A method for on-line regulation and control of surface crack inhibition based on casting blank structure

Abstract

The application discloses a method for online regulation and control of surface crack inhibition based on casting blank structure, which comprises the following steps: establishing a continuous cooling transformation database of steel; and establishing a casting blank structure regulation and control system from the horizontal section of continuous casting to the furnace mouth, and regulating and controlling the casting blank structure based on cooling process control. The application has the beneficial effects that: the surface layer structure of the casting blank is adjusted through cooling process control at the horizontal section of the continuous casting, on the one hand, the continuous cooling transformation database of the steel is established to provide accurate data for the structure regulation and control based on the temperature system; on the other hand, the starting temperature and the ending temperature are called in real time from the established continuous cooling transformation database of the steel according to the continuous casting steel grade, and the cooling speed in the regulation and control process is dynamically calculated according to the steel structure requirement and the real-time temperature of the casting blank, so that the regulation and control for different steel grades and target structures are more accurate; and the surface structure of the casting blank is regulated and controlled, and automatic control is completely adopted, so that the advantages of accuracy, high efficiency and convenience are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of iron and steel metallurgy, and in particular to a method for suppressing surface cracks based on online regulation of ingot structure. Background Art

[0002] The global warming problem caused by excessive greenhouse gas emissions resulting from carbon dioxide emissions has become an indisputable fact. Currently, developing a low-carbon economy and achieving energy conservation and emission reduction have become major trends in the international community's sustainable development. China's steel industry accounts for approximately 16% of the nation's total carbon emissions, making low-carbon development in the steel industry of great significance. In the steel production process, most ingots are first cooled off the production line before being heated in a reheating furnace to approximately 1200°C for rolling. Reheating furnaces typically use a mixture of blast furnace gas, converter gas, or coke oven gas for heating, consuming significant energy and resulting in significant carbon emissions. Hot charging and hot delivery allows continuous casting ingots to be fed directly into the reheating furnace without cooling off the production line. By utilizing the waste heat of the ingots and eliminating the need for off-line cooling, hot charging and hot delivery improves production efficiency, reduces energy consumption, and reduces carbon emissions. However, the difficulty with hot charging and hot delivery lies in the fact that improper hot charging procedures can lead to the formation of abnormal microstructures and surface cracks in the ingots, increasing scrap rates and reducing economic benefits.

[0003] Patent CN202310632573.5 discloses an online quenching method for improving hot-feed cracking during the continuous casting billet charging process. It uses the end temperature A1 of the transformation from austenite to ferrite, pearlite or bainite as the basic basis for process design. The shortcomings of this method are, on the one hand, that its transformation temperature is calculated by an empirical formula using the composition of steel, and the influence of cooling rate is not considered. However, continuous casting of steel is a cooling process, and the cooling rate has a great influence on the transformation temperature; on the other hand, it does not specify a method for automatically detecting and controlling the temperature of the billet; on the other hand, patent CN202210914994.2 is a hot-feeding and hot-charging production method for micro-alloyed low-alloy structural steel. It simply divides the hot-charging temperature into 400-650°C or 800-900°C or 400-900°C according to the Nb and Ti content in the steel. On the one hand, it does not consider the influence of cooling rate on the precipitation of carbonitrides, and on the other hand, it does not specify how to achieve online control of this classification temperature.

[0004] In summary, how to suppress surface cracks through online regulation of ingot structure and achieve precise hot charging and hot delivery of ingots while meeting the requirements of high efficiency, high quality, low cost and low carbon emission production is of great importance to the green and sustainable development of the steel industry. Summary of the Invention

[0005] The purpose of the present invention is to address the deficiencies and defects in the prior art and provide a method for suppressing surface cracks based on online regulation of the ingot structure. The present invention provides a method for suppressing surface cracks based on online regulation of the ingot structure. At the end of continuous casting, the surface structure of the ingot is adjusted by controlling the cooling process in the horizontal section of the ingot. On the one hand, a continuous cooling transformation database of steel is established to provide accurate data for the structure regulation based on the temperature system; on the other hand, according to the type of continuously cast steel, the start temperature and the end temperature are regulated in real time from the established continuous cooling transformation database of steel. The cooling rate in the regulation process is dynamically calculated according to the structure requirements of the steel and the real-time temperature of the ingot, and the regulation for different steel types and target structures is more accurate; not only the surface structure of the ingot is regulated, but also the structure within 20 mm below the skin is regulated considering the surface burn of the ingot in the heating furnace, thereby avoiding the generation of surface cracks during hot delivery and hot loading. It is fully automatically controlled and has the advantages of accuracy, efficiency and convenience.

