Method for controlling comprehensive quality of thin-gauge ultrahigh-strength steel plate

Abstract

This invention discloses a method for controlling the overall quality of thin-gauge ultra-high-strength steel plates, belonging to the field of steel plate production. It includes the following steps: 1) Heating: The slab is fed into a heating furnace for heating; 2) Rolling: Rolling is performed using a 2-stand roughing mill and a 7-stand finishing mill hot continuous rolling mill; 3) Cooling: After rolling, the slab undergoes three-stage cooling: ultra-rapid cooling, air cooling, and water cooling, followed by coiling after water cooling; 4) Tension straightening: The coiled steel, cooled to room temperature, is sequentially uncoiled, laser-welded, and tension straightened; 5) Pickling: After tension straightening, the strip is pickled using a three-stage continuous hydrochloric acid pickling process; 6) Leveling: After pickling, the strip is rinsed, dried, and then leveled online. This invention effectively improves the overall quality of steel plates and solves the problems of poor surface quality, large fluctuations in mechanical properties, and difficulty in shape control in phase transformation strengthened thin-gauge ultra-high-strength hot-rolled steel plates.

Description

Technical Field

[0001] This invention belongs to the field of steel plate production, and more specifically, relates to a method for controlling the overall quality of thin-gauge ultra-high-strength steel plates. Background Technology

[0002] With the development of high-strength steel for special-purpose vehicles and construction machinery, and the upgrading of rolling cooling technology, especially ultra-fast cooling equipment, in recent years, phase transformation strengthened hot-rolled ultra-high-strength steel (tensile strength R) has become increasingly popular. m ≥1000MPa) has become a research hotspot. The main product strengthening method is to achieve online direct quenching through an ultra-fast cooling system after rolling. The main product strengthening method is phase transformation strengthening.

[0003] Compared to traditional grain refinement strengthening, precipitation strengthening, and dislocation strengthening, phase transformation strengthening contributes most significantly to improving material strength. It can reduce the amount of alloying elements required and produces products with a lower yield strength, which is beneficial for improving cold bending performance. Therefore, materials produced through phase transformation strengthening have advantages such as high strength, ease of forming, and low production cost. However, the production or application of phase transformation strengthened hot-rolled ultra-high strength steel has the following problems, mainly the following three points: (1) In order to ensure that the air cooling section of the product can form a certain proportion of soft phase ferrite structure, a high Si (Si content ≥1.0%) chemical composition design is adopted, and the material surface is all red iron oxide scale, with poor surface quality; (2) The cooling adopts a segmented cooling mode. Due to the influence of factors such as fast cooling rate, narrow cooling process window, and large influence of temperature fluctuation on phase transformation, the mechanical properties of phase transformation strengthened hot-rolled ultra-high strength steel fluctuate greatly. The yield strength and tensile strength fluctuate up to 200MPa, and the performance uniformity of phase transformation strengthened hot-rolled ultra-high strength steel is difficult to control; (3) The thickness specification is thin (≤6mm), the rolling pressure is large, the cooling rate after rolling is fast, the coiling temperature is low (≤300℃) and the coiling temperature hit rate is poor. The plate shape problem after rolling and cooling is prominent, and the wave height is as high as 20-30mm / m.

[0004] Regarding phase transformation strengthened hot-rolled ultra-high strength steel (R) m Patent applications for materials with a strength of ≥1000MPa, such as those with publication numbers CN103233161B, CN110331326A, CN104532126A, and CN110257725A, primarily address the technical challenge of achieving coordinated control of ultra-high strength, high wear resistance, and easy formability through a design that reduces alloy composition and optimizes rolling and cooling processes. These applications do not simultaneously address technical issues related to material surface quality, performance uniformity, or plate shape.

[0005] The patent with publication number CN108411203B discloses NM300 wear-resistant steel for high-silicon and high-alumina concrete mixer trucks and its production method. Its plate shape control strategy mainly involves cold rolling and annealing of hot-rolled steel coils, which requires adding a process to the existing production line. The process is long and does not involve the control of surface quality and performance uniformity.

