VD furnace low-sulfur smelting method

Abstract

The invention relates to the technical field of metal smelting, and discloses a VD furnace low-sulfur smelting method which comprises the steps that molten iron is blown with a magnesium-based desulfurizing agent, and the magnesium-based desulfurizing agent comprises magnesium powder and lime; conveying the molten iron into a converter, and adding lime and fluorite into the molten iron; smelting the molten iron into molten steel through a converter; the molten steel is poured into a steel ladle, and pre-melted slag is added into the steel ladle; and the steel ladle is in butt joint with a vacuum cover of a VD furnace, and molten steel is subjected to a slag-steel reaction under the vacuum condition. Through combination of molten iron pre-desulfurization, converter end point dynamic control and VD furnace slag steel synergistic reaction, the VD furnace directly realizes low-sulfur smelting, the LF furnace pretreatment process is omitted, the smelting cost is effectively reduced, and the low-cost production requirement of common deformed steel bars can be met.

Description

Technical Field

[0001] The present application relates to the technical field of metal smelting, and in particular to a low-sulfur smelting method in a VD furnace. Background Art

[0002] In related technologies, the desulfurization technology of VD furnace (Vacuum Decarburization) smelting is usually aimed at high-end steel grades and needs to be pre-treated in conjunction with LF furnace (Ladle Furnace). It relies on LF furnace refining and RH vacuum treatment, resulting in high smelting costs and is not suitable for the low-cost production needs of ordinary rebar. Summary of the Invention

[0003] This application aims to solve at least one of the technical problems existing in the prior art or related art.

[0004] The technical solution of the present application proposes a low-sulfur smelting method for a VD furnace, which includes: spraying molten iron with a magnesium-based desulfurizer, the magnesium-based desulfurizer including magnesium powder and lime; transporting the molten iron to a converter, adding lime and fluorite to the molten iron; smelting the molten iron into molten steel through the converter; pouring the molten steel into a ladle, and adding pre-melted slag into the ladle; connecting the ladle to the vacuum cover of the VD furnace, and allowing the molten steel to undergo a slag-steel reaction under vacuum conditions.

[0005] In some technical solutions provided in this application, the step of spraying molten iron with a magnesium-based desulfurizer specifically includes: the mass ratio of magnesium powder and lime is 1:2, the spraying rate is 8kg / min to 12kg / min, the spraying carrier gas pressure is 0.5MPa to 0.8MPa, and the spraying time is proportional to the initial sulfur content of the molten iron.

[0006] In some technical solutions provided in this application, after the step of spraying the molten iron with a magnesium-based desulfurizer, the following steps are further included: blowing nitrogen gas to the bottom of the molten iron for stirring, with a nitrogen flow rate of 0.3 Nm 3 / min to 0.5Nm 3 / min, and the nitrogen blowing time is 3 minutes to 5 minutes.

[0007] In some technical solutions provided in this application, after the step of blowing nitrogen to the bottom of the molten iron for stirring, it also includes: performing slag skimming operation on the molten iron, the slag skimming rate of the molten iron is ≥95%, the slag amount is ≤2kg / ton of molten iron, and the temperature of the molten iron is controlled to be ≥1300℃.

[0008] In some technical solutions provided in this application, the step of adding lime and fluorite to molten iron specifically includes: the amount of lime added Q 石灰 =40+100×([S] 铁水-0.010), the amount of fluorite added is Q 石灰 8% to 10%; control the basicity of the final slag of the converter R = CaO / SiO2 ≥ 3.5, and the sulfur capacity in the final slag ≥ 50.

[0009] In some technical solutions provided in the present application, after the step of adding lime and fluorite to the molten iron, the method further includes: obtaining a predicted sulfur content of the molten steel; when the predicted sulfur content is greater than 0.020%, the oxygen blowing time of the converter is extended by 1 minute to 2 minutes; and controlling the sulfur content of the steel tapped from the converter to be ≤0.015%.

[0010] In some technical solutions provided in this application, the step of pouring molten steel into the ladle specifically includes: using slag blocking cones and slag blocking balls to perform slag blocking operations, controlling the slag layer thickness of the ladle to ≤30mm, and controlling the final temperature of the converter to ≥1680°C.

[0011] In some technical solutions provided in the present application, the step of adding pre-melted slag into the ladle specifically includes: the components of the pre-melted slag are: 50% CaO, 40% Al2O3, 10% SiO2, and the amount of pre-melted slag added is 3kg / ton of steel to 5kg / ton of steel.

