Cold-rolled low-carbon steel plate produced through BOF-VD-LF and steelmaking process

Abstract

The invention relates to a BOF-VD-LF cold-rolled low-carbon steel plate production and steelmaking process, which comprises the following steps: adopting converter smelting BOF to carry out oxygen blowing decarburization on first molten steel to obtain second molten steel; the second molten steel is subjected to deep decarburization through VD vacuum refining, Al strong deoxidation and modification treatment are conducted after deep decarburization, and third molten steel is obtained; and the third molten steel is subjected to heating and component adjusting treatment through LF refining, fourth molten steel is obtained, the fourth molten steel is further treated, and the cold-rolled low-carbon steel plate is obtained. The process can reduce the surface defects of the cold-rolled steel sheet and improve the cold-rolled sheet product production capacity and product quality of an enterprise. The LF process is adopted to heat the molten steel, the chemical components of the molten steel are adjusted, and the requirements of continuous casting on the temperature and the chemical components of the molten steel are met.

Description

Technical Field

[0001] The invention belongs to the technical field of steelmaking, and in particular relates to a BOF-VD-LF production of cold-rolled low-carbon steel plates and a steelmaking process. Background Art

[0002] Low-carbon aluminum-killed cold-rolled steel sheets are widely used in the automotive, home appliance and other industries, requiring low carbon and nitrogen content and high cleanliness to meet strict cold stamping and other processing requirements and ensure that the steel sheets have good surface quality. The current main steelmaking process for cold-rolled low-carbon steel sheets is converter (BOF)-RH vacuum refining or converter (BOF)-ladle furnace heating (LF)-RH vacuum refining. The steelmaking steps are mainly: BOF smelting oxygen decarburizes the molten steel, and the ladle top slag is modified during BOF steelmaking to reduce the oxidizing property of the slag; RH vacuum refining further reduces the carbon content in the steel, and after the RH decarburization is completed, the molten steel is subjected to Al strong deoxidation; since some RH vacuum refining devices do not have a molten steel temperature compensation function, in order to compensate for the temperature drop of the molten steel during the RH decarburization process, some process flows use LF refining to heat the molten steel after converter smelting, and then perform RH decarburization. At present, in addition to RH, domestic plate production lines are equipped with some VD vacuum refining equipment. The development of VD process to produce cold-rolled low-carbon steel plates can release the capacity of equipment, which is conducive to improving the company's high-quality steel production capacity and product structure upgrading.

[0003] Prior art 1 CN202210994963.2 mentions a method for manufacturing ultra-high strength cold-rolled steel sheets, whose steelmaking process route is converter smelting-refining outside the furnace (LF+RH); Prior art 2 CN201510229460.6 mentions a method for producing cold-rolled steel sheets for electrogalvanizing, whose steelmaking process is converter smelting-alloy fine-tuning station-RH furnace refining; Prior art 3 CN201010252335.4 mentions a method for producing ultra-deep drawing grade cold-rolled steel sheets based on the ASP process, and the steelmaking process The prior art four CN200910272575.8 mentions a low-carbon phosphorus-added high-yield strength cold-rolled steel sheet and its manufacturing method, the smelting steps are hot metal desulfurization-converter composite blowing-argon blowing; the prior art five CN200610098397.8 mentions a stamping grade cold-rolled steel sheet production method based on the CSP process flow, its smelting process is BOF-LF, RH vacuum treatment is not used, and the carbon content of 0.02-0.05% DQ grade stamping automobile steel is produced efficiently and at low cost. However, none of these patents mentions the use of VD devices as cold-rolled steel sheet deep decarburization production devices.

[0004] Prior art 6 (CN114381575B) and prior art 7 (CN113512618A) both adopt BOF-LF furnace-VD furnace process, and in the BOF-LF-VD process, the role of LF is heating, and the role of VD is deep decarburization, and this order of LF first and VD later does not take into account that the molten steel can no longer be heated after the VD is completed, so that the temperature drop of the molten steel generated after the deep decarburization of the VD process is difficult to stably control, which is not conducive to the stable control of the molten steel temperature in the continuous casting process. At present, there are no patents and reports related to the production of cold-rolled low-carbon steel sheets using the BOF-VD-LF process. Summary of the invention

[0005] In order to overcome the problems existing in the prior art, the present invention provides a BOF-VD-LF production of cold-rolled low-carbon steel plates and a steelmaking process.

