Method for increasing the number of straight rolling continuous casting furnaces for Q355B steel

Abstract

The application belongs to the technical field of steelmaking, and particularly relates to a method for improving the number of straight rolling continuous casting furnaces for Q355B steel. The stopper head is prone to erosion, nodulation and even fracture under the action of high-temperature molten steel scouring and Al2O3 deposition sintering, which is a key restricting factor for limiting the number of straight rolling continuous casting furnaces for Q355B steel and difficult to realize long-casting continuous production. The embodiment of the application breaks through the traditional single deoxidization or fixed aluminum content control mode, constructs a synergistic protection mechanism of barium-based initial deoxidization-periodic aluminum deoxidization-high speed induction enrichment-stopper position monitoring feedback, and through process timing coupling and dynamic regulation, converts Al2O3 inclusions from harmful nodules into controllable protective resources, so as to replace passive corrosion resistance with active film formation, and solve the technical contradiction that the straight rolling process is limited by temperature drop to cause poor castability and long service life of the stopper.

Description

Technical Field

[0001] This application belongs to the field of steelmaking technology, and in particular relates to a method for increasing the number of continuous casting heats of Q355B steel in direct rolling. Background Technology

[0002] In the direct rolling process without heating, Q355B steel requires increased continuous casting speed to ensure the direct rolling temperature. When the continuous casting speed is increased, the molten steel flow velocity in the tundish increases, leading to greater impact on the tundish stopper rod and increasing its erosion rate. This results in unstable flow control by the stopper rod in the later stages of a casting cycle (around 20 heats), causing fluctuations in product quality, unstable direct rolling temperature, and even safety accidents due to the stopper rod failing to control the flow. In such cases, production must be interrupted, resulting in a low number of consecutive casting heats.

[0003] The stopper rod can be raised and lowered via a hydraulic control system to adjust the gap with the internal nozzle and regulate the molten steel flow rate, thus matching the continuous casting billet pulling speed. If the stopper rod is severely corroded, or even if pieces break off from the rod head, the molten steel flow rate cannot be effectively controlled even when the stopper rod is lowered to its lowest position. This will cause fluctuations in the casting speed, and if the nozzle needs to be replaced, the stopper rod cannot shut off the steel flow, potentially leading to a safety accident. In such cases, a copper plug cone is typically used to block the flow, forcing a production shutdown. Summary of the Invention

[0004] This application provides a method for increasing the number of consecutive hot-rolled Q355B steel to solve the following technical problem: how to extend the life of the stopper rod to increase the number of consecutive hot-rolled Q355B steel.

[0005] This application provides a method for increasing the number of continuous casting heats in direct rolling of Q355B steel, the method comprising the following steps: The Q355B molten steel is smelted in a converter, and the final carbon content, final temperature and final harmful element content of the Q355B molten steel are controlled. The Q355B steel smelted in the converter is deoxidized and alloyed after tapping, and the deoxidation and alloying is carried out by deoxidation using a barium-containing deoxidizer. The deoxidized and alloyed Q355B steel is subjected to periodic aluminum deoxidation treatment to form dispersed Al2O3 inclusions in the Q355B steel. The periodic aluminum deoxidation treatment includes feeding aluminum wire in the start-up heat to control the aluminum content in the Q355B steel within a first target range, and feeding aluminum wire again in a subsequent specific heat when stopper erosion characteristics are detected to control the aluminum content in the Q355B steel back to the first target range, thus forming a periodic cyclic protection. The molten Q355B steel after the periodic aluminum deoxidation treatment was stirred by argon blowing. The molten Q355B steel, after being stirred by argon blowing, is hoisted to the continuous casting process for tundish casting. The continuous casting speed during tundish casting is controlled to be higher than the conventional continuous casting speed, so that the Al2O3 inclusions are enriched in the head of the stopper rod to form a dense protective layer. The position change of the stopper rod is monitored, and the erosion state of the stopper rod is determined based on the position change. The cyclic execution of the periodic aluminum deoxidation treatment is triggered based on the erosion state of the stopper rod until the casting cycle ends.

[0006] Optionally, the final carbon content of the Q355B molten steel is 0.07wt% to 0.17wt%, the final temperature of the Q355B molten steel is 1670℃ to 1690℃, and the final harmful element content of the Q355B molten steel is phosphorus content ≤ 0.025wt% and sulfur content ≤ 0.025wt%.

[0007] Optionally, the barium-containing deoxidizer is silicon-calcium-barium, and the amount of silicon-calcium-barium added is 2.0 kg / ton of Q355B molten steel; The method of adding the barium-containing deoxidizer includes adding refining slag and the silicon-calcium-barium compound to the bottom of the ladle before tapping, and adding the remaining silicon-calcium-barium compound with the steel stream.

[0008] Optionally, the amount of added silicon-calcium-barium further includes: When the final carbon content of the Q355B molten steel is less than 0.07wt%, the amount of silicon, calcium and barium is increased by 10kg / furnace for every 0.01wt% below the carbon content.

[0009] Optionally, the aluminum content in the first target range is 0.005wt%-0.008wt%, and the amount of aluminum wire added is 0.5-0.8Kg / ton·Q355B molten steel; The periodic aluminum deoxidation treatment also includes feeding aluminum wire into the second furnace after the initial casting to control the aluminum content in the Q355B molten steel to be within a second target range, wherein the aluminum content in the second target range is lower than the aluminum content in the first target range.

[0010] Optionally, the aluminum content in the second target range is 0.003wt%-0.005wt%, and the amount of aluminum wire added to the second furnace after the start of casting is 0.3-0.5Kg / ton·Q355B molten steel; the final temperature of the second furnace after the start of casting is 5-10℃ lower than the final temperature of the first furnace.

[0011] Optionally, the aluminum wire feeding process is not used in the subsequent furnaces after the second furnace after the start of casting, and the final temperature of the subsequent furnaces after the second furnace after the start of casting gradually decreases compared to the final temperature of the second furnace after the start of casting.

[0012] Optionally, the argon blowing and stirring includes strong argon blowing and soft argon blowing, wherein the strong argon blowing pressure is 0.2-0.8 MPa and the strong argon blowing time is not less than 3 minutes; The soft blowing time of the argon is not less than 2 minutes, and the argon flow rate is controlled during the soft blowing process to ensure that the surface of the Q355B molten steel is not exposed. The forced argon blowing also includes: when adjusting the composition based on the analysis results of the reference sample, the forced argon blowing time before resampling shall not be less than 2 minutes.

[0013] Optionally, the temperature of the molten steel in the tundish during casting is in the range of 30°C to 45°C above the liquidus temperature, the liquidus temperature is 1510°C, and the continuous casting speed is 2.5-2.7 m / min.

[0014] Optionally, the monitoring of stopper rod position changes includes: The change in the scale of the stopper rod position data is monitored. When the number displayed on the stopper rod position returns to the initial position or is 1-3 mm lower than the initial position, it is determined that the stopper rod has been eroded, triggering the next round of aluminum wire feeding operation of the periodic aluminum deoxidation treatment.

[0015] The technical solution provided in this application has the following advantages compared with the prior art: Because the stopper head is prone to erosion, nodule formation, and even breakage under the scouring of high-temperature molten steel and the deposition and sintering of Al2O3, it is a key constraint that limits the number of continuous castings of Q355B steel and makes it difficult to achieve continuous production of long casting cycles.

[0016] This application embodiment controls the carbon content, temperature, and harmful elements at the converter endpoint to stabilize the initial cleanliness and superheat of the molten steel, thereby reducing the chemical corrosion and thermal shock damage of the stopper rod material by the molten steel, laying the compositional foundation for subsequent protection mechanisms. Furthermore, a barium-containing deoxidizer is used for deoxidation alloying at the tapping stage. The strong deoxidizing properties of barium reduce the dissolved oxygen activity in the steel, inhibiting the premature and excessive formation of initial Al2O3 and preventing severe nodulation and blockage at the stopper rod head in the early stages. Subsequently, through periodic aluminum deoxidation treatment, aluminum wire is fed into the furnace during startup to maintain the aluminum content within the first target range. Aluminum reacts with residual oxygen to generate dispersed Al2O3 inclusions. When stopper rod erosion characteristics are detected, aluminum is fed again in subsequent specific furnaces to restore this range, forming a periodic cyclical protection system. This dynamically compensates for aluminum loss and the attenuation of the protective effect caused by the removal of inclusions during continuous casting. The thermodynamic driving force for Al2O3 formation in steel is continuously maintained. Furthermore, argon blowing and stirring promote uniform dispersion and moderate flotation of inclusions, optimizing their size distribution and movement. Additionally, the continuous casting speed is controlled to be higher than conventional levels, enhancing the scouring effect of the steel flow on the stopper head. This causes dispersed Al2O3 inclusions to accumulate and sinter at the stopper head, forming a dense protective layer. This protective layer physically isolates the high-temperature molten steel from direct contact with the stopper matrix, significantly reducing the rate of thermal erosion and mechanical scouring of the stopper. Furthermore, by real-time monitoring of the stopper position changes to determine the erosion state and triggering periodic aluminum deoxidation cycles, dynamic feedback and precise replenishment of the protective effect are achieved, ensuring the dense protective layer remains effective throughout the entire casting cycle. Thus, without needing to stop casting and replace the stopper, the service life of the stopper is significantly extended, effectively increasing the number of continuous casting heats in the Q355B steel direct rolling process.

