Low-stress hot rolled steel coil production method

Abstract

The invention discloses a low-stress hot rolled steel coil production method which comprises the following steps: controlling the rigidity difference of two sides of a rolling mill within a set range and setting the convexity of a steel plate in the rolling process to realize the stability of the manufacturing process and the original shape of the steel plate; the convexity of the final-state steel plate is determined according to the steel plate middle temperature, the steel plate transmission side edge temperature and the steel plate operation side edge temperature in the strip steel rolling process; the rolling mill cooling system comprises side spraying cooling valves arranged on the two side edges of the strip steel, so that the pressure flow of the side spraying cooling valves enables cooling water on the surface of a steel plate not to be gathered on the edges, and the edge cooling strength and the middle cooling strength of the strip steel are uniform. The method can meet the requirements for low stress and high plate shape of the steel coil, and is particularly suitable for treatment of strip steel with the thickness of 3-8 mm of the steel coil.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to a method for producing a low-stress hot-rolled steel coil. Background Art

[0002] Plate shape is an important visible and measurable macro-quality indicator of hot-rolled strip, while the internal stress of the steel plate is a micro-technical indicator that is difficult to monitor. The essence of plate shape is the distribution of residual internal stress. When the residual internal stress is higher than a certain critical value, it will directly lead to plate shape deformation. The uneven distribution of residual internal stress will also cause potential deformation problems of the steel plate during subsequent processing and application. Therefore, improving the plate shape quality of hot-rolled strip and reducing the internal stress of the original steel plate through technological means are of vital importance to the quality of hot-rolled strip. The process flow of the hot rolling unit is roughly divided into heating, rough rolling, finishing rolling, coiling and other processes. The quality of hot-rolled plate shape, internal internal stress and each process of hot rolling technology are correlated. Different from the single-rolled plate of the medium and thick plate production line, the hot-rolled strip steel has its own process characteristics. The hot-rolled steel coil generally has large internal stress, especially there are three problems: (1) the rolling cooling internal stress caused by uneven deformation and uneven cooling of the strip steel during rolling; (2) the curvature distribution along the length direction during the coiling process is uneven, resulting in uneven stress from the inner ring to the outer ring of the hot-rolled strip steel, as well as the upper and lower surfaces during the coiling process; (3) after the hot-rolled strip steel is coiled, various uneven residual stresses will be formed due to uneven cooling inside and outside the coil. This patent controls the internal stress of the plate shape from the rolling, cooling and insulation process of the strip steel, and proposes a low-stress production method for thin-gauge hot-rolled steel coils. Summary of the invention

[0003] The purpose of the present invention is to provide a method for producing a low-stress hot-rolled steel coil, which can meet the requirements of low stress and high plate shape for the steel coil, and is particularly suitable for processing steel coils with a strip thickness of 3 to 8 mm.

[0004] The technical solution adopted by the present invention is: A method for producing a low-stress hot-rolled steel coil, comprising: By controlling the difference in rigidity on both sides of the rolling mill and setting the convexity of the steel plate during the rolling process, the manufacturing process is stabilized and the original shape of the steel plate is maintained, thus reducing the internal stress during rolling. The crown of the steel plate is determined according to the temperature of the middle part of the steel plate, the temperature of the transmission side of the steel plate, and the temperature of the operating side of the steel plate during the strip rolling process; The rolling mill cooling system includes side spray cooling valves arranged on both sides of the strip. The nozzle angles connected to the side spray cooling valves avoid the overcooled parts of the strip edges, and the pressure flow of the side spray cooling valves is achieved so that the cooling water on the surface of the steel plate does not gather at the edges, so that the cooling intensity of the strip edges and the middle of the strip is uniform.

[0005] Preferably, the final steel plate convexity Y = K*[T 中 -1 / 2(T传动侧 +T 操作侧 )] Where K is the high temperature plastic constant of rolled steel, T 中 is the temperature in the middle of the steel plate, T 传动侧 is the temperature of the transmission side of the steel plate, T 操作侧 It is the temperature of the side edge of the steel plate.

[0006] Preferably, the stability of the manufacturing process and the original shape of the steel plate are controlled by the stiffness difference on both sides of the rolling mill, the internal stress of rolling is reduced, and the stiffness difference on both sides of the rolling mill (drive side and working side) is controlled within 30 tons / mm.

