A process for mixed casting and billet cutting between multiple steel grades

Abstract

The present invention discloses a process for mixed casting and billet division among multiple steel grades. The specific process is as follows: First, when the compositions of the steel grades are similar for mixed casting and the rolling processes have little difference, the liquid level control in the tundish is not reduced, the mixed-cast billets are not divided, and the billets are directly divided by furnace and sent for rolling according to the steel grade with the lower composition. Second, when the compositions of the steel grades are similar for mixed casting but the rolling processes have great differences, the liquid level control in the tundish is not reduced, the mixed-cast billets are divided separately, a new furnace number is created, and the billets are judged and sent for rolling according to the steel grade with the lower composition. Third, when the compositions of the steel grades have large differences for mixed casting, the mixed casting is organized by reducing the liquid level control in the tundish, and the mixed-cast billets are divided separately in combination with the walking position of the cast billet after passing through the flame cutting machine. The process for mixed casting and billet division among multiple steel grades of the present invention not only realizes the accuracy of the composition of the divided mixed casting and ensures the stability of the composition of the mixed-cast heat, but also can reduce the number of tundish replacements, thereby reducing the number of tundishes used.

Description

Technical Field

[0001] The present invention specifically relates to a process for mixed casting and billet dividing between multiple steel grades, belonging to the technical field of mixed casting processes for multiple steel grades. Background Art

[0002] The tundish of a continuous casting machine is an intermediate link in the steelmaking production process, with functions such as storing molten steel, stabilizing flow, diverting flow, equalizing temperature, and removing inclusions. During the process of changing ladles, the molten steel stored in the tundish can ensure the smooth operation of continuous casting, and it is the connection point for the transition of molten steel from intermittent operation to continuous operation; during production, when changing from one steel grade to another after producing a certain steel grade, it is necessary to replace the tundish with a new one, which can effectively avoid the mixing between different steel grades and prevent the generation of mixed-cast billets; however, with the increase in orders for different steel grades from customers, when changing steel grades, replacing the tundish with a new one, especially for small-batch orders, will result in a relatively low number of continuous casting heats with a single tundish, greatly reducing the service life of the tundish of the continuous casting machine; at the same time, due to frequent start-up and shutdown operations, the amount of cut heads and cut tails of the cast billets during start-up and shutdown increases, increasing the waste of cast billets and reducing the metal yield; in summary, it greatly reduces production efficiency and increases the process production cost.

[0003] As people's requirements for the working efficiency of the continuous casting process are getting higher and higher, and at the same time to meet the continuous production of multiple steel grades during continuous casting, therefore, continuous casting of multiple steel grades is carried out on the same continuous casting machine, that is, after pouring one steel grade in the same tundish, continue to pour another steel grade without the need to replace the tundish with a new one, and continuous casting can be carried out. Especially for large-batch and multiple-steel-grade production, it can effectively reduce the production cost during continuous casting; however, during mixed casting between different steel grades, there is still the composition of the previous heat of molten steel remaining in the tundish for continuous pouring. After the ladle change is completed, when pouring the next steel grade from the ladle, there will be partial mixing of molten steel with two compositions in the tundish. Due to the difference in composition, it is necessary to divide the mixed-cast billets, resulting in mixed-cast billets; if the mixed casting is not properly controlled during the process, it will not only affect the smooth production but also cause problems with the composition and quality of the cast billets. Therefore, there is an urgent need for a process for mixed casting and billet dividing between multiple steel grades to stabilize production and meet the production and quality requirements of large-batch and multiple-steel-grade production. Summary of the Invention

[0004] To solve the above problems, the present invention proposes a process for mixed casting and billet dividing between multiple steel grades, which can effectively reduce the replacement frequency of the tundish, stabilize the service life of the tundish during large-batch and multiple-steel-grade production; reduce the amount of discarded billets caused by tundish replacement, improve the metal yield, reduce the production cost, increase the production efficiency, and in addition, the accurate method of mixed casting and billet dividing can effectively ensure the composition requirements of the mixed-cast billets.