[0017] This application breaks through the traditional single deoxidation or fixed aluminum content control mode and constructs a synergistic protection mechanism of barium-based initial deoxidation - periodic aluminum deoxidation - high-speed induced enrichment - rod position monitoring feedback. Through process timing coupling and dynamic regulation, Al2O3 inclusions are transformed from harmful nodules into controllable protective resources. Active film formation replaces passive corrosion resistance, solving the technical contradiction between poor castability and long life of stopper rods caused by temperature drop limitations in direct rolling process. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings required in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other related drawings can be derived from these drawings without creative effort.

[0020] Figure 1This is a schematic diagram of the continuous casting tundish and stopper rod provided in an embodiment of this application. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within the range. For example, a range description of 1 to 6 or 1~6 covers all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms used herein, including terms such as "include" to indicate, but not limited to, "first," "second," etc., are used only to distinguish different entities or steps and do not imply an actual order or relationship; and / or to indicate that multiple situations can exist alone or simultaneously; expressions such as "at least one," "more than one," etc., refer to any combination of the corresponding objects, including combinations of single or multiple objects. Proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as a correspondence between the antecedent and consequent of a proportional expression, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0023] This application provides a method for increasing the number of continuous casting heats in direct rolling of Q355B steel, the method comprising the following steps: The Q355B molten steel is smelted in a converter, and the final carbon content, final temperature and final harmful element content of the Q355B molten steel are controlled. The Q355B steel smelted in the converter is deoxidized and alloyed after tapping, and the deoxidation and alloying is carried out by deoxidation using a barium-containing deoxidizer. The deoxidized and alloyed Q355B steel is subjected to periodic aluminum deoxidation treatment to form dispersed Al2O3 inclusions in the Q355B steel. The periodic aluminum deoxidation treatment includes feeding aluminum wire in the start-up heat to control the aluminum content in the Q355B steel within a first target range, and feeding aluminum wire again in a subsequent specific heat when stopper erosion characteristics are detected to control the aluminum content in the Q355B steel back to the first target range, thus forming a periodic cyclic protection. The molten Q355B steel after the periodic aluminum deoxidation treatment was stirred by argon blowing. The molten Q355B steel, after being stirred by argon blowing, is hoisted to the continuous casting process for tundish casting. The continuous casting speed during tundish casting is controlled to be higher than the conventional continuous casting speed, so that the Al2O3 inclusions are enriched in the head of the stopper rod to form a dense protective layer. The position change of the stopper rod is monitored, and the erosion state of the stopper rod is determined based on the position change. The cyclic execution of the periodic aluminum deoxidation treatment is triggered based on the erosion state of the stopper rod until the casting cycle ends.

[0024] Stopper rod erosion characteristics: refers to the identifiable phenomenon of changes in the stopper rod position caused by the scouring and chemical erosion of the stopper rod head by molten steel in the tundish during continuous casting. Conventional continuous casting speed: refers to the continuous casting speed when no heating-free direct rolling process is used, typically 1.85-1.95 m / min. Start-up heat: refers to the first heat of molten steel in a casting cycle. Subsequent specific heat: refers to the specific heat that triggers the next aluminum wire feeding operation when stopper rod erosion characteristics are detected during periodic aluminum deoxidation treatment; this specific heat is determined by the change in stopper rod position. Casting cycle: refers to the collection of consecutive casting cycles from the start of casting in the tundish to the end of casting in the tundish during the continuous casting process.

[0025] The Q355B molten steel is smelted in a converter, and the final carbon content, final temperature, and final harmful element content of the Q355B molten steel are controlled, so as to provide Q355B molten steel with qualified composition for subsequent deoxidation and alloying, and thus create chemical conditions for the formation of dispersed Al2O3 inclusions.

[0026] The Q355B molten steel after converter smelting is deoxidized and alloyed at the tapping stage. The deoxidation and alloying process uses a barium-containing deoxidizer to reduce the oxygen content in the Q355B molten steel. This reduces the probability of free oxygen in the Q355B molten steel reacting with the subsequently fed aluminum to form coarse Al2O3 inclusions, thus providing a deoxidation basis for the formation of dispersed Al2O3 inclusions.

[0027] After deoxidation and alloying, Q355B molten steel undergoes periodic aluminum deoxidation treatment. This periodic aluminum deoxidation treatment includes feeding aluminum wire during the start-up heat to control the aluminum content in the Q355B molten steel within a first target range, and feeding aluminum wire again in subsequent specific heats when stopper erosion characteristics are detected to control the aluminum content in the Q355B molten steel back to the first target range, forming a periodic cyclic protection. This allows the aluminum element in the Q355B molten steel to form dispersed Al2O3 inclusions, which in turn provide a source of inclusions for migration and enrichment towards the stopper head during the tundish casting process. When stopper erosion causes the protective layer to thin, aluminum wire is fed again to replenish the aluminum content and restore it to the first target range. This periodically reforms a dense protective layer at the stopper head, thereby slowing down the erosion rate of the stopper head matrix, extending the stopper life, and increasing the number of consecutive heats of Q355B steel.

[0028] The molten Q355B steel after periodic aluminum deoxidation is stirred by argon blowing, thereby homogenizing the chemical composition of the molten Q355B steel, and thus ensuring that the Al2O3 inclusions are evenly distributed in the molten Q355B steel. This ensures that the thickness of the dense protective layer formed at the head of the stopper rod is uniform, thereby ensuring the stability of the stopper rod flow control, extending the life of the stopper rod, and thus increasing the number of continuous casting heats of Q355B steel in direct rolling.

[0029] After being stirred by argon, the molten Q355B steel is hoisted to the continuous casting process for tundish casting. The casting speed during tundish casting is controlled to be higher than that of conventional continuous casting. This allows Al2O3 inclusions to accumulate towards the stopper head under the action of the high-velocity steel flow, forming a dense protective layer on the stopper head. This layer covers the substrate of the stopper head, reducing the direct scouring and chemical corrosion of the stopper head by the high-temperature molten steel, thus slowing down the erosion rate of the stopper, extending the stopper life, and ultimately increasing the number of heats that can be cast in the direct rolling process of Q355B steel.

[0030] The system monitors the position changes of the stopper rod and determines the erosion status of the stopper rod based on these changes. It then triggers a cyclical aluminum deoxidation process based on the erosion status until the end of the casting cycle. This allows for timely replenishment of aluminum content to form a new dense protective layer before the dense protective layer fails due to stopper rod erosion. This enables the periodic regeneration of the stopper rod protective layer, thereby continuously slowing down the erosion rate of the stopper rod, extending its lifespan, and ultimately increasing the number of consecutive castings of Q355B steel in direct rolling.

[0031] Existing technologies employ a constant deoxidation process, which cannot dynamically replenish the protective layer during stopper rod erosion. This application establishes a periodic cycle mechanism by feeding aluminum wire to form Al2O3 inclusions—Al2O3 inclusions enrich to form a dense protective layer—monitoring the stopper rod position to determine the erosion state—and feeding aluminum wire again to replenish the protective layer. This mechanism achieves active regeneration of the stopper rod protective layer and periodic extension of its lifespan, thereby overcoming the limitation of existing technologies where the stopper rod lifespan monotonically decreases with each casting cycle.

[0032] In some embodiments, the final carbon content of the Q355B molten steel is 0.07wt% to 0.17wt%, the final temperature of the Q355B molten steel is 1670℃ to 1690℃, and the final harmful element content of the Q355B molten steel is phosphorus content ≤ 0.025wt% and sulfur content ≤ 0.025wt%.

[0033] By controlling the final carbon content of Q355B steel to 0.07wt%~0.17wt%, the Q355B steel achieves a moderate carbon content level at the end of converter smelting. This provides a stable deoxidation reaction basis for the Q355B steel during the deoxidation and alloying stage, ensuring the stability of the deoxidation effect of the barium-containing deoxidizer. This, in turn, ensures the stability of the reaction conditions for the formation of dispersed Al2O3 inclusions by aluminum elements in the subsequent periodic aluminum deoxidation treatment. This, in turn, ensures the quality of the formation of a dense protective layer at the stopper head, thereby extending the stopper life and increasing the number of continuous casting heats of Q355B steel.

[0034] By controlling the final temperature of Q355B molten steel to 1670℃~1690℃, the molten steel has sufficient superheat at tapping to ensure its fluidity. This ensures that even after temperature loss during transport to the continuous casting process, the molten steel still meets the requirements for the initial pouring temperature in the tundish. Consequently, the molten steel temperature at the start of pouring in the tundish is guaranteed to be 30℃~45℃ higher than the liquidus temperature. This also ensures that the molten steel maintains good fluidity even when the continuous casting speed is increased to 2.5-2.7m / min. Furthermore, this ensures that Al2O3 inclusions are effectively enriched at the stopper head at higher casting speeds, forming a dense protective layer that delays stopper erosion, extends stopper life, and ultimately increases the number of heats that can be directly rolled and continuously cast Q355B steel.

[0035] By controlling the final phosphorus content and final sulfur content of Q355B molten steel to ≤0.025wt%, the content of harmful elements in Q355B molten steel is reduced, thereby reducing the adverse effects of phosphorus and sulfur on the mechanical properties of Q355B steel, ensuring the quality of Q355B steel products, avoiding interruptions in casting due to quality problems, ensuring the realization of the number of consecutive casting heats, and increasing the number of consecutive casting heats of Q355B steel direct rolling.

[0036] The endpoint carbon content has a lower limit of 0.07 wt% and an upper limit of 0.17 wt%, including but not limited to 0.07 wt%, 0.10 wt%, 0.12 wt%, 0.15 wt%, and 0.17 wt%. The endpoint temperature has a lower limit of 1670℃ and an upper limit of 1690℃, including but not limited to 1670℃, 1675℃, 1680℃, 1685℃, and 1690℃. The endpoint phosphorus content has an upper limit of 0.025 wt%, including but not limited to 0.010 wt%, 0.015 wt%, 0.020 wt%, and 0.025 wt%. The endpoint sulfur content has an upper limit of 0.025 wt%, including but not limited to 0.010 wt%, 0.015 wt%, 0.020 wt%, and 0.025 wt%.

