A method for producing a steel slab

Abstract

The application relates to the field of steel production, in particular to a preparation method of a steel plate casting blank. The method comprises the following steps: converter smelting of molten iron, and control of the TFe content in a ladle top slag to obtain first molten steel; RH vacuum refining of the first molten steel to obtain target molten steel; wherein the weight ratio of Als and Alt in the target molten steel is controlled; tundish molten steel is obtained through the target molten steel, and the total oxygen content of the tundish molten steel, the Als loss amount of the tundish molten steel and the weight ratio of Als and Alt in the tundish molten steel are controlled to perform continuous casting pouring to obtain a first casting blank; wherein the process parameters of the continuous casting pouring include: intermediate ladle superheat, argon blowing flow and the amount of protective slag; the first casting blank is in-furnace heated, and the surface temperature of the first casting blank when entering the furnace and the in-furnace time are controlled to obtain a steel plate casting blank. The method reduces the surface defects of the casting blank, and can realize cleaning-free casting blank.

Description

Technical Field

[0001] This application relates to the field of steelmaking production, and more particularly to a method for preparing steel plate billets. Background Technology

[0002] High-grade alloyed galvanized steel sheets have stringent requirements regarding the distribution of surface defects and inclusions. In industrial production, flame cleaning of cast billets is commonly used to remove more than 3mm of surface defects to reduce surface defects in the final product. However, flame cleaning of cast billets increases costs, reduces efficiency, and increases the probability of surface defects generated during flame cleaning.

[0003] Therefore, there is an urgent need to prepare a steel plate billet with high surface quality. Summary of the Invention

[0004] This application provides a method for preparing steel plate billets to solve the technical problem of serious surface defects in existing high-grade steel plate billets.

[0005] In a first aspect, this application provides a method for preparing a steel plate billet, the method comprising:

[0006] The molten iron is smelted in a converter, and the content of TFe in the top slag of the ladle is controlled to obtain the first molten steel.

[0007] The first molten steel is subjected to RH vacuum refining to obtain the target molten steel; wherein, the weight ratio of Als to Alt in the target molten steel is controlled.

[0008] The target molten steel is used to obtain tundish molten steel, and the total oxygen content, Als loss, and Als to Alt weight ratio of the tundish molten steel are controlled for continuous casting to obtain the first billet; wherein the process parameters of continuous casting include: tundish superheat, argon blowing flow rate, and amount of protective slag.

[0009] The first billet is heated in the furnace, and the surface temperature and furnace time of the first billet are controlled when it enters the furnace to obtain a steel plate billet.

[0010] Optionally, the TFe content in the ladle top slag is 2%-4% by weight.

[0011] Optionally, the weight ratio of Als to Alt in the target molten steel is ≥90%.

[0012] Optionally, the total oxygen content of the molten steel in the tundish is ≤15ppm.

[0013] Optionally, the Al loss of the molten steel in the tundish is ≤80ppm, and the weight ratio of Al to Alt in the molten steel in the tundish is ≥90%.

[0014] Optionally, the superheat of the intermediate ladle is ≥30°C.

[0015] Optionally, the argon blowing flow rate is ≤3L / min.

[0016] Optionally, the amount of protective slag includes: a liquid slag layer thickness of ≥10mm at 1 / 4 position in the width direction, provided that the liquid level fluctuation in the crystallizer is within ±5mm.

[0017] Optionally, the physical properties of the protective slag include: a melting point of 1150℃-1210℃ and a viscosity of 0.35Pa.s-0.50Pa.s.

[0018] Optionally, the surface temperature of the first billet when it enters the furnace is ≥600℃, and the time spent in the furnace is ≥160min.

[0019] The technical solutions provided in this application have the following advantages compared with the prior art:

[0020] The method for preparing the steel slab billet provided in this application ensures high steel purity by controlling the TFe content in the steel slag and the total oxygen content in the steel; it ensures sufficient flotation of inclusions in the steel by quantitatively evaluating the Als / Alt ratio and process aluminum loss in the molten steel; it achieves stable and controllable size and subsurface depth of inclusions on the billet surface through high-superheat casting, low-flow argon blowing, and sufficient liquid slag protection; and it achieves stable control of iron scale burn-off by controlling the high-temperature billet entry temperature and residence time in the heating furnace, thus eliminating shallow surface inclusions in the billet. This comprehensive control of the smelting and continuous casting processes reduces surface defects in the billet, effectively lowers product surface defects caused by billet quality problems, eliminates the need for billet cleaning, and saves production costs. Attached Figure Description

[0021] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0022] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic flowchart illustrating a method for preparing a steel plate billet according to an embodiment of this application. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0025] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0026] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this application, terms such as "comprising" and "including" mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than one" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0027] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0028] Firstly, this application provides a method for preparing steel plate castings; please refer to [link to relevant documentation]. Figure 1 The method includes:

[0029] S1. The molten iron is smelted in a converter, and the content of TFe in the top slag of the ladle is controlled to obtain the first molten steel.

