Control method for reducing handover blank steel change in bale replacement process

Abstract

The invention discloses a control method for reducing handing-over billet steel change in a large ladle replacement process, which comprises the following steps: in a continuous casting pouring process, when a large ladle is replaced and the liquid level of molten steel in a tundish begins to drop, carrying out rare earth treatment on the molten steel in a crystallizer by adopting a rare earth wire until the molten steel in the tundish rises to a set tonnage of the tundish. In the bale replacement process, the inclusions are modified through the rare earth, the inclusions in the molten steel are reduced, the slab quality is improved, and steel modification of the connecting part in bale replacement is further reduced.

Description

Technical Field

[0001] The invention relates to the technical field of continuous casting production, and in particular to a control method for reducing the number of handover billets and steel changes during the replacement of large packages. Background Art

[0002] During the continuous casting production process, large ladles are generally replaced to maintain normal continuous casting production. During the large ladle replacement process, the large ladle water inlet needs to be closed. After the new large ladle is rotated into place, the large ladle water inlet is opened for pouring. During this process, there is no molten steel replenishment within a few minutes, so the tonnage of the tundish is constantly decreasing. Due to the decrease in the tonnage of the tundish and the decrease in the static pressure of the crystallizer, the liquid level in the crystallizer will fluctuate greatly, and the fluctuation of the liquid level in the crystallizer will cause the crystallizer protective slag to be involved. In addition, during the large ladle replacement process, the tonnage of the tundish first decreases and then increases, and the tundish liquid level also fluctuates, and the tundish slag in the tundish will be involved. Whether it is the fluctuation of the crystallizer liquid level or the fluctuation of the tundish liquid level, the technical means of rapid replacement of large ladles are generally used to minimize the unstable production state time, but it cannot fundamentally solve the problem.

[0003] The steel industry often uses rare earth to solve problems in steel metallurgy. Chinese patent publication number CN 112063930A proposes rare earth treatment of low-cost, high-toughness low-temperature pressure vessel steel plates. By adding a trace amount of lanthanum-cerium rare earth alloy to improve the toughness of the steel plate, the alloy cost and manufacturing cost of the low-temperature pressure vessel steel plate are reduced. The rare earth content added is 20-40ppm, and the process is in the refining process. In view of the need for rust prevention of steel for unpainted steel structure projects in outdoor atmospheric environments of construction projects, indoor projects, and arid and rainless areas, Chinese Patent Publication No. CN110983156A provides a rare earth corrosion-resistant steel rich in alloyed rare earth elements and a method for manufacturing the same, in which the rare earth elements used are one or more of cerium Ce, lanthanum La, and yttrium Y, and are controlled at 50 to 450 ppm through a steelmaking rare earth wire feeding process, to obtain an economical corrosion-resistant steel having a yield strength level of more than 235 MPa or a yield strength level of more than 355 MPa, and a relative corrosion rate of less than 70% (compared with Q235B in the national standard "Ordinary Carbon Steel" GB / T700) in a 96-hour periodic immersion corrosion test. Low-alloy martensitic wear-resistant steel is the most widely used wear-resistant steel in my country's coal machinery industry. Compared with medium and high manganese austenitic wear-resistant steel and bainitic wear-resistant steel, it has obvious advantages such as simple production process, low cost, excellent and stable comprehensive performance, etc. It represents the development direction of wear-resistant steel for coal mining. However, traditional low-alloy martensitic steel improves wear resistance by simply increasing hardness, which leads to poor processing performance of steel and a significant increase in the cracking tendency of wear-resistant parts. How to improve wear resistance without increasing hardness and reducing processing performance is a key technical problem faced by the development of high-wear-resistant steel for coal mining and transportation. In view of the high problem of high wear-resistant production in the coal industry, Chinese patent CN111676418B uses rare earth to treat high-strength wear-resistant quenched and tempered steel plates, specifically involving treated HB500 grade high wear-resistant steel plates and their production methods. During RH vacuum treatment, the vacuum treatment time is 20 minutes, and rare earth Ce-Fe alloy is added during vacuum treatment (experiments have confirmed that the recovery rate of rare earth can reach more than 50% by adding Ce-Fe alloy, which is significantly higher than the recovery rate obtained by directly adding rare earth elements to the system (less than 30%)), and the amount of added rare earth is about 15ppm. In the above technology, rare earth is basically added in the steelmaking process, and the problem of quality fluctuation of the handover billet during the replacement of the big bag is not solved. In addition, adding rare earth in the steelmaking process will cause a large increase in the number of inclusions and bring about the problem of difficulty in casting. In addition, the above technology does not elaborate on the mechanism changes in the amount of rare earth added, the prevention of rare earth oxidation, and the change of inclusions.