[0037] In some embodiments, the barium-containing deoxidizer is barium silicate calcium silicate, and the amount of barium silicate calcium silicate added is 2.0 kg / ton of Q355B molten steel; The method of adding the barium-containing deoxidizer includes adding refining slag and the silicon-calcium-barium compound to the bottom of the ladle before tapping, and adding the remaining silicon-calcium-barium compound with the steel stream.

[0038] Silicon-calcium-barium: Refers to a barium-containing deoxidizer whose chemical composition includes silicon, calcium, and barium. Refining slag: Refers to the slag material added to the bottom of the ladle before tapping from the converter.

[0039] The deoxidation alloying process at the tapping stage employs a barium-containing deoxidizer, specifically a silicon-calcium-barium deoxidizer. This deoxidizes the barium, calcium, and silicon elements in the silicon-calcium-barium deoxidizer, causing a deoxidation reaction with the oxygen in the Q355B molten steel. This reduces the oxygen content of the Q355B molten steel, creating a low-oxygen environment for the formation of dispersed Al2O3 inclusions during subsequent periodic aluminum deoxidation treatment. This prevents aluminum from reacting with excessive free oxygen to form coarse Al2O3 inclusions, ensuring that the formed Al2O3 inclusions have a dispersed distribution. Consequently, the Al2O3 inclusions are effectively enriched at the stopper head during the tundish casting process, forming a dense protective layer that delays stopper erosion, extends stopper life, and ultimately increases the number of consecutive castings of Q355B steel.

[0040] The addition of silicon-calcium-barium alloy is controlled at 2.0 kg / ton of Q355B molten steel. This ensures that the deoxidation capacity of silicon-calcium-barium alloy matches the oxygen content in Q355B molten steel, thereby fully removing free oxygen from the Q355B molten steel. This avoids insufficient deoxidation, which would lead to the formation of large inclusions during subsequent aluminum deoxidation. Conversely, it avoids excessive deoxidation, which would result in wasted alloy costs and a decrease in steel purity. This ensures the effectiveness of subsequent periodic aluminum deoxidation treatment, guarantees the quality of the dense protective layer formed on the stopper head, extends the stopper life, and ultimately increases the number of continuous casting heats of Q355B steel.

[0041] The method of adding barium-containing deoxidizer involves adding refining slag and barium silicate to the bottom of the ladle before tapping, and adding the remaining barium silicate to the ladle with the steel flow. This allows some of the barium silicate to be placed at the bottom of the ladle before tapping and react fully with the molten steel that enters the ladle earlier. As a result, the remaining barium silicate reacts continuously with the molten steel that is added with the steel flow, thus achieving uniform distribution and thorough deoxidation of barium silicate in the ladle. This ensures the uniformity and thoroughness of deoxidation of Q355B steel, provides a uniform steel base for subsequent periodic aluminum deoxidation treatment, ensures the uniform distribution of Al2O3 inclusions, ensures the uniformity of the dense protective layer at the stopper head, extends the stopper life, and increases the number of continuous casting heats of Q355B steel.

[0042] The addition amount of silicon, calcium, and barium is 2.0 kg / ton of Q355B molten steel. For converters of different tonnages, the single-furnace addition amount includes, but is not limited to, 140 kg / furnace (70-ton converter), 160 kg / furnace (80-ton converter), 180 kg / furnace (90-ton converter), and 200 kg / furnace (100-ton converter).

[0043] In some embodiments, the amount of added silica-calcium-barium further includes: When the final carbon content of the Q355B molten steel is less than 0.07wt%, the amount of silicon, calcium and barium is increased by 10kg / furnace for every 0.01wt% below the carbon content.

[0044] When the final carbon content of Q355B steel is below 0.07wt%, 10kg / heat of silicon-calcium-barium is added for every 0.01wt% below the final carbon content. This increases the amount of silicon-calcium-barium added as the final carbon content decreases, thus compensating for the increase in oxygen content in the steel caused by the decrease in final carbon content. This ensures that the oxygen content in Q355B steel can still be removed to a suitable level even when the final carbon content is low. This also prevents the steel from being too oxidized under low final carbon conditions, which would lead to the formation of coarse Al2O3 inclusions during subsequent aluminum deoxidation. Furthermore, it ensures that dispersed Al2O3 inclusions can still be formed under low final carbon conditions. This ensures that the Al2O3 inclusions are effectively enriched at the stopper head during the tundish casting process, forming a dense protective layer that delays stopper erosion, extends stopper life, and ultimately increases the number of consecutive casting heats of Q355B steel.

[0045] The difference between the final carbon content and the actual carbon content is less than 0.07wt% includes, but is not limited to, 0.01wt%, 0.02wt%, 0.03wt%, 0.04wt%, and 0.05wt%.

[0046] In some embodiments, the aluminum content in the first target range is 0.005wt%-0.008wt%, and the amount of aluminum wire added is 0.5-0.8Kg / ton·Q355B molten steel; The periodic aluminum deoxidation treatment also includes feeding aluminum wire into the second furnace after the initial casting to control the aluminum content in the Q355B molten steel to be within a second target range, wherein the aluminum content in the second target range is lower than the aluminum content in the first target range.

[0047] The second furnace after the start of casting: refers to the second furnace of molten steel after the start of the furnace operation.

[0048] The first target range for aluminum content is 0.005wt%-0.008wt%, and the amount of aluminum wire fed is 0.5-0.8 kg / ton of Q355B molten steel. This ensures that the amount of aluminum wire fed into the start-up furnace matches the target aluminum content range, thus placing the aluminum content in the Q355B molten steel within a range that can form sufficiently dispersed Al2O3 inclusions without causing turbulence in the molten steel. This allows the Al2O3 inclusions to form an effective and dense protective layer at the stopper head, preventing nozzle blockage due to excessive aluminum content and insufficient protective layer due to insufficient aluminum content. This ensures effective protection of the stopper head during start-up furnace operation, extends stopper life, and ultimately increases the number of continuous casting furnaces for Q355B steel.

[0049] Periodic aluminum deoxidation treatment also includes feeding aluminum wire into the second heat after the first casting to control the aluminum content in the Q355B steel to be within the second target range, and the aluminum content in the second target range is lower than that in the first target range. This allows the aluminum content in the second heat after the first casting to transition from the first target range to a lower level, thereby achieving a gradient reduction in aluminum content. This prepares the composition for subsequent heats after the second heat without using the aluminum wire feeding process, thus avoiding process fluctuations caused by a sudden drop in aluminum content. It also ensures a smooth transition and continued effectiveness of the dense protective layer at the stopper head, thereby extending the stopper life and increasing the number of consecutive heats of Q355B steel direct rolling.

[0050] The aluminum content within the first target range has a lower limit of 0.005 wt% and an upper limit of 0.008 wt%, including but not limited to 0.005 wt%, 0.006 wt%, 0.007 wt%, and 0.008 wt%. The aluminum wire feeding rate has a lower limit of 0.5 kg / ton of Q355B molten steel and an upper limit of 0.8 kg / ton of Q355B molten steel, including but not limited to 0.5 kg / ton of Q355B molten steel, 0.6 kg / ton of Q355B molten steel, 0.7 kg / ton of Q355B molten steel, and 0.8 kg / ton of Q355B molten steel.

[0051] In some embodiments, the aluminum content in the second target range is 0.003wt%-0.005wt%, and the amount of aluminum wire added to the second furnace after the start of casting is 0.3-0.5 kg / ton of Q355B molten steel; the final temperature of the second furnace after the start of casting is 5-10°C lower than the final temperature of the first furnace.

[0052] The aluminum content in the second target range is 0.003wt%-0.005wt%. After the start of casting, the amount of aluminum wire fed into the second heat is 0.3-0.5 kg / ton of Q355B molten steel. This ensures that the amount of aluminum wire fed into the second heat matches the aluminum content in the second target range, thus making the aluminum content in the second heat lower than the aluminum content in the first target range of the start-up heat. This achieves a gradient reduction in aluminum content, thereby reducing the oxidizability of the molten steel in the second heat. This prepares the process for subsequent heats without using the aluminum wire feeding process, ensures a smooth transition of the dense protective layer at the stopper head, extends the stopper life, and increases the number of consecutive heats of Q355B steel.

[0053] The final temperature of the second heat after the start of casting is 5-10℃ lower than that of the first heat after the start of casting. This lowers the temperature of the molten steel in the second heat, thereby reducing the superheat of the molten steel and the thermal erosion intensity of the stopper head. This slows down the thermal erosion rate of the stopper head. Combined with the reduced aluminum content in the second heat after the start of casting, this achieves coordinated control of temperature and aluminum content, ensuring the stability of the dense protective layer on the stopper head, extending the stopper life, and increasing the number of consecutive heats of Q355B steel.

[0054] The second target range has an aluminum content limit of 0.003 wt% and an upper limit of 0.005 wt%, including but not limited to 0.003 wt%, 0.004 wt%, and 0.005 wt%. The amount of aluminum wire fed into the second furnace after casting is limited to 0.3 kg / ton of Q355B molten steel and 0.5 kg / ton of Q355B molten steel, including but not limited to 0.3 kg / ton of Q355B molten steel, 0.4 kg / ton of Q355B molten steel, and 0.5 kg / ton of Q355B molten steel. The final temperature of the second furnace after casting is limited to a decrease of 5°C and an upper limit of 10°C compared to the final temperature of the first furnace, including but not limited to decreases of 5°C, 6°C, 7°C, 8°C, 9°C, and 10°C.

