Method for controlling carbide mesh grade of medium-specification GCr15 bearing steel

Abstract

The invention discloses a method for controlling the carbide mesh grade of medium-specification GCr15 bearing steel, and belongs to the technical field of bearing steel production. Comprising the following steps: (1) heating a continuous casting billet in a heating furnace; (2) rolling the continuous casting billet into a squared billet by adopting a large reduction process, wherein the compression ratio is 2-4; (3) heating the squared billet in a heating furnace; and (4) the round steel is rolled through a controlled rolling process, water cooling and re-reddening are conducted before finish rolling, after the temperature is uniform, finish rolling is conducted through a three-roller mill, the temperature before finish rolling is controlled to be 720-740 DEG C, the temperature after finish rolling is controlled to be 700-720 DEG C, and water cooling is not conducted after finish rolling. The method is suitable for GCr15 bearing steel with the specification of phi 40 mm-phi 60 mm, the production process is simple, the hardness value of a product is 360-370 HBW, network carbide is stably controlled within the level 1.5, meanwhile, martensite is not contained, the subsequent annealing procedure can be omitted, and the requirement of a user for direct machining and using is met.

Description

Technical Field

[0001] The invention belongs to the technical field of bearing steel production, and in particular relates to a method for controlling the carbide network level of medium-specification GCr15 bearing steel. Background Art

[0002] Bearings are one of the most important key basic components in various transmission equipment. They are widely used in major equipment fields such as mining machinery, precision machine tools, metallurgical equipment, heavy equipment, and emerging industries such as wind power generation, high-speed trains, and aerospace. Their function is to support the rotational motion of rotating shafts or other moving bodies. They are indispensable "joints" of mechanical equipment and play a vital role in national economic construction.

[0003] The contact area between the rolling element and the raceway of the bearing ring is very small. The compressive stress of the rolling element is extremely high during normal operation, reaching tens of thousands of cycles per minute. Therefore, the working conditions of the bearing are relatively harsh. The rolling element is also subject to additional loads caused by centrifugal force when rotating, and sliding friction is also generated between the bearing rings. Therefore, the performance of the bearing steel used to manufacture the bearing rolling element must reach an extremely high level to meet the requirements of stable operation of the equipment.

[0004] GCr15 bearing steel is a hypereutectoid steel with relatively high carbon and chromium content. If the relevant process control is not proper during the production process, its carbides will easily precipitate from the austenite and grow along the austenite grain boundaries, eventually forming a network of carbides. As the level of network carbides increases, the brittleness of the steel increases after heat treatment, and the contact fatigue strength will be significantly reduced, seriously weakening the comprehensive performance of the steel. The general standard "GB / T18254-2016 High Carbon Chromium Bearing Steel" currently in force has clear provisions on the network level. The requirements for the network level of bearing steel used to process bearing rings are relatively loose. However, the requirements for the network level of bearing steel used to process bearing rolling elements are relatively strict, and the spectrum rating requires that the network level should not exceed 2.5.

[0005] At present, the general method is to quickly cool the steel after rolling to below 700℃ to inhibit the precipitation of carbides, thereby reducing the mesh level. However, this process is suitable for smaller specifications. At the same time, rapid cooling after rolling will cause the surface temperature of the steel to drop sharply, causing martensite structure to appear on the surface of the steel, resulting in very high hardness. It is impossible to directly test the depth of the decarburization layer. Annealing is required to meet the requirements of decarburization testing and user processing.

[0006] The invention patent application with application number 201610750155.6 discloses a rolling method for controlling the precipitation of network carbides in large-section GCr15 bearing steel. The total heating time of the continuous casting billet is 10 to 15 hours, the heating time in the soaking section at 1200 to 1230°C is 5 to 8 hours, the start rolling temperature is controlled at 1050 to 1100°C, and the final rolling temperature is 830 to 850°C; the final rolling preferably has a relative reduction of 35 to 75%; and the final rolling is cooled to 550 to 670°C through water. This patent is suitable for rolling bars with specifications of φ50 to φ90 mm, but not for medium-sized bearing steel bars. In addition, the continuous casting billet heating time is relatively long, and the energy consumption is relatively high.

