming elements may be constituted by chromium, molybdenum, tungsten, niobium, zirconium, tantalum, silicon or mixtures thereof. Carbon-containing compounds include diphenyl, naphthalene, anthracene, pyrene, triphenylene,
It may also be 3.4-benzopyrene. In addition to the above organic compounds, other solid organic compounds of the hydrocarbon class may be used; this organic compound should be in the solid state at room temperature and its boiling point or sublimation temperature should be in the range 100 to 700°C. be. The function of the activator is
This may be accomplished by ammonium chloride, ammonium fluoride, ammonium iodide, ammonium bromide. Aluminum oxide, magnesium oxide or silicon dioxide may be used for inert fillers.

The powder mixture is prepared by sieving the components, taken separately in powder form, through a vibrating sieve with a mesh size of less than 50 μm. The particle size of the sieved portion should not exceed 50 μm. Particles of this size ensure a high degree of saturation of the surface with carbon during the carburizing stage and with carbide-forming elements during the diffusion saturation stage.
Moreover, using a powder mixture with particles of this particle size prevents sticking of the mixture particles to the surface of the workpiece. After sieving, each component is weighed out in the following mass percentages.

Carbide-forming elements 40-70 Carbon-containing compounds 0.5-2.5 Activators 0.2-5.0 Inert fillers remainder After weighing, each component of the powder mixture is dried under certain conditions, depending on the nature of the components. The carbide-forming element powder is dried at 140° C. for 4 hours. The inert filler powder is calcined at 1200° C. for 2 hours. Carbon-containing compounds are dried within 0.5-1.0 hours at 60°C. Then, the activator powder was heated at 140℃ for 4 hours.
Dry for an hour. All ingredients are then cooled to 40°C and thoroughly mixed in a bicone mixer for 1-2 hours.

The moisture content in powder mixtures intended for use in the preparation process of diffusion carbide coatings should not exceed 5-6%. Place the powder mixture into a stainless steel container. The product must have a distance of at least 20 mm from the bottom of the container to the product and 10 mm from the side wall of the container to the container.
, a distance of at least 15 mm between the products and a distance of at least 30 mm from the products to the first container cover.

After immersing the product into the powder mixture, the container is capped with a first cover made of stainless steel and a layer of silica sand at least 30 mm thick is poured on top.
Then close the second cover and add boron oxide B ₂ O ₃ (approx.
A substance with a melting temperature of 450 °C) is poured on top of it.

placing the container containing the powder mixture and product in a resistance furnace and heating to a temperature of 560 to 720°C;
The surface of the product is then carburized; according to the invention, the carburization is carried out at a given temperature within the limits of 0.6 to 1.2 hours. The mechanism of the chemical reactions that take place inside the vessel during this process can be illustrated by the example of a saturating powder mixture consisting of chromium, diphenyl, ammonium fluoride, and aluminum oxide. Aluminum oxide is an inert filler and does not participate in chemical reactions.

During heating, diphenyl begins to decompose from a temperature of about 256°C: 2C ₁₂ H ₁₀ →5CH ₄ +19C (1) The carbon interacts with the oxygen inside the container: C+O ₂ →CO ₂ (2) The decomposition of ammonium chloride starts at a temperature of 335°C: NH ₄ F→NH ₃ +HF (3) 2NH ₃ →N ₂ +3H ₂ (4) Then, the saturated hydrocarbon (methane) produced during the decomposition of diphenyl is It interacts with some of the hydrogen fluoride, thus producing carbon tetrafluoride. This carbon tetrafluoride is adsorbed on the surface of the product and produces active carbon atoms that saturate the surface of the product: CH ₄ +4HF→CF ₄ +4H ₂ (5) CF ₄ +4Fe→2FeF ₂ +C (6) Reaction ( 5) and (6) mainly occur during carburization.

When the temperature in the furnace reaches 450℃, boron oxide
The B ₂ O ₃ melts to form a dense layer that seals the container and prevents air from penetrating into the container along with the contained oxygen.

