Preparation method of continuous casting and rolling high-carbon chromium bearing steel wire rod

Abstract

The invention relates to a preparation method of a continuous casting and rolling high-carbon chromium bearing steel wire rod, and belongs to the technical field of metallurgical wire rods. The production process comprises the steps of KR molten iron pretreatment, BOF converter smelting, LF refining, RH vacuum degassing, 390 * 510 mm < 2 > bloom arc-shaped continuous casting, high-temperature diffusion, 150 * 150 mm < 2 >-200 * 200 mm < 2 > intermediate billet rolling, billet peeling and coping, heating, wire rod rolling and spheroidizing annealing. A blooming mode of continuous casting and continuous rolling is achieved by direct furnace entering high-temperature diffusion of blooms through continuous casting, an intermediate billet is obtained, rolling is conducted through secondary heating, and after spheroidizing annealing is conducted on a finished wire rod, the hardness difference between the core and the surface is not larger than 15 Hv, the spheroidizing structure is 2-3 levels, the oxygen content is not larger than 6 ppm, and the size of Ds type non-metallic inclusions is not larger than 15 micrometers. And the depth of a decarburized layer of the high-quality high-carbon chromium bearing steel wire rod is not greater than 0.05 mm.

Description

Technical Field

[0001] This invention belongs to the field of wire rod manufacturing in the metallurgical industry, and specifically relates to a method for preparing high-carbon chromium bearing steel wire rod. Background Technology

[0002] High-carbon chromium bearing steel wire rod is one of the important products of the modern steel industry, widely used in the processing and application of rolling elements and miniature bearing rings. The uniformity of the material's microstructure, non-metallic inclusions, oxygen content, and the depth of the decarburized layer directly affect the service life of bearing rolling elements and rings. Therefore, strict requirements are placed on the control of various indicators during the smelting and rolling processes.

[0003] Patent publication number CN114789194A discloses a method for heating and rolling bearing steel wire rods using a two-stage heating process. It describes a method that uses continuously cast billets for secondary heating and rolling, controlling the angle between the nozzle and the billet in the heating furnace by adjusting the composition of the combustion atmosphere, and simultaneously controlling cooling after rolling to achieve excellent surface decarburization and carbide control. This technology only describes the heating of the billet and the cooling control of the wire rod, and does not cover the control of non-metallic inclusions, oxygen content, and microstructure uniformity in bearing steel.

[0004] Patent publication number CN105925909A discloses a method for producing bearing steel wire rod. After continuous casting, the wire rod is slowly cooled and then reheated. The temperature of the heating process is controlled at 1100~1200℃ for wire rod rolling. The high-temperature diffusion temperature of liquid carbides in high-carbon chromium bearing steel products needs to reach above 1200℃ to be improved. However, the 1100~1200℃ in this technology does not improve the quality of liquid carbides. Summary of the Invention

[0005] The present invention aims to provide a method for preparing high-carbon chromium bearing steel wire rod by continuous casting and rolling, which improves the segregation quality of the material, enhances the uniformity and purity of the material structure, and extends the service life of bearing rolling elements and raceways.

