A method for controlling inclusions in titanium-containing ultra-low carbon steel

Abstract

This invention discloses a method for controlling inclusions in titanium-containing ultra-low carbon steel. The steelmaking process is as follows: converter process – LF process – RH process – slab continuous casting process. After aluminum deoxidation and alloying in the RH process, low-reactive slag is added. As the vacuum molten steel circulates, this slag floats to the surface and remains at the steel-slag interface, hindering oxygen transfer from the ladle slag to the molten steel. Simultaneously, this substance has the ability to adsorb inclusions in the steel. By controlling the process parameters of the RH process, oxygen transfer from the ladle slag to the molten steel is effectively prevented, avoiding secondary oxidation of titanium and aluminum elements in the deoxidized steel and controlling the inclusion content in the steel. This invention's control method effectively prevents oxygen transfer from the ladle slag to the molten steel and avoids secondary oxidation of easily oxidized elements such as titanium and aluminum in the deoxidized steel, resulting in significant economic and social benefits.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel smelting and refining technology, and specifically relates to a method for controlling inclusions in titanium-containing ultra-low carbon steel. Background Technology

[0002] Because the RH treatment process for ultra-low carbon steels such as IF steel requires the reaction between oxygen and carbon in the steel to reduce the [C] content to 30 × 10⁻⁶. -6 The levels are even lower. Therefore, ultra-low carbon steel undergoes little or no deoxidation of the ladle slag during converter tapping and LF refining, resulting in high oxidizability of the ladle slag. Typically, after RH decarburization, the TFe content in the ladle slag remains above 8%, with some top domestic companies achieving around 5%, still significantly higher than that of medium or high carbon steel (where TFe is generally less than 1% in deoxidized steel). This leads to a large amount of oxygen transfer from the slag into the steel during the alloying process after decarburization and during continuous casting, resulting in substantial loss of alloying elements such as titanium and aluminum, and a significant increase in inclusion content.

[0003] For a long time, metallurgists at home and abroad have conducted a lot of research on how to effectively reduce the oxidizing properties of ladle slag in ultra-low carbon steel and have achieved results. However, they can only reduce the TFe content of ladle slag to about 5%, and still cannot avoid the secondary oxidation of molten steel by ladle slag.

[0004] Patent CN116287566A discloses an ultra-low carbon steel top slag modification process. Through staged modification and reasonable control of the oxidizability of the ladle top slag, the oxidizability of the top slag is utilized as a resource. The entire process is controlled without generating large amounts of instantaneous smoke and dust, making it environmentally friendly and precise in its modification. After RH cavitation, the top slag T.Fe ≤ 8%, and the CaO / Al2O3 ratio is in the range of 1.3–1.8.

[0005] Patent CN113528757A discloses a ladle refining slag and its smelting method. The ladle refining slag, by weight percentage, comprises: SiO2: 6%–8.5%, Al2O3: 23%–27.5%, CaO: 45%–51%, MgO: 5%–8%, and T(Fe+Mn) ≤ 0.5%, wherein the CaO / Al2O3 ratio is controlled within the range of 1.5–1.9. By rationally controlling the basicity and alumina content of the refining slag, and maintaining the CaO / Al2O3 ratio within the range of 1.5–1.9, the desulfurization effect is ensured while also considering the deoxidation capacity of the slag system, which is beneficial for the adsorption of inclusions.

[0006] Patent CN105821178A discloses a method for smelting ultra-low carbon steel, comprising: smelting molten iron through a converter; adding high-calcium aluminum slag balls to reduce the TFe content in the top slag when tapping the steel from the converter, based on the oxygen content at the converter endpoint, thereby obtaining molten steel; refining the molten steel through RH vacuum refining; and uniformly sprinkling high-calcium aluminum slag balls on the slag surface at the end of RH vacuum refining to further reduce the TFe content in the slag. After the application of this technology, the TFe content in the slag before ladle hoisting at the end of RH can be reduced to 3.4% to 5.0%.