[0007] The cooling system includes an ultra-fast cooling unit, an encrypted cooling unit and a compensating cooling unit which are arranged in sequence along the conveying direction of the rolling mill steel strip. A cross-section temperature detector is arranged behind the ultra-fast cooling unit. The cross-section temperature detector is used for real-time collection of cross-section temperature data of the steel strip. The cross-section temperature detector is respectively connected to the ultra-fast cooling unit, the encrypted cooling unit and the compensating cooling unit.

[0008] Preferably, the ultrafast cooling unit is arranged in the front 1 / 3 of the rolling mill conveyor, the encrypted cooling unit is arranged in the middle 1 / 3 of the rolling mill conveyor, and the compensating cooling unit is arranged in the rear 1 / 3 of the rolling mill conveyor. A special section temperature monitor is set behind the head 1 / 3 ultra-fast cooling in the cooling rolling direction, and the section temperature data is collected in real time. For the section uneven data, the rear section compensating cooling control is designed in the rear 1 / 3 compensating cooling system. After the steel strip is cooled, the section cooling effect is fed back to the ultrafast cooling device by the terminal section temperature monitor to realize the cooling parameter correction of the next steel strip. The cooling capacities of the ultrafast cooling unit, the encrypted cooling unit and the compensating cooling unit decrease successively.

[0009] Preferably, the water spraying amount of the upper strip cooling system and the lower strip cooling system is set to 1:1~1:1.5, and the asymmetric water ratio is uniformly cooled in the thickness direction. This ratio should be adjusted for wide strip steel plates of different thicknesses, and horizontal fine-tuning corrections should be made in combination with the uniformity of the steel plate's organizational properties to determine the final optimized water ratio. Preferably, in order to solve the problem of internal stress difference between the upper and lower surfaces caused by different curvatures in the length direction of the steel coil, a reverse flattening or straightening process is used to further reduce the tension in the length direction by reverse bending the curvature of the steel coil.

[0010] Preferably, in view of the difference in residual stress in the width direction of the steel coil, the steel coil is insulated as a whole after being curled, and the steel coil is stacked and stored at its own temperature or annealed (500-650°C) through an insulation wall or a relatively uniform temperature in the room. Such stacking and sealing insulation measures can effectively solve the difference in internal and external stress of the steel strip.

[0011] Preferably, the temperature for annealing the steel coil is 500-650°C.

[0012] Preferably, the strip thickness of the steel coil is 3-8 mm. The beneficial effects of the present invention are: 1. Through the control of steel plate crown and temperature matching during the rolling and coiling process, combined with the internal stress characteristics of the rolled steel coil, it can meet the requirements of low stress and high plate shape for the steel coil, and is especially suitable for the processing of steel coils with a strip thickness of 3~8mm.

[0013] 2. The mill precision and the steel coil insulation are matched with the convexity and temperature of the steel plate in the rolling and coiling process. Different from the stress elimination method of the unrolled flat plate through heat treatment, the present invention provides a heat treatment-free process, which reduces the residual stress of the strip through uniform plastic deformation of small convexity and stable rolling of the rolling mill, uniform surface cooling, low-tension coiling, and self-tempering treatment of the steel coil. DETAILED DESCRIPTION

[0014] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0016] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection. It can be a mechanical connection or an electrical connection. It can be directly connected or indirectly connected through an intermediate medium. It can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0017] A method for producing a low-stress hot-rolled steel coil, comprising: achieving stability of the manufacturing process and the original shape of the steel plate by controlling the stiffness difference between the two sides of the rolling mill and setting the convexity of the steel plate during the rolling process, thereby reducing the internal stress of rolling; The crown of the steel plate is determined according to the temperature of the middle part of the steel plate, the temperature of the transmission side of the steel plate, and the temperature of the operating side of the steel plate during the strip rolling process; The rolling mill cooling system includes side spray cooling valves arranged on both sides of the strip. The nozzle angles connected to the side spray cooling valves avoid the overcooled parts of the strip edges (the overcooled parts of the edges refer to the parts with larger temperature drop at the edges, generally within 100mm of the edges), and the pressure flow of the side spray cooling valves is achieved so that the cooling water on the surface of the steel plate does not gather at the edges, so that the cooling intensity of the strip edges and the middle of the strip is uniform.

