A method for skin passing a ferritic-martensitic dual phase ultra-high strength hot-rolled coil

Abstract

The application mainly researches and analyzes the shape improvement and surface protection of the hot-rolled strip steel leveling process of ferrite-martensite bidirectional high-strength steel, and summarizes a set of leveling production method; 1, through the variable tension, the use of various process rollers increases the shape improvement effect of the head and tail no-tension coiling section, ensures the shape consistency of the strip steel in the length direction, and improves the shape opening and leveling pass rate; 2, through the addition of the inlet water blowing pipe, the limitation of the running speed of the production line, the water entanglement of the work roll surface caused by the residual cooling water on the surface of the strip steel is prevented, and the roll printing of the leveling is avoided. After the application is implemented, the opening and leveling pass rate of the ferrite-martensite bidirectional high-strength steel hot-rolled strip steel can be effectively improved from 60% to 90%.

Description

Technical Field

[0001] This invention belongs to the field of plate shape quality control technology in hot-rolled steel coil leveling production line, and relates to a leveling method for ferritic martensitic dual-phase ultra-high strength hot-rolled coils. Background Technology

[0002] Lightweighting and extended lifespan are the industry trends for construction machinery and commercial vehicles, requiring continuous upgrades in raw materials to meet this demand. Due to limitations in processes and equipment, traditional hot rolling mills cannot produce hot-rolled steel plates with tensile strengths exceeding 800MPa online. The first quenching machine from Dongda, installed on the heat treatment line at the Linfen branch, cannot produce quenched plates that meet general industry requirements, hindering the development of such products.

[0003] Ferritic-martensitic biaxial ultra-high strength steel hot-rolled coils were developed by Taiyuan Iron & Steel Group (TISCO) to address this issue. These hot-rolled steel plates, with tensile strengths exceeding 800 MPa, are produced using a forced-cooling, room-temperature coiling process. This process, while ensuring high strength, results in highly unstable plate shape, particularly in the tension-free sections (approximately 130 meters each). The plate shape differs significantly from the tension-coated sections. Even using the same leveling parameters, the shape improvement varies considerably, with the tension-free sections showing poor shape improvement and failing to meet delivery quality requirements.

[0004] On the other hand, this type of high-strength steel is produced by hot rolling at room temperature with strong cooling. Due to the low coiling temperature, the cooling water will remain on the surface of the strip for a long time and cannot evaporate. During the leveling process, it is very easy to cause iron scale to stick to the surface of the leveling rolls, resulting in leveling roll marks. This problem needs to be overcome and solved during the leveling process.

[0005] To address the above problems, this invention summarizes a method for controlling the leveling process parameters in stages. Different uncoiling / rewinding tensions and operating speeds are used at different positions along the strip length, and auxiliary process rollers such as deep bending rollers, anti-wrinkle rollers, and straightening rollers are employed to improve the shape improvement capability of the beginning and end sections, ensuring the consistency of the final strip shape quality throughout the entire length. Controlling the operating speed of the leveling production line and adding water blowing ducts at the leveling unit inlet prevents water adhesion during the rapid operation of the leveling work rollers, eliminating the generation of leveling roller marks and improving the subsequent flattening shape and surface qualification rate. Summary of the Invention

[0006] The purpose of this invention is to address the above-mentioned problems by providing a method for leveling ferritic-martensitic dual-phase ultra-high strength hot-rolled coils.

[0007] The objective of this invention is achieved as follows: A method for leveling ferritic martensitic duplex ultra-high strength hot-rolled coils, comprising the following steps: Step 1: After the hot rolling of ferritic martensitic duplex ultra-high strength steel is completed, leveling production is arranged within one week; Step 2: Before production, new work rolls are replaced, and production proceeds from wide to narrow after the work rolls are replaced; Step 3: According to the width specification, the minimum allowable roll position is set; Step 4: A water blowing duct is added at the entrance of the straightener on the leveling line, and compressed air with a pressure of 0.5-0.8 MPa is supplied during production to quickly dry the residual cooling water adhering to the surface of the strip; Step 5: The uncoiling tension of the incoming material stabilization section is 1. 5-2.0 kg / mm²; the coiler tension is set to 2.5-3.5 kg / mm². During the flattening process of the incoming material without tension, the tension of the flattening uncoiler is increased to 2.6-3.2 kg / mm², and the tension of the coiler is increased to 3.5-6.0 kg / mm². Step 6: Initial pressure setting; Step 7: Control the maximum flattening line speed at 60-100 m / min; Step 8: Use anti-wrinkle rollers and deep bending rollers for sections with poor sheet shape; Step 9: Check the upper and lower surfaces twice for each roll: check the length of the upper and lower surfaces 10-15 meters when starting the machine; check the upper and lower surfaces 5-10 meters after automatic speed reduction.

