Low-phosphorus steel and smelting method thereof

Abstract

The invention discloses low-phosphorus steel and a smelting method thereof. The technical problem that in the prior art, the phosphorus content is high is solved. The smelting method comprises the following steps that tapping is conducted after smelting of a steel smelting furnace is finished, a slag former is added in the tapping process to make oxidizing slag with the alkalinity being 4-10, and primary molten steel is obtained; carrying out VD vacuum refining on the primary smelting molten steel to obtain refined molten steel; and after slagging-off treatment is conducted on the refined molten steel, LF refining is conducted, and the low-phosphorus molten steel is obtained. According to the smelting method, the mass fraction of phosphorus is 8-20 ppm, and the dephosphorization effect is good.

Description

Technical Field

[0001] The present application belongs to the technical field of low-phosphorus steel smelting, and specifically relates to a low-phosphorus steel and a smelting method thereof. Background Art

[0002] With the high-quality development of the steel industry, the new generation of advanced steel materials has higher and higher requirements for the cleanliness of molten steel, especially the phosphorus content in steel, which poses new challenges to the control level of steelmaking process. Phosphorus is considered a harmful element in most steel grades. On the one hand, phosphorus is prone to segregation during the solidification process of molten steel, affecting the internal quality of the ingot; on the other hand, the increase in phosphorus content in steel will significantly reduce the low-temperature toughness and temper brittleness resistance of the material, and at the same time reduce the welding performance and corrosion fatigue resistance of the steel plate.

[0003] In the related technology, the patent with application number 202310776165.7 provides a smelting method for producing low-phosphorus steel based on a BOF converter. In the converter smelting process, the double slag retention steelmaking technology is used to obtain a dephosphorization rate of more than 95%, and then the argon blowing station oxidizing slag stirring dephosphorization technology is used to make the argon blowing station dephosphorization rate reach more than 50%, and an ultra-low phosphorus steel liquid with P≤0.005% can be obtained.

[0004] This smelting method allows the P content to be removed to 20-50ppm, and there is still room for improvement. Summary of the invention

[0005] In order to solve the current technical problem of smelting high P content, the present application provides a low-phosphorus steel and a smelting method thereof.

[0006] In a first aspect of the present application, a method for smelting low-phosphorus steel is provided, comprising the following steps:

[0007] After the steelmaking furnace is finished smelting, the steel is tapped. During the tapping process, a slag-making agent is added to make an oxidizing slag with a basicity of 4 to 10 to obtain primary molten steel;

[0008] Vacuum refining the primary molten steel by VD to obtain refined molten steel;

[0009] The refined molten steel is subjected to LF refining after slagging treatment to obtain low-phosphorus molten steel.

[0010] In some embodiments, the composition of the oxidizing slag is: CaO: 45-55%, SiO2: 5.5-12.0%, FeO: 17-35%, MgO: 6-10%, MnO: 1.5-5.0%, Al2O3: 1.5-3.0%, and the rest are unavoidable impurities.

[0011] In some embodiments, the amount of the oxidizing slag is 5-8 Kg / t steel.

[0012] In some embodiments, the difference between the tapping temperature and the liquidus temperature of the smelting steel is 130°C to 150°C; the difference between the temperature of the molten steel at the end of the VD refining and the liquidus temperature of the smelting steel is 85°C to 105°C; the difference between the temperature of the molten steel at the end of the LF refining and the liquidus temperature of the smelting steel is 50°C to 70°C; the intensity of argon blowing at the bottom of the ladle during the tapping process is 0.5-1.0NL / (min·t steel).

[0013] In some embodiments, the steelmaking furnace has an endpoint carbon content of 0.02-0.06% and an oxygen activity of 200-1000 ppm.

[0014] In some embodiments, during the VD vacuum refining process, the vacuum degree is ≤67 Pa, the intensity of the bottom blowing argon is 1.5-4.0NL / (min·t steel), and the vacuum refining time is >12 min.

[0015] In some embodiments, the VD vacuum refining end temperature is 1600° C. to 1620° C., and after the VD vacuum refining is completed, the slag is removed so that the area of ​​the exposed bright surface of the molten steel accounts for no less than 90%.

[0016] In some embodiments, during the LF refining process: the mass fraction of aluminum in the molten steel is ≥0.03%, and the intensity of the bottom blowing argon is 2.0-7.0 NL / (min·t steel).

