A method for improving the blockage of submerged nozzle in the continuous casting process of duplex steel

Abstract

The present invention provides a method for improving the blockage of an immersed nozzle in a continuous casting process of duplex steel. The improvement method comprises: adding pure aluminum balls during the AOD refining process, controlling the [Al] concentration at the endpoint of the AOD refining to be ≥0.12%; after completing the AOD refining, allowing the molten steel to enter the ladle for ladle refining, specifically comprising: performing a ladle bottom blowing and opening operation; controlling [Si] to be ≥0.45% after complete slagging, adding CaF2 and CaO; then adding a pure calcium wire for quantitative pretreatment, and performing temperature measurement and sampling; adding an iron alloy for temperature adjustment, with the continuous casting target at 1500°C (+10,-5), adding a Ca-Si alloy for quantitative final treatment (when the mass concentration of Si is >0.65%, adding a pure calcium wire); the ladle bottom blowing time in the later stage of the second calcium treatment is ≥30min, and the [Ca] content is ≥27ppm at the end of the ladle bottom blowing.

Description

Technical Field

[0001] The present invention relates to a method for improving the blockage of a continuous casting nozzle, in particular to a method for improving the blockage of an immersion nozzle in a dual-phase steel continuous casting process, and belongs to the technical field of steel material casting. Background Art

[0002] Duplex steel is a high-chromium, low-carbon, medium-nickel, low-sulfur stainless steel. The smelting process includes: EAF melting process, AOD refining process, LT ladle treatment process and continuous casting.

[0003] EAF smelting completes the melting of scrap steel and alloys. The molten steel is then fed into an AOD refining furnace for decarburization, chromium retention, and other alloying adjustments. The AOD decarburization process is affected by the chromium component, resulting in lower decarburization efficiency than standard 304 stainless steel. Oxygen decarburization takes a long time, and high smelting temperatures contribute to high levels of residual oxygen in the molten steel. Deoxidation of the molten steel is primarily carried out through precipitation deoxidation. Using a deoxidizer (FeSi) results in weak deoxidation, slow deoxidation, prolonged reduction desulfurization, and inadequate deoxidation, which is sufficient for general stainless steel smelting.

[0004] The stainless steel deoxidation process primarily uses precipitation deoxidation. The key steps in this process include: 1. After the AOD furnace completes its decarburization and chromium conservation tasks, deoxidizers (FeSi, aluminum pellets) with strong oxygen affinity and low inclusion formation are used to deoxidize and reduce the molten steel; 2. Calcium treatment: The deoxidation products (SiO2, Al2O3) in the molten steel are denatured through this calcium treatment process, allowing inclusions in the molten steel to fully analyze and float, reducing the precipitation of inclusions at the submerged nozzle during the casting process, thereby reducing the occurrence of submerged nozzle blockage.

[0005] The existing methods to reduce the blockage of submerged nozzles are generally:

[0006] 1. Improve the structure of the nozzle: This method is not conducive to the stability of the crystallizer liquid level and is likely to cause the mold slag to mix in and form surface steelmaking inclusion defects;

[0007] 2. Improve the material of the nozzle: The improvement of the nozzle material cannot be maintained for a long time. Melting loss is easy to occur at the end of continuous casting, and the melted refractory material mixes into the billet to form inclusions;

[0008] 3. Improve the purity of molten steel: This method generally improves the purity of molten steel by reducing the aluminum content in the steel and treating it with calcium. It is effective in general ferritic stainless steel, but not obvious in high chromium duplex steel. Summary of the Invention

[0009] In order to solve the above technical problems, the purpose of the present invention is to provide a method that can effectively improve the clogging of the submerged nozzle in the continuous casting process of duplex steel. This method can solve the problem of continuous casting nozzle clogging caused by insufficient deoxidation and incomplete calcium treatment of high chromium duplex steel.

