Method for continuously casting dissimilar steel by sharing same tundish

Abstract

The invention provides a method for continuously casting dissimilar steel by sharing the same tundish, which is characterized by comprising the following process steps of: 1) when high-carbon steel is smelted and cast to the last but one furnace, controlling the temperature of high-carbon molten steel to be 5-10 DEG C lower than the temperature of normal molten steel, and controlling the temperature of a continuous casting large ladle to be 1570-1575 + / -7 DEG C; the method comprises the following steps of (1) pouring molten high-carbon steel into a continuous casting tundish through a large continuous casting ladle, (2) pouring the last but one furnace of molten high-carbon steel into the continuous casting tundish through the large continuous casting ladle, and raising the liquid level of the molten high-carbon steel in the tundish, (3) putting a covering agent into the continuous casting tundish after deslagging of the last but one furnace of molten high-carbon steel in the continuous casting tundish is completed, and (4) before pouring of the last furnace of molten high-carbon steel, replacing a quick-change water gap of the continuous casting tundish with a water gap with the diameter phi of 17.5 mm, and reducing the pulling speed from 2.5 m / min to 2.0 m / min.

Description

Technical Field

[0001] This invention relates to the field of continuous casting technology for small billets, and in particular to a method for continuous casting of dissimilar steels using the same tundish, in order to reduce losses during continuous casting of dissimilar steels. Background Technology

[0002] In recent years, with changes in the demand patterns of steel market users, planned production based on sales orders has become the main production mode for steel enterprises. Under this mode, steelmaking production has shifted from long-cycle production of the same steel grade and specifications to short-cycle production of different steel grades and specifications. With the same output requirements, this mode increases the number of continuous casting tundishes and the energy consumption resulting from frequent start-ups and shutdowns of converters, refining furnaces, and continuous casting machines on the main production line. It also reduces production efficiency, significantly impacting steelmaking cost control, operational efficiency, and the labor intensity of employees. Particularly in industrial wire rod production, due to the lack of large-scale production capacity, tundishes that are available for 30 hours often only complete their production plan in 12 hours, requiring replacement to produce another 12 hours' worth of steel grades and specifications. This results in tundish utilization rates falling below 50% and an increased need for new tundishes, further complicating steelmaking cost control.

[0003] With the continuous increase in the output, variety, and specifications of industrial wire rod, the production mode of sharing a single tundish with dissimilar steels can fundamentally solve the contradiction in existing technologies, which on the one hand result in a tundish utilization rate of less than 50%, and on the other hand require increasing the number of tundishes, laying the operational foundation for subsequent "product differentiation" production. However, in the process of implementing the production of dissimilar steels using a single tundish, due to the different chemical compositions of different steel grades, such as HPB300 and Q195 steels, the significant difference in carbon content can easily cause production fluctuations such as steel leakage and nozzle formation during the connection process due to factors such as temperature changes, casting speed changes, cooling changes, and billet shrinkage changes, leading to quality fluctuations. This is the difficulty in continuous casting production of dissimilar steels using a single tundish. Therefore, it is necessary to improve the existing technology. Summary of the Invention

[0004] In view of the problems existing in the prior art, and in combination with the steel grades produced, this invention provides a method for continuous casting of dissimilar steels using the same tundish through process control and operation optimization, which is suitable for large-scale production of multiple steel grades, and has low cost and controllable quality.

