A method for producing a dual-phase steel strip for a battery case cover

Abstract

The application discloses a production method of a dual-phase steel strip for a battery box cover, and specifically comprises the following steps: (1) top and bottom combined blowing smelting of a converter, wherein the composition of the molten steel for a casting machine is as follows: C: 0.08-0.15%, Si: 0.20-0.75%, Mn: 1.8-2.5%, P≤0.070%, S≤0.035%, Alt: 0.010-0.070%, Cr: 0.10-0.40%, Ca: 0.0005-0.0050%, and the rest is Fe and impurities; the slab continuous casting superheat is 5-30 DEG C, and the drawing speed is controlled to be 0.2-2.0 m / min; (2) hot rolling; (3) pickling and cold rolling; and (4) continuous hot galvanizing and finishing process. The dual-phase steel strip for the battery box cover has the characteristics of high strength, high strain hardening index, good matching of strength and ductility and high corrosion resistance, and meets the material selection requirement of automobile light weight and the differentiated application of users.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical sheet technology, and particularly relates to a method for producing duplex steel strips for battery box covers. Background Technology

[0002] In recent years, the global greenhouse effect, energy shortages, and environmental pollution have become increasingly prominent, making energy conservation, emission reduction, and green development a common trend across all industries. In the automotive sector, more and more products are focusing on the development and application of high-quality, low-carbon-emission ultra-high-strength steel, achieving weight reduction while improving safety performance. Furthermore, as people's demands for automotive quality and aesthetics continue to rise, the shapes of automotive parts are becoming increasingly complex, leading to a surge in demand for galvanized products. Therefore, there is an urgent need to develop galvanized high-strength steel with superior comprehensive performance, which represents the future innovation trend of high-strength automotive steel. 590MPa grade galvanized duplex steel is a widely used advanced high-strength steel in the automotive field. Its microstructure consists of two phases: ferrite and martensite. Ferrite provides ductility, while martensite provides strength. It features high strength, a high work hardening index, a high initial work hardening rate, a good balance of strength and ductility, and high corrosion resistance, making it one of the preferred materials for lightweight automotive steel. It is mainly used in high-strength structural parts and connectors in automobiles, such as crossbeams, connecting plates, anti-collision bars, etc. The development of 590MPa grade galvanized duplex steel for high yield strength automotive structures can meet users' lightweight material selection needs and realize differentiated product applications.

[0003] Application number CN202410787686.7 discloses a method for producing 780MPa grade high-strength cold-rolled duplex steel for automotive structures. The method is characterized by the following chemical composition by mass percentage: C: 0.085-0.135%, Si: 0.35-0.55%, Mn: 1.9-2.3%, P≤0.020%, S≤0.015%, Alt: 0.010-0.050%, Cr: 0.2-0.5%, Nb: 0.01-0.04%, Ti: 0.01-0.04%, Ca: 0.0010-0.0030%, N≤0.0070%. The production method includes: smelting-continuous casting, hot rolling, pickling and cold rolling, and continuous annealing. The 780MPa grade high-strength cold-rolled dual-phase steel for automotive structures of this invention has advantages such as low yield strength ratio, high initial work hardening rate, and good strength and ductility balance.

[0004] Application number CN202211222061.3 discloses a 600MPa grade hot-dip galvanized duplex steel for automotive structures and its production method. The chemical composition of the provided 600MPa grade hot-dip galvanized duplex steel for automotive structures, by mass percentage, is as follows: C: 0.10–0.12%, Si: 0.28–0.35%, Mn: 1.50–1.65%, P: ≤0.020%, S: ≤0.003%, Alt: 0.020–0.050%, Cr: 0.30–0.40%, Ca: 0.0008–0.0020%, with the remainder being Fe and unavoidable impurities. The 600MPa grade hot-dip galvanized duplex steel for automotive structures provided by this invention possesses comprehensive properties such as continuous yield strength, high strength, low yield strength ratio, high work hardening rate, good uniform deformation, excellent bake hardening ability, and corrosion resistance. Summary of the Invention

[0005] The purpose of this invention is to provide a method for producing duplex steel strip for battery box covers. The duplex steel strip for battery box covers of this invention features high strength, a high strain hardening index, good strength-ductility matching, and high corrosion resistance, meeting the material selection requirements for automotive lightweighting and user-differentiated applications. Its mechanical properties meet the following requirements: yield strength Rp0.2: 351-383 MPa, tensile strength Rm: 642-660 MPa, elongation A... 50 21.5-27.0%, strain hardening index n 90： 0.19-0.21.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] This invention discloses a method for producing duplex steel strip for battery box covers, specifically comprising:

[0008] (1) During the top and bottom blowing smelting of the converter, oxygen blowing is used for decarburization and heating. During the tapping process of the converter, aluminum ferromanganese, ferrosilicon and ferrochrome are added for deoxidation and alloying. The P and S composition is controlled to prevent the steel liquid from over-oxidizing. The tapping temperature is ≥1600℃. The LF ladle refining adopts the LF full-process argon blowing process. The composition is adjusted to the target composition according to the steel liquid composition. The composition of the steel liquid supplied to the casting machine by mass percentage is C: 0.08-0.15%, Si: 0.20-0.75%, Mn: 1.8-2.5%, P≤0.070%, S≤0.035%, Alt: 0.010-0.070%, Cr: 0.10-0.40%, Ca: 0.0005-0.0050%, and the remainder is Fe and impurities. The superheat of the slab continuous casting is 5-30℃, and the casting speed is controlled at 0.2-2.0m / min.

