Method for improving pitted surface on surface of hot-rolled steel plate

Abstract

The invention discloses a method for improving pitted surfaces on the surface of a hot-rolled steel plate, which belongs to the technical field of steel smelting, and specifically comprises the following steps: (1) reducing the descaling height of nozzles on a rolling mill, improving the hitting power of the nozzles, adjusting the number of the nozzles, and ensuring the overlapping amount D of the adjacent nozzles; (2) the striking force of the upper and lower nozzles is adjusted, so that the striking force F lower of the lower nozzle is higher than the striking force F upper of the upper nozzle by more than 10%, and the descaling quality of the lower surface is facilitated; (3) the flow Q < lower > of a rolling mill descaling lower header is larger than the flow Q < upper > of an upper header, the temperature drop of the lower surface of a rolled piece is changed to be larger than that of the upper surface through descaling water, the lower surface temperature of the rolled piece is lower than that of the upper surface, and the head warping degree of the rolled piece is improved; the method is simple to operate, effectively reduces the generation amount of pitted surfaces on the lower surface of the steel plate, improves the product surface quality, effectively changes the head warping degree of the rolled piece by changing the temperature drop of the upper surface and the lower surface of the rolled piece, and reduces the accidents of collision and damage of the head warping steel plate to a rolling mill guide.

Description

Technical Field

[0001] The invention relates to a method for improving defects, in particular to a method for improving the surface pitting of a hot-rolled steel plate, and belongs to the technical field of steel smelting. Background Art

[0002] Hot rolled steel plate is made of continuous casting slab or initial rolling slab as raw material, heated by a step-beam heating furnace, descaled by high pressure water and then enters the rough rolling mill. The rough rolled material is cut and then enters the finishing mill for computer controlled rolling. After the final rolling, it is cooled by laminar flow (computer controls the cooling rate) and coiled by the coiler to become a straight coil. The head and tail of the straight coil are often tongue-shaped and fish-tail-shaped, with poor thickness and width accuracy, and the edges often have defects such as wave shape, folded edge, and tower shape. The coil weight is heavy and the inner diameter of the steel coil is 760mm.

[0003] The high-pressure water descaling process uses high-pressure water provided by the system to spray out through the descaling nozzle to cause the iron oxide scale on the surface of the steel plate to crack and fall off. If the descaling is not clean, product defects such as pitting, pitting, and iron oxide intrusion will form on the surface of the steel plate, causing product degradation or scrapping, affecting production costs; especially when the bottom surface of the steel plate has pitting, it is not easy to be found, which is easy to cause quality disputes and affect the corporate image. In addition, when designing the descaling of wide and thick plate mills, the upper and lower headers generally adopt the same flow rate and impact force. It is also easy to appear buckled heads during the rolling process. The impact of the buckled head plate on the rolling mill guide may cause damage to the rolling mill guide.

[0004] Patent CN119237482A discloses a method for reducing hot-rolled pitting defects. The method reduces the occurrence of pitting by ensuring the dephosphorization pressure, the quality of the working roll surface and the head-to-tail temperature difference. However, the pressure is controlled by adding a dephosphorization water tank. The specific control method and the optimization method for adjusting the height and angle of the water nozzle are not disclosed. It is simply described that the pressure is controlled to 19MPa by adding a water tank. There is no specific control process, and the amount of pitting on the lower surface of the steel plate cannot be controlled. The improvement of the pitting needs to be improved. It also needs to be controlled in combination with the working roll surface and the head-to-tail temperature difference. The process is more complicated and the cost is high.

[0005] Therefore, developing a method for improving the surface roughness of hot-rolled steel plates that can overcome the above defects has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for improving the surface roughness of hot-rolled steel plates. The method is simple to operate, effectively reduces the amount of roughness on the lower surface of the steel plate, improves the surface quality of the product, and effectively changes the degree of warping of the rolled piece by changing the temperature drop between the upper and lower surfaces of the rolled piece, thereby reducing the accidents of warped steel plates colliding with and damaging the rolling mill guides.