[0005] This invention is achieved through the following technical solution: a method for continuous casting of dissimilar steels using the same tundish, comprising the following process steps: 1) When smelting and casting high-carbon steel to the penultimate heat, control the temperature of the high-carbon steel molten steel to be 5-10℃ lower than the normal molten steel temperature, and control the continuous casting ladle temperature to 1570-1575±7℃. 2) After pouring the second-to-last heat of high-carbon steel into the tundish through the continuous casting ladle, raise the molten steel level in the tundish until slag is discharged from the molten steel side of the tundish, thereby reducing the slag content in the molten steel and improving the purity of the molten steel. 3) After the second-to-last heat of high-carbon steel has completed slag removal in the continuous casting tundish, add a covering agent with the following chemical composition by mass percentage to the continuous casting tundish: C: 5-10%, SiO2: 33-43%, CaO: 13-23%, MgO≤7%, Al2O3≤7%, Fe2O3≤5%, flux 10-20%. Continue until there is no exposed surface of the molten steel to prevent the steel from cooling down and to avoid secondary oxidation of the exposed steel. 4) Before pouring the last batch of high-carbon steel, the quick-change nozzle of the continuous casting tundish was replaced with a φ17.5mm nozzle, and the casting speed was reduced from 2.5m / min to 2.0m / min to reduce the changes in solidification temperature, billet shell shrinkage, and billet shell strength during the connection stage. 5) When the last batch of high-carbon steel is poured from the continuous casting ladle to the continuous casting tundish, the temperature of the steel should be controlled to be 10-20℃ higher than the normal temperature, and the temperature of the continuous casting ladle should be controlled to 1590-1600±7℃. 6) When the last batch of high-carbon steel is poured from the continuous casting ladle to the continuous casting tundish, add the following chemical composition by mass percentage to the continuous casting tundish: C: 5-10%, SiO2: 33-43%, CaO: 13-23%, MgO≤7%, Al2O3≤7%, Fe2O3≤5%, and flux 10-20%, until the surface of the molten steel is continuously kept free of exposed steel. 7) Before the last batch of high-carbon steel is poured into the continuous casting ladle, replace the high-carbon steel protective slag in the protective slag bin with low-carbon steel protective slag until the high-carbon steel continuous casting is completed. 8) When the first batch of low-carbon steel is poured from the continuous casting ladle to the continuous casting tundish, the secondary cooling intensity K value of the continuous casting is controlled to be increased from 1.12 to 1.25, and low-carbon steel protective slag is added in the crystallizer until the liquid slag layer thickness reaches 8-12mm. 9) After the first batch of low-carbon steel is poured from the continuous casting ladle into the continuous casting tundish, the molten steel level in the tundish is controlled to be lower than the normal level. Then, the low-carbon steel grade continues to be smelted and cast until the last batch of low-carbon steel is poured from the continuous casting ladle into the continuous casting tundish, and the continuous casting of low-carbon steel is completed.

[0006] The flux in the covering agent in steps 3) and 6) is a conventional product.

[0007] The high-carbon steel protective slag and low-carbon steel protective slag in step 7) are both conventional protective slags.

[0008] Before the last batch of high-carbon steel in step 6) is poured into the continuous casting tundish, the residual amount of high-carbon steel in the tundish is controlled to be ≤15t, so as to reduce the amount of high-carbon steel in the tundish and facilitate the rapid replacement of the high-carbon steel after the subsequent low-carbon steel enters the tundish.

[0009] After the first batch of low-carbon steel is poured from the continuous casting ladle to the continuous casting tundish, the steel level in the tundish is controlled to be lower than the normal level. This allows the inclusions in the low-carbon steel to have sufficient space to float and be removed.

[0010] The technical challenge of this invention lies in the fact that different steel grades have significant differences in composition and temperature. To achieve production in the same tundish, it is necessary to first solve the problems of solidification temperature changes, billet shell shrinkage changes, billet shell strength changes, and phase transformations in steel that occur at least two steel grades in the connection section due to changes in temperature and composition. Otherwise, steel leakage is very likely to occur, causing production interruption.

[0011] The present invention has the following advantages and effects: by adopting the above technical solution, production efficiency is greatly improved, steel loss caused by casting machine start-up and shutdown is reduced, labor intensity of workers is reduced, costs are saved, and the flexibility and adaptability of the production line are improved, effectively meeting the needs of phased order production, helping to optimize resource allocation, reduce production costs, enhance the market competitiveness of enterprises, realize the continuous casting production of dissimilar steels using the same tundish with controllable operation and stable quality, and effectively control steel leakage at the steel grade connection section. Detailed Implementation

[0012] The present invention will be further described below with reference to embodiments. Example 1

