Method for rapid slag formation during first heat of patched converter

Abstract

The present invention belongs to the technical field of steelmaking, and specifically relates to a method for rapid slag formation during the first heat of a patched converter. The method comprises: adding, along with scrap steel, hot slag from a converter into the converter at the beginning of the first heat of the converter that has been patched; and then adding molten iron and an appropriate amount of lime and light-calcined dolomite into the converter to perform rapid slag formation. In the present invention, the hot slag from the converter is used to replace part of lime and dolomite to perform slag formation, which can achieve rapid slag formation within 5 minutes and yields a dephosphorization rate of 45% or higher. Since the hot slag contains a great amount of TFe and basic CaO and has a high temperature and a good fluidity, the hot slag is added into the converter in the early stages of steelmaking. TFe and CaO have high concentrations, and can thus be combined with acidic oxides and participate in an early dephosphorization reaction, thereby avoiding the problems of poor fluidity, a long melting time, low basicity, a slow slag formation speed, etc., of room-temperature solid slag; therefore, the problems of the low dephosphorization efficiency in the early stage of converter steelmaking and the erosion of a basic furnace lining by acidic slag are ameliorated.

Description

A rapid slag formation method for smelting the first heat of steel after converter repair Technical Field

[0001] This invention belongs to the field of steelmaking technology, and in particular relates to a rapid slag formation method for smelting the first batch of steel after converter repair. Background Technology

[0002] Converter lining repair involves adding magnesia-based lining material to the converter after tapping and slag removal, followed by baking and sintering to bond the lining material with the converter lining. This process significantly extends converter life and reduces steelmaking costs. However, during the first heat of steel produced after lining repair, MgO from the magnesia-based lining material, which is not tightly bonded to the lining, can enter the slag, resulting in higher slag melting temperatures and greater viscosity, which negatively impacts dephosphorization. Furthermore, during the first heat of steel produced after lining repair, auxiliary materials such as 30-50mm lumps of lime and lightly calcined dolomite at room temperature are required for slag formation. These materials require a long melting time and absorb significant heat within the furnace to reach a molten state before forming a fluid slag. Currently, the optimization and improvement of the slag-forming and dephosphorization process during the first heat of steel produced after converter lining repair primarily involves adjusting the amount of lightly calcined dolomite and slagging agents added, as well as the initial slag formation temperature. However, in the early stages of the first heat of steelmaking, the severe oxidation of Si and Mn, resulting in acidic oxides such as SiO2 and MnO, inevitably leads to serious corrosion of the basic furnace lining. Furthermore, these acidic oxides preferentially react with the added auxiliary material, lime (primarily CaO, a basic oxide), causing a dephosphorization reaction during steelmaking: 2[P] + 5(FeO) + 4(CaO) = (4CaO·P2O5) + 5[Fe]. This reduces the reactant concentration and reaction rate, significantly hindering the forward dephosphorization reaction. Therefore, rapidly forming high-basicity, highly fluid slag in the early stages of converter smelting the first heat after furnace repair is of significant practical importance.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a rapid slag formation method for the first heat of steel after converter repair, in order to solve the problems of long time, poor fluidity, low basicity, and slow slag formation rate of slag-forming auxiliary materials such as lime and lightly calcined dolomite added during the first heat of steel smelting after repair, when they are transformed from solid at room temperature to molten at high temperature. This improves the dephosphorization efficiency in the early stage of converter steelmaking and the erosion of basic furnace lining by acidic slag.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A rapid slag-forming method for the first heat of steel after converter repair includes: adding hot converter slag along with scrap steel to the converter furnace at the start of the first heat of steel smelting after converter repair; then adding molten iron and appropriate amounts of lime and lightly calcined dolomite to the converter furnace to rapidly form slag.

[0007] Furthermore, the temperature of the hot slag is 600–1100°C, and even more specifically, 800–1100°C.

[0008] Furthermore, the amount of hot slag added is 25-67 kg / ton of steel.

