Screw-down method for improving center quality of continuous casting billet

Abstract

The invention discloses a pressing method for improving the center quality of a continuous casting billet, and belongs to the technical field of steel continuous casting. The method comprises the following steps: (1) selecting a reduction model according to the solid fraction s of the core part of a continuous casting billet simulated and calculated by a solidification model; when s is smaller than or equal to 0.3, pressing is not carried out; when s is larger than 0.3 and smaller than 0.8, soft reduction is adopted, and the reduction of a single roller ranges from 0.5 mm to 5 mm; when s is larger than or equal to 0.8 and smaller than 1.0, heavy reduction is adopted, and the reduction of a single roller is 5-15 mm; (2) after heavy reduction, large reduction is adopted within the temperature difference range of 300-400 DEG C between the surface and the core of the continuous casting billet, and the reduction of a single roller is 20-30 mm; and (3) the rotating speed of the withdrawal and straightening machine is automatically calculated by the press-down control model according to a withdrawal and straightening machine rotating speed formula. By adopting multiple pressing modes, the center quality of the continuous casting billet can be effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of steel continuous casting, and in particular relates to a pressing method for improving the center quality of a continuous casting billet. Background Art

[0002] The center quality of continuous casting ingots includes center segregation, center porosity, and center shrinkage. Center segregation is caused by the presence of enriched segregated elements near the end of solidification. Once formed, it cannot be completely eliminated through subsequent processes, affecting the uniformity and performance of the steel. Center porosity is caused by the volume shrinkage of molten steel during solidification without timely replenishment of molten steel. Severe center porosity forms a center shrinkage cavity. Center shrinkage cavity has a significant impact on ingot quality. After continuous casting ingots are heated in a heating furnace, the shrinkage cavity is prone to oxidation. During the rolling process, the shrinkage cavity cannot be welded together, forming cracks, which seriously affect the mechanical properties of the product. With the development of high-end manufacturing, the performance requirements for products are becoming increasingly higher, especially the requirements for the center quality of products. Therefore, it is urgent to reduce and eliminate the defects of center segregation, center porosity, and center shrinkage cavity in ingots and improve the center quality of ingots.

[0003] Chinese patent application 201911101751.1, "A Combined Reduction Method for Continuously Casting Ingots," establishes a solidification model before reducing the ingot to determine the end point of solidification and the center solid fraction. This model then predicts the critical solid fraction at the final formation point of central macrosegregation and the critical solid fraction at the onset of central porosity. Dynamic light reduction is performed at the end of solidification in the region where the center solid fraction is less than the critical solid fraction at the final formation point of macrosegregation, while heavy reduction is performed in the region where the center solid fraction is greater than the critical solid fraction at the onset of central porosity. The reduction model is then used to predict the effects of different reduction amounts on central segregation and porosity, thereby determining the optimal reduction location and amount. While this method demonstrates significant improvements in central porosity and segregation in the ingot, it does not address high reductions or how to control mold level instability caused by changes in the steel throughput of the straightener due to ingot deformation after reduction.

[0004] Chinese patent application 201310386312.6 discloses a method for improving the internal quality of large square billets. During the continuous casting process, a high reduction scheme is employed in a straightening machine with a casting speed between 0.6 and 0.85 m / min and a solid-to-solid ratio between 0.7 and 0.9. The roll gap opening of the straightening machine is precisely controlled to maintain a reduction of 10 to 20 mm. A circumferential boss is centrally located on the straightening machine surface, with slopes of 1:3 to 1:10 positioned between each end of the boss and the straightening machine roll surface. The patent's use of the circumferential boss during the reduction roll creates a corresponding concave surface within the billet's inner arc, which is prone to surface cracking.

