Submersed nozzle for reducing inclusion defect rate of rolled plate and application method of submersed nozzle

Abstract

The invention relates to the technical field of continuous casting, in particular to a submersed nozzle for reducing the inclusion defect rate of a rolled plate, which comprises a body, a molten steel channel and a tapping hole, the body comprises a nozzle outer layer and an internal foamed ceramic layer, and the internal foamed ceramic layer is made of zirconia-based foamed ceramic. The thickness of the internal foamed ceramic layer ranges from 10 mm to 20 mm. The zirconium oxide-based foamed ceramic comprises the following components in percentage by mass: 40%-50% of zirconium oxide and 10%-20% of yttrium oxide. 10%-20% of calcium carbonate; 10%-20% of magnesium oxide; 20%-30% of cerium oxide; the heat-resistant temperature of the zirconia-based foamed ceramic is 1700-2000 DEG C, the aperture of the foamed ceramic is 200 [mu] m-2mm, and the porosity is 60-80%. A layer of foamed ceramic is added to the inner wall of the submersed nozzle, the net-shaped foamed ceramic structure plays a role in actively adsorbing inclusions in molten steel, the existing form of the fine inclusions on the inner wall of the submersed nozzle is changed, the existing mode is changed into the mode that the fine inclusions are stored on the inner wall of the foamed ceramic, and the purity of the molten steel is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of continuous casting, and particularly relates to a submerged nozzle for reducing the inclusion defect rate of rolled plates. Background Art

[0002] Nozzle clogging is a serious problem existing in the continuous casting of aluminum-killed steel. The reason for clogging is the precipitation of solid micro-inclusions in the molten steel. During continuous casting, taking alumina as an example, alumina inclusions gradually form on the wall of the submerged nozzle and periodically fall off into the mold, thereby increasing the content of harmful inclusions in the cast slab. Nozzle clogging causes premature end of casting, reduction of the number of continuous casting heats, and reduction of the efficiency of the continuous casting machine. Although argon is blown into the tundish nozzle and refractory brick sleeve through the stopper rod to remove some of the clogging substances, loose non-metallic inclusions and meniscus disturbance will still increase the inclusion content in the continuous casting slab, thereby reducing the surface quality of the rolled plate and forming inclusion defects in the rolled plate.

[0003] The literature "Production Practice of Reducing Tundish Nozzle Clogging" - Zhao Dengbao - Continuous Casting - No. 2, 2008, analyzes that when casting low-carbon high-aluminum steel, the clogging substances in the tundish nozzle show an obvious three-layer structure, from the inside to the outside are the piled-up Al 2 O 3 loose layer, the net-like Al 2 O 3 dense layer and decarburized layer. The net-like Al 2 O 3 dense layer and decarburized layer are the products of the reaction between the refractory of the tundish nozzle and the molten steel, and their thicknesses do not reach the degree of clogging the nozzle, while the piled-up Al 2 O 3 mainly adsorbs the included Al 2 O 3The formation of molten steel is the main reason for the blockage of the nozzle. In view of the above reasons, measures such as controlling the inclusion content in the molten steel and reducing the oxidation of the molten steel are proposed. By reducing the slag of the converter, improving the ladle bottom blowing effect and self-opening rate, protecting the casting throughout the process, blowing argon at the plug rod and nozzle, and stabilizing the casting speed, the blockage of the tundish nozzle is greatly reduced. The document "Optimization Design and Research on the Structure and Performance of the Continuous Casting Tundish Nozzle" - Mou Jining, Yu Yanwen - 2018 International Refractory Academic Conference, proposed to reduce the contact area between the molten steel and the nozzle by changing the inner diameter of the nozzle, thereby reducing the blockage: using a flat-bottom nozzle (i.e., the nozzle has no slope) can reduce the blockage; using an annular stepped nozzle can reduce the accumulation of alumina and the impact of the steel flow on the wide surface of the crystallizer; rounding the nozzle inlet, and reducing the blockage at the nozzle inlet by eliminating the diversion; improving the joint sealing, reducing air inhalation, thereby reducing blockage and oxide inclusions and oxygenation; strengthening the surrounding insulation, preheating and heating at the easily blocked parts can reduce the nozzle blockage. However, the improved nozzle is subject to certain limitations in application and cannot effectively prevent nozzle blockage. The paper "Research on Improving the Castability of Low-Carbon Aluminum Killed Steel" - Su Duxing, Ma Jianchao, Zhao Weijie, Lu Jianhui - Shanghai Metal - May 2014, proposed that a large amount of high melting point Al in molten steel 2 O 3 The main reason for the blockage of the nozzle is that the inclusions gather and stick to the inner wall of the nozzle. By improving the LF refining bottom argon blowing process, optimizing the calcium treatment effect and reducing the secondary oxidation of molten steel, the castability of molten steel is improved, and the nozzle blockage rate is reduced from the original 13.9% to 4.2%.

