A long nozzle for preventing secondary oxidation of molten steel and its application method

Abstract

This invention relates to a long nozzle for a ladle and its method of use for preventing secondary oxidation of molten steel. The nozzle includes: a long nozzle body; an internal fluid cavity comprising a receiving seat, a fluid inlet, a straight section, a narrowing section, an expanding section, and a fluid outlet, connected sequentially; the receiving seat is used to connect to the ladle outlet; the fluid inlet is centered and connected to the ladle outlet via the receiving seat; the inner diameter of the straight section is the same as the inner diameter of the ladle outlet; a slag line is located on the lower outer side of the long nozzle body; the narrowing section is located at the slag line, and the minimum inner diameter of the narrowing section is smaller than the inner diameter of the straight section; the outlet inner diameter of the expanding section is larger than the inner diameter of the straight section; and the fluid outlet is connected to the tundish. This structure avoids air intake from gaps, reduces the risk of secondary oxidation of molten steel in the tundish, and improves the service life of the nozzle.

Description

Technical Field

[0001] This invention relates to the field of secondary oxidation control technology for molten steel in continuous casting, specifically to a long nozzle for a ladle used to prevent secondary oxidation of molten steel and its application method. Background Technology

[0002] The cleanliness of steel is a core indicator determining the mechanical properties, corrosion resistance, and service life of high-end steel. Controlling the secondary oxidation behavior of molten steel during the casting process is the main technical bottleneck in improving the cleanliness of molten steel. As a core component of continuous casting with full protection, the long nozzle is a key process channel that blocks the contact between molten steel and air, inhibiting secondary oxidation of molten steel from the source.

[0003] During the casting process, the long nozzle of the ladle is connected to the bottom nozzle, and molten steel from the ladle enters the tundish through the long nozzle. Traditionally, the inner diameter of the long nozzle is approximately 25mm-30mm larger than that of the bottom nozzle. After the molten steel is ejected at high speed through the bottom nozzle, it enters the expansion channel. The central jet detaches from the inner wall of the long nozzle and entrains interstitial gas. Combined with the incomplete recovery of static pressure during the expansion flow, a negative pressure forms in the annular area at the connection between the bottom nozzle and the long nozzle, making it highly susceptible to air intake and secondary oxidation. To prevent secondary oxidation of the molten steel, modern steel companies generally use a sealing bowl between the long nozzle and the bottom nozzle, followed by argon gas filling for argon sealing to isolate air. However, in actual use, the argon flow rate is difficult to control. If the argon flow rate is too low, it will not effectively isolate air; if the argon flow rate is too high, it will create large openings in the tundish covering agent, leading to subsequent inclusions and secondary oxidation of the steel in the tundish.

[0004] Therefore, there is an urgent need to provide a long nozzle for ladles and its usage method to prevent secondary oxidation of molten steel, in order to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings and defects of the prior art and provide a long nozzle for a ladle and its usage method to prevent secondary oxidation of molten steel, avoid air intake in the gaps, reduce the risk of secondary oxidation of molten steel in the tundish, and improve the service life of the nozzle.

[0006] The objective of this invention is achieved through the following technical solution: A long nozzle for preventing secondary oxidation of molten steel includes a long nozzle body. The internal fluid cavity of the long nozzle body includes a receiving seat, a fluid inlet, a straight section, a narrowing section, an expanding section, and a fluid outlet connected in sequence. The receiving seat is used to connect with the ladle outlet. The fluid inlet is centered and connected to the ladle outlet through the receiving seat. The inner diameter of the straight section is the same as the inner diameter of the ladle outlet. A slag line is provided on the lower outer side of the long nozzle body. The narrowing section is located at the slag line, and the minimum inner diameter of the narrowing section is smaller than the inner diameter of the straight section. The outlet inner diameter of the expanding section is larger than the inner diameter of the straight section. The fluid outlet is connected to the tundish.

[0007] Optionally, the length of the straight section is 700~900mm.

[0008] Optionally, the length of the reduced diameter section is 150~250mm, and the minimum inner diameter of the reduced diameter section is 0.5~0.75 times the inner diameter of the straight section.