[0007] The invention patent application with application number 202110849617.0 discloses a production process method for reducing the carbide network level of GCr15 bearing steel bars. The process requires the use of a two-fire controlled rolling and controlled cooling process. The total heating time of the continuous casting billet is 20 to 30 hours, the heating time of the square billet is 6 hours, and water cooling is carried out before and after the final rolling. The final rolling temperature is controlled at 780 to 820°C, the final rolling deformation is ≥35%, and the red return temperature after the final rolling is below 650°C. This patent is suitable for rolling smaller bars of φ16 to φ40mm, but is not suitable for medium-sized bearing steel bars. The heating time of the ingot is relatively long and the fuel consumption is relatively high. The process requires rapid cooling through water after rolling, and a martensitic structure is formed on the surface of the steel. The depth of the decarburization layer cannot be directly tested, which has a certain impact on direct processing and use. Summary of the invention

[0008] In order to solve the above technical problems, the present invention provides a method for controlling the carbide network level of medium-specification GCr15 bearing steel, which can solve the problems that the network carbide level of medium-specification bearing steel is too high, martensitic structure appears after water penetration, controlled rolling and controlled cooling, and the hardness is too high to be used directly.

[0009] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is: A method for controlling the carbide network level of medium-sized GCr15 bearing steel comprises the following steps: (1) The continuous casting billet is heated in a heating furnace; (2) The continuous casting billet is rolled into open square billet by a large reduction process, and the compression ratio (i.e., the cross-sectional area before rolling / the cross-sectional area after rolling) is controlled at 2 to 4; (3) Open the square billet and put it into the heating furnace for heating; (4) The steel is rolled into round steel using a controlled rolling process. Water cooling is performed before final rolling. After the steel returns to red and the temperature is uniform, a three-roll mill is used for final rolling. The temperature before final rolling is controlled at 720-740°C, and the temperature after final rolling is controlled at 700-720°C. No water cooling is performed after final rolling.

[0010] Furthermore, in step (1), the soaking section temperature is 1200-1235° C., and the soaking time is 3-4 hours; so that the carbides formed during the continuous casting of the ingot are fully dissolved in the soaking section and diffused into the austenite.

[0011] Furthermore, in step (2), the maximum reduction in a single pass is 25-30% to fully eliminate continuous casting defects such as center segregation and porosity of the ingot and coarse as-cast structure.

[0012] Furthermore, in step (3), the temperature of the soaking section is 1200-1235° C., and the soaking time is 1.5-2.5 h.

[0013] Furthermore, in step (4), the compression ratio is ≥9.

[0014] Furthermore, in step (4), the reduction ratio of the finishing mill is controlled at 25-33%.

[0015] Furthermore, the GCr15 bearing steel has a specification of φ40mm~φ60mm, a hardness of 360~370HBW, and a carbide network level ≤1.5.

[0016] The beneficial effect of adopting the above technical scheme is that the present invention adopts a large reduction process to roll the continuous casting billet into a square billet, and implements large reduction rolling in the width and height directions to ensure that the central defects of the billet are eliminated and the coarse structure of the continuous casting state is broken under the premise of a smaller compression ratio requirement. In the process of rolling round steel from the square billet, water cooling is performed before the final rolling to inhibit the precipitation of network carbides. The surface temperature after water cooling is generally around 500°C, which can avoid the martensite formation temperature. The final rolling temperature is 720-740°C and a three-roll mill is used for rolling. The network carbides formed before the final rolling can be completely broken by rolling deformation to reduce the network level. The temperature after the final rolling is 700-720°C, which completely avoids the temperature range where a large amount of carbides precipitate. At this time, the temperature is relatively low and the amount of carbide precipitation is very small. The conventional process of cooling, sawing and collecting can ensure that the network level does not exceed 1.5 levels. After final rolling, no water-penetrating rapid cooling is performed, which can ensure that there is no martensite structure on the surface of the steel, and the depth of the decarburized layer can be normally tested. Compared with the GCr15 bearing steel produced by conventional processes, the hardness of the GCr15 bearing steel of the present invention has no obvious fluctuation. At the same time, because it does not contain martensite, it does not need to go through the subsequent annealing process, meeting the requirements of users for direct processing and use.

[0017] The present invention is suitable for GCr15 bearing steel with a specification of φ40mm to φ60mm. The production process is relatively simple, the product quality is good, and the hardness value is 360 to 370 HBW. While ensuring the hardness of the steel, the network carbide can be stably controlled within level 1.5, meeting the needs of users for direct processing and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a high-magnification picture of the carbide network of the GCr15 bearing steel produced in Example 1; Figure 2 This is a high-magnification picture of the carbide network of the GCr15 bearing steel produced in Example 2; Figure 3 This is a high-magnification picture of the carbide network of the GCr15 bearing steel produced in Example 3; Figure 4 This is a high-magnification picture of the carbide network of the GCr15 bearing steel produced in Example 4; Figure 5 This is a high-magnification picture of the carbide network of the GCr15 bearing steel produced in Example 5; Figure 6 This is a high-magnification picture of the carbide network of the GCr15 bearing steel produced in Example 6; Figure 7 This is a high-magnification picture of the carbide network of the GCr15 bearing steel produced in Example 7; Figure 8 This is a high-magnification picture of the carbide network of the GCr15 bearing steel produced in Example 8. DETAILED DESCRIPTION

[0019] Example 1: The method of controlling the carbide network level of medium-sized GCr15 bearing steel in this example is described in detail as follows.