[0006] To achieve the above-mentioned purpose, the present invention adopts the following technical solution: a method for suppressing surface cracks based on online regulation of ingot structure, comprising the following steps: establishing a continuous cooling transformation database of steel; establishing an ingot structure regulation system from the beginning of the continuous casting horizontal section to the heating furnace mouth, and regulating the ingot structure based on cooling process control.

[0007] Furthermore, the steel used for continuous cooling transformation in the steel continuous cooling transformation database is obtained by cutting continuous casting billets with qualified composition and quality in the direction of drawing speed.

[0008] Furthermore, the continuous cooling transformation parameters of the steel in the continuous cooling transformation database for steel are obtained by analyzing the relationship between temperature and expansion of the steel using a thermal simulator.

[0009] Furthermore, the thermal simulator can be a Gleeble thermal / mechanical simulation tester, a high-temperature rapid quenching and deformation phase change instrument, or other device that can control the cooling rate and continuously measure the temperature and expansion amount.

[0010] Furthermore, in the steel continuous cooling transformation database, the relationship between the steel temperature and the steel expansion determined at different cooling rates is used to determine the steel type, cooling rate, and different phase transformation start and end temperature parameters.

[0011] Furthermore, in the establishment of the continuous cooling transformation database of steel, a database of the determined parameters is established based on a computer language such as SQL.

[0012] Furthermore, the slab structure control system from the horizontal section of continuous casting to the heating furnace mouth is established, and the slab structure control system is composed of a temperature control system, a spraying system, and a slab transportation system for controlling the slab structure based on the cooling process control.

[0013] The temperature control system is established based on the mathematical model of solidification heat transfer of the slab. The initial condition of the model is the temperature of the slab at the beginning of the horizontal section called by the secondary cooling system.

[0014] The spraying system mainly consists of multiple rows of nozzles arranged perpendicular to the throwing direction and a spraying water control system, where the nozzles can be opened row by row according to spraying needs.

[0015] Furthermore, the temperature control system calls relevant parameters in the continuous cooling transformation database for different steel grades, combines the target temperatures for the start and end of the billet spraying required for the target structure control calculated by the temperature control system, and reversely calculates the spraying water volume and spraying time of the spraying device when the cooling rate required for the target structure control within 10mm of the billet surface is achieved.

[0016] Furthermore, the spraying time in the temperature control system is preferentially adjusted by automatically adjusting the number of rows of nozzles used for spraying. When the adjustment of the number of rows of nozzles cannot meet the requirements, the spraying time is adjusted by the billet running speed of the billet transportation system.

[0017] After adopting the above technical scheme, the beneficial effects of the present invention are as follows: the present invention provides a method for suppressing surface cracks based on online regulation of the ingot structure, and adjusts the surface structure of the ingot by controlling the cooling process at the end of continuous casting in the horizontal section of the ingot. On the one hand, the established continuous cooling transformation database of steel provides accurate data for the structure regulation based on the temperature system; on the other hand, according to the type of continuous casting steel, the start temperature and the end temperature are regulated in real time from the established continuous cooling transformation database of steel, and the cooling rate in the regulation process is dynamically calculated according to the structure requirements of the steel and the real-time temperature of the ingot, so that the regulation for different steel types and target structures is more accurate; not only the surface structure of the ingot is regulated, but also the structure within 20 mm below the skin is regulated considering the surface burn of the ingot in the heating furnace, thereby avoiding the generation of surface cracks during hot delivery and hot loading, and it is fully automatically controlled, with the advantages of accuracy, efficiency and convenience. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 This is the surface structure of the ingot in Example 1 of the present invention.

[0020] Figure 2 This is the surface structure of the ingot in Example 2 of the present invention. DETAILED DESCRIPTION

[0021] The technical solution adopted in this specific embodiment is: comprising the following steps:

[0022] S1. Establish a database of continuous cooling transformation of steel;

[0023] S2. Establish a system for regulating the structure of the slab from the horizontal section of continuous casting to the heating furnace mouth, and regulate the structure of the slab based on the cooling process control.

[0024] As a more specific explanation of the present invention, the steel used for continuous cooling transformation in S1 is obtained by intercepting a continuous casting billet with qualified composition and quality in the direction of pulling speed, and the continuous cooling transformation parameters of the steel are obtained by analyzing the relationship between temperature and expansion of the steel with a thermal simulator (the thermal simulator can be a Gleeble thermal / mechanical simulation testing machine, a high-temperature rapid quenching and deformation phase transformer, etc., which can control the cooling rate and continuously measure the temperature and expansion).

