A method for controlling the shape of phase-change strengthened hot-rolled high-strength steel plates

Abstract

The invention discloses a method for controlling the shape of a phase-change strengthened hot-rolled high-strength steel plate, and belongs to the field of steel plate production. The process comprises the following steps: 1) rolling, using a 2-stand rough rolling and a 7-stand finishing hot rolling mill, with the finishing rolling temperature being 850-900°C; 2) cooling, after the slab is rolled, the slab is cooled in three stages, namely ultra-fast cooling, air cooling and water cooling, and then coiled to form a steel coil; 3) leveling, for the outer ring of the steel coil, the leveling rolling force is 7000-8000kN, and the working roll bending force is 700-900kN; for the middle position of the steel coil, the leveling rolling force is 6000-7000kN, and the working roll bending force is 500-700kN; for the inner ring of the steel coil, the leveling rolling force is 5000-6000kN, and the working roll bending force is 400-600kN; 4) leveling, cross-cutting the leveled coil. The present invention can significantly improve the plate shape quality of phase transformation strengthened hot rolled high-strength steel, increase the plate shape qualification rate, and reduce production costs.

Description

Technical Field

[0001] The present invention belongs to the field of steel plate production, and more specifically, relates to a method for controlling the shape of phase-change strengthened hot-rolled high-strength steel plates. Background Art

[0002] With the increasing trend toward high-strength steel for special vehicles and engineering machinery, coupled with advancements in rolling cooling technology, particularly ultra-rapid cooling equipment, phase transformation-strengthened hot-rolled high-strength steel with tensile strengths of 1000 MPa and above has become a research hotspot in recent years. This strengthening approach primarily involves in-line direct quenching in post-rolling ultra-rapid cooling systems. Phase transformation strengthening effectively addresses the challenge of achieving both high strength and formability. However, due to factors such as the high intensity of ultra-rapid cooling, the narrow cooling process window, and the significant impact of temperature fluctuations on phase transformation, controlling the plate shape of phase transformation-strengthened hot-rolled high-strength steel has been a persistent industry challenge, primarily manifested in the presence of double-sided and single-sided waves in the produced steel plates.

[0003] About phase transformation strengthened hot rolled high strength steel (tensile strength R m ≥1000MPa), such as patents with publication numbers CN103233161B, CN104532126B, CN110331326A, CN110578095A, CN104532126A, CN110760752A, and CN111334720A. The technical problems solved by the above patents are mainly concentrated on the design of alloy reduction composition, optimization of controlled rolling and controlled cooling process, coordinated control of ultra-high strength and easy formability, etc., and none of them involve how to improve the plate shape.

[0004] Regarding the method of improving the shape of hot-rolled strip, the methods currently disclosed in the patents are mainly as follows:

[0005] (1) Micro-wave rolling compensation

[0006] Patents with publication numbers CN101372018A, CN102581025B, CN104511483A, CN110404978B, and CN108817101B disclose that controlling strip flatness and micro-waving in the final stand of finishing mills can effectively address the problem of poor strip shape caused by uneven cooling. The methods disclosed in these patents focus on strip rolling and the optimization of strip micro-waving methods or control models. Flatness compensation values ​​typically range from -50 to 0I, with values ​​as high as -100I. These methods are suitable for low-strength steels that undergo single- or two-stage cooling, undergo only a single-phase transformation from austenite to ferrite and bainite, and are subjected to high-temperature coiling. However, plate shape control involves the entire process of heating-rolling-cooling-coiling-flattening-flattening. The above solution is not applicable to high-strength steel of phase transformation strengthening type with complex cooling mode, complex phase transformation from austenite to ferrite, martensite, etc. during the cooling process, and low-temperature coiling. The main reason is that the flatness compensation value of phase transformation strengthening type high-strength steel is within -50I, which cannot offset the double-sided waves caused by uneven cooling of the strip. If the flatness compensation value reaches -100I or even greater, it will lead to a decrease in the stability of the finishing rolling process, a decrease in the plate shape quality of the strip after finishing rolling, and even worse plate shape after cooling of the strip, and increase the probability of steel piling risk.

