Electromagnetic launching special protective slag for duplex stainless steel

Abstract

The present application relates to the technical field of protecting slag, in particular to a kind of electromagnetic catapulting dual-phase stainless steel special protecting slag, comprising the following raw materials: red mud, wollastonite, modified fluorite, borax, spodumene and blast furnace slag.The present application handles fluorite by yttrium oxide modification and forsterite coating process, effectively inhibits the release of harmful fluorine ion at high temperature, substantially reduces the erosion to refractory material;At the same time, forsterite coating enhances the stability of particles, improves the comprehensive use effect of protecting slag;In addition, modified fluorite helps to form a better lubricity slag film, reduces the slag and casting blank surface defects.

Description

Technical Field

[0001] This invention relates to the field of protective slag technology, and more specifically, to a protective slag specifically for electromagnetic catapults used in duplex stainless steel. Background Technology

[0002] In electromagnetic catapult systems, duplex stainless steel is widely used in the manufacture of key components, such as guide rails and catapult structural parts, due to its excellent comprehensive properties, such as high strength, good corrosion resistance, and toughness. Duplex stainless steel has a two-phase structure of austenitic and ferritic components, which gives it excellent mechanical properties and corrosion resistance. However, during its processing and manufacturing, especially in hot working processes such as continuous casting and rolling, duplex stainless steel is susceptible to oxidation and gas absorption, which can affect its final performance and quality. Therefore, a special protective slag is required to protect it.

[0003] Although traditional stainless steel protective slag performs well in reducing melting point and viscosity, the fluoride ions released at high temperatures can corrode refractory materials, and excessive fluoride can lead to excessively high slag film crystallization rate, reducing lubrication performance. In view of this, we propose a special protective slag for electromagnetic catapult duplex stainless steel. Summary of the Invention

[0004] The purpose of this invention is to provide a special protective slag for electromagnetic catapult duplex stainless steel, in order to solve the problems mentioned in the background art, which are that although traditional stainless steel protective slags perform well in reducing melting point and viscosity, the fluoride ions released at high temperatures will corrode refractory materials, and excessive fluoride will lead to excessively high slag film crystallization rate, reducing lubrication performance.

[0005] To achieve the above objectives, the present invention provides a special protective slag for electromagnetic catapult duplex stainless steel, comprising the following raw materials: red mud, wollastonite, modified fluorite, borax, spodumene, and blast furnace slag.

[0006] The modified fluorite is prepared by reacting yttrium oxide with fluorite in a solid phase and then coating it with magnesium olivine.

[0007] Preferably, the red mud comprises 35-40 parts by weight, wollastonite comprises 30-36 parts by weight, modified fluorite comprises 5-8 parts by weight, borax comprises 3-7 parts by weight, spodumene comprises 3-5 parts by weight, and blast furnace slag comprises 3-7 parts by weight.

[0008] Preferably, the preparation process of the modified fluorite is as follows:

[0009] Fluorite powder and yttrium oxide are dry-mixed in a mixer at 20-30 rpm for 30-40 min to obtain a mixture; polyvinyl alcohol is added to the mixture and pressed into a green body with a diameter of 18-20 mm; the green body is placed in a tube furnace and subjected to a high-temperature solid-phase reaction under nitrogen protection, heated to 1100-1150℃ at a rate of 4-6℃ / min, held at that temperature for 2-3 h, and then cooled to room temperature with the furnace to obtain the reaction product;

[0010] The reaction product was preheated to 75-85℃, and magnesium olivine sol was spray-deposited. Each batch was cycled 18-22 times. After spraying, it was cured at 105-110℃ for 1-1.5h. Finally, it was calcined and strengthened in a tube furnace, heated to 1180-1220℃ at a rate of 4-6℃ / min and held for 1-1.5h. After cooling to 300℃ in the furnace, it was naturally cooled to room temperature to obtain modified fluorite.

[0011] Yttrium oxide effectively binds fluoride ions in fluorite by altering the lattice parameters and electronic structure of the fluorite crystals, thereby reducing their migration ability and activity in the external environment (such as high-temperature melts). Magnesia olivine forms a solid film on the surface of fluorite particles, which acts as a physical barrier and prevents the internal fluorite or its decomposition products from directly contacting the external environment (such as molten steel and refractory materials), thus effectively controlling the diffusion and release path of fluoride ions.