[0004] A Chinese patent with publication number CN 111940716 A discloses a method for preventing the blockage of the nozzle of rare earth steel continuous casting. The method heats the nozzle and the plug rod, increases the temperature of the part, reduces the viscosity of the rare earth inclusions, increases their fluidity, and ensures normal casting by dynamically adjusting the plug rod, thereby achieving a good effect of improving nozzle nodules and blockage. However, for rare earth steel, in addition to the adhesion of high-melting-point rare earth inclusions leading to nodules, the rare earth elements in the steel will also react with the nozzle to generate rare earth aluminates, resulting in an increase in nozzle thickness.

[0005] A Chinese patent with publication number CN 109732072 B discloses a method for applying like charges to suppress nodules on the inner wall of an immersion nozzle. A stable positive current is applied to the inner wall of the immersion nozzle, so that the inclusion particles that generate transient charges due to friction cannot adhere to the inner wall of the nozzle to form adherent slag and nodules due to the repulsive force, so that the sintering and adhesion behavior of the inclusions on the inner wall of the immersion nozzle is limited, thereby suppressing nodules. However, the same and continuous current has a more obvious effect on the removal of large-sized inclusions, but the removal effect is not ideal for small-sized and high-density rare earth inclusions, and a larger current is required to work.

[0006] Chinese Patent No. CN111906266 A discloses a method for suppressing the clogging of submerged entry nozzles in rare earth steel casting, characterized in that the method includes inserting electrodes into the rare earth molten steel, applying pulsed current to the electrodes by a power supply device, intervening in the erosion reaction at the interface between the inner wall of the nozzle and the rare earth molten steel through the pulsed current, improving the corrosion resistance of the inner wall of the nozzle to rare earth molten steel, and further preventing inclusions in the rare earth molten steel from adhering to the inner wall of the nozzle.

[0007] Currently, the existing ideas for dealing with the clogging of submerged entry nozzles mainly focus on reducing inclusions in molten steel, improving the purity of molten steel, and avoiding the adhesion of inclusions to the wall of the submerged entry nozzle. Although it has played a certain role, it is impossible to achieve the goal of zero inclusions in improving the purity of molten steel. Avoiding the adsorption of inclusions on the inner wall of the nozzle, the inclusions will inevitably flow into the mold with the molten steel and finally remain in the slab, forming defects after rolling, and cannot solve the problem of rolling plate defects caused by the accumulated substances in the nozzle. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a submerged entry nozzle that reduces the inclusion defect rate of rolled plates, actively adsorbs inclusions in molten steel, and improves the purity of molten steel.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] A submerged entry nozzle for reducing the inclusion defect rate of rolled plates, including a body, a molten steel passage, and a tapping port. The body includes an outer layer of the nozzle and an inner foam ceramic layer, and the material of the inner foam ceramic layer is zirconia-based foam ceramic.

[0011] The thickness of the inner foam ceramic layer is 10 mm to 20 mm.

[0012] The mass percentage of the components of the zirconia-based foam ceramic is as follows: zirconia: 40% - 50%, yttrium oxide: 10% - 20%; calcium carbonate: 10% - 20%; magnesium oxide: 10% - 20%; cerium oxide: 20% - 30%; the heat-resistant temperature of the zirconia-based foam ceramic is 1700°C to 2000°C, the pore diameter of the foam ceramic is 200 μm to 2 mm, and the porosity is 60% - 80%.

[0013] An application method of a submerged entry nozzle for reducing the inclusion defect rate of rolled plates includes:

[0014] 1) When the oxygen content in the tundish molten steel is 0.003% - 0.005%, the thickness of the internal foam ceramic layer of the submerged entry nozzle used is 15 mm - 25 mm, the pore diameter of the zirconia-based foam ceramic is 1 mm - 2 mm, and the porosity is 60% - 65%; when the oxygen content in the tundish molten steel < 0.003%, the thickness of the internal foam ceramic layer of the submerged entry nozzle used is 10 mm - 15 mm, the pore diameter of the zirconia-based foam ceramic is 200 μm - 1 mm, and the porosity is 65% - 80%.

