Dynamic soft reduction and on-line quenching synergistic process for continuous casting billet and application of dynamic soft reduction and on-line quenching synergistic process
Through the collaborative process of light pressure and online quenching during continuous casting, the heat consumption and control problems of offline quenching are solved, efficient quenching and tissue improvement of continuous casting billets are achieved, and the mechanical properties and internal density of steel products are improved.
Patent Information
- Application Number
- CN202510530707.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-25
- Publication Date
- 2025-07-11
AI Technical Summary
In the prior art, continuous casting billets need to be quenched offline before rolling, resulting in large heat consumption, difficult to accurately control the temperature and cooling speed, and are susceptible to external environment, affecting the steel structure and mechanical properties.
The dynamic light pressure and online quenching collaborative process of continuous casting billets is adopted, including online quenching after light pressure treatment, through gradient light pressure and controlling the cooling process, online quenching is achieved, and the continuous casting billets are quenched by heat themselves, reducing heat consumption and improving internal density and tissue uniformity.
It improves the structural uniformity and mechanical properties of steel products, refines grains, reduces cracks caused by concentration of quenching stress, and improves product quality.
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Figure CN120286670A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of steel smelting, and in particular, to a dynamic soft reduction and on-line quenching collaborative process for continuous casting billets and its application. Background Art
[0002] In the process of steel smelting, after the refined molten steel enters the mold for continuous casting, it needs to be rolled. The current treatment method is to directly send the continuous casting billet to the rolling process after continuous casting. In order to ensure good tissue performance of the steel during rolling and prevent cracking, etc., the continuous casting billet needs to be pre-quenched offline before rolling starts.
[0003] Offline quenching is to cool the casting blank to room temperature, reheat it to the quenching temperature, and then perform quenching treatment, so additional heat consumption is required. In addition, it is difficult to achieve precise control of temperature and cooling rate during offline quenching, resulting in unsatisfactory transformation of steel structure. At the same time, during offline quenching, the casting blank is more vulnerable to the influence of external environmental factors such as oxidation and decarburization, thereby reducing mechanical properties.
[0004] In view of this, the present invention is specifically proposed. Summary of the Invention
[0005] The purpose of the present invention is to provide a dynamic soft reduction and on-line quenching collaborative process for continuous casting billets and its application.
[0006] The present invention is implemented as follows:
[0007] In a first aspect, the present invention provides a dynamic soft reduction and on-line quenching collaborative process for continuous casting billets, including performing soft reduction on the continuous casting billet and then performing on-line quenching.
[0008] The soft reduction treatment includes gradient soft reduction, and the total reduction amount of the gradient soft reduction is 1.0 - 1.5% of the thickness of the continuous casting billet. After the soft reduction treatment, the surface temperature of the continuous casting billet ≥ 950 °C, and the core temperature ≥ 850 °C.
[0009] The cooling process of on-line quenching includes a strong cooling process, a slow cooling process, and an air cooling process. After the strong cooling process ends, the temperature of the continuous casting billet is 550 - 600 °C; after the slow cooling process ends, the temperature of the continuous casting billet is 250 - 300 °C.
[0010] In an optional embodiment, the cooling time of the strong cooling process is less than or equal to 5 s, and the cooling time of the slow cooling process is 8 - 10 s.
[0011] In an optional embodiment, the cooling water volume of the strong cooling process is 450 - 550 L / m 2 ·s, and the cooling rate ≥ 50 °C / s.
[0012] The cooling water volume during the slow cooling process is 150 - 250 L / m 2 ·s, the cooling rate is 20 - 30 °C / s, and the equilibrium core-surface temperature difference ≤ 100 °C.
[0013] The cooling rate during the air cooling process ≤ 10 °C / s.
[0014] In an alternative embodiment, the cooling water volume during the forced cooling process is 500 L / m 2 ·s, and the cooling water volume during the slow cooling process is 200 L / m 2 ·s.
[0015] In an alternative embodiment, when the solid fraction of the continuous casting billet is 0.68 - 0.72, soft reduction treatment is started.
[0016] In an alternative embodiment, the soft reduction treatment is carried out with 2 - 4 sets of reduction rolls for gradient soft reduction.
[0017] In an alternative embodiment, the soft reduction treatment is carried out with 3 sets of reduction rolls for gradient soft reduction, and the roll spacing of the roll system is 1 - 2 m.
