Rapid slagging method for smelting first furnace steel after converter fettling

Abstract

The invention belongs to the technical field of steelmaking, and particularly relates to a rapid slagging method for smelting first furnace steel after converter fettling, which comprises the following steps of: adding hot-state slag of a converter into a converter along with scrap steel when the smelting of the first furnace steel after converter fettling begins; and then molten iron is added into the converter, a proper amount of lime and light-burned dolomite are added, and rapid slagging is carried out. According to the method, the hot-state slag of the converter is used for replacing part of lime and dolomite for slagging, rapid slagging can be achieved within 5 min, and the dephosphorization rate reaches 45% or above. As the hot-state slag contains more TFe and alkaline CaO, and is higher in temperature and better in fluidity, the hot-state slag is added into the converter in the initial stage of smelting, and the TFe and the CaO are high in concentration, can be combined with acidic oxides and participate in an early-stage deP reaction, so that the problems of poor fluidity, long melting time, low alkalinity and low slagging rate of normal-temperature solid-state slag charge are solved; therefore, the problems of low deP efficiency in the early stage of converter steelmaking and alkaline lining erosion by acid slag are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of steelmaking, and in particular relates to a rapid slag forming method for smelting the first heat of steel after a converter is replenished. Background Art

[0002] The converter restocking is a furnace protection process in which magnesium restocking materials are added to the converter furnace after the converter is tapped and the slag is poured, and the magnesium restocking materials are baked and sintered to combine with the converter lining. This process can greatly increase the converter life and reduce the converter steelmaking cost. However, when the first batch of steel is smelted after the converter is restocked, the MgO in the magnesium restocking materials that are not tightly combined with the lining will enter the slag, resulting in a high melting temperature and high viscosity of the slag, which is unfavorable for converter dephosphorization. In addition, when smelting the first batch of steel after the restocking, auxiliary materials such as Φ30-50mm blocks and room temperature lime and light-burned dolomite need to be added for slag making. Therefore, the auxiliary materials need to be melted for a long time and need to absorb more heat in the furnace to be transformed into a molten state, and then a slag with good fluidity can be formed. At present, when smelting the first batch of steel after the converter is restocked, the slag making and dephosphorization process is mainly optimized and improved by adjusting the amount of light-burned dolomite and slag-removing agent added and the initial slag forming temperature. However, in the early stage of the first steelmaking, the problem of acidic oxides such as SiO2 and MnO generated by the violent oxidation of Si and Mn seriously corroding the alkaline furnace lining cannot be avoided. Moreover, acidic oxides such as SiO2 and MnO will preferentially react with the added auxiliary material lime (main component CaO, which is an alkaline oxide), which leads to the dephosphorization reaction of steelmaking: 2[P]+5(FeO)+4(CaO)=(4CaO·P2O5)+5[Fe]. The concentration of reactants decreases, the reaction rate decreases, and the forward progress of the dephosphorization reaction is greatly hindered. Therefore, how to quickly form the early converter slag with high basicity and good fluidity when smelting the first steel after the furnace is replenished has a good practical significance.

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

[0004] The object of the present invention is to provide a rapid slag forming method for smelting the first heat of steel after a converter is repaired, so as to solve the problems of long time for slag forming auxiliary materials such as lime and light-burned dolomite added during the smelting of the first heat of steel after the repair to transform from a solid state at room temperature to a high-temperature molten state, poor fluidity, low basicity and slow slag forming rate, thereby improving the P removal efficiency in the early stage of converter steelmaking and the corrosion of acidic slag on the basic furnace lining.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A rapid slag forming method for smelting the first heat of steel after a converter is replenished comprises: adding hot converter slag together with scrap steel into the converter at the beginning of smelting the first heat of steel after the converter is replenished; then adding molten iron into the converter and adding appropriate amounts of lime and light-burned dolomite to form slag rapidly.

[0007] Furthermore, the temperature of the hot slag is 600-1100°C, and further 800-1100°C.

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

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

[0010] Furthermore, the composition of the hot slag includes, 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 of the hot slag is R≥2.5.

