A method for reducing carbon segregation and improving banded microstructure in large-section rectangular billets of gear steel

Abstract

This invention discloses a method for reducing carbon segregation and improving banded microstructure in large-section rectangular billets of gear steel. This method addresses the problem of secondary banded microstructure caused by dendritic segregation of carbon and alloying elements due to the large billet size and long solidification time in (380~400) mm × (490~520) mm large-section gear steel. Without increasing equipment investment, changing the rolling process, or affecting the overall uniformity of carbon composition in the billet and round steel cross-section, this method employs a combined process of "weakening electromagnetic stirring in the crystallizer + stopping electromagnetic stirring at the end of solidification + optimizing light reduction at the end of solidification." This achieves a reduction in the banded microstructure level of the round steel to 0.5 while maintaining a central porosity of 0.5 and a shrinkage cavity of 0.

Description

Technical Field

[0001] This invention relates to the fields of steelmaking technology and continuous casting technology, and more particularly to a method for reducing carbon segregation and improving banded structure in large-section rectangular billets of gear steel. Background Technology

[0002] Gear steel is a core material for gearboxes in automobiles and construction machinery. Its microstructure uniformity directly affects gear performance and service life. Banding is a common microstructural defect in gear steel, characterized by alternating bands of ferrite and pearlite along the rolling direction. The presence of banding often leads to uneven hardness across the carburized layer and tooth surface, resulting in inconsistent fatigue performance of the carburized layer. It also exacerbates heat treatment deformation and, in severe cases, can cause quenching cracks. Therefore, gear manufacturers have placed high demands on the banding structure of automotive gear steel.

[0003] To meet the high requirements of gear steel for banded structure, the rolling process must ensure a sufficient compression ratio, making large-section rectangular billets a trend in gear steel production. However, due to their large size and long solidification time, large-section rectangular billets exhibit particularly prominent dendritic segregation of carbon and alloying elements during the solidification process, fundamentally exacerbating the difficulty of controlling the subsequent banded structure. Therefore, controlling dendritic segregation in continuously cast billets is key to improving the banded structure at its source. Currently, traditional processes mostly rely on weak crystallizer electromagnetic stirring and strong solidification end electromagnetic stirring to macroscopically control segregation from the source. Chinese patent CN120480127A discloses a high-homogeneity medium-low carbon alloy steel large-section rectangular billet and its preparation method. For cross-sections of 320~390mm×385~510mm, a combined process of "weak crystallizer electromagnetic stirring + strong solidification end electromagnetic stirring + light reduction + heavy reduction" is used to improve the uniformity of the billet cross-section composition and improve frame-type segregation by improving center segregation. Chinese patent CN118832130A discloses a production method for improving the segregation of large-section rectangular gear steel frames. The method employs a process of "minimizing the intensity of electromagnetic stirring in the crystallizer (100A / 2.5Hz) + end electromagnetic stirring (400~600A / 3.5Hz)" to reduce the influence of the axial crystal region on the segregation frame.

[0004] However, traditional processes are difficult to apply to gear steel with a cross-sectional size of (380~400) mm × (490~520) mm, where a significant banded structure still exists in the area near 1 / 2R (where R is the radius of the round steel). During gear machining, the tooth root is usually located near 1 / 2R (where R is the radius of the round steel) of the cross-section of this round steel. The level of banded structure here directly affects the performance of the gear (the banded structure inspection location is at 1 / 2R), which is also the quality evaluation location that gear steel users are most concerned about. Therefore, a method is needed to optimize the banded structure near 1 / 2R of gear steel with a cross-sectional size of (380~400) mm × (490~520) mm, reduce the banded structure level in this area, and thus ensure the service performance of the tooth root. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for reducing carbon segregation and improving banded microstructure in large-section rectangular billets of gear steel. This method addresses the issue of secondary banded structures at the 1 / 2R position of large-section gear steel (380~400) mm × (490~520) mm, which is susceptible to dendritic segregation in the billet. Without increasing equipment investment, changing the rolling process, or affecting the overall carbon composition uniformity of the billet and round steel cross-section, this method employs a combined process of "weakening the electromagnetic stirring in the crystallizer + stopping the electromagnetic stirring at the end of solidification + optimizing the light reduction at the end of solidification." This avoids the impact of the electromagnetic stirring rotation at the end of solidification on the carbon segregation uniformity at the 1 / 4 thickness position of the billet, eliminating the uneven distribution of carbon elements and microstructure caused by the internal flow of molten steel. Simultaneously, by weakening the current and frequency of the electromagnetic stirring in the crystallizer and optimizing the reduction amount at the end of solidification, the method reduces negative segregation on the billet surface and the overall carbon gradient, compensating for the risk of central porosity caused by stopping the electromagnetic stirring at the end of solidification. While ensuring a central porosity level of 0.5 and a shrinkage cavity level of 0, the method reduces the banded structure level of the round steel to 0.5.

