A method for vacuum induction melting and desulfurization of high-purity stainless steel

Abstract

The application discloses a high-purity stainless steel vacuum induction melting desulfurization method, which comprises the following steps: S1, preparing materials; S2, charging and melting; S3, refining; S4, deoxidizing and desulfurizing: after the refining is completed, deoxidizing alloy and desulfurizing agent are added into the molten steel, and after stirring for 5-10 minutes, argon is filled into the furnace until the pressure reaches 80-90 KPa, the temperature is controlled at 1580-1610 DEG C, and deoxidizing and desulfurizing are performed for 40-50 minutes; S5, secondary refining; and S6, pouring. The high-purity stainless steel vacuum induction melting desulfurization method provided by the application firstly pre-treats raw materials, then performs charging and melting, reduces the contact between molten steel and air through the vacuum induction melting method, improves the desulfurizing and deoxidizing efficiency, and through twice refining and adding specific desulfurizing agent, the sulfur content of the finally obtained high-purity stainless steel is less than 7 ppm, the effect of deep desulfurization is achieved, and the demand of the steel industry is met.

Description

Technical Field

[0001] This invention belongs to the field of vacuum metallurgy technology, specifically relating to a method for desulfurization of high-purity stainless steel through vacuum induction melting. Background Technology

[0002] Sulfur exists in steel in the form of sulfides (MnS, FeS, etc.), and its effects on mechanical properties are: (1) the strength, plasticity, and toughness of steel in the transverse and thickness directions are significantly lower than those in the rolling direction (longitudinal direction), especially the low-temperature impact performance of steel plates; (2) it significantly reduces the steel's resistance to hydrogen-induced cracking, therefore it is used in marine engineering, railway bridges, high-rise buildings, and large hydrogen storage tanks. [S]≤50×10 -6 Sulfur also affects the corrosion resistance of steel. For steel used in oil and gas pipelines transporting acidic media such as H2S, the [S] content is reduced to (5-10)×10⁻⁶. -6 Furthermore, sulfur adversely affects the hot working properties and weldability of steel. Therefore, for some steel grades, desulfurization during the smelting process is crucial.

[0003] Based on market demand, high-strength steel, high-purity stainless steel, and high-purity mold steel are currently produced using a vacuum induction melting + vacuum arc remelting process. Since vacuum arc remelting lacks the desulfurization capabilities of electroslag remelting, and vacuum induction melting has poor desulfurization effects, the industry typically uses low-sulfur raw materials to control the sulfur content of the finished product when producing these materials using a dual-vacuum melting process. However, low-sulfur raw materials are expensive, leading to high production costs. Therefore, how to achieve desulfurization during vacuum induction melting is a major research direction.

[0004] The basic working principle of a vacuum induction melting furnace is based on the principles of electromagnetic induction and the thermal effect of electric current. That is, electromagnetic induction induces a current within the metal charge; as this current flows through the charge, it generates heat due to resistance, thus heating and melting the metal. Vacuum induction furnace smelting is a smelting method that involves heating, melting, refining, alloying, and casting under negative pressure. Because the entire metallurgical process is carried out in isolation from the atmosphere, atmospheric contamination of the molten steel is avoided. Refining the molten steel under vacuum significantly improves its purity and allows for precise control of its chemical composition.

[0005] Chinese Patent Application No. 201010579832.5 discloses an ultra-pure smelting process for low-alloy high-strength steel. The specific method involves using a CaO refractory crucible and employing vacuum induction melting to obtain ultra-pure low-alloy high-strength steel. During the melting period, deoxidation and denitrification of the carbon in the alloy raw materials are performed in the early stages. During the refining period, the refining temperature is increased to enhance the thermodynamic and kinetic conditions for deoxidation and desulfurization, effectively deoxidizing and desulfurizing the crucible wall and the surface of the molten steel. During the deoxidation and desulfurization period, a strong deoxidizing and desulfurizing agent is added to perform final deoxidation and desulfurization of the alloy, further reducing the oxygen and sulfur content in the alloy to below 10 ppm, below 30 ppm, and below 30 ppm. This invention can effectively improve the low-temperature impact toughness of low-alloy high-strength steel, further reduce the ductile-brittle transition temperature, expand the application fields of low-alloy high-strength steel, improve the hot working performance of the alloy, and obtain high-quality low-alloy high-strength steel. However, this method requires the use of a high-purity calcium oxide crucible and a high vacuum (less than 1 Pa) during desulfurization, making the process conditions quite demanding.

