A method for controlling slag overflow in a VD refining ladle of CrMo steel

Abstract

This invention relates to the field of alloy production technology, specifically disclosing a method for controlling slag overflow in the ladle during the VD refining of CrMo steel. In the electric arc furnace tapping stage, aluminum ingots, alloys, and slag are added in batches for rapid deoxidation and initial adjustment of slag composition and basicity. After tapping, aluminum wire is fed in to further reduce oxygen content, creating conditions for subsequent refining. In the LF refining process, a silica-calcium wire is fed in to transform alumina into easily floating calcium aluminate. Combined with precise control of the proportions of each component in the slag system, slag viscosity and surface tension are reduced, improving dephosphorization and desulfurization efficiency and reducing foam slag formation. In the VD vacuum smelting stage, the argon flow rate is dynamically adjusted according to the vacuum level and slag surface condition to achieve a balance between efficient degassing and slag surface stability. This process reduces the slag overflow rate in the VD refining process from 100% to below 3%, the temperature drop from 80℃ to 50℃, significantly reduces the hydrogen content in the molten steel, and lowers the level of inclusions. This not only effectively controls the risk of slag overflow but also improves the purity of the molten steel.

Description

Technical Field

[0001] This invention relates to the field of alloy production technology, and in particular to a method for controlling slag overflow in the ladle during VD refining of CrMo steel. Background Technology

[0002] In modern steel metallurgy, CrMo steel, with its high strength, high toughness, and good fatigue resistance, is widely used in key industries such as machinery manufacturing and energy chemicals. VD (vacuum degassing) refining, as a core process for improving the quality of CrMo steel, significantly optimizes the purity and performance of the steel through degassing, desulfurization, and inclusion removal in a vacuum environment. However, during VD refining, ladle overflow occurs frequently, severely restricting production efficiency and product quality.

[0003] Currently, during the VD refining of CrMo steel, the molten steel boils violently in a vacuum environment, making it difficult to maintain a stable slag layer and causing it to easily overflow from the ladle. Slag overflow not only wastes slag and increases production costs, but can also exacerbate the erosion of the ladle's refractory materials, shortening the ladle's service life and even leading to equipment failures and safety accidents. Existing control methods largely rely on experience to adjust the argon blowing intensity and vacuum level, lacking precise control mechanisms. These methods are ill-suited to the complex composition and violently reacting characteristics of CrMo steel and cannot fundamentally solve the slag overflow problem.

[0004] Furthermore, in actual production, there is a difficult contradiction between reducing inclusions in steel and controlling slag overflow. To effectively remove inclusions, it is usually necessary to increase the argon blowing intensity to enhance the stirring effect of the molten steel and promote the floating of inclusions to the slag layer; however, excessively high argon blowing intensity will intensify the boiling of the molten steel, causing violent fluctuations in the slag layer and significantly increasing the risk of slag overflow. Conversely, if the argon blowing intensity or vacuum degree is reduced to suppress slag overflow, the molten steel will not be stirred sufficiently, and inclusions will not be able to float to the surface for removal, failing to achieve the ideal refining effect. This dilemma in process operation makes it difficult for existing technologies to simultaneously meet the dual requirements of efficient slag overflow control and deep purification of molten steel.

[0005] Therefore, there is an urgent need to develop a scientific and efficient method for controlling slag overflow in VD refining of CrMo steel, which can not only avoid the problem of slag overflow, but also effectively reduce the content of inclusions in the steel, achieve stability in the refining process, and improve the quality and production efficiency of CrMo steel products. Summary of the Invention

[0006] To address the challenge of simultaneously meeting the dual requirements of efficient slag control and deep steel purification in existing VD refining techniques, this invention provides a method for controlling slag overflow in CrMo steel VD refining. This method precisely controls the amount and timing of Al ingot addition during tapping, the timing of silicon-calcium wire addition during LF refining, and ensures the FeO+MnO content in the LF refining slag does not exceed 0.5%. Furthermore, it controls the vacuum level during VD refining, thus avoiding slag overflow during VD refining. Simultaneously, it reduces the content of inclusions in the steel, which is of great significance for improving the quality stability of CrMo steel products, reducing production costs, and extending the service life of the ladle.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0008] A method for controlling slag overflow in VD refining of CrMo steel includes the following steps:

[0009] S1. When the electric furnace taps steel to 5%~8% of the total amount, add 50%~60% of the total amount of aluminum ingots. When the electric furnace taps steel to 10%~12% of the total amount, add the remaining aluminum ingots. When the electric furnace taps steel to 15%~30% of the total amount, add carbon raiser and silicon-manganese alloy. When the electric furnace taps steel to 33%~43% of the total amount, add pre-melted refining slag, fluorite and alloying elements. When the electric furnace taps steel to 45%~55% of the total amount, add lime. After tapping, feed aluminum wire into the ladle.