[0055] In some embodiments, the subsequent furnaces after the second furnace after the initial casting do not employ the aluminum wire feeding process, and the final temperature of the subsequent furnaces after the second furnace after the initial casting gradually decreases compared to the final temperature of the second furnace after the initial casting.

[0056] After the second heat following the initial casting, the aluminum wire feeding process is not used in subsequent heats. This prevents an additional increase in the aluminum content of the molten steel in these heats. Consequently, the Al2O3 inclusions formed during the initial and second heats maintain a dense protective layer on the stopper head, reducing alloy consumption and process complexity. Furthermore, periodic aluminum deoxidation treatment triggers the aluminum wire feeding operation again when stopper erosion characteristics are detected. This allows for periodic, concentrated aluminum deoxidation rather than per heat, optimizing the overall casting process rhythm. This ensures that the stopper protection effect is maintained while reducing the frequency of aluminum wire feeding operations, thus extending the stopper life and increasing the number of consecutive heats of Q355B steel.

[0057] The final temperature of subsequent heats after the second heat after the initial casting is gradually lower than that of the second heat after the initial casting. This causes the superheat of the molten steel in subsequent heats to gradually decrease with each casting, thereby gradually reducing the thermal erosion intensity of the molten steel on the stopper head. This, combined with the gradually decreasing aluminum content, achieves synchronous gradient control of temperature and aluminum content, thus slowing down the erosion rate of the stopper head, extending the effective maintenance time of the dense protective layer on the stopper head, extending the stopper life, and ultimately increasing the number of consecutive heats of Q355B steel.

[0058] The final temperature of subsequent furnaces after the first pour is gradually lower than the final temperature of the second pour. The gradual decrease includes, but is not limited to, a decrease of 5℃, 10℃, 15℃, or 20℃.

[0059] In some embodiments, the argon blowing stirring includes strong argon blowing and soft argon blowing, wherein the strong argon blowing pressure is 0.2-0.8 MPa and the strong argon blowing time is not less than 3 minutes; The soft blowing time of the argon is not less than 2 minutes, and the argon flow rate is controlled during the soft blowing process to ensure that the surface of the Q355B molten steel is not exposed. The forced argon blowing also includes: when adjusting the composition based on the analysis results of the reference sample, the forced argon blowing time before resampling shall not be less than 2 minutes.

[0060] Strong argon blowing: refers to the use of high argon pressure and large argon flow rate during argon blowing and stirring to promote the homogenization of the composition of Q355B molten steel and the floating of inclusions. Soft argon blowing: refers to the use of low argon pressure and small argon flow rate during argon blowing and stirring to maintain the flow state of Q355B molten steel without exposing the surface of the molten steel.

[0061] Argon blowing agitation includes strong argon blowing and soft argon blowing, thus implementing the argon blowing agitation process in two stages. Strong argon blowing achieves rapid homogenization of the composition of Q355B molten steel and sufficient flotation of inclusions, while soft argon blowing maintains the static state of Q355B molten steel and promotes further flotation of residual inclusions, thereby improving the purity of Q355B molten steel. This ensures that the subsequently formed Al2O3 inclusions have appropriate size and distribution, thus ensuring the formation quality of the dense protective layer at the stopper rod head, extending the stopper rod life, and ultimately increasing the number of continuous casting heats of Q355B steel.

[0062] The argon blowing pressure is 0.2-0.8 MPa, and the argon blowing time is no less than 3 minutes. This ensures sufficient stirring intensity and duration in the argon blowing process, thereby fully homogenizing the chemical composition of the Q355B molten steel. It also allows inclusions in the Q355B molten steel to collide, aggregate, and float to the surface for removal. This avoids insufficient stirring due to excessively low argon blowing pressure or short blowing time, and avoids splashing and secondary oxidation of molten steel due to excessively high argon blowing pressure. This ensures the uniformity and purity of the Q355B molten steel composition, which in turn ensures the effectiveness of subsequent periodic aluminum deoxidation treatment, guarantees the quality of the formation of a dense protective layer on the stopper rod head, extends the stopper rod life, and ultimately increases the number of continuous casting heats of Q355B steel.

[0063] The soft blowing time of argon is not less than 2 minutes. During the soft blowing process, the argon flow rate is controlled to ensure that the surface of the Q355B molten steel is not exposed, thereby maintaining an appropriate weak stirring state during the soft blowing process. This allows residual inclusions in the Q355B molten steel to float and be removed further, thus avoiding the exposure of the molten steel surface and secondary oxidation caused by excessive soft blowing argon flow rate, and avoiding insufficient floating force of inclusions caused by insufficient soft blowing argon flow rate, thus avoiding the oxidation loss of aluminum element caused by exposure of the molten steel surface. This ensures the stability of aluminum content in the Q355B molten steel, thus ensuring the effective enrichment of Al2O3 inclusions during subsequent tundish casting, thus ensuring the formation quality of the dense protective layer at the stopper head, thus extending the stopper life, and thus increasing the number of continuous casting heats of Q355B steel.

[0064] The forced argon blowing also includes ensuring that the forced argon blowing time is no less than 2 minutes before resampling when adjusting the composition based on the analysis results of the reference sample. This allows the molten steel after composition adjustment to have sufficient forced argon blowing stirring time, thereby ensuring that the added alloying elements are fully dissolved and evenly distributed. This, in turn, ensures the uniformity of the composition of the Q355B molten steel after composition adjustment, thus ensuring the process stability of subsequent periodic aluminum deoxidation treatment, ensuring the formation quality of the dense protective layer on the stopper head, extending the stopper life, and increasing the number of continuous casting heats of Q355B steel.

[0065] The lower limit of the forced argon blowing pressure is 0.2 MPa, and the upper limit is 0.8 MPa, including but not limited to 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa, and 0.8 MPa. The forced argon blowing time is not less than 3 minutes, including but not limited to 3 minutes, 4 minutes, 5 minutes, and 6 minutes. The soft argon blowing time is not less than 2 minutes, including but not limited to 2 minutes, 3 minutes, 4 minutes, and 5 minutes. When adjusting the composition based on the analysis results of the reference sample, the forced argon blowing time before resampling is not less than 2 minutes, including but not limited to 2 minutes, 3 minutes, 4 minutes, and 5 minutes.

[0066] In some embodiments, the temperature of the molten steel in the tundish during casting is in the range of 30°C to 45°C above the liquidus temperature, the liquidus temperature is 1510°C, and the continuous casting speed is 2.5-2.7 m / min.

[0067] The temperature of the molten steel in the tundish during initial casting is 30℃~45℃ higher than the liquidus temperature, with a liquidus temperature of 1510℃. This ensures that the Q355B molten steel has sufficient superheat to guarantee its fluidity. Consequently, even when the continuous casting speed is increased to 2.5-2.7m / min, the Q355B molten steel can still smoothly fill the crystallizer. This avoids the risk of casting speed fluctuations or steel leakage caused by excessively low molten steel temperature. Furthermore, it ensures that Al2O3 inclusions are effectively enriched at the stopper head under the action of the steel flow at higher casting speeds, forming a dense protective layer that delays stopper erosion, extends stopper life, and ultimately increases the number of continuous casting heats of Q355B steel.

[0068] The continuous casting speed is 2.5-2.7 m / min, which is higher than the conventional continuous casting speed of 1.85-1.95 m / min. This increases the flow rate of molten steel in the ladle to meet the temperature requirements of direct rolling without heating. As a result, Al2O3 inclusions migrate and accumulate towards the head of the stopper rod under the action of the higher flow rate of the steel. This leads to the rapid formation of a dense protective layer of Al2O3 inclusions at the head of the stopper rod, thereby improving the formation efficiency and coverage density of the dense protective layer. This enhances the protective effect of the stopper rod head, slows down the erosion rate of the stopper rod, extends the life of the stopper rod, and increases the number of heats that can be cast in the direct rolling of Q355B steel.

[0069] The range above the liquidus temperature has a lower limit of 30℃ and an upper limit of 45℃. The temperature of molten steel in the tundish includes, but is not limited to, 1540℃, 1545℃, 1550℃, and 1555℃. The continuous casting speed has a lower limit of 2.5m / min and an upper limit of 2.7m / min, including but not limited to 2.5m / min, 2.6m / min, and 2.7m / min.

[0070] In some embodiments, monitoring the position change of the stopper rod includes: The change in the scale of the stopper rod position data is monitored. When the number displayed on the stopper rod position returns to the initial position or is 1-3 mm lower than the initial position, it is determined that the stopper rod has been eroded, triggering the next round of aluminum wire feeding operation of the periodic aluminum deoxidation treatment.

[0071] Initial position: refers to the initial setting position of the stopper rod when the furnace starts casting at the beginning of a casting cycle, which serves as the reference position for subsequent determination of the stopper rod erosion status.

[0072] Monitoring the stopper rod position changes includes monitoring the change in the stopper rod position data scale. When the stopper rod position display number returns to the initial position or falls below the initial position by 1-3 mm, it is determined that the stopper rod has eroded, triggering the next round of aluminum wire feeding operation for periodic aluminum deoxidation treatment. This allows the determination of the stopper rod erosion state to be based on quantifiable rod position data changes, thus providing a clear operational standard for the determination of stopper rod erosion. This avoids delays or advances in the timing of aluminum wire feeding due to subjective judgment, ensuring timely replenishment of aluminum content before the dense protective layer at the stopper rod head thins and fails. This restores the aluminum content in the Q355B molten steel to the first target range, allowing new dispersed Al2O3 inclusions to form and accumulate at the stopper rod head, thereby reforming the dense protective layer at the stopper rod head. This achieves periodic regeneration of the stopper rod protective layer, continuously slowing down the stopper rod erosion rate, extending the stopper rod life, and ultimately increasing the number of continuous casting heats for Q355B steel.