[0006] Patent CN114011885A discloses a method for controlling the shape of hot-rolled high-strength steel in the gigapascal grade. It mainly emphasizes the use of edge heaters, fine rolling with micro-waves, and intensive continuous cooling. However, on the one hand, it directly and continuously cools the strip to 150~300℃ for coiling after rolling, making it difficult to control the uniformity of the coiling temperature. The coiling temperature will significantly affect the yield strength and yield ratio of the material, thus making it difficult to control the uniformity of the material's mechanical properties. On the other hand, the use of continuous cooling during rolling increases the residence time of the strip in the cooling section and increases the inconsistency of phase transformation in the width or length direction, thus increasing the difficulty of controlling the material's shape. Moreover, it does not address the aspects of material surface quality and performance uniformity.

[0007] Patents concerning the improvement of material performance uniformity, such as those with publication numbers CN107824619A, CN107983784B, CN109576467B, CN103031419B, CN113249557A, CN112063815A, and CN103031419B, fall into the following categories: (1) The research focuses on fine-grained or precipitation-strengthened hot-rolled high-strength steel (Rm≤700MPa) or medium-thick plates with relatively thick thicknesses, and there are no patents concerning thin-gauge (≤6mm) phase transformation-strengthened hot-rolled ultra-high-strength steel (Rm≥1 (1) 000MPa); 2) The research object is 780MPa grade phase transformation strengthened cold-rolled high-strength steel. The product strength level is relatively low and the performance uniformity of the strip in the length direction is mainly improved by optimizing the subsequent annealing process. The optimization of hot rolling process parameters and the width direction are not involved; (3) The performance uniformity of the strip in the length direction is improved by segmented head and tail shielding or U-shaped cooling process. The performance uniformity in the width direction is not involved; (4) By adding an online heat preservation cover device after the coiler, this method is only applicable to the performance uniformity improvement of precipitation strengthened high-strength steel, not applicable to phase transformation strengthened ultra-high-strength steel, and requires additional equipment investment.

[0008] In summary, existing technologies are not yet perfect in improving the phase transformation strengthened hot-rolled ultra-high strength steel (R... m Technical solutions for improving the surface quality, performance uniformity, and plate shape quality of steel plates with a strength of ≥1000MPa and a thickness of ≤6mm are needed to address the overall quality challenges in improving thin-gauge ultra-high-strength steel plates in phase transformation-strengthened slabs. Summary of the Invention

[0009] 1. The problem to be solved

[0010] To address the problem that existing technologies struggle to effectively improve the overall quality of thin-gauge ultra-high-strength steel plates with phase transformation strengthening, this invention provides a method for controlling the overall quality of thin-gauge ultra-high-strength steel plates. By optimizing the heating, rolling, cooling, tension leveling, pickling, and leveling processes, the overall quality of the steel plate can be effectively improved, solving the problems of poor surface quality, large fluctuations in mechanical properties, and difficulty in shape control of thin-gauge ultra-high-strength hot-rolled steel plates with phase transformation strengthening.

[0011] 2. Technical Solution

[0012] To solve the above problems, the present invention adopts the following technical solution.

[0013] A method for controlling the overall quality of thin-gauge ultra-high-strength steel plates includes the following steps:

[0014] 1) Heating

[0015] The slab is fed into a heating furnace and heated. The slab exits the furnace at a temperature of 1250~1300℃.

[0016] 2) Rolling

[0017] The strip is rolled using a 2-stand roughing mill and a 7-stand finishing mill hot continuous rolling mill. The finishing mill F7 exit temperature is 840~890℃, the centerline control is -20~+20mm, the crown C40 is 20-30μm, the symmetry and straightness is -50~0I, and the final rolling speed is ≥8m / s. C40 is the difference between the thickness at the midpoint of the strip cross-section and the average thickness at a position 40mm away from both sides.

[0018] 3) Cooling

[0019] After the slab is rolled, it is cooled in three stages: ultra-rapid cooling, air cooling and water cooling. After water cooling, it is coiled.

[0020] 4) Straightening

[0021] The steel coils, after being coiled and cooled to room temperature, are sequentially uncoiled, laser-welded, and tension-straightened.

[0022] 5) Pickling

[0023] After the strip is straightened, it is pickled using a three-stage continuous hydrochloric acid pickling method. The acid temperature is 70~80℃ and the pickling rate is 30-50m / min.

[0024] 6) Flat

[0025] After pickling, the product is rinsed and dried, and then leveled online using an elongation mode, with a leveling elongation rate of 0.4-0.8%.