[0007] (2) Edge occlusion

[0008] By installing water baffles on both sides of the water beam on the laminar cooling line to block the laminar cooling water on both sides of the strip, the temperature gradient in the width direction of the strip is reduced, which is beneficial to plate shape control. However, the existing edge shielding adopts symmetrical shielding with the same laminar cooling water shielding amount on both sides, and does not take into account the movement of the head or tail of the strip in the width direction during the actual rolling process, resulting in inconsistent actual shielding amount on both sides of the strip, and thus poor temperature uniformity on both sides of the strip, resulting in on-site edge shielding for strip shape control effect is not ideal, and the actual equipment maintenance amount is large, which increases the difficulty of equipment maintenance.

[0009] (3) Add insulation or tempering process after strip coiling

[0010] After the strip is coiled, an insulation slow cooling or tempering process or a hood annealing process is added to make the overall temperature of the strip uniform. However, on the one hand, it requires the construction of a new insulation pit, insulation wall and online insulation cover, such as the contents disclosed in patents with publication numbers CN110106322B, CN110624954B, CN112063815A and CN110614280A, which requires additional equipment investment and increases costs; on the other hand, for phase transformation strengthened hot-rolled high-strength steel coiled at low temperature (CT≤250℃), the insulation pit slow cooling or low-temperature tempering effect is basically ineffective, while the strength of the high-temperature tempered (CT≥400℃) material decreases significantly, which will lead to unqualified strip performance.

[0011] (4) Adding a leveling process

[0012] As disclosed in the patents with publication numbers CN111215454A and CN111215455A, the existing leveling process has the following criteria for judging the excellent strip shape: the unevenness is 0 and there is no visible wave shape. However, after leveling, the strip is in a state of high tension, and the defects in the strip shape are concealed to a certain extent, which cannot accurately reflect the actual situation of the strip shape. The strip shape is good during leveling, but it is not necessarily good when it is finally cross-cut and flattened in a tension-free state.

[0013] In summary, currently published patents are either unsuitable, require additional equipment investment, or require the addition of a flattening process. The criterion for good strip shape after flattening is zero flatness, making them unsuitable for phase transformation-strengthened hot-rolled high-strength steel. Strip shape issues stem from uniformity control of temperature and residual stress, which involves the entire process of rolling, cooling, coiling, flattening, and flattening. Shape control requires a comprehensive approach, rather than relying solely on individual steps of rolling, cooling, coiling, or flattening for optimization. Summary of the Invention

[0014] 1. Problems to be solved

[0015] For the existing technology for phase transformation strengthened hot rolled high strength steel (tensile strength R m ≥1000MPa) is not good at controlling the plate shape. The present invention provides a method for controlling the plate shape of phase change strengthened hot-rolled high-strength steel. The method can significantly improve the plate shape quality of phase change strengthened hot-rolled high-strength steel, increase the plate shape qualification rate and reduce production costs by optimizing the plate shape of the entire process such as rolling, cooling, coiling, flattening and opening without adding new equipment.

[0016] 2. Technical solution

[0017] To solve the above problems, the present invention adopts the following technical solutions.

[0018] A method for controlling the shape of a phase transformation strengthened hot-rolled high-strength steel plate comprises the following steps:

[0019] 1) Rolling

[0020] It adopts a 2-stand rough rolling and 7-stand finishing hot rolling mill, with the finishing temperature of 850-900℃;

[0021] 2) Cooling

[0022] After slab rolling, the slab is cooled in three stages, namely ultra-rapid cooling, air cooling and water cooling, and then coiled to form a steel coil.