[0005] Chinese patent application 200710048924.9 discloses a dynamic soft reduction process for continuous casting of heavy rail steel blooms. The technical measures include controlling the casting speed and molten steel temperature. The continuous casting casting speed is 0.6-0.80 m / min, the molten steel superheat is 15-40°C, the specific water content is 0.25-0.3 L / kg, the surface temperature of the soft-reduction continuous casting bloom is controlled at 900-1020°C, the solidification rate in the soft-reduction zone is 30%-100%, and the total reduction is 1.6-7.0 mm. The total reduction required by this patent is too small, and the effect of improving the center quality of steels with higher carbon content is limited.

[0006] Chinese patent application 201811578543.6, "A method for improving the internal quality of continuous casting high-carbon steel blooms," involves controlling the casting speed of the continuous casting to 0.45-0.6 m / min; adjusting the water content in the secondary cooling zone to 0.15-0.30 L / kg, with a water content ratio of 1:1-3:1 across the width and thickness of the continuous casting; controlling the surface temperature of the continuous casting to 600-800°C across the width and 700-900°C across the thickness within the reduction zone; implementing electromagnetic stirring before the first reduction roller; and determining the reduction zone using the solid fraction calculated from the distance between the liquidus and solidus points. Within this reduction zone, the reduction of each reduction roller is determined based on the solid fraction, total reduction, and the coefficient k. The total reduction is 10-25 mm, resulting in minimal deformation at the center of the continuous casting.

[0007] At present, the method of pressing down the billet is used to solve the center defect of the billet, but it does not take into account that as the billet reduction amount increases, the amount of steel passed through the straightening machine at the same speed gradually decreases, which can easily cause the "steel pile" phenomenon, resulting in unstable liquid level in the crystallizer and affecting product quality. Summary of the Invention

[0008] In order to solve the above technical problems, the present invention provides a reduction method for improving the center quality of the continuous casting billet. By adopting the speed compensation of the straightening machine, the "steel piling" phenomenon caused by large reduction is solved; different degrees of light reduction, heavy reduction and large reduction are performed in different solidification stages of the continuous casting billet to reduce the center segregation, center porosity and center shrinkage defects of the continuous casting billet.

[0009] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0010] A method for improving the center quality of a continuous casting billet comprises the following operations:

[0011] (1) Select the reduction model based on the solid phase fraction s in the core of the continuous casting billet calculated by solidification model simulation;

[0012] When s≤0.3, no pressing is performed;

[0013] When 0.3<s<0.8, light reduction is adopted, and the reduction of single roller in light reduction is 0.5~5mm;

[0014] When 0.8≤s<1.0, heavy pressure is used, and the single roller pressure reduction under heavy pressure is 5~15mm;

[0015] (2) After heavy reduction, the temperature difference between the surface and the core of the continuous casting billet is calculated based on the solidification model simulation. When the temperature difference between the two is within the range of 300-400°C, a large reduction is used, and the reduction of a single roll in the large reduction is 20-30 mm;

[0016] (3) The speed of the straightening machine is automatically calculated by the press-down control model according to the speed formula of the straightening machine, which is as follows:

[0017]

[0018] Z n ——Current speed of the tension and leveling machine, rpm;

[0019] Z n-1 ——Speed of the previous straightening machine, rpm;

[0020] a——the thickness of the continuous casting slab before the current straightening machine is pressed down, mm;

[0021] b——width of continuous casting billet before being pressed down by the current straightening machine, mm;

[0022] f——slab width deformation coefficient, ranging from 0.1 to 0.3;

[0023] Δs——the current tension and leveling machine's pressure reduction, mm.

[0024] Furthermore, the total reduction of the light reduction is 10 to 20 mm, and the number of tension and leveling machines is 3 to 6.

[0025] Furthermore, the total reduction under heavy pressure is 15 to 30 mm, and the number of tension and leveling machines is 2.

[0026] Furthermore, the total reduction of the large reduction is 20 to 30 mm, and the number of tension and leveling machines is one.

[0027] Furthermore, after being pressed by the above method, the center segregation index of the continuous casting billet is 0.97-1.03, and the center shrinkage cavity is level 0.