[0013] A method for continuous casting of dissimilar steels using the same tundish includes the following process steps: 1) When smelting and casting high-carbon steel HPB300 to the penultimate heat, control the temperature of the high-carbon steel molten steel to be 5℃ lower than the normal molten steel temperature, and control the temperature of the continuous casting ladle to 1570±7℃. 2) After pouring the second-to-last heat of high-carbon steel into the tundish through the continuous casting ladle, raise the molten steel level in the tundish until slag is discharged from the molten steel side of the tundish, thereby reducing the slag content in the molten steel and improving the purity of the molten steel. 3) After the slag is removed from the tundish of the second-to-last heat of high-carbon steel, a covering agent with the following chemical composition is added to the tundish: C: 5%, SiO2: 43%, CaO: 15%, MgO: 7%, Al2O3: 6%, Fe2O3: 5%, and flux 19%, until there is no exposed surface of the molten steel, to prevent the molten steel from cooling down and avoid secondary oxidation of the exposed molten steel; 4) Before pouring the last batch of high-carbon steel, the quick-change nozzle of the continuous casting tundish was replaced with a φ17.5mm nozzle, and the casting speed was reduced from 2.5m / min to 2.0m / min to reduce the changes in solidification temperature, billet shell shrinkage, and billet shell strength during the connection stage. 5) When the last batch of high-carbon steel is poured from the continuous casting ladle to the continuous casting tundish, the temperature of the steel is controlled to be 10°C higher than the normal temperature, and the temperature of the continuous casting ladle is controlled to 1590±7°C. 6) When the last batch of high-carbon steel is poured from the continuous casting ladle to the continuous casting tundish, a covering agent with the following chemical composition by mass percentage is added to the continuous casting tundish: C: 5%, SiO2: 43%, CaO: 15%, MgO: 7%, Al2O3: 6%, Fe2O3: 5%, and flux 19%, until the surface of the molten steel is continuously kept free of exposed steel. 7) Before the last heat of high-carbon steel is poured into the continuous casting ladle, the high-carbon steel protective slag in the protective slag bin is replaced with low-carbon steel protective slag until the high-carbon steel continuous casting is completed; both the high-carbon steel protective slag and the low-carbon steel protective slag are conventional protective slags; before the last heat of high-carbon steel is poured into the continuous casting tundish, the residual amount of high-carbon steel in the tundish is controlled to be ≤15t, reducing the residual amount of high-carbon steel in the tundish, so that it can be quickly replaced after the subsequent low-carbon steel enters the tundish; 8) When the first batch of low-carbon steel Q195 molten steel is poured from the continuous casting ladle to the continuous casting tundish, the secondary cooling intensity K value of the continuous casting is controlled to be increased from 1.12 to 1.25, and low-carbon steel protective slag is added in the crystallizer until the liquid slag layer thickness reaches 8-12mm. 9) After the first batch of low-carbon steel is poured from the continuous casting ladle into the continuous casting tundish, the molten steel level in the tundish is controlled to be lower than the normal level, so that the inclusions in the low-carbon steel have sufficient space to float to the surface and be removed. Then, the low-carbon steel grade continues to be smelted and cast until the last batch of low-carbon steel is poured from the continuous casting ladle into the continuous casting tundish, until the continuous casting of low-carbon steel is completed. Example 2

