Four-hole submersed nozzle special for large round billet and using method of four-hole submersed nozzle

Abstract

The invention discloses a four-hole submersed nozzle special for a large round billet and a using method of the four-hole submersed nozzle. The through hole extends from the first end of the nozzle body to the position near the second end, and the through hole penetrates through the first end of the nozzle body; the open hole is formed in the side face of the second end of the water gap body, and the open hole extends from the side face of the water gap body to be communicated with the through hole; a plurality of open holes are evenly formed in the side face of the nozzle body. Design is carried out by improving the hole number, the hole angle and the like of the submersed nozzle, insertion depth optimization is carried out according to the design, the retention time of molten steel in a crystallizer is prolonged, sufficient time is provided for floating of inclusions, a flow field and a temperature field in the crystallizer are homogenized, uniform distribution of alloy solute elements is promoted, and the homogenization level of a casting blank is improved; melting of casting powder is promoted, liquid slag evenly flows into a gap between a casting blank and a crystallizer, and the surface quality of the casting blank is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of continuous casting, and in particular relates to a four-hole submerged nozzle specially used for large round billets and a use method thereof. Background Art

[0002] In the process of implementing the present invention, the inventors discovered that the prior art has at least the following problems:

[0003] With the development of efficient continuous casting technology and the increasingly high requirements of downstream customers for steel products, the technical level of homogenization and cleanliness of continuous casting billets has been continuously improved. At present, the uniformity of solidification components of billets is mainly achieved by controlling electromagnetic stirring parameters, low superheat, pressure reduction and other process technologies, and the cleanliness level of molten steel is improved by refining, vacuum and tundish technologies. However, after the molten steel passes through the immersion nozzle in the tundish to the crystallizer, due to the addition of protective slag to the molten steel surface in the crystallizer, when the immersion nozzle is unreasonable and the insertion depth is not appropriate, especially for large round billets of high-quality steel Generally speaking, due to the segregation effect during the solidification process, the following defects are prone to occur: 1) The flow field of molten steel in the crystallizer is disordered, resulting in fluctuations in the liquid level of the molten steel and slag rolls, which affects the cleanliness of the molten steel; 2) When the molten steel passes through the secondary cooling section, the solidified shell of the ingot is uneven, resulting in segregation of solute elements, which affects the homogenization level of the ingot; 3) The temperature of the molten steel surface is low, resulting in poor melting of the protective slag and reduced consumption, which affects the heat transfer and lubrication function of the protective slag, uneven primary shell of the ingot, increased demoulding resistance, surface defects, etc. In severe cases, there will be a risk of steel leakage.

