Preparation method of crucible for smelting stainless steel in vacuum induction furnace

Abstract

The invention relates to the field of smelting of vacuum induction furnaces, in particular to a preparation method of a crucible for smelting stainless steel in a vacuum induction furnace. The preparation method comprises the following steps: I, preparing a ramming refractory material; iI, ramming the furnace bottom of the crucible; iII, placing a crucible lining; iV, ramming the outer lining of the crucible; v, knotting at a furnace mouth; vI, baking the crucible; and VII, inspecting and judging. The crucible prepared by the invention is good in thermal stability, and cracks caused by rapid cooling and rapid heating change of the crucible are avoided; the prepared crucible has enough high refractoriness and high-temperature structural strength, is enough to bear high temperature and molten steel furnace charge impact, and can ensure the stability and safety in the stainless steel smelting process. The use verifies that the service life of the crucible is obviously prolonged, the furnace life of the crucible is prolonged from the original 15 furnace times to the present 25 furnace times or more, the furnace life is stable, the problem of steel leakage is avoided, the service life of the crucible is prolonged, the times of furnace disassembly, furnace ramming and furnace baking are reduced, the research and development period is greatly shortened, and the research and development cost is reduced.

Description

Technical Field

[0001] The invention relates to the field of vacuum induction furnace smelting, and in particular to a method for preparing a crucible for smelting stainless steel in a vacuum induction furnace. Background Art

[0002] 50Kg vacuum induction furnace is widely used in the research and development of stainless steel materials. When using 50Kg vacuum induction furnace for stainless steel smelting, the manufacture of crucible is a very critical link. The quality of crucible manufacturing has an important impact on the smelting process and steel quality of stainless steel. Since the crucible is in direct contact with molten steel, with the increase of smelting time and furnace number, the crucible is particularly severely eroded and eroded by molten steel, and it is easy to crack. During the smelting process, the crucible may not be able to withstand the pressure generated by the molten steel and break. In severe cases, steel leakage will occur, posing a safety risk. Due to the short life of the crucible (the furnace age is only 15 furnaces), the furnace needs to be dismantled and rebuilt, which increases the R&D cycle and cost, which is not conducive to the development of high-quality scientific and technological innovation. Therefore, it is of great significance to develop a long-life, safe, reliable and economical crucible.

[0003] The purpose of the present invention is to overcome the problems of short furnace life and easy cracking of crucibles used in vacuum induction furnaces for smelting stainless steel in the prior art, and to provide a method for preparing a crucible used in vacuum induction furnaces for smelting stainless steel, so as to achieve long life, safe, reliable and economical use of the crucible. Summary of the invention

[0004] The purpose of the present invention is to solve the above problems and provide a method for preparing a crucible for smelting stainless steel in a vacuum induction furnace.