[0018] When the solid fraction of the continuous casting billet is 0.68 - 0.8, the first set of reduction rolls performs soft reduction on the continuous casting billet, and the reduction amount of the first set of reduction rolls is 0.3 - 0.5% of the thickness of the continuous casting billet.
[0019] When the solid fraction of the continuous casting billet is 0.8 - 0.85, the second set of reduction rolls performs soft reduction on the continuous casting billet, and the reduction amount of the second set of reduction rolls is 0.5 - 0.7% of the thickness of the continuous casting billet.
[0020] When the solid fraction of the continuous casting billet is 0.85 - 0.9, the third set of reduction rolls performs soft reduction on the continuous casting billet, and the reduction amount of the third set of reduction rolls is 0.4 - 0.6% of the thickness of the continuous casting billet.
[0021] In an alternative embodiment, during the soft reduction process, when the difference between the actual surface temperature of the continuous casting billet and the target surface temperature of the steel grade is greater than 20 °C, the reduction amount reduction value is 0.1% of the thickness of the continuous casting billet.
[0022] In an alternative embodiment, the casting speed of the continuous casting billet is 1.0 - 1.5 m / min, and the roll gap of the reduction rolls for the soft reduction treatment satisfies: S = 0.12vt.
[0023] Wherein, S is the roll gap, the unit is mm; v is the casting speed of the continuous casting billet, the unit is mm / s; t is the time of the soft reduction treatment, the unit is s.
[0024] In a second aspect, the present invention provides an application of a process according to any one of the foregoing embodiments in improving the tissue uniformity of steel products during the steel smelting process.
[0025] The present invention has the following beneficial effects:
[0026] The present invention provides a dynamic soft reduction and on-line quenching collaborative process for continuous casting billets and its application. By adding an on-line quenching process during continuous casting, the heat of the continuous casting billet itself can be directly utilized for the quenching process, reducing heat consumption. At the same time, due to the addition of the on-line quenching process, during continuous casting, soft reduction treatment is adopted to improve the internal density of the billet, providing a uniform matrix structure for subsequent on-line quenching and avoiding cracks caused by quenching stress concentration. By controlling the temperature of the continuous casting billet after soft reduction treatment and the temperature of the continuous casting billet during on-line quenching, it is beneficial to refine the grains and improve the mechanical properties of the product. Brief Description of the Drawings
[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.
[0028] Figure 1 Microstructure metallographic diagram of the product obtained by the method provided in Embodiment 1 of the present invention;
[0029] Figure 2 Microstructure metallographic diagram of the product obtained by the method provided in Comparative Example 1 of the present invention. Detailed Description of the Embodiments
[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments not specified by the manufacturer are all conventional products that can be obtained through commercial purchase.
[0031] The features and properties of the present invention will be further described in detail below in conjunction with the embodiments.
[0032] In a first aspect, the present invention provides a dynamic soft reduction and on-line quenching collaborative process for continuous casting billets, including subjecting the continuous casting billet to soft reduction treatment and then performing on-line quenching.
[0033] By adopting soft reduction treatment, during continuous casting, a slight pressing operation is performed on the billet to compensate for solidification shrinkage and reduce internal defects. Then on-line quenching is carried out to refine the grains, improve the mechanical properties of the billet, and facilitate subsequent rolling treatment.
[0034] The soft reduction process includes gradient soft reduction. The total reduction amount of gradient soft reduction is 1.0 - 1.5% of the thickness of the continuous casting billet. After the soft reduction process, the surface temperature of the continuous casting billet is ≥950°C, and the core temperature is ≥850°C.
[0035] The cooling process of online quenching includes a strong cooling process, a slow cooling process, and an air cooling process. After the strong cooling process ends, the temperature of the continuous casting billet is 550 - 600°C; after the slow cooling process ends, the temperature of the continuous casting billet is 250 - 300°C.
[0036] By controlling the total reduction amount of the soft reduction process, the internal defects of the continuous casting billet during solidification are reduced, and the structural density is improved, which is beneficial to the subsequent online quenching process. By controlling the temperature of the online quenching process, the solidification phase transformation process of the microstructure can be transformed as expected, which is beneficial to the refinement of the microstructure grains and the improvement of the performance of the continuous casting billet.
[0037] In an alternative embodiment, the cooling time of the strong cooling process is less than or equal to 5 s, and the cooling time of the slow cooling process is 8 - 10 s.