[0017] In some embodiments, when the LF refining is completed, the slag consists of the following components: CaO: 50-58%, SiO2: 5-10%, (FeO+MnO)%<1%, MgO: 6-10%, Al2O3: 25-30%, P2O5<0.2%, and the rest are unavoidable impurities, and the basicity of the slag is 5-12.

[0018] In a second aspect of the present application, there is provided a low-phosphorus steel obtained by smelting using the aforementioned low-phosphorus steel smelting method.

[0019] According to the embodiment of the present application, the low-phosphorus steel and the smelting method thereof provided include the following steps: tapping the steel after the smelting in the steelmaking furnace is completed, adding a slag-making agent during the tapping process to make an oxidizing slag with a basicity of 4 to 10 to obtain a primary molten steel; subjecting the primary molten steel to VD vacuum refining to obtain a refined molten steel; and subjecting the refined molten steel to LF refining after slagging treatment to obtain a low-phosphorus molten steel.

[0020] The present application performs VD and then LF on the molten steel after preliminary smelting, and at the same time controls the basicity of the oxidizing slag entering the VD station, and utilizes the thermodynamic conditions of high basicity of the oxidizing slag, the kinetic conditions of good VD vacuum reaction, and the thermodynamic conditions of low VD vacuum stirring temperature, so that the phosphorus in the molten steel can be removed to below 0.002%, thereby improving the dephosphorization effect; without adding additional production processes, and without increasing the burden on the dephosphorization link of steelmaking furnaces such as converters or electric furnaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A process step diagram of a method for smelting low-phosphorus steel in one or more embodiments of the present application is shown. DETAILED DESCRIPTION

[0022] In order to make the technical personnel in the technical field to which the present application belongs to understand the present application more clearly, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0023] The first aspect of the present application provides a method for smelting low-phosphorus steel, which can stably produce low-phosphorus steel with a phosphorus content not exceeding 0.002%, and the smelting process is not complicated, and the production process and smelting cycle are not increased.

[0024] See also Figure 1 The smelting method of low-phosphorus steel provided in the embodiment of the present application comprises the following steps:

[0025] S1: After the steelmaking furnace is finished smelting, steel is tapped. During the tapping process, a slag-making agent is added to make an oxidizing slag with a basicity of 4 to 10 to obtain primary molten steel;

[0026] S2: vacuum refining the primary molten steel VD to obtain refined molten steel;

[0027] S3: performing LF refining on the refined molten steel after slagging treatment to obtain low-phosphorus molten steel.

[0028] The present application adopts a process of first VD vacuum refining and then LF refining. Before VD vacuum refining, high-basicity and high-oxidizing slag is produced. During the VD vacuum refining process, the oxidizing slag can absorb the heat of the molten steel and melt quickly, while reducing the temperature of the molten steel, thereby creatively creating good dephosphorization thermodynamic conditions of high basicity, high oxidizing property and low temperature. At the same time, the slag and steel are fully stirred and mixed during the VD vacuum refining, which provides good dephosphorization kinetic conditions, so that the phosphorus content after the VD vacuum refining can be reduced to below 0.002%; after the VD refining is completed, the slag is removed to avoid rephosphorization, thereby ensuring the dephosphorization effect of the VD vacuum refining.

[0029] The basicity of oxidizing slag refers to the ratio of calcium oxide to silicon dioxide in the slag. Controlling the basicity of oxidizing slag to 4-10 increases the basicity of dephosphorization slag, which is beneficial to improving the dephosphorization effect. If the basicity of oxidizing slag is too high, the melting temperature of slag increases, the liquid phase rate decreases, and the fluidity deteriorates, which affects the dephosphorization reaction from a kinetic perspective. If the basicity of oxidizing slag is too low, the CaO content in the slag is low, which affects the dephosphorization reaction from a thermodynamic perspective. The use of oxidizing slag with a high FeO content is beneficial to improving the dephosphorization effect during VD vacuum refining.

