A method for controlling large size liquid inclusions in the lf refining stage

Abstract

The application discloses a method for controlling large-size liquid inclusions in a LF refining stage, comprising the following steps: S1: obtaining the O content, Ca content and Al content in molten steel in the LF refining process; S2: calculating the large-size liquid inclusion index Y of the molten steel by using formula (I); and S3: controlling the O, Ca and Al contents according to the calculated large-size liquid inclusion index Y. According to the inclusion control characteristics of multiple steel types, the O, Ca and Al contents are accurately controlled in the refining stage, 100% of the large-particle spherical oxide Ds-type inclusions are controlled to be less than 19 microns, the Ds-type inclusion is less than or equal to 0.5 level in the GB / T 10561-2023 'Standard Grading Diagram Microscopic Test Method for Determining Nonmetallic Inclusion Content in Steel', and the large-size liquid inclusion is accurately controlled.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, and in particular to a method for controlling large-sized liquid inclusions in the LF refining stage. Background Technology

[0002] Non-metallic inclusions are an inevitable byproduct of steelmaking and cannot be completely removed. Inclusions remaining in the steel matrix negatively impact the quality and performance of the steel. During steelmaking, inclusions collide, aggregate, and grow under the influence of molten steel flow. The aggregation tendencies exhibited by inclusions of different compositions differ significantly. Studies show that solid inclusions can be significantly removed during RH vacuum refining, while liquid inclusions, primarily composed of Ca and Al, are difficult to remove. These inclusions ultimately precipitate, aggregate, grow, and detach during casting and cooling, leading to a decline in product quality and purity.

[0003] CN111172351B, "A Method for Controlling Ds Inclusions in Medium-Carbon Sulfur-Containing Aluminum Deoxidized Non-Quenched and Tempered Steel," proposes a method to control Ds inclusions in medium-carbon, sulfur-containing, aluminum-containing deoxidized non-quenched and tempered steel by adjusting the location of sulfur addition, optimizing the multi-component composition of refining slag and the composition of molten steel, and transforming inclusions into a solid phase that is easy to float, thereby avoiding the formation of liquid inclusions and CaS and improving the removal efficiency of inclusions, especially large Ds-type inclusions, in molten steel. However, this method is only applicable to medium-carbon, sulfur-containing, aluminum-containing deoxidized non-quenched and tempered steel, and no further research has been conducted on non-sulfur-containing steel. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for controlling large-sized liquid inclusions in the LF refining stage.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention includes the following steps: S1: In the LF refining process, the O content, Ca content and Al content in the molten steel are obtained; S2: The large-size liquid inclusion index Y of molten steel is calculated using the following formula (Ⅰ); Y=X [Al] -X [O] ×ln(X [Ca] / X [O] (I); In the formula, X [O] O content in molten steel during the LF refining process, expressed in ppm; X [Ca] : The Ca content of molten steel in the LF refining process, expressed in ppm; X [Al] Al content of molten steel during the LF refining process, in units of 10. -5 ; S3: Control the refining process based on the calculated large-size liquid inclusion index Y.

[0006] Furthermore, in step S3, the content of O, Ca, and Al in the refining process is controlled to reduce the index Y of large-size liquid inclusions.

[0007] Furthermore, the control process for step S3 is as follows: Y≤40: Refined using conventional processes; 40<Y≤50: Add 50~100m of aluminum wire during the LF refining process; 50 < Y < 60: Add 50-150m of aluminum wire during the LF refining process, and extend the RH high vacuum refining time by 1-3 minutes; Y≥60: Add 50-200m of aluminum wire during the LF refining process and extend the RH high vacuum refining time by 1-5min.

[0008] Furthermore, the composition and mass percentage of the applicable steel grade are as follows: C 0.3%~1.0%, Si 0.1%~0.25%, Mn 0.5%~1.0%, Al 0.02%~0.04%, P≤0.010%, S≤0.02%, Cr 0.05%~1.0%, Ca≤0.0005%, with the balance being Fe and unavoidable impurities.

