Efficient demanganizing agent, preparation method thereof and molten steel demanganizing method after converter tapping

Abstract

The invention discloses an efficient demanganizing agent, a preparation method of the efficient demanganizing agent and a molten steel demanganizing method after converter tapping. The efficient demanganizing agent comprises the following raw material components: CaF2 and FeO / Al2O3 composite particles, wherein the FeO / Al2O3 composite particles comprise a FeO inner core and a nano Al2O3 coating, and the surface of the FeO inner core is coated with the nano Al2O3 coating. According to the method, the efficient demanganizing agent is added after converter tapping, the purpose of deep demanganizing is achieved by increasing the oxidability of the top slag of the molten steel, the low-manganese steel production process is simplified, the purpose of deep demanganizing of the low-manganese steel can be achieved without purchasing low-manganese iron ore, adopting converter duplex or double-slag smelting and demanganizing in modes such as over-blowing, and the method is safe, reliable and low in cost. The production cost of the low-manganese steel can be reduced, and meanwhile furnace lining erosion can be effectively avoided.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, and more specifically, to a highly efficient demanganese agent, its preparation method, and a method for demanganese removal from molten steel after tapping from a converter. Background Technology

[0002] Low-manganese steel is increasingly favored by users due to its excellent physical properties. Currently, the internationally accepted method for smelting low-manganese steel in converters is to use low-manganese molten iron for smelting, employing either double-slag or double-slag smelting in converters. The endpoint relies on large slag volume, low temperature, and high oxidizing properties for demanganese removal. The disadvantages are as follows: First, the cost of smelting low-manganese steel is high. Low-manganese molten iron requires the purchase of special low-manganese ore, which increases the cost of molten iron. Double-slag or double-slag smelting results in significant iron loss and high steel material costs. Second, the endpoint relies on over-blowing to remove manganese, which leads to severe corrosion of the furnace lining refractory materials and poses a significant safety risk in production. Summary of the Invention

[0003] The purpose of this invention is to overcome the above-mentioned defects in the prior art and to provide a highly efficient demanganese agent, its preparation method, and a method for demanganese removal from molten steel after tapping from a converter.

[0004] To achieve the above objectives, the technical solution of the present invention is as follows: A high-efficiency manganese removal agent, wherein the raw material components of the high-efficiency manganese removal agent include CaF2 and FeO / Al2O3 composite particles; wherein the FeO / Al2O3 composite particles include an FeO core and a nano-Al2O3 coating covering the surface of the FeO core; based on the total mass of the high-efficiency manganese removal agent, the mass percentage content of the FeO core is ≥90%, the mass percentage content of the nano-Al2O3 coating is 2%~3%, and the mass percentage content of CaF2 is 5%~8%.

[0005] Optionally, the particle size of the high-efficiency manganese removal agent is 10~30mm.

[0006] Optionally, in the FeO / Al2O3 composite microparticles, the particle size of the FeO core is 10~30mm, and the thickness of the nano-Al2O3 coating is 10~20μm; the Fe3O4 content in the FeO core is <5%.

[0007] This invention also discloses a method for preparing the above-described highly efficient manganese-removing agent, comprising the following steps: (1) In an inert gas atmosphere, iron oxide scale is pre-oxidized at 1200~1300℃ for 2~5h to obtain FeO core; (2) The FeO core is crushed and the surface of the crushed FeO core is sprayed with nano Al2O3 suspension, dried and then mixed with CaF2 to form balls to obtain the high-efficiency manganese removal agent.

[0008] Optionally, in step (1), the inert gas is argon or nitrogen.