[0020] The cross-sectional size of the continuous casting billet is 300mm×340mm, and it is heated by a walking beam heating furnace, and the heating time in the 1200℃ soaking section is 3 hours. The continuous casting billet is rolled into a 225mm×225mm cross-sectional billet, with a compression ratio of 2.0, and a maximum single-pass reduction of 25% in the width and height directions of the billet. After the billet is cooled to room temperature in a windproof pile, it enters a walking beam heating furnace for heating. After heating in a 1200℃ soaking section for 1.5 hours, it is rolled into a φ40mm specification bar with a compression ratio of 40.3. It is water-cooled before final rolling. After returning to red and the temperature is uniform, it is final rolled by a three-roll mill, with a final rolling temperature of 720℃, a final rolling mill reduction rate of 25%, and a final rolling temperature of 700℃. After final rolling, it is directly cooled on a cooling bed, and sawed and collected according to normal processes.

[0021] The carbide network level of the longitudinal and cross-sectional GCr15 bearing steel bars produced by this process does not exceed level 1.5 (such as Figure 1 As shown in the figure), it meets the requirements of GB / T18254-2016 High Carbon Chromium Bearing Steel. The hardness is 360HBW, which meets the requirements of direct processing by users. There is no martensitic structure on the surface, and the depth of the decarburized layer can be directly tested.

[0022] Example 2: The method of controlling the carbide network level of medium-sized GCr15 bearing steel in this example is described in detail as follows.

[0023] The cross-sectional size of the continuous casting billet is 300mm×340mm, and it is heated by a walking beam heating furnace, and the heating time in the 1210℃ soaking section is 3.5 hours. The continuous casting billet is rolled into a 200mm×200mm cross-sectional billet, with a compression ratio of 2.55 and a maximum single-pass reduction of 28% in the billet width and height directions. After the billet is cooled to room temperature in a windproof pile, it enters a walking beam heating furnace for heating. After heating in a 1220℃ soaking section for 2 hours, it is rolled into a φ41mm specification bar with a compression ratio of 30.3. It is water-cooled before final rolling. After returning to red and the temperature is uniform, a three-roll rolling mill is used for final rolling. The final rolling temperature is 730℃, the final rolling mill group reduction rate is 30%, and the final rolling temperature is 710℃. After final rolling, it is directly cooled on a cooling bed, and sawed and collected according to normal processes.

[0024] The carbide network level of the GCr15 bearing steel bars produced by this process does not exceed level 1.0 in both longitudinal and cross sections (such as Figure 2 As shown in the figure), it meets the requirements of GB / T18254-2016 High Carbon Chromium Bearing Steel. The hardness is 365HBW, which meets the requirements of direct processing by users. There is no martensitic structure on the surface, and the depth of the decarburized layer can be directly tested.

[0025] Example 3: The method of controlling the carbide network level of medium-sized GCr15 bearing steel in this example is described in detail as follows.

[0026] The cross-sectional size of the continuous casting billet is 300mm×340mm, and it is heated by a walking beam heating furnace, and the heating time in the 1220℃ soaking section is 4 hours. The continuous casting billet is rolled into a 200mm×200mm cross-sectional billet, with a compression ratio of 2.55 and a maximum single-pass reduction of 29% in the width and height directions of the billet. After the billet is cooled to room temperature in a windproof pile, it enters a walking beam heating furnace for heating. After heating in a 1230℃ soaking section for 1.5 hours, it is rolled into a φ42mm specification bar with a compression ratio of 28.8. It is water-cooled before final rolling, and after returning to red and the temperature is uniform, a three-roll rolling mill is used for final rolling. The final rolling temperature is 725℃, the final rolling mill group reduction rate is 28%, and the final rolling temperature is 705℃. After final rolling, it is directly cooled on a cooling bed, and sawing and collection are carried out according to normal processes.

[0027] The carbide network level of the longitudinal and cross-sectional GCr15 bearing steel bars produced by this process does not exceed level 1.5 (such as Figure 3 As shown in the figure), it meets the requirements of GB / T18254-2016 High Carbon Chromium Bearing Steel. The hardness is 370HBW, which meets the requirements of direct processing by users. There is no martensitic structure on the surface, and the depth of the decarburized layer can be directly tested.