[0006] A steelmaking process for producing cold-rolled low-carbon steel sheets by BOF-VD-LF, comprising the following steps: S1. using a converter smelting BOF to perform oxygen blowing decarburization on a first molten steel to obtain a second molten steel;

[0007] S2. The second molten steel is subjected to deep decarburization by VD vacuum refining, and Al strong deoxidation and modification treatment is performed after deep decarburization to obtain a third molten steel;

[0008] S3. The third molten steel is subjected to LF refining to increase the temperature and adjust the composition to obtain a fourth molten steel, and the fourth molten steel is further processed to obtain a cold-rolled low-carbon steel sheet.

[0009] According to the aspects and any possible implementations described above, an implementation is further provided, wherein the oxygen content in the first molten steel is between 0.03-0.08%, the carbon content is between 0.02-0.07%, and the temperature of the molten steel is between 1600-1670°C.

[0010] According to the above aspects and any possible implementation, there is further provided an implementation, wherein the carbon content in the second molten steel after deep deoxidation in S2 is ≤0.0080%.

[0011] According to the aspects and any possible implementations described above, an implementation is further provided, wherein the modification treatment in S2 includes adding lime, aluminum particles or aluminum slag balls to the second molten steel after Al strong deoxidation to modify the ladle top slag therein.

[0012] According to the above aspects and any possible implementation, there is further provided an implementation, in which the T.Fe of the slag in the third molten steel is ≤8%.

[0013] According to the above aspects and any possible implementation, an implementation is further provided, wherein the [N] content in the fourth molten steel is ≤35ppm and the T[O] is ≤25ppm.

[0014] According to the aspects and any possible implementations described above, an implementation is further provided, wherein the mass percentages of the components in the cold-rolled steel sheet are: C≤0.12, Mn≤0.60, P≤0.030, S≤0.030, Alt>0.020, and the remainder is Fe.

[0015] According to the aspects and any possible implementations described above, there is further provided an implementation, wherein the oxygen content in the first molten steel is 0.03%, the carbon content is 0.026%, and the temperature of the molten steel is 1660°C.

[0016] The present invention also provides a cold-rolled low-carbon steel plate, which is prepared by the process of the present invention.

[0017] According to the above aspects and any possible implementation, there is further provided an implementation, wherein the maximum size of the inclusions in the cold-rolled low-carbon steel plate is less than or equal to 50 microns.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The steelmaking process of producing cold-rolled low-carbon steel plates by BOF-VD-LF of the present invention comprises the following steps: using converter smelting BOF to blow oxygen and decarburize the first molten steel to obtain the second molten steel; using VD vacuum refining to perform deep decarburization on the second molten steel, and after deep decarburization, performing Al strong deoxidation and modification treatment to obtain the third molten steel; using LF refining to heat up and adjust the composition of the third molten steel to obtain the fourth molten steel, and further treating the fourth molten steel to obtain the cold-rolled low-carbon steel plate. The process of the present invention can reduce the surface defects of cold-rolled steel plates, improve the ability of enterprises to produce cold-rolled plate products and product quality. The present invention uses the LF process to heat up the molten steel and adjust the chemical composition of the molten steel to meet the requirements of continuous casting for the temperature and chemical composition of the molten steel. The method of the present invention can meet the requirements of the production of low-carbon aluminum-killed steel cold-rolled steel plates including DC01, DC03, etc. for the control of molten steel temperature, chemical composition and cleanliness. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the morphology and size of typical calcium magnesium aluminate inclusions in a 0.2 mm thick cold-rolled steel plate in Example 1;

[0021] Figure 2 Schematic diagram of the morphology and size of typical calcium magnesium aluminate inclusions in a 0.2 mm thick cold-rolled steel plate in Example 2;

[0022] Figure 3 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0023] In order to better understand the technical solution of the present invention, the content of the present invention includes but is not limited to the specific implementation methods described below, and similar technologies and methods should be considered to be within the scope of protection of the present invention. In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments.