[0005] The object of the present invention is achieved as follows: 1. A method for preparing a crucible for smelting stainless steel in a vacuum induction furnace, comprising the following steps: Step 1: pounding a refractory material configuration: the refractory material is fused magnesia, the MgO content of the fused magnesia is ≥96%, fused magnesia with a particle size of 2 to 4 mm and fused magnesia with a particle size of 0.05 to 0.07 mm are mixed in a ratio of 7:3, the amount of the binder water glass added is controlled at 10% to 12% of the total amount of the fused magnesia, and stirring is performed at a temperature of 20±5°C for 30 to 35 minutes to ensure that the fused magnesias of different particle sizes are evenly mixed; Step 2: Crucible furnace bottom ramming: Attach a layer of mica paper with a thickness of 2-3mm to the inner side of the induction coil, lay a piece of asbestos cloth on the crucible furnace bottom, add the configured refractory material magnesia sand in 5-6 batches, and add the same amount of each batch to ensure that the thickness of each layer is 8-9mm. Add the configured refractory material and ram it with a pointed steel chisel with a diameter of 10-12mm. Each ramming time is 15-16min. The number of ramming and feeding times of the furnace bottom is 5-6 times, and the thickness of the furnace bottom is 40-54mm. Step 3: Placement of the crucible lining: The crucible lining is an alkaline material Al2O3, and the compressive strength at room temperature is 15M-17 MPa, put the prefabricated crucible lining into the induction coil, so that the center of the crucible lining coincides with the center of the induction coil, and the distance between the crucible lining and the mica paper inside the induction coil is 11-12 cm; Step 4: Ramming of the crucible lining: add refractory magnesia sand layer by layer into the gap between the crucible lining and the inside of the induction coil and tamp it, and tamp it with a pointed steel chisel with a diameter of 8-10 mm. Each ramming time is 18-20 min, and the thickness of each layer is 21-25 mm; Step 5: Knotting at the furnace mouth: Use 2-4 mm fused magnesia sand and 0.05-0.07 mm fused magnesia sand in a ratio of 6:4, and add a binder water glass in an amount of 15-16 of the total amount of fused magnesia sand. % control, ramming with a pointed steel chisel with a diameter of 12 to 14 mm, each ramming time is 22 to 23 minutes, and the thickness of each layer is 18 to 20 mm; finally, the upper opening is sealed with a mixture of water glass and corundum powder, and the ratio of water glass to corundum powder is 3:25; Step six: crucible baking: first use a low-power 20 to 25KW furnace to heat to 550±10℃, keep warm for 2.5 to 3 hours, then use a medium-power 60 to 70KW furnace to heat to 1000±10℃, keep warm for 1 to 1.5 hours, and finally use a high-power 90 to 100KW furnace to heat to 1600±10℃, and keep warm for 4 to 5 hours, then stop the furnace to cool; Step seven: inspection and judgment.

[0006] The inspection and judgment of step seven are as follows: the prepared crucible has no deformation and cracks, and the stainless steel is continuously vacuum-induced melted until the inner wall of the crucible is covered with a thick mixture of magnesium-aluminum crystal stone and steel slag, which cannot be removed.

[0007] The beneficial effects of the present invention are as follows: the method for preparing a crucible for smelting stainless steel in a vacuum induction furnace of the present invention has good thermal stability of the prepared crucible, which avoids cracks caused by rapid cooling and heating of the crucible; the prepared crucible has sufficiently high refractoriness and high-temperature structural strength, which is sufficient to withstand high temperature and impact of molten steel charge, prevent changes in the composition of molten steel, and have no effect on the content of harmful trace elements, providing basic conditions for obtaining high purity steel, and ensuring the stability and safety of the stainless steel smelting process. It has been verified by use that the life of the crucible has been significantly improved, and the crucible furnace age has been increased from only 15 furnaces to more than 25 furnaces now, and the furnace age is stable, and there has been no steel leakage problem. The extension of the crucible life reduces the number of furnace dismantling, furnace construction, and furnace baking, greatly shortening the R&D cycle and reducing R&D costs. DETAILED DESCRIPTION

