A steel material having a small amount of fine inclusions and a method for producing the same

Abstract

The application relates to a steel material with a small amount of micro-inclusions and a preparation method thereof, and belongs to the technical field of steel material preparation.The method comprises the following steps: converter smelting of molten iron to obtain converter molten steel; refining of the converter molten steel to obtain refined molten steel; continuous casting of the refined molten steel to obtain a steel billet; and adding refining slag in the tapping process of the converter smelting, wherein the refining slag comprises lime, and the amount of the lime satisfies a set amount to increase the CaO / Al2O3 ratio of the slag; by controlling the adding amount of the lime, increasing the CaO / Al2O3 ratio of the slag promotes the adsorption and removal of inclusions, strengthens the removal of micro-inclusions, and solves the problem that the current steel material has a large amount of micro-inclusions.

Description

Technical Field

[0001] This invention belongs to the field of steel preparation technology, and specifically relates to a steel with low content of micro-inclusions and its preparation method. Background Technology

[0002] Tinplate (commonly known as tinplate) refers to steel sheets with a thin layer of metallic tin plated on their surface. The finished tinplate is approximately 0.2mm thick when rolled. The process involves pickling, cold rolling, electrolytic cleaning and annealing, leveling, edge trimming, followed by cleaning, electroplating, remelting, passivation, oiling, and finally cutting into finished tinplate sheets. Tinplate has a wide range of applications, from food and raw material packaging to oil cans, chemical cans, and other miscellaneous cans. The steel used in tinplate manufacturing requires strict control over the types, properties, and content of various residual metallic and non-metallic impurities during smelting. Cold-rolled tinplate products are typically thin, ranging from 0.18mm to 0.24mm, and the thickness is further reduced during stamping, reaching as low as 0.06mm in some areas. Tin inclusions from the steelmaking process can become hidden dangers for cracks, holes, and corrosion during the processing of the sheet into cans or the preservation of canned food. Summary of the Invention

[0003] The purpose of this application is to provide a steel with low content of micro-inclusions and a method for preparing the same, so as to solve the problem of high content of micro-inclusions in current steel products.

[0004] This invention provides a method for preparing steel with low content of minute inclusions, the method comprising:

[0005] Molten iron is smelted in a converter to obtain converter steel;

[0006] The molten steel from the converter is refined to obtain refined molten steel;

[0007] The refined steel is continuously cast to obtain a billet;

[0008] Refining slag, including lime, is added during the tapping process of the converter smelting. The amount of lime used meets the set requirements to increase the CaO / Al2O3 ratio of the slag.

[0009] Optionally, the set amount is 7 kg / t steel to 9 kg / t steel.

[0010] Optionally, the refining slag also includes fluorite, and the amount of fluorite used is 1.5 kg / t steel to 2.5 kg / t steel.

[0011] Optionally, strong Al deoxidation is used during the tapping process of the converter smelting.

[0012] Optionally, the bottom blowing flow rate during the tapping process in the converter smelting meets the set flow rate.

[0013] Optionally, the set flow rate is 1000 Nm. 3 / h-1500Nm 3 / h.

[0014] Optionally, the final temperature of the converter smelting is 1670℃-1685℃.

[0015] Optionally, the oxygen content at the end of the converter smelting process is 300ppm-600ppm.

[0016] Optionally, high-calcium aluminum slag balls are added during the tapping process of the converter smelting, and the amount of high-calcium aluminum slag balls added is 0.4 kg / t steel to 0.5 kg / t steel.

[0017] Based on the same inventive concept, this embodiment of the invention also provides a steel with low content of micro-inclusions, which is prepared by the method for preparing steel with low content of micro-inclusions as described above.

[0018] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0019] The method for preparing steel with low micro-inclusion content provided in this invention increases the CaO / Al2O3 ratio in the slag by controlling the amount of lime added, thereby promoting the adsorption and removal of inclusions, enhancing the removal of micro-inclusions, and solving the problem of high micro-inclusion content in current steel products.

[0020] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a flowchart of the method provided in an embodiment of the present invention. Detailed Implementation

[0023] The present invention will be described in detail below with reference to specific embodiments and examples, thereby making the advantages and various effects of the present invention more clearly apparent. Those skilled in the art should understand that these specific embodiments and examples are for illustrative purposes only and are not intended to limit the present invention.

[0024] Throughout this specification, unless otherwise specified, the terminology used herein should be understood as having the meaning commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In the event of any conflict, this specification shall prevail.