[0005] Process for mixed casting and billet dividing among multiple steel grades of the present invention. The process is to formulate the process of mixed casting and billet dividing among different steel grades according to the steel grade composition to complete the continuous casting of different steel grades. Specifically, the process is as follows:

[0006] First, when the compositions between steel grades are similar for mixed casting and the rolling processes have little difference, the liquid level control in the tundish is not reduced, the mixed-cast billets are not divided, and the billets are directly divided by furnace and sent for rolling according to the steel grade with lower composition;

[0007] Second, when the compositions between steel grades are similar for mixed casting and the rolling processes have great differences, the liquid level control in the tundish is not reduced, the mixed-cast billets are separately divided, a new furnace number is created, and the billets are judged and sent for rolling according to the steel grade with lower composition;

[0008] Third, when the compositions between steel grades have great differences for mixed casting, the mixed casting is organized by reducing the liquid level control in the tundish, and in combination with the walking position of the cast billet after passing through the flame cutting machine, the mixed-cast billets are separately divided. Composition samples are taken from the head of the first billet and the tail of the last billet of the mixed-cast billets, a new furnace number is created, and the billets are judged and sent for rolling according to the composition results;

[0009] Finally, when the compositions between steel grades have great differences, no mixed casting is carried out, or the mixed casting is carried out in the way of making a joint and secondary teeming. The head and tail of the first billet after the joint are verified for composition, and the billets are judged and sent for rolling according to the composition results.

[0010] Further, when the compositions between steel grades are similar and the rolling processes have little difference for mixed casting, specifically: the billets of HRB400E-2G, HRB400E-3, HRB400E-5, HRB400E-6 and HRB400E-7 are mixed-cast, the mixed-cast billets are not separately divided, but directly divided by furnace and sent for rolling according to the principle of taking the lower composition;

[0011] When the compositions between steel grades are similar for mixed casting and the rolling processes have great differences, the mixed casting is carried out as follows:

[0012] HRB400E-1 is mixed-cast with HRB400E-2G / HRB400E-2. The continuous casting machine organizes the mixed casting of billets according to the following process: the tapping temperature of the two furnace charges for mixed casting is increased by 3-5°C compared with the normal furnace charge. Before mixed casting, the liquid level of the tundish molten steel is controlled at 480-530 mm. The ladle of the mixed-cast furnace charge starts teeming. After the teeming of the mixed-cast furnace charge, the main control operator records the running position of the billets and notifies the billet discharging worker to divide the billets. The billet discharging worker starts to divide the billets according to the running position of the billets provided by the main control operator; the mixed-cast billets are separately divided and judged according to the principle of taking the lower composition;

[0013] When pouring molten steel of steel grades with large compositional differences, it is organized in the way of pouring with decreasing liquid level. For example, when pouring molten steel of two groups of steel grades: HRB400E series steel grades (HRB400E-3 / HRB400E-5 / HRB400E-6 / HRB400E-7) and HRB500E series steel grades (HRB500E-2 / HRB500E-3 / HRB500E-2G / HRB500E-5 / HRB500E-4 / HRB500E-6 / HRB500E-7), the continuous caster organizes the pouring of billets according to the following process:

[0014] a. Requirements for pouring operation: The tapping temperature of the refining furnace for two consecutive pouring heats is increased by 3 - 5°C compared with the normal heat. Before pouring, the liquid level of the tundish molten steel is controlled at 380 - 430 mm. When the ladle of the pouring heat starts pouring, after the pouring heat starts pouring, the main control operator records the running position of the billet and notifies the billet discharging worker to cut the billet. The billet discharging worker starts cutting the billet according to the running position of the billet provided by the main control operator;

[0015] b. Requirements for sampling of poured billets: Samples are taken from the head of the first billet of each strand in the poured part and the tail of the last poured billet for chemical composition analysis. Requirements for marking the sampled billets and the taken billet samples: Strand number - which billet - head or tail, where head and tail are represented by 1 and 2 respectively; for example, for the head of the first billet in strand 2, both the billet and the corresponding billet sample are marked with "2-1-1"; for the tail of the third billet in strand 2, both the billet and the corresponding billet sample are marked with "2-3-2";

[0016] c. Judgment of poured billets: After the composition inspection of the poured billets is completed, it is judged and sent for rolling.