[0010] S2, after the aluminum wire feeding is completed, the molten steel is transferred to the LF refining furnace, argon gas is introduced, and then 1m / t~1.5m / t of silicon-calcium wire is fed into the ladle. After power is supplied, lime, aluminum granules and silicon carbide are added to the ladle in sequence for refining. The mass percentage of each component in the refined steel slag system is as follows: CaO 50%~55%, SiO2 7.5%~10.5%, Al2O3 22%~27%, MgO 4.5%~7.5%, FeO+MnO≤0.5%.

[0011] S3. After refining, the molten steel is transferred to the VD vacuum smelting furnace. When the vacuum degree is >67Pa, if the molten steel does not submerge the slag surface, control the argon flow rate to 5NL / min~8NL / min. If the molten steel submerges the slag surface, control the argon flow rate to 80NL / min~100NL / min and maintain it for 2min~3min. When the vacuum degree is ≤67Pa, control the argon flow rate to 40NL / min~50NL / min. If there is no bubbling in the slag layer, maintain it for 8min~10min and then break the vacuum. If bubbling occurs in the slag layer, increase the vacuum degree to above 67Pa, adjust the argon flow rate to 80NL / min~100NL / min and maintain it for 2min~3min. When the vacuum degree is ≤67Pa, adjust the argon flow rate to 40NL / min~50NL / min and maintain it for 8min~10min and then break the vacuum.

[0012] The applicant experienced a slag overflow rate of up to 100% during the VD refining of CrMo steel with a carbon content of 0.16%~0.45% and an aluminum content of 0.01%~0.04%, which severely restricted production efficiency.

[0013] Controlling VD overflow in CrMo steel faces the following challenges:

[0014] (1) In order to ensure the purity of molten steel and reduce inclusions in steel, oxides in molten steel need to be fully removed. At this time, the FeO content in the slag before the steel ladle is put into VD refining is required to ensure that the non-metallic inclusions in molten steel are controllable. However, when the FeO content is less than 1%, the foaming index of slag increases significantly, which can easily cause slag overflow during the VD process. Therefore, there is a certain contradiction between the deoxidation method for molten steel purity and the control of slag overflow.

[0015] (2) The process from the LF refining furnace to the VD refining is a process in which the temperature of the molten steel and slag decreases. The LF refining station has a high temperature and the slag has good fluidity. As the VD refining proceeds, the slag temperature decreases and the fluidity deteriorates. Gas does not easily pass through the slag layer, resulting in slag overflow. The temperature drop in VD vacuum refining is inevitable.

[0016] (3) In order to efficiently reduce the hydrogen content in the molten steel, the vacuum level needs to be reduced to below 67 Pa. As VD refining proceeds, the vacuum level in the VD refining furnace decreases, the volume of the blowing argon bubbles increases, which increases the difficulty of them penetrating the slag layer and leads to the occurrence of slag overflow.

[0017] Compared to existing technologies, the method for controlling slag overflow in VD refining of CrMo steel provided by this invention involves adding a portion of aluminum ingots when the steel reaches 5% to 8% of its charge. This early addition, while ensuring the aluminum ingots are fully melted, avoids adding a large amount of aluminum ingots at once, as incompletely melted ingots floating on the molten steel surface will not provide deoxidation. Furthermore, the heat released from the pre-oxidation and deoxidation of some aluminum ingots accelerates the melting and deoxidation of the subsequently added ingots, achieving thorough deoxidation. This prevents excessive oxides from increasing slag viscosity and foaming tendency, and avoids CO bubbles generated by the reaction of the recarburizing agent with oxygen, which can cause slag overflow during tapping. When the steel reaches 15% to 30% of its charge, a recarburizing agent and silicon-manganese alloy are added for further deoxidation, improving the purity of the molten steel. This method is applied at the tapping point. When the slag content reaches 33%~43%, pre-melted refining slag and fluorite are added. At this point, the pre-melted slag can quickly form slag, and the fluorite lowers the slag melting point, improves fluidity, and prevents the formation of foamy slag due to excessive slag viscosity when gas escapes. When the slag content reaches 45%~55%, lime is added to gradually increase the slag basicity, laying the groundwork for the slag system composition in the LF refining stage and ensuring that the slag has good dephosphorization, desulfurization capabilities and stability. After tapping, aluminum wire is fed in to further reduce the oxygen content in the molten steel. At the same time, the aluminum wire melts inside the molten steel, forming a thin layer of alumina film covering the surface of the molten steel, reducing the contact area between the molten steel and air, reducing the risk of secondary oxidation during the transfer to the LF furnace, and avoiding the increase in slag viscosity and foaming tendency caused by the formation of FeO and other oxides due to secondary oxidation.

[0018] In the LF refining process, a specific amount of silica-calcium wire is fed into the molten steel to modify the alumina in the molten steel, transforming it into low-melting-point, easily floating calcium aluminate. This improves the purity of the molten steel and reduces the content of solid Al2O3 in the refining slag, thereby lowering the viscosity and surface tension of the refining slag. This reduces the foamy slag expansion caused by gas escape during VD vacuum degassing. In addition, calcium aluminate inclusions float sufficiently, resulting in fewer residual inclusions in the molten steel. During the VD stage vacuum degassing, the molten steel boils more evenly, preventing the slag layer from breaking through the ladle edge due to violent local gas escape. The refining slag system of LF refining has advantages such as low melting point, good fluidity, and high basicity, which can stably adsorb inclusions while effectively controlling slag foaming.

