Method for controlling cross-sectional profile of high carbon steel in ultra-thin gauge produced by thin slab continuous casting and rolling line

Abstract

The present application relates to the production process technical field of very thin gauge high carbon steel, and particularly discloses a thin slab continuous casting and rolling production line very thin gauge high carbon steel cross section profile control method, local hot crown compensation finishing high carbon steel differentiation roll shape design: each rack of finishing installation is provided with a high carbon steel work roll shape with local hot crown compensation, and differentiation design is performed according to the hot crown size of different racks; the support roll shape is in a variable contact chamfer form; the full-rack high-speed steel roll is used for producing high carbon steel strips on a endless rolling production line: the finishing rack is provided with a full-rack high-speed steel roll, and is matched with a hot crown compensation high-speed steel roll shape; high carbon steel strip cooling control: through layer cooling steel organization homogenization control, strip offline slow cooling setting and thin gauge slow cooling area position selection, uniform slow cooling of each area of the steel coil is realized; and the present application realizes batch stable production of 65Mn and below grade high carbon steel limit thin gauge ≤1.2mm steel strips on a hot rolling continuous casting and rolling production line.

Description

Technical Field

[0001] This invention relates to the field of production technology for ultra-thin high-carbon steel, specifically to a method for controlling the cross-sectional profile of ultra-thin high-carbon steel in a thin slab continuous casting and rolling production line. Background Technology

[0002] Currently, there are no records of hot-rolled high-carbon steel production lines producing steel grades of 65Mn and below with an extreme thinness of ≤1.25mm.

[0003] Although the specification for producing 65Mn high-carbon steel using a thin slab continuous casting and rolling production line has been reduced to 1.25mm, several production technology issues prevent the stable mass production of high-carbon steel ≤1.25mm from being feasible. The main problems are as follows:

[0004] (1) The unstable pulling speed and centerline fluctuation of 65Mn lead to extremely unstable rolling conditions for the thinnest specifications, resulting in a high risk of rolling failure in the finishing mill.

[0005] (2) The large transverse temperature difference and large centerline fluctuation of the billet result in high points on both sides of the finished product section, large wedge shape and small convexity. The average convexity of the 1.25mm specification is less than 5um, resulting in a high defect rate of finished strip steel and unsatisfactory customer trial results.

[0006] (3) The cooling rate of the strip is inconsistent between the edge and the middle after the strip is unloaded, resulting in local differences in the strip structure, which leads to severe rib formation and waviness at the edge of the strip.

[0007] Therefore, it is necessary to design a method for controlling the cross-sectional profile of ultra-thin high-carbon steel in a thin slab continuous casting and rolling production line, in order to solve the problems of insufficient convexity of thin strip, high risk of breakage during finishing rolling, and high rejection rate of finished strip quality in the production of ultra-thin high-carbon steel. Summary of the Invention

[0008] To address the problems existing in the prior art, the purpose of this invention is to provide a method for controlling the cross-sectional profile of ultra-thin high-carbon steel in a thin slab continuous casting and rolling production line. Based on previous experiments on ultra-thin high-carbon steel, it has been verified that the thinner the specification, the more obvious the change in convexity caused by uneven local thermal expansion in the width direction of the steel passage zone. This results in insufficient convexity of thin-specification strip steel, and the production of bright strips in steel coils does not meet the conditions for mass production. This problem cannot be solved simply by adjusting the process such as temperature difference. Therefore, starting from the original roll shape, a roll shape design concept for thin-specification high-carbon steel is proposed.

[0009] The technical solution adopted by this invention to solve its technical problem is: a method for controlling the cross-sectional profile of ultra-thin high-carbon steel in a thin slab continuous casting and rolling production line, comprising the following steps:

[0010] S1. Differentiated roll shape design for high carbon steel finishing mill with local thermal crown compensation: The roll shape of high carbon steel work rolls with local thermal crown compensation is installed on each stand of the finishing mill, and the design is differentiated according to the thermal crown size of different stands.