[0018] The strip thickness of the steel coil is 3~8mm.

[0019] Furthermore, the final steel plate convexity Y = K*[T 中 -1 / 2(T 传动侧 +T 操作侧 )] Where K is the high temperature plastic constant of rolled steel, T 中 is the temperature in the middle of the steel plate, T 传动侧 is the temperature of the transmission side of the steel plate, T 操作侧 It is the temperature of the operating side edge of the steel plate, and the convexity of the steel plate is determined according to the temperature gradient in the width direction of the plate during strip rolling.

[0020] Furthermore, the temperature in the middle of the steel plate specifically refers to: the temperature in the middle of the steel plate during rolling, the temperature on the transmission side of the steel plate specifically refers to: the temperature of the edge of the strip close to the transmission side of the rolling mill during rolling; the temperature on the operating side of the steel plate specifically refers to: the temperature of the edge of the strip close to the operating side of the rolling mill during rolling.

[0021] Furthermore, it is necessary to precisely control the plastic deformation of the slab during the rolling process, especially during the finishing rolling process. In order to ensure the stability of the rolling process, a certain convexity design is performed during the strip rolling process, which also exacerbates the unevenness of the residual internal stress to a certain extent; due to the existence of the plate convexity, the thickness of the edge of the strip is less than that of the middle. After layer-by-layer accumulation in the later stage of coiling, it will show a deformation in the width direction with a high middle and two sides bent downward. When this bending deformation exceeds a certain degree, the strip will undergo plastic deformation to form lateral warping, which is also easy to cause stress caused by uneven plastic deformation during coiling.

[0022] Furthermore, in actual production, the hot-rolled strip head and tail are bent, sickle-shaped, and the strip has large left-right mobility, and the thin-gauge steel strip head is folded, which will lead to defects such as head tower shape and overflow edge in the coil shape. Such defects are often accompanied by large internal stress, resulting in poor original rolled plate shape. Therefore, it is necessary to improve the coil shape quality by controlling the rolling process, specifically to find out the corresponding relationship between the sickle-shaped rolled plate shape and the stiffness, pressure difference, and precision cracking of the equipment such as the AGC oil cylinder of each finishing rolling frame. During the rolling process, under the action of the rolling force, the rolled piece undergoes plastic deformation, and its thickness size and cross-sectional shape change. The reaction force of the rolled piece causes a series of parts such as the roll, roll bearing, bearing seat, pad, press cylinder and arch in the working machine seat to undergo corresponding elastic deformation. The sum of the elastic deformations produced by this series of force-bearing parts is usually called the bounce value of the rolling mill. The stiffness of a rolling mill refers to its ability to resist elastic deformation caused by rolling pressure, also known as the mill modulus or mill modulus, which has a great influence on the adjustment of the rolling mill and the dimensional accuracy of the rolled product. The difference in elastic deformation on both sides of the rolling mill is also one of the important factors that lead to wedge shape, sickle bend, and rolling instability during the rolling process. When the difference in stiffness on both sides of the rolling mill (drive side and working side) exceeds 30 tons / mm, the rolling mill will experience obvious rolling instability and wedge-shaped out-of-control phenomena. Therefore, in actual production, the difference in stiffness on both sides of the rolling mill equipment can be used to control the stability of the manufacturing process and the original shape of the steel plate, thereby reducing the internal stress of rolling.

[0023] The cooling system includes an ultra-fast cooling unit, an encrypted cooling unit and a compensating cooling unit which are arranged in sequence along the conveying direction of the rolling mill steel strip. A cross-section temperature detector is arranged behind the ultra-fast cooling unit. The cross-section temperature detector is used for real-time collection of cross-section temperature data of the steel strip. The cross-section temperature detector is respectively connected to the ultra-fast cooling unit, the encrypted cooling unit and the compensating cooling unit.

