A method for improving the head and tail performance of black coils in a hot rolling mill

Abstract

This invention discloses a method for improving the head and tail performance of stainless steel black coils produced by a hot rolling mill, belonging to the field of stainless steel hot rolling processing technology. By optimizing the heating air-fuel ratio (2.00-2.20 in the heating section and 2.25-2.45 in the soaking section), reducing the cooling water volume in the roughing / finishing mills (150±10 m³ / h and 120±10 m³ / h respectively), shortening the water seal plate replacement cycle to 4 days, using high-temperature coiling with coke oven gas (1150±5℃), and prohibiting 30m of layer cooling at the head and tail, the temperature uniformity at the head and tail is significantly improved. Through these adjustments to process parameters, this invention effectively solves the problem of abnormal head and tail performance of black coils, thereby improving head and tail performance and yield. This method results in stainless steel produced by a hot rolling mill having better performance and quality.

Description

Technical Field

[0001] This invention belongs to the field of stainless steel hot working, specifically relating to a method for improving the abnormal head and tail performance of hot-rolled black coils by optimizing the process parameters of the hot-rolled coil mill, applicable to the production of stainless steel strip. Background Technology

[0002] Abnormal performance at the beginning and end of hot-rolled black coils refers to the fact that during the hot rolling process, the sheet undergoes multiple stages, including high-temperature heating, deformation, and cooling, each affecting the sheet's microstructure and properties. The beginning and end of the coil are typically in 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 beginning and end (within 0-30 meters) and the normal parts. These differences in hardness at the beginning and end of the hot-rolled coil can lead to uneven product performance, finished product quality problems, and difficulties in subsequent processing.

[0003] The beginning and end sections (0-30 meters) of hot-rolled stainless steel black coils often exhibit hardness differences (above ±15HB) due to uneven heating, rolling, and cooling conditions, leading to difficulties in subsequent processing (such as cold rolling fracture) and a decrease in yield. Traditional methods, such as adjusting the cooling water volume of the rolls or using a layer cooling process, have failed to systematically solve the problems of rapid temperature drop and uneven microstructure at the beginning and end sections.

[0004] The existing technology has the following drawbacks:

[0005] The air-fuel ratio control of the heating furnace is not zoned, resulting in uneven heating at the beginning and end; the cooling water volume of the roughing / finishing mill is too high (180m³ / h for conventional roughing mill and 150m³ / h for finishing mill), which aggravates the temperature drop at the beginning and end; the coiling temperature fluctuates greatly (±20℃), and the contact of the mandrel leads to heat loss at the beginning and end. Summary of the Invention

[0006] The purpose of this invention is to provide a method for improving the head and tail performance of hot-rolled black coils in a hot-rolled stainless steel mill. By adjusting the process to address the abnormal head and tail performance of hot-rolled black coils in a hot-rolled stainless steel mill, the invention aims to improve the head and tail performance and increase the yield.

[0007] The process of this invention mainly adopts the following technical steps:

[0008] Process flow: heating - rough rolling → finish rolling → coiling → annealing → packaging and warehousing.

[0009] 1. Heating: The air-fuel ratio in the heating section is controlled between 2.00 and 2.20, and the air-fuel ratio in the soaking section is controlled between 2.25 and 2.45, while the furnace pressure is controlled within the range of 7-10 Pa. The zoned control of the air-fuel ratio in the heating section (2.00-2.20 in the heating section and 2.25-2.45 in the soaking section) is coordinated with the furnace pressure to ensure the uniformity of the slab temperature at both ends; the setting of the coiling furnace temperature at 1150±5℃ is used to avoid temperature drop at both ends caused by contact between the strip and the mandrel.

[0010] 2. Roughing: Reduce the cooling water volume of the roughing rolls to 150±10m. 3 Cooling adjustments are made within a range of / h to increase the temperature at the beginning and end of the steel coil.

[0011] 3. Finishing Roll: Similarly, reduce the cooling water volume of the finishing rolls to 120±10m. 3 Cooling adjustments are made within a range of / h to increase the temperature at the beginning and end of the steel coil.

[0012] 4. Water sealing: Replace the water sealing plate to enhance the water sealing effect, and adjust the water sealing plate replacement cycle from 7 days to 4 days.

[0013] 5. Coiling: The coiling furnace uses coke oven gas to provide high calorific value, thereby increasing the coiling temperature and controlling it at 1150±5℃. No cooling is applied to the first and last 30m sections, raising the coiling temperature to 710±5℃. A high-speed coiling method is used, with a coiling speed of 6 meters per second.

[0014] 6. Cooling: When the steel coil comes off the production line, a slow cooling method is adopted, with a cooling rate of 5℃ / hour. After adjusting the process parameters, the hardness fluctuation within a 30m range between the beginning and end of the black coil is ≤10HV.

[0015] The beneficial effects of this invention are:

[0016] 1. Adjust the air-fuel ratio of the heating section to be between 2.00 and 2.20, and the air-fuel ratio of the soaking section to be between 2.25 and 2.45, to increase the temperature of the slab head and tail.

[0017] 2. Reduce the cooling water volume of the roughing and finishing mill rolls; the cooling water volume of the roughing mill rolls should be 150±10m³. 3 / h, Cooling water volume for finishing mill rolls: 120±10m 3 / h, increasing the surface temperature of the steel plate, especially the temperature of the beginning and end parts, can increase by 20℃, thus improving the performance of the beginning and end parts of the black coil.

