High cleanliness low carbon steel and method of making the same

Abstract

This application discloses a high-purity low-carbon steel and its preparation method. The high-purity low-carbon steel comprises the following components by mass percentage: C: 0.02wt%~0.07wt%, Si≤0.03wt%, Mn: 0.15wt%~0.25wt%, P≤0.015wt%, S≤0.01wt%, Alt: 0.04wt%~0.06wt%, N≤0.004wt%, Ni≤0.06wt%, Cr≤0.06wt%, Cu≤0.06wt%, As≤0.01wt%, Sn≤0.02wt%, Cr+Ni+Cu≤0.09wt%, with the remainder being Fe and unavoidable trace elements. The high-purity low-carbon steel of this application has fewer inclusions and higher mechanical properties, exhibiting good machinability.

Description

Technical Field

[0001] This application belongs to the field of metallurgical technology, and in particular relates to a high-purity low-carbon steel and its preparation method. Background Technology

[0002] The current production process for battery casing steel mainly adopts the process route of "KR hot metal desulfurization → converter smelting → LF / RH refining → continuous casting". In this process, the control of inclusions mainly relies on traditional deoxidation alloying and secondary refining technologies. However, the low-carbon steel produced by existing technologies contains too many inclusions, making it difficult to meet the stamping performance requirements of high-end battery casings. Summary of the Invention

[0003] This application provides a high-purity low-carbon steel and its preparation method. The high-purity low-carbon steel of this application has fewer inclusions and higher mechanical properties, and has good processing performance.

[0004] In a first aspect, embodiments of this application provide a high-purity low-carbon steel, which, by mass percentage, comprises the following components: C: 0.02wt%~0.07wt%, Si≤0.03wt%, Mn: 0.15wt%~0.25wt%, P≤0.015wt%, S≤0.01wt%, Alt: 0.04wt%~0.06wt%, N≤0.004wt%, Ni≤0.06wt%, Cr≤0.06wt%, Cu≤0.06wt%, As≤0.01wt%, Sn≤0.02wt%, Cr+Ni+Cu≤0.09wt%, with the remainder being Fe and unavoidable trace elements.

[0005] According to the embodiments of this application, the high-purity low-carbon steel of this application, by limiting the content standards of P ≤ 0.015wt% and S ≤ 0.01wt%, can effectively suppress the formation of brittle or low-melting-point inclusions such as FeS, MnS, and AlP, and avoid such inclusions forming stress concentration points or fracture sources inside the steel. Furthermore, by controlling the Alt content within the range of 0.04wt% to 0.06wt%, the strong deoxidizing effect of Al can be fully utilized to remove free oxygen in the molten steel and reduce Al content. O The precipitation of oxide inclusions can avoid the formation of a large number of coarse Al particles due to excessive Alt content. O Inclusion aggregation, coupled with strict control of N ≤ 0.004 wt%, prevents the formation and growth of AlN inclusions, ensuring that the inclusions inside the steel are characterized by "few in number, small in size, and uniformly distributed." Furthermore, by controlling the Mn content between 0.15 wt% and 0.25 wt%, the plasticity and toughness of the steel can be significantly improved while ensuring its basic strength. This avoids the problems of increased hardness and decreased plasticity due to excessive Mn content, or insufficient structural strength requirements after battery casing molding due to insufficient Mn content. This significantly improves the pass rate and reliability of battery casing products. In addition, by controlling the total content of Cr+Ni+Cu ≤ 0.09 wt% in the high-purity low-carbon steel of this application, the formation of enriched layers or compounds of these elements on the steel surface can be avoided, ensuring that the steel has good corrosion resistance and surface treatment performance.

[0006] In some optional embodiments, the high-cleanliness low-carbon steel meets at least one of the following: (1) the high-cleanliness low-carbon steel contains less than or equal to 15 inclusions / mm. 2 (2) The number of inclusions with an average particle size ≥10μm in high-purity low-carbon steel is less than or equal to 0.5 particles / mm. 2 (3) The metallographic structure of high-purity low-carbon steel includes ferrite and carbides. (4) Cr+Ni+Cu≤0.06wt%.

[0007] In some optional embodiments, the high-purity low-carbon steel satisfies at least one of the following: (1) the yield strength of the high-purity low-carbon steel is 220 MPa to 350 MPa. (2) the tensile strength of the high-purity low-carbon steel is 300 MPa to 420 MPa. (3) the elongation A50 of the high-purity low-carbon steel is greater than or equal to 26%. (4) the hardness of the high-purity low-carbon steel is 100 HV5 to 130 HV5.

[0008] Secondly, embodiments of this application provide a method for preparing high-purity low-carbon steel according to the first aspect, comprising: Provide molten iron with a temperature of 1300℃ or higher.

[0009] After KR desulfurization treatment and converter smelting treatment, low-carbon steel is obtained, wherein the temperature of the low-carbon steel is 1620℃~1650℃.