As the temperature rises to 814° C., the chromium in the container begins to evaporate, interacts with hydrogen fluoride and creates an active gaseous medium for diffusion saturation.

Cr+2HF→CrF ₂ +H ₂ (7) Chromium fluoride is adsorbed on the surface of the product to form active chromium atoms, which diffuse into the surface layer of the product: CrF ₂ +Fe→FeF ₂ +C (8) CrF ₂ + H ₂ → 2HF + Cr (9) Activated chromium atoms interact with the carbon diffused on the surface of the product during the carburizing stage to form a diffused carbide coating: 23Cr + 6C → Cr ₂₃ C ₆ (10) Reaction (7 )−(10) proceeds extremely vigorously at temperatures chosen from the range 950−1100°C.

Carburizing allows the surface layer of the product to be saturated with carbon that diffuses from the powder mixture into the product, thus ensuring enhanced formation of a diffused carbide layer during subsequent heating. A diffused carbide layer is formed solely by carbon that has diffused from the powder mixture to the surface of the product. The carbon contained in the material of the product is
Does not diffuse to the surface of the product to create a carbide layer. This practically prevents the formation of a decarburization zone under the coating that is present in other prior art methods. During the carburization stage, carbon-containing compounds are decomposed to produce large amounts of gaseous saturated hydrocarbons and also some amount of carbon dioxide which is obtained by interacting with the oxygen in the air and with the steam. hydrocarbons and carbon dioxide in reactions (1) and (2)
Therefore, a small amount is present in the container. The interaction of the hydrogen halide formed during the decomposition of the activator according to reaction (3) with the decomposition products of the carbon-containing component results in the formation of gaseous compounds of carbon and one of the halogens, e.g. carbon tetrafluoride. , which increases the saturation of the surface with carbon. The product is held at these temperatures to bring about saturation of the surface layer with carbon, thereby ensuring early formation of a carbide layer during subsequent heating. If the above temperature and time limits are not adhered to, the desired effect will not be achieved. Carburizing at temperatures below 560° C. does not ensure sufficient carbon diffusion flow from the decomposition products of the carbon-containing compounds of the mixture to the surface layer of the product. 720
Carburizing at temperatures higher than 0.degree. C. results in premature deposition and subsequent diffusion of carbide-forming elements at the surface of the product. If the carburization time is shorter than 0.6 hours, the carbon concentration on the product surface will decrease, causing the formation of a decarburized zone under the diffusion coating. The decarburization zone reduces the strength and tribological properties of products with diffused carbide coatings. The carburizing stage
If it takes longer than 1.2 hours, this is unsuitable from an economic point of view. This is because the strength and tribological properties are no longer increased and there is an unreasonable consumption of power.

Once the carburization time has expired, the product is heated to the diffusion saturation temperature. Heating is carried out at a rate selected from 0.8 to 2.4°/s. This treatment procedure ensures a constant concentration of carbon on the surface layer of the product, saturated with carbon diffused from the powder mixture into the product during the carburization stage, and a diffusion carbide coating during the diffusion saturation stage. The formation of decarburization zones under the conditions is prevented. Heating to the diffusion saturation temperature at a rate higher than 2.4°/s is not practical from an economic point of view since it requires a large amount of energy which would be consumed by more powerful heaters. Conversely, heating carried out at a rate lower than 0.8°/s results in a diffusive dispersion of carbon from the surface layer; the carbon begins to diffuse into the product, i.e. into the matrix, thereby reducing the concentration of carbon in the surface layer. decreases. In the diffusion saturation stage, this results in the amount of carbon diffused into the surface layer in the carburizing stage being insufficient to form a diffusion carbide layer; as a result, carbon begins to diffuse out of the steel;
A decarburization zone is thereby created below the carbide layer.