[0030] The smelting process of low-phosphorus steel is steelmaking, VD vacuum refining and LF refining, and then sent to continuous casting for casting. In some embodiments, in order to reduce the sulfur content of the smelted steel, the molten iron may be pre-desulfurized first, and then steelmaking, VD vacuum refining and LF refining are carried out. The "content" in this application refers to the mass fraction of a certain element in the molten steel. For example, the carbon content of the molten steel refers to the mass fraction of carbon in the molten steel. After understanding the meaning of the above "content", the specific process of each step is described in detail below:

[0031] Hot metal pre-desulfurization is used to desulfurize hot metal provided by an ironmaking furnace such as a blast furnace. In some embodiments, the smelting steel grade has extremely low sulfur content requirements. Therefore, hot metal pre-desulfurization is performed before converter smelting to reduce the sulfur content of the source hot metal and reduce the desulfurization pressure of subsequent processes. After the hot metal pre-desulfurization is completed, the desulfurization slag can be removed to avoid resulfurization. In some embodiments, the bright surface area of ​​the hot metal surface after the desulfurization slag is removed can be no less than 95%, and the sulfur content in the hot metal after the hot metal pretreatment is completed does not exceed 0.002%.

[0032] Steelmaking mainly involves decarburization and heating of molten iron, which can be done by converter or electric furnace. In some embodiments, the composition of the oxidizing slag is: CaO: 45-55%, SiO2: 5.5-12.0%, FeO: 17-35%, MgO: 6-10%, MnO: 1.5-5.0%, Al2O3: 1.5-3.0%, and the rest are unavoidable impurities.

[0033] The higher the FeO mass fraction, the stronger the oxidizing property of the oxidizing slag, which is more conducive to the dephosphorization of molten steel in the VD vacuum refining stage. If the FeO mass fraction is too high, on the one hand, the metal recovery rate will be reduced, and on the other hand, the converter lining will be seriously corroded; if the FeO mass fraction is too low, the oxidizing property of the oxidizing slag will be reduced, which will directly affect the dephosphorization reaction of the slag.

[0034] In some embodiments, the slag amount of the oxidizing slag is 5-8 kg / t steel. The large slag amount of the oxidizing slag is beneficial to the dephosphorization of the molten steel in the VD vacuum refining stage. If the slag amount of the oxidizing slag is too small, the dephosphorization effect will be reduced to a certain extent. If the slag amount of the oxidizing slag is too large, slag overflow will occur during the VD vacuum stirring process, affecting normal production. In some embodiments, the slag-making agent may include materials such as lime and fluorite, and the ratio of lime to fluorite may be 4:1.

[0035] In some embodiments, the difference between the converter tapping temperature and the liquidus temperature of the smelting steel is 130°C to 150°C. The purpose is that on the one hand, the converter tapping at a lower temperature will ensure the dephosphorization effect of the converter process; on the other hand, it can ensure that the temperature of the molten steel is low during the VD vacuum refining stage, which is convenient for dephosphorization and can catch up with casting. If the converter tapping temperature is too high, it will cause the VD vacuum refining molten steel temperature to be high to a certain extent, which is not conducive to the dephosphorization of the molten steel. If the converter tapping temperature is too low, it will cause the molten steel to fail to catch up with the casting to a certain extent.

[0036] In order to improve the dephosphorization effect, in some embodiments, the converter smelting can also adopt one of the duplex method, double slag method and single slag method, so that the phosphorus content at the end of the converter smelting is ≤0.01%, and the sulfur content of the molten steel at the end of the converter smelting is ≤0.008%.

[0037] In some embodiments, the carbon content at the converter end point is 0.02-0.06%, and the oxygen activity is 200-1000ppm; the slag amount at the converter tapping does not exceed 10kg / t steel. The purpose of controlling the oxygen activity in the molten steel at the converter end point is to remove carbon from the steel through the carbon-oxygen reaction in the VD vacuum refining process to produce low-carbon steel. If the oxygen activity is too high, it will, to a certain extent, cause a large amount of deoxidizer to be added after decarburization is completed to remove excess oxygen, increasing costs. If the oxygen activity is too low, to a certain extent, it will not provide enough carbon-oxygen reaction to remove carbon from the steel, so that the carbon content will not drop to the required range.

[0038] In some embodiments, the intensity of argon blowing at the bottom of the ladle during the converter steel tapping process is 0.5-1.0NL / (min·t steel), that is, soft blowing is performed on the molten steel to prevent the added slag from agglomerating and promote slag removal.

[0039] VD vacuum refining is a process of removing carbon from molten steel through slag steel circulation. In some embodiments, the difference between the temperature of the molten steel at the end of VD refining and the liquidus temperature of the smelting steel grade is 85°C to 105°C, in order to minimize the temperature drop during the VD vacuum process and reduce the subsequent LF temperature rise burden.