[0011] S2. Variable contact support roller shape design with large circular arc composite transition chamfer: The support roller shape is a variable contact chamfer form;

[0012] S3. High-carbon strip steel is produced on a headless rolling production line using full-stand high-speed steel rolls: the finishing mill uses full-stand high-speed steel rolls, and is matched with high-speed steel rolls with thermal crown compensation.

[0013] S4. Cooling control of high carbon strip: By controlling the uniformity of strip structure in layer cooling, setting up slow cooling of strip after it leaves the production line, and selecting the location of the slow cooling zone for thin specifications, uniform slow cooling of all areas of the steel coil is achieved.

[0014] Specifically, in step S1, the thermal convexity of different racks is designed differently. For racks F1-F5, the compensation range is determined according to the width of the temperature difference band, which is 50-200mm, and the local thermal convexity compensation range is 20-150um.

[0015] Specifically, the variable contact chamfering in step S2 consists of a first segment that is a variable contact segment. The length and curvature of the variable contact segment are adjusted to match the requirements of the support roller shape of different frames. According to the design of the work rollers of different frames, the length of the variable contact segment of frames F1-F5 is 30-220mm, and the convexity is increased by 30-100um. The second segment is a chamfered segment, where the chamfer taper remains unchanged, while improving the distribution shape of the strip along the width direction.

[0016] Specifically, in step S4, the homogenization control of the microstructure of the laminated strip steel involves opening the last set of cooling water for the laminated strip steel with a thickness of less than 1.5mm, so that the temperature of the transverse cross section of the strip steel is uniform, and the laminated strip cooling temperature is controlled to be ≥620℃ by adjusting the water volume.

[0017] Specifically, in step S4, the slow cooling of strip steel is set to take a long time from unloading the steel coil to the finished product warehouse. It takes 55 minutes to transport the steel coil from the No. 1 walking beam to the finished product warehouse. When producing ultra-thin high-carbon steel, a detachable slow cooling cover is installed on the No. 1 walking beam.

[0018] Specifically, in step S4, the location of the thin-gauge slow cooling zone is selected to be slow cooling of the extreme thin-gauge ≤1.2mm, the slow cooling time of the extreme thin-gauge is ≥48 hours, and the slow cooling zone is placed as the second layer of the middle slow cooling zone to ensure that there are steel coils in the upper, lower, left and right areas, and that the steel coils are slow cooled evenly in each area.

[0019] The present invention has the following beneficial effects:

[0020] The present invention relates to a method for controlling the cross-sectional profile of ultra-thin high-carbon steel in a thin slab continuous casting and rolling production line. This method enables stable batch production of ≤1.2mm strip steel of 65Mn and below high-carbon steel grades in hot rolling continuous casting and rolling production lines. It meets the thinning requirements of some end customers, saves pickling, cold rolling and annealing costs, and achieves the goal of "replacing cold with hot" for high-carbon steel.

[0021] The present invention provides a method for controlling the cross-sectional profile of ultra-thin high-carbon steel in a thin slab continuous casting and rolling production line. This method addresses factors affecting the cross-sectional profile of high-carbon finished steel coils, such as unstable casting speed, large cross-sectional temperature difference, centerline deviation, edge warping in the finishing roll section, and coiling, in the production of thin-gauge high-grade 65Mn and below steels. This method aims to meet the quality requirements of end customers for high-carbon steel with a thickness of ≤1.2mm. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be described clearly, completely, and in further detail below. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0023] A method for controlling the cross-sectional profile of ultra-thin high-carbon steel in a thin slab continuous casting and rolling production line includes the following steps:

[0024] I. The innovative design of ultra-thin high-carbon steel rolls solves the convexity problem.

