A protective slag and granulation device for solving the slag inclusion problem of 310 steel

Abstract

The present invention relates to the field of protective slag technology, and in particular to a protective slag and a granulating device thereof for solving the slag inclusion problem of 310 steel grades. The protective slag is a hollow spherical particle with a particle size of 0.2mm-0.5mm. The raw materials of the protective slag include 6%-10% soda ash, 7%-11% fluorite, 6%-10% bauxite, 5%-12% B2O3, 3%-5% MnO, 2%-4% carbon black, 1%-3% MgO, and the rest are magnesium slag, heavy calcium powder, and wollastonite. The slag basicity is 1.2-1.5 in terms of CaO / SiO2, and the viscosity is 0.12-0.15 Pa·s at 1300°C. The particle size of carbon black is 500 nanometers-5 microns, and the particle size of other raw materials is 45 microns-55 microns. The carbon black is coated on the outside of other raw materials and evenly distributed in each hollow spherical particle. The protective slag is used for 310 steel grades to reduce the occurrence of slag inclusion problems.

Description

Technical Field

[0001] The present invention relates to the technical field of mold slag, and in particular to a mold slag and a granulating device thereof for solving the slag inclusion problem of 310 grade steel. Background Art

[0002] During the continuous casting production of austenitic stainless steel, slag inclusion is a factor that has a greater impact on product quality. During production, slag inclusion in 310 steel is more serious and needs to be dealt with comprehensively from multiple aspects. In addition to equipment reasons, nozzle depth and other reasons, protective slag is also the main reason affecting slag inclusion in 310 steel.

[0003] In the prior art, there are many protective slags for slag inclusion, such as stainless steel continuous casting protective slag and its preparation method with application number 201810730725.4, and stainless steel die casting protective slag with application number 201811521731.5. The above patents have universal applicability and can also reduce slag inclusion to a certain extent, but the effect is not obvious for 310 steel.

[0004] Therefore, it is necessary to use protective slag to reduce slag inclusion for 310 steel grade. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a protective slag and a granulation device for solving the slag inclusion problem of 310 steel. The protective slag and a granulation device are used for 310 steel to reduce the occurrence of the slag inclusion problem. The present invention also provides a granulation device for granulating the protective slag of the present invention to solve the problem of poor drying effect when the existing granulation device is applied to the granulation production of the present invention.

[0006] The technical solution adopted in this application to solve this technical problem is:

[0007] A protective slag for solving the slag inclusion problem of 310 steel grade. The protective slag is hollow spherical particles with a particle size of 0.2 mm-0.5 mm. The raw materials of the protective slag include, by weight percentage, 6%-10% soda ash, 7%-11% fluorite, 6%-10% bauxite, 35%-12% B2O, 3%-5% MnO, 2%-4% carbon black, 1%-3% MgO, and the rest are magnesium slag, heavy calcium powder, and wollastonite. The slag basicity is 1.2-1.5 in terms of CaO / SiO2, and the viscosity is 0.12-0.15 Pa·s at 1300°C. The particle size of carbon black is 500 nanometers-5 microns, and the particle size of other raw materials is 45 microns-55 microns. The carbon black is coated on the outside of other raw materials and evenly distributed in each hollow spherical particle.

[0008] Furthermore, the magnesium slag includes at least Fe2O3, and the Fe2O3 in the protective slag does not exceed 3%.

[0009] Furthermore, the method for preparing the mold slag comprises the following steps:

[0010] Step S1: grinding and balling, wherein the grinding and balling is to grind magnesium slag, heavy calcium powder, wollastonite, fluorite, bauxite, B2O3, MnO, carbon black, and MgO, mix them with soda ash and water, and press them into spherical particles;

[0011] Step S2: sintering, drying the spherical particles obtained in step S1, and performing oxygen-insulated sintering at 850-900° C. to obtain pre-sintered particles;

[0012] Step S3: crushing, crushing the pre-burned particles obtained in step S2 into 325 meshes, with the sieve residue less than 5%, to obtain pre-burned powder;

[0013] Step S4: slurrying, slurrying the pre-burned powder obtained in step S3 using an aqueous solution of hydroxymethyl cellulose to obtain slurry;

[0014] Step S5: spray granulation, the slurry obtained in step S4 is spray granulated to obtain protective slag.