[0012] In some technical solutions provided in the present application, the step of carrying out slag-steel reaction of molten steel under vacuum conditions specifically includes: the vacuum degree of the vacuum conditions is ≤1 mbar, and the sulfur distribution ratio in the slag is 80 to 100.

[0013] In some technical solutions provided in this application, the step of slag-steel reaction of molten steel under vacuum conditions specifically includes: blowing argon into the VD furnace to stir the molten steel, controlling the flow rate of argon according to the state of the VD furnace, and the total stirring time is ≥25 minutes.

[0014] Compared with the related art, the present invention has at least the following beneficial effects:

[0015] By combining molten iron pre-desulfurization, dynamic control of the converter endpoint and synergistic reaction of VD slag and steel, the VD furnace can directly achieve low-sulfur smelting, omitting the LF furnace pretreatment process, effectively reducing the smelting cost, and meeting the low-cost production needs of ordinary rebar. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of some embodiments below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference numerals are used throughout the accompanying drawings to denote the same components. In the accompanying drawings:

[0017] Figure 1 This is one of the flow diagrams of a VD furnace low-sulfur smelting method according to an embodiment of the present application;

[0018] Figure 2 This is the second flow chart of the VD furnace low-sulfur smelting method according to an embodiment of the present application. DETAILED DESCRIPTION

[0019] In order to better understand the above technical solution, the technical solution of the embodiment of the present application is described in detail below through the accompanying drawings and specific embodiments. It should be understood that the embodiment of the present application and the specific features in the embodiment are detailed descriptions of the technical solution of the embodiment of the present application, rather than limitations on the technical solution of the present application. In the absence of conflict, the embodiment of the present application and the technical features in the embodiment can be combined with each other.

[0020] The embodiment of the present application provides a VD furnace low sulfur smelting method, such as Figure 1 As shown, the VD furnace low-sulfur smelting method includes:

[0021] Step 101, spraying molten iron with a magnesium-based desulfurizer, the magnesium-based desulfurizer comprising magnesium powder and lime;

[0022] Step 102: transporting molten iron to a converter and adding lime and fluorite to the molten iron;

[0023] Step 103, smelting the molten iron into molten steel through a converter;

[0024] Step 104, pouring molten steel into a ladle and adding pre-melted slag into the ladle;

[0025] Step 105: docking the ladle with the vacuum cover of the VD furnace, and the molten steel undergoes slag-steel reaction under vacuum conditions.

[0026] In this embodiment, molten iron is first poured into a molten iron ladle and pretreated before smelting. A magnesium-based desulfurizer comprising magnesium powder and lime is then sprayed onto the molten iron. Magnesium powder has a direct desulfurization effect. Due to its strong affinity for sulfur, the solid MgS generated by the reaction of magnesium with sulfur in the molten iron can float to the slag layer and be removed, thereby achieving rapid desulfurization. Lime has an auxiliary desulfurization effect. Lime reacts with sulfur to form CaS, which, in conjunction with magnesium powder, can improve desulfurization efficiency. Lime can neutralize acidic oxides (such as SiO2), increase the alkalinity of the slag system, and inhibit sulfur re-dissolution.

[0027] The molten iron is then fed into the converter for the steelmaking process, entering the converter smelting stage. Scrap steel is also added to the converter through a hopper. Oxygen is blown into the molten iron using a deoxidation lance to remove carbon, phosphorus, and sulfur. Meanwhile, bulk material from the converter's overhead hopper is weighed and added to the converter, where it gradually melts and reacts with oxidized impurities in the molten pool, removing harmful substances from the molten steel. Secondary sulfur control is achieved by adding lime and fluorite to the converter's molten iron. Lime neutralizes inherent acidic oxides within the furnace. Residual MgS after pre-desulfurization of the molten iron is further fixed by lime in the converter. Fluorite lowers the melting point of the slag. Fluorite reacts with high-melting-point lime to form a eutectic (such as CaO·CaF2), lowering the melting point of the slag system from over 1700°C to 1400-1500°C, improving the fluidity of the molten iron. Furthermore, it promotes sulfur mass transfer. The low-viscosity slag accelerates the diffusion of sulfur ions from the molten steel into the slag, increasing the desulfurization reaction rate. The synergistic effect of lime and fluorite can reduce the final sulfur content of the converter to ≤0.015%, laying the foundation for subsequent VD furnace deep desulfurization.