[0009] Optionally, the length of the expansion section is 200~300mm, and the outlet inner diameter of the expansion section is 1.5~2 times the inner diameter of the straight section.

[0010] Optionally, the connection between the straight section and the reduced diameter section, and the connection between the reduced diameter section and the expanded diameter section, are all circular arc transition connections.

[0011] Optionally, the material of the main body of the large-sized nozzle is aluminum carbon, the material of the slag line part is zirconium carbon, and the mass percentage of graphite in the zirconium carbon is 20%~25%.

[0012] Optionally, at the joint between the receiving seat and the ladle drain outlet, a first sealing gasket and a second sealing gasket are sequentially provided from the inside out.

[0013] Optionally, the first sealing gasket is a metallurgical putty sealing gasket, and the second sealing gasket is an aluminum silicate fiber sealing gasket.

[0014] A method for using a long nozzle on a ladle to prevent secondary oxidation of molten steel includes the following steps: S1: Control of drainage sand; control the particle size of drainage sand to be 0.8~2mm, and the moisture content to be <0.1%; S2: Initial control during casting; During the initial casting stage, the depth of the long nozzle of the ladle inserted into the tundish should not exceed 150mm, and the opening degree of the casting valve should be 0.2~0.25 to control the slow start of the steel flow. S3: Argon sealing control; After the molten steel flows out, argon gas is introduced into the joint between the receiving seat and the ladle outlet to maintain a slight positive pressure argon seal. The argon gas pressure is 0.3~0.5MPa and the flow rate is 3~5L / min. S4: Immersion depth control; after the steel flow stabilizes, insert the ladle's long nozzle into the working position.

[0015] Optionally, in step S2, the depth to which the long nozzle of the large package is inserted into the intermediate package is 80~120mm.

[0016] Compared with the prior art, the present invention has the following beneficial effects: In this invention, by using the same inner diameter of the straight section as the ladle's outlet, there is no abrupt change in cross-section when the molten steel enters the long nozzle from the outlet, avoiding the negative pressure zone at the connection point in traditional structures, reducing air intake, and thus reducing secondary oxidation of the molten steel. Furthermore, placing the narrowing section at the slag line increases the molten steel flow velocity and reduces turbulence in this area, creating a self-cleaning effect. Inclusions and protective slag are less likely to adhere and deposit at the slag line, reducing local erosion; the use of high-graphite-content zirconium-carbon materials at the slag line effectively extends the service life of the nozzle; the narrowing section rectifyes the upstream steel flow, eliminating eddies and pulsations; the widening section reduces the outlet velocity of the molten steel and allows for smooth diffusion, reducing the impact on the refractory material of the tundish and the disturbance to the liquid surface, further reducing the risk of secondary oxidation and slag entrapment of the molten steel in the tundish, and improving the purity of the steel. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the present invention.

[0018] Figure 2 This is a schematic diagram of the structure of a large package with a long nozzle in the prior art.

[0019] The above figures include the following reference numerals: 1. Ladle drain outlet; 2. Ladle long outlet body; 21. Slag line section; 3. Receiver; 31. Metallurgical mortar gasket; 32. Aluminum silicate fiber gasket; 4. Fluid inlet; 5. Straight section; 6. Reduction section; 7. Expansion section; 8. Fluid outlet; 9. Tundish. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0021] The present invention proposes a long nozzle for a ladle to prevent secondary oxidation of molten steel and its usage method.

[0022] Reference Figures 1 to 2In this embodiment, the system includes: a large ladle nozzle body 2, the internal fluid cavity of which includes a receiving seat 3, a fluid inlet 4, a straight section 5, a narrowing section 6, an expanding section 7, and a fluid outlet 8 connected in sequence; the receiving seat 3 is used to connect with the ladle outlet 1; the fluid inlet 4 is centered and connected to the ladle outlet 1 through the receiving seat 3; the inner diameter of the straight section 5 is the same as the inner diameter of the ladle outlet 1; a slag line portion 21 is provided on the lower outer side of the large ladle nozzle body 2, the narrowing section 6 is located at the slag line portion 21, and the minimum inner diameter of the narrowing section 6 is smaller than the inner diameter of the straight section 5; the outlet inner diameter of the expanding section 7 is larger than the inner diameter of the straight section 5, and the fluid outlet 8 is connected to the tundish 9.