[0009] (2) Hot rolling production process: billet heating—rough rolling—finish rolling—coiling; billet time in the furnace is 180-250 min, furnace exit temperature is 1200-1250℃, rough rolling adopts 3+3 mode 2-stand rolling mill rough rolling, finish rolling adopts 7-stand rolling mill finish rolling, finish rolling start temperature is 950-1050℃, finish rolling end temperature is 890-930℃; cooling adopts laminar flow cooling equipment, coiling temperature is 500-600℃;

[0010] (3) Pickling and cold rolling process: After the hot-rolled steel strip is pickled to remove the surface iron oxide scale, it is cold rolled by a 5-stand cold rolling mill with a cold rolling reduction rate of 68-72% and a thickness of 0.7mm.

[0011] (4) Continuous hot-dip galvanizing and finishing process: After uncoiling the cold-hardened steel strip, it is welded for continuous production. The furnace speed is 100-150m / min, the soaking temperature is 790-860℃, the slow cooling is 650-750℃, the rapid cooling is 450-500℃, the temperature of entering the zinc pot is 430-490℃, the temperature of the top roller cooling tower is ≤270℃, the finishing elongation is 0.6%-1.0%, and the tension leveling elongation is ≤0.8%.

[0012] Furthermore, the chemical composition of the duplex steel by mass percentage is: C: 0.08-0.10%, Si: 0.20-0.40%, Mn: 1.8-2.1%, P≤0.070%, S≤0.035%, Alt: 0.015-0.050%, Cr: 0.10-0.30%, Ca: 0.0005-0.0035%, with the remainder being Fe and impurities.

[0013] Furthermore, the thickness of the hot-rolled steel strip is 2.5 mm.

[0014] Furthermore, the mechanical properties of the duplex steel satisfy the following: tensile strength R m 642-660MPa.

[0015] Furthermore, the mechanical properties of the duplex steel satisfy the following: yield strength Rp 0.2 351-383 MPa.

[0016] Furthermore, the mechanical properties of the duplex steel satisfy the following: elongation A 50： 21.5-27.0%.

[0017] Furthermore, the mechanical properties of the duplex steel satisfy the following: strain hardening exponent n 90： 0.19-0.21.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0019] The dual-phase steel strip for automotive structures of this invention has characteristics such as low yield strength ratio, good corrosion resistance, weldability, no room temperature aging, and high elongation, which can meet users' requirements for lightweight and highly corrosion-resistant materials.

[0020] The dual-phase steel used for the battery box cover of this invention features high strength, high strain hardening index, good strength-ductility balance, and high corrosion resistance, meeting the requirements for lightweight automotive materials and diverse user applications. Mechanical properties: Yield strength Rp 0.2 351-383MPa, tensile strength R m： 642-660MPa, elongation A 50： 21.5-27.0%, strain hardening index n 90： 0.19-0.21. Detailed Implementation

[0021] According to the requirements of the steelmaking production process, the actual chemical composition of the slab is shown in Table 1.

[0022] Table 1 Chemical composition (wt%) of embodiments of the present invention

[0023] Element C Si Mn P S Alt Cr Ca scope 0.080-0.15 0.20-0.75 1.80-2.50 ≤0.070 ≤0.035 0.010-0.070 0.10-0.40 0.0005-0.0050 Example 0.080-0.100 0.20-0.40 1.80-2.10 ≤0.070 ≤0.035 0.015-0.050 0.10-0.30 0.0005-0.0035

[0024] According to the above hot rolling process requirements, the hot rolling thickness is 2.5mm, and the actual process is shown in Table 2.

[0025] Table 2 Hot rolling process of embodiments of the present invention

[0026] Hot-rolled thickness (mm) Furnace time (min) Furnace temperature (°C) Finishing rolling temperature (°C) Final rolling temperature ℃ Winding temperature ℃ 2 .5 180-250 1200-1250 950-1050 890-930 500-600

[0027] Based on the above requirements for cold rolling, hot-dip galvanizing, and finishing processes, the cold rolling thickness is 0.7 mm. The actual hot-dip galvanizing and finishing processes are shown in Table 3.