[0026] As a further improvement to the technical solution, after the slab is fed into the heating furnace, it enters the preheating section, the primary heating section, the secondary heating section and the soaking section in sequence. The temperature at the end of the primary heating section is 980~1030℃, the temperature at the end of the secondary heating section is 1180~1230℃, the temperature in the soaking section is 1250~1300℃, and the soaking time is 20-30min.

[0027] As a further improvement to the technical solution, during rolling, the slab undergoes a high-pressure water descaling process after exiting the heating furnace, with a descaling water pressure of 180-230 bar. The first and third passes of the R1 stand and the second and fourth passes of the R2 stand of the roughing mill are equipped with pass-by-pass descaling water. After the intermediate slabs finish roughing, they undergo a second high-pressure water descaling process after passing through the heat insulation cover, with a descaling water pressure of 300-350 bar.

[0028] As a further improvement to the technical solution, the ultra-fast cooling section adopts centralized cooling and side shielding process, with a cooling rate of ≥80℃ / s, a side shielding distance of 100~150mm, and a cooling water flow ratio of (1:1.15)~(1:1.30) on the upper and lower surfaces of the strip. The side spraying water is symmetrical cross side spraying.

[0029] As a further improvement to the technical solution, the air-cooled section is air-cooled to 640-680℃ and then water-cooled.

[0030] As a further improvement to the technical solution, the water cooling section adopts a sparse cooling method, with the cooling water flow ratio between the upper and lower surfaces of the strip being (1:1.05) to (1:1.15), and the side spraying water is symmetrical and cross-side spraying, with a cooling rate of 50~80℃ / s.

[0031] As a further improvement to the technical solution, the winding temperature is ≤100℃.

[0032] As a further improvement to the technical solution, the tension leveler is a two-bend-one-straightening type, with a tension leveling elongation of 0.8~1.2% and a tension leveler tension of 50~80kN.

[0033] As a further improvement to the technical solution, the bending roller force of the leveling machine is 400-600kN, the inlet tension is 140-160kN, and the outlet tension is 180-200kN.

[0034] 3. Beneficial effects

[0035] (1) The present invention provides a method for controlling the overall quality of thin-gauge ultra-high strength steel plates. The ultra-high strength steel has good surface quality after pickling and no obvious color difference, which can eliminate the need for the subsequent tile-making process of downstream manufacturers and reduce the manufacturing cost of downstream manufacturers.

[0036] (2) The present invention provides a method for controlling the overall quality of thin-gauge ultra-high-strength steel plates. Without adding new equipment, the method can effectively improve the overall quality of steel plates by optimizing the heating, rolling, cooling, tension leveling, pickling and leveling processes. The product yield strength is ≥700MPa, tensile strength is ≥1000MPa, and the yield strength fluctuation range in the width and length directions is ≤70MPa, the tensile strength fluctuation range is ≤60MPa, and the flatness of the cut plate is ≤6mm / m. This method effectively solves the problems of large fluctuations in mechanical properties and difficulty in plate shape control of phase transformation strengthened thin-gauge ultra-high-strength hot-rolled steel plates. Attached Figure Description

[0037] Figure 1 This is a process flow diagram of the control method of the present invention;

[0038] Figure 2 The graphs show the fluctuations in mechanical properties of the strip steel in Example 1 in the width and length directions, respectively.

[0039] Figure 3 The graphs show the fluctuations in mechanical properties of the strip steel in the width and length directions of Example 2.

[0040] Figure 4 The graphs show the fluctuations in mechanical properties of the strip steel in Example 3 in the width and length directions, respectively.

[0041] Figure 5 The graphs show the fluctuations in mechanical properties of the strip in the width and length directions of Comparative Example 1.

[0042] Figure 6 The graphs show the fluctuations in mechanical properties of the strip in Comparative Example 2 in the width and length directions, respectively.

[0043] Figure 7 The graphs show the fluctuations in mechanical properties of the strip in Comparative Example 3 in the width and length directions, respectively.

[0044] Figure 8 This is a diagram of an ultra-high strength steel plate after pickling and leveling. Detailed Implementation

[0045] Exemplary embodiments of the present invention are described in detail below. While these exemplary embodiments have been 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 various changes may be made to the invention without departing from its spirit and scope. The more detailed description of embodiments of the invention below is not intended to limit the scope of the claimed invention, but is merely illustrative and does not limit the description of the features and characteristics of the invention, in order to suggest the best mode for carrying out the invention and to enable those skilled in the art to practice it. Therefore, the scope of the invention is defined only by the appended claims.

