Continuous casting slab ending method

Abstract

The invention discloses a continuous casting sheet billet ending method which comprises the following steps: S1, for a sheet billet with the size thickness of 210-230 mm and the width of 1.0-1.8 m, the total slag layer thickness of casting powder in a crystallizer is not greater than 60 mm when molten steel of a large ladle is poured; s2, after the molten steel in the large ladle is poured, the molten steel in the tundish is used for pouring, the pulling speed is controlled to be gradually reduced to 0.4 m / min, meanwhile, the retention time is adjusted, the pulling speed is matched with consumption of casting powder, and the pulling speed is matched with the liquid level height of the tundish, so that the situation that vortexes are generated due to the high pulling speed and the low liquid level is avoided; and S3, when the thickness of the casting powder is smaller than or equal to 20 mm, the tundish and the crystallizer are disconnected, the pulling speed is adjusted to be 0.2 m / min, the remaining liquid casting powder and the copper plate form slag strips, and the slag strips are removed. According to the continuous casting sheet billet ending method, the thickness of a covering slag layer can be reduced without stirring, and tail billet solidification is effectively accelerated.

Description

Technical Field

[0001] The present invention relates to the technical field of steelmaking, and in particular to a method for finishing a continuous casting slab. Background Art

[0002] Continuous casting slab production involves continuously pouring molten steel into billets of fixed specifications. Existing factories producing slabs with a thickness of 210-230mm and a width of 1.0-1.8m typically leave a significant amount of molten steel in the tundish. This molten steel needs to be processed during the subsequent finishing process. Furthermore, due to the thick mold slag, to increase the cooling rate of the slab and avoid steel overflow caused by squeezing the hull during the downward pull of the slab before it solidifies, which could lead to safety hazards, the molten steel in the crystallizer is typically stirred with a steel pipe during the casting machine shutdown to accelerate solidification. This stirring requires operators to stand next to the crystallizer, posing a safety hazard. Furthermore, during the stirring process, slag can fall between the copper plate and the slab shell, potentially scratching the copper plate as the slab moves downward.

[0003] In view of this, it is necessary to design a continuous casting slab finishing method to solve the above problems. Summary of the Invention

[0004] The purpose of the present invention is to provide a continuous casting slab finishing method that utilizes the residual molten steel in the tundish to reduce the thickness of the protective slag layer, effectively accelerates the solidification of the tail slab, and at the same time ensures the safety of the operator and avoids the situation where the steel slag scratches the copper plate due to stirring.

[0005] To achieve the above-mentioned object of the invention, the present invention provides a method for finishing a continuous casting slab, comprising the following steps: S1. For slabs with a thickness of 210-230mm and a width of 1.0-1.8m, the total thickness of the protective slag layer in the crystallizer shall not exceed 60mm after the ladle of molten steel is poured; S2. After the molten steel in the ladle is poured, a certain amount of molten steel in the tundish is poured into the crystallizer. The pulling speed is gradually reduced to 0.4 m / min. At the same time, the residence time at different pulling speeds is adjusted to match the pulling speed with the consumption of the mold slag and the pulling speed with the tundish liquid level to avoid vortexes caused by high pulling speed and low liquid level, which may lead to slag rolls and steel leakage. S3. When the protective slag thickness is consumed to less than or equal to 20 mm under molten steel pouring, disconnect the tundish and the crystallizer, adjust the pulling speed to 0.2 m / min, and maintain it for a certain time so that the remaining liquid protective slag and the copper plate form slag strips, and further clean up the slag strips to make the protective slag thickness in the crystallizer less than 10 mm.

[0006] As a further improvement to the present invention, step S1 further requires that the slag layer thickness within the tundish be no greater than 60 mm. The specific operation for achieving this is to perform slag removal on the tundish in the furnace preceding the finishing furnace to control the slag thickness within the tundish. By controlling the slag thickness within the tundish before pouring molten steel, inclusion quality issues with the slab can be avoided during the finishing process. The slag thickness within the tundish refers to the thickness of the covering agent and the slag below the ladle.

[0007] As a further improvement of the present invention, in step S2, the casting speed is matched with the consumption of the protective slag by using a certain amount of molten steel in the tundish to reduce the thickness of the protective slag to less than or equal to 20 mm within the predetermined total residence time.

