Production method of saving type extra-thick Q345R steel plate

Abstract

The invention discloses a production method of a saving type extra-thick Q345R steel plate. The production method comprises the following steps: step 1, adopting a process combining molten iron pretreatment, converter smelting and LF furnace and RH furnace external refining; secondly, a continuous casting machine is adopted in the continuous casting process, and molten steel is treated; 3, a heating procedure is conducted, pile cooling treatment is conducted after the continuous casting billets are offline, heating is conducted through a walking beam furnace after pile cooling is completed, and heating is divided into a preheating section, a heating section and a soaking section; 4, a rolling procedure is conducted through a rolling mill, and an uncontrolled rolling large reduction technology is adopted for treatment; 5, a cooling procedure after rolling is conducted, and water cooling treatment is conducted immediately after rolling is completed; sixthly, heat treatment is conducted, and normalizing treatment is conducted through a continuous normalizing furnace; according to the method, the process of combining molten iron pretreatment, converter smelting and LF + RH external refining is adopted, precise control is achieved, the purity of molten steel is improved, and the quality and performance of the steel plate are improved.

Description

Technical Field

[0001] This invention relates to the field of steel plate production, specifically to a method for producing economical extra-thick Q345R steel plates. Background Technology

[0002] With the rapid development of industries such as petrochemicals and energy equipment, pressure vessels are moving towards larger size and higher parameters, which places higher demands on the extra-thick steel plates used in manufacturing pressure vessels. In modern industrial fields, extra-thick Q345R steel plates are widely used as important structural materials in key industries such as pressure vessels, nuclear power equipment, petrochemicals, and large-scale engineering machinery. Their quality and performance are directly related to the safe operation and service life of equipment. As the industry continues to increase its requirements for equipment reliability and safety, higher standards are being set for the comprehensive mechanical properties, internal quality uniformity, and welding performance of extra-thick Q345R steel plates.

[0003] However, traditional methods for producing extra-thick Q345R steel plates have many limitations. In the smelting process, the lack of precise control over temperature, reduction rate and cooling rate in rolling and heat treatment processes can easily lead to uneven steel plate structure and coarse grains, which in turn reduces the strength and toughness of the steel plate. In addition, traditional production methods have high energy consumption and low yield, which cannot meet the current industrial production requirements for green, efficient and low-cost production.

[0004] To address the aforementioned issues, there is an urgent need to develop a cost-effective production method for extra-thick Q345R steel plates that can precisely control and optimize production process parameters. This would improve the overall performance and production efficiency of the steel plates, reduce production costs, and meet the pressing demand of modern industry for high-quality extra-thick steel plates. Summary of the Invention

[0005] The purpose of this invention is to solve the problems mentioned above, and therefore a method for producing extra-thick Q345R steel plates that saves resources is proposed.

[0006] The objective of this invention can be achieved through the following technical solution: a method for producing economical extra-thick Q345R steel plates, comprising:

[0007] Step 1: The process combines molten iron pretreatment, converter smelting, and LF furnace plus RH ladle refining.

[0008] Step 2: The continuous casting process uses a continuous casting machine to process the molten steel;

[0009] Step 3: Heating process. After the continuously cast billet comes off the line, it undergoes a heat treatment. After the heat treatment is completed, it is heated by a walking beam furnace. The heating process is divided into a preheating section, a heating section, and a soaking section.

[0010] Step 4: The rolling process involves uncontrolled rolling with large reduction using a rolling mill.

[0011] Step 5: Post-rolling cooling process. Immediately after rolling, water cooling is performed using a laminar flow cooling system with a cooling water volume of 1500-2000 m³ / h and a cooling rate of 5-15℃ / s. Water cooling is stopped after the steel plate is cooled to 650-700℃, followed by slow cooling in stacks. During the slow cooling process, the temperature of the core of the steel plate is monitored by thermocouples to ensure that the temperature slowly drops below 200℃.

[0012] Step Six: Heat Treatment Process. A continuous normalizing furnace is used for normalizing treatment. The normalizing temperature is 890±10℃, the heating rate is 5~10℃ / min, and the holding time is calculated according to the formula 1.5-2.0min / mm×t+40min, where t is the thickness of the steel plate. After normalizing, water mist cooling is used for rapid cooling. The cooling water temperature is 20~30℃, and the water pressure is 0.3~0.5MPa. The temperature of the steel plate is reduced to 600~650℃ within 5min. Then, it is air-cooled to room temperature on a cooling bed. The temperature of the cooling bed table is ≤50℃.

[0013] Furthermore, the method also includes a seventh step, a flaw detection process, in which ultrasonic testing is performed after the heat treatment process is completed. The detection sensitivity is Φ2mm flat-bottomed hole to ensure that there are no defects ≥Φ2mm inside the steel plate. The steel plate that passes the flaw detection is then trimmed with an edge width of 50-100mm to ensure that there are no burrs or missing corners on the edge and that the edge perpendicularity is ≤1mm / m.

[0014] Furthermore, in the heat treatment process, a nitrogen protective atmosphere is used in the normalizing furnace, with a nitrogen purity of ≥99.99% and an oxygen content of ≤50ppm, to prevent oxidation of the steel plate surface. When water is poured to cool the steel plate after it is taken out of the furnace, multiple sets of nozzles are used to spray water evenly to ensure uniform cooling of the upper and lower surfaces of the steel plate and avoid the generation of thermal stress.