[0028] Next, the molten steel is poured from the converter's taphole into a ladle for auxiliary desulfurization in a VD furnace. Under vacuum, oxygen is removed from the molten steel, driving the desulfurization reaction. Pre-melted slag rapidly forms a high-sulfur content slag phase within the VD furnace. The synergistic effect of the pre-melted slag and vacuum ensures efficient desulfurization, adsorbs inclusions, and purifies the molten steel.

[0029] By combining molten iron pre-desulfurization, dynamic control of the converter endpoint and synergistic reaction of VD slag and steel, the VD furnace can directly achieve low-sulfur smelting, and can achieve a sulfur content of rebar ≤ 0.025%. The LF furnace pretreatment process is omitted, effectively reducing the smelting cost and meeting the low-cost production needs of ordinary rebar.

[0030] In some embodiments provided in the present application, step 101 of spraying molten iron with a magnesium-based desulfurizer specifically includes: a mass ratio of magnesium powder to lime is 1:2, a spraying rate is 8kg / min to 12kg / min, a spraying carrier gas pressure is 0.5MPa to 0.8MPa, and the spraying time is proportional to the initial sulfur content of the molten iron.

[0031] In this embodiment, magnesium powder and lime are mixed in a mass ratio of 1:2 to ensure that the magnesium-based desulfurizer has high reactivity and good fluidity. The desulfurizer delivery rate is regulated by a variable frequency feeder or a rotary feed valve to ensure stable injection. Nitrogen or argon can be used as the carrier gas. The spray gun is inserted 1.5 to 2.0 meters below the molten iron surface to ensure sufficient dispersion of the desulfurizer in the molten iron.

[0032] According to the initial sulfur content of the molten iron, the injection rate is dynamically adjusted. Specifically, the injection rate is proportional to the initial sulfur content of the molten iron. The higher the sulfur content of the molten iron, the faster the injection rate. The injection rate is reasonably limited to avoid the desulfurization reaction being insufficient and prolonging the time due to too low a rate, and to avoid the increase in magnesium vapor escaping due to too high a rate, thereby reducing the utilization rate of magnesium powder and causing the molten iron to splash. The carrier gas pressure of the injection is reasonably limited to ensure that the desulfurizer penetrates the molten iron layer and avoids gathering near the liquid surface. At the same time, it is avoided that the pressure is too low and the injection is not smooth, and it is avoided that the pressure is too high and causes the molten iron to splash. The time of the injection is dynamically adjusted according to the initial sulfur content of the molten iron, so that the higher the sulfur content of the molten iron, the longer the injection time is, to meet the target sulfur content. The specific injection time is shown in Table 1.

[0033] Table 1

[0034]

[0035] In some embodiments provided in the present application, after step 101 of spraying molten iron with a magnesium-based desulfurizer, the following steps are further included:

[0036] Step 106: Blow nitrogen gas to the bottom of the molten iron for stirring. The nitrogen flow rate is 0.3 Nm 3 / min to 0.5Nm 3 / min, and the nitrogen blowing time is 3 minutes to 5 minutes.

[0037] In this embodiment, during the molten iron pretreatment stage, blowing nitrogen after the spraying is completed can prevent the escape of magnesium vapor and disperse unreacted desulfurizer particles. The nitrogen bubbles generate strong turbulence during the rising process, allowing the molten iron to fully contact the top slag layer, accelerating the mass transfer of sulfur from the molten iron to the slag phase, and the nitrogen bubbles adsorb fine solid sulfide particles and carry them to the slag layer. In addition, stirring can improve the utilization rate of the desulfurizer and avoid incomplete reaction caused by excessive local sulfur concentration. In addition, when spraying the desulfurizer, a "static zone" is easily formed at the bottom of the molten iron. Nitrogen stirring can prevent the formation of dead corners in the spraying and ensure that the sulfur content in the entire area is uniformly reduced. By physically stirring the molten iron-slag interface, the desulfurization reaction is ensured to be completed efficiently, and molten iron with uniform composition and low sulfur is provided for subsequent processes. Bottom-blown nitrogen stirring loosens the slag layer, reducing the slag layer thickness to below 20 mm, reducing the resistance of subsequent slag removal operations.

