Production control method for reducing net-shaped cracks during hot-fed casting blank rolling of steel plate

Abstract

The invention relates to the technical field of metallurgy, in particular to a production control method for reducing net cracks in the process of rolling a steel plate by a red-fed casting blank, the steel plate production steps comprise the procedures of converter smelting, refining, continuous casting and rolling, and the specific operation comprises the following steps: (1) controlling the nitrogen content of molten steel in the converter smelting procedure; (2) controlling the content of acid-soluble aluminum in molten steel in a refining process; (3) in the molten steel pouring process of the continuous casting procedure, whole-process protection pouring is adopted, the pulling speed is controlled, and nitrogen content detection is conducted on molten steel in a tundish; and (4) performing a forced cooling mode on a bending section of a continuous casting machine in a continuous casting process, and controlling the surface temperature of a casting blank to be not more than 610 DEG C when the casting blank enters a steel rolling heating furnace. The compactness and uniformity of the casting blank can be improved, the fine grain proportion of the casting blank is increased, coarse grains are avoided, precipitation of nitrides and inclusions in a high-temperature two-phase region of the casting blank is reduced, and grain boundary cracking of a steel plate during steel rolling is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to a production control method for reducing web cracks occurring when hot-cast billets are rolled into steel plates. Background Art

[0002] Steel plate production generally includes converter smelting, refining, continuous casting, rolling, and post-processing processes. Among them, the hot rolling process of the ingot is a production process in which the high-temperature ingot produced by continuous casting is directly hot-sent to the steel rolling process for rolling. The use of the hot rolling process in the steel production process can greatly reduce energy consumption by heating the high-temperature ingot to the rolling temperature, which meets the development requirements of energy conservation and emission reduction; on the other hand, it reduces the time waste in the intermediate links, shortens the production cycle of the steel plate, and improves production efficiency.

[0003] In the prior art, the specific operation process of the hot-rolling rolling process is as follows: the high-temperature billet produced by the continuous casting machine is quickly transported to the steel rolling heating furnace workshop using special conveying equipment (such as a heat-insulating roller), and the conveying process is also called hot-rolling; then the steel rolling workshop adjusts the rolling process parameters according to the temperature and state of the billet to carry out efficient rolling. During the hot-rolling process, the surface temperature and conveying time of the billet must be strictly controlled to ensure that the billet remains within the appropriate high temperature range when entering the heating furnace.

[0004] However, in the hot rolling process of the ingot, the temperature of the ingot is high and the thermal stress inside the ingot is large. It is easily affected by multiple factors such as the composition, temperature and production process of the ingot, resulting in uneven composition or structure inside the ingot. Under the interaction of uneven composition or morphology with high temperature and high thermal stress, there is a high risk of network cracking defects. Summary of the invention

[0005] In view of the problem that in the hot-feeding and rolling process of the ingot, the temperature of the ingot is high and the thermal stress inside the ingot is large during the hot-feeding process, and the ingot is easily affected by various factors, resulting in uneven composition or organization inside the ingot, and a high risk of network cracking defects. The present invention provides a production method for reducing the occurrence of network cracks when rolling steel plates after the ingot is hot-feeded. The method can improve the density and uniformity of the ingot, increase the proportion of fine grains in the ingot, avoid coarse grains, reduce the precipitation of nitrides and inclusions in the high-temperature two-phase zone of the ingot, avoid the formation of grain boundary cracks in the steel plate during rolling, and reduce the risk of network cracks in the steel plate.

[0006] The technical solution of the present invention is: A production control method for reducing the occurrence of web cracks when rolling steel plates from hot-rolled billets, wherein the steel plate production steps include converter smelting, refining, continuous casting, and rolling processes, and the specific operations include: (1) Controlling nitrogen content in molten steel during converter smelting process; (2) Control the acid-soluble aluminum content in molten steel during the refining process; (3) The molten steel pouring process of the continuous casting process adopts full protection pouring, controls the casting speed, and tests the nitrogen content of the molten steel in the tundish; (4) The continuous casting process implements the strong cooling mode in the bending section of the continuous casting machine, and controls the surface temperature of the cast billet not to exceed 610℃ when it enters the steel rolling heating furnace.

[0007] Furthermore, in step (1), the nitrogen content in the molten steel is controlled to be ≤38ppm in the converter smelting process, and specific measures include not adding high-nitrogen scrap steel during the converter smelting process, and the high-nitrogen scrap steel includes steel bar briquettes.

[0008] Furthermore, in step (2), the acid-soluble aluminum content in the molten steel is controlled to be below 0.03% during the refining process.

[0009] Furthermore, in step (3), the head and tail billets of the continuous casting and the corresponding billets with a pulling speed fluctuation exceeding 0.3 m / min are taken off-line and cooled to room temperature. After these billets are trial-fired and confirmed to be free of crack defects, they are loaded into the steel rolling heating furnace for rolling.