[0030] In some embodiments, the TFe content in the ladle top slag is 2%-4% by weight.

[0031] In this embodiment, an aluminum-containing slag modifier is added near the end of converter tapping. The amount added is determined based on the estimated slag charge from the converter, aiming for a TFe content of 2%-4% in the modified slag. The addition is completed after the converter tapping is finished. Controlling the TFe weight content in the ladle top slag to 2%-4% has the following positive effects: it effectively reduces the oxidizing properties of the slag and prevents the formation of magnesium aluminum spinel in the steel. Excessive TFe content can exacerbate the oxidation of molten steel by the slag, increasing alumina inclusions in the steel. Insufficient TFe content can increase steel production costs and generate magnesium aluminum spinel inclusions, which can clog the top nozzle during continuous casting. Specifically, the TFe weight content in the ladle top slag can be 2%, 3%, 4%, etc.

[0032] S2. The first molten steel is subjected to RH vacuum refining to obtain the target molten steel; wherein, the weight ratio of Als to Alt in the target molten steel is controlled.

[0033] In this embodiment, the refining process uses the RH process, and aluminum deoxidation and alloying are completed in one aluminum addition. The pure circulation time after adding the last batch of material is 4-6 minutes.

[0034] In some embodiments, the weight ratio of Als to Alt in the target molten steel is ≥90%.

[0035] In this embodiment, sampling and analysis are performed near the end of refining, and the Als / Alt ratio must be ≥90%; otherwise, vacuum treatment continues. Controlling the Als / Alt weight ratio in the molten steel to be ≥90% after refining has the positive effect of reducing alumina inclusions in the steel. If the Als / Alt weight ratio is too low, it will increase the alumina inclusions in the molten steel to some extent, causing immersion nozzle blockage during continuous casting. Specifically, the target Als / Alt weight ratio in the molten steel can be 90%, 92%, 94%, 96%, 98%, etc.

[0036] S3. A tundish molten steel is obtained from the target molten steel, and the total oxygen content, Als loss, and Als to Alt weight ratio of the tundish molten steel are controlled for continuous casting to obtain the first billet; wherein the process parameters of the continuous casting include: tundish superheat, argon blowing flow rate, and the amount of protective slag.

[0037] In this embodiment, continuous casting employs fully protected casting.

[0038] In some embodiments, the total oxygen content (T[O]) of the molten steel in the tundish is ≤15ppm.

[0039] In this embodiment, controlling the total oxygen content of the molten steel in the tundish to ≤15ppm has the positive effect of reducing the mass percentage of free oxygen and oxygen-containing inclusions in the steel. If the total oxygen content is too high, it indicates a high density of various oxide inclusions in the steel, which can easily lead to nozzle blockage during continuous casting. Specifically, the total oxygen content of the molten steel in the tundish can be 15ppm, 14ppm, 13ppm, 12ppm, 11ppm, 10ppm, etc.

[0040] In some embodiments, the Al loss of the molten steel in the ladle is ≤80ppm, and the weight ratio of Al to Alt in the molten steel in the ladle is ≥90%.

[0041] In this embodiment, controlling the Als loss of molten steel in the ladle to ≤80ppm has the positive effect that the oxidation of molten steel from refining to continuous casting is stable and controllable. If the Als loss is too high, it indicates that the molten steel is undergoing severe secondary oxidation, and the oxide inclusions in the molten steel are in an abnormally high process. Specifically, the Als loss of the molten steel in the ladle can be 80ppm, 75ppm, 70ppm, etc.

[0042] In some embodiments, the superheat of the intermediate ladle is ≥30°C.