[0009] The present invention also discloses a method for demanganese removal from molten steel after tapping from a converter, wherein the method uses the high-efficiency demanganese remover as described above, or the high-efficiency demanganese remover prepared by the preparation method described above; the method includes the following steps; S1. Converter final carbon temperature control: S11. Using molten iron and scrap steel as raw materials, the converter adopts the single slag method for smelting. The amount of quicklime added to the converter is controlled at 20-60 kg / t steel, and the amount of lightly calcined dolomite added is controlled at 10-50 kg / t steel. S12, the converter process temperature is controlled at 1550~1590℃, and the process carbon mass content is controlled at 0.10%~0.60%; S13. The converter endpoint temperature is controlled at 1660~1680℃, the converter endpoint oxygen is controlled within 450~700ppm, the endpoint phosphorus content is ≤0.015%, the endpoint sulfur content is ≤0.005%, and the converter endpoint Mn content is determined. S2, Argon Station Manganese Removal Control: S21. Converter boiling tapping; no alloying or deoxidizing agents are added during the tapping process; S22. Determine the amount of Mn removed, wherein the amount of Mn removed is the Mn content at the converter endpoint minus the Mn content of the finished product; S23. Based on the amount of Mn removed, determine the amount of the high-efficiency manganese removal agent to be added, and then add the high-efficiency manganese removal agent to carry out manganese removal treatment, wherein the amount of the high-efficiency manganese removal agent added is controlled to be 2-15 kg / t steel; S24. Add quicklime to the lidded container, and start the bottom purge of argon gas into the large container. The argon gas flow rate is 90~150 Nm. 3 Stir for 90-120 seconds per hour, then turn off the argon gas; after the argon blowing is completed, the molten steel is hoisted to the refining station for processing.

[0010] Optionally, in step S23, when the amount of Mn removed is <0.01%, the amount of the high-efficiency manganese removal agent added is 2-4 kg / t steel; when 0.01% ≤ the amount of Mn removed is <0.02%, the amount of the high-efficiency manganese removal agent added is 5-7 kg / t steel; when 0.02% ≤ the amount of Mn removed is <0.03%, the amount of the high-efficiency manganese removal agent added is 8-11 kg / t steel; and when the amount of Mn removed is ≥0.03%, the amount of the high-efficiency manganese removal agent added is 12-15 kg / t steel.

[0011] Optionally, in step S23, the high-efficiency demanganese agent is fed into the converter's intermediate material silo via an alloy chute at a rate of 1.5~2.0 t / min.

[0012] Optionally, in step S24, the amount of quicklime added to the lid can is controlled to be 4~6 kg / t steel.

[0013] Optionally, in step S11, the mass of scrap steel accounts for 8% to 10% of the total mass of molten iron and scrap steel; Implementing the embodiments of the present invention will have the following beneficial effects: (1) This invention discloses a high-efficiency manganese removal agent, the raw material components of which include CaF2 and FeO / Al2O3 composite particles; wherein, the FeO / Al2O3 composite particles include an FeO core and a nano-Al2O3 coating on the surface of the FeO core; this invention first uses FeO after pre-oxidation treatment as the core, controls the Fe3O4 content to be <5%, and uses a nano-Al2O3 coating to coat the FeO core to inhibit high-temperature decomposition and improve reaction activity; and uses CaF2 to lower the melting point of the slag system and promote the reaction between FeO and Mn.

[0014] (2) The present invention achieves deep demanganese removal by adding the above-mentioned demanganese agent after the steel is tapped from the converter, thereby increasing the oxidizing property of the top slag of the molten steel. The demanganese-removed molten steel is then subjected to slag removal treatment to remove the high-manganese slag from the surface of the molten steel, so that the molten steel with qualified composition can be cast into the machine.

[0015] (3) The present invention simplifies the production process of low manganese steel. The converter does not need to adopt the double-slag or double-slag smelting method to achieve the purpose of deep demanganese removal of low manganese steel.

[0016] (4) The present invention is safe and reliable. It does not require the purchase of low-manganese iron ore, the use of double converter or double slag smelting, or the removal of manganese through overblowing. It can reduce the production cost of low-manganese steel and effectively avoid furnace lining erosion. Detailed Implementation

[0017] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0018] This invention discloses a high-efficiency manganese removal agent, the raw material components of which include CaF2 and FeO / Al2O3 composite particles; wherein, the FeO / Al2O3 composite particles include an FeO core and a nano-Al2O3 coating on the surface of the FeO core; based on the total mass of the high-efficiency manganese removal agent, the mass percentage of the FeO core is ≥90%, the mass percentage of the nano-Al2O3 coating is 2%~3%, and the mass percentage of CaF2 is 5%~8%.