[0007] As can be seen from the existing technology, in the refining process of titanium-containing ultra-low carbon steel such as automotive steel sheets, both domestically and internationally, a large amount of aluminum-containing modifiers are added to deoxidize the ladle slag. However, after RH refining, the oxidizing properties of the ladle slag cannot be reduced to the level of medium-carbon or high-carbon steel. During continuous casting, oxygen transfer from the ladle slag to the molten steel still occurs, leading to the loss of alloying elements such as titanium and aluminum, resulting in a significant increase in inclusion content and a deterioration in steel quality. Summary of the Invention

[0008] The purpose of this invention is to provide a method for controlling inclusions in titanium-containing ultra-low carbon steel. This method is applied to high-quality titanium-containing ultra-low carbon steel such as automotive steel sheets, and is used for the stable control of inclusions in the steel.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows:

[0010] A method for controlling inclusions in titanium-containing ultra-low carbon steel is disclosed. The steelmaking process is as follows: converter process - LF process - RH process - slab continuous casting process. After aluminum deoxidation and alloying in the RH process, low-reactive slag is added. As the vacuum molten steel circulates, the slag floats to the surface and remains at the steel-slag interface, hindering oxygen transfer from the ladle slag to the molten steel. At the same time, this substance has the ability to adsorb inclusions in the steel. The process parameters of the RH process are controlled to prevent oxygen transfer from the ladle slag to the molten steel, avoid secondary oxidation of titanium and aluminum elements in the deoxidized steel, and control the inclusion content in the steel.

[0011] The low-reactive slag composition, by mass percentage, is as follows: CaO: 60%–63%, Al2O3: 26.3%–31%, MgO: 1.5%–4.5%, SiO2: 0%–2.9%, TiO2: 2%–4.8%, vermiculite: 2%–4%, CaO / Al2O3: 2.1%–2.4%, with the remainder being unavoidable impurities.

[0012] Furthermore, in the above technical solution, the low-reactive slag material is added in two stages. 2 to 4 minutes after the aluminum deoxidation and alloying of the RH process is completed, the low-reactive slag material is added for the first time from the high-level silo in the vacuum chamber. 2 to 4 minutes after the addition is completed, ferrotitanium or sponge titanium is added to the steel to alloy the molten steel with titanium. 1 to 3 minutes after the addition of titanium, the low-reactive slag material is added for the second time. After the second addition of the low-reactive slag material to the steel, the vacuum treatment time of the molten steel is 5 to 10 minutes.

[0013] Furthermore, in the above technical solution, the first addition of low-reactive slag material is 0.2 kg / t steel to 0.5 kg / t steel, and the second addition of low-reactive slag material is 0.2 kg / t steel to 0.5 kg / t steel.

[0014] Furthermore, in the above technical solution, the process parameters for controlling the RH process are as follows: from the start of adding low-reactive slag to the end of the RH process, the entire process involves bottom argon blowing from the ladle, with the argon blowing position below the riser pipe, and the line connecting the bottom argon blowing permeable brick of the ladle and the center line of the RH insertion pipe forming an angle of 25 to 35 degrees, the argon blowing flow rate being 50 NL / min to 70 NL / min, and the boosting gas flow rate being controlled at 1500 NL / min to 1700 NL / min.

[0015] Furthermore, in the above technical solution, before the first addition of low-reactive slag material, the gas flow rate is controlled at 1400NL / min to 1600NL / min.

[0016] The beneficial effects of this invention are as follows:

[0017] This invention involves adding a low-reactive slag material to the steel in two batches immediately after the aluminum deoxidation and alloying process in the RH stage. As the vacuum molten steel circulates, this slag material floats to the surface and remains at the steel-slag interface, hindering oxygen transfer from the ladle slag to the molten steel. Simultaneously, this substance has the ability to adsorb Al2O3 inclusions in the steel. Based on the steel composition requirements and through thermodynamic calculations, the slag is designed to contain a certain amount of TiO2 to ensure a certain TiO2 activity in the slag system, preventing the oxidation of titanium in the steel and lowering the steel's melting point. The formation of titanium-aluminum inclusions results in Al2O3 inclusions being the main component in the steel. These inclusions have high surface tension and tend to aggregate and float in the steel, which is beneficial to improving the cleanliness of ultra-low carbon steel. By controlling the RH treatment parameters, the aggregation and floating of inclusions in the steel can be promoted for removal without disrupting the interface structure of "molten steel - low reactive slag - original slag in the ladle". This effectively prevents oxygen transfer from the ladle slag to the molten steel and avoids secondary oxidation of easily oxidized elements such as titanium and aluminum in the deoxidized steel, resulting in significant economic and social benefits. Attached Figure Description

