RU2198954C2 - Method of hardening parts surfaces - Google Patents

Abstract

FIELD: hardening of parts; applicable for increasing wear resistance of friction surfaces. SUBSTANCE: method includes cold plastic deformation of surface, its subsequent thermochemical treatment. In so doing, surface to be hardened is subjected to plastic deformation with continuous supply of radical-forming substance to zone of deformation up to attainment of preset value of cold-work hardening of surface layer material. Then part is heated up to temperature of chemical modification of radical-forming substance at which destruction of its molecules takes place, and part is held at said temperature with continuous supply of radical-forming substance for period of time required for limited saturation of hardened surface layer with radicals. EFFECT: formation of strong, wear- and corrosion-resistant layer on surface of part. 1 tbl

Description

 The invention relates to hardening processing of parts and can be used to increase the wear resistance of friction surfaces.

 Known methods of mechanical hardening of the surface layers of metals and alloys, based on surface plastic deformation (PPD) [1], in which the increase in mechanical characteristics is achieved due to hardening, grinding grain, the formation of favorable texture and residual stresses in the surface layer. One of the important disadvantages of mechanical hardening is a decrease in the corrosion resistance of rubbing surfaces.

 Known methods for increasing the strength of the surface layers by chemical-thermal treatment (CTO): nitriding, cementation, etc. [2]. In this case, diffusion processes occur on the surface, during which the crystal lattice of metal grains in the surface layer is saturated with interstitial atoms, which create an energy barrier for the formation and slip of a dislocation. Surface layers treated in this way are characterized by high strength and corrosion resistance. A significant drawback of XTO is the energy intensity and processing time.

 The prototype of the invention is a method of combined mechanical and chemical-thermal effects [3] on hardened surfaces, in which, to increase the wear resistance of parts of friction units, a grid of hexagonal channels is applied to the working surface by deformation shaping, after which the samples are nitrided. In this case, the process of chemical-thermal treatment is intensified and the depth of the diffusion zone increases.

 The specified method has the disadvantages noted above.

 The essence of the invention lies in the fact that the process of saturation with interstitial atoms produced during XTO is proposed to be replaced by the process of diffusion saturation of the surface layer with radicals during the mechanical-thermal treatment.

 The proposed method uses radicals generated during the destruction of lubricants, which, as you know, are a chain of chemically bonded atoms containing an incomplete atomic bond at the end, which determines their high strength and chemical activity. The sizes of the radicals are larger than the atomic ones; therefore, their penetration into the crystal lattice by ordinary diffusion is difficult, however, radicals can penetrate deeper into the surface layer through larger material defects located at the grain boundaries or at the pits of dislocations that surface. The radicals migrate deeper into the surface layer due to their own excess free energy of radicals, dislocation nuclei, grain boundaries and proceeds according to the principle of minimum free energy. In addition, this process is intensified due to the mechanical activation of the material during its surface deformation.

 The observed effect of increasing the strength of the surface layer is due to the "reinforcement" of the surface layer material with chains of radical atoms, the bond strength of which exceeds the metal one, as well as the barrier action of the introduced radicals on the formation and sliding of new dislocations, which prevents the accumulation of defects and slows down the development of fatigue and destruction of the material.

 The formation of radicals on a metal surface in the proposed method is carried out by initiating the destruction of long molecules of organic compounds during mechanical and thermal effects due to mechanical grinding of molecules and their thermal decomposition. In both cases, the dissociation of the weakest covalent bonds in the chain of principal valencies is observed, and the metal surface has a catalytic effect on the destruction of adsorbed molecules.

 The claimed method of hardening metal surfaces is carried out in the following steps.

 1. Produce cold surface plastic deformation of the workpiece in any traditional way (rolling by ball, roller, vibratory rolling, etc.) in a medium of a radical-forming substance. At this stage, a favorable texture, microrelief is formed, activation and mechanical hardening of the surface layer takes place, as well as partial saturation of the surface with radicals formed during the mechanical destruction of the molecules of the radical-forming substance in the contact zone of the indenter (ball, roller) with the surface. In addition, during plastic deformation of the surface layer, a large number of dislocations are formed that promote the introduction of radicals in the next stage of processing.