[0006] Therefore, developing a method to improve the deep desulfurization of stainless steel in vacuum induction melting is of great significance to this field. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a method for desulfurization of high-purity stainless steel through vacuum induction melting, thereby improving desulfurization efficiency, achieving deep desulfurization, and further reducing the sulfur content in high-purity stainless steel to meet the needs of the steel industry.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A method for desulfurization of high-purity stainless steel by vacuum induction melting includes the following steps:

[0010] S1. Material preparation: Select raw materials according to the composition of stainless steel, remove the oxide layer or rust layer on the surface, clean with anhydrous ethanol, and dry after cleaning for later use.

[0011] S2, Charging and Melting: Add the raw materials prepared in step S1 into the magnesium oxide crucible. After the vacuum degree in the vacuum induction melting chamber is reduced to below 10 Pa, start powering on to melt the materials.

[0012] S3. Refining: After the main alloy material is melted, it is refined once.

[0013] S4. Deoxidation and desulfurization: After refining, add deoxidizing alloy and desulfurizing agent to the molten steel, stir for 5-10 minutes, and then fill the furnace with argon gas until the pressure reaches 80-90KPa. Control the temperature at 1580-1610℃ and carry out deoxidation and desulfurization for 40-50 minutes.

[0014] S5. Secondary refining: The furnace is evacuated again to below 10Pa to perform secondary refining on the deoxidized and desulfurized molten steel.

[0015] S6. Casting: After the secondary refining is completed, the power is turned off and the temperature is lowered. The casting temperature is adjusted to 1480℃ for casting to complete the high-purity stainless steel smelting.

[0016] Preferably, the temperature of the first refining step S3 is 1630-1680℃ and the time is 35-50 min.

[0017] More preferably, the temperature of the first refining step S3 is 1650-1670°C, and the time is 40-45 minutes.

[0018] Preferably, the deoxidizing alloy in step S4 is one or more of silicon, aluminum, and titanium; the amount of deoxidizing alloy used is 0.5-1 wt% of the molten steel.

[0019] More preferably, the deoxidizing alloy in step S4 is one or more of silicon, aluminum, and titanium; the amount of deoxidizing alloy used is 0.7-0.9 wt% of the molten steel.

[0020] Preferably, the amount of desulfurizing agent used in step S4 is 1-2% of the molten steel.

[0021] More preferably, the amount of desulfurizing agent used in step S4 is 1.5-2% of the molten steel.

[0022] Preferably, the desulfurizing agent in step S4 is prepared as follows:

[0023] (a) Add calcium carbonate powder to deionized water, then add polyvinylpyrrolidone, stir and disperse evenly to obtain a calcium carbonate suspension;

[0024] (b) Add aluminum nitrate to deionized water, and after dissolution, add fatty alcohol polyoxyethylene ether AEO-9, adjust the pH to 5-6, age at room temperature, freeze dry, and obtain pretreated aluminum nitrate.

[0025] (c) Add pretreated aluminum nitrate to calcium carbonate suspension, disperse by ultrasonication, and then carry out hydrothermal reaction. After the reaction is completed, filter, wash, dry and sinter to obtain solid powder.

[0026] (d) The solid powder is impregnated in a mixed solution of zirconium nitrate and nickel nitrate. After impregnation, the powder is filtered, dried and calcined to obtain the desulfurizing agent.

[0027] Preferably, the mass ratio of calcium carbonate, deionized water, and polyvinylpyrrolidone in step (a) is 50:400-500:0.3-0.5.

[0028] More preferably, the mass ratio of calcium carbonate, deionized water, and polyvinylpyrrolidone in step (a) is 50:450-500:0.4-0.5.