[0019] By controlling different argon flow rates at different vacuum stages, appropriate stirring intensity can be provided to achieve a balance between efficient degassing and slag surface stability, promoting the migration of inclusions and gases to the slag layer while controlling the risk of slag overflow.

[0020] Through the above process control, the slag overflow rate in the VD refining process was reduced from 100% to below 3%, the temperature drop in the VD process was reduced from 80℃ to 50℃, and the hydrogen content in the molten steel was reduced from 1.5~1.8ppm to 0.6~1.2ppm. After the steel obtained by the above process was continuously cast and molded, the average inclusion level was reduced, which met the dual requirements of controlling slag overflow and deeply purifying the molten steel. This helps to ensure the smooth progress of production and improve the quality of CrMo steel products, and has high practical value.

[0021] In some embodiments, in S1, the total amount Y of aluminum ingots is calculated according to the following formula:

[0022] Y=

[0023] In the formula, T is the electric arc furnace tapping temperature, 1610℃~1640℃; Wc is the carbon content at the end of electric arc furnace smelting, 0.05%~0.08%; W 目标Al To achieve the target aluminum content of 0.015%~0.025% in the LF refining furnace; G EAF Total steel output from the electric arc furnace: 84,000 kg to 88,000 kg; W Al含量 The aluminum content in the aluminum ingot is ≥99.9%; η Al Y represents the aluminum yield, ranging from 45% to 60%; Y is measured in kg.

[0024] Using the above formula, the amount of deoxidized aluminum ingots added can be calculated based on real-time steel tapping conditions. This ensures that the amount of aluminum ingots added is minimized while ensuring that the oxygen content in the molten steel is fully removed and the inclusions in the steel are reduced, thereby lowering production costs.

[0025] It should be noted that when calculating the above formula, Wc and W 目标Al and η Al All values ​​are percentages and not converted to decimals. For example, if the Wc content is 0.05%, then the Wc value should be 0.05 when substituting into the formula. η Al When it is 50%, then when substituting into the formula, η Al The value is 50. W Al含量 When substituting values ​​into the formula, the values ​​need to be converted to decimals, such as 99.9% being substituted into 0.999.

[0026] In the above formula, 10 （2.236-1303 / T-logWc） The formula represents the oxygen content in the molten steel that reacts with the aluminum ingot, derived from the carbon-oxygen concentration product. This is converted to the Al content required for deoxidation using the chemical formula. Adding this to the target Al content in the molten steel gives the amount of aluminum ingot required per 1 kg of molten steel. The total amount of aluminum ingots required for electric arc furnace smelting can then be calculated from the amount of aluminum ingots needed for 1 unit of molten steel.

[0027] In some embodiments, in S1, the Al content of the aluminum ingot is ≥99.9%.

[0028] In some embodiments, in S1, the carbon raiser is carbon particles.

[0029] In some embodiments, in S1, the pre-melted refining slag comprises the following components by mass percentage: CaO 32%~40%, SiO2 5%~10%, Al2O3 46%~54%, and MgO ≤1%.

[0030] In some embodiments, in S1, the amount of pre-melted refining slag added is 3.7 kg / t to 4.3 kg / t, and the amount of fluorite added is 1.0 kg / t to 1.4 kg / t.

[0031] In some embodiments, in S1, the fluorite contains ≥75% CaF2 and ≤23% SiO2.

[0032] In some embodiments, in S1, the amount of lime added is 3.7 kg / t to 4.3 kg / t.

[0033] In some embodiments, in S1, the lime contains CaO ≥ 88%, SiO2 ≤ 3%, MgO ≤ 7%, and S ≤ 0.05%.

[0034] In some embodiments, in S1, the feeding amount of the aluminum wire is 0.2 kg / t to 0.3 kg / t, and the feeding speed is 3 m / s to 3.5 m / s.

[0035] The optimal aluminum wire feed rate and feed speed can uniformly integrate aluminum into the molten steel, ensuring that the aluminum reacts fully with the oxygen in the molten steel.

[0036] In some embodiments, in S1, the aluminum wire contains ≥99.9% Al.

[0037] In some embodiments, in S2, the pressure of the introduced argon gas is 1.2MPa~1.3MPa, the flow rate is 500NL / min~600NL / min, and the holding time is 2min~3min.

[0038] In some embodiments, in S2, the specific steps after power supply are as follows: lime is added while power is supplied, argon gas is turned on for stirring, and aluminum particles and silicon carbide are added 2 to 3 minutes after power supply.

[0039] In some embodiments, in S2, the amount of lime added is 4.5 kg / t to 5 kg / t, the amount of aluminum granules added is 0.4 kg / t to 0.6 kg / t, and the amount of silicon carbide added is 0.4 kg / t to 0.6 kg / t.