[0014] A method for continuous casting of dissimilar steels using the same tundish includes the following process steps: 1) When smelting and casting high-carbon steel HPB300 to the penultimate heat, control the temperature of the high-carbon steel molten steel to be 10℃ lower than the normal molten steel temperature, and control the continuous casting ladle temperature to 1575±7℃. 2) After pouring the second-to-last heat of high-carbon steel into the tundish through the continuous casting ladle, raise the molten steel level in the tundish until slag is discharged from the molten steel side of the tundish, thereby reducing the slag content in the molten steel and improving the purity of the molten steel. 3) After the slag is removed from the tundish of the second-to-last heat of high-carbon steel, a covering agent with the following chemical composition is added to the tundish: C: 10%, SiO2: 33%, CaO: 23%, MgO: 5%, Al2O3: 5%, Fe2O3: 5%, and flux 19%, until there is no exposed surface of the molten steel, to prevent the molten steel from cooling down and avoid secondary oxidation of the exposed molten steel; 4) Before pouring the last batch of high-carbon steel, the quick-change nozzle of the continuous casting tundish was replaced with a φ17.5mm nozzle, and the casting speed was reduced from 2.5m / min to 2.0m / min to reduce the changes in solidification temperature, billet shell shrinkage, and billet shell strength during the connection stage. 5) When the last batch of high-carbon steel is poured from the continuous casting ladle to the continuous casting tundish, the temperature of the steel is controlled to be 20°C higher than the normal temperature, and the temperature of the continuous casting ladle is controlled to 1600±7°C. 6) When the last batch of high-carbon steel is poured from the continuous casting ladle to the continuous casting tundish, a covering agent with the following chemical composition is added to the continuous casting tundish: C: 10%, SiO2: 33%, CaO: 23%, MgO: 5%, Al2O3: 5%, Fe2O3: 5%, flux 19%, until the surface of the molten steel is continuously kept without any exposed steel. 7) Before the last heat of high-carbon steel is poured into the continuous casting ladle, the high-carbon steel protective slag in the protective slag bin is replaced with low-carbon steel protective slag until the high-carbon steel continuous casting is completed; both the high-carbon steel protective slag and the low-carbon steel protective slag are conventional protective slags; before the last heat of high-carbon steel is poured into the continuous casting tundish, the residual amount of high-carbon steel in the tundish is controlled to be ≤15t, reducing the residual amount of high-carbon steel in the tundish, so that it can be quickly replaced after the subsequent low-carbon steel enters the tundish; 8) When the first batch of low-carbon steel Q195 molten steel is poured from the continuous casting ladle to the continuous casting tundish, the secondary cooling intensity K value of the continuous casting is controlled to be increased from 1.12 to 1.25, and low-carbon steel protective slag is added in the crystallizer until the liquid slag layer thickness reaches 8-12mm. 9) After the first batch of low-carbon steel is poured from the continuous casting ladle into the continuous casting tundish, the molten steel level in the tundish is controlled to be lower than the normal level, so that the inclusions in the low-carbon steel have sufficient space to float to the surface and be removed. Then, the low-carbon steel grade continues to be smelted and cast until the last batch of low-carbon steel is poured from the continuous casting ladle into the continuous casting tundish, until the continuous casting of low-carbon steel is completed. Example 3

[0015] A method for continuous casting of dissimilar steels using the same tundish includes the following process steps: 1) When smelting and casting high-carbon steel HPB300 to the penultimate heat, control the temperature of the high-carbon steel molten steel to be 7℃ lower than the normal molten steel temperature, and control the temperature of the continuous casting ladle to 1572±7℃. 2) After pouring the second-to-last heat of high-carbon steel into the tundish through the continuous casting ladle, raise the molten steel level in the tundish until slag is discharged from the molten steel side of the tundish, thereby reducing the slag content in the molten steel and improving the purity of the molten steel. 3) After the slag is removed from the tundish of the second-to-last heat of high-carbon steel, add a covering agent with the following chemical composition to the tundish: C: 8%, SiO2: 38%, CaO: 19%, MgO: 7%, Al2O3: 7%, Fe2O3: 5%, and flux 16% until there is no exposed surface of the molten steel, to prevent the molten steel from cooling down and avoid secondary oxidation of the exposed molten steel; 4) Before pouring the last batch of high-carbon steel, the quick-change nozzle of the continuous casting tundish was replaced with a φ17.5mm nozzle, and the casting speed was reduced from 2.5m / min to 2.0m / min to reduce the changes in solidification temperature, billet shell shrinkage, and billet shell strength during the connection stage. 5) When the last batch of high-carbon steel is poured from the continuous casting ladle to the continuous casting tundish, the temperature of the steel is controlled to be 15°C higher than the normal temperature, and the temperature of the continuous casting ladle is controlled to 1595±7°C. 6) When the last batch of high-carbon steel is poured from the continuous casting ladle to the continuous casting tundish, a covering agent with the following chemical composition is added to the continuous casting tundish: C: 8%, SiO2: 38%, CaO: 19%, MgO: 7%, Al2O3: 7%, Fe2O3: 5%, and flux 16%, until the surface of the molten steel is continuously kept without any exposed steel. 7) Before the last heat of high-carbon steel is poured into the continuous casting ladle, the high-carbon steel protective slag in the protective slag bin is replaced with low-carbon steel protective slag until the high-carbon steel continuous casting is completed; both the high-carbon steel protective slag and the low-carbon steel protective slag are conventional protective slags; before the last heat of high-carbon steel is poured into the continuous casting tundish, the residual amount of high-carbon steel in the tundish is controlled to be ≤15t, reducing the residual amount of high-carbon steel in the tundish, so that it can be quickly replaced after the subsequent low-carbon steel enters the tundish; 8) When the first batch of low-carbon steel Q195 molten steel is poured from the continuous casting ladle to the continuous casting tundish, the secondary cooling intensity K value of the continuous casting is controlled to be increased from 1.12 to 1.25, and low-carbon steel protective slag is added in the crystallizer until the liquid slag layer thickness reaches 8-12mm. 9) After the first batch of low-carbon steel is poured from the continuous casting ladle into the continuous casting tundish, the molten steel level in the tundish is controlled to be lower than the normal level, so that the inclusions in the low-carbon steel have sufficient space to float to the surface and be removed. Then, the low-carbon steel grade continues to be smelted and cast until the last batch of low-carbon steel is poured from the continuous casting ladle into the continuous casting tundish, until the continuous casting of low-carbon steel is completed. Example 4