[0008] As a further improvement of the present invention, the pulling speed control process is divided into a high-speed section with a pulling speed greater than 0.9 m / min and a low-speed section with a pulling speed less than or equal to 0.9 m / min, with 0.9 m / min as the boundary, and the total residence time of the high-speed section and the low-speed section does not exceed 6 minutes.

[0009] As a further improvement of the present invention, in step S2, the pulling speed is gradually reduced to 0.4 m / min in an increment of 0.1 or 0.2.

[0010] As a further improvement of the present invention, in step S2, according to different cross-sectional dimensions, when the initial pulling speed is 1.6, 1.5, 1.4, 1.3 or 1.2 m / min, the corresponding relationship between the pulling speed and the tundish liquid level is as follows: when the pulling speed is 1.6 m / min, the corresponding minimum liquid level of the tundish is 1200 mm, when the pulling speed is 1.5 m / min, the corresponding minimum liquid level of the tundish is 1100 mm, when the pulling speed is 1.4 m / min, the corresponding minimum liquid level of the tundish is 1000 mm, when the pulling speed is 1.3 m / min, the corresponding minimum liquid level of the tundish is 950 mm, when the pulling speed is 1.2 m / min, the corresponding minimum liquid level of the tundish is 900 mm, and when the pulling speed is 1.1 m / min, the corresponding minimum liquid level of the tundish is 1 min when the minimum liquid level of the tundish is 800mm, when the pulling speed is 1.0m / min, the minimum liquid level of the tundish is 600mm, when the pulling speed is 0.9m / min, the minimum liquid level of the tundish is 550mm, when the pulling speed is 0.8m / min, the minimum liquid level of the tundish is 500mm, when the pulling speed is 0.7m / min, the minimum liquid level of the tundish is 450mm, when the pulling speed is 0.6m / min, the minimum liquid level of the tundish is 400mm, when the pulling speed is 0.5m / min, the minimum liquid level of the tundish is 300mm, and when the pulling speed is 0.4m / min, the minimum liquid level of the tundish is 200mm.

[0011] By matching the tundish liquid level with the drawing speed, it is possible to avoid slag rolling and steel leakage caused by high drawing speed when the molten steel level is low. Further, by limiting the residence time, it is possible to avoid the situation where the molten steel level is high and the drawing speed is low, resulting in a total residence time that is too long to consume the protective slag, thereby increasing the slab strength and damaging the equipment.

[0012] As a further improvement of the present invention, the calculation formula for the consumption of molten steel at different casting speeds is: V=v i ×t i ×w Among them, V is the consumption of molten steel at different drawing speeds, in tons, v i is the pulling speed, in m / min (meters per minute), t i is the residence time at the corresponding pulling speed, in minutes; w is the weight per meter, in tons / meter.

[0013] Specifically, the formula for calculating the weight of a meter is: w=L1×L2×ρ Where w is the weight per meter, in tons / meter; L1 and L2 are the width and thickness of the slab, in meters; and ρ is the density of molten steel, in tons / cubic meter.

[0014] Since molten steel consumption is related to the drawing speed and residence time, as the molten steel is poured, the liquid level in the tundish gradually decreases. By limiting the total residence time and changing the liquid level in the tundish, the drawing speed and the residence time at different drawing speeds can be regulated. This can ensure orderly consumption of protective slag while avoiding slag coiling and steel leakage, as well as increased slab strength that may damage the casting machine equipment.

[0015] As a further improvement of the present invention, the amount of molten steel in the tundish used to pour into the crystallizer is such that at least 2 tons of molten steel remain in the tundish when the tundish is disconnected from the crystallizer. This arrangement of at least 2 tons of molten steel remaining in the tundish ensures the purity of the final slab at the end of the process.

[0016] As a further improvement of the present invention, in step S3, the pulling speed is adjusted to 0.2 m / min and maintained for 20-40 s.

[0017] As a further improvement of the present invention, in step S3, the specific operation of disconnecting the tundish from the crystallizer is: closing the tundish stopper rod and removing the water outlet on the tundish car.

[0018] As a further improvement of the present invention, step S4 is further included. Step S4 specifically comprises: cooling the tail billet with a spray device to further accelerate the solidification of the tail billet, and after confirming that the tail billet is solidified, gradually increasing the drawing speed to the normal drawing speed.