[0025] As a more specific description of the present invention, S1 determines the steel type, cooling rate, and the start and end temperature parameters of different phase changes based on the relationship between the temperature of the steel determined at different cooling rates and the expansion of the steel, and establishes a database of the determined parameters based on computer languages ​​such as SQL.

[0026] As a more specific description of the present invention, the slab structure control system in S2 is composed of a temperature control system, a spraying system, and a slab transportation system:

[0027] The temperature control system is established based on the mathematical model of solidification heat transfer of the slab. The initial condition of the model is the temperature of the slab at the beginning of the horizontal section called by the secondary cooling system.

[0028] The spraying system mainly consists of multiple rows of nozzles arranged perpendicular to the throwing direction and a spraying water control system, where the nozzles can be opened row by row according to spraying needs.

[0029] As a more specific explanation of the present invention, the temperature control system calls the relevant parameters in the continuous cooling transformation database for different steel grades, combines the target temperatures for the start and end of the billet spraying required for the target structure control calculated by the temperature control system, and reversely calculates the spraying water volume and spraying time of the spraying device when the cooling rate required for the target structure control within 10 mm of the billet surface is reached.

[0030] As a more specific description of the present invention, the spraying time in the temperature control system is preferably adjusted by automatically adjusting the number of rows of nozzles used for spraying. When the adjustment of the number of rows of nozzles cannot meet the requirements, it is adjusted by the billet running speed of the billet transportation system.

[0031] The working principle of the present invention is as follows: during the process of transporting the billet from the casting machine to the heating furnace, the cooling process of the billet is regulated by spraying water, thereby regulating the surface structure of the billet and achieving control of surface cracks. The principle of online regulation of the billet structure to suppress surface cracks in the present invention is as follows: during the cooling process of the billet after continuous casting, the structure undergoes a series of transformations with temperature changes. The structure and precipitation phase of the billet are different at different hot charging temperatures. When the billet charging temperature is higher than the Ar3 temperature, the billet structure does not undergo γ-α phase transformation and remains high-temperature coarse austenite grains; when the billet charging temperature is lower than the A At the r3 temperature, austenite undergoes ferrite transformation and is in the two-phase region. Film-like ferrite forms at the austenite grain boundaries. After heating in the furnace, the proeutectoid ferrite does not completely transform into austenite, and proeutectoid ferrite films are still retained at the grain boundaries, reducing the thermoplasticity of the steel. When subjected to external forces, cracks are easily caused. When the billet charging temperature drops below the Ar1 temperature, the austenite has completely transformed into ferrite and pearlite. After heating in the heating furnace, it transforms into finer austenite grains, forming fine grain strengthening and inhibiting the formation of cracks. It can be seen that effective control of cracks lies in precise control of the organization through precise temperature control.

[0032] The technical solution of the present invention is further described below with reference to specific embodiments:

[0033] Example 1

[0034] See Figure 1 As shown, a method for suppressing surface cracks based on online regulation of ingot structure includes the following steps:

[0035] S1. Establishment of a continuous cooling transformation database for steel

[0036] Q355B steel was used as raw material, with the composition of C≤0.24wt%, Si≤0.55wt%, Mn≤1.60wt%, P≤0.035wt%, S≤0.035wt%, and the balance being Fe. Samples with a diameter of 3mm and a length of 10mm for continuous cooling transformation were cut along the drawing direction of the continuous casting billet. The start and end temperature parameters of the phase transformation at different cooling rates were continuously measured by high-temperature rapid quenching and deformation phase transformer instrument to establish a continuous cooling transformation parameter database.

[0037] S2. Establish a system for regulating the structure of the slab from the horizontal section of continuous casting to the heating furnace mouth, and regulate the structure of the slab based on the cooling process control.

[0038] When the casting speed is 1.1m / min, the surface temperature of the Q355B continuous casting ingot at the beginning of the horizontal section is 975℃, and the temperature control system calculates that the spraying start temperature when entering the spraying section is 758℃. The relevant parameters of Q355B in the continuous cooling transformation parameter database are called. When the cooling rate is 2℃ / s, the temperature at the end of spraying is not higher than 600℃. When there is no ferrite precipitation within 10mm of the surface of the ingot, the spraying water volume of the spraying device is not less than 40m3 / h and the spraying time is not less than 90s. Combined with the casting speed calculation, it is determined that the length of the open nozzle is not less than 1.65m. The calculated spraying water volume, spraying time and open nozzle length are fed back to the spraying system to realize the control of the spraying. The temperature before entering the heating furnace after the spraying is 645℃. Figure 1 This is the surface structure of the ingot in the embodiment of the present invention. It can be seen that the grain boundary film-like proeutectoid ferrite has been basically eliminated.