[0006] To achieve the above objectives, the present invention is accomplished through the following technical solutions.

[0007] A method for reducing carbon segregation and improving banded microstructure in large-section rectangular billets of gear steel includes the following steps: converter smelting → LF refining → continuous casting → slow cooling of billet → heated rolling; The continuous casting process stops using electromagnetic stirring at the solidification end. Instead, electromagnetic stirring in the crystallizer and light pressure at the solidification end are used for the molten steel leaving the LF refining station to ensure that the superheat in the continuous casting tundish is 10~30℃; the casting speed is 0.40~0.45m / min; and the secondary cooling water ratio is 0.13~0.15L / kg, resulting in a billet with a cross-section of (380~400)mm×(490~520)mm. The current controlling the electromagnetic stirring of the crystallizer is 150~350A, and the frequency is 1.4~1.6Hz; The light pressing at the end of solidification, using pressing rollers and their corresponding positions and pressing amounts, are as follows: Roll #1: Distance from the meniscus is 18.17~18.19m, and the reduction is 0.8~1.2mm; #2 roller: distance from the meniscus is 19.63~19.65m, and the reduction is 2.8~3.2mm; Roller #3: Distance from the meniscus is 21.09~21.1m, and the reduction is 5.8~6.2mm; Roller #4: Distance from the meniscus is 22.55~22.57m, and the reduction is 1.8~2.2mm.

[0008] In the above technical solution, the carbon content of the gear steel is 0.17wt%~0.23wt%.

[0009] In the above technical solution, the gear steel includes: 20CrMnTiH, 22CrMoH and SAE8620H.

[0010] In the above technical solution, the converter smelting involves: adding steel feedstock into the converter for blowing, controlling the carbon content at the tapping endpoint to be ≥0.06wt% and the phosphorus content to be ≤0.020wt%, using double-slag tapping to achieve a slag discharge target of ≤3t / furnace; when the tapping amount reaches 1 / 4 of the total steel volume, aluminum ingots, ferrosilicon, medium carbon ferrochrome, pre-melted calcium aluminate, refined (top) lime, and carbon raiser are added sequentially to ensure that the charging ends before the tapping amount reaches 3 / 4 of the total steel volume, controlling the carbon content in the molten steel at the converter outlet to be 0.11wt%~0.15wt%, the manganese content to be 0.77wt%~0.83wt%, the silicon content to be 0.15wt%~0.21wt%, and the chromium content to be 0.97wt%~1.03wt%.

[0011] In the above technical solution, the LF refining process involves: blowing argon onto the molten steel after converter smelting; adding slag-forming materials in batches and applying electricity to form a thin slag; adding deoxidizer to the slag surface in batches for diffusion deoxidation; continuing to apply electricity for 8-12 minutes; dipping the slag to confirm its whiteness and then measuring the temperature and taking samples; adjusting the alloy composition; adding ferrotitanium; feeding calcium wire according to the acid-soluble aluminum (Als) content to control the carbon content, manganese content, silicon content, and chromium content in the molten steel leaving the station to be 0.17wt%~0.20wt%, 0.81wt%~0.87wt%, 0.21wt%~0.27wt%, and 1.01wt%~1.07wt%.