[0018] Figure 1 Front view of the RH equipment;

[0019] Figure 2 This is a top view of the ladle in the RH process of the present invention;

[0020] In the diagram: ①, the angle between the bottom permeable brick of the ladle and the line connecting the centerline of the RH insertion pipe; ②, the riser pipe; ③, the downcomer pipe; ④, the bottom permeable brick of the ladle. Detailed Implementation

[0021] The following detailed embodiments further illustrate the above-mentioned content of the present invention. Given that those skilled in the art have conducted extensive research in the field of RH (hydrophobic reaction) and accumulated a wealth of experience in both theory and practice, after carefully reading these embodiments and their corresponding analyses, one can certainly, based on other specific conditions, and within the range of the process scheme and slag composition design ratio proposed in this invention, conduct at most a few limited conventional experiments to specifically select several sets of process technology schemes that meet other conditions, thereby achieving the technical effects described in this invention. Therefore, only some embodiments are given below. However, this should not be construed as limiting the scope of the above-mentioned subject matter of this invention to the following examples; all technologies implemented based on the above-mentioned content of this invention fall within the scope of this invention.

[0022] Comparative Example 1

[0023] The steelmaking process adopts the process flow of "converter process - LF process - RH process - slab continuous casting process". The product composition is shown in Table 1.

[0024] Table 1 Steel Grade Composition Requirements / wt%

[0025] C Si Mn P S Al Ti ≤0.0035 ≤0.020 0.11～0.15 ≤0.010 ≤0.012 0.02～0.05 0.05～0.07

[0026] After vacuum decarburization, metallic aluminum is directly added to deoxidize the molten steel and simultaneously alloy it with aluminum. At the same time, argon is blown into the bottom throughout the RH treatment process, with an argon flow rate of 80 NL / min to 100 NL / min. The bottom-blowing permeable brick of the ladle is directly opposite the riser of the RH insertion pipe, and the RH boosting gas flow rate remains at 1800 NL / min to 2200 NL / min, which is the flow rate during the decarburization stage.

[0027] The 100mm inclusion analysis of RH steel samples was performed using the ASPEX fully automated inclusion analyzer. 2 The surface scan yielded the unit area (mm²) of the molten steel in the tundish. 2 The area of ​​inclusions larger than 1 μm is 52.8 μm. 2 Six consecutive furnaces were successfully poured, and the inner wall of the nozzle after pouring was severely lumped but not completely blocked.

[0028] Example 1

[0029] The steelmaking process adopts the process flow of "converter process - LF process - RH process - slab continuous casting process". The product composition is shown in Table 1.

[0030] Two minutes after the RH aluminum deoxidation alloying is completed, 0.21 kg / t of low-reactive slag (composition: CaO: 61.2 wt%, Al2O3: 27.6 wt%, MgO: 3.5 wt%, SiO2: 0.3 wt%, TiO2: 0.5 wt%, vermiculite: 2.1 wt%, CaO / Al2O3: 2.2) is immediately added from the high-level silo in the vacuum chamber. Two minutes after the addition, ferrotitanium or sponge titanium is added to the steel to alloy the molten steel with titanium. One minute after the addition of titanium, 0.48 kg / t of low-reactive slag is added a second time. After the second addition of low-reactive slag, the molten steel is vacuum treated for 10 minutes before the treatment is completed and the steel is discharged from the station.

[0031] Before adding the low-reactive slag for the first time, adjust the RH booster gas flow rate to 1500 NL / min. From the start of adding the low-reactive slag to the end of the RH treatment, bottom blowing argon is carried out throughout the process, with an argon flow rate of 67 NL / min. The line connecting the bottom blowing permeable brick of the ladle and the centerline of the RH insertion pipe forms an angle of 25 to 35 degrees.