[0024] It should be clear that the embodiments described in the present invention are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "said" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0026] like Figure 3 As shown, the present invention provides a steelmaking process for producing cold-rolled low-carbon steel sheets by BOF-VD-LF, comprising the following steps: S1. using a converter smelting BOF to blow oxygen and decarburize the first molten steel to obtain a second molten steel, wherein the first molten steel is the object to be processed by this process;

[0027] S2. The second molten steel is subjected to deep decarburization by VD vacuum refining, and Al strong deoxidation and modification treatment is performed after deep decarburization to obtain a third molten steel;

[0028] S3. The third molten steel is subjected to LF refining to increase the temperature and adjust the composition to obtain a fourth molten steel, and the fourth molten steel is further processed to obtain a cold-rolled low-carbon steel sheet.

[0029] Specifically, the process of the present invention mainly includes converter smelting, VD vacuum refining, LF refining, including the following processes:

[0030] (1) Converter smelting: oxygen blowing decarburization is performed on the molten steel obtained by cold-rolled steel plate smelting. The oxygen content of the molten steel after decarburization at the converter end point is controlled between [0.03, 0.08%], the end point carbon content is between [0.02, 0.07%], and the molten steel temperature is controlled between [1600, 1670°C]. Since the converter smelting BOF end point is not processed under vacuum conditions, deep decarburization cannot be achieved, and only preliminary decarburization can be achieved, which requires VD process to process;

[0031] (2) A VD vacuum refining device is used to perform deep decarburization on the molten steel. After deep decarburization, the carbon content in the molten steel is ≤0.0080%. Since the final cold-rolled sheet is required to have certain deep drawing properties, a lower carbon content is required during the process. A high carbon content will increase the strength of the steel, but it is difficult to form by cold stamping. During the VD process, with the help of vacuum conditions, C+O=CO occurs in the device, and then the vacuum pump is used to evacuate the air to reduce the amount of the product CO, thereby promoting the chemical reaction to generate CO, thereby achieving deep decarburization and obtaining molten steel with a lower carbon content.

[0032] (3) After VD vacuum deep decarburization is completed, the molten steel is subjected to Al strong deoxidation, and lime, aluminum particles, aluminum slag balls, etc. are added to the ladle obtained by Al strong deoxidation to modify the top slag in the ladle, reduce the oxidizability of the slag, and make the T.Fe in the slag ≤8%; there are two main deoxidation processes in the steelmaking process, one is Si deoxidation and the other is Al deoxidation. The present invention requires that the final cold-rolled sheet has good cold stamping performance, but when Si deoxidation is used, the Si content in the steel will increase, thereby reducing the cold stamping forming performance of the steel. Therefore, the present invention uses Al strong deoxidation to avoid reducing the cold stamping forming performance.

[0033] (4) The molten steel obtained after the treatment in step (3) is heated by an LF refining furnace, and the chemical composition of the molten steel is adjusted to control the [N] content of the molten steel to be ≤35ppm and the T[O] content to be ≤25ppm. After the LF refining is completed, the ladle (in the steel ladle) is lifted to the continuous casting platform by an overhead crane, and placed on the turntable of the continuous casting platform to wait for casting.

[0034] In order to ensure that the final molten steel temperature is appropriate, the above-mentioned process flow of the present invention adopts the BOF-VD-LF process, performs BOF, and then adopts LF treatment after the VD is completed. LF can more accurately and stably control the molten steel temperature and stably meet the temperature requirements of continuous casting for the molten steel.

[0035] Furthermore, the metallurgical operation units covered by the steelmaking process are converter smelting (BOF)-VD vacuum refining-LF refining.

[0036] Furthermore, BOF is used to blow oxygen into the molten steel for decarburization, thereby achieving preliminary removal of carbon; at the same time, the temperature of the molten steel is also increased (the reaction of C and O produces a large amount of chemical heat, which can effectively increase the temperature of the molten steel); from the perspective of carbon content control, the task of VD decarburization in the next step can be reduced.

[0037] Furthermore, after BOF smelting, the molten steel is subjected to vacuum deep decarburization by a VD device. As mentioned above, BOF does not operate under vacuum conditions, and therefore, the C content in the molten steel is difficult to reduce. However, after the molten steel is subjected to vacuum deep decarburization by VD, the C content in the molten steel can be reduced to the content range required for cold-rolled plates.