[0046] A method for controlling the overall quality of thin-gauge ultra-high-strength steel plates, specifically for plates with a thickness ≤6mm and a tensile strength R... m Phase transformation strengthened ultra-high strength steel plates with a strength ≥1000MPa can effectively improve their overall quality. The chemical composition and mass percentage of the steel plate are as follows: C: 0.08~0.13%, Si: 0.80-1.50%, Mn: 1.20~1.80%, P: ≤0.015%, S: ≤0.005%, Als: 0.30~0.50%, Ti: 0.015~0.040%, B: 0.0006~0.0012%, with the remainder being Fe and unavoidable inclusions. The process and principle are described in detail below.

[0047] like Figure 1 As shown, the method includes the following steps:

[0048] 1) Heating

[0049] After the slab enters the heating furnace, it sequentially enters the preheating section, primary heating section, secondary heating section, and soaking section. The temperature and time in the preheating section are not limited, as long as the preheating effect specified in this field is achieved. The final temperature of the primary heating section is 980~1030℃, the final temperature of the secondary heating section is 1180~1230℃, and the temperature of the soaking section is 1250~1300℃, with a soaking time of 20-30 minutes. It should be noted that at the end of the primary and secondary heating sections, the slab needs to be held at that temperature for 5~10 minutes to allow changes in its microstructure, preparing it for subsequent rolling, cooling, pickling, and leveling processes. The total heating time of the slab in the heating furnace is generally 180~210 minutes.

[0050] In this step, the purpose of high-temperature heating is to control the slab temperature to >1173℃ during high-pressure water descaling before rough rolling, ensuring that the iron oxide Fe2SiO4 is in a molten state and easy to remove, and preventing Fe2SiO4 from sticking to the surface of the steel plate matrix and being difficult to remove. Taking into account factors such as slab burn-through and the amount of iron oxide scale generated, the high-temperature soaking time of the slab should not be too long, and should be controlled within 20-30 minutes.

[0051] 2) Rolling

[0052] The strip is rolled using a 2-stand roughing mill and a 7-stand finishing mill hot continuous rolling mill. The finishing mill F7 exit temperature is 840~890℃. The centerline control during rolling is -20~+20mm, the crown C40 is 20-30μm, the symmetry and straightness is -50~0I, and the final rolling speed is ≥8m / s. C40 is the difference between the thickness at the midpoint of the strip cross-section and the average thickness at a position 40mm away from both sides.

[0053] During rolling, the slab undergoes a first high-pressure water descaling process after exiting the heating furnace, with a descaling water pressure of 180-230 bar. The first and third passes of the R1 stand and the second and fourth passes of the R2 stand in the roughing mill are equipped with this pass-by-pass descaling water. In this embodiment, RX represents the Xth stand in the rolling direction of the continuous rolling mill. After roughing, the intermediate slab undergoes a second high-pressure water descaling process after passing through an insulation hood, with a descaling water pressure of 300-350 bar.

[0054] In this step, the use of high-pressure water descaling before roughing and finishing, descaling between roughing passes, increasing the finishing mill exit rolling speed, and employing low-temperature rolling are all aimed at controlling and reducing the amount of iron oxide scale generated during rolling and the residual amount of iron oxide scale after high-pressure water descaling, thus providing a foundation for improving the surface quality of the steel plate after pickling. Controlling the rolling centerline within -20 to +20 mm is primarily based on ensuring equal cooling water shielding on both sides of the ultra-fast cooling section in the width direction, and improving the edge shielding for temperature and performance uniformity in the width direction. The strip crown at the F7 stand exit is 20-30 μm mainly to avoid double-sided waves in the strip rolling and to improve the thickness dimensional accuracy in the width direction, which is beneficial for controlling the temperature uniformity in the width direction of laminar cooling of the strip. The symmetrical flatness is -50~0I in order to adopt micro-wave rolling, so that the strip steel forms a small wave, increases the deformation in the middle position of the strip steel in the width direction, avoids the double wave caused by uneven deformation in the width direction of the strip steel during cooling (large deformation at both sides and small deformation in the middle), and thus helps to improve the strip shape quality.