[0008] The initial pressure settings in step six are as follows: width 1600-2000mm, pressure 850-1000 tons; width 1200-1600mm, pressure 750-900 tons.

[0009] The beneficial effects of this invention are: it can effectively ensure the flatness of ultra-high strength steel, improve the shape and surface quality of the flattened line, and increase the yield of high-quality ultra-high strength steel after leveling. Taiyuan Iron & Steel Group's hot rolling mill began to implement this invention gradually in March 2022, and the yield of high-quality cross-cutting and leveling has been greatly improved. Detailed Implementation

[0010] This invention belongs to the field of strip shape quality control technology in hot-rolled steel coil leveling production lines. Addressing the instability of strip shape when high-strength hot-rolled coils are wound without tension at both ends, the leveling process employs variable tension and speed operation methods at both ends to enhance the strip shape improvement effect and ensure consistent strip shape quality throughout its length. Furthermore, to address the problem of iron scale adhesion and leveling roll marks caused by water on the work roll surface during leveling, this invention utilizes methods such as adding a water-blowing duct at the leveling machine inlet and limiting the leveling speed to prevent water from adhering to the work roll surface and thus improve the strip surface quality.

[0011] The main characteristics of this hot-rolled coil include the following aspects: 1. Hot rolling adopts forced cooling and low temperature coiling, resulting in high thermal stress and unstable plate shape of the strip.

[0012] 2. Due to the influence of the strip shape, the cooling of the strip is more uneven in the tension-free winding section at the beginning and end, resulting in a worse strip shape.

[0013] 3. Since the winding is done at room temperature, the cooling water on the surface cannot evaporate fully. It is necessary to ensure timely leveling during production to dry the surface moisture. In addition, the moisture adhering to the surface during production can easily contaminate the leveling work roller, causing the roller surface to stick and produce roller mark defects.

[0014] 4. Due to the influence of the plate shape of the tension-free sections at the beginning and end, the steel coil exhibits a relatively severe tower shape at both the beginning and end.

[0015] 5. High strength, close to the strength required for flattening production capacity, making it difficult to meet the requirements for improving plate shape with high pressure alone.

[0016] To address the above characteristics, the technical solution and concept adopted in this invention are as follows: 1. A water-blowing air duct is added at the inlet of the straightening machine on the leveling line to deliver compressed air at a pressure of 0.6 MPa during production, quickly drying the residual cooling water adhering to the surface of some strip steel, preventing residual water from adhering to the surface of the work rolls during operation; 2. The maximum running speed of the leveling line is controlled to not exceed 100 m / min to prevent water marks adhering to the surface of the work rolls from accumulating under the centrifugal force of high-speed rotation, reducing the risk of roll surface adhesion; 3. During the tensionless winding and leveling production of the beginning and end sections of the rolling line, the tension of the leveling uncoiler is increased to 3.0 kg / mm², and the tension of the coiler is increased to 5.0 kg / mm², improving the elongation rate of the leveling line and enhancing the leveling shape improvement effect; 4. During the tensionless winding and leveling production of the beginning and end sections of the rolling line, the production line running speed is reduced to below 30 m / min, and deep bending rolls and anti-wrinkle rolls are introduced to increase online tension and improve the leveling shape improvement effect of the beginning and end sections.

[0017] This invention is only applicable to the leveling process of hot-rolled ferritic martensitic dual-phase ultra-high strength steel strip. Its main purpose is to improve the original plate shape quality of the coil and avoid the generation of surface defects in the leveling process. It is mainly for high-strength varieties with strength levels close to the capabilities of the leveling line equipment, where the plate shape at the beginning and end of the tension-free section is poor. It ensures the consistency of the plate shape in the final length direction and improves the yield of finished products after leveling.

