Production method for top slag modification and optimization of ultra-low carbon single-link process

Abstract

The invention discloses a production method for top slag modification optimization of an ultra-low carbon single connection process, and belongs to the technical field of metallurgical materials. The production process flow of the method comprises the steps of KR desulfurization, BOF converter, RH vacuum refining and machine casting. In view of the special situation of ultra-low carbon steel, top slag modification of an ultra-low carbon single connection process is developed according to the technological process, namely converter process steel ladle top slag modification and RH process steel ladle top slag modification; through top slag modification optimization of the ultra-low carbon single connection process, the content of FeO + MnO in the slag is smaller than or equal to 3% through modification treatment under the original process route condition of ultra-low carbon steel, and the top slag oxidability of the ultra-low carbon steel meets the requirements of molten steel purity and continuous pouring.

Description

Technical Field

[0001] The present invention belongs to the technical field of metallurgical materials, and in particular relates to a production method for optimizing top slag modification in an ultra-low carbon single-link process. Background Art

[0002] Ultra-low carbon steel (ULCS) is a key branch of clean steel and a key development direction for future clean steel grades. The cleanliness of ULCS is crucial to the quality of steel products. Improving its cleanliness, controlling inclusion precipitation, and harmlessly treating it are key issues that need to be addressed during the steelmaking process. The oxidizability of slag during steelmaking is a key indicator of the purity of ULCS, and the purity of ULCS is closely related to the quality of the steel. The oxidizability of the ladle top slag directly affects the total oxygen content in the molten steel, thereby affecting its cleanliness and, in turn, the product quality of ULCS. The production of ULCS places stringent requirements on controlling the oxidizability (e.g., FeO and MnO content) and basicity of the top slag. Traditional modifiers (e.g., aluminum granules and silicon carbide) can easily lead to increased carbonization or inclusions in the molten steel. The slag-metal reaction time in the single-stage process is short, making it difficult to achieve rapid slag formation and efficient inclusion adsorption using traditional step-by-step modification. Existing processes consume a large amount of slag, placing significant environmental and cost pressures.

[0003] The production process for ultra-low carbon steel is unique and significantly different from other steel grades. Its smelting and production process follows the following steps: KR desulfurization, BOF converter, RH vacuum refining, and casting machine. Unlike other processes, the molten steel for ultra-low carbon steel does not pass through the LF refining furnace. Instead, it is fed directly from the BOF converter to the RH vacuum refining furnace for treatment before being fed to the casting machine for casting. Omitting the LF refining furnace prevents the top slag from being fully reduced as it would be during the LF refining process. During normal LF refining, the top slag is fully reduced, reducing the FeO and MnO content in the slag. However, under this unique process for ultra-low carbon steel, the FeO and MnO content in the slag remains high after RH refining, resulting in a highly oxidizing ladle top slag. During continuous casting, the oxygen in this highly oxidizing slag is transferred to the molten steel in large quantities, reacting with elements in the molten steel in a series of chemical reactions, resulting in the formation of numerous inclusions. Because these inclusions are difficult to remove in a timely manner during the continuous casting process, they accumulate in the molten steel, significantly affecting its cleanliness and reducing product quality. More seriously, the large number of inclusions can also cause flocculation in the molten steel. This flocculation disrupts the normal flow of the molten steel, affecting the stability of the continuous casting process and making it difficult to continue pouring the molten steel smoothly. This has a number of adverse effects on production, increasing production difficulty and cost, and reducing production efficiency. Summary of the Invention

[0004] The purpose of the present invention is to provide a production method for optimizing the top slag modification of an ultra-low carbon single process. In view of the special situation of ultra-low carbon steel, we have developed a top slag modification of an ultra-low carbon single process according to the process flow, namely, the top slag modification of the ladle in the converter process + the top slag modification of the ladle in the RH process.

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

[0006] The present invention provides a production method for optimizing top slag modification in an ultra-low carbon single-link process, comprising:

[0007] 1) Converter process

[0008] In order to reduce the MnO content in the ladle top slag, pre-deoxidation of ferromanganese is no longer performed during the converter tapping process. Instead, CaO-based synthetic slag or small-grained lime is added during the tapping process using the dilution and slag adjustment method to increase the basicity of the ladle top slag. The amount of slag added is adjusted appropriately based on the amount of slag discharged from the converter, but should not be too large. At the same time, the addition time should be as early as possible to ensure that the slag is fully melted at the end of tapping.

[0009] After tapping, a modifier should be added to the ladle slag surface quickly. The amount of modifier to be added should first be estimated based on the actual slag amount and the amount of modified lime added, and then adjusted appropriately based on the FeO content of the converter end slag. After adding the modifier, weak argon blowing should be used to fully melt the modifier. The argon blowing time should not be too long.

[0010] 2) RH vacuum refining process

[0011] In order to reduce the FeO and Al2O3 contents in the ladle top slag, under the premise of reducing the MnO content as much as possible, a certain amount of ferrosilicon alloy is added in the early stage of RH decarburization treatment to utilize the carbon contained in ferrosilicon for deoxidation, achieving the purpose of deoxidation without increasing the Al2O3 and MnO contents.