[0024] Furthermore, the cooling in the width direction is uneven: Generally speaking, the edge of the steel plate cools faster, and the phase change occurs earlier than the middle part, and the volume enters the expansion stage, while the middle part has not yet undergone a phase change, and the volume is still in the contraction process. As the temperature continues to drop, this contradiction gradually intensifies, so that there will be a certain stress between the edge and the middle part of the steel plate. When this stress increases to exceed the steel plate's deformation resistance, the steel plate will have edge wave defects. Solution: (1) Side spray cooling valve angle and flow control: special side spray cooling valves are set on both sides, and the nozzle angle avoids the overcooled part of the edge, and the pressure flow of the side spray water valve is made to ensure that the cooling water on the steel plate surface does not gather at the edge, so that the edge cooling and middle cooling intensity are uniform; (2) The cooling system is divided into the head 1 / 3 ultra-fast cooling, the middle 1 / 3 dense cooling, and the rear 1 / 3 compensatory cooling. A special section temperature monitor is set behind the head 1 / 3 ultra-fast cooling in the cooling rolling direction. The section temperature data is collected in real time. For the uneven section data, the rear section compensatory cooling control is designed in the rear 1 / 3 compensatory cooling system. After the steel strip is cooled, the section cooling effect is fed back to the ultra-fast cooling device by the terminal section temperature monitor to realize the cooling parameter correction of the next piece of steel strip. The cooling capacity of the ultra-fast cooling unit, dense cooling unit and compensatory cooling unit decreases in sequence.

[0025] Furthermore, the cooling in the thickness direction is uneven: during the cooling process, the upper surface of the steel plate cools faster than the lower surface, enters the phase change zone earlier, expands in volume, and forms a turtle back on the steel plate. When the lower surface subsequently changes phase and expands in volume, the metal unit is subjected to compressive stress and cannot eliminate the arch. When this residual stress is large, L warping, C warping or four-corner warping may form during finishing shearing. Solution: Cooling symmetry in the thickness direction is mainly to ensure that the upper and lower surfaces of the steel plate receive the same cooling effect during the cooling process. For different steel grades and thickness specifications, the upper and lower water spray volumes are set to an asymmetric water ratio of 1:1~1:1.5 for uniform cooling in the thickness direction. This ratio should be adjusted to a certain extent for wide-band steel plates of different thicknesses, and horizontal fine-tuning corrections should be made in combination with the uniformity of the steel plate's organizational properties to determine the final optimized water ratio.

[0026] Furthermore, the tension control from the inner and outer rings to the upper and lower surfaces during the coiling process: the residual stress value is in an increasing relationship with the yield point and original curvature of the steel, and the degree of warping varies with the strength and original curvature of the steel plate. The higher the strength and the larger the original curvature, the more serious the warping degree, and the warping direction of each strip after longitudinal slitting is likely to be in the same direction, which is consistent with the actual warping situation. Analysis shows that to solve the warping problem of longitudinal slitting of hot-rolled steel plates, it is first necessary to eliminate the difference in internal stress on the upper and lower surfaces caused by the curvature of the strip along the length direction, and then make the residual stress in the width direction uniform. Conventional straightening can obtain a whole straight steel plate, but it is not obvious to prevent warping after longitudinal slitting. To address the internal stress difference between the upper and lower surfaces caused by different curvatures in the length direction, the reverse direction flattening or straightening process is used to make the curvature of the steel coil further reduce the tension in the length direction through reverse bending; to address the residual stress difference in the width direction, the steel coil is insulated as a whole, and the steel coil is stacked and stored at its own temperature or annealed (500~650℃) at a relatively uniform temperature on an insulation wall or indoors. This stacking and sealing insulation measure can effectively solve the internal and external stress differences of the strip.

[0027] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with the examples in Table 1, but the present invention is not limited to the following examples. Examples 1 to 8 and Comparative Examples 1 to 4: A 230 mm thick slab is rolled into a 6 mm hot-rolled steel plate by using a hot rolling process for producing high-strength ship plate AH36 with controlled rolling and controlled cooling treatment on a 2250 mm hot rolling mill.