 2. Without removing a layer of a radical-forming substance from the surface, the workpiece is heated to a temperature close to the temperature of the chemical modification of this substance, at which the destruction of the molecules begins, and active centers - radicals appear, which are separate fragments of the original molecule with incomplete atomic bonds. In addition, heating promotes intense interaction of radicals with the treated surface. In this case, the bulk of the radicals penetrates the surface layer, strengthening it, and some of the radicals oxidize, forming a lacquer film on the surface, or evaporate into the atmosphere. The speed and method of heating the part must ensure uniform and quick heating of the surface, so as not to cause tempering of the metal. After hardening is completed, mechanical or chemical cleaning of the treated surface from traces of soot is carried out.

 As a result of the described method, a durable, wear-resistant corrosion-resistant layer of the material of the part is formed on the surface.

 As radical-forming substances, industrial lubricants are used. With the PPD of the workpiece, they simultaneously serve as a cutting fluid, and with thermal degradation it is a radical-forming material.

 To increase the temperature resistance, an antioxidant additive is added to the lubricant, which prevents the unwanted reaction of radicals and juvenile surface areas with oxygen dissolved in the lubricant.

 The temperature stability of the radical-forming liquid is increased because the oxidized radicals turn into varnishes, and the oxide film formed on the surface prevents the diffusion of radicals, which turns the proposed process into a known method of surface burnishing.

 In the patent [4], the proposed method is used for a control procedure - estimating the activation energy of thermomechanical destruction of lubricants, since the destruction of lubricants on a metal surface causes an increase in the activation energy of plastic deformation of the surface layer material by an amount characterizing the bond strength of the molecules of the tested lubricant. In the claimed method, this effect is used to harden the surfaces of parts.

 Implementation example.

 Samples of steel 12X18H10T in an amount of 10 pcs. (material in the delivery state) was processed by grinding on a surface grinding machine, and then rubbed on a cast-iron plate to obtain a high-quality contact plane.

 After grinding, Vickers microhardness and the activation energy of plastic deformation of the surface layer by sclerometry were evaluated. The activation energy of plastic deformation was calculated as the specific work spent on plastic displacement of 1 mole of the substance of the surface layer.

Then, the samples were subjected to plastic deformation (PPD) by rolling a ⌀10 mm ball, the load on the 100N ball in a medium of a radical-forming liquid (industrial oil I-40A). After PPD, the samples were heated in the same oil at T = 200 ^° C for 10 minutes. Then, according to the same methodology, the activation energy of plastic deformation of the surface layer after hardening by the proposed method, the SHS method and explosion hardening was evaluated. The results of evaluating the effectiveness of the proposed method are shown in the table.

LITERARY SOURCES
1. Hardening and finishing of parts by surface plastic deformation / Reference. -M .: Mechanical Engineering, 1987. -328 p.

 2. Chemical-thermal treatment of metals and alloys / Reference. -M .: Metallurgy, 1981. -424 p.

 3. A.S. 1497269, “Method for hardening the surface of parts” // Gromakovsky D. G., Kirilenko L.N., Otrazhiy V.I., Kuritsyn V.N., class. C 23 C 8/24, 8/26, 1987

 4. RF patent 2119165. "A method for evaluating the activation energy of thermomechanical destruction of lubricants" / Gromakovsky DG, Belenkikh EV, Ibatullin I.D., Karpov A.S., Kovshov A.G., Sorokin A. N., Torrens A.A .; publ. 09/20/98, Bull. //Discoveries. Inventions. 1998

Claims (1)

 The method of hardening the surfaces of parts, which consists in the fact that the surface is subjected to cold plastic deformation, and then thermo-chemical treatment, characterized in that the hardened surface is subjected to plastic deformation by continuously supplying a radical-forming substance to the deformation zone until a predetermined hardening value of the surface layer material is achieved, and then the part is heated to the temperature of the chemical modification of the radical-forming substance, at which the destruction begins of molecules, and is kept at this temperature part with a continuous feed of radical substances for the time required for the saturation limit radicals hardenable surface layer.

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