[0023] 3) Leveling

[0024] For the outer ring of the steel coil, the temper rolling force is 7000-8000kN, and the work roll bending force is 700-900kN; for the middle position of the steel coil, the temper rolling force is 6000-7000kN, and the work roll bending force is 500-700kN; for the inner ring of the steel coil, the temper rolling force is 5000-6000kN, and the work roll bending force is 400-600kN;

[0025] The length of the outer ring and the inner ring of the steel coil each accounts for 1 / 6 to 1 / 5 of the total length of the steel coil, and the remaining part is the middle part. The total length of the steel coil is 500 to 600 meters.

[0026] 4) Kaiping

[0027] The flattened roll is cut horizontally.

[0028] As a further improvement of the technical solution, after leveling, the wave value of the strip is 2 to 5 mm / m.

[0029] As a further improvement of the technical solution, the working rolls of the leveling machine adopt convex rolls with a convexity of 40-60μm and a leveling rate of 50-80m / min.

[0030] As a further improvement of the technical solution, edge heaters are used at the finishing rolling entrance, and the edge heating temperature is set at 30-50℃.

[0031] As a further improvement of the technical solution, during finishing rolling, the exit convexity C of the F7 stand 40 The target value is 20-30μm, wedge shape 40 The target value is 0-20μm, and the symmetric straightness is -50~0I; among them, C 40 w is the difference between the thickness at the midpoint of the strip cross section and the average thickness at a position 40 mm away from both sides of the strip. 40 It is the thickness difference between the strip cross section at a position 40 mm away from the operating side and the position 40 mm away from the transmission side.

[0032] As a further improvement of the technical solution, during finishing rolling, the rolling speed of the F7 stand adopts a constant acceleration control strategy, with a constant acceleration of ≤0.01m / s 2 , rolling speed ≥7.5m / s.

[0033] As a further improvement of the technical solution, the ultra-fast cooling section adopts centralized cooling with a cooling rate ≥80℃ / s, the cooling water flow ratio of the upper and lower surfaces of the strip is (1:1.15)~(1:1.30), and the side water spray is symmetrical cross-side spray; the air cooling section time is 4~8s; the water cooling section adopts sparse cooling method, the cooling water flow ratio of the upper and lower surfaces of the strip is (1:1.05)~(1:1.15), the side water spray is symmetrical cross-side spray, and the cooling rate is 50~80℃ / s.

[0034] As a further improvement of the technical solution, after cooling, the coiling temperature of the strip is ≤100°C.

[0035] As a further improvement of the technical solution, Kaiping uses a 7-roll rough straightening machine and an 11-roll fine straightening machine. The lifting amount of the first lower roller of the two straightening machines is lower than the lifting amount of the second lower roller, and the lifting amount gradually decreases from the second lower roller to the last lower roller.

[0036] As a further improvement of the technical solution, for the 7-roller rough straightening machine: the lifting amount of the first lower roller is 6-8mm, the lifting amount of the second lower roller is 18-20mm, the lifting amount of the third lower roller is 10-12mm, and the lifting amount of the fourth lower roller is 4-6mm;

[0037] For the 11-roller fine straightening machine: the lifting amount of the first lower roller is 2-4mm, the lifting amount of the second lower roller is 10-12mm, the lifting amount of the third lower roller is 8-10mm, the lifting amount of the fourth lower roller is 4-6mm, the lifting amount of the fifth lower roller is 3-5mm, and the lifting amount of the sixth lower roller is 2-4mm.

[0038] 3. Beneficial effects

[0039] (1) The present invention provides a method for controlling the plate shape of phase change strengthened hot-rolled high-strength steel. The method can significantly improve the plate shape quality of phase change strengthened hot-rolled high-strength steel and improve the plate shape qualification rate without adding new equipment through reasonable optimization of the plate shape in the entire process of rolling, cooling, coiling, flattening, and opening. It also significantly reduces the product re-evaluation loss and production cost. The unevenness is controlled to be ≤6 mm / m, preferably 0 mm / m, and the plate shape qualification rate is ≥88%.

