Extra-thick steel plate blank heating process

Abstract

The invention provides an extra-thick steel plate blank heating process, which relates to the technical field of extra-thick steel plate blank heating, and comprises the following steps: S1, plate blank treatment: scanning the whole surface of a plate blank by adopting an industrial visual inspection system to confirm that no crack with the length of more than 5mm and the depth of more than 3mm and no concentrated oil stain or corrosion with the area of more than 0.5 m exist; and all corners of the plate blank are subjected to arc chamfering through the numerical control chamfering machine. According to the ultra-thick steel plate blank heating process, in the plate blank treatment stage, industrial visual inspection is adopted to remove out-of-standard cracks, oil stains and rust, and the problem of cracks caused by corner stress concentration in the heating process is thoroughly solved in cooperation with arc chamfers with the radius larger than or equal to 20 mm and roughness control with the Ra smaller than or equal to 12.5 microns; in the preheating and heating stage, the heating rate, the furnace temperature interval and the heat preservation time are set according to the thickness difference of the plate blank, the total cross-section temperature difference is strictly controlled to be smaller than or equal to 50 DEG C in combination with dual monitoring of infrared temperature measurement and a plug-in thermocouple, and the situation that the core part is not heated thoroughly is avoided.

Description

Technical Field

[0001] This invention relates to the field of heating technology for extra-thick steel slabs, specifically to a heating process for extra-thick steel slabs. Background Technology

[0002] Extra-thick steel slabs (typically referring to those with a thickness ≥ 200 mm) are core materials in fields such as major equipment manufacturing, marine engineering, high-rise buildings, and bridge construction. Their quality directly determines the structural safety and service life of the final product. Due to their large thickness and wide cross-sectional dimensions, these slabs face technical challenges during heating, including long heat conduction paths, difficulty in controlling internal and external temperature differences, and stress concentration leading to cracking. This places extremely high demands on the precision, uniformity, and stability of the heating process.

[0003] In traditional heating processes, extra-thick slabs generally suffer from the following prominent problems: First, the heating strategy lacks specificity, failing to perform graded preheating based on slab thickness and furnace charging temperature (cold / hot charging). This results in overheating of thin slabs, leading to increased oxidation loss, while the core temperature of thick slabs lags behind, with the temperature difference across the entire cross-section often exceeding 100°C. Subsequent rolling processes are prone to defects such as delamination and cracks. Second, furnace atmosphere control is rudimentary, often employing a single oxidizing atmosphere. For steel grades containing easily oxidized elements such as Cr, Ni, and Mn, the surface oxidation loss rate can reach 3%-5%, wasting steel resources and affecting slab surface quality. Third, temperature monitoring methods are limited, relying heavily on surface temperature measurement, making it difficult to accurately grasp core temperature changes. This leads to the homogenization time being set based on experience, resulting in either insufficient heat preservation causing uneven temperature or excessive heat preservation increasing energy consumption. Finally, the slab edges and corners are not specifically treated. During heating, rapid heat dissipation and stress concentration at the edges and corners easily generate microcracks, requiring additional removal during subsequent processing and reducing production efficiency. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a heating process for extra-thick steel slabs to solve the problems mentioned in the background art. To achieve the above objectives, the present invention provides the following technical solution: a heating process for extra-thick steel slabs, comprising the following steps: S1. Slab processing: An industrial vision inspection system is used to scan the entire surface of the slab to confirm that there are no cracks with a length >5mm and a depth >3mm, and no concentrated oil stains or rust with an area >0.5m². All edges and corners of the slab are rounded using a CNC chamfering machine, with a chamfer surface roughness Ra≤12.5μm to avoid stress concentration at the edges and corners during heating and thus prevent cracks. The slab is then smoothly fed into the heating furnace by a steel loading machine, and the slabs are arranged at intervals. If it is a hot-charged slab for continuous casting, the temperature of the hot-charged slab is 400-700℃, and it is directly loaded into the heating furnace with a shortened preheating time. Cold-charged slabs need to be slowly loaded into the furnace. S2. Slab preheating treatment: Heat treatment is performed on slabs of different thicknesses. Slabs with a thickness of less than 400 mm are preheated, while slabs with a thickness of more than 400 mm are deep preheated. S3, Slab heating stage: Slabs smaller than 400mm and slabs larger than 400mm are heated without any additional heating process, both using a zone heating method, divided into a first heating stage and a second heating stage. For slabs smaller than 400mm, the heating method involves zone heating. In the first heating stage, the furnace temperature is 1000-1150℃, and the heating rate is 80-120℃ / h, mainly to increase the surface temperature. In the second heating stage, the furnace temperature is 1150-1250℃, and the heating rate is 60-100℃ / h, to promote heat conduction to the core of the slab. Oxygen-enriched air is introduced into the heating furnace and mixed with fuel for combustion to control the atmosphere inside the furnace to be weakly oxidizing. At the same time, the contents of O2, CO, CO2 and H2 are monitored in real time using a linear gas analyzer. S4, Heating Phase: The furnace temperature is maintained at the target temperature of 1150-1300℃, and the holding time is 2-6 hours. The holding time is calculated according to the thickness of the slab, and 1-1.5 hours is held for every 100mm of thickness. In addition, the temperature is monitored in real time by the temperature measuring device in the heating furnace to ensure that the temperature difference of the entire cross section of the slab is ≤50℃. For steel slabs containing easily oxidized elements, atmosphere control, temperature limitation and spray coating are carried out. S5. Regulation and control: Oxygen-enriched air is introduced into the heating furnace and mixed with fuel for combustion to control the atmosphere inside the furnace to be weakly oxidizing. At the same time, the contents of O2, CO, CO2 and H2 are monitored in real time by a gas monitor. In addition, the controller works together to keep the various parameters inside the heating furnace stable.