[0040] In some embodiments, the VD vacuum refining end temperature is 1600° C. to 1620° C. If the temperature of the molten steel at the end of VD refining is too high, the dephosphorization effect of the molten steel in the VD vacuum refining will be reduced to a certain extent. If the temperature of the molten steel at the end of VD refining is too low, the molten steel will not be able to keep up with the casting to a certain extent.

[0041] In certain embodiments, during the VD vacuum refining process, the vacuum degree is ≤67Pa, the intensity of the bottom blowing argon is 1.5-4.0NL / (min·t steel), and the vacuum refining time is greater than 12min. Controlling the vacuum degree is beneficial to removing carbon from the molten steel, strengthening stirring, and promoting the slag and steel to be fully mixed to cause dephosphorization reaction. If the intensity of the bottom blowing argon is too high, it will cause severe churning of the molten steel to a certain extent, increasing the temperature drop. If the bottom blowing argon is too low, it will cause the slag and steel to not be fully mixed to a certain extent, affecting the efficiency of the dephosphorization reaction. If the vacuum refining time is too long, the temperature drop of the molten steel will increase to a certain extent. If the vacuum refining time is too short, the effect of slag dephosphorization will be affected to a certain extent due to the short sufficient contact time between the slag and steel.

[0042] In order to avoid rephosphorization in the LF refining stage, in some embodiments, the slag is removed after the VD vacuum refining, so that the exposed bright surface area of ​​the molten steel accounts for no less than 90%. If the slag is not removed thoroughly after the VD vacuum refining, it will not only cause rephosphorization, but also affect the desulfurization effect.

[0043] The LF refining stage heats up the molten steel for desulfurization. In some embodiments, the difference between the temperature of the molten steel at the end of the LF refining and the liquidus temperature of the smelting steel grade is 50°C to 70°C. In some embodiments, the temperature of the molten steel at the end of the LF refining is 1570-1590°C. The purpose is to improve the desulfurization effect and ensure smooth continuous casting. If the temperature of the molten steel is too high at the end of the LF refining, it will increase the burden of LF heating to a certain extent. On the other hand, it will increase the superheat of the molten steel during continuous casting and affect the quality of the ingot. If the temperature of the molten steel is too low at the end of the LF refining, it will reduce the temperature of the molten steel during continuous casting to a certain extent, affecting the smooth continuous casting.

[0044] In certain embodiments, during the LF refining process: the mass fraction of aluminum in the molten steel is ≥0.03%, the intensity of the bottom blowing argon is 2.0-7.0NL / (min·t steel), and the amount of slag material added is 8-10Kg / t steel. The purpose of controlling the mass fraction of aluminum in LF refining is to reduce the oxygen content in the steel and ensure the smooth progress of desulfurization. If the mass fraction of aluminum is too high, the cost of the deoxidizer will increase to a certain extent. On the other hand, the aluminum content exceeds the requirements of the steel grade, affecting the product quality. If the mass fraction of aluminum is too low, deoxidation will be incomplete to a certain extent, because desulfurization must be preceded by deoxidation, which in turn affects the normal progress of the desulfurization reaction. The role of bottom blowing argon is to promote the mixing of slag and steel in the LF refining process and ensure that the refined slag fully removes sulfur from the steel. If the intensity of argon is too high, the temperature drop of the molten steel will increase to a certain extent. On the other hand, excessive stirring will increase the exposure of the molten steel and cause secondary oxidation of the molten steel by air. If the intensity of argon is too low, the stirring and mixing between the slag and steel will be weakened to a certain extent, and the mass transfer of sulfur in the steel will be reduced, which will kinetically limit the progress of the desulfurization reaction.

[0045] Slag-making materials are used to make reducing slag for desulfurization in the LF refining process. If the quality of slag-making materials is too high, it will increase the difficulty of slagging to a certain extent, increase the LF temperature rise burden, and increase the cost. If the quality of slag-making materials is too low, it will reduce the sulfur content of the refined slag to a certain extent and reduce the desulfurization rate.

[0046] In some embodiments, at the end of the LF refining, the slag consists of the following components: CaO: 50-58%, SiO2: 5-10%, (FeO+MnO)% <1%, MgO: 6-10%, Al2O3: 25-30%, P2O5 <0.2%, and the rest is impurity elements, and the basicity of the slag is 5-12. The high-basicity, low-reducibility slag has a super desulfurization ability on the one hand, and on the other hand, the control of P2O5 in the slag <0.2% inhibits the phosphorus in the slag from entering the molten steel again, causing the molten steel to rephosphorize, thereby ensuring the ultra-low phosphorus content of the molten steel.

