A method of thin slab semi-endless mode continuous casting and rolling

Abstract

The application relates to the technical field of steel metallurgy, in particular to a thin slab semi-endless mode continuous casting and rolling method.The method comprises the following steps: continuously casting molten steel and controlling the casting speed to obtain a slab; dividing the slab into two parts, then heating, and controlling the heating calorific value of gas and the heating time of the divided slab; under the condition of setting a rolling force, first rolling the heated slab; second rolling the first-rolled slab and controlling the flow of spalling cooling water in the second rolling; wherein the second rolling comprises the following steps: rough rolling the first-rolled slab to obtain an intermediate slab with a target thickness; finish rolling the intermediate slab, adopting a double-row descaling mode in the finish rolling process, and controlling the pressure of the descaling. The application solves the technical problem that the existing thin slab continuous casting and rolling production line is prone to producing strip buckling in the semi-endless mode production process.

Description

Technical Field

[0001] This application relates to the field of iron and steel metallurgy technology, and in particular to a method for continuous casting and rolling of thin slabs in a semi-endless mode. Background Technology

[0002] Thin slab continuous casting and rolling is a major innovative technology developed by the world's steel industry in the late 1980s. Compared with the conventional headless production mode, the semi-headless mode generally rolls thicknesses of 3.0 mm and above. When using the semi-headless mode, there is no need to use induction heaters, which is of great significance for energy saving and consumption reduction in production lines.

[0003] However, during the production process, rolling defects frequently occur at the edges, ranging from 10 to 50 times, and in severe cases, the number of rolling defects can reach hundreds. Once this defect occurs, it fails to meet the supply standards for pickling raw materials, leading to the downgrading of steel coils. This not only increases process costs and extends the delivery cycle, but also significantly impacts the strip steel yield. Summary of the Invention

[0004] This application provides a method for continuous casting and rolling of thin slabs in a semi-endless mode to solve the technical problem of strip peeling that easily occurs in the semi-endless mode production process of existing thin slab continuous casting and rolling production lines.

[0005] In a first aspect, this application provides a method for continuous casting and rolling of thin slabs in a semi-endless mode, the method comprising:

[0006] Molten steel is continuously cast, and the casting speed is controlled to obtain a slab;

[0007] The slab is cut, then heated, and the calorific value of the heating gas is controlled; wherein the slab includes a first slab and a second slab, and the heating time of the first slab and the second slab are controlled respectively;

[0008] Under a set rolling force, the heated slab is subjected to a first rolling process;

[0009] The slab after the first rolling is subjected to a second rolling process, and the flow rate of the stripping cooling water during the second rolling process is controlled; wherein, the second rolling process includes:

[0010] The slab after the first rolling is rough rolled to obtain an intermediate slab; wherein the intermediate slab has a target thickness;

[0011] The intermediate billet is precision rolled, and a double descaling mode is adopted during the precision rolling process, and the descaling pressure is controlled.

[0012] Optionally, the casting speed is 5.0-5.2 m / min.

[0013] Optionally, the calorific value of the heated gas is ≥2400 Kcal / m³. 3 .

[0014] Optionally, the heating time of the first slab is 105-110s.

[0015] Optionally, the heating time of the second slab is 99-103 seconds.

[0016] Optionally, the rolling force is set to 350-370 kN.

[0017] Optionally, the target thickness is 18-20 mm.

[0018] Optionally, the flow rate of the anti-stripping cooling water in the second rolling process includes: the anti-stripping water flow rate at the edge of the strip and the anti-stripping water flow rate at the middle of the strip.

[0019] Optionally, the anti-stripping water flow rate at the edge of the steel strip is 10-15 m³ / h. 3 / h, and / or the anti-stripping water flow rate in the middle of the strip is 20-25m³ / h. 3 / h.

[0020] Optionally, the descaling pressure is ≥375MPa.

[0021] The technical solutions provided in this application have the following advantages compared with the prior art:

[0022] The method for continuous casting and rolling of thin slabs in a semi-endless mode provided in this application effectively reduces the number of strip edge peelings by adjusting the slab heating time in the furnace, the vertical roll rolling force, the thickness of the intermediate slab, and the strategy for preventing water stripping. After applying this method, the number of strip edges peelings in the entire coil is reduced, and the cutting loss caused by strip edge peelings during rolling is reduced. While improving the yield, the turnover cycle of the steel coil is shortened, effectively reducing costs, improving the core competitiveness of the production line, and increasing efficiency. Attached Figure Description

[0023] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0024] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1A schematic flowchart illustrating a method for semi-endless continuous casting and rolling of thin slabs provided in this application embodiment;

[0026] Figure 2 A schematic diagram of a "dog bone" and a "fish tail" provided for this application;

[0027] Figure 3 A surface image of a rolled strip provided as comparative example 1 of this application;