[0029] Preferably, in step (b), the mass ratio of aluminum nitrate, deionized water, and fatty alcohol polyoxyethylene ether AEO-9 is 50:150-200:0.4-0.8; and the aging time is 4-6 hours.

[0030] More preferably, in step (b), the mass ratio of aluminum nitrate, deionized water, and fatty alcohol polyoxyethylene ether AEO-9 is 50:180-200:0.5-0.7; and the aging time is 5-6 hours.

[0031] Preferably, in step (c), the mass ratio of the pretreated aluminum nitrate to calcium carbonate suspension is 40-50:450-550; the hydrothermal reaction temperature is 150-180℃ and the time is 7-10h; and the sintering temperature is 550-650℃ and the time is 3-5h.

[0032] More preferably, in step (c), the mass ratio of the pretreated aluminum nitrate to calcium carbonate suspension is 45-50:500-550; the hydrothermal reaction temperature is 160-170℃ and the time is 8-10h; and the sintering temperature is 580-620℃ and the time is 4-5h.

[0033] Preferably, in step (d), the concentration of zirconium nitrate in the mixed solution is 30-40 g / L, and the concentration of nickel nitrate is 60-70 g / L; the impregnation temperature is 60-70°C, and the time is 1-2 h; the calcination temperature is 850-900°C, and the time is 4-6 h.

[0034] More preferably, in step (d), the concentration of zirconium nitrate in the mixed solution is 35-40 g / L, and the concentration of nickel nitrate is 60-65 g / L; the impregnation temperature is 65-70°C, and the time is 1.5-2 h; the calcination temperature is 870-890°C, and the time is 5-6 h.

[0035] Preferably, the temperature of the secondary refining in step S5 is controlled at 1500-1540℃, and the time is 20-30 minutes.

[0036] More preferably, the temperature of the secondary refining in step S5 is controlled at 1520-1540℃, and the time is 20-25 minutes.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] (1) The method for desulfurization of high-purity stainless steel by vacuum induction melting provided by the present invention first pre-treats the raw materials and then charges and melts them. By using vacuum induction melting, the contact between the molten steel and the air is reduced, the desulfurization and deoxidation efficiency is improved, and by refining twice and adding a specific desulfurizing agent, the sulfur content of the final high-purity stainless steel is less than 7ppm, achieving the effect of deep desulfurization, thereby meeting the needs of the steel industry.

[0039] (2) The desulfurization method for high-purity stainless steel vacuum induction melting provided by the present invention uses calcium carbonate and aluminum nitrate as the main raw materials for the added desulfurizing agent. First, calcium carbonate powder is dispersed in deionized water to form a suspension. Then, aluminum nitrate is mixed with fatty alcohol polyoxyethylene ether and aged to pretreat the aluminum nitrate. This pretreatment can improve the mixing uniformity of aluminum nitrate and fatty alcohol polyoxyethylene ether, which is beneficial for the subsequent soft template method to prepare hollow alumina. It can also improve the heat resistance temperature of hollow alumina, making it less prone to cracking during calcination. Then, the pretreated aluminum nitrate is added to the calcium carbonate suspension for hydrothermal reaction, causing the aluminum nitrate to hydrolyze and form amorphous alumina. Then, sintering is performed to obtain alumina / calcium carbonate. Compared to direct blending, the composite material involves partially coating calcium carbonate with alumina, thereby increasing the bonding strength between the two. Another portion forms hollow alumina, improving the fluidity of the desulfurizing agent and thus enhancing its overall desulfurization performance. Finally, the alumina / calcium carbonate composite is impregnated in a solution of zirconium nitrate and nickel nitrate, and then calcined at high temperature to introduce zirconium and nickel rare earth metals. Simultaneously, calcium carbonate decomposes into calcium oxide, yielding the desulfurizing agent. This desulfurizing agent introduces hollow alumina and rare earth zirconium and nickel elements into the calcium oxide through hydrothermal and sintering methods. This improves the fluidity of the desulfurizing agent in molten steel, and the addition of alumina and zirconium / nickel accelerates the desulfurization reaction, increasing the utilization rate of calcium oxide and thus achieving deep desulfurization of the molten steel. Detailed Implementation

[0040] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. 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.