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

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

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

[0015] The present invention provides a rapid slag forming method for smelting the first heat of steel after a converter is replenished. Part of the hot slag of the converter can be transferred to a scrap steel bucket or a scrap steel tank. When the first furnace starts to add scrap steel after the furnace is replenished, the hot slag of the converter is added to the converter furnace together with the scrap steel for smelting. The advantages and effects of the present invention are:

[0016] a. The rapid slag forming method of the present invention is to add the hot slag of the converter together with the scrap steel into the converter furnace for smelting, which can not only recycle the components and heat of the converter slag at the same time, but also fully recycle the TFe and CaO in the slag so that they can participate in the early P removal reaction in the early stage of smelting, and can also reduce the consumption of lime (mainly 85% CaO) in the first furnace of the replenishment furnace, reduce production costs, and be green, low-carbon and environmentally friendly.

[0017] b. The hot slag used in the rapid slag forming method of the present invention is alkaline, with a basicity of ≥2.5. The alkaline hot slag can react with the acidic product in the early stage of converter smelting, thereby better protecting the alkaline converter lining and reducing the maintenance cost of the lining. Due to the intense oxidation of Si\Mn in the early stage of steelmaking, SiO2\MnO oxides are generated, which are acidic; and the main material of the converter lining is MgO, which is easy to react with acidic substances to cause acid-base neutralization reaction, causing lining erosion. The present invention adds alkaline slag along with scrap steel to effectively resist the corrosion of the lining by the SiO2\MnO acidic oxides generated by the early reaction of converter smelting, better protect the converter lining and reduce the maintenance cost of the lining.

[0018] c. The hot slag used in the rapid slag-forming method of the present invention contains rich physical heat. By adding some lime, light-burned dolomite and other slag-forming auxiliary materials, slag with a temperature exceeding 1400°C, good fluidity and a certain basicity can be formed in the converter earlier, which promotes the dephosphorization of the converter, improves the dephosphorization efficiency in the early stage of converter smelting, reduces the number of reblowing times, and reduces the consumption of oxygen, lime and metal materials. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention. The process parameters of the following embodiments that do not specify specific conditions are usually based on conventional conditions.

[0020] A rapid slag forming method for smelting the first heat of steel after a converter is replenished comprises: adding hot converter slag together with scrap steel into the converter at the beginning of smelting the first heat of steel after the converter is replenished; then adding molten iron into the converter and adding appropriate amounts of lime and light-burned dolomite to form slag rapidly.

[0021] The rapid slag forming method of the present invention can rapidly form slag within the first 5 minutes and the dephosphorization rate reaches more than 45% by using the hot slag of the converter to replace part of the lime (main component CaO, CaO content is 85%) and lightly burned dolomite (main component MgO, MgO content is 15-50%) for slag forming. Since the TFe (FeO, Fe2O3) and CaO contained in the hot slag are both alkaline, and the temperature is relatively high and the fluidity is relatively good, after being added in the early stage of smelting, the TFe and CaO concentrations are high and the dispersion is relatively good, and they can directly and fully participate in the early dephosphorization reaction and react with the acidic oxides (SiO2\MnO oxides) at the same time, avoiding the problems of poor fluidity, long melting time and slow slag forming rate of the solid slag at room temperature due to low basicity, and at the same time improving the dephosphorization efficiency in the early stage of converter steelmaking and the problem of corrosion of the acidic slag on the alkaline furnace lining and reducing the cost of adding slag lime. In addition, magnesium balls (MgO prefabricated into spherical materials) do not need to be added during the rapid slag formation in the first batch of steel after the furnace repair of the present invention, because the MgO in the magnesium furnace repair material (MgO content is 60-90%) that is not tightly combined with the furnace lining will enter the slag, so there is no need to add additional magnesium balls, which reduces production costs and prevents the MgO content in the slag from being too high, resulting in an increase in the melting point of the slag and an increase in viscosity, which is not conducive to the de-P and decarburization reactions of the converter.

[0022] As an optional implementation of the rapid slag forming method of the present invention, the temperature of the hot slag is 600-1100°C, further 800-1100°C.

[0023] In the above technical solution, if the slag temperature is too low, the CaO, FeO and Fe2O3 in the slag need to undergo a longer endothermic reaction and raise the temperature to 1130°C to 1420°C to form a slag with a low melting point and good fluidity such as (CaO·FeO). If the slag temperature is too high, the slag fluidity is good, 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 huge heat and generating a large amount of CO2, and even explosion in severe cases. Therefore, the temperature of the hot slag is typically but not limitatively selected to be 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C.