[0005] S6. Slab unloading from the furnace: The slab is smoothly moved out of the heating furnace by the tapping machine and quickly sent into the rolling process. The interval between tapping and rolling is ≤30 minutes to avoid excessive temperature drop.

[0006] S7. Waste heat recovery: Install a regenerative heat exchanger or tubular heat exchanger in the flue gas duct of the heating furnace to recover the heat from the flue gas. The recovered heat is used to preheat the combustion air in the heating furnace or the boiler feedwater. After preheating, the air temperature is ≥300℃, which is used to increase the water temperature.

[0007] Furthermore, in step S1, the chamfer radius of the slab edge corners is ≥20mm.

[0008] Furthermore, in step S2, the preheating method for slabs with a thickness of less than 400 mm is as follows: the furnace temperature in the preheating section is controlled at 800-900℃, the heating rate is 50-80℃ / h, the lower limit furnace temperature of 800 degrees Celsius is used for cold-charged slabs, the upper limit furnace temperature of 900 degrees Celsius is used for hot-charged slabs, and the cold-charged slabs are cold-charged for ≥1h.

[0009] Furthermore, in step S2, the core is preheated to a depth greater than 400 mm with a heating rate of 40-50℃ / h and a duration of 2-3 hours to ensure that the core temperature gradually follows.

[0010] Furthermore, in step S3, the first stage of heating for slabs larger than 400mm is carried out at a furnace temperature of 1050-1100℃, a heating rate of 70-80℃ / h, and a duration of 1.5-2h. The second stage of heating is carried out at a furnace temperature of 1200-1250℃, a heating rate of 50-60℃ / h, and a duration of 2-3h.

[0011] Furthermore, in step S3, the temperature measuring device inside the heating furnace adopts infrared temperature measurement and insertion thermocouple for real-time monitoring, and the temperature difference across the entire cross section of the slab is ≤50℃.

[0012] Furthermore, the movable thermocouple is inserted into the preset hole position of the slab for measurement, and the movable thermocouple is inserted into the preset hole position of the slab for measurement once every 30 minutes.