[0010] Molten low-carbon steel is subjected to argon station treatment to obtain argon-treated molten steel, wherein the argon station treatment time is less than or equal to 30 minutes.

[0011] The molten steel treated by the argon station is then continuously cast to obtain a billet.

[0012] The billet is rolled, cooled, and degreased to obtain high-purity low-carbon steel.

[0013] According to the embodiments of this application, the preparation method of this application controls the content range of key elements such as Mn, P, S, Al, and N without adding any other alloying elements, and adopts a direct converter-continuous casting process route, that is, the molten steel directly enters the continuous casting process after desulfurization treatment and converter smelting. Compared with refining processes such as LF or RH, the preparation method of this application does not require refining treatment with an external heating source, which simplifies the production process and significantly reduces the carbon emission intensity during the production process, effectively reducing secondary pollution during the steel refining process. In addition, the argon station treatment time is controlled within ≤30 minutes, which can not only achieve homogenization of steel composition and temperature, but also avoid problems such as steel gas absorption and insufficient flotation of inclusions caused by excessive treatment time, further improving the stability of the production process.

[0014] In some alternative embodiments, the steps of rolling, cooling, and degreasing the billet to obtain high-purity low-carbon steel include: The billet is subjected to heat treatment and hot rolling to obtain hot-rolled steel plate, wherein the heat treatment temperature is greater than or equal to 1200℃.

[0015] Hot-rolled steel sheets are coiled to obtain hot-rolled steel coils.

[0016] Hot-rolled steel coils are pickled and then cold-rolled to obtain cold-rolled steel sheets.

[0017] Cold-rolled steel sheets are degreased in an alkaline degreasing agent at 50℃~60℃ to obtain degreased cold-rolled steel sheets. Preferably, the residual oil on the surface of the degreased cold-rolled steel sheets is ≤5mg / m².

[0018] The degreased cold-rolled steel sheet is subjected to a bell-type annealing treatment to obtain the annealed steel sheet.

[0019] The annealed steel plate is flattened to obtain high-purity low-carbon steel.

[0020] In some optional embodiments, the step of heating and hot rolling the billet to obtain a hot-rolled steel sheet includes roughing rolling and finishing rolling, and the hot rolling process satisfies at least one of the following: (1) The number of passes in the rough rolling process is 5 or 7.

[0021] (2) The thickness of the intermediate billet produced by rough rolling is 30mm~50mm.

[0022] (3) The final rolling temperature of the finishing rolling is 870℃~920℃.

[0023] In the above optional embodiments, the preparation method of this application can refine the grain structure of steel by precisely controlling the roughing rolling passes, intermediate billet thickness and finishing rolling temperature, avoiding the decrease in plasticity caused by coarse grains, while ensuring the uniformity of steel thickness and dimensional accuracy.

[0024] In some optional embodiments, in the step of coiling the hot-rolled steel sheet to obtain a hot-rolled steel coil, the coiling temperature is 600℃~680℃. Controlling the coiling temperature at 600℃~680℃ can effectively suppress the formation of hard and brittle phases in the steel structure and improve the plasticity and toughness of the steel.

[0025] In some optional embodiments, in the step of pickling and cold rolling hot-rolled steel coils to obtain cold-rolled steel sheets, the total reduction rate of the cold rolling process is 75% to 90%. The design of a total reduction rate of 75% to 90% in cold rolling can further refine the grains, improve the strength and surface finish of the steel, and meet the stringent requirements of high-end battery casings for steel flatness and forming precision.

[0026] In some optional embodiments, the degreased cold-rolled steel sheet is subjected to a bell-type annealing treatment to obtain an annealed steel sheet. The annealing temperature is 660℃~720℃. The bell-type annealing treatment at 660℃~720℃ can eliminate work hardening generated during cold rolling, restore the plasticity and toughness of the steel, refine the microstructure, improve the stamping performance of the steel, and avoid defects such as cracking and springback during stamping.

[0027] In some optional embodiments, in the step of leveling the annealed steel sheet to obtain high-purity low-carbon steel, the leveling process employs wet leveling rolling with a leveling elongation of 0.5% to 3%. The wet leveling rolling process, combined with a leveling elongation of 0.5% to 3%, can further improve the surface flatness and shape of the steel, eliminate defects such as surface oxide scale, and enhance the surface hardness and wear resistance of the steel. This improves the surface quality and structural stability of the formed battery casing, providing a good surface foundation for subsequent processing steps. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a metallographic diagram of high-purity low-carbon steel in one embodiment of this application. Detailed Implementation

[0030] To make the purpose, technical solution, and beneficial technical effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the implementation details described in this specification are merely for illustrative purposes and are not intended to limit the scope of this application.

[0031] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, although not explicitly stated, every point or individual value between the endpoints of the range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit and combined with any other point or individual value or with other lower or upper limits to form a range not explicitly stated.