[0038] Precise control of stirring flow parameters and time parameters is the key to balancing desulfurization efficiency and temperature drop. By reasonably limiting the nitrogen flow rate and blowing time, the stirring intensity can be moderate to prevent molten iron splashing, avoid insufficient stirring intensity that leads to slow floating of sulfides and reduced desulfurization efficiency, and avoid excessive temperature drop that leads to slag roll-up and sulfur re-dissolution.

[0039] In some embodiments provided in the present application, after step 106 of blowing nitrogen to the bottom of the molten iron for stirring, it also includes: performing a slag skimming operation on the molten iron, the slag skimming rate of the molten iron is ≥95%, the slag amount is ≤2kg / ton of molten iron, and the temperature of the molten iron is controlled to be ≥1300℃.

[0040] In this embodiment, a hydraulic slag scraper or a robotic slag scraper arm is used to ensure that the slag scraping operation covers the entire liquid surface of the molten iron ladle. The laser thickness gauge or image analysis system is controlled to monitor the thickness of the slag layer in real time. The slag scraping force is guided by visual detection combined with laser thickness measurement to control the slag amount, slag layer thickness and slag scraping rate of the molten iron. The slag scraping rate is the ratio of the slag scraped out to the total slag amount of the molten iron. The sulfides generated after desulfurization are enriched in the slag. Slag scraping can reduce the decomposition of residual sulfides in subsequent high-temperature smelting and avoid sulfur dissolving back into the molten iron (the "back-sulfurization" phenomenon). In addition, phosphorus and oxides may be enriched in the slag. The slag scraping operation can reduce the pollution of the molten steel by harmful elements and inclusions. The sulfur content of the molten iron is stable after slag scraping, which is convenient for the subsequent converter to accurately calculate the amount of lime to be added.

[0041] Since hot molten iron has good fluidity, controlling the molten iron temperature allows for more thorough slag-iron separation, while also minimizing the temperature drop during the skimming process. This prevents incomplete skimming due to increased slag viscosity caused by low-temperature skimming. If the molten iron temperature is close to the lower limit of 1300°C, a small amount of heat-insulating agent (such as carbonized rice hulls) can be added before the skimming operation in step 107.

[0042] In some embodiments provided herein, step 102 of adding lime and fluorite to molten iron specifically includes: adding an amount of lime Q 石灰 =40+100×([S] 铁水- 0.010), the amount of fluorite added is Q 石灰 8% to 10%; control the basicity of the final slag of the converter R = CaO / SiO2 ≥ 3.5, and the sulfur capacity in the final slag ≥ 50.

[0043] In this embodiment, during the molten iron converter smelting process, the amount of lime and fluorite added is precisely controlled. The amount of lime needs to cover both sulfur components (residual sulfur in the molten iron + newly generated sulfur). Specifically, the amount of lime added is 35kg / ton to 45kg / ton of steel. The amount of lime added corresponds to the basic requirement when the initial sulfur content of the molten iron is 0.010%. For every 0.001% increase in the sulfur content of the molten iron, the amount of lime needs to be increased by 10kg / ton of steel to provide sufficient lime to react with sulfur to form CaS. For example: when the molten iron sulfur [S] 铁水 When Q is 0.015%, 石灰= 40 + 100 × (0.015 - 0.010) = 45 kg / ton of steel, fluorite = 3.6 kg to 4.5 kg. Dynamically adjusting the amount of lime and fluorite can offset fluctuations in the initial sulfur content of the molten iron, reduce the basicity of the final converter slag, ensure good slag fluidity, avoid hindered sulfur mass transfer that affects desulfurization efficiency, and prevent excessive erosion of the furnace lining caused by excessive addition, thereby making the addition of lime and fluorite more reasonable.

[0044] The final slag basicity at the converter end point is controlled to R = CaO / SiO2 ≥ 3.5 to meet the necessary conditions for desulfurization. The sulfur capacity CS = [%S] / (%S) ≥ 50. This achieves efficient desulfurization while avoiding cost waste or lining damage caused by excessive auxiliary materials, improving process stability and providing molten steel with controllable composition for subsequent refining steps.