[0040] In some embodiments, in S2, the lime contains CaO ≥ 88%, SiO2 ≤ 3%, MgO ≤ 7%, and S ≤ 0.05%.

[0041] In some embodiments, in S2, the Al content in the aluminum particles is ≥99.9%.

[0042] In some embodiments, in S2, the feeding speed of the silicon-calcium wire is 3m / s to 3.5m / s.

[0043] In some embodiments, in S2, the silicon-calcium wire contains SiC ≥ 75%, SiO2 ≤ 10%, and free carbon ≤ 10%.

[0044] In some embodiments, the refining time in S2 is 20 min to 25 min.

[0045] It should be noted that in S2, no carbon addition operation is performed 5 minutes before steel tapping to avoid carbon-oxygen reaction causing slag foaming.

[0046] It should be noted that in S3, a camera is used to observe in real time whether the molten steel submerges the slag surface or whether the slag layer is bubbling, so as to adjust the argon flow rate in time and reduce the slag overflow rate.

[0047] In summary, the method for controlling ladle overflow during VD refining of CrMo steel provided by this invention involves adding aluminum ingots, alloys, and slag in batches during the electric arc furnace tapping stage to rapidly deoxidize and initially adjust the slag composition and basicity. After tapping, aluminum wire is fed in to further reduce the oxygen content, creating conditions for subsequent refining. In the LF refining process, a silica-calcium wire is fed in to transform alumina into easily floating calcium aluminate. Combined with precise control of the proportions of each component in the slag system, slag viscosity and surface tension are reduced, improving dephosphorization and desulfurization efficiency and reducing foam slag formation. In the VD vacuum smelting stage, the argon flow rate is dynamically adjusted according to the vacuum level and slag surface condition to achieve a balance between efficient degassing and slag surface stability. This process reduces the overflow rate in the VD refining process from 100% to below 3%, the temperature drop from 80℃ to 50℃, significantly reduces the hydrogen content in the molten steel, and lowers the level of inclusions. It not only effectively controls the risk of overflow but also improves the purity of the molten steel, providing a new solution for controlling overflow during VD refining of CrMo steel, which can significantly enhance enterprise production efficiency and market competitiveness. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0049] To better illustrate the present invention, further examples are provided below.

[0050] The aluminum ingots, aluminum granules, and aluminum wires used in the following examples have an Al content of ≥99.9%.

[0051] In the following examples, the total amount Y of aluminum ingots used in the LF refining process is calculated according to the following formula:

[0052] Y (Kg) =

[0053] In the formula, T is the electric arc furnace tapping temperature, 1610℃~1640℃; Wc is the carbon content at the end of electric arc furnace smelting, 0.05%~0.08%; W 目标Al To achieve the target aluminum content of 0.015%~0.025% in the LF refining furnace; G EAF Total steel output from the electric arc furnace: 84,000 kg to 88,000 kg; W Al含量 The aluminum content in the aluminum ingot is ≥99.9%; η Al The aluminum yield is 45% to 60%.

[0054] Example 1

[0055] This invention provides a method for controlling slag overflow in the ladle during VD refining of CrMo steel. The steel grade is 27CrMo48V, and the heat number is 2511032. The method includes the following steps:

[0056] Electric furnace process: The carbon content W at the end of the tapping process in this electric furnace C The content of Al in the aluminum ingot is 0.06%, the tapping temperature T is 1630℃, and the content of Al in the ingot is W. Al含量 The yield is 99.9%, the aluminum ingot recovery rate is 55%, the target aluminum content of this steel grade to the LF refining furnace is 0.020%, the electric furnace output is 85,500 kg, and the total amount of aluminum ingots used for deoxidation is calculated to be 110.8 kg according to the above formula. When the electric arc furnace taps to 6% of the total steel volume, add 50.4 kg of aluminum ingots to the ladle. When the steel volume reaches 10% of the total steel volume, add the remaining aluminum ingots to the ladle. When the steel volume reaches 15% of the total steel volume, add carbon particles and ferrosilicon manganese according to the target composition. When the steel volume reaches 35% of the total steel volume, add 4.2 kg / t of pre-melted refining slag (CaO 38%, SiO2 8%, Al2O3 53%, MgO ≤ 1%) and 1.2 kg / t of fluorite (CaF2 75%, SiO2 12.5%) to the ladle, and add high-carbon ferromanganese, ferromolybdenum, ferrochrome, and ferrovanadium according to the target composition. When the steel volume reaches 45% of the total steel volume, add 5 kg / t of lime (CaO 89%, SiO2 3%, MgO 7%, S...) to the ladle. 0.05%), after tapping, 0.25 kg / t of aluminum wire is fed into the ladle at a feeding speed of 3.5 m / s. After the aluminum wire is fed, it is transferred to the LF refining furnace.