[0073] The stopper rod position display number returns to the initial position, or is lower than the initial position by a value including but not limited to 1mm, 2mm, 3mm, etc.

[0074] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards. If there is no corresponding industry standard, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0075] Example 1 The Q355B molten steel is smelted in a converter, and the final carbon content of the Q355B molten steel is controlled to be 0.12wt%, the final temperature to be 1680℃, the final phosphorus content to be 0.015wt%, and the final sulfur content to be 0.012wt%.

[0076] The Q355B steel smelted in the converter is deoxidized and alloyed at tapping. The deoxidation and alloying at tapping is carried out using a barium-containing deoxidizer. The barium-containing deoxidizer is silicon-calcium-barium, and the amount of silicon-calcium-barium added is 2.0 kg / ton of Q355B steel. The method of adding the barium-containing deoxidizer includes adding 100 kg of refining slag and 100 kg of silicon-calcium-barium to the bottom of the ladle before tapping, and adding the remaining silicon-calcium-barium with the steel stream.

[0077] The deoxidized and alloyed Q355B steel is subjected to periodic aluminum deoxidation treatment; the periodic aluminum deoxidation treatment includes feeding aluminum wire during the start-up furnace cycle to control the aluminum content in the Q355B steel within a first target range; the aluminum content in the first target range is 0.006wt%, and the amount of aluminum wire added is 0.6Kg / ton·Q355B steel.

[0078] The Q355B molten steel after the periodic aluminum deoxidation treatment is subjected to argon blowing and stirring. The argon blowing and stirring includes strong argon blowing and soft argon blowing. The strong argon blowing pressure is 0.5 MPa and the strong argon blowing time is 3 min. The soft argon blowing time is 2 min. During the soft argon blowing process, the argon flow rate is controlled so that the surface of the Q355B molten steel is not exposed.

[0079] The molten Q355B steel, after being stirred by argon blowing, is hoisted to the continuous casting process for tundish casting. The continuous casting speed during tundish casting is controlled to be higher than the conventional continuous casting speed. The temperature of the molten steel in the tundish during casting is 35°C higher than the liquidus temperature, which is 1510°C. The continuous casting speed is 2.6 m / min, so that the Al2O3 inclusions accumulate on the head of the stopper rod to form a dense protective layer.

[0080] The position change of the stopper rod is monitored, and the erosion status of the stopper rod is determined based on the position change. The monitoring of the position change of the stopper rod includes monitoring the change of the stopper rod position data scale. When the number displayed on the stopper rod position returns to the initial position or is 2mm lower than the initial position, it is determined that the stopper rod has been eroded, triggering the next round of aluminum wire feeding operation of the periodic aluminum deoxidation treatment until the casting cycle ends.

[0081] The periodic aluminum deoxidation treatment also includes feeding aluminum wire into the second furnace after the initial casting to control the aluminum content in the Q355B molten steel within a second target range; the aluminum content in the second target range is 0.004 wt%, and the amount of aluminum wire added in the second furnace after the initial casting is 0.4 kg / ton of Q355B molten steel; the final temperature of the second furnace after the initial casting is 7°C lower than the final temperature of the initial furnace.

[0082] The aluminum wire feeding process is not used in the subsequent furnaces after the second furnace after the start of casting, and the final temperature of the subsequent furnaces after the second furnace after the start of casting gradually decreases compared to the final temperature of the second furnace after the start of casting.

[0083] Results data: The number of consecutive casting furnaces reached 35, the stopper rod life was extended, and there was no phenomenon of unstable flow control by the stopper rod.

[0084] Example 2 (Second Furnace Operation After Initial Casting) The Q355B molten steel is smelted in a converter, and the final carbon content of the Q355B molten steel is controlled to be 0.10wt%, the final temperature to be 1675℃, the final phosphorus content to be 0.018wt%, and the final sulfur content to be 0.015wt%.

[0085] The Q355B steel smelted in the converter is deoxidized and alloyed at tapping. The deoxidation and alloying at tapping is carried out using a barium-containing deoxidizer. The barium-containing deoxidizer is silicon-calcium-barium, and the amount of silicon-calcium-barium added is 2.0 kg / ton of Q355B steel. The method of adding the barium-containing deoxidizer includes adding 100 kg of refining slag and 100 kg of silicon-calcium-barium to the bottom of the ladle before tapping, and adding the remaining silicon-calcium-barium with the steel stream.

[0086] The deoxidized and alloyed Q355B steel is subjected to periodic aluminum deoxidation treatment; the periodic aluminum deoxidation treatment includes feeding aluminum wire during the start-up furnace cycle to control the aluminum content in the Q355B steel within a first target range; the aluminum content in the first target range is 0.007wt%, and the amount of aluminum wire added is 0.7Kg / ton·Q355B steel.

[0087] The Q355B molten steel after the periodic aluminum deoxidation treatment is subjected to argon blowing and stirring. The argon blowing and stirring includes strong argon blowing and soft argon blowing. The strong argon blowing pressure is 0.6 MPa and the strong argon blowing time is 4 min. The soft argon blowing time is 3 min. During the soft argon blowing process, the argon flow rate is controlled so that the surface of the Q355B molten steel is not exposed.

[0088] The molten Q355B steel, after being stirred by argon blowing, is hoisted to the continuous casting process for casting in the tundish. The casting speed during casting in the tundish is controlled to be higher than the conventional casting speed. The temperature of the molten steel in the tundish during casting is 40°C higher than the liquidus temperature, which is 1510°C. The casting speed is 2.5 m / min, so that the Al2O3 inclusions accumulate on the head of the stopper rod to form a dense protective layer.

[0089] The position change of the stopper rod is monitored, and the erosion status of the stopper rod is determined based on the position change. The monitoring of the position change of the stopper rod includes monitoring the change of the stopper rod position data scale. When the number displayed on the stopper rod position returns to the initial position or is 1 mm lower than the initial position, it is determined that the stopper rod has been eroded, triggering the next round of aluminum wire feeding operation of the periodic aluminum deoxidation treatment until the casting cycle ends.

[0090] The periodic aluminum deoxidation treatment also includes feeding aluminum wire into the second furnace after the initial casting to control the aluminum content in the Q355B molten steel within a second target range; the aluminum content in the second target range is 0.005wt%, and the amount of aluminum wire added in the second furnace after the initial casting is 0.5Kg / ton·Q355B molten steel; the final temperature of the second furnace after the initial casting is 5℃ lower than the final temperature of the initial furnace.

[0091] The aluminum wire feeding process is not used in the subsequent furnaces after the second furnace after the start of casting, and the final temperature of the subsequent furnaces after the second furnace after the start of casting gradually decreases compared to the final temperature of the second furnace after the start of casting.

[0092] Performance data: The number of consecutive casting heats reached 32, the flow control of the stopper rod was stable, and the direct rolling temperature was stable.

[0093] Example 3 (Upper limit of the first target range) The Q355B molten steel is smelted in a converter, and the final carbon content of the Q355B molten steel is controlled to be 0.15wt%, the final temperature to be 1685℃, the final phosphorus content to be 0.020wt%, and the final sulfur content to be 0.018wt%.

[0094] The Q355B steel smelted in the converter is deoxidized and alloyed at tapping. The deoxidation and alloying at tapping is carried out using a barium-containing deoxidizer. The barium-containing deoxidizer is silicon-calcium-barium, and the amount of silicon-calcium-barium added is 2.0 kg / ton of Q355B steel. The method of adding the barium-containing deoxidizer includes adding 100 kg of refining slag and 100 kg of silicon-calcium-barium to the bottom of the ladle before tapping, and adding the remaining silicon-calcium-barium with the steel stream.

[0095] The deoxidized and alloyed Q355B steel is subjected to periodic aluminum deoxidation treatment; the periodic aluminum deoxidation treatment includes feeding aluminum wire during the start-up furnace cycle to control the aluminum content in the Q355B steel within a first target range; the aluminum content in the first target range is 0.008wt%, and the amount of aluminum wire added is 0.8Kg / ton·Q355B steel.

[0096] The Q355B molten steel after the periodic aluminum deoxidation treatment is subjected to argon blowing and stirring. The argon blowing and stirring includes strong argon blowing and soft argon blowing. The strong argon blowing pressure is 0.8 MPa and the strong argon blowing time is 5 min. The soft argon blowing time is 4 min. During the soft argon blowing process, the argon flow rate is controlled so that the surface of the Q355B molten steel is not exposed.

[0097] The molten Q355B steel, after being stirred by argon blowing, is hoisted to the continuous casting process for casting in the tundish. The casting speed during casting in the tundish is controlled to be higher than the conventional casting speed. The temperature of the molten steel in the tundish during casting is 45°C higher than the liquidus temperature, which is 1510°C. The casting speed is 2.7 m / min, so that the Al2O3 inclusions accumulate on the head of the stopper rod to form a dense protective layer.

[0098] The position change of the stopper rod is monitored, and the erosion status of the stopper rod is determined based on the position change. The monitoring of the position change of the stopper rod includes monitoring the change of the stopper rod position data scale. When the number displayed on the stopper rod position returns to the initial position or is 3mm lower than the initial position, it is determined that the stopper rod has been eroded, triggering the next round of aluminum wire feeding operation of the periodic aluminum deoxidation treatment until the casting cycle ends.