[0013] Furthermore, in step S4, the atmosphere is controlled such that the soaking zone uses a strong reducing atmosphere with CO = 3%-5% and O2 ≤ 1%. The target temperature for temperature limitation is 30-50°C lower than that for ordinary steel grades; The spray coating is an Al2O3-SiO2 based coating with a thickness of 0.1-0.2 mm.

[0014] Furthermore, in step S4, before spraying Al2O3-SiO2-based coating onto steel slabs containing easily oxidized elements, the slab surface needs to be sandblasted. The sandblasting pressure is controlled at 0.4-0.6 MPa, and the surface roughness Ra reaches 3.2-6.3 μm to ensure that the bonding strength between the coating and the slab surface is ≥15 MPa.

[0015] Furthermore, in step S7, the flue gas inlet and outlet temperatures of the regenerative heat exchanger are controlled to be ≤800℃ and ≥150℃, respectively.

[0016] Compared with existing technologies, this invention has the following advantages: In the slab processing stage, industrial visual inspection is used to remove excessive cracks, oil stains, and rust. Combined with chamfered edges with a radius of ≥20mm and roughness control of Ra≤12.5μm, the problem of cracks caused by stress concentration at the edges and corners during heating is completely solved. In the preheating and heating stages, the heating rate, furnace temperature range, and holding time are set according to the slab thickness differences. Combined with dual monitoring of infrared thermometry and insertion thermocouples, the temperature difference across the entire cross-section is strictly controlled to ≤50℃, avoiding problems such as incomplete core heating and surface overheating. For easily oxidized steel grades, a strong reducing atmosphere (CO=3%-5%, O2≤1%), temperature adjustment of 30-50℃, and Al2O3-SiO2-based coating protection effectively suppress the loss of easily oxidized elements. Simultaneously, sandblasting ensures a coating bonding strength of ≥15MPa, further improving the slab's oxidation resistance and the stability of subsequent rolling quality. Hot-charged slabs can be directly fed into the furnace, shortening the preheating time. Cold-charged slabs are preheated with a slow charging time of ≥1 hour and a low furnace temperature, balancing heating safety and efficiency. Slabs with a thickness >400mm are preheated deeply and slowly in stages, with a preheating rate of 40-50℃ / h and a second-stage heating rate of 50-60℃ / h, ensuring that the core temperature keeps pace and avoiding excessively long heating cycles due to excessive thickness. Strict control of the interval between slab exiting the furnace and rolling is ≤30 minutes, reducing the cost of secondary heating caused by temperature loss. At the same time, the design of zoned heating and precise temperature control makes the total heating and homogenization time more reasonable, greatly improving the production flow efficiency of extra-thick slabs and adapting to the needs of large-scale production. By utilizing waste heat recovery and efficient combustion control, energy utilization efficiency is significantly improved, reducing production energy consumption and environmental costs. Regenerative or tubular heat exchangers are installed in the flue gas ducts of the heating furnace to recover heat from the flue gas for preheating combustion air or boiler feedwater, effectively recovering waste heat and reducing energy waste. During the heating and control phase, oxygen-enriched air is mixed with fuel for combustion, and a linear gas analyzer monitors the O2, CO, CO2, and H2 content in real time, precisely controlling the weakly oxidizing or strongly reducing furnace atmosphere to ensure complete combustion while reducing fuel consumption. The flue gas inlet and outlet temperatures of the regenerative heat exchanger are controlled at ≤800℃ and ≥150℃, further optimizing waste heat recovery efficiency. The overall process, through energy recycling and precise energy consumption control, significantly reduces energy consumption and carbon emissions during the heating of extra-thick slabs. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this application clearer, the following description and illustration are provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0018] Obviously, the following description is merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios without any inventive effort. Furthermore, it is understood that although the effort involved in such development may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0019] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0020] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0021] A heating process for extra-thick steel slabs includes the following steps: S1. Slab processing: An industrial vision inspection system is used to scan the entire surface of the slab to confirm the absence of cracks longer than 5mm and deeper than 3mm, and the absence of concentrated oil stains or rust with an area greater than 0.5m². A CNC chamfering machine is then used to round the corners of the slab, ensuring a surface roughness Ra≤12.5μm. This prevents stress concentration at the corners during heating, thus avoiding cracks. The slab is then smoothly fed into the heating furnace using a steel loading machine, with the slabs spaced apart. For continuously cast hot-charged slabs (400-700℃), they are directly loaded into the heating furnace with a shortened preheating time. Cold-charged slabs are loaded slowly. In step S1, the chamfer radius of the slab corners is ≥20mm. During the slab processing stage, industrial vision inspection is used to remove excessive cracks, oil stains, and rust. Combined with the ≥20mm radius rounded chamfer and Ra≤12.5μm surface roughness control, the problem of cracks caused by stress concentration at the corners during heating is thoroughly solved. S2. Slab preheating treatment: Heat treatment is performed on slabs of different thicknesses. Slabs with a thickness less than 400 mm are preheated, while slabs with a thickness