Heat treatment method for high-carbon chromium bearing steel

Abstract

The invention discloses a heat treatment method of high-carbon chromium bearing steel, which comprises the following steps: step 1, carrying out spheroidizing annealing treatment on a high-carbon chromium bearing steel raw material through a bearing part formed by forging or a steel pipe, heating the bearing part manufactured by turning forming to 840 + / -20 DEG C in a heat treatment furnace, keeping the temperature for 30-60 minutes, taking out the bearing part, and carrying out air cooling to room temperature; and secondly, the bearing part treated in the first step is reheated to 860 DEG C + / -20 DEG C through a surface induction heating method for induction quenching, then induction tempering is conducted, and an effective hardened layer is formed on the surface of the bearing part. According to the heat treatment method for the high-carbon-chromium bearing steel, through the first step and the second step, the heat treatment process of carburizing, quenching and tempering of carburizing steel can be effectively replaced.

Description

Technical Field

[0001] The invention relates to a heat treatment method, and more particularly to a heat treatment method for high carbon chromium bearing steel. Background Art

[0002] During the processing of bearing steel, heat treatment operations are required. The current existing method mainly uses high-temperature carburizing to achieve heat treatment. However, the existing high-temperature carburizing equipment has high investment and complex process. High-temperature carburizing may cause large deformation, especially in the ordinary carburizing process, due to the inevitable introduction of oxygen, it is easy to cause intergranular oxidation or the appearance of black structure. In order to reduce deformation and oxidation, a vacuum carburizing furnace is usually required, which increases the investment and maintenance cost of the equipment. The carburizing process requires strict control of temperature, time and carbon potential to ensure the expected structure and performance, which puts high demands on process control. At the same time, some carburizing processes may produce harmful gases, which require corresponding environmental protection measures to deal with. Summary of the invention

[0003] In view of the shortcomings of the prior art, the object of the present invention is to provide a high carbon chromium bearing steel heat treatment method which can reduce investment and maintenance costs and is more environmentally friendly.

[0004] To achieve the above object, the present invention provides the following technical solution: a high carbon chromium bearing steel heat treatment method, characterized in that it comprises the following steps: Step 1: subjecting the high carbon chromium bearing steel raw material to forging or steel tube forming bearing parts to spheroidizing annealing treatment, and heating the bearing parts manufactured by turning forming to 840±20°C in a heat treatment furnace and keeping the temperature for 30 to 60 minutes, and then taking out and air cooling to room temperature; Step 2: reheat the bearing parts processed in step 1 to 860°C ± 20 by surface induction heating for induction quenching, and then perform induction tempering to form an effective hardened layer on the surface of the bearing parts.

[0005] As a further improvement of the present invention, in step 1, the process is heated to 840±20° C. in a heat treatment furnace and kept warm for 30 to 60 minutes, and then rapidly cooled to room temperature using nitrogen.

[0006] As a further improvement of the present invention, the induction quenching equipment used in the step 2 includes a machine body and a quenching coil. The quenching coil is fixed on one side of the machine body and connected to the electrical components inside the machine body to receive the high-frequency current output by the machine body and generate heat to induction quench the bearing parts. A quenching base is provided under the quenching coil. The quenching base can be lifted and lowered on the side of the machine body. The bearing parts are placed on the quenching base so that they are sent into the quenching coil for quenching as the quenching base rises.

[0007] As a further improvement of the present invention, the quenching base includes a fixture column and a lifting base plate, the fixture column is fixedly installed on the upper side of the lifting base plate, and the side of the lifting base plate can be lifted and installed on the side of the machine body.

[0008] As a further improvement of the present invention, a protective cover with an opening at the lower side is fixed on the side of the machine body, and the protective cover accommodates the quenching coil inside.

[0009] As a further improvement of the present invention, a clamping column is coaxially fixed to the upper end of the clamp column, a plurality of sliding channels are provided in the clamping column, and the plurality of sliding channels are circumferentially distributed in the clamping column. A clamping rod is slidably provided in the sliding channel, a cylindrical cavity is provided in the clamping column, and the ends of the plurality of sliding channels are connected to the cylindrical cavity. The end of the clamping rod is a piston structure, and the cylindrical cavity is filled with hydraulic oil.