[0009] Further, the amount of lime added is 8-25 kg / ton of steel; preferably, the lime is added within 2 minutes of the start of oxygen supply to the converter; and / or, the amount of light-burned dolomite added is 15-45 kg / ton of steel, preferably, the light-burned dolomite is added within 2 minutes of the start of oxygen supply to the converter.

[0010] Furthermore, the hot slag comprises, by mass percentage, 10–25% TFe, 22–50% CaO, 1.0–5.0% Al2O3, 4–15% MgO, 10–25% SiO2, 1–4% P2O5, 0–10% TiO2, 2–12% MnO, and 0–8% Cr2O3.

[0011] Furthermore, the basicity R of the hot slag is ≥2.5.

[0012] Furthermore, the composition of the molten iron, by mass percentage, includes: C: 3.8-4.5wt%, Si: 0.18-0.7wt%, P: <0.130wt%, Cr: ≤0.25wt%, with the balance being Fe and unavoidable impurities.

[0013] Furthermore, the temperature of the molten iron is 1250–1400°C;

[0014] And / or, the amount of molten iron added accounts for 70-100% of the total mass of molten iron and scrap steel.

[0015] This invention provides a rapid slag-forming method for the first heat of steel smelting after converter repair. Part of the hot slag from the converter can be transferred to a scrap hopper or trough. When scrap steel is added for the first heat after repair, the hot slag from the converter is added along with the scrap steel into the converter for smelting. The advantages and effects of this invention are:

[0016] a. The rapid slag formation method of this invention involves adding the hot slag from the converter along with the scrap steel into the converter for smelting. This not only allows for the simultaneous recovery and utilization of the composition and heat of the converter slag, but also fully recovers the TFe and CaO in the slag, enabling it to participate in the early dephosphorization reaction in the initial stage of smelting. Furthermore, it reduces the consumption of lime (mainly 85% CaO) in the first batch of furnace repairs, thereby reducing production costs and making the method green, low-carbon, and environmentally friendly.

[0017] b. The hot slag used in the rapid slag formation method of this invention is inherently alkaline, with an alkalinity ≥ 2.5. This alkaline hot slag can react with acidic products in the early stages of converter smelting, thus effectively protecting the alkaline converter lining and reducing lining maintenance costs. Due to the intense oxidation of Si and Mn in the early stages of steelmaking, SiO2 and MnO oxides are generated, which are acidic. Currently, the main material of the converter lining is MgO, which easily undergoes acid-base neutralization reactions with acidic substances, causing lining erosion. This invention adds alkaline slag along with the scrap steel, effectively resisting the erosion of the converter lining by the acidic SiO2 and MnO oxides generated in the early stages of converter smelting, thus better protecting the converter lining and reducing lining maintenance costs.

[0018] c. The hot slag used in the rapid slag formation method of this invention contains abundant physical heat. With the addition of some lime and lightly calcined dolomite and other slag-forming auxiliary materials, slag with a temperature exceeding 1400℃, good fluidity, and a certain degree of alkalinity can be formed in the converter earlier. This promotes dephosphorization in the converter, improves the dephosphorization efficiency in the early stage of converter smelting, reduces the number of reblowing cycles, and reduces the consumption of oxygen, lime, and metal materials. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0020] A rapid slag-forming method for the first heat of steel after converter repair includes: adding hot converter slag along with scrap steel to the converter furnace at the start of the first heat of steel smelting after converter repair; then adding molten iron and appropriate amounts of lime and lightly calcined dolomite to the converter furnace to rapidly form slag.