[0023] In this embodiment, see Figure 1 The long nozzle of the ladle, designed to prevent secondary oxidation of molten steel, includes a long nozzle body 2. The internal fluid cavity of the long nozzle body 2 includes a receiving seat 3, a fluid inlet 4, a straight section 5, a narrowing section 6, an expanding section 7, and a fluid outlet 8, which are connected sequentially in the vertical direction. The receiving seat 3 is used to connect with the ladle outlet 1, and the fluid inlet 4 is aligned and connected to the ladle outlet 1 through the receiving seat 3. The inner wall of the receiving seat 3 is provided with a slope that matches the outer wall of the outlet to ensure alignment accuracy and sealing contact area. The inner diameter of the straight section 5 is the same as the inner diameter of the ladle outlet 1, and its length is 700~900mm. This ensures that the flow channel cross-section does not change abruptly when the molten steel enters the long nozzle from the outlet, avoiding the negative pressure zone caused by the Venturi effect in traditional abrupt expansion structures, reducing the possibility of air being sucked in from the joint, and reducing the possibility of secondary oxidation of the steel. The lower outer side of the long nozzle body 2 of the tundish has a slag line section 21, which is the part of the long nozzle that is inserted into the molten steel in the tundish 9 during use. This area is in direct contact with the molten steel and the molten protective slag. The narrowing section 6 is set at the slag line section 21, with a length of 150~250mm, and the minimum inner diameter of the narrowing section 6 is 0.5~0.75 times the inner diameter of the straight section 5. By setting the narrowing section 6 at the slag line section 21, the narrowing leads to an increase in the flow velocity of the molten steel and a reduction in turbulence. The resulting self-cleaning effect makes it difficult for Al2O3 inclusions, protective slag, etc. to adhere and deposit at the slag line, reducing local erosion. At the same time, the lowest pressure zone of the narrowing section 6 is located in the area with the best liquid sealing effect, forming a strong negative pressure flow at the moment of pouring, improving the self-opening rate.

[0024] The expansion section 7 is located downstream of the contraction section 6, with a length of 200~300mm. Its outlet inner diameter is 1.5~2 times the inner diameter of the straight section 5. The fluid outlet 8 is connected to the tundish 9. The expansion section 7 allows the molten steel accelerated by the contraction section 6 to smoothly decelerate and diffuse, reducing the outlet flow rate and the impact on the bottom refractory material of the tundish 9. At the same time, it reduces the fluctuation of the liquid surface in the tundish 9, thereby reducing the risk of secondary oxidation and slag entrapment of the molten steel in the tundish 9.

[0025] In this embodiment, the connection between the straight section 5 and the reduced diameter section 6, as well as the connection between the reduced diameter section 6 and the expanded diameter section 7, are all arc transition connections. The arc transition can avoid dead zones in the flow channel, reduce turbulence and eddies in the molten steel, make the flow more stable, and at the same time reduce the scouring and wear on the connection.

[0026] In this embodiment, the material of the main body 2 of the large nozzle is aluminum carbon, which has good thermal shock resistance and low cost; the material of the slag line part 21 is zirconium carbon, and the graphite mass percentage is 20%~25%. The high graphite content gives the zirconium carbon material good slag erosion resistance and thermal shock resistance, which can effectively resist the high steel pressure and scouring caused by the narrow diameter design and extend the service life of the nozzle.