[0040] (2) The present invention provides a method for controlling the shape of phase-change strengthened hot-rolled high-strength steel plates, which can expand the product variety, thickness specification range, and strength level of conventional cross-cutting lines with insufficient flattening equipment capacity without the need for additional investment or equipment modification. It can enable conventional cross-cutting lines to produce thin-gauge high-strength steel flat plates with high flattening quality and high flattening qualification rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 The figure is a flat plate shape diagram of hot-rolled high-strength steel processed by the method of the present invention;

[0042] Figure 2 This is a flat plate shape diagram of hot-rolled high-strength steel processed using the comparative example method. DETAILED DESCRIPTION

[0043] Exemplary embodiments of the present invention are described in detail below. Although these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be implemented and that various changes may be made to the invention without departing from the spirit and scope of the invention. The following more detailed description of the embodiments of the invention is not intended to limit the scope of the claimed invention, but is merely for illustrative and non-limiting purposes, to describe the features and characteristics of the invention, to set forth the best mode for carrying out the invention, and to enable those skilled in the art to practice the invention. Therefore, the scope of the invention is limited solely by the appended claims.

[0044] A control method for the shape of phase-change strengthened hot-rolled high-strength steel plate, targeting the tensile strength R m Phase transformation-hardened high-strength steel plates with a strength of ≥1000 MPa can significantly improve their flatness. The chemical composition and percentage by mass of this steel plate are: C: 0.12-0.16%, Si: 1.00-1.50%, Mn: 1.2-2.0%, Cr: 0.20-0.40%, P: ≤0.012%, S: ≤0.005%, Als: 0.30-0.50%, Ti: 0.015-0.050%, with the remainder being Fe and unavoidable inclusions. The specific process and principles are described in detail below.

[0045] The method comprises the following steps:

[0046] 1) Rolling

[0047] The hot rolling mill with 2 stands roughing and 7 stands finishing is used. The roughing is carried out in 3+5 passes. The heat preservation covers between the roughing and finishing mills are all used. The edge heater is used at the finishing entrance. The edge heating temperature is set at 30-50℃. The convexity of the finishing F7 stand outlet is C 40 Target value 20-30μm, wedge shape 40 Controlled within 0-20μm, symmetrical straightness is -50~0I. Among them, FX represents the X-th stand of the rolling mill group in the rolling direction, C 40 w is the difference between the thickness at the midpoint of the strip cross section and the average thickness at a position 40 mm away from both sides of the strip. 40 The thickness difference between the cross section of the strip at a position 40 mm from the operating side and the position 40 mm from the transmission side is used. The rolling speed of the F7 stand adopts a constant acceleration control strategy, that is, a constant acceleration is maintained, and the constant acceleration is ≤ 0.01 m / s.2 , rolling speed ≥ 7.5m / s, finishing rolling temperature FDT = 850 ~ 900 ℃, the steel plate rolled through this step will produce fine waves.

[0048] In this step, the finishing rolling adopts a plate shape control strategy of small crown, small wedge, and slight medium wave, as well as a speed control strategy of high rolling speed and constant acceleration.

[0049] The main purpose of adopting a small crown and small wedge control strategy is to avoid single-sided waves or sickle bends during strip rolling and to improve the thickness dimensional accuracy in the width direction. The purpose of adopting micro-wave rolling is to increase the deformation in the middle position of the strip in the width direction and reduce the double-sided waves caused by uneven deformation in the width direction during strip cooling, which is beneficial to improving the plate shape quality and laying the foundation for improving the plate shape in the flattening process. The symmetrical flatness is -50 to 0I because the micro-wave compensation should not be too large, otherwise it will be difficult to ensure the stability of the rolling process. It is also to echo the micro-wave rolling strategy that can form micro-waves on the strip.