[0019] The beneficial effects of the present invention are: 1. The present invention utilizes the remaining molten steel in the tundish to consume the protective slag, and matches the molten steel consumption with the protective slag consumption by controlling the cross-section pulling speed and residence time, and further coordinates the protective slag to react with the copper plate to form a large slag strip, which can reduce the thickness of the protective slag to less than 10 mm within a predetermined time, effectively accelerating the solidification of the tail billet. Compared with the existing technology, the present invention does not require molten steel stirring, can ensure the safety of operators, and avoid slag coiling and steel leakage incidents that affect the billet casting process.

[0020] 2. The present invention controls the section pulling speed and residence time to match the molten steel consumption with the protection slag consumption. On the one hand, the molten steel in the tundish can be used to consume the protection slag to a certain thickness to accelerate the solidification of the tail slab. On the other hand, it can also avoid the occurrence of slag coiling and steel leakage caused by high pulling speed when the molten steel level is low, and avoid the occurrence of high molten steel level and low pulling speed, resulting in excessively long residence time for achieving protection slag consumption, which increases the strength of the slab and damages the equipment.

[0021] 3. The continuous casting slab finishing method of the present invention utilizes the residual molten steel in the tundish to consume the protective slag, which can realize the recycling of the molten steel in the tundish, and no longer needs to consume manpower and material resources to treat the molten steel in the tundish. The method is simple to operate and can ensure the safety of the operator. At the same time, compared with the existing stirring method to accelerate the solidification of the tail slab, the method can also avoid the situation where the steel slag scratches the copper plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the process of finishing the continuous casting slab of Example 1. DETAILED DESCRIPTION

[0023] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] It should also be noted here that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the solutions of the present invention are shown in the drawings, while other details that are not closely related to the present invention are omitted.

[0025] In addition, it should be noted that the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0026] Example 1 like Figure 1As shown, this embodiment provides a method for finishing a continuous casting slab, which is described by taking the production of a slab of steel grade SPHC-1R with a cross-sectional size of 220×1250 mm as an example, and includes the following steps: S1. Control the total slag thickness of the mold slag layer when the ladle of molten steel is poured: When the ladle of molten steel is poured, reduce the amount of mold slag added to the crystallizer to keep the total slag thickness in the mold at 55mm. At the same time, perform slag removal on the tundish in the furnace before the finishing furnace to make the slag layer thickness in the tundish 60mm. S2. Molten steel pouring and casting speed control: After the ladle of molten steel is poured, the amount of molten steel in the tundish is 23.2 tons. The molten steel in the tundish is continued to be poured into the crystallizer. The casting speed and residence time are controlled as shown in Table 1 to match the casting speed with the consumption of mold slag and the casting speed with the tundish liquid level to avoid vortexes caused by high casting speed and low liquid level, which may lead to slag roll and steel leakage; S3. Use the remaining liquid mold slag and copper plate to form large slag strips to further consume the mold slag: When the total slag layer thickness of the mold slag drops to 20mm, stop and finish. At this time, close the tundish stopper and remove the drain port on the tundish car to disconnect the tundish from the crystallizer. Then, adjust the casting speed to 0.2m / min and maintain it for 30s to allow the remaining liquid mold slag and copper plate to form large slag strips. After the tundish is driven away, use a small oxygen tube to pick out the large slag strips hanging on the copper plate of the crystallizer. At this time, the thickness of the mold slag in the crystallizer is less than 10mm, which will not affect the normal solidification of the tail billet. S4. Further processing of the tail billet: Use a spray device to cool the tail billet to further accelerate the solidification of the tail billet. After confirming that the tail billet is solidified, the drawing speed is gradually increased to the normal drawing speed. The degree of speed increase is: 0.4 (60) -0.6 (30) -0.8 (30) -1.0 (30) -1.2 (30) -1.4 (30) -1.6 (30), wherein 0.4 (60) is used for illustration, 0.4 represents the drawing speed, the unit is m / min, 60 represents the residence time, the unit is s, and the spraying to accelerate the solidification of the tail billet and the speed increase of the drawing speed can be processed by conventional operations in the existing technology, which will not be repeated here.

[0027] Specifically, the tundish has an inverted isosceles trapezoidal structure. When viewed from the front and side, the tundish is an inverted isosceles trapezoidal structure. When viewed from the front, the bottom length of the tundish is 800 mm, and the top length is 1190 mm. When viewed from the side, the bottom length of the tundish is 3750 mm, and the top length is 3930 mm. The height of the tundish is 1300 mm.