[0041] A method for desulfurization of high-purity stainless steel by vacuum induction melting includes the following steps:

[0042] S1. Material preparation: Select raw materials according to the composition of stainless steel, remove the oxide layer or rust layer on the surface, clean with anhydrous ethanol, and dry at 90-120℃ to remove anhydrous ethanol for later use.

[0043] S2, Charging and Melting: Add the raw materials prepared in step S1 into the magnesium oxide crucible. After the vacuum degree in the vacuum induction melting chamber is reduced to below 10 Pa, start powering on to melt the materials.

[0044] S3. Refining: After the main alloy material is melted, the temperature of the molten steel is heated to 1630-1680℃ and refined for 35-50 minutes.

[0045] S4. Deoxidation and desulfurization: After refining, add 0.5-1wt% of deoxidizing alloy and 1-2wt% of desulfurizing agent to the molten steel. Stir for 5-10 minutes, then fill the furnace with argon gas until the pressure reaches 80-90 kPa. Control the temperature at 1580-1610℃ and carry out deoxidation and desulfurization for 40-50 minutes.

[0046] S5. Secondary refining: Vacuum the furnace again to below 10Pa, control the temperature at 1500-1540℃, and refine the deoxidized and desulfurized molten steel again for 20-30 minutes.

[0047] S6. Casting: After refining, power is cut off and the temperature is reduced to 1480℃ for casting, thus completing the high-purity stainless steel smelting.

[0048] The deoxidizing alloy mentioned in step S4 is one or more of silicon, aluminum, and titanium;

[0049] The desulfurizing agent is prepared as follows:

[0050] (a) Add 50g of calcium carbonate powder to 400-500g of deionized water, then add 0.3-0.5g of polyvinylpyrrolidone, stir at 150-200r / min for 0.5-1h to disperse evenly and obtain a calcium carbonate suspension.

[0051] (b) Add 50g of aluminum nitrate to 150-200g of deionized water. After dissolution, add 0.4-0.8g of fatty alcohol polyoxyethylene ether AEO-9. Adjust the pH to 5-6 using sodium hydroxide solution and hydrochloric acid solution. Aged at room temperature for 4-6 hours and freeze-dried to obtain pretreated aluminum nitrate.

[0052] (c) Add 40-50g of pretreated aluminum nitrate to 450-550g of calcium carbonate suspension, disperse ultrasonically for 10-20min, and then hydrothermally react at 150-180℃ for 7-10h. After the reaction is completed, filter, wash, dry, and sinter at 550-650℃ for 3-5h to obtain solid powder.

[0053] (d) Add 50g of solid powder to 300mL of a mixed solution of zirconium nitrate and nickel nitrate (the concentration of zirconium nitrate is 30-40g / L and the concentration of nickel nitrate is 60-70g / L), and impregnate at 60-70℃ for 1-2h. After impregnation, filter and dry, and calcine at 850-900℃ for 4-6h to obtain the desulfurizing agent.

[0054] The present invention will be further described below through specific embodiments.

[0055] Example 1

[0056] A method for desulfurization of high-purity stainless steel by vacuum induction melting includes the following steps:

[0057] S1. Material preparation: Select raw materials according to the stainless steel composition, remove the oxide layer or rust layer on the surface, clean with anhydrous ethanol, and dry at 110℃ to remove the anhydrous ethanol for later use.

[0058] S2, Charging and Melting: Add the raw materials prepared in step S1 into the magnesium oxide crucible. After the vacuum degree in the vacuum induction melting chamber is reduced to below 10 Pa, start powering on to melt the materials.

[0059] S3. Refining: After the main alloy material is melted, a sample is taken to test the sulfur content. The temperature of the molten steel is heated to 1600℃ and refined for 40 minutes.

[0060] S4. Deoxidation and desulfurization: After refining, add 0.8wt% of metallic silicon and 1.5wt% of desulfurizing agent to the molten steel. Stir for 8 minutes, then fill the furnace with argon gas until the pressure reaches 80-90 kPa. Control the temperature at 1600℃ and carry out deoxidation and desulfurization for 45 minutes.