[0008] During the smelting process, the crucible itself is subjected to various forces, including the impact force of the charge on the crucible, the static pressure of the molten steel, the force of the electromagnetic stirring when the molten steel moves, the temperature difference stress inside and outside the crucible, the internal stress caused by the rapid cooling and heating changes, etc. Due to the action of these forces, the crucible must have a higher strength at high temperature and room temperature to prevent cracking and steel leakage. In order to solve the above technical problems, the technical scheme adopted by the present invention is a method for preparing a crucible for smelting stainless steel in a vacuum induction furnace. Three measures are mainly adopted to work together to improve the life of the crucible. Measure 1, the prepared crucible consists of an inner lining and an outer lining. The inner lining is made of alkaline material Al2O3, which has the advantages of less impurities and good chemical stability. Its main function is to resist the scouring and corrosion of high-temperature molten steel, prevent the composition of molten steel from changing, and have no effect on the content of harmful trace elements, providing a basic condition guarantee for obtaining high purity steel. The outer lining is configured with fused magnesia sand refractory material, which mainly realizes high strength of crucible and prevents steel leakage; measure two, the particle size ratio of the refractory material of the outer lining of the crucible affects the service life of the furnace lining, and it is necessary to mix refractory materials of different particle sizes in a certain proportion and mix them evenly with high-temperature binders. The proportion needs to be accurately controlled during the batching to ensure the uniformity and stability of the refractory material; measure three, formulate a scientific and reasonable crucible baking process system to remove moisture and residual organic matter in the material, improve its high temperature resistance and corrosion resistance and high temperature strength, and the drying process needs to be gradually heated up to make the temperature inside the crucible uniform, avoid cracks and deformation, so as to ensure the long life of the crucible and safe and reliable use. In order to achieve the above-mentioned invention purpose, the technical solution adopted by the present invention is to provide a method for preparing a crucible for smelting stainless steel in a vacuum induction furnace, and its process includes ramming refractory material configuration, ramming the bottom of the crucible, placing the inner lining of the crucible, ramming the outer lining of the crucible, tying the furnace mouth, and baking the crucible.

[0009] The present invention describes the configuration of rammed refractory materials, ramming of the bottom of the crucible, placement of the inner lining of the crucible, ramming of the outer lining of the crucible, knotting of the furnace mouth and baking of the crucible in the manufacturing process of the crucible. The prepared crucible consists of an inner lining and an outer lining. The inner lining is made of an alkaline material Al2O3, and the outer lining is a configured fused magnesia sand refractory material. The inner lining is made of an alkaline material Al2O3, which has the advantages of less impurities and good chemical stability. Its main function is to resist the scouring and corrosion of high-temperature molten steel, prevent the change of the composition of the molten steel, and have no effect on the content of harmful trace elements, providing a basic condition guarantee for obtaining high purity of steel. The outer lining is a configured fused magnesia sand refractory material, which mainly realizes high strength of the crucible and prevents steel leakage. It is sufficient to withstand high temperature and impact of molten steel charge, prevent changes in the composition of molten steel, and have no effect on the content of harmful trace elements. It can effectively solve the problems of deoxidation and inclusions in the vacuum smelting process, provide a basic condition guarantee for obtaining high purity of steel, and ensure the stability and safety of the stainless steel smelting process. The particle size ratio of the refractory material of the crucible outer lining affects the service life of the furnace lining. Different refractory materials need to be mixed in a certain proportion and evenly mixed with high-temperature binders. The proportion needs to be precisely controlled during mixing to ensure the balance and stability of the materials. The stronger the lining's corrosion resistance.

[0010] Formulate a scientific and reasonable crucible baking process system to remove moisture and residual organic matter in the material, improve its high temperature resistance, corrosion resistance and high temperature strength. The drying process needs to gradually increase the temperature to make the temperature inside the crucible uniform and avoid cracks and deformation to ensure the long life of the crucible and safe and reliable use.

[0011] Specifically, the following main steps are adopted: Ⅰ. Ramming refractory material configuration: The refractory material is fused magnesia, and its MgO content is ≥96%. 2-4mm fused magnesia and 0.05-0.07mm fused magnesia are mixed in a ratio of 7:3. The amount of binder water glass added is controlled at 10%-12% of the total amount of fused magnesia. Stir at a temperature of 20±5℃ for 30-35 minutes to ensure that fused magnesia of different particle sizes are evenly mixed.