[0010] The beneficial effect of the present invention is that the bearing parts of high carbon chromium bearing steel treated by this heat treatment process can completely replace the bearing parts of carburized steel carburized quenched and tempered in terms of performance. The induction quenching process is easy to realize mechanization and automation, has a short process cycle, high production efficiency, small deformation of bearing parts and energy saving. The product with a certain depth of effective hardened layer obtained by surface induction quenching after being heated to austenitization and rapidly cooled by a multi-purpose furnace or other heat treatment equipment can completely replace the carburized steel carburized quenched and tempered under some impact-resistant working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a schematic diagram of the microstructure of fine-flaked troostite and spherulitic carbide after treatment in step 1; Figure 2 Schematic diagram of the heat treatment method of high carbon chromium bearing steel of the present invention; Figure 3 A schematic diagram of the surface martensite structure of the surface induction quenching of the present invention; Figure 4 A schematic diagram of transition zone martensite and troostite of the present invention; Figure 5 It is a schematic diagram of the core troostite and granular carbide of the present invention; Figure 6 It is a structural schematic diagram of the induction quenching equipment of the present invention; Figure 7 for Figure 6 Schematic diagram of the structure of the middle fixture column part. DETAILED DESCRIPTION

[0012] The present invention will be further described below in detail with reference to the embodiments shown in the accompanying drawings.

[0013] Reference Figure 1 As shown, a high carbon chromium bearing steel heat treatment method of this embodiment includes the following steps: Step 1: subject the high carbon chromium bearing steel raw material to forging or steel tube forming bearing parts to spheroidizing annealing treatment, and heat the bearing parts manufactured by turning forming to 840±20℃ in a heat treatment furnace and keep it at this temperature for 30-60min before taking it out and air cooling it to room temperature. The cooling to room temperature can be used to increase the nucleation rate of austenite by heating as in the normalizing operation, and to form a microstructure of fine lamellar troostite and spheroidal carbide that is conducive to nucleation by rapid cooling (see the microstructure). Figure 1 ), the hardness obtained after rapid cooling is similar to the matrix hardness of carburized steel after carburizing, quenching and tempering, and the hardness value is 35-48HRC; Step 2: reheat the bearing parts treated in step 1 to austenitizing temperature (860℃±20) by surface induction heating for induction quenching. Figure 2 As shown, induction tempering is then performed to form an effective hardened layer on the surface of the bearing parts. The effective hardened layer depth of the bearing parts in this embodiment can be adjusted according to the use conditions. Generally, the effective hardened layer depth is controlled to be 1.0mm to 6.0mm. The surface of the bearing parts after induction quenching and tempering can obtain high surface hardness while the core still maintains the low hardness matrix structure of the previous process (see the microstructure Figure 3 , 4 , 5).

[0014] Therefore, after the heat treatment process in the above steps, the bearing parts of high carbon chromium bearing steel treated by this heat treatment process can completely replace the bearing parts of carburized steel carburized quenched and tempered in terms of performance. The induction quenching process is easy to realize mechanization and automation, with a short process cycle, high production efficiency, small deformation of bearing parts and energy saving. Moreover, the product with a certain depth of effective hardened layer obtained by surface induction quenching after heating to austenitization and rapid cooling through multi-purpose furnace or other heat treatment equipment can completely replace carburized steel carburized quenched and tempered in some impact-resistant working conditions.

[0015] Furthermore, in order to avoid high-temperature oxidation reaction after leaving the furnace, nitrogen is also used in this embodiment to quickly cool the bearing parts to room temperature.

[0016] This embodiment provides a device for applying the above-mentioned induction hardening, referring to Figure 6As shown, the equipment includes a body 1 and a quenching coil 2. The quenching coil 2 is fixed on one side of the body 1 and connected to the electrical components inside the body 1 to receive the high-frequency current output by the body 1 and generate heat to induction quench the bearing parts. A quenching base 3 is provided below the quenching coil 2. The quenching base 3 can be installed on the side of the body 1 in a liftable manner. The bearing parts are placed on the quenching base 3 so that they can be sent into the quenching coil 2 for quenching as the quenching base 3 rises. The quenching base 3 includes a clamp column 31 and a lifting base plate 32. The clamp column 31 is fixedly installed on the upper side of the lifting base plate 32. The side of the lifting base plate 32 can be lifted and installed on the side of the body 1. In this way, the lifting effect of the lifting base plate 32 is utilized to realize sending the bearing parts into the quenching coil 2 for quenching, or sending the bearing parts out after quenching is completed, thereby realizing mechanization and automation.