[0025] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0026] The technical solution of this application embodiment is to solve the above-mentioned technical problems, and the general idea is as follows:

[0027] During the invention process, the applicant discovered that, considering the requirements of tinplate varieties and the characteristics of inclusion control, the key and challenge in controlling micro-inclusions lies in: inhibiting the aggregation of micro-inclusions into coarse, large inclusions; recognizing that the removal mechanisms of micro-inclusions (<20μm) differ from those of large inclusions; and strengthening the removal of micro-inclusions; and improving the wettability of Al2O3 inclusions with molten steel. For tinplate varieties, Al2O3 is the most significant inclusion component in the steel, and it is one of the main issues affecting the cleanliness of molten steel and the quality of the final product. Because the wetting angle between Al2O3 inclusions and molten steel is 140°, the interfacial energy between them is relatively large, which objectively leads to poor wettability between Al2O3 inclusions and molten steel. During slab continuous casting and molten steel solidification, Al2O3 has a tendency to spontaneously aggregate. On the one hand, it easily causes nodule formation in the immersion nozzle (SEN) of continuous casting, changing the internal size of the nozzle. When molten steel enters the crystallizer from the SEN, it causes abnormal fluctuations in the liquid level of the crystallizer, turbulent flow field, and even uncontrollability, affecting the stable and smooth operation of continuous casting production and the quality of the cast billet. On the other hand, when the aggregate size of Al2O3 inclusions remaining in the steel exceeds 20μm, such large inclusions will cause a serious decline in the surface quality of tinplate products.

[0028] Currently, one of the effective measures to control the hazards of Al2O3 inclusions in cold-rolled steel products is the RH vacuum refining method. However, RH refining cannot guarantee the complete removal of Al2O3 inclusions. More importantly, current RH refining methods cannot solve the problem of Al2O3 inclusion aggregation during the solidification process of molten steel. Due to the poor wettability of Al2O3 inclusions with molten steel, this aggregation tendency is a strong spontaneous behavior, and the degree of aggregation during solidification is uncontrollable, resulting in significant quality risks. The above aspects are common problems faced by the steelmaking industry, and effective low-cost control measures have long been lacking.

[0029] This application optimizes the slag modification process during steelmaking to enhance the adsorption and removal of micro-inclusions, improve their wettability, and inhibit their spontaneous aggregation and growth. This minimizes the harm caused by micro-inclusions in the steel. Based on the interfacial characteristics between inclusions and slag, the application improves the adsorption conditions of inclusions in the slag, promotes their adsorption and removal by the slag, reduces the return of inclusions from the slag to the molten steel, significantly improves the quality of tinplate products, and better meets customer requirements.

[0030] According to a typical embodiment of the present invention, a method for preparing steel with low content of minute inclusions is provided, the process flow being: KR—BOF—RH—CC, the method comprising:

[0031] S1. The molten iron is smelted in a converter to obtain molten steel; during the tapping process of the converter smelting, refining slag is added, the refining slag including lime, and the amount of lime used meets the set amount to increase the CaO / Al2O3 ratio of the slag.

[0032] In some embodiments, the set amount is 7 kg / t steel to 9 kg / t steel.

[0033] Increasing the amount of fine-grained lime used during the converter tapping process increases the CaO / Al2O3 ratio in the slag, promoting the adsorption and removal of inclusions.

[0034] In some embodiments, the refining slag also includes fluorite, wherein the amount of fluorite used is 1.5 kg / t steel to 2.5 kg / t steel.

[0035] In this embodiment, strong Al deoxidation is used during the tapping process of converter smelting.

[0036] Strong Al deoxidation is performed during steel tapping, with the addition of lime (7-9 kg / t) and fluorite (1.5-2.5 kg / t) to reduce the FeO content in the slag and increase the CaO / Al2O3 ratio in the slag, ultimately reducing the FeO activity in the slag.

[0037] In some embodiments, the bottom blowing flow rate during the tapping process in converter smelting meets a set flow rate. Specifically, the set flow rate is 1000 Nm³. 3 / h-1500Nm 3 / h.

[0038] Strong stirring during the killed tapping process ensures good bottom blowing effect; bottom blowing flow rate is 1000-1500 Nm³. 3 / h, to enhance the removal of single particles and tiny inclusions with a size of (5-10)μm.

[0039] In this embodiment, the steel is a tin-plated sheet product. Of course, in other embodiments, it can also play a certain role in controlling inclusions in other similar low-carbon cold-rolled products.

[0040] By adopting the above design, the surface tension of the ladle top slag is increased by optimizing the composition of the ladle top slag, which promotes the separation and removal of the ladle top slag from the molten steel. The composition of inclusions is finely adjusted to improve the tendency of spontaneous aggregation of Al2O3, reduce the surface wettability of Al2O3 inclusions (contact angle 140°), and inhibit the aggregation of small inclusions during solidification.