[0028] Figure 4 This is an image of the surface of a rolled strip provided in Embodiment 1 of this application. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0030] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0031] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this application, terms such as "comprising" and "including" mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than one" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0032] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0033] Firstly, this application provides a method for semi-endless continuous casting and rolling of thin slabs; please refer to [link to relevant documentation]. Figure 1 The method includes:

[0034] S1. Continuously cast molten steel and control the casting speed to obtain a slab;

[0035] Before implementing step S1, the following steps are also included: checking the water leakage and sealing effect in the roughing rolling area, checking whether the vertical roll cooling water cools to the edge of the slab under rolling conditions, and checking the descaling sealing effect in the roughing rolling to ensure that the descaling water does not flow back into the heating furnace and the edge of the slab, so as not to affect the rolling stability.

[0036] In some embodiments, the casting speed is 5.0-5.2 m / min.

[0037] The positive effects of controlling the casting speed in continuous casting at 5.0-5.2 m / min are as follows: To ensure the slab's entry temperature in the furnace remains within a certain range, the casting speed is set during semi-endless production. Higher casting speeds result in higher slab entry temperatures, and as the slab's acceleration point shifts later, the furnace dwell time is extended, effectively ensuring the slab's temperature within the furnace. Within the aforementioned casting speed range, the occurrence of surface skidding is minimized. It also ensures that the finishing mill entry temperature is controlled within the range of 980-1000℃, thereby avoiding rolling in the two-phase zone at the edges and reducing the risk of surface skidding. Specifically, this casting speed can be 5.0 m / min, 5.1 m / min, 5.2 m / min, etc.

[0038] S2. The slab is cut and then heated, and the calorific value of the heating gas is controlled; wherein the slab includes a first slab and a second slab, and the heating time of the first slab and the second slab are controlled respectively;

[0039] In some embodiments, the calorific value of the heated gas is ≥2400 Kcal / m³. 3 .

[0040] The calorific value of the gas used for heating is ≥2400 kcal / m³ 3 The positive effects include: improving the heating capacity of the heating furnace, controlling the furnace temperature to 1180℃, ensuring effective heating of the slab in the furnace, and reducing the temperature difference between the edges and center of the slab. This heating step is carried out in a tunnel furnace. The MCCR production line's tunnel furnace gas is a mixture of coke oven gas, blast furnace gas, and converter gas in a ratio of 4:4:2. Due to the higher proportion of coke oven gas, the calorific value of the gas can be maintained at a high level. Within this range of gas calorific value, it ensures that the temperature difference of the slab is controlled within an ideal range, and also prevents the slab from developing iron oxide scale defects due to excessively high furnace temperatures. Specifically, the calorific value of the heating gas can be 2400 Kcal / m³. 3 2410 kcal / m 3 2420 kcal / m 3 wait.

[0041] In some embodiments, the heating time of the first slab is 105-110 s.

[0042] In some embodiments, the heating time of the second slab is 99-103 seconds.

[0043] Under the existing process, it was found that the number of peeling sheets on the second and third slabs in the semi-headless production process was significantly higher than that on the first slab. This was positively correlated with the fact that the temperatures of the second and third slabs were lower than those of the first slab. Research revealed that this was directly related to the furnace time of the subsequent slabs, especially the third slab. (In the semi-headless production process on the MCCR line, when the slab length reaches three times the standard length (one standard length is generally 22m), the swing shear at the exit of the fan-shaped section cuts the slab. The cut slab undergoes a period of acceleration, creating a certain distance between its head and the uncut slabs. This is done to prevent collisions between the two slabs at high drawing speeds due to insufficient spacing. Because of this acceleration, the furnace time of the third slab in the semi-headless mode is shorter than that of the first two slabs (because the first two slabs enter the furnace more quickly). In the tunnel furnace, before the slab length reaches three times the fixed length and before the shearing process, the third slab experiences a shorter heating time under the same furnace atmosphere and temperature. This results in a lower overall temperature for the third slab compared to the first and second slabs, leading to a significant temperature drop at the edges, particularly at the second and third slabs. This causes edge peeling defects during subsequent rolling. Previously, the slab acceleration point was 5m from the tunnel furnace entrance; this has now been adjusted to 9m inside the furnace. This ensures a proper temperature difference between the first and last slabs, effectively controlling the peeling defect.

[0044] In this embodiment, the positive effect of cutting the slab in half is to reduce edge peeling defects during rolling. The positive effect of controlling the heating time of the first slab to 105-110 s and the heating time of the second slab to 99-103 s is to extend the slab's time in the furnace and ensure more uniform heating. Specifically, the heating time of the first slab can be 105 s, 107 s, 109 s, 110 s, etc., and the heating time of the second slab can be 99 s, 101 s, 103 s, etc.