[0012] In the above technical solution, the slag-forming materials include: lime and pre-melted calcium aluminate, with the mass of each batch of slag-forming materials ≤100kg; the deoxidizer is added in batches by a loose mixture of calcium carbide, aluminum granules, and silicon carbide.

[0013] In the above technical solution, the temperature is measured at 1545~1555℃, and the white slag retention time is ≥20min.

[0014] In the above technical solution, titanium iron is added before feeding calcium and then energized for 3-5 minutes.

[0015] In the above technical solution, during LF refining, after the ladle is placed at the soft blowing station, strong argon blowing is started with an argon flow rate of 600~700 NL / min. After 50~70 seconds, it is adjusted to soft argon blowing before entering the refining station with an argon flow rate of 200~300 NL / min. When the ladle enters the refining station, the argon flow rate is adjusted to 400~500 NL / min, and argon is blown throughout the process.

[0016] In the above technical solution, the alloy composition adjustment operation includes: when the acid-soluble aluminum (Als) is ≤0.022wt%, the acid-soluble aluminum (Als) is adjusted to 0.022wt%~0.027wt%; diffusion deoxidation is continued; medium carbon ferromanganese, ferrosilicon and medium carbon ferrochrome are added to the diffusion-deoxidized molten steel.

[0017] In the above technical solution, calcium wire is fed according to the acid-soluble aluminum (Als) content of the molten steel before calcium wire feeding. The reference amount is Als × 3~5, rounded to the nearest integer. The calcium wire feed is ≥50m and the feeding speed is 1.5m / s. After the calcium wire feeding is completed, the machine is moved to the soft blowing station to add a covering agent. At the same time, the argon gas is adjusted to prevent the molten steel from being exposed due to the creeping surface. The soft blowing argon time is ≥20min.

[0018] In the above technical solution, the water volume of the crystallizer is 80~86m wide. 3 / h, narrow face 68~74m 3 / h.

[0019] In the above technical solution, the billet slow cooling is as follows: the billet after continuous casting is sent into a slow cooling pit for slow cooling. The temperature of the billet entering the pit after continuous casting is ≥600℃, the temperature exiting the pit is ≤350℃, and the slow cooling time is ≥24h.

[0020] In the above technical solution, the heated rolling process involves heating and rolling the slowly cooled billet, controlling the initial rolling temperature to be 1020~1150℃ and the final rolling temperature to be 920~1000℃.

[0021] In the above technical solution, during the heated rolling process, the temperature of heating section I is 650~850℃, the temperature of heating section II is 950~1100℃, the temperature of heating section III is 1190~1250℃, and the temperature of the soaking section is 1160~1240℃.

[0022] In the above technical solution, the round steel is slowly cooled after heating and rolling, and the slow cooling time is ≥36h.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention targets a specific cross-section of (380~400)mm×(490~520)mm, and reveals the correspondence between the solidification thickness of the billet, the 1 / 4 thickness of the billet, and the 1 / 2R position of the round steel at the installation position of the electromagnetic stirring at the solidification end. Based on this, a reverse process combination of "weakening the electromagnetic stirring of the crystallizer + stopping the electromagnetic stirring at the solidification end + optimizing the light pressing at the solidification end" is proposed, which realizes the synergistic optimization of carbon segregation, banded structure and central compactness at the 1 / 2R position of the round steel.

[0024] (2) The method of the present invention avoids the influence of the rotational motion scouring and cleaning on the carbon segregation uniformity at the 1 / 4 thickness position of the billet by stopping the electromagnetic stirring at the end of solidification, eliminates the uneven distribution of carbon elements and structure caused by the internal flow of molten steel, and at the same time, with the weakening current and frequency of the electromagnetic stirring of the crystallizer, and the optimized control of the amount of pressure reduction under the light pressure at the end of solidification, the negative segregation on the surface of the billet and the overall carbon difference are reduced, and the risk of central porosity caused by stopping the electromagnetic stirring at the end of solidification is compensated. While optimizing the banded structure at the 1 / 2R position of the gear steel round bar, the central porosity can be controlled at level 0.5 and the shrinkage cavity at level 0, realizing the synergistic improvement of surface / near surface structure uniformity and core density.