[0015] Furthermore, in the post-rolling cooling process, a temperature monitoring system is used during the slow cooling of the stack. Thermocouples are placed at the center and edge of the stack to record temperature changes in real time, ensuring that the slow cooling process meets the process requirements. After the stacking cooling is completed, the steel plate surface is shot blasted to remove oxide scale. The shot blasting intensity is 0.2 to 0.3 MPa, and the surface roughness Ra is controlled at 5 to 15 μm.

[0016] Furthermore, in the heating process, the stepping cycle of the walking beam furnace is 30-40 seconds to ensure that the billet moves evenly in the furnace. A temperature measuring device is installed at the furnace outlet to detect the temperature of each billet and ensure that the temperature deviation at the furnace outlet is ≤ ±20℃.

[0017] Furthermore, the hot metal pretreatment stage involves injecting a desulfurizing agent, specifically a CaO-based composite desulfurizing agent. The injection pressure is controlled at 0.4–0.6 MPa, and the treatment time is 15–25 minutes, ensuring that the sulfur content of the hot metal is ≤0.008% when it enters the converter.

[0018] Furthermore, the converter smelting adopts a top-bottom combined blowing process, with an oxygen flow rate of 2500-3000 m³ / h, a bottom blowing nitrogen flow rate of 50-80 m³ / h, a final carbon content controlled at 0.08%-0.12%, and a tapping temperature of 1620-1680℃. During the tapping process, a double slag-blocking method using slag-blocking balls and slag-blocking cones is adopted to ensure that the slag discharge is ≤5 kg / t.

[0019] Furthermore, the LF furnace refining stage adopts an alkaline slag system, with a slag-forming time of ≥20 min and a white slag retention time of ≥10 min. Deoxidation is carried out by feeding aluminum wire, with an aluminum wire feeding amount of 170-200 meters / furnace, to ensure that the acid-soluble aluminum content in the molten steel reaches 0.02% to 0.06%.

[0020] Furthermore, the RH furnace refining vacuum degree is ≤3.0mbar, the vacuum holding time is ≥20min, the circulating argon flow rate is 100~150Nm³ / h, and the hydrogen content of the treated molten steel is ≤0.0002% and the nitrogen content is ≤0.006%.

[0021] Furthermore, the steel treatment in step two specifically includes:

[0022] Dynamic light reduction technology is used to carry out the reduction operation within the solidification end range of 0.2-1.0, with a total reduction of 10-20 mm;

[0023] Control the cooling water flow rate at 320-350 m³ / h, the inlet water temperature at 30-35℃, and the outlet water temperature at 45-50℃;

[0024] Secondary cooling is achieved using an aerosol cooling method. The specific water volume is 1.0-1.2 L / kg in Zone 1, 0.8-1.0 L / kg in Zone 2, and 0.6-0.8 L / kg in Zone 3.

[0025] The billet is pulled and stirred at a speed of 0.5-0.8 m / min. After the billet exits the crystallizer, it is electromagnetically stirred with a stirring current of 250-400 A and a frequency of 6 Hz.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] The process combines hot metal pretreatment, converter smelting, and LF+RH ladle refining. The hot metal pretreatment uses CaO-based composite desulfurizer for precise sulfur control. The converter top and bottom blowing controls oxygen and nitrogen flow rates, final carbon content, and tapping temperature. It also features double slag blocking. The LF furnace uses basic slag refining, aluminum wire deoxidation, and RH furnace refining controls vacuum and argon flow rates. This effectively reduces sulfur, phosphorus, hydrogen, nitrogen impurities, and gas content in the steel, precisely controls these processes, improves the purity of the molten steel, and enhances the quality and performance of the steel plates.

[0028] After the continuous casting billet is cooled, it is heated in a walking beam furnace in three sections: preheating, heating, and soaking. The heating time, heating coefficient, air-fuel ratio, and furnace pressure are controlled in each section to ensure uniform heating of the billet, reduce oxidation loss to ≤0.5%, provide good billet conditions for subsequent rolling, and ensure rolling quality.

[0029] Ultrasonic testing is performed according to standards. After passing the test, the edges are trimmed. The trimmed edge width and edge perpendicularity are controlled to ensure that there are no defects inside the steel plate, guarantee edge quality, and meet the usage requirements. Attached Figure Description

[0030] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings.

[0031] Figure 1 This is a flowchart of a method for producing an economical extra-thick Q345R steel plate according to the present invention. Detailed Implementation

[0032] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] In the existing technology, the pressure vessel manufacturing field has long faced technical bottlenecks in the production of extra-thick steel plates. Traditional production processes have problems such as inaccurate temperature control and uneven cooling rate in the smelting, rolling and heat treatment stages, resulting in coarse internal structure and unstable mechanical properties of the steel plate. A pressure vessel manufacturing company once tried to produce extra-thick Q345R steel plates using conventional rolling processes. The final product developed heat-affected zone cracks during the welding process. After testing, it was found that there was obvious banded segregation in the core of the steel plate, which seriously affected the safety performance of the equipment.

[0034] To address the aforementioned issues, technicians discovered that the temperature gradient control in the heating section of the traditional process was insufficient, resulting in an excessive temperature difference between the core and surface of the billet. By analyzing the heat conduction law of the post-rolling cooling process, they found that uneven distribution of thermal stress during the rapid cooling stage could induce microscopic defects. After multiple process experiments, it was finally determined that a staged temperature control system needed to be established, and the synergistic mechanism between rolling and cooling needed to be optimized.