[0004] In view of the fact that conventional technical means have not fundamentally solved the problem of the unstable state of large bag replacement, and the rare earth processing technology has not considered the technical measures for corrosion prevention and has not adopted targeted processing technology in the face of the unstable state of large bags, the present invention proposes a rare earth processing method for the unstable stage of large bag replacement to solve the problem of inclusion entanglement. Summary of the invention

[0005] In view of the problem in the prior art that inclusions are entangled in the joint due to the fluctuation of the liquid level in the tundish or the liquid level in the crystallizer during the replacement of the large ladle, the purpose of the present invention is to provide a control method for reducing the steel modification of the handover slab during the replacement of the large ladle. During the replacement of the large ladle, rare earths are used to modify the inclusions, reduce the inclusions in the molten steel, improve the quality of the slab, and further reduce the steel modification of the handover slab during the replacement of the large ladle.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] The present invention provides a control method for reducing the conversion of billets into steel during the replacement of large ladles. During the continuous casting process, when the large ladles are replaced and the molten steel level in the tundish begins to drop, rare earth wires are used to perform rare earth treatment on the molten steel in the crystallizer until the molten steel in the tundish rises to the set tonnage of the tundish.

[0008] Preferably, the rare earth wire is an alloy of lanthanum and cerium.

[0009] Preferably, the rare earth wire is wrapped with a protective iron sheet, and the inner diameter of the rare earth wire is 2.0-4.0 mm.

[0010] Preferably, the protective iron sheet wrapped around the outside of the rare earth wire is cast iron sheet, and the thickness of the protective iron sheet is 0.05-0.25 mm.

[0011] Preferably, in the rare earth silk, the weight ratio of lanthanum to cerium is 2:1.

[0012] Preferably, the feeding speed of the rare earth wire into the crystallizer is 0.5-2.0 m / min, and the feeding amount of the rare earth wire is 5-50 ppm measured according to the content of cerium in molten steel.

[0013] Preferably, during the continuous casting process, argon protection is used for casting, the argon sealing flow rate of the long shroud is 20-60 L / h, the continuous casting speed is 1.0-1.8 m / min, and the width of the crystallizer is 800-1950.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] 1. The control method for reducing the steel conversion of the handover slab during the ladle replacement process of the present invention can prevent the inclusions caused by the large liquid level fluctuations during the ladle replacement process during the continuous casting production process, and can be widely used in the production process of continuous steel casting, reduce inclusions, improve the quality of slabs, further reduce steel conversion, and improve enterprise benefits;

[0016] 2. The control method of the present invention for reducing the change of steel from the handover billet during the replacement of the large package mainly utilizes rare earth to modify the inclusions to reduce their harmfulness. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0018] Figure 1 It is a schematic diagram of the structure of the protective iron sheet wrapped around the rare earth wire used in the control method for reducing the transfer of billets and steel during the replacement of large packages of the present invention;

[0019] Figure 2 This is a morphology diagram of inclusions in molten steel being eroded by rare earth after rare earth treatment during ladle replacement in Example 1;

[0020] Figure 3 This is the morphology of inclusions in the molten steel without rare earth treatment during the ladle replacement process. DETAILED DESCRIPTION

[0021] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form.