[0055] 3) Cooling

[0056] After rolling, the slab undergoes three-stage cooling: ultra-rapid cooling, air cooling, and water cooling. The ultra-rapid cooling stage employs centralized cooling with edge shielding, achieving a cooling rate ≥80℃ / s. The edge shielding distance is 100~150mm, and the cooling water flow ratio between the upper and lower surfaces of the strip is (1:1.15)~(1:1.30). Side water spraying is symmetrical and cross-sprayed. In the air cooling stage, the strip is air-cooled to 640-680℃ before water cooling. This water cooling stage uses a sparse cooling method, with a cooling water flow ratio between the upper and lower surfaces of the strip at (1:1.05)~(1:1.15). Side water spraying is symmetrical and cross-sprayed, and the cooling rate is 50~80℃ / s. After water cooling, the strip is coiled at a temperature CT≤100℃.

[0057] In this step, the three-stage cooling mode of ultra-fast cooling-air cooling-water cooling is mainly used to obtain a ferrite + martensite dual-phase microstructure. To control the temperature uniformity of the strip across its width in the ultra-fast cooling and water cooling sections, measures such as controlling the ratio of upper and lower cooling water, cross-symmetrical side spraying, and edge shielding are employed. The purpose of using less upper cooling water than lower cooling water in the ultra-fast cooling and water cooling sections is to avoid excessive upper cooling water residue and accumulation on the strip surface, which would lead to uneven temperature distribution across the strip width and negatively impact performance uniformity. Edge shielding in the ultra-fast cooling section is primarily used to improve temperature and performance uniformity across the strip width. The water cooling section employs sparse cooling and a water cooling rate of 50~80℃ / s, mainly to minimize the cooling rate and prevent structural stress and phase transformation stress caused by excessive cooling rates, which could lead to cooling ripples on one or both sides of the strip, detrimental to temperature and performance uniformity across the width.

[0058] The air-cooling section ends at 640~680℃. This is done for two reasons: firstly, to control the material's microstructure and properties, ensuring a certain proportion of ferrite in the material; and secondly, to control the proportion of loose FeO phase in the iron oxide scale on the strip surface, preventing FeO from undergoing eutectoid transformation. Loose FeO is easily removed during pickling, which is beneficial for improving surface quality after pickling. Furthermore, the low-temperature coiling process is mainly used to control the uniformity of coiling temperature in both the width and length directions of the strip, avoiding the adverse effects of width-direction temperature fluctuations on the material's mechanical properties and shape.

[0059] 4) Straightening

[0060] The hot coil, after being wound and cooled to room temperature, is then unwound, laser-welded, and tension-straightened in sequence. The tension-straightening machine is a two-bend-one-straightening type, with a tension-straightening elongation of 0.8~1.2% and a tension of 50~80kN.

[0061] 5) Pickling

[0062] After the strip is straightened, it is pickled using a three-stage continuous hydrochloric acid pickling method. The acid temperature is 70~80℃ and the pickling rate is 30-50m / min.

[0063] 6) Flat

[0064] After pickling, the strip is rinsed and dried, then subjected to online leveling using an elongation mode. The leveling elongation is 0.4-0.8%, the bending roller force is 400-600kN, the inlet tension of the leveling machine is 140-160kN, and the outlet tension is 180-200kN. The strip surface is not oiled after leveling. Figure 2 As shown, the final product obtained is an ultra-high strength hot-rolled pickled steel sheet.

[0065] This embodiment employs a pre-pickling tension leveling process followed by online leveling after pickling. The main purpose is to improve the shape and performance uniformity of ultra-high strength hot-rolled strip steel using tension leveling and leveling processes, which is also the innovation of this embodiment. Under the tension of the tension leveling unit, the strip steel continuously passes through alternating small-diameter bending rolls and undergoes severe bending. Under the combined effect of tensile and bending stresses, the lengths of the longitudinal fiber units in the width direction of the strip steel tend to be consistent, thereby reducing the unevenness of internal stress distribution and helping to reduce shape defects such as double-sided and single-sided waviness. Simultaneously, the online leveling process after pickling, through the coordinated operation of leveling elongation, bending roll force, and tension, further improves the shape and width-direction performance uniformity.