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

[0025] In the above technical scheme, the hot slag can be transferred to the scrap steel bucket or scrap steel trough before the furnace is replenished, and added to the converter furnace together with the scrap steel when the converter is added with scrap steel after the furnace is replenished. The transfer method can be carried out according to the existing equipment and tooling conditions of the steel plant, such as transferring to the scrap steel bucket or scrap steel trough by means of a forklift, a dump truck, or a container hoisting. The amount of hot slag added is mainly based on three points: 1. The nominal capacity of the converter used; 2. The size of the scrap steel bucket or scrap steel trough, such as the remaining space after the scrap steel bucket is loaded with scrap steel; 3. The heat balance of steelmaking added by molten iron and scrap steel, i.e., raw and auxiliary materials. For a 120t nominal capacity converter, the amount of hot slag added is approximately 3 to 8t (further selected as 3 to 6t), that is, the amount of hot slag used to produce each ton of qualified steel is (3 to 8) / 120t≈25 to 67Kg. Therefore, the amount of hot slag added can be typically but not limitedly selected as 26Kg / ton steel, 30Kg / ton steel, 35Kg / ton steel, 40Kg / ton steel, 45Kg / ton steel, 50Kg / ton steel, 55Kg / ton steel, 60Kg / ton steel, and 65Kg / ton steel.

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

[0027] As an optional implementation of the rapid slagging 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 the light-burned dolomite added is 15-45 kg / ton of steel, and the light-burned dolomite is 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 are preferentially oxidized to generate SiO2 and MnO. The Φ30-50 mm block lime and lightly burned dolomite added in batches react chemically with SiO2, as shown in (1) and (2):

[0030] 2CaO(s)+SiO2(s)=2CaO·SiO2(s) ΔG 0 (1) =118800-11.3T (1)

[0031] 3CaO(s)+SiO2(s)=3CaO·SiO2(s) ΔG 0 (1) =118800-6.7T (2)

[0032] The melting point of (3CaO·SiO2) is 1550℃, and the melting point of (2CaO·SiO2) is 2130℃. Since the temperature of molten iron is usually 1250~1400℃, the temperature of the molten pool is difficult to rise to 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 and only occurs on the surface of the lime block, which is not conducive to the further melting and slag formation of lime. In addition, the added Φ30~50mm block lime is at room temperature and needs to absorb more heat to raise the temperature to 1130℃~1420℃. Since the added hot slag has a relatively high temperature and contains abundant heat, it greatly makes up for the lack of heat required for lime melting, effectively promoting the rapid dissolution and rapid slag formation of lime.

[0033] It is preferred that within 2 minutes after the start of oxygen supply to the converter, lime is added early, melted early and P is removed early, but if too much is added at one time, there will be a large number of piles piled together and hardened, forming large floating islands, which is not conducive to improving fluidity, thus reducing the contact area of ​​slag and reducing the P removal efficiency. Therefore, in the early rapid slag formation, the amount of lime added can be typically but not limited to 9Kg / ton steel, 11Kg / ton steel, 13Kg / ton steel, 15Kg / ton steel, 17Kg / ton steel, 19Kg / ton steel, 21Kg / ton steel, 23Kg / ton steel. The amount of light-burned dolomite added can be typically but not limited to 16Kg / ton steel, 20Kg / ton steel, 25Kg / ton steel, 30Kg / ton steel, 35Kg / ton steel, 40Kg / ton steel, 44Kg / ton steel.