[0022] In the production and application field of IF steel, in the production of ultra-low carbon aluminum killed steel, especially in the cold-pressed steel with relatively high plasticity requirements, such as automobile engine outer panels, automobile side panels, home appliance panels and battery shell steel, during the continuous casting production process, the replacement of the ladle will cause the liquid level of the tundish and the crystallizer to fluctuate, which will lead to the continuous casting inclusions being captured by the ingot. In view of the unstable stage of the ladle replacement, in order to reduce the steel modification at the junction during the ladle replacement, the present invention uses rare earth to modify the inclusions to reduce their harmfulness.

[0023] In order to reduce the problem of inclusions in the corner joints when replacing large ladles, the present invention provides a control method for reducing the change of steel from the handover billets during the replacement of large ladles. During the continuous casting process, when the large ladles are replaced and the molten steel level in the tundish begins to drop, rare earth wires are used to perform rare earth treatment on the molten steel in the crystallizer until the molten steel in the tundish rises to the set tonnage of the tundish.

[0024] In combination with the steelmaking process, when replacing large packages, the handover section shall carry out relevant rare earth treatment:

[0025] (1) Rare earth silk

[0026] To prevent oxidation of rare earth wire, it is necessary to first protect the rare earth wire to prevent oxidation by air. The rare earth wire adopts lanthanum and cerium associated alloy, and the weight ratio of lanthanum to cerium is 2:1. The outside of the rare earth wire is wrapped with protective iron sheet, such as cast iron sheet with good plasticity, to prevent oxidation by air; the inner diameter of the rare earth wire is 2.0-4.0mm, and the thickness of the protective iron sheet wrapped outside the rare earth wire is 0.05-0.25mm.

[0027] The above-mentioned rare earth wire can be wound on a hollow sleeve using a wire rolling barrel, with one roll being 600 to 800 meters, for the convenience of production management and calculation of relevant wire feeding process parameters. The rare earth wire is then fed from the top of the crystallizer into the inside of the crystallizer through a wire feeder. After the rare earth wire enters the crystallizer, it melts and enters the molten steel, thereby realizing rare earth treatment of the molten steel.

[0028] (2) Production process and finished product ingredients

[0029] When preparing ultra-low carbon aluminum killed steel, hot metal pretreatment desulfurization - converter smelting - RH refining - continuous casting pouring is adopted, and this process belongs to the conventional production process. The finished ultra-low carbon aluminum killed steel includes the following components by weight percentage: C is 0.0015-0.0045%, Si≤0.15%, Mn is between 0.10% and 0.65%, Al is between 0.03% and 0.65%, S≤0.020%, P≤0.030%, TO≤0.0025%.

[0030] (3) Production process parameters

[0031] During converter smelting, the stop blowing temperature is 1630-1650℃, the stop blowing free oxygen is 400-900ppm, and the stop blowing carbon is 0.02-0.05%; 200-700kg of lime is added during converter tapping, and 200-500kg of aluminum slag is added after tapping. After RH refining and constant temperature oxygen measurement, a 20-30min vacuum cycle is carried out, followed by decarburization. After decarburization, metallic aluminum is added for deoxidation, and alloying is carried out after deoxidation for 2-4min. During continuous casting, argon protection casting is adopted, the long water nozzle argon seal flow rate is 20-60L / h, the continuous casting pulling speed is 1.0-1.8m / min, and the continuous casting crystallizer width is 800mm-1950mm.