[0018] This invention was implemented in March 2022 at the 2250 leveling unit of the Taiyuan Iron & Steel Group's hot strip mill. The specific implementation steps are as follows: 1. After the hot rolling of ferritic martensitic duplex ultra-high strength steel is completed, leveling production must be arranged within one week to avoid long-term residual cooling water on the strip surface causing rust on the steel plate surface; 2. Before production, new work rolls must be replaced, and after replacing the work rolls, production must be carried out from wide to narrow; 3. According to the width specification, the minimum roll shifting position allowed by the width is set. 4. Add a water-blowing air duct at the entrance of the straightening machine on the leveling line. During production, it delivers compressed air at a pressure of 0.5-0.8 MPa to quickly dry any residual cooling water adhering to the surface of the strip. In the section where the strip shape is stable, the uncoiling tension is 1.5-2.0 kg / mm², and the coiling tension is 2.5-3.5 kg / mm². When the strip shape is abnormal in the tensionless sections at the beginning and end, adjust the uncoiling tension to 2.6-3.2 kg / mm², and the coiling tension can be 3.5-6.0 kg / mm² until fully stretched. 5. Initial pressure settings: 850-1000 tons for a width of 1600-2000 mm, and 750-900 tons for a width of 1200-1600 mm. During the leveling process, the pressure can be appropriately increased based on changes in the strip shape, combined with adjustments to the bending rollers. 6. When the time between leveling and hot rolling completion is greater than 5 days, the leveling speed should be 80-100 m / min under stable sheet shape conditions. The speed should be reduced after the length reaches 400 meters. When abnormal fluctuations in sheet shape occur, the production speed should be 50-80 m / min until automatic speed reduction is completed. When the time between leveling and hot rolling completion is less than 5 days, the maximum leveling speed should be 60-80 m / min. 7. Anti-wrinkle rollers must be used, and deep bending rollers must be used for sections with poor sheet shape. 8. Inspect the upper and lower surfaces of each coil twice: inspect the upper and lower surfaces for 10-15 meters immediately after starting the machine; inspect the upper and lower surfaces for 5-10 meters after automatic speed reduction. 9. Before production, the water blowing pipes on the upper and lower surfaces after the inlet pinch rollers must be opened. Example 1

[0019] Taiyuan Iron & Steel Group's 2250 leveling unit produces high-strength wear-resistant steel TWR300TP, with specifications of 3.0×1290mm. The specific implementation steps are as follows: 1. Leveling production must be arranged within one week after the completion of hot rolling. 2. The width of the transition material produced by replacing the work rolls must be within the range of 1290-2000mm. 3. Before production, the upper and lower surface water blowing pipes after the inlet pinch rolls must be opened, with an air pressure of 0.6Mpa. 4. In the stable section of the plate shape, the uncoiling tension is 2.0kg / mm²; the coiling tension is 3.0kg / mm². When the plate shape is abnormal in the tensionless section at the beginning and end, the uncoiling tension is adjusted to 3.0kg / mm², and the coiling tension can be 6.0kg / mm². 5. Initial pressure setting: 750 tons. During the leveling process, the pressure can be appropriately increased according to the changes in plate shape, combined with the bending roll adjustment. 6. When the time between leveling and hot rolling completion is greater than 5 days, the leveling speed is 100 m / min under stable sheet shape conditions. The speed is reduced after the length reaches 400 meters. When abnormal fluctuations in sheet shape occur, the production speed is reduced to 80 m / min until automatic speed reduction is completed. When the time between leveling and hot rolling completion is less than 5 days, the maximum leveling speed is 80 m / min. 7. Anti-wrinkle rollers are used before starting the machine; deep bending rollers are used when the sheet shape begins to deteriorate. 8. The upper and lower surfaces of each coil are inspected twice: 15 meters at the start of the machine; and 10 meters after automatic speed reduction. Example 2