[0032] 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 a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0033] Unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application). Unless otherwise stated, the test temperature for all parameters mentioned in this application is 25°C and the test pressure is standard atmospheric pressure.

[0034] The foregoing description of this application is not intended to describe every disclosed implementation or method. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments, which can be used in various combinations. The examples listed are representative only and should not be construed as exhaustive.

[0035] The current production process for battery casing steel mainly adopts the process route of "KR hot metal desulfurization → converter smelting → LF / RH refining → continuous casting". In this process, inclusion control primarily relies on traditional deoxidation alloying and secondary refining technologies. However, existing technologies have several core shortcomings, making it difficult to meet the stamping performance requirements of high-end battery casings: during hot rolling, Al... O Brittle inclusions tend to form chain-like distributions. For example, during the stamping process of a 0.35mm thick sheet, sand holes or microcracks may appear, resulting in a scrap rate as high as 5% to 8%. Although current steelmaking technology can control harmful elements such as N, O, S, Ca, and Mg in steel to below 0.005%, the control of inclusions larger than 10μm is still not stable enough. The current RH refining process has difficulties in removing dispersed oxides larger than 10μm, and silicate inclusions in the billet are prone to forming glassy defects during solidification, leading to strip peeling. Currently, the inclusion rating of battery casing steel produced using existing technology generally reaches or exceeds Class B 1.5.

[0036] To address the problems in the prior art, this application provides a high-purity low-carbon steel and its preparation method. The high-purity low-carbon steel of this application has fewer inclusions and higher mechanical properties, as well as good processing performance.

[0037] The high-purity low-carbon steel and its preparation method of this application will be described below with reference to embodiments.

[0038] High-purity low-carbon steel A high-purity low-carbon steel, by mass percentage, comprises the following components: C: 0.02wt%~0.07wt%, Si≤0.03wt%, Mn: 0.15wt%~0.25wt%, P≤0.015wt%, S≤0.01wt%, Alt: 0.04wt%~0.06wt%, N≤0.004wt%, Ni≤0.06wt%, Cr≤0.06wt%, Cu≤0.06wt%, As≤0.01wt%, Sn≤0.02wt%, Cr+Ni+Cu≤0.09wt%, with the remainder being Fe and unavoidable trace elements.

[0039] Optionally, Cr+Ni+Cu≤0.085wt%, Cr+Ni+Cu≤0.08wt%, Cr+Ni+Cu≤0.075wt%, Cr+Ni+Cu≤0.07wt%, Cr+Ni+Cu≤0.065wt%, and Cr+Ni+Cu≤0.06wt%.

[0040] According to the embodiments of this application, the high-purity low-carbon steel of this application, by limiting the content standards of P ≤ 0.015wt% and S ≤ 0.01wt%, can effectively suppress the formation of brittle or low-melting-point inclusions such as FeS, MnS, and AlP, and avoid such inclusions forming stress concentration points or fracture sources inside the steel. Furthermore, by controlling the total aluminum content (Alt) within the range of 0.04wt% to 0.06wt%, the strong deoxidizing effect of Al can be fully utilized to remove free oxygen in the molten steel and reduce Al content. O The precipitation of oxide inclusions can avoid the formation of a large number of coarse Al particles due to excessive Alt content. O Inclusion aggregation, coupled with strict control of N ≤ 0.004 wt%, prevents the formation and growth of AlN inclusions, ensuring that the inclusions inside the steel are characterized by "few in number, small in size, and uniformly distributed." Furthermore, by controlling the Mn content between 0.15 wt% and 0.25 wt%, the plasticity and toughness of the steel can be significantly improved while ensuring its basic strength. This avoids the problems of increased hardness and decreased plasticity due to excessive Mn content, or insufficient structural strength requirements after battery casing molding due to insufficient Mn content. This significantly improves the pass rate and reliability of battery casing products. In addition, by controlling the total content of Cr+Ni+Cu ≤ 0.09 wt% in the high-purity low-carbon steel of this application, the formation of enriched layers or compounds of these elements on the steel surface can be avoided, ensuring that the steel has good corrosion resistance and surface treatment performance.

[0041] In some embodiments, the inclusions in high-cleanliness low-carbon steel are less than or equal to 15 per mm. 2 .

[0042] In some embodiments, the number of inclusions with an average particle size ≥10μm in the high-cleanliness low-carbon steel is less than or equal to 0.5 inclusions / mm. 2 .

[0043] In some embodiments, the high-cleanliness low-carbon steel meets the standards of B0.5 to B1 in GB / T 10561-2019.

[0044] In some embodiments, please refer to Figure 1 The metallographic structure of high-purity low-carbon steel includes ferrite and carbide precipitates.

[0045] In some embodiments, the yield strength of the high-cleanliness low-carbon steel is 220 MPa to 350 MPa. For example, the yield strength of the high-cleanliness low-carbon steel can be 220 MPa, 250 MPa, 280 MPa, 300 MPa, 320 MPa, 350 MPa, or any range of the above values.