[0032] (4) Wire feeding process

[0033] During the continuous casting process, rare earth wire is fed according to the cross-section and the drawing speed. The rare earth wire adopts lanthanum and cerium associated alloy, and the weight ratio is La:Ce=2:1. The feeding speed of the rare earth wire into the crystallizer is 0.5-2.0m / min, and the feeding amount of the rare earth wire is measured according to the content of cerium in the molten steel, which is 5-50ppm (that is, the weight percentage of cerium in the molten steel is 0.0005-0.0050%). Specifically, different contents of rare earth can be fed according to different sections of the continuous casting crystallizer. The timing of wire feeding is: when the ladle is replaced and the molten steel level in the tundish begins to drop, the rare earth wire is fed; when the ladle is transferred to the pouring position and pouring begins, the tonnage of the tundish slowly rises until the molten steel in the tundish rises to the set tundish tonnage, and the wire feeding ends. That is, the rare earth feeding starts when the previous ladle ends, and the new ladle is transferred to the pouring position and pouring begins until the tundish liquid level reaches a stable stage, and the feeding of rare earth wire is stopped.

[0034] The role of rare earth is: due to the instability in the continuous casting process, the slag and inclusions are brought into the molten steel, and the MeO inclusions can be denatured and reduced in size through the following reaction:

[0035] MeO+Ce(La)=M+Ce2O3

[0036] Since rare earth Ce (La) is very active, it can corrode large inclusions and reduce the size of harmful inclusions during the rolling process of steel, so that destructive plastic deformation does not occur during the subsequent rolling process.

[0037] The following is a further introduction to a control method for reducing the change of billets during the replacement of large packages with a specific example.

[0038] Example 1

[0039] The present embodiment provides a control method for reducing the number of steel changes from handover billets during the replacement of large packages, which is implemented in combination with the steelmaking process as follows.

[0040] Ultra-low carbon aluminum killed steel was produced on a certain day, and the operation steps are as follows:

[0041] (1) Rare earth wire protection. Figure 1 As shown, the rare earth wire used has rare earth A as the inner layer and protective iron sheet B as the outer layer, which is wrapped with cast iron sheet with good plasticity. The inner diameter D1 of the rare earth wire is 2.5mm, and the outer layer is wrapped with cast iron sheet (with a thickness of 0.15mm) to prevent oxidation by air. The rare earth wire is wound on the hollow sleeve with a rolling barrel, and one roll is wound according to 650m, so as to facilitate production management and calculate relevant wire feeding process parameters.

[0042] (2) Production process and finished product composition. Ultra-low carbon aluminum-killed steel adopts the conventional production process of hot metal pretreatment desulfurization - converter smelting - RH refining - continuous casting. The finished steel composition (wt%) is: C is 0.001%, Si is 0.12%, Mn is 0.15%, Al is 0.035%, S is 0.015%, P is 0.020%, TO ≤ 0.0020%.

[0043] (3) Production process parameter control. The stop-blowing temperature of the converter smelting is 1650℃, the stop-blowing free oxygen is 700ppm, and the stop-blowing carbon is 0.03%; 400kg of lime is added during the converter tapping process, and 350kg of aluminum slag is added after the tapping is completed. After RH refining and constant temperature oxygen measurement, a 20-minute vacuum cycle is carried out for decarburization; after decarburization, metallic aluminum is added for deoxidation, and alloying is carried out after deoxidation for 2 minutes. In the continuous casting production process, argon protection casting is adopted, the long water gate argon seal flow rate is 24L / h, the continuous casting pulling speed is 1.5m / min, and the continuous casting crystallizer width is 1400mm.

[0044] (4) Wire feeding process parameters. During the continuous casting process, rare earth wire is fed according to the 1400mm section and the drawing speed. The rare earth wire is a lanthanum and cerium associated alloy with a weight ratio of La:Ce=2:1. The feeding speed is 0.5m / min, and the feeding amount of rare earth wire is measured as 5ppm according to the Ce content in the molten steel (the weight percentage of Ce in the molten steel is 0.0005%). The timing of wire feeding is when the ladle is replaced and the tundish liquid level begins to drop, and the rare earth wire is fed; when the ladle is transferred to the pouring position and pouring begins, the tundish tonnage slowly increases until the set tundish tonnage is reached, and the wire feeding ends. The entire process of rare earth treatment is mainly aimed at the process of the tundish tonnage decreasing and increasing. Figure 1 It is a rare earth wire protection measure of an embodiment. Figure 2 This is the morphology of inclusions being corroded by rare earth after rare earth is fed.

