Manufacturing method of silicon steel continuous casting billet

Abstract

The invention discloses a manufacturing method of a silicon steel continuous casting billet, which comprises the following steps: the thickness of a liquid slag layer of adopted casting powder is within 10-18mm, the viscosity of the casting powder is within 0.20-0.29 Pa.S, and the melting point is within 1000-1110 DEG C; the liquid level fluctuation of the molten steel is kept within + / -3mm; and the secondary cooling area is cooled by adopting a process system that the cooling water amount is sequentially reduced in the casting blank drawing direction. According to the method, parameters such as the thickness of a casting powder liquid slag layer, the viscosity of the casting powder, the melting point, the superheat degree of tundish molten steel, stirring current and the like are controlled, and a secondary cooling area is divided into a high-temperature strong cooling process system and a low-temperature weak cooling process system in the throwing direction for cooling. And silicon steel production has the characteristics of high pulling speed, few defects, high equiaxed crystal rate, high casting blank temperature and the like.

Description

Technical Field

[0001] The invention relates to the field of metal alloy material processing, and in particular to a method for manufacturing a silicon steel continuous casting billet. Background Art

[0002] One of the important signs of modern continuous casting technology is high drawing speed, especially in the production of ordinary carbon steel continuous casting machines, which generally adopts high drawing speed production mode. The purpose of organizing production at high drawing speed is to achieve the purpose of headless rolling. The benefit of headless rolling is to avoid the impact of the rolling head and tail, achieve uniform temperature and size on the entire rolling line, reduce roll wear, reduce impact on equipment, and do not require flying shear cutting between units, thereby improving steel dimensional accuracy and yield rate.

[0003] Silicon steel is a functional soft magnetic material, mainly used in the manufacture of iron cores for various motors, transformers, new energy vehicles and green home appliances, and is a major product for energy conservation and emission reduction. High-quality (oriented and non-oriented high-grade) silicon steel products are difficult to manufacture, have complex processes, long process flows and high costs. If high-speed and high-quality manufacturing can be achieved, the yield rate, quality and performance levels can be greatly improved.

[0004] With the continuous advancement of continuous casting technology, continuous casting technology and equipment are developing towards high efficiency, high quality and low cost. The efficiency of silicon steel production is mainly based on the basic principle of maintaining furnace-machine matching. The converters of Baosteel Qingshan Base and Masteel are 150 tons, and the continuous casting speed is 1.0-1.1m / min. The converter of Baoshan Base is 300 tons, and the continuous casting speed is medium and low grade silicon steel, and the continuous casting speed is 1.0-1.2m / min. The production speed of silicon steel is relatively low, and the pouring time of a single furnace is long, which has a great impact on the increase in production capacity. The average pouring time per furnace of silicon steel is 63.4min, and the average pouring time of other steel grades is 47.5min. The average pouring time per furnace of silicon steel is 1.37 times the average of other steel grades. The continuous casting section of silicon steel is small, the pulling speed is low, and the middle package cannot be quickly changed, which greatly prolongs the production and preparation time, and seriously restricts the improvement of production efficiency. With the further release of silicon steel production capacity, it is particularly important to increase the pulling speed of silicon steel.

[0005] For a long time, people have had an inherent understanding of silicon steel, namely: high silicon content, poor matrix thermal conductivity, low billet shell forming ability compared to low carbon steel, low hot strength of the ingot at high temperature, high brittleness, and unable to achieve high-speed production like ordinary carbon steel, especially short-process CSP, ESP, MCCR, etc. cannot achieve headless rolling. With the advancement of technology, the conventional process of high (oriented, non-oriented high grade) silicon steel continuous casting billet drawing speed has increased from the original 0.85-1.0m / min to 1.05-1.2m / min, but compared with the drawing speed of 1.5-1.7m / min of low carbon steel, it is 30-50% lower, and it is easy to produce defects such as bulging, segregation, and low equiaxed crystal rate. Therefore, there is still a lot of room for improvement in the drawing speed of silicon steel.

[0006] In order to solve the problems of bulging, segregation and other defects that silicon steel continuous casting is prone to, as well as low equiaxed crystal rate, patent CN114734007B discloses a method for controlling the bulging of the narrow side of a high-grade silicon steel continuous casting billet. The method for solving the bulging of the narrow side of the continuous casting billet is mainly to reduce the continuous casting pulling speed, so that the molten steel inside the billet can solidify quickly, accelerate the formation of the billet shell, and increase the thickness to resist the pressure brought by the intermediate molten steel. However, a reduction in the pulling speed will lead to a reduction in the production capacity of the continuous casting machine, and due to poor thermal conductivity, the pulling speed of high-grade silicon steel is already low. Further reducing the pulling speed will cause the molten steel to be overcooled in the crystallizer, resulting in adhesion between the molten steel and the crystallizer, and damage to the copper plate of the crystallizer. It can be seen that reducing the pulling speed cannot effectively solve the problems of bulging, segregation and low equiaxed crystal rate that continuous casting is prone to, but instead reduces production capacity.