[0012] Ⅱ. Ramming of the crucible furnace bottom: clean the impurities attached to the upper surface of the induction coil (Note: the induction coil is made of copper coil, which is coiled in circles. When preparing the crucible, it is placed inside the furnace body. The prepared crucible is inside the induction coil. The induction coil is energized to generate an electromagnetic field to melt the charge inside the crucible). To ensure that the furnace lining has good thermal insulation and insulating properties, a layer of mica paper with a thickness of 2 to 3 mm is attached to the inside of the induction coil. The top of the mica paper should be higher than the induction coil. A piece of asbestos cloth should be laid on the bottom of the crucible furnace to fix the charge and provide insulation. The asbestos cloth should be laid flat and wrinkle-free. Add the configured refractory material magnesia sand in 5 to 6 batches. The amount added in each batch is the same to ensure that the thickness of each layer is 8 to 9 mm. Use a pointed steel chisel with a diameter of 10 to 12 mm to ram. Each ramming time is 15 to 16 minutes. The number of ramming and feeding times is 5 to 6 times. The thickness of the furnace bottom is 40 to 54 mm (Note: Step II is only for making the furnace bottom. The purpose of preparing the crucible furnace bottom is to prevent the molten metal steel from burning through the furnace bottom and causing steel leakage accidents).

[0013] Ⅲ Placement of crucible lining: The crucible lining is alkaline material Al2O3, with a room temperature compressive strength of 15M~17 MPa. Place the prefabricated crucible lining into the induction coil so that its center coincides with the center of the induction coil, and the distance between it and the mica paper inside the induction coil is 11~12cm.

[0014] IV. Ramming of crucible outer lining: Add the configured refractory fused magnesia sand layer by layer into the gap between the crucible lining and the inner side of the induction coil and tamp it down. Use a pointed steel chisel with a diameter of 8 to 10 mm to ram. Each ramming time is 18 to 20 minutes, and the thickness of each layer is 21 to 25 mm. During the ramming process, check whether the crucible lining is centered frequently to prevent the crucible lining from tilting and causing uneven thickness of the crucible wall, which will reduce its service life. During the ramming process, do not damage the kraft paper or asbestos cloth. Repeat the tamping until the furnace wall height is flush with the induction coil, and then proceed to the knotting operation at the furnace mouth.

[0015] Ⅴ Knotting at the furnace mouth: Since the furnace mouth area is not easy to dry, in order to obtain a stronger furnace mouth, the proportion of fine powder must be increased in the refractory material. Use fused magnesia with a particle size of 2-4 mm and fused magnesia with a particle size of 0.05-0.07 mm in a ratio of 6:4. The amount of binder water glass added is controlled at 15-16% of the total amount of fused magnesia. Use a pointed steel chisel with a diameter of 12-14 mm to ram. Each ramming time is 22-23 minutes, and the thickness of each layer is 18-20 mm. Finally, seal the upper mouth with a mixture of water glass and corundum powder to make it strong and durable after drying. The configuration ratio of water glass to corundum powder is 3:25.

[0016] Ⅵ Crucible baking: Control the temperature rise and fall speed to avoid deformation and cracks of the crucible due to rapid temperature changes. First use a low-power 20-25KW furnace to heat to 550±10℃ and keep warm for 2.5-3 hours, then use a medium-power 60-70KW furnace to heat to 1000±10℃ and keep warm for 1-1.5 hours, and finally use a high-power 90-100KW furnace to heat to 1600±10℃ and keep warm for 4-5 hours, then stop the furnace to cool.

[0017] Ⅶ Inspection and judgment: In order to ensure that the prepared crucible meets the requirements of long-life safe and reliable use, the quality of the prepared crucible needs to be inspected and evaluated. The main technical indicators of the crucible for smelting stainless steel in the vacuum induction furnace manufactured by the present invention are as follows: the prepared crucible has no deformation and cracks, and the stainless steel is continuously smelted by vacuum induction until the inner wall of the crucible is covered with a thick mixture of magnesium-aluminum crystal stone and steel slag, which cannot be eliminated, seriously affecting the subsequent addition of furnace charges, and a new furnace needs to be re-tied. The original crucible expires and is terminated. The crucible life is ≥25 furnaces, and the chemical composition control of the smelted stainless steel meets the technical requirements.