greater than 400 mm are deep preheated. In step S2, the preheating method for slabs with a thickness less than 400 mm is as follows: the furnace temperature in the preheating section is controlled at 800-900℃, the heating rate is 50-80℃ / h, the lower limit furnace temperature of 800℃ is used for cold-charged slabs, and the upper limit furnace temperature of 900℃ is used for hot-charged slabs. The cold-charged slabs are cold-charged for ≥1h. In step S2, slabs with a thickness greater than 400 mm are deep preheated at a heating rate of 40-50℃ / h for 2-3h to ensure that the core temperature gradually follows. S3, Slab heating stage: Slabs smaller than 400mm and larger than 400mm are heated using a separate heating process, employing a zoned heating method, consisting of a first heating stage and a second heating stage. For slabs smaller than 400mm, the heating process involves zoned heating. The first heating stage maintains a furnace temperature of 1000-1150℃ with a heating rate of 80-120℃ / h, primarily focusing on increasing the surface temperature. The second heating stage maintains a furnace temperature of 1150-1250℃ with a heating rate of 60-100℃ / h, promoting heat transfer to the slab's core. Oxygen-enriched air is introduced into the furnace and mixed with fuel for combustion, maintaining a weakly oxidizing atmosphere. Simultaneously, a linear gas analyzer monitors O2, CO, and CO levels in real time. Regarding the O2 and H2 content, during the heating and control stage, oxygen-enriched air is mixed with fuel for combustion. A linear gas analyzer is used to monitor the O2, CO, CO2, and H2 content in real time, precisely controlling the weakly oxidizing or strongly reducing furnace atmosphere to ensure complete combustion while reducing fuel consumption. In step S3, for slabs larger than 400mm, the first heating stage is performed at a furnace temperature of 1050-1100℃, a heating rate of 70-80℃ / h, and a duration of 1.5-2 hours. The second heating stage is performed at a furnace temperature of 1200-1250℃, a heating rate of 50-60℃ / h, and a duration of 2-3 hours. Hot-charged slabs (400-700℃) can be directly fed into the furnace with a shortened preheating time. Cold-charged slabs require ≥1 hour of preheating. The loading time is slowed down and preheating is carried out at a low furnace temperature (800℃) to balance heating safety and efficiency. For slabs with a thickness > 400mm, deep preheating and segmented slow heating are used, with a preheating rate of 40-50℃ / h and a second-stage heating rate of 50-60℃ / h to ensure that the core temperature keeps up and avoids excessively long heating cycles due to excessive thickness. The interval between slab exiting the furnace and rolling is ≤ 30min. Strict control reduces the cost of secondary heating caused by temperature loss. At the same time, the design of zoned heating and precise temperature control makes the total heating and homogenization time more reasonable, greatly improving the production flow efficiency of extra-thick slabs and adapting to the needs of large-scale production. In step S3, the temperature measuring device in the heating furnace adopts infrared temperature measurement and insertion thermocouple for real-time monitoring. The temperature difference of the entire cross section of the slab is ≤50℃. The heating rate, furnace temperature range and holding time are set according to the difference in slab thickness during the preheating and heating stages. Combined with the dual monitoring of infrared temperature measurement and insertion thermocouple, the temperature difference of the entire cross section is strictly controlled to be ≤50℃ to avoid problems such as incomplete heating of the core and overheating of the surface. The moving thermocouple is inserted into the preset hole position of the slab for measurement, and the moving thermocouple is inserted into the preset hole position of the slab for measurement once every 30 minutes. S4, Heating Phase: The furnace temperature is maintained at the target temperature of 1150-1300℃, and the holding time is 2-6 hours. The holding time is calculated according to the slab thickness, with 1-1.5 hours of holding time per 100mm thickness. In addition, the temperature is monitored in real time by a temperature measuring device inside the heating furnace to ensure that the temperature difference across the entire cross section of the slab is ≤50℃. For steel slabs containing easily oxidized elements, atmosphere control, temperature limitation, and coating are applied. In step S4, the atmosphere control uses a strong reducing atmosphere of CO=3%-5% and O2≤1% in the soaking zone. The target temperature for temperature limitation is 30-50°C lower than that for ordinary steel grades; The spray coating is an Al2O3-SiO2 based coating with a thickness of 0.1-0.2 mm. For easily oxidized steel grades, the loss of easily oxidized elements is effectively suppressed by using a strong reducing atmosphere (CO=3%-5%, O2≤1%), temperature adjustment of 30-50℃, and protection with an Al2O3-SiO2 based coating. At the same time, sandblasting treatment ensures that the coating bonding strength is ≥15MPa, further improving the oxidation resistance of the slab and the stability of subsequent rolling quality. In step S4, before spraying the Al2O3-SiO2 based coating on the steel grade slab containing easily oxidized elements, the slab surface needs to be sandblasted. The sandblasting pressure is controlled at 0.4-0.6MPa, and the surface roughness Ra reaches 3.2-6.3μm to ensure that the bonding strength between the coating and the slab surface is ≥15MPa. S5. Regulation and control: Oxygen-enriched air is introduced into the heating furnace and mixed with fuel for combustion to control the atmosphere inside the furnace to be weakly oxidizing. At the same time, the contents of O2, CO, CO2 and H2 are monitored in real time by a gas monitor. In addition, the controller works together to keep the various parameters inside the heating furnace stable.