[0061] S5. Secondary refining: Vacuum the furnace again to below 10Pa, control the temperature at 1520℃, and refine the deoxidized and desulfurized molten steel for 25 minutes.

[0062] S6. Casting: After refining, power is cut off and the temperature is reduced to 1480℃ for casting to complete the high-purity stainless steel smelting. Sampling is performed again to test the sulfur content.

[0063] The preparation method of the desulfurizing agent in step S4 is as follows:

[0064] (a) Add 50g of calcium carbonate powder to 450g of deionized water, then add 0.4g of polyvinylpyrrolidone, stir at 180r / min for 1h to disperse evenly, and obtain a calcium carbonate suspension.

[0065] (b) Add 50g of aluminum nitrate to 150g of deionized water. After dissolution, add 0.6g of fatty alcohol polyoxyethylene ether AEO-9. Adjust the pH to 6 using sodium hydroxide solution and hydrochloric acid solution. Aged at room temperature for 5h and freeze-dried to obtain pretreated aluminum nitrate.

[0066] (c) Add 40g of pretreated aluminum nitrate to 500g of calcium carbonate suspension, disperse ultrasonically for 15min, and then hydrothermally react at 170℃ for 8h. After the reaction is completed, filter, wash, dry, and sinter at 600℃ for 4h to obtain solid powder.

[0067] (d) Add 50g of solid powder to 300mL of a mixed solution of zirconium nitrate and nickel nitrate (the concentration of zirconium nitrate is 35g / L and the concentration of nickel nitrate is 65g / L), and impregnate at 65℃ for 1.5h. After impregnation, filter and dry, and calcine at 880℃ for 5h to obtain the desulfurizing agent.

[0068] Example 2

[0069] A method for desulfurization of high-purity stainless steel by vacuum induction melting includes the following steps:

[0070] S1. Material preparation: Select raw materials according to the composition of stainless steel, remove the oxide layer or rust layer on the surface, clean with anhydrous ethanol, and dry at 100℃ to remove anhydrous ethanol for later use.

[0071] S2, Charging and Melting: Add the raw materials prepared in step S1 into the magnesium oxide crucible. After the vacuum degree in the vacuum induction melting chamber is reduced to below 10 Pa, start powering on to melt the materials.

[0072] S3. Refining: After the main alloy material is melted, a sample is taken to test the sulfur content. The temperature of the molten steel is heated to 1640℃ and refined for 45 minutes.

[0073] S4. Deoxidation and desulfurization: After refining, add 0.8wt% of metallic aluminum and 1.5wt% of desulfurizing agent to the molten steel. Stir for 10 minutes, then fill the furnace with argon gas until the pressure reaches 80-90 kPa. Control the temperature at 1590℃ and carry out deoxidation and desulfurization for 45 minutes.

[0074] S5. Secondary refining: Vacuum the furnace again to below 10Pa, control the temperature at 1530℃, and refine the deoxidized and desulfurized molten steel for 25 minutes.

[0075] S6. Casting: After refining, power is cut off and the temperature is reduced to 1480℃ for casting to complete the high-purity stainless steel smelting. Sampling is performed again to test the sulfur content.

[0076] The preparation method of the desulfurizing agent in step S4 is as follows:

[0077] (a) Add 50g of calcium carbonate powder to 450g of deionized water, then add 0.4g of polyvinylpyrrolidone, stir at 180r / min for 0.5h to disperse evenly and obtain a calcium carbonate suspension.

[0078] (b) Add 50g of aluminum nitrate to 200g of deionized water. After dissolution, add 0.6g of fatty alcohol polyoxyethylene ether AEO-9. Adjust the pH to 5 using sodium hydroxide solution and hydrochloric acid solution. Aged at room temperature for 5h and freeze-dried to obtain pretreated aluminum nitrate.

[0079] (c) Add 50g of pretreated aluminum nitrate to 500g of calcium carbonate suspension, disperse ultrasonically for 15min, and then hydrothermally react at 160℃ for 9h. After the reaction is completed, filter, wash, dry, and sinter at 600℃ for 4h to obtain solid powder.