[0035] Therefore, please refer to Figure 1 As shown, this application proposes a smelting process including hot metal pretreatment and composite refining, steel treatment technology for continuous casting, a billet heat treatment process with staged heating, a large reduction rolling method, a cooling system combining laminar cooling and slow stacking cooling, and a normalizing treatment scheme including temperature control and cooling method optimization.

[0036] Among them, molten iron pretreatment refers to reducing impurity content through multi-process combined treatment. The combination of converter and refining furnace can be used to effectively remove sulfur and phosphorus elements. The molten steel treatment in the continuous casting process involves solidification process control. The flow state of molten steel is adjusted through specific equipment to ensure the uniformity of the billet. Staged heating refers to dividing the heating process into different temperature zones. For example, the preheating section can adopt a gradient heating method to eliminate residual stress in the billet. High reduction rolling refers to high deformation processing under the condition of not controlling the rolling temperature. It can refine the grain structure through plastic deformation. The laminar flow cooling system achieves uniform heat dissipation on the surface of the steel plate by adjusting the water flow distribution. Stacking slow cooling utilizes the residual heat of the material itself for slow cooling. The normalizing treatment scheme includes temperature curve design and cooling medium selection. For example, a specific heating rate is used to ensure austenite homogenization.

[0037] Specifically, the smelting stage controls the purity of molten steel through multi-stage refining processes; the continuous casting process uses dynamic control technology to optimize the internal quality of the billet; the heating process eliminates temperature stress through staged treatment; the rolling stage improves the material density through large deformation processing; the post-rolling cooling uses a combination of rapid water cooling and slow cooling to balance the structural transformation stress; the heat treatment process obtains stable mechanical properties through precise temperature control; the various processes work synergistically; the smelting quality assurance lays the foundation for subsequent processing; the temperature control system runs through the entire production process; and finally, the uniformity of the steel plate structure and the stability of its performance are improved simultaneously.

[0038] Compared with existing technologies, traditional processes typically use a single air cooling method after rolling, and the uncontrollable cooling rate can easily lead to differences in the microstructure between the surface and the core. This solution combines laminar flow cooling and slow stacking cooling, which ensures the necessary cooling intensity while avoiding internal stress caused by excessively rapid cooling. Existing technologies for normalizing treatment mostly use fixed holding times, which are difficult to adapt to the heat treatment requirements of steel plates of different thicknesses. This solution achieves dynamic adjustment of process parameters by establishing a time calculation model.

[0039] Through the above technical solutions, this application effectively solves the problem of large differences in the core and surface properties of extra-thick steel plates, improves the banded segregation defect, reduces energy consumption loss through coordinated control of each process during production, reduces the probability of subsequent processing cracks through optimization of the slow cooling process, adapts the dynamic parameter adjustment in the heat treatment stage to the quality requirements of products of different specifications, and significantly improves the overall process stability.

[0040] This application further proposes to perform ultrasonic testing after the heat treatment process, with a testing sensitivity of Φ2mm flat-bottomed hole, to ensure that there are no defects ≥Φ2mm inside the steel plate. The steel plate that passes the flaw detection is then trimmed with an edge width of 50-100mm to ensure that there are no burrs or missing corners on the edge and that the edge perpendicularity is ≤1mm / m.

[0041] Ultrasonic testing refers to non-destructive testing that utilizes the principle of high-frequency sound waves reflecting off defects when they propagate inside a material. Specifically, it can be achieved using a multi-channel digital flaw detector in conjunction with a linear array probe. By setting a Φ2mm flat-bottom hole as the reference sensitivity, it can effectively identify minute defects inside the steel plate. Edge trimming refers to the mechanical cutting and trimming of the steel plate edges. Specifically, it can be achieved using a hydraulic shearing machine or a flame cutting machine in conjunction with a subsequent grinding process. By controlling the edge width and perpendicularity parameters, it can eliminate irregular edge shapes generated during the rolling process.

[0042] Specifically, after the steel plate has been normalized and cooled to room temperature, the entire steel plate is scanned by an ultrasonic testing device arranged on the conveyor rollers. During the testing process, an automatic coupling agent spraying system is used to ensure good contact between the probe and the surface of the steel plate. When the reflected wave amplitude exceeds the equivalent size of the Φ2mm flat bottom hole, the defect location is automatically marked. For the steel plate that passes the test, it is continuously cut on both sides along the length direction. The cut edges are chamfered by a grinding wheel unit, and the straightness of the edges is monitored online by a laser rangefinder.

[0043] Compared with existing technologies, conventional production processes often only perform local flaw detection by sampling after rolling and lack systematic edge cutting quality control. By adding a full-surface ultrasonic testing process, comprehensive screening of defects can be achieved, and precise control of the edge cutting process can effectively avoid subsequent processing problems caused by poor edge quality, such as welding undercut or abnormal assembly gaps.

[0044] Through the above technical solution, this application can reliably eliminate excessive defects inside the steel plate, eliminate stress concentration caused by edge defects, ensure the welding accuracy during subsequent pressure vessel assembly, and reduce material loss caused by edge trimming.

[0045] This application further proposes that in the heat treatment process, a nitrogen protective atmosphere is used in the normalizing furnace, with the nitrogen purity controlled at above 99.99% and the oxygen content in the furnace controlled at below 50ppm, in order to prevent oxidation of the steel plate surface; when water is poured to cool down after exiting the furnace, multiple sets of nozzles are used to spray water evenly to ensure uniform cooling of the upper and lower surfaces of the steel plate and avoid the generation of thermal stress.