[0017] Furthermore, when the steel grades of the HRB500E pouring heats have similar compositions, the continuous caster organizes the pouring of billets according to the following process: The tapping temperature of the refining furnace for two consecutive pouring heats is increased by 3 - 5°C compared with the normal heat. Before pouring, the tundish liquid level is controlled at 480 - 530 mm. When the ladle of the pouring heat starts pouring, after the pouring heat starts pouring, the main control operator records the running position of the billet and notifies the billet discharging worker to cut the billet. The billet discharging worker starts cutting the billet according to the running position of the billet provided by the main control operator; The poured billets can be judged according to the principle of taking the lower composition:

[0018] If the steel grades HRB500E-3 and HRB500E-2 are poured together, the poured billet shall be rolled according to HRB500E-2; if the steel grades HRB500E-3 and HRB500E-4 are poured together, the poured billet shall be rolled according to HRB500E-3; if the steel grades HRB500E-5 and HRB500E-3 are poured together, the poured billet shall be rolled into steel bars of the HRB500E-3 specification; if the steel grades HRB500E-5 and HRB500E-2 are poured together, the poured billet shall be rolled according to HRB500E-2; if the steel grades HRB500E-6 and HRB500E-4 are poured together, or if the steel grades HRB500E-7 and HRB500E-4 are poured together, both shall be sent for rolling according to the steel grade HRB500E-4; if the steel grades HRB500E-7 and HRB500E-6 are poured together, for the poured billet of the front and rear furnace charges, both shall be sent for rolling according to the steel grade HRB500E-6; for other steel grades not specified in the HPB300 series, HRB400E series, and HRB500E series, mixed pouring is not allowed.

[0019] Compared with the prior art, the process of mixed pouring and billet division among multiple steel grades of the present invention can not only achieve the accuracy of the mixed pouring composition and ensure the stability of the composition of the mixed pouring furnace charges, but also reduce the number of tundish replacements, thereby reducing the number of tundishes used. Description of the Drawings

[0020] Figure 1 It is a detailed drawing of the division of steel grades for direct sub-furnace pouring of steel grades with similar compositions in the mixed pouring furnace charges of the present invention.

[0021] Figure 2 It is a schematic diagram of billet division for mixed pouring of steel grades with similar compositions (with large differences in rolling processes) in the mixed pouring furnace charges of the present invention.

[0022] Figure 3 It is a schematic diagram for judging the poured billet of steel grades with large differences in compositions among different steel grades in the mixed pouring furnace charges of the present invention.

[0023] Figure 4 It is a schematic diagram of the billet division method for mixed pouring with large differences in compositions among different steel grades in the mixed pouring furnace charges of the present invention.

[0024] Figure 5 It is a trend chart of the average service life of tundishes from January to July in the process of the present invention.

[0025] Figure 6 It is a trend chart of the change in the yield of continuous casting billets from January to July in the present invention.

[0026] Figure 7 It is a schematic diagram of the composition control requirements for the steel grades HRB400E-3 and HRB500E-5 of the present invention.

[0027] Figure 8 It is a schematic diagram of the verification of the sampling compositions of the head and tail samples of the poured billets of two furnace charges of the steel grades HRB400E-3 and HRB500E-5 of the present invention. Detailed implementation mode

[0028] Example 1:

[0029] For the process of mixed casting and billet division among multiple steel grades of the present invention, the process is to formulate the mixed casting and billet division processes among different steel grades according to the steel grade components to complete the continuous casting of different steel grades. The specific process is as follows:

[0030] First, when the components between steel grades are similar for mixed casting and the rolling processes have little difference, there is no need to lower the tundish control liquid level, and the mixed casting billets are not divided. Instead, the billets are directly divided by furnace and sent for rolling according to the steel grade with lower components;

[0031] Secondly, when the components between steel grades are similar for mixed casting and the rolling processes have large differences, there is no need to lower the tundish control liquid level. The mixed casting billets are separately divided, a new furnace number is created, and the billets are sent for rolling according to the judgment of the steel grade with lower components;

[0032] Thirdly, when the components between steel grades have large differences for mixed casting, the mixed casting is organized by lowering the tundish control liquid level. Combining with the walking position of the cast billet after passing through the overheating cutting machine, the mixed casting billets are separately divided. Composition samples are taken from the head of the first billet and the tail of the last billet of the mixed casting billets. A new furnace number is created, and the billets are sent for rolling according to the composition results;

[0033] Finally, when the components between steel grades have large differences, no mixed casting is carried out, or the mixed casting is carried out in the way of making a joint and pouring again. The head and tail of the first billet after the joint are verified for composition, and the billets are sent for rolling according to the composition results.