[0012] Preferably, the mass ratio of fluorite powder to yttrium oxide is 1:0.15-0.19.

[0013] Preferably, the amount of polyvinyl alcohol added is 0.4-0.6% of the mass of the mixture.

[0014] Preferably, the forsterite sol is prepared by mixing tetraethyl orthosilicate, magnesium nitrate, anhydrous ethanol and water in a molar ratio of 1:1.2:20:4 and adjusting the pH to 4 with hydrochloric acid at a mass concentration of 0.1 mol / L.

[0015] Preferably, the spray deposition is carried out using a fluidized bed spray coating machine, with a bed temperature of 78-82℃, an atomization pressure of 0.28-0.32MPa, a sol feed rate of 9-11mL / min, and nitrogen as the fluidizing gas at a flow rate of 7.5-8.5m. 3 / h.

[0016] As a preferred embodiment, the preparation process of the special protective slag for electromagnetic catapult duplex stainless steel is as follows:

[0017] S1.1 Weigh the following raw materials in parts by weight: 35-40 parts red mud, 30-36 parts wollastonite, 5-8 parts modified fluorite, 3-7 parts borax, 3-5 parts spodumene, and 3-7 parts blast furnace slag.

[0018] S1.2 Add red mud, wollastonite, and blast furnace slag to a mixer and mix at 20-30 rpm for 25-35 minutes to obtain a preliminary dry mixture; spray polyvinyl alcohol solution onto the preliminary dry mixture, mix well, add borax and modified fluorite, and continue mixing at 20-30 rpm for 15-20 minutes; finally add spodumene and mix at 10-15 rpm for 5-10 minutes to obtain a uniform wet mixture;

[0019] S1.3. The wet mixture is fed into a granulator to prepare wet granules, and the feeding rate is controlled at 18-22 kg / h. Then the wet granules are fed into a fluidized bed at 105-110℃ to dry for 1-1.5 h, and sieved to obtain granules with a particle size of 0.1-1.5 mm.

[0020] S1.4 Place the granules in an atmosphere furnace, introduce nitrogen gas at a flow rate of 5-8 L / min, raise the temperature to 580-620℃, and hold for 1-1.5 h; continue to raise the temperature to 900-950℃ and hold for 15-30 min; cool with the furnace to obtain a special protective slag for electromagnetic catapult duplex stainless steel.

[0021] Preferably, in step S1.2, the mass concentration of the polyvinyl alcohol solution is 2.5-5.0%.

[0022] Preferably, in step S1.3, the inlet air temperature of the centrifugal spray drying tower is 280-300℃, the outlet air temperature is 100-110℃, and the atomization pressure is 0.3-0.4MPa.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] In this electromagnetic catapult-specific protective slag for duplex stainless steel, fluorite is treated with yttrium oxide modification and magnesium olivine coating, which effectively inhibits the release of harmful fluoride ions at high temperatures and significantly reduces the corrosion of refractory materials. At the same time, magnesium olivine coating enhances the stability of the particles and improves the overall performance of the protective slag. In addition, modified fluorite helps to form a slag film with better lubricity, reducing slag entrapment and surface defects of the cast billet. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] This invention provides a special protective slag for electromagnetic catapult duplex stainless steel, comprising the following raw materials: red mud, wollastonite, modified fluorite, borax, spodumene, and blast furnace slag;

[0027] The modified fluorite is prepared by reacting yttrium oxide with fluorite in a solid phase and then coating it with magnesium olivine.

[0028] Preparation steps of fluorite powder: After soaking fluorite in a 10% hydrochloric acid solution for 2 hours, it is washed with water until neutral, dried at 120℃, and finally pulverized by an air jet mill to obtain fluorite powder.

[0029] Magnesia olivine sol is prepared by mixing tetraethyl orthosilicate, magnesium nitrate, anhydrous ethanol and water in a molar ratio of 1:1.2:20:4 and adjusting the pH to 4 with 0.1 mol / L hydrochloric acid.

[0030] Example 1: A preparation process for a special protective slag for electromagnetic catapult duplex stainless steel, comprising the following steps:

[0031] S1.1 Weigh the following raw materials by weight: 35 parts red mud, 30 parts wollastonite, 5 parts modified fluorite, 3 parts borax, 3 parts spodumene, and 3 parts blast furnace slag.