[0047] The second aspect of the present application provides a low-phosphorus steel obtained by smelting the low-phosphorus steel smelting method according to any embodiment of the first aspect.

[0048] The low-phosphorus steel smelting method provided in the present application will be further described below in conjunction with specific embodiments.

[0049] Embodiment 1:

[0050] Steel type: Ultra-low temperature container steel. The process route adopted is: KR molten iron desulfurization—200-ton converter smelting—VD—LF—continuous casting.

[0051] KR hot metal desulfurization pretreatment: KR stirring desulfurization is used, and the [S] in the hot metal after desulfurization is 0.0005%; slag removal treatment is carried out after desulfurization, and the slag bright surface reaches 98%.

[0052] Converter smelting: double slag method is used for dephosphorization. The phosphorus content of molten steel at the end of smelting is 0.008%, the sulfur content is 0.0070%, the carbon content of molten steel is 0.04%, the oxygen activity is 550ppm, and the converter tapping temperature is 1665℃. 7Kg / t of slag material is added with the steel flow during converter tapping, in which the ratio of lime to fluorite in the slag material is 4:1. The argon gas flow rate of the ladle bottom during tapping is controlled at 0.9NL / (min·t steel), and the slag amount under tapping is 6kg / t steel.

[0053] VD vacuum refining: The composition R of the VD incoming slag is 5.7, and the contents of each component are shown in Table 1. The rest are impurity element contents. The bottom blowing argon flow rate during the VD vacuum refining process is 2.3NL / (min·t steel). When the VD vacuum degree is ≤67Pa, the deep vacuum treatment time is 12min, the carbon content of the molten steel is 0.005%, the phosphorus content of the molten steel is 0.0019%, and the temperature of the molten steel is 1605℃. After VD refining, the dephosphorization slag is removed, and the slag bright surface reaches 92%.

[0054] LF furnace refining: LF refining is carried out by heating deoxidation, slagging and deep desulfurization. The amount of slag material added in refining is 9kg / t steel. The basicity R of the slag at the end of refining is 8, and the composition is shown in Table 2. The rest are impurity elements. The bottom blowing flow rate during the refining and desulfurization process is controlled at 3.5NL / (min·t steel). The aluminum content of the molten steel is 0.035%. At the end of refining, the sulfur content of the molten steel is 0.0020%, the phosphorus content of the molten steel is 0.0020%, and the carbon content of the molten steel is 0.02%.

[0055] Continuous Casting: Continuous casting is normal casting.

[0056] Embodiment 2:

[0057] Steel type: low temperature pipeline steel, the process route adopted is: magnesium injection molten iron desulfurization - 100-ton electric furnace smelting - VD - LF - continuous casting.

[0058] Magnesium spraying hot metal desulfurization pretreatment: Magnesium spraying hot metal desulfurization pretreatment is used, and the [S] in the hot metal after desulfurization is 0.0020%; slag removal treatment is carried out after desulfurization, and the slag bright surface reaches 98%.

[0059] Electric furnace smelting: The phosphorus content of the molten steel at the end of smelting is 0.007%, the sulfur content is 0.0075%, the carbon content of the molten steel is 0.03%, the oxygen activity is 800ppm, and the tapping temperature is 1657℃. 8Kg / t of slag material is added with the steel flow, in which the ratio of lime to fluorite in the slag material is 4:1, and the argon gas flow rate of the ladle bottom blowing during the tapping process is controlled to 0.9NL / (min·t steel).

[0060] VD vacuum refining: The composition R of VD incoming slag is 6, and the composition can be seen in Table 1. The rest is the content of impurity elements. The bottom blowing argon flow rate during VD vacuum refining is 3.0NL / (min·t steel). When the VD vacuum degree is ≤67Pa, the deep vacuum treatment time is 18min, the carbon content of the molten steel is 0.003%, the phosphorus content of the molten steel is 0.0007%, and the temperature of the molten steel is 1609℃. After VD refining, the dephosphorization slag is removed, and the slag bright surface reaches 97%.