[0032] The 100mm inclusion analysis of RH steel samples was performed using the ASPEX fully automated inclusion analyzer. 2 The surface scan yielded the unit area (mm²) of the molten steel in the tundish. 2 The area of ​​inclusions larger than 1 μm is 23.8 μm. 2 The quality of molten steel was significantly improved compared to the original process, enabling the successful continuous casting of 8 heats, and the inner wall of the nozzle after casting was smooth and unblocked.

[0033] Example 2

[0034] The steelmaking process adopts the process flow of "converter process - LF process - RH process - slab continuous casting process". The product composition is shown in Table 1.

[0035] Two minutes after the RH aluminum deoxidation alloying is completed, 0.48 kg / t of low-reactive slag (composition: CaO: 62.3 wt%, Al2O3: 27.5 wt%, MgO: 2.1 wt%, SiO2: 1.3 wt%, TiO2: 3.8 wt%, vermiculite: 2.0 wt%, CaO / Al2O3: 2.3) is immediately added from the high-level silo in the vacuum chamber. Two and a half minutes after the addition, ferrotitanium or sponge titanium is added to the steel to alloy the molten steel with titanium. Four minutes after the addition of titanium, 0.43 kg / t of low-reactive slag is added a second time. After the second addition of low-reactive slag, the molten steel is vacuum treated for 8 minutes before the treatment is completed and the steel is discharged from the station.

[0036] Before the first addition of low-reactive slag, the RH booster gas flow rate was adjusted to 1450 NL / min. From the start of adding the low-reactive slag to the end of the RH treatment, bottom blowing argon was carried out throughout the process, with an argon flow rate of 55 NL / min. The line connecting the bottom blowing permeable brick of the ladle and the centerline of the RH insertion pipe was at an angle of 25 to 35 degrees.

[0037] The 100mm inclusion analysis of RH steel samples was performed using the ASPEX fully automated inclusion analyzer. 2 The surface scan yielded the unit area (mm²) of the molten steel in the tundish. 2 The area of ​​inclusions larger than 1 μm is 26.7 μm. 2 The quality of molten steel was significantly improved compared to the original process, enabling the successful casting of nine heats in a row, and the inner wall of the nozzle after casting was smooth and unblocked.

[0038] Example 3

[0039] The steelmaking process adopts the process flow of "converter process - LF process - RH process - slab continuous casting process". The product composition is shown in Table 1.

[0040] Three minutes after the RH aluminum deoxidation alloying is completed, 0.36 kg / t of low-reactive slag (composition: CaO: 60.1 wt%, Al2O3: 29.3 wt%, MgO: 2.2 wt%, SiO2: 2.5 wt%, TiO2: 2.4 wt%, vermiculite: 2.5 wt%, CaO / Al2O3: 2.1) is immediately added from the high-level silo in the vacuum chamber. Three minutes after the addition, ferrotitanium or sponge titanium is added to the steel to alloy the molten steel with titanium. Three minutes after the addition of titanium, 0.40 kg / t of low-reactive slag is added a second time. After the second addition of low-reactive slag, the molten steel is vacuum treated for 7 minutes before the treatment is completed and the steel is discharged from the station.

[0041] Before adding the low-reactive slag for the first time, adjust the control RH boost gas flow rate to 1420 NL / min. From the start of adding the low-reactive slag to the end of the RH treatment, bottom blowing argon is carried out throughout the process, with an argon flow rate of 55 NL / min. The line connecting the bottom blowing permeable brick of the ladle and the centerline of the RH insertion pipe forms an angle of 25 to 35 degrees.

[0042] The 100mm inclusion analysis of RH steel samples was performed using the ASPEX fully automated inclusion analyzer. 2 The surface scan yielded the unit area (mm²) of the molten steel in the tundish. 2 The area of ​​inclusions larger than 1 μm is 31.2 μm. 2 The quality of molten steel was significantly improved compared to the original process, enabling the successful casting of nine heats in a row, and the inner wall of the nozzle after casting was smooth and unblocked.

[0043] Example 4

[0044] The steelmaking process adopts the process flow of "converter process - LF process - RH process - slab continuous casting process". The product composition is shown in Table 1.