[0099] The periodic aluminum deoxidation treatment also includes feeding aluminum wire into the second furnace after the initial casting to control the aluminum content in the Q355B molten steel within a second target range; the aluminum content in the second target range is 0.003wt%, and the amount of aluminum wire added in the second furnace after the initial casting is 0.3Kg / ton·Q355B molten steel; the final temperature of the second furnace after the initial casting is 10℃ lower than the final temperature of the initial furnace.

[0100] The aluminum wire feeding process is not used in the subsequent furnaces after the second furnace after the start of casting, and the final temperature of the subsequent furnaces after the second furnace after the start of casting gradually decreases compared to the final temperature of the second furnace after the start of casting.

[0101] Results data: The number of consecutive casting furnaces reached 33, and an effective protective layer was formed on the head of the stopper rod.

[0102] Example 4 (Lower Limit of First Target Range) The Q355B molten steel is smelted in a converter, and the final carbon content of the Q355B molten steel is controlled to be 0.08wt%, the final temperature to be 1670℃, the final phosphorus content to be 0.012wt%, and the final sulfur content to be 0.010wt%.

[0103] The Q355B steel smelted in the converter is deoxidized and alloyed at tapping. The deoxidation and alloying at tapping is carried out using a barium-containing deoxidizer. The barium-containing deoxidizer is silicon-calcium-barium, and the amount of silicon-calcium-barium added is 2.0 kg / ton of Q355B steel. The method of adding the barium-containing deoxidizer includes adding 100 kg of refining slag and 100 kg of silicon-calcium-barium to the bottom of the ladle before tapping, and adding the remaining silicon-calcium-barium with the steel stream.

[0104] The deoxidized and alloyed Q355B steel is subjected to periodic aluminum deoxidation treatment; the periodic aluminum deoxidation treatment includes feeding aluminum wire during the start-up furnace cycle to control the aluminum content in the Q355B steel within a first target range; the aluminum content in the first target range is 0.005wt%, and the amount of aluminum wire added is 0.5Kg / ton·Q355B steel.

[0105] The Q355B molten steel after the periodic aluminum deoxidation treatment is subjected to argon blowing and stirring. The argon blowing and stirring includes strong argon blowing and soft argon blowing. The strong argon blowing pressure is 0.2 MPa and the strong argon blowing time is 3 min. The soft argon blowing time is 2 min. During the soft argon blowing process, the argon flow rate is controlled so that the surface of the Q355B molten steel is not exposed.

[0106] The molten Q355B steel, after being stirred by argon blowing, is hoisted to the continuous casting process for casting in the tundish. The casting speed during casting in the tundish is controlled to be higher than the conventional casting speed. The temperature of the molten steel in the tundish during casting is 30°C higher than the liquidus temperature, which is 1510°C. The casting speed is 2.5 m / min, so that the Al2O3 inclusions accumulate on the head of the stopper rod to form a dense protective layer.

[0107] The position change of the stopper rod is monitored, and the erosion status of the stopper rod is determined based on the position change. The monitoring of the position change of the stopper rod includes monitoring the change of the stopper rod position data scale. When the number displayed on the stopper rod position returns to the initial position or is 2mm lower than the initial position, it is determined that the stopper rod has been eroded, triggering the next round of aluminum wire feeding operation of the periodic aluminum deoxidation treatment until the casting cycle ends.

[0108] The periodic aluminum deoxidation treatment also includes feeding aluminum wire into the second furnace after the initial casting to control the aluminum content in the Q355B molten steel within a second target range; the aluminum content in the second target range is 0.004 wt%, and the amount of aluminum wire added in the second furnace after the initial casting is 0.4 kg / ton of Q355B molten steel; the final temperature of the second furnace after the initial casting is 8°C lower than the final temperature of the initial furnace.

[0109] The aluminum wire feeding process is not used in the subsequent furnaces after the second furnace after the start of casting, and the final temperature of the subsequent furnaces after the second furnace after the start of casting gradually decreases compared to the final temperature of the second furnace after the start of casting.

[0110] Results data: The number of consecutive casting furnaces reached 30, and the life of the stopper rod was effectively extended.

[0111] Example 5 (Low Endpoint Carbon Compensation) The Q355B molten steel is smelted in a converter, and the final carbon content of the Q355B molten steel is controlled to be 0.05wt%, the final temperature to be 1680℃, the final phosphorus content to be 0.015wt%, and the final sulfur content to be 0.012wt%.

[0112] The Q355B steel smelted in the converter is deoxidized and alloyed at tapping. The deoxidation and alloying at tapping is carried out using a barium-containing deoxidizer. The barium-containing deoxidizer is silicon-calcium-barium, and the amount of silicon-calcium-barium added is 2.0 kg / ton of Q355B steel. When the final carbon content of the Q355B steel is less than 0.07 wt%, 10 kg / heat of silicon-calcium-barium is added for every 0.01 wt% below the carbon content, and the total increase in the amount of silicon-calcium-barium is 20 kg / heat. The method of adding the barium-containing deoxidizer includes adding 100 kg of refining slag and 100 kg of silicon-calcium-barium to the bottom of the ladle before tapping, and adding the remaining silicon-calcium-barium with the steel stream.

[0113] The deoxidized and alloyed Q355B steel is subjected to periodic aluminum deoxidation treatment; the periodic aluminum deoxidation treatment includes feeding aluminum wire during the start-up furnace cycle to control the aluminum content in the Q355B steel within a first target range; the aluminum content in the first target range is 0.006wt%, and the amount of aluminum wire added is 0.6Kg / ton·Q355B steel.

[0114] The Q355B molten steel after the periodic aluminum deoxidation treatment is subjected to argon blowing and stirring. The argon blowing and stirring includes strong argon blowing and soft argon blowing. The strong argon blowing pressure is 0.5 MPa and the strong argon blowing time is 3 min. The soft argon blowing time is 2 min. During the soft argon blowing process, the argon flow rate is controlled so that the surface of the Q355B molten steel is not exposed.

[0115] The molten Q355B steel, after being stirred by argon blowing, is hoisted to the continuous casting process for tundish casting. The continuous casting speed during tundish casting is controlled to be higher than the conventional continuous casting speed. The temperature of the molten steel in the tundish during casting is 35°C higher than the liquidus temperature, which is 1510°C. The continuous casting speed is 2.6 m / min, so that the Al2O3 inclusions accumulate on the head of the stopper rod to form a dense protective layer.

[0116] The position change of the stopper rod is monitored, and the erosion status of the stopper rod is determined based on the position change. The monitoring of the position change of the stopper rod includes monitoring the change of the stopper rod position data scale. When the number displayed on the stopper rod position returns to the initial position or is 2mm lower than the initial position, it is determined that the stopper rod has been eroded, triggering the next round of aluminum wire feeding operation of the periodic aluminum deoxidation treatment until the casting cycle ends.

[0117] The periodic aluminum deoxidation treatment also includes feeding aluminum wire into the second furnace after the initial casting to control the aluminum content in the Q355B molten steel within a second target range; the aluminum content in the second target range is 0.004 wt%, and the amount of aluminum wire added in the second furnace after the initial casting is 0.4 kg / ton of Q355B molten steel; the final temperature of the second furnace after the initial casting is 7°C lower than the final temperature of the initial furnace.

[0118] The aluminum wire feeding process is not used in the subsequent furnaces after the second furnace after the start of casting, and the final temperature of the subsequent furnaces after the second furnace after the start of casting gradually decreases compared to the final temperature of the second furnace after the start of casting.

[0119] Performance data: The number of consecutive casting furnaces reached 31, and the stopper rod protection effect was good under low endpoint carbon conditions.

[0120] Comparative Example 1 (without direct rolling process) The Q355B molten steel is smelted in a converter, and the final carbon content of the Q355B molten steel is controlled to be 0.12wt%, the final temperature to be 1680℃, the final phosphorus content to be 0.015wt%, and the final sulfur content to be 0.012wt%.

[0121] The Q355B steel smelted in the converter is deoxidized and alloyed at tapping. The deoxidation and alloying at tapping is carried out using a barium-containing deoxidizer. The barium-containing deoxidizer is silicon-calcium-barium, and the amount of silicon-calcium-barium added is 2.0 kg / ton of Q355B steel. The method of adding the barium-containing deoxidizer includes adding 100 kg of refining slag and 100 kg of silicon-calcium-barium to the bottom of the ladle before tapping, and adding the remaining silicon-calcium-barium with the steel stream.

[0122] The deoxidized and alloyed Q355B steel is stirred by argon blowing; the argon blowing includes strong argon blowing and soft argon blowing, the strong argon blowing pressure is 0.5MPa and the strong argon blowing time is 3min; the soft argon blowing time is 2min, and the argon flow rate is controlled during the soft argon blowing process to ensure that the surface of the Q355B steel is not exposed.

[0123] The molten Q355B steel, after being stirred by argon, is hoisted to the continuous casting process for casting in the tundish, and the casting speed during casting in the tundish is controlled to be the conventional continuous casting speed of 1.9 m / min; the temperature of the molten steel in the tundish during casting is within 35°C above the liquidus temperature, and the liquidus temperature is 1510°C.

[0124] Results data: The number of consecutive castings was 25, but the temperature at the head of the billet was too low to meet the requirements for direct rolling without heating.

[0125] Comparative Example 2 (using direct rolling but without periodic aluminum deoxidation) The Q355B molten steel is smelted in a converter, and the final carbon content of the Q355B molten steel is controlled to be 0.12wt%, the final temperature to be 1680℃, the final phosphorus content to be 0.015wt%, and the final sulfur content to be 0.012wt%.