[0015] Furthermore, in step S1, the particle size of magnesium slag, heavy calcium powder, wollastonite, fluorite, bauxite, B2O3, MnO and MgO after grinding is 325 mesh.

[0016] Furthermore, the mass ratio of the pre-burned powder to the aqueous solution of hydroxymethyl cellulose is 3-4:6-7, and the aqueous solution of hydroxymethyl cellulose contains 2%-3% of hydroxymethyl cellulose.

[0017] A protective slag granulating device for solving the slag inclusion problem of 310 steel grade comprises a spray granulator and a cyclone separator, wherein the lower end of the spray granulator is connected to the cyclone separator via a conveying pipeline, a separation pipe is provided on the conveying pipeline, one end of the separation pipe is connected to the conveying pipeline, and the other end is connected to the lower part of the cyclone separator, a high-temperature resistant breathable fabric is provided at the lower part of the cyclone separator, the high-temperature resistant breathable fabric is connected to the inner side wall of the cyclone separator to form a buffer chamber connected to the separation pipe, and a discharge pipe with a discharge valve is provided at the lower end of the cyclone separator.

[0018] Furthermore, a flow regulating valve is provided on the separation tube, and a filter screen is provided at the connection point between the delivery pipeline and the separation tube.

[0019] Furthermore, an adjusting tube is connected to the discharge pipe above the discharge valve, and the adjusting tube can be adjusted upward and downward relative to the discharge pipe, and the upper end of the adjusting tube is higher than the lower end of the buffer cavity.

[0020] Furthermore, an internal thread is provided on the inner wall of the discharge pipe above the discharge valve, an external thread is provided on the lower end of the outer wall of the regulating pipe, the regulating pipe and the discharge pipe are connected via threads, and a row of discharge holes is arranged on the regulating pipe above the external thread.

[0021] Furthermore, an openable and closable inspection door is provided at the lower portion of the side wall of the cyclone separator, and the lower end of the inspection door is lower than the upper end of the regulating pipe.

[0022] Beneficial Effects

[0023] 1. The protective slag for solving the slag inclusion problem of 310 steel grade of the present invention has high basicity, high crystallinity, relatively low melting temperature and reasonable viscosity, and is not prone to slag inclusion. Compared with the existing protective slag, the present invention adds B2O3 and MnO to reduce the melting temperature of the protective slag, inhibit the accumulation of Al2O3 in the slag liquid layer, and reduce F — content, reducing environmental pollution, and using magnesium slag as the raw material for protective slag. The impurities contained in it promote the performance of the protective slag, adjust the melting speed, and reduce carbon increase in steel grades.

[0024] 2. The preparation method of the protective slag of the present invention can make the protective slag more uniform, with a stable melting rate and better use effect compared with the prior art. The thickness of the slag liquid layer, the molten slag layer and the powder slag layer are uniform and not easy to fluctuate when the molten steel impacts, thereby reducing slag inclusion.

[0025] 3. The granulation device of the present invention is specially modified to address the problem that the protective slag of the present invention is difficult to dry. It can greatly prolong the drying time of the protective slag particles, shorten the production process, and improve the drying effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a SEM electron microscope image of the protective slag in Example 1 of the present invention;

[0027] Figure 2 This is a SEM electron microscope image of the protective slag in Example 2 of the present invention;

[0028] Figure 3 This is a SEM electron microscope image of the protective slag in Example 3 of the present invention;

[0029] Figure 4 This is a SEM electron microscope image of the protective slag of Example 4 of the present invention;

[0030] Figure 5 This is a SEM electron microscope image of the protective slag in Example 5 of the present invention;

[0031] Figure 6 It is a schematic structural diagram of a granulation device of the present invention;

[0032] Figure 7is a sectional front view of the granulation device of the present invention;

[0033] Figure 8 yes Figure 7 A magnified view of part A;

[0034] Fig. 9 yes Figure 8 Enlarged view of part B.