[0066] For thin-gauge high-Si ultra-high-strength steel, an excessively small elongation rate during leveling results in insufficient improvement in strip shape and scale breaking effect. Conversely, an excessively large elongation rate not only increases the leveling tension and the risk of strip breakage in the pickling unit but also causes uneven deformation due to imbalance, which is detrimental to improving strip shape. Considering all factors, the elongation rate during leveling is controlled between 0.8% and 1.2%, and the tension of the leveling machine is controlled between 50 and 80 kN. The strip surface is not coated with oil after leveling primarily to prevent oil from affecting the adhesion and aesthetic appearance of the final finished product when paint is applied.

[0067] In the pickling process, the surface quality is mainly controlled by parameters such as the elongation of the straightening, the pickling rate, and the acid temperature. Considering the thick iron oxide scale of high-Si steel and the stability of the flattening process after pickling, the pickling rate is controlled at 30-50 m / min. The pickling rate should not be too fast, otherwise the surface quality and plate shape will be difficult to guarantee.

[0068] In summary, this method for controlling the overall quality of thin-gauge ultra-high-strength steel plates, without adding new equipment, can effectively improve the overall quality of the steel plates through reasonable optimization of heating, rolling, cooling, tension leveling, pickling, and leveling processes. The product yield strength is ≥700MPa, tensile strength is ≥1000MPa, and the yield strength fluctuation range in the width and length directions is ≤70MPa, the tensile strength fluctuation range is ≤60MPa, the flatness of the cut plate is ≤6mm / m, and the surface quality is good. This method solves the problems of poor surface quality, large fluctuations in mechanical properties, and difficulty in shape control of phase transformation strengthened thin-gauge ultra-high-strength hot-rolled steel plates.

[0069] It must be noted that this method emphasizes improving the overall quality of transformation-strengthened ultra-high-strength steel plates from the perspective of the entire process—heating, rolling, cooling, coiling, tension leveling, pickling, and leveling—rather than optimizing and controlling a single process parameter within any one of these steps. Therefore, comprehensive quality control of transformation-strengthened ultra-high-strength steel plates must be implemented from the perspective of the entire process to obtain steel coils with the desired properties.

[0070] The technical solution of the present invention will be described below through specific embodiments and comparative examples.

[0071] The chemical composition and weight percentage of Examples 1-3 and Comparative Examples 1-3 are as follows: 0.11% C, 1.10% Si, 1.74% Mn, 0.011% P, 0.002% S, 0.45% Als, 0.023% Ti, and 0.0008% B. The remainder is Fe and unavoidable inclusions. The specific process parameters for the examples and comparative examples are shown in Tables 1-3, including heating, rolling, cooling, tension leveling, pickling, and leveling.

[0072] The method for evaluating the uniformity of mechanical properties is as follows: After pickling, one full-width sample is taken from the head and tail of the strip. Ten longitudinal tensile test specimens are cut from each full-width sample at equal intervals along the width direction, for a total of 20 specimens. The yield strength and tensile strength of the material are obtained by conducting room temperature tensile tests according to GB / T 228.1. The uniformity of mechanical properties is indicated by the fluctuation range of yield strength and tensile strength in the width and length directions. The fluctuation range of yield strength in the width direction = Max(yield strength of 10 tensile test specimens) - Min(yield strength of 10 tensile test specimens), and the fluctuation range of tensile strength in the width direction = Max(tensile strength of 10 tensile test specimens) - Min(tensile strength of 10 tensile test specimens). The fluctuation range of yield strength in the length direction = Max(yield strength of the head and tail at the same width position) - Min(yield strength of the head and tail at the same width position), and the fluctuation range of tensile strength in the length direction = Max(tensile strength of the head and tail at the same width position) - Min(tensile strength of the head and tail at the same width position).

[0073] The width and length direction property distributions of the ultra-high strength steels corresponding to Examples 1-3 and Comparative Examples 1-3 are shown in the figure. Figure 3-7 As shown in Table 4, the yield strength and tensile strength fluctuation ranges in the width and length directions are as follows: the yield strength fluctuation range of the ultra-high strength steel corresponding to the embodiment is ≤70MPa and the tensile strength fluctuation range is ≤60MPa.

[0074] Table 5 shows the flatness of the ultra-high strength steel plate cutters corresponding to Examples 1-3 and Comparative Examples 1-3. The flatness of the ultra-high strength steel plate cutters after pickling in the examples is ≤6mm / m.