[0028] Example 4: The method of controlling the carbide network level of medium-sized GCr15 bearing steel in this example is described in detail as follows.

[0029] The cross-sectional size of the continuous casting billet is 300mm×340mm, and it is heated by a walking beam heating furnace, and the heating time in the 1225℃ soaking section is 3.5 hours. The continuous casting billet is rolled into a 200mm×200mm cross-sectional billet, with a compression ratio of 2.55 and a maximum single-pass reduction of 27% in the billet width and height directions. After the billet is cooled to room temperature in a windproof pile, it enters a walking beam heating furnace for heating. After heating in a 1235℃ soaking section for 2 hours, it is rolled into a φ43mm specification bar with a compression ratio of 27.5. It is water-cooled before final rolling, and after returning to red and the temperature is uniform, a three-roll rolling mill is used for final rolling. The final rolling temperature is 730℃, the final rolling mill group reduction rate is 27%, and the final rolling temperature is 710℃. After final rolling, it is directly cooled on a cooling bed, and sawed and collected according to normal processes.

[0030] The carbide network level of the longitudinal and cross-sectional GCr15 bearing steel bars produced by this process does not exceed level 1.5 (such as Figure 4 As shown in the figure), it meets the requirements of GB / T18254-2016 High Carbon Chromium Bearing Steel. The hardness is 370HBW, which meets the requirements of direct processing by users. There is no martensitic structure on the surface, and the depth of the decarburized layer can be directly tested.

[0031] Example 5: The method of controlling the carbide network level of medium-sized GCr15 bearing steel in this example is described in detail as follows.

[0032] The cross-sectional size of the continuous casting billet is 300mm×340mm, and it is heated by a walking beam heating furnace, and the heating time in the 1220℃ soaking section is 4 hours. The continuous casting billet is rolled into a 200mm×200mm cross-sectional billet, with a compression ratio of 2.55 and a maximum single-pass reduction of 29% in the billet width and height directions. After the billet is cooled to room temperature in a windproof pile, it enters a walking beam heating furnace for heating. After heating in a 1230℃ soaking section for 1.5 hours, it is rolled into a φ45mm specification bar with a compression ratio of 25.1. It is water-cooled before final rolling. After returning to red and the temperature is uniform, a three-roll mill is used for final rolling. The final rolling temperature is 730℃, the final rolling mill group reduction rate is 26%, and the final rolling temperature is 710℃. After final rolling, it is directly cooled on a cooling bed, and sawing and collection are carried out according to normal processes.

[0033] The carbide network level of the GCr15 bearing steel bars produced by this process does not exceed level 1.0 in both longitudinal and cross sections (such as Figure 5 As shown in the figure), it meets the requirements of GB / T18254-2016 High Carbon Chromium Bearing Steel. The hardness is 369HBW, which meets the requirements of direct processing by users. There is no martensitic structure on the surface, and the depth of the decarburized layer can be directly tested.

[0034] Example 6: The method of controlling the carbide network level of medium-sized GCr15 bearing steel in this example is described in detail as follows.

[0035] The cross-sectional size of the continuous casting billet is 300mm×340mm, and it is heated by a walking beam heating furnace, and the heating time in the 1230℃ soaking section is 3 hours. The continuous casting billet is rolled into a 200mm×200mm cross-sectional billet, with a compression ratio of 2.55 and a maximum single-pass reduction of 26% in the billet width and height directions. After the billet is cooled to room temperature in a windproof pile, it enters a walking beam heating furnace for heating. After heating in a 1235℃ soaking section for 1.5 hours, it is rolled into a φ50mm specification bar with a compression ratio of 20.4. It is water-cooled before final rolling. After returning to red and the temperature is uniform, a three-roll rolling mill is used for final rolling. The final rolling temperature is 740℃, the final rolling mill group reduction rate is 32%, and the final rolling temperature is 720℃. After final rolling, it is directly cooled on a cooling bed, and sawed and collected according to normal processes.

[0036] The carbide network level of the longitudinal and cross-sectional GCr15 bearing steel bars produced by this process does not exceed level 1.5 (such as Figure 6 As shown in the figure), it meets the requirements of GB / T18254-2016 High Carbon Chromium Bearing Steel. The hardness is 365HBW, which meets the requirements of direct processing by users. There is no martensitic structure on the surface, and the depth of the decarburized layer can be directly tested.

[0037] Example 7: The method of controlling the carbide network level of medium-sized GCr15 bearing steel in this example is described in detail as follows.