[0010] In order to achieve the above technical objectives, the present invention provides a method for improving the blockage of submerged nozzles in the continuous casting process of duplex steel, wherein the method comprises the steps of EAF (electric arc furnace) melting, AOD (argon oxygen furnace) refining, LT (ladle) refining, and continuous casting, wherein:

[0011] Pure aluminum balls are added during the AOD refining process, and the mass concentration of [Al] at the end point of AOD refining is controlled to be ≥0.12%;

[0012] After AOD refining, the molten steel enters the ladle for LT ladle treatment, which includes:

[0013] Carry out the early bottom blowing and hole opening operation of the ladle;

[0014] After the ladle is completely deslagging (S / K), the mass concentration of molten steel [Si] is ≥0.45%, and CaF2 and CaO (powder) are added;

[0015] Then the pure calcium line was put into use for quantitative pretreatment for the first time, and temperature was measured and sampled;

[0016] Add alloy iron to adjust the temperature, and the target continuous casting temperature is 1500℃ (+10℃, -5℃);

[0017] Ca-Si alloy is added for quantitative 2-time calcium treatment. When the mass concentration of molten steel [Si] is greater than 0.65%, pure calcium line is added for 2-time calcium treatment.

[0018] After the second calcium treatment, the ladle bottom blowing time is ≥30min, and the [Ca] content is controlled to be ≥27ppm at the end of the ladle bottom blowing.

[0019] In the above method, preferably, the duplex steel is 329 duplex steel or 2507 super duplex steel.

[0020] In the above method, preferably, the amount of molten steel refined by AOD is 145-155 tons.

[0021] In the above method, preferably, the calculation formula for the addition amount of pure aluminum balls is as follows:

[0022] The amount of pure aluminum balls added (kg) = 1.61 × the amount of oxygen consumed by metal oxidation (Nm 3 )÷Al actual recovery rate+0.15×steel output (kg) / 100.

[0023] In the above method, preferably, when the amount of molten steel refined by AOD is 145-155 tons, the input amount of CaF2 is 50 kg, and the input amount of CaO (powder) is 50 kg.

[0024] In the above method, preferably, when the amount of molten steel refined by AOD is 145-155 tons, the amount of pure calcium wire put into the first time is 120 kg.

[0025] In the above method, preferably, when the amount of molten steel refined by AOD is 145-155 tons, the input amount of the Ca-Si alloy is 350 kg.

[0026] In the above method, preferably, the time of the early bottom blowing P / P opening operation of the ladle is at least 20 minutes, and the pressure is 2.5 Bar.

[0027] In the above method, preferably, the reaction time after adding CaF2 and CaO (powder) is 5 minutes.

[0028] In the above method, preferably, when performing quantitative pretreatment, if the molten steel [Si]>0.65%, the second input amount of pure calcium wire is 280 kg.

[0029] According to a specific embodiment of the present invention, the method for improving the blockage of the submerged nozzle in the dual-phase steel continuous casting process provided by the present invention may include the following specific steps:

[0030] The steps of smelting duplex steel are sequentially performed: EAF melting, AOD refining, LT ladle treatment, and continuous casting;

[0031] During AOD refining, pure aluminum balls and Fe-Si alloy are added to control the mass concentration of [Al] at the AOD refining end point to be ≥0.12%, and the amount of molten steel refined by AOD is 145-155 tons;

[0032] LT ladle processing is carried out in the following steps:

[0033] Ladle bottom blowing P / P opening, at least 20 minutes, pressure 2.5Bar;

[0034] After complete slagging, control the mass concentration of [Si] to ≥0.45%, add 50 kg of CaF2, and react for 5 minutes;

[0035] 120 kg of pure calcium wire was added for quantitative pretreatment, the reaction lasted for 10 minutes, and the temperature was measured and sampled;

[0036] Add alloy iron to adjust the temperature and react for 5 minutes;

[0037] 350 kg of Ca-Si alloy was added for quantitative final treatment. When the mass concentration of Si was greater than 0.65%, 280 kg of pure Ca wire was added for replacement.

[0038] After the second Ca treatment, the ladle bottom blowing time is ≥30min, and [Ca] is ≥27ppm at the end of bottom blowing.

[0039] In the method for improving the clogging of the submerged nozzle in the continuous casting process of dual-phase steel of the present invention, the purpose of adding Fe-Si alloy during AOD refining is to make the silicon content in the molten steel meet the standard.