[0046] In some embodiments, the tensile strength of the high-cleanliness low-carbon steel is 300 MPa to 420 MPa. For example, the tensile strength of the high-cleanliness low-carbon steel can be 300 MPa, 320 MPa, 350 MPa, 380 MPa, 400 MPa, 420 MPa, or any range of the above values.

[0047] In some embodiments, the elongation A50 of the high-cleanliness low-carbon steel is greater than or equal to 26%.

[0048] In some embodiments, the hardness of the high-cleanliness low-carbon steel is 100 HV5 to 130 HV5. For example, it can be 100 HV5, 105 HV5, 110 HV5, 115 HV5, 120 HV5, 125 HV5, 130 HV5, or any range of the above values.

[0049] Preparation method of high-purity low-carbon steel This application provides a method for preparing the above-mentioned high-purity low-carbon steel, comprising: Provide molten iron with a temperature of 1300℃ or higher.

[0050] After KR desulfurization treatment and converter smelting treatment, low-carbon steel is obtained, wherein the temperature of the low-carbon steel is 1620℃~1650℃.

[0051] Molten low-carbon steel is subjected to argon station treatment to obtain argon-treated molten steel, wherein the argon station treatment time is less than or equal to 30 minutes.

[0052] The molten steel treated by the argon station is then continuously cast to obtain a billet.

[0053] The billet is rolled, cooled, and degreased to obtain high-purity low-carbon steel.

[0054] According to the embodiments of this application, the preparation method of this application controls the content range of key elements such as Mn, P, S, Al, and N without adding any other alloying elements, and adopts a direct converter-continuous casting process route, that is, the molten steel directly enters the continuous casting process after desulfurization treatment and converter smelting. Compared with refining processes such as LF or RH, the preparation method of this application does not require refining treatment with an external heating source, which simplifies the production process and significantly reduces the carbon emission intensity during the production process, effectively reducing secondary pollution during the steel refining process. In addition, the argon station treatment time is controlled within ≤30 minutes, which can not only achieve homogenization of steel composition and temperature, but also avoid problems such as steel gas absorption and insufficient flotation of inclusions caused by excessive treatment time, further improving the stability of the production process.

[0055] In some embodiments, during the step of providing molten iron, the molten iron may include the following components by mass percentage: Si ≥ 0.30 wt%, S ≤ 0.07 wt%, Ni ≤ 0.035 wt%, Cr ≤ 0.035 wt%, Cu ≤ 0.035 wt%, As ≤ 0.007 wt%, Sn ≤ 0.015 wt%, Cr + Ni + Cu ≤ 0.085 wt%.

[0056] In some embodiments, the steps of rolling, cooling, and degreasing the billet to obtain high-purity low-carbon steel include: The billet is subjected to heat treatment and hot rolling to obtain hot-rolled steel plate, wherein the heat treatment temperature is greater than or equal to 1200℃.

[0057] Hot-rolled steel sheets are coiled to obtain hot-rolled steel coils.

[0058] Hot-rolled steel coils are pickled and then cold-rolled to obtain cold-rolled steel sheets.

[0059] Cold-rolled steel sheets are degreased in an alkaline degreasing agent at 50℃~60℃ to obtain degreased cold-rolled steel sheets.

[0060] The degreased cold-rolled steel sheet is subjected to a bell-type annealing treatment to obtain the annealed steel sheet.

[0061] The annealed steel plate is flattened to obtain high-purity low-carbon steel.

[0062] In some embodiments, the residual oil content on the surface of the degreased cold-rolled steel sheet is ≤5mg / m².

[0063] In some embodiments, the hot rolling process, which involves heating and hot rolling of a billet to obtain a hot-rolled steel plate, includes roughing and finishing rolling.

[0064] In some embodiments, the roughing rolling process consists of 5 or 7 passes.

[0065] In some embodiments, the thickness of the intermediate billet rolled in the roughing mill is 30 mm to 50 mm. For example, it can be 30 mm, 32 mm, 35 mm, 38 mm, 40 mm, 42 mm, 45 mm, 48 mm, 50 mm, or any range of the above values.

[0066] In some embodiments, the final rolling temperature of the finishing rolling is 870°C to 920°C. For example, it can be 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, or any range of the above values.

[0067] In the above embodiments, the preparation method of this application can refine the grain structure of steel by precisely controlling the roughing rolling passes, intermediate billet thickness and finishing rolling temperature, avoid the decrease in plasticity caused by coarse grains, and at the same time ensure the uniformity of steel thickness and dimensional accuracy.

[0068] In some embodiments, in the step of coiling hot-rolled steel sheet to obtain hot-rolled steel coil, the coiling temperature is 600℃~680℃. For example, it can be 600℃, 610℃, 620℃, 630℃, 640℃, 650℃, 660℃, 670℃, 680℃, or any range of the above values. Controlling the coiling temperature at 600℃~680℃ can effectively suppress the formation of hard and brittle phases in the steel structure and improve the plasticity and toughness of the steel.