[0025] (3) The method of the present invention achieves quality improvement without increasing equipment, changing the rolling process, or reducing energy consumption; the method is applicable to conventional continuous casting machines without heavy pressure equipment, and has the characteristics of low equipment investment, simple operation and strong engineering applicability. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of carbon segregation points on the cross-section of the billet in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram showing the carbon segregation points on the cross-section of the round steel in Embodiment 1 of the present invention; Figure 3 This is a low-magnification microstructure photograph of the cast billet in Embodiment 1 of the present invention; Figure 4 This is a low-magnification microstructure photograph of the cast billet in Comparative Example 1 of this invention; Figure 5 This is a metallographic photograph of the strip-shaped microstructure of the round steel in Embodiment 1 of the present invention; Figure 6 This is a metallographic photograph of the strip-shaped microstructure of a round steel bar, Comparative Example 1 of this invention; Figure 7 This is a schematic diagram of the billet tracking point location in Embodiment 1 of the present invention; Figure 8 This is a solidification cloud diagram of the billet in Embodiment 1 of the present invention. Detailed Implementation

[0027] The following examples are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0028] Unless otherwise specified, the materials used in the embodiments of the present invention can be obtained commercially or prepared according to conventional methods known to those skilled in the art.

[0029] In the following embodiments, the steel ladle double-permeable bricks used are of good quality; Example 1 A method for reducing carbon segregation and improving banded microstructure in large-section rectangular billets of gear steel includes the following steps: converter smelting → LF refining → continuous casting → slow cooling of billet → heated rolling; Converter smelting: 125t of molten iron and 6.5t of scrap steel are added to the converter for blowing. The carbon content at the end of tapping is 0.08wt% and the phosphorus content is 0.014wt%. Double slag tapping is used to achieve a slag discharge of 3t / furnace. When the tapping amount reaches 1 / 4 of the total steel, 144kg of aluminum ingots, 1446kg of silicon-manganese alloy, 1989kg of medium carbon ferrochrome, 476kg of pre-melted calcium aluminate, 400kg of refined (top) lime, and 30kg of carbon raiser are added in sequence to ensure that the charging ends before the tapping amount reaches 3 / 4 of the total steel. The carbon content, manganese content, silicon content, and chromium content in the molten steel composition at the time of exiting the converter are controlled to be 0.13wt%, 0.80wt%, 0.17wt%, and 0.99wt%. Argon is purged throughout the process from tapping to ladle hoisting.

[0030] LF Refining: After placing the ladle containing molten steel from the converter at the soft-blowing station, start strong argon blowing at a flow rate of 650 NL / min. After 1 minute, adjust to soft argon blowing and proceed to the refining station at a flow rate of 250 NL / min. Once the ladle is in the refining station, adjust the argon flow rate to 450 NL / min, apply electricity to form a thin slag, and add slag-forming materials in batches (including 480 kg of refined lime and 400 kg of pre-melted calcium aluminate). Add a deoxidizer (130 kg of calcium carbide, 25 kg of aluminum granules, and 60 kg of silicon carbide, mixed in bulk and added in batches) to the slag surface for diffusion deoxidation. Continue energizing for 10 minutes. After confirming the formation of a white slag with good molten fluidity by dipping the ladle in slag, measure the temperature, which is 1550℃. Stop the power, blow argon for 2 minutes, and then take the first sample for analysis. Adjust the overall temperature... To prevent the addition of aluminum later, continue diffusion deoxidation and maintain a reducing atmosphere until the molten steel leaves the station, keeping the white slag for 25 minutes. After good deoxidation, add medium-carbon ferromanganese (100 kg), ferrosilicon (32 kg), and medium-carbon ferrochrome (45 kg) according to the target composition. After the composition is qualified, add 380 kg of ferrotitanium before feeding the calcium wire. After energizing for 4 minutes, feed 120 m of calcium wire at a feeding speed of 1.5 m / s. After feeding the calcium wire, move to the soft blowing station and add a covering agent. At the same time, adjust the argon gas to prevent the molten steel from being exposed due to surface peristalsis. The soft blowing argon time is 25 minutes. Control the molten steel composition (target composition) at the time of leaving the LF refined molten steel station to have a carbon content of 0.20 wt%, a manganese content of 0.86 wt%, a silicon content of 0.25 wt%, and a chromium content of 1.07 wt%.