[0021] This invention discloses a rapid slag-forming method that utilizes hot converter slag to replace a portion of the lime (main component CaO, CaO content 85%) and lightly calcined dolomite (main component MgO, MgO content 15-50%) for slag formation. This method enables rapid slag formation within the first 5 minutes, achieving a dephosphorization rate of over 45%. Because the hot converter slag contains TFe (FeO, Fe2O3) and CaO, which are alkaline and have high temperature and good fluidity, their addition at the initial stage of smelting results in high concentrations and good dispersion of TFe and CaO. This allows them to directly and sufficiently participate in the early dephosphorization reaction and react with acidic oxides (SiO2 / MnO oxides), avoiding the problems of poor fluidity, long melting time, and slow slag-forming rate associated with room-temperature solid slag. Simultaneously, it improves the dephosphorization efficiency in the early stages of converter steelmaking and addresses the erosion of the alkaline furnace lining by acidic slag, while also reducing the cost of adding lime to the slag. Furthermore, during the rapid slag formation of the first heat of steel after furnace repair according to this invention, magnesium balls (MgO pre-formed into spherical shapes) do not need to be added. This is because MgO in the magnesium furnace repair material (MgO content of 60-90%) that is not tightly bonded to the furnace lining will enter the slag. Therefore, there is no need to add magnesium balls, which reduces production costs and prevents the slag from having an excessively high MgO content, which would lead to an increase in the slag melting point and viscosity, thus hindering the dephosphorization and decarburization reactions in the converter.

[0022] As an optional embodiment of the rapid slag formation method of the present invention, the temperature of the hot slag is 600-1100℃, and more specifically 800-1100℃.

[0023] In the above technical solutions, if the slag temperature is too low, the CaO, FeO, and Fe2O3 in the slag need to undergo a longer endothermic reaction, requiring the temperature to rise to 1130℃~1420℃ to form low-melting-point, well-flowing slag such as (CaO·FeO). If the slag temperature is too high, the slag has good fluidity, and the FeO in the high-temperature hot slag added to the converter will undergo a violent reduction reaction with the C in the molten iron, releasing a huge amount of heat and generating a large amount of CO2, which may even lead to an explosion in severe cases. Therefore, the typical, but not limited, temperature of the hot slag is selected as 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, and 1050℃.

[0024] As an optional embodiment of the rapid slag formation method of the present invention, the amount of hot slag added is 25-67 kg / ton of steel.

[0025] In the above technical solution, the hot slag can be transferred to the scrap hopper or scrap trough before furnace repair, and then added to the converter along with the scrap steel when adding scrap steel after furnace repair. The transfer method can be based on the existing equipment and tooling conditions of the steel plant, such as using a loader, dump truck, or container hoisting to transfer it to the scrap hopper or scrap trough. The amount of hot slag added mainly depends on three points: 1. The nominal capacity of the converter used; 2. The size of the scrap hopper or scrap trough, such as the remaining space after the scrap steel is loaded into the scrap hopper; 3. The heat balance of steelmaking when molten iron and scrap steel, i.e., raw materials and auxiliary materials are added. For a 120t nominal capacity converter, the amount of hot slag added is approximately 3-8t (further selected 3-6t), that is, the amount of hot slag used to produce one ton of qualified steel is (3-8) / 120t≈25-67Kg. Therefore, the typical but not limited amount of hot slag added can be 26Kg / ton of steel, 30Kg / ton of steel, 35Kg / ton of steel, 40Kg / ton of steel, 45Kg / ton of steel, 50Kg / ton of steel, 55Kg / ton of steel, 60Kg / ton of steel, or 65Kg / ton of steel.

[0026] In this invention, "ton of steel" refers to the amount of qualified molten steel.

[0027] As an optional embodiment of the rapid slag formation method of the present invention, the amount of lime added is 8-25 kg / ton of steel; preferably, the lime is added within 2 minutes after the start of oxygen supply to the converter;

[0028] And / or, the amount of lightly calcined dolomite added is 15-45 kg / ton of steel, preferably added within 2 minutes of the start of oxygen supply to the converter.