[0027] Furthermore, at the joint between the receiving seat 3 and the ladle outlet 1, a first sealing gasket and a second sealing gasket are sequentially arranged from the inside out; wherein, the first sealing gasket is a metallurgical mortar sealing gasket 31, and the second sealing gasket is an aluminum silicate fiber sealing gasket 32. The composition (by mass percentage) of the metallurgical mortar sealing gasket 31 is preferably: 20%~25% sintered magnesia, 50%~60% corundum powder, 5%~8% expanded graphite, and 5%~7% dibutyl phthalate. During the casting process, the magnesia and corundum in the metallurgical mortar undergo a sintering reaction to generate magnesium aluminum spinel. This reaction is accompanied by a 5%~8% volume expansion, which actively blocks the sealing gaps and forms a dense magnesium aluminum spinel sintered layer at the joint, improving the sealing strength and erosion resistance at the interface, and effectively resisting the increase in pressure above the outlet caused by the reduced diameter design.

[0028] The aluminum silicate fiber sealing gasket 32 ​​is disposed on the outer layer of the metallurgical putty sealing gasket 31 and has a certain degree of air permeability. On the one hand, it serves as a mechanical sealing layer to fill the joint gap, and on the other hand, it serves as an argon pressure transmission medium, so that the outer layer argon pressure is evenly distributed to the joint interface, assisting in compacting the inner layer metallurgical putty. Argon gas is introduced into the joint for argon sealing, forming a third sealing barrier. By using the inner layer metallurgical putty sealing gasket 31 and the outer layer aluminum silicate fiber sealing gasket 32 ​​in conjunction with argon gas to seal the joint, air isolation is achieved, reducing the risk of air being drawn into the joint.

[0029] A method for using a long ladle nozzle to prevent secondary oxidation of molten steel, comprising the following steps: S1: Control of guiding sand; Strictly control the particle size and moisture content of the guiding sand. The particle size of the guiding sand should be 0.8~2.0mm, and the moisture content should be <0.1%. If the particle size is too large or too small, it will affect the guiding effect and the self-opening rate; if the moisture content is too high, it will cause the guiding sand to clump or generate water vapor at high temperature, which will cause secondary oxidation of the molten steel.

[0030] S2: Initial Casting Control; In the initial casting stage, the depth of the long nozzle of the ladle inserted into the tundish 9 should not exceed 150mm, preferably 80~120mm. At the same time, the opening degree of the casting valve should be controlled at 0.2~0.25 (i.e., 1 / 5~1 / 4 opening) to control the slow start of the steel flow. By initially shallowly inserting the nozzle and slowly starting the flow, the molten steel enters the tundish 9 smoothly, avoiding violent fluctuations in the liquid surface of the tundish 9 due to excessive flow, thereby reducing slag entrapment and secondary oxidation. At the same time, under the shallow insertion state, the negative pressure drainage effect formed by the necking section 6 in the slag line area is most significant, which is conducive to the smooth discharge of drainage sand and improves the self-starting rate.

[0031] S3: Argon sealing control; after the molten steel flows out, argon gas is introduced into the joint between the receiving seat 3 and the ladle outlet 1 to maintain a slightly positive pressure argon seal; the argon gas pressure is 0.3~0.5MPa and the flow rate is 3~5L / min; by designing the straight section 5 and the ladle outlet 1 to have the same diameter, the negative pressure source at the joint is eliminated from the structure. Argon gas only needs to maintain a slightly positive pressure environment to block air intake, without the need for a large flow of argon to overcome the negative pressure, thus avoiding the problems of open-hole coating agent and slag entrapment in the tundish 9 caused by the large flow of argon gas in traditional technology.

[0032] S4: Immersion depth control; After the steel flow stabilizes, insert the ladle nozzle into the working position, which is the insertion depth required for normal casting (determined according to the liquid level height of the tundish 9). At this time, the necking section 6 is completely submerged in the molten steel, and the slag line 21 is located at the junction of the slag layer and the molten steel, giving full play to its self-cleaning and anti-corrosion functions.

[0033] Example 1: Industrial trials were conducted on a six-strand continuous casting machine at a steel plant, with a ladle capacity of 120 tons. The casting speed was 1.6 m / min, the steel grade used was 42CrMo, the casting cross-section was 160 mm × 225 mm, and the tundish superheat was 20~30℃.