[0031] Continuous casting: Electromagnetic stirring at the solidification end (F-EMS) is discontinued. For the LF refined steel exiting the station, electromagnetic stirring in the crystallizer and light pressure at the solidification end are used to ensure the superheat in the continuous casting tundish is 20~25℃; casting speed is 0.41m / min; secondary cooling water flow rate is 0.13L / kg; and the crystallizer water flow rate is 85m wide. 3 / h, narrow face 71m 3 / h, the mold flux used is a special mold flux for large square billets of 20CrMnTiH steel, resulting in a 390mm × 510mm cross-section slab (20CrMnTiH slab). The electromagnetic stirring parameters are as follows: The current of the weakened electromagnetic stirring in the crystallizer is 250A and the frequency is 1.5Hz. The electromagnetic stirring in the crystallizer agitates the molten steel and scours the solidification front, bringing the high concentration of solute at the solidification front to the liquid phase region, resulting in the formation of a negative segregation zone under the surface of the billet. Weakening the intensity of the electromagnetic stirring in the crystallizer helps to reduce the negative segregation on the surface of the billet and the overall carbon difference. To mitigate the risk of center segregation caused by stopping electromagnetic stirring at the solidification end and weakening electromagnetic stirring in the crystallizer, a gentle pressing method at the solidification end is employed. The pressing method at the solidification end utilizes pressing rollers and their corresponding positions and pressing amounts, as shown in Table 1. Table 1

[0032] The mechanism of light pressure at the end of solidification is adopted: light pressure compensates for the volume shrinkage at the end of solidification through mechanical extrusion, improves the core density of the billet, reduces dendrite spacing, and reduces microsegregation, thereby compensating for the risk of central porosity caused by stopping electromagnetic stirring at the end of solidification and weakening electromagnetic stirring in the crystallizer, and achieving dual optimization of the 1 / 2R position quality and the center quality.

[0033] Slow cooling of the billet: The 20CrMnTiH billet after continuous casting is sent to a slow cooling pit for slow cooling. The temperature upon entering the pit is 610℃, and the temperature upon exiting the pit is 270℃. The slow cooling time is 48 hours. This ensures that the billet cools slowly and evenly in the slow cooling pit, fully releasing stress.

[0034] The 20CrMnTiH billet after continuous casting was subjected to carbon segregation testing. The locations of the carbon segregation testing points are shown in [reference needed]. Figure 1 The carbon composition at each test point is shown in Table 2.

[0035] Table 2

[0036] Heating and rolling: The slowly cooled billet is heated and rolled in a regenerative walking beam furnace to obtain φ200mm round steel. The temperature of heating section I is controlled at 747℃, heating section II at 1012℃, heating section III at 1230℃, and soaking section at 1220℃.

[0037] Rolling was performed using a φ1150mm two-roll reversible billet mill, followed by rolling on a 4-stand φ850mm + 4-stand φ750mm finishing mill. The initial rolling temperature was 1109℃, and the final rolling temperature was 950℃. After rolling, the round bars were placed in a slow cooling pit for 45 hours to cool slowly.

[0038] Inspect φ200mm round steel for carbon segregation. The locations for carbon segregation testing are shown below. Figure 2 The carbon composition at each test point is shown in Table 3.

[0039] Table 3

[0040] Comparative Example 1 A method for reducing carbon segregation and improving banded structure in large-section rectangular billets of gear steel (traditional method) is basically the same as that in Example 1, except that it is a continuous casting process. In the continuous casting process, electromagnetic stirring at the end of solidification is turned on in Comparative Example 1, and the current is set to 400A and the frequency is 5.5Hz.