[0045] For example, when basicity < 3.5, this is usually due to insufficient lime addition. Add 3kg to 5kg of lime per ton of steel and extend the blowing time by 1 minute. When sulfur capacity (CS) < 50, this is usually due to excessive FeO in the slag (> 15%). Add ferrosilicon from 2kg to 3kg per ton of steel to reduce FeO, and lower the oxygen lance height. When tapping sulfur is > 0.015%, this is usually due to both low basicity and low sulfur capacity. Add aluminum pellets (0.5kg per ton of steel) during the tapping process to improve the desulfurization rate.

[0046] In some embodiments provided in the present application, after step 102 of adding lime and fluorite to the molten iron, the method further includes: obtaining a predicted sulfur content of the molten steel; when the predicted sulfur content is greater than 0.020%, extending the oxygen blowing time of the converter by 1 minute to 2 minutes; and controlling the sulfur content of the steel tapped from the converter to be ≤0.015%.

[0047] In this embodiment, the sulfur content of the molten steel is predicted based on the furnace gas analysis. When the sulfur content is greater than 0.020%, the oxygen blowing time is extended, the oxygen lance is lowered to 1.2m to 1.5m from the liquid surface, and the oxygen supply intensity is increased to 3.5Nm 3 / (min·t) to promote the reaction between oxygen and molten steel, utilizing the oxidation period to enhance the desulfurization effect. Extending the oxygen blowing time can improve desulfurization efficiency, reduce slag viscosity, accelerate sulfur ion diffusion, enhance the impact of oxygen blowing, increase the slag-steel interface area, and shorten the reaction time.

[0048] The sulfur content of the steel tapped from the converter is monitored in real time by means of a secondary lance or a post-furnace rapid sulfur analyzer, and the sulfur content of the steel tapped from the converter is controlled to be ≤0.015%. If the sulfur content of the steel tapped is too high, a lime desulfurizer of 2 kg / ton of steel is added to the molten steel.

[0049] In some embodiments provided in the present application, step 104 of pouring molten steel into the ladle specifically includes: using slag blocking cones and slag blocking balls to perform slag blocking operations, controlling the slag layer thickness of the ladle to ≤30 mm, and controlling the final temperature of the converter to ≥1680°C.

[0050] In this embodiment, sulfur backflow is prevented during the tapping process by controlling the thickness of the slag layer in the ladle through a slag barrier. This controls the amount of slag in the molten steel, reduces the amount of residual slag, ensures an extremely low total amount of sulfur in the slag, and reduces the probability of sulfur back dissolution. When the converter is shut down, the endpoint temperature of the molten steel is measured by a secondary lance. This endpoint temperature is maintained at a high temperature, ensuring more complete slag-steel separation. This also reduces the temperature drop during the slag removal process, preventing incomplete slag removal due to increased slag viscosity caused by low-temperature slag removal.

[0051] In some embodiments provided in the present application, step 104 of adding pre-melted slag into the ladle specifically includes: the components of the pre-melted slag are: 50% CaO, 40% Al2O3, 10% SiO2, and the amount of pre-melted slag added is 3kg / ton of steel to 5kg / ton of steel.

[0052] In this embodiment, the components of the pre-melted slag are limited so that the melting point of the pre-melted slag can be as low as 1300°C to 1450°C, thereby enabling the pre-melted slag to melt quickly in the low temperature environment of the VD furnace. In addition, the pre-melted slag achieves a high sulfur distribution ratio. The sulfur distribution ratio of the CaO-Al2O3-SiO2 slag system can reach 80 to 100. Compared with the sulfur distribution of 50 to 60 components of conventional slag, it is easier to further remove the sulfur in the molten steel from 0.015% to ≤0.005%. The pre-melted slag can quickly form a high-sulfur capacity slag phase. The addition of Al2O3 can reduce the slag viscosity, improve the slag fluidity, accelerate the mass transfer of sulfur from the molten steel to the slag, and increase the mass transfer coefficient. In addition, the high content of 40% Al2O3 has a strong adsorption capacity for Al2O3 inclusions in the steel, purifies the molten steel by adsorbing the inclusions, and reduces the damage of Ds-type inclusions (such as Al2O3 clusters) to the performance of the steel.

[0053] Reasonable limits on the amount of pre-melted slag added can form a 20mm to 30mm slag layer and meet ultra-low sulfur requirements, balancing desulfurization and cost. Avoid insufficient addition, which results in an incomplete slag layer and reduces desulfurization efficiency. Avoid excessive slag volume, which causes slag rolls and affects the vacuum effect in subsequent operations.