[0034] The parameters for the long nozzle are as follows: Straight section 5 has an inner diameter of φ60mm and a length of 700mm; narrowing section 6 has a minimum inner diameter of φ30mm (0.5d) and a length of 150mm; expanding section 7 has a length of 200mm and an outlet inner diameter of φ90mm (1.5d). The main body of the long nozzle is made of alumina-carbon, while the slag line section 21 is made of zirconium-carbon, with a graphite content of 20%~25%. The connections between straight section 5 and narrowing section 6, and between narrowing section 6 and expanding section 7, are all rounded transitions.

[0035] Sealing method: The joint between the receiving seat 3 and the drain outlet is sealed with an inner metallurgical mortar gasket 31 and an outer aluminum silicate fiber gasket 32, and argon gas is introduced for argon sealing. The argon gas flow rate is 5L / min and the pressure is 0.5MPa.

[0036] Instructions for use: The particle size of the guiding sand should be 0.8~2.0mm, and the moisture content should be <0.1%; at the initial stage of pouring, the valve should be opened to 1 / 5 and the long nozzle should be inserted to a depth of 80mm; after the molten steel flows out, maintain the argon seal; after stabilization, lower the nozzle to the working position.

[0037] Example 2: Industrial trials were conducted on a six-strand continuous casting machine at a steel plant, with a ladle capacity of 120 tons. The casting speed was 1.4 m / min, the steel grade used was 42CrMo, the casting cross-section was 220 mm × 220 mm, and the tundish superheat was 20~30℃.

[0038] Parameters of the long nozzle: Straight section 5 has an inner diameter of φ60mm and a length of 900mm; narrowing section 6 has a minimum inner diameter of φ45mm (i.e., 0.75d) and a length of 250mm; expanding section 7 has a length of 300mm and an outlet inner diameter of φ120mm (i.e., 2d). The long nozzle body is made of alumina-carbon, while the slag line section 21 is made of zirconium-carbon, with a graphite content of 20%~25%.

[0039] The sealing method and usage are the same as in Example 1, wherein the argon flow rate is 3L / min and the pressure is 0.3MPa; the initial insertion depth is 120mm.

[0040] Comparative Example 1: The traditional long nozzle was used for casting, and the remaining test conditions were the same as in Example 2. The traditional long nozzle has a trumpet-shaped structure with an inner diameter of φ70mm, no necking section 6, and no special design for the slag line section 21. The sealing method is a single-layer aluminum silicate fiber sealing gasket 32 ​​+ argon gas sealing, with an argon gas flow rate of 18L / min and a pressure of 0.3MPa. The initial insertion depth was 100mm, without staged depth control.

[0041] Comparison of experimental results and effects: The following table compares the technical specifications of the above embodiments with those of the comparative examples:

[0042] Among them, the change in the gaseous nitrogen content in the molten steel is an important indicator for judging the severity of secondary oxidation. The smaller the difference between the tundish [N] and the ladle [N], the lighter the degree of secondary oxidation.

[0043] The results above show that the argon consumption using this method is significantly reduced. The argon consumption in Examples 1 and 2 is 1.85 L / ton of steel and 0.94 L / ton of steel, respectively, which is 67% and 83% lower than that in Comparative Example 1 (5.64 L / ton of steel). The straight section 5 equal diameter design of this invention eliminates the negative pressure at the joint from a structural perspective, and only a slightly positive pressure argon seal is needed to meet the sealing requirements.

[0044] Service life significantly extended: The service life of the nozzles in Examples 1 and 2 was 64 hours and 58 hours, respectively, which is 52% and 38% higher than that of Comparative Example 1 (42 hours). This is due to the self-cleaning design of the necking section coinciding with the slag line and the excellent erosion resistance of the high-graphite-content zirconium-carbon material in the slag line area.

[0045] The ladle self-opening rate reached 100%: The ladle self-opening rate of both Example 1 and Example 2 was 100%, a significant improvement over the 85% of Comparative Example 1. The reduced diameter section was set in the slag line liquid seal zone, forming a strong negative pressure to guide the flow at the moment of pouring. Combined with strict control of the guiding sand and the staged insertion depth and slow flow start operation, the smooth discharge of the guiding sand and the smooth flow of molten steel were ensured, thereby significantly improving the ladle self-opening rate.