[0006] The technical solution adopted by this invention to solve the above problems is: a method for preparing high-carbon chromium bearing steel wire rod by continuous casting and rolling, characterized in that it includes: Step 1: KR molten iron pretreatment, controlling the original sulfur content of the molten iron to ≤0.003% and the phosphorus content to ≤0.10%, while the molten iron temperature to ≥1280℃; Step 2: BOF converter smelting, controlling the final carbon content to be above 15%; Step 3: LF refining, smelting time ≥ 55 min, superheat control 15~30℃; Step 4: RH vacuum degassing, vacuum circulation time ≥45min, after circulation, adjust argon flow rate to promote the floating of inclusions, ensuring that the molten steel is not exposed; Step 5: Arc-shaped continuous casting, argon blowing and sealing of the tundish to prevent molten steel from contacting oxygen, liquid level fluctuation in the crystallizer ≤6mm, control the total reduction during continuous casting to ≥12mm, and control the casting speed ≤0.5m / min; Step 6: Three machines, three flow meters, 390×510mm 2 Large billets are hot-charged into the furnace for high-temperature diffusion. The furnace temperature is ≥700℃, the high-temperature diffusion time is ≥7 hours, and the temperature of the soaking zone and the high-temperature zone is 1200~1280℃. After diffusion, the billets are rolled to ensure that the rolling temperature is ≥1050℃. Step 7: Roll the billet to 150×150mm. 2 ~200×200mm 2 The intermediate billet has a carbon bias index of 0.93~1.05 in the core. The billet surface is peeled to eliminate surface defects and decarburized layer. Step 8: The billet is heated in the furnace using blast furnace gas. The residual oxygen content in the furnace is controlled to be ≤4%. The billet temperature is raised to 960~1050℃ and held for 40~80 minutes. The initial rolling temperature is not lower than 900℃. The rolling process adopts a controlled cooling process. The final rolling temperature is controlled at 870~930℃, and the wire drawing temperature is 780~820℃. After wire drawing, the cooling rate of the wire is controlled at 4.0℃ / s~9℃ / s. The wire is slowly cooled off the production line at 600~630℃. By controlling the cooling rate on site, the material is rapidly reduced to below the temperature range for secondary carbide precipitation during the microstructure transformation process, thereby reducing the precipitation of secondary carbides. The temperature control during the rolling process is to ensure the initial temperature for rapid cooling during the post-rolling cooling process. Step 9: Spheroidizing annealing. Before annealing, pickling is used to remove the surface iron oxide scale. The spheroidizing temperature is 790±10℃. Spheroidizing is held at this temperature for 24-30 hours. After cooling to below 600℃, the annealing furnace is removed.

[0007] Preferably, in step 7: the peeling depth of the billet is ≥0.8mm.

[0008] Preferably, in step 8: the rolling process uses online water cooling to control the cooling of the billet, and after wire drawing, the wire rod is air-cooled on the Steyrmo line.

[0009] Preferably, the chemical composition of the bearing steel wire rod to which this method is applicable, by mass percentage, is: C 0.95–1.05%, Si 0.15–0.35%, Mn 0.25–0.45%, Cr 1.30–1.65%, Mo ≤0.10%, Ni ≤0.25%, Al ≤0.050%, P ≤0.025%, S ≤0.020%, Cu ≤0.25%, Ca ≤0.0010%, O ≤0.0012%, Ti ≤0.0050%, As ≤0.040%, Pb ≤0.002%, As+Sn+Sb ≤0.075%, with the balance being Fe and unavoidable impurities.

[0010] This application ultimately achieves uniformity and purity of the microstructure of high carbon chromium bearing steel wire rod. After spheroidizing annealing, the hardness difference between the core and the surface of the wire rod is ≤15Hv, the spheroidization microstructure is grade 2-3, the oxygen content is ≤6ppm, the size of Ds-type non-metallic inclusions is ≤15μm, and the decarburized layer depth is ≤0.05mm. Attached Figure Description

[0011] Figure 1 Example 1: Decarburization after spheroidizing annealing; Figure 2 Example 2: Decarburization after spheroidizing annealing; Figure 3 Example 3: Decarburization after spheroidizing annealing; Figure 4 Example 1: Core microstructure after spheroidizing annealing; Figure 5 Example 1: Edge microstructure after spheroidizing annealing; Figure 6 Example 2: Core microstructure after spheroidizing annealing; Figure 7 Example 2: Edge microstructure after spheroidizing annealing; Figure 8 Example 3: Core microstructure after spheroidizing annealing; Figure 9 Example 3: Edge microstructure after spheroidizing annealing; Figure 10 Example 1-3: Carbon bias index trend of billets. Detailed Implementation

[0012] The present invention will be further described in detail below with reference to the embodiments. The embodiments are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention.

[0013] The production process of high-carbon chromium bearing steel wire rod is as follows: KR hot metal pretreatment → BOF converter smelting → LF refining → RH vacuum degassing → 390×510mm 2 Large square billet arc continuous casting → high temperature diffusion → rolling into 150×150mm2 ~200×200mm 2 Intermediate billet → Billet peeling and grinding → Heating + rolling into wire rod → Spheroidizing annealing. Example 1

[0014] The product manufactured is a φ14.5mm high-carbon chromium bearing steel wire rod. The smelting composition is: C 1.00%, Si 0.29%, Mn 0.35%, Cr 1.44%, Mo 0.02%, Ni 0.02%, Al 0.014%, P 0.018%, S 0.002%, Cu 0.01%, Ca≤0.0010%, O≤5.3PPM, Ti≤0.0050%, As≤0.040%, Pb≤0.002%, As+Sn+Sb≤0.075%, with the balance being Fe and unavoidable impurities. KR hot metal pretreatment controls the S content to 0.001% and P content to 0.06%, with a hot metal temperature of 1310℃. After BOF smelting, the final carbon content is 0.18%. LF smelting time is 63 minutes, with superheat controlled at 20℃. RH vacuum degassing process involves a vacuum circulation time of 47 minutes. The continuous casting wire drawing speed is 0.5 m / min, the reduction amount of the light pressing process is 16.5 mm, and the measured liquid level fluctuation is ≤3 mm.