[0029] In the above technical solution, as smelting begins, oxygen is blown in, and Si and Mn will preferentially oxidize to generate SiO2 and MnO. The Φ30~50mm block lime and lightly calcined dolomite added in batches will react chemically with SiO2, as shown in (1) and (2): 2CaO(s) + SiO2(s) = 2CaO·SiO2(s) ΔG 0 (1) =118800-11.3T (1) 3CaO(s)+SiO2(s)=3CaO·SiO2(s) ΔG 0 (1) =118800-6.7T (2)

[0030] Among them, (3CaO·SiO2) has a melting point of 1550℃ and (2CaO·SiO2) has a melting point of 2130℃. Since the temperature of molten iron is usually 1250~1400℃, the temperature of the molten pool is difficult to rise above 1550℃ within 4 minutes before smelting. The (3CaO·SiO2) and (2CaO·SiO2) generated by chemical reactions (1) and (2) are solid below 1550℃ and have poor fluidity. Moreover, this reaction mainly occurs on the surface of lime blocks, which is not conducive to the further melting of lime into slag. Furthermore, the added Φ30~50mm block lime is in a room temperature state and needs to absorb a lot of heat to raise the temperature to 1130℃~1420℃. However, since the added hot slag has a relatively high temperature and contains abundant heat, it greatly makes up for the lack of heat absorption required for lime melting and effectively promotes the rapid dissolution of lime and rapid slag formation.

[0031] Ideally, lime should be added within 2 minutes of the start of oxygen supply to the converter to facilitate early melting and dephosphorization. However, adding too much lime at once can lead to large-scale clumping and caking, forming large floating islands that hinder fluidity and reduce the steel-slag contact area, thus lowering dephosphorization efficiency. Therefore, in the early rapid slag formation, the typical but not limited amount of lime added can be 9 kg / ton of steel, 11 kg / ton of steel, 13 kg / ton of steel, 15 kg / ton of steel, 17 kg / ton of steel, 19 kg / ton of steel, 21 kg / ton of steel, or 23 kg / ton of steel. The typical but not limited amount of lightly calcined dolomite added can be 16 kg / ton of steel, 20 kg / ton of steel, 25 kg / ton of steel, 30 kg / ton of steel, 35 kg / ton of steel, 40 kg / ton of steel, or 44 kg / ton of steel.

[0032] As an optional embodiment of the rapid slag formation method of the present invention, the hot slag comprises, by mass percentage, 10-25% TFe, 22-50% CaO, 1.0-5.0% Al2O3, 4-15% MgO, 10-25% SiO2, 1-4% P2O5, 0-10% TiO2, 2-12% MnO and 0-8% Cr2O3. Among them, TFe can typically, but not limited to, be 11%, 13%, 15%, 17%, 19%, 21%, or 23%; CaO can typically, but not limited to, be 23%, 25%, 27%, 29%, 31%, 33%, 35%, 37%, 39%, 41%, 43%, 45%, 47%, or 49%; MgO can typically, but not limited to, be 5%, 7%, 9%, 11%, or 13%; P2O5 can typically, but not limited to, be 1.5%, 2%, 2.5%, 3%, or 3.5%, etc. The main forms of 10-25% TFe include one or more of elemental iron, Fe2O3, Fe3O4, and FeO. Although both Fe2O3 and FeO can undergo eutectic chemical reactions with CaO, the three in hot slag do not undergo eutectic reactions because the eutectic reaction temperature of (CaO·FeO) is 1130℃, that of (CaO·Fe2O3) is 1220℃, that of (CaO·2Fe2O3) is 1240℃, and that of (2CaO·Fe2O3) is 1420℃. The temperature of hot slag is no higher than 1100℃. Therefore, even if hot slag contains all three, eutectic reactions will not occur between them. When molten iron is added, because the temperature of the molten iron is higher than that of the hot slag, the CaO and FeO components in the hot slag can reach the eutectic temperature of 1130°C with less temperature increase under hot conditions (900-1100°C), and begin to appear in a molten state or even a liquid state. Since the molten or liquid slag has better fluidity than the solid slag, it has a larger contact area with the molten steel, which is conducive to the dephosphorization reaction at the interface between the molten steel and the slag. In addition, the addition of molten iron raises the temperature and also dilutes the hot slag more thoroughly. Therefore, the Fe2O3 in TFe in the hot slag is more likely to react with C in the molten iron to form FeO. The FeO formed and in TFe are more likely to undergo a eutectic chemical reaction with CaO in the newly added room-temperature slag-forming auxiliary material lime. It can utilize its own heat and through a small amount of endothermic reaction to effectively promote the dissolution of the added room-temperature slag-forming auxiliary material—lime—to form a molten slag with good fluidity. The specific reactions are shown in (3) and (4): 2CaO(s) + Fe2O3(s) = 2CaO·Fe2O3(s) ΔG 0 (1) =53100-2.51T (3) CaO(s)+Fe2O3(s)=CaO·Fe2O3(s) ΔG0 (1) =29700-4.81T (4)