[0075] Table 1 Heating and rolling process parameters for the examples and comparative examples

[0076]

[0077] Table 2 Cooling process parameters for the examples and comparative examples

[0078]

[0079] Table 3. Process parameters for straightening, pickling, and leveling in the examples and comparative examples.

[0080]

[0081] Table 4. Performance fluctuations of ultra-high strength steel in the width and length directions for the examples and comparative examples.

[0082]

[0083] Table 5. Unevenness of ultra-high strength steel sheet metal in the examples and comparative examples

[0084]

[0085] The examples described herein are merely preferred embodiments of the invention and are not intended to limit the concept and scope of the invention. Any modifications and improvements made by those skilled in the art to the technical solutions of the invention without departing from the design concept of the invention should fall within the protection scope of the invention.

Claims

1. A method for controlling the overall quality of thin-gauge ultra-high-strength steel plates, characterized in that: Includes the following steps: 1) Heating The slab is fed into a heating furnace and heated. The slab exits the furnace at a temperature of 1250~1300℃. 2) Rolling The strip is rolled using a 2-stand roughing mill and a 7-stand finishing mill hot continuous rolling mill. The finishing mill F7 exit temperature is 840~890℃, the centerline control is -20~+20mm, the crown C40 is 20-30μm, the symmetry and straightness is -50~0I, and the final rolling speed is ≥8m / s. C40 is the difference between the thickness at the midpoint of the strip cross-section and the average thickness at a position 40mm away from both sides. 3) Cooling After the slab is rolled, it is cooled in three stages: ultra-rapid cooling, air cooling and water cooling. After water cooling, it is coiled. The ultra-fast cooling section adopts centralized cooling and side shielding technology, with a cooling rate ≥80℃ / s, a side shielding distance of 100~150mm, a cooling water flow ratio of 1:1.15~1:1.30 on the upper and lower surfaces of the strip, and symmetrical cross-side spraying of side water. After the air-cooled section reaches 640-680℃, it is then water-cooled. The water-cooling section adopts a sparse cooling method, with the cooling water flow ratio between the upper and lower surfaces of the strip being 1:1.05~1:1.

15. The side spraying is symmetrical and cross-side spraying, with a cooling rate of 50~80℃ / s. 4) Straightening The steel coils, after being coiled and cooled to room temperature, are sequentially uncoiled, laser-welded, and tension-straightened. 5) Pickling After the strip is straightened, it is pickled using a three-stage continuous hydrochloric acid pickling method. The acid temperature is 70~80℃ and the pickling rate is 30-50m / min. 6) Flat After pickling, the product is rinsed and dried, and then leveled online using an elongation mode, with a leveling elongation rate of 0.4-0.8%.

2. The method for controlling the overall quality of thin-gauge ultra-high-strength steel plates according to claim 1, characterized in that: After the slab is fed into the heating furnace, it enters the preheating section, the primary heating section, the secondary heating section and the soaking section in sequence. The temperature at the end of the primary heating section is 980~1030℃, the temperature at the end of the secondary heating section is 1180~1230℃, the temperature in the soaking section is 1250~1300℃, and the soaking time is 20-30 minutes.

3. The method for controlling the overall quality of thin-gauge ultra-high-strength steel plates according to claim 2, characterized in that: During rolling, the slab undergoes a high-pressure water descaling process after exiting the heating furnace, with a descaling water pressure of 180-230 bar. The first and third passes of the R1 stand and the second and fourth passes of the R2 stand of the roughing mill are equipped with descaling water. After the intermediate slabs finish roughing, they undergo a second high-pressure water descaling process after passing through the heat insulation cover, with a descaling water pressure of 300-350 bar.

4. The method for controlling the overall quality of thin-gauge ultra-high-strength steel plates according to claim 3, characterized in that: Winding temperature ≤100℃.

5. The method for controlling the overall quality of thin-gauge ultra-high-strength steel plates according to claim 4, characterized in that: The tension leveling machine is a two-bend-one-straightening type, with a tension leveling elongation of 0.8~1.2% and a tension of 50~80kN.

6. The method for controlling the overall quality of thin-gauge ultra-high-strength steel plates according to claim 5, characterized in that: The bending roller force of the leveling machine is 400-600kN, the inlet tension is 140-160kN, and the outlet tension is 180-200kN.

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