[0046] Nitrogen protective atmosphere refers to the introduction of high-purity nitrogen into the furnace during the normalizing process of steel plates to isolate oxygen. This can be achieved by using a nitrogen generator or a liquid nitrogen vaporization system. The nitrogen flow rate is adjusted by real-time monitoring of oxygen content, thereby inhibiting the oxidation reaction on the steel plate surface. Uniform water spraying from multiple nozzles refers to the arrangement of multiple water spraying units at intervals along the length of the steel plate. This can be achieved by using a matrix arrangement of fan-shaped nozzles. By adjusting the water pressure and angle of each nozzle, the water flow coverage areas overlap to ensure a consistent cooling rate on the steel plate surface.

[0047] Specifically, during the normalizing process, the continuous supply of nitrogen protective atmosphere can effectively reduce the proportion of oxidizing atmosphere in the furnace and reduce the formation of oxide scale on the surface of the steel plate. After the steel plate is taken out of the furnace, water is sprayed onto the upper and lower surfaces of the steel plate simultaneously through a symmetrically arranged nozzle array. The uniformity of water flow distribution eliminates local temperature differences and prevents internal stress concentration caused by uneven cooling.

[0048] Compared with existing technologies, traditional processes often use air atmosphere for normalizing, which easily forms a thick oxide layer on the surface of the steel plate, requiring subsequent shot blasting or pickling. At the same time, single-sided water spraying or fixed nozzles can easily cause differences in cooling rates, leading to an increase in residual stress inside the steel plate. This solution reduces the generation of oxidation defects and avoids stress concentration problems during the cooling process by using nitrogen protection and multi-nozzle coordinated control.

[0049] Through the above technical solutions, this application can significantly reduce the degree of oxidation on the surface of steel plates, reduce the workload of subsequent surface treatment processes, and at the same time, through uniform cooling control, effectively eliminate residual stress inside the steel plates, and improve the dimensional stability and mechanical property consistency of the products.

[0050] This application further proposes that during the slow cooling process after rolling, a temperature monitoring system is used, with thermocouples placed at the center and edge of the stack to record temperature changes in real time, ensuring that the slow cooling process meets the process requirements. After the slow cooling is completed, the steel plate surface is shot blasted to remove oxide scale. The shot blasting intensity is 0.2 to 0.3 MPa, and the surface roughness Ra is controlled at 5 to 15 μm.

[0051] The temperature monitoring system refers to a device that collects temperature data at different locations in the stack via thermocouples and feeds it back to the control terminal in real time. Specifically, it can be implemented by combining a multi-point distributed temperature measurement module with a data logger. This system is used to monitor the internal temperature gradient of the stack and avoid stress concentration inside the steel plate due to uneven cooling. Shot blasting is a process that uses high-speed shot to impact the surface of the steel plate to remove oxide scale and impurities. Specifically, it can be implemented by using a centrifugal shot blasting machine in conjunction with steel shot blasting. The shot blasting intensity is controlled by adjusting the shot projection speed and density, and the surface roughness is adjusted by controlling the shot particle size and processing time. This is used to improve the surface cleanliness of the steel plate and its subsequent processing performance.

[0052] Specifically, during the slow cooling process of stacking, thermocouples are placed at the center and edge of the stack to simultaneously acquire temperature change data in different areas. For example, the difference between the temperature drop rate in the central area and the edge area can be monitored in real time, thereby dynamically adjusting the stacking environment conditions to ensure the overall uniformity of cooling of the steel plate. After the stacking cooling is completed, the shot blasting stage can effectively remove oxide scale and form a uniform surface morphology by controlling the shot blasting intensity and surface roughness range. For example, by using a combination of process parameters with a steel shot particle size of 0.8-1.2mm and a projection angle of 45°-60°, the oxide layer can be effectively removed and a uniform surface morphology can be formed, avoiding the impact of residual oxide layer on the subsequent processing quality.

[0053] Compared with existing technologies, traditional stacking slow cooling processes usually rely on a single temperature measurement point or manual sampling, which cannot fully reflect the internal temperature distribution of the stack and is prone to local cooling rate exceeding the standard. Furthermore, the lack of precise control over shot blasting parameters may result in excessive surface roughness or incomplete cleaning. This application achieves controllability of the cooling process and consistency of surface treatment through multi-point temperature monitoring and optimization of shot blasting process parameters.

[0054] Through the above technical solution, this application can effectively eliminate the differences in internal structure of steel plates caused by uneven temperature distribution during the stacking and slow cooling process. At the same time, by precisely controlling the shot blasting parameters, it can ensure that the surface quality of the steel plate meets the requirements of subsequent processing and avoid processing defects caused by oxide scale residue or abnormal surface roughness.

[0055] This application further proposes that in the heating process, the stepping cycle of the walking beam furnace is 30 to 40 seconds to ensure that the billet moves evenly in the furnace. A temperature measuring device is installed at the outlet of the heating furnace to detect the temperature of each billet and ensure that the temperature deviation at the outlet does not exceed ±20℃.

[0056] The stepping cycle refers to the time interval between the movement of the billet in the walking beam furnace. Specifically, it can be achieved by controlling the movement frequency of the walking beam using a hydraulic drive system. By adjusting the stepping cycle, uneven heating caused by differences in the residence time of the billet in the furnace can be avoided. The temperature measuring device refers to the temperature detection equipment installed at the outlet of the furnace. Specifically, it can be an infrared thermometer or a thermocouple for real-time temperature acquisition. This device is used to monitor the surface temperature distribution of the billet and ensure that the temperature uniformity of each area meets the process requirements.