[0035] The numbers in the attached figure are: 1. spray granulator; 2. cyclone separator; 3. conveying pipeline; 4. separation pipe; 5. breathable fabric; 6. buffer chamber; 7. unloading valve; 8. discharge pipe; 9. flow regulating valve; 10. filter screen; 11. regulating pipe; 12. discharge hole; 13. inspection door. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be noted that, in the principle part of this embodiment, "carbon black" refers to carbon raw materials, and "C" refers to carbon element.

[0037] A protective slag for solving the slag inclusion problem of 310 steel, the protective slag is a hollow spherical particle with a particle size of 0.2mm-0.5mm, and the raw materials of the protective slag include 6%-10% soda ash, 7%-11% fluorite, 6%-10% bauxite, 35%-12% B2O, 3%-5% MnO, 2%-4% carbon black, MgO 1%-3%, and the rest are magnesium slag, heavy calcium powder, and wollastonite. Those skilled in the art can calculate the mass percentages of magnesium slag, heavy calcium powder, and wollastonite according to the slag basicity. Specifically, in this embodiment, the magnesium slag is 20%-30%, the heavy calcium powder is 17%-25%, and the wollastonite is 11%-15%, wherein the slag basicity is 1.2-1.5 in terms of CaO / SiO2, and the viscosity at 1300°C is 0.12-0.15 Pa·s. In the protective slag of the present invention, the carbon black particle size is 500 nanometers-5 microns, and the particle size of other raw materials is 45 microns-55 microns. The carbon black is coated on the outside of other raw materials and is evenly distributed in each hollow spherical particle.

[0038] 310 steel is a high chromium-nickel austenitic stainless steel. Its main components are as follows: Cr: 24.0% (wt) -26.0% (wt), Ni: 19.0% (wt) -22.0% (wt), C: ≤0.25% (wt), Si: ≤1.50% (wt), Mn: ≤2.00% (wt), P: ≤0.045% (wt), S: ≤0.0.03% (wt), and the rest is Fe. During the continuous casting process, because the composition of 310 steel is complex, it is easy to produce impurities during the continuous casting process. Measures need to be taken to control impurities in the smelting and casting process. In addition to adjusting the equipment and production parameters, improving the various properties of the protective slag is also an important way.

[0039] Because 310 steel has better flowability in the molten state, its impact on the meniscus of the crystallizer is stronger than other steel grades, and the possibility of slag inclusion is higher. 310 steel contains a higher proportion of Cr and Ni, and its thermal expansion coefficient is large, so uniform weak cooling is very important.

[0040] Therefore, the protective slag needs to have a relatively high basicity, a relatively high crystallinity, a relatively low melting temperature and a reasonable viscosity. Compared with the existing protective slag, the present invention adds B2O3 and MnO to reduce the melting temperature of the protective slag, inhibit the accumulation of Al2O3 in the slag liquid layer, prevent the protective slag from absorbing impurities in the molten steel and precipitating high melting point substances, and reduce F — content, reducing environmental pollution, and using magnesium slag as the raw material of protective slag to promote the performance of protective slag.

[0041] The magnesium slag includes at least Fe2O3. According to the ratio calculation, the Fe2O3 in the protective slag does not exceed 3%.

[0042] Fe2O3 is an impurity component in magnesium slag. Introducing it into the protective slag can consume part of the carbon in the slag process, avoiding excessive accumulation of C in the slag layer (the accumulation concentration of C between the slag liquid layer and the slag layer is usually 5-10 times higher than the C concentration in the protective slag), which is beneficial to maintain a stable slag liquid layer thickness and a stable protective slag melting time, and reduce slag inclusion and carbon increase in continuous casting of 310 steel.

[0043] The method for preparing the protective slag comprises the following steps:

[0044] Step S1: grinding and balling, wherein the grinding and balling is to grind magnesium slag, heavy calcium powder, wollastonite, fluorite, bauxite, B2O3, MnO, carbon black, and MgO, mix with soda ash and water, and press them into spherical particles; the water content of the spherical particles is 15%-18%, and the particle size is 2cm-5cm;

[0045] Step S2: sintering, drying the spherical particles obtained in step S1, and performing oxygen-insulated sintering at 850-900° C. for 2 h to obtain pre-sintered particles;

[0046] Step S3: crushing, crushing the pre-burned particles obtained in step S2 into 325 meshes, with the sieve residue less than 5%, to obtain pre-burned powder;

[0047] Step S4: slurrying, slurrying the pre-burned powder obtained in step S3 using an aqueous solution of hydroxymethyl cellulose to obtain slurry;

[0048] Step S5: spray granulation, the slurry obtained in step S4 is spray granulated to obtain protective slag.

