Method for improving cooling uniformity of medium-carbon high-strength ultrathin strip steel in double-roller cast rolling production

Abstract

The invention belongs to the field of hot-rolled thin strip steel production, and relates to a device and method for improving cooling uniformity of medium-carbon high-strength ultrathin strip steel in double-roller cast rolling production. The medium-carbon high-strength ultrathin strip steel is produced by adopting a double-roller casting and rolling process, molten steel meeting the requirement forms a cast strip through a casting roller, then hot-rolled thin-strip high-strength steel is formed through one-pass hot rolling, aerial fog cooling and coiling, and by optimizing relevant parameters such as the angle and the arrangement mode of aerial fog cooling nozzles, the high-strength ultrathin strip steel can be obtained. And the problem of uneven cooling of the medium-carbon high-strength ultrathin strip steel is solved, and the tensile strength fluctuation in the plate width direction is within + / -30 MPa.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel rolling, in particular to a device and method for improving the cooling uniformity of high-carbon high-strength ultra-thin strip steel in double-roller casting production, specifically, the device and method are used for producing high-carbon high-strength ultra-thin strip steel by a double-roller casting method, and the problem of uneven cooling of the high-carbon high-strength ultra-thin strip steel is improved by optimizing related parameters such as the gas mist cooling nozzle and the arrangement mode. BACKGROUND

[0002] The double-roller casting process has a short production line and low carbon emission, and only has 50 meters from the ladle rotating table to the coiler. The double-roller casting process has natural advantages for producing thin-gauge strip steel. The thinnest hot-rolled strip steel produced by the process can be 0.6 mm, and the hot strip can be cooled. Molten steel is cooled by copper casting rolls with cooling water to form a cast strip of 1.8-2.5 mm, and then is rolled by one pass to form a rolled strip of 0.6-2.0 mm, and then is cooled by gas mist to the required process temperature, and finally is coiled.

[0003] In the double-roller casting production process, the temperature of the strip steel from the outlet of the rolling mill is as high as 780-900℃, and needs to be rapidly cooled to the coiling temperature of 300-500℃ by the gas mist cooling section to ensure the subsequent shape quality and mechanical properties. Due to the compact design requirements of the production line, the effective length of the gas mist cooling section is only 10 meters. To achieve an ultra-high cooling speed of 100℃ / s, high-density nozzles are arranged on the upper and lower cross beams of the cooling equipment, a total of 22 rows of nozzles, each row having 7 one-dimensional nozzles, the nozzles are distributed in a cross shape, the water mist sprayed by the nozzles is distributed in a fan shape, and the fan shape is perpendicular to the rolling direction of the strip steel. Due to the inevitable overlapping of the fan-shaped spray areas of adjacent nozzles, the cooling water quantity in the overlapping area is significantly higher than that in other areas, resulting in prominent local overcooling of the strip steel. This uneven cooling in the width direction can form significant local stress concentration in the strip steel, directly leading to shape defects such as waves and warping, and seriously affecting the product qualification rate and profit level.

[0004] Patent CN110523786B "A uniform cooling type laminar cooling system for strip steel", provides a uniform cooling type laminar cooling system and method for strip steel, including rolling module and cooling module; the rolling module is used for rolling the intermediate strip blank to form the strip steel; the cooling module includes the first cooling area and the second cooling area; the rolling strip steel is obtained, and the strip steel is water-cooled through the first cooling area and the second cooling area respectively; the first cooling area includes at least one encryption cooling unit and a general cooling unit; under the same water flow pressure, the unit area water flow density of the encryption cooling unit is greater than that of the general cooling unit, which is the main cooling equipment to ensure the cooling effect and performance of the strip steel. The second cooling area is a fine adjustment cooling area, which can finely adjust the temperature of the strip steel. In the laminar cooling process of the strip steel, the nozzle with a small diameter is arranged in the encryption laminar cooling section of the first cooling area, so that the strip steel can be uniformly cooled. However, this scheme is suitable for conventional hot rolling production line and is not suitable for double roll casting process production line. SUMMARY

[0005] In view of the above problems, the present application provides a device and method for improving the cooling uniformity of high-carbon high-strength ultra-thin strip steel in double-roll casting production, which improves the problem of uneven cooling of high-carbon high-strength ultra-thin strip steel by optimizing related parameters such as gas mist cooling nozzle and arrangement.

[0006] Specifically, the technical scheme adopted by the present application is:

[0007] According to one aspect of the present application, a method for improving the cooling uniformity of high-carbon high-strength ultra-thin strip steel in double-roll casting production is provided, characterized in that the high-carbon high-strength ultra-thin strip steel is produced by double-roll casting process, the molten metal passes through the casting machine, the rolling mill, the gas mist cooling section to the required process temperature, and then enters the coiler to form a hot rolled coil, and the finished product thickness is 0.5-2.0mm.

[0008] According to the method of the present application, preferably, the C content of the molten metal is 0.21-0.30%, the silicon content is 0.1-0.5%, and the Mn content is 0.4-2.0%, and the molten steel passes through two casting rolls with cooling water distributed in the inner part of the relative rotation, and forms a cast strip with a thickness of 1.8-2.5mm.

[0009] According to the method of the present application, preferably, the cast strip is sent to the rolling mill after passing through the hot box with inert gas protection, and is rolled into a rolling strip with a thickness of 0.6-2.0mm.

