Method for modifying smelting industrial pure iron top slag

Abstract

The invention discloses a method for modifying smelting industrial pure iron top slag, and belongs to the technical field of ferrous metallurgy steelmaking processes. A top slag modification process is carried out mainly by adopting a three-step method, that is, the top slag modification process is carried out after tapping is finished, an LF treatment process and an RH treatment process are finished, and reasonable steel slag chemical components of the IF steel are obtained according to calculation and simulation; the influence of the adding amount of the modifier on the oxygen activity in the molten steel and the oxidability of the steel slag after converter tapping is studied; the slag forming effect of the steel slag after tapping is controlled; the steel slag oxidability change rule after RH oxygen blowing is analyzed; controlling the steel slag oxidability at the smelting end point; the optimal adding amount of the modifier and the deoxidizing agent is obtained; the influence of the oxidability of the steel slag on nozzle nodulation and the number of continuous casting furnaces is explained; and the influence of steel slag oxidability on aluminum loss is researched.

Description

Technical Field

[0001] This invention belongs to the field of steelmaking process technology in iron and steel metallurgy, and particularly relates to a method for modifying the top slag of pure iron in the smelting industry. Background Technology

[0002] Domestic and international research indicates that highly oxidizing slag will deteriorate the cleanliness of molten steel and the surface quality of cast billets during industrial pure iron smelting. When the TFe mass fraction in the slag exceeds 15%, it will oxidize alloying elements such as Al and Ti dissolved in the molten steel, forming secondary oxide inclusions, which can easily cause nozzle nodules and surface inclusion defects in the product. Top slag modification has been widely recognized and used as an effective means to reduce the oxidizing properties of refining slag.

[0003] The current industrial pure iron production route is BOF-LF-RH-CCM. This route requires LF treatment, which places demands on the slag-forming process to produce well-formed, homogeneous slag with good fluidity and low oxidizing properties. Top slag modification technology is highly effective in reducing the total iron content of steel slag, which is significant for improving the cleanliness of molten steel. Summary of the Invention

[0004] The purpose of this invention is to provide a method for modifying top slag in the smelting of pure iron. The method mainly employs a three-step process: top slag modification after tapping, during LF treatment, and after RH treatment. Calculations and simulations are used to obtain a reasonable chemical composition of IF steel slag. The invention also investigates the effects of the amount of modifier added after converter tapping on the oxygen activity and oxidizability of the slag in the molten steel; controls the slag formation effect after tapping; analyzes the change in slag oxidizability after RH oxygen blowing; controls the slag oxidizability at the smelting endpoint; obtains the optimal amount of modifier and deoxidizer added; explains the influence of slag oxidizability on nozzle nodule formation and the number of consecutive castings; studies the influence of slag oxidizability on aluminum loss; and improves the cleanliness of molten steel while simultaneously increasing the yield of industrial pure iron.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] This invention discloses a method for upgrading top slag in the smelting industry of pure iron, comprising:

[0007] Converter primary reforming:

[0008] The final tapping temperature of the converter must be ≥1590℃. Before tapping, the furnace must be turned over and slag discharged. 200-300kg of dolomite thick slag must be added to the vertical furnace. 600±20kg of quicklime and 200±20kg of pre-melted slag must be added to the top slag of the ladle during converter tapping. Double-sliding slag-blocking tapping is used to avoid slag falling. Argon blowing is performed during converter tapping. Large argon gas is used for stirring in the early stage of tapping. After 2 / 3 of the steel has been tapped, the argon gas flow rate is reduced for slag blocking.

[0009] Secondary modification in LF refining furnace:

[0010] The LF refining process involves heating for 15 minutes, during which 600±20 kg of quicklime is added in batches, with each batch controlled at 200±20 kg. The LF refining process is then heated a second time, during which 800±20 kg of quicklime is added in batches, with each batch controlled at 200±20 kg. Before the LF is removed from its position, the argon gas is turned off, and 100±10 kg of aluminum granules are added to the slag surface for slag modification.

[0011] RH vacuum treatment with three stages of modification:

[0012] The RH vacuum treatment process involves three modifications. After the RH decarburization is completed, the final oxygen content is controlled at the end of the decarburization process. If the final oxygen content is above 350ppm after the decarburization is completed, aluminum is added in small batches during the treatment process to control the final oxygen content of the decarburization to within 350ppm, thereby reducing the oxygen content of the molten steel. After the RH treatment is completed, 120±10kg of aluminum modifier is added, and the TFe content in the slag is controlled to within 6%.

[0013] Furthermore, 600 kg of quicklime and 200 kg of pre-melted slag are added to the top slag of the ladle at the converter tapping.

[0014] Furthermore, the LF refining furnace undergoes secondary modification: during the heating process, 600 kg of quicklime is added in batches, with each batch containing 200 kg.

[0015] Furthermore, LF refining secondary heating: 800 kg of quicklime is added in batches during the heating process, with each batch containing 200 kg.