[0050] The use of constant acceleration is primarily to improve rolling stability along the strip's length and temperature uniformity along the length of the subsequent cooling section, thereby contributing to improved strip shape stability. High-speed rolling, with a rolling speed of ≥7.5m / s on the finishing rolling stand F7, is primarily intended to reduce the temperature drop gradient between the head and tail of the intermediate strip, preventing excessively low strip temperature at the tail, excessive rolling forces, and unstable rolling, which can lead to double-sided waves and compromise strip shape control. The use of insulation hoods and edge heaters is intended to improve temperature and performance uniformity across the strip's width, contributing to rolling stability.

[0051] 2) Cooling

[0052] After rolling, the steel undergoes three cooling stages: ultra-rapid cooling, air cooling, and water cooling. The ultra-rapid cooling stage utilizes centralized cooling, with a cooling rate of ≥80°C / s. The cooling water flow ratio between the upper and lower surfaces of the strip is (1:1.15) to (1:1.30), and the side spraying is symmetrical and cross-sprayed, meaning the spraying devices on both sides are arranged crosswise. After ultra-rapid cooling, air cooling is performed, and after 4 to 8 seconds of air cooling, water cooling is performed. The water cooling stage uses a sparse cooling method, with a cooling water flow ratio between the upper and lower surfaces of the strip of (1:1.05) to (1:1.15), a symmetrical and cross-sprayed side spraying, and a cooling rate of 50 to 80°C / s.

[0053] In this step, in order to control the temperature uniformity of the strip in the ultra-fast cooling section and the water-cooling section in the width direction, measures such as controlling the upper and lower cooling water ratio and cross-symmetrical side spraying are mainly adopted. The purpose of having less upper cooling water than lower cooling water in the ultra-fast cooling section and the water-cooling section is mainly to avoid excessive upper cooling water remaining and accumulating on the upper surface of the strip, resulting in uneven temperature distribution in the width direction of the strip, which is not conducive to strip shape control.

[0054] The water-cooling section uses sparse cooling at a cooling rate of 50-80°C / s. This is primarily to minimize the cooling rate and avoid the generation of structural stress and phase transformation stress due to excessive cooling rates, which can lead to single-sided and double-sided cooling waves in the strip. The low-temperature coiling control strategy is primarily intended to control the uniformity of the coiling temperature across the width and length of the strip and improve the coiling temperature hit rate. Because the existing cooling model does not fully consider the effect of internal heat conduction generated by phase transformation during strip cooling on the surface heat transfer coefficient, the coiling temperature fluctuates significantly across the width and length of the strip when the coiling temperature is between 200-400°C, resulting in a poor hit rate and unfavorable shape control.

[0055] 3) Leveling

[0056] After coiling, the steel plate is air-cooled to room temperature before being leveled at a rate of 50-80 m / min. The leveling mill's work rolls are convex with a crown of 40-60 μm. During this step, the leveling rolling force and bending force are dynamically coordinated based on the incoming hot coil shape at the leveling mill inlet. The shape of the strip at the leveling exit is micro-controlled, keeping the leveling strip's wave value within 2-5 mm / m. The specific control strategy is as follows: for the outer ring of the coil, the leveling rolling force is 7000-8000 kN, and the work roll bending force is 700-900 kN; for the middle of the coil, the leveling rolling force is 6000-7000 kN, and the work roll bending force is 500-700 kN; for the inner ring of the coil, the leveling rolling force is 5000-6000 kN, and the work roll bending force is 400-600 kN.

[0057] Among them, the length of the outer ring and the inner ring of the steel coil each accounts for 1 / 6 to 1 / 5 of the total length of the steel coil, and the remaining part is the middle part. The total length of the steel coil is 500 to 600 meters.