[0045] S3. Under the condition of setting the rolling force, the heated slab is subjected to a first rolling process;

[0046] In some embodiments, the set rolling force is 350-370 kN.

[0047] The positive effects of controlling the rolling force to 350-370KN: After the strip exits the tunnel furnace, it undergoes rolling with vertical rolls. Vertical roll rolling reduces the slab width, resulting in a "dog-bone" shape. This "dog-bone" shape, after being rolled by the roughing mill, develops a noticeable "fishtail" shape. If the vertical roll rolling force is too high, both the "dog-bone" and "fishtail" shapes become more pronounced, affecting edge quality and causing excessively low temperatures at the edges and corners of the slab, leading to peeling defects (after the slab forms a dog-bone shape, it is then rolled by a pair of parallel rolls; the protruding parts at the edges are pressed into the strip edge. If the vertical roll rolling force is very high, the protruding edges are more pronounced, and the deeper the edges are pressed in after rolling, the more peeling defects occur). See also... Figure 2 When the vertical roll rolling force is within the above range, the dog-bone shape formed by the slab is uniform and smooth. At this time, the fishtail shape is not obvious after passing through the roughing mill, which can effectively reduce the occurrence of edge peeling. Specifically, the rolling force can be 350KN, 360KN, 370KN, etc.

[0048] S4. Perform a second rolling process on the slab after the first rolling, and control the flow rate of the stripping cooling water during the second rolling; wherein the second rolling process includes:

[0049] The slab after the first rolling is rough rolled to obtain an intermediate slab; wherein the intermediate slab has a target thickness;

[0050] The intermediate billet is precision rolled, and a double descaling mode is adopted during the precision rolling process, and the descaling pressure is controlled.

[0051] In some implementations, the target thickness is 18-20 mm.

[0052] "Target thickness" refers to the thickness of the intermediate slab. Controlling the thickness of the intermediate slab to 18-20mm has the positive effect of effectively controlling its thickness. The slab before entering the finishing mill after passing through the roughing mill is called the intermediate slab. The thickness of the intermediate slab is a crucial parameter in slab rolling, significantly impacting the microstructure and mechanical properties of the steel plate at room temperature. The selection of the intermediate slab thickness is directly related to the steel grade being rolled, the rolling control method, the thickness of the finished steel plate, and the temperature control method for the intermediate slab. If the intermediate slab thickness is too large, while increasing the deformation during finishing rolling, it also slows down the temperature drop rate. Without a water-cooling process for the intermediate slab, this not only increases the waiting time and reduces production efficiency, but also significantly reduces the impact of excessive deformation on the final microstructure and properties. If the intermediate slab thickness is too small, the deformation degree increases in the roughing stage, and the temperature drop in the finishing stage is faster but the deformation degree is slightly smaller. This can lead to an unbalanced load distribution between the two mills (or the roughing and finishing stages), potentially reducing the finishing stage's impact on refining recrystallized austenite grains, increasing the effective grain boundary area, and promoting the transformation to ferrite. Furthermore, an excessively thin intermediate slab will lead to excessive temperature drop at the slab edges. After passing through the descaling machine, the temperature drop at the strip edges will be further amplified, resulting in an increase in the amount of rolled surface peeling. Specifically, the target thickness can be 18mm, 19mm, 20mm, etc.

[0053] In some embodiments, the flow rate of the anti-stripping cooling water in the second rolling process includes: the anti-stripping water flow rate at the edge of the strip and the anti-stripping water flow rate at the middle of the strip.

[0054] In some embodiments, the anti-stripping water flow rate at the edge of the steel strip is 10-15 m³ / h. 3 / h, and / or the anti-stripping water flow rate in the middle of the strip is 20-25m³ / h. 3 / h.

[0055] The anti-stripping water flow rate at the edge of the strip is controlled to be 10-15m. 3 / h, the anti-stripping water flow rate in the middle of the strip is 20-25m³ / h. 3The positive effects of the / h flow rate: The anti-stripping water is the cooling water for the rolls. After the rolls come into contact with the high-temperature strip steel, an oxide film forms on the roll surface. This not only effectively reduces roll wear but also significantly increases the rolling mileage of the production line. Therefore, to ensure the continuous existence of the oxide film on the rolls, the rolls are cooled. (If the roll temperature is too high, the oxide film on the rolls will be too thick, which can easily cause the outer oxide film to peel off and affect the surface quality of the strip steel; if the temperature is too low, the oxide film on the rolls will be too thin, and the strip steel will easily scrape against the roll surface during rolling, leading to pits on the rolls and affecting the surface quality of the strip steel). Due to the temperature difference in the cross-section of the strip steel, the temperature at the edge is lower than that in the middle, resulting in the temperature at the edge of the rolls being lower than that in the middle. Based on this, the cooling of the rolls is carried out in segments, that is, the cooling capacity at the edge of the rolls is lower than that in the middle. This can effectively ensure the temperature uniformity of the rolls along the length direction and avoid the generation of rolling skin. Specifically, the anti-stripping water flow rate at the edge of the strip steel can be 10m³ / h. 3 / h、12m 3 / h, 14m 3 / h, 15m 3 The anti-stripping water flow rate in the middle of the strip can be 20m³ / h, etc. 3 / h、22m 3 / h、24m 3 / h, 25m 3 / h etc.