[0061] LF furnace refining: LF refining is carried out by heating, deoxidation, slag making and deep desulfurization. The amount of slag material added is 10kg / t steel. The composition of slag after refining is as follows: basicity R is 9. The contents of various components in the slag are shown in Table 2. The rest are impurity elements. The bottom blowing flow rate during the refining and desulfurization process is controlled at 5.0NL / (min·t steel). The aluminum content of the molten steel is 0.04%. At the end of refining, the sulfur content of the molten steel is 0.0016%, the phosphorus content of the molten steel is 0.0008%, and the carbon content of the molten steel is 0.01%.

[0062] Continuous Casting: Continuous casting is normal casting.

[0063] Embodiment 3:

[0064] Steel type: Ultra-low temperature container steel. The process route adopted is: KR molten iron desulfurization—200-ton converter smelting—VD—LF—continuous casting.

[0065] KR hot metal desulfurization pretreatment: KR stirring desulfurization is used, and the [S] in the hot metal after desulfurization is 0.0005%; slag removal treatment is carried out after desulfurization, and the slag bright surface reaches 98%.

[0066] Converter smelting: double slag method is used for dephosphorization. The phosphorus content of molten steel at the end of smelting is 0.008%, the sulfur content is 0.0070%, the carbon content of molten steel is 0.04%, the oxygen activity is 550ppm, and the converter tapping temperature is 1665℃. 6Kg / t of slag material is added with the steel flow during converter tapping, in which the ratio of lime to fluorite in the slag material is 4:1. The argon gas flow rate of the ladle bottom during tapping is controlled at 0.8NL / (min·t steel), and the slag amount under tapping is 6kg / t steel.

[0067] VD vacuum refining: The composition R of the VD incoming slag is 7.3, and the contents of each component are shown in Table 1. The rest are impurity element contents. The bottom blowing argon flow rate during the VD vacuum refining process is 2.6NL / (min·t steel). When the VD vacuum degree is ≤67Pa, the deep vacuum treatment time is 13min, the carbon content of the molten steel is 0.004%, the phosphorus content of the molten steel is 0.0014%, and the temperature of the molten steel is 1608℃. After VD refining, the dephosphorization slag is removed, and the slag bright surface reaches 92%.

[0068] LF furnace refining: LF refining is carried out by heating deoxidation, slagging and deep desulfurization. The amount of slag material added in refining is 8kg / t steel. The basicity R of the slag after refining is 9.1. The composition is shown in Table 2, and the rest are impurity elements. The bottom blowing flow rate during refining and desulfurization is controlled at 4NL / (min·t steel). The aluminum content of the molten steel is 0.035%. The sulfur content of the molten steel at the end of refining is 0.0011%, the phosphorus content of the molten steel is 0.0015%, and the carbon content of the molten steel is 0.02%.

[0069] Continuous Casting: Continuous casting is normal casting.

[0070] Example 4

[0071] Steel type: Ultra-low temperature container steel. The process route adopted is: KR molten iron desulfurization—200-ton converter smelting—VD—LF—continuous casting.

[0072] KR hot metal desulfurization pretreatment: KR stirring desulfurization is used, and the [S] in the hot metal after desulfurization is 0.0005%; slag removal treatment is carried out after desulfurization, and the slag bright surface reaches 98%.

[0073] Converter smelting: double slag method is used for dephosphorization. The phosphorus content of molten steel at the end of smelting is 0.008%, the sulfur content is 0.007%, the carbon content of molten steel is 0.02%, the oxygen activity is 550ppm, and the converter tapping temperature is 1665℃. 6Kg / t of slag material is added with the steel flow during converter tapping, in which the ratio of lime to fluorite in the slag material is 4:1. The argon gas flow rate of the ladle bottom during tapping is controlled at 0.8NL / (min·t steel), and the slag amount under tapping is 6kg / t steel.

[0074] VD vacuum refining: The composition R of VD incoming slag is 8.7, and the contents of each component are shown in Table 1. The rest are impurity elements. The bottom blowing argon flow rate during VD vacuum refining is 2.6NL / (min·t steel). When the VD vacuum degree is ≤67Pa, the deep vacuum treatment time is 13min, the carbon content of the molten steel is 0.003%, the phosphorus content of the molten steel is 0.0011%, and the temperature of the molten steel is 1610℃. After VD refining, the dephosphorization slag is removed, and the slag bright surface reaches 92%.