[0028] Table 1 Example serial number Rolling crown μm Finishing load stiffness difference t / mm Cooling uniformity (℃) Slow cooling and heat preservation temperature (℃) Average internal stress of steel plate (MPa) Example 1 10 15 10 650 -16 Example 2 18 20 5 630 -16 Example 3 25 17 15 610 -47 Example 4 28 20 11 600 -38 Example 5 32 25 18 580 -50 Example 6 35 30 13 550 -72 Example 7 40 35 20 500 -74 Example 8 25 10 14 580 -60 Comparative Example 1 80 39 25 400 -148 Comparative Example 2 90 31 19 430 -133 Comparative Example 3 45 70 40 510 -157 Comparative Example 4 40 38 24 No insulation and slow cooling measures -180 For the stiffness difference of multi-stand finishing rolling load, the maximum stiffness difference between multiple stands is used as the recording parameter. For the uniformity of the thickness direction of the rolled steel plate, the upper and lower water ratio of the plate thickness is used for control, and the temperature difference of the plate width is used to evaluate the cooling uniformity of the rolled steel plate in the width direction. The average temperature is used for the slow cooling and insulation temperature. The average internal stress of the steel plate is measured by the residual stress of the X-ray method after the steel coil is uncoiled, and the stress of the whole plate width is tested at multiple points, and the average value is calculated.

[0029] It can be seen from Examples 1-8 and Comparative Examples 1-4 that the residual stress of the strip can be reduced to ≤74MPa by small convexity uniform plastic deformation rolling, precision control of finishing rolling load, uniform surface cooling, low tension coiling, and self-tempering treatment of the steel coil, while the residual stress is ≥100Mpa when the comparative process is used.

[0030] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0031] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all these improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. A method for producing a low stress hot rolled steel coil, characterized in that: include: The manufacturing process is stable and the original shape of the steel plate is achieved by controlling the difference in rigidity on both sides of the rolling mill within a set range and setting the steel plate crown during the rolling process; The crown of the steel plate is determined according to the temperature of the middle part of the steel plate, the temperature of the transmission side of the steel plate, and the temperature of the operating side of the steel plate during the strip rolling process; The rolling mill cooling system includes side spray cooling valves arranged on both sides of the strip, so that the pressure flow of the side spray cooling valves is achieved so that cooling water on the steel plate surface does not gather at the edges, and the cooling intensity of the strip edges and the middle of the strip is uniform.

2. The method for producing a low stress hot rolled steel coil according to claim 1, characterized in that: Steel plate convexity Y = K*[T 中 -1 / 2(T 传动侧 +T 操作侧 )] Where K is the high temperature plastic constant of rolled steel, T 中 is the temperature in the middle of the steel plate, T 传动侧 is the temperature of the transmission side of the steel plate, T 操作侧 It is the temperature of the side edge of the steel plate.

3. The method for producing a low stress hot rolled steel coil according to claim 1, characterized in that: The stiffness difference on both sides of the rolling mill is controlled within 30 tons / mm.

4. The method for producing a low stress hot rolled steel coil according to claim 1, characterized in that: The cooling system includes an ultra-fast cooling unit, an encrypted cooling unit and a compensating cooling unit which are arranged in sequence along the conveying direction of the rolling mill steel strip. A cross-section temperature detector is arranged behind the ultra-fast cooling unit. The cross-section temperature detector is used for real-time collection of cross-section temperature data of the steel strip. The cross-section temperature detector is respectively connected to the ultra-fast cooling unit, the encrypted cooling unit and the compensating cooling unit.

5. The method for producing a low stress hot rolled steel coil according to claim 1, characterized in that: The water spraying amount of the upper strip cooling system and the lower strip cooling system is set to 1:1~1:1.

5.

6. The method for producing a low stress hot rolled steel coil according to claim 1, characterized in that: The reverse leveling or straightening process is used to reduce the tension in the length direction by reverse bending the steel coil curvature.

7. The method for producing a low stress hot rolled steel coil according to claim 1, characterized in that: The coils are kept warm as a whole after the strip is coiled, and the coils are stacked and stored at their own temperature or annealed through insulation walls or relatively uniform temperature in the room.

8. The method for producing a low stress hot rolled steel coil according to claim 7, characterized in that: The annealing temperature of the steel coil is 500~650℃.

9. The method for producing a low stress hot rolled steel coil according to claim 1, characterized in that: The strip thickness of the steel coil is 3~8mm.