[0049] The existing pre-melted protective slag still generally has the problems of uneven melting and high consumption of slag liquid. Although the use of spray granulation to make hollow sphere particles can produce a certain degree of spreadability and reduce some melting speed, spray granulation requires the material to be slurried with water. Graphite or carbon black is usually used as the source of C, which is insoluble in water and difficult to disperse. It usually floats in the slurry, which leads to uneven distribution of C in the slurry. In the production process, the uneven distribution of C also leads to uneven use effects even for the same batch of protective slag. After adding materials, the melting speed of the protective slag is sometimes fast, sometimes slow, or some areas are slow to melt, and some areas are slow to melt. The melting speed in some areas is fast, resulting in that part of the slag liquid layer is exposed when the protective slag is used. Due to the lack of upper protective slag coverage, it is impacted by molten steel and causes large fluctuations, thereby generating slag inclusions. The technical solution mixes carbon black with other raw materials, makes them physically uniform, and then makes balls and sinters them, so that the carbon black can be evenly dispersed, stably combined with other materials after sintering, and is not easy to float up after crushing. The carbon black can be fully and evenly dispersed in each hollow sphere particle, and C is more evenly distributed, with better use effect. The melting speed of the protective slag can be stably controlled, and the thickness of the slag liquid layer, molten slag layer and powder slag layer is uniform, which is not easy to fluctuate when impacted by molten steel, thereby reducing slag inclusions and carbon increase.

[0050] In the step S1, the magnesium slag, heavy calcium powder, wollastonite, fluorite, bauxite, B2O3, MnO and MgO are ground to a particle size of 325 mesh.

[0051] In the formula of the present invention, carbon black is in excess. On the one hand, it can ensure that the carbon black is evenly coated on the outside of other raw materials. On the other hand, in order to compensate for the C loss during the pre-sintering process, in this technical solution, each component in the raw materials of the protective slag has a strict particle size standard, that is, the carbon black particle size is about 500 nanometers-5 microns, and the particle size of other raw materials is about 55 microns. The carbon black is evenly coated on the outside of other raw materials to produce a separation effect, which is used to control the melting rate of the protective slag.

[0052] The mass ratio of the pre-burned powder to the aqueous solution of hydroxymethyl cellulose is 3-4:6-7, and the aqueous solution of hydroxymethyl cellulose contains 2%-3% of hydroxymethyl cellulose.

[0053] The addition of hydroxymethyl cellulose in the present technical solution is because, on the one hand, hydroxymethyl cellulose can be fully dispersed in water and, as a binder, also serves as a source of C in the protective slag. On the other hand, hydroxymethyl cellulose dehydrates slowly after swelling, making the evaporation rate of water faster than the migration rate of water, which can fully complete the encrustation of the particles in the spray granulation to form relatively standard concentric spherical particles.

[0054] Embodiment 1:

[0055] The protective slag includes, by weight percentage, 30 parts of magnesium slag, 15 parts of heavy calcium powder, 13 parts of wollastonite, 10 parts of soda ash, 11 parts of fluorite, 6 parts of bauxite, 5 parts of B2O3, 5 parts of MnO, 3 parts of carbon black, and 2 parts of MgO.

[0056] During the granulation process, the mass ratio of the pre-burnt powder to the aqueous solution of hydroxymethyl cellulose is 3.5:6.5, and the aqueous solution of hydroxymethyl cellulose contains 2.5% of hydroxymethyl cellulose.

[0057] Embodiment 2:

[0058] The protective slag includes, by weight percentage, 20 parts of magnesium slag, 25 parts of heavy calcium powder, 15 parts of wollastonite, 6 parts of soda ash, 7 parts of fluorite, 9 parts of bauxite, 10 parts of B2O3, 3 parts of MnO, 2 parts of carbon black, and 3 parts of MgO.