[0038] In an alternative embodiment, both the strong cooling process and the slow cooling process use water cooling to cool the continuous casting billet, and the air cooling process is to place the continuous casting billet in the air for natural cooling.
[0039] Therefore, the cooling water volume of the strong cooling process is 450 - 550 L / m 2 ·s, and the cooling rate is ≥50°C / s.
[0040] The cooling water volume of the slow cooling process is 150 - 250 L / m 2 ·s, the cooling rate is 20 - 30°C / s, and the equilibrium core-surface temperature difference is ≤100°C.
[0041] The cooling rate of the air cooling process is ≤10°C / s. Especially when the temperature of the continuous casting billet is 200 - 300°C, it is necessary to strictly control the cooling rate of the air cooling process to be ≤10°C / s to prevent cracking during the online quenching process.
[0042] In an alternative embodiment, the cooling water volume of the strong cooling process is 500 L / m 2 ·s, and the cooling water volume of the slow cooling process is 200 L / m 2 ·s.
[0043] In an alternative embodiment, when the solid fraction of the continuous casting billet is 0.68 - 0.72, the soft reduction process is started. Preferably, when the solid fraction of the casting billet is 0.7, the soft reduction process is started.
[0044] Among them, the solid fraction can be monitored by an infrared thermal imager for the surface temperature of the continuous casting billet, and calculated in real time in combination with solidification models such as the Chvorinov model, the KGT model, and the finite element solidification model, etc.
[0045] In an alternative embodiment, the soft reduction treatment is carried out with 2 - 4 sets of reduction rolls for gradient soft reduction.
[0046] In an alternative embodiment, the soft reduction treatment is carried out with 3 sets of reduction rolls for gradient soft reduction, and the roll spacing is 1 - 2 m, preferably 1.5 m.
[0047] When the solid fraction of the continuous casting billet is 0.68 - 0.8, the first set of reduction rolls performs soft reduction on the continuous casting billet, and the reduction amount of the first set of reduction rolls is 0.3 - 0.5% of the thickness of the continuous casting billet.
[0048] When the solid fraction of the continuous casting billet is 0.8 - 0.85, the second set of reduction rolls performs soft reduction on the continuous casting billet, and the reduction amount of the second set of reduction rolls is 0.5 - 0.7% of the thickness of the continuous casting billet.
[0049] When the solid fraction of the continuous casting billet is 0.85 - 0.9, the third set of reduction rolls performs soft reduction on the continuous casting billet, and the reduction amount of the third set of reduction rolls is 0.4 - 0.6% of the thickness of the continuous casting billet.
[0050] Preferably, when the solid fraction of the continuous casting billet is 0.68 - 0.8, the first set of reduction rolls performs soft reduction on the continuous casting billet, and the reduction amount of the first set of reduction rolls is 0.4% of the thickness of the continuous casting billet.
[0051] When the solid fraction of the continuous casting billet is 0.8 - 0.85, the second set of reduction rolls performs soft reduction on the continuous casting billet, and the reduction amount of the second set of reduction rolls is 0.6% of the thickness of the continuous casting billet.
[0052] When the solid fraction of the continuous casting billet is 0.85 - 0.9, the third set of reduction rolls performs soft reduction on the continuous casting billet, and the reduction amount of the third set of reduction rolls is 0.5% of the thickness of the continuous casting billet.
[0053] Since the soft reduction process is a continuous process, therefore, during the soft reduction process, when the solid fraction of the continuous casting billet is 0.68 - 0.72, the first set of reduction rolls starts to perform soft reduction, when it is detected that the solid fraction of the continuous casting billet is greater than or equal to 0.8, the second set of reduction rolls starts to perform soft reduction, and when it is detected that the solid fraction of the continuous casting billet is greater than or equal to 0.85, the third set of reduction rolls performs soft reduction.
[0054] In an alternative embodiment, during the soft reduction process, when the difference between the actual surface temperature of the continuous casting billet and the target surface temperature of the steel grade is greater than 20 °C, the reduction amount reduction value is 0.1% of the thickness of the continuous casting billet to prevent cracks in the continuous casting billet.
[0055] In an alternative embodiment, the casting speed of the continuous casting billet is 1.0 to 1.5 m / min, and the roll gap of the reduction rolls for soft reduction treatment satisfies: S = 0.12vt.
[0056] Wherein, S is the roll gap, in mm; v is the casting speed of the continuous casting billet, in mm / s; t is the time of soft reduction treatment, in s.