[0016] A method for continuous casting of dissimilar steels using the same tundish includes the following process steps: 1) When smelting and casting high-carbon steel HPB300 to the penultimate heat, control the temperature of the high-carbon steel molten steel to be 8℃ lower than the normal molten steel temperature, and control the continuous casting ladle temperature to 1573±7℃. 2) After pouring the second-to-last heat of high-carbon steel into the tundish through the continuous casting ladle, raise the molten steel level in the tundish until slag is discharged from the molten steel side of the tundish, thereby reducing the slag content in the molten steel and improving the purity of the molten steel. 3) After the slag is removed from the tundish of the second-to-last heat of high-carbon steel, a covering agent with the following chemical composition is added to the tundish: C: 7%, SiO2: 40%, CaO: 20%, MgO: 7%, Al2O3: 6%, Fe2O3: 5%, and flux 15%, until there is no exposed surface of the molten steel, to prevent the molten steel from cooling down and avoid secondary oxidation of the exposed molten steel; 4) Before pouring the last batch of high-carbon steel, the quick-change nozzle of the continuous casting tundish was replaced with a φ17.5mm nozzle, and the casting speed was reduced from 2.5m / min to 2.0m / min to reduce the changes in solidification temperature, billet shell shrinkage, and billet shell strength during the connection stage. 5) When the last batch of high-carbon steel is poured from the continuous casting ladle to the continuous casting tundish, the temperature of the steel is controlled to be 12°C higher than the normal temperature, and the temperature of the continuous casting ladle is controlled to 1590±7°C. 6) When the last batch of high-carbon steel is poured from the continuous casting ladle to the continuous casting tundish, a covering agent with the following chemical composition is added to the continuous casting tundish: C: 7%, SiO2: 40%, CaO: 20%, MgO: 7%, Al2O3: 6%, Fe2O3: 5%, and flux 15%, until the surface of the molten steel is kept completely covered. 7) Before the last heat of high-carbon steel is poured into the continuous casting ladle, the high-carbon steel protective slag in the protective slag bin is replaced with low-carbon steel protective slag until the high-carbon steel continuous casting is completed; both the high-carbon steel protective slag and the low-carbon steel protective slag are conventional protective slags; before the last heat of high-carbon steel is poured into the continuous casting tundish, the residual amount of high-carbon steel in the tundish is controlled to be ≤15t, reducing the residual amount of high-carbon steel in the tundish, so that it can be quickly replaced after the subsequent low-carbon steel enters the tundish; 8) When the first batch of low-carbon steel Q195 molten steel is poured from the continuous casting ladle to the continuous casting tundish, the secondary cooling intensity K value of the continuous casting is controlled to be increased from 1.12 to 1.25, and low-carbon steel protective slag is added in the crystallizer until the liquid slag layer thickness reaches 8-12mm. 9) After the first batch of low-carbon steel is poured from the continuous casting ladle into the continuous casting tundish, the molten steel level in the tundish is controlled to be lower than the normal level, so that the inclusions in the low-carbon steel have sufficient space to float to the surface and be removed. Then, the low-carbon steel grade continues to be smelted and cast until the last batch of low-carbon steel is poured from the continuous casting ladle into the continuous casting tundish, until the continuous casting of low-carbon steel is completed. Example 5