Diffusion saturation temperature range (bracket) from 950 to 1100℃
When the temperature within 1.2 is reached, stop heating and
Diffusion saturation is performed within a period selected from 1 to 1.8 hours. This procedure creates a diffused carbide layer on the surface of the product. The formation of the diffused carbide layer is ensured by the interaction between the carbide-forming elements attached to the surface and the carbon that has saturated the surface layer of the product according to reaction (1). The carbon contained within the material of the product does not practically take part in the formation of the diffused carbide layer during this period, which prevents the formation of a decarburized zone below the diffused carbide layer. It should be noted that since the surface layer of the product is saturated with carbon, the carbide layer is formed more actively than in previously known methods. If the above temperature and time intervals are not observed, the desired effect will not be obtained. 950
Diffusion saturation carried out at temperatures below °C results in a decrease in the thickness of the diffused carbide layer due to insufficient diffusion of carbide-forming elements into the coating, which reduces the strength and tribological properties of the coating. . Diffusion saturation carried out at temperatures above 1100°C is likewise unsuitable. This is because at such temperatures the size of the particles of the product material increases, thereby reducing the mechanical properties of the product, ie its impact strength. If the diffusion saturation is carried out within a time period shorter than 1.2 hours, this will lead to an insufficient deposition rate of carbide-forming elements on the surface of the product and the formation of a thinner diffusion saturation layer, thereby reducing the coating. Strength and tribological properties are impaired. Conversely, extending the time of diffusion saturation beyond 1.8 hours results in the formation of a diffuse carbide layer with a lower concentration of carbon. This is because under these conditions carbon diffuses through the carbide layer that was already formed and this diffusion process loses its strength due to the reduced carbon concentration in the surface layer. . Additionally, at such diffusion saturation times, carbon may diffuse from the matrix to the coating. This is because the entire amount of carbon introduced to the surface during the carburization stage would have already been used up to create the carbide layer while the diffusion of the carbide-forming elements continues. This effect causes the formation of a decarburized zone under the coating.

Once the diffusion saturation time has expired, the container containing the product is cooled according to the invention to a temperature selected from 300 to 500° C. at a rate selected within the limits of 1.2 to 2.4°/s.

This technique makes it possible to avoid the effects of carbon redistribution under the diffused carbide layer and the formation of decarburized zones under the coating. At these cooling rates, carbide-forming elements and carbon stop precipitating from the powder mixture onto the surface of the product, so that there is no diffusion of carbon from the matrix to the surface of the product. Cooling after diffusion saturation at rates higher than 2.4°/s is not economically practical as it requires the use of special cooling systems. Conversely, cooling the vessel after diffusion saturation at a rate lower than 1.2°/s results in the deposition of carbide-forming elements on the surface, although at a lower rate it This results in a diffusive redistribution of carbon within the diffusing carbide layer, creating a highly undesirable decarburization zone beneath the carbide coating.

After cooling to a temperature selected from the range 300 to 500°C, all steps of the above treatment are carried out according to the invention.
It is repeated for a number of cycles ranging from at least 1 to 7. The number of cycles within these limits is
It should be selected to suit the conditions of use of the product with the diffusion coating. If the cycle is repeated 6 or 7 times, the resulting coating is characterized by high strength and tribological properties.

Upon cycling the above treatment steps by carburizing within 560-720 °C, the diffused carbide layer created in the previous cycle becomes saturated with carbon from the powder mixture, and during heating on it, the deposited carbide-forming elements are removed. It diffuses into the layer and then its carbide is formed.
The circulation promotes the growth of the diffused carbide layer without reducing the concentration of carbon in the lower zone. In addition, the cyclic nature of the saturated temperature conditions with periodic cooling to a temperature chosen from the range 300-500° C. results in the formation of a diffused carbide layer with a more dispersed structure. This is achieved by repeating the two-stage heating cycle after cooling to a temperature of 300-500°C, rather than the growth of pre-existing carbide crystals.
This is due to the fact that this results in the formation of new species of crystallization of carbide-forming elements on the treated surface and the development of carbides. This produces a large number of fine carbide crystals that improve the strength and tribological properties of the product.

Completion of the cooling step at temperatures above 500 °C precludes the possibility of the formation of new crystallized species, so that subsequent heating and carburization
Only the growth of the existing carbide crystals is induced, without the creation of fine dispersed structures.