[0032] S1.2 Add red mud, wollastonite, and blast furnace slag to a mixer and mix at 25 rpm for 30 minutes to obtain a preliminary dry mixture. Spray a 3.5% polyvinyl alcohol solution onto the preliminary dry mixture, mix well, add borax and modified fluorite, and continue mixing at 25 rpm for 20 minutes. Finally, add spodumene and mix at 15 rpm for 5 minutes to obtain a uniform wet mixture.

[0033] S1.3. The wet mixture is fed into a granulator to prepare wet granules, and the feeding rate is controlled at 20 kg / h. Then the wet granules are fed into a fluidized bed at 105-110℃ and dried for 1.5 h. The granules are then sieved to obtain granules with a particle size of 0.1-1.5 mm.

[0034] S1.4 Place the granules in an atmosphere furnace, introduce nitrogen gas at a flow rate of 6 L / min, heat to 600℃, and hold for 1 hour; continue heating to 950℃ and hold for 30 minutes; cool with the furnace to obtain a special protective slag for electromagnetic catapult duplex stainless steel.

[0035] Furthermore, the preparation process of modified fluorite is as follows:

[0036] Fluorite powder and yttrium oxide (mass ratio 1:0.15) were dry-mixed in a mixer at 30 rpm for 30 min to obtain a mixture. Polyvinyl alcohol at 0.5% of the mixture mass was added to the mixture, and the mixture was pressed into a green body with a diameter of 20 mm. The green body was placed in a tube furnace and subjected to a high-temperature solid-phase reaction under nitrogen protection. The mixture was heated to 1120 °C at a rate of 5 °C / min and held at that temperature for 3 h. The mixture was then cooled to room temperature with the furnace to obtain the reaction product.

[0037] The reaction products were preheated to 80°C, and then a magnesium olivine sol was deposited using a fluidized bed spray coating machine. The bed temperature was 80°C, the atomization pressure was 0.3 MPa, the sol feed rate was 10 mL / min, the fluidizing gas was nitrogen, and the flow rate was 8.0 m / s. 3 / h, each batch is cycled 20 times, and after spraying, it is cured at 110℃ for 1h; finally, it is calcined and strengthened in a tube furnace, heated to 1200℃ at a rate of 5℃ / min and held for 1h, cooled to 300℃ in the furnace and then naturally cooled to room temperature to obtain modified fluorite.

[0038] Example 2: A preparation process for a special protective slag for electromagnetic catapult duplex stainless steel, comprising the following steps:

[0039] S1.1 Weigh the following raw materials by weight: 38 parts red mud, 33 parts wollastonite, 6 parts modified fluorite, 5 parts borax, 4 parts spodumene and 5 parts blast furnace slag.

[0040] S1.2 Add red mud, wollastonite, and blast furnace slag to a mixer and mix at 25 rpm for 30 minutes to obtain a preliminary dry mixture. Spray a 3.5% polyvinyl alcohol solution onto the preliminary dry mixture, mix well, add borax and modified fluorite, and continue mixing at 25 rpm for 20 minutes. Finally, add spodumene and mix at 15 rpm for 5 minutes to obtain a uniform wet mixture.

[0041] S1.3. The wet mixture is fed into a granulator to prepare wet granules, and the feeding rate is controlled at 20 kg / h. Then the wet granules are fed into a fluidized bed at 105-110℃ and dried for 1.5 h. The granules are then sieved to obtain granules with a particle size of 0.1-1.5 mm.

[0042] S1.4 Place the granules in an atmosphere furnace, introduce nitrogen gas at a flow rate of 6 L / min, heat to 600℃, and hold for 1 hour; continue heating to 950℃ and hold for 30 minutes; cool with the furnace to obtain a special protective slag for electromagnetic catapult duplex stainless steel.