[0019] Specifically, the high-efficiency manganese removal agent of the present invention comprises CaF2 and FeO / Al2O3 composite particles as raw material components. The present invention first uses FeO that has undergone pre-oxidation treatment as the core and coats the FeO core with a nano-Al2O3 coating to inhibit high-temperature decomposition and enhance reaction activity. CaF2 is used to lower the melting point of the slag system and promote the reaction between FeO and Mn.

[0020] In one specific embodiment, the particle size of the high-efficiency manganese removal agent is 10~30mm.

[0021] In one specific embodiment, the FeO / Al2O3 composite microparticles have a FeO core particle size of 10~30mm and a nano-Al2O3 coating thickness of 10~20μm; the Fe3O4 content in the FeO core is <5%.

[0022] This invention also discloses a method for preparing the above-described highly efficient manganese-removing agent, comprising the following steps: (1) In an inert gas environment, the iron oxide scale is pre-oxidized at 1200~1300℃ for 2~5h to stabilize the FeO phase, with the Fe3O4 content <5%, to obtain the FeO core.

[0023] (2) The FeO core is crushed and the surface of the crushed FeO core is sprayed with nano Al2O3 suspension, dried and then mixed with CaF2 to form a ball to obtain a high-efficiency manganese removal agent.

[0024] In one specific embodiment, in step (1), the inert gas is argon or nitrogen.

[0025] This invention also discloses a method for demanganese removal from molten steel after tapping from a converter, using the high-efficiency demanganese remover as described above, or the high-efficiency demanganese remover prepared by the preparation method described above; the process route includes converter—argon station—LF refining—casting machine; S1. Converter final carbon temperature control: S11. Using molten iron and scrap steel as raw materials, the converter charging amount is reduced by 5% year-on-year. The converter adopts the single slag method for smelting. The amount of quicklime added to the converter is controlled at 20-60 kg / t steel, and the amount of lightly calcined dolomite added is controlled at 10-50 kg / t steel.

[0026] S12, Sub-lance process test: Converter process temperature controlled at 1550~1590℃, process carbon mass content controlled at 0.10%~0.60%.

[0027] S13. The converter endpoint temperature is controlled at 1660~1680℃, the converter endpoint oxygen is controlled within 450~700ppm, the endpoint phosphorus content is ≤0.015%, the endpoint sulfur content is ≤0.005%, and the converter endpoint Mn content is determined.

[0028] S2, Argon Station Manganese Removal Control: S21. Converter boiling tapping; no alloys or deoxidizers are added during the tapping process.

[0029] S22. Determine the amount of Mn removed. The amount of Mn removed is the Mn content at the converter endpoint minus the Mn content of the finished product (determine the amount of Mn removed = Mn content at the converter endpoint - Mn content of the finished product).

[0030] S23. Determine the amount of high-efficiency manganese removal agent to be added based on the amount of Mn removed, and then add the high-efficiency manganese removal agent to carry out manganese removal treatment. The amount of high-efficiency manganese removal agent added is controlled to be 2-15 kg / t steel.

[0031] S24. Add quicklime to the lidded container, and start the bottom purge of argon gas into the large container. The argon gas flow rate is 90~150 Nm. 3 Stir for 90-120 seconds per hour, then turn off the argon gas; after the argon blowing is completed, the molten steel is hoisted to the refining station for processing.

[0032] In one specific embodiment, in step S23, when the amount of Mn removed is <0.01%, the amount of high-efficiency manganese removal agent added is 2-4 kg / t steel; when 0.01% ≤ Mn removal amount <0.02%, the amount of high-efficiency manganese removal agent added is 5-7 kg / t steel; when 0.02% ≤ Mn removal amount <0.03%, the amount of high-efficiency manganese removal agent added is 8-11 kg / t steel; and when the amount of Mn removal is ≥0.03%, the amount of high-efficiency manganese removal agent added is 12-15 kg / t steel.

[0033] In one specific embodiment, in step S23, the high-efficiency demanganese agent is fed into the converter's intermediate material silo via an alloy chute at a rate of 1.5~2.0 t / min.

[0034] In one specific embodiment, in step S24, the amount of quicklime added to the lid is controlled to be 4~6 kg / t steel.

[0035] In one specific embodiment, in step S11, the mass of scrap steel accounts for 8% to 10% of the total mass of molten iron and scrap steel.

[0036] In one specific embodiment, in step S24, if unmelted material is found in the container, argon blowing can continue for 30 seconds to ensure that the material melts.