[0017] A method for continuous casting of dissimilar steels using the same tundish includes the following process steps: 1) When smelting and casting high-carbon steel HPB300 to the penultimate heat, control the temperature of the high-carbon steel molten steel to be 9℃ lower than the normal molten steel temperature, and control the temperature of the continuous casting ladle to 1571±7℃. 2) After pouring the second-to-last heat of high-carbon steel into the tundish through the continuous casting ladle, raise the molten steel level in the tundish until slag is discharged from the molten steel side of the tundish, thereby reducing the slag content in the molten steel and improving the purity of the molten steel. 3) After the slag is removed from the tundish of the second-to-last heat of high-carbon steel, a covering agent with the following chemical composition is added to the tundish: C: 9%, SiO2: 39%, CaO: 22%, MgO: 6%, Al2O3: 7%, Fe2O3: 5%, and flux 12%, until there is no exposed surface of the molten steel, to prevent the molten steel from cooling down and avoid secondary oxidation of the exposed molten steel; 4) Before pouring the last batch of high-carbon steel, the quick-change nozzle of the continuous casting tundish was replaced with a φ17.5mm nozzle, and the casting speed was reduced from 2.5m / min to 2.0m / min to reduce the changes in solidification temperature, billet shell shrinkage, and billet shell strength during the connection stage. 5) When the last batch of high-carbon steel is poured from the continuous casting ladle to the continuous casting tundish, the temperature of the steel is controlled to be 18°C ​​higher than the normal temperature, and the temperature of the continuous casting ladle is controlled to 1600±7°C. 6) When the last batch of high-carbon steel is poured from the continuous casting ladle to the continuous casting tundish, a covering agent with the following chemical composition is added to the continuous casting tundish: C: 9%, SiO2: 39%, CaO: 22%, MgO: 6%, Al2O3: 7%, Fe2O3: 5%, and flux 12%, until the surface of the molten steel is continuously kept without any exposed steel. 7) Before the last heat of high-carbon steel is poured into the continuous casting ladle, the high-carbon steel protective slag in the protective slag bin is replaced with low-carbon steel protective slag until the high-carbon steel continuous casting is completed; both the high-carbon steel protective slag and the low-carbon steel protective slag are conventional protective slags; before the last heat of high-carbon steel is poured into the continuous casting tundish, the residual amount of high-carbon steel in the tundish is controlled to be ≤15t, reducing the residual amount of high-carbon steel in the tundish, so that it can be quickly replaced after the subsequent low-carbon steel enters the tundish; 8) When the first batch of low-carbon steel Q195 molten steel is poured from the continuous casting ladle to the continuous casting tundish, the secondary cooling intensity K value of the continuous casting is controlled to be increased from 1.12 to 1.25, and low-carbon steel protective slag is added in the crystallizer until the liquid slag layer thickness reaches 8-12mm. 9) After the first batch of low-carbon steel is poured from the continuous casting ladle into the continuous casting tundish, the molten steel level in the tundish is controlled to be lower than the normal level, so that the inclusions in the low-carbon steel have sufficient space to float to the surface and be removed. Then, the low-carbon steel grade continues to be smelted and cast until the last batch of low-carbon steel is poured from the continuous casting ladle into the continuous casting tundish, until the continuous casting of low-carbon steel is completed.

[0018] The method of using the same tundish for continuous casting of dissimilar steels, as described in this invention, effectively resolves the contradiction between production efficiency and cost control for two steel grades, achieving the following significant results: 1. After exploration in 2023, the operation method was standardized starting in April 2023. Since April 2023, a total of 337 heats of (Q195) have been cast in 10 groups, with a maximum of 58 heats cast in a row. It is estimated that 10 tundishes were saved in continuous casting, which effectively reduced the energy consumption caused by tundish baking, the metal loss caused by casting machine start-up and shutdown, and reduced the labor intensity of employees.

[0019] 2. Since the implementation of this invention, there has been no unplanned shutdown of the casting machine caused by steel leakage accidents during the steel grade transition stage, and steel leakage in the steel grade transition section has been effectively controlled. No steel leakage has occurred in the steel grade transition section since 2024.

[0020] 3. Since the implementation of this invention, the casting billets in the connecting section have been handled by taking samples one by one according to the online sampling and judgment process due to composition reasons. The composition of the connecting part fluctuates greatly and is packaged as Q195 strip steel for rolling. No defective products have been found.

