Smelting method for efficient demanganization of converter

Abstract

The invention belongs to the technical field of converter steelmaking, and particularly discloses a smelting method for efficient demanganization of a converter, which comprises the following steps of: removing S content in molten iron to be below 0.002% by adopting a deep desulfurization process on the molten iron, adding the molten iron and scrap steel into the converter to replace high-sulfur slag in the converter, and carrying out oxygen blowing smelting, the adding amount of lime, magnesite and fluorite and the lance position of an oxygen lance are accurately controlled in the smelting period, and converter tapping is conducted after oxygen blowing smelting is completed. The method aims at solving the problems that in the duplex method demanganizing process, the slag material consumption is remarkably increased, meanwhile, the molten steel smelting time is prolonged, and consequently the production cost is increased. According to the method, two-converter smelting of a duplex method is optimized into single-converter-base smelting, the use frequency of converter equipment is reduced, the consumption of steel slag per ton is reduced, the production efficiency is remarkably improved, the iron and steel production rhythm is balanced, meanwhile, the deoxidation effect of the subsequent RH procedure is improved, and the problems that the deoxidation difficulty is large and bubbles exist under the surface of a slab due to the fact that the oxygen content of molten steel is too high are solved.

Description

Technical Field

[0001] The invention relates to the technical field of converter steelmaking, and in particular to a converter high-efficiency manganese removal smelting method. Background Art

[0002] During the steelmaking process, effective control of manganese is crucial to steel product quality. With increasing market demand for low-manganese steel, efficiently reducing the manganese content in molten steel has become a pressing issue to expand this market. Traditional converter demanganization methods suffer from low demanganization efficiency, high energy consumption, and inadequate slag control, making them difficult to meet the demands of large-scale low-manganese steel production. Some methods fail to fully utilize the reaction between slag and manganese during the blowing process, resulting in inadequate manganese oxidation. Alternatively, improper slag basicity and composition during slagging prevent the effective dissolution of manganese oxides, thus compromising demanganization effectiveness.

[0003] Currently, the "double method" is used for demanganese removal. Utilizing the oxidation sequence of the smelting process, which is "silicon-manganese oxidation in the early stage, and decarburization and heating in the middle and late stages," and leveraging the advantages of the 120t production line system, two converters are used for secondary demanganese removal. The specific process is as follows: pretreatment of molten iron desulfurization → primary demanganese removal to below 0.15% in the 1# converter → ladle transfer → decarburization, demanganese removal, and heating in the 2# converter → argon stirring in the ladle → LF heating → RH vacuum degassing and demanganese removal → continuous casting, ultimately producing billets whose composition meets the design requirements of the steel grade.

[0004] However, during the "double-process" demanganeseization process, two converters are required to complete the molten steel smelting, which significantly increases the slag consumption and prolongs the molten steel smelting time, thereby leading to rising production costs. Summary of the Invention

[0005] The purpose of the present invention is to provide a smelting method for efficient demanganeseization in a converter, so as to solve the problem that in the demanganeseization process of the "double method", the slag consumption is significantly increased, the smelting time of the molten steel is prolonged, and the production cost is increased.

[0006] To achieve the above object, the present invention provides a basic solution: a smelting method for efficient manganese removal in a converter, comprising the following steps:

[0007] S1. The molten iron adopts deep desulfurization process to remove the S content in the molten iron to below 0.002%, and the slag skimming standard is that more than 90% of the molten iron is exposed;

[0008] S2. Adding molten iron and scrap steel into the converter to replace the high-sulfur slag in the converter, controlling the smelting end point S≤0.005%, wherein the amount of molten iron added is 110-115t, and the amount of scrap steel added is 20-25t;

[0009] S3, the molten iron and scrap steel in the converter are subjected to oxygen blowing smelting, smelting early stage: add 70% lime, oxygen lance gun position is controlled at 1600mm from the liquid level, blowing 30s, after the lime is melted, add 70% magnesite, the blowing temperature is 1350-1400 ℃, smelting mid-term: adjust the oxygen lance gun position to drop to 1200mm from the liquid level, add 15% lime and magnesite in small batches at the same time, treat that the molten steel temperature is raised to above 1400 ℃, add 200-300kg fluorite, simultaneously the oxygen lance gun position is controlled at 1600mm from the liquid level, add the remaining 15% lime and magnesite, blowing late stage: the terminal gun position is controlled at 1000mm from the liquid level, the terminal temperature is controlled at 1560-1600 ℃, and the terminal C is controlled at 0.06-0.08%;

[0010] S4. After oxygen blowing smelting is completed, steel is tapped from the converter. When the molten steel volume reaches 40-60t, 200kg of active lime is added and the argon is adjusted to a medium stirring state. After the active lime melts, the argon is adjusted to a soft blowing state until the tapping is completed. The tapping time is 3'00"-5'30".