[0043] Furthermore, the preparation process of modified fluorite is as follows:

[0044] Fluorite powder and yttrium oxide (mass ratio 1:0.17) were dry-mixed in a mixer at 30 rpm for 30 min to obtain a mixture. Polyvinyl alcohol at 0.5% of the mass of the mixture was added to the mixture, and the mixture was pressed into a green body with a diameter of 20 mm. The green body was placed in a tube furnace and subjected to a high-temperature solid-phase reaction under nitrogen protection. The mixture was heated to 1120 °C at a rate of 5 °C / min and held at that temperature for 3 h. The mixture was then cooled to room temperature with the furnace to obtain the reaction product.

[0045] The reaction products were preheated to 80°C, and then a magnesium olivine sol was deposited using a fluidized bed spray coating machine. The bed temperature was 80°C, the atomization pressure was 0.3 MPa, the sol feed rate was 10 mL / min, the fluidizing gas was nitrogen, and the flow rate was 8.0 m / s. 3 / h, each batch is cycled 20 times, and after spraying, it is cured at 110℃ for 1h; finally, it is calcined and strengthened in a tube furnace, heated to 1200℃ at a rate of 5℃ / min and held for 1h, cooled to 300℃ in the furnace and then naturally cooled to room temperature to obtain modified fluorite.

[0046] Example 3: A preparation process for a special protective slag for electromagnetic catapult duplex stainless steel, comprising the following steps:

[0047] S1.1 Weigh the following raw materials by weight: 40 parts red mud, 36 parts wollastonite, 8 parts modified fluorite, 7 parts borax, 5 parts spodumene and 7 parts blast furnace slag.

[0048] S1.2 Add red mud, wollastonite, and blast furnace slag to a mixer and mix at 25 rpm for 30 minutes to obtain a preliminary dry mixture. Spray a 3.5% polyvinyl alcohol solution onto the preliminary dry mixture, mix well, add borax and modified fluorite, and continue mixing at 25 rpm for 20 minutes. Finally, add spodumene and mix at 15 rpm for 5 minutes to obtain a uniform wet mixture.

[0049] S1.3. The wet mixture is fed into a granulator to prepare wet granules, and the feeding rate is controlled at 20 kg / h. Then the wet granules are fed into a fluidized bed at 105-110℃ and dried for 1.5 h. The granules are then sieved to obtain granules with a particle size of 0.1-1.5 mm.

[0050] S1.4 Place the granules in an atmosphere furnace, introduce nitrogen gas at a flow rate of 6 L / min, heat to 600℃, and hold for 1 hour; continue heating to 950℃ and hold for 30 minutes; cool with the furnace to obtain a special protective slag for electromagnetic catapult duplex stainless steel.

[0051] Furthermore, the preparation process of modified fluorite is as follows:

[0052] Fluorite powder and yttrium oxide (mass ratio 1:0.19) were dry-mixed in a mixer at 30 rpm for 30 min to obtain a mixture. Polyvinyl alcohol at 0.5% of the mixture mass was added to the mixture, and the mixture was pressed into a green body with a diameter of 20 mm. The green body was placed in a tube furnace and subjected to a high-temperature solid-phase reaction under nitrogen protection. The furnace was heated to 1120 °C at a rate of 5 °C / min and held for 3 h. The furnace was then cooled to room temperature to obtain the reaction product.

[0053] The reaction products were preheated to 80°C, and then a magnesium olivine sol was deposited using a fluidized bed spray coating machine. The bed temperature was 80°C, the atomization pressure was 0.3 MPa, the sol feed rate was 10 mL / min, the fluidizing gas was nitrogen, and the flow rate was 8.0 m / s. 3 / h, each batch is cycled 20 times, and after spraying, it is cured at 110℃ for 1h; finally, it is calcined and strengthened in a tube furnace, heated to 1200℃ at a rate of 5℃ / min and held for 1h, cooled to 300℃ in the furnace and then naturally cooled to room temperature to obtain modified fluorite.

[0054] Example 4: A preparation process for a special protective slag for electromagnetic catapult duplex stainless steel, comprising the following steps:

[0055] S1.1 Weigh the following raw materials by weight: 38 parts red mud, 33 parts wollastonite, 10 parts modified fluorite, 5 parts borax, 4 parts spodumene and 5 parts blast furnace slag.

[0056] S1.2 Add red mud, wollastonite, and blast furnace slag to a mixer and mix at 25 rpm for 30 minutes to obtain a preliminary dry mixture. Spray a 3.5% polyvinyl alcohol solution onto the preliminary dry mixture, mix well, add borax and modified fluorite, and continue mixing at 25 rpm for 20 minutes. Finally, add spodumene and mix at 15 rpm for 5 minutes to obtain a uniform wet mixture.