[0075] LF furnace refining: LF refining is carried out by heating, deoxidation, slag making and deep desulfurization. The amount of slag making material added in refining is 8kg / t steel. The basicity R of the slag at the end of refining is 9.7. The composition is shown in Table 2, and the rest are impurity elements. The bottom blowing flow rate during the refining and desulfurization process is controlled at 4NL / (min·t steel). The aluminum content of the molten steel is 0.035%. At the end of refining, the sulfur content of the molten steel is 0.0012%, the phosphorus content of the molten steel is 0.0012%, and the carbon content of the molten steel is 0.01%.

[0076] Continuous Casting: Continuous casting is normal casting.

[0077] Comparative Example 1 :

[0078] Comparative Example 1 provides a smelting method, which is based on Example 1. The difference between Comparative Example 1 and Example 1 is that the amount of slag added along with the steel flow during the converter steel tapping process is 4 kg / t steel, and the other smelting process controls are the same as those in Example 1.

[0079] Comparative Example 2 :

[0080] Comparative Example 2 provides a smelting method, which is based on Example 2. The difference between Comparative Example 1 and Example 2 is that the bright surface area after slag removal after VD refining is 85%, and other smelting process controls are the same as those in Example 2.

[0081] Table 1 Oxidizing slag composition serial number R CaO / % <![CDATA[SiO2 / %]]> FeO / % MgO / % MnO / % <![CDATA[Al2O3 / %]]> Example 1 5.7 57 10 21 8 1.9 2.1 Example 2 6 56.2 9.4 23 8 1.5 1.9 Example 3 7.3 54.3 7.4 27 7 2.1 2.2 Example 4 8.7 48.8 5.6 30 9 3.2 2.4 Comparative Example 1 3.9 49.0 12.6 26 8 2.3 2.1 Comparative Example 2 8.1 53.2 6.5 29 7 2.0 2.3

[0082] Table 2 LF refined slag composition serial number R CaO / % <![CDATA[SiO2 / %]]> (FeO+MnO) / % MgO / % <![CDATA[Al2O3 / %]]> <![CDATA[P2O5 / %]]> Example 1 7.6 53.9 7.1 0.74 7 26 0.16 Example 2 8.3 57.1 6.9 0.83 7 28 0.17 Example 3 9.1 55.0 6.0 0.95 9 29 0.15 Example 4 9.7 57.2 5.8 0.82 6 30 0.18 Comparative Example 1 4.9 57.1 11.7 1.04 8 22 0.16 Comparative Example 2 8.6 57.9 6.7 1.17 7 27 0.23

[0083] Table 3

[0084] Table 3 shows the control of carbon, phosphorus and sulfur elements in the smelting process of low-phosphorus steel provided by Examples 1 to 4 and Comparative Examples 1 to 2.

[0085] As can be seen from Table 3, in the smelting methods of low-phosphorus steel provided in Examples 1 to 4 of the present application, the mass fraction of phosphorus after VD refining is 7-19 ppm, and the mass fraction of phosphorus after LF refining is 8-20 ppm, which is low in phosphorus content. The mass fraction of carbon after LF refining is 0.01-0.02%, which is low in carbon content.

[0086] In the low-phosphorus steel smelting method provided in Comparative Example 1, the amount of oxidizing slag is too small, the mass fraction of phosphorus after VD refining is 52 ppm, and the mass fraction of phosphorus after LF refining is 54 ppm, and the phosphorus content is high.

[0087] In the low-phosphorus steel smelting method provided in Comparative Example 2, the proportion of bright surface after VD refining is 85%, the slag removal is not thorough enough, the mass fraction of phosphorus after VD refining is 7ppm, and the mass fraction of phosphorus after LF refining is 10ppm. The phosphorus content is low, and the surface slag removal is not thorough, which will cause phosphorus regeneration. The mass fraction of sulfur after LF refining is 33ppm, and the incomplete surface slag removal will also affect the desulfurization effect to a certain extent.

[0088] The smelting method of low-phosphorus steel provided in this application has at least the following advantages:

[0089] (1) After the preliminary smelting, the molten steel is first subjected to VD and then to LF, and the basicity of the oxidizing slag entering the VD station is controlled at the same time. By utilizing the thermodynamic conditions of high basicity of the oxidizing slag, the kinetic conditions of good VD vacuum reaction, and the thermodynamic conditions of low VD vacuum stirring temperature, the phosphorus in the molten steel can be removed to below 0.002%, thereby improving the dephosphorization effect and ensuring the decarburization effect. No additional production process is added, and the burden of the dephosphorization link of the steelmaking furnace, such as the converter or electric furnace, is not increased.