[0057] By adjusting the roll gap in real time using the above formula, the reduction amount of soft reduction is ensured to meet the above requirements, thereby obtaining a dense structure.
[0058] In an alternative embodiment, if the reduction rolls are jammed during the soft reduction process, it is necessary to immediately switch to the standby roll system and compensate the reduction amount to the subsequent roll groups to ensure that the total reduction amount remains consistent.
[0059] In a second aspect, the present invention provides an application of a process according to any one of the foregoing embodiments in improving the tissue uniformity of steel products during the steel smelting process.
[0060] Example 1
[0061] This example provides a dynamic soft reduction and online quenching collaborative process for continuous casting billets, and the specific steps are as follows:
[0062] S01. Soft reduction stage
[0063] Use an infrared thermal imager to monitor the surface temperature of the semi-solid continuous casting billet pulled out from the mold, and calculate the solid fraction f of the continuous casting billet at a position about 12 m from the meniscus in real time in combination with the solidification model. When the solid fraction is 0.7, start the soft reduction program.
[0064] The total thickness of the continuous casting billet is 200 mm, the total reduction amount of soft reduction treatment is 3 mm, and 3 sets of reduction rolls are used for gradient soft reduction, and the roll system spacing is 1.5 m.
[0065] The reduction amount of the first set of reduction rolls is 0.8 mm, and the corresponding solid fraction of the continuous casting billet is 0.7 to 0.8.
[0066] The reduction amount of the second set of reduction rolls is 1.2 mm, and the corresponding solid fraction of the continuous casting billet is 0.8 to 0.85.
[0067] The reduction amount of the third set of reduction rolls is 1.0 mm, and the corresponding solid fraction of the continuous casting billet is 0.85 to 0.9.
[0068] The casting speed of the continuous casting billet is v = 1.2 m / min, and the time t of soft reduction treatment is 0.5 s. Therefore, the roll gap is adjusted in real time during the soft reduction process according to the casting speed of the continuous casting billet, and the roll gap S = 0.12×1.2÷60×1000×0.5 = 1.2 mm.
[0069] After the continuous casting billet is completely solidified, the surface temperature of the continuous casting billet is 964 °C and the core temperature is ≥872 °C, and then online quenching is started.
[0070] S02. Online quenching stage
[0071] The continuous casting billet undergoes a strong cooling process, a slow cooling process, and an air cooling process in sequence for online quenching.
[0072] Among them, the strong cooling process is the first two meters of the cooling roll. The cooling water volume in the strong cooling process is 500 L / m 2 ·s, the cooling rate is 53 °C / s, the cooling time is 5 s. After cooling, the temperature of the continuous casting billet is 580 °C.
[0073] The cooling water volume in the slow cooling process is 200 L / m 2 ·s, the cooling rate is 26 °C / s, the equilibrium core-surface temperature difference is 74 °C, the cooling time is 8 s. After cooling, the temperature of the continuous casting billet is 280 °C.
[0074] The air cooling process is to place the continuous casting billet in the air for natural cooling, and the cooling rate is ≤10 °C / s.
[0075] Example 2
[0076] This example provides a coordinated process of dynamic soft reduction and online quenching for continuous casting billets. The specific steps are as follows:
[0077] S01. Soft reduction stage
[0078] Use an infrared thermal imager to monitor the surface temperature of the semi-solid continuous casting billet pulled out from the mold, and combine with the solidification model to calculate the solid fraction f at about 12 m from the meniscus of the continuous casting billet in real time. When the solid fraction is 0.7, start the soft reduction program.
[0079] The total thickness of the continuous casting billet is 200 mm, the total reduction amount of the soft reduction treatment is 2 mm, and 3 sets of reduction rolls are used for gradient soft reduction, and the roll spacing is 1.5 m.
[0080] The reduction amount of the first set of reduction rolls is 0.6 mm, and the corresponding solid fraction of the continuous casting billet is 0.7 - 0.8.
[0081] The reduction amount of the second set of reduction rolls is 0.8 mm, and the corresponding solid fraction of the continuous casting billet is 0.8 - 0.85.
[0082] The reduction amount of the third set of reduction rolls is 0.6 mm, and the corresponding solid fraction of the continuous casting billet is 0.85 - 0.9.