[0045] Figure 3 This is the morphology of inclusions without rare earth feed. Figure 2 and Figure 3 look, Figure 2 The rare earths corrode the inclusions, reduce their particle size and reduce their harmfulness.

[0046] Example 2

[0047] The present embodiment provides a control method for reducing the number of steel changes from handover billets during the replacement of large packages, which is implemented in combination with the steelmaking process as follows.

[0048] Ultra-low carbon aluminum killed steel was produced on a certain day, and the operation steps are as follows:

[0049] (1) Rare earth wire protection. Figure 1As shown in the figure, the rare earth wire used has rare earth as the inner layer and protective iron sheet as the outer layer, which is wrapped with cast iron sheet with good plasticity. The inner diameter of the rare earth wire is 3.0mm, and the outer layer is wrapped with cast iron sheet (with a thickness of 0.25mm) to prevent oxidation by air. The rare earth wire is wound on the hollow sleeve with a wire rolling barrel, and one roll is wound according to 700m, so as to facilitate production management and calculate relevant wire feeding process parameters.

[0050] (2) Production process and finished product composition. Ultra-low carbon aluminum-killed steel adopts the conventional production process of hot metal pretreatment desulfurization - converter smelting - RH fine - continuous casting. The finished steel composition (wt%) is: C is 0.001%, Si is 0.10%, Mn is 0.18%, Al is 0.055%, S is 0.012%, P is 0.015%, TO ≤ 0.0018%.

[0051] (3) Production process parameter control. The stop-blowing temperature of the converter smelting is 1630℃, the stop-blowing free oxygen is 650ppm, and the stop-blowing carbon is 0.04%; 350kg of lime is added during the converter tapping process, and 300kg of aluminum slag is added after the tapping is completed. After RH refining and constant temperature oxygen measurement, a 22-minute vacuum cycle is carried out for decarburization; after decarburization, metallic aluminum is added for deoxidation, and alloying is carried out after deoxidation for 3 minutes. During the continuous casting production process, argon protection pouring is adopted, the long water gate argon seal flow rate is 30L / h, the continuous casting pulling speed is 1.2m / min, and the continuous casting crystallizer width is 1600mm.

[0052] (4) Wire feeding process parameters. During the continuous casting process, rare earth wire is fed according to the 1600mm cross-section and the drawing speed. The rare earth wire is a lanthanum and cerium associated alloy with a weight ratio of La:Ce=2:1. The feeding speed is 1.0m / min, and the amount of wire fed is measured as 8ppm according to the Ce content in the molten steel (the weight percentage of Ce in the molten steel is 0.0008%). The timing of wire feeding is when the ladle is replaced and the tundish liquid level begins to drop, and the rare earth wire is fed; when the ladle is transferred to the pouring position and pouring begins, the tundish tonnage slowly increases until the set tundish tonnage is reached, and the wire feeding ends. The entire process of rare earth treatment is aimed at the process of the tundish tonnage decreasing and increasing.

[0053] Example 3

[0054] The present embodiment provides a control method for reducing the number of steel changes from handover billets during the replacement of large packages, which is implemented in combination with the steelmaking process as follows.

[0055] Ultra-low carbon aluminum killed steel was produced on a certain day, and the operation steps are as follows:

[0056] (1) Rare earth wire protection. Figure 1As shown, the rare earth wire used has rare earth as the inner layer and protective iron sheet as the outer layer, which is wrapped with cast iron sheet with good plasticity. The inner diameter of the rare earth wire is 4.0mm, and the outer layer is wrapped with cast iron sheet (with a thickness of 0.20mm) to prevent oxidation by air. The rare earth wire is wound on the hollow shaft sleeve with a rolling barrel, and one roll is wound according to 800m, so as to facilitate production management and calculate relevant wire feeding process parameters.