[0016] Furthermore, the LF refining furnace undergoes secondary slag modification: 100 kg of aluminum granules are added to the slag surface for slag modification.

[0017] Furthermore, after the RH treatment is completed, 120 kg of aluminum modifier is added.

[0018] Furthermore, the molten iron in the KR desulfurization process needs to undergo KR deep desulfurization treatment. The sulfur content of the molten iron entering the converter is required to be ≤0.001%, the desulfurization slag removal area is greater than 95%, the slag removal of the molten iron is done until it is mirror-like, and visual inspection shows that there is no slag on the surface of the molten iron. The sulfur content of the molten iron entering the furnace is ≤0.002%.

[0019] Furthermore, continuous casting protection: the long nozzle of the ladle is protected by an asbestos bowl and argon seal, and the argon flow rate is controlled to 1.0-3.0 m³ / h.

[0020] Further, the process flow is as follows: blast furnace—converter—refining LF furnace—RH vacuum furnace—280*380mm casting machine.

[0021] Furthermore, the conditions for molten iron:

[0022] The requirements for the composition of molten iron, including non-oxidizing elements such as silicon, manganese, phosphorus, and sulfur, should be lower than the internal control requirements for finished products in the quality plan. The temperature of the molten iron after arriving at the inlet station should be ≥1350℃. The composition requirements for molten iron are shown in the table below:

[0023] Iron composition requirements (unit: %)

[0024] Element Si Mn P S Temperature (°C) scope 0.2~0.6 ≤0.50 ≤0.100 ≤0.040 ≥1350

[0025] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0026] Currently, the steel plant has begun small-batch production of industrial pure iron and has gained some experience. Research on the modification of top slag in industrial pure iron steelmaking provides a reference for further research and development of high-quality industrial pure iron production. The implementation of this patent has improved the yield of industrial pure iron, enriching the product structure while significantly increasing the company's profitability and enhancing its market competitiveness. Detailed Implementation

[0027] This experiment optimized the top slag modification process for industrial pure iron steelmaking, controlling the TFe content in the slag to within 6%, thereby improving the cleanliness and castability of the molten steel.

[0028] Example 1:

[0029] The steel plant produces four heats of industrial pure iron. The process route is: No. 9 converter — No. 4 refining — RH vacuum furnace — No. 5 casting machine (280*380mm). The specific details are as follows:

[0030] 1. KR desulfurization

[0031] Molten iron from the torpedo ladle is transferred to a ladle at the ladle-turning station and then transported to the desulfurization station. The processing flow is "removing pre-slag—stirring desulfurization—removing post-slag." Desulfurization involves deep desulfurization and the use of slag-forming agents. The slag removed has a mirror-like finish. The sulfur content (S%) of the molten iron entering the furnace is all 0.002%, and the iron temperature is between 1365℃ and 1371℃. Specific desulfurization parameters are shown in Table 1.

[0032] Table 1 KR Desulfurization Parameters

[0033]

[0034] 2. Converter primary tempering

[0035] Clean scrap steel is used in the converter, and a single-slag process is employed. Slag is blocked at the tapping point using sliding plates (front and rear plates) to ensure the slag runoff is less than 50mm. The final tapping temperature is ≥1594℃. Before tapping, the furnace is turned over and slag is removed. 300kg of dolomite slag is added to the vertical furnace. 600kg of quicklime and 200kg of pre-melted slag are added to the top slag of the ladle during tapping. Double sliding plates are used for tapping to prevent slag runoff. Argon blowing is performed during tapping. A large amount of argon gas is used for stirring in the early stages of tapping, and the argon flow is reduced to block slag after 2 / 3 of the steel has been tapped. Specific carbon removal and steel composition are shown in the table below.

[0036] Table 2 Converter Endpoint Parameters

[0037]

[0038] 3. Secondary upgrading of LF refining furnace

[0039] LF refining is heated in place for 15 minutes. During the heating process, 600 kg of quicklime is added in batches, with each batch controlled at 200 kg. After stirring for 8 minutes, samples are taken, temperature is measured, and oxygen content is determined. Details are shown in Tables 3 and 4.

[0040] Table 3. First heating condition

[0041]

[0042] Table 4. In-situ components (%)

[0043]

[0044] The LF furnace is reheated for 19-30 minutes. During the heating process, 800 kg of quicklime is added in batches, stirred for 5-6 minutes, with each batch added in 200 kg. Before the LF furnace is removed, the argon gas is turned off, and 100 kg of aluminum granules are added to the slag surface for slag modification. The details of the second heating are shown in Table 5, and the composition of the LF furnace after removal is shown in Table 6.