[0083] The drawing speed of the continuous casting billet is v = 1.5 m / min, and the time of soft reduction treatment is t = 0.5 s. Therefore, the roll gap is adjusted in real time according to the drawing speed of the continuous casting billet during the soft reduction process. The roll gap S = 0.12×1.5÷60×1000×0.5 = 1.5 mm.
[0084] After the continuous casting billet is completely solidified, the surface temperature of the continuous casting billet is ≥950 °C, and the core temperature is ≥850 °C, and then online quenching is started.
[0085] S02. Online quenching stage
[0086] The continuous casting billet undergoes online quenching through a strong cooling process, a slow cooling process, and an air cooling process in sequence.
[0087] Among them, the strong cooling process is the first two meters of the cooling roller. The cooling water volume in the strong cooling process is 500 L / m 2 ·s, the cooling rate is 53 °C / s, the cooling time is 5 s. After cooling, the temperature of the continuous casting billet is 570 °C.
[0088] The cooling water volume in the slow cooling process is 200 L / m 2 ·s, the cooling rate is 26 °C / s, the equilibrium core-surface temperature difference is 74 °C, the cooling time is 8 s. After cooling, the temperature of the continuous casting billet is 280 °C.
[0089] The air cooling process is to place the continuous casting billet in the air for natural cooling, and the cooling rate is ≤10 °C / s.
[0090] Comparative example 1
[0091] This comparative example provides a method for treating a continuous casting billet, including the following steps:
[0092] The molten steel enters the mold and solidifies to obtain a semi-solid continuous casting billet. After the semi-solid continuous casting billet is cooled in the secondary cooling zone, it is cut, and then slowly cooled for 24 h to room temperature.
[0093] Then the slowly cooled continuous casting billet is heated to 950 °C by an electric furnace, held for 2 h, and then quenched (water quenching). The strong cooling process is adopted during the quenching process, and the cooling water volume is 400 L / m 2 ·s, the cooling rate is 40 °C / s, the cooling time is 10 s. After quenching, the surface temperature of the continuous casting billet drops to 600 °C, and then it is naturally cooled to room temperature in the air.
[0094] Comparative example 2
[0095] This comparative example provides a method for treating a continuous casting billet. Compared with Example 1, the only difference is that after the strong cooling process, the temperature of the continuous casting billet is 650 °C.
[0096] Comparative example 3
[0097] This comparative example provides a method for treating continuous casting billets. Compared with Example 1, the only difference is that the cooling time during the intensive cooling process is 8 s.
[0098] Comparative Example 4
[0099] This comparative example provides a method for treating continuous casting billets. Compared with Example 1, the only difference is that the total reduction amount during the soft reduction stage is 1.6 mm; the reduction amount of the first group of reduction rolls is 0.8 mm, the reduction amount of the second group of reduction rolls is 0.4 mm, and the reduction amount of the third group of reduction rolls is 0.4 mm.
[0100] Comparative Example 5
[0101] This comparative example provides a method for treating continuous casting billets. Compared with Example 1, the only difference is that a fixed roll gap is adopted during the soft reduction stage, and the roll gap width is 3.6 mm.
[0102] Test Example 1
[0103] The continuous casting billets obtained by the methods of Examples 1 - 2 and Comparative Examples 1 - 5 were post - treated by the same method to obtain steel products. Then, the tensile strength, grain size, and crack rate of each steel product were detected respectively, and the results shown in Table 1 were obtained; in addition, the micro - morphology diagrams of the steel products taken during the grain size detection process are as Figures 1 - 2 shown.
[0104] Among them, the detection method for the tensile strength is: GB / T 228.1 - 2021, and both the grain size and the crack rate were statistically detected by a metallographic microscope.