[0010] According to the method of the present application, preferably, the strip is cooled to the process required temperature of 500±20℃ by the gas mist cooling device, the gas mist cooling device is divided into upper side spraying and lower side spraying, each side has 20-25 rows, each row is composed of 6-10 nozzles, the adjacent nozzles are distributed in star shape staggered, the water flow is avoided to cross and overlap, the angle between the direction of the nozzle and the transverse direction of the strip is 0-20°.

[0011] According to the method of the present application, preferably, the spray form of the nozzle of the gas mist cooling device is in the form of a linear fan, the angle between the direction of the nozzle and the transverse direction of the strip is 5±2°.

[0012] According to the method of the present application, preferably, the gas pressure of the gas mist cooling device is controlled at 2-3bar, and the water pressure is controlled at 6-8bar.

[0013] According to the method of the present application, preferably, the obtained medium carbon high strength ultra-thin strip has a tensile strength of ≥620MPa, and the metallographic microstructure is mainly bainite, and the tensile strength fluctuation in the plate width direction is within ±30MPa. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings described below only relate to some embodiments of the present application, and are not a limitation on the present application.

[0015] Figure 1 is a schematic diagram of nozzle fan water flow intersection and production line well-shaped nozzle arrangement.

[0016] Figure 2 is the surface state of the strip after cooling of the comparative example.

[0017] Figure 3 is the mechanical property data of the strip in the plate width direction.

[0018] Figure 4 is the nozzle angle of the optimized production line and the schematic diagram of the star-shaped nozzle arrangement.

[0019] Figure 5 is the surface state of the strip after cooling of the embodiment.

[0020] Figure 6 is the mechanical property data of the strip in the plate width direction. DETAILED DESCRIPTION

[0021] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the described embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without any creative effort belong to the scope of protection of the present application.

[0022] Unless otherwise defined, the technical terms or scientific terms used in the present application shall have the meanings commonly understood by those of ordinary skill in the art to which the present application belongs.

[0023] The following are embodiments of the present application, and the described embodiments are only part of the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without any creative effort belong to the scope of protection of the present application.

[0024] The technical solutions of the present application will be further described in detail below through specific embodiments and comparative examples.

[0025] Comparative Example

[0026] Figure 1 is a schematic diagram of nozzle fan-shaped water flow intersection and a schematic diagram of line well-shaped nozzle arrangement. Figure 2 is the surface state of the strip after cooling in the comparative example. Figure 3 is the mechanical property data of the strip in the plate width direction.

[0027] The molten metal meeting the component requirements is cast and rolled into 1.0 mm rolling strip, and after passing through the gas mist cooling device of Figure 1 , the surface of the strip is as shown in Figure 2 , and obvious supercooled strips appear at the overlapping parts of the nozzles, and the performance in the plate width direction fluctuates greatly, as shown in Figure 3 , the tensile strength deviation in the plate width direction is ± 150 MPa.

[0028] Embodiment

[0029] Figure 4 is a schematic diagram of the nozzle angle and star-shaped nozzle arrangement after optimization. Figure 5 is the surface state of the strip after cooling in the embodiment. Figure 6 is the mechanical property data of the strip in the plate width direction. The molten metal meeting the component requirements is cast and rolled into 0.9 mm rolling strip, and after passing through the gas mist cooling device after optimization of Figure 4 , the surface of the strip is as shown in Figure 5 , and the strip surface is good without obvious supercooled strips. The tensile strength in the plate width direction is uniform, and the fluctuation is within ± 25 MPa, as shown in Figure 6 .

[0030] The above description is merely a specific embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for improving the cooling uniformity of high-carbon, ultra-thin strip steel in twin-roll casting and rolling production, characterized in that, The medium-carbon high-strength ultra-thin strip steel is produced by twin-roll casting and rolling process. The molten metal passes through the casting machine, rolling mill, and air mist cooling section to the required process temperature, and then enters the coiler to form hot-rolled coils. The finished product thickness is 0.5-2.0mm.

2. The method according to claim 1, characterized in that: The molten metal has a C content of 0.21-0.30%, a silicon content of 0.1-0.5%, and a Mn content of 0.4-2.0%. The molten steel passes through two relatively rotating casting rolls with internally distributed cooling water and is cast and rolled to form a casting strip with a thickness of 1.8-2.5 mm.

3. The method according to claim 1, characterized in that: After passing through a hot box protected by inert gas, the cast strip is sent to the rolling mill and rolled into a strip with a thickness of 0.6-2.0 mm.

4. The method according to claim 1, characterized in that: The strip is cooled to the required process temperature of 500±20℃ by an air mist cooling device. The air mist cooling device is divided into upper spray and lower spray, with 20-25 rows on each side. Each row consists of 6-10 nozzles, with a spacing of 200-300mm between adjacent nozzles. They are staggered in a star shape to avoid water flow crossing and overlapping. The angle between the nozzles in a straight line and the transverse direction of the strip is 0-20°.

5. The method according to claims 1-4, characterized in that: The nozzle of the aerosol cooling device has a straight fan-shaped spray pattern, and the angle between the nozzle direction and the transverse direction of the strip is 5±2°.

6. The method according to claims 1-5, characterized in that: The air pressure of the aerosol cooling device is controlled at 2-3 bar, and the water pressure is controlled at 6-8 bar.

7. The method according to claims 1-6, characterized in that: The obtained medium-carbon high-strength ultra-thin strip steel has a tensile strength ≥620MPa, and the metallographic microstructure is mainly bainite. The tensile strength in the width direction fluctuates within ±30MPa.

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