[0041] In this embodiment, after the converter is charged and tapped, top slag is modified by adding 7-9 kg / t of fine lime and 1.5-2.5 kg / t of fluorite to improve its adsorption capacity for alumina inclusions. The converter's final temperature is controlled at 1670-1685℃, and the final oxygen content is 300-600 ppm. 0.4-0.5 kg / ton of high-calcium alumina slag balls are added at the tapping point. Front and rear sliding plates must be used for slag blocking at the converter tapping point, and the bottom blowing flow rate is 1000-1500 Nm³. 3 / h, after the steel ladle is discharged, blow strong agitation at the bottom for 3-5 minutes to ensure that there is no unmelted slag or alloy on the slag surface.

[0042] S2. The molten steel from the converter is refined to obtain refined molten steel;

[0043] In this embodiment, refining is carried out using RH refining. Specifically, RH deep vacuum circulation treatment is performed, alloying is carried out to adjust aluminum and manganese, pure circulation is performed for ≥6 minutes, and the steel is discharged from the station after breaking the vacuum. The RH treatment cycle time is guaranteed to be ≥25 minutes. After the RH treatment is completed, 0.5-0.8 kg / ton of high calcium aluminum slag balls are added.

[0044] Under the premise of the slag modification process, the content of (MgO) in the inclusions gradually increases during the RH treatment process. The inclusions in the molten steel are transformed from the deoxidation product Al2O3 into MgO·Al2O3 spinel, thus completing the removal of inclusions.

[0045] S3. The refined molten steel is continuously cast to obtain a billet.

[0046] This method optimizes the slag modification process during converter steelmaking to enhance the adsorption and removal of micro-inclusions, reduce (dilute) the FeO content in the slag, and increase the CaO / Al2O3 ratio in the slag. Ultimately, it reduces the FeO activity in the slag and controls the inclusions in the molten steel into MgO·Al2O3 spinel through a steel-slag reaction. This invention has high technological application value, is simple to operate, and eliminates the problem of large amounts of Al2O3 inclusions in steel under traditional processes.

[0047] According to another typical embodiment of the present invention, a steel with low content of micro-inclusions is provided, which is prepared by the method for preparing steel with low content of micro-inclusions as described above.

[0048] The following will provide a detailed description of the steel with low content of minute inclusions and its preparation method, in conjunction with embodiments, comparative examples and experimental data.

[0049] Example 1

[0050] A method for preparing steel with low content of minute inclusions, the method comprising:

[0051] The process flow for tinplate is as follows: BOF—RH—CC. After the converter is quenched and tapped, 141 kg of high-calcium aluminum slag balls, 2.4 t of small-particle quicklime, and 500 kg of fluorite are added. The converter tapping process must use front and rear sliding plates to block slag. After tapping, the bottom of the ladle is blown and strongly stirred for 3 minutes to ensure that there is no unmelted slag or alloy on the slag surface, thereby improving the adsorption capacity of the top slag for alumina inclusions. The final temperature of the converter is controlled at 1681℃, and the final oxygen content of the converter is 471 ppm.

[0052] The RH inlet temperature was 1615℃, the RH inlet TFe content was 2.5%, the CaO / Al2O3 ratio was 1.54, the RH was subjected to deep vacuum circulation treatment, alloying and adjusting aluminum and manganese, pure circulation for 6 minutes, and then the RH was discharged from the station. The RH treatment circulation time was 26 minutes. At the end of the RH treatment, 198 kg of high calcium aluminum slag balls were added. The RH discharge slag TFe content was 1.32, and the RH discharge slag C / A ratio was 1.36.

[0053] During RH refining, the total oxygen (TO) content in the steel was 13.9 ppm, lower than the 23.2 ppm TO content under conventional processes. Adjustments to the RH top slag composition allowed for control of inclusion composition. During RH refining, the maximum MgO content in Al2O3 inclusions increased from 1% to 13.3%, with over 95% of inclusions concentrated in the 1–5 μm range, inhibiting particle aggregation. The increased CaO content in the RH top slag improved the actual CaO / Al2O3 ratio, which is beneficial for inclusion adsorption. Despite the increased total slag volume, the slag melting point (1550℃) remained unchanged. The reduced T and Fe content and increased basicity further promoted the reduction of FeO activity in the slag, increasing the slag's ability to adsorb inclusions.

[0054] Example 2

[0055] A method for preparing steel with low content of minute inclusions, the method comprising:

[0056] The process flow for tinplate is as follows: BOF—RH—CC. After the converter is quenched and tapped, 145 kg of high-calcium aluminum slag balls, 2.34 t of small-particle quicklime, and 520 kg of fluorite are added. The converter must use front and rear sliding plates to block slag during tapping. After tapping, the ladle is blown and strongly stirred for 3.5 min to ensure that there is no unmelted slag or alloy on the slag surface and to improve the adsorption capacity of the top slag for alumina inclusions. The final temperature of the converter is 1672℃ and the final oxygen content is 455 ppm.