[0069] In some embodiments, in the step of pickling and cold rolling hot-rolled steel coils to obtain cold-rolled steel sheets, the total reduction rate of the cold rolling process is 75% to 90%. For example, it can be 75%, 78%, 80%, 82%, 85%, 88%, 90%, or any range of the above values. The design of a total reduction rate of 75% to 90% in cold rolling can further refine the grains, improve the strength and surface finish of the steel, and meet the stringent requirements of high-end battery casings for steel flatness and forming precision.

[0070] In some embodiments, the degreased cold-rolled steel sheet is subjected to a bell-type annealing treatment to obtain an annealed steel sheet. The annealing temperature is 660℃~720℃. For example, it can be 660℃, 670℃, 680℃, 690℃, 700℃, 710℃, 720℃, or any range of the above values. The bell-type annealing treatment at 660℃~720℃ can eliminate work hardening generated during cold rolling, restore the plasticity and toughness of the steel, refine the microstructure, improve the stamping performance of the steel, and avoid defects such as cracking and springback during stamping.

[0071] In some optional embodiments, in the step of leveling the annealed steel sheet to obtain high-purity low-carbon steel, the leveling process employs wet leveling rolling with a leveling elongation of 0.5% to 3%. For example, it can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or any range of the above values. The wet leveling rolling process, combined with a leveling elongation of 0.5% to 3%, can further improve the surface flatness and shape of the steel, eliminate defects such as surface oxide scale, and enhance the surface hardness and wear resistance of the steel. This improves the surface quality and structural stability of the formed battery casing, providing a good surface foundation for subsequent processing steps.

[0072] Example The following embodiments describe the disclosure of this application in more detail. These embodiments are for illustrative purposes only, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing. The instruments used in the embodiments are also commercially available. The magnetic properties of the non-oriented silicon steel were detected in a magnetic property detector.

[0073] Example 1 A high-purity low-carbon steel, comprising the following components by mass percentage: C: 0.047wt%, Si: 0.013wt%, Mn: 0.233wt%, P: 0.014wt%, S: 0.006wt%, Alt: 0.055wt%, N: 0.0029wt%, Ni: 0.009wt%, Cr: 0.028wt%, Cu: 0.015wt%, As: 0.005wt%, Sn: 0.004wt%; the remainder being Fe and unavoidable trace elements.

[0074] The above-mentioned high-purity low-carbon steel is prepared by the following method: Molten iron is provided at a temperature of 1323℃.

[0075] After KR desulfurization treatment and converter smelting, low-carbon steel is obtained, with the tapping temperature of the low-carbon steel being 1635℃.

[0076] Molten low-carbon steel was subjected to argon treatment to obtain argon-treated molten steel, with the argon treatment time being 28 minutes.

[0077] The molten steel treated by the argon station was then continuously cast to obtain a billet. The billet, by mass percentage, comprises the following components: C: 0.047 wt%, Si: 0.013 wt%, Mn: 0.233 wt%, P: 0.014 wt%, S: 0.006 wt%, Alt: 0.055 wt%, N: 0.0029 wt%, Ni: 0.009 wt%, Cr: 0.028 wt%, Cu: 0.015 wt%, As: 0.005 wt%, Sn: 0.004 wt%; the remainder being Fe and unavoidable trace elements.

[0078] The cast billet is subjected to heat treatment and hot continuous rolling to obtain hot-rolled steel plate. The temperature of the slab after heat treatment is 1203℃. In the hot continuous rolling process, the roughing rolling has 5 passes, the intermediate slab thickness is 40mm, and the finishing rolling temperature is 907℃.

[0079] Hot-rolled steel sheets are coiled to obtain hot-rolled steel coils. The coiling temperature is 679℃.

[0080] Hot-rolled steel coils are pickled and then subjected to cold rolling to obtain cold-rolled steel sheets. The total reduction rate of the cold rolling process is 85.0%, and the thickness of the cold-rolled steel sheets is 0.3 mm.

[0081] A 7% alkaline degreasing agent was used to immerse the cold-rolled steel sheet at 53°C to obtain the degreased cold-rolled steel sheet.

[0082] The degreased cold-rolled steel sheet was subjected to a bell-type annealing treatment to obtain the annealed steel sheet. The annealing temperature was 720℃.

[0083] The annealed steel plate was wet-leveled and rolled, with a leveling elongation of 1.2%, to obtain high-purity low-carbon steel.

[0084] The mechanical properties of the high-purity low-carbon steel were tested using the methods described in GB / T 228.1-2021, GB / T 5213-2019 and GB / T 4340.1-2009. The yield strength of the high-purity low-carbon steel was 232 MPa, the tensile strength was 369 MPa, the elongation (A50) was 37.7%, and the hardness was 112 HV5. The material properties and mechanical properties of the high-purity low-carbon steel meet the processing requirements of battery casings for new energy vehicles.