[0041] The low-magnification microstructure of the 20CrMnTiH billet from Comparative Example 1 and Example 1, and the banded microstructure of the rolled φ200mm round steel were examined. The results are shown in Table 4. The low-magnification microstructure of the 20CrMnTiH billet from Example 1 is as follows: Figure 3 As shown, the low-magnification microstructure of the 20CrMnTiH billet in Comparative Example 1 is as follows: Figure 4 As shown, the φ200mm round steel strip structure of Example 1 is as follows: Figure 5 As shown, the microstructure of the φ200mm round steel strip in Comparative Example 1 is as follows: Figure 6 As shown.

[0042] Table 4

[0043] To characterize the relative position change of the tracking point within the billet during rolling, it is calculated using the following formula: a = (L / H) × 100%, where H represents half the billet thickness (mm); L represents the distance (mm) from the rolling tracking point to the center point. The position of the billet tracking point is shown in the figure. Figure 7 As shown.

[0044] Taking the rolling of φ200mm round steel in Example 1 as an example, the relative position changes of the tracking nodes before and after rolling are shown in Table 5.

[0045] Table 5

[0046] Calculations revealed that before and after rolling, the 1 / 4 thickness position of the billet deviated from the 1 / 2R position of the round steel by 4mm. This can be approximated as the 1 / 4 thickness position of the billet corresponding to the 1 / 2R position of the round steel. However, ANSYS numerical simulations showed that the existing solidification end electromagnetic stirrer installation position corresponds to a billet solidification thickness of 126mm, i.e., the 1 / 4 thickness position of the billet (e.g., ...). Figure 8 As shown), the results of Comparative Example 1 and Example 1 are analyzed as follows: 1) In the method of Comparative Example 1, under the action of electromagnetic stirring at the end of solidification, the rotational motion of the molten steel in the horizontal section will increase the non-uniformity of carbon segregation at the 1 / 4 thickness position of the billet. However, after stopping the electromagnetic stirring at the end of solidification using the method of Example 1 of this invention, the carbon segregation range of the billet cross section decreased from 0.060% to 0.054%; the carbon segregation range of the round steel cross section decreased from 0.040% to 0.036%; the carbon segregation range at the 1 / 4 thickness position of the billet decreased from 0.045% to 0.028%; and the carbon segregation range at the 1 / 2R position of the round steel decreased from 0.031% to 0.020%.

[0047] 2) In the method of Comparative Example 1, electromagnetic stirring at the end of solidification causes the internal molten steel to flow. This flow leads to increased non-uniformity in carbon distribution and microstructure, resulting in increased non-uniformity in interdendritic segregation. Interdendritic segregation directly affects the grade of the banded microstructure. However, in the method of Example 1 of this invention, after stopping the electromagnetic stirring at the end of solidification, the grade of the banded microstructure decreased from 1.5 to 0.5.

[0048] 3) In the method of Embodiment 1 of the present invention, under the action of light pressure at the end of solidification, the low magnification structure of the cast billet after stopping the electromagnetic stirring at the end of solidification did not show obvious shrinkage cavities, and the central porosity rating was 0.5.

[0049] Compared to existing technologies that generally rely on and strengthen end-solidation electromagnetic stirring to improve billet segregation, forming an inherent process approach of "end-stage electromagnetic stirring is indispensable," this invention breaks through the traditional approach of strengthening end-stage electromagnetic stirring to break dendrites and expand the equiaxed grain region when improving center segregation. It reveals the correspondence between the installation position of the end-stage electromagnetic stirring, the 1 / 4 thickness position of the billet, and the 1 / 2R position of the round steel in a specific cross-section of 390mm × 510mm. By disabling end-solidation electromagnetic stirring in continuous casting, segregation at the 1 / 4 thickness position of the billet is avoided, thereby improving the quality of the 1 / 2R position of the round steel. It also verifies that under specific process windows, end-solidation light pressure, originally considered complementary to end-solidation electromagnetic stirring, can replace it to achieve center densification. Therefore, this invention effectively reduces carbon segregation at the 1 / 4 thickness position of the billet while ensuring no significant deterioration in the overall carbon gradient of the billet, ultimately improving the microstructure quality and banded microstructure grade of the 1 / 2R position of the round steel.