[0040] The present invention provides a method for improving the blockage of the submerged nozzle in the continuous casting process of duplex steel. The deoxidation intensity of the full Al deoxidation process used in AOD refining is large and the deoxidation speed is fast. 329 is a high-Cr low-carbon steel grade. [Cr] in the molten steel will react with [O] before [C] at a certain temperature. The oxidation product Cr2O3 will inhibit the decarburization reaction. With the high temperature conditions in the later stage of decarburization, the [C] element will react with the [Cr] element before the [O] element, but a large amount of residual oxygen has accumulated in the molten steel. Deoxidation by [SI] elements can no longer meet the deoxidation requirements. At the same temperature, the residual oxygen in the molten steel can be greatly reduced by using pure Al for deoxidation.

[0041] The present invention provides a method for improving clogging of submerged nozzles in the duplex steel continuous casting process. During the Ca treatment process (LT) in the Ladle Treatment (LT) step, CaO, an oxidation product of Ca, combines with Al2O3 to form large, low-melting-point inclusions, enabling the deoxidation reaction to proceed continuously. During the LT step, Al2O3 is denatured into large, spherical, low-melting-point inclusions. This significantly reduces the accumulation of Al2O3 on the inner wall of the submerged nozzle, thereby preventing clogging.

[0042] The technical solution of the present invention can bring beneficial effects:

[0043] 1. The present invention achieves efficient deoxidation by reducing ferrosilicon and aluminum in an argon-oxygen furnace and controlling the aluminum content at the reduction endpoint, thereby solving the difficult problem of deoxidation of high-chromium steel liquid.

[0044] 2. The present invention completely deslagging the molten steel slag before ladle treatment to remove the argon oxygen furnace slag with high Al2O3 content;

[0045] 3. The present invention solves the problem of newly generated Al2O3 inclusions in molten steel tapped from an argon-oxygen furnace by adding a calcium pretreatment process in the ladle. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a process flow chart for the LT ladle treatment in Example 1.

[0047] Figure 2This is the composition and melting point analysis results of inclusions. DETAILED DESCRIPTION

[0048] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be understood as limiting the scope of implementation of the present invention.

[0049] Example 1

[0050] This embodiment provides a method for improving the clogging of the submerged nozzle in the continuous casting process of dual-phase steel. The process is as follows: Figure 1 The method includes EAF melting, AOD refining, LT ladle processing, continuous casting and other steps; wherein:

[0051] Using EAF melting;

[0052] Then perform AOD Heat NO.SF72987, SF72988;

[0053] The molten steel is injected into an AOD argon oxygen furnace for refining, wherein the amount of the AOD molten steel is 146-150 tons; during the refining process of the AOD argon oxygen furnace, reducing Al pellets are added in an amount of 4779 kg to 4676 kg, and the mass concentration of Al at the end point of the AOD argon oxygen furnace refining is controlled to be 0.14% to 0.15%;

[0054] After AOD refining, the molten steel enters the ladle for LT refining, which includes:

[0055] Perform ladle bottom blowing (P / P) tapping operation for at least 20 minutes at a pressure of 2.5 Bar;

[0056] The endpoint of complete slag removal (S / K) is controlled by the ladle to reach a [Si] mass concentration of 0.49%-0.51%, and 50 kg of CaF2 and 50 kg of CaO powder are added and reacted for 5 minutes;

[0057] Then 120 kg of pure Ca was added for quantitative pretreatment, and the reaction was carried out for 10 minutes, after which the temperature was measured and samples were taken;

[0058] Add alloy iron to adjust the temperature, and the continuous casting temperature is 1500℃ (+10, -5);

[0059] 350 kg of Ca-Si alloy was added for quantitative final treatment. When the mass concentration of Si was greater than 0.65%, 280 kg of pure Ca was added.

[0060] The late ladle bottom blowing time (late B / B) is ≥30min, and the [Ca] content is controlled to be ≥27ppm when the ladle treatment is completed and the subsequent steps are started.

[0061] The inventors of the present invention have found that the main reasons for the blockage of the continuous immersion nozzle are as follows:

[0062] 1. Normal refractory materials should be CaO-SiO2-Al2O3, with CaO and Al2O3 as the main components. However, in the blockage, the Al2O3 component is too much, and the blockage is mainly CaO-Al2O3-MgO. The specific analysis results are shown in Table 1.

