Thin slab continuous casting and rolling production line ultra-thin specification high-carbon steel section contour control method

Abstract

The invention relates to the technical field of ultra-thin specification high-carbon steel production processes, and particularly discloses a thin slab continuous casting and rolling production line ultra-thin specification high-carbon steel section profile control method, which comprises the following steps of: designing differential roll shapes of finish rolling high-carbon steel with local thermal convexity compensation: mounting roll shapes of special high-carbon steel working rolls with local thermal convexity compensation on all finish rolling racks; differentiated design is carried out according to the thermal convexity of different racks; the roll shape of the back-up roll is optimized into a variable contact chamfer form; the full-rack high-speed steel roller is used for producing high-carbon strip steel on an endless rolling production line, specifically, the full-rack high-speed steel roller is applied to a finishing mill rack, and meanwhile, an original thermal convexity compensation high-speed steel special roller shape is matched; high-carbon strip steel cooling control is conducted, specifically, uniform slow cooling of all areas of a steel coil is achieved through layer cooling strip steel structure homogenization control, strip steel offline slow cooling optimization and thin specification slow cooling area position selection; according to the invention, the batch stable production of the hot-rolling continuous casting and rolling production line 65Mn and below high-carbon steel strip steel with the ultimate thin specification of less than or equal to 1.2 mm is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of production technology of ultra-thin high-carbon steel, and in particular to a method for controlling the cross-sectional profile of ultra-thin high-carbon steel on a thin slab continuous casting and rolling production line. Background Art

[0002] At present, there is no record of hot rolling production line producing ultra-thin high carbon steel of 65Mn and below with a thickness of ≤1.25mm.

[0003] Based on the thin slab continuous casting and rolling production line, 65Mn high carbon steel is produced. Although the specification has been reduced to 1.25mm, there are many production technology problems that make it impossible to have stable batch production conditions for ≤1.25mm high carbon steel. The main problems are as follows:

[0004] (1) The unstable pulling speed and centerline fluctuation of 65Mn lead to the extremely unstable rolling state of the extreme thin gauge and a high risk of finishing rolling.

[0005] (2) Factors such as large lateral temperature difference of the ingot and large fluctuation of the center line lead to high points on both sides of the cross section of the finished product, large wedge shape of the cross section, small convexity, and the average convexity of the 1.25mm specification is less than 5um. The quality defect rate of the finished strip is high, and the customer trial effect is not ideal.

[0006] (3) The cooling rate of the strip edge and the middle after it comes off the line is inconsistent, resulting in differences in the local structure of the strip and severe rib wave shape at the edge of the strip.

[0007] Therefore, it is necessary to design a method for controlling the cross-sectional profile of extremely thin high-carbon steel in a thin slab continuous casting and rolling production line to solve the problems of insufficient convexity of thin-gauge strip steel, high risk of blowout in finishing rolling, and high defective rate of finished strip steel products in the production of the above-mentioned extremely thin-gauge high-carbon steel. Summary of the invention

[0008] In view of the problems existing in the prior art, the purpose of the present 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. According to the previous ultra-thin high-carbon steel downward exploration experiment, the thinner the specification, the more obvious the convexity change caused by the local uneven thermal expansion in the width direction of the steel zone, resulting in insufficient convexity of thin-gauge strip steel and bright strips in the steel coils that do 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 roller shape, a special roller shape design concept for thin-gauge high-carbon steel is proposed.

[0009] The technical solution adopted by the present invention to solve the 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 of high carbon steel for finishing rolling with local thermal crown compensation: Each finishing rolling stand is equipped with a special work roll shape of high carbon steel with local thermal crown compensation, and a differentiated design is performed according to the thermal crown size of different stands;

[0011] S2. Design of variable contact support roller shape with large arc composite transition chamfer: The support roller shape is optimized to a variable contact chamfer form;

[0012] S3, full-frame high-speed steel rolls are used to produce high-carbon strip steel in the headless rolling production line: the finishing mill uses full-frame high-speed steel rolls, and is matched with the original thermal crown compensation high-speed steel special roll shape;

[0013] S4. Cooling control of high carbon strip steel: uniform slow cooling of each area of ​​the steel coil is achieved through the homogenization control of the layer-cooled strip steel structure, optimization of the slow cooling of the strip steel off the line, and selection of the location of the slow cooling zone for thin specifications.