[0015] Bloom 390×510mm 2 The intermediate billet was diffused at a high temperature of 1245℃~1255℃ for 7.5 hours, with a total heating time of 11 hours. The rolling specification of the intermediate billet was 200×200mm. 2 After peeling and finishing, the billet is heated to 1020℃ and rolled. The high-temperature holding time is 65-78 minutes, and the final rolling temperature is 870℃. During the rolling process, online water tanks are used for controlled cooling to ensure that the temperature during the finishing rolling process is controlled at 900℃±30℃. The wire drawing temperature is 802℃, and the controlled cooling after wire drawing adopts the XDWP controlled cooling process with a cooling rate of 4.5℃ / s. The slow cooling temperature after entering the annealing furnace is 623℃. The finished wire rod is then placed in a annealing furnace for spheroidizing annealing. Example 2

[0016] We produce high-carbon chromium bearing steel wire rods with a diameter of φ5.5mm. The smelting composition is: C 1.01%, Si 0.30%, Mn 0.33%, Cr 1.45%, Mo 0.02%, Ni 0.02%, Al 0.015%, P 0.020%, S 0.002%, Cu 0.01%, Ca≤0.0010%, O≤5.6PPM, Ti≤0.0050%, As≤0.040%, Pb≤0.002%, As+Sn+Sb≤0.075%, with the balance being Fe and unavoidable impurities. Through KR hot metal pretreatment, the S content is controlled to 0.001%, and the P content to 0.08%, with a hot metal temperature of 1302℃. The final carbon content after BOF smelting is 0.19%, the LF smelting time is 62 minutes, and the superheat is controlled at 23℃; the RH vacuum degassing process has a vacuum circulation time of 49 minutes. The continuous casting wire drawing speed is 0.5m / min, the reduction amount of the light pressing process is 18mm, and the measured liquid level fluctuation is ≤3mm.

[0017] Bloom 390×510mm 2 The intermediate billet was diffused at 1240~1260℃ for 7.3 hours, with a total heating time of 11.3 hours. The rolling specification of the intermediate billet was 200×200mm. 2 After peeling and finishing, the billet is heated to 1010℃ and rolled. The high-temperature holding time exceeds 67-80 minutes, and the final rolling temperature is 876℃. During the rolling process, online water tanks are used for controlled cooling to ensure that the temperature during the finishing rolling process is controlled at 900℃±30℃. The wire drawing temperature is 788℃, and the controlled cooling after wire drawing adopts the Stellmor air cooling process, with a cooling rate of 2.6℃ / s. The slow cooling temperature after entering the annealing furnace is 610℃. The finished wire rod is then placed in a annealing furnace for spheroidizing annealing. Example 3

[0018] We produce high-carbon chromium bearing steel wire rods with a diameter of φ17mm. The smelting composition is: C 1.00%, Si 0.30%, Mn 0.35%, Cr 1.44%, Mo 0.03%, Ni 0.01%, Al 0.012%, P 0.018%, S 0.002%, Cu 0.04%, Ca≤0.0010%, O≤5.3PPM, Ti≤0.0050%, As≤0.040%, Pb≤0.002%, As+Sn+Sb≤0.075%, with the balance being Fe and unavoidable impurities. Through KR hot metal pretreatment, the S content is controlled to 0.001%, and the P content to 0.08%, with a hot metal temperature of 1292℃. The final carbon content after BOF smelting is 0.16%, the LF smelting time is 65 minutes, and the superheat is controlled at 19℃; the RH vacuum degassing process has a vacuum circulation time of 45 minutes. The continuous casting wire drawing speed is 0.5 m / min, the reduction amount of the light pressing process is 16.5 mm, and the measured liquid level fluctuation is ≤3 mm.

