A method for improving cleanliness of pre-deoxidized steel

Abstract

The application discloses a method for improving cleanliness of pre-deoxidized steel. The technological process of molten steel smelting is as follows: converter process-LF process-RH process-slab continuous casting process, after the end of vacuum decarburization in the RH process, a steel-slag interface barrier agent is added, and the treatment process parameters of the RH process are controlled, so that oxygen transmission from the ladle slag to the molten steel is effectively prevented, secondary oxidation of titanium and aluminum elements in the deoxidized steel is avoided, and the content of inclusions in the steel is controlled. The application effectively solves the problem of secondary oxidation of the molten steel by the ladle slag after the end of the RH decarburization of the existing pre-deoxidized steel to the continuous casting pouring process, and has remarkable 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 improving the cleanliness of pre-deoxidized steel. Background Technology

[0002] Because the RH treatment process for pre-deoxidized steels such as IF steel utilizes 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, pre-deoxidized 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-performing domestic companies achieving around 5%, still significantly higher than that of deoxidized steel (which generally contains less than 1% TFe). 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 pre-deoxidized 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. This reasonable control of the refining slag basicity and Al2O3 content, with the CaO / Al2O3 ratio maintained within the range of 1.5–1.9, ensures desulfurization 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 pre-deoxidized steels such as ultra-low carbon steel, 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 deoxidized 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 improving the cleanliness of pre-deoxidized steel. This method can be applied to various pre-deoxidized steel grades that require high cleanliness, and it is of great significance for improving steel cleanliness, reducing the amount of deoxidation products generated, and reducing the consumption of deoxidizing alloys.

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

[0010] A method for improving the cleanliness of pre-deoxidized steel, wherein the steelmaking process is as follows: converter process - LF process - RH process - slab continuous casting process. After vacuum decarburization in the RH process, a steel-slag interface barrier agent is added, and 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 content of inclusions in the steel.

[0011] The steel-slag interface barrier agent comprises the following components by mass percentage: CaO: 63.1%–67%, Al2O3: 27.7%–33%, MgO: 2%–4.8%, SiO2: 0–2.9%, Na2O: 0.5%–2.5%, vermiculite: 2%–4%, CaO / Al2O3: 2.1–2.4, with the remainder being unavoidable impurities.

[0012] Furthermore, in the above technical solution, the steel-slag interface barrier is added in two stages. After vacuum decarburization, the steel-slag interface barrier is added for the first time from the high-level silo in the vacuum chamber. After the addition, metallic aluminum is added to the molten steel 1 to 2 minutes to deoxidize the molten steel and simultaneously alloy the aluminum element. 2 to 3 minutes after adding aluminum, the steel-slag interface barrier is added for the second time. After the second addition of the steel-slag interface barrier, the vacuum treatment time of the molten steel is greater than 5 minutes.

[0013] Furthermore, in the above technical solution, the steel-slag interface barrier agent is added for the first time at a rate of 0.1 kg / t steel to 0.3 kg / t steel, and for the second time at a rate of 0.3 kg / t steel to 0.6 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 the steel-slag interface barrier agent 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 permeable brick of the ladle and the centerline of the RH insertion pipe forming a 90-100 degree angle, 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 steel-slag interface barrier agent is added for the first time, the gas flow rate is controlled at 1500NL / min to 1700NL / min.

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

[0017] This invention involves adding a low-reactivity substance as a steel-slag interface barrier twice after decarburization in the RH process. This substance, added to the vacuum chamber, rises to the steel-slag interface with the molten steel during circulation, preventing the oxidizing ladle slag from contacting the molten steel. Simultaneously, the low alumina activity in the steel-slag interface barrier allows it to adsorb Al2O3 inclusions in the steel. Furthermore, controlling the argon flow rate and booster gas flow rate at the bottom of the ladle during the RH process generates tiny Ar bubbles within the ladle, promoting the rise of Al2O3 and other inclusions to the steel-slag interface, where they are absorbed and dissolved by the barrier. The barrier maintains stable performance after absorbing Al2O3 inclusions. Vermiculite has a certain foaming effect, reducing oxygen transfer from the molten slag to the barrier.

[0018] This invention effectively solves the problem of secondary oxidation of molten steel by ladle slag during the continuous casting process after RH decarburization of pre-deoxidized steel, and has significant economic and social benefits. Attached Figure Description

[0019] Figure 1 Front view of the RH equipment;

[0020] Figure 2 This is a top view of the ladle in the RH process of the present invention;

[0021] 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

[0022] 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.