[0004] The disadvantages of the existing technology are: currently, in order to improve the homogenization and cleanliness level of large-section continuous casting billets through the crystallizer immersion nozzle, a special multi-hole nozzle, pouring temperature and immersion nozzle insertion depth are designed. However, the multi-hole immersion nozzle is generally used on slab continuous casting machines, while large-section round billet continuous casting machines generally use single-hole straight-cylinder immersion nozzles. There are few reports on the application of multi-hole immersion nozzles for large-section round billet continuous casting machines. For example, 1. Add an electromagnetic swirl control device to the immersion nozzle (such as invention patent CN202311717780.7) to control the residence time of the molten steel in the crystallizer, improve the time for removing inclusions in the molten steel, and make the solute elements in the molten steel evenly distributed through the swirl effect of the molten steel. Its disadvantages are: 1) Excessive swirl of the molten steel can easily cause vortex slag to form on the molten steel surface in the crystallizer; 2) As the content of high-quality alloying elements continues to increase, its solidification shrinkage conditions continue to increase, and the centrifugal effect of each element is different, which will cause the alloy to swell. The aggregation of gold elements is not conducive to the improvement of the homogenization technology of the ingot; 2. The side holes of the submerged nozzle are subjected to swirl (such as the utility model patent CN201820406645.9). The core technology is to open three side holes and perform swirl design, and open a hole at the bottom. A buffer platform is designed at the bottom hole to slow down the impact of the molten steel injection on the liquid center, and the opening is downward to reduce the buffering of the molten steel surface and reduce the risk of slag rolling on the liquid surface of the crystallizer. The disadvantage is that the design size of the bottom opening will be smaller, and the molten steel will pass through the submerged nozzle after being injected. The impact of the molten steel entering the solidifying liquid core from the bottom hole is greater and deeper. Due to the swirl effect of the side holes, the molten steel inclusions entering the deeper liquid core cannot float up and are more likely to precipitate in the solidifying liquid core, resulting in an increase in inclusions in the core of the ingot; 3. By improving the centering of the submerged nozzle to reduce the stress gradient of the ingot shell caused by thermal shrinkage (such as the invention patent CN201811140920.8), its core technology is that the distance between the submerged nozzle and the outer arc side is greater than the distance between the submerged nozzle and the inner arc side, and the process of solidification shrinkage is improved by eliminating the characteristics of gravity, preventing The slab will have quality defects such as surface cracks in the second cooling section due to the excessive temperature gradient. Its disadvantages are: the offset and misalignment of the immersed nozzle in the crystallizer can easily cause uneven flow and temperature fields in the crystallizer, which is more likely to cause slag rolling. In addition, the growth rates of the inner and outer shells of the ingot are inconsistent, and the strength of the shell cannot be guaranteed. When the ingot leaves the crystallizer, defects such as dents may be caused. This method is suitable for slabs. For the solidification shrinkage characteristics of large round billets, the gravity affects the growth of columnar crystals more significantly, and the proportion of columnar crystals on the inner arc side is greater than that on the outer arc side. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a four-hole submerged nozzle specially used for large round billets and a method for using the same. The design is carried out by improving the number of openings and the opening angle of the submerged nozzle, and the insertion depth is optimized according to the design, thereby increasing the residence time of molten steel in the crystallizer, providing sufficient time for inclusions to float up, uniformizing the flow field and temperature field in the crystallizer, promoting the uniform distribution of alloy solute elements, improving the homogenization level of the billet, and promoting the melting of protective slag, so that the liquid slag flows evenly into the gap between the billet and the crystallizer, thereby improving the surface quality of the billet.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a four-hole immersion nozzle specially used for large round billets, having:

[0007] Shuikou body;

[0008] a through hole extending from the first end of the nozzle body to near the second end, the through hole penetrating the first end of the nozzle body;

[0009] An opening is provided on the side of the second end of the nozzle body, and the opening extends from the side of the nozzle body to communicate with the through hole; a plurality of openings are evenly provided on the side of the nozzle body.

[0010] Four openings are evenly arranged on the side of the nozzle body.

[0011] The inclination angle of the opening is 15°.

[0012] The opening is a waist-shaped hole with a length of 48 mm, a width of 27 mm, and a fillet radius of 13.5 mm.

[0013] The overall length of the nozzle body is 1250 mm ± 5 mm, and the opening is 25 mm away from the second end of the nozzle body.

[0014] The outer diameter of the second end of the nozzle body is φ98mm, and the inner diameter of the through hole is φ42mm.

[0015] The insertion depth of the nozzle body is 100 mm to 120 mm.

[0016] The material of the slag line erosion position of the nozzle body is ZrO2-C.

[0017] The method for using the above-mentioned four-hole submerged nozzle for large round billets includes the following steps:

[0018] 1) The tundish baking time is ≥5h, the baking temperature is ≥1100℃, and the immersion nozzle wall temperature measured by the infrared temperature measuring gun is >750℃;

[0019] 2) After baking, the tundish car is driven to the pouring position to ensure that the nozzle is centered and not offset;

[0020] 3) During the pouring process, the tundish is lowered to the pouring position and the stopper rod is used to control the pouring;

[0021] 4) Turn on the crystallizer vibration, electromagnetic stirring 100A / 2HZ~200A / 2HZ, and the crystallizer cooling water 3600~4600L / min;

[0022] 5) Add protective slag. Add protective slag frequently and in small amounts to prevent the slag interface from being unstable or the molten steel from being exposed, causing secondary oxidation of the molten steel.

[0023] One of the above technical solutions has the following advantages or beneficial effects. It is designed by improving the number of openings and the opening angle of the submerged nozzle, and optimizing the insertion depth according to the design, thereby increasing the residence time of the molten steel in the crystallizer, providing sufficient time for inclusions to float up, uniformizing the flow field and temperature field in the crystallizer, promoting the uniform distribution of alloy solute elements, improving the homogenization level of the ingot, and promoting the melting of the protective slag, so that the liquid slag flows evenly into the gap between the ingot and the crystallizer, and improving the surface quality of the ingot. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic structural diagram of a four-hole submerged nozzle specifically for large round billets provided in an embodiment of the present invention;

[0025] The markings in the above figures are: 1. nozzle body, 2. through hole, 3. opening. DETAILED DESCRIPTION

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention 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 making creative efforts are within the scope of protection of the present invention.