[0038] Furthermore, after VD vacuum deep decarburization, the molten steel is subjected to Al strong deoxidation, and the ladle top slag is modified to reduce the oxidizability of the top slag. During the VD vacuum decarburization process, the C+O=CO (mainly) or C+2O=CO2 reaction is promoted by the vacuum conditions and the O content in the steel. Therefore, when the deep decarburization is completed, the O content in the steel is very high. If the molten steel is not deoxidized, the steel will become very "brittle" after cooling, making it difficult to meet practical use. Therefore, after VD vacuum deep decarburization, the molten steel is deoxidized again, and the top slag needs to be modified to reduce the FeO content in the slag and reduce the indirect oxygen transfer of the slag to the molten steel, which is beneficial to reduce the oxygen content in the molten steel.

[0039] Furthermore, after vacuum deep decarburization, LF is used to increase the temperature and adjust the composition of the molten steel, effectively controlling the [N] and T[O] contents of the molten steel to meet the requirements of cold-rolled steel sheets for composition and cleanliness control. If the molten steel does not go through this process and directly reaches the continuous casting platform, the temperature and composition cannot be adjusted. Therefore, LF is used to adjust the temperature and composition of the molten steel so that the temperature and chemical composition of the final molten steel meet the requirements.

[0040] Furthermore, the mass percentage of each component in the cold-rolled steel plate is: C≤0.12, Mn≤0.60, P≤0.030, S≤0.030, Alt>0.020, and the balance is Fe. Specifically, DC01 steel and DC03 steel are used, and both of these steels meet this composition requirement.

[0041] As an embodiment disclosed in the present invention, the present invention also provides a cold-rolled low-carbon steel plate, which is prepared by the process described in the present invention. The maximum size of inclusions in the cold-rolled low-carbon steel plate prepared by the process of the present invention is less than or equal to 50 microns, which is beneficial to reducing surface defects during the cold rolling process.

[0042] The steelmaking process of producing cold-rolled low-carbon steel plates by BOF-VD-LF of the present invention comprises the following steps: converter smelting, oxygen blowing decarburization of molten steel, controlling the final oxygen content of the converter between 0.03-0.08%, the final carbon content between 0.02-0.07%, and controlling the temperature of the molten steel between 1600-1670 DEG C; VD vacuum refining for deep decarburization of the molten steel, controlling the carbon content in the molten steel to be less than or equal to 0.0080%, performing Al strong deoxidation on the molten steel after the deep decarburization, and modifying the ladle top slag to reduce the oxidizability of the slag, controlling T.Fe in the slag to be less than or equal to 8%; using an LF refining furnace to heat the molten steel and accurately adjust the content of each chemical component in the steel, controlling the molten steel [N] to be less than or equal to 35ppm and T[O] to be less than or equal to 0.0025%, controlling the maximum size of inclusions in the steel to be less than 50 microns, reducing the surface defects of the cold-rolled steel plates, and improving the production capacity and product quality of the cold-rolled plate products of the enterprise.

[0043] The present invention is specifically described below using embodiments:

[0044] Example 1

[0045] The cold-rolled steel sheet used in the production of this embodiment is DC01 steel, and the steel composition is shown in Table 1 below. At the end of converter smelting, the oxygen content of the molten steel is 0.030%, the carbon content is 0.026%, and the temperature of the molten steel is 1660°C; when the VD leaves the station, the carbon content of the molten steel is 0.0047%, the nitrogen content is 0.0018%, and the [Al] content is 0.035%; the LF refining process heats the molten steel and adjusts the composition of the molten steel. At the end of LF, the carbon content of the steel is 0.011%, the nitrogen content is 0.0030%, the oxygen content is 0.0023%, and the temperature of the molten steel is 1585°C. See Table 2 below for details. Inclusions in 0.2mm cold-rolled steel sheet such as Figure 1 As shown, the inclusions are small in size, less than 20 μm, the junction between the inclusions and the steel matrix is ​​dense, and no surface defects caused by the inclusions are observed.