[0028] Table 3 Hot-dip galvanizing and finishing processes of embodiments of the present invention

[0029] Thickness (mm) Furnace zone speed (m / min) Isotropic temperature (°C) Slow cooling temperature ℃ Rapid cooling temperature ℃ Zinc pot temperature ℃ Top roller cooling tower top temperature (°C) Finishing elongation % Stretching elongation % 0.7 100-150 790-860 650-750 450-500 430-490 ≤270 0 .6％-1.0 ≤0 .8

[0030] The mechanical properties of the steel strip in this embodiment of the invention were tested, and the test results are shown in Table 4.

[0031] Table 4 Mechanical properties of steel strip in embodiments of the present invention

[0032] Example Thickness (mm) Yield strength MPa Tensile strength (MPa) <![CDATA[A 50 Elongation % <![CDATA[Strain hardening index n 90 > Require 340-460 ≥590 ≥20 ≥0.15 1 0.7 383 660 22.5 0.20 2 0.7 370 651 24.0 0.21 3 0.7 369 642 26.5 0.21 4 0.7 351 644 20.5 0.19 5 0.7 370 649 21.5 0.20 6 0.7 368 644 27.0 0.20

[0033] As shown in Table 4, the mechanical properties of the dual-phase steel strip for the battery box cover of this invention are as follows: yield strength Rp 0 .2 351-383MPa, tensile strength R m 642-660MPa, elongation A 5021.5-27.0%, strain hardening index n 90 The value is 0.19-0.21. In summary, the steel strip products obtained through this process have shown suitable performance after user testing and are suitable for widespread application.

[0034] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for producing a duplex steel strip for a battery box cover, characterized in that: Specifically, it includes: (1) During the top and bottom blowing smelting of the converter, oxygen blowing is used for decarburization and heating. During the tapping process of the converter, aluminum ferromanganese, ferrosilicon and ferrochrome are added for deoxidation and alloying. The P and S composition is controlled to prevent the steel liquid from over-oxidizing. The tapping temperature is ≥1600℃. The LF ladle refining adopts the LF full-process argon blowing process. The composition is adjusted to the target composition according to the steel liquid composition. The composition of the steel liquid supplied to the casting machine by mass percentage is C: 0.08-0.15%, Si: 0.20-0.75%, Mn: 1.8-2.5%, P≤0.070%, S≤0.035%, Alt: 0.010-0.070%, Cr: 0.10-0.40%, Ca: 0.0005-0.0050%, and the remainder is Fe and impurities. The superheat of the slab continuous casting is 5-30℃, and the casting speed is controlled at 0.2-2.0m / min. (2) Hot rolling production process: billet heating—rough rolling—finish rolling—coiling; billet time in the furnace is 180-250 min, furnace exit temperature is 1200-1250℃, rough rolling adopts 3+3 mode 2-stand rolling mill rough rolling, finish rolling adopts 7-stand rolling mill finish rolling, finish rolling start temperature is 950-1050℃, finish rolling end temperature is 890-930℃; cooling adopts laminar flow cooling equipment, coiling temperature is 500-600℃; (3) Pickling and cold rolling process: After the hot-rolled steel strip is pickled to remove the surface iron oxide scale, it is cold rolled by a 5-stand cold rolling mill with a cold rolling reduction rate of 68-72% and a thickness of 0.7mm. (4) Continuous hot-dip galvanizing and finishing process: After uncoiling the cold-hardened steel strip, it is welded for continuous production. The furnace speed is 100-150m / min, the soaking temperature is 790-860℃, the slow cooling is 650-750℃, the rapid cooling is 450-500℃, the temperature of entering the zinc pot is 430-490℃, the temperature of the top roller cooling tower is ≤270℃, the finishing elongation is 0.6%-1.0%, and the tension leveling elongation is ≤0.8%.

2. The method for producing duplex steel strip for battery box cover according to claim 1, characterized in that: The chemical composition of the duplex steel by mass percentage is: C: 0.08-0.10%, Si: 0.20-0.40%, Mn: 1.8-2.1%, P≤0.070%, S≤0.035%, Alt: 0.015-0.050%, Cr: 0.10-0.30%, Ca: 0.0005-0.0035%, with the remainder being Fe and impurities.

3. The method for producing duplex steel strip for battery box cover according to claim 1, characterized in that: Hot-rolled steel strip thickness 2.5mm.

4. The method for producing duplex steel strip for battery box cover according to claim 1, characterized in that: The mechanical properties of the duplex steel satisfy: tensile strength R m 642-660MPa.

5. The method for producing duplex steel strip for battery box cover according to claim 1, characterized in that: The mechanical properties of the duplex steel satisfy: yield strength Rp 0.2 351-383 MPa.

6. The method for producing duplex steel strip for battery box cover according to claim 1, characterized in that: The mechanical properties of the duplex steel satisfy: elongation A 50： 21.5-27.0%.

7. The method for producing duplex steel strip for battery box cover according to claim 1, characterized in that: The mechanical properties of the duplex steel satisfy: strain hardening exponent n 90： 0.19-0.21.