[0018] The specific implementation of the present invention is described in detail below in conjunction with the embodiments, but the specific implementation of the present invention is not limited to the following embodiments. Example 1

[0019] Prepare crucibles for vacuum induction furnaces and carry out stainless steel smelting.

[0020] This embodiment includes the following steps in sequence: Ⅰ. Ramming refractory material configuration: the refractory material is fused magnesia, and its MgO content is ≥96%. 2.5mm fused magnesia and 0.05mm fused magnesia are mixed in a ratio of 7:3. The amount of binder water glass added is controlled at 10% of the total amount of fused magnesia. Stir at a temperature of 23°C for 30 minutes to ensure that fused magnesia of different particle sizes are evenly mixed.

[0021] Ⅱ Crucible furnace bottom ramming: clean the impurities attached to the upper surface of the induction coil. To ensure that the furnace lining has good thermal insulation and insulation performance, attach a layer of 2mm thick mica paper to the inside of the induction coil. The upper side of the mica paper should be higher than the induction coil. A piece of asbestos cloth should be laid on the bottom of the crucible to achieve the function of fixing the charge and insulation. The laying of the asbestos cloth should be flat and wrinkle-free. Add the configured refractory material magnesia sand in 5 batches, and the amount added in each batch is the same to ensure that each layer is 8mm thick. Ramming with a pointed steel chisel with a diameter of 10mm, each ramming time is 15min, the number of ramming and feeding times of the furnace bottom is 5 times, and the thickness of the furnace bottom is 40mm.

[0022] III. Placement of crucible lining: The crucible lining is alkaline material Al2O3, with a room temperature compressive strength of 15MPa. Place the prefabricated crucible lining into the induction coil so that its center coincides with the center of the induction coil, and the distance between it and the mica paper inside the induction coil is 11cm.

[0023] IV. Ramming of crucible outer lining: Add the configured refractory fused magnesia sand layer by layer into the gap between the crucible lining and the inner side of the induction coil and tamp it down. Use a pointed steel chisel with a diameter of 8mm to ram. The ramming time is 18min each time and the thickness of each layer is 21mm. During the ramming process, the crucible lining should be checked frequently to see if it is centered to prevent the crucible lining from tilting and causing uneven thickness of the crucible wall, which will reduce its service life. During the ramming process, the kraft paper and asbestos cloth should not be damaged. Repeatedly tamp the filler until the furnace wall height is flush with the induction coil, and then proceed to the knotting operation at the furnace mouth.

[0024] Ⅴ Knotting at the furnace mouth: As the furnace mouth area is not easy to dry, in order to obtain a stronger furnace mouth, the proportion of fine powder must be increased in the refractory material. Use 2.5mm fused magnesia and 0.05mm fused magnesia in a ratio of 6:4. The amount of binder water glass added is controlled at 15% of the total amount of fused magnesia. Use a pointed steel chisel with a diameter of 12 to ram. Each ramming time is 23 minutes and the thickness of each layer is 18mm. Finally, seal the upper mouth with a mixture of water glass and corundum powder to make it strong and durable after drying. The configuration ratio of water glass to corundum powder is 3:25.

[0025] Ⅵ Crucible baking: Control the temperature rise and fall speed to avoid the crucible from breaking due to too fast temperature change. First use a low-power 20KW furnace to heat to 540℃ and keep warm for 2.5 hours, then use a medium-power 60KW furnace to heat to 990℃ and keep warm for 1 hour, and finally use a high-power 90KW furnace to heat to 1590℃ and keep warm for 4 hours, then stop the furnace to cool.

[0026] Ⅶ Inspection and judgment: In order to ensure that the prepared crucible meets the requirements of long-life, safe and reliable use, the quality of the prepared crucible needs to be inspected and evaluated. After inspection, the prepared crucible has no deformation and inner wall cracks. After continuous vacuum induction melting of 25 furnaces of stainless steel, the crucible did not crack or leak during this process. At this time, the inner wall of the crucible is covered with a thick mixture of magnesium-aluminum crystal stone and steel slag, which cannot be eliminated, seriously affecting the subsequent addition of furnace materials. A new furnace needs to be re-tied. The original crucible expires and is no longer used. The chemical composition control of the 25 furnaces of stainless steel melted meets the technical requirements. Example 2

[0027] Prepare crucibles for vacuum induction furnaces and carry out stainless steel smelting.