[0063] 2. Excessive Al input results in an inappropriate ratio of Ca input to Al input during LT ladle processing.

[0064] The mechanism of nozzle blockage may be: the [Al] in the molten steel increases, resulting in an increase in the Al2O3 content in the inclusions, making it easy for the SEN molten steel to be adsorbed on the surface of the nozzle refractory when passing through the nozzle.

[0065] Table 1 Analysis results of blockage components (unit: %)

[0066] CaO <![CDATA[Al2O3]]> <![CDATA[SiO2]]> MgO Water outlet blockage 16 77 1 5 Normal nozzle refractory 42 40 15 4

[0067] The present invention can solve the above-mentioned problems by lowering the melting point of inclusions (i.e., increasing the amount of Ca treatment during the T ladle treatment process to lower the melting point of inclusions) and reducing the number of inclusions (preventing the secondary oxidation of molten steel to generate new inclusions during the ladle Top Slag operation and increasing the post-ladle bubbling time to increase the aggregation and floating of inclusions).

[0068] The changes in inclusion components after improvement using the method of the present invention are shown in Table 2.

[0069] Table 2 Inclusion composition analysis results (unit: %)

[0070] <![CDATA[SiO2]]> CaO <![CDATA[Al2O3]]> MgO Current situation (before improvement) 2 17 77 5 After improvement 1 48 44 5

[0071] The melting point of inclusions dropped from 1700-1800℃ before improvement to below 1550℃, such as Figure 2 shown.

Claims

1. A method for improving the blockage of submerged nozzles in a continuous casting process of duplex steel, wherein: The method comprises electric arc furnace smelting AOD argon oxygen furnace refining LT ladle refining Continuous casting, where: The duplex steel is high chromium duplex steel; Pure aluminum balls are added during the AOD refining process. The endpoint of AOD refining controls the mass concentration of [Al] to be ≥0.12%. The calculation formula for the amount of pure aluminum balls added is as follows: The amount of pure aluminum balls added = 1.61 × oxygen consumed by metal oxidation ÷ Al actual recovery rate + 0.15 × steel output / 100. The amount of pure aluminum balls added is measured in kg, and the amount of oxygen consumed by metal oxidation is measured in Nm 3 The unit of measurement is kg. After AOD refining, the molten steel enters the ladle for LT ladle refining, which includes: Carry out ladle bottom blowing and hole opening operations; Completely skim off the molten steel slag to remove the argon-oxygen furnace slag with high Al2O3 content; After the ladle is completely deslagging, the mass concentration of molten steel [Si] is controlled to be ≥0.45%, and CaF2 and CaO are added; Then the pure calcium line was put into use for the first time for quantitative pretreatment, temperature measurement and sampling; Add ferroalloy and adjust the temperature. The target continuous casting temperature is 1500℃+10℃ to 1500℃-5℃. Ca-Si alloy is added for quantitative 2-time calcium treatment. When the mass concentration of molten steel [Si] is greater than 0.65%, pure calcium wire is added for 2-time calcium treatment. After the second calcium treatment, the ladle bottom blowing time is ≥30min, and the [Ca] content at the end of the ladle bottom blowing is controlled to be ≥27ppm.

2. The method according to claim 1, wherein The duplex steel is 329 duplex steel or 2507 super duplex steel.

3. The method according to claim 1, wherein The amount of molten steel refined by AOD is 145-155 tons.

4. The method according to claim 1, wherein The input amount of CaF2 is 50Kg, and the input amount of CaO is 50Kg.

5. The method according to claim 1, wherein When the amount of molten steel refined by AOD is 145-155 tons, the first input amount of pure calcium line is 120 kg.

6. The method according to claim 1, wherein The input amount of the Ca-Si alloy is 350 kg.

7. The method according to claim 1, wherein The ladle bottom blowing and hole opening operation takes at least 20 minutes, and the pressure is 2.5 Bar.

8. The method according to claim 1, wherein The reaction time after adding CaF2 and CaO is 5 minutes.

9. The method according to claim 1, wherein When performing the second calcium treatment, if the molten steel [Si]>0.65%, the second input of pure Ca is 280Kg.

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