Completing the cooling at temperatures below 300° C. is unsuitable from an economic point of view, since this involves an extra amount of power for the subsequent heating. If the number of cycles is less than two, the concept of a "cyclic process" loses its meaning. For more than 8 cycles,
The powder mixture becomes depleted, i.e. the amount of carbon that diffuses from the powder mixture to the product surface decreases, which subsequently leads to longer holding times between each cycle and overall unreasonable prolongation of the process and power consumption. This results in additional consumption of

Once the required number of cycles have been completed, heating is discontinued and the container is allowed to cool to room temperature in air. The container is then opened and the product and powder mixture removed. The product is shipped to the customer, while the saturating powder mixture is sent for recycling. Regeneration involves grinding the powder mixture in a ball mill, sieving it through a vibrating sieve (50 μm mesh), drying it at 140 °C for 4 hours, and dissolving the dried activator and carbon-containing compound in the following proportions (% by mass): carbon-containing compounds 0.5−2.5,
The active agent should be added at 0.2-5.0. The mixture used is carefully mixed with the activator and the carbon-containing substance. The freshly prepared and dried powder mixture is then added in a proportion of 10% of the initial weight of the mixture and carefully mixed again. In addition,
Powder mixtures can be used upon request. The mixture can be recycled up to 15 times before disposal.

The method proposed herein is based on a dense non-porous diffusion carbide coating with a thickness of 21.0-40.0 μm;
Microhardness of 27.0GPa, average height of carbide crystals of 4.2−5.4μm, substrate hardness of 4.2−7.4GPa, 4.2−
Minimum hardness in the lower zone of 7.4 GPa, no decarburized zone under the carbide coating and 12.5−15.6
A coating is produced having a relative wear rate at sliding friction of g/m ² s.

The carbide coating has an attractive silver-gray surface with a surface roughness Ra of less than 0.32 μm. Therefore, once the process is completed, the product does not require any finishing treatment or subsequent machining. The coating is evenly spread over the entire surface of the product, including the interior space, and effectively adheres to the material of the product.

The process does not require the use of vacuum equipment, nor does it use gases (hydrogen and argon) that require the provision of special fire and explosion protection equipment. The process does not involve any substantial hazards to handling personnel or the environment.

Although the process can be repeated up to 7 times, its total duration does not exceed 20-22 hours due to the short duration of its individual stages.

The invention will be further elucidated by an example embodiment of a method for depositing a carbide diffusion coating on an iron-carbon alloy article.

Example 1 In a stainless steel container with an inner diameter of 80 mm, a height of 110 mm, and a wall thickness of 5 mm, 195 g (65%) of chromium powder is placed.
Diphenyl C ₁₂ H ₁₀ 3 g (1%), ammonium chloride NH ₄ Cl 1.5 g (0.5%) and aluminum oxide
Powder mixture containing 100.5 g (33.5%) of Al ₂ O ₃
300g was charged. These components had previously been milled, sieved to yield a particle size fraction below 50 μm, weighed out according to formulation and mixed in a mixer.

Next, carbon and alloy steel test pieces with a diameter of 15 mm and a height of 5 mm were placed with a distance of 20 mm between the container bottom and the test piece, a distance of 10 mm between the container side wall and the test piece, and a distance between the test pieces.
15 mm and 30 mm between the specimen and the first cover of the container.
It was immersed into the mixture leaving a distance of mm. The test pieces were arranged in a line. Once the specimens were placed in the powder mixture, the container was closed with a first stainless steel cover and a 30 mm thick layer of silica sand was poured on top of the cover. The second stainless steel cover of the vessel was then closed, a 10 mm thick layer of boron oxide was poured on top of the cover, and the vessel was moved into a resistance furnace. The container was heated to 650°C, and carburization was performed at this temperature for 1.0 hour. The surface of the specimen was saturated with carbon. The carburized specimen was then heated to the diffusion saturation temperature (1000°C) at a rate of 1.5°/s.