[0027] Example 1

[0028] See also Figure 1A four-hole immersion nozzle specially designed for large round billets comprises: a nozzle body; a through hole extending from the first end of the nozzle body to near the second end, the through hole penetrating the first end of the nozzle body; an opening provided on the side of the second end of the nozzle body, the opening extending from the side of the nozzle body to communicate with the through hole; and a plurality of openings evenly provided on the side of the nozzle body. By improving the number of openings and the opening angle of the immersion nozzle and optimizing the insertion depth according to the design, the residence time of the molten steel in the crystallizer is increased, sufficient time is provided for the floating of inclusions, the flow field and temperature field in the crystallizer are uniformed, the uniform distribution of alloy solute elements is promoted, the homogenization level of the ingot is improved, and the melting of the protective slag is promoted, so that the liquid slag flows evenly into the gap between the ingot and the crystallizer, thereby improving the surface quality of the ingot.

[0029] The side of the nozzle body is evenly distributed with four openings. The four-hole immersion nozzle can effectively even out the temperature of the molten steel in the crystallizer, which is conducive to the uniform growth of the solidified shell.

[0030] The opening is tilted at a 15° angle. Adjusting the four-hole submerged nozzle opening angle downward by 15° can effectively even out the flow field of the molten steel in the mold, control the molten steel flow rate at the mold surface, reduce the risk of slag roll-off caused by excessive molten steel flow rate at the mold surface, and improve the cleanliness of the molten steel.

[0031] The opening is a waist-shaped hole, 48mm long and 27mm wide, with a fillet radius of 13.5mm. The overall length of the nozzle body is 1250mm ± 5mm, and the opening is located 25mm from the second end of the nozzle body. The outer diameter of the second end of the nozzle body is φ98mm, and the inner diameter of the through hole is φ42mm.

[0032] The insertion depth of the nozzle body is 100mm to 120mm. Controlling the insertion depth of the crystallizer immersion nozzle to 100mm to 120mm promotes the melting of the mold slag, gives full play to the heat transfer and lubrication effects of the mold slag, and reduces the resistance to demolding of the billet.

[0033] The material for the slag line erosion position of the nozzle body is ZrO2-C.

[0034] The existing single-hole straight-cylinder submerged nozzle for large round billet crystallizer is redesigned and optimized. The number of openings and the opening angle of the submerged nozzle are improved, and the insertion depth is optimized according to the design. The residence time of molten steel in the crystallizer is increased, sufficient time is provided for inclusions to float up, the flow field and temperature field in the crystallizer are uniform, the uniform distribution of alloy solute elements is promoted, the homogenization level of the billet is improved, and the melting of protective slag is promoted, so that the liquid slag flows evenly into the gap between the billet and the crystallizer, thereby improving the surface quality of the billet.

[0035] The continuous casting machine involved is a 17m 4-machine 4-strand arc continuous casting machine, the cross-section of the billet is a φ600mm round billet continuous casting machine, the conventional drawing speed is 0.22~0.30m / min, the length of the crystallizer copper tube is 800mm, the water volume of the crystallizer is 3600~4600L / min, the crystallizer adopts a new four-hole submerged nozzle, the submerged nozzle adopts two slag lines, the tundish adopts an integral bag, and the four-hole nozzle is baked together with the tundish. The production process of the large round billet steel grade involved is converter-LF refining-RH vacuum degassing-continuous casting.

[0036] Example 2

[0037] This embodiment provides a design and application method of a new four-hole submerged nozzle specially used for large round billets, which is used to produce large-section continuous casting billets with a diameter of 600 mm. The liquidus temperature of 42CrMoA steel is 1494°C, the water volume of the crystallizer is 4000L / min, and a new four-hole submerged nozzle is used. The four-hole nozzles are all symmetrically opened on the side holes, with a downward inclination angle of 15°, an insertion depth of 100 mm, an average pulling speed of 0.26 m / min, an average superheat control of 25°C, and an electric stirring parameter of the crystallizer of 150A / 2HZ.