[0028] Furthermore, in the two reduction models of heavy reduction and large reduction, the rotational speed of the first straightening machine performing heavy reduction and large reduction is calculated according to: straightening machine rotational speed = pulling speed ÷ straightening machine circumference.

[0029] The beneficial effects of adopting the above technical solution are:

[0030] The speed of the straightening machine of the present invention is calculated by a formula according to the reduction amount of the reduction model, and the speed of the straightening machine is adjusted in real time. By adopting the speed compensation of the straightening machine, the "steel piling" phenomenon caused by the large reduction amount is solved, and the quality problems caused by the unstable liquid level of the crystallizer are reduced.

[0031] The present invention increases the reduction amount of the continuous casting billet by adopting multiple reduction modes, is more conducive to the transmission of the deformation amount to the core of the continuous casting billet, and can more effectively improve the center quality of the continuous casting billet.

[0032] The continuous casting slab obtained by the present invention has a central segregation index of 0.97-1.03, and the proportion of central porosity of the continuous casting slab ≤ level 1.5 is as high as 98%. The central shrinkage cavity defect of the continuous casting slab is eliminated, and the performance of the product is greatly improved. DETAILED DESCRIPTION

[0033] The present invention takes bearing steel as an example, 1-7# drawing and straightening machine is a light pressure drawing and straightening machine, 8-9# drawing and straightening machine is a heavy pressure drawing and straightening machine, 10# drawing and straightening machine is a large pressure drawing and straightening machine, the original cross-sectional size of the continuous casting billet is 300×340mm, the drawing speed is 0.6m / min, the diameter of the light pressure drawing and straightening machine is 420mm, the diameter of the heavy pressure drawing and straightening machine is 450mm, the diameter of the large pressure drawing and straightening machine is 550mm, and the billet width deformation coefficient f=0.18 is taken as an example.

[0034] When no pressing is performed, the speed of the straightening machine = pulling speed ÷ the circumference of the straightening machine; thus,

[0035] When no pressing is performed, the speed of the light pressure straightening machine = 0.6÷(0.42×π) = 0.455 rpm.

[0036] Example 1: The specific operation of the pressing method for improving the center quality of the continuous casting billet in this embodiment is as follows:

[0037] (1) Select the reduction model based on the solid phase fraction s in the core of the continuous casting billet calculated by solidification model simulation;

[0038] When s≤0.3, no pressing is performed;

[0039] When 0.3<s<0.8, light reduction is adopted, with a total reduction of 20mm; 6 tension and leveling machines are used for light reduction, and the reductions of 2#-7# tension and leveling machines are: 2mm, 4mm, 4mm, 4mm, 4mm, 2mm in sequence;

[0040] When 0.8≤s<1.0, heavy pressure is used, with a total pressure reduction of 25mm; the 8# tensioning and leveling machine presses down 15mm, and the 9# tensioning and leveling machine presses down 10mm.

[0041] (2) After heavy pressure reduction, the temperature difference between the surface and the core of the continuous casting billet is calculated based on the solidification model simulation. When the temperature difference between the two is within the range of 300-400℃, large pressure reduction is adopted. The pressure reduction of the 10# straightening machine is 20mm, and the number of straightening machines is 1.

[0042] (3) The speed of the straightening machine is automatically calculated by the press-down control model according to the speed formula of the straightening machine. The speed of the straightening machine in this embodiment is as follows:

[0043] The speed of the 1# straightening machine is 0.455 rpm. According to the speed formula of the straightening machine, the speed of the 2# straightening machine is 0.457 rpm. Similarly, the speeds of the 3#, 4#, 5#, 6#, and 7# straightening machines are 0.463 rpm, 0.468 rpm, 0.474 rpm, 0.479 rpm, and 0.482 rpm respectively.