[0126] The Q355B steel smelted in the converter is deoxidized and alloyed at tapping. The deoxidation and alloying at tapping is carried out using a barium-containing deoxidizer. The barium-containing deoxidizer is silicon-calcium-barium, and the amount of silicon-calcium-barium added is 2.0 kg / ton of Q355B steel. The method of adding the barium-containing deoxidizer includes adding 100 kg of refining slag and 100 kg of silicon-calcium-barium to the bottom of the ladle before tapping, and adding the remaining silicon-calcium-barium with the steel stream.

[0127] The deoxidized and alloyed Q355B steel is stirred by argon blowing; the argon blowing includes strong argon blowing and soft argon blowing, the strong argon blowing pressure is 0.5MPa and the strong argon blowing time is 3min; the soft argon blowing time is 2min, and the argon flow rate is controlled during the soft argon blowing process to ensure that the surface of the Q355B steel is not exposed.

[0128] The molten Q355B steel, after being stirred by argon blowing, is hoisted to the continuous casting process for casting in the tundish, and the casting speed during casting in the tundish is controlled to be higher than the conventional casting speed. The temperature of the molten steel in the tundish during casting is 35°C higher than the liquidus temperature, the liquidus temperature is 1510°C, and the casting speed is 2.6 m / min.

[0129] Results data: In the later stages of a casting cycle (more than 20 heats), the flow control of the stopper rod became unstable, resulting in 22 consecutive heats being cast, forcing a production halt.

[0130] Comparative Example 3 (Excessive aluminum content leading to nozzle nodule formation) The Q355B molten steel is smelted in a converter, and the final carbon content of the Q355B molten steel is controlled to be 0.12wt%, the final temperature to be 1680℃, the final phosphorus content to be 0.015wt%, and the final sulfur content to be 0.012wt%.

[0131] The Q355B steel smelted in the converter is deoxidized and alloyed at tapping. The deoxidation and alloying at tapping is carried out using a barium-containing deoxidizer. The barium-containing deoxidizer is silicon-calcium-barium, and the amount of silicon-calcium-barium added is 2.0 kg / ton of Q355B steel. The method of adding the barium-containing deoxidizer includes adding 100 kg of refining slag and 100 kg of silicon-calcium-barium to the bottom of the ladle before tapping, and adding the remaining silicon-calcium-barium with the steel stream.

[0132] The deoxidized and alloyed Q355B steel is subjected to periodic aluminum deoxidation treatment; the periodic aluminum deoxidation treatment includes feeding aluminum wire during the start-up furnace cycle to control the aluminum content in the Q355B steel to be 0.010wt%, and the amount of aluminum wire added is 1.0Kg / ton·Q355B steel.

[0133] The Q355B molten steel after the periodic aluminum deoxidation treatment is subjected to argon blowing and stirring. The argon blowing and stirring includes strong argon blowing and soft argon blowing. The strong argon blowing pressure is 0.5 MPa and the strong argon blowing time is 3 min. The soft argon blowing time is 2 min. During the soft argon blowing process, the argon flow rate is controlled so that the surface of the Q355B molten steel is not exposed.

[0134] The molten Q355B steel, after being stirred by argon blowing, is hoisted to the continuous casting process for casting in the tundish, and the casting speed during casting in the tundish is controlled to be higher than the conventional casting speed. The temperature of the molten steel in the tundish during casting is 35°C higher than the liquidus temperature, the liquidus temperature is 1510°C, and the casting speed is 2.6 m / min.

[0135] Results data: Molten steel turbulent flow occurred, forming nozzle blockages, resulting in only 8 consecutive heats being cast, forcing production to be interrupted.

[0136] Comparative Example 4 (too low aluminum content provides no protection) The Q355B molten steel is smelted in a converter, and the final carbon content of the Q355B molten steel is controlled to be 0.12wt%, the final temperature to be 1680℃, the final phosphorus content to be 0.015wt%, and the final sulfur content to be 0.012wt%.

[0137] The Q355B steel smelted in the converter is deoxidized and alloyed at tapping. The deoxidation and alloying at tapping is carried out using a barium-containing deoxidizer. The barium-containing deoxidizer is silicon-calcium-barium, and the amount of silicon-calcium-barium added is 2.0 kg / ton of Q355B steel. The method of adding the barium-containing deoxidizer includes adding 100 kg of refining slag and 100 kg of silicon-calcium-barium to the bottom of the ladle before tapping, and adding the remaining silicon-calcium-barium with the steel stream.

[0138] The deoxidized and alloyed Q355B steel is subjected to periodic aluminum deoxidation treatment; the periodic aluminum deoxidation treatment includes feeding aluminum wire during the start-up furnace cycle to control the aluminum content in the Q355B steel to be 0.002wt%, and the amount of aluminum wire added is 0.2Kg / ton·Q355B steel.

[0139] The Q355B molten steel after the periodic aluminum deoxidation treatment is subjected to argon blowing and stirring. The argon blowing and stirring includes strong argon blowing and soft argon blowing. The strong argon blowing pressure is 0.5 MPa and the strong argon blowing time is 3 min. The soft argon blowing time is 2 min. During the soft argon blowing process, the argon flow rate is controlled so that the surface of the Q355B molten steel is not exposed.

[0140] The molten Q355B steel, after being stirred by argon blowing, is hoisted to the continuous casting process for casting in the tundish, and the casting speed during casting in the tundish is controlled to be higher than the conventional casting speed. The temperature of the molten steel in the tundish during casting is 35°C higher than the liquidus temperature, the liquidus temperature is 1510°C, and the casting speed is 2.6 m / min.

[0141] Monitor the position change of the stopper rod and determine the erosion state of the stopper rod based on the position change.

[0142] Results data: The aluminum content was too low to provide adequate protection for the expansion bar, resulting in severe corrosion of the stopper bar. The number of consecutive casting furnaces was 18, and the flow could not be controlled by the stopper bar.

[0143] Comparative Example 5 (without barium-containing deoxidizer) The Q355B molten steel is smelted in a converter, and the final carbon content of the Q355B molten steel is controlled to be 0.12wt%, the final temperature to be 1680℃, the final phosphorus content to be 0.015wt%, and the final sulfur content to be 0.012wt%.

[0144] The Q355B steel smelted in the converter is deoxidized and alloyed at the tapping stage. The deoxidation and alloying process uses an aluminum deoxidizer and does not use a barium-containing deoxidizer.

[0145] The deoxidized and alloyed Q355B steel is subjected to periodic aluminum deoxidation treatment; the periodic aluminum deoxidation treatment includes feeding aluminum wire during the start-up furnace cycle to control the aluminum content in the Q355B steel within a first target range; the aluminum content in the first target range is 0.006wt%, and the amount of aluminum wire added is 0.6Kg / ton·Q355B steel.

[0146] The Q355B molten steel after the periodic aluminum deoxidation treatment is subjected to argon blowing and stirring. The argon blowing and stirring includes strong argon blowing and soft argon blowing. The strong argon blowing pressure is 0.5 MPa and the strong argon blowing time is 3 min. The soft argon blowing time is 2 min. During the soft argon blowing process, the argon flow rate is controlled so that the surface of the Q355B molten steel is not exposed.

[0147] The molten Q355B steel, after being stirred by argon blowing, is hoisted to the continuous casting process for tundish casting. The continuous casting speed during tundish casting is controlled to be higher than the conventional continuous casting speed. The temperature of the molten steel in the tundish during casting is 35°C higher than the liquidus temperature, which is 1510°C. The continuous casting speed is 2.6 m / min, so that the Al2O3 inclusions accumulate on the head of the stopper rod to form a dense protective layer.

[0148] Monitor the position change of the stopper rod and determine the erosion state of the stopper rod based on the position change.

[0149] Results data: The distribution of Al2O3 inclusions was uneven, the protective layer at the head of the stopper rod was not dense, the number of consecutive casting furnaces was 24, and the life of the stopper rod was not effectively extended.

[0150] Experimental methods for evaluating results: 1. Method for determining the number of consecutive casting furnaces Record the number of consecutive castings from the start of casting in the tundish to the end of casting in the tundish. The starting point is the normal start of casting in the tundish, and the ending point is the forced interruption of production due to unstable flow control of the stopper rod or a safety accident. Count the number of consecutive castings.

[0151] 2. Method for determining the flow control state of the stopper rod The change in the scale of the stopper rod position data is monitored by the stopper rod controller in the continuous casting main control room, and the fluctuation range of the stopper rod position display number is recorded. When the fluctuation of the stopper rod position display number exceeds ±2mm or the phenomenon that the steel flow cannot be effectively controlled even when the stopper rod is lowered to the lowest position is observed, it is determined that the stopper rod flow control is unstable.

[0152] 3. Method for determining nodule formation at the sprue Observe the flow state of molten steel at the tundish nozzle during continuous casting. When the molten steel flow is obstructed, the flow rate is reduced, or it is completely blocked, and inspection confirms that there is Al2O3 deposits blocking the nozzle, it is determined to be nozzle nodule formation.

[0153] 4. Method for determining direct rolling temperature requirements The temperature of the 12m billet head is measured at the hydraulic shear segment shearing position. When the billet head temperature meets the temperature requirements for direct rolling without heating, it is determined that the direct rolling temperature requirements are met; when the billet head temperature is lower than the temperature required for direct rolling without heating, it is determined that the direct rolling temperature requirements are not met.

[0154] 5. Method for determining the life condition of stopper rods The erosion status of the stopper rod is determined by the change in the stopper rod position data scale. When the stopper rod position display number returns to the initial position or is 1-3 mm lower than the initial position, it is determined that the stopper rod has eroded. The number of furnace cycles from the start of casting to the occurrence of stopper rod erosion is counted to evaluate the stopper rod life status.