[0011] The beneficial effects of the present invention are: 1) Optimizing the two converter smelting of the "double-connection method" into a single-furnace smelting, reducing the frequency of converter equipment use and reducing the consumption of ton steel slag;

[0012] ② Compared with the original "double-link method", the average smelting time per furnace is saved by 48 minutes, which significantly improves production efficiency;

[0013] ③ The original "double-process" converter group consumed 4,000 tons of molten iron, which was lower than the 5,600 tons of molten iron output of the blast furnace group. After adopting a single-furnace smelting method, the blast furnace molten iron can be fully consumed, balancing the rhythm of iron and steel production;

[0014] ④ The oxygen content of molten steel in the converter process is reduced by about 100ppm compared with the previous period, which improves the deoxidation effect of the subsequent RH process and solves the problem of difficult deoxidation and subcutaneous bubbles in the slab caused by excessively high oxygen content in the molten steel.

[0015] Option 2 is the preferred option of the basic option. In S2, the scrap steel adopts cold-rolled sheared materials and hot-rolled cutting scrap plates with S < 0.030% and Mn ≤ 0.50% for internal circulation; by internally circulating low-S, low-Mn cold-rolled sheared materials and hot-rolled cutting scrap plates, the S and Mn recovery phenomena of high-Mn and high-S scrap steel during the smelting process can be suppressed. At the same time, demanganeseization in converter smelting is a reversible reaction, and excessive Mn will inhibit the reaction.

[0016] Option 3 is the preferred option of the basic option. In S2, the CaO content in the high-sulfur slag is controlled to 50%-60%, the SiO2 content is controlled to 15%-20%, the FeO content is controlled to 15-25%, and the MgO content is controlled to 9-10% through molten iron and scrap steel. The basicity of the high-sulfur slag is R = 3.5-5.0. The slag composition with high basicity (R = 3.5-5.0) and high FeO (15-25%) can provide favorable conditions for the demanganese reaction, promote manganese oxidation, and improve the demanganese efficiency. At the same time, a reasonable combination of CaO, SiO2, and MgO contents can improve the fluidity and stability of the slag, which is conducive to the full occurrence of the demanganese reaction.

[0017] Option 4 is the preferred option of the basic option. In S2, after the molten iron and scrap steel are replaced with high-sulfur slag, the Si content in the molten iron is 0.10-0.60%, Mn ≤ 0.55%, P < 0.120%, S < 0.045%, and the molten iron temperature is > 1280°C. Lower sulfur and phosphorus contents can reduce the adverse effects of resulfurization and rephosphorization on manganese removal and molten steel quality during the smelting process. At the same time, the appropriate silicon content helps to form a reasonable slag composition in the early stage of smelting, assisting in manganese removal.

[0018] Option 5 is the preferred option of the basic option. In S3, the amount of lime and magnesite added in each batch is 200 kg, and the number of batches added is 4-6 times; adding slag in small batches can avoid excessive fluctuations in furnace temperature and composition caused by adding too much at one time, which is conducive to maintaining the early low temperature, high alkalinity, and high FeO environment, and continuously meeting the demanganeseization requirements.

[0019] Option six is the preferred option of the basic option. In S4, the medium stirring state is an argon blowing diameter of 200mm, and the soft blowing state is an argon blowing diameter of 400-600mm. During the steel tapping process, the argon blowing diameter is 200mm, which can quickly melt the active lime and promote the full reaction of the steel slag. The argon blowing diameter of 400-600mm can gently stir the molten steel after the lime melts, making the molten steel composition and temperature more uniform, while avoiding the splashing of molten steel caused by violent stirring.

[0020] Option seven is the preferred option of the basic option. In S4, the slag blocking method during the steel-making process is a slide slag blocking method. This can effectively block the slag with high MnO content from entering the molten steel and prevent the manganese oxides in the slag from being reduced back to the molten steel.