[0034] As an optional embodiment of the rapid slag forming method of the present invention, the composition of the hot slag includes, 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 be typically but not limitedly selected as 11%, 13%, 15%, 17%, 19%, 21%, 23%; CaO can be typically but not limitedly selected as 23%, 25%, 27%, 29%, 31%, 33%, 35%, 37%, 39%, 41%, 43%, 45%, 47%, 49%; MgO can be typically but not limitedly selected as 5%, 7%, 9%, 11%, 13%; P2O5 can be typically but not limitedly selected as 1.5%, 2%, 2.5%, 3%, 3.5%, and so on. The main forms of 10-25% TFe include one or more of elemental iron, Fe2O3, Fe3O4 and FeO. Although Fe2O3 and FeO will undergo eutectic chemical reaction with CaO, the three in the hot slag will not undergo eutectic reaction because the eutectic reaction temperature of (CaO·FeO) is 1130°C, the eutectic reaction temperature of (CaO·Fe2O3) is 1220°C, the eutectic reaction temperature of (CaO·2Fe2O3) is 1240°C, and the eutectic reaction temperature of (2CaO·Fe2O3) is 1420°C, while the temperature of hot slag is not higher than 1100°C. Therefore, even if the hot slag contains the three at the same time, no eutectic reaction will occur between them. After the addition of molten iron, since the temperature of the molten iron is higher than that of the hot slag, the CaO and FeO components in the hot slag can be heated up less in the hot state (900-1100°C), that is, reach the eutectic temperature of 1130°C, and begin to melt or even liquid. Because the molten state 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 increases the temperature and dilutes the hot slag more fully. Therefore, the Fe2O3 in TFe in the hot slag is more likely to react with C in the molten iron to generate FeO, and the generated FeO in TFe is more likely to react with the CaO in the newly added room temperature slag-making auxiliary material lime to generate eutectic chemical reaction, which can utilize its own heat and a small amount of endothermic reaction to effectively promote the dissolution of the added room temperature slag-making auxiliary material - lime, and generate molten slag with good fluidity. The specific reactions are shown in (3) and (4):

[0035] 2CaO(s)+Fe2O3(s)=2CaO·Fe2O3(s) ΔG 0 (1) =53100-2.51T (3)

[0036] CaO(s)+Fe2O3(s)=CaO·Fe2O3(s) ΔG 0 (1) =29700-4.81T (4)

[0037] Furthermore, CaO in lime, light-burned dolomite and hot slag, as well as FeO in TFe and FeO converted from Fe2O3, will participate in the P removal reaction as follows:

[0038] 2[P]+5(FeO)+4(CaO)=(4CaO·P2O5)+5[Fe] ΔG 0 (1) =-267750+61.05T (5)

[0039] The CaO and TFe (Fe2O3 and FeO) added to the hot slag in the rapid slag-forming method of the first furnace after the above-mentioned furnace repair can effectively and quickly increase the concentration of reactants in the dephosphorization reaction (5) and improve the reaction rate. At the same time, since the added CaO effectively participates in the dephosphorization reaction and can replace part of the lime, the consumption of lime auxiliary materials is saved. In addition, reaction (5) is similar to the combustion reaction of C. The reaction starts because the molten iron temperature is high enough to support the reaction. And this dephosphorization reaction releases a large amount of heat, and the released heat can be used to increase the temperature of the molten iron and the slag to promote the melting of the slag.

[0040] As an optional implementation of the rapid slag forming method of the present invention, the hot slag has a certain basicity. Furthermore, the basicity of the hot slag is R≥2.5 (such as 2.6, 2.8, 3.0, 3.2, 3.4, 3.6, 3.8, 4.0, etc.).

[0041] In the present invention, the basicity of the slag is calculated as follows: the sum of the mass percentages of CaO and MgO in the material composition is divided by the sum of the mass percentages of SiO2 and P2O5, that is, the basicity R = (CaO% + MgO%) / (SiO2% + P2O5%). Because of the intense oxidation of Si\Mn in the early stage of steelmaking, SiO2\MnO oxides are generated, which are acidic; and the main material of the converter lining is MgO, which is easy to react with acidic substances to cause acid-base neutralization reaction, causing lining corrosion. The hot slag added in the present invention has a basicity R (basic oxide / acidic oxide) ≥ 2.5, which is alkaline and can preferentially react with the oxides generated in the early stage, thereby avoiding acidic oxides from corroding the lining and reducing the maintenance cost of the converter. In addition, since the converter slag is a waste slag with high basicity, it usually needs to be transported and harmlessly treated by the steel plant, so the method of the present invention fully recycles the hot slag of the converter, saves production costs, and is low-carbon and environmentally friendly.

[0042] As an optional embodiment of the rapid slag forming method of the present invention, the composition of the molten iron includes, by mass percentage: C: 3.8-4.5wt%, Si: 0.18-0.7wt%, P: <0.130wt%, Cr: ≤0.25wt%, and the balance is Fe and inevitable impurities. Among them, C can be typically but not limitedly selected to be 3.9wt%, 4.0wt%, 4.1wt%, 4.2wt%, 4.3wt%, 4.4wt%, etc.