[0057] (2) Production process and finished product composition. Ultra-low carbon aluminum-killed steel adopts the conventional production process of hot metal pretreatment desulfurization - converter smelting - RH fine - continuous casting. The finished steel composition (wt%) is: C is 0.001%, Si is 0.10%, Mn is 0.18%, Al is 0.055%, S is 0.012%, P is 0.015%, TO ≤ 0.0018%.

[0058] (3) Production process parameter control. The stop-blowing temperature of the converter smelting is 1640℃, the stop-blowing free oxygen is 900ppm, and the stop-blowing carbon is 0.05%; 700kg of lime is added during the converter tapping process, and 500kg of aluminum slag is added after the tapping is completed. After RH refining and constant temperature oxygen measurement, a 30-minute vacuum cycle is carried out for decarburization; after decarburization, metallic aluminum is added for deoxidation, and alloying is carried out after deoxidation for 4 minutes. During the continuous casting production process, argon protection pouring is adopted, the long water gate argon seal flow rate is 60L / h, the continuous casting pulling speed is 1.8m / min, and the continuous casting crystallizer width is 1950mm.

[0059] (4) Wire feeding process parameters. During the continuous casting process, rare earth wire is fed according to the 1950mm cross-section and the drawing speed. The rare earth wire is a lanthanum and cerium associated alloy with a weight ratio of La:Ce=2:1. The feeding speed is 2.0m / min, and the amount of wire fed is measured as 50ppm according to the Ce content in the molten steel (the weight percentage of Ce in the molten steel is 0.0050%). The timing of wire feeding is when the ladle is replaced and the tundish liquid level begins to drop, and the rare earth wire is fed; when the ladle is transferred to the pouring position and pouring begins, the tundish tonnage slowly increases until the set tundish tonnage is reached, and the wire feeding ends. The entire process of rare earth treatment is aimed at the process of the tundish tonnage decreasing and increasing.

[0060] In summary, the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A control method for reducing the number of steel changes during the large package replacement process, characterized in that: During the continuous casting process, when the large ladle is replaced and the molten steel level in the tundish begins to drop, rare earth wire is used to perform rare earth treatment on the molten steel in the crystallizer until the molten steel in the tundish rises to the set tonnage of the tundish.

2. The control method for reducing the number of steel transfers during the large package replacement process according to claim 1 is characterized in that: The rare earth wire is an alloy of lanthanum and cerium.

3. The control method for reducing the number of steel transfers during the large package replacement process according to claim 2, characterized in that: The rare earth wire is wrapped with protective iron sheet on the outside, and the inner diameter of the rare earth wire is 2.0-4.0 mm.

4. The control method for reducing the number of steel transfers during the large package replacement process according to claim 3 is characterized in that: The protective iron sheet wrapped outside the rare earth wire is cast iron sheet.

5. The control method for reducing the number of steel transfers during the large package replacement process according to claim 2, characterized in that: In the rare earth silk, the weight ratio of lanthanum to cerium is 2:

1.

6. The control method for reducing the number of steel changes during the large package replacement process according to claim 5, characterized in that: The feeding speed of the rare earth wire into the crystallizer is 0.5-2.0 m / min, and the feeding amount of the rare earth wire is 5-50 ppm measured according to the content of cerium in molten steel.

7. The control method for reducing the number of steel transfers during the large package replacement process according to claim 1, characterized in that: During the continuous casting process, argon protection is used for casting, the argon sealing flow rate of the long shroud is 20-60 L / h, the continuous casting speed is 1.0-1.8 m / min, and the width of the crystallizer is 800-1950.

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