[0007] In view of this, it is necessary to increase the drawing speed of silicon steel to avoid defects such as bulging, segregation, and low equiaxed grain rate. Summary of the invention

[0008] The purpose of the present application is to provide a method for manufacturing high-speed and high-quality continuous casting billets of silicon steel, which has the characteristics of high pulling speed, few defects, high equiaxed crystal ratio, high billet temperature, etc., and provides conditions for realizing casting-rolling integration. It is also applicable to conventional processes, CSP, ESP, MCCR and other short processes, especially ESP, MCCR and other processes can realize headless rolling of high silicon steel.

[0009] The present application provides a method for manufacturing a silicon steel continuous casting billet, comprising:

[0010] The thickness of the mold slag liquid slag layer used is within 10 to 18 mm, the viscosity of the mold slag is within 0.20 Pa·S to 0.29 Pa·S, and the melting point is within 1000°C to 1110°C;

[0011] Keep the molten steel level fluctuation within ±3mm;

[0012] The secondary cooling zone is divided into at least two cooling zones, and cooling is performed by adopting a process system in which the amount of cooling water decreases successively along the direction of the casting and drawing.

[0013] Optionally, for conventional process technology, the pulling speed of high silicon steel can reach 1.3-1.7 m / min.

[0014] Optionally, for short process high silicon steel drawing speed can be increased to 5.0-6.0 m / min.

[0015] Optionally, the superheat of the molten steel in the tundish is controlled within the range of 10 to 15°C.

[0016] Optionally, the stirring current is controlled within 450-500A.

[0017] Optionally, the second cooling zone is divided into first to fourth cooling zones, and the second cooling zone passes through the first cooling zone, the second cooling zone, the third cooling zone, and the fourth cooling zone in sequence along the casting billet drawing direction, the first cooling zone and the second cooling zone have the same cooling water volume, or the second cooling zone has more cooling water than the first cooling zone, and the third cooling zone and the fourth cooling zone have 15 to 80% less cooling water than the second cooling zone.

[0018] Compared with the prior art, this application has the following beneficial effects:

[0019] This application controls the thickness of the protective slag layer, the viscosity of the protective slag, the melting point, the superheat of the molten steel in the tundish, the stirring current and other parameters, and divides the secondary cooling zone into a high-temperature strong cooling and a low-temperature weak cooling process system for cooling along the billet drawing direction. It can make the silicon steel production have the characteristics of high drawing speed, few defects, high equiaxed crystal rate, high billet temperature, etc., and provide conditions for realizing casting-rolling integration. It is also applicable to conventional processes, CSP, ESP, MCCR and other short processes, especially ESP, MCCR and other processes can realize headless rolling of high silicon steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a graph of thermal conductivity of different grades of silicon steel and low carbon steel at different temperatures;

[0021] Figure 2 It is the thermoplasticity curve of oriented silicon steel;

[0022] Figure 3 It is the strength curve of oriented silicon steel;

[0023] Figure 4 This is the thermoplasticity and strength curve of Q235. DETAILED DESCRIPTION

[0024] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] The method for manufacturing the silicon steel continuous casting billet of this embodiment comprises:

[0026] In step S1, the thickness of the protective slag liquid slag layer is within 10 to 18 mm, the viscosity of the protective slag is within 0.20 Pa·S to 0.29 Pa·S, and the melting point is within 1000°C to 1110°C. By controlling the parameters of the protective slag layer within this range, defects such as slag curling, heavy skin, scarring, and holes can be controlled.

[0027] Step S2, the fluctuation of the molten steel level is stabilized within ±3mm to ensure stable casting.

[0028] Step S3, the superheat of the molten steel in the tundish is controlled within 10-25°C, and is controlled as close to the lower limit as possible to increase the equiaxed grain rate;

[0029] Step S4, increasing the electromagnetic stirring current. Under the condition that the electromagnetic stirring frequency is 5 Hz, the stirring current is controlled within 200 A to 500 A, and is controlled near the upper limit as much as possible to increase the equiaxed crystal ratio and reduce segregation.

[0030] Step S5, during continuous casting, in the second cooling zone, cooling is carried out in sequence by adopting a process system of high-temperature strong cooling and low-temperature weak cooling according to the front and rear partitions. Specifically, for example, along the direction of billet drawing, the second cooling zone passes through the first cooling zone, the second cooling zone, the third cooling zone, and the fourth cooling zone in sequence, then the cooling water volume of the first cooling zone and the second cooling zone passed first is the same, or the cooling water volume of the second cooling zone is slightly increased than that of the first cooling zone. Exemplarily, the cooling water volume of the first cooling zone is 300L / min, and the cooling water volume of the second cooling zone is 300L / min, or 305L / min.