[0059] During the granulation process, the mass ratio of the pre-burnt powder to the aqueous solution of hydroxymethyl cellulose is 4:6, and the aqueous solution of hydroxymethyl cellulose contains 3% of hydroxymethyl cellulose.

[0060] Embodiment three:

[0061] The protective slag includes, by weight percentage, 25 parts of magnesium slag, 21 parts of heavy calcium powder, 15 parts of wollastonite, 8 parts of soda ash, 8 parts of fluorite, 7 parts of bauxite, 7 parts of B2O3, 4 parts of MnO, 3 parts of carbon black, and 2 parts of MgO.

[0062] During the granulation process, the mass ratio of the pre-burnt powder to the aqueous solution of hydroxymethyl cellulose is 4:6, and the aqueous solution of hydroxymethyl cellulose contains 2% of hydroxymethyl cellulose.

[0063] Embodiment 4:

[0064] The protective slag includes, by weight percentage, 24 parts of magnesium slag, 18.5 parts of heavy calcium powder, 11.5 parts of wollastonite, 9 parts of soda ash, 9 parts of fluorite, 10 parts of bauxite, 8 parts of B2O3, 5 parts of MnO, 3 parts of carbon black, and 2 parts of MgO.

[0065] During the granulation process, the mass ratio of the pre-burnt powder to the aqueous solution of hydroxymethyl cellulose is 3:7, and the aqueous solution of hydroxymethyl cellulose contains 2% of hydroxymethyl cellulose.

[0066] Embodiment five:

[0067] The protective slag includes, by weight percentage, 30 parts of magnesium slag, 17 parts of heavy calcium powder, 13 parts of wollastonite, 7 parts of soda ash, 6 parts of fluorite, 8 parts of bauxite, 10 parts of B2O3, 4 parts of MnO, 4 parts of carbon black, and 1 part of MgO.

[0068] During the granulation process, the mass ratio of the pre-burnt powder to the aqueous solution of hydroxymethyl cellulose is 3:7, and the aqueous solution of hydroxymethyl cellulose contains 3% of hydroxymethyl cellulose.

[0069]

[0070] The above-mentioned embodiments are produced according to the preparation method of the present invention to form protective slag, and its performance is tested as follows:

[0071] Figure 1 - Figure 5 The SEM electron microscope images of the protective slag of the five embodiments of the present invention from the first embodiment to the fifth embodiment. It can be seen from the figure that the grains inside the particles are not uniform. This is because the spray granulation raw material of the present invention is pre-sintered, not pre-melted, and the carbon and other components are evenly distributed and connected. After the pre-sintered particles are broken, these carbon black particles are not easy to separate. Therefore, it can be seen from the SEM electron microscope image that the particle size gradient is about 10 times, that is, the large particle size material is about 10 times the small particle size.

[0072] It can be seen from the figure that the protective slag in each of Examples 1 to 5 is spherical and relatively regular in shape. Due to the different material-liquid ratios before spray granulation in each embodiment and the different hydroxymethyl cellulose contents in the aqueous solution of hydroxymethyl cellulose, the transfer rates in the particles are different during the spray granulation process, thus resulting in differences in the concentricity of the hollow part inside the particles.

[0073] like Figure 6 and Figure 7As shown, a protective slag granulating device for solving the slag inclusion problem of 310 steel grade comprises a spray granulator 1 and a cyclone separator 2, wherein the lower end of the spray granulator 1 is connected to the cyclone separator 2 via a conveying pipe 3, a separation pipe 4 is provided on the conveying pipe 3, one end of the separation pipe 4 is connected to the conveying pipe 3, and the other end is connected to the lower part of the cyclone separator 2, a high temperature resistant breathable fabric 5 is provided at the lower part of the cyclone separator 2, the breathable fabric 5 is a breathable fabric made of a stainless steel filter mesh, a carbon fiber cloth or a basalt fiber, the breathable fabric 5 is connected to the inner side wall of the cyclone separator 2 to form a buffer chamber 6 connected to the separation pipe 4, the hot air in the separation pipe 4 enters the buffer chamber 6, and is discharged from the breathable fabric 5 to form a fluidized bed, so that the protective slag particles are in a fluidized state, thereby achieving a uniform drying effect, and a discharge pipe 8 with a discharge valve 7 is provided at the lower end of the cyclone separator 2.