[0045] Table 5 Second heating conditions

[0046]

[0047] Table 6. LF Ex-situ Components (%)

[0048]

[0049] 4. RH vacuum treatment with three-stage modification

[0050] The RH vacuum treatment process involves three modification steps. The in-situ RH temperature is measured at 1612–1687℃, the oxygen content is constant at 524–1021 ppm, the circulation flow rate is set at 80–150 Nm³ / h, and the oxygen content at the end of decarburization is 427–810 ppm. 150–360 kg of aluminum granules are added based on the oxygen content of the molten steel, and the pure degassing time is at least 5 minutes. The vacuum treatment time is 25–44 minutes, and the temperature at the end of the vacuum treatment is 1592–1653℃. After the RH treatment is completed, 120 kg of aluminum modifier is added, and the TFe content in the slag is controlled between 5.1% and 5.8%. The RH furnace treatment details and off-situ composition are shown in Tables 7 and 8.

[0051] Table 7 RH Vacuum Treatment Status

[0052]

[0053] Table 8. RH-depleted components (%)

[0054]

[0055] 5. Continuous casting protective casting

[0056] The casting speed of the casting machine is 0.75 m / min. The superheat of the first heat is relatively high at 46℃, and the superheat of the other heats are 36℃, 27℃ and 32℃ respectively. The ladle long nozzle is protected by asbestos bowl and argon seal. The argon flow rate is controlled at 2.6 m³ / h, so that the steel surface is not exposed to prevent secondary oxidation of the steel. The composition of the tundish is shown in Table 9.

[0057] Table 9 Composition of ladle in casting machine (%)

[0058]

[0059] By introducing a method for modifying pure iron top slag in the smelting industry, the scheme for modifying pure iron top slag in steelmaking production was optimized. The TFe content in the slag was controlled within 5.8%, which improved the cleanliness and castability of molten steel and improved the quality of cast billets.

[0060] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for modifying top slag in the smelting industry for pure iron, characterized in that: include: Converter primary reforming: The final tapping temperature of the converter must be ≥1590℃. Before tapping, the furnace must be turned over and slag discharged. 200-300kg of dolomite thick slag must be added to the vertical furnace. 600±20kg of quicklime and 200±20kg of pre-melted slag must be added to the top slag of the ladle during converter tapping. Double-sliding slag-blocking tapping is used to avoid slag falling. Argon blowing is performed during converter tapping. Large argon gas is used for stirring in the early stage of tapping. After 2 / 3 of the steel has been tapped, the argon gas flow rate is reduced for slag blocking. Secondary modification in LF refining furnace: The LF refining process involves heating for 15 minutes, during which 600±20 kg of quicklime is added in batches, with each batch controlled at 200±20 kg. The LF refining process is then heated a second time, during which 800±20 kg of quicklime is added in batches, with each batch controlled at 200±20 kg. Before the LF is removed from its position, the argon gas is turned off, and 100±10 kg of aluminum granules are added to the slag surface for slag modification. RH vacuum treatment with three stages of modification: The RH vacuum treatment process involves three modifications. After the RH decarburization is completed, the final oxygen content is controlled at the end of the decarburization process. If the final oxygen content is above 350ppm after the decarburization is completed, aluminum is added in small batches during the treatment process to control the final oxygen content of the decarburization to within 350ppm, thereby reducing the oxygen content of the molten steel. After the RH treatment is completed, 120±10kg of aluminum modifier is added, and the TFe content in the slag is controlled to within 6%.

2. The method for upgrading the top slag of pure iron smelting industry according to claim 1, characterized in that: Add 600 kg of quicklime and 200 kg of pre-melted slag to the top slag of the ladle at the converter tapping.

3. The method for upgrading the top slag of pure iron smelting industry according to claim 1, characterized in that: Secondary modification of LF refining furnace: 600 kg of quicklime is added in batches during the heating process, with each batch adding 200 kg.

4. The method for upgrading the top slag of pure iron smelting industry according to claim 1, characterized in that: LF refining secondary heating: 800 kg of quicklime is added in batches during the heating process, with each batch adding 200 kg.

5. The method for upgrading the top slag of pure iron smelting industry according to claim 1, characterized in that: Secondary slag modification in LF refining furnace: 100 kg of aluminum granules are added to the slag surface for slag modification.

6. The method for upgrading the top slag of pure iron smelting industry according to claim 1, characterized in that: After the RH treatment is completed, add 120 kg of aluminum modifier.

7. The method for upgrading the top slag of pure iron smelting industry according to claim 1, characterized in that: The molten iron in the KR desulfurization process needs to undergo KR deep desulfurization treatment. The sulfur content of the molten iron entering the converter is required to be ≤0.001%, the desulfurization slag removal area is greater than 95%, the slag removal of the molten iron is to the point of being mirror-like, and visual inspection shows that there is no slag on the surface of the molten iron. The sulfur content of the molten iron entering the furnace is ≤0.002%.

8. The method for upgrading the top slag of pure iron smelting industry according to claim 1, characterized in that: Continuous casting protective casting: The long nozzle of the ladle is protected by an asbestos cup and argon sealing, with the argon flow rate controlled at 1.0-3.0 m³ / s. 3 / h.

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