[0057] Specifically, in the heating process, by setting the stepping cycle range, the billet moves in the furnace at a constant rhythm to prevent overheating or underheating in local areas due to excessive dwell time. The temperature measuring device at the furnace outlet scans the full width of each billet. When the temperature deviation is detected to exceed the allowable range, it can be compensated by adjusting the burner power or the billet moving speed. For example, if the head temperature of a billet is lower than the target value, the gas supply in that area can be temporarily increased to ensure the uniformity of the furnace exit temperature of the entire billet.

[0058] Compared with existing technologies, the billet movement speed fluctuates greatly in traditional heating processes, which can easily lead to uneven temperature distribution in the furnace. Furthermore, there is a lack of real-time temperature detection methods, and it is difficult to control the overall temperature deviation by relying solely on manual sampling. This solution achieves stability of billet movement rhythm and comprehensive temperature detection by using a fixed stepping cycle and an automated temperature measurement system, effectively solving the problem of uneven microstructure caused by temperature fluctuations in traditional processes.

[0059] Through the above technical solution, this application can accurately control the heating process of the billet in the heating furnace, reduce the grain size difference caused by temperature deviation, thereby improving the consistency of the mechanical properties of the steel plate. At the same time, through real-time temperature feedback adjustment, energy waste is avoided and production costs are further reduced.

[0060] This application further proposes to inject a desulfurizing agent during the hot metal pretreatment stage. The desulfurizing agent is a CaO-based composite desulfurizing agent, the injection pressure is controlled at 0.4-0.6 MPa, and the treatment time is 15-25 min, to ensure that the sulfur content of the hot metal is ≤0.008% when it enters the converter.

[0061] The CaO-based composite desulfurizer refers to a powder with calcium oxide as the main component and magnesium and fluorite components. Specifically, it can be a powder mixture with a particle size of 0.1-0.5mm. The desulfurization efficiency is improved through the synergistic effect of calcium and magnesium. The injection pressure is controlled at 0.4-0.6MPa, which means adjusting the carrier gas pressure through a pneumatic conveying system. Specifically, nitrogen can be used as the carrier gas medium. This pressure range can ensure sufficient contact between the desulfurizer and molten iron, and avoid molten iron loss caused by splashing. The treatment time of 15-25min refers to the continuous reaction time of the desulfurizer and molten iron in the molten iron ladle. Specifically, it can be achieved by monitoring the change of sulfur content in molten iron in real time through an online sulfur content detection device to ensure that the desulfurization reaction reaches a balanced state.

[0062] Specifically, in the hot metal pretreatment stage, CaO-based composite desulfurizer is uniformly injected into the hot metal ladle at a specific pressure using a pneumatic injection device. The active calcium in the desulfurizer reacts chemically with the sulfur in the hot metal to generate calcium sulfide slag phase. During the treatment time of 15-25 minutes, the reaction kinetics are promoted by mechanical stirring or gas stirring to ensure that the sulfur is fully transferred to the slag phase. After the treatment, the sulfur-containing slag layer is removed by slag skimming to ensure that the sulfur content of the hot metal meets the requirements of the converter smelting process.

[0063] Compared with existing technologies, traditional methods often use a single lime desulfurizing agent and the injection pressure is less than 0.3 MPa, resulting in insufficient desulfurization reaction and a processing time of more than 30 minutes. In contrast, this solution achieves a lower final sulfur content while shortening the processing time by optimizing the composition of the composite desulfurizing agent and matching the pressure parameters.

[0064] Through the above technical solutions, this application effectively reduces the impact of sulfur elements in molten iron on subsequent steelmaking processes, reduces the desulfurization load of converters and slag consumption, and avoids the problem of increased sulfide inclusions in steel due to excessive sulfur content, laying the foundation for the production of high-purity extra-thick steel plates.

[0065] This application further proposes that the converter smelting adopts a top and bottom blowing process, with an oxygen flow rate of 2500-3000 m³ / h, a bottom blowing nitrogen flow rate of 50-80 m³ / h, a final carbon content controlled at 0.08%-0.12%, a tapping temperature of 1620-1680℃, and a double slag blocking process using slag-blocking balls and slag-blocking cones to ensure that the slag discharge is ≤5 kg / t.

[0066] Among them, the top and bottom combined blowing process refers to strengthening the stirring of the molten pool by combining oxygen blowing from the top of the converter with nitrogen blowing from the bottom. Specifically, it can be achieved by using a split oxygen lance and bottom blowing permeable bricks. The metallurgical reaction kinetics are optimized by adjusting the flow ratio of oxygen from the top and nitrogen from the bottom. The endpoint carbon content control refers to the target carbon concentration range that the molten steel needs to reach at the end of the converter smelting. Specifically, it can be achieved by dynamically detecting the carbon-oxygen accumulation in the molten pool and adjusting the oxygen supply intensity. Its function is to balance the decarburization efficiency and the oxidizing properties of the molten steel. The double slag blocking of slag ball plus slag blocking cone refers to the use of two different slag blocking devices with different structures during the tapping process. Specifically, slag blocking balls can be made of ceramic composite materials with a density between that of molten steel and slag, and combined with conical slag blocking devices to form a physical isolation layer to reduce the probability of slag entering the ladle.