[0034] As Figure 1 shown, when the components between steel grades are similar and the rolling processes have little difference for mixed casting, it is specifically as follows: The billets of HRB400E-2G, HRB400E-3, HRB400E-5, HRB400E-6 and HRB400E-7 are mixed cast. The mixed casting billets are not separately divided, but directly divided by furnace and sent for rolling according to the principle of taking the lower component;

[0035] As Figure 2 and Figure 3 shown, when the components between steel grades are similar for mixed casting and the rolling processes have large differences, the specific mixed casting is as follows:

[0036] HRB400E-1 is mixed cast with HRB400E-2G / HRB400E-2. The continuous caster organizes the mixed casting of steel billets according to the following process: The tapping temperature of the two furnace charges for mixed casting is increased by 3-5°C compared with the normal furnace charge. Before mixed casting, the tundish molten steel liquid level is controlled at 480-530 mm. The ladle of the mixed casting furnace charge starts pouring. After the pouring of the mixed casting furnace charge, the main control operator records the running position of the steel billet and notifies the billet discharging worker to divide the billet. The billet discharging worker starts to divide the billet according to the running position of the steel billet provided by the main control operator; The mixed casting billets are separately divided and judged according to the principle of taking the lower component;

[0037] When the chemical compositions of the steel grades are quite different and mixed casting is carried out, it is organized in the way of mixing at the descending liquid level. For example, for two groups of steel grades for mixed casting: HRB400E series steel grades (HRB400E-3 / HRB400E-5 / HRB400E-6 / HRB400E-7) and HRB500E series steel grades (HRB500E-2 / HRB500E-3 / HRB500E-2G / HRB500E-5 / HRB500E-4 / HRB500E-6 / HRB500E-7) are mixed cast, the continuous caster organizes the billet mixed casting according to the following process:

[0038] a. Requirements for mixed casting operation: The tapping temperature of the refining for two consecutive heats for mixed casting is increased by 3-5°C compared with the normal heat. Before mixed casting, the tundish molten steel level is controlled at 380-430 mm. For the ladle of the mixed casting heat to start pouring, after the ladle of the mixed casting heat starts pouring, the main control operator records the running position of the billet and notifies the billet discharging worker to mark the billet. The billet discharging worker starts to mark the billet according to the running position of the billet provided by the main control operator, as Figure 4 shown;

[0039] b. Requirements for sampling of mixed-cast billets: Samples are taken from the head of the first billet of each strand in the mixed-cast part and the tail of the last billet in the mixed casting to analyze the chemical composition; Requirements for marking the sampled billets and the taken billet samples: Strand number - the nth billet - head or tail, and the head and tail are represented by 1 and 2 respectively; For example, for the head of the first billet in strand 2, both the billet and the corresponding billet sample are marked with "2-1-1"; For the tail of the third billet in strand 2, both the billet and the corresponding billet sample are marked with "2-3-2";

[0040] c. Judgment of mixed-cast billets: After the composition inspection of the mixed-cast billets is completed, it is judged and sent for rolling.

[0041] Among them, when the steel grade compositions of the HRB500E mixed-cast heats are similar, the continuous caster organizes the billet mixed casting according to the following process: The tapping temperature of the refining for two consecutive heats for mixed casting is increased by 3-5°C compared with the normal heat. Before mixed casting, the tundish liquid level is controlled at 480-530 mm. For the ladle of the mixed casting heat to start pouring, after the ladle of the mixed casting heat starts pouring, the main control operator records the running position of the billet and notifies the billet discharging worker to mark the billet. The billet discharging worker starts to mark the billet according to the running position of the billet provided by the main control operator, as Figure 4As shown in the figure, the mixed-cast billets can be judged according to the principle of taking the lower grade in terms of composition. For example, when HRB500E-3 and HRB500E-2 are mixed-cast, the mixed-cast billets are rolled according to HRB500E-2; when HRB500E-3 and HRB500E-4 are mixed-cast, the mixed-cast billets are rolled according to HRB500E-3; when HRB500E-5 and HRB500E-3 are mixed-cast, the mixed-cast billets are processed into steel products of HRB500E-3 specifications; when HRB500E-5 and HRB500E-2 are mixed-cast, the mixed-cast billets are rolled according to HRB500E-2; when HRB500E-6 and HRB500E-4 are mixed-cast, and when HRB500E-7 and HRB500E-4 are mixed-cast, they are all sent for rolling according to the HRB500E-4 steel grade; when HRB500E-7 and HRB500E-6 are mixed-cast, for the mixed-cast billets in the previous and subsequent furnace batches, they are all sent for rolling according to the HRB500E-6 steel grade; for other steel grades not specified in the HPB300 series, HRB400E series, and HRB500E series, mixed-casting is not allowed.

