Method for improving head and tail performance of black coil of steckel mill

Abstract

The invention discloses a method for improving the head and tail performance of a steckel mill stainless steel black coil, and belongs to the technical field of stainless steel hot rolling machining. By optimizing the heating air-fuel ratio (the heating section is 2.00-2.20, and the soaking section is 2.25-2.45), reducing the rough / finish rolling cooling water amount (150 + / -10 m / h and 120 + / -10 m / h), shortening the replacement period of a water sealing plate to 4 days, adopting coke oven gas high-temperature coiling (1150 + / -5 DEG C), forbidding stratified cooling at the head and the tail of 30 m and the like, the temperature uniformity of the head and the tail is remarkably improved. By adjusting the process parameters, the problem that the head and tail performance of the black coil is abnormal is effectively solved, and therefore the head and tail performance and the yield are improved. According to the method, the stainless steel produced by the steckel mill has better performance and quality.

Description

Technical Field

[0001] The invention belongs to the field of stainless steel hot processing, and specifically relates to a method for improving abnormal performance of hot-rolled black coil heads and tails by optimizing process parameters of a furnace coil mill, and is suitable for the production of stainless steel strips. Background Art

[0002] The abnormal performance of the head and tail of hot-rolled black coil means that during the hot rolling process, the plate undergoes multiple stages such as high-temperature heating, deformation and cooling, and each stage affects the structure and performance of the plate. The head and tail are usually in the earlier or later stages of the hot rolling process, and are affected by different heating, cooling and plastic deformation conditions, resulting in differences in hardness between the head and tail of the plate within 0-30 meters and the normal part. The difference in hardness between the head and tail of hot rolling can cause uneven product performance, finished product quality problems, and subsequent processing difficulties.

[0003] The head and tail parts (0-30 meters) of hot-rolled stainless steel black coils often have different hardness (±15HB or more) due to uneven heating, rolling and cooling conditions, which leads to subsequent processing difficulties (such as cold rolling fracture) and reduced yield. Traditional methods adjust the cooling water volume of the rolls or the layer cooling process, but fail to systematically solve the problems of fast temperature drop and uneven structure at the head and tail.

[0004] The prior art has the following defects: The air-fuel ratio control of the heating furnace is not divided into different zones, resulting in uneven heating at the head and tail. The cooling water volume for roughing / finishing rolling is too high (180m³ / h for conventional roughing rolling and 150m³ / h for finishing rolling), which aggravates the temperature drop at the head and tail. The coiling temperature fluctuates greatly (±20℃), and the contact between the mandrels causes heat loss at the head and tail. Summary of the invention

[0005] The purpose of the present invention is to provide a method for improving the head and tail performance of black coils of a Steckel rolling mill. Aiming at the abnormal head and tail performance of black coils hot-rolled by the Steckel rolling mill of stainless steel, process adjustment is carried out to achieve the purpose of improving the head and tail performance and increasing the yield rate.

[0006] The process of the present invention mainly adopts the following technical steps: Process flow: heating-rough rolling→finishing rolling→coiling→annealing→packaging and warehousing.

[0007] 1. Heating: The air-fuel ratio of the heating section is controlled between 2.00-2.20, the air-fuel ratio of the soaking section is controlled between 2.25-2.45, and the furnace pressure is controlled within the range of 7-10 Pa. The zone control of the air-fuel ratio of the heating section (heating section 2.00-2.20, soaking section 2.25-2.45) is coordinated with the furnace pressure to ensure the uniformity of the head and tail temperature of the slab; the setting of the coiling furnace temperature of 1150±5℃ is used to avoid the head and tail temperature drop caused by the contact between the strip and the mandrel.

[0008] 2. Rough rolling: Reduce the cooling water volume of the rough rolling rolls to 150±10m 3 / h to adjust the cooling to increase the temperature of the head and tail of the steel coil.

[0009] 3. Finishing rolling: Similarly, reduce the cooling water volume of the finishing rolling rolls to 120±10m 3 / h to adjust the cooling to increase the temperature of the head and tail of the steel coil.

[0010] 4. Water sealing: Replace the water sealing board to enhance the water sealing effect, and adjust the replacement cycle of the water sealing board from 7 days to 4 days.

[0011] 5. Coiling: The coiling furnace uses coke oven gas to provide high calorific value to increase the coiling temperature and control the temperature at 1150±5℃. No layer cooling is applied for the first 30m to the tail, raising the coiling temperature to 710±5℃. High-speed coiling is adopted, with a coiling speed of 6 meters / second.

[0012] 6. Cooling: When the steel coil is off the line, it is slowly cooled at a rate of 5℃ / hour. After the process parameters are adjusted, the hardness fluctuation within 30m from the head to the tail of the black coil is ≤10HV.

[0013] Beneficial effects of the present invention: 1. Adjust the air-fuel ratio of the heating section to between 2.00-2.20 and the air-fuel ratio of the soaking section to between 2.25-2.45 to increase the head and tail temperatures of the slab.

[0014] 2. Reduce the cooling water volume of roughing and finishing rolls. The cooling water volume of roughing rolls is 150±10m 3 / h, cooling water volume of finishing rolls: 120±10m 3 / h, increasing the surface temperature of the steel plate, especially the temperature of the head and tail parts can be increased by 20℃, improving the performance of the head and tail of the black roll.

[0015] 3. Adjust the replacement cycle of the water sealing plate from 7 days to 4 days to enhance the water sealing effect, increase the temperature of the head and tail of the strip, and improve the performance of the head and tail of the black coil.