[0022] S6. Slab unloading from the furnace: The slab is smoothly moved out of the heating furnace by the tapping machine and quickly sent into the rolling process. The interval between tapping and rolling is ≤30 minutes to avoid excessive temperature drop.

[0023] S7. Waste heat recovery: A regenerative heat exchanger or tubular heat exchanger is installed in the flue gas duct of the heating furnace to recover the heat from the flue gas. The recovered heat is used to preheat the combustion air in the heating furnace or the boiler feedwater. After preheating, the air temperature is ≥300℃, which is used to increase the water temperature. In step S7, the flue gas inlet and outlet temperatures of the regenerative heat exchanger are controlled at ≤800℃ and ≥150℃, respectively. Through waste heat recovery and efficient combustion control, the energy utilization rate is significantly improved, reducing production energy consumption and environmental protection costs. The installation of a regenerative or tubular heat exchanger in the flue gas duct of the heating furnace to recover the heat from the flue gas for preheating the combustion air or boiler feedwater effectively recovers the waste heat from the flue gas and reduces energy waste. The flue gas inlet and outlet temperatures of the regenerative heat exchanger are controlled at ≤800℃ and ≥150℃ to further optimize the waste heat recovery efficiency. The overall process significantly reduces energy consumption and carbon emissions during the heating process of extra-thick slabs through energy recycling and precise energy consumption control. Based on the above description, the heating process for extra-thick steel slabs starts with slab pretreatment, using industrial visual inspection to remove defects and rounded corners to avoid stress cracks. Then, a targeted preheating and segmented heating scheme is developed based on the slab thickness and furnace loading status. Combined with infrared temperature measurement and real-time thermocouple monitoring, the temperature difference across the entire cross-section is strictly controlled to ≤50℃. Simultaneously, atmosphere control, temperature limits, and coating protection address the loss of easily oxidized steel grades, comprehensively ensuring the slab heating quality and subsequent rolling stability. The design of direct furnace entry of hot-charged slabs from continuous casting, scientific preheating of cold-charged slabs, and a furnace exit to rolling interval of ≤30 minutes significantly improves production adaptability and flow efficiency, avoiding unnecessary time consumption and secondary heating. Precise temperature control through oxygen-enriched combustion and recovery of waste heat from flue gas using regenerative / tubular heat exchangers reduce fuel consumption and carbon emissions while achieving energy recycling.