[0058] The innovation in this step lies in the proposed flattening micro-wavy strip shape control strategy, and the coordinated compensation segmented control of the flattening rolling force and the bending roll force is adopted according to the incoming material shape, controlling the strip wave value after flattening to 2-5mm / m. The main purpose is to, on the one hand, the strip shape detected after flattening is in a state of high tension, which to a certain extent conceals the strip shape defects and cannot accurately reflect the actual strip shape and make timely and accurate adjustments. Therefore, to ensure that the strip does not have double-sided waves after flattening, the strip shape is compensated for micro-wavy during flattening. On the other hand, the existing cross-cutting unit is a conventional cross-cutting line, and its designed thinnest flattening product thickness is 5mm. The straightening ability for thin-gauge (≤4mm) high-strength steel is relatively weak, especially the ability to improve double-sided waves. In order to ensure the flatness of the strip shape after flattening, the strip shape needs to be compensated for micro-wavy in advance during the flattening process. At the same time, in order to control the strip shape stability and performance uniformity during the leveling process, the leveling rolling force and bending roll force should not be too large, and the leveling rate should be controlled at 50-80m / min.

[0059] 4) Kaiping

[0060] After leveling, the flattened coils are cut horizontally using conventional cross-cutting methods. Specifically, a 7-roll rough straightener and an 11-roll fine straightener are used. Both the rough and fine straighteners utilize a large deformation straightening scheme, with the straightening roll diameters of both machines being 220 mm. The specific control strategy is shown in Table 1-2 below. It should be noted that the upper and lower rollers of the straighteners are arranged in a staggered arrangement. The lower roller is a movable roller that can be raised, while the upper roller is a fixed roller that remains in a fixed position. In this embodiment, the rollers are numbered according to the direction of steel plate movement, with odd-numbered rollers representing the lower rollers and even-numbered rollers representing the upper rollers.

[0061] Table 1 Rough straightening machine control method

[0062] Straightening roller serial number 1# roller 3# roller 5# roller 7# roller Lifting amount / mm 6-8 18-20 10-12 4-6

[0063] Table 2 Control method of fine straightening machine

[0064] Straightening roller serial number 1# roller 3# roller 5# roller 7# roller 9# roller 11# roller Lifting amount / mm 2-4 10-12 8-10 4-6 3-5 2-4

[0065] In this step, both the rough and fine straightening machines adopt a large deformation straightening scheme, mainly based on the fact that the existing conventional cross-cutting line has a relatively weak straightening ability for thin-gauge (≤4mm) high-strength steel, severe buckling after rough or fine straightening, and poor plate flatness. Increasing the lifting amount of the 1, 3, and 5# straightening rollers of the rough straightening machine and the 1, 3, 5, 7, 9, and 11# straightening rollers of the fine straightening machine can allow the strip to undergo multiple continuous large deformations, and ultimately balance the internal stress of the strip during the straightening process, which is beneficial to improving the flatness of the open plate and improving the plate quality. At the same time, the use of this open flat control method can improve the flatness of the plate with higher strength (R m ≥1000MPa) and the equipment with insufficient Kaiping capacity can also complete the straightening of this type of high-strength plates without the need for new investment or equipment modification, saving costs.

[0066] In summary, the method for controlling the plate shape of phase change strengthened hot-rolled high-strength steel in this embodiment can significantly improve the plate shape quality of phase change strengthened hot-rolled high-strength steel, improve the plate shape qualification rate, and reduce production costs by optimizing the plate shape of the entire process including rolling, cooling, coiling, flattening, and opening without adding new equipment. The flatness is controlled to be ≤6 mm / m, and can preferably reach 0 mm / m, and the plate shape qualification rate is ≥88%.