[0155] As shown by the above performance data, the technological advancements of this application's technical solution include: 1. The number of consecutive casting heats in Examples 1 to 5 reached 35, 32, 33, 30, and 31 heats respectively, with an average of 32.2 heats. Comparative Example 2 (using direct rolling but without periodic aluminum deoxidation) had 22 heats, and Comparative Example 4 (with excessively low aluminum content) had 18 heats. The technical solution of this application increases the number of consecutive casting heats by 45.5% to 59.1% compared to Comparative Example 2, and by 66.7% to 94.4% compared to Comparative Example 4, significantly increasing the number of consecutive casting heats for Q355B steel direct rolling.

[0156] 2. In Examples 1 to 5, the stopper rod lifespan was "extended" or "good," and the stopper rod flow control was "stable." In Comparative Example 2, the stopper rod lifespan was "not extended," and unstable flow control occurred in the later stages of casting. In Comparative Example 4, the stopper rod lifespan was "severely eroded," and the stopper rod could not control the flow. The technical solution of this application uses periodic aluminum deoxidation treatment to continuously form a dense protective layer on the stopper rod head, effectively slowing down the stopper rod erosion rate and extending the stopper rod lifespan.

[0157] 3. Examples 1 to 5 all meet the direct rolling temperature requirements, and the continuous casting speed is higher than the conventional continuous casting speed (2.5-2.7 m / min). Although Comparative Example 1 achieves 25 consecutive heats, it does not meet the direct rolling temperature requirements. The technical solution of this application, while ensuring an increase in the number of consecutive heats, continuously meets the temperature requirements for direct rolling without heating by using a tundish opening speed higher than the conventional continuous casting speed, thus achieving synergistic optimization of the number of consecutive heats and the direct rolling temperature.

[0158] 4. No nozzle clogging occurred in Examples 1 to 5; in Comparative Example 3, the high aluminum content (0.010 wt%) caused turbulent steel flow and nozzle clogging, resulting in only 8 consecutive heats. The technical solution of this application limits the aluminum content within the first target range to 0.005 wt%-0.008 wt%, effectively forming a stopper rod while avoiding the risk of nozzle clogging caused by excessive aluminum content, thus achieving a balance between protective effect and process smoothness.

[0159] 5. In Example 5, under low endpoint carbon conditions (0.05 wt%), by increasing the amount of silicon, calcium, and barium added (20 kg / furnace), 31 consecutive furnaces were still achieved with good stopper rod protection. The technical solution of this application, by establishing a dynamic compensation relationship between the endpoint carbon content and the amount of silicon, calcium, and barium added, adapts to smelting conditions with fluctuations in endpoint carbon content, thereby enhancing the stability and operability of the process.

[0160] 6. In Comparative Example 2, which did not employ periodic aluminum deoxidation treatment, the stopper rod exhibited unstable flow control after approximately 20 heats. Examples 1 to 5 all employed periodic aluminum deoxidation treatment, triggering the next round of aluminum wire feeding operation by monitoring changes in the stopper rod position, thus enabling periodic regeneration of the stopper rod protection and extending the number of consecutive casting heats to over 30. The periodic cycle mechanism of "rod expansion protection - rod drop erosion - re-feeding aluminum wire to restore protection" established by the technical solution of this application overcomes the limitation of the existing technology where the stopper rod life monotonically decreases with the extension of casting cycles.

[0161] Detailed explanation of the attached diagram: Figure 1 This is a schematic diagram of the continuous casting tundish and stopper rod provided in an embodiment of this application. As can be seen from the figure: The tundish is a container for holding molten steel at high temperatures. A stopper rod is vertically positioned inside the tundish, its head extending above the internal nozzle. The internal nozzle is located at the bottom of the tundish, connecting the interior of the tundish to the drain outlet. The drain outlet is located below the internal nozzle, connecting it to the crystallizer. The crystallizer is located below the drain outlet and receives molten steel from it.

[0162] The stopper rod can be raised and lowered via a hydraulic control system, thereby adjusting the gap between the stopper rod head and the internal nozzle, and thus adjusting the flow rate of high-temperature molten steel from the internal nozzle to the lower nozzle, so as to match the flow rate of high-temperature molten steel with the continuous casting billet pulling speed.

[0163] During the casting process in the tundish, Al2O3 inclusions in the high-temperature molten steel accumulate at the stopper head as the steel flows, forming a dense protective layer on the surface of the stopper head. This dense protective layer covers the stopper head substrate, thereby reducing the direct scouring and chemical corrosion of the stopper head substrate by the high-temperature molten steel, thus slowing down the erosion rate of the stopper and extending its service life.

[0164] When the stopper rod is severely corroded, pieces fall off the head of the stopper rod. Even if the stopper rod is lowered to the lowest position, the gap between the head of the stopper rod and the internal nozzle cannot be effectively closed, which leads to uncontrolled flow of high-temperature molten steel, resulting in casting speed fluctuations or safety accidents.

[0165] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for increasing the number of continuous casting heats in direct rolling of Q355B steel, characterized in that, The method includes the following steps: The Q355B molten steel is smelted in a converter, and the final carbon content, final temperature and final harmful element content of the Q355B molten steel are controlled. The Q355B steel smelted in the converter is deoxidized and alloyed after tapping, and the deoxidation and alloying is carried out by deoxidation using a barium-containing deoxidizer. The deoxidized and alloyed Q355B steel is subjected to periodic aluminum deoxidation treatment to form dispersed Al2O3 inclusions in the Q355B steel. The periodic aluminum deoxidation treatment includes feeding aluminum wire in the start-up heat to control the aluminum content in the Q355B steel within a first target range, and feeding aluminum wire again in a subsequent specific heat when stopper erosion characteristics are detected to control the aluminum content in the Q355B steel back to the first target range, thus forming a periodic cyclic protection. The molten Q355B steel after the periodic aluminum deoxidation treatment was stirred by argon blowing. The molten Q355B steel, after being stirred by argon blowing, is hoisted to the continuous casting process for tundish casting. The continuous casting speed during tundish casting is controlled to be higher than the conventional continuous casting speed, so that the Al2O3 inclusions are enriched in the head of the stopper rod to form a dense protective layer. The position change of the stopper rod is monitored, and the erosion state of the stopper rod is determined based on the position change. The cyclic execution of the periodic aluminum deoxidation treatment is triggered based on the erosion state of the stopper rod until the casting cycle ends.

2. The method according to claim 1, characterized in that, The final carbon content of the Q355B molten steel is 0.07wt% to 0.17wt%, the final temperature of the Q355B molten steel is 1670℃ to 1690℃, and the final harmful element content of the Q355B molten steel is phosphorus content ≤ 0.025wt% and sulfur content ≤ 0.025wt%.

3. The method according to claim 1, characterized in that, The barium-containing deoxidizer is silicon-calcium-barium, and the amount of silicon-calcium-barium added is 2.0 kg / ton of Q355B molten steel; The method of adding the barium-containing deoxidizer includes adding refining slag and the silicon-calcium-barium compound to the bottom of the ladle before tapping, and adding the remaining silicon-calcium-barium compound with the steel stream.

4. The method according to claim 3, characterized in that, The amount of added silicon-calcium-barium also includes: When the final carbon content of the Q355B molten steel is less than 0.07wt%, the amount of silicon, calcium, and barium is increased by 10kg / furnace for every 0.01wt% below the carbon content.

5. The method according to claim 1, characterized in that, The aluminum content in the first target range is 0.005wt%-0.008wt%, and the amount of aluminum wire added is 0.5-0.8Kg / ton·Q355B molten steel; The periodic aluminum deoxidation treatment also includes feeding aluminum wire into the second furnace after the initial casting to control the aluminum content in the Q355B molten steel to be within a second target range, wherein the aluminum content in the second target range is lower than the aluminum content in the first target range.

6. The method according to claim 5, characterized in that, The aluminum content in the second target range is 0.003wt%-0.005wt%, and the amount of aluminum wire added to the second furnace after the start of casting is 0.3-0.5Kg / ton·Q355B molten steel; the final temperature of the second furnace after the start of casting is 5-10℃ lower than the final temperature of the furnace start-up.

7. The method according to claim 5, characterized in that, The aluminum wire feeding process is not used in the subsequent furnaces after the second furnace after the start of casting, and the final temperature of the subsequent furnaces after the second furnace after the start of casting gradually decreases compared to the final temperature of the second furnace after the start of casting.

8. The method according to claim 1, characterized in that, The argon blowing and stirring includes strong argon blowing and soft argon blowing. The strong argon blowing pressure is 0.2-0.8 MPa, and the strong argon blowing time is not less than 3 minutes. The soft blowing time of the argon is not less than 2 minutes, and the argon flow rate is controlled during the soft blowing process to ensure that the surface of the Q355B molten steel is not exposed. The forced argon blowing also includes: when adjusting the composition based on the analysis results of the reference sample, the forced argon blowing time before resampling shall not be less than 2 minutes.

9. The method according to claim 1, characterized in that, The temperature of the molten steel in the tundish during casting is 30°C to 45°C higher than the liquidus temperature, the liquidus temperature is 1510°C, and the continuous casting speed is 2.5-2.7 m / min.

10. The method according to claim 1, characterized in that, The monitoring of stopcock position changes includes: The change in the scale of the stopper rod position data is monitored. When the number displayed on the stopper rod position returns to the initial position or is 1-3 mm lower than the initial position, it is determined that the stopper rod has been eroded, triggering the next round of aluminum wire feeding operation of the periodic aluminum deoxidation treatment.

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