[0010] Furthermore, in step (3), the method for detecting the nitrogen content includes spectral detection and / or gas detection. When the nitrogen content of the detected sample is higher than 38 ppm, the corresponding ingot is taken offline and cooled to room temperature. After the ingot is trial-fired and confirmed to be free of crack defects, it is loaded into the steel rolling heating furnace for rolling.

[0011] The head and tail billets, corresponding billets with a pulling speed fluctuation exceeding 0.3m / min, and billets with excessive nitrogen content are processed offline and trial-fired to ensure the quality of billets entering the rolling process. This helps reduce production interruptions and quality fluctuations caused by unqualified billets entering subsequent processes, and improves production stability and continuity.

[0012] Furthermore, step (3) further includes: when the continuous casting machine is shut down for more than 3 hours, the fan-shaped segment nozzle is inspected, and the fan-shaped segment nozzle is replaced when the nozzle is blocked or the spraying is poor. Timely maintenance of the nozzle can ensure uniform and stable cooling effect during the continuous casting process, and avoid defects in the casting caused by uneven cooling.

[0013] Furthermore, step (4) further includes providing a forced cooling device on the roller of the billet discharge area of ​​the continuous casting machine, and when the produced billet is a non-peritectic steel billet, using the forced cooling device to quickly cool the non-peritectic steel billet to reduce the surface temperature of the non-peritectic steel billet to below 480°C; when the produced billet is a peritectic steel billet, slowly cooling the peritectic steel billet off the line to ≤610°C on the roller of the billet discharge area.

[0014] Furthermore, step (4) also includes regularly calibrating the surface temperature measuring device of the ingot in front of the heating furnace, with the calibration cycle being at least once a week.

[0015] The beneficial effects of the present invention are: 1. The production control method for reducing the occurrence of network cracks when rolling steel plates from hot-rolled ingots provided by the present invention controls the nitrogen content in molten steel in the converter smelting process, which can reduce the adverse effects of nitrogen on the quality of steel, effectively improve the density and uniformity of the ingots, and reduce the precipitation of nitrides; controlling the acid-soluble aluminum content in the molten steel in the refining process helps to optimize the purity and fluidity of the molten steel, reduce the formation of inclusions, make the internal structure of the ingot more uniform, and reduce the risk of network cracks in the ingot.

[0016] 2. The present invention adopts full-process protective pouring and controlled pulling speed in the continuous casting process. Protective pouring can prevent secondary oxidation of molten steel and reduce the introduction of inclusions; stable pulling speed is conducive to uniform cooling and solidification of the ingot, avoiding uneven internal stress and quality problems caused by pulling speed fluctuations, ensuring the stable molding quality of the ingot and further reducing the risk of ingot network cracks.

[0017] 3. The present invention implements a strong cooling mode in the bending section of the continuous casting machine, and controls the surface temperature of the ingot to be no less than 610°C when entering the steel rolling heating furnace, which can increase the fine grain ratio of the ingot, avoid coarse grains, reduce the precipitation of nitrides and inclusions in the high-temperature two-phase zone of the ingot, avoid the formation of grain boundary cracks in the steel plate during steel rolling, and reduce the risk of network cracks in the steel plate. DETAILED DESCRIPTION

[0018] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0019] Example 1 A production control method for reducing web cracks when rolling steel plates from hot-rolled ingots is used to produce Q345qD peritectic steel. The steel plate production steps include converter smelting, refining, continuous casting, and rolling processes. The refining process is LF+RH refining. The mass percentages of the raw material components of the ingot are shown in Table 1, and the remainder is Fe and unavoidable impurities.

[0020] Table 1 Q345qD peritectic steel raw material composition

[0021] The specific operations are: (1) The nitrogen content in molten steel should be controlled to be ≤38ppm in the converter smelting process. Specific measures include not adding high-nitrogen scrap steel such as steel bars during the converter smelting process; (2) The refining process controls the acid-soluble aluminum content in the molten steel to 0.015%-0.03%; (3) The molten steel pouring process of the continuous casting process adopts full-process protection pouring, and the pulling speed is controlled. The head and tail billets of the continuous casting and the corresponding billets with a pulling speed fluctuation exceeding 0.3m / min are taken off the line and cooled to room temperature. After these billets are trial-fired and confirmed to have no crack defects, they are loaded into the steel rolling heating furnace for rolling; The nitrogen content of the molten steel in the tundish is tested. The methods of nitrogen content testing include spectrum detection and gas detection. When the nitrogen content of the test sample is higher than 38ppm, the corresponding ingot will be taken off-line and cooled to room temperature. After the ingot is trial-fired and confirmed to be free of cracks, it will be loaded into the steel rolling heating furnace for rolling. When the continuous casting machine is shut down for more than 3 hours, check the fan-shaped segment nozzles and replace the fan-shaped segment nozzles if there are problems such as nozzle blockage or poor spraying; (4) The continuous casting process implements the strong cooling mode in the bending section of the continuous casting machine, and the peritectic steel ingot is slowly cooled to ≤610℃ on the roller in the billet discharge area; The surface temperature measuring device of the ingot in front of the heating furnace should be calibrated regularly, at least once a week.