[0067] It must be pointed out that this method emphasizes the uniformity control of the mechanical properties of phase transformation strengthened ultra-high strength steel plates from the perspective of the entire process of rolling-cooling-coiling-flattening, rather than optimizing and controlling a single process parameter of a single process among rolling, cooling, coiling, and flattening. The root cause of the strip shape problem lies in the uniformity control of temperature and residual stress, which involves the entire process of rolling, cooling, coiling, flattening, and flattening, as well as the actual shape control level of each process. If the shape control capability of the rolling and cooling processes is strong, it can provide a better foundation for the shape control of the subsequent finishing process; if the shape control capability of the flattening and straightening processes is strong, the shape requirements of the incoming material in the rolling and cooling processes can be reduced; if the shape control level of the rolling, cooling, flattening, and straightening processes is average, it is necessary to coordinate the shape control from the perspective of the entire process, and explore reasonable process parameters that match the previous and subsequent processes under the conditions of excellent shape control. This method significantly improves the plate shape quality of phase change strengthened hot-rolled high-strength steel by coordinating the plate shape of the entire process angles of rolling, cooling, flattening and straightening, combined with precise parameter control.

[0068] The technical solution of the present invention is described below through specific embodiments and comparative examples.

[0069] The tensile strength level of the corresponding steel grades of Examples 1-3 and Comparative Examples 1-3 is 1100 MPa, and their chemical composition and weight percentage content are: 0.13% C, 1.13% Si, 1.62% Mn, 0.30% Cr, 0.010% P, 0.002% S, 0.41% Als, 0.025% Ti, and the rest is Fe and unavoidable inclusions.

[0070] Through the optimization control of the whole process of rolling, cooling, coiling, flattening and unrolling, the specific process parameters of the embodiment and comparative example are shown in Table 3-7.

[0071] The flatness and plate shape qualification rates of the embodiments and comparative examples are shown in Table 8. Among them, the flatness of the flat plate ≤ 8mm / m is a qualified finished product, and the plate shape qualification rate = the weight of the qualified finished product of the flat plate / the weight of the hot coil.

[0072] It can be clearly seen from the table that the steel plate produced by this method has a certain medium wave value, and the quality of the plate shape after final flattening is significantly improved, the unevenness is controlled to ≤6mm / m, and can best reach 0mm / m, and the qualified rate is significantly increased. Figure 1 As shown in the figure, the flatness data of the hot-rolled high-strength steel plate processed by the comparative method is significantly lower in comparison. The actual situation of the product is as follows Figure 2 shown.

[0073] Table 3 Rolling process parameters of the embodiment and comparative example

[0074]

[0075] Table 4 Cooling process parameters of the embodiments and comparative examples

[0076]

[0077] Table 5 Leveling process parameters of the embodiment and comparative example

[0078]

[0079] Table 6 Process parameters of straightening process of rough straightening roller in embodiment and comparative example

[0080] serial number 1# roller lifting amount (mm) 3# roller lifting amount (mm) 5# roller lifting amount (mm) 7# roller lifting amount (mm) Example 1 6.5 18.2 10.5 4.8 Example 2 7.0 19.0 11.0 5.5 Example 3 7.6 19.5 11.5 6.0 Comparative Example 1 5.0 10.0 5.0 3.0 Comparative Example 2 6.0 12.0 6.0 4.0 Comparative Example 3 7.0 14.0 7.0 5.0

[0081] Table 7 Straightening process parameters of the fine straightening machine of the embodiment and comparative example

[0082]

[0083] Table 8 Example and comparative example flatness

[0084]

[0085] The examples described in the present invention are merely descriptions of the preferred embodiments of the present invention and are not intended to limit the concept and scope of the present invention. Without departing from the design concept of the present invention, various modifications and improvements made to the technical solutions of the present invention by engineers and technicians in this field should fall within the scope of protection of the present invention.