[0014] Specifically, the thermal convexity sizes of different racks in step S1 are differentiatedly designed so that the compensation range of racks 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 convexity compensation range is 20-150um.

[0015] Specifically, the variable contact chamfering form in step S2 is that the first section is a variable contact section, and the requirements of the roll shape of different frame support rollers are matched by adjusting the length and curvature of the variable contact section. According to the design of working rolls of different frames, 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 a chamfering section, and the chamfering taper remains unchanged, while improving the distribution shape of the strip along the width direction.

[0016] Specifically, the layer cooling strip structure homogenization control in step S4 is to open the last group of cooling water for the layer cooling with a thickness of less than 1.5 mm to make the temperature uniformity of the transverse section of the strip consistent, and at the same time control the layer cooling temperature ≥ 620°C by adjusting the water volume.

[0017] Specifically, the slow cooling optimization of the strip steel off-line in step S4 is that the time from unloading of the steel coil to storage of the finished product is long, and it takes 55 minutes for the steel coil to be transported from the No. 1 walking beam to the finished product warehouse. When producing extremely thin-gauge high-carbon steel, a detachable slow cooling cover of the No. 1 walking beam is installed.

[0018] Specifically, the position of the thin-gauge slow cooling zone in step S4 is selected as the slow cooling of the extreme thin gauge ≤1.2mm, the slow cooling time of the extreme thin gauge ≥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 each area of ​​the steel coil is evenly cooled.

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

[0020] The method for controlling the cross-sectional profile of extremely thin high-carbon steel in a thin slab continuous casting and rolling production line designed in the present invention can realize stable batch production of extremely thin strip steel of grades 65Mn and below of high-carbon steel ≤1.2mm in a hot rolling continuous casting and rolling production line, meet the thinning needs of some end customers, save the cost of pickling, cold rolling and annealing, and realize the purpose of "replacing cold with heat" for high-carbon steel.

[0021] The method for controlling the cross-sectional profile of ultra-thin high-carbon steel in a thin slab continuous casting and rolling production line designed in the present invention solves the problems affecting the cross-sectional profile of high-carbon finished steel coils, such as unstable drawing speed, large cross-sectional temperature difference, center line deviation, warping of the finishing section, and coiling, in the production of thin-sized high-grade 65Mn and below steel grades, and meets the quality requirements of end customers for high-carbon steel of ≤1.2mm. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present invention are described in detail below. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work 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 comprises the following steps:

[0024] 1. The innovative design of the roller shape for ultra-thin high-carbon steel solves the convexity problem.

[0025] 1. Differentiated roller shape design for finishing high carbon steel with local thermal crown compensation: Each finishing rolling stand is equipped with a special high carbon steel work roll with local thermal crown compensation, and is designed differently according to the thermal crown size of different stands; F1-F5 stands determine the compensation range according to the width of the temperature difference band, the temperature difference band width is 50-200mm, and the local thermal crown compensation range is 20-150um. This roller shape compensates for the poor cross-sectional profile caused by uneven thermal expansion of the roller due to uneven cross-sectional temperature difference from the source, and directly and effectively solves the problem of local high points on both sides of the strip cross-sectional profile.

[0026] 2. Variable contact support roller shape design with large arc composite transition chamfer: The support roller shape is optimized as a variable contact chamfer; the first section is the variable contact section, and the requirements of the support roller shape of different frames are matched by adjusting the length and curvature of the variable contact section. According to the design of working rolls of different frames, 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 to avoid the support roller shape from forming a local contact stress area due to the adjustment of the working roller shape, resulting in fatigue loss of the support roller, shoulder loss and other abnormalities, while improving the distribution shape of the strip along the width direction, achieving the purpose of optimizing the plate shape and section, and better matching the special working roll shape of high carbon steel.

[0027] 3. Full-frame high-speed steel rolls are used in headless rolling lines to produce high-carbon strip steel: The finishing mill uses full-frame high-speed steel rolls, and is matched with an original thermal crown compensation high-speed steel special roll shape; the wear of the rolls on the machine 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 stage of casting meets the quality requirements. In addition to the stable batch rolling of ≤1.2mm, the mileage of a single casting is increased by 30km.

[0028] 2. Strip cooling control solves the problem of poor cross-sectional profile caused by uneven cooling of steel coils.

[0029] Due to the fact that the fine rolling section is normal during the thin gauge rolling process, the bright strip of the steel coil appears during the process from unloading to slow cooling, resulting in abnormal cross-sectional profile of the final product. Based on the concept of uniform cooling of the strip after rolling, the following process control innovations are proposed.