[0009] The beneficial effects of adopting the above technical solution are as follows: This invention can optimize the LF refining process based on the O, Ca, and Al content detected in the early stage of refining, according to the characteristics of inclusion control of multiple steel types. It can convert large Ds-type liquid inclusions into Al2O3 solid inclusions, and then remove them significantly in the RH vacuum refining process. Finally, it can achieve 100% control of large spherical oxide Ds-type inclusions <19μm, which meets the requirement of Ds-type inclusions ≤0.5 grade in GB / T 10561-2023 "Standard Rating Chart Microscopic Examination Method for Determination of Non-metallic Inclusion Content in Steel", and achieve precise control of large-size liquid inclusions. Attached Figure Description

[0010] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0011] Figure 1 This is a schematic diagram illustrating the rating results of Ds-type inclusions using the present invention and conventional methods. Detailed Implementation

[0012] This method for controlling large-size liquid inclusions in the LF refining stage is applicable to steel grades with the following composition and mass percentage: C 0.3%~1.0%, Si 0.1%~0.25%, Mn 0.5%~1.0%, Al 0.02%~0.04%, P≤0.010%, S≤0.02%, Cr 0.05%~1.0%, Ca≤0.0005%, with the balance being Fe and unavoidable impurities. The production process adopted is: converter / electric furnace smelting → LF ladle refining → RH / VD vacuum refining → continuous casting.

[0013] The method for controlling large-size liquid inclusions in the LF refining stage includes the following steps: S1: During the LF refining process, samples are taken and tested within 5 to 10 minutes of LF refining to obtain the O content, Ca content and Al content in the molten steel.

[0014] S2: The large-size liquid inclusion index Y of molten steel is calculated using the following formula (Ⅰ); Y=X [Al] -X [O] ×ln(X [Ca] / X [O] (I); In the formula, X [O] The O content of molten steel in the LF refining process, i.e. the O content obtained in step S1, is expressed in ppm. X [Ca] : The Ca content of molten steel in the LF refining process, i.e. the Ca content obtained in step S1, in ppm; X [Al] Al content of molten steel in the LF refining process, i.e., Al content obtained in step S1, in units of 10. -5 ×100%.

[0015] The relationship between the large-size liquid inclusion index Y and Ds-type inclusions in steel is as follows: Y≤40: The steel contains few Ds-type inclusions and has good purity. 40<Y≤50: The steel contains a small amount of Ds-type inclusions, and the purity of the molten steel is relatively good; 50 < Y < 60: The steel contains more Ds-type inclusions, and the purity of the molten steel is poor. Y≥60: The steel contains a large number of Ds-type inclusions, and the purity of the molten steel is poor.

[0016] S3: Based on the calculated large-size liquid inclusion index Y, control the O, Ca, and Al content during the refining process. The refining process control is as follows: Y≤40: Refined using conventional processes, without additional operations; 40<Y≤50: Add 50~100m of aluminum wire during the LF refining process; 50 < Y < 60: Add 50-150m of aluminum wire during the LF refining process, and extend the RH high vacuum refining time by 1-3 minutes; Y≥60: Add 50-200m of aluminum wire during the LF refining process and extend the RH high vacuum refining time by 1-5min.

[0017] In summary, based on this method, by precisely controlling the contents of O, Ca, and Al during the refining stage, large-sized liquid inclusions can be precisely controlled, with Ds-type inclusions ≤ 0.5 grade. Figure 1 This is a schematic diagram of the Ds-type inclusion rating results of the present invention and the conventional method. The conventional method (before optimization) rates the Ds-type inclusions as 0.5, 1 and 1.5, while the present method (after optimization) rates the Ds-type inclusions as 0 and 0.5. Example

[0018] The steel production process in this embodiment is as follows: electric furnace → LF ladle refining → RH vacuum refining → continuous casting; after the LF-refined molten steel is energized for 5 minutes, the molten steel is taken for composition analysis, and the results are shown in Table 1: Table 1. Results of steel liquid composition analysis in Example 1

[0019] Substituting the O, Ca, and Al contents of the above-mentioned LF refined molten steel into formula (Ⅰ), the large-size liquid inclusion index Y is calculated: Y=X [Al] -X [O] ×ln(X [Ca] / X [O] =40.0.

[0020] Y≤40, therefore, the steel is refined using conventional processes without additional operations: no aluminum wire is added during the LF refining process, and the RH high-vacuum refining process is carried out for 22 minutes. The final RH refining endpoint and the T.[O] and Ca composition in the steel are shown in Table 1. The steel has T.[O]=5ppm, the D coarse inclusion rating is 0, and the Ds type inclusion rating is 0. Example

[0021] The steel production process in this embodiment is as follows: electric furnace → LF ladle refining → RH vacuum refining → continuous casting; after the LF-refined molten steel is energized for 7 minutes, the molten steel is taken for composition analysis, and the results are shown in Table 2: Table 2. Results of steel liquid composition analysis in Example 2

[0022] Substituting the O, Ca, and Al contents of the above-mentioned LF refined molten steel into formula (Ⅰ), the large-size liquid inclusion index Y is calculated: Y=X[Al] -X [O] ×ln(X [Ca] / X [O] =44.2.