[0016] 4. Raise the coiling furnace temperature to 1150±5℃, mainly to increase the coiling mandrel temperature and avoid the contact between the strip and the coiling mandrel, which will cause the head and tail temperatures to drop.

[0017] 5. No layer cooling for 30m between the head and tail, increasing the winding speed to 6m / s, can increase the head and tail temperature by 20℃, greatly alleviating the performance abnormality caused by the temperature difference between the head and tail. High-speed winding (6m / s) and no layer cooling for 30m between the head and tail can further reduce the temperature difference between the head and tail.

[0018] 6. When the steel coil is off the line, a slow cooling method is adopted, and the slow cooling rate is 5℃ / hour. By controlling the slow cooling rate, the rolling stress at the head and tail is eliminated and the structure of the head and tail is improved.

[0019] The present invention significantly improves the abnormal performance problem of the head and tail of the black coil by optimizing the heating, rolling, cooling and coiling process of the Steckel mill in producing stainless steel. The main beneficial effects include: 1. Improve temperature uniformity: optimize the air-fuel ratio (2.00-2.45) and furnace pressure (7-10Pa) of the heating section / soaking section to improve the head-to-tail temperature uniformity by 10-15°C; reduce the cooling water volume of rough rolling (150±10m³ / h) and finishing rolling (120±10m³ / h), increase the head-to-tail temperature by 20°C, and the hardness fluctuation is ≤10HV.

[0020] 2. Improve the yield rate and quality: Coiling temperature control (1150±5℃) and high-speed coiling (6m / s) reduce the temperature difference between the head and the tail, and increase the yield rate by 2%-5%; 3. Optimize organizational properties: The slow cooling process (5°C / hour) eliminates residual stress and refines grains; 1 million tons of mass production has been verified, and the head and tail performance qualification rate is ≥98%. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a comparison chart before and after optimization of the head and tail hardness. DETAILED DESCRIPTION

[0022] The present invention will be further described below through specific implementation modes. Example

[0023] 1. Heating phase Parameter settings: Air-fuel ratio in heating section: 2.00-2.20 (to ensure rapid heating); Air-fuel ratio in the equalizing section: 2.25-2.45 (to maintain temperature uniformity); Furnace pressure: 7-10Pa (reduce heat loss).

[0024] Effect: The temperature difference between the head and tail of the slab is reduced from ±35℃ to ±10℃.

[0025] 2. Rolling stage Rough rolling: cooling water volume 150±10m³ / h (originally 180m³ / h), head and tail temperatures increased by 10℃; Finishing rolling: cooling water volume 120±10m³ / h (original 150m³ / h), surface temperature uniformity improved by 15%.

[0026] 3. Coiling and cooling Coiler: Coke oven gas is used, the temperature is 1150±5℃, to avoid the mandrel absorbing heat; Layer cooling control: the layer cooling is closed at 30m from the head to the tail, and the coiling temperature is 710±5℃ (originally 690℃); Slow cooling process: After leaving the production line, slow cooling is performed at 5℃ / h to eliminate residual stress.

[0027] This process has been verified through continuous batch production of 1 million tons of stainless steel strip. The tail performance is good, the hardness difference between the head and tail is controlled within ±10HV, the yield rate is increased by 2.3%, the water sealing plate cycle is shortened to reduce downtime, the annual production capacity is increased by 15,000 tons, and the slow cooling process reduces the subsequent annealing energy consumption by 8%. 1 million tons of stainless steel strip has been produced continuously, and the head and tail performance qualification rate has been increased from 90% to 98%.

[0028] These measures cover heating, rolling, cooling and other links, with the goal of making the hardness of the head and tail more uniform. It is necessary to determine the best parameters and process control solutions based on actual production conditions and requirements, combined with tests and optimization. During the operation, please follow the relevant process specifications and operating guidelines, and it is recommended to cooperate with professionals.

Claims

1. A method for improving the performance of the head and tail of the black coil of the Steckel rolling mill, characterized in that: The following steps are involved: (1) Heating stage: The air-fuel ratio in the heating section is controlled at 2.00-2.20, the air-fuel ratio in the soaking section is controlled at 2.25-2.45, and the furnace pressure is controlled at 7-10Pa; (2) Rolling stage: The cooling water volume of the rough rolling rolls is adjusted to 150±10m³ / h, and the cooling water volume of the finishing rolling rolls is adjusted to 120±10m³ / h; (3) Coiling stage: The coiling furnace uses coke oven gas, the coiling temperature is controlled at 1150±5℃, no layer cooling is applied for 30m from the head to the tail, the coiling temperature is increased to 710±5℃, and the coiling speed is 6m / s; (4) Cooling stage: After the steel coil comes off the line, it is slowly cooled at a rate of 5℃ / h.

2. The method according to claim 1, characterized in that: By reducing the amount of cooling water in rough rolling and finishing rolling, the temperature of the head and tail of the steel coil can be increased by 20°C; the replacement cycle of the water sealing plate is shortened from 7 days to 4 days to enhance the water sealing effect.

3. The method according to claim 1 or 2, characterized in that: The zoned control of the air-fuel ratio in the heating section is coordinated with the furnace pressure to ensure the uniformity of the head and tail temperatures of the slab; the setting of the coiling furnace temperature of 1150±5°C is used to avoid the head and tail temperature drop caused by the contact between the strip and the mandrel.

4. The method according to any one of claims 1 to 3, characterized in that: The slow cooling rate of 5°C / h is used to eliminate rolling stress and refine the head and tail structures.

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