[0007] To solve the above technical problems, the present invention provides a method for improving the surface pitting of hot-rolled steel plates, which specifically includes the following steps: (1) Reduce the descaling height of the nozzles on the rolling mill, increase the impact force of the nozzles, and at the same time adjust the number of nozzles to ensure that the overlap D of adjacent nozzles is 7 - 20 mm; (2) Adjust the impact forces of the upper and lower nozzles so that the impact force F of the lower nozzle 下 is higher than the impact force F of the upper nozzle 上 by more than 10%, which is beneficial to the descaling quality of the lower surface; (3) The flow rate Q of the lower header of the rolling mill descaling 下 is greater than the flow rate Q of the upper header 上 , and the temperature drop of the lower surface of the rolled piece changed by the descaling water is greater than that of the upper surface, and the temperature of the lower surface of the rolled piece is lower than that of the upper surface, so as to improve the degree of warping of the rolled piece.

[0008] The further limited technical solution of the present invention is: Further, in the method for improving the surface pitting of hot-rolled steel plates described above, in step (1), the installation dimension of the upper and lower headers of the rolling mill is 200 mm, so that the vertical distance from the lower nozzle to the lower surface of the steel plate is 170 mm.

[0009] In the method for improving the surface pitting of hot-rolled steel plates described above, add 3 - 4 nozzles to the lower header to ensure the overlap of adjacent nozzles.

[0010] Technical effect: The present invention adds 3 - 4 nozzles to the lower header, reduces the distance between the nozzles, ensures the overlap of adjacent nozzles, ensures the descaling effect, and at the same time increases the descaling water flow rate of the lower header.

[0011] In the method for improving the surface pitting of hot-rolled steel plates described above, in step (2), the nozzle impact force F 下 = (1.1 - 1.2)F 上 .

[0012] In the method for improving the surface pitting of hot-rolled steel plates described above, in step (3), the ratio of the flow rate Q of the lower header to the flow rate Q of the upper header during rolling mill descaling 下 is specifically Q 上 = 1.1Q 下 . 上 .

[0013] In the method for improving the surface pitting of hot-rolled steel plates described above, the temperature of the lower surface of the rolled piece is 10 - 20 °C lower than that of the upper surface.

[0014] The beneficial effects of the present invention are: Improving the impact force of descaling nozzles can reduce the scale on the surface of steel plates. According to the theoretical calculation of the impact force of nozzles for descaling, there are four main factors affecting the impact force F of the nozzles: water pressure P, flow rate Q, spray angle α, and spray height H. The impact force F is proportional to the descaling pressure P and the flow rate Q; it is inversely proportional to the spray angle α. The smaller the spray angle, the smaller the impact area and the greater the impact force; the impact force is inversely proportional to the square of the spray height H. To achieve a better descaling effect, the spray distance should be reduced as much as possible within the allowable range. Therefore, in the present invention, by adjusting the water consumption of the upper and lower manifolds of the mill descaling, adjusting the number and impact force of the nozzles, changing the temperature drop on the upper and lower surfaces of the rolled piece through descaling water, changing the degree of warping of the rolled piece, reducing the accidents of the warped steel plate hitting and damaging the guide guards of the mill, and also reducing the occurrence of pitted surfaces on the lower surface of the steel plate that are not easy to clean, improving the surface quality of the product, and meeting the needs of users.

[0015] In the present invention, only by improving the nozzles and water collecting pipes on the mill can the occurrence of pitted surfaces on the lower surface of the steel plate be reduced, the surface quality of the product be improved, and the degree of warping of the rolled piece be improved. The process is simple, the cost is low, and it is easy to use. Brief Description of the Drawings

[0016] Figure 1 It is a partial structural schematic diagram of a mill with lower nozzles in the prior art; Figure 2 It is a structural schematic diagram of the improved mill with lower nozzles in the embodiment of the present invention; Detailed Description of the Invention Embodiment 1