[0033] Furthermore, CaO in lime, lightly calcined dolomite, and hot slag, as well as FeO from the conversion of FeO and Fe2O3 in TFe, will participate in the dephosphorization reaction, as follows: 2[P] + 5(FeO) + 4(CaO) = (4CaO·P2O5) + 5[Fe] ΔG 0 (1) =-267750+61.05T (5)

[0034] The addition of CaO and TFe (Fe2O3 and FeO) from the hot slag in the rapid slag formation method of the first furnace after the above-mentioned furnace repair effectively and rapidly increases the reactant concentration in the dephosphorization reaction (5), thereby increasing the reaction rate. Simultaneously, since the added CaO effectively participates in the dephosphorization reaction, it can replace some of the lime, thus saving on lime auxiliary material consumption. Furthermore, reaction (5) is similar to the combustion reaction of C, and the reaction begins at a high enough temperature in the molten iron to support its progress. Moreover, this dephosphorization reaction releases a large amount of heat, which can be used to increase the temperature of the molten iron and the slag, promoting slag melting.

[0035] As an optional embodiment of the rapid slag formation method of the present invention, the hot slag has a certain alkalinity, and more specifically, the alkalinity R of the hot slag is ≥2.5 (e.g., 2.6, 2.8, 3.0, 3.2, 3.4, 3.6, 3.8, 4.0, etc.).

[0036] In this invention, the basicity of the slag is calculated as follows: the sum of the mass percentages of CaO and MgO in the material is divided by the sum of the mass percentages of SiO2 and P2O5, i.e., basicity R = (CaO% + MgO%) / (SiO2% + P2O5%). Because of the intense oxidation of Si and Mn in the early stages of steelmaking, SiO2 and MnO oxides are generated, which are acidic. Currently, the main material of the converter lining is MgO, which easily undergoes acid-base neutralization reactions with acidic substances, causing lining erosion. The hot slag added in this invention has a basicity R (basic oxides / acidic oxides) ≥ 2.5, exhibiting a certain degree of alkalinity, and can preferentially combine and react with the oxides generated in the early stages, avoiding acidic oxide erosion of the lining and reducing converter maintenance costs. Furthermore, since converter slag is a high-basicity waste slag, it usually requires steel plants to transfer and treat it harmlessly. Therefore, the method of this invention fully recycles the hot converter slag, saving production costs and being low-carbon and environmentally friendly.

[0037] As an optional embodiment of the rapid slag formation method of the present invention, the composition of the molten iron, by mass percentage, includes: C: 3.8-4.5 wt%, Si: 0.18-0.7 wt%, P: <0.130 wt%, Cr: ≤0.25 wt%, with the balance being Fe and unavoidable impurities. The C content is typically, but not limited to, 3.9 wt%, 4.0 wt%, 4.1 wt%, 4.2 wt%, 4.3 wt%, 4.4 wt%, etc.

[0038] As an optional embodiment of the rapid slag formation method of the present invention, the temperature of the molten iron is 1250-1400℃ (e.g., 1260℃, 1280℃, 1300℃, 1320℃, 1340℃, 1360℃, 1380℃).