[0038] The cross-sectional size of the continuous casting billet is 300mm×340mm, and it is heated by a walking beam heating furnace, and the heating time in the 1220℃ soaking section is 4 hours. The continuous casting billet is rolled into a 200mm×200mm cross-sectional billet, with a compression ratio of 2.55 and a maximum single-pass reduction of 30% in the billet width and height directions. After the billet is cooled to room temperature in a windproof pile, it enters a walking beam heating furnace for heating. After heating in a 1230℃ soaking section for 2 hours, it is rolled into a φ55mm specification bar with a compression ratio of 16.8. It is water-cooled before final rolling. After returning to red and the temperature is uniform, a three-roll mill is used for final rolling. The final rolling temperature is 730℃, the final rolling mill group reduction rate is 33%, and the final rolling temperature is 710℃. After final rolling, it is directly cooled on a cooling bed, and sawing and collection are carried out according to normal processes.

[0039] The carbide network grade of the GCr15 bearing steel bars produced by this process is 1.5 in both longitudinal and cross sections (such as Figure 7 As shown in the figure), it meets the requirements of GB / T18254-2016 High Carbon Chromium Bearing Steel. The hardness is 370HBW, which meets the requirements of direct processing by users. There is no martensitic structure on the surface, and the depth of the decarburized layer can be directly tested.

[0040] Example 8: The method of controlling the carbide network level of medium-sized GCr15 bearing steel in this example is described in detail as follows.

[0041] The cross-sectional size of the continuous casting billet is 300mm×340mm, and it is heated by a walking beam heating furnace, and the heating time in the 1235℃ soaking section is 4 hours. The continuous casting billet is rolled into a 160mm×160mm cross-sectional billet, with a compression ratio of 4.0 and a maximum single-pass reduction of 30% in the width and height directions of the billet. After the billet is cooled to room temperature in a windproof pile, it enters a walking beam heating furnace for heating. After heating in the 1235℃ soaking section for 2.5 hours, it is rolled into a φ60mm specification bar with a compression ratio of 9.0. It is water-cooled before final rolling. After returning to red and the temperature is uniform, a three-roll rolling mill is used for final rolling. The final rolling temperature is 740℃, the final rolling mill group reduction rate is 33%, and the final rolling temperature is 720℃. After final rolling, it is directly cooled on a cooling bed, and sawed and collected according to normal processes.

[0042] The carbide network level of the longitudinal and cross-sectional GCr15 bearing steel bars produced by this process does not exceed level 1.5 (such as Figure 8 As shown in the figure), it meets the requirements of GB / T18254-2016 High Carbon Chromium Bearing Steel. The hardness is 361HBW, which meets the requirements of direct processing by users. There is no martensitic structure on the surface, and the depth of the decarburized layer can be directly tested.

[0043] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for controlling the carbide network level of medium-sized GCr15 bearing steel, characterized in that: The steps include: (1) The continuous casting billet is heated in a heating furnace; (2) The continuous casting billet is rolled into open square billet by a large reduction process, and the compression ratio is controlled at 2 to 4; (3) Open the square billet and put it into the heating furnace for heating; (4) The steel is rolled into round steel using a controlled rolling process. It is water-cooled before final rolling. After the steel returns to red and the temperature is uniform, it is final rolled using a three-roll mill. The temperature before final rolling is controlled at 720-740°C, and the temperature after final rolling is controlled at 700-720°C. No water cooling is performed after final rolling.

2. The method for controlling the carbide network level of medium-sized GCr15 bearing steel according to claim 1, characterized in that: In step (1), the temperature of the soaking section is 1200-1235° C., and the soaking time is 3-4 hours.

3. The method for controlling the carbide network level of medium-sized GCr15 bearing steel according to claim 2, characterized in that: In step (2), the maximum pressure reduction per single pass is 25-30%.

4. The method for controlling the carbide network level of medium-sized GCr15 bearing steel according to claim 3, characterized in that: In step (3), the temperature of the soaking section is 1200-1235° C., and the soaking time is 1.5-2.5 h.

5. The method for controlling the carbide network level of medium-sized GCr15 bearing steel according to claim 4, characterized in that: In step (4), the compression ratio is ≥9.

6. The method for controlling the carbide network level of medium-sized GCr15 bearing steel according to claim 5, characterized in that: In step (4), the reduction ratio of the finishing mill is controlled at 25-33%.

7. The method for controlling the carbide network level of medium-sized GCr15 bearing steel according to any one of claims 1 to 6, characterized in that: The GCr15 bearing steel has a specification of φ40mm~φ60mm, a hardness of 360~370HBW, and a carbide network level ≤1.5.

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