[0057] The RH inlet temperature was 1617℃, the RH inlet TFe content was 2.7%, the CaO / Al2O3 ratio was 1.46, the RH was subjected to deep vacuum circulation treatment, alloying and adjusting aluminum and manganese, pure circulation for 6 minutes, and then the RH was discharged from the station. The RH treatment circulation time was 25.5 minutes. At the end of the RH treatment, 212 kg of high calcium aluminum slag balls were added. The RH discharge slag TFe content was 1.32%, and the RH discharge slag C / A ratio was 1.34.

[0058] When the RH slag is broken, the TO content in the steel is 14.3 ppm, which is lower than the 23.2 ppm TO content in the steel under conventional processes. Based on the adjustment of the RH top slag composition, the inclusion composition can be controlled. More than 95% of the inclusions are concentrated in 1-5 μm, which inhibits the aggregation behavior of inclusion particles.

[0059] Comparative Examples 1-N

[0060] A method for preparing steel, the method comprising:

[0061] The process flow for tinplate is as follows: BOF—RH—CC. After the converter is quenched and tapped, 135 kg of high-calcium aluminum slag balls, 2.0 t of small-particle quicklime, and 600 kg of fluorite are added. The converter must use front and rear sliding plates to block slag during tapping. After tapping, the ladle is blown and stirred strongly for 4 minutes to ensure that there is no unmelted slag or alloy on the slag surface, thereby improving the adsorption capacity of the top slag for alumina inclusions. The final temperature of the converter is 1675℃, and the final oxygen content of the converter is 465 ppm.

[0062] The RH inlet temperature was 1620℃, the RH inlet TFe content was 4.5%, the CaO / Al2O3 ratio was 1.24, the RH was subjected to deep vacuum circulation treatment, alloying and adjusting aluminum and manganese, pure circulation for 6 minutes, and then the RH was discharged from the station. The RH treatment circulation time was 25.5 minutes. At the end of the RH treatment, 208 kg of high calcium aluminum slag balls were added. The RH discharge slag had a TFe content of 4.32% and a C / A ratio of 1.06.

[0063] When the RH process is activated, the TO content in the steel is 23.9 ppm, which is higher than the 23.2 ppm TO content in the steel under conventional processes, making it difficult to stably control small inclusions.

[0064] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0065] (1) The method provided in this embodiment of the invention optimizes the process of adjusting the slag modification mode in the converter tapping process to enhance the adsorption and removal of micro inclusions, reduce the FeO content in the slag and increase the CaO / Al2O3 ratio in the slag, and finally reduce the FeO activity in the slag, and control the inclusions in the molten steel to MgO·Al2O3 spinel through the steel slag reaction.

[0066] (2) The method provided in this embodiment of the invention has high process application value, is easy to operate, can significantly suppress the tendency of inclusions to spontaneously aggregate and grow, can minimize the harm of small inclusions in steel, improve the adsorption conditions of inclusions in slag, promote the adsorption and removal of inclusions by slag, significantly improve the quality of tinplate products, and better meet customer requirements.

[0067] Finally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0068] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0069] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing steel with low content of minute inclusions, characterized in that, The method includes: Molten iron is smelted in a converter to obtain converter steel; The molten steel from the converter is refined to obtain refined molten steel; The refined steel is continuously cast to obtain a billet; During the tapping process of the converter smelting, refining slag is added and strong Al deoxidation is adopted. The refining slag includes lime and fluorite. The amount of lime used is 7 kg / t steel to 9 kg / t steel to increase the CaO / Al2O3 ratio of the slag. The amount of fluorite used is 1.5 kg / t steel to 2.5 kg / t steel. The bottom blowing flow rate during the tapping process in the converter smelting is 1000 Nm³. 3 / h-1500Nm 3 / h; The oxygen content at the end of the converter smelting process is 300ppm-600ppm; the temperature at the end of the converter smelting process is 1670℃-1685℃. High-calcium aluminum slag balls are added during the tapping process of the converter smelting, and the amount of high-calcium aluminum slag balls added is 0.4 kg / t steel to 0.5 kg / t steel; The micro-inclusions are Al2O3-type inclusions with a size <20μm, and the steel is tin-plated sheet.

2. A type of steel with low content of minute inclusions, characterized in that, The steel is prepared by the method for preparing steel with low content of micro-inclusions as described in claim 1.

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