[0057] LF refining process: Molten steel is transferred from the ladle to the refining furnace. Argon gas is introduced for breaking and blowing at a pressure of 1.3 MPa and a flow rate of 550 NL / min for 2.5 min. Then, 1.5 m / t of silicon-calcium alloy cored wire (Ca 32%, Si 58%) is fed into the ladle at a speed of 3.1 m / s. Power is supplied, and 4.7 kg / t of lime (CaO 91.5%, SiO 23%, MgO 5%, S...) is added to the ladle. 0.05%), and simultaneously turn on argon gas for stirring at a flow rate of 260 NL / min. After 3 minutes of power supply, add 0.5 kg / t aluminum granules and 0.5 kg / t silicon carbide (SiC≥75%, SiO2≤10%, free carbon≤10%) to create white slag. Refine for 23 minutes while maintaining the white slag. Do not perform carbon addition operation for 5 minutes before steelmaking. The content of each component in the refined steel slag system is: CaO 53.5%, SiO2 8.5%, Al2O3 25%, MgO 5%, (FeO+MnO) 0.5%;

[0058] VD refining process: After refining, the ladle is hoisted into the VD tank and argon gas is introduced for VD vacuum smelting. When the vacuum degree is >67Pa, the argon gas flow rate is 6NL / min when the molten steel does not submerge the slag surface, and 85NL / min when the molten steel submerges the slag surface, and the holding time is 2.5min. When the vacuum degree is ≤67Pa, the argon gas flow rate is 43NL / min. During the process, slag bubbling occurs. The vacuum degree is adjusted to above 67Pa, and the argon gas flow rate is adjusted to 87NL / min, and held for 2min. When the vacuum degree is ≤67Pa, the argon gas flow rate is adjusted to 43NL / min, and the holding time is 8.8min, and the vacuum is broken.

[0059] The entire VD process was free of overflow, with a temperature drop of 45°C and a hydrogen content of 0.8 ppm.

[0060] The molten steel obtained from the above VD refining process was cast into a billet using conventional processes. The billet was sampled and tested for inclusions according to ASTM E45-18a(2023). The results are shown in Table 1.

[0061] Table 1

[0062]

[0063] Example 2

[0064] This invention provides a method for controlling slag overflow in the ladle during VD refining of CrMo steel. The steel grade is 35CrMo, and the heat number is 2511552. The method includes the following steps:

[0065] Electric furnace process: The carbon content W at the end of the tapping process in this electric furnace CThe content of Al in the aluminum ingot is 0.07%, the tapping temperature T is 1625℃, and the content of Al in the aluminum ingot is W. Al含量 The yield is 99.9%, the aluminum ingot recovery rate is 50%, the target aluminum content of this steel grade to the LF refining furnace is 0.015%, the electric furnace output is 84,500 kg, and the total amount of aluminum ingots used for deoxidation is calculated to be 100.2 kg according to the above formula. When the electric arc furnace taps to 7.5% of the total steel volume, add 50.1 kg of aluminum ingots to the ladle. When the steel volume reaches 11%, add the remaining aluminum ingots to the ladle. When the steel volume reaches 18%, add carbon particles and ferrosilicon manganese according to the target composition. When the steel volume reaches 40%, add 3.8 kg / t of pre-melted refining slag (CaO 38.5%, SiO2 6.5%, Al2O3 51.5%, MgO ≤ 1%) and 1.3 kg / t of fluorite (CaF2 75%, SiO2 12.5%) to the ladle, and add high-carbon ferromanganese, ferromolybdenum, and ferrochrome according to the target composition. When the steel volume reaches 50%, add 4.5 kg / t of lime (CaO 89%, SiO2 3%, MgO 7%, S...) to the ladle. 0.05%), after the steel tapping is completed, 0.2 kg / t of aluminum wire is fed into the ladle at a feeding speed of 3.2 m / s. After the aluminum wire is fed, it is transferred to the LF refining furnace.

[0066] LF Refining Process: Molten steel is transferred from the ladle to the refining furnace. Argon gas is introduced for breaking and blowing at a pressure of 1.25 MPa and a flow rate of 500 NL / min for 2 minutes. Then, 1.3 m / t of silicon-calcium alloy cored wire (Ca 32%, Si 58%) is fed into the ladle at a speed of 3.3 m / s. Power is supplied, and 4.5 kg / t of lime (CaO 89.5%, SiO2 2.5%, MgO 6%, S 0.05%) is added to the ladle. Argon gas is simultaneously introduced for stirring at a flow rate of 255 NL / min. After 3 minutes of power supply, 0.6 kg / t of aluminum granules and 0.6 kg / t of silicon carbide (SiC ≥ 75%, SiO2 ≤ 10%, free carbon ≤ 10%) are added to create white slag. Refining is carried out for 20 minutes while maintaining the white slag. No further carbon addition is performed in the last 5 minutes before tapping. The composition of the refined steel slag is as follows: CaO 54.5%, SiO28.6%, Al2O325.4%, MgO 4.5%, (FeO+MnO) 0.5%;

[0067] VD refining process: After refining, the ladle is hoisted into the VD tank and argon gas is introduced for VD vacuum smelting. When the vacuum degree is >67Pa, the argon gas flow rate is 7.8NL / min when the molten steel does not submerge the slag surface, and 90NL / min when the molten steel submerges the slag surface, and the holding time is 2min. When the vacuum degree is ≤67Pa, the argon gas flow rate is 45NL / min. No slag layer bubbling occurs during the process, and the holding time is 10min before the vacuum is broken.