[0021] 4. This invention and its subsequent processing procedures provide a feasible reference for the joint casting of other types of different steel grades. In particular, in actively responding to the company's "differentiated" competitive development, it has successfully extended the continuous production of SWRH82B (8mm, 11.5mm, 12.5mm, 13mm) and medium and high carbon steel (45 steel, 55 steel, 60 steel, 65 steel), and also laid the foundation for subsequent sales and market demand.

Claims

1. A method for continuous casting of dissimilar steels using the same tundish, characterized in that... Including the following process steps: 1) When smelting and casting high-carbon steel to the penultimate heat, control the temperature of the high-carbon steel molten steel to be 5-10℃ lower than the normal molten steel temperature, and control the continuous casting ladle temperature to 1570-1575±7℃. 2) After pouring the second-to-last heat of high-carbon steel into the tundish through the continuous casting ladle, raise the molten steel level in the tundish until slag is discharged from the molten steel side of the tundish, thereby reducing the slag content in the molten steel and improving the purity of the molten steel. 3) After the slag is removed from the tundish of the second-to-last heat of high-carbon steel, add a covering agent with the following chemical composition by mass percentage to the tundish: C: 5-10%, SiO2: 33-43%, CaO: 13-23%, MgO≤7%, Al2O3≤7%, Fe2O3≤5%, flux 10-20%, until there is no exposed surface of the molten steel, to prevent the molten steel from cooling down and avoid secondary oxidation of the exposed molten steel; 4) Before pouring the last batch of high-carbon steel, the quick-change nozzle of the continuous casting tundish was replaced with a φ17.5mm nozzle, and the casting speed was reduced from 2.5m / min to 2.0m / min to reduce the changes in solidification temperature, billet shell shrinkage, and billet shell strength during the connection stage. 5) When the last batch of high-carbon steel is poured from the continuous casting ladle to the continuous casting tundish, the temperature of the steel should be controlled to be 10-20℃ higher than the normal temperature, and the temperature of the continuous casting ladle should be controlled to 1590-1600±7℃. 6) When the last batch of high-carbon steel is poured from the continuous casting ladle to the continuous casting tundish, add the following chemical composition by mass percentage to the continuous casting tundish: C: 5-10%, SiO2: 33-43%, CaO: 13-23%, MgO≤7%, Al2O3≤7%, Fe2O3≤5%, and flux 10-20%, until the surface of the molten steel is continuously kept free of exposed steel. 7) Before the last batch of high-carbon steel is poured into the continuous casting ladle, replace the high-carbon steel protective slag in the protective slag bin with low-carbon steel protective slag until the high-carbon steel continuous casting is completed. 8) When the first batch of low-carbon steel is poured from the continuous casting ladle to the continuous casting tundish, the secondary cooling intensity K value of the continuous casting is controlled to be increased from 1.12 to 1.25, and low-carbon steel protective slag is added in the crystallizer until the liquid slag layer thickness reaches 8-12mm. 9) After the first batch of low-carbon steel is poured from the continuous casting ladle into the continuous casting tundish, the molten steel level in the tundish is controlled to be lower than the normal level. Then, the low-carbon steel grade continues to be smelted and cast until the last batch of low-carbon steel is poured from the continuous casting ladle into the continuous casting tundish, and the continuous casting of low-carbon steel is completed.

2. The method for continuous casting of dissimilar steels using the same tundish according to claim 1, characterized in that... Both the high-carbon steel protective slag and the low-carbon steel protective slag are conventional protective slags.

3. The method for continuous casting of dissimilar steels using the same tundish according to claim 1, characterized in that... Before the last batch of high-carbon steel is poured into the tundish, the residual amount of high-carbon steel in the tundish is controlled to be ≤15t, so as to reduce the amount of high-carbon steel in the tundish and facilitate the rapid replacement of the high-carbon steel after the subsequent low-carbon steel enters the tundish.

4. The method for continuous casting of dissimilar steels using the same tundish according to claim 1, characterized in that... After the first batch of low-carbon steel is poured from the continuous casting ladle to the continuous casting tundish, the steel level in the tundish is controlled to be lower than the normal level. This allows the inclusions in the low-carbon steel to have sufficient space to float and facilitates their removal.