[0044] After the soft pressing is completed, the speed of the 7# straightening machine is 0.482 rpm. According to the formula of "straightening machine speed = pulling speed ÷ straightening machine circumference", the pulling speed of the 8# straightening machine is 0.636 m / min. According to the formula of "straightening machine speed = pulling speed ÷ straightening machine circumference", the pulling speed of the 8# straightening machine is 0.45 rpm. According to the formula of straightening machine speed Z n Calculation shows that the speed of 9# tension leveler is 0.465 rpm;

[0045] After the heavy pressure is over, the speed of the 9# straightening machine is 0.465 rpm. According to the reverse calculation of "straightening machine speed = pulling speed ÷ straightening machine circumference", the pulling speed of the 10# straightening machine is 0.657 m / min. According to the calculation of "straightening machine speed = pulling speed ÷ straightening machine circumference", the speed of the 10# straightening machine is 0.380 rpm.

[0046] The continuous casting billet after being pressed using the above method was tested, and the test results showed that the center segregation index was 0.98-1.03, the center porosity was level 1.0, and the center shrinkage cavity was level 0.

[0047] Example 2: The specific operation of the pressing method for improving the center quality of the continuous casting billet in this embodiment is as follows:

[0048] (1) Select the reduction model based on the solid phase fraction s in the core of the continuous casting billet calculated by solidification model simulation;

[0049] When s≤0.3, no pressing is performed;

[0050] When 0.3<s<0.8, use light reduction, with a total reduction of 10mm; 3#-5# three tension levelers perform light reduction, with reductions of 2.5mm, 3.5mm, and 4mm respectively;

[0051] When 0.8≤s<1.0, heavy pressure is used, with a total pressure reduction of 30mm; the 8# tensioning and leveling machine presses down 15mm, and the 9# tensioning and leveling machine presses down 15mm.

[0052] (2) After heavy pressure reduction, the temperature difference between the surface and the core of the continuous casting billet is calculated based on the solidification model simulation. When the temperature difference between the two is within the range of 300-400℃, large pressure reduction is adopted. The pressure reduction of the 10# straightening machine is 30mm, and the number of straightening machines is 1.

[0053] (3) The speed of the straightening machine is automatically calculated by the press-down control model according to the speed formula of the straightening machine. The speed of the straightening machine in this embodiment is as follows:

[0054] The speed of 1# and 2# tension and straightening machines is 0.455 rpm. According to the speed formula of tension and straightening machine, the speed of 3# tension and straightening machine is 0.458 rpm. Similarly, the speed of 4# and 5# tension and straightening machines are 0.463 rpm and 0.468 rpm respectively. 6# and 7# tension and straightening machines do not press down, and the speed is 0.468 rpm.

[0055] The same calculation as in Example 1 shows that the speed of the 8# straightening machine is 0.437 rpm. According to the speed formula of the straightening machine Z n Calculation shows that the speed of the 9# tension leveler is 0.459 rpm;

[0056] The same calculation as in Example 1 shows that the rotation speed of the 10# tension and leveling machine is 0.375 rpm.

[0057] The continuous casting billet after being pressed using the above method was tested, and the test results showed that the center segregation index was 0.97-1.02, the center porosity was level 1.0, and the center shrinkage cavity was level 0.

[0058] Example 3: The specific operation of the pressing method for improving the center quality of the continuous casting billet in this embodiment is as follows:

[0059] (1) Select the reduction model based on the solid phase fraction s in the core of the continuous casting billet calculated by solidification model simulation;

[0060] When s≤0.3, no pressing is performed;

[0061] When 0.3<s<0.8, use light reduction, with a total reduction of 15mm; 2#-5# four-stand tension levelers perform light reduction, with the reductions being 1.5mm, 3.5mm, 5mm, and 5mm respectively;

[0062] When 0.8≤s<1.0, heavy pressure is used, with a total reduction of 27mm; the 8# tensioning and leveling machine reduces the pressure by 12mm, and the 9# tensioning and leveling machine reduces the pressure by 15mm.