[0090] (2) Prolonging the VD deep vacuum time can reduce the phosphorus content to below 0.001%. After the VD is completed, the highly oxidizing dephosphorization slag is removed, which, on the one hand, avoids the rephosphorization in the subsequent LF refining process, and on the other hand, creates conditions for desulfurization in the LF refining process.

[0091] (3) Hot metal desulfurization pretreatment takes advantage of low-cost and high-efficiency deep desulfurization to reduce the sulfur content of hot metal entering the primary smelting furnace to below 0.001%, laying the foundation for controlling the sulfur content of molten steel in the entire process.

[0092] (4) Without increasing the production process and cycle, the low-phosphorus steel smelting method provided in the present application can stably produce low-carbon, low-phosphorus, and low-sulfur steel grades with C≤0.02%, S≤0.002%, and P≤0.002%, providing a guarantee for the production of ultra-clean steel.

[0093] In the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0094] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise" and "counterclockwise" indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0095] In this application, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0096] In addition, the descriptions of "first", "second", etc. in this application are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include one or more features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0097] Although the embodiments of the present application have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present application, and that the scope of the present application is defined by the claims and their equivalents.

Claims

1. A method for smelting low-phosphorus steel, characterized in that: The steps include: After the steelmaking furnace is finished smelting, the steel is tapped. During the tapping process, a slag-making agent is added to make an oxidizing slag with a basicity of 4 to 10 to obtain primary molten steel; Vacuum refining the primary molten steel by VD to obtain refined molten steel; The refined molten steel is subjected to LF refining after slagging treatment to obtain low-phosphorus molten steel.

2. The method for smelting low-phosphorus steel according to claim 1, characterized in that: The composition of the oxidizing slag is: CaO: 45-55%, SiO2: 5.5-12.0%, FeO: 17-35%, MgO: 6-10%, MnO: 1.5-5.0%, Al2O3: 1.5-3.0%, and the rest are inevitable impurities.

3. The smelting method of low-phosphorus steel according to claim 1, characterized in that: The amount of the oxidizing slag is 5-8 kg / t steel.

4. The method for smelting low-phosphorus steel according to claim 1, characterized in that: The difference between the steel tapping temperature and the liquidus temperature of the smelting steel grade is 130°C to 150°C; the difference between the temperature of the molten steel at the end of the VD refining and the liquidus temperature of the smelting steel grade is 85°C to 105°C; the difference between the temperature of the molten steel at the end of the LF refining and the liquidus temperature of the smelting steel grade is 50°C to 70°C; the intensity of argon blowing at the bottom of the ladle during the steel tapping process is 0.5-1.0NL / (min·t steel).

5. The method for smelting low-phosphorus steel according to any one of claims 1 to 4, characterized in that: The steelmaking furnace has an endpoint carbon content of 0.02-0.06% and an oxygen activity of 200-1000 ppm.

6. The method for smelting low-phosphorus steel according to any one of claims 1 to 4, characterized in that: During the VD vacuum refining process, the vacuum degree is ≤67Pa, the intensity of the bottom blowing argon is 1.5-4.0NL / (min·t steel), and the vacuum refining time is >12min.

7. The method for smelting low-phosphorus steel according to any one of claims 1 to 4, characterized in that: The VD vacuum refining end temperature is 1600° C. to 1620° C. After the VD vacuum refining is finished, the slag is removed so that the exposed bright surface area of ​​the molten steel accounts for no less than 90%.

8. The method for smelting low-phosphorus steel according to any one of claims 1 to 4, characterized in that: In the LF refining process, the mass fraction of aluminum in the molten steel is ≥0.03%, the intensity of bottom blowing argon is 2.0-7.0NL / (min·t steel), and the amount of slag material added is 8-10Kg / t steel.

9. The method for smelting low-phosphorus steel according to claim 8, characterized in that: in, When the LF refining is finished, the slag consists of the following components: CaO: 50-58%, SiO2: 5-10%, (FeO+MnO)%<1%, MgO: 6-10%, Al2O3: 25-30%, P2O5<0.2%, and the rest are inevitable impurities. The basicity of the slag is 5-12.

10. A low-phosphorus steel, characterized in that: The steel is obtained by smelting using the low-phosphorus steel smelting method described in any one of claims 1 to 9.

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