[0039] Example 2

[0040] See Figure 2 As shown, a method for suppressing surface cracks without online regulation of the ingot structure comprises the following steps:

[0041] S1. Establishment of a continuous cooling transformation database for steel

[0042] The comparative example does not adjust the solidification structure, so there is no need to establish a continuous cooling transformation database for Q355B steel (composition: C≤0.24wt%, Si≤0.55wt%, Mn≤1.60wt%, P≤0.035wt%, S≤0.035wt%, and the balance is Fe).

[0043] S2. Establish a system for regulating the structure of the ingot from the horizontal section of continuous casting to the heating furnace mouth, and use traditional methods for cooling without specifically regulating the structure of the ingot through cooling process control.

[0044] When the casting speed is 1.1m / min, the surface temperature of the Q355B continuous casting horizontal section started by the secondary cooling system is 994℃. The temperature when entering the spray section is calculated by the temperature control system to be 767℃. The spray system is not started after entering the spray section, and the temperature before entering the heating furnace is 658℃. Figure 2 This is the surface structure of the ingot in the comparative example of the present invention, in which a large amount of proeutectoid ferrite can be seen.

[0045] The main difference in structure between Example 1 and Example 2 of the present invention is proeutectoid ferrite. The generation and existence of proeutectoid ferrite will reduce the thermoplasticity of steel and increase crack sensitivity. In the embodiment, due to the combination of the established continuous cooling transformation database, a cooling system for controlling the precipitation of proeutectoid ferrite is obtained, and then the structure of the ingot is regulated through cooling process control, thereby suppressing the precipitation of proeutectoid ferrite and suppressing the generation of cracks in the ingot. The present invention regulates the structure of the ingot to suppress the generation of cracks through online automatic control, without the need for ingot offline cooling, thereby improving production efficiency and ingot quality, reducing production costs, being simple and easy to implement, and having obvious effects.

[0046] The above description is only used to illustrate the technical solution of the present invention and is not intended to limit it. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in this field should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for suppressing surface cracks based on online regulation of ingot structure, characterized by: The steps include: S1. Establish a database of continuous cooling transformation of steel; S2. Establish a system for controlling the structure of the slab from the horizontal section of continuous casting to the heating furnace mouth, and control the structure of the slab based on the cooling process control; In said S1, based on the relationship between the temperature of the steel determined at different cooling rates and the expansion of the steel, the steel type, cooling rate, and different phase transformation start and end temperature parameters are determined; The slab structure control system in S2 is composed of a temperature control system, a spraying system, and a slab transportation system: The temperature control system is established based on the mathematical model of solidification heat transfer of the slab. The initial condition of the model is the temperature of the slab at the beginning of the horizontal section called by the secondary cooling system. The spraying system mainly consists of multiple rows of nozzles arranged perpendicular to the throwing direction and a spraying water control system, in which the nozzles can be opened row by row according to the spraying needs; The temperature control system calls relevant parameters in the continuous cooling transformation database for different steel grades, combines the target temperatures for the start and end of the slab spraying required for the target microstructure control calculated by the temperature control system, and reversely calculates the spraying water volume and spraying time of the spraying device when the cooling rate required for the target microstructure control within 10 mm of the slab surface is achieved; The spraying time in the temperature control system is preferably adjusted by automatically adjusting the number of rows of nozzles used for spraying. When the adjustment of the number of rows of nozzles cannot meet the requirements, it is adjusted by the billet running speed of the billet transportation system.

2. The method for suppressing surface cracks based on online regulation of ingot structure according to claim 1, characterized in that: The steel used for the continuous cooling transformation in S1 is obtained by cutting a continuous casting billet with qualified composition and quality in the direction of drawing speed.

3. The method for suppressing surface cracks based on online regulation of ingot structure according to claim 1, characterized in that: The continuous cooling transformation parameters of the steel in S1 are obtained by analyzing the relationship between temperature and steel expansion using a thermal simulator.

4. The method for suppressing surface cracks based on online regulation of ingot structure according to claim 3, characterized in that: The thermal simulator is a Gleeble thermal / mechanical simulation tester or a high-temperature rapid quenching and deformation phase change instrument.

5. The method for suppressing surface cracks based on online regulation of ingot structure according to claim 1, characterized in that: In the S1, a database of the determined parameters is established based on SQL.

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