[0012] When the RH treatment is just finished, that is, when the riser and downcomer just leave the ladle liquid surface, add the modifier to the slag active area just below the double tubes. The amount of modifier added should be enough to cover the entire area.

[0013] After the RH refining treatment is completed, the final top slag modification is carried out. One modification method is to use a special container to add the top slag modifier and perform calcium treatment at the same time to make the modifier fully melt in the top slag.

[0014] Furthermore, the method ensures that FeO+MnO in the ultra-low carbon steel top slag is ≤3%, so that the oxidizability of the ultra-low carbon steel top slag meets the requirements of molten steel purity and continuous casting.

[0015] Furthermore, the basicity of the ladle top slag is increased to 1.5-1.8.

[0016] Furthermore, the weak argon blowing flow rate is 45-50NL / min.

[0017] Furthermore, the addition amount of ferrosilicon alloy is 0.15-0.35%.

[0018] Furthermore, the argon blowing time is controlled at 2-3 minutes.

[0019] Furthermore, the top slag modification of the ultra-low carbon single process is an organic combination of two modification methods: converter top slag modification and RH top slag modification.

[0020] Compared with the prior art, the present invention has the following beneficial technical effects:

[0021] The top slag modification of the ultra-low carbon single-link process reduces the FeO content in the slag by about 7%, and the MnO content is also stabilized at around 2.6%. The (FeO+MnO) in the slag is ≤3%. The oxidizability of the top slag of ultra-low carbon steel meets the requirements of molten steel purity and continuous pouring.

[0022] By taking a series of measures, it can now be ensured that (FeO+MnO) in the top slag of ultra-low carbon steel is ≤3%, so that the oxidation property of the top slag of ultra-low carbon steel meets the purity and continuity of molten steel. DETAILED DESCRIPTION

[0023] The processing route for ultra-low carbon steel differs from other steel grades. Because the molten steel bypasses the LF refining furnace and instead flows directly from the BOF converter to the RH vacuum refining process before being poured into the casting machine, the slag after RH refining contains high levels of FeO and MnO, and the ladle top slag remains highly oxidizing. During the continuous casting process, a large amount of oxygen in the slag is transferred to the molten steel, reacting with elements in the steel to produce numerous inclusions that are difficult to remove. This significantly impacts steel cleanliness and can even cause flocculence, hindering continuous pouring. Given the unique characteristics of ultra-low carbon steel, we have developed a single-step process for top slag modification, combining ladle top slag modification in the converter and RH stages. The production process follows the following steps: KR desulfurization → BOF converter → RH vacuum refining → casting machine.

[0024] Through top slag modification and optimization in the ultra-low carbon single-link process, the (FeO+MnO) content in the slag of ultra-low carbon steel can be reduced to ≤3% under the original process conditions. The oxidizing properties of the top slag of ultra-low carbon steel meet the requirements for molten steel purity and continuous pouring. The process route for ultra-low carbon steel is: desulfurization → converter → vacuum refining → casting machine. Because the molten steel does not pass through the LF refining furnace but is directly supplied from the BOF converter to the RH vacuum refining process before being poured into the casting machine, the FeO and MnO contents in the slag after RH refining are very high, and the ladle top slag is still highly oxidizing. This causes a large amount of oxygen in the slag to be transferred to the molten steel during the continuous casting process, where it reacts with elements in the steel to produce a large number of inclusions that are difficult to remove, significantly affecting the cleanliness of the molten steel and even causing flocculent flow, which affects the continuous pouring of the molten steel. The original top slag modification and optimization of ultra-low carbon steel is insufficient, and the (FeO+MnO) content in the ultra-low carbon silicon steel slag is far greater than 5%, resulting in the oxygen content in the molten steel being higher than the requirement of ultra-low carbon silicon steel, the castability of the molten steel cannot meet the continuous casting requirements, and the purity of the molten steel cannot meet the product quality requirements.

[0025] (1) Converter process

[0026] In order to reduce the MnO content in the ladle top slag, pre-deoxidation of ferromanganese is no longer carried out during the converter tapping process. Only CaO-based synthetic slag or small-particle white ash is added by dilution and slag adjustment method during the tapping process to increase the basicity of the ladle top slag. The amount of addition is adjusted appropriately according to the amount of slag under the converter, but it should not be too large. At the same time, the addition time should be as early as possible to ensure that it can be fully melted at the end of tapping.

[0027] After tapping is complete, a modifier should be quickly added to the ladle slag surface. The amount of modifier added should first be estimated based on the actual slag volume and the amount of modified lime added, and then adjusted appropriately based on the FeO content of the converter end slag. After adding the modifier, a weak argon blow is used to fully melt the modifier. The argon blow time should not be too long, generally controlled at 2-3 minutes. After the above top slag modification treatment, the composition of the converter end slag has undergone significant changes. The specific slag sample composition is shown in Table 1 below:

[0028] Table 1 Changes in converter top slag fraction before and after modification (%)

[0029]

[0030] As shown in Table 1, the FeO content of the converter top slag is reduced by approximately 7% before and after reforming, significantly reducing the oxidizing properties of the top slag. However, some heats still have high FeO contents, which can contaminate the molten steel during pouring and cause slight steel flocculation. Therefore, secondary RH top slag reforming is essential.