[0031] The cooling water volume of the third and fourth cooling zones is significantly reduced compared to the cooling water volume of the first and second cooling zones, and is reduced by 15-80% compared to the cooling water volume of the second cooling zone. For example, if the cooling water volume of the first and second cooling zones is 300L / min, and the cooling water volume of the third and fourth cooling zones is reduced by 80% compared to the cooling water volume of the second cooling zone, the cooling water volume of the third and fourth cooling zones is 60L / min.

[0032] This method is adopted because the applicant has found through a large number of experimental studies that although the hot strength of the ingot is low and the brittleness is large, it is not obvious compared with ordinary carbon steel. Figures 2 to 4 shown. Figure 2 , Figure 3 The section reduction ratio (Z) and tensile strength (R) of three silicon steel samples Q1, Q2 and Q3 are shown in Figure 2. m ) changes with temperature, Figure 4 Q235 thermoplasticity and strength curve. Figures 2 to 4 It can be seen that in the I zone (1200℃~liquidus)-ductile-brittle transition zone, the cross-sectional shrinkage (Z) and tensile strength (R m ) There is almost no difference; in the range of 1200-900℃, both oriented silicon steel and Q235 have good plasticity, with Z value above 60%, and no II brittle zone appears, which fully demonstrates that silicon steel has good high-temperature plasticity and the continuous casting process is easier to control; in zone III (600-900℃) - low plasticity zone, oriented silicon steel and Q235 have the same change trend. During the cooling process from 900 to 600℃, the cross-sectional shrinkage rate (Z) decreases from ≥60% to about 30% at 750℃, and the plasticity decreases. In this range, the thermal conductivity of high-grade silicon steel (W350, W250, QG085) reaches the second extreme value (minimum value). At this time, the heat dissipation of the ingot is fast, the heat conduction is slow, the temperature difference between the inside and the outside is large, and the plasticity is reduced and the brittleness is increased. If no insulation or slow cooling measures are taken, cracks or ingot breaks are very likely to occur.

[0033] Therefore, the applicant conducted an experimental study on the relationship between the silicon content, temperature and thermal conductivity of silicon steel, and found that there is a nonlinear coupling relationship between the silicon content, temperature and thermal conductivity of silicon steel, such as Figure 1 As shown in the figure, it is confirmed that the thermal conductivity of silicon steel at room temperature decreases with the increase of silicon content, but with the increase of temperature, the thermal conductivity of silicon steel with silicon content ≤1.8% (W1000, W600) gradually decreases, reaching the lowest point at about 1000℃, and then slowly increases; the thermal conductivity of silicon steel with silicon content ≥1.8% (W470, W350, W250, QG085) first increases slowly, reaching the first extreme value (maximum value) at 400-500℃, then slightly decreases, reaching the second extreme value (minimum value) at 780-910℃, and finally slowly increases. After the temperature of all silicon steel varieties exceeds 1080℃, their thermal conductivity is greater than that of low-carbon steel, and the higher the temperature, the greater the difference. This fully demonstrates that the thermal conductivity of silicon steel is higher than that of low-carbon steel during the continuous casting stage (1200-1500°C), and the cooling intensity of the second cooling zone of continuous casting should not be increased, but should be appropriately reduced, otherwise the columnar crystal area will expand and the equiaxed crystal area will decrease. Therefore, the present application significantly reduces the cooling water volume of the third and fourth cooling zones relative to the cooling water volume of the first and second cooling zones, which can reduce the columnar crystal area, increase the equiaxed crystal area, and avoid defects such as bulging and segregation.

[0034] Step S6, the drawing speed can be increased by 30-60% compared with the prior art, and the drawing speed can be greater than or equal to that of low carbon steel. For conventional process technology, the drawing speed of high silicon steel can reach 1.3-1.7 m / min; for short process technology, the drawing speed of high silicon steel can reach 5.0-6.0 m / min; the casting temperature is increased by more than 25°C.

[0035] The following is a method for manufacturing a silicon steel high-speed and high-quality continuous casting billet according to the present invention, with reference to specific examples.

