RU2539128C1 - Method for surface boration of parts from steel 40 - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: first, preliminary local surface boration is performed using laser heating from a coating material containing boron or its compounds. Then, thermodiffusion boron saturation process is performed at heating to the temperature T=850-950°C with exposure during 3-4 hours.

EFFECT: reduction of brittleness of borated layers; reduction of duration and temperature of a thermodiffusion saturation process of surface of parts at maintaining high hardness.

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Description

The invention relates to the field of metallurgy and mechanical engineering, in particular to combined methods of surface hardening of metals, and can be used in the manufacture of parts operating under conditions of wear in aggressive environments, as well as parts exposed to aggressive environmental influences during operation.

A known method of laser alloying the surface of low-carbon and medium-carbon alloy steels with boron. Saturation of the surface with boron is carried out using laser heating, the essence of which is to melt a portion of the steel surface together with a slip containing boron previously applied to the treated area (see Rykalin N.N., Uglov A.A., Kokora A.N. Laser processing of materials. ”-M.:“ Mechanical Engineering ”, 1975, p.296).

The method allows, by varying the options, processing conditions and coating thickness, it is possible to obtain doped layers with different phase composition and structure, and therefore with different properties. To increase the wear resistance, it is advisable to carry out processing without overlapping, which creates a surface morphology that satisfies the Charpy principle. To achieve the corrosion resistance of the surface layer, it is necessary to carry out overlapping processing, which is associated with additional time and energy costs and is not always economically justified.

The disadvantage of this method is the increased fragility of the hardened layer due to the high hardness of iron borides.

Closest to the claimed method according to the technical essence is the method of boronation of steel parts adopted as a prototype by thermal diffusion saturation of the surface with boron, which consists in applying a coating containing the alloying element to the surface of the part and holding it in an oven at a temperature of T = 950-1150 ° C for 6-10 hours, followed by cooling in the furnace (see L. G. Voroshnin. “Boroning of industrial steels and cast irons.” - Minsk: “Belarus”, 1981, S. 19-21).

The disadvantage of this method is the duration of the process, high temperatures, while borated layers are brittle.

The technical problem solved by the present invention is to reduce the fragility of the diffusion layer, reducing the duration and temperature of the process of thermal diffusion saturation of the surface of parts of steel 40 while maintaining high hardness.

The specified technical problem is solved by the fact that in the method of surface boronation of parts made of steel 40, which consists in thermal diffusion saturation of the surface with boron of parts with a coating applied to their surface containing boron or its compounds, including heating the prepared parts to a given temperature, holding and cooling, according to the invention Initially, a preliminary surface local boronization process is carried out using laser heating from the coating, and subsequent thermal diffusion saturation lead when heated to a temperature T = 850-950 ° C where it was held for 3-4 hours.

The solution of the technical problem is achieved due to the fact that initially carry out the process of preliminary surface local boration, using laser heating of the prepared parts. As a result, local boron regions are formed which, at the stage of thermal diffusion saturation during heating and holding, accelerate surface diffusion processes. In this case, the diffusion of alloying elements occurs both on the surface and deep into the part. Due to the preliminary laser action, a local process of preliminary diffusion of boron occurs, which allows the process of thermal diffusion saturation at lower temperatures and lower shutter speed, while maintaining high hardness due to the high concentration of the alloying element in the surface layer.

The method of surface boronation of parts made of steel 40 consists in thermal diffusion saturation of the surface with boron. First, a coating containing boron or its compounds is applied to the surface of the parts. The process of thermal diffusion saturation includes heating the prepared parts to a predetermined temperature, holding and cooling in the furnace. According to the invention, at the initial stage, a preliminary surface local boration process is carried out using laser heating from plaster. Then, subsequent thermal diffusion saturation is carried out in the furnace when heated to a temperature of T = 850-950 ° C with holding for 3-4 hours, followed by cooling in the furnace.

The proposed method is implemented as follows.

Initially, a preliminary surface local boration process is carried out using laser heating. Before this, a coating is applied to the surface of the parts, consisting of a suspension consisting of amorphous boron powder, pure carbon and a binder, for example, zaponlak or BF-2 glue. Then a laser beam is applied to the surface. As a result of heating, local doped regions are formed that accelerate the processes of surface diffusion during subsequent thermal diffusion saturation, which is carried out by heating the prepared parts in a furnace to a temperature of T = 850-950 ° C with holding for 3-4 hours. This is followed by cooling parts together with the furnace to room temperature. Thus, during processing, boron diffusion occurs both on the surface and in the interior of the part.

This method of surface doping allows one to obtain a diffusion layer with a boride zone 150 μm thick and a transition zone 50 μm thick is formed.

To compare the proposed method with the prototype, studies were carried out on sample parts made of steel 40 subjected to thermal diffusion without prior laser alloying and laser alloying. Feasibility and advantages of the proposed method can be considered in the examples below.