[0080] (d) Add 50g of solid powder to 300mL of a mixed solution of zirconium nitrate and nickel nitrate (the concentration of zirconium nitrate is 35g / L and the concentration of nickel nitrate is 65g / L), and impregnate at 65℃ for 2h. After impregnation, filter and dry, and calcine at 870℃ for 5h to obtain the desulfurizing agent.

[0081] Example 3

[0082] A method for desulfurization of high-purity stainless steel by vacuum induction melting includes the following steps:

[0083] S1. Material preparation: Select raw materials according to the composition of stainless steel, remove the oxide layer or rust layer on the surface, clean with anhydrous ethanol, and dry at 90℃ to remove anhydrous ethanol for later use.

[0084] S2, Charging and Melting: Add the raw materials prepared in step S1 into the magnesium oxide crucible. After the vacuum degree in the vacuum induction melting chamber is reduced to below 10 Pa, start powering on to melt the materials.

[0085] S3. Refining: After the main alloy material is melted, a sample is taken to test the sulfur content. The temperature of the molten steel is heated to 1630℃ and refined for 50 minutes.

[0086] S4. Deoxidation and desulfurization: After refining, add 0.5wt% of metallic titanium and 2wt% of desulfurizing agent to the molten steel. Stir for 5 minutes, then fill the furnace with argon gas until the pressure reaches 80-90 kPa. Control the temperature at 1610℃ and carry out deoxidation and desulfurization for 40 minutes.

[0087] S5. Secondary refining: Vacuum the furnace again to below 10Pa, control the temperature at 1500℃, and refine the deoxidized and desulfurized molten steel again for 30 minutes.

[0088] S6. Casting: After refining, power is cut off and the temperature is reduced to 1480℃ for casting to complete the high-purity stainless steel smelting. Sampling is performed again to test the sulfur content.

[0089] The preparation method of the desulfurizing agent in step S4 is as follows:

[0090] (a) Add 50g of calcium carbonate powder to 400g of deionized water, then add 0.3g of polyvinylpyrrolidone, stir at 150r / min for 0.5h to disperse evenly and obtain a calcium carbonate suspension.

[0091] (b) Add 50g of aluminum nitrate to 150g of deionized water. After dissolution, add 0.4g of fatty alcohol polyoxyethylene ether AEO-9. Adjust the pH to 6 using sodium hydroxide solution and hydrochloric acid solution. Aged at room temperature for 6h and freeze-dried to obtain pretreated aluminum nitrate.

[0092] (c) Add 4g of pretreated aluminum nitrate to 450g of calcium carbonate suspension, disperse ultrasonically for 10min, and then hydrothermally react at 150℃ for 10h. After the reaction is completed, filter, wash and dry, and sinter at 550℃ for 5h to obtain solid powder.

[0093] (d) Add 50g of solid powder to 300mL of a mixed solution of zirconium nitrate and nickel nitrate (the concentration of zirconium nitrate is 30g / L and the concentration of nickel nitrate is 70g / L), and impregnate at 60℃ for 2h. After impregnation, filter and dry, and calcine at 850℃ for 6h to obtain the desulfurizing agent.

[0094] Example 4

[0095] A method for desulfurization of high-purity stainless steel by vacuum induction melting includes the following steps:

[0096] S1. Material preparation: Select raw materials according to the composition of stainless steel, remove the oxide layer or rust layer on the surface, clean with anhydrous ethanol, and dry at 120℃ to remove anhydrous ethanol for later use.

[0097] S2, Charging and Melting: Add the raw materials prepared in step S1 into the magnesium oxide crucible. After the vacuum degree in the vacuum induction melting chamber is reduced to below 10 Pa, start powering on to melt the materials.

[0098] S3. Refining: After the main alloy material is melted, a sample is taken to test the sulfur content. The temperature of the molten steel is heated to 1680℃ and refined for 35 minutes.

[0099] S4. Deoxidation and desulfurization: After refining, add 0.4wt% aluminum, 0.4wt% titanium and 1wt% desulfurizing agent to the molten steel. Stir for 10 minutes, then fill the furnace with argon gas until the pressure reaches 80-90 kPa. Control the temperature at 1610℃ and carry out deoxidation and desulfurization for 50 minutes.