[0085] Example 2 A high-purity low-carbon steel, comprising the following components by mass percentage: C: 0.043wt%, Si: 0.014wt%, Mn: 0.266wt%, P: 0.014wt%, S: 0.004wt%, Alt: 0.052wt%, N: 0.0026wt%, Ni: 0.009wt%, Cr: 0.026wt%, Cu: 0.015wt%, As: 0.006wt%, Sn: 0.004wt%; the remainder being Fe and unavoidable trace elements.

[0086] The above-mentioned high-purity low-carbon steel is prepared by the following method: Molten iron is provided at a temperature of 1312℃.

[0087] After KR desulfurization treatment and converter smelting treatment, low-carbon steel is obtained, and the tapping temperature of the low-carbon steel is 1633℃.

[0088] Molten low-carbon steel was subjected to argon treatment to obtain argon-treated molten steel, wherein the argon treatment time was 26 minutes.

[0089] The molten steel treated by the argon station is then continuously cast to obtain a billet. The billet comprises the following components by mass percentage: C: 0.043 wt%, Si: 0.014 wt%, Mn: 0.266 wt%, P: 0.014 wt%, S: 0.004 wt%, Alt: 0.052 wt%, N: 0.0026 wt%, Ni: 0.009 wt%, Cr: 0.026 wt%, Cu: 0.015 wt%, As: 0.006 wt%, Sn: 0.004 wt%; the remainder being Fe and unavoidable trace elements.

[0090] The cast billet is subjected to heat treatment and hot continuous rolling to obtain hot-rolled steel plate. The slab temperature for heat treatment is 1248℃. In the hot continuous rolling process, the roughing rolling has 5 passes, the intermediate slab thickness is 40mm, and the finishing rolling temperature is 907℃.

[0091] Hot-rolled steel sheets are coiled to obtain hot-rolled steel coils. The coiling temperature is 679℃.

[0092] Hot-rolled steel coils are pickled and then subjected to cold rolling to obtain cold-rolled steel sheets. The total reduction rate of the cold rolling process is 82.2%, and the thickness of the cold-rolled steel sheet is 0.4 mm.

[0093] A 7% alkaline degreasing agent was used to immerse the cold-rolled steel sheet at 53°C to obtain the degreased cold-rolled steel sheet.

[0094] The degreased cold-rolled steel sheet was subjected to a bell-type annealing treatment to obtain the annealed steel sheet. The annealing temperature was 720℃.

[0095] The annealed steel plate was wet-leveled and rolled, with a leveling elongation of 1.2%, to obtain high-purity low-carbon steel.

[0096] The mechanical properties of the high-purity low-carbon steel were tested using the methods described in GB / T 228.1-2021, GB / T 5213-2019, and GB / T 4340.1-2009. The yield strength of the high-purity low-carbon steel was 235 MPa, the tensile strength was 375 MPa, the elongation (A50) was 38.5%, and the hardness was 116 HV5. The material properties and mechanical properties of the high-purity low-carbon steel meet the processing requirements for battery casings of new energy vehicles.

[0097] Example 3 A high-purity low-carbon steel, comprising the following components by mass percentage: C: 0.045wt%, Si: 0.012wt%, Mn: 0.201wt%, P: 0.012wt%, S: 0.005wt%, Alt: 0.058wt%, N: 0.0026wt%, Ni: 0.008wt%, Cr: 0.021wt%, Cu: 0.011wt%, As: 0.005wt%, Sn: 0.006wt%; the remainder being Fe and unavoidable trace elements.

[0098] The above-mentioned high-purity low-carbon steel is prepared by the following method: Molten iron is provided at a temperature of 1316℃.

[0099] After KR desulfurization treatment and converter smelting treatment, low-carbon steel is obtained, and the tapping temperature of the low-carbon steel is 1631℃.

[0100] Molten low-carbon steel was subjected to argon treatment to obtain argon-treated molten steel, wherein the argon treatment time was 26 minutes.

[0101] The molten steel treated by the argon station is then continuously cast to obtain a billet. The billet comprises the following components by mass percentage: C: 0.045 wt%, Si: 0.012 wt%, Mn: 0.201 wt%, P: 0.012 wt%, S: 0.005 wt%, Alt: 0.058 wt%, N: 0.0026 wt%, Ni: 0.008 wt%, Cr: 0.021 wt%, Cu: 0.011 wt%, As: 0.005 wt%, Sn: 0.006 wt%; the remainder being Fe and unavoidable trace elements.

[0102] The cast billet is subjected to heat treatment and hot continuous rolling to obtain hot-rolled steel plate. The slab temperature for heat treatment is 1248℃. In the hot continuous rolling process, the roughing rolling has 5 passes, the intermediate slab thickness is 40mm, and the finishing rolling temperature is 905℃.