[0015] 2) Baking: The tundish and the submerged entry nozzle are baked simultaneously. The total baking time is 80 min - 100 min. The temperature of the submerged entry nozzle meets ≥ 900 °C, and the temperature of the tundish meets ≥ 1000 °C; after baking for ≥ 30 min, open the tundish stopper rod and continue baking until the end.

[0016] 3) Replacement of the submerged entry nozzle:

[0017] When the drawing speed is constant and the change rate K of the tundish stopper rod opening c > 20%, replace the submerged entry nozzle.

[0018] K c Calculate according to the formula ;

[0019] where: K c is the change rate of the tundish stopper rod opening;

[0020] K r is the actual monitored value of the tundish stopper rod opening;

[0021] K b is the basic value of the tundish stopper rod opening; during steady-state casting, under the condition of constant drawing speed and no fluctuation of the molten steel surface, the actual monitored value of the tundish stopper rod opening is defined as the basic value K of the tundish stopper rod opening b ;

[0022] When the fluctuation of the molten steel surface ≥ 5 mm, replace the submerged entry nozzle.

[0023] Compared with the existing technology, the beneficial effects of the present invention are:

[0024] In this application, a layer of foam ceramic is added to the inner wall of the submerged entry nozzle. The reticulated foam ceramic structure plays a role in actively adsorbing inclusions in the molten steel, changing the existence form of fine inclusions on the inner wall of the submerged entry nozzle, from the original retention form to being stored on the inner wall of the foam ceramic. This not only improves the purity of the molten steel but also avoids the shedding of the nozzle retention material into the molten steel in the mold, causing defects after rolling, and can greatly reduce the inclusion defects of the rolled plate.

[0025] By monitoring the data of the drawing speed and the opening degree of the stopper rod, the inclusion adsorption situation of the submerged nozzle is judged, providing a basis for replacing the submerged nozzle. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic structural diagram of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the 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 thus cannot be understood as a limitation of the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, the features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more.

[0028] Unless otherwise clearly defined and limited, the terms "installation", "connection", "connection" shall be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific situations.

[0029] Such as Figure 1 , a submerged nozzle for reducing the inclusion defect rate of rolled plates, including a body 1, a molten steel channel 2, and a tapping hole 3. The body 1 includes a nozzle outer layer 11 and an internal foam ceramic layer 12, and the material of the internal foam ceramic layer 12 is zirconia-based foam ceramic.

[0030] The thickness of the internal foam ceramic layer is 10 mm to 20 mm.

[0031] The mass percentage of the components of the zirconia-based foam ceramic is: zirconia: 40% to 50%, yttrium oxide: 10% to 20%; calcium carbonate: 10% to 20%; magnesium oxide: 10% to 20%; cerium oxide: 20% to 30%; the heat-resistant temperature of the zirconia-based foam ceramic is 1700 °C to 2000 °C, the pore diameter of the foam ceramic is 200 μm to 2 mm, and the porosity is 60% to 80%.

[0032] An application method of an immersion nozzle for reducing the inclusion defect rate of rolled plates, comprising:

[0033] 1) When the oxygen content of the molten steel in the tundish is 0.003% - 0.005%, the thickness of the internal foam ceramic layer of the used immersion nozzle is 15 mm - 25 mm, the pore diameter of the zirconia-based foam ceramic is 1 mm - 2 mm, and the porosity is 60% - 65%; when the oxygen content of the molten steel in the tundish < 0.003%, the thickness of the internal foam ceramic layer of the used immersion nozzle is 10 mm - 15 mm, the pore diameter of the zirconia-based foam ceramic is 200 μm - 1 mm, and the porosity is 65% - 80%;

[0034] 2) Baking: The tundish and the immersion nozzle are baked simultaneously. The total baking time is 80 min - 100 min. The temperature of the immersion nozzle meets ≥ 900 °C, and the temperature of the tundish meets ≥ 1000 °C; after baking for ≥ 30 min, open the tundish stopper rod and continue baking until the end;

[0035] 3) Replacement of the immersion nozzle:

[0036] When the drawing speed is constant and the change rate K of the tundish stopper rod opening c > 20%, replace the immersion nozzle;

[0037] K c Calculate according to the formula ;

[0038] where: K c is the change rate of the tundish stopper rod opening;

[0039] K r is the actual monitored value of the tundish stopper rod opening;

[0040] K b is the basic value of the tundish stopper rod opening; during steady-state casting, under the condition of constant drawing speed and no fluctuation of the molten steel surface, the actual monitored value of the tundish stopper rod opening is defined as the basic value K of the tundish stopper rod opening b ;

[0041] When the fluctuation of the molten steel surface ≥ 5 mm, replace the immersion nozzle.