[0050] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A method for reducing carbon segregation and improving banded structure in a large section rectangular bloom of gear steel, comprising the steps of: The process involves converter smelting → LF refining → continuous casting → slow cooling of the billet → heated rolling; characterized in that the electromagnetic stirring at the solidification end is stopped during continuous casting, and the molten steel exiting the LF refining station is subjected to electromagnetic stirring in the crystallizer and light pressure at the solidification end; ensuring that the superheat in the continuous casting tundish is 10~30℃, the casting speed is 0.40~0.45m / min, and the secondary cooling water ratio is 0.13~0.15L / kg, resulting in a billet with a cross-section of (380~400)mm×(490~520)mm; The current controlling the electromagnetic stirring of the crystallizer is 150~350A, and the frequency is 1.4~1.6Hz; The light pressing at the end of solidification, using pressing rollers and their corresponding positions and pressing amounts, are as follows: Roll #1: Distance from the meniscus is 18.17~18.19m, and the reduction is 0.8~1.2mm; #2 roller: distance from the meniscus is 19.63~19.65m, and the reduction is 2.8~3.2mm; Roller #3: Distance from the meniscus is 21.09~21.1m, and the reduction is 5.8~6.2mm; Roller #4: Distance from the meniscus is 22.55~22.57m, and the reduction is 1.8~2.2mm.

2. The method of claim 1, wherein, The carbon content of the gear steel is 0.17wt%~0.23wt%.

3. The method according to claim 2, characterized in that, The gear steels include: 20CrMnTiH, 22CrMoH and SAE8620H.

4. The method according to claim 1, characterized in that, The converter smelting process involves adding steel feedstock into the converter for blowing, controlling the carbon content at the tapping endpoint to be ≥0.06wt% and the phosphorus content to be ≤0.020wt%, using a double-slag tapping method to achieve a slag discharge target of ≤3t / furnace; when the tapping amount reaches 1 / 4 of the total steel volume, aluminum ingots, ferrosilicon, medium carbon ferrochrome, pre-melted calcium aluminate, refined lime, and carbon raiser are added sequentially, ensuring that the charging ends before the tapping amount reaches 3 / 4 of the total steel volume, and controlling the carbon content, manganese content, silicon content, and chromium content in the molten steel at the converter outlet to be 0.11wt%~0.15wt%, 0.77wt%~0.83wt%, 0.15wt%~0.21wt%, and 0.97wt%~1.03wt% of the chromium content.

5. The method according to claim 1, characterized in that, The LF refining process involves: blowing argon onto the molten steel after converter smelting; adding slag-forming materials in batches and applying electricity to form a thin slag; adding deoxidizer to the slag surface in batches for diffusion deoxidation; continuing to apply electricity for 8-12 minutes; dipping the slag in water to confirm its whiteness and then measuring the temperature and taking samples; adjusting the alloy composition; adding ferrotitanium; feeding calcium wire according to the acid-soluble aluminum content; and controlling the carbon content, manganese content, silicon content, and chromium content in the molten steel leaving the LF refining station to be 0.17wt%~0.20wt%, 0.81wt%~0.87wt%, 0.21wt%~0.27wt%, and 1.01wt%~1.07wt%.

6. The method according to claim 1, characterized in that, The crystallizer water quantity is 80~86m 3 / h on the wide side and 68~74m 3 / h on the narrow side.

7. The method according to claim 1, characterized in that, The billet slow cooling: The billet after continuous casting is sent into a slow cooling pit for slow cooling. The temperature of the billet entering the pit is ≥600℃, the temperature exiting the pit is ≤350℃, and the slow cooling time is ≥24h.

8. The method according to claim 1, characterized in that, The heated rolling process involves heating and rolling the slowly cooled billet, controlling the initial rolling temperature at 1020~1150℃ and the final rolling temperature at 920~1000℃.

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