[0018] 3. The replacement cycle of the water sealing plate was adjusted from 7 days to 4 days to enhance the water sealing effect, increase the temperature of the strip head and tail, and improve the performance of the black coil head and tail.

[0019] 4. Increasing the coiling furnace temperature to 1150±5℃ is mainly to increase the temperature of the coiling mandrel and prevent the strip from contacting the coiling mandrel, which would cause the head and tail temperatures to drop.

[0020] 5. Without initial cooling for the first and last 30 meters, increasing the winding speed to 6 meters per second can raise the temperature at the beginning and end by 20°C, significantly mitigating performance abnormalities caused by temperature differences between the beginning and end. The combination of high-speed winding (6 meters per second) and no initial cooling for the first and last 30 meters further reduces the temperature difference between the beginning and end.

[0021] 6. When the steel coil is unloaded from the production line, a slow cooling method is adopted, with a slow cooling rate of 5℃ / hour. By controlling the slow cooling rate, the rolling stress at the beginning and end is eliminated and the microstructure at the beginning and end is improved.

[0022] This invention significantly improves the abnormal performance of the beginning and end of stainless steel coils by optimizing the heating, rolling, cooling, and coiling processes of the hot-roll mill. The main beneficial effects include:

[0023] 1. Improve temperature uniformity: Optimize the air-fuel ratio (2.00-2.45) and furnace pressure (7-10Pa) in the heating / soaking section to improve the temperature uniformity of the beginning and end by 10-15℃; reduce the cooling water volume of the roughing (150±10m³ / h) and finishing (120±10m³ / h) rolling mills to increase the temperature of the beginning and end by 20℃ and reduce the hardness fluctuation to ≤10HV.

[0024] 2. Improve yield and quality: Winding temperature control (1150±5℃) and high-speed winding (6 m / s) reduce the temperature difference between the beginning and end, increasing the yield by 2%-5%;

[0025] 3. Optimize microstructure and properties: Slow cooling process (5℃ / hour) eliminates residual stress and refines grains; mass production has been verified at 1 million tons, with a head and tail performance qualification rate of ≥98%. Attached Figure Description

[0026] Figure 1 Comparison images before and after optimizing the head and tail hardness. Detailed Implementation

[0027] The present invention will be further described below through specific embodiments. Example

[0028] 1. Heating stage

[0029] Parameter settings:

[0030] Air-fuel ratio in the heating section: 2.00-2.20 (to ensure rapid heating);

[0031] Air-fuel ratio in the soaking zone: 2.25-2.45 (to maintain temperature uniformity);

[0032] Furnace pressure: 7-10 Pa (to reduce heat loss).

[0033] Effect: The temperature difference between the beginning and end of the slab decreased from ±35℃ to ±10℃.

[0034] 2. Rolling stage

[0035] Rough rolling: Cooling water volume 150±10m³ / h (original 180m³ / h), head and tail temperatures increased by 10℃;

[0036] Finishing rolling: Cooling water volume 120±10m³ / h (originally 150m³ / h), surface temperature uniformity improved by 15%.

[0037] 3. Winding and Cooling

[0038] Coiling furnace: uses coke oven gas at a temperature of 1150±5℃ to avoid heat absorption by the mandrel;

[0039] Laminar cooling control: Laminar cooling is turned off for the first and last 30m, and the winding temperature is 710±5℃ (originally 690℃).

[0040] Slow cooling process: After the product is taken off the production line, it is slowly cooled at 5℃ / h to eliminate residual stress.

[0041] The process has been validated through continuous batch production of 1 million tons of stainless steel strip. The tail performance is good, the difference in hardness 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, the slow cooling process reduces the energy consumption of subsequent annealing by 8%, and it has been continuously produced for 1 million tons of stainless steel strip. The head and tail performance qualification rate has increased from 90% to 98%.

[0042] These measures cover multiple stages, including heating, rolling, and cooling, with the goal of achieving more uniform hardness across the beginning and end sections. The optimal parameters and process control scheme need to be determined through experimentation and optimization, based on actual production conditions and requirements. During operation, please follow relevant process specifications and operating guidelines, and collaboration with professionals is recommended.

Claims

1. A method for improving the head and tail performance of black coils in a hot rolling mill, characterized in that, Includes the following steps: (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 7-10 Pa; (2) Rolling stage: The cooling water volume of the roughing rolls is adjusted to 150±10m³ / h, and the cooling water volume of the finishing 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℃, the first and last 30m are not cooled, 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 production line, it is cooled slowly at a rate of 5℃ / h; By reducing the amount of cooling water in the roughing and finishing rolling processes, the temperature at the beginning and end of the steel coil is increased by 20°C; the replacement cycle of the sealing plate is shortened from 7 days to 4 days to enhance the sealing effect.

2. The method according to claim 1, characterized in that: The zoned control of the air-fuel ratio during the heating stage, in conjunction with the coordinated adjustment of the furnace pressure, ensures the uniformity of the slab temperature at both ends. The setting of the coiling furnace temperature at 1150±5℃ is used to avoid temperature drop at both ends caused by contact between the strip and the mandrel.

3. The method according to claim 1 or 2, characterized in that: A slow cooling rate of 5℃ / h is used to eliminate rolling stress and refine the head and tail structure.

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