[0042] The preferred embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention. In addition, it should be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without conflict. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods. In addition, any combination can be made between various different embodiments of the present invention, as long as it does not violate the idea of the present invention, and it should also be regarded as the content disclosed by the present invention.

[0043] To make the objectives, technical solutions, and technical effects of the present invention clearer, the technical solutions in the embodiments of the present invention will now be described clearly and completely. However, the embodiments described below are only some embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art in combination with the embodiments of the present invention without making creative efforts fall within the protection scope of the present invention.

[0044] An immersion nozzle for reducing the inclusion defect rate of rolled plates, comprising a body 1, a molten steel channel 2, and a tapping port 3. The body 1 includes a nozzle outer layer 11 and an internal foam ceramic layer 12, and the material of the internal foam ceramic layer 12 is zirconia-based foam ceramic. The zirconia-based foam ceramic will adsorb the inclusions in the molten steel and retain them therein, and the molten steel flows into the mold through the tapping port 3.

[0045] Example 1:

[0046] The test steel grade is SPCC, and the process route is BOF-RH-CC. A total of two casting trials were carried out, with 10 ladles of steel in each casting trial. The main component information is shown in Table 1:

[0047] Table 1: Composition information of SPCC steel grade (mass percentage %)

[0048] C Si Mn p S Als 0.071 0.01 0.28 0.0188 0.013 0.02

[0049] A casting trial using an immersion nozzle without an internal foam ceramic layer:

[0050] A total of 10 ladle-casts were carried out, and the immersion nozzle was replaced during the 4th ladle in the middle. The inclusion defect rate of the rolled plate was statistically 1.06%.

[0051] Steel samples were taken during the steady state of the tundish (ladle numbers 1-5), and the total oxygen content in the tundish was chemically analyzed as shown in Table 2:

[0052] Table 2: Total oxygen content T[O] of molten steel in the SPCC tundish (mass percentage %)

[0053] Batch number of cans 1 2 3 4 5 T[O] 0.0028 0.0020 0.0019 0.0014 0.0015

[0054] Heat tapping times using the submerged entry nozzle with an internal foam ceramic layer according to the present invention:

[0055] For the same process route of SPCC steel grade, according to the chemical analysis results, during the casting of SPCC, the tundish T[O] < 0.003%, and the composition information of the foam ceramic of the selected submerged entry nozzle is shown in Table 3:

[0056] Table 3: Composition information of foam ceramic (mass percentage%)

[0057] Zirconia Yttrium oxide Calcium carbonate Magnesium oxide Cerium oxide 40 10 10 20 20

[0058] The pore size of the foam ceramic is 500 μm, the porosity is 70%, and the thickness of the foam ceramic is 10 mm.

[0059] The baking information of the tundish and the submerged entry nozzle is shown in Table 4:

[0060] Table 4: Baking information

[0061]

[0062] During the casting process, monitor the changes of the tundish stopper rod and the molten steel level at a constant casting speed. The basic value K of the tundish stopper rod opening b = 60 mm. When the 7th ladle is at a constant casting speed and the molten steel level does not fluctuate, the actual value K of the tundish stopper rod opening r = 75 mm, and the change rate K of the tundish stopper rod opening c = 25%. At this time, replace the submerged entry nozzle with a new one until the casting is completed. The inclusion defect rate of the rolled plate is statistically 0.37%.

[0063] Comparing the test results of the two heat tapping times, after using the submerged entry nozzle with an internal foam ceramic layer, the inclusion defect rate of the rolled plate is reduced from 1.06% to 0.37%, indicating that the use of the submerged entry nozzle of the present invention significantly reduces the inclusion defect rate of the rolled plate.

[0064] Example 2:

[0065] The test steel grade is the automotive steel grade AB6R1B of a certain steel plant, and the process route is BOF - RH - CC. A total of two heat tapping times of tests are carried out, with 10 ladles of steel for each heat tapping time. The main composition information is shown in Table 5:

[0066] Table 5: Composition information of AB6R1B steel grade (mass percentage%)

[0067] C Si Mn p S Als 0.0018 0.014 0.13 0.010 0.003 0.037

[0068] Heat tapping times without using the submerged entry nozzle with an internal foam ceramic layer:

[0069] A total of 10 ladle castings of steel were carried out. The submerged entry nozzle was replaced during the 4th ladle in the middle. The inclusion defect rate of the rolled plate was statistically 1.74%.