[0067] Specifically, in the top-bottom combined blowing process, the top oxygen lance injects oxygen into the molten pool at a specific flow rate for decarburization reaction, while the bottom nitrogen forms a bubble cluster through the permeable elements distributed at the bottom of the furnace, enhancing the material exchange between the upper and lower parts of the molten pool. For example, the oxygen flow rate can be controlled at around 2800 m³ / h, and the bottom blowing nitrogen flow rate can be adjusted to around 65 m³ / h. The synergistic effect of the two shortens the molten pool mixing time. The final carbon content is controlled by real-time monitoring of the molten pool composition through an online detection system. When the carbon content enters the target range, blowing is stopped immediately. The tapping temperature is kept stable by adjusting the amount of coolant added, for example, it can be kept at around 1650℃. The slag blocking operation is implemented in stages after the tapping port is opened. First, slag blocking balls are put in to block the flow of large slag particles, and then slag blocking cones are used to further block fine slag from entering the steel flow.

[0068] Compared with existing technologies, traditional converter smelting mostly adopts a single top-blowing process, which is prone to compositional segregation due to insufficient stirring intensity of the molten pool and the single slag-blocking measures result in a high slag discharge. This solution strengthens the stirring of the molten pool through top and bottom combined blowing, making the composition of the molten steel more uniform. At the same time, the double slag-blocking structure forms a multi-stage filtration, effectively reducing the content of inclusions in the steel.

[0069] Through the above technical solutions, this application can improve the uniformity of steel composition in the converter smelting process, reduce carbon segregation caused by insufficient stirring of the molten pool, and at the same time avoid steel over-oxidation by precisely controlling the carbon content at the end point. The application of the double slag-blocking device significantly reduces the thickness of the slag layer in the ladle, creating cleaner steel conditions for subsequent refining processes, and ultimately improving the internal quality of the steel plate.

[0070] This application further proposes the use of an alkaline slag system in the refining stage of the LF furnace, with a slag-forming time of no less than 20 minutes and a white slag retention time of no less than 10 minutes. Deoxidation is carried out by feeding aluminum wire, with an aluminum wire feeding rate of 170-200 meters / furnace, to ensure that the acid-soluble aluminum content in the molten steel reaches 0.02% to 0.06%.

[0071] Among them, the alkalinity slag system refers to the formation of a high alkalinity environment by controlling the ratio of CaO to SiO2 in the slag. Specifically, it can be achieved by adjusting the slag system composition with auxiliary materials such as lime and fluorite. Its function is to enhance the desulfurization and deoxidation capabilities. The slag-forming time of not less than 20 minutes refers to the duration from the initial addition of slag-forming materials to the formation of a stable slag phase. Specifically, it can be achieved by batch feeding and real-time monitoring of the slag layer state to ensure sufficient slag system reaction. The white slag retention time of not less than 10 minutes refers to the duration of maintaining the white slag phase with low oxidation and good fluidity after its formation. Specifically, it can be achieved by adjusting the intensity and temperature of argon gas stirring to continuously adsorb inclusions in the molten steel.

[0072] Specifically, in the LF furnace refining process, a high-basicity slag system is first formed by adding slag-forming materials. After a slag-forming reaction of more than 20 minutes, a stable white slag phase is formed. The white slag state is then maintained for at least 10 minutes to continuously purify the molten steel. During this process, aluminum wire is continuously added at a feed rate of 170 to 200 meters per furnace of molten steel. The aluminum element combines with the oxygen in the molten steel to form alumina inclusions, which are then adsorbed by the slag. Ultimately, the acid-soluble aluminum content in the molten steel is stabilized within the range of 0.02% to 0.06%.

[0073] Compared with existing technologies, traditional LF furnace refining often results in insufficient slag reaction due to insufficient slag-forming time, and the short white slag retention time leads to low inclusion removal efficiency. Inaccurate control of aluminum wire addition can easily cause fluctuations in acid-soluble aluminum content. This solution achieves a dual improvement in steel purity and composition stability by extending the slag-forming and white slag retention time and combining it with quantitative aluminum wire feeding process.

[0074] Through the above technical solutions, this application effectively controls the oxygen content and the number of inclusions in molten steel, avoids internal defects in steel plates caused by insufficient deoxidation, and improves the grain refinement ability and mechanical property uniformity of steel by stabilizing the acid-soluble aluminum content.

[0075] This application further proposes that the vacuum degree of RH furnace refining is ≤3.0 mbar, the vacuum holding time is ≥20 min, the circulating argon flow rate is 100~150 Nm³ / h, and the hydrogen content of the treated molten steel is ≤0.0002% and the nitrogen content is ≤0.006%.

[0076] Among them, vacuum degree refers to the pressure control range inside the furnace during the refining process, which can be achieved through a vacuum pump system. The pressure is kept stable by adjusting the pumping rate. Vacuum holding time refers to the processing time of molten steel under a set vacuum degree, which can be monitored by a timing device to ensure that the degassing reaction is fully carried out. Circulating argon flow rate refers to the amount of gas injected into the bottom of the ladle through the permeable bricks. It can be controlled by a flow meter and a regulating valve to promote the circulation of molten steel. Hydrogen content control is achieved through the vacuum degassing mechanism, which promotes the escape of dissolved hydrogen from the molten steel under low pressure. Nitrogen content control is achieved through the combined action of argon gas covering and vacuum to block the contact between molten steel and air.

[0077] Specifically, in the RH refining stage, after the molten steel is introduced into the vacuum chamber, the pressure is reduced to a set threshold by a vacuum pump. During this process, argon gas is continuously injected from the bottom of the ladle at a specific flow rate, forming an upward bubble flow that drives the molten steel to circulate. The molten steel stays in the vacuum environment for a sufficient time, allowing the dissolved hydrogen atoms to diffuse to the surface of the bubbles and be carried away from the system. At the same time, the protective atmosphere formed by the argon gas effectively isolates the air and prevents the molten steel from increasing nitrogen content. By precisely controlling the vacuum degree and the argon gas flow rate, the hydrogen and nitrogen content of the molten steel can be reduced simultaneously.