[0028] Specifically, after the total slag layer thickness of the protective slag is reduced to 20 mm by pouring molten steel, the remaining liquid protective slag and copper plate are used to remove the protective slag, which can promote the solidification of the tail billet. That is, the method of using molten steel in combination with the casting speed control of the present invention can effectively reduce the total slag layer thickness of the protective slag in the crystallizer, and there is no need to accelerate the solidification of the tail billet by stirring, which not only ensures the safety of the operator, but also avoids the situation where the steel slag scratches the copper plate of the crystallizer.

[0029] Table 1 Casting speed control program for a section size of 220×1250mm

[0030] Example 2 This embodiment provides a method for finishing a continuous casting slab. Compared with Example 1, the slab size of Example 2 is 220×1500 mm, and the casting speed control in step S2 of Example 2 is as shown in Table 2. The remaining steps are the same as those in Example 1 and will not be repeated here.

[0031] Table 2 Casting speed control program for a section size of 220×1500mm

[0032] Example 3 This embodiment provides a method for finishing a continuous casting slab. Compared with Example 1, the slab size of Example 3 is 220×1800 mm, and the casting speed control in step S2 of Example 3 is as shown in Table 3. The remaining steps are the same as those in Example 1 and will not be repeated here.

[0033] Table 3 Casting speed control program for a section size of 220×1800mm

[0034] The weight of each section of rice in Examples 1-3 is shown in Table 4.

[0035] Table 4 Weight of each section of rice in Examples 1-3

[0036] Comparative Example 1 This comparative example provides a method for finishing a continuous casting slab. Compared with Example 1, in Comparative Example 1, before pouring molten steel, the total slag layer thickness of the protective slag in the crystallizer is maintained at 80 mm. The remaining steps are consistent with Example 1 and are not repeated here.

[0037] In Examples 1-3, the density of molten steel is 7.6 tons / cubic meter, and the total amount of molten steel in the tundish is about 23.2 tons. According to the methods of Examples 1-3, when the connection between the tundish and the crystallizer is disconnected, when there are still about 4 tons of molten steel left in the tundish, the corresponding amount of molten steel is used and the pulling speed and residence time are regulated to reduce the total slag layer thickness of the protective slag in the crystallizer to 20 mm. At the same time, the protective slag layer is regulated under the condition that the total residence time in the high-speed section and the low-speed section does not exceed 6 minutes. In addition, the liquid level in the tundish after the corresponding residence time at each pulling speed in Examples 1-3 is equal to or slightly greater than the minimum liquid level of the tundish corresponding to each pulling speed, that is, the liquid level of the tundish can match the pulling speed of each section. There is no slag rolling or steel leakage in the entire finishing process, and the solidification of the tail billet is effectively promoted while ensuring the strength of the slab.

[0038] Regarding the drawing speed control in Examples 1-3, since the initial drawing speed of the cross-sectional dimensions of 220×1250mm and 220×1500mm is relatively high, the drawing speed can be gradually reduced to 0.4m / min by an amplitude of 0.2 in Example 1-2, and the residence time is controlled during the deceleration process to match the molten steel consumption with the protection slag consumption, and at the same time, the drawing speed is matched with the liquid level height of the tundish; the cross-sectional dimension of the slab in Example 3 is 220×1800mm, and its initial drawing speed is relatively low. In order to ensure that the protection slag is consumed to less than 10mm within the predetermined total residence time, the drawing speed needs to be gradually reduced by an amplitude of 0.1 in the high-speed section, and the molten steel pouring gradient in the high-speed section is lengthened to effectively consume the protection slag in the high-speed section, so as to avoid the overall residence time being too long due to the small amount of protection slag consumed in the high-speed section to ensure that the protection slag is finally consumed to less than 10mm.

[0039] In Comparative Example 1, before pouring molten steel, the total slag layer thickness of the protective slag in the crystallizer was maintained at 80 mm, and the final protective slag thickness in the crystallizer was 30 mm. In order to promote the solidification of the tail billet, manual stirring was required to reduce the thickness of the protective slag, which posed a safety hazard to the operator and may cause damage to the copper plate.