[0070] Steel samples were taken during the steady state of the tundish (ladle numbers 1 - 5), and the total oxygen content in the tundish was chemically analyzed as shown in Table 6:

[0071] Table 6: Total oxygen content T[O] (mass percentage %) of molten steel in the tundish of AB6R1B

[0072] Batch number of cans 1 2 3 4 5 T[O] 0.0053 0.0044 0.0040 0.0035 0.0033

[0073] Ladle casting times using the submerged entry nozzle with an internal foam ceramic layer according to the present invention:

[0074] For the same process route of steel grade AB6R1B, according to the chemical analysis results, when casting AB6R1B, the total oxygen content T[O] in the tundish ≥ 0.003%. The component information of the foam ceramic of the selected submerged entry nozzle is shown in Table 7:

[0075] Table 7: Component information of foam ceramic (mass percentage %)

[0076] Zirconia Yttrium oxide Calcium carbonate Magnesium oxide Cerium oxide 45 10 15 10 20

[0077] The pore diameter of the foam ceramic is 1.5 mm, the porosity is 60%, and the thickness of the foam ceramic is 20 mm.

[0078] The baking information of the tundish and the submerged entry nozzle is as follows:

[0079] Table 8: Baking information

[0080]

[0081] During the casting process, the changes of the tundish stopper rod and the molten steel level were monitored under constant casting speed. The basic value K of the tundish stopper rod opening b = 70 mm. When the casting speed was constant and the molten steel level did not fluctuate during the 8th ladle, the actual value K of the tundish stopper rod opening r = 91 mm. The change rate K of the tundish stopper rod opening c = 30%. At this time, a new foam ceramic submerged entry nozzle was replaced and used until the casting was completed. The inclusion defect rate of the rolled plate was statistically 0.64%.

[0082] Comparing the test results of the two ladle casting times, after using the foam ceramic submerged entry nozzle, the inclusion defect rate of the rolled plate decreased from 1.74% to 0.64%, indicating that the use of the submerged entry nozzle with an internal foam ceramic layer significantly reduces the inclusion defect rate of the rolled plate.

[0083] Although embodiments of the present invention have been shown and described, those of ordinary skill in the art will appreciate that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An immersion nozzle for reducing the defect rate of inclusions in rolled plates, characterized in that: It includes a body, a molten steel channel and a steel outlet. The body includes an outer nozzle layer and an inner foam ceramic layer. The inner foam ceramic layer is made of zirconia-based foam ceramic.

2. The submerged nozzle for reducing the inclusion defect rate of rolled plate according to claim 1 is characterized in that: The thickness of the internal foam ceramic layer is 10 mm to 20 mm.

3. The submerged nozzle for reducing the inclusion defect rate of rolled plate according to claim 1, characterized in that: The mass percentages of the zirconia-based foam ceramic components are: zirconia: 40% to 50%, yttrium oxide: 10% to 20%; calcium carbonate: 10% to 20%; magnesium oxide: 10% to 20%; cerium oxide: 20% to 30%; the heat-resistant temperature of the zirconia-based foam ceramic is 1700° C. to 2000° C., the pore size of the foam ceramic is 200 μm to 2 mm, and the porosity is 60% to 80%.

4. An application method of the submerged nozzle for reducing the inclusion defect rate of rolled plate according to claim 1, characterized in that: include: 1) When the oxygen content of the tundish steel liquid is 0.003% to 0.005%, the thickness of the internal foam ceramic layer of the immersion nozzle is 15mm to 25mm, the pore size of the zirconia-based foam ceramic is 1mm to 2mm, and the porosity is 60% to 65%; when the oxygen content of the tundish steel liquid is less than 0.003%, the thickness of the internal foam ceramic layer of the immersion nozzle is 10mm to 15mm, the pore size of the zirconia-based foam ceramic is 200μm to 1mm, and the porosity is 65% to 80%; 2) Baking: The tundish and the immersion nozzle are baked at the same time, the total baking time is 80min to 100min, the immersion nozzle temperature meets ≥900℃, and the tundish temperature meets ≥1000℃; the baking time is ≥30min, the tundish plug rod is opened, and the baking is continued until the end; 3) Replacement of immersion nozzle: a. Casting speed is constant, the opening change rate of the tundish plug K c When the temperature is greater than 20%, the submerged nozzle should be replaced; K c By formula calculate; Where: K c is the opening change rate of the tundish plug; K r It is the actual monitoring value of the opening of the tundish plug; K b is the basic value of the tundish plug opening; during steady-state casting, when the casting speed is constant and the steel liquid level does not fluctuate, the actual monitoring value of the tundish plug opening is defined as the basic value of the tundish plug opening K b ; b. When the steel liquid level fluctuation is ≥5mm, the submerged nozzle should be replaced.

Images