[0024] The following embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

Example

[0025] Table 1 Table 2 shows the process parameters for graded preheating at different furnace loading temperatures. (Example)

[0026] Table 2 Therefore, compared with existing technologies, the extra-thick steel slab heating process of this invention solves the problems of a lack of targeted heating strategies, failure to perform graded preheating based on slab thickness and furnace charging temperature (cold / hot charging), resulting in overheating of thin slabs leading to increased oxidation loss, and lagging core temperature follow-up of thick slabs, with the temperature difference across the entire cross-section often exceeding 100°C, easily causing defects such as delamination and cracks in subsequent rolling. Secondly, the furnace atmosphere control is crude, often using a single oxidizing atmosphere. For steel grades containing easily oxidized elements such as Cr, Ni, and Mn, the surface oxidation loss rate is as high as 3%-5%, which not only wastes steel resources but also affects the surface quality of the slab. In addition, the temperature monitoring method is limited, relying mainly on surface temperature measurement, making it difficult to accurately grasp the core temperature changes. This leads to the homogenization time being set based on experience, resulting in either insufficient heat preservation causing uneven temperature or excessive heat preservation increasing energy consumption. Finally, the slab edges and corners are not specially treated. During the heating process, the edges and corners dissipate heat quickly and stress concentrate, easily generating micro-cracks, requiring additional removal in subsequent processing and reducing production efficiency.

[0027] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A heating process for extra-thick steel slabs, characterized in that: Includes the following steps: S1. Slab processing: An industrial vision inspection system is used to scan the entire surface of the slab to confirm that there are no cracks with a length >5mm and a depth >3mm, and no concentrated oil stains or rust with an area >0.5m². All edges and corners of the slab are rounded using a CNC chamfering machine, with a chamfer surface roughness Ra≤12.5μm to avoid stress concentration at the edges and corners during heating and thus prevent cracks. The slab is then smoothly fed into the heating furnace by a steel loading machine, and the slabs are arranged at intervals. If it is a hot-charged slab for continuous casting, the temperature of the hot-charged slab is 400-700℃, and it is directly loaded into the heating furnace with a shortened preheating time. Cold-charged slabs need to be slowly loaded into the furnace. S2. Slab preheating treatment: Heat treatment is performed on slabs of different thicknesses. Slabs with a thickness of less than 400 mm are preheated, while slabs with a thickness of more than 400 mm are deep preheated. S3, Slab heating stage: Slabs smaller than 400mm and slabs larger than 400mm are heated without any additional heating process, both using a zone heating method, divided into a first heating stage and a second heating stage. For slabs smaller than 400mm, the heating method involves zone heating. In the first heating stage, the furnace temperature is 1000-1150℃, and the heating rate is 80-120℃ / h, mainly to increase the surface temperature. In the second heating stage, the furnace temperature is 1150-1250℃, and the heating rate is 60-100℃ / h, to promote heat conduction to the core of the slab. Oxygen-enriched air is introduced into the heating furnace and mixed with fuel for combustion to control the atmosphere inside the furnace to be weakly oxidizing. At the same time, the contents of O2, CO, CO2 and H2 are monitored in real time using a linear gas analyzer. S4, Heating Phase: The furnace temperature is maintained at the target temperature of 1150-1300℃, and the holding time is 2-6 hours. The holding time is calculated according to the thickness of the slab, and 1-1.5 hours is held for every 100mm of thickness. In addition, the temperature is monitored in real time by the temperature measuring device in the heating furnace to ensure that the temperature difference of the entire cross section of the slab is ≤50℃. For steel slabs containing easily oxidized elements, atmosphere control, temperature limitation and spray coating are carried out. S5. Regulation and control: Oxygen-enriched air is introduced into the heating furnace and mixed with fuel for combustion to control the atmosphere inside the furnace to be weakly oxidizing. At the same time, the contents of O2, CO, CO2 and H2 are monitored in real time by a gas monitor. In addition, the controller works together to keep the various parameters inside the heating furnace stable. S6. Slab unloading from the furnace: The slab is smoothly moved out of the heating furnace by the tapping machine and quickly sent into the rolling process. The interval between tapping and rolling is ≤30 minutes to avoid excessive temperature drop. S7. Waste heat recovery: Install a regenerative heat exchanger or tubular heat exchanger in the flue gas duct of the heating furnace to recover the heat from the flue gas. The recovered heat is used to preheat the combustion air in the heating furnace or the boiler feedwater. After preheating, the air temperature is ≥300℃, which is used to increase the water temperature.