[0074] Due to the addition of hydroxymethyl cellulose, the migration speed of water slows down. Although the conventional spray granulation device can still complete the granulation, the evaporation of water is incomplete, resulting in a high water content of the protective slag particles and substandard quality. Therefore, the granulation device needs to be improved. The present invention changes the cyclone separator of the granulation device to complete the drying operation of the protective slag particles for a longer time with a smaller structural change, so that the moisture content of the protective slag meets the standard.

[0075] The separation pipe 4 separates a part of the hot air on the conveying pipe 3 and passes it into the lower part of the cyclone separator 2, which does not affect the conveying and separation of the protective slag. However, the hot air separated by the separation pipe 4 enters the lower part of the cyclone separator 2, and cooperates with the interception effect of the discharge valve 7 to re-dry the protective slag particles. The drying time can be adjusted by the opening and closing of the discharge valve 7 or the rotating discharge speed, so as to fully dry the protective slag particles.

[0076] like Figure 8 As shown, a flow regulating valve 9 is provided on the separation pipe 4 , and a filter screen 10 is provided at the connection point between the delivery pipeline 3 and the separation pipe 4 .

[0077] The flow regulating valve 9 is used to adjust the flow in the separation tube 4 to make the hot air drying effect more prominent.

[0078] Even if the breathable fabric 5 produces the effect of a fluidized bed, because there is no fluidized bed exhaust at the discharge pipe 8, the protective slag particles will quickly transfer to the top of the discharge pipe 8 to form a pile state after being fluidized by the fluidized bed, and will no longer be fluidized by the airflow, and the drying effect will be reduced. If you want to get a better drying effect, you can only do so by slowing down the unloading and allowing the particles to accumulate at the bottom of the cyclone separator 2. However, after accumulation, it also compresses the breathable fabric, which can easily lead to uneven airflow distribution and affect the drying effect. Therefore, the structure needs to be improved.

[0079] like Figure 8 and Fig. 9 As shown, an adjusting pipe 11 is connected to the discharge pipe 8 above the discharge valve 7 . The adjusting pipe 11 can be adjusted upward and downward relative to the discharge pipe 8 . The upper end of the adjusting pipe 11 is higher than the lower end of the buffer chamber 6 .

[0080] The setting of the regulating pipe 11 separates the undried and dried materials, dries the particles more evenly, and improves the drying effect. Because of the interception of the regulating pipe 11, the protective slag particles sliding down the side wall of the cyclone separator 2 are concentrated between the regulating pipe 11 and the breathable fabric 5, thereby improving the fluidization effect. At the same time, as the moisture in the particles is lost, the rising height of the particles will also increase, and they can enter the regulating pipe 11 from the top of the regulating pipe 11. Therefore, the height of the regulating pipe 11 can be adjusted up and down in coordination with the flow regulating valve 9 on the separation pipe 4 to control the drying effect and achieve a better drying effect.

[0081] The inner wall of the discharge pipe 8 above the discharge valve 7 is provided with an internal thread, and the lower end of the outer wall of the regulating pipe 11 is provided with an external thread. The regulating pipe 11 is connected to the discharge pipe 8 via threads, and a row of discharge holes 12 located above the external thread is arrayed on the regulating pipe 11.

[0082] The above arrangement discloses a specific method for adjusting the adjusting tube 11 up and down, and the arrangement of the discharge hole 12 can completely discharge the protective slag from the cyclone separator 2 at the end of production without generating any residue.

[0083] An openable and closable inspection door 13 is provided at the lower portion of the side wall of the cyclone separator 2 , and the lower end of the inspection door 13 is lower than the upper end of the regulating pipe 11 .

[0084] The inspection door can not only inspect the cyclone separator, but also adjust the regulating pipe through the inspection door.