[0078] In some specific implementations, the vacuum pump unit can be configured with a pressure feedback control system, such as a combination of a Roots pump and a steam jet pump, to adjust the pumping power in real time to maintain the target vacuum level. Argon flow control can be achieved by using a mass flow meter in conjunction with a proportional valve to automatically adjust the gas supply parameters according to the steel processing volume. Steel composition monitoring can be performed by online sampling, such as by rapidly detecting hydrogen and nitrogen content using a spectrometer.

[0079] Compared with existing technologies, traditional RH refining processes typically use a vacuum of 80-100 Pa and a holding time of less than 15 minutes, with a large fluctuation range in argon flow rate. This results in low dehydrogenation efficiency of molten steel, and insufficient argon coverage can easily lead to excessive nitrogen content. This solution significantly improves the degassing effect by increasing the vacuum standard, extending the processing time, and precisely controlling the argon parameters.

[0080] Through the above technical solution, this application effectively reduces the gas inclusion content in molten steel, avoids hydrogen embrittlement cracks and nitride inclusion defects in the subsequent rolling process, and lays the foundation for the high density microstructure of extra-thick steel plates.

[0081] This application further proposes the use of dynamic light reduction technology in the continuous casting process, performing reduction operations within the solidification end range of 0.2-1.0, with a total reduction of 10-20 mm; controlling the cooling water flow rate at 320-350 m³ / h, the inlet water temperature at 30-35℃, and the outlet water temperature at 45-50℃; employing air mist cooling for secondary cooling, with a specific water volume of 1.0-1.2 L / kg in zone one, 0.8-1.0 L / kg in zone two, and 0.6-0.8 L / kg in zone three; implementing a billet pulling speed of 0.5-0.8 m / min; and performing electromagnetic stirring after the billet exits the crystallizer, with a stirring current of 250-400 A and a frequency of 6 Hz.

[0082] Among them, dynamic light pressure reduction technology refers to applying mechanical pressure by adjusting the roll gap at the end of the billet solidification. Specifically, it can be achieved by controlling the contraction of the roll gap in the fan-shaped section through a hydraulic servo system. This technology can compensate for the voids generated by solidification shrinkage and suppress center segregation. Among them, the air mist cooling method refers to mixing compressed air with water mist to form a uniform cooling medium. Specifically, it can be achieved by using a dual-fluid nozzle system. This method can precisely adjust the heat transfer intensity of different cooling zones. Among them, electromagnetic stirring refers to generating circulation in molten steel through an alternating magnetic field. Specifically, it can be achieved by using a low-frequency rotating magnetic field generator. This measure can promote the transformation of columnar crystals to equiaxed crystals.

[0083] Specifically, during continuous casting, when the billet enters the solidification end, a light pressing operation is implemented by dynamically adjusting the roll gap of the fan-shaped section to compensate for the volume change caused by solidification shrinkage. The cooling system adjusts the air-mist mixing ratio in zones to create a gradient cooling intensity on the billet surface. During the billet pulling process, the electromagnetic stirring device arranged at the crystallizer outlet generates a rotating magnetic field, which promotes directional flow inside the molten steel. In this process, the solute distribution at the solidification front is effectively controlled, and the liquid flow between dendrites is improved.

[0084] Compared with existing technologies, traditional continuous casting processes do not implement dynamic reduction at the end of solidification, resulting in a high rate of central porosity defects; conventional water cooling methods are difficult to achieve zoned control of cooling intensity, which easily causes surface temperature fluctuations; the lack of electromagnetic stirring results in insufficient proportion of equiaxed crystals inside the billet, affecting subsequent rolling performance. This solution systematically improves the uniformity of solidification structure through multi-stage coordinated control.

[0085] Through the above technical solutions, this application effectively suppresses the defects of center segregation and shrinkage cavity in the billet, thereby reducing the hardness deviation of the steel plate cross section; the zoned control of air mist cooling avoids the phenomenon of surface reheating and reduces the concentration of internal thermal stress; electromagnetic stirring promotes grain refinement and provides a uniform original microstructure basis for subsequent rolling processes.

[0086] Using the above method, Q345R steel plates were produced with the following chemical composition and weight percentages: C: 0.10%~0.16%, Mn: 1.30%~1.60%, P≤0.015%, S≤0.005%, Si: 0.15%~0.40%, Cr≤0.30%, Ni: 0.10%~0.30%, V≤0.05%, Ti≤0.03%, Alt: 0.02%~0.06%, N≤0. .006%, H≤0.0002%C: 0.10%~0.16%, Mn: 1.30%~1.60%, P≤0.015%, S≤0.005%, Si: 0.15%~0.40% , Cr≤0.30%, Ni:0.10%~0.30%, V≤0.05%, Ti≤0.03%, Alt: 0.02%~0.06%, N≤0.006%, H≤0.0002%.