[0023] Since 40 < Y ≤ 50, 30m of aluminum wire was added during the LF refining process, and the RH high-vacuum refining was maintained for 22min. The final RH refining endpoint and the T.[O] and Ca composition in the steel are shown in Table 2. The steel has T.[O] = 4ppm, D coarse inclusions are rated as grade 0, and Ds inclusions are rated as grade 0.5. Example

[0024] The steel production process in this embodiment is as follows: electric furnace → LF ladle refining → RH vacuum refining → continuous casting; after the LF-refined molten steel is energized for 5 minutes, the molten steel is taken for composition analysis, and the results are shown in Table 2: Table 3. Composition analysis results of molten steel in Example 3

[0025] Substituting the O, Ca, and Al contents of the above-mentioned LF refined molten steel into formula (Ⅰ), the large-size liquid inclusion index Y is calculated: Y=X [Al] -X [O] ×ln(X [Ca] / X [O] )=52.1 Since 50 < Y < 60, 50m of aluminum wire was added during the LF refining process, and the RH high-vacuum refining was carried out for 24min. The final RH refining endpoint and the T.[O] and Ca composition in the steel are shown in Table 3. The steel has T.[O] = 7ppm, D coarse inclusions are rated as grade 0, and Ds inclusions are rated as grade 0. Example

[0026] The steel production process in this embodiment is as follows: electric furnace → LF ladle refining → RH vacuum refining → continuous casting; after the LF-refined molten steel is energized for 10 minutes, the molten steel is taken for composition analysis, and the results are shown in Table 2: Table 3. Composition analysis results of molten steel in Example 3

[0027] Substituting the O, Ca, and Al contents of the above-mentioned LF refined molten steel into formula (Ⅰ), the large-size liquid inclusion index Y is calculated: Y=X [Al] -X [O] ×ln(X [Ca] / X [O] =74.9.

[0028] Y≥60, therefore 150m of aluminum wire was added during the LF refining process, and RH high vacuum refining was carried out for 26min. The final RH refining endpoint and the T.[O] and Ca composition in the steel are shown in Table 4. The steel has T.[O]=9ppm, D coarse inclusion rating is 0, and Ds type inclusion rating is 0.5.

Claims

1. A method for controlling large-size liquid inclusions in the LF refining stage, characterized in that, The process includes the following steps: S1: During the LF refining process, the O content, Ca content and Al content in the molten steel are obtained; S2: The large-size liquid inclusion index Y of molten steel is calculated using the following formula (Ⅰ); Y=X [Al] -X [O] ×ln(X [Ca] / X [O] ) (Ⅰ); In the formula, X [O] O content in molten steel during the LF refining process, expressed in ppm; X [Ca] : The Ca content of molten steel in the LF refining process, expressed in ppm; X [Al] Al content of molten steel during the LF refining process, in units of 10. -5 ; S3: Control the refining process based on the calculated large-size liquid inclusion index Y.

2. The method for controlling large-size liquid inclusions in the LF refining stage according to claim 1, characterized in that: Step S3 controls the content of O, Ca, and Al during the refining process to reduce the index Y of large-size liquid inclusions.

3. The method for controlling large-size liquid inclusions in the LF refining stage according to claim 1, characterized in that, The control process for step S3 is as follows: Y≤40: Refined using conventional processes; 40<Y≤50: Add 50~100m of aluminum wire during the LF refining process; 50 < Y < 60: Add 50-150m of aluminum wire during the LF refining process, and extend the RH high vacuum refining time by 1-3 minutes; Y≥60: Add 50-200m of aluminum wire during the LF refining process and extend the RH high vacuum refining time by 1-5min.

4. A method for controlling large-size liquid inclusions in the LF refining stage according to claim 1, 2, or 3, characterized in that, The applicable steel grades and their mass percentages are as follows: C 0.3%~1.0%, Si 0.1%~0.25%, Mn 0.5%~1.0%, Al 0.02%~0.04%, P≤0.010%, S≤0.02%, Cr 0.05%~1.0%, Ca≤0.0005%, with the balance being Fe and unavoidable impurities.

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