[0054] In some embodiments provided in the present application, step 105 of subjecting the molten steel to a slag-steel reaction under vacuum conditions specifically includes: a vacuum degree of the vacuum conditions ≤ 1 mbar, and a sulfur distribution ratio in the slag of 80 to 100.

[0055] In this embodiment, sufficient vacuum is ensured in the ladle, overcoming thermodynamic limitations of the desulfurization reaction and improving desulfurization efficiency, laying the foundation for the production of ultra-low-sulfur steel. The sulfur distribution ratio LS = [%S] / (%S) = 80 to 100. This limiting sulfur distribution ratio ensures a reasonable ratio of sulfur in the slag to sulfur in the molten steel.

[0056] In some embodiments provided in the present application, step 105 of performing a slag-steel reaction on the molten steel under vacuum conditions specifically includes: blowing argon into the VD furnace to stir the molten steel, controlling the flow rate of the argon according to the state of the VD furnace, and the total stirring time is ≥25 minutes.

[0057] In this embodiment, the addition of pre-melted slag is combined with bottom-blown argon to promote slag-steel mixing through argon stirring, shortening the desulfurization reaction time. The argon flow rate is controlled in stages to improve the rationality of the bottom-blowing argon operation.

[0058] Specifically, the step of blowing argon into the VD furnace includes: determining that the vacuum is in the initial state, and the pressure is 0.5Nm 3 / min to 0.8Nm 3 / min; Make sure the VD furnace is in the vacuum holding period and control the argon flow rate to 0.3Nm 3 / min to 0.5Nm 3 / min; Make sure the VD furnace is in the soft blowing state after breaking the vacuum, and control the flow rate of argon to 0.1Nm 3 / min to 0.2Nm 3 / min. The argon flow rate is high during the initial vacuuming phase to quickly mix the molten steel and slag. During the vacuum holding period, the argon flow rate is reduced to promote the transfer of sulfur to the slag phase. During the soft blow after vacuum is broken, the argon flow rate is further reduced to allow slag droplets to float upward and reduce slag entrainment.

[0059] The total stirring time with argon should be ≥ 25 minutes to ensure that sulfur is fully transferred to the slag phase, promote the floating of inclusions, and reduce the residual sulfur and inclusions. The stirring time in the vacuum state should be ≥ 15 minutes, and the stirring time in the soft blowing state should be ≥ 10 minutes.

[0060] In a specific embodiment, Figure 2 As shown, a VD furnace direct smelting process is provided in which the LF furnace is omitted. Through molten iron pre-desulfurization, dynamic control of the converter endpoint and VD furnace slag-steel synergistic reaction, the sulfur content of ordinary rebar is achieved to be ≤0.025%.

[0061] 1. Molten iron pretreatment stage:

[0062] First, the hot metal is pre-desulfurized by injecting a magnesium-based desulfurizer, followed by bottom-blowing nitrogen for stirring to enhance agitation and promote slag-iron separation. The hot metal is then skimmed.

[0063] 2. Converter smelting stage:

[0064] First, optimize the converter slag-making system, limit the amount of lime and fluorite added, and control the final slag basicity. Then, implement converter endpoint sulfur control and a dynamic stop-blowing model. When the predicted sulfur content in the molten steel exceeds 0.020%, extend the oxygen blowing time by 1 to 2 minutes, utilizing the oxidation period for desulfurization to keep the tapping sulfur content ≤ 0.015%. Finally, prevent sulfur reversion during the tapping process by implementing slag blocking operations, using slag blocking cones and balls, and ensuring that the amount of slag carried over the tapping is ≤ 5kg / ton of steel. The final tapping temperature is controlled at ≥ 1680°C to prevent sulfur from re-dissolving into the molten steel due to low-temperature tapping.

[0065] 3. VD furnace assisted desulfurization

[0066] Perform VD slag modification treatment, add pre-melted slag, add low melting point pre-melted slag (composition: CaO50%-A l2 O3 40% - SiO2 10%), and conduct the slag-steel reaction under vacuum conditions. The argon flow rate is controlled in stages. The total stirring time is ≥ 25 minutes.

[0067] In the present invention, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The term "plurality" refers to two or more, unless expressly limited otherwise. Terms such as "installed," "connected," "connected," and "fixed" should be interpreted broadly. For example, "connected" can mean a fixed connection, a detachable connection, or an integral connection; "connected" can mean a direct connection or an indirect connection through an intermediary. Those skilled in the art will understand the specific meanings of these terms in the present invention based on specific circumstances.