[0068] The entire VD process was free of overflow, with a temperature drop of 47°C and a hydrogen content of 1.1 ppm.

[0069] The molten steel obtained from the above VD refining process was cast into a billet using conventional processes. The billet was sampled and tested for inclusions according to ASTM E45-18a(2023). The results are shown in Table 2.

[0070] Table 2

[0071]

[0072] Example 3

[0073] This invention provides a method for controlling slag overflow in the ladle during VD refining of CrMo steel. The steel grade is 42CrMo, and the heat number is 2511880. The method includes the following steps:

[0074] Electric furnace process: The carbon content W at the end of the tapping process in this electric furnace C The content of Al in aluminum ingots is 0.05%, the tapping temperature T is 1630℃, and the content of Al in the ingots is W. Al含量 The yield is 99.9%, the aluminum ingot recovery rate is 50%, the target aluminum content of this steel grade to the LF refining furnace is 0.018%, the electric furnace output is 85,000 kg, and the total amount of aluminum ingots used for deoxidation is calculated to be 136.5 kg according to the above formula. When the electric arc furnace taps to 5% of the total steel volume, add 80 kg of aluminum ingots to the ladle. When the steel volume reaches 12% of the total steel volume, add the remaining aluminum ingots to the ladle. When the steel volume reaches 20% of the total steel volume, add carbon particles and ferromanganese according to the target composition. When the steel volume reaches 42% of the total steel volume, add 4.3 kg / t of pre-melted refining slag (CaO 38.5%, SiO2 6.5%, Al2O3 51.5%, MgO ≤ 1%) and 1.1 kg / t of fluorite (CaF2 75%, SiO2 12.5%) to the ladle, and add high-carbon ferromanganese, ferromolybdenum, and ferrochrome according to the target composition. When the steel volume reaches 52% of the total steel volume, add 4.8 kg / t of lime (CaO 89%, SiO2 3%, MgO 7%, S...) to the ladle. 0.05%), after tapping, 0.28 kg / t of aluminum wire is fed into the ladle at a feeding speed of 3.4 m / s. After the aluminum wire is fed, it is transferred to the LF refining furnace.

[0075] LF refining process: Molten steel is transferred from the ladle to the refining furnace. Argon gas is introduced for breaking and blowing at a pressure of 1.24 MPa and a flow rate of 530 NL / min for 2.2 min. Then, 1.1 m / t of silicon-calcium alloy cored wire (Ca 32%, Si 58%) is fed into the ladle at a speed of 3.5 m / s. Power is supplied, and 4.6 kg / t of lime (CaO 90.5%, SiO2 2.5%, MgO 5.5%, S...) is added to the ladle. 0.05%), and simultaneously turn on argon gas for stirring at a flow rate of 260 NL / min. After energizing for 2 minutes, add 0.55 kg / t aluminum granules and 0.4 kg / t silicon carbide (SiC≥75%, SiO2≤10%, free carbon≤10%) to create white slag. Refine for 23 minutes while maintaining the white slag. Do not add carbon for the last 5 minutes before steelmaking. The content of each component in the refined steel slag system is: CaO 54.5%, SiO2 7.6%, Al2O3 24.4%, MgO 6.5%, (FeO+MnO) 0.5%;

[0076] VD refining process: After refining, the ladle is hoisted into the VD tank and argon gas is introduced for VD vacuum smelting. When the vacuum degree is >67Pa, the argon gas flow rate is 7.5NL / min when the molten steel does not submerge the slag surface, and 95NL / min when the molten steel submerges the slag surface, and maintained for 2 minutes. When the vacuum degree is ≤67Pa, the argon gas flow rate is 45NL / min. During the process, slag bubbling occurs. The vacuum degree is adjusted to above 67Pa, and the argon gas flow rate is adjusted to 95NL / min, maintained for 2.5 minutes. When the vacuum degree is ≤67Pa, the argon gas flow rate is adjusted to 45NL / min, maintained for 8.2 minutes, and the vacuum is broken.

[0077] The entire VD process was free of overflow, with a temperature drop of 45°C and a hydrogen content of 0.7 ppm.

[0078] The molten steel obtained from the above VD refining process was cast into a billet using conventional processes. The billet was sampled and tested for inclusions according to ASTM E45-18a(2023). The results are shown in Table 3.