[0057] S1.3. The wet mixture is fed into a granulator to prepare wet granules, and the feeding rate is controlled at 20 kg / h. Then the wet granules are fed into a fluidized bed at 105-110℃ and dried for 1.5 h. The granules are then sieved to obtain granules with a particle size of 0.1-1.5 mm.

[0058] S1.4 Place the granules in an atmosphere furnace, introduce nitrogen gas at a flow rate of 6 L / min, heat to 600℃, and hold for 1 hour; continue heating to 950℃ and hold for 30 minutes; cool with the furnace to obtain a special protective slag for electromagnetic catapult duplex stainless steel.

[0059] Furthermore, the preparation process of modified fluorite is as follows:

[0060] Fluorite powder and yttrium oxide (mass ratio 1:0.17) were dry-mixed in a mixer at 30 rpm for 30 min to obtain a mixture. Polyvinyl alcohol at 0.5% of the mass of the mixture was added to the mixture, and the mixture was pressed into a green body with a diameter of 20 mm. The green body was placed in a tube furnace and subjected to a high-temperature solid-phase reaction under nitrogen protection. The mixture was heated to 1120 °C at a rate of 5 °C / min and held at that temperature for 3 h. The mixture was then cooled to room temperature with the furnace to obtain the reaction product.

[0061] The reaction products were preheated to 80°C, and then a magnesium olivine sol was deposited using a fluidized bed spray coating machine. The bed temperature was 80°C, the atomization pressure was 0.3 MPa, the sol feed rate was 10 mL / min, the fluidizing gas was nitrogen, and the flow rate was 8.0 m / s. 3 / h, each batch is cycled 20 times, and after spraying, it is cured at 110℃ for 1h; finally, it is calcined and strengthened in a tube furnace, heated to 1200℃ at a rate of 5℃ / min and held for 1h, cooled to 300℃ in the furnace and then naturally cooled to room temperature to obtain modified fluorite.

[0062] Example 5: A preparation process for a special protective slag for electromagnetic catapult duplex stainless steel, comprising the following steps:

[0063] S1.1 Weigh the following raw materials by weight: 38 parts red mud, 33 parts wollastonite, 6 parts modified fluorite, 5 parts borax, 4 parts spodumene and 5 parts blast furnace slag.

[0064] S1.2 Add red mud, wollastonite, and blast furnace slag to a mixer and mix at 25 rpm for 30 minutes to obtain a preliminary dry mixture. Spray a 3.5% polyvinyl alcohol solution onto the preliminary dry mixture, mix well, add borax and modified fluorite, and continue mixing at 25 rpm for 20 minutes. Finally, add spodumene and mix at 15 rpm for 5 minutes to obtain a uniform wet mixture.

[0065] S1.3. The wet mixture is fed into a granulator to prepare wet granules, and the feeding rate is controlled at 20 kg / h. Then the wet granules are fed into a fluidized bed at 105-110℃ and dried for 1.5 h. The granules are then sieved to obtain granules with a particle size of 0.1-1.5 mm.

[0066] S1.4 Place the granules in an atmosphere furnace, introduce nitrogen gas at a flow rate of 6 L / min, heat to 600℃, and hold for 1 hour; continue heating to 950℃ and hold for 30 minutes; cool with the furnace to obtain a special protective slag for electromagnetic catapult duplex stainless steel.

[0067] Furthermore, the preparation process of modified fluorite is as follows:

[0068] Fluorite powder and yttrium oxide (mass ratio 1:0.20) were dry-mixed in a mixer at 30 rpm for 30 min to obtain a mixture. Polyvinyl alcohol at 0.5% of the mass of the mixture was added to the mixture, and the mixture was pressed into a green body with a diameter of 20 mm. The green body was placed in a tube furnace and subjected to a high-temperature solid-phase reaction under nitrogen protection. The mixture was heated to 1120 °C at a rate of 5 °C / min and held at that temperature for 3 h. The mixture was then cooled to room temperature with the furnace to obtain the reaction product.