[0063] (2) After heavy pressure reduction, the temperature difference between the surface and the core of the continuous casting billet is calculated based on the solidification model simulation. When the temperature difference between the two is within the range of 300-400℃, large pressure reduction is adopted. The pressure reduction of the 10# straightening machine is 25mm, and the number of straightening machines is 1.

[0064] (3) The speed of the straightening machine is automatically calculated by the press-down control model according to the speed formula of the straightening machine. The speed of the straightening machine in this embodiment is as follows:

[0065] The speed of the 1# straightening machine is 0.455 rpm. According to the speed formula of the straightening machine, the speed of the 2# straightening machine is 0.457 rpm. Similarly, the speeds of the 3#, 4#, and 5# straightening machines are 0.461 rpm, 0.468 rpm, and 0.475 rpm respectively. The 6# and 7# straightening machines do not press down, and their speeds are the same as that of the 5# straightening machine, which is 0.475 rpm.

[0066] The same calculation as in Example 1 shows that the speed of the 8# straightening machine is 0.443 rpm. According to the speed formula Z n Calculation shows that the speed of 9# tension leveler is 0.466 rpm;

[0067] The same calculation as in Example 1 shows that the rotation speed of the 10# tension and leveling machine is 0.381 rpm.

[0068] The continuous casting billet after being pressed using the above method was tested, and the test results showed that the center segregation index was 0.97-1.02, the center porosity was level 1.0, and the center shrinkage cavity was level 0.

[0069] Example 4: The specific operation of the pressing method for improving the center quality of the continuous casting billet in this embodiment is as follows:

[0070] (1) Select the reduction model based on the solid phase fraction s in the core of the continuous casting billet calculated by solidification model simulation;

[0071] When s≤0.3, no pressing is performed;

[0072] When 0.3<s<0.8, light reduction is adopted, with a total reduction of 17mm; the five tension levelers 2#-6# are used for light reduction, with the reductions being 5mm, 4.5mm, 3.5mm, 2.5mm, and 1.5mm respectively;

[0073] When 0.8≤s<1.0, heavy pressure is used, with a total pressure reduction of 25mm; the 8# tensioning and leveling machine presses down 12mm, and the 9# tensioning and leveling machine presses down 13mm.

[0074] (2) After heavy pressure reduction, the temperature difference between the surface and the core of the continuous casting billet is calculated based on the solidification model simulation. When the temperature difference between the two is within the range of 300-400℃, large pressure reduction is adopted. The pressure reduction of the 10# straightening machine is 25mm, and the number of straightening machines is 1.

[0075] (3) The speed of the straightening machine is automatically calculated by the press-down control model according to the speed formula of the straightening machine. The speed of the straightening machine in this embodiment is as follows:

[0076] The speed of the 1# straightening machine is 0.455 rpm. According to the speed formula of the straightening machine, the speed of the 2# straightening machine is 0.461 rpm. Similarly, the speeds of the 3#, 4#, 5#, and 6# straightening machines are 0.467 rpm, 0.472 rpm, 0.475 rpm, and 0.478 rpm, respectively. The 7# straightening machine does not press down, and its speed is the same as that of the 6# straightening machine, which is 0.478 rpm.

[0077] The same calculation as in Example 1 shows that the speed of the 8# straightening machine is 0.446 rpm. According to the speed formula of the straightening machine Z n Calculation shows that the speed of the 9# tension and leveling machine is 0.469 rpm;

[0078] The same calculation as in Example 1 shows that the rotation speed of the 10# tension and leveling machine is 0.383 rpm.

[0079] The continuous casting billet after being pressed using the above method was tested, and the test results showed that the center segregation index was 0.99-1.03, the center porosity was level 1.0, and the center shrinkage cavity was level 0.