[0079] Table 3

[0080]

[0081] Example 4

[0082] This embodiment provides a method for controlling slag overflow in the ladle during VD refining of CrMo steel. The steel grade is 27CrMo48V, and the furnace number is 2511035. The only difference from Embodiment 1 is the change in the amount of aluminum ingots added; otherwise, the method is exactly the same as Embodiment 1. The specific steps are as follows:

[0083] Electric furnace process: The carbon content W at the end of the tapping process in this electric furnace C The content of Al in the aluminum ingot is 0.06%, the tapping temperature T is 1630℃, and the content of Al in the ingot is W. Al含量 The aluminum ingot yield is 55%, and the target aluminum content for this steel grade in the LF refining furnace is 0.020%. The electric arc furnace tapping rate is 85,500 kg. When the electric arc furnace tapping reaches 6% of the total, 68 kg of aluminum ingots are added to the ladle. When the tapping reaches 10% of the total, 68 kg of aluminum ingots are added to the ladle. When the tapping reaches 15% of the total, carbon particles and silicon manganese are added according to the target composition. When the tapping reaches 35% of the total, 4.2 kg / t of pre-melted refining slag (CaO 38%, SiO2 8%, Al2O3 53%, MgO ≤ 1%) and 1.2 kg / t of fluorite (CaF2 75%, SiO2 12.5%) are added to the ladle. High-carbon ferromanganese, ferromolybdenum, ferrochrome, and ferrovanadium are added according to the target composition. When the tapping reaches 45% of the total, 5 kg / t of lime (CaO 89%, SiO2 3%, MgO 7%, S...) is added to the ladle. 0.05%), after tapping, 0.25 kg / t of aluminum wire is fed into the ladle at a feeding speed of 3.5 m / s. After the aluminum wire is fed, it is transferred to the LF refining furnace.

[0084] The other procedures are the same as in Example 1, and will not be repeated here.

[0085] Based on multi-furnace tests, the probability of VD refining overflow in this embodiment is approximately 35%. The VD process temperature drop is 70°C, and the hydrogen content is 1.8 ppm.

[0086] The molten steel obtained from the above VD refining process was cast into a billet using conventional processes. The billet was sampled and tested for inclusions according to ASTM E45-18a(2023). The results are shown in Table 4.

[0087] Table 4

[0088]

[0089] Comparative Example 1

[0090] This comparative example provides a method for controlling slag overflow in the ladle during VD refining of CrMo steel. The steel grade is 35CrMo, and the heat number is 2511553. The only difference from Example 2 is that the aluminum ingot is added all at once. The specific steps are as follows:

[0091] Electric furnace process: The carbon content W at the end of the tapping process in this electric furnace C The content of Al in the aluminum ingot is 0.07%, the tapping temperature T is 1625℃, and the content of Al in the aluminum ingot is W. Al含量The yield is 99.9%, the aluminum ingot recovery rate is 50%, the target aluminum content of this steel grade to the LF refining furnace is 0.015%, the electric furnace output is 84,500 kg, and the total amount of aluminum ingots used for deoxidation is calculated to be 100.2 kg according to the above formula. When the electric furnace taps 11% of the total steel volume, 100.2 kg of aluminum ingots are added to the ladle. When the steel volume reaches 18%, carbon particles and silicon manganese are added according to the target composition. When the steel volume reaches 40%, 3.8 kg / t of pre-melted refining slag (CaO 38.5%, SiO2 6.5%, Al2O3 51.5%, MgO ≤ 1%) and 1.3 kg / t of fluorite (CaF2 75%, SiO2 12.5%) are added to the ladle, along with high-carbon ferromanganese, ferromolybdenum, and ferrochrome according to the target composition. When the steel volume reaches 50%, 4.5 kg / t of lime (CaO 89%, SiO2 3%, MgO 7%, S 0.05%) is added to the ladle. After tapping, 0.2 kg / t of aluminum wire is fed into the ladle at a speed of 3.2 m / s. After the aluminum wire is fed, it is transferred to the LF refining furnace.

[0092] The other procedures are the same as in Example 2, and will not be repeated here.

[0093] The initial stage of the entire VD refining process was characterized by severe slag overflow, a temperature drop of 88°C during the VD process, and a hydrogen content of 1.1 ppm.

[0094] The molten steel obtained from the above VD refining process was cast into a billet using conventional processes. The billet was sampled and tested for inclusions according to ASTM E45-18a(2023). The results are shown in Table 5.

[0095] Table 5

[0096]

[0097] Comparative Example 2

[0098] This comparative example provides a method for controlling slag overflow in the ladle during VD refining of CrMo steel. The steel grade is 42CrMo and the heat number is 2511880. The only difference from Example 3 is that the amount of silicon-calcium wire fed in during the LF refining process is changed to 0.5m / t. The rest is exactly the same and will not be described again here.

[0099] Slag overflow occurred in the early stage of VD refining. After multiple furnace tests, the probability of slag overflow in VD refining in this comparative example was about 60%. The temperature drop in the VD process was 80℃, and the hydrogen content was 1.7ppm.

[0100] The molten steel obtained from the above VD refining process was cast into a billet using conventional processes. The billet was sampled and tested for inclusions according to ASTM E45-18a(2023). The results are shown in Table 6.