[0069] The reaction products were preheated to 80°C, and then a magnesium olivine sol was deposited using a fluidized bed spray coating machine. The bed temperature was 80°C, the atomization pressure was 0.3 MPa, the sol feed rate was 10 mL / min, the fluidizing gas was nitrogen, and the flow rate was 8.0 m / s. 3 / h, each batch is cycled 20 times, and after spraying, it is cured at 110℃ for 1h; finally, it is calcined and strengthened in a tube furnace, heated to 1200℃ at a rate of 5℃ / min and held for 1h, cooled to 300℃ in the furnace and then naturally cooled to room temperature to obtain modified fluorite.

[0070] Comparative Example 1: Using the method of Example 2, in the preparation process of the special protective slag for electromagnetic catapult duplex stainless steel, modified fluorite was not used, and fluorite was used directly.

[0071] Comparative Example 2: The method of Example 2 was used, but no forsterite was used for coating in the preparation process of the modified fluorite.

[0072] Comparative Example 3: Using the method of Example 2, no borax was added in the preparation process of the special protective slag for electromagnetic catapult duplex stainless steel.

[0073] This invention introduces a special protective slag for electromagnetic catapult duplex stainless steel, prepared by modifying fluorite, during the preparation process. The performance indicators and testing standards for the electromagnetic catapult duplex stainless steel prepared using this special protective slag are as follows:

[0074] The samples were taken from electromagnetic catapult duplex stainless steel (such as the weld heat-affected zone), with dimensions of 20mm×20mm×3mm and a surface roughness Ra of less than 1.6μm. Sensitization treatment was performed by holding the samples at 650±10℃ for 1 hour and then air cooling. In the corrosion test, the samples were immersed in a boiling copper-copper sulfate-16% sulfuric acid solution (containing copper shavings) for no less than 24 hours. The mass of the samples before and after the test was weighed, and the intergranular corrosion rate was calculated.

[0075] Take a sample of electromagnetic catapult duplex stainless steel, remove surface oil and oxide layer with acetone or alcohol to ensure no impurities; electromagnetically energize the workpiece to form a leakage magnetic field on the surface; spray fluorescent / black magnetic powder, the magnetic powder accumulates at the crack; the fluorescent magnetic powder shows bright green crack traces under ultraviolet light; take pictures to mark the crack location, measure the crack length, and calculate the surface crack rate.

[0076] The electromagnetic catapult duplex stainless steels prepared using the special protective slag for electromagnetic catapult stainless steel in Examples 1-5 and Comparative Examples 1-3 were tested according to the above standards, and the data obtained are shown in Table 1:

[0077] Table 1 Performance data of electromagnetic catapult duplex stainless steel in Examples 1-5 and Comparative Examples 1-3

[0078] Implementation / Comparative Example Intergranular corrosion rate % Surface crack rate % Example 1 1.70% 2.00% Example 2 1.20% 1.50% Example 3 1.40% 1.80% Example 4 3.90% 3.70% Example 5 4.00% 3.20% Comparative Example 1 7.80% 4.20% Comparative Example 2 5.30% 5.60% Comparative Example 3 6.50% 4.40%

[0079] Examples 1-3 and 4 show that when the other components of the special protective slag for electromagnetic catapult duplex stainless steel remain unchanged, and the weight of modified fluorite is continuously increased, the intergranular corrosion rate and surface cracks of electromagnetic catapult duplex stainless steel first decrease and then increase. Modified fluorite can effectively inhibit the excessive release of fluoride ions at high temperatures. An appropriate amount of fluoride ions helps stabilize the liquid phase and form complex inclusions with harmful oxygen and sulfur, thereby reducing their negative impact on the cleanliness of molten steel and thus reducing the risk of intergranular corrosion. When the amount of modified fluorite added is too high, a large amount of fluoride ions will enter the molten steel and slag layer, forming highly active chlorine-fluoride complex anions. These complex anions are extremely destructive and will preferentially accumulate along the grain boundaries, directly eroding and destroying the passivation film on the surface of stainless steel, significantly reducing the electrochemical stability at the grain boundaries, and inducing severe intergranular corrosion. At the same time, the slag film undergoes drastic changes in its melting point, viscosity and other physical properties due to excessive fluoride content, making crystallization behavior difficult to control, reducing lubricity, and even causing inclusions to be drawn in, increasing the risk of surface cracks.

