A method for treating cold rolled strip for sticking in batch annealing

Abstract

The application discloses a method for treating cold-rolled strip steel sticking in a bell-type furnace annealing, and belongs to the technical field of bell-type furnace annealing. The cold-rolled strip steel sticking is put into a bell-type furnace for heat treatment, and after heat preservation for a period of time, the cold-rolled strip steel is cooled with a cover, and is taken out of the furnace after the temperature of the cold-rolled strip steel is reduced to a temperature at which the cold-rolled strip steel does not react with air, so that the cold-rolled strip steel sticking is separated. Before the method is used, at least 48-72 hours are needed for hoisting and transporting the cold-rolled strip steel after the cold-rolled strip steel is separated; after the method is used, the cold-rolled strip steel can be separated only after 24 hours or so, the time for treating the fault is obviously shortened, the fault of the cold-rolled strip steel sticking is quickly treated, the production efficiency is improved, and the stable operation of the unit and the product quality meeting the requirements are ensured.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of bell-type furnace annealing, and particularly relates to a method for treating cold-rolled strip steel sticking in bell-type furnace annealing. BACKGROUND

[0002] After cold-rolled strip steel is rolled, the internal organization of the steel is elongated, broken and increased in defects, the strength and hardness of the steel plate are increased, and the plasticity, toughness and stamping performance are greatly reduced, which is called work hardening. Work hardening brings further difficulties to the processing of the metal. In order to eliminate the internal stress and work hardening caused by cold rolling and make the steel plate have the required mechanical properties to ensure the quality requirements of the cold-rolled product, the cold-rolled strip steel needs to be recrystallized annealed. The cold-rolled strip steel can eliminate the work hardening and internal stress generated in the cold deformation process through a bell-type annealing furnace or a continuous annealing furnace. After adopting a full-hydrogen protective atmosphere technology, the mechanical properties and the uniformity of the metallographic structure of the product have been greatly improved. At the same time, due to the flexibility of the bell-type furnace in production organization, the bell-type annealing furnace still has certain advantages in the cold-rolled annealing production mode. However, for the bell-type furnace annealing form, since the steel coils are produced in a whole coil stacking mode, the steel coils are connected to the convection plates and stick together at the end of the annealing process, which causes the crane to be unable to lift the steel coils, and the steel coils can only be placed and then lifted after the temperature is reduced to a certain extent for the next process production. However, the cooling rate of the steel coil is very slow in the natural environment, which greatly reduces the production efficiency. Therefore, it is urgent to establish a method for treating cold-rolled strip steel sticking in bell-type furnace annealing, so that the stuck steel coils can be quickly separated to ensure the continuity of production and improve the production efficiency. SUMMARY

[0003] In view of this, the purpose of the present application is to provide a method for treating cold-rolled strip steel sticking in bell-type furnace annealing, which significantly shortens the treatment failure time and improves the production efficiency.

[0004] To achieve the above-mentioned purpose, the present application adopts the following technical scheme:

[0005] The present application provides a method for treating cold-rolled strip steel sticking in bell-type furnace annealing, which comprises the following steps: placing the cold-rolled steel coil with sticking into a bell-type furnace for heat treatment, cooling with a cover after a certain period of heat preservation, and taking out the furnace after the temperature of the cold-rolled strip steel coil is reduced to a level that does not cause oxidation reaction with air, so that the cold-rolled strip steel coil with sticking is separated.

[0006] Based on the above technical scheme, further, the medium in the bell-type furnace is hydrogen, the oxygen content in the hydrogen is <5ppm, the dew point is <-60℃, and the purity is >=99.999%.

[0007] Based on the above technical scheme, further, the steel grade of the cold-rolled strip steel coil is low carbon steel.

[0008] Based on the above technical scheme, further, the chemical elements and mass percentage of the low carbon steel are as follows: C≤0.1%, Si≤0.05%, Mn≤0.5%, P≤0.03%, S≤0.067%, the balance being Fe and unavoidable impurities.

[0009] Based on the above technical scheme, further, the holding temperature is calculated by formula (1),

[0010] T=23.262ln(w·d)+397.79 (1)

[0011] T is the holding temperature;

[0012] w is the maximum width of the coil in the same furnace;

[0013] d is the maximum thickness of the coil in the same furnace.

[0014] Based on the above technical scheme, further, the holding time is calculated by formula (2),

[0015] t=1.6226ln(w·d)-7.2892 (2)

[0016] t is the holding time;

[0017] w is the maximum width of the coil in the same furnace;

[0018] d is the maximum thickness of the coil in the same furnace.

[0019] Based on the above technical scheme, further, the holding temperature is 540-610℃, and the holding time is 3-7 hours.

[0020] Based on the above technical scheme, further, the heating speed is controlled at 30-50℃ / h.

[0021] Based on the above technical scheme, further, when the coil is cooled to below 500℃, a fast cooling cover is used for shunt rapid cooling or a fast cooling cover is used for water spray cooling, and the cooling speed is controlled at 10-30℃ / h.

[0022] Based on the above technical scheme, further, the discharge temperature is controlled at 30-160℃.

[0023] The present application has the following beneficial effects relative to the prior art:

[0024] This invention establishes a method for handling low-carbon steel coil adhesion. Before using this method, it would take at least 48-72 hours for the steel coils to separate and be fully hoisted after adhesion. With this method, the steel coils can be separated in about 24 hours, significantly shortening the troubleshooting time, enabling rapid handling of coil adhesion problems, improving production efficiency, ensuring stable unit operation, and meeting product quality requirements. Detailed Implementation

[0025] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.