[0101] Table 6

[0102]

[0103] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for controlling slag overflow in the ladle during VD refining of CrMo steel, characterized in that, Includes the following steps: S1. When the electric furnace taps steel to 5%~8% of the total amount, add 50%~60% of the total amount of aluminum ingots. When the electric furnace taps steel to 10%~12% of the total amount, add the remaining aluminum ingots. When the electric furnace taps steel to 15%~30% of the total amount, add carbon raiser and silicon-manganese alloy. When the electric furnace taps steel to 33%~43% of the total amount, add pre-melted refining slag, fluorite and alloying elements. When the electric furnace taps steel to 45%~55% of the total amount, add lime. After tapping, feed aluminum wire into the ladle. S2, after the aluminum wire feeding is completed, the molten steel is transferred to the LF refining furnace, argon gas is introduced, and then 1m / t~1.5m / t of silicon-calcium wire is fed into the ladle. After power is supplied, lime, aluminum granules and silicon carbide are added to the ladle in sequence for refining. The mass percentage of each component in the refined steel slag system is as follows: CaO 50%~55%, SiO2 7.5%~10.5%, Al2O3 22%~27%, MgO 4.5%~7.5%, FeO+MnO≤0.5%. S3. After refining, the molten steel is transferred to the VD vacuum smelting furnace. When the vacuum degree is >67Pa, if the molten steel does not submerge the slag surface, control the argon flow rate to 5NL / min~8NL / min. If the molten steel submerges the slag surface, control the argon flow rate to 80NL / min~100NL / min and maintain it for 2min~3min. When the vacuum degree is ≤67Pa, control the argon flow rate to 40NL / min~50NL / min. If there is no bubbling in the slag layer, maintain it for 8min~10min and then break the vacuum. If bubbling occurs in the slag layer, increase the vacuum degree to above 67Pa, adjust the argon flow rate to 80NL / min~100NL / min and maintain it for 2min~3min. When the vacuum degree is ≤67Pa, adjust the argon flow rate to 40NL / min~50NL / min and maintain it for 8min~10min and then break the vacuum.

2. The method for controlling ladle overflow during VD refining of CrMo steel as described in claim 1, characterized in that, In S1, the total amount of aluminum ingots Y is calculated according to the following formula: Y= In the formula, T is the electric arc furnace tapping temperature, 1610℃~1640℃; Wc is the carbon content at the end of electric arc furnace smelting, 0.05%~0.08%; W 目标Al To achieve the target aluminum content of 0.015%~0.025% in the LF refining furnace; G EAF Total steel output from the electric arc furnace: 84,000 kg to 88,000 kg; W Al含量 The aluminum content in the aluminum ingot is ≥99.9%; η Al Y represents the aluminum yield, ranging from 45% to 60%; Y is measured in kg.

3. The method for controlling ladle overflow during VD refining of CrMo steel as described in claim 1, characterized in that, In S1, the pre-melted refining slag comprises the following components by mass percentage: CaO 32%~40%, SiO2 5%~10%, Al2O3 46%~54%, and MgO≤1%.

4. The method for controlling ladle overflow during VD refining of CrMo steel as described in claim 3, characterized in that, In S1, the amount of pre-melted refining slag added is 3.7 kg / t to 4.3 kg / t, and the amount of fluorite added is 1.0 kg / t to 1.4 kg / t.

5. The method for controlling ladle overflow during VD refining of CrMo steel as described in claim 1, characterized in that, In S1, the amount of lime added is 3.7 kg / t to 4.3 kg / t; and / or In S1, the aluminum wire feeding rate is 0.2 kg / t to 0.3 kg / t, and the feeding speed is 3 m / s to 3.5 m / s.

6. The method for controlling slag overflow in VD refining of CrMo steel as described in claim 1, characterized in that, In S2, the pressure of argon gas introduced is 1.2MPa~1.3MPa, the flow rate is 500NL / min~600NL / min, and the holding time is 2min~3min.

7. The method for controlling ladle overflow during VD refining of CrMo steel as described in claim 1, characterized in that, In S2, the specific steps after power supply are as follows: lime is added at the same time as power supply, argon gas is turned on for stirring, and aluminum particles and silicon carbide are added 2 to 3 minutes after power supply.

8. The method for controlling ladle overflow during VD refining of CrMo steel as described in claim 7, characterized in that, In S2, the amount of lime added is 4.5 kg / t to 5 kg / t, the amount of aluminum granules added is 0.4 kg / t to 0.6 kg / t, and the amount of silicon carbide added is 0.4 kg / t to 0.6 kg / t.

9. The method for controlling slag overflow in VD refining of CrMo steel as described in claim 1, characterized in that, In S2, the feeding speed of the silicon-calcium wire is 3m / s to 3.5m / s.

10. The method for controlling ladle overflow during VD refining of CrMo steel as described in claim 1, characterized in that, In S2, the refining time is 20 min to 25 min.

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