[0042] The process of mixed-casting and billet classification among multiple steel grades of the present invention has the following advantages:

[0043] As Figure 5 shown, in the process of the present invention, during continuous casting production of large quantities and multiple steel grades, planned mixed-casting can be organized according to the mixed-cast steel grade compositions required before and after. Without replacing the tundish, the replacement frequency of the tundish can be reduced, and the average service life of the tundish can be stably increased. The average service life of the tundish has increased from 35.5 hours in January 2022 to 42.5 hours in July 2022, with a 12.8% increase in life; therefore, the present technology can effectively increase the service life of the tundish, reduce the number of tundishes used, and further reduce the refractory material usage cost of the tundish.

[0044] As Figure 6 shown, the process of the present invention effectively reduces the start-up and shutdown frequencies of the tundish, enables continuous mixed-casting of different steel grades, reduces the waste of cutting heads and tails during the process, improves the metal yield rate, and the metal yield rate has increased from 99.42% in January 2022 to 99.80% in July 2022, which can reduce production costs and improve the continuous casting production efficiency.

[0045] In the process of the present invention, the molten steel at the mixed-casting point forms a mixed-cast billet whose composition belongs neither to the previous furnace of steel nor to the subsequent furnace of steel. Through the effective control of the tundish liquid level height at the mixed-casting point and the walking position of the billets under the platform, the billets of the previous furnace, the mixed-cast billets, and the subsequent furnace are classified, and accurate billet classification can be achieved with obvious effects, effectively ensuring the stability of the mixed-cast steel grade composition.

[0046] As Figure 7 and Figure 8 shown, when steel grade HRB400E-3 and steel grade HRB500E-5 are mixed-cast, as Figure 7As shown in the figure, it is the composition control requirements for two steel grades. Before mixed casting, the tundish molten steel level is controlled at 380 - 430 mm. For the ladle tapping of the mixed casting heat, after the tapping of the heat to be mixed cast, the main control operator records (takes a photo) the running position of the billet and notifies the billet discharging worker to mark the billet. The billet discharging worker starts to mark the billet according to the running position of the billet provided by the main control operator; according to the billet marking plan, the distance that the head of the billet runs past the flame cutting machine is X meters. When 0 ≤ X ≤ 4 meters, 3 mixed-cast billets are continuously marked per strand; when 4 < X < 10 meters, 2 mixed-cast billets are continuously marked per strand; when X ≥ 10 meters, 2 mixed-cast billets are continuously marked per strand. The first head sample of the 1st / 3rd / 5th / 7th strand of the mixed-cast billets and the last tail sample of the mixed-cast billets are taken for composition inspection. The composition results are as Figure 8 shown. The composition of the head sample meets the composition requirements of the steel grade HRB400E-3, and the composition of the tail sample meets the composition requirements of the steel grade HRB500E-5. The division of the mixed-cast billets is successful;

[0047] In summary, the process of the present invention organizes mixed casting based on the difference in composition between the two mixed-cast steel grades, and effectively marks the billets by controlling the height of the tundish liquid level at the mixed-casting point and combining the walking position of the billets under the platform. It not only achieves the effective division of the mixed-cast billets and ensures the steel grade composition after mixed casting, but also reduces the number of tundishes used, improves the average service life of the tundish, reduces the loss of billets during the process, and achieves the purpose of improving the steel yield.

[0048] The above embodiments are only the preferred embodiments of the present invention. Therefore, any equivalent changes or modifications made according to the structure, characteristics, and principles described in the scope of the present invention patent application are included in the scope of the present invention patent application.