Claims

1. A method for controlling the shape of phase transformation strengthened hot-rolled high-strength steel plate, characterized by: The following steps are involved: 1) Rolling The hot rolling mill with 2 stands for rough rolling and 7 stands for finishing rolling is used, and the finishing temperature is 850~900℃; During finishing rolling, the exit convexity C of F7 stand is 40 The target value is 20-30μm, wedge shape 40 The target value is 0-20μm, and the symmetric straightness is -50~0I; Among them, C 40 w is the difference between the thickness at the midpoint of the strip cross section and the average thickness at a position 40 mm away from both sides of the strip. 40 The thickness difference between the strip cross section at a position 40 mm from the operating side and the position 40 mm from the transmission side; During finishing rolling, the rolling speed of the F7 stand adopts a constant acceleration control strategy, with a constant acceleration of ≤0.01m / s 2 , rolling speed ≥7.5m / s; 2) Cooling After slab rolling, the slab is cooled in three stages, namely ultra-rapid cooling, air cooling and water cooling, and then coiled to form a steel coil. 3) Leveling For the outer ring of the steel coil, the temper rolling force is 7000-8000kN, and the work roll bending force is 700-900kN; for the middle position of the steel coil, the temper rolling force is 6000-7000kN, and the work roll bending force is 500-700kN; for the inner ring of the steel coil, the temper rolling force is 5000-6000kN, and the work roll bending force is 400-600kN; The outer and inner rings of the steel coil each account for 1 / 6 to 1 / 5 of the total length of the steel coil, and the remaining portion is the middle portion. The total length of the steel coil is 500 to 600 meters. 4) Kaiping The flattened roll is cut horizontally.

2. The method for controlling the shape of a phase transformation strengthened hot rolled high strength steel plate according to claim 1, characterized in that: After leveling, the strip wave value is 2~5mm / m.

3. The method for controlling the shape of a phase transformation strengthened hot rolled high strength steel plate according to claim 2, characterized in that: The working rolls of the leveling machine are convex rolls with a convexity of 40-60μm and a leveling rate of 50-80m / min.

4. The method for controlling the shape of a phase transformation strengthened hot rolled high strength steel plate according to claim 3, characterized in that: The edge heater is used at the finishing rolling entrance, and the edge heating temperature is set at 30-50℃.

5. The method for controlling the shape of a phase transformation strengthened hot rolled high strength steel plate according to claim 1, characterized in that: The ultra-fast cooling section adopts centralized cooling with a cooling rate ≥80℃ / s. The cooling water flow ratio of the upper and lower surfaces of the strip is (1:1.15)~(1:1.30), and the side water spray is symmetrical cross-side spray; the air cooling section time is 4~8s; the water cooling section adopts sparse cooling method, the cooling water flow ratio of the upper and lower surfaces of the strip is (1:1.05)~(1:1.15), the side water spray is symmetrical cross-side spray, and the cooling rate is 50~80℃ / s.

6. The method for controlling the shape of a phase transformation strengthened hot rolled high strength steel plate according to claim 5, characterized in that: After cooling, the coiling temperature of the strip is ≤100℃.

7. The method for controlling the shape of a phase transformation strengthened hot rolled high strength steel plate according to claim 6, characterized in that: Kaiping uses a 7-roll rough straightening machine and an 11-roll fine straightening machine. The lifting amount of the first lower roller of the two straightening machines is lower than the lifting amount of the second lower roller, and the lifting amount gradually decreases from the second lower roller to the last lower roller.

8. The method for controlling the shape of phase transformation strengthened hot rolled high strength steel plate according to claim 7, characterized in that: For 7-roller rough straightening machine: the lifting amount of the first lower roller is 6-8mm, the lifting amount of the second lower roller is 18-20mm, the lifting amount of the third lower roller is 10-12mm, and the lifting amount of the fourth lower roller is 4-6mm; For the 11-roller fine straightening machine: the lifting amount of the first lower roller is 2-4mm, the lifting amount of the second lower roller is 10-12mm, the lifting amount of the third lower roller is 8-10mm, the lifting amount of the fourth lower roller is 4-6mm, the lifting amount of the fifth lower roller is 3-5mm, and the lifting amount of the sixth lower roller is 2-4mm.

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