2. The heating process for extra-thick steel slabs according to claim 1, characterized in that: In step S1, the chamfer radius of the slab edge corners is ≥20mm.

3. The heating process for extra-thick steel slabs according to claim 1, characterized in that: In step S2, the preheating method for slabs with a thickness of less than 400 mm is as follows: the furnace temperature in the preheating section is controlled at 800-900℃, the heating rate is 50-80℃ / h, the lower limit furnace temperature of 800 degrees Celsius is used for cold-charged slabs, the upper limit furnace temperature of 900 degrees Celsius is used for hot-charged slabs, and the cold-charged slabs are cold-charged for ≥1h.

4. The heating process for extra-thick steel slabs according to claim 1, characterized in that: In step S2, the core is preheated to a depth greater than 400 mm at a rate of 40-50 °C / h for 2-3 hours to ensure that the core temperature gradually increases.

5. The heating process for extra-thick steel slabs according to claim 1, characterized in that: In step S3, the first stage of heating for slabs larger than 400 mm is carried out at a furnace temperature of 1050-1100℃, a heating rate of 70-80℃ / h, and a duration of 1.5-2h. The second stage of heating is carried out at a furnace temperature of 1200-1250℃, a heating rate of 50-60℃ / h, and a duration of 2-3h.

6. The heating process for extra-thick steel slabs according to claim 1, characterized in that: In step S3, the temperature measuring device inside the heating furnace uses infrared temperature measurement and insertion thermocouple for real-time monitoring, and the temperature difference across the entire cross section of the slab is ≤50℃.

7. The heating process for extra-thick steel slabs according to claim 6, characterized in that: The movable thermocouple is inserted into the preset hole position of the slab for measurement, and the movable thermocouple is inserted into the preset hole position of the slab for measurement once every 30 minutes.

8. The heating process for extra-thick steel slabs according to claim 1, characterized in that: In step S4, the atmosphere is controlled, and the soaking zone uses a strong reducing atmosphere with CO=3%-5% and O2≤1%; The target temperature for temperature limitation is 30-50°C lower than that for ordinary steel grades; The spray coating is an Al2O3-SiO2 based coating with a thickness of 0.1-0.2 mm.

9. The heating process for extra-thick steel slabs according to claim 1, characterized in that: In step S4, before spraying Al2O3-SiO2-based coating onto steel slabs containing easily oxidized elements, the slab surface needs to be sandblasted. The sandblasting pressure is controlled at 0.4-0.6 MPa, and the surface roughness Ra reaches 3.2-6.3 μm to ensure that the bonding strength between the coating and the slab surface is ≥15 MPa.

10. The heating process for extra-thick steel slabs according to claim 1, characterized in that, In step S7, the flue gas inlet and outlet temperatures of the regenerative heat exchanger are controlled to be ≤800℃ and ≥150℃, respectively.

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