[0043] As an optional implementation of the rapid slag forming method of the present invention, the temperature of the molten iron is 1250-1400°C (such as 1260°C, 1280°C, 1300°C, 1320°C, 1340°C, 1360°C, 1380°C).

[0044] As an optional implementation of the rapid slag forming method of the present invention, the amount of molten iron added accounts for 70-100% (such as 75%, 80%, 85%, 90%, 95%) of the total mass of molten iron and scrap steel.

[0045] The specific implementation of the present invention is further explained below in conjunction with examples and comparative examples:

[0046] Example 1

[0047] During the converter restocking process, the hot slag of the converter is added to the scrap steel bucket by means of a forklift or the like. After the restocking is completed, when the first batch of steel is smelted, the hot slag is first added to the converter with a nominal capacity of 120t at a rate of 42kg / ton of steel, and 28.1t of scrap steel is added at the same time; then the temperature is 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: 0.02%, Mo: 0.01%, V: 0.025%, Ti: 0.0524, the rest are Fe and trace inevitable impurity elements, weighing 106t of molten iron (molten iron ratio is 79.06%, molten iron ratio = molten iron mass / (molten iron mass + scrap steel mass)); finally, within 2 minutes after the start of oxygen supply, 40.92kg / ton of steel lime and 21.8kg / ton of steel light-burned dolomite are added in batches, and magnesium balls are not added, and smelting begins. The temperature of the added converter hot slag is about 930℃, and its main components are calculated by mass percentage as follows:

[0048] Element <![CDATA[Al2O3]]> MgO <![CDATA[SiO2]]> CaO <![CDATA[P2O5]]> <![CDATA[TiO2]]> MnO <![CDATA[Cr2O3]]> TFe content% 1.81 9.28 14.49 45.58 2.324 1.186 2.25 2.22 14.86

[0049] Its basicity R = (CaO% + MgO%) / (SiO2% + P2O5%) = 3.3.

[0050] At 3 minutes and 30 seconds of smelting, a sample of the slag from the early stage of converter steelmaking was taken, and the results were:

[0051] Element <![CDATA[Al2O3]]> MgO <![CDATA[SiO2]]> CaO <![CDATA[P2O5]]> <![CDATA[TiO2]]> MnO TFe content% 3.66 5.34 18.13 37.96 2.06 1.172 7.83 17.86

[0052] The initial slag basicity R = (CaO% + MgO%) / (SiO2% + P2O5%) = 2.14.

[0053] At the same time, take the molten steel sample in the converter furnace, and the inspection results are as follows (the rest are Fe and trace amounts of unavoidable impurity elements):

[0054] Element C Si Mn P S Cr Ni Cu Mo V Ti content% 3.66 0.01 0.16 0.065 0.040 0.06 0.02 0.02 0.01 0.01 0.01

[0055] The above results show that when the first furnace after the repair furnace is smelted by the rapid slag forming method of the present invention, the basicity of the early slag at 3min30s of steelmaking is R=(CaO%+MgO%) / (SiO2%+P2O5%)=2.14, and the P removal efficiency in the early stage of the converter is=(0.121%-0.065%) / 0.121%×100%=46.28%.

[0056] Comparative Example 1

[0057] In the comparative test of Example 1, during the converter restocking process, the hot slag of the converter was added into the scrap steel bucket by a forklift or other means. After the restocking was completed, when the first batch of steel was smelted, the slag prepared above was first added to the converter with a nominal capacity of 120t at an amount of 42.5Kg / ton of steel, and 28.4t of scrap steel was added at the same time; then the 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, the rest are Fe and trace inevitable impurity elements, 105.3t of molten iron (molten iron ratio is 78.83%), after oxygen supply starts, 22.0kg / ton of steel light-burned dolomite and 48.0kg / ton of steel lime are added to the converter in batches within 2 minutes, and magnesium balls are not added, and smelting begins. The temperature of the hot converter slag added is about 560℃, and its main components are calculated by mass percentage as follows:

[0058] Element <![CDATA[Al2O3]]> MgO <![CDATA[SiO2]]> CaO <![CDATA[P2O5]]> <![CDATA[TiO2]]> MnO <![CDATA[Cr2O3]]> TFe content% 1.81 9.28 14.49 45.58 2.324 1.186 2.25 2.22 14.86

[0059] Its basicity R = (CaO% + MgO%) / (SiO2% + P2O5%) = 3.3.