[0043] In this embodiment, the refining temperature is controlled to achieve a superheat of ≥30°C during continuous casting. The positive effects of controlling the tundish superheat to ≥30°C include: better floating conditions for inclusions in the molten steel; shorter solidification hooks during crystallizer cooling; and a positive effect on the melting of the protective slag and the uniform spreading of the molten slag. If the superheat is too low, it will increase slag entrapment defects on the surface of the coil to some extent. Specifically, the tundish superheat can be 30°C, 34°C, 38°C, 40°C, etc.

[0044] In some embodiments, the argon blowing flow rate is ≤3L / min.

[0045] In the embodiments of this application, the positive effects of controlling the argon blowing flow rate to ≤3L / min are: it may reduce the amount of argon gas blown into the crystallizer and the size of the bubbles, and restrict the use of low-flow argon blowing for the stopper rod and the water inlet; if the argon blowing flow rate is too high, it will excessively disturb the flow of molten steel in the crystallizer to a certain extent, severely emulsify the liquid slag at the top of the crystallizer, and significantly increase the slag defects on the surface of the plate coil. Specifically, the argon blowing flow rate can be 3L / min, 2.8L / min, 2.5L / min, 2.3L / min, 2L / min, etc.

[0046] In some embodiments, the amount of protective slag includes: a liquid slag layer thickness of ≥10mm at 1 / 4 position in the width direction, provided that the liquid level fluctuation in the crystallizer is within ±5mm.

[0047] In this embodiment, the thickness of the liquid slag layer at 1 / 4 of the width direction is set under the condition that the liquid level fluctuation in the crystallizer is within ±5mm.

[0048] The purpose of a thickness of ≥10mm is to ensure that the process of molten steel transforming into a preliminary solidified billet shell is effectively protected by slag when the fluctuation of the liquid level in the crystallizer is within the normal range. Specifically, under the condition that the fluctuation of the liquid level in the crystallizer is within ±5mm, the thickness of the slag layer at 1 / 4 position in the width direction can be 10mm, 12mm, 14mm, 16mm, etc.

[0049] In some embodiments, the physical properties of the protective slag include: a melting point of 1150℃-1210℃ and a viscosity of 0.35Pa.s-0.50Pa.s.

[0050] In this embodiment, controlling the melting point of the protective slag to be between 1150℃ and 1210℃ has the following positive effects: ensuring a good melting state of the protective slag. If the melting point of the protective slag is too high, it will cause difficulties in melting to some extent, resulting in a thin layer of liquid slag in the crystallizer; if the melting point of the protective slag is too low, it will increase the fluidity of the slag to some extent, making it easier for liquid slag droplets to be entrained in the molten steel. Specifically, the melting point of the protective slag can be 1150℃, 1170℃, 1180℃, 1200℃, 1210℃, etc.

[0051] The positive effects of controlling the viscosity of the protective slag to 0.35 Pa·s-0.50 Pa·s include: ensuring effective lubrication of the cast billet and the copper plate in the crystallizer, and controlling the appropriate thickness of the liquid slag layer. If the viscosity of the protective slag is too high, it will, to some extent, worsen the lubrication between the cast billet and the copper plate in the crystallizer, causing the billet to stick to the copper plate; if the viscosity is too low, it will, to some extent, exacerbate the consumption of liquid slag, significantly reducing the thickness of the liquid slag layer in the crystallizer, thereby increasing the risk of slag entrapment defects. Specifically, the viscosity of the protective slag can be 0.35 Pa·s, 0.40 Pa·s, 0.45 Pa·s, 0.50 Pa·s, etc.

[0052] S4. The first billet is heated in the furnace, and the surface temperature and furnace time of the first billet are controlled when it enters the furnace to obtain a steel plate billet.

[0053] In some embodiments, the surface temperature of the first billet when it is fed into the furnace is ≥600°C, and the time spent in the furnace is ≥160 min.

[0054] In this embodiment, controlling the surface temperature of the first billet to be ≥600℃ upon entering the furnace has the following positive effects: it reduces fluctuations in the burning loss of the billet's sheet, as the billet must be loaded into the heating furnace at a high temperature; if the surface temperature of the billet is too low, it will reduce the burning loss of the billet in the heating furnace to a certain extent. Specifically, the surface temperature of the first billet upon entering the furnace can be 600℃, 620℃, 640℃, 650℃, 680℃, 700℃, etc.