[0036] Embodiment 1:

[0037] Using conventional process, two grades of non-oriented high-grade silicon steel 50W250 and 50W350 were selected for experiment;

[0038] Control the thickness of the protective slag liquid slag layer within 12-15mm; adjust the viscosity of the protective slag within 0.20Pa·S-0.23Pa·S and the melting point within 1040℃-1060℃;

[0039] The fluctuation of molten steel level is stable within ±3mm;

[0040] The superheat of molten steel in the tundish is controlled within 12-15℃;

[0041] The electromagnetic stirring frequency is 5Hz, and the stirring current is controlled within 400A~450A;

[0042] The continuous casting adopts the process system of high temperature strong cooling and low temperature weak cooling, that is, the two-cooling water distribution process of strong top and weak bottom is adopted, that is, the cooling water volume of the first cooling zone and the second cooling zone is the same, and the cooling water volume of the third cooling zone and the fourth cooling zone is reduced by 50% compared with the cooling water volume of the second cooling zone;

[0043] Under the implementation conditions of the aforementioned process parameters, the pulling speed of silicon steel can be increased to 1.4 m / min and the casting temperature can reach 900°C.

[0044] The changes in the silicon steel casting cycle before and after the implementation of the statistical analysis are shown in Table 1. The increase in the casting speed increases the equiaxed grain rate, reduces the casting cycle, and increases the hourly output.

[0045] Table 1 Changes in silicon steel casting cycle before and after implementation

[0046]

[0047] The ingot is sent down normally and the product is produced according to the conventional process. The performance comparison of silicon steel products before and after the implementation of the patent is shown in Table 2. The increase in the drawing speed improves the magnetic properties of the product.

[0048] Table 2 Product performance of silicon steel before and after implementation

[0049]

[0050] Embodiment 2:

[0051] The conventional process was adopted and the low temperature and high magnetic induction oriented silicon steel grade 23QG085 was selected for the experiment;

[0052] Control the thickness of the protective slag liquid slag layer within 12-15mm; adjust the viscosity of the protective slag within 0.21Pa·S-0.23Pa·S and the melting point within 1040℃-1080℃;

[0053] The fluctuation of molten steel level is stable within ±3mm;

[0054] The superheat of molten steel in the tundish is controlled within 11-15℃;

[0055] The electromagnetic stirring frequency is 5Hz, and the stirring current is controlled within 350A~400A;

[0056] The continuous casting adopts the process system of high temperature strong cooling and low temperature weak cooling, that is, the two-cooling water distribution process of strong top and weak bottom is adopted, that is, the cooling water volume of the first cooling zone and the second cooling zone is the same, and the cooling water volume of the third cooling zone and the fourth cooling zone is reduced by 55% compared with the second cooling zone;

[0057] Under the implementation conditions of the aforementioned process parameters, the pulling speed of silicon steel can be increased to 1.5 m / min, and the casting temperature is 915°C.

[0058] The changes in the silicon steel casting cycle before and after the implementation of statistical analysis are shown in Table 3. The increase in casting speed increased the equiaxed crystal rate, reduced the casting cycle, and increased the hourly output.

[0059] Table 3 Changes in silicon steel casting cycle before and after implementation

[0060]

[0061] The ingot is sent down normally and the product is produced according to the conventional process. The performance comparison of silicon steel products before and after the implementation of the patent is shown in Table 4. The increase in the drawing speed improves the magnetic properties of the product.

[0062] Table 4 Product performance of silicon steel before and after implementation

[0063]

[0064] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may make various corresponding changes and deformations according to the present invention, but these corresponding changes and deformations shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for manufacturing a silicon steel continuous casting billet, characterized in that: include: The thickness of the mold slag liquid slag layer used is within 10 to 18 mm, the viscosity of the mold slag is within 0.20 Pa·S to 0.29 Pa·S, and the melting point is within 1000°C to 1110°C; Keep the molten steel level fluctuation within ±3mm; The secondary cooling zone is divided into at least two cooling zones, and cooling is performed by adopting a process system in which the amount of cooling water decreases successively along the direction of the casting and drawing.

2. The method for manufacturing silicon steel continuous casting billet according to claim 1, characterized in that: For conventional process technology, the pulling speed of high silicon steel reaches 1.3-1.7 m / min.

3. The method for manufacturing silicon steel continuous casting billet according to claim 1, characterized in that: For short process technology, the pulling speed of high silicon steel is reached to 5.0~6.0m / min.

4. The method for manufacturing silicon steel continuous casting billet according to claim 1, characterized in that: The superheat of molten steel in the tundish is controlled within the range of 10 to 25°C.

5. The method for manufacturing silicon steel continuous casting billet according to claim 1, characterized in that: The stirring current is controlled within 200~500A.

6. The method for manufacturing silicon steel continuous casting billet according to claim 1, characterized in that: The second cooling zone is divided into the first to fourth cooling zones. The second cooling zone passes through the first cooling zone, the second cooling zone, the third cooling zone and the fourth cooling zone in sequence along the casting billet drawing direction. The cooling water volume of the first cooling zone and the second cooling zone is the same, or the cooling water volume of the second cooling zone is increased than that of the first cooling zone, and the cooling water volume of the third cooling zone and the fourth cooling zone is reduced by 15 to 80% compared with the cooling water volume of the second cooling zone.

Images