[0040] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for finishing a continuous casting slab, characterized in that: The following steps are involved: S1. For slabs with a thickness of 210-230mm and a width of 1.0-1.8m, the total thickness of the protective slag layer in the crystallizer shall not exceed 60mm after the ladle of molten steel is poured; S2. After the molten steel in the ladle is poured, a certain amount of molten steel in the tundish is poured into the crystallizer. The pulling speed is gradually reduced to 0.4 m / min. At the same time, the residence time at different pulling speeds is adjusted to match the pulling speed with the consumption of the mold slag, and the pulling speed with the height of the tundish liquid to avoid vortexes caused by high pulling speed and low liquid level. S3. When the protective slag thickness is consumed to less than or equal to 20 mm under molten steel pouring, disconnect the tundish and the crystallizer, adjust the pulling speed to 0.2 m / min, and maintain it for a certain time so that the remaining liquid protective slag and the copper plate form slag strips, and further clean up the slag strips to make the protective slag thickness in the crystallizer less than 10 mm.

2. The method for finishing a continuous casting slab according to claim 1, wherein: In step S1, it is also necessary to limit the thickness of the slag layer in the tundish to no more than 60 mm.

3. The method for finishing a continuous casting slab according to claim 1, wherein: The pulling speed control process is divided into a high-speed section with a pulling speed greater than 0.9 m / min and a low-speed section with a pulling speed less than or equal to 0.9 m / min, with 0.9 m / min as the boundary. The total residence time of the high-speed section and the low-speed section does not exceed 6 minutes.

4. The method for finishing a continuous casting slab according to claim 1, wherein: In step S2, the pulling speed is gradually reduced to 0.4 m / min in increments of 0.1 or 0.

2.

5. The method for finishing a continuous casting slab according to claim 4, characterized in that: According to the different cross-sectional dimensions, when the initial pulling speed is 1.6, 1.5, 1.4, 1.3 or 1.2 m / min, the corresponding relationship between the pulling speed and the tundish liquid level is: when the pulling speed is 1.6 m / min, the corresponding minimum liquid level of the tundish is 1200 mm, when the pulling speed is 1.5 m / min, the corresponding minimum liquid level of the tundish is 1100 mm, when the pulling speed is 1.4 m / min, the corresponding minimum liquid level of the tundish is 1000 mm, when the pulling speed is 1.3 m / min, the corresponding minimum liquid level of the tundish is 950 mm, when the pulling speed is 1.2 m / min, the corresponding minimum liquid level of the tundish is 900 mm, when the pulling speed is 1.1 m / min, the corresponding minimum liquid level of the tundish is 900 mm. The minimum liquid level in the tundish is 800mm, the minimum liquid level in the tundish corresponding to the pulling speed of 1.0m / min is 600mm, the minimum liquid level in the tundish corresponding to the pulling speed of 0.9m / min is 550mm, the minimum liquid level in the tundish corresponding to the pulling speed of 0.8m / min is 500mm, the minimum liquid level in the tundish corresponding to the pulling speed of 0.7m / min is 450mm, the minimum liquid level in the tundish corresponding to the pulling speed of 0.6m / min is 400mm, the minimum liquid level in the tundish corresponding to the pulling speed of 0.5m / min is 300mm, and the minimum liquid level in the tundish corresponding to the pulling speed of 0.4m / min is 200mm.

6. The method for finishing a continuous casting slab according to claim 1, wherein: The calculation formula for molten steel consumption at different drawing speeds is: V=v i ×t i ×w Among them, V is the consumption of molten steel at different drawing speeds, vi is the drawing speed, ti is the residence time at the corresponding drawing speed, and w is the weight per meter.

7. The method for finishing a continuous casting slab according to claim 1, wherein: The amount of molten steel in the tundish used for pouring into the crystallizer is such that when the tundish is disconnected from the crystallizer, at least 2 tons of molten steel remains in the tundish.

8. The method for finishing a continuous casting slab according to claim 1, wherein: In step S3, the pulling speed is adjusted to 0.2 m / min and maintained for 20-40 seconds.

9. The method for finishing a continuous casting slab according to claim 1, wherein: In step S3, the specific operation of disconnecting the tundish from the crystallizer is: closing the tundish stopper rod and removing the water outlet on the tundish car.

10. The method for finishing a continuous casting slab according to claim 1, characterized in that: The method further includes step S4, which specifically comprises: cooling the tail billet with a spray device to further accelerate the solidification of the tail billet, and after confirming that the tail billet is solidified, gradually increasing the drawing speed to the normal drawing speed.

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