Steel surface decarburizing method for finishing the surface of steel parts with smoothing

Abstract

The invention relates to the mechanical engineering industry and can be used for the production of articles as a finishing operation in order to achieve the smoothness of the steel surface of the articles, increase the resistance to wear and corrosion. The method of decarburization a hardened steel surface for finishing surface of steel articles with smoothing, comprises the steps of (i) providing one or more steel surfaces, at least of which is to be treated; (ii) introducing a decarburization agent between two contacting surfaces, at least of which is to be treated; (iii) compressing said surfaces together and moving them relative to each other, resulting in decarburization and smoothening of the treated steel surface. An introduction of the decarburization agent between the two contacting surfaces at the step (ii) can be made gradually or at once. The decarburization agent can be introduced between the two contacting surfaces at the step (ii) so that the surfaces to be treated are entirely covered with the decarburization agent. According to the preferred embodiment the force applied to compress the surfaces together at the step (iii) can be selected in the range of 0.5-2.5 kg / cm2.

Description

[0001] STILL SURFACE DECARBURIZING METHOD WITH SMOOTHING

[0002] Technical Field

[0003] The invention relates to the mechanical engineering industry and can be used for the production of articles as a finishing operation in order to achieve the smoothness of the steel surface of the articles, increase the resistance to wear and corrosion.

[0004] Background Art

[0005] Decarburization, or decarbonization is a process that reduces the amount of carbon constituents in a material, usually steels. Typically, decarburization occurs when the metal is heated to temperatures above 700 °C and when carbon in the metal reacts with gases containing oxygen or hydrogen. The removal of carbon removes hard carbide phases resulting in a softening of the metal, primarily atthe surfaces which are in contact with the decarburizing gas. Decarburization may have desirable or adverse effects. In general, the decarburization mechanism can be described as three events: the reaction at the steel surface, the interstitial diffusion of carbon atoms and the dissolution of carbides within the steel.

[0006] There is known a cast iron member surface decarbonization device and decarburization process (CN104831341A). The known process is carried out by hydrolysis, transferring carbon from the casting surface to the molten salt. The process is only applicable to steel castings.

[0007] KR20010060769 describes a method for improving the surface of steel wires during their manufacture. The known method provides for decarburizing steel wire rod for rail clip by heating it to 900-970 °C and its subsequent air-cooling. The method is only applicable for manufacturing of the steel wire in varnish. The surface decarburization of carbon-containing alloys described in CA528602A involves heating an article at a temperature of 1050 °C to 1300 °C and subjecting such an article to a gaseous mixture of hydrogen and hydrogen chloride. The implementation of the known method requires complex equipment. The process takes place at high temperatures, which causes undesirable changes in the article’s properties.

[0008] There is also known a surface decarburizing method described in US5628837, where an article is placed on a protective environment, heated in this environmentto a temperature of 600-1100 °C, and maintaining this temperature for a period of 15-120 minutes. The known method is relatively complicated and requires complex equipment. Processing takes place at elevated temperatures, which significantly affects the properties of an article, which it can be subjected to deformation during cooling. Moreover, not only the surface of the article is subject to deformation, but also its deepest layers.

[0009] Summary of the Invention

[0010] The object of the invention is to overcome the drawbacks of the prior art solutions and to achieve the smoothness, wear resistance and corrosion resistance of a surface of a steel article by means of a single finish operation, without the need of any surface polishing or any other additional treatment. This set goal is achieved by the proposed method of decarburization a hardened steel surface for finishing surface of steel articles with smoothing, comprising the steps of (i) providing one or more steel surfaces, at least of which is to be treated; (ii) introducing a decarburization agent between two contacting surfaces, at least of which is to be treated; (hi) compressing said surfaces together and moving them relative to each other, resulting in decarburization and smoothening of the treated steel surface. An introduction of the decarburization agent between the two contacting surfaces at the step (ii) can be made gradually or at once. The decarburization agent can be introduced between the two contacting surfaces at the step (ii) so that the surfaces to be treated are entirely covered with the decarburization agent. According to the preferred embodiment the force applied to compress the surfaces together at the step (hi) can be selected in the range of 0.5-2.5 kg / cm2. The decarburization agent can be a powder selected from the group consisting of steel powder, aluminium powder, magnesium powder, copper powder, a mineral powder or a combination thereof. The decarburization agent is preferably a powder, having particles size in the range of 3-100 pm, preferably, 3-10 pm. If the decarburization agent selected comprises a mineral powder, it should have hardness under the Mohs’ hardness scale in the range of 1-5.