[0056] In some embodiments, the descaling pressure is ≥375MPa.

[0057] The positive effects of controlling the descaling pressure to ≥375MPa: During the rolling process, the finishing mill uses a double-row descaling water system, with the descaling water pressure controlled at ≥375MPa. The cooling water at the inlet and outlet quarters of the finishing mill descaling system is not turned on. The MCCR production line has two rows of manifolds for finishing descaling. When using double-row manifold descaling and a pressure ≥375MPa, the impact force of the descaling water increases, and the fan-shaped pattern formed by the descaling water ensures a more uniform temperature across the slab cross-section. The cooling water positions at the inlet and outlet quarters of the finishing mill are located on both sides of the strip at a distance of 1 / 4 from the edge. In semi-endless production, turning on the quarters of the cooling water will cause a significant temperature drop on both sides of the strip, potentially leading to two distinct black marks on the strip, which is detrimental to controlling rolling defects such as peeling. Specifically, the descaling pressure can be 375MPa, 376MPa, 377MPa, etc.

[0058] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0059] Specific implementation steps:

[0060] S1. Continuously cast molten steel and control the casting speed to obtain a slab;

[0061] S2. The slab is cut and then heated, and the calorific value of the heating gas is controlled; wherein the slab includes a first slab and a second slab, and the heating time of the first slab and the second slab are controlled respectively;

[0062] S3. Under the condition of setting the rolling force, the heated slab is subjected to a first rolling process;

[0063] S4. Perform a second rolling process on the slab after the first rolling, and control the flow rate of the stripping cooling water during the second rolling; wherein the second rolling process includes:

[0064] The slab after the first rolling is rough rolled to obtain an intermediate slab; wherein the intermediate slab has a target thickness;

[0065] The intermediate slab is precision rolled, and a double descaling mode is used during the precision rolling process, while the descaling pressure is controlled. Specific process parameters are shown in Table 1, and the results of the semi-endless continuous casting and rolling of thin slabs are shown in Table 2.

[0066] Table 1. Process parameters for semi-endless continuous casting and rolling of thin slabs

[0067]

[0068] Table 2 Quantity of Steel Strip Peeling

[0069] Serial Number Number of steel strips with peeling (locations) Example 1 6 Example 2 8 Example 3 10 Comparative Example 1 75

[0070] The method of semi-endless continuous casting and rolling of thin slabs according to the embodiments of this application is shown in Table 2 and... Figure 4 It can be seen that the amount of strip peeling was reduced, and the surface quality of the strip in the embodiment was good; from Figure 3 As can be seen from the data, the strip steel in Comparative Example 1 has obvious surface peeling defects.

[0071] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for continuous casting and rolling of thin slabs in a semi-endless mode, characterized in that, The method includes: Molten steel is continuously cast, and the casting speed is controlled to obtain a slab; The slab is cut, then heated, and the calorific value of the heating gas is controlled; wherein the slab includes a first slab and a second slab, and the heating time of the first slab and the second slab are controlled respectively; Under a set rolling force, the heated slab is subjected to a first rolling process; The slab after the first rolling is subjected to a second rolling process, and the flow rate of the stripping cooling water during the second rolling process is controlled; wherein, the second rolling process includes: The slab after the first rolling is rough rolled to obtain an intermediate slab; wherein the intermediate slab has a target thickness; The intermediate billet is precision rolled, and a double descaling mode is adopted during the precision rolling process, and the descaling pressure is controlled. The casting speed is 5.0-5.2 m / min; The calorific value of the heated gas is ≥2400 kcal / m³. 3 ; The heating time for the first slab is 105-110 seconds; The heating time for the second slab is 99-103 seconds; The set rolling force is 350-370KN; The target thickness is 18-20 mm; The descaling pressure is ≥375MPa.

2. The method according to claim 1, characterized in that, The flow rate of the anti-stripping cooling water in the second rolling process includes: the anti-stripping water flow rate at the edge of the strip and the anti-stripping water flow rate in the middle of the strip.

3. The method according to claim 2, characterized in that, The anti-stripping water flow rate at the edge of the steel strip is 10-15m. 3 / h, and / or the anti-stripping water flow rate in the middle of the strip is 20-25m³ / h. 3 / h.

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