Claims

1. A process for mixed casting and billet division between multiple steel grades, characterized in that, The process is to formulate the processes of mixed casting and billet division between different steel grades according to the steel grade composition to complete the continuous casting of different steel grades. The specific process is as follows: First, when the compositions between steel grades are similar for mixed casting and the rolling processes have little difference, there is no need to lower the tundish control liquid level, and there is no need to divide the mixed-cast billets. The billets are directly divided by furnace and sent to rolling according to the steel grade with lower composition. Second, when the compositions between steel grades are similar for mixed casting and the rolling processes have large differences, there is no need to lower the tundish control liquid level. The mixed-cast billets are separately divided, a new furnace number is created, and they are sent to rolling according to the judgment of the steel grade with lower composition. Third, when the compositions between steel grades have large differences for mixed casting, the mixed casting is organized in the way of lowering the tundish control liquid level. Combined with the walking position of the cast billet after passing through the flame cutting machine, the mixed-cast billets are separately divided. Composition samples are taken from the head of the first billet and the tail of the last billet of the mixed-cast billets. A new furnace number is created, and they are sent to rolling according to the composition results. Finally, when the compositions between steel grades have large differences, there is no mixed casting, or the mixed casting is carried out in the way of making a joint and secondary pouring. The head and tail of the first billet after the joint are verified for composition, and they are sent to rolling according to the composition results. When the compositions between steel grades are similar and the rolling processes have little difference for mixed casting, specifically: the billets of HRB400E-2G, HRB400E-3, HRB400E-5, HRB400E-6 and HRB400E-7 are mixed-cast. The mixed-cast billets are not separately divided, but directly divided by furnace and sent to rolling according to the principle of taking the lower composition. When the compositions between steel grades are similar for mixed casting and the rolling processes have large differences, the specific mixed casting is as follows: HRB400E-1 is mixed-cast with HRB400E-2G or HRB400E-2. The continuous casting machine organizes the mixed casting of steel billets according to the following process: the refining tapping temperatures of the two mixed-cast heats are 3-5°C higher than those of the normal heats. Before mixed casting, the tundish molten steel liquid level is controlled at 480-530 mm. The ladle of the mixed-cast heat starts pouring. After the pouring of the mixed-cast heat starts, the main control operator records the running position of the steel billet and notifies the billet discharging worker to divide the billets. The billet discharging worker starts to divide the billets according to the running position of the steel billet provided by the main control operator; the mixed-cast billets are separately divided and judged according to the principle of taking the lower composition. When the compositions between steel grades have large differences for mixed casting, it is organized in the way of mixed casting with lowered liquid level. Specifically: the steel grades of the HRB400E series are mixed-cast with the steel grades of the HRB500E series. The continuous casting machine organizes the mixed casting of steel billets according to the following process: a. Requirements for mixed casting operation: The refining tapping temperatures of the two mixed-cast heats are 3-5°C higher than those of the normal heats. Before mixed casting, the tundish molten steel liquid level is controlled at 380-430 mm. The ladle of the mixed-cast heat starts pouring. After the pouring of the mixed-cast heat starts, the main control operator records the running position of the steel billet and notifies the billet discharging worker to divide the billets. The billet discharging worker starts to divide the billets according to the running position of the steel billet provided by the main control operator; b. Requirements for sampling of mixed-cast billets: Samples are taken from the head of the first billet of each strand of the mixed-cast part and the tail of the last billet of the mixed casting for chemical composition analysis; Requirements for the identification of the sampled steel billets and the taken steel billet samples: strand number - which billet - head or tail, the head is represented by 1 and the tail is represented by 2; c. Judgment of mixed-cast billets: After the composition inspection of the mixed-cast billets is completed, it is judged and sent to rolling.

2. The process of mixed casting and billet cutting between multiple steel grades according to claim 1, characterized in that: When the steel grades of the HRB500E mixed casting heats are similar, the continuous caster organizes the billet mixed casting according to the following process: The tapping temperature of the refining for the two mixed casting heats is increased by 3-5°C compared with the normal heat. Before mixed casting, the tundish liquid level is controlled at 480-530 mm. For the mixed casting heat, the ladle is tapped. After the start of tapping of the heat to be mixed, the main control operator records the running position of the billet and notifies the billet discharging operator to mark the billet. The billet discharging operator starts to mark the billet according to the running position of the billet provided by the main control operator.

Images