[0019] Bloom 390×510mm 2 The intermediate billet was diffused at a high temperature of 1242℃~1258℃ for 8.0 hours, with a total heating time of 12 hours. The rolling specification of the intermediate billet was 150×150mm. 2 After peeling and finishing, the billet is heated to 1013℃ and rolled. The high-temperature holding time exceeds 60-85 minutes, and the final rolling temperature is 880℃. During the rolling process, online water tanks are used for controlled cooling to ensure that the temperature during the finishing rolling process is controlled at 900℃±30℃. The wire drawing temperature is 813℃, and the controlled cooling after wire drawing adopts the XDWP controlled cooling process, with a cooling rate of 4.8℃ / s. The slow cooling temperature after entering the annealing furnace is 628℃. The finished wire rod is then placed in a annealing furnace for spheroidizing annealing.

[0020] Table 1. Inspection performance of high carbon chromium bearing steel wire rods in Examples 1-3 .

Claims

1. A method for preparing high-carbon chromium bearing steel wire rod by continuous casting and rolling, characterized in that: include, Step 1: KR molten iron pretreatment, controlling the original sulfur content of the molten iron to ≤0.003% and the phosphorus content to ≤0.10%, while the molten iron temperature to ≥1280℃; Step 2: BOF converter smelting, controlling the final carbon content to be above 15%; Step 3: LF refining, smelting time ≥ 55 min, superheat control 15~30℃; Step 4: RH vacuum degassing, vacuum circulation time ≥45min, after circulation, adjust argon flow rate to promote the floating of inclusions, ensuring that the molten steel is not exposed; Step 5: Arc-shaped continuous casting, argon blowing and sealing of the tundish to prevent molten steel from contacting oxygen, liquid level fluctuation in the crystallizer ≤6mm, control the total reduction during continuous casting to ≥12mm, and control the casting speed ≤0.5m / min; Step 6: Three machines, three flow meters, 390×510mm 2 Large billets are hot-charged into the furnace for high-temperature diffusion. The furnace temperature is ≥700℃, the high-temperature diffusion time is ≥7 hours, and the temperature of the soaking zone and the high-temperature zone is 1200~1280℃. After diffusion, the billets are rolled to ensure that the rolling temperature is ≥1050℃. Step 7: Roll the billet to 150×150mm. 2 ~200×200mm 2 The intermediate billet has a carbon bias index of 0.93~1.05 in the core. The billet surface is peeled to eliminate surface defects and decarburized layer. Step 8: The billet is heated in the furnace using blast furnace gas. The residual oxygen content in the furnace is controlled to be ≤4%. The billet temperature is raised to 960~1050℃ and held for 40~80 minutes. The initial rolling temperature is not lower than 900℃. The rolling process adopts a controlled cooling process. The final rolling temperature is controlled to be 870~930℃ and the wire drawing temperature is 780~820℃. After wire drawing, the wire cooling rate is controlled to be 4.0℃ / s~9℃ / s. The wire is slowly cooled and removed from the production line at 600~630℃. Step 9: Spheroidizing annealing. Before annealing, pickling is used to remove the surface iron oxide scale. The spheroidizing temperature is 790±10℃. Spheroidizing is held at this temperature for 24-30 hours. After cooling to below 600℃, the annealing furnace is removed.

2. The method according to claim 1, characterized in that: Step 7: Peeling depth of the billet ≥ 0.8mm.

3. The method according to claim 1, characterized in that: Step 8: The rolling process uses online water cooling to control the cooling of the billet. After the wire is drawn, the wire rod is air-cooled on the Steyrmo line.

4. The method according to claim 1, characterized in that: The chemical composition of the bearing steel wire rod to which this method is applicable, by mass percentage, is: C 0.95–1.05%, Si 0.15–0.35%, Mn 0.25–0.45%, Cr 1.30–1.65%, Mo≤0.10%, Ni≤0.25%, Al≤0.050%, P≤0.025%, S≤0.020%, Cu≤0.25%, Ca≤0.0010%, O≤0.0012%, Ti≤0.0050%, As≤0.040%, Pb≤0.002%, As+Sn+Sb≤0.075%, with the balance being Fe and unavoidable impurities.

5. The method according to claim 1, characterized in that: After spheroidizing annealing, the hardness difference between the core and the surface of the wire rod is ≤15Hv, the spheroidization structure is grade 2~3, the oxygen content is ≤6ppm, the size of Ds-type non-metallic inclusions is ≤15μm, and the decarburized layer depth is ≤0.05mm.

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