[0038] In the above embodiment, the liquid level of the crystallizer is tracked, and the surface velocity is measured by interpolation. The protective slag melting effect is good. The average surface velocity of the molten steel is measured to be 0.08 m / s, wherein the average residence time of 50 μm-sized inclusions is 68 s, the average residence time of 100 μm-sized inclusions is 60 s, the inclusion density is 10.3 pieces / mm2, and the equiaxed grain ratio of the ingot is 28.4%. The data table is shown in Table 1.

[0039] Example 3

[0040] This embodiment provides a design and application method of a new four-hole submerged nozzle specially designed for large round billets, which produces large-section continuous casting billets with a diameter of 600 mm. The liquidus temperature of 27SiMn steel is 1494°C, the water volume of the crystallizer is 3800L / min, and a new four-hole submerged nozzle is adopted. The four-hole nozzles are all symmetrically opened on the side holes, and their downward inclination angles are all 15°. The insertion depth is 100 mm, the average pulling speed is 0.26 m / min, the average superheat is controlled at 23°C, and the electric stirring parameter of the crystallizer is 150A / 2HZ.

[0041] In the above embodiment, the liquid level of the crystallizer is tracked, and the surface velocity is measured by interpolation. The protective slag melting effect is good. The average surface velocity of the molten steel is measured to be 0.08 m / s, wherein the average residence time of 50 μm-sized inclusions is 65 s, the average residence time of 100 μm-sized inclusions is 62 s, the inclusion density is 9.4 pieces / mm2, and the equiaxed grain ratio of the ingot is 27.2%. The data table is shown in Table 1.

[0042] Example 4

[0043] This embodiment provides a design and application method of a new four-hole submerged nozzle specially used for large round billets, which produces large-section continuous casting billets of φ600mm. The liquidus temperature of 30CrMo steel is 1505℃, the water volume of the crystallizer is 3800L / min, and a new four-hole submerged nozzle is adopted. The four-hole nozzles are all symmetrically opened on the side holes, and their downward inclination angles are all 15°. The insertion depth is 100mm, the average pulling speed is 0.26m / min, the average superheat is controlled at 25℃, and the electric stirring parameter of the crystallizer is 150A / 2HZ.

[0044] In the above embodiment, the liquid level of the crystallizer is tracked, and the surface velocity is measured by interpolation. The protective slag melting effect is good. The average surface velocity of the molten steel is measured to be 0.09 m / s, wherein the average residence time of 50 μm-sized inclusions is 66 s, the average residence time of 100 μm-sized inclusions is 61 s, the inclusion density is 9.6 pieces / mm2, and the equiaxed grain ratio of the ingot is 28.8%. The data table is shown in Table 1.

[0045] Comparative Example 1

[0046] This embodiment provides a new four-hole submerged nozzle design and application method for large round billets, which is used to produce large-section continuous casting billets with a diameter of 600 mm. The liquidus temperature of 27SiMn steel is 1494°C, the water volume of the crystallizer is 3800 L / min, and a downward-opening single-hole straight-cylinder submerged nozzle is used. The insertion depth is 100 mm, the average pulling speed is 0.26 m / min, the average superheat is controlled at 23°C, and the electric stirring parameter of the crystallizer is 150 A / 2 Hz.

[0047] In the above embodiment, the liquid level of the crystallizer is tracked, and the surface velocity is measured by interpolation. The protective slag melting effect is good. The average surface velocity of the molten steel is measured to be 0.12 m / s, wherein the average residence time of 50 μm inclusions is 332 s, the average residence time of 100 μm inclusions is 295 s, the inclusion density is 13.5 / mm2, and the equiaxed grain ratio of the ingot is 21.8%. The data table is shown in Table 1.

[0048] Comparative Example 2

[0049] This embodiment provides a new four-hole submerged nozzle design and application method for large round billets, which is used to produce large-section continuous casting billets with a diameter of 600 mm. The liquidus temperature of 42CrMoA steel is 1494°C, the water volume of the crystallizer is 4000L / min, and a four-hole submerged nozzle is used. The four-hole nozzles are all symmetrically opened on the side holes, with an upward inclination angle of 15°, an insertion depth of 100 mm, an average pulling speed of 0.26 m / min, an average superheat control of 23°C, and an electric stirring parameter of the crystallizer of 150A / 2HZ.