[0031] (2) RH vacuum refining process

[0032] In order to reduce the FeO and Al2O3 contents in the ladle top slag, and on the premise of reducing the MnO content as much as possible, a certain amount of ferrosilicon alloy is added in the early stage of RH decarburization treatment, and the carbon contained in ferrosilicon is used for deoxidation, so as to achieve the purpose of deoxidation without increasing the Al2O3 and MnO contents.

[0033] When the RH treatment is just completed, that is, when the riser and downcomer just leave the ladle liquid surface, add the modifier to the slag active area just below the double tubes. The amount of modifier added should be enough to cover this area completely.

[0034] After the RH refining treatment is completed, the final top slag modification is carried out. One modification method is to use a special container to add the top slag modifier and perform calcium treatment at the same time to make the modifier fully melt in the top slag.

[0035] The top slag modification of the ultra-low carbon single process is an organic combination of converter top slag modification and RH top slag modification. After the top slag modification, the changes in the FeO content in the top slag were analyzed and the top slag data of the original process and the current process were compared. The results are shown in Table 2.

[0036] Table 2 Comparison of top slag data of the original process and the current process in the "two-step method" top slag modification

[0037]

[0038] The top slag modification of the ultra-low carbon single-link process reduces the FeO content in the slag by about 7%, and the MnO content is also stabilized at around 2.6%. The (FeO+MnO) in the slag is ≤3%. The oxidizability of the top slag of ultra-low carbon steel meets the requirements of molten steel purity and continuous pouring.

[0039] By taking a series of measures, it can now be ensured that (FeO+MnO) in the top slag of ultra-low carbon steel is ≤3%, so that the oxidation property of the top slag of ultra-low carbon steel meets the purity and continuity of molten steel.

[0040] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A production method for optimizing top slag modification in an ultra-low carbon single-link process, characterized by: include: 1) Converter process In order to reduce the MnO content in the ladle top slag, pre-deoxidation of ferromanganese is no longer performed during the converter tapping process. Instead, CaO-based synthetic slag or small-grained lime is added during the tapping process using the dilution and slag adjustment method to increase the basicity of the ladle top slag. The amount of slag added is adjusted appropriately based on the amount of slag discharged from the converter, but should not be too large. At the same time, the addition time should be as early as possible to ensure that the slag is fully melted at the end of tapping. After tapping, a modifier should be added to the ladle slag surface quickly. The amount of modifier to be added should first be estimated based on the actual slag amount and the amount of modified lime added, and then adjusted appropriately based on the FeO content of the converter end slag. After adding the modifier, weak argon blowing should be used to fully melt the modifier. The argon blowing time should not be too long. 2) RH vacuum refining process In order to reduce the FeO and Al2O3 contents in the ladle top slag, under the premise of reducing the MnO content as much as possible, a certain amount of ferrosilicon alloy is added in the early stage of RH decarburization treatment to utilize the carbon contained in ferrosilicon for deoxidation, achieving the purpose of deoxidation without increasing the Al2O3 and MnO contents. When the RH treatment is just finished, that is, when the riser and downcomer just leave the ladle liquid surface, add the modifier to the slag active area just below the double tubes. The amount of modifier added should be enough to cover the entire area. After the RH refining treatment is completed, the final top slag modification is carried out. One modification method is to use a special container to add the top slag modifier and perform calcium treatment at the same time to make the modifier fully melt in the top slag.

2. The production method for optimizing top slag modification in an ultra-low carbon single-link process according to claim 1, characterized in that: The method ensures that FeO+MnO in the ultra-low carbon steel top slag is less than or equal to 3%, so that the oxidizability of the ultra-low carbon steel top slag meets the requirements of molten steel purity and continuous pouring.

3. The production method for optimizing top slag modification in an ultra-low carbon single-link process according to claim 1, characterized in that: Increase the basicity of ladle top slag to 1.5-1.

8.

4. The production method for optimizing top slag modification in an ultra-low carbon single-link process according to claim 1, characterized in that: The weak argon blowing flow rate is 45-50NL / min.

5. The production method for optimizing top slag modification in an ultra-low carbon single-link process according to claim 1, characterized in that: The addition amount of ferrosilicon alloy is 0.15-0.35%.

6. The production method for optimizing top slag modification in an ultra-low carbon single-link process according to claim 1, characterized in that: The argon blowing time is controlled at 2-3 minutes.

7. The production method for optimizing top slag modification in an ultra-low carbon single-link process according to claim 1, characterized in that: The top slag modification of the ultra-low carbon single process is an organic combination of two modification methods: converter top slag modification and RH top slag modification.

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