[0103] Hot-rolled steel sheets are coiled to obtain hot-rolled steel coils. The coiling temperature is 678℃.

[0104] Hot-rolled steel coils are pickled and then subjected to cold rolling to obtain cold-rolled steel sheets. The total reduction rate of the cold rolling process is 80.8%, and the thickness of the cold-rolled steel sheets is 0.5 mm.

[0105] A 7% alkaline degreasing agent was used to immerse the cold-rolled steel sheet at 53°C to obtain the degreased cold-rolled steel sheet.

[0106] The degreased cold-rolled steel sheet was subjected to a bell-type annealing treatment to obtain the annealed steel sheet. The annealing temperature was 720℃.

[0107] The annealed steel plate was wet-leveled and rolled, with a leveling elongation of 1.2%, to obtain high-purity low-carbon steel.

[0108] The mechanical properties of the high-purity low-carbon steel were tested using the methods described in GB / T 228.1-2021, GB / T 5213-2019 and GB / T 4340.1-2009. The yield strength of the high-purity low-carbon steel was 255 MPa, the tensile strength was 390 MPa, the elongation (A50) was 38%, and the hardness was 119 HV5. The material properties and mechanical properties of the high-purity low-carbon steel meet the processing requirements of battery casings for new energy vehicles.

[0109] Comparative Example 1 Comparative Example 1 is a low-carbon steel with grade DC01. By mass percentage, it comprises the following components: C: 0.04 wt%, Si: 0.016 wt%, Mn: 0.253 wt%, P: 0.018 wt%, S: 0.016 wt%, Alt: 0.035 wt%, N: 0.0028 wt%, Ni: 0.016 wt%, Cr: 0.028 wt%, Cu: 0.025 wt%, As: 0.008 wt%, Sn: 0.014 wt%; the remainder is Fe and unavoidable trace elements.

[0110] The above-mentioned high-purity low-carbon steel is prepared by the following method: Molten iron is provided at a temperature of 1331℃.

[0111] After KR desulfurization treatment and converter smelting, low-carbon steel is obtained, with the tapping temperature of the low-carbon steel being 1635℃.

[0112] Low-carbon steel molten steel is subjected to LF refining treatment.

[0113] The molten steel refined by LF was subjected to continuous casting to obtain a billet. The billet, by mass percentage, comprises the following components: C: 0.04wt%, Si: 0.016wt%, Mn: 0.253wt%, P: 0.018wt%, S: 0.016wt%, Alt: 0.035wt%, N: 0.0028wt%, Ni: 0.016wt%, Cr: 0.028wt%, Cu: 0.025wt%, As: 0.008wt%, Sn: 0.014wt%; the remainder being Fe and unavoidable trace elements.

[0114] The cast billet is subjected to heat treatment and hot continuous rolling to obtain hot-rolled steel plate. The temperature of the slab after heat treatment is 1213℃. In the hot continuous rolling process, the roughing rolling has 5 passes, the intermediate slab thickness is 40mm, and the finishing rolling temperature is 895℃.

[0115] Hot-rolled steel sheets are coiled to obtain hot-rolled steel coils. The coiling temperature is 626℃.

[0116] Hot-rolled steel coils are pickled and then subjected to cold rolling to obtain cold-rolled steel sheets. The total reduction rate of the cold rolling process is 82.2%, and the thickness of the cold-rolled steel sheet is 0.4 mm.

[0117] A 7% alkaline degreasing agent was used to immerse the cold-rolled steel sheet at 53°C to obtain the degreased cold-rolled steel sheet.

[0118] The degreased cold-rolled steel sheet was subjected to a bell-type annealing treatment to obtain the annealed steel sheet. The annealing temperature was 720℃.

[0119] The annealed steel plate was wet-leveled and rolled, with a leveling elongation of 1.2%, to obtain high-purity low-carbon steel.

[0120] The mechanical properties of the above-mentioned high-cleanliness low-carbon steel were tested using the methods described in GB / T 228.1-2021, GB / T 5213-2019 and GB / T 4340.1-2009. The yield strength of the high-cleanliness low-carbon steel was 212 MPa, the tensile strength was 363 MPa, the elongation A50 was 38.1%, and the hardness was 111HV5. The material and mechanical properties of the low-carbon steel met the processing requirements of DC01.

[0121] The inclusions in the high-cleanliness low-carbon steel sample of Example 1 and the low-carbon steel sample of Comparative Example 1 treated with conventional LF process were statistically compared using electron microscopy (SEM) and Image Pro Plus 6.0 software. The results are shown in Table 1.

[0122] Table 1. Statistical Table of Sample Inclusions According to Table 1, the inclusion area ratio in the high-cleanliness low-carbon steel of Example 1 is significantly lower than that of the sample treated by the traditional LF process (Comparative Example 1), indicating a significant improvement in cleanliness. In this application, the high-cleanliness low-carbon steel exhibits a similar inclusion area ratio from the edge to the center, demonstrating good uniformity, and very few inclusions exceeding 10 μm in size. The composition and production process are rationally designed, resulting in high material cleanliness and excellent processing performance, meeting the requirements of battery casing steel users for material surface quality and ultra-deep drawing performance.