[0046] The degree of secondary oxidation was significantly reduced: the difference between the intermediate ladle [N] and the steel ladle [N] in Examples 1 and 2 was 3 ppm and 5 ppm, respectively, which was significantly reduced compared to 26 ppm in Comparative Example 1. This indicates that the structural design and usage method can effectively suppress the secondary oxidation of molten steel during the casting process.

[0047] The embodiments described above merely illustrate implementation methods of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A long nozzle for a ladle to prevent secondary oxidation of molten steel, characterized in that, The system includes a large ladle nozzle body. The internal fluid cavity of the large ladle nozzle body comprises a receiving seat, a fluid inlet, a straight section, a narrowing section, an expanding section, and a fluid outlet, connected sequentially. The receiving seat is used to connect to the ladle outlet. The fluid inlet is centered and connected to the ladle outlet via the receiving seat. The inner diameter of the straight section is the same as the inner diameter of the ladle outlet. A slag line is located on the lower outer side of the large ladle nozzle body. The narrowing section is located at the slag line, and the minimum inner diameter of the narrowing section is smaller than the inner diameter of the straight section. The outlet inner diameter of the expanding section is larger than the inner diameter of the straight section. The fluid outlet is connected to the tundish.

2. The long nozzle for preventing secondary oxidation of molten steel according to claim 1, characterized in that, The length of the straight section is 700~900mm.

3. The long nozzle for preventing secondary oxidation of molten steel according to claim 1, characterized in that, The length of the reduced diameter section is 150~250mm, and the minimum inner diameter of the reduced diameter section is 0.5~0.75 times the inner diameter of the straight section.

4. The long nozzle for preventing secondary oxidation of molten steel according to claim 1, characterized in that, The length of the expansion section is 200~300mm, and the inner diameter of the outlet of the expansion section is 1.5~2 times the inner diameter of the straight section.

5. The long nozzle for preventing secondary oxidation of molten steel according to claim 1, characterized in that, The connection between the straight section and the reduced diameter section, and the connection between the reduced diameter section and the expanded diameter section, are all circular arc transition connections.

6. The long nozzle for preventing secondary oxidation of molten steel according to claim 1, characterized in that, The material of the main body of the large-capacity water nozzle is aluminum carbon, the material of the slag line part is zirconium carbon, and the mass percentage of graphite in the zirconium carbon is 20%~25%.

7. The long nozzle for preventing secondary oxidation of molten steel according to claim 1, characterized in that, At the joint between the receiving seat and the ladle drain outlet, a first sealing gasket and a second sealing gasket are sequentially installed from the inside out.

8. The long nozzle for preventing secondary oxidation of molten steel according to claim 7, characterized in that, The first sealing gasket is a metallurgical putty sealing gasket, and the second sealing gasket is an aluminum silicate fiber sealing gasket.

9. A method for using a long nozzle on a ladle to prevent secondary oxidation of molten steel, characterized in that, The large package with a long sprue as described in any one of claims 1-8 includes the following steps: S1: Control of drainage sand; control the particle size of drainage sand to be 0.8~2mm, and the moisture content to be <0.1%; S2: Initial control during casting; During the initial casting stage, the depth of the long nozzle of the ladle inserted into the tundish should not exceed 150mm, and the opening degree of the casting valve should be 0.2~0.25 to control the slow start of the steel flow. S3: Argon sealing control; After the molten steel flows out, argon gas is introduced into the joint between the receiving seat and the ladle outlet to maintain a slight positive pressure argon seal. The argon gas pressure is 0.3~0.5MPa and the flow rate is 3~5L / min. S4: Immersion depth control; after the steel flow stabilizes, insert the ladle's long nozzle into the working position.

10. The method for using a long nozzle on a ladle to prevent secondary oxidation of molten steel according to claim 9, characterized in that, In step S2, the depth to which the long nozzle of the large package is inserted into the intermediate package is 80~120mm.

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