[0030] 1. Layer-cooling strip steel structure homogenization control: For layer-cooling strip steel with a thickness of less than 1.5 mm, open the last group of cooling water to make the temperature uniformity of the transverse section of the strip steel consistent. At the same time, the layer-cooling temperature is controlled to be ≥620℃ by adjusting the water volume.

[0031] 2. Optimization of slow cooling of strip steel off the line: It takes a long time from unloading the steel coil to the storage of the finished product. It takes 55 minutes for the steel coil to be transported from the No. 1 walking beam to the finished product warehouse. When producing 65Mn ultra-thin high-carbon steel, a detachable slow cooling cover of the No. 1 walking beam is installed to reduce the thermal stress of the transverse section of the strip caused by the excessive cooling speed of the strip edge at the walking beam, and the uneven structural stress causes the strip to bend, wave shape and local uneven thickness. The plate shape defects.

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

[0033] The invention provides a method for controlling the cross-sectional profile of extremely thin high-carbon steel in a thin slab continuous casting and rolling production line. A single pouring of 65Mn≤1.2mm thin specifications can stably produce more than 300 tons in batches. At the same time, the cross-sectional profile control capability of pouring is greatly improved. The average convexity of 1.5mm and below strip steel is increased from 0um to 28um, and the maximum thickness difference within 200mm of the strip steel edge is reduced from 40um to within 10um; at the same time, the wedge shape of the strip steel is stabilized within ±10. After the control method is applied, the number of kilometers of 65Mn pouring can be increased to 150km, and the defective product re-judgment caused by the cross-sectional profile of thin-gauge production pouring before and after the research is reduced from 65 tons to 0 tons.

[0034] The present invention is not limited to the above-mentioned implementation modes, and anyone should be aware of the structural changes made under the enlightenment of the present invention, and all those having the same or similar technical solutions as the present invention fall within the protection scope of the present invention.

[0035] The techniques, shapes, and structural parts not described in detail in the present invention are all well-known techniques.

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: The following steps are involved: S1. Differentiated roll shape design of high carbon steel for finishing rolling with local thermal crown compensation: Each finishing rolling stand is equipped with a special work roll shape of high carbon steel with local thermal crown compensation, and a differentiated design is performed according to the thermal crown size of different stands; S2. Design of variable contact support roller shape with large arc composite transition chamfer: The support roller shape is optimized to a variable contact chamfer form; S3, full-frame high-speed steel rolls are used to produce high-carbon strip steel in the headless rolling production line: the finishing mill uses full-frame high-speed steel rolls, and is matched with the original thermal crown compensation high-speed steel special roll shape; S4. Cooling control of high carbon strip steel: uniform slow cooling of each area of ​​the steel coil is achieved through the homogenization control of the layer-cooled strip steel structure, optimization of the slow cooling of the strip steel off the line, and selection of the location of the slow cooling zone for thin specifications.

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 thermal convexity sizes of different racks in step S1 are differentiatedly designed so that the compensation range of racks 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 convexity compensation range is 20-150um.

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: The variable contact chamfering form in step S2 is that the first section is a variable contact section, and the requirements of the roll shape of different frame support rollers are matched by adjusting the length and curvature of the variable contact section. According to the design of different frame working rolls, the length of the F1-F5 frame variable contact section is 30-220mm, and the convexity is increased by 30-100um; the second section is a chamfering section, and the chamfering taper remains unchanged, while improving the distribution shape of the strip along the width direction.

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 layer cooling strip steel structure homogenization control in step S4 is to open the last group of cooling water for the layer cooling with a thickness of less than 1.5 mm to make the temperature uniformity of the transverse section of the strip steel consistent, and at the same time control the layer cooling temperature ≥ 620°C by adjusting the water volume.

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: The optimization of the slow cooling of the strip steel off-line in step S4 is that the time from unloading the steel coil to the storage of the finished product is long. It takes 55 minutes for the steel coil to be transported from the No. 1 walking beam to the finished product warehouse. When producing extremely thin-gauge high-carbon steel, a detachable slow cooling cover of the No. 1 walking beam is installed.

6. 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 position of the thin-gauge slow cooling zone in step S4 is selected as the slow cooling of the extreme thin-gauge ≤1.2mm, the slow cooling time of the extreme thin-gauge ≥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 each area of ​​the steel coil is evenly slow cooled.