[0080] Example 5: The specific operation of the pressing method for improving the center quality of the continuous casting billet in this embodiment is as follows:

[0081] (1) Select the reduction model based on the solid phase fraction s in the core of the continuous casting billet calculated by solidification model simulation;

[0082] When s≤0.3, no pressing is performed;

[0083] When 0.3<s<0.8, light reduction is adopted, and the total reduction is 18.5mm; 1#-5# five-stand tension levelers are used for light reduction, and the reductions are: 4.5mm, 3.5mm, 2.5mm, 3.5mm, 4.5mm;

[0084] When 0.8≤s<1.0, heavy pressure is used, with a total pressure reduction of 20mm; the 8# tensioning and straightening machine presses down 10mm, and the 9# tensioning and straightening machine presses down 10mm.

[0085] (2) After heavy pressure reduction, the temperature difference between the surface and the core of the continuous casting billet is calculated based on the solidification model simulation. When the temperature difference between the two is within the range of 300-400℃, large pressure reduction is adopted. The pressure reduction of the 10# straightening machine is 30mm, and the number of straightening machines is 1.

[0086] (3) The speed of the straightening machine is automatically calculated by the press-down control model according to the speed formula of the straightening machine. The speed of the straightening machine in this embodiment is as follows:

[0087] The speed of the 1# straightening machine is 0.455 rpm. According to the speed formula of the straightening machine, the speed of the 2# straightening machine is 0.459 rpm. Similarly, the speeds of the 3#, 4#, and 5# straightening machines are 0.463 rpm, 0.467 rpm, and 0.474 rpm respectively. The 6# and 7# straightening machines do not press down, and their speeds are the same as that of the 5# straightening machine, which is 0.474 rpm.

[0088] The same calculation as in Example 1 shows that the speed of the 8# straightening machine is 0.442 rpm. According to the speed formula of the straightening machine Z n Calculation shows that the speed of 9# tension leveler is 0.456 rpm;

[0089] The same calculation as in Example 1 shows that the rotation speed of the 10# tension and leveling machine is 0.373 rpm.

[0090] The continuous casting billet after being pressed using the above method was tested, and the test results showed that the center segregation index was 0.99-1.03, the center porosity was level 1.0, and the center shrinkage cavity was level 0.

[0091] Example 6: The specific operation of the pressing method for improving the center quality of the continuous casting billet in this embodiment is as follows:

[0092] (1) Select the reduction model based on the solid phase fraction s in the core of the continuous casting billet calculated by solidification model simulation;

[0093] When s≤0.3, no pressing is performed;

[0094] When 0.3<s<0.8, light reduction is adopted, with a total reduction of 15mm; 3#-7# five-stand tension levelers are used for light reduction, with the reductions being 1mm, 2.5mm, 3.5mm, 4.5mm, and 3.5mm respectively;

[0095] When 0.8≤s<1.0, heavy pressure is used, with a total pressure reduction of 15mm; the 8# tensioning and leveling machine presses down 10mm, and the 9# tensioning and leveling machine presses down 5mm.

[0096] (2) After heavy pressure reduction, the temperature difference between the surface and the core of the continuous casting billet is calculated based on the solidification model simulation. When the temperature difference between the two is within the range of 300-400℃, large pressure reduction is adopted. The pressure reduction of the 10# straightening machine is 30mm, and the number of straightening machines is 1.

[0097] (3) The speed of the straightening machine is automatically calculated by the press-down control model according to the speed formula of the straightening machine. The speed of the straightening machine in this embodiment is as follows:

[0098] The speed of 1# and 2# tension and straightening machines is 0.455 rpm. According to the speed formula of tension and straightening machine, the speed of 3# tension and straightening machine is 0.459 rpm. Similarly, the speeds of 4#, 5#, 6# and 7# tension and straightening machines are 0.456 rpm, 0.459 rpm, 0.464 rpm, 0.470 rpm and 0.475 rpm respectively.