[0080] Furthermore, a comparison of Examples 1-3 and Example 5 shows that: when other components of the protective slag for electromagnetic catapult duplex stainless steel remain unchanged, and the mass ratio of fluorite powder to yttrium oxide continuously increases, the intergranular corrosion rate and surface cracks of the electromagnetic catapult duplex stainless steel first decrease and then increase. Yttrium oxide can react with oxygen, aluminum, etc. in the steel to generate high-melting-point, more stable, and dispersed oxide inclusions that are not easily aggregated at grain boundaries, thus significantly reducing the risk of intergranular corrosion. At the same time, yttrium oxide helps to form a more uniform and stable slag film, improves lubrication and heat transfer uniformity, and reduces the generation of surface cracks. However, excessive yttrium oxide will significantly increase the melting point and viscosity of the protective slag, and may lead to the formation of excessive oxide inclusions in the molten steel. Excessively high slag viscosity will hinder uniform heat transfer, leading to increased differences in cooling rates, generating thermal stress, and easily forming surface cracks. If too many inclusions agglomerate at grain boundaries, they will disrupt the continuity of the matrix, becoming preferential initiation points for corrosion, leading to an increased risk of intergranular corrosion.

[0081] Based on the above test experiments, Example 2 is considered the optimal example.

[0082] A comparison of Example 2 and Comparative Example 1 shows that when fluorite is used directly without modification, the intergranular corrosion rate of electromagnetic catapult duplex stainless steel increases significantly. Under the high-temperature environment of the protective slag, fluorite decomposes to a certain extent and reacts with active elements in the molten steel and other components in the protective slag to generate low-melting-point fluoride / silicate inclusions. These inclusions are easily enriched at the austenite and ferrite grain boundaries of duplex stainless steel, physically isolating adjacent grains and forming chromium-depleted regions around them. The inclusions gathered on the grain boundaries form a micro-battery system with the surrounding chromium-depleted grain boundary regions and the intact austenite / ferrite grains, leading to preferential intergranular corrosion in the chromium-depleted grain boundary regions.

[0083] A comparison of Example 2 and Comparative Example 2 shows that: in the preparation process of modified fluorite, the surface crack rate of electromagnetic catapult duplex stainless steel is significantly increased when forsterite is not used for coating; forsterite has a low coefficient of thermal expansion, which can effectively buffer the shrinkage stress during the cooling process of the billet; when forsterite is missing, the difference in the coefficient of thermal expansion between the slag film and the billet increases, leading to interface stress concentration, and the local tensile stress exceeds the tensile strength of the duplex steel, thereby triggering the initiation of surface microcracks; in addition, the forsterite coating layer helps to form a uniform glassy slag film, and if it is missing, the crystallization rate of the slag film increases, and the brittleness increases; under electromagnetic field disturbance, the probability of slag film fracture also increases significantly; magnesium oxide and silicon dioxide in forsterite can form a low-viscosity liquid phase at high temperature, and its absence will lead to increased viscosity fluctuation of the protective slag, which will further aggravate the friction between the billet and the crystallizer, causing surface scratches and cracks.

[0084] A comparison of Example 2 and Comparative Example 3 shows that: without the addition of borax, the intergranular corrosion rate of electromagnetic catapult duplex stainless steel is significantly increased; borax (mainly B2O3) is an excellent flux and glass network former, which can effectively reduce the melting point and viscosity of the protective slag and promote the formation of a uniform and dense glassy slag film; without borax, the melting point of the protective slag increases and its properties deteriorate, making it difficult to provide good lubrication and heat homogenization, which may lead to a decrease in the surface quality of the billet, and the grain boundaries are more easily eroded by stress or high-temperature oxidation, inducing intergranular corrosion; in addition, the presence of B2O3 helps to increase the solubility of nitrogen in the slag, thereby stabilizing the nitrogen content in the steel and playing a positive role in maintaining the austenite-ferrite phase ratio; without the addition of borax, nitrogen atoms may escape more from the molten steel, resulting in an abnormally high ferrite content, and the ferrite phase is more prone to selective corrosion in some media; boron can also inhibit the precipitation of carbides at grain boundaries to a certain extent and prevent the formation of chromium-depleted zones.