[0037] The following are specific embodiments. Example 1 The high-efficiency manganese removal agent (particle size 10~30mm) in this embodiment has the following raw material components: CaF2 and FeO / Al2O3 composite microparticles. The FeO / Al2O3 composite microparticles include an FeO core and a nano-Al2O3 coating on the surface of the FeO core. Based on the total mass of the high-efficiency manganese removal agent, the FeO core has a mass percentage of 92%, the nano-Al2O3 coating has a mass percentage of 3%, and the CaF2 has a mass percentage of 5%.

[0038] Among them, the FeO / Al2O3 composite microparticles have a FeO core particle size of 10~30mm and a nano Al2O3 coating thickness of 10~20μm; the Fe3O4 content in the FeO core is <5%.

[0039] The preparation method of the high-efficiency manganese removal agent in this embodiment includes the following steps: (1) In argon, the iron oxide scale was pre-oxidized at 1200℃ for 2h to stabilize the FeO phase, with the Fe3O4 content <5%, and the FeO core was obtained.

[0040] (2) The FeO core is crushed and the surface of the crushed FeO core is sprayed with nano Al2O3 suspension, dried and then mixed with CaF2 to form a ball to obtain a high-efficiency manganese removal agent.

[0041] Example 2 The high-efficiency manganese removal agent (particle size 10~30mm) in this embodiment has the following raw material components: CaF2 and FeO / Al2O3 composite microparticles; wherein, the FeO / Al2O3 composite microparticles include an FeO core and a nano-Al2O3 coating on the surface of the FeO core; based on the total mass of the high-efficiency manganese removal agent, the mass percentage of the FeO core is 90%, the mass percentage of the nano-Al2O3 coating is 2%, and the mass percentage of CaF2 is 8%.

[0042] Among them, the FeO / Al2O3 composite microparticles have a FeO core particle size of 10~30mm and a nano Al2O3 coating thickness of 10~20μm; the Fe3O4 content in the FeO core is <5%.

[0043] The preparation method of the high-efficiency manganese removal agent in this embodiment includes the following steps: (1) In nitrogen, the iron oxide scale was pre-oxidized at 1300℃ for 2.5h to stabilize the FeO phase, with the Fe3O4 content <5%, and the FeO core was obtained.

[0044] (2) The FeO core is crushed and the surface of the crushed FeO core is sprayed with nano Al2O3 suspension, dried and then mixed with CaF2 to form a ball to obtain a high-efficiency manganese removal agent.

[0045] Example 3 This embodiment discloses a method for demanganese removal from molten steel after tapping from a converter, using the high-efficiency demanganese removal agent of Example 1; the process route includes converter—argon station—LF refining—casting machine, smelting low-manganese steel DDCT-1, with a tapping rate of 260t and a finished product Mn≤0.02%, including the following steps: S1. Converter final carbon temperature control: S11. Using molten iron and scrap steel as raw materials, the converter charge is controlled at 285t. The scrap steel accounts for 8% of the total mass of molten iron and scrap steel. The converter adopts the single-slag method for smelting. The amount of quicklime added to the converter feed is controlled at 40kg / t steel, and the amount of lightly calcined dolomite added is controlled at 30kg / t steel. The composition of the molten iron is: C: 4.4%, Si: 0.31%, Mn: 0.145%, P: 0.115%, S: 0.030%, with the balance being iron and unavoidable impurities.

[0046] S12, Sub-lance process test: Converter process temperature controlled at 1590℃, process carbon mass content controlled at 0.40%.

[0047] S13, the converter endpoint temperature is controlled at 1680℃, the converter endpoint oxygen is controlled at 600ppm, the endpoint phosphorus content is 0.010%, the endpoint sulfur content is 0.003%, and the endpoint manganese content is 0.05%.

[0048] S2, Argon Station Manganese Removal Control: S21. Converter boiling tapping; no alloying or deoxidizing agents are added during the tapping process. The converter slag composition obtained by converter boiling tapping is: CaO: 40%, SiO2: 15%, MgO: 8.0%, TFe: 17%, MnO: 2.8%, P2O5: 3.2%, with the balance being unavoidable impurities.