[0039] As an optional embodiment of the rapid slag formation method of the present invention, the amount of molten iron added accounts for 70% to 100% (e.g., 75%, 80%, 85%, 90%, 95%) of the total mass of molten iron and scrap steel.

[0040] The specific embodiments of the present invention will be further explained below with reference to examples and comparative examples:

[0041] Example 1

[0042] During converter repair, the hot slag is added to the scrap hopper using a loader or similar method. After repair, when smelting the first heat of steel, the hot slag is first added to the 120t nominal capacity converter at a rate of 42kg / ton of steel, along with 28.1t of scrap steel. The temperature is then set at 1376℃, and the composition (by mass percentage) includes: C: 4.48%, Si: 0.51%, P: 0.121%, Cr: 0.13%, S: 0.042%, Mn: 0.28%, Ni: 0.02%, Cu: The composition of the molten iron is as follows: 0.02% Mo, 0.01% V, 0.025% Ti, with the remainder being Fe and trace amounts of unavoidable impurities. The weight of the molten iron is 106 tons (molten iron ratio is 79.06%, molten iron ratio = molten iron mass / (molten iron mass + scrap steel mass)). Finally, within 2 minutes of the start of oxygen supply, 40.92 kg / ton of lime and 21.8 kg / ton of lightly calcined dolomite are added in batches. Magnesium shavings are not required, and smelting begins immediately. The temperature of the hot converter slag added is approximately 930℃. Its main components, by mass percentage, are shown in the table below.

[0043] Its alkalinity R = (CaO% + MgO%) / (SiO2% + P2O5%) = 3.3.

[0044] At 3 minutes and 30 seconds into the smelting process, a slag sample was taken from the early stage of converter steelmaking. The results were as follows:

[0045] Its initial slag basicity R = (CaO% + MgO%) / (SiO2% + P2O5%) = 2.14.

[0046] Simultaneously, samples of molten steel were taken from the converter furnace, and the results are as follows (the remainder consisted of Fe and trace amounts of unavoidable impurity elements):

[0047] The above results show that, in the first furnace after remelting using the rapid slag formation method of the present invention, the basicity of the slag in the early stage after 3 minutes and 30 seconds of steelmaking is R = (CaO% + MgO%) / (SiO2% + P2O5%) = 2.14, and the dephosphorization efficiency in the early stage of the converter is (0.121% - 0.065%) / 0.121% × 100% = 46.28%.

[0048] Comparative Example 1

[0049] In the comparative experiment of Example 1, during the converter repair process, the hot slag from the converter was added to the scrap steel hopper using a loader or similar method. After the repair was completed, when starting to smelt the first batch of steel, the prepared slag was first added to the 120t nominal capacity converter at a rate of 42.5 kg / ton of steel, along with 28.4t of scrap steel. The addition temperature was 1368℃, and the composition (by mass percentage) included: C: 4.41%, Si: 0.48%, P: 0.115%, Cr: 0.14%, S: 0.037%, Mn: 0.22%. Ni: 0.02%, Cu: 0.02%, Mo: 0.01%, V: 0.024%, Ti: 0.0624%, with the remainder being Fe and trace amounts of unavoidable impurities. 105.3 tons of molten iron (78.83% iron-to-metal ratio) was added to the converter in batches within 2 minutes after oxygen supply began. 22.0 kg / ton of lightly calcined dolomite and 48.0 kg / ton of lime were added to the converter in batches. Magnesium balls were not added, and smelting commenced immediately. The temperature of the added hot converter slag was approximately 560°C. Its main components, by mass percentage, are shown in the table below.

[0050] Its alkalinity R = (CaO% + MgO%) / (SiO2% + P2O5%) = 3.3.

[0051] When the smelting process reaches 3 minutes and 30 seconds, a sample of the initial slag is taken, and the results are as follows:

[0052] Its initial slag basicity R = (CaO% + MgO%) / (SiO2% + P2O5%) = 1.20.