[0017] In order to further increase the safety of the induction quenching equipment, in this embodiment, a protective cover 11 is also provided on the side wall of the body 1, and the protective function of the protective cover 11 is utilized to avoid problems caused by accidental touch by human hands during the quenching process.

[0018] In order to further facilitate the loading and unloading of the inner and outer rings of the bearing during quenching, a clamping column 33 is coaxially fixed to the upper end of the clamping column 31 in this embodiment, and a plurality of sliding channels 34 are provided in the clamping column 33, and the plurality of sliding channels 34 are circumferentially distributed in the clamping column 33. A clamping rod 35 is slidably provided in the sliding channel 34, and a cylindrical cavity 36 is provided in the clamping column 33. The ends of the plurality of sliding channels 34 are connected to the cylindrical cavity 36, and the end of the clamping rod 35 is a piston structure, and the cylindrical cavity 36 is filled with hydraulic oil. In this way, on the one hand, the thermal expansion and contraction effect of the hydraulic oil is utilized to realize the clamping and positioning of the inner and outer rings of the bearing, and on the other hand, the centrifugal force generated during the quenching rotation process can be utilized to further increase the clamping and positioning effect of the inner and outer rings of the bearing, thereby effectively facilitating people's loading and unloading of the inner and outer rings of the bearing.

[0019] In summary, the high carbon chromium bearing steel heat treatment method of this embodiment, which is heated to austenitization once by a multi-purpose furnace or other heat treatment equipment and then rapidly cooled by surface induction quenching to obtain a certain depth of effective hardened layer depth, can completely replace carburizing quenching and tempering of carburized steel under some impact-resistant working conditions.

[0020] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A heat treatment method for high carbon chromium bearing steel, characterized in that: The steps include: Step 1: subjecting the high carbon chromium bearing steel raw material to forging or steel tube forming bearing parts to spheroidizing annealing treatment, and heating the bearing parts manufactured by turning forming to 840±20°C in a heat treatment furnace and keeping the temperature for 30 to 60 minutes, and then taking out and air cooling to room temperature; Step 2: reheat the bearing parts processed in step 1 to 860°C ± 20 by surface induction heating for induction quenching, and then perform induction tempering to form an effective hardened layer on the surface of the bearing parts.

2. The heat treatment method of high carbon chromium bearing steel according to claim 1, characterized in that: In the step 1, the heat treatment furnace is heated to 840±20° C. and kept warm for 30 to 60 minutes, and then nitrogen is used to quickly cool the mixture to room temperature.

3. The heat treatment method for high carbon chromium bearing steel according to claim 2, characterized in that: The induction hardening equipment used in the step 2 comprises a machine body (1) and a quenching coil (2), wherein the quenching coil (2) is fixed on one side of the machine body (1) and connected to the electrical components inside the machine body (1) so as to receive the high-frequency current output by the machine body (1) and generate heat to perform induction hardening on the bearing parts, and a quenching base (3) is provided below the quenching coil (2), wherein the quenching base (3) is movably mounted on the side of the machine body (1), and the bearing parts are placed on the quenching base (3) so as to be sent into the quenching coil (2) for quenching as the quenching base (3) rises.

4. The heat treatment method for high carbon chromium bearing steel according to claim 3, characterized in that: The quenching base (3) comprises a fixture column (31) and a lifting base plate (32), wherein the fixture column (31) is fixedly mounted on the upper side of the lifting base plate (32), and the side of the lifting base plate (32) is liftably mounted on the side of the machine body (1).

5. The heat treatment method for high carbon chromium bearing steel according to claim 4, characterized in that: A protective cover (11) with an opening at the bottom is fixed on the side of the machine body (1), and the protective cover (11) accommodates the quenching coil (2) therein.

6. The heat treatment method for high carbon chromium bearing steel according to claim 5, characterized in that: A clamping column (33) is coaxially fixed to the upper end of the clamping column (31), and a plurality of sliding channels (34) are provided in the clamping column (33). The plurality of sliding channels (34) are circumferentially distributed in the clamping column (33), and a clamping rod (35) is slidably provided in the sliding channel (34). A cylindrical cavity (36) is provided in the clamping column (33), and the ends of the plurality of sliding channels (34) are connected to the cylindrical cavity (36). The end of the clamping rod (35) is a piston structure, and the cylindrical cavity (36) is filled with hydraulic oil.

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