[0021] Option 8 is the preferred basic option. In S4, the oxygen content of the molten steel in the ladle is 500-600ppm after tapping is completed. This provides a good foundation for subsequent processes and effectively solves problems such as excessive oxygen content in the molten steel, which leads to difficulty in deoxidation and subcutaneous bubbles in the slab. DETAILED DESCRIPTION

[0022] The present invention will be further described in detail below through specific embodiments:

[0023] A smelting method for efficient manganese removal in a converter comprises the following steps:

[0024] S1. The molten iron adopts deep desulfurization process to remove the S content in the molten iron to below 0.002%, inhibiting the return of sulfur during the molten steel smelting process. The slag skimming standard is more than 90% of the molten iron exposed to reduce the phenomenon of desulfurization slag reducing sulfur during the smelting process;

[0025] S2. Adding molten iron and scrap steel into a converter to replace the high-sulfur slag in the converter, suppressing the return of S and Mn in the high-Mn and high-S scrap steel during the smelting process, controlling the CaO content, SiO2 content, FeO content, and MgO content in the high-sulfur slag to 50%, 20%, 20%, and 10%, and the basicity of the high-sulfur slag to R=4.5, and controlling the smelting end point S≤0.005%. After the molten iron and scrap steel are replaced with the high-sulfur slag, the Si content, Mn content, P content, and S content in the molten iron are 0.20%, 0.50%, 0.10%, and 0.033%, and the molten iron temperature is 1300° C., wherein the amount of molten iron added is 115 t, the amount of scrap steel added is 25 t, and the scrap steel adopts cold-rolled sheared materials and hot-rolled cutting scrap plates with S<0.030% and Mn≤0.50% that are internally circulated;

[0026] S3. Oxygen blowing is performed on the molten iron and scrap steel in the converter. In the early stage of smelting, 70% of lime is added, and the oxygen lance position is controlled at 1600mm from the liquid surface. The blowing is performed for 30s. After the lime is melted, 70% of magnesite is added. The blowing temperature is 1380℃. The active lime with low melting point is matched with magnesite to quickly form high alkalinity and low temperature conditions, quickly enrich (MnO) in the slag, and at the same time, the high heat absorption efficiency of magnesite is used to extend the low temperature duration. In the middle stage of smelting, the oxygen lance position is adjusted to 1200mm from the liquid surface to improve the stirring ability of the oxygen stream in the furnace on the molten steel. At the same time, 15% of lime and magnesite are added in small batches. The amount of lime and magnesite added in each batch is 200kg. The number of batches is 5 to uniformly increase the composition and temperature of the molten steel. When the temperature of the molten steel reaches above 1400°C, the FeO content in the slag in the converter is at a low level, which is not conducive to demanganeseization. 200-300kg of fluorite is added, and the oxygen lance is controlled at 1600mm from the liquid surface to help improve the fluidity of the slag. The remaining 15% of lime and magnesite are added to accelerate the [Mn]+O=[MnO] reaction at the "steel-slag" interface. In the late blowing stage, the end point lance is controlled at 1000mm from the liquid surface, the end point temperature is controlled at 1590°C, the end point C is controlled at 0.06%, and the smelting end point S is controlled at 0.005%. After the furnace is turned over and the temperature is sampled, additional blowing is performed based on the end point composition temperature.

[0027] S4. After the oxygen blowing smelting is completed, the converter is tapped. When the molten steel volume reaches 50t, 200kg of active lime is added and the argon is adjusted to the medium stirring state. The medium stirring state means that the argon blows open a diameter of 200mm. After the active lime melts, the argon is adjusted to the soft blowing state until the tapping is completed. The soft blowing state means that the argon blows open a diameter of 400mm. The tapping time is 4'30". The slag blocking method during the tapping process is the slide block. After the tapping is completed, the oxygen content of the molten steel in the ladle is 500ppm.