[0060] When the smelting reaches 3 minutes and 30 seconds, the early slag sample is taken, and the result is:

[0061] Element <![CDATA[Al2O3]]> MgO <![CDATA[SiO2]]> CaO <![CDATA[P2O5]]> <![CDATA[TiO2]]> MnO TFe content% 2.35 4.35 23.56 25.08 1.02 1.03 9.95 20.05

[0062] The initial slag basicity R = (CaO% + MgO%) / (SiO2% + P2O5%) = 1.20.

[0063] At the same time, take the molten steel sample in the converter furnace, and the inspection results are as follows (the rest are Fe and trace amounts of unavoidable impurity elements):

[0064] Element C Si Mn P S Cr Ni Cu Mo V Ti content% 3.77 0.01 0.10 0.090 0.036 0.07 0.02 0.02 0.01 0.01 0.01

[0065] The above results show that in the first furnace after the repair, the basicity of the slag in the early stage of steelmaking is R = (CaO% + MgO%) / (SiO2% + P2O5%) = 1.20, and the P removal efficiency in the early stage of the converter is = (0.115% - 0.090%) / 0.115% × 100% = 21.7%.

[0066] From the above, it can be seen that during the first smelting of the converter replenishment furnace, a total of about 5t of hot slag with a basicity of 3.3 is added together with the scrap steel, among which the hot slag at about 930°C has a relatively high basicity than the converter slag at a temperature of about 560°C. The initial slag at the early stage of smelting for about 3 minutes and 30 seconds has a relatively high basicity. The hot slag at 930°C can absorb less heat to form molten slag, which promotes the dephosphorization effect of the early slag of converter steelmaking from 21.7% to 46.28%, and the converter lime is similar.

[0067] Comparative Example 2

[0068] In the comparative test of Example 1, during the converter restocking process, the hot slag of the converter was added into the scrap steel bucket by a forklift or the like. After the restocking was completed, when the first batch of steel was smelted, the slag prepared above was first added to the converter with a nominal capacity of 120t at an amount of 15Kg / ton of steel, and 27.3t of scrap steel was added at the same time; then the temperature of the slag was 1360°C, 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 i: 0.02%, Cu: 0.02%, Mo: 0.01%, V: 0.02%, Ti: 0.055, the rest are Fe and trace inevitable impurity elements, the weight is 105.8t of molten iron (molten iron ratio is 79.49%); finally, after the oxygen supply starts, 21.5kg / ton of steel light-burned dolomite and 47.2kg / ton of steel lime are added to the converter in batches within 2 minutes, and magnesium balls are not added, and smelting begins. The temperature of the hot converter slag added is about 930°C, and its main components are kept similar to those in Example 1 in terms of mass percentage.

[0069] Element <![CDATA[Al2O3]]> MgO <![CDATA[SiO2]]> CaO <![CDATA[P2O5]]> <![CDATA[TiO2]]> MnO <![CDATA[Cr2O3]]> TFe content% 1.81 9.28 14.49 45.58 2.324 1.186 2.25 2.22 14.86

[0070] Its basicity R = (CaO% + MgO%) / (SiO2% + P2O5%) = 3.3. When the smelting reaches 3 minutes and 30 seconds, the early slag sample is taken, and the result is:

[0071] Element <![CDATA[Al2O3]]> MgO <![CDATA[SiO2]]> CaO <![CDATA[P2O5]]> <![CDATA[TiO2]]> MnO TFe content% 2.20 5.31 23.06 30.48 1.03 1.11 9.88 19.35

[0072] The initial slag basicity R = (CaO% + MgO%) / (SiO2% + P2O5%) = 1.49.

[0073] At the same time, take the molten steel sample in the converter furnace, and the inspection results are as follows (the rest are Fe and trace amounts of unavoidable impurity elements):

[0074] Element C Si Mn P S Cr Ni Cu Mo V Ti content% 3.47 0.01 0.09 0.070 0.036 0.08 0.02 0.02 0.01 0.01 0.01

[0075] The above results show that in the first furnace after the repair, the slag basicity R in the early stage of steelmaking is (CaO% + MgO%) / (SiO2% + P2O5%) = 1.49, and the P removal efficiency in the early stage of the converter is = (0.113% - 0.070%) / 0.113% × 100% = 38%.