[0046] Table 1 DC01 national standard composition (mass percentage %)

[0047] C Mn P S Alt Fe other ≤0.12 ≤0.60 ≤0.030 ≤0.030 >0.020 margin National Standard

[0048] Table 2 Chemical composition (mass percentage) and temperature information of molten steel in DC01 production process

[0049]

[0050] At the end of LF, the slag T.Fe is 0.91%, thereby reducing the oxidizability of the slag, reducing the oxygen content in the steel, reducing the reaction of Al and O to generate Al2O3 inclusions, improving the surface quality of the cold-rolled sheet, and reducing surface quality defects.

[0051] Example 2

[0052] The cold-rolled steel sheet used in the production of this embodiment is DC03 steel, and the steel composition is shown in Table 3 below. After converter smelting, the oxygen content of the molten steel is 0.063%, the carbon content is 0.030%, and the molten steel temperature is 1630°C; the VD inlet temperature is 1595°C, and the carbon content of the molten steel is 0.003%, the nitrogen content is 0.0022%, and the [Al] content is 0.04% when the VD leaves the station; the LF refining process heats the molten steel and adjusts the molten steel composition. At the end of LF, the carbon content of the steel is 0.018%, the nitrogen content is 0.0031%, and the oxygen content is 0.0022%, and the molten steel temperature is 1588°C, as shown in Table 4 below. Inclusions in 0.2mm cold-rolled steel sheet are as follows Figure 2 As shown in the figure, the inclusions are small in size, less than 30 μm, the junction between the inclusions and the steel matrix is ​​dense, and no surface defects caused by the inclusions are observed.

[0053] Table 3 DC03 national standard composition (mass percentage %)

[0054] C Mn P S Alt Fe other ≤0.10 ≤0.45 ≤0.025 ≤0.025 >0.020 margin National Standard

[0055] Table 4 Chemical composition (mass percentage) and temperature information of molten steel in DC03 production process

[0056]

[0057] At the end of LF, the T.Fe in the slag is 0.85%, thus achieving a better effect than that of Example 1.

[0058] The above description shows and describes several preferred embodiments of the present invention, but as mentioned above, it should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the application concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art shall not depart from the spirit and scope of the present invention, and shall be within the scope of protection of the claims attached to the present invention.

Claims

1. A steelmaking process for producing cold-rolled low-carbon steel sheets by BOF-VD-LF, characterized in that: The steps include: S1. using a converter BOF to decarburize the first molten steel by blowing oxygen to obtain a second molten steel; S2. The second molten steel is subjected to deep decarburization by VD vacuum refining, and Al strong deoxidation and modification treatment is performed after deep decarburization to obtain a third molten steel; S3. The third molten steel is subjected to LF refining to increase the temperature and adjust the composition to obtain a fourth molten steel, and the fourth molten steel is further processed to obtain a cold-rolled low-carbon steel sheet.

2. The process according to claim 1, characterized in that The oxygen content in the first molten steel is between 0.03-0.08%, the carbon content is between 0.02-0.07%, and the temperature of the molten steel is between 1600-1670°C.

3. The process according to claim 1 or 2, characterized in that The carbon content in the second molten steel after deep deoxidation in S2 is ≤0.0080%.

4. The process according to claim 2, characterized in that The modification treatment in S2 includes adding lime, aluminum particles or aluminum slag balls to the second molten steel after Al strong deoxidation to modify the ladle top slag therein.

5. The process according to claim 4, characterized in that The T.Fe of the slag in the third molten steel is ≤ 8%.

6. The process according to claim 1, characterized in that The [N] content in the fourth molten steel is ≤35ppm and the T[O] content is ≤25ppm.

7. The process according to claim 1, characterized in that The mass percentages of the components in the cold-rolled steel sheet are: C≤0.12, Mn≤0.60, P≤0.030, S≤0.030, Alt>0.020, and the balance is Fe.

8. The process according to claim 2, characterized in that The oxygen content in the first molten steel is 0.03%, the carbon content is 0.026%, and the temperature of the molten steel is 1660°C.

9. A cold-rolled low-carbon steel sheet, characterized in that: The cold-rolled low-carbon steel sheet is prepared by the process described in any one of claims 1-8.

10. The cold-rolled low-carbon steel sheet according to claim 9, characterized in that: The maximum size of the inclusions in the cold-rolled low-carbon steel plate is less than or equal to 50 microns.

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