[0028] Table 1 Comparison of molten steel composition between the “double-link method” and the present application

[0029]

[0030] Table 2 Comparison of the time required for the converter process of the "double method" and this application

[0031]

[0032] Table 3 Cost comparison between the “double-link method” and this application

[0033]

[0034] In summary, the present application achieves a demanganeseization efficiency equivalent to that of the "double-link method" through a single-furnace process, while having a lower sulfur content, which significantly improves the purity of the molten steel. The oxygen content of the molten steel is controlled at 500-600ppm, which reduces the deoxidation burden of the subsequent RH process and solves the problem of subcutaneous bubbles in the slab. At the same time, the smelting cycle is shortened from 50.7 minutes to 37.27 minutes, saving about 13.4 minutes per furnace, and increasing daily production capacity by about 20%, which is compatible with the output rhythm of blast furnace molten iron. The use of ferrosilicon and magnesium balls in the slag is eliminated, the unit consumption of lime is optimized, the cost of slag per ton of steel is reduced by about 15%, and the comprehensive cost of a single furnace is reduced by about 308 yuan. Therefore, compared with the "double-link method", the cost is higher, the efficiency is lower, and the process is simpler.

[0035] The above is only an embodiment of the present invention, and the common knowledge such as the specific structure and characteristics of the scheme is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A smelting method for efficient demanganese removal in a converter, characterized in that: The following steps are involved: S1. The molten iron adopts deep desulfurization process to remove the S content in the molten iron to below 0.002%, and the slag skimming standard is that more than 90% of the molten iron is exposed; S2. Adding molten iron and scrap steel into the converter to replace the high-sulfur slag in the converter, controlling the smelting end point S≤0.005%, wherein the amount of molten iron added is 110-115t, and the amount of scrap steel added is 20-25t; S3, the molten iron and scrap steel in the converter are subjected to oxygen blowing smelting, smelting early stage: add 70% lime, oxygen lance gun position is controlled at 1600mm from the liquid level, blowing 30s, after the lime is melted, add 70% magnesite, the blowing temperature is 1350-1400 ℃, smelting mid-term: adjust the oxygen lance gun position to drop to 1200mm from the liquid level, add 15% lime and magnesite in small batches at the same time, treat that the molten steel temperature is raised to above 1400 ℃, add 200-300kg fluorite, simultaneously the oxygen lance gun position is controlled at 1600mm from the liquid level, add the remaining 15% lime and magnesite, blowing late stage: the terminal gun position is controlled at 1000mm from the liquid level, the terminal temperature is controlled at 1560-1600 ℃, and the terminal C is controlled at 0.06-0.08%; S4. After oxygen blowing smelting is completed, steel is tapped from the converter. When the molten steel volume reaches 40-60t, 200kg of active lime is added and the argon is adjusted to a medium stirring state. After the active lime melts, the argon is adjusted to a soft blowing state until the tapping is completed. The tapping time is 3'00"-5'30".

2. The smelting method of a converter with high efficiency manganese removal according to claim 1, characterized in that: In S2, the scrap steel adopts cold-rolled sheared materials and hot-rolled cutting scrap plates with internal circulation of S < 0.030% and Mn ≤ 0.50%.

3. The smelting method of a converter with high efficiency manganese removal according to claim 1, characterized in that: In S2, the CaO content in the high-sulfur slag is controlled at 50%-60%, the SiO2 content is controlled at 15%-20%, the FeO content is controlled at 15-25%, and the MgO content is controlled at 9-10% through molten iron and scrap steel, and the basicity of the high-sulfur slag is R=3.5-5.

0.

4. The smelting method of a converter with high efficiency manganese removal according to claim 1, characterized in that: In S2, after the molten iron and scrap steel are replaced with high-sulfur slag, the Si content in the molten iron is 0.10-0.60%, Mn≤0.55%, P<0.120%, S<0.045%, and the molten iron temperature is>1280℃.

5. The smelting method for high-efficiency manganese removal in a converter according to claim 1, characterized in that: In S3, the amount of lime and magnesite added in each batch is 200 kg, and the number of batches added is 4-6 times.

6. The smelting method for high-efficiency manganese removal in a converter according to claim 1, characterized in that: In S4, the medium stirring state is an argon gas blowing state with a diameter of 200 mm, and the soft blowing state is an argon gas blowing state with a diameter of 400-600 mm.

7. The smelting method for high-efficiency manganese removal in a converter according to claim 1, characterized in that: In S4, the slag blocking method during the steel tapping process is slide block slag blocking.

8. The smelting method for high-efficiency manganese removal in a converter according to claim 1, characterized in that: In S4, the oxygen content of the molten steel in the ladle is 500-600ppm after tapping is completed.

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