[0085] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A special protective slag for electromagnetic catapult duplex stainless steel, characterized in that, The raw materials include: 35-40 parts by weight of red mud, 30-36 parts by weight of wollastonite, 5-8 parts by weight of modified fluorite, 3-7 parts by weight of borax, 3-5 parts by weight of spodumene, and 3-7 parts by weight of blast furnace slag. The modified fluorite is prepared by reacting yttrium oxide with fluorite in a solid phase and then coating it with magnesium olivine. The preparation process of modified fluorite is as follows: Fluorite powder and yttrium oxide are dry-mixed in a mixer at 20-30 rpm for 30-40 min to obtain a mixture; polyvinyl alcohol is added to the mixture and pressed into a green body with a diameter of 18-20 mm; the green body is placed in a tube furnace and subjected to a high-temperature solid-phase reaction under nitrogen protection, heated to 1100-1150℃ at a rate of 4-6℃ / min, held at that temperature for 2-3 h, and then cooled to room temperature with the furnace to obtain the reaction product; Tetraethyl orthosilicate, magnesium nitrate, anhydrous ethanol and water were mixed in a molar ratio of 1:1.2:20:4 and the pH was adjusted to 4 with 0.1 mol / L hydrochloric acid to obtain forsterite sol. The reaction product was preheated to 75-85℃, and magnesium olivine sol was spray-deposited. Each batch was cycled 18-22 times. After spraying, it was cured at 105-110℃ for 1-1.5h. Finally, it was calcined and strengthened in a tube furnace, heated to 1180-1220℃ at a rate of 4-6℃ / min and held for 1-1.5h. After cooling to 300℃ in the furnace, it was naturally cooled to room temperature to obtain modified fluorite.

2. The special protective slag for electromagnetic catapult duplex stainless steel according to claim 1, characterized in that, The mass ratio of fluorite powder to yttrium oxide is 1:0.15-0.

19.

3. The special protective slag for electromagnetic catapult duplex stainless steel according to claim 1, characterized in that, The amount of polyvinyl alcohol added is 0.4-0.6% of the mass of the mixture.

4. The special protective slag for electromagnetic catapult duplex stainless steel according to claim 1, characterized in that, The spray deposition was carried out using a fluidized bed spray coating machine, with a bed temperature of 78-82℃, an atomization pressure of 0.28-0.32MPa, a sol feed rate of 9-11mL / min, and nitrogen as the fluidizing gas at a flow rate of 7.5-8.5m. 3 / h.

5. The special protective slag for electromagnetic catapult duplex stainless steel according to claim 1, characterized in that, The preparation process of the special protective slag for electromagnetic catapult duplex stainless steel is as follows: S1.1 Weigh the following raw materials in parts by weight: 35-40 parts red mud, 30-36 parts wollastonite, 5-8 parts modified fluorite, 3-7 parts borax, 3-5 parts spodumene, and 3-7 parts blast furnace slag. S1.2 Add red mud, wollastonite, and blast furnace slag to a mixer and mix at 20-30 rpm for 25-35 minutes to obtain a preliminary dry mixture; spray polyvinyl alcohol solution onto the preliminary dry mixture, mix well, add borax and modified fluorite, and continue mixing at 20-30 rpm for 15-20 minutes; finally add spodumene and mix at 10-15 rpm for 5-10 minutes to obtain a uniform wet mixture; S1.

3. The wet mixture is fed into a granulator to prepare wet granules, and the feeding rate is controlled at 18-22 kg / h. Then the wet granules are fed into a fluidized bed at 105-110℃ to dry for 1-1.5 h, and sieved to obtain granules with a particle size of 0.1-1.5 mm. S1.4 Place the granules in an atmosphere furnace, introduce nitrogen gas at a flow rate of 5-8 L / min, raise the temperature to 580-620℃, and hold for 1-1.5 h; continue to raise the temperature to 900-950℃ and hold for 15-30 min; cool with the furnace to obtain a special protective slag for electromagnetic catapult duplex stainless steel.

6. The electromagnetic catapult-specific protective slag for duplex stainless steel as described in claim 5, characterized in that, In step S1.2, the mass concentration of the polyvinyl alcohol solution is 2.5-5.0%.