[0020] Taiyuan Iron & Steel Group's 2250 leveling unit produces high-strength wear-resistant steel TWR400, with specifications of 4.0×1800mm. The specific implementation steps are as follows: 1. Leveling production must be arranged within one week after the completion of hot rolling. 2. The width of the transition material produced by replacing the work rolls must be within the range of 1800-2000mm. 3. Before production, the upper and lower surface water blowing pipes after the inlet pinch rolls must be opened, with an air pressure of 0.65Mpa. 4. In the stable section of the plate shape, the uncoiling tension is 1.8kg / mm², and the coiling tension is 3.2kg / mm². When the plate shape is abnormal in the tensionless section at the beginning and end, the uncoiling tension is adjusted to 2.8kg / mm², and the coiling tension is 5.5kg / mm². 5. The initial pressure setting is 850 tons. During the leveling process, the pressure can be appropriately increased according to the changes in plate shape, combined with the bending roll adjustment. 6. When the time between leveling and hot rolling completion is greater than 5 days, the leveling speed is 100 m / min under stable sheet shape conditions. The speed is reduced after the length reaches 350 meters. When abnormal fluctuations in sheet shape occur, the production speed is reduced to 60 m / min until automatic speed reduction is completed. When the time between leveling and hot rolling completion is less than 5 days, the maximum leveling speed is 60 m / min. 7. Anti-wrinkle rollers are used before starting the machine; deep bending rollers are used when the sheet shape begins to deteriorate. 8. The upper and lower surfaces of each coil are inspected twice: 12 meters at the start of the machine; and 10 meters after automatic speed reduction. Example 3

[0021] Taiyuan Iron & Steel Group's 2250 leveling unit produces high-strength magnetic yoke steel 1000TM162, with specifications of 4.0×1500mm. The specific implementation steps are as follows: 1. Leveling production must be arranged within one week after the completion of hot rolling. 2. The width of the transition material produced after replacing the new work rolls must be within the range of 1800-2000mm. 3. Set the minimum allowable roll shift position to 40mm for a width of 1500mm. 4. Before production, the upper and lower surface water blowing pipes after the inlet pinch rolls must be opened, with an air pressure of 0.6Mpa. 5. In the stable section of the plate shape, the uncoiling tension is 1.5kg / mm², and the coiling tension is 3.0kg / mm². When the plate shape is abnormal in the tensionless sections at the beginning and end, the uncoiling tension is adjusted to 2.6kg / mm², and the coiling tension is 3.5kg / mm². 6. Initial pressure setting: 950 tons. During the leveling process, the pressure can be appropriately increased according to the changes in plate shape, combined with the bending roll adjustment. 7. When the time between leveling and hot rolling completion is greater than 5 days, the leveling speed is 100 m / min under stable sheet shape conditions. The speed is reduced after the length reaches 400 meters. When abnormal fluctuations in sheet shape occur, the production speed is reduced to 80 m / min until automatic speed reduction is completed. When the time between leveling and hot rolling completion is less than 5 days, the maximum leveling speed is 80 m / min. 8. Use anti-wrinkle rollers before starting the machine and deep bending rollers immediately after starting. 9. Inspect the upper and lower surfaces of each coil twice: inspect the upper and lower surfaces for a length of 15 meters immediately after starting the machine; inspect the upper and lower surfaces for a length of 10 meters after automatic speed reduction.

[0022] The above description is only a specific embodiment of the present invention, but the structural features protected by the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A method for leveling ferritic-martensitic dual-phase ultra-high strength hot-rolled coils, characterized in that: Includes the following steps: Step 1: After the hot rolling of ferritic martensitic dual-phase ultra-high strength steel is completed, leveling production will be arranged within one week. Step 2: Replace the work roll with a new one before production, and then produce from wide to narrow after replacing the work roll; Step 3: Based on the width specification, set the minimum allowable roller position; Step 4: Add a water blowing duct at the inlet of the leveling line straightener to deliver compressed air with a pressure of 0.5-0.8 MPa during production to quickly dry the residual cooling water adhering to the surface of the strip steel. Step 5: The uncoiling tension of the incoming material plate stabilization section is 1.5-2.0 kg / mm²; the tension of the coiler is set to 2.5-3.5 kg / mm². During the production process of flattening the head and tail sections of the incoming material without tension, the tension of the flattening uncoiling machine is increased to 2.6-3.2 kg / mm², and the tension of the coiler is increased to 3.5-6.0 kg / mm². Step Six: Initial Pressure Setting; Step 7: Control the maximum running speed of the leveling line to 60-100m / min; Step 8: Use anti-wrinkle rollers and deep bending rollers for sections with poor plate shape; Step 9: Check the top and bottom surfaces twice per roll: check the length of the top and bottom surfaces for 10-15 meters when the machine starts; check the length of the top and bottom surfaces for 5-10 meters after the machine automatically slows down.

2. The method for leveling ferritic martensitic dual-phase ultra-high strength hot-rolled coils according to claim 1, characterized in that: The initial pressure settings in step six are as follows: width 1600-2000mm, pressure 850-1000 tons; width 1200-1600mm, pressure 750-900 tons.