[0087] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for producing an economical extra-thick Q345R steel plate, characterized in that, include: Step 1: The process combines molten iron pretreatment, converter smelting, and LF furnace plus RH ladle refining. Step 2: The continuous casting process uses a continuous casting machine to process the molten steel; Step 3: Heating process. After the continuously cast billet comes off the line, it undergoes a heat treatment. After the heat treatment is completed, it is heated by a walking beam furnace. The heating process is divided into a preheating section, a heating section, and a soaking section. Step 4: The rolling process involves uncontrolled rolling with large reduction using a rolling mill. Step 5: Post-rolling cooling process. Immediately after rolling, water cooling is performed using a laminar flow cooling system with a cooling water volume of 1500-2000 m³ / h and a cooling rate of 5-15℃ / s. Water cooling is stopped after the steel plate is cooled to 650-700℃, followed by slow cooling in stacks. During the slow cooling process, the temperature of the core of the steel plate is monitored by thermocouples to ensure that the temperature slowly drops below 200℃. Step Six: Heat Treatment Process. A continuous normalizing furnace is used for normalizing treatment at a temperature of 890±10℃. The furnace time is calculated using the formula 1.5-2.0 min / mm×t+40 min, where t is the thickness of the steel plate. After normalizing, water mist cooling is used for rapid cooling. The cooling water temperature is 20~30℃ and the water pressure is 0.3~0.5MPa. The steel plate temperature is reduced to 600~650℃ within 5 minutes. Subsequently, the plate is air-cooled to room temperature on a cooling bed, with the cooling bed surface temperature ≤50℃.

2. The method for producing an economical extra-thick Q345R steel plate according to claim 1, characterized in that, The method also includes a seventh step, a flaw detection process, in which ultrasonic testing is performed after the heat treatment process is completed. The detection sensitivity is Φ2mm flat-bottomed hole to ensure that there are no defects ≥Φ2mm inside the steel plate. The steel plate that passes the flaw detection is then trimmed with an edge width of 50-100mm to ensure that there are no burrs or missing corners on the edge and that the edge perpendicularity is ≤1mm / m.

3. The method for producing an economical extra-thick Q345R steel plate according to claim 1, characterized in that, In the heat treatment process, a nitrogen protective atmosphere is used in the normalizing furnace, with a nitrogen purity of ≥99.99% and an oxygen content of ≤50ppm, to prevent oxidation of the steel plate surface. When water is poured to cool the steel plate after it is taken out of the furnace, multiple sets of nozzles are used to spray water evenly to ensure uniform cooling of the upper and lower surfaces of the steel plate and avoid the generation of thermal stress.

4. The method for producing an economical extra-thick Q345R steel plate according to claim 1, characterized in that, In the post-rolling cooling process, a temperature monitoring system is used during the slow cooling of the stack. Thermocouples are placed at the center and edge of the stack to record temperature changes in real time, ensuring that the slow cooling process meets the process requirements. After the stacking cooling is completed, the steel plate surface is shot blasted to remove oxide scale. The shot blasting intensity is 0.2 to 0.3 MPa, and the surface roughness Ra is controlled at 5 to 15 μm.

5. The method for producing an economical extra-thick Q345R steel plate according to claim 1, characterized in that, In the heating process, the stepping cycle of the walking beam furnace is 30-40 seconds to ensure that the billet moves evenly in the furnace. A temperature measuring device is installed at the furnace outlet to detect the temperature of each billet and ensure that the temperature deviation at the furnace outlet is ≤ ±20℃.

6. The method for producing an economical extra-thick Q345R steel plate according to claim 1, characterized in that, The hot metal pretreatment stage involves spraying a desulfurizing agent, specifically a CaO-based composite desulfurizing agent. The spraying pressure is controlled at 0.4–0.6 MPa, and the treatment time is 15–25 min, ensuring that the sulfur content of the hot metal is ≤0.008% when it enters the converter.

7. The method for producing an economical extra-thick Q345R steel plate according to claim 1, characterized in that, The converter smelting adopts a top-bottom combined blowing process, with an oxygen flow rate of 2500-3000 m³ / h and a bottom blowing nitrogen flow rate of 50-80 m³ / h. The final carbon content is controlled at 0.08%-0.12%, and the tapping temperature is 1620-1680℃. During the tapping process, a double slag-blocking method using slag-blocking balls and slag-blocking cones is adopted to ensure that the slag discharge is ≤5 kg / t.

8. The method for producing an economical extra-thick Q345R steel plate according to claim 1, characterized in that, The refining stage of the LF furnace adopts an alkaline slag system, with a slag-forming time of ≥20 min and a white slag retention time of ≥10 min. Deoxidation is carried out by feeding aluminum wire, with an aluminum wire feeding amount of 170-200 meters / furnace, to ensure that the acid-soluble aluminum content in the molten steel reaches 0.02% to 0.06%.

9. The method for producing an economical extra-thick Q345R steel plate according to claim 1, characterized in that, The RH furnace refining vacuum degree is ≤3.0mbar, the vacuum holding time is ≥20min, the circulating argon flow rate is 100~150Nm³ / h, and the hydrogen content of the treated molten steel is ≤0.0002% and the nitrogen content is ≤0.006%.

10. A method for producing an economical extra-thick Q345R steel plate according to claim 1, characterized in that, The steel treatment in step two specifically includes: Dynamic light reduction technology is used to carry out the reduction operation within the solidification end range of 0.2-1.0, with a total reduction of 10-20 mm; Control the cooling water flow rate at 320-350 m³ / h, the inlet water temperature at 30-35℃, and the outlet water temperature at 45-50℃; Secondary cooling is achieved using an aerosol cooling method. The specific water volume is 1.0-1.2 L / kg in Zone 1, 0.8-1.0 L / kg in Zone 2, and 0.6-0.8 L / kg in Zone 3. The billet is pulled and stirred at a speed of 0.5-0.8 m / min. After the billet exits the crystallizer, it is electromagnetically stirred with a stirring current of 250-400 A and a frequency of 6 Hz.

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