[0022] Example 2 A production control method for reducing web cracks when rolling steel plates from hot-cast billets is used to produce Q460C non-peritectic steel. The steel plate production steps include converter smelting, refining, continuous casting, and rolling processes, wherein the refining process is LF+RH refining. The mass percentages of the raw material components of the steel billet are shown in Table 1, and the remainder is Fe and unavoidable impurities.

[0023] Table 2 Q460C non-peritectic steel raw material composition

[0024] The specific operations are: (1) The nitrogen content in molten steel should be controlled to be ≤38ppm in the converter smelting process. Specific measures include not adding high-nitrogen scrap steel such as steel bars during the converter smelting process; (2) The refining process controls the acid-soluble aluminum content in the molten steel to 0.015%-0.03%; (3) The molten steel pouring process of the continuous casting process adopts full-process protection pouring, and the pulling speed is controlled. The head and tail billets of the continuous casting and the corresponding billets with a pulling speed fluctuation exceeding 0.3m / min are taken off the line and cooled to room temperature. After these billets are trial-fired and confirmed to have no crack defects, they are loaded into the steel rolling heating furnace for rolling; The nitrogen content of the molten steel in the tundish is tested. The methods of nitrogen content testing include spectrum detection and gas detection. When the nitrogen content of the test sample is higher than 38ppm, the corresponding ingot will be taken off-line and cooled to room temperature. After the ingot is trial-fired and confirmed to be free of cracks, it will be loaded into the steel rolling heating furnace for rolling. When the continuous casting machine is shut down for more than 3 hours, check the fan-shaped segment nozzles and replace the fan-shaped segment nozzles if there are problems such as nozzle blockage or poor spraying; (4) The continuous casting process implements a strong cooling mode in the bending section of the continuous casting machine, and a forced cooling device is set on the roller table of the billet discharge area of ​​the continuous casting machine. The forced cooling device is used to quickly cool the billet and reduce the surface temperature of the billet to below 480°C; The surface temperature measuring device of the ingot in front of the heating furnace should be calibrated regularly, at least once a week.

[0025] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and such modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily conceive of changes or substitutions within the technical scope disclosed by the present invention, and such changes or substitutions shall be within the scope of protection of the present invention.

Claims

1. A production control method for reducing the occurrence of web cracks when rolling steel plates from hot-cast billets, wherein the steel plate production steps include converter smelting, refining, continuous casting, and rolling processes, characterized in that: Specific operations include: (1) Controlling nitrogen content in molten steel during converter smelting process; (2) Control the acid-soluble aluminum content in molten steel during the refining process; (3) The molten steel pouring process of the continuous casting process adopts full protection pouring, controls the casting speed, and tests the nitrogen content of the molten steel in the tundish; (4) The continuous casting process implements the strong cooling mode in the bending section of the continuous casting machine, and controls the surface temperature of the cast billet not to exceed 610℃ when it enters the steel rolling heating furnace.

2. The production control method according to claim 1, characterized in that: Step (1) in the converter smelting process, the nitrogen content in the molten steel is controlled to be ≤38ppm. The specific measures include not adding high-nitrogen scrap steel during the converter smelting process, and the high-nitrogen scrap steel includes steel bar briquettes.

3. The production control method according to claim 1, characterized in that: Step (2) controls the acid-soluble aluminum content in the molten steel to below 0.03% during the refining process.

4. The production control method according to claim 1, characterized in that: In step (3), the head and tail billets of continuous casting and the corresponding billets with a pulling speed fluctuation exceeding 0.3 m / min are taken off-line and cooled to room temperature. After these billets are trial-fired and confirmed to be free of crack defects, they are loaded into the steel rolling heating furnace for rolling.

5. The production control method according to claim 1, characterized in that: In step (3), the method for detecting the nitrogen content includes spectral detection and / or gas detection. When the nitrogen content of the detected sample is higher than 38 ppm, the corresponding ingot is taken offline and cooled to room temperature. After the ingot is trial-fired and confirmed to be free of crack defects, it is loaded into the steel rolling heating furnace for rolling.

6. The production control method according to claim 1, characterized in that: Step (3) also includes: when the continuous casting machine is shut down for more than 3 hours, the fan-shaped segment nozzle is inspected, and the fan-shaped segment nozzle is replaced when the nozzle is blocked or the injection is poor.

7. The production control method according to claim 1, characterized in that: Step (4) further comprises providing a forced cooling device on the roller conveyor of the billet discharge zone of the continuous casting machine, and when the produced billet is a non-peritectic steel billet, using the forced cooling device to rapidly cool the non-peritectic steel billet, so as to reduce the surface temperature of the non-peritectic steel billet to below 480°C; when the produced billet is a peritectic steel billet, slowly cooling the peritectic steel billet off the line to ≤610°C on the roller conveyor of the billet discharge zone.

8. The production control method according to claim 1, characterized in that: Step (4) also includes regularly calibrating the surface temperature measuring device of the ingot in front of the heating furnace, with the calibration cycle being at least once a week.

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