[0105] Table 1 Properties of Steel Products
[0106] Tensile strength (MPa) Grain size (μm) Crack rate (%) Example 1 650 8 0.3 Example 2 680 7 0.2 Comparative Example 1 540 18 3.5 Comparative Example 2 580 12 1.8 Comparative Example 3 620 10 2.5 Comparative Example 4 600 9 1.2 Comparative Example 5 630 8～15 4.2
[0107] From Table 1 and Figures 1 - 2It can be seen that after the continuous casting billet prepared by the method provided in the embodiment of the present invention is made into a steel product, the product has good mechanical properties, relatively fine grain size and low crack rate. In Comparative Example 1, the traditional process is adopted, first continuous casting, and then quenching before rolling. The thickness of the surface oxide layer is relatively large, which easily leads to a decrease in the mechanical properties of the product, an increase in grain size and an increase in crack rate; in Comparative Example 2, the temperature of the continuous casting billet after intensive cooling is too high, the tensile strength decreases, the grain size increases, and the crack rate increases; in Comparative Example 3, the intensive cooling time is increased, resulting in supercooling on the surface of the continuous casting billet, and the temperature difference between the core and the surface is as high as 150 °C, resulting in an increase in the crack rate; in Comparative Example 4, the total reduction is low, the interior of the continuous casting billet is loose, the density decreases, and the internal defects of the continuous casting billet increase; in Comparative Example 5, a fixed roll gap is adopted, resulting in a local temperature deviation of the continuous casting billet greater than 50 °C, an increase in the crack rate, and uneven grain size, distributed in the range of 8-15 μm. It shows that the mechanical properties of the product are poor, and at the same time, the grain size is coarser than that of the embodiment, and the crack rate is increased, indicating that the method provided in the embodiment of the present invention can significantly optimize the product performance.
[0108] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.
Claims
1. A dynamic soft reduction and online quenching collaborative process for continuous casting billets, characterized in that It includes subjecting the continuous casting slab to soft reduction and then performing online quenching; The soft reduction includes gradient soft reduction, and the total reduction amount of the gradient soft reduction is 1.0-1.5% of the thickness of the continuous casting slab. After the soft reduction, the surface temperature of the continuous casting slab is ≥950°C, and the core temperature is ≥850°C; The cooling process of the online quenching includes a strong cooling process, a slow cooling process and an air cooling process. After the strong cooling process ends, the temperature of the continuous casting slab is 550-600°C; after the slow cooling process ends, the temperature of the continuous casting slab is 250-300°C.
2. The process according to claim 1, characterized in that, The cooling time of the strong cooling process is less than or equal to 5s, and the cooling time of the slow cooling process is 8-10s.
3. The process according to claim 1 or 2, characterized in that, The cooling water volume in the strong cooling process is 450 - 550 L / m 2 ·s, and the cooling rate ≥ 50℃ / s; The cooling water volume in the slow cooling process is 150 - 250 L / m 2 ·s, the cooling rate is 20 - 30 °C / s, and the equilibrium temperature difference between the core and the surface ≤ 100 °C; The cooling rate of the air cooling process is ≤10°C / s.
4. The process according to claim 1 or 2, characterized in that, The cooling water volume in the intensive cooling process is 500 L / m 2 ·s, and the cooling water volume in the slow cooling process is 200 L / m 2 ·s.
5. The process according to claim 1, characterized in that, When the solid fraction of the continuous casting slab is 0.68-0.72, the soft reduction is started.
6. The process according to claim 5, characterized in that, The soft reduction uses 2-4 sets of reduction rolls for gradient soft reduction.
7. The process according to claim 6, characterized in that, The soft reduction uses 3 sets of reduction rolls for gradient soft reduction, and the roll spacing of the roll system is 1-2m; When the solid fraction of the continuous casting slab is 0.68-0.8, the first set of reduction rolls subjects the continuous casting slab to soft reduction, and the reduction amount of the first set of reduction rolls is 0.3-0.5% of the thickness of the continuous casting slab; When the solid fraction of the continuous casting slab is 0.8-0.85, the second set of reduction rolls subjects the continuous casting slab to soft reduction, and the reduction amount of the second set of reduction rolls is 0.5-0.7% of the thickness of the continuous casting slab; When the solid fraction of the continuous casting slab is 0.85-0.9, the third set of reduction rolls subjects the continuous casting slab to soft reduction, and the reduction amount of the third set of reduction rolls is 0.4-0.6% of the thickness of the continuous casting slab.
8. The process according to claim 7, characterized in that, During the soft reduction process, when the difference between the actual surface temperature of the continuous casting slab and the target surface temperature of the steel grade is greater than 20°C, the reduction value of the reduction amount is 0.1% of the thickness of the continuous casting slab.
9. The process according to claim 7, characterized in that, The casting speed of the continuous casting slab is 1.0-1.5m / min, and the roll gap of the reduction rolls for the soft reduction satisfies: S = 0.12vt; Wherein, S is the roll gap, with the unit of mm; v is the casting speed of the continuous casting slab, with the unit of mm / s; t is the time of the soft reduction process, with the unit of s.
10. Application of the process according to any one of claims 1-9 in improving the tissue uniformity of steel products during the process of steel smelting.