[0026] Example 1

[0027] This embodiment provides a method for handling the sticking of cold-rolled strip steel coils during bell-type furnace annealing. The chemical elements and mass percentages of the cold-rolled strip steel are as follows: C≤0.1%, Si≤0.05%, Mn≤0.5%, P≤0.03%, S≤0.067%, with the balance being Fe and unavoidable impurities. The specific process is as follows: The sticking cold-rolled strip steel coils are placed in a bell-type furnace for heat treatment. After holding at that temperature for a period of time, the furnace is cooled under the hood. Once the temperature of the cold-rolled strip steel coils has decreased to a level where they no longer oxidize with air, they are removed from the furnace, thus separating the sticking cold-rolled strip steel coils. The medium in the bell-type furnace is hydrogen gas with an oxygen content <5ppm, a dew point <-60℃, and a purity ≥99.999%. To ensure that product performance is not affected and to separate the sticking steel coils as quickly as possible, thereby improving production efficiency, the process is optimized in the following aspects.

[0028] Determining the heating rate: The heating rate of steel is mainly determined by its thermal conductivity. The steel's composition is the primary consideration when determining the heating rate. The chemical composition of steel, particularly carbon content and alloy content, significantly affects thermal conductivity. Higher carbon and alloy content result in lower thermal conductivity, requiring a slower heating rate to avoid excessive internal and external temperature differences that could lead to uneven microstructure and properties. Therefore, the heating rate is controlled at 30–50 °C / h.

[0029] Determination of holding temperature and holding time: The recrystallization temperature of steel is not a fixed temperature, but is related to the internal microstructure of the strip. The greater the amount of processing deformation, the more severe the phenomenon of grain elongation and crushing, and the greater the internal energy of the strip. Recrystallization can then be carried out at a lower temperature. The holding temperature and holding time also depend on the steel grade and the thickness of the strip. Combined with the on-site equipment, the holding temperature is set to 540-610℃ and the holding time is set to 3-7 hours.

[0030] Determining the cooling rate: The cooling rate should be as fast as possible, because a faster cooling rate improves the efficiency of the furnace platform and allows for adjustments to the platform-to-hood ratio without affecting the properties of certain steel grades. For steel grades with special performance requirements, slow cooling is necessary to prevent performance degradation. When the strip coil is cooled to below 500℃, the cooling rate should be increased as much as possible. Since the bell-type furnace uses a rapid cooling hood with diversion cooling or a rapid cooling hood with a water spray cooling device, the cooling rate is controlled at 10–30℃ / h.

[0031] Determination of tapping temperature: The main basis is that the strip coil does not oxidize when it exits the furnace and is exposed to air. Considering the utilization efficiency and output of the furnace platform, the tapping temperature is controlled at 30-160℃.

[0032] Table 1. Characteristics and Processing Parameters of the Steel Coil to be Processed

[0033]

[0034]

[0035] The processing is directly related to the heat treatment temperature, heat treatment time, and product specifications. Therefore, by establishing models relating the heat treatment process parameters, such as heat treatment temperature and time, to product specifications, and calculating the optimal heat treatment process parameters based on the product's width and thickness, intelligent and rapid handling of sticking / coiling faults can be achieved. The relationships are as follows:

[0036] T = 23.262ln(w·d(+397.79 (1))

[0037] T—Insulation temperature;

[0038] w—Maximum width of the steel coil in the same furnace;

[0039] d—Maximum thickness of the steel coil in the same furnace;

[0040] t=1.6226ln(w·d)-7.2892 (2)

[0041] t—Insulation time;

[0042] w—Maximum width of the steel coil in the same furnace;

[0043] d—Maximum thickness of the steel coil in the same furnace;

[0044] The heat treatment temperature and time are positively correlated with the product thickness and width. By determining the maximum thickness and width of the steel coils in the same furnace, the optimal heat treatment parameters can be matched to quickly resolve coil sticking issues. Using this intelligent method, coil sticking problems can be resolved quickly, improving production efficiency and ensuring stable unit operation and product quality that meets requirements.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for treating the sticking and coiling of cold-rolled strip steel during bell-type furnace annealing, characterized in that, Includes the following steps: The cold-rolled strip coils that have become stuck together are placed in a bell-type furnace for heat treatment. After being held at a certain temperature for a period of time, they are cooled with a bell. Once the temperature of the cold-rolled strip coils has dropped to a level where they no longer oxidize with air, they are taken out of the furnace, thus separating the stuck cold-rolled strip coils. The cold-rolled strip steel coil is made of low-carbon steel; the chemical elements and mass percentages of the low-carbon steel are as follows: C≤0.1%, Si≤0.05%, Mn≤0.5%, P≤0.03%, S≤0.067%, with the balance being Fe and unavoidable impurities; The insulation temperature is 540~610℃, and the insulation time is 3~7 hours.

2. The method according to claim 1, characterized in that, The medium in the bell-type furnace is hydrogen, with an oxygen content of <5ppm, a dew point of <-60℃, and a purity of ≥99.999%.

3. The method according to claim 1, characterized in that, The heating rate is controlled at 30~50℃ / h.

4. The method according to claim 1, characterized in that, When the steel coil is cooled to below 500℃, a rapid cooling hood with diversion cooling or a rapid cooling hood with water spray cooling is used, and the cooling rate is controlled at 10~30℃ / h.

5. The method according to claim 1, characterized in that, The oven temperature should be controlled between 30 and 160℃.

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