Claims

1. A protective slag for solving the slag inclusion problem of 310 steel, characterized in that: The protective slag is a hollow spherical particle with a particle size of 0.2mm-0.5mm. The raw materials of the protective slag include, by weight percentage, 6%-10% soda ash, 7%-11% fluorite, 6%-10% bauxite, 5%-12% B2O3, 3%-5% MnO, 2%-4% carbon black, 1%-3% MgO, and the rest are magnesium slag, heavy calcium powder, and wollastonite. The slag basicity is 1.2-1.5 in terms of CaO / SiO2, and the viscosity is 0.12-0.15 Pa·s at 1300°C. The particle size of carbon black is 500 nanometers-5 microns, and the particle size of other raw materials is 45 microns-55 microns. The carbon black is coated on the outside of other raw materials and is evenly distributed in each hollow spherical particle.

2. The mold slag for solving the slag inclusion problem of 310 steel according to claim 1, characterized in that: The magnesium slag includes at least Fe2O3, and the Fe2O3 in the protective slag does not exceed 3%.

3. The mold slag for solving the slag inclusion problem of 310 steel according to claim 1, characterized in that: The method for preparing the protective slag comprises the following steps: Step S1: grinding and balling, wherein the grinding and balling is to grind magnesium slag, heavy calcium powder, wollastonite, fluorite, bauxite, B2O3, MnO, carbon black, and MgO, mix them with soda ash and water, and press them into spherical particles; Step S2: sintering, drying the spherical particles obtained in step S1, and performing oxygen-insulated sintering at 850-900° C. to obtain pre-sintered particles; Step S3: crushing the pre-burned particles obtained in step S2 to obtain pre-burned powder; Step S4: slurrying, slurrying the pre-burned powder obtained in step S3 using an aqueous solution of hydroxymethyl cellulose to obtain slurry; Step S5: spray granulation, the slurry obtained in step S4 is spray granulated to obtain protective slag.

4. The mold slag for solving the slag inclusion problem of 310 steel according to claim 3, characterized in that: In the step S1, the magnesium slag, heavy calcium powder, wollastonite, fluorite, bauxite, B2O3, MnO and MgO are ground to a particle size of 325 mesh.

5. The mold slag for solving the slag inclusion problem of 310 steel according to claim 3, characterized in that: The mass ratio of the pre-burned powder to the aqueous solution of hydroxymethyl cellulose is 3-4:6-7, and the aqueous solution of hydroxymethyl cellulose contains 2%-3% of hydroxymethyl cellulose.

6. A granulation device for mold slag to solve the slag inclusion problem of 310 steel, characterized in that: The invention comprises a spray granulator (1) and a cyclone separator (2), wherein the lower end of the spray granulator (1) is connected to the upper end of the cyclone separator (2) via a conveying pipe (3), a separation pipe (4) is provided on the conveying pipe (3), one end of the separation pipe (4) is connected to the conveying pipe (3), and the other end is connected to the lower part of the cyclone separator (2), the lower part of the cyclone separator (2) is provided with a high-temperature resistant breathable fabric (5), the high-temperature resistant breathable fabric (5) is connected to the inner side wall of the cyclone separator (2) to form a buffer chamber (6) connected to the separation pipe (4), and the lower end of the cyclone separator (2) is provided with a discharge pipe (8) with a discharge valve (7); An adjusting pipe (11) is connected to the discharge pipe (8) above the discharge valve (7). The adjusting pipe (11) can be adjusted to move upward and downward relative to the discharge pipe (8). The upper end of the adjusting pipe (11) is higher than the lower end of the buffer chamber (6).

7. A mold slag granulating device for solving the slag inclusion problem of 310 steel according to claim 6, characterized in that: The separation pipe (4) is provided with a flow regulating valve (9), and a filter screen (10) is provided at the connection point between the delivery pipe (3) and the separation pipe (4).

8. The granulation device for mold slag for solving the slag inclusion problem of 310 steel according to claim 6, characterized in that: An internal thread is provided on the inner wall of the discharge pipe (8) above the discharge valve (7), and an external thread is provided on the lower end of the outer wall of the regulating pipe (11). The regulating pipe (11) is connected to the discharge pipe (8) via threads, and a row of discharge holes (12) is arranged on the regulating pipe (11) above the external thread.

9. A granulation device for mold slag for solving the slag inclusion problem of 310 steel according to claim 6, characterized in that: An openable and closable inspection door (13) is provided at the lower portion of the side wall of the cyclone separator (2), and the lower end of the inspection door (13) is lower than the upper end of the regulating pipe (11).

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