As soon as a temperature of 1000°C is achieved, this temperature is
It was maintained for 1.5 hours. Once diffusion saturation with chromium was completed, the specimen was cooled to 400°C at a rate of 1.8°/s. Then, the above operations like heating up to carburization temperature, carburization proper, heating up to diffusion saturation point, diffusion saturation and cooling are repeated once again, after which the container containing the specimen is brought to ambient temperature in air. Cooled. The container was then opened, the powder-saturated mixture was directed for regeneration, and the specimens were tested by conventional methods to determine the physico-mechanical and physico-chemical properties of the resulting carbide-chromium coating.

Test results: - the carbide coating is dense, ie practically pore-free; - the thickness of the carbide coating, 21.0 μm; - the microhardness of the carbide coating, 21.6 GPa; - the average height of the carbide crystals, 5.2 μm; - Hardness of the substrate, 5.6 GPa; - Minimum hardness of the lower zone, 5.6 GPa; - Relative wear rate, 12.5 g/m ^<2> s.

Example 2 A diffusion carbide coating was prepared in the vessel described in Example 1. Container contains 195 g of titanium powder (65%), 3 g of anthracene C ₁₄ H ₁₀ (1%), and ammonium bromide.
NH ₄ Br 1.5g (0.5%) and magnesium oxide
300 g of a mixture containing 100.5 g (33.5%) was charged. A powder mixture was prepared as in Example 1. The specimens were used as in Example 1 and placed in a container. The container containing the powder mixture and specimen was placed in a resistance furnace and heated to 560°C.
At this temperature, the specimens were carburized for 1.2 hours, resulting in carburization of their surfaces.

The carburized specimen was heated to 950°C at a rate of 2.4°/s. This temperature is the temperature at which the surface of the product becomes diffusion saturated with titanium. Diffusion saturation lasted for 1.8 hours. Once diffusion saturation with titanium was completed, the specimen was cooled to 500°C at a rate of 1.2°/s. Next, heating to the carburizing temperature, original carburization, heating to the diffusion saturation stage, and original diffusion saturation.
The above operations such as saturation proper) and cooling were repeated three more times. Then open the container and
The saturating powder mixture was subjected to regeneration and the specimens were tested in the usual manner to determine the physico-mechanical and physico-chemical properties of the deposited titanium-carbide coating.

Test results: - the carbide coating was dense, i.e. virtually pore-free; - the thickness of the carbide coating, 28.8 μm; - the microhardness of the carbide coating, 26.8 GPa; - the average height of the carbide crystals, 4.7 μm; - Hardness of the substrate, 4.2 GPa; - Minimum hardness in the lower zone, 4.2 GPa; - Relative wear rate, 18.2 g/m ² s.

Example 3 A diffusion carbide coating was prepared in the vessel described in Example 1. In a container, silicon powder 195g (65%), naphthalene C ₁₀ H ₈ 3g (1%), ammonium iodide
NH ₄ I 1.5g (0.5%) and aluminum oxide
300 g of powder mixture containing 100.5 g (33.5%) of Al ₂ O ₃
was loaded. A powder mixture was prepared as in Example 1. The test specimens were used and placed in a container just as in Example 1. The container containing the powder mixture and the test piece immersed therein was then placed in a resistance furnace and heated to 720°C. At this temperature, the specimen was carburized for 0.6 hours.
The surfaces of these test pieces were carburized. Next, the carburized specimen was heated to 1100°C at a speed of 0.8°/s.
heated to. This temperature is the temperature at which diffusion is saturated by silicon on the surface of the test piece. Diffusion saturation was performed for 1.2 hours. Once diffusion saturation with silicon was completed, the specimen was cooled to 300°C at a rate of 2.4°/s. Then heating to carburizing temperature, original carburizing,
The above operations of heating to the stage of diffusion saturation, original diffusion saturation, and cooling were repeated seven more times.
The container was then opened, the powder mixture was directed for regeneration, and the specimens were tested to determine the physico-mechanical and physico-chemical properties of the deposited silicon carbide coating.

Test results: - the carbide coating was dense, i.e. practically pore-free; - the thickness of the carbide coating, 39.8 μm; - the microhardness of the carbide coating, 22.3 GPa; - the average height of the carbide crystals, 4.3 μm; - Hardness of the substrate, 7.4 GPa; - Minimum hardness of the lower zone, 7.4 GPa; - Relative wear rate, 20.9 g/m ² s.