[0023] Comparative Example 1

[0024] 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.

[0025] Table 1 Steel Grade Composition Requirements / wt%

[0026] C Si Mn P S Al ≤0.0030 ≤0.030 0.16～0.30 ≤0.010 ≤0.012 0.04～0.08

[0027] 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.

[0028] The 100mm inclusion analysis of RH steel samples was performed using the ASPEX fully automated inclusion analyzer. 2 The surface scan revealed that the number of inclusions larger than 1 μm in the molten steel was 11.2 per mm. 2 The number of inclusions larger than 5μm is 3.8 per mm. 2 .

[0029] Example 1

[0030] 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.

[0031] After vacuum decarburization, 0.12 kg / t of steel-slag interface barrier agent (composition: CaO: 63.2 wt%, Al2O3: 27.4 wt%, MgO: 3.5 wt%, SiO2: 1.2 wt%, Na2O: 0.5 wt%, vermiculite: 3.2 wt%, CaO / Al2O3: 2.3) is immediately added from the high-level silo of the vacuum chamber. One minute after the addition, metallic aluminum is added to the steel to deoxidize the molten steel and simultaneously alloy the aluminum element. Two minutes after the addition of aluminum, 0.6 kg / t of steel-slag interface barrier agent (with the same composition as the first addition) is added for the second time. After the second addition of the barrier agent to the steel, the molten steel is vacuum treated for 10 minutes.

[0032] Before adding the steel-slag interface barrier agent for the first time, the control RH boosting gas flow rate was adjusted to 1500 NL / min. From the start of the barrier agent addition to the end of the RH treatment, bottom blowing argon was carried out throughout the process, with an argon blowing 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 was at a 90-100 degree angle.

[0033] The 100mm inclusion analysis of RH steel samples was performed using the ASPEX fully automated inclusion analyzer. 2 The surface scan revealed that the number of inclusions larger than 1 μm in the molten steel was 5.4 per mm. 2 The number of inclusions larger than 5μm is 1.5 per mm. 2 The quality of molten steel has been significantly improved compared to the original process.

[0034] Example 2

[0035] The steelmaking process adopts the process flow of "converter process - RH process - slab continuous casting process". The product composition is shown in Table 1.

[0036] After vacuum decarburization, 0.16 kg / t of steel is immediately added from the high-level silo of the vacuum chamber as a steel-slag interface barrier agent (composition: CaO: 65wt%, Al2O3: 27.0wt%, MgO: 2.1wt%, SiO2: 0.4wt%, Na2O: 2.5wt%, vermiculite: 2wt%, CaO / Al2O3: 2.4). Two minutes after the addition, metallic aluminum is added to the steel to deoxidize it and simultaneously alloy it with aluminum. One minute after the addition of aluminum, 0.5 kg / t of steel is added a second time as a steel-slag interface barrier agent (with the same composition as the first addition). After the second addition of the barrier agent, the vacuum treatment time of the molten steel is 7 minutes.

[0037] Before the first addition of the steel-slag interface barrier agent, the control RH boosting gas flow rate was adjusted to 1620 NL / min. From the start of the barrier agent addition to the end of the RH treatment, bottom blowing argon was carried out throughout the process, with an argon flow rate of 62 NL / min. The bottom blowing permeable brick of the ladle and the line connecting the centerline of the RH insertion pipe were at an angle of 90 to 100 degrees.

[0038] The 100mm inclusion analysis of RH steel samples was performed using the ASPEX fully automated inclusion analyzer. 2 The surface scan revealed that the number of inclusions larger than 1 μm in the molten steel was 5.2 per mm. 2 The number of inclusions larger than 5μm is 1.1 per mm. 2 The quality of molten steel has been significantly improved compared to the original process.

[0039] Example 3

[0040] 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.

[0041] After vacuum decarburization, 0.22 kg / t of steel is immediately added from the high-level silo of the vacuum chamber as a steel-slag interface barrier agent (composition: CaO: 60wt%, Al2O3: 28wt%, MgO: 4.5wt%, SiO2: 2.5wt%, Na2O: 1.5wt%, vermiculite: 2.5wt%, CaO / Al2O3: 2.1). 1.5 min after the addition, metallic aluminum is added to the steel to deoxidize it and simultaneously alloy it with aluminum. 1.5 min after the addition of aluminum, 0.4 kg / t of steel-slag interface barrier agent (with the same composition as the first addition) is added a second time. After the second addition of the barrier agent, the molten steel is vacuum treated for 5 min.