[0049] S22. Determine the amount of Mn removed. The amount of Mn removed is the Mn content at the end of the converter minus the Mn content of the finished product (determine the amount of Mn removed 0.03% = Mn content at the end of the converter 0.05% - Mn content of the finished product 0.02%).

[0050] S23. Based on the amount of Mn removed, the amount of high-efficiency demanganese agent added is determined to be 12 kg / t steel. Then, the high-efficiency demanganese agent is added for demanganese treatment. The addition method is as follows: the high-efficiency demanganese agent is placed in the middle material bin of the converter and added through the alloy chute at a rate of 1.5 t / min.

[0051] S24. Add 5 kg / t of quicklime to the steel-coated tank, open the bottom of the large tank and purge with argon gas at a flow rate of 90~150 Nm. 3If unmelted material is found in the tank at / h, continue blowing argon for 30 seconds to ensure the material melts. Stir for 90-120 seconds, then turn off the argon gas. After argon blowing, take a sample for temperature measurement and send it to the laboratory for analysis. The manganese content after desulfurization is 0.018%. The molten steel is hoisted to the refining station for processing. After the composition and temperature meet the requirements, it is put into operation.

[0052] Example 4 This embodiment discloses a method for demanganese removal from molten steel after tapping from a converter, using the high-efficiency demanganese removal agent of Example 2; the process route includes converter—argon station—LF refining—casting machine, smelting low-manganese steel DYCT-1, with a tapping rate of 260t and a finished product Mn≤0.03%, including the following steps: S1. Converter final carbon temperature control: S11. Using molten iron and scrap steel as raw materials, the converter charge is controlled at 287t. The scrap steel accounts for 10% of the total mass of molten iron and scrap steel. The converter adopts the single-slag method for smelting. The amount of quicklime added to the converter feed is controlled at 30kg / t steel, and the amount of lightly calcined dolomite added is controlled at 20kg / t steel. The composition of the molten iron is: C: 4.5%, Si: 0.35%, Mn: 0.140%, P: 0.115%, S: 0.025%, with the balance being iron and unavoidable impurities.

[0053] S12, Sub-lance process test: Converter process temperature controlled at 1580℃, process carbon mass content controlled at 0.40%.

[0054] S13, the converter endpoint temperature is controlled at 1660℃, the converter endpoint oxygen is controlled at 650ppm, the endpoint phosphorus content is 0.011%, the endpoint sulfur content is 0.004%, and the endpoint manganese content is 0.04%.

[0055] S2, Argon Station Manganese Removal Control: S21. Converter boiling tapping; no alloying or deoxidizing agents are added during the tapping process. The converter slag composition obtained by converter boiling tapping is: CaO: 42%, SiO2: 14%, MgO: 7.8%, TFe: 18%, MnO: 2.6%, P2O5: 3.1%, with the balance being unavoidable impurities.

[0056] S22. Determine the amount of Mn removed. The amount of Mn removed is the Mn content at the converter endpoint minus the Mn content in the finished product (determine the amount of Mn removed 0.01% = Mn content at the converter endpoint 0.04% - Mn content in the finished product 0.03%).

[0057] S23. Based on the amount of Mn removed, the amount of high-efficiency demanganese agent added is determined to be 5 kg / t of steel. Then, the high-efficiency demanganese agent is added for demanganese treatment. The addition method is as follows: the high-efficiency demanganese agent is placed in the middle material bin of the converter and added through the alloy chute at a rate of 1.5 t / min.

[0058] S24. Add 5 kg / t of quicklime to the steel-coated tank, open the bottom of the large tank and purge with argon gas at a flow rate of 90~150 Nm. 3 If unmelted material is found in the tank at / h, continue blowing argon for 30s to ensure the material melts. Stir for 90-120s and then turn off the argon gas. After blowing argon, take a sample for temperature measurement and send it to the laboratory for analysis. The manganese content after desulfurization is 0.022%. The molten steel is hoisted to the refining station for processing. After the composition and temperature are qualified, it is put into the machine.

[0059] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A highly efficient manganese removal agent, characterized in that, The raw material components of the high-efficiency manganese removal agent include CaF2 and FeO / Al2O3 composite particles; The FeO / Al2O3 composite microparticles include an FeO core and a nano-Al2O3 coating covering the surface of the FeO core. Based on the total mass of the highly efficient manganese removal agent, the mass percentage of the FeO core is ≥90%, the mass percentage of the nano-Al2O3 coating is 2%~3%, and the mass percentage of the CaF2 is 5%~8%.