[0099] The same calculation as in Example 1 shows that the speed of the 8# straightening machine is 0.443 rpm. According to the speed formula Z n Calculation shows that the speed of 9# tension leveler is 0.450 rpm;

[0100] The same calculation as in Example 1 shows that the rotation speed of the 10# tension and leveling machine is 0.369 rpm.

[0101] The continuous casting billet after being pressed using the above method was tested, and the test results showed that the center segregation index was 0.98-1.02, the center porosity was level 1.0, and the center shrinkage cavity was level 0.

[0102] Comparative test: Five heats of bearing steel before the implementation of the present invention were randomly selected as a control group and any five heats of the above embodiments 1-5 were tested and analyzed. The test and analysis contents included center segregation, center porosity, and center shrinkage.

[0103] (1) Central segregation: comparison of central segregation index between the control group and the embodiment;

[0104] (2) Central porosity: comparison of central porosity levels between the control group and the embodiment;

[0105] (3) Central shrinkage: comparison of central shrinkage levels between the control group and the example;

[0106] (4) Test and analysis methods:

[0107] ① Take a longitudinal sample of the continuous casting billet, polish it, take 5 points in the longitudinal direction of the cross section, drill some samples for infrared analysis of composition, and the ratio of the analyzed composition to the finished sample composition is the central segregation index.

[0108] ② Take low-magnification samples of the test continuous casting billets, carry out pickling inspection to check the center porosity and center shrinkage, and grade them.

[0109] (5) Through testing and analysis, the results are shown in Tables 1 to 3.

[0110] Table 1: Comparison of central segregation index between control group and example

[0111]

[0112] Table 2: Central looseness test results of control group and embodiment

[0113]

[0114] Table 3: Central shrinkage pore detection results of control group and embodiment

[0115]

[0116] It can be seen from Tables 1 to 3 that the method effectively improves the center segregation of the continuous casting billet, reduces the center porosity of the continuous casting billet, and eliminates the shrinkage cavity defect in the center of the continuous casting billet.

Claims

1. A method for improving the center quality of a continuous casting billet, characterized in that: The following operations are included: (1) Select the reduction model based on the solid phase fraction s in the core of the continuous casting billet calculated by solidification model simulation; When s≤0.3, no pressing is performed; When 0.3<s<0.8, light reduction is adopted, and the reduction of single roller in light reduction is 0.5~5mm; When 0.8≤s<1.0, heavy pressure is used, and the single roller pressure reduction under heavy pressure is 5~15mm; (2) After heavy reduction, the temperature difference between the surface and the core of the continuous casting billet is calculated based on the solidification model simulation. When the temperature difference between the two is within the range of 300-400°C, a large reduction is used, and the reduction of a single roll in the large reduction is 20-30 mm; (3) The speed of the straightening machine is automatically calculated by the press-down control model according to the speed formula of the straightening machine, which is as follows: Z n ——Current speed of the tension and leveling machine, rpm; Z n-1 ——Speed of the previous straightening machine, rpm; a——the thickness of the continuous casting slab before the current straightening machine is pressed down, mm; b——width of continuous casting billet before being pressed down by the current straightening machine, mm; f——slab width deformation coefficient, ranging from 0.1 to 0.3; Δs——the current tension and leveling machine's pressure reduction, mm.

2. The method for improving the center quality of continuous casting billets according to claim 1, characterized in that: The total reduction under light pressure is 10 to 20 mm, and the number of tension and leveling machines is 3 to 6.

3. The method for improving the center quality of continuous casting billets according to claim 2, characterized in that: The total reduction under heavy pressure is 15 to 30 mm, and there are two straightening machines.

4. The method for improving the center quality of continuous casting billets according to claim 3, characterized in that: The total reduction of the maximum reduction is 20 to 30 mm, and the number of tension and leveling machines is 1.

5. The method for improving the center quality of a continuous casting slab according to any one of claims 1 to 4, characterized in that: After being pressed by the method, the center segregation index of the continuous casting billet is 0.97-1.03, and the center shrinkage cavity is level 0.

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