[0076] From the above, it can be seen that during the first smelting of the converter replenishment furnace, hot slag with a temperature of 930°C is added together with the scrap steel. The amount added is 15Kg / ton of steel. The total amount added to the 120t converter is about 1.8t. Compared with the hot slag of 5t added in Example 1, the basicity of the initial slag in the early stage of smelting for 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 of converter steelmaking to a certain extent, but the effect is not as good as that in Example 1.

[0077] Comparative Example 3

[0078] The comparative test of Example 1 does not add hot slag, specifically as follows: at the beginning of the first heat after the furnace repair, 27 tons of scrap steel is added to a nominal capacity 120t converter at a temperature of 1375°C, and the composition (by mass percentage) includes: 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: 0.02%, Cu ... :0.01%, V:0.024%, Ti:0.0624, the rest are Fe and trace inevitable impurity elements, the weight is 104.6t of molten iron (molten iron ratio is 79.48%); after the start of oxygen supply, 21.7kg / ton of steel light-burned dolomite and 63.02kg / ton of steel lime are added to the converter in batches within 2 minutes, without adding magnesium balls, and smelting begins. When smelting reaches 3 minutes and 30 seconds, the early slag sample is taken, and the result is:

[0079] Element <![CDATA[Al2O3]]> MgO <![CDATA[SiO2]]> CaO <![CDATA[P2O5]]> <![CDATA[TiO2]]> MnO TFe content% 2.85 4.38 22.07 26.58 1.06 1.172 10.03 19.86

[0080] The initial slag basicity R = (CaO% + MgO%) / (SiO2% + P2O5%) = 1.34.

[0081] At the same time, take the molten steel sample in the converter furnace, and the inspection results are as follows (the rest are Fe and trace amounts of unavoidable impurity elements):

[0082]

[0083]

[0084] The above results show that in the first furnace after the repair, the basicity of the slag in the early stage of steelmaking is R = (CaO% + MgO%) / (SiO2% + P2O5%) = 1.34, and the P removal efficiency in the early stage of the converter is = (0.110% - 0.097%) / 0.110% × 100% = 11.8%.

[0085] From the above, it can be seen that during the first smelting of the converter replenishment furnace, Example 1 adds hot converter slag together with scrap steel for smelting in the converter furnace. Compared with the furnace without heated slag, in the early period of about 3 minutes and 30 seconds of smelting, the initial slag has a relatively high basicity, and the hot slag can absorb less heat to form molten slag, which promotes the dephosphorization effect of the early slag of converter steelmaking from 11.8% to 46.28%. At the same time, the converter lime consumption is reduced from 63.02 kg / ton of steel to 40.92 kg / ton of steel.

[0086] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A rapid slag forming method for smelting the first heat of steel after a converter repair, characterized in that: include: The hot slag of the converter is added into the converter furnace together with the scrap steel at the beginning of the first steelmaking after the converter is replenished; Then, molten iron is added into the converter furnace and an appropriate amount of lime and light-burned dolomite are added for rapid slag formation.

2. The rapid slag forming method according to claim 1, characterized in that: The temperature of the hot slag is 600-1100°C.

3. The rapid slag forming method according to claim 2, characterized in that: The temperature of the hot slag is 800-1100°C.

4. The rapid slag forming method according to claim 1, characterized in that: The amount of hot slag added is 25-67 kg / ton of steel.

5. The rapid slag forming method according to 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 after 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 after the start of oxygen supply to the converter.

6. The rapid slag forming method according to claim 1, characterized in that: The composition of the hot slag includes, 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 forming method according to claim 1, characterized in that: The basicity of the hot slag is R≥2.

5.

8. The rapid slag forming method according to claim 1, characterized in that: The components of the molten iron include, by mass percentage: C: 3.8-4.5wt%, Si: 0.18-0.7wt%, P: <0.130wt%, Cr: ≤0.25wt%, and the remainder is Fe and unavoidable impurities.

9. The rapid slag forming method according to claim 1, characterized in that: The temperature of the molten iron is 1250-1400° C.; the amount of the molten iron added accounts for 70-100% of the total mass of the molten iron and scrap steel.

10. The rapid slag forming method according to claim 1, characterized in that: The rapid slag forming time does not exceed 5 minutes, and the obtained dephosphorization efficiency is not less than 45%.

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