Example 4 A diffusion carbide coating was deposited in the container described in Example 1. Container contains chromium powder 195g (65%), polyvinyl chloride 3g (1%), ammonium fluoride
NH ₄ F 1.5g (0.5%) and magnesium chloride
300 g of a powder mixture containing 100.5 g (33.5%) of MgO was charged. A powder mixture was prepared as in Example 1. The specimens were also used and placed in a container as in Example 1. The container containing the powder mixture and specimen was placed in a resistance furnace and heated to 600°C. At this temperature, the specimen was allowed to carburize for 1.1 hours, and the carburized specimen
It was heated to 1000°C at a rate of 2.1°/s. At this temperature, the surface of the specimen was diffusion saturated with chromium. Diffusion saturation was performed for 1.7 hours. After diffusion saturation with chromium is completed, the specimen is moved at 2.1°/s.
It was cooled down to 450°C at a rate of . Next, the above operations of heating to the carburizing temperature, original carburizing, heating to the stage of diffusion saturation, original diffusion saturation, and cooling were repeated four more times. The container was then opened, the saturating powder mixture was directed for regeneration, and the specimens were tested to determine the physico-mechanical and physico-chemical properties of the deposited chromium carbide coating.

Test results: - the carbide coating was dense, i.e. virtually pore-free; - the thickness of the carbide coating, 23.7 μm; - the microhardness of the carbide coating, 22.0 GPa; - the average height of the carbide crystals, 5.4 μm; - Hardness of the substrate, 5.6 GPa; - Minimum hardness of the lower zone, 5.6 GPa; - Relative wear rate, 15.6 g/m ² s.

Example 5 This example uses a regenerated powder mixture of composition according to Example 1 and is utilized according to Example 1.

Once the process was completed, the powder mixture was regenerated. For this purpose, the powder mixture was ground in a geocrusher and sieved through a vibrating sieve with a mesh size not exceeding 50 .mu.m in order to obtain a powder portion with a particle size not below 50 .mu.m. Once the mixture was sieved, it was dried at 140°C for 4 hours. 266.5 g (88.8%) of this mixture was then added with the following ingredients: diphenyl pre-dried for 0.5 h at 60°C.
3.3 g (1.1%) of C ₁₂ H ₁₀ , 1.65 g (10%) of ammonium chloride first dried at 140° C. for 4 hours, 19.5 g (6.5%) of dry chromium powder and 9.05 g (3%) of dry aluminum oxide. Added. All ingredients were then carefully mixed and the prepared powder mixture was charged into the container described in Example 1. The specimen described in Example 1 was placed in a container containing the powder mixture, and the container was placed in a resistance furnace. Heat the container to 630℃,
The specimens were carburized at this temperature for 0.9 hours.
The surface of the specimen was saturated with carbon. The carburized specimen was then heated to 1020°C at a rate of 1.5°/s.
This temperature is the temperature at which the surface of the specimen undergoes diffusion saturation with chromium. The step of diffusion saturation with chromium is carried out for 1.4 hours. The specimen was then cooled to 350°C at a rate of 2.2°/s. Finally, the above operations of heating to the carburizing temperature, carburizing, heating to the stage of diffusion saturation, original diffusion saturation, and cooling were repeated once more. The container was then opened, the saturating powder mixture was directed for regeneration, and the specimens were tested for physico-mechanical and physico-chemical properties of the deposited chromium-carbide coating.

Test results: - the carbide coating was dense, i.e. virtually pore-free; - the thickness of the carbide coating, 20.9 μm; - the microhardness of the carbide coating, 22.5 GPa; - the average height of the carbide crystals, 5.1 μm; - Hardness of the substrate, 4.2 GPa; - Minimum hardness of the lower zone, 4.2 GPa; - Relative wear rate, 14.1 g/m ² s.

Example 6 This example shows the deposition of a diffusion carbide coating carried out according to previously known methods.