2. The high-efficiency manganese removal agent according to claim 1, characterized in that, The particle size of the high-efficiency manganese removal agent is 10~30mm.

3. The high-efficiency manganese removal agent according to claim 1, characterized in that, In the FeO / Al2O3 composite microparticles, the FeO core has a particle size of 10~30mm, and the thickness of the nano-Al2O3 coating is 10~20μm; the Fe3O4 content in the FeO core is <5%.

4. A method for preparing a highly efficient manganese-removing agent as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) In an inert gas atmosphere, iron oxide scale is pre-oxidized at 1200~1300℃ for 2~5h to obtain FeO core; (2) The FeO core is crushed and the surface of the crushed FeO core is sprayed with nano Al2O3 suspension, dried and then mixed with CaF2 to form balls to obtain the high-efficiency manganese removal agent.

5. The method for preparing the high-efficiency manganese removal agent according to claim 4, characterized in that, In step (1), the inert gas is argon or nitrogen.

6. A method for demanganese removal from molten steel after tapping from a converter, characterized in that, The method uses the high-efficiency manganese removal agent as described in any one of claims 1-3, or the high-efficiency manganese removal agent prepared by the preparation method as described in any one of claims 4-5; The method includes the following steps; S1. Converter final carbon temperature control: S11. Using molten iron and scrap steel as raw materials, the converter adopts the single slag method for smelting. The amount of quicklime added to the converter is controlled at 20-60 kg / t steel, and the amount of lightly calcined dolomite added is controlled at 10-50 kg / t steel. S12, the converter process temperature is controlled at 1550~1590℃, and the process carbon mass content is controlled at 0.10%~0.60%; S13. The converter endpoint temperature is controlled at 1660~1680℃, the converter endpoint oxygen is controlled within 450~700ppm, the endpoint phosphorus content is ≤0.015%, the endpoint sulfur content is ≤0.005%, and the converter endpoint Mn content is determined. S2, Argon Station Manganese Removal Control: S21, Converter boiling tapping; S22. Determine the amount of Mn removed, wherein the amount of Mn removed is the Mn content at the converter endpoint minus the Mn content of the finished product; S23. Based on the amount of Mn removed, determine the amount of the high-efficiency manganese removal agent to be added, and then add the high-efficiency manganese removal agent to carry out manganese removal treatment, wherein the amount of the high-efficiency manganese removal agent added is controlled to be 2-15 kg / t steel; S24. Add quicklime to the lidded container, and start the bottom purge of argon gas into the large container. The argon gas flow rate is 90~150 Nm. 3 Stir for 90-120 seconds per hour, then turn off the argon gas; after the argon blowing is completed, the molten steel is hoisted to the refining station for processing.

7. The method for demanganese removal from molten steel after tapping from a converter according to claim 6, characterized in that, In step S23, when the amount of Mn removed is <0.01%, the amount of the high-efficiency manganese removal agent added is 2-4 kg / t steel; when 0.01% ≤ the amount of Mn removed is <0.02%, the amount of the high-efficiency manganese removal agent added is 5-7 kg / t steel; when 0.02% ≤ the amount of Mn removed is <0.03%, the amount of the high-efficiency manganese removal agent added is 8-11 kg / t steel; and when the amount of Mn removed is ≥0.03%, the amount of the high-efficiency manganese removal agent added is 12-15 kg / t steel.

8. The method for demanganese removal from molten steel after tapping from a converter according to claim 6, characterized in that, In step S23, the high-efficiency demanganese agent is fed into the converter's intermediate material silo and added through an alloy chute at a rate of 1.5~2.0 t / min.

9. The method for demanganese removal from molten steel after tapping from a converter according to claim 6, characterized in that, In step S24, the amount of quicklime added to the lid is controlled to be 4~6 kg / t steel.

10. The method for demanganese removal from molten steel after tapping from a converter according to claim 6, characterized in that, In step S11, the mass of scrap steel accounts for 8% to 10% of the total mass of molten iron and scrap steel.