[0011] The method may optionally comprise the step of controlling and maintenance a temperature during movement of the treated surfaces relative to each other at the step (hi), so that the temperature on the treated surfaces is kept in the range of 800°C and 900°C.

[0012] According to yet another embodiment of the invention a carrier means can be introduced between the two contacting surfaces before, simultaneously with, or after introduction of the decarburization agent. Said carrier means can be oil, gel or a combination thereof.

[0013] Brief Description of Drawings

[0014] Fig. 1 is a picture of a steel surface polished with stone having 125pm grain;

[0015] Fig. 2 - a picture of a steel surface polished with a polishing paste having 0.3-0.1pm grain; Fig. 3 - ground surface during the decarbonisation and simultaneous ironing process;

[0016] Fig. 4 - electron microscope image of the ground surface during the decarbonization and simultaneous ironing process;

[0017] Fig. 5 - a surface smoothed during the decarbonisation and simultaneous ironing process;

[0018] Fig. 6 - smoothed surface profile;

[0019] Fig. 7 - decarbonized surface with amorphous layer scratching;

[0020] Fig. 8 - a decarbonized surface with a deep scratch of the amorphous layer reaching the granular base metal;

[0021] Fig. 9 - partially decarbonized surface with corrosion areas. Detailed Description of the Invention

[0022] The method of decarburization a hardened steel surface for finishing surface of steel articles with smoothing, comprising the steps of (i) providing one or more steel surfaces, at least of which is to be treated; (ii) introducing a decarburization agent between two contacting surfaces, at least of which is to be treated; (hi) compressing said surfaces together and moving them relative to each other, resulting in decarburization and smoothening of the treated steel surface.

[0023] Once the effective amount of decarburization agent has been placed between the two surfaces, they are compressed with a certain force (e.g. 0.5-2.5 kg / cm2) and moved relative each other, causing decarburization and smoothening of the treated steel surface. The placement of the decarburization agent between the two surfaces can gradual or whole amount at once. The decarburization agent can be different (specially prepared powder of iron, aluminium and certain other metals or various minerals), which is introduced between the surfaces to be treated, optionally with aid of the carrier means. The decarburization agent should preferably have particles size in the range of 3-100 pm, preferably, 3-10 pm. The minerals, comprising in the decarburization agent should preferably have hardness on the Mohs’ hardness scale in the range of 1-5.

[0024] The decarburization agent can be introduced between the two contacting surfaces before, after, or together with carrier means. The carrier means can be selected from the group consisting of oil, gel or a combination thereof. The aim of the carrier means is to carry (transport) the decarburization agent and simultaneously cool the surfaces to be treated.

[0025] The substances of the decarburization agent and the carrier means are selected depending on the required end result and the properties of the surface to be treated. The method i.a. has been tested for carbon steel hardened parts with hardness HRC 20 - 70. The treatment time and the decarburization agent differ depending on the hardness, but the result is analogous. When the dispersed particle of the decarburization agent gets between the compressed surfaces, which are moving towards each other, it is either being deformed or destroyed. As a result, heat is released. According to the invention, it should be preferably in the range of 800-900 °C. Various substances of the decarburization agent comply to this temperature criteria. Each individual particle decarbonizes a point of its size on both moving surfaces. Due to introduction of the effective amount of the decarburization agent there are many such points. They preferably completely cover the surfaces to be treated during processing. The carrier means simultaneously cools the surfaces to be treated. Only the individual points on the surface heat up temporarily until they have cooled down with the carrier means. The articles, which surfaces are treated practically do not heat up. They do not change their properties after treatment and are fully usable without further treatment. The only thing that is changed is their surfaces. They become smooth. The surfaces now have a modified structure - it is an amorphous metal. This means that pitting of the metal due to friction is not happening. Generally, hard, hardened articles with high hardness are not resistant to microcracks, which cause these articles to break under impulse loads. Because even when polishing them with fine-grained pastes, scratches are formed from the abrasive of these pastes, which, although not as deep as grinding, also promotes the formation of microcracks (Fig. 1-2).