As in Example 1, a powder mixture was prepared and charged into a container, and a test specimen was placed into the container.

The container containing the powder mixture and specimen was placed in a resistance furnace and heated to 800°C. At this temperature, the specimens were carburized for 3.5 hours, allowing their surfaces to become carburized. Once the carburizing period is completed, the specimen is heated to the temperature of diffusion saturation, i.e.
Heated to 1050°C. At this temperature, the surface
Diffusion saturation was allowed for 3.5 hours. The container was then removed from the oven and allowed to cool to room temperature. After cooling, the container was opened, the powder mixture was sent for regeneration, and the specimens were tested to determine the physico-mechanical and physico-chemical properties of the deposited chromium carbide coating.

Test results: - the carbide coating is dense, i.e. does not have practically any pores; - the thickness of the carbide coating, 12.3 μm; - the microhardness of the carbide coating, 21.3 GPa; - the average height of the carbide crystals. , 7.1 μm; - hardness of the substrate, 6.4 GPa; - minimum hardness in the lower (decarburized) zone,
5.8 GPa; - Depth of decarburization zone, 17 μm: - Relative wear rate, 36.4 g/m ² s.

Comparing the physico-mechanical and physico-chemical properties of specimens with diffused carbide coatings deposited by the method proposed here and previously known methods, it is found that the physico-mechanical and physico-chemical properties obtained according to the invention It can be concluded that the physico-mechanical properties of the coated coatings are significantly higher than in the case of coatings applied according to previously known methods.

Thus, the wear resistance under abrasive conditions of a diffusion carbide coating produced in accordance with the disclosed invention is
The wear resistance is 2.8-3.3 times higher than that of diffusion carbide coatings produced by known methods. Moreover, products with diffused carbide coatings deposited by the method of the invention do not have any decarburization zone beneath the coating.

EFFECTS OF THE INVENTION Iron-carbon alloy articles with coatings deposited according to the disclosed method of the invention have high surface hardness up to 24.0 GPa, and have low sliding friction with coatings deposited by known methods. than in the case of products that receive
Wear resistance at sliding friction 1.3−1.5 times higher than in the case of coatings made by known methods, 2.8−
Features 3.3 times higher abrasion resistance. The coatings obtained by the process of the invention have a thickness of up to 35 μm and are virtually free of any pores and without any decarburization zone beneath the coating.

According to the invention, in order to make particularly important parts,
It became possible to use ordinary carbon steel instead of expensive high alloys. This saves on hard-to-obtain high alloys. Depending on the usage and conditions of use of the product, the service life of the product can be extended by a factor of 2-10.

Claims (1)

[Claims] 1. A powder mixture containing solid components such as carbide-forming elements, carbon-containing compounds, activators, and inert fillers is charged to a container, and an iron-carbon alloy product is placed in the mixture. heating the products to a carburizing temperature of their surfaces; causing the surfaces of the products to be carburized at the carburizing temperature; heating the carburized products to a temperature of diffusion saturation of their product surfaces with carbide-forming elements; A method for applying a diffusion carbide coating to an iron-carbon alloy product comprising diffusion saturating the surface of the product with a carbide-forming element at a temperature selected within the range from 950 to 1100°C, comprising: carburizing the surface of the product; heating the carburized product to a diffusion saturation temperature selected from within 950 to 1100°C at a temperature selected from 560 to 720°C for a period of time selected from 0.6 to 1.2 hours; be carried out at a speed of 2.4°/s; the diffusion saturation of the product surface by carbide-forming elements is
carried out at a temperature selected within the range of 950 to 1100°C for a time selected from 1.2 to 1.8 hours; after diffusion saturation of the product surface, the product
be cooled to a selected temperature within the range 300 to 500°C at a rate selected from 2.4°/s; the above operations are repeated at least once, starting with heating the product to the carburizing temperature; A method for depositing a diffusion carbide coating on an iron-carbon alloy product characterized by: 2. A method for applying a diffusion carbide coating to an iron-carbon alloy product according to claim 1, characterized in that said operation is repeated up to seven times.