[0053] Simultaneously, samples of molten steel were taken from the converter furnace, and the results are as follows (the remainder consisted of Fe and trace amounts of unavoidable impurity elements):

[0054] The above results indicate that in the first furnace after the furnace repair, the basicity of the slag in the early stage of steelmaking is R = (CaO% + MgO%) / (SiO2% + P2O5%) = 1.20, and the dephosphorization efficiency in the early stage of the converter is (0.115% - 0.090%) / 0.115% × 100% = 21.7%.

[0055] As can be seen from the above, during the first heat of smelting in the converter, approximately 5 tons of hot slag with a basicity of 3.3 were added along with the scrap steel. The hot slag at approximately 930°C had a relatively higher basicity than the converter slag at approximately 560°C during the initial smelting period of about 3 minutes and 30 seconds. The hot slag at 930°C could absorb less heat to form molten slag, which increased the dephosphorization effect of the early slag in the converter steelmaking process from 21.7% to 46.28%. At the same time, the converter lime was similar.

[0056] Comparative Example 2

[0057] In the comparative experiment of Example 1, during the converter repair process, the hot slag from the converter was added to the scrap steel hopper using a loader or similar method. After the repair was completed, when starting to smelt the first batch of steel, the prepared slag was first added to the 120t nominal capacity converter at a rate of 15 kg / ton of steel, along with 27.3t of scrap steel. The temperature was then set at 1360℃, and the composition (by mass percentage) included: C: 4.42%, Si: 0.46%, P: 0.113%, Cr: 0.13%, S: 0.035%, Mn: 0.21%, N... The composition of the molten iron was 0.02% i, 0.02% Cu, 0.01% Mo, 0.02% V, 0.05% Ti, with the remainder being Fe and trace amounts of unavoidable impurities. The weight of the molten iron was 105.8 t (molten iron ratio 79.49%). After oxygen supply was initiated, 21.5 kg / ton of lightly calcined dolomite and 47.2 kg / ton of lime were added to the converter in batches within 2 minutes. Magnesium balls were not added, and smelting commenced immediately. The temperature of the hot converter slag added was approximately 930°C, and its main components, by mass percentage, remained similar to those in Example 1.

[0058] Its basicity R = (CaO% + MgO%) / (SiO2% + P2O5%) = 3.3. When smelting reaches 3 minutes and 30 seconds, a slag sample is taken from the initial stage, and the results are as follows:

[0059] Its initial slag basicity R = (CaO% + MgO%) / (SiO2% + P2O5%) = 1.49.

[0060] Simultaneously, samples of molten steel were taken from the converter furnace, and the results are as follows (the remainder consisted of Fe and trace amounts of unavoidable impurity elements):

[0061] The above results indicate that in the first furnace after the furnace repair, the slag basicity R in the early stage of steelmaking is (CaO% + MgO%) / (SiO2% + P2O5%) = 1.49, and the dephosphorization efficiency in the early stage of the converter is (0.113% - 0.070%) / 0.113% × 100% = 38%.

[0062] As can be seen from the above, during the first heat of smelting in the converter, hot slag at a temperature of 930°C is added along with the scrap steel. The addition amount is 15 kg / ton of steel, and the total amount added in a 120t converter is about 1.8t. Compared with the addition amount of 5t of hot slag in Example 1, the basicity of the initial slag in the early stage of smelting, about 3 minutes and 30 seconds, is relatively low. Adding a small amount of hot slag at 930°C can absorb less heat to form molten slag, which can improve the dephosphorization effect of the early slag in converter steelmaking to a certain extent, but the effect is not as good as that in Example 1.