[0026] The surface treatment process is as follows. Decarburization agent is introduced between two surfaces, where at least one is to be treated. The amount of the decarburization agent between the surfaces has to be effective. If it is too little, then the process will not happen. If there is too much of the decarburization agent, the pressure will be distributed to all particles in contact between the plates. The pressure on each of them will be insufficient to release the required heat in case of deformation and / or destruction and reach the required 800-900 °C. As the particles are of different sizes, the larger ones will be compressed first and then the rest. This allows a wider range of decarburization agent to be placed. One or more articles are provided with a ground surface (e.g. abrasive grain size 125pm) and matched with an opposite surface, which can be another article, which surface is to be treated, or a tool used for treatment of an article’s surface. The configuration of the second surface can completely replicate the surface of the article to be treated, or it can be a rotating body that slides along the surface to be treated and thus compresses the decarburization agent’s particles. There may be a difference between the hardness of the surface to be treated and the tool’s surface. If two flat surfaces or two cylindrical surfaces, which are in contact in operation are treated, a decarburization agent is introduced between them and they are smoothed together (Fig. 3, 4).

[0027] At the start of the treatment process, the decarburization agent’s particles contact the protrusions of the part and decarbonize the individual contact points. The carbon-free metal at these points has become amorphous and accordingly soft. When the entire surface of the protrusion is decarbonized, it smoothes and fills the gaps with amorphous metal (Fig. 3, 4). The result is a very smooth surface with a roughness of a few tens of nm (Fig. 5, 6). Some characteristics of the height profile of Fig. 6 are shown in Table 1.

[0028] Table 1. Characteristics of the height profile show on Fig. 5

[0029] By continuing the ironing process, the surface roughness can be further reduced compared to the ones shown in the pictures (Fig. 5). The properties of the surface treated are characterized by scratching with a hard, hardened steel needle. The pictures (Fig. 7, 8) show that the top layer is soft, amorphous and is scraped along the edges of the scratch. Approximating the microscope objective to the sample, it can be seen that where the needle touches the solid base layer, there is a grainy structure, which indicates that only a thin surface layer is decarbonized. The thickness of this layer can reach up to a few nm. Thus, it does not affect the properties of the article, but only removes the graininess of the surface and eliminates sanding marks, significantly reduces the possibility of microcracks and increases corrosion resistance. Ifthe amorphous layer in friction pairs is thick enough, then even if an abrasive grain enters it, it will only leave an indentation on the surface, which will be smoothed out during the work after the grain has been removed. There will be no surface crushing or adhesion with subsequent avalanche wear.

[0030] The formed amorphous layer has a high resistance to corrosion. The Fig. 9 shows that the part of the part that has been treated has not corroded while in the water for 24 hours, but the untreated part has corroded. The part was degreased before immersion into the water.

[0031] Judging by the fact that the surface roughness can be achieved within a few nanometers, the individual crystals of the base metal are also decarbonized gradually and it is possible to smooth these crystals in parts. Half of the crystal remains hard, while the other half becomes amorphous and fills the adjacent abrasive scratches and other irregularities.

[0032] Friction pairs that have undergone decarbonisation due to surface smoothness retain the boundary layer of grease on their surfaces even when the movement is complete and there is no longer a dynamic layer of grease, because the pressure on the surface units is low surfaces.

[0033] If it is necessary for the part to have no amorphous metal layer on the surface, then it can be treated by spark carbonization or some other carbonation method, restoring the surface hardness. The surface thus smoothed is i.a. suitable for coating with graphene.

Claims

8Claims1. A method of decarburization a hardened steel surface for finishing surface of steel articles with smoothing, comprising the steps of(i) providing one or more steel surfaces, at least of which is to be treated;(ii) introducing a decarburization agent between two contacting surfaces, at least of which is to be treated;(hi) compressing said surfaces together and moving them relative to each other, resulting in decarburization and smoothening of the treated steel surface.

2. The method according to claim 1, wherein the force applied to compress the surfaces together at the step (hi) is selected in the range of 0.5-2.5 kg / cm2.

3. The method according to any preceding claims, wherein the decarburization agent is a powder selected from the group consisting of steel powder, aluminium powder, magnesium powder, copper powder, a mineral powder or a combination thereof.

4. The method according to claim 3, wherein the decarburization agent is a powder, having particles size in the range of 3-100 pm, preferably, 3-10 pm.

5. The method according to claim 3, wherein the decarburization agent comprises a mineral powder having hardness on the Mohs’ hardness scale in the range of 1-5.

6. The method according to claim 1, wherein introduction a decarburization agent between the two contacting surfaces at the step (ii) is made gradually.

7. The method according to claim 1, wherein introduction a decarburization agent between the two contacting surfaces at the step (ii) is made so that the surfaces to be treated are entirely covered with the decarburization agent.

98. The method according to any preceding claims, wherein a carrier means is introduced between the two contacting surfaces before, simultaneously with, or after introduction of the decarburization agent.

9. The method according to claim 8, wherein the carrier means is selected from the group consisting of oil, gel or a combination thereof.

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