[0050] In the above embodiment, the liquid level of the crystallizer is tracked, and the surface velocity is measured by interpolation. The protective slag melting effect is good. The average surface velocity of the molten steel is measured to be 0.08 m / s. The average residence time of 50 μm inclusions is 139 s, the average residence time of 100 μm inclusions is 121 s, the inclusion density is 11.8 / mm2, and the equiaxed grain ratio of the ingot is 23.4%. The data table is shown in Table 1.

[0051] Table 1 Gas content and inclusions corresponding to each example

[0052]

[0053] By designing and applying a submerged nozzle in a continuous casting mold, the residence time of inclusions in the mold molten steel is increased, improving the removal of inclusions. By optimizing the inclination angle and insertion depth of the submerged nozzle during use, the melting effect of the mold slag is improved, allowing the mold slag to maximize its metallurgical function. The four-hole submerged nozzle is more optimized for uniform molten steel temperature and flow field, increasing the equiaxed grain ratio of the ingot to a certain extent and improving the homogenization level. This method can significantly reduce molten steel processing costs and improve the quality of steel products.

[0054] The existing single-hole straight-cylinder submerged nozzle for large round billet crystallizer is redesigned and optimized. The number of openings and the opening angle of the submerged nozzle are improved, and the insertion depth is optimized according to the design. The residence time of molten steel in the crystallizer is increased, sufficient time is provided for inclusions to float up, the flow field and temperature field in the crystallizer are uniform, the uniform distribution of alloy solute elements is promoted, the homogenization level of the billet is improved, and the melting of protective slag is promoted, so that the liquid slag flows evenly into the gap between the billet and the crystallizer, thereby improving the surface quality of the billet.

[0055] In the description of the present invention, it should be understood that the terms "coaxial", "bottom", "one end", "top", "middle", "the other end", "upper", "one side", "top", "inside", "front", "center", "both ends", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0056] In the present invention, unless otherwise clearly stipulated and limited, the terms "install", "set", "connect", "fix", "screw" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integrated connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements. Unless otherwise clearly defined, ordinary technicians in this field can understand the specific meanings of the above terms in the present invention according to the specific circumstances.

[0057] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A four-hole immersion nozzle specially designed for large round billets, characterized in that: have: Shuikou body; a through hole extending from the first end of the nozzle body to near the second end, the through hole penetrating the first end of the nozzle body; An opening is provided on the side of the second end of the nozzle body, and the opening extends from the side of the nozzle body to communicate with the through hole; a plurality of openings are evenly provided on the side of the nozzle body.

2. The four-hole immersion nozzle for large round billets according to claim 1, characterized in that: Four openings are evenly arranged on the side of the nozzle body.

3. The four-hole submerged nozzle for large round billets according to claim 2, characterized in that: The inclination angle of the opening is 15°.

4. The four-hole submerged nozzle for large round billets as claimed in claim 3, characterized in that: The opening is a waist-shaped hole with a length of 48 mm, a width of 27 mm, and a fillet radius of 13.5 mm.

5. The four-hole submerged nozzle for large round billets according to claim 4, characterized in that: The overall length of the nozzle body is 1250 mm ± 5 mm, and the opening is 25 mm away from the second end of the nozzle body.

6. The four-hole submerged nozzle for large round billets according to claim 5, characterized in that: The outer diameter of the second end of the nozzle body is φ98mm, and the inner diameter of the through hole is φ42mm.

7. The four-hole submerged nozzle for large round billets according to claim 6, characterized in that: The insertion depth of the nozzle body is 100 mm to 120 mm.

8. The four-hole submerged nozzle for large round billets according to claim 7, characterized in that: The material of the slag line erosion position of the nozzle body is ZrO2-C.

9. The method for using the four-hole submerged nozzle for large round billets according to claim 8, characterized in that: The steps include: 1) The tundish baking time is ≥5h, the baking temperature is ≥1100℃, and the immersion nozzle wall temperature measured by the infrared temperature measuring gun is >750℃; 2) After baking, the tundish car is driven to the pouring position to ensure that the nozzle is centered and not offset; 3) During the pouring process, the tundish is lowered to the pouring position and the stopper rod is used to control the pouring; 4) Turn on the crystallizer vibration, electromagnetic stirring 100A / 2HZ~200A / 2HZ, and the crystallizer cooling water 3600~4600L / min; 5) Add protective slag.

Images