[0028] This embodiment includes the following steps in sequence: Ⅰ. Ramming refractory material configuration: the refractory material is fused magnesia, and its MgO content is ≥96%. 4mm fused magnesia and 0.07mm fused magnesia are mixed in a ratio of 7:3. The amount of binder water glass added is controlled at 12% of the total amount of fused magnesia. Stirring is carried out at a temperature of 25°C for 35 minutes to ensure that fused magnesia of different particle sizes are evenly mixed.

[0029] Ⅱ Crucible furnace bottom ramming: clean the impurities attached to the upper surface of the induction coil. To ensure that the furnace lining has good thermal insulation and insulation performance, attach a layer of 3mm thick mica paper to the inside of the induction coil. The upper side of the mica paper should be higher than the induction coil. A piece of asbestos cloth should be laid on the bottom of the crucible to achieve the function of fixing the charge and insulation. The laying of the asbestos cloth requires flatness without wrinkles. Add the configured refractory material magnesia in 6 batches, and the amount added in each batch is the same to ensure that each layer is 9mm thick. Ramming with a pointed steel chisel with a diameter of 12mm, each ramming time is 16min, the number of ramming and feeding times of the furnace bottom is 6 times, and the thickness of the furnace bottom is 54mm.

[0030] III. Placement of crucible lining: The crucible lining is alkaline material Al2O3, with a room temperature compressive strength of 17MPa. Place the prefabricated crucible lining into the induction coil so that its center coincides with the center of the induction coil, and the distance between it and the mica paper on the inner side of the induction coil is 12cm.

[0031] IV. Ramming of crucible outer lining: Add the configured refractory fused magnesia sand layer by layer into the gap between the crucible lining and the inner side of the induction coil and tamp it down. Use a pointed steel chisel with a diameter of 10mm to ram. Each ramming time is 20min and the thickness of each layer is 25mm. During the ramming process, the crucible lining should be checked frequently to see if it is centered to prevent the crucible lining from tilting and causing uneven thickness of the crucible wall, which will reduce its service life. During the ramming process, the kraft paper and asbestos cloth should not be damaged. Repeatedly tamp the filler until the furnace wall height is flush with the induction coil, and then proceed to the knotting operation at the furnace mouth.

[0032] Ⅴ Knotting at the furnace mouth: Since the furnace mouth area is not easy to dry, in order to obtain a stronger furnace mouth, the proportion of fine powder must be increased in the refractory material. Use 4mm fused magnesia and 0.07mm fused magnesia in a ratio of 6:4. The amount of binder water glass added is controlled at 16% of the total amount of fused magnesia. Use a pointed steel chisel with a diameter of 14 to pound. Each pounding time is 22 minutes, and the thickness of each layer is 20mm. Finally, use a mixture of water glass and corundum powder to seal the upper mouth to make it strong and durable after drying. The configuration ratio of water glass to corundum powder is 3:25.

[0033] Ⅵ Crucible baking: Control the temperature rise and fall speed to avoid the crucible from breaking due to too fast temperature change. First use a low-power 25KW furnace to heat to 560℃ and keep warm for 3 hours, then use a medium-power 70KW furnace to heat to 1010℃ and keep warm for 1.5 hours, and finally use a high-power 100KW furnace to heat to 1610℃ and keep warm for 5 hours, then stop the furnace to cool.