[0100] S5. Secondary refining: Vacuum the furnace again to below 10Pa, control the temperature at 1540℃, and refine the deoxidized and desulfurized molten steel for 20 minutes.

[0101] S6. Casting: After refining, power is cut off and the temperature is reduced to 1480℃ for casting to complete the high-purity stainless steel smelting. Sampling is performed again to test the sulfur content.

[0102] The preparation method of the desulfurizing agent in step S4 is as follows:

[0103] (a) Add 50g of calcium carbonate powder to 500g of deionized water, then add 0.5g of polyvinylpyrrolidone, stir at 200r / min for 1h to disperse evenly, and obtain a calcium carbonate suspension.

[0104] (b) Add 50g of aluminum nitrate to 200g of deionized water. After dissolution, add 0.8g of fatty alcohol polyoxyethylene ether AEO-9. Adjust the pH to 5 using sodium hydroxide solution and hydrochloric acid solution. Aged at room temperature for 4 hours and freeze-dried to obtain pretreated aluminum nitrate.

[0105] (c) Add 50g of pretreated aluminum nitrate to 550g of calcium carbonate suspension, disperse ultrasonically for 20min, and then hydrothermally react at 180℃ for 7h. After the reaction is completed, filter, wash, dry, and sinter at 650℃ for 3h to obtain solid powder.

[0106] (d) Add 50g of solid powder to 300mL of a mixed solution of zirconium nitrate and nickel nitrate (the concentration of zirconium nitrate is 40g / L and the concentration of nickel nitrate is 60g / L), and impregnate at 70℃ for 1h. After impregnation, filter and dry, and calcine at 900℃ for 4h to obtain the desulfurizing agent.

[0107] Comparative Example 1

[0108] A method for desulfurization of high-purity stainless steel by vacuum induction melting includes the following steps:

[0109] S1. Material preparation: Select raw materials according to the stainless steel composition, remove the oxide layer or rust layer on the surface, clean with anhydrous ethanol, and dry at 110℃ to remove the anhydrous ethanol for later use.

[0110] S2, Charging and Melting: Add the raw materials prepared in step S1 into the magnesium oxide crucible. After the vacuum degree in the vacuum induction melting chamber is reduced to below 10 Pa, start powering on to melt the materials.

[0111] S3. Refining: After the main alloy material is melted, a sample is taken to test the sulfur content. The temperature of the molten steel is heated to 1600℃ and refined for 40 minutes.

[0112] S4. Deoxidation and desulfurization: After refining, add 0.8wt% of metallic silicon and 1.5wt% of desulfurizing agent to the molten steel. Stir for 8 minutes, then fill the furnace with argon gas until the pressure reaches 80-90 kPa. Control the temperature at 1600℃ and carry out deoxidation and desulfurization for 45 minutes.

[0113] S5. Secondary refining: Vacuum the furnace again to below 10Pa, control the temperature at 1520℃, and refine the deoxidized and desulfurized molten steel for 25 minutes.

[0114] S6. Casting: After refining, power is cut off and the temperature is reduced to 1480℃ for casting to complete the high-purity stainless steel smelting. Sampling is performed again to test the sulfur content.

[0115] The preparation method of the desulfurizing agent in step S4 is as follows:

[0116] (a) Add 50g of calcium carbonate powder to 450g of deionized water, then add 0.4g of polyvinylpyrrolidone, stir at 180r / min for 1h to disperse evenly, and obtain a calcium carbonate suspension.

[0117] (b) Add 40g of aluminum nitrate to 500g of calcium carbonate suspension, disperse by ultrasonication for 15min, and then hydrothermally react at 170℃ for 8h. After the reaction is completed, filter, wash and dry, and sinter at 600℃ for 4h to obtain the desulfurizing agent.