[0025] 1. Differentiated roll shape design for high-carbon steel finishing mill with localized thermal crown compensation: Each stand of the finishing mill is equipped with high-carbon steel work rolls with localized thermal crown compensation, and the design is differentiated according to the thermal crown size of different stands; for stands F1-F5, the compensation range is determined based on the width of the temperature difference band, which is 50-200mm, and the localized thermal crown compensation range is 20-150µm. This roll shape compensates for the problem of uneven thermal expansion of the rolls caused by uneven cross-sectional temperature difference at the source, resulting in poor cross-sectional profile, and directly and effectively solves the problem of localized high points on both sides of the strip cross-sectional profile.

[0026] 2. Variable Contact Support Roll Shape Design with Large Arc Composite Transition Chamfer: The support roll shape is a variable contact chamfer type; the first section is the variable contact section, and the length and arc of the variable contact section are adjusted to match the requirements of the support roll shape of different frames. According to the design of different frame work rolls, the length of the variable contact section of F1-F5 frames is 30-220mm, and the convexity is increased by 30-100um; the second section is the chamfer section, and the chamfer taper remains unchanged, so as to avoid the support roll shape from forming a local contact stress zone due to the adjustment of the work roll shape, which would cause fatigue, chipping, and other abnormalities of the support roll. At the same time, it improves the distribution shape of the strip along the width direction, and achieves the purpose of optimizing the strip shape and cross-section, which can better match the high carbon steel work roll shape.

[0027] 3. High-carbon strip production using full-stand high-speed steel rolls in a headless rolling production line: The finishing mill uses full-stand high-speed steel rolls, and is matched with high-speed steel rolls with thermal crown compensation; the wear of the rolls is reduced by more than 2 / 3, alleviating the uneven wear of the rolls caused by batch rolling of extremely thin specifications, ensuring that the cross-sectional profile of the strip in the later stages of casting meets the quality requirements, and increasing the single casting mileage by 30km except for stable batch rolling of ≤1.2mm.

[0028] II. Strip cooling control solves the problem of poor cross-sectional profile caused by uneven cooling of steel coils.

[0029] Due to a situation where the strip section appeared normal multiple times during the thin-gauge rolling process, but a bright strip appeared on the coil after uncoiling and during slow cooling, resulting in an abnormal profile of the final finished product, the following process control innovations are proposed based on the concept of uniform cooling of the strip after rolling.

[0030] 1. Control of uniformity of strip structure in laminar cooling: For strips with a thickness of less than 1.5mm, the last set of cooling water is turned on in laminar cooling to make the temperature uniformity of the transverse cross section of the strip consistent. At the same time, the laminar cooling temperature is controlled to be ≥620℃ by adjusting the water volume.

[0031] 2. Slow cooling setting for strip steel unloading: The time from unloading the steel coil to the finished product warehouse is long. It takes 55 minutes to transport the steel coil from No. 1 walking beam to the finished product warehouse. When producing 65Mn ultra-thin high carbon steel, a detachable slow cooling cover is installed on No. 1 walking beam to reduce the strip shape defects such as warping, waviness and local thickness unevenness caused by the uneven thermal stress and structural stress in the transverse section of the strip steel due to the excessively rapid cooling rate of the strip edge at the walking beam.

[0032] 3. Selection of the location of the slow cooling zone for thin specifications: For 65Mn with an extreme thin specification of ≤1.2mm, the slow cooling time is ≥48 hours. The slow cooling zone is placed as the second layer of the middle slow cooling zone to ensure that there are steel coils in the upper, lower, left and right areas, and to ensure that the steel coils are cooled evenly in all areas.

[0033] The present invention provides a method for controlling the cross-sectional profile of ultra-thin high-carbon steel in a thin slab continuous casting and rolling production line. This method enables stable batch production of over 300 tons of 65Mn steel with a thickness of ≤1.2mm in a single casting. Simultaneously, it significantly improves the cross-sectional profile control capability per casting, increasing the average crown of strip steel with a thickness of 1.5mm and below from 0µm to 28µm, and reducing the maximum thickness difference within a 200mm radius of the strip edge from 40µm to less than 10µm. Furthermore, the wedge shape of the strip steel is stabilized within ±10. After applying this control method, the casting mileage for 65Mn steel can be increased to 150km, and the amount of defective products requiring re-judgment due to cross-sectional profile issues in thin-gauge production castings has decreased from 65 tons to 0 tons.