[0045] Two minutes after the RH aluminum deoxidation alloying is completed, 0.44 kg / t of low-reactive slag (main components: CaO: 63 wt%, Al2O3: 26.3 wt%, MgO: 4.2 wt%, SiO2: 0 wt%, TiO2: 3.5 wt%, vermiculite: 2.0 wt%, CaO / Al2O3: 2.4) is immediately added from the high-level silo in the vacuum chamber. Two and a half minutes after the addition, ferrotitanium or sponge titanium is added to the steel to alloy the molten steel with titanium. Three and a half minutes after the addition of titanium, 0.23 kg / t of low-reactive slag is added a second time. After the second addition of low-reactive slag, the molten steel is vacuum treated for 8 minutes before the treatment is completed and the steel is discharged from the station.

[0046] Before the first addition of low-reactive slag, the RH booster gas flow rate was adjusted to 1450 NL / min. From the start of adding the low-reactive slag to the end of the RH treatment, bottom blowing argon was carried out throughout the process, with an argon flow rate of 55 NL / min. The line connecting the bottom blowing permeable brick of the ladle and the centerline of the RH insertion pipe was at an angle of 25 to 35 degrees.

[0047] The 100mm inclusion analysis of RH steel samples was performed using the ASPEX fully automated inclusion analyzer. 2 The surface scan yielded the unit area (mm²) of the molten steel in the tundish. 2 The area of ​​inclusions larger than 1 μm is 35.6 μm. 2 The quality of molten steel was significantly improved compared to the original process, enabling the successful casting of 9 heats in a row. Furthermore, the inner wall of the nozzle after casting showed slight nodules but no blockage.

[0048] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A method for controlling inclusions in titanium-containing ultra-low carbon steel, characterized in that, The steelmaking process is as follows: converter process - LF process - RH process - slab continuous casting process. After the aluminum deoxidation and alloying in the RH process, low reactive slag is added. As the vacuum molten steel circulates, the slag floats to the surface and remains at the steel-slag interface, preventing oxygen transfer from the ladle slag to the molten steel. At the same time, the slag has the ability to adsorb inclusions in the steel. The process parameters of the RH process are controlled to prevent oxygen transfer from the ladle slag to the molten steel, avoid secondary oxidation of titanium and aluminum elements in the deoxidized steel, and control the inclusion content in the steel. The low-reactive slag composition, by mass percentage, is as follows: CaO: 60%~63%, Al2O3: 26.3%~31%, MgO: 1.5%~4.5%, SiO2: 0~2.9%, TiO2: 2%~4.8%, vermiculite: 2%~4%, CaO / Al2O3: 2.1~2.3, with the remainder being unavoidable impurities.

2. The method for controlling inclusions in titanium-containing ultra-low carbon steel according to claim 1, characterized in that: The low-reactive slag is added in two stages. 2-4 minutes after the aluminum deoxidation and alloying process in the RH step is completed, the low-reactive slag is added for the first time from the high-level silo in the vacuum chamber. 2-4 minutes after the addition, ferrotitanium or sponge titanium is added to the steel to alloy the molten steel with titanium. 1-3 minutes after the addition of titanium, the low-reactive slag is added for the second time. After the second addition of the low-reactive slag, the vacuum treatment time for the molten steel is 5-10 minutes.

3. The method for controlling inclusions in titanium-containing ultra-low carbon steel according to claim 2, characterized in that: The first addition of low-reactive slag is 0.2 kg / t steel to 0.5 kg / t steel, and the second addition of low-reactive slag is 0.2 kg / t steel to 0.5 kg / t steel.

4. The method for controlling inclusions in titanium-containing ultra-low carbon steel according to claim 1, characterized in that: The process parameters for controlling the RH process are as follows: from the initial addition of low-reactive slag to the end of the RH process, argon is blown from the bottom of the ladle throughout the process, and the argon blowing position is below the riser pipe. The line connecting the bottom-blowing permeable brick of the ladle and the centerline of the RH insertion pipe forms an angle of 25 to 35 degrees. The argon blowing flow rate is 50 NL / min to 70 NL / min, and the riser gas flow rate is controlled at 1500 NL / min to 1700 NL / min.

5. The method for controlling inclusions in titanium-containing ultra-low carbon steel according to claim 1, characterized in that: Before adding the low-reactive slag for the first time, the gas flow rate should be controlled at 1400NL / min~1600NL / min.

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