[0042] Before adding the first steel-slag interface barrier agent, the control RH boosting gas flow rate was adjusted to 1550 NL / min. From the start of the barrier agent addition to the end of the RH treatment, bottom blowing argon was 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 was at an angle of 90 to 100 degrees.

[0043] The 100mm inclusion analysis of RH steel samples was performed using the ASPEX fully automated inclusion analyzer. 2 The surface scan revealed that the number of inclusions larger than 1 μm in the molten steel was 4.6 per mm. 2 The number of inclusions larger than 5μm is 1.3 per mm. 2 The quality of molten steel has been significantly improved compared to the original process.

[0044] Example 4

[0045] 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.

[0046] After vacuum decarburization, 0.3 kg / t of steel is immediately added from the high-level silo of the vacuum chamber as a steel-slag interface barrier agent (main components: CaO: 64.5 wt%, Al2O3: 30 wt%, MgO: 2 wt%, SiO2: 0 wt%, Na2O: 0.5 wt%, vermiculite: 2 wt%, CaO / Al2O3: 2.2). Two minutes after the addition, metallic aluminum is added to the steel to deoxidize it and simultaneously alloy it with aluminum. Two minutes after the addition of aluminum, 0.3 kg / t of steel-slag interface barrier agent (with the same composition as the first addition) is added a second time. After the second addition of the barrier agent, the vacuum treatment time of the molten steel is 7 minutes.

[0047] Before the first addition of the steel-slag interface barrier agent, the control RH boosting gas flow rate was adjusted to 1700 NL / min. From the start of the barrier agent addition to the end of the RH treatment, bottom blowing argon was carried out throughout the process, with an argon flow rate of 52 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 90 to 100 degrees.

[0048] The 100mm inclusion analysis of RH steel samples was performed using the ASPEX fully automated inclusion analyzer. 2 The surface scan revealed that the number of inclusions larger than 1 μm in the molten steel was 4.8 per mm. 2 The number of inclusions larger than 5μm is 1.5 per mm. 2 The quality of molten steel has been significantly improved compared to the original process.

[0049] 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 improving the cleanliness of pre-deoxidized steel, characterized in that, The steelmaking process is as follows: converter process - LF process - RH process - slab continuous casting process. After vacuum decarburization in the RH process, a steel-slag interface barrier is added, and 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 content of inclusions in the steel. The steel-slag interface barrier agent comprises, by mass percentage: CaO: 63.1%~67%, Al2O3: 27.7%~33%, MgO: 2%~4.8%, SiO2: 0~2.9%, Na2O: 0.5%~2.5%, vermiculite: 2%~4%, CaO / Al2O3: 2.1~2.4, with the remainder being unavoidable impurities.

2. The method for improving the cleanliness of pre-deoxidized steel according to claim 1, characterized in that: The steel-slag interface barrier is added in two stages. After vacuum decarburization, the steel-slag interface barrier is added for the first time from the high-level silo in the vacuum chamber. After the addition, 1 to 2 minutes later, metallic aluminum is added to the molten steel to deoxidize the steel and simultaneously alloy the aluminum element. 2 to 3 minutes after the addition of aluminum, the steel-slag interface barrier is added for the second time. After the second addition of the steel-slag interface barrier, the vacuum treatment time of the molten steel is greater than 5 minutes.

3. The method for improving the cleanliness of pre-deoxidized steel according to claim 2, characterized in that: The first addition of steel-slag interface barrier agent is 0.1 kg / t steel to 0.3 kg / t steel, and the second addition is 0.3 kg / t steel to 0.6 kg / t steel.

4. The method for improving the cleanliness of pre-deoxidized steel according to claim 1, characterized in that: The process parameters for controlling the RH process are as follows: from the start of adding the steel-slag interface barrier agent 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 permeable brick of the ladle and the centerline of the RH insertion pipe forming a 90-100 degree angle. 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 improving the cleanliness of pre-deoxidized steel according to claim 2, characterized in that: Before adding the steel-slag interface barrier for the first time, the boost gas flow rate should be controlled at 1500NL / min~1700NL / min.

Images