[0118] The sulfur content detection results of the samples before and after desulfurization in Examples 1-4 and Comparative Example 1 are shown in Table 1 below:

[0119] Table 1

[0120] Example 1 62 5 91.9 Example 2 65 6 90.7 Example 3 61 7 88.5 Example 4 53 5 90.5 Comparative Example 1 57 16 71.9

[0121] As can be seen from Table 1 above, the vacuum induction melting desulfurization method provided by the present invention has a desulfurization rate of up to 91.9%, and the sulfur content of the final high-purity stainless steel is below 7 ppm. It has a deep desulfurization effect on molten steel and has good application prospects.

[0122] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for desulfurization of high-purity stainless steel by vacuum induction melting, characterized in that, Includes the following steps: S1. Material preparation: Select raw materials according to the composition of stainless steel, remove the oxide layer or rust layer on the surface, clean with anhydrous ethanol, and dry after cleaning for later use. S2, Charging and Melting: Add the raw materials prepared in step S1 into the magnesium oxide crucible. After the vacuum degree in the vacuum induction melting chamber is reduced to below 10 Pa, start powering on to melt the materials. S3. Refining: After the main alloy material is melted, it is refined once. S4. Deoxidation and desulfurization: After refining, add deoxidizing alloy and desulfurizing agent to the molten steel, stir for 5-10 minutes, and then fill the furnace with argon gas until the pressure reaches 80-90KPa. Control the temperature at 1580-1610℃ and carry out deoxidation and desulfurization for 40-50 minutes. S5. Secondary refining: The furnace is evacuated again to below 10Pa to perform secondary refining on the deoxidized and desulfurized molten steel. S6. Casting: After the secondary refining is completed, the power is turned off and the temperature is reduced. The casting temperature is adjusted to 1480℃ and the casting is carried out to complete the high-purity stainless steel smelting. The preparation method of the desulfurizing agent in step S4 is as follows: (a) Add calcium carbonate powder to deionized water, then add polyvinylpyrrolidone, stir and disperse evenly to obtain a calcium carbonate suspension; (b) Add aluminum nitrate to deionized water, and after dissolution, add fatty alcohol polyoxyethylene ether AEO-9, adjust the pH to 5-6, age at room temperature, and freeze dry to obtain pretreated aluminum nitrate; (c) Add pretreated aluminum nitrate to calcium carbonate suspension, disperse ultrasonically, and then carry out hydrothermal reaction. After the reaction is completed, filter, wash, dry and sinter to obtain solid powder. (d) The solid powder is impregnated in a mixed solution of zirconium nitrate and nickel nitrate. After impregnation, the powder is filtered, dried and calcined to obtain the desulfurizing agent.

2. The method according to claim 1, characterized in that, The refining temperature in step S3 is 1630-1680℃, and the time is 35-50 minutes.

3. The method according to claim 1, characterized in that, The deoxidizing alloy mentioned in step S4 is one or more of silicon, aluminum, and titanium; the amount of deoxidizing alloy used is 0.5-1 wt% of the molten steel.

4. The method according to claim 1, characterized in that, The amount of desulfurizing agent used in step S4 is 1-2% of the molten steel.

5. The method according to claim 1, characterized in that, The mass ratio of calcium carbonate, deionized water, and polyvinylpyrrolidone in step (a) is 50:400-500:0.3-0.

5.

6. The method according to claim 1, characterized in that, In step (b), the mass ratio of aluminum nitrate, deionized water, and fatty alcohol polyoxyethylene ether AEO-9 is 50:150-200:0.4-0.8; the aging time is 4-6 hours.

7. The method according to claim 1, characterized in that, In step (c), the mass ratio of the pretreated aluminum nitrate and calcium carbonate suspension is 40-50:450-550; the hydrothermal reaction temperature is 150-180℃ and the time is 7-10h; the sintering temperature is 550-650℃ and the time is 3-5h.

8. The method according to claim 1, characterized in that, In step (d), the concentration of zirconium nitrate in the mixed solution is 30-40 g / L, and the concentration of nickel nitrate is 60-70 g / L; the impregnation temperature is 60-70℃, and the time is 1-2 h; the calcination temperature is 850-900℃, and the time is 4-6 h.

9. The method according to claim 1, characterized in that, In step S5, the temperature of the secondary refining is controlled at 1500-1540℃, and the time is 20-30 minutes.