[0055] The positive effects of controlling the furnace dwell time to ≥160 min include: stabilizing the burn-off of the billet in the heating furnace, as the billet has a high heat content; if the furnace dwell time is too short, it will reduce the burn-off of the billet in the heating furnace to a certain extent, leading to an increase in surface inclusions and defects. Simultaneously, the increased temperature drop at the corners of the billet will produce fine line defects at the rolled edges. Specifically, the furnace dwell time can be 160℃, 165℃, 170℃, 180℃, etc. Furthermore, the furnace exit temperature after this heating should be ≥1180℃.

[0056] Using the above methods, the depth fluctuation of inclusions on the surface of the billet is effectively controlled and identified, and the shedding and burning of the billet's scale are controlled, reducing surface defects and effectively minimizing product surface defects caused by billet quality issues. This allows for billet cleaning-free production. Subsequent rolling and galvanizing processes on the above-mentioned steel plate billet can yield high-grade alloyed galvanized sheets with excellent surface quality.

[0057] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0058] This application provides a method for preparing a steel plate billet, the method comprising:

[0059] S11. The molten iron is smelted in a converter, and the content of TFe in the top slag of the ladle is controlled to obtain the first molten steel.

[0060] S21. The first molten steel is subjected to RH vacuum refining to obtain the target molten steel; wherein, the weight ratio of Als to Alt in the target molten steel is controlled.

[0061] S31. A tundish molten steel is obtained from the target molten steel, and the total oxygen content, Als loss, and Als to Alt weight ratio of the tundish molten steel are controlled for continuous casting to obtain a first billet; wherein the process parameters for continuous casting include: tundish superheat, argon blowing flow rate, and the amount of protective slag.

[0062] S41. The first billet is heated in the furnace, and the surface temperature and furnace time of the first billet are controlled when it enters the furnace to obtain a steel plate billet. Please refer to Table 1-2 for specific process parameters.

[0063] Table 1. Process parameters for converter smelting, RH refining, and continuous casting.

[0064]

[0065]

[0066] Table 2 Process parameters for billet heating

[0067] Serial Number The surface temperature of the billet when it enters the furnace is ℃ Total heating time (min) Furnace temperature (°C) Example 1 600 160 1180 Example 2 700 170 1182 Example 3 650 165 1185 Comparative Example 1 350 145 1180

[0068] The surface defects of the cast billets prepared in Examples 1-3 and Comparative Example 1 were evaluated, and the results are shown in Table 3.

[0069] Table 3 Evaluation results of surface defects in cast billets

[0070] Serial Number Defect rate % Example 1 5.10 Example 2 6.12 Example 3 3.39 Comparative Example 1 13.67

[0071] Based on the analysis in Tables 1-3 above, the steel plate billet preparation method provided in this application, through comprehensive control of the smelting and continuous casting processes, reduces surface defects of the billet and effectively reduces product surface defects caused by billet quality problems, thus achieving billet cleaning-free operation; while Comparative Example 1, which did not adopt the method of the embodiment of this application, has a higher defect rate of the billet.

[0072] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing a steel plate billet, characterized in that, The method includes: The molten iron is smelted in a converter, and the content of TFe in the top slag of the ladle is controlled to be 2%-4% to obtain the first molten steel. The first molten steel is subjected to RH vacuum refining to obtain the target molten steel; wherein the weight ratio of Als to Alt in the target molten steel is controlled to be ≥90%; The target molten steel is used to obtain tundish molten steel, and the total oxygen content of the tundish molten steel is controlled to be ≤15ppm, the Al loss of the tundish molten steel is controlled to be ≤80ppm, and the weight ratio of Al to Alt of the tundish molten steel is controlled to be continuous casting to obtain the first billet; wherein, the process parameters of the continuous casting include: tundish superheat, argon blowing flow rate ≤3L / min, and the amount of protective slag is such that the thickness of the liquid slag layer at 1 / 4 position in the width direction is ≥10mm under the condition that the liquid level fluctuation in the crystallizer is within ±5mm. The physical properties of the protective slag include: melting point of 1150℃-1210℃, viscosity of 0.35Pa·s-0.50Pa·s; The first billet is heated in a furnace, and the surface temperature of the first billet is controlled to be ≥600℃ and the furnace time is ≥160min when it enters the furnace, so as to obtain a steel plate billet, wherein the steel plate is a high-grade alloyed galvanized plate.

2. The method according to claim 1, characterized in that, The weight ratio of Als to Alt in the molten steel in the ladle is ≥90%.

3. The method according to claim 1, characterized in that, The superheat of the intermediate ladle is ≥30℃.

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