[0034] Ⅶ Inspection and judgment: In order to ensure that the prepared crucible meets the requirements of long-life, safe and reliable use, the quality of the prepared crucible needs to be inspected and evaluated. After inspection, the prepared crucible has no deformation and inner wall cracks. After continuous vacuum induction melting of 28 furnaces of stainless steel, the crucible did not crack or leak during this process. At this time, the inner wall of the crucible is covered with a thick mixture of magnesium-aluminum crystal stone and steel slag, which cannot be eliminated, seriously affecting the subsequent addition of furnace materials. A new furnace needs to be re-tied. The original crucible expires and is no longer used. The chemical composition control of the 26 furnaces of stainless steel melted meets the technical requirements.

[0035] The above description is only a specific embodiment of the present invention, but the structural features of the protection scope of the present invention are not limited thereto. Any changes or modifications made by any technician in the field of the present invention are all covered by the patent scope of the present invention.

Claims

1. A method for preparing a crucible for smelting stainless steel in a vacuum induction furnace, characterized in that: The following steps are involved: Step 1: Ramming refractory material configuration: The refractory material is fused magnesia, the MgO content of the fused magnesia is ≥96%, and the fused magnesia with a particle size of 2-4 mm and the fused magnesia with a particle size of 0.05-0.07 mm are mixed in a ratio of 7:3, and the amount of the binder water glass added is controlled at 10%-12% of the total amount of the fused magnesia. Stir at a temperature of 20±5°C for 30-35 minutes to ensure that the fused magnesia of different particle sizes are evenly mixed; Step 2: Ramming the crucible furnace bottom: attach a layer of mica paper with a thickness of 2 to 3 mm on the inner side of the induction coil, lay a piece of asbestos cloth on the crucible furnace bottom, add the configured refractory material magnesia sand in 5-6 batches, add the same amount of each batch, ensure that the thickness of each layer is 8 to 9 mm, add the configured refractory material, and ram with a pointed steel chisel with a diameter of 10 to 12 mm. Each ramming time is 15 to 16 minutes, the number of ramming and feeding times of the furnace bottom is 5 to 6 times, and the thickness of the furnace bottom is 40 to 54 mm; Step 3: Place the crucible lining: The crucible lining is an alkaline material Al2O3, with a room temperature compressive strength of 15M~17 MPa. Place the prefabricated crucible lining into the induction coil so that the center of the crucible lining coincides with the center of the induction coil, and the distance between the crucible lining and the mica paper inside the induction coil is 11~12cm; Step 4: Ramming the crucible outer lining: Add refractory magnesia sand layer by layer into the gap between the crucible inner lining and the inner side of the induction coil and tamp it down, ramming it with a pointed steel chisel with a diameter of 8 to 10 mm, each ramming time is 18 to 20 minutes, and the thickness of each layer is 21 to 25 mm; Step 5: Tie the furnace mouth: Mix fused magnesia with a particle size of 2-4 mm and fused magnesia with a particle size of 0.05-0.07 mm in a ratio of 6:4, and control the amount of water glass as the binder to be added at 15-16% of the total amount of fused magnesia. Ram with a pointed steel chisel with a diameter of 12-14 mm, and each ramming time is 22-23 minutes, and the thickness of each layer is 18-20 mm; finally, seal the upper mouth with a mixture of water glass and corundum powder, and the configuration ratio of water glass to corundum powder is 3:25; Step 6: Crucible baking: first use a low-power 20-25KW furnace to heat to 550±10℃, keep warm for 2.5-3 hours, then use a medium-power 60-70KW furnace to heat to 1000±10℃, keep warm for 1-1.5 hours, and finally use a high-power 90-100KW furnace to heat to 1600±10℃, keep warm for 4-5 hours, then stop the furnace to cool; Step 7: Inspection and judgment.

2. The method for preparing a crucible for smelting stainless steel in a vacuum induction furnace according to claim 1, characterized in that: The inspection and judgment of step seven are as follows: the prepared crucible has no deformation and cracks, and the stainless steel is continuously vacuum-induced melted until the inner wall of the crucible is covered with a thick mixture of magnesium-aluminum crystal stone and steel slag, which cannot be removed.