[0017] A method for improving the pitted surface of hot-rolled steel plates provided in this embodiment specifically includes the following steps: (1) Reduce the descaling height of the nozzles on the mill, increase the impact force of the nozzles, and at the same time adjust the number of nozzles to ensure that the overlap D of adjacent nozzles is 7 - 20 mm; (2) In the prior art, as shown in Figure 1 , the size of the lower manifold is 185 mm. By increasing the installation size of the lower manifold as shown in Figure 2 , where ② is changed to 200 mm, ensure the vertical distance ① from the nozzle to the lower surface of the steel plate, which is closer to the lower surface, and adjust the impact forces of the upper and lower nozzles so that the impact force F of the lower nozzle 下 is more than 10% higher than the impact force F of the upper nozzle 上 , and the impact force F of the nozzle 下 = (1.1 - 1.2)F 上 , which is beneficial to the descaling quality of the lower surface; (3) The flow rate Q of the lower manifold of the mill descaling is 下 greater than the flow rate Q of the upper manifold 上 , Q 下 = 1.1Q 上, the temperature drop of the lower surface of the rolled piece is changed by descaling water to be greater than that of the upper surface, and the temperature of the lower surface of the rolled piece is 10 - 20 °C lower than that of the upper surface, improving the degree of warping of the rolled piece.

[0018] The following table shows the comparison of the parameters of the descaling upper and lower header nozzles of the rolling mill before and after modification: Table 1 Parameters of the descaling upper and lower header nozzles of the rolling mill before modification As can be seen from Table 1, (1) by modifying the design of the lower header, the vertical distance from the nozzle to the lower surface of the steel plate is changed from 185 mm to 170 mm, and the impact force of the nozzle is increased from 0.73 N / mm 2 to 0.86 N / mm 2 , and the impact force is increased by 18%; (2) 3 nozzles are added to the lower header, and the nozzle spacing is reduced from 126 mm to 112 mm, ensuring that the overlap of nozzle impacts changes from 18.5 mm to 20.7 mm without affecting the descaling effect; (3) the flow rate Q 下 of the lower header = 43 * 140.72 = 6050.96; Q 上 of the other part = 49 * 113.84 = 5578.16. The flow rate Q 下 of the descaling header = 1.085Q 上 , meeting the requirements.

[0019] After the implementation of this invention, the descaling quality is improved, the surface quality of the steel plate is improved, especially the quality of the lower surface of the steel plate. The occurrence of pitted surface is reduced by 150 t / month, 1800 t in a year, and the affected benefit is 180,000 yuan; if there is one equipment accident, it will cause a downtime of 24 h, affect the production capacity of 5000 t, and reduce the benefit by 750,000 yuan.

[0020] Except for the above embodiments, the present invention may have other implementation manners. All technical solutions formed by equivalent replacement or equivalent transformation fall within the protection scope required by the present invention.

Claims

1. A method for improving the surface pitting of hot-rolled steel sheets, characterized in that, Specifically, it includes the following steps: (1) Reduce the descaling height of the nozzles on the rolling mill, and at the same time adjust the number of nozzles to ensure that the overlap of adjacent nozzles is D7 - 20 mm; (2)Adjust the impact forces of the upper and lower nozzles so that the impact force F of the lower nozzle 下 is higher than the impact force F of the upper nozzle 上 ; (3)Flow rate Q of the lower manifold of the mill descaling system 下 is greater than the flow rate Q of the upper manifold 上 , such that the temperature drop of the lower surface of the rolled piece changed by the descaling water is greater than that of the upper surface, and the temperature of the lower surface of the rolled piece is lower than that of the upper surface.

2. The method for improving the surface pitting of hot-rolled steel sheets according to claim 1, characterized in that: The installation dimension of the upper and lower headers of the rolling mill is 200 mm, so that the vertical distance from the lower nozzle to the lower surface of the steel plate is 170 mm.

3. The method for improving the surface pitting of hot-rolled steel sheets according to claim 1, characterized in that: Add 3 - 4 nozzles to the lower header nozzle to ensure the overlap of adjacent nozzles.

4. The method for improving the surface pitting of hot-rolled steel sheets according to claim 1, characterized in that: The nozzle impact force F in the step (2) 下 = (1.1 - 1.2)F 上 .

5. The method for improving the surface pitting of hot-rolled steel sheets according to claim 1, characterized in that: The flow rate Q of the lower header during descaling by the rolling mill in step (3) 下 and the flow rate Q of the upper header 上 The specific ratio is Q 下 = 1.1Q 上 .

6. The method for improving the surface pitting of hot-rolled steel sheets according to claim 1, characterized in that: In step (3), the temperature of the lower surface of the rolled piece is 10 - 20 °C lower than that of the upper surface.

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