[0034] This invention is not limited to the above-described embodiments. Anyone should know that any structural changes made under the guidance of this invention, and any technical solutions that are the same as or similar to this invention, fall within the protection scope of this invention.

[0035] The technologies, shapes, and structures not described in detail in this invention are all known technologies.

Claims

1. A method for controlling the cross-sectional profile of ultra-thin high-carbon steel in a thin slab continuous casting and rolling production line, characterized in that, Includes the following steps: S1. Differentiated roll shape design for high carbon steel finishing mill with local thermal crown compensation: Each stand of the finishing mill is equipped with high carbon steel work rolls with local thermal crown compensation. The design is differentiated according to the thermal crown size of different stands. The compensation range of stands F1-F5 is determined according to the width of the temperature difference band. The width of the temperature difference band is 50-200mm, and the local thermal crown compensation range is 20-150um. S2. Variable contact support roller shape design with large circular arc composite transition chamfer: The support roller shape is a variable contact chamfer form; S3. High-carbon strip steel is produced on a headless rolling production line using full-stand high-speed steel rolls: the finishing mill uses full-stand high-speed steel rolls, and is matched with high-speed steel rolls with thermal crown compensation. S4. Cooling control of high carbon strip: By controlling the uniformity of strip structure in layer cooling, setting up slow cooling of strip after it leaves the production line, and selecting the location of the slow cooling zone for thin specifications, uniform slow cooling of all areas of the steel coil is achieved.

2. The method for controlling the cross-sectional profile of ultra-thin high-carbon steel in a thin slab continuous casting and rolling production line according to claim 1, characterized in that, The variable contact chamfering in step S2 consists of a first segment that is a variable contact segment. The length and curvature of the variable contact segment are adjusted to match the requirements of the support roller shape of different frames. According to the design of the work rollers of different frames, the length of the variable contact segment of frames F1-F5 is 30-220mm, and the convexity is increased by 30-100um. The second segment is a chamfered segment. The chamfered taper remains unchanged, while improving the distribution shape of the strip along the width direction.

3. The method for controlling the cross-sectional profile of ultra-thin high-carbon steel in a thin slab continuous casting and rolling production line according to claim 1, characterized in that, In step S4, the homogenization control of the microstructure of the laminated strip is achieved by opening the last set of cooling water for the laminated strip with a thickness of less than 1.5 mm, so that the temperature of the transverse cross section of the strip is uniform. At the same time, the temperature of the laminated strip is controlled to be ≥620℃ by adjusting the amount of water.

4. The method for controlling the cross-sectional profile of ultra-thin high-carbon steel in a thin slab continuous casting and rolling production line according to claim 1, characterized in that, The slow cooling of strip steel in step S4 is designed to take a long time from unloading the steel coil to the finished product warehouse. It takes 55 minutes to transport the steel coil from the No. 1 walking beam to the finished product warehouse. When producing ultra-thin high carbon steel, a detachable slow cooling cover is installed on the No. 1 walking beam.

5. The method for controlling the cross-sectional profile of ultra-thin high-carbon steel in a thin slab continuous casting and rolling production line according to claim 1, characterized in that, In step S4, the location of the thin-gauge slow cooling zone is selected to be slow cooling of the minimum thin gauge ≤ 1.2mm, and the slow cooling time of the minimum thin gauge is ≥ 48 hours. The slow cooling zone is placed as the second layer of the middle slow cooling zone to ensure that there are steel coils in the upper, lower, left and right areas, and that the steel coils are slow cooled evenly in all areas.