[0063] Comparative Example 3

[0064] The comparative test in Example 1, without the addition of hot slag, was as follows: At the beginning of the first heat after the furnace was repaired, 27 tons of scrap steel were added to a 120t nominal capacity converter at a temperature of 1375℃. The composition (by mass percentage) included: C: 4.37%, Si: 0.62%, P: 0.110%, Cr: 0.15%, S: 0.038%, Mn: 0.22%, Ni: 0.02%, Cu: 0.02%, Mo... The iron content was 0.01%, V 0.024%, Ti 0.0624%, with the remainder being Fe and trace amounts of unavoidable impurities. The molten iron weighed 104.6 t (iron ratio 79.48%). After oxygen supply began, 21.7 kg / ton of lightly calcined dolomite and 63.02 kg / ton of lime were added to the converter in batches within 2 minutes. Magnesium balls were not added, and smelting began immediately. When smelting reached 3 minutes and 30 seconds, a slag sample was taken, and the results were as follows:

[0065] Its initial slag basicity R = (CaO% + MgO%) / (SiO2% + P2O5%) = 1.34.

[0066] Simultaneously, samples of molten steel were taken from the converter furnace, and the results are as follows (the remainder consisted of Fe and trace amounts of unavoidable impurity elements):

[0067] The above results indicate that in the first furnace after the furnace repair, the basicity of the slag in the early stage of steelmaking is R = (CaO% + MgO%) / (SiO2% + P2O5%) = 1.34, and the dephosphorization efficiency in the early stage of the converter is (0.110% - 0.097%) / 0.110% × 100% = 11.8%.

[0068] As can be seen from the above, in the first heat of smelting in the converter, the addition of hot converter slag along with the scrap steel in Example 1 results in a relatively high basicity of the initial slag in the early stage of smelting (approximately 3 minutes and 30 seconds) compared to the heat of unheated slag. The hot slag can absorb less heat to form molten slag, which increases the dephosphorization effect of the early slag in converter steelmaking from 11.8% to 46.28%. At the same time, the lime consumption in the converter decreases from 63.02 kg / ton of steel to 40.92 kg / ton of steel.

[0069] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A rapid slag formation method for smelting a first heat of steel after a converter top-up, characterized in that, include: The hot slag from the converter is added into the converter along with the scrap steel at the start of the first heat of steelmaking after the converter is repaired. Then, molten iron is added to the converter furnace along with appropriate amounts of lime and lightly calcined dolomite to rapidly form slag.

2. The rapid slag formation method as claimed in claim 1, wherein, The temperature of the hot slag is 600–1100°C.

3. The rapid slag formation method as claimed in claim 2, wherein, The temperature of the hot slag is 800–1100℃.

4. The rapid slag formation method as described in claim 1, characterized in that, The amount of hot slag added is 25-67 kg / ton of steel.

5. The rapid slag formation method as described in claim 1, characterized in that, The amount of lime added is 8-25 kg / ton of steel; preferably, the lime is added within 2 minutes of the start of oxygen supply to the converter; and / or, the amount of light-burned dolomite added is 15-45 kg / ton of steel; preferably, the light-burned dolomite is added within 2 minutes of the start of oxygen supply to the converter.

6. The rapid slag formation method as described in claim 1, characterized in that, The hot slag comprises, by mass percentage, 10–25% TFe, 22–50% CaO, 1.0–5.0% Al2O3, 4–15% MgO, 10–25% SiO2, 1–4% P2O5, 0–10% TiO2, 2–12% MnO, and 0–8% Cr2O3.

7. The rapid slag formation method as described in claim 1, characterized in that, The basicity R of the hot slag is ≥2.

5.

8. The rapid slag formation method as described in claim 1, characterized in that, The composition of the molten iron, by mass percentage, includes: C: 3.8-4.5wt%, Si: 0.18-0.7wt%, P: <0.130wt%, Cr: ≤0.25wt%, with the balance being Fe and unavoidable impurities.

9. The rapid slag formation method as described in claim 1, characterized in that, The temperature of the molten iron is 1250-1400℃; the amount of molten iron added accounts for 70-100% of the total mass of molten iron and scrap steel.

10. The rapid slag formation method as described in claim 1, characterized in that, The rapid slag formation time shall not exceed 5 minutes, and the resulting dephosphorization efficiency shall not be less than 45%.

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