[0068] In the description of the present invention, it should be understood that the directions or positional relationships indicated by terms such as "up", "down", "left", "right", "front" and "back" are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or unit referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they should not be understood as limiting the present invention.

[0069] Throughout this specification, terms such as "one embodiment," "some embodiments," and "specific embodiments" mean that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0070] The above are merely some embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A VD furnace low-sulfur smelting method, characterized in that: include: Spraying the molten iron with a magnesium-based desulfurizer, wherein the magnesium-based desulfurizer comprises magnesium powder and lime; transporting the molten iron into a converter, and adding lime and fluorite to the molten iron; smelting the molten iron into molten steel through the converter; pouring the molten steel into a ladle, and adding pre-melted slag into the ladle; The ladle is docked with the vacuum cover of the VD furnace, and the molten steel undergoes slag-steel reaction under vacuum conditions.

2. The VD furnace low-sulfur smelting method according to claim 1, characterized in that: The step of spraying the molten iron with a magnesium-based desulfurizer specifically includes: The mass ratio of the magnesium powder to the lime is 1:2, the injection rate is 8kg / min to 12kg / min, the injection carrier gas pressure is 0.5MPa to 0.8MPa, and the injection time is proportional to the initial sulfur content of the molten iron.

3. The VD furnace low-sulfur smelting method according to claim 1, characterized in that: After the step of spraying the molten iron with a magnesium-based desulfurizer, the method further comprises: Blow nitrogen gas to the bottom of the molten iron for stirring, and the flow rate of the nitrogen gas is 0.3Nm 3 / min to 0.5Nm 3 / min, and the blowing time of the nitrogen is 3 minutes to 5 minutes.

4. The VD furnace low-sulfur smelting method according to claim 3, characterized in that: After the step of blowing nitrogen to the bottom of the molten iron for stirring, the method further comprises: The molten iron is subjected to a slag skimming operation, wherein the slag skimming rate is ≥95%, the slag amount is ≤2kg / ton of molten iron, and the temperature of the molten iron is controlled to be ≥1300°C.

5. The VD furnace low-sulfur smelting method according to claim 1, characterized in that: The step of adding lime and fluorite to the molten iron specifically comprises: Control the amount of lime added Q 石灰 =40+100×([S] 铁水 -0.010), the amount of fluorite added is Q 石灰 8% to 10%; The basicity of the final slag of the converter is controlled to be R=CaO / SiO2≥3.5, and the sulfur capacity in the final slag is controlled to be ≥50.

6. The VD furnace low-sulfur smelting method according to claim 1, characterized in that: After the step of adding lime and fluorite to the molten iron, the method further comprises: Obtaining a predicted value of sulfur content in the molten steel; When the predicted sulfur content is greater than 0.020%, the oxygen blowing time of the converter is extended from 1 minute to 2 minutes; The sulfur content of the steel tapped from the converter is controlled to be ≤0.015%.

7. The VD furnace low-sulfur smelting method according to claim 1, characterized in that: The step of pouring the molten steel into the ladle specifically comprises: Slag blocking operation is performed using slag blocking cones and slag blocking balls, the slag layer thickness of the ladle is controlled to be ≤30mm, and the terminal temperature of the converter is controlled to be ≥1680°C.

8. The VD furnace low-sulfur smelting method according to claim 1, characterized in that: The step of adding pre-melted slag into the ladle specifically comprises: The components of the pre-melted slag are: 50% CaO, 40% Al2O3, 10% SiO2, and the addition amount of the pre-melted slag is 3kg / ton steel to 5kg / ton steel.

9. The VD furnace low-sulfur smelting method according to claim 1, characterized in that: The step of carrying out slag-steel reaction of the molten steel under vacuum conditions specifically comprises: The vacuum degree of the vacuum condition is ≤1 mbar, and the sulfur distribution ratio in the slag is 80 to 100.

10. The VD furnace low-sulfur smelting method according to claim 1, characterized in that: The step of carrying out slag-steel reaction of the molten steel under vacuum conditions specifically comprises: Argon gas is blown into the VD furnace to stir the molten steel. The flow rate of the argon gas is controlled according to the state of the VD furnace. The total stirring time is ≥25 minutes.

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