Examples

1. The processing of parts-samples of steel 40 subjected to thermal diffusion saturation, according to the method described in the prototype: the prepared parts-samples were heated to a temperature T = 1000-1150 ° C, kept for 6-10 hours, then cooled in an oven. The thickness of the diffusion layer was 150 ... 250 μm, and the microhardness was 13500 ... 15000 MPa.

2. Processing of sample parts made of steel 40 subjected to thermal diffusion boarding without prior alloying with a laser according to the proposed method: the prepared sample parts were heated to a temperature of T = 850 ° C, held for 3-4 hours, then cooled in an oven. The thickness of the diffusion layer was 50 ... 70 μm, and the microhardness was 9000 ... 10000 MPa.

3. Processing of sample parts from steel 40 subjected to thermal diffusion with laser doping according to the proposed method: the prepared sample parts were heated to a temperature of T = 850 ° C, held for 3-4 hours, then cooled in an oven. The thickness of the diffusion layer was 170 ... 300 microns, i.e. increased due to diffusion of the alloying element from the zones of laser alloying, and microhardness - 13500 ... 15000 MPa.

4. The processing of parts-samples of steel 40 subjected to thermal diffusion with laser doping according to the proposed method: the prepared parts-samples were heated to a temperature of T = 900 ° C, kept for 3-4 hours, then cooled in an oven. The thickness of the diffusion layer was 190 ... 350 microns, i.e. increased due to further diffusion of the alloying element from the zones of laser alloying, and microhardness - 13500 ... 15000 MPa.

5. The processing of parts-samples of steel 40 subjected to thermal diffusion with laser doping according to the proposed method: the prepared parts-samples were heated to a temperature of T = 950 ° C, kept for 3-4 hours, then cooled in an oven. The thickness of the diffusion layer was 200 ... 370 μm, and the microhardness was 13500 ... 15000 MPa.

6. Processing of sample parts made of steel 40 subjected to thermal diffusion with laser alloying according to the proposed method: the prepared sample parts were heated to a temperature of T = 1000 ° C, held for 3-4 hours, then cooled in an oven. The thickness of the diffusion layer was 380 μm, and the microhardness was 12000 MPa. A further temperature increase of more than 950 ° C leads to some slowdown in the growth rate of the diffusion layer due to a decrease in the concentration of the alloying element in the zones of laser alloying.

7. Processing of sample parts made of steel 40 subjected to thermal diffusion with laser doping according to the proposed method: the prepared sample parts were heated to a temperature of T = 1100 ° C, held for 3-4 hours, then cooled in an oven. The thickness of the diffusion layer was 400 μm, and the microhardness was 10,000 MPa. An increase in temperature of more than 1000 ° C leads to a decrease in the microhardness of the alloyed layer due to the growth of austenite grain and a sharp decrease in the concentration of the alloying element from the surface deeper.

The research results are shown in the table.

 Example No. T, ° С t hour h, μm Microhardness (MPa) to a depth of 100 microns 1. Prototype 1000-1150 6-9 150 ... 250 15500 ... 21500 2. Thermodiffusion boration without laser alloying 850 3-4 50 ... 70 9000 ... 10000 3. The proposed method 3 170 850 3,5 230 13500 ... 15000 four 300 4. The proposed method 3 190 900 3,5 270 13500 ... 15000 four 350 5. The proposed method 3 200 950 3,5 285 13500 ... 15000 four 380 6. The proposed method 1000 3-4 380 12000 7. The proposed method 1100 3-4 400 10,000

The table shows that the thickness of the diffusion layer without preliminary doping with a laser does not exceed 70 microns, and with zones of laser doping - 190 ... 380 microns. The microhardness of the alloyed layer after combined treatment is 13500 ... 15000 MPa. An increase in temperature of more than 950 ° C leads to an increase in the thickness of the diffusion layer, however, the growth rate of the thickness of the diffusion layer decreases, while the hardness decreases slightly. The optimal temperature range is 850-950 ° C from the point of view of maintaining high hardness and high concentration of the alloying element of the surface layer.

The table also shows that the claimed method in comparison with the prototype allows to achieve large values of the thickness of the diffusion layer while reducing the duration of the process of thermal diffusion boration to 3-4 hours at a temperature T = 850-950 ° C while maintaining high hardness.

Thus, the invention allows to obtain an increase in the thickness of the diffusion layer, to reduce the duration and reduce the temperature of the thermal diffusion boronation of the surface of parts made of steel 40, while reducing the fragility of the layer while maintaining high hardness.

Claims (1)

The method of surface boronation of parts made of steel 40, including thermal diffusion saturation with boron of the surfaces of the parts by applying a coating of boron or its compounds on their surface, heating the prepared parts to a predetermined temperature, exposure and cooling, characterized in that they initially carry out a process of preliminary surface local boronization with using laser heating from the said coating, and subsequent thermal diffusion saturation is carried out when heated to a temperature of T = 850-950 ° C with Coy for 3-4 hours.