[0123] The above description is merely a specific implementation of this application. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working process described above can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here. It should be understood that the protection scope of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the protection scope of this application.

Claims

1. A high-purity low-carbon steel, characterized in that, The high-purity low-carbon steel comprises the following components by weight percentage: C: 0.02wt%~0.07wt%, Si≤0.03wt%, Mn: 0.15wt%~0.25wt%, P≤0.015wt%, S≤0.01wt%, Alt: 0.04wt%~0.06wt%, N≤0.004wt%, Ni≤0.06wt%, Cr≤0.06wt%, Cu≤0.06wt%, As≤0.01wt%, Sn≤0.02wt%, Cr+Ni+Cu≤0.09wt%, with the remainder being Fe and unavoidable trace elements.

2. The high-purity low-carbon steel according to claim 1, characterized in that, The high-purity low-carbon steel meets at least one of the following requirements: (1) The inclusions in the high-purity low-carbon steel are less than or equal to 15 per mm. 2 ; (2) The inclusions with an average particle size ≥10μm in the high-purity low-carbon steel are less than or equal to 0.5 particles / mm. 2 ; (3) The metallographic structure of the high-purity low-carbon steel includes ferrite and carbides; (4) Cr+Ni+Cu≤0.06wt%.

3. The high-purity low-carbon steel according to claim 1 or 2, characterized in that, The high-purity low-carbon steel meets at least one of the following requirements: (1) The yield strength of the high-purity low-carbon steel is 220MPa~350MPa; (2) The tensile strength of the high-purity low-carbon steel is 300MPa~420MPa; (3) The elongation A50 of the high-purity low-carbon steel is greater than or equal to 26%; (4) The hardness of the high-purity low-carbon steel is 100 HV5~130 HV5.

4. A method for preparing high-purity low-carbon steel as described in any one of claims 1 to 3, characterized in that, include: Molten iron is provided, wherein the temperature of the molten iron is greater than or equal to 1300°C; After the molten iron is subjected to KR desulfurization treatment and converter smelting treatment, low carbon steel molten steel is obtained, wherein the temperature of the low carbon steel molten steel is 1620℃~1650℃. The molten low-carbon steel is subjected to argon station treatment to obtain argon-treated molten steel, wherein the argon station treatment time is less than or equal to 30 minutes; The molten steel treated by the argon station is then subjected to continuous casting to obtain a cast billet; The billet is rolled, cooled, and degreased to obtain the high-purity low-carbon steel.

5. The preparation method according to claim 4, characterized in that, The steps of rolling, cooling, and degreasing the billet to obtain the high-purity low-carbon steel include: The billet is subjected to heat treatment and hot continuous rolling to obtain hot-rolled steel plate, wherein the heat treatment temperature is greater than or equal to 1200℃; The hot-rolled steel sheet is coiled to obtain a hot-rolled steel coil; The hot-rolled steel coil is subjected to pickling and cold continuous rolling to obtain cold-rolled steel sheet; The cold-rolled steel sheet is degreased in an alkaline degreasing agent at 50℃~60℃ to obtain a degreased cold-rolled steel sheet. Preferably, the residual oil on the surface of the degreased cold-rolled steel sheet is ≤5mg / m². The degreased cold-rolled steel sheet is subjected to a bell-type annealing treatment to obtain an annealed steel sheet; The annealed steel plate is flattened to obtain the high-purity low-carbon steel.

6. The preparation method according to claim 5, characterized in that, In the step of heating and hot rolling the billet to obtain hot-rolled steel plate, the hot rolling process includes roughing rolling and finishing rolling, and the hot rolling process satisfies at least one of the following: (1) The roughing rolling process consists of 5 or 7 passes; (2) The thickness of the intermediate billet produced by rough rolling is 30mm~50mm; (3) The final rolling temperature of the finishing rolling is 870℃~920℃.

7. The preparation method according to claim 5, characterized in that, In the step of coiling the hot-rolled steel sheet to obtain a hot-rolled steel coil, the temperature of the coiling process is 600℃~680℃.

8. The preparation method according to claim 5, characterized in that, In the step of pickling and cold rolling the hot-rolled steel coil to obtain cold-rolled steel sheet, the total reduction rate of the cold rolling process is 75% to 90%.

9. The preparation method according to claim 5, characterized in that, The step of performing a bell-type annealing treatment on the degreased cold-rolled steel sheet to obtain an annealed steel sheet, wherein the annealing temperature is 660℃~720℃.

10. The preparation method according to claim 5, characterized in that, In the step of leveling the annealed steel plate to obtain the high-purity low-carbon steel, the leveling process is performed by wet leveling rolling with a leveling elongation of 0.5% to 3%.

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