Production method of cold-rolled dual-phase steel strip with tensile strength of 450 MPa

Abstract

The invention discloses a production method of a cold-rolled dual-phase steel strip with the tensile strength of 450 MPa. The cold-rolled dual-phase steel strip comprises the following chemical components in percentage by mass: 0.05-0.08% of C, 0.1-0.35% of Si, 1.10-1.40% of Mn, less than or equal to 0.020% of P, less than or equal to 0.010% of S, 0.010-0.050% of Alt, 0.0010-0.0030% of Ca, less than or equal to 0.0070% of N and the balance of Fe and impurities. The invention further discloses a main process and parameter setting of the production method. The produced cold-rolled dual-phase steel strip with the tensile strength of 450 MPa has the characteristics of being low in yield ratio, high in work hardening capacity, good in welding performance, free of yield elongation and room-temperature aging, high in elongation and the like, can meet the requirement of a user for lightweight material selection, and is widely applied to complex forming structural parts needing certain strength requirements.

Description

Technical Field

[0001] This invention relates to the field of metallurgical sheet technology, and in particular to a method for producing cold-rolled duplex steel strip with a tensile strength of 450 MPa. Background Technology

[0002] With the rapid development of industries such as automobiles and home appliances, the demand for high-strength, high-ductility steel is increasing daily. Cold-rolled duplex steel strip, as a material that combines high strength and good formability, has been widely used in automobile manufacturing, structural components, and other fields. However, existing cold-rolled duplex steel strips still need improvement in terms of product strength, toughness, and formability to meet higher engineering standards. Especially when tensile strength reaches the 450MPa level, maintaining good ductility and formability of the steel strip becomes crucial for developing products at this level, and has significant guiding implications for improving product performance and market competitiveness in related industries.

[0003] Currently, the 450MPa grade cold-rolled duplex steel (a method for preparing 450MPa grade automotive cold-rolled duplex steel sheet with tensile strength, application number 201210277421.X) produced by Maanshan Iron & Steel (Group) Holding Co., Ltd. has a composition design of C: 0.03-0.06%, Mn: 1.4-1.6%, and Ti: 0.003-0.020%, which differs from the composition design of this invention. The higher Mn and Ti content affects product cost, and the yield strength is 200-250MPa, which is different from the performance of this invention. The 450MPa grade cold-rolled duplex steel (a 450MPa grade automotive lightweight cold-rolled duplex steel and its production method, application number 201811) produced by Baotou Steel (Group) Co., Ltd. In the composition design of 240068.1), Mn: 1.05~1.15%, Cr: 0.2~0.3%, and coiling temperature 650℃, there are differences from the composition and process design of this invention. The higher Cr content affects the product cost, and the higher coiling temperature may affect the product performance. In the composition design of 450MPa grade cold-rolled duplex steel (manufacturing method of 450MPa grade cold-rolled duplex steel with tensile strength, application number 201710418616.4) produced by Wuhan Iron and Steel Co., Ltd., Si < 0.06% and slow cooling temperature 610~650℃, there are differences from the composition and process design of this invention. The lower Si content affects the product's plasticity and toughness, and the lower slow cooling temperature may lead to a decrease in cooling rate, affecting the product strength. Summary of the Invention

[0004] The purpose of this invention is to provide a method for producing cold-rolled duplex steel strip with a tensile strength of 450 MPa. The produced cold-rolled duplex steel strip with a tensile strength of 450 MPa possesses characteristics such as low yield strength ratio, high work hardening ability, good weldability, no yield elongation, no room temperature aging, and high elongation. It can meet users' requirements for lightweight materials and is widely used in complex formed structural parts requiring certain strength. Mechanical properties satisfy: Yield strength R p0.2 250~340MPa, tensile strength R m ≥450MPa, yield strength ratio ≤0.65, elongation A 80 ≥27%, n≥0.16.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] This invention discloses a method for producing cold-rolled duplex steel strip with a tensile strength of 450 MPa, comprising:

[0007] (1) Smelting-continuous casting production process: hot metal pretreatment—converter—LF refining—slab continuous casting; oxygen blowing for decarburization and heating is carried out in the top and bottom blowing smelting of the converter. During the tapping process of the converter, aluminum iron, manganese iron and silicon iron are added for deoxidation and alloying. The P and S composition is controlled to prevent the steel liquid from over-oxidation. The tapping temperature is ≥1620℃; the LF ladle refining adopts the LF full-process argon blowing process. After calcium treatment, the soft blowing time is ≥10min. The composition is adjusted to the target composition according to the steel liquid composition; the superheat of slab continuous casting is 15~35℃, and the casting speed is controlled at 1.0~1.8m / min;

[0008] (2) Hot rolling production process: billet heating—rough rolling—finish rolling—coiling; billet time in the furnace is 160-260 min, furnace exit temperature is 1220-1280℃, rough rolling adopts 3+3 mode 2-stand rolling mill, finish rolling adopts 7-stand rolling mill, finish rolling start temperature is 960-1040℃, finish rolling end temperature is 860-905℃, hot rolled steel strip thickness is 2.8-4.8mm; cooling adopts laminar flow cooling equipment, coiling temperature is 560-610℃;

[0009] (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 55-70% and a thickness of 0.8-2.0 mm.

[0010] (4) Continuous annealing process: production speed 60~130m / min, after uncoiling the cold hardened steel strip, heat it to 790~840℃, slowly cool it to 660~690℃, then cool it to 270~300℃, over-aging temperature 260~300℃, after over-aging treatment, finally cool it to room temperature, and the elongation of the leveling machine is 0.4~0.8%;

[0011] The chemical composition of the cold-rolled duplex steel strip by mass percentage is: C: 0.05-0.08%, Si: 0.1-0.35%, Mn: 1.10-1.40%, P≤0.020%, S≤0.010%, Alt: 0.010-0.050%, Ca: 0.0010-0.0030%, N≤0.0070%, with the remainder being Fe and impurities.

[0012] Furthermore, the chemical composition of the cold-rolled duplex steel strip by mass percentage is C: 0.08%, Si: 0.33%, Mn: 1.35%, P: 0.010%, S: 0.001%, Alt: 0.036%, Ca: 0.0015%, N: 0.0046%, with the remainder being Fe and impurities.

[0013] Furthermore, the chemical composition of the cold-rolled duplex steel strip by mass percentage is C: 0.07%, Si: 0.26%, Mn: 1.32%, P: 0.017%, S: 0.002%, Alt: 0.027%, Ca: 0.0022%, N: 0.0035%, with the remainder being Fe and impurities.

[0014] Furthermore, the chemical composition of the cold-rolled duplex steel strip by mass percentage is C: 0.07%, Si: 0.23%, Mn: 1.23%, P: 0.015%, S: 0.006%, Alt: 0.043%, Ca: 0.0011%, N: 0.0056%, with the remainder being Fe and impurities.

[0015] Furthermore, the chemical composition of the cold-rolled duplex steel strip by mass percentage is C: 0.06%, Si: 0.13%, Mn: 1.32%, P: 0.015%, S: 0.002%, Alt: 0.036%, Ca: 0.0011%, N: 0.0035%, with the remainder being Fe and impurities.

[0016] Furthermore, the initial rolling temperature for finishing is 977–1028℃, the final rolling temperature for finishing is 866–900℃, and the coiling temperature is 565–600℃.

[0017] Furthermore, with a production speed of 75–124 m / min, the cold-hardened steel strip is uncoiled and heated to 801–826°C, slowly cooled to 664–681°C, then rapidly cooled to 275–292°C, and over-aging at 267–289°C. After over-aging treatment, it is finally cooled to room temperature, and the elongation of the leveling machine is 0.52–0.874%.

[0018] Further, the mechanical properties of cold-rolled duplex steel strip: yield strength R p0.2 284~301MPa, tensile strength R m 491~498MPa, elongation A80 : 29.5%~34.5%, n value 0.19~0.21, yield strength ratio 0.58~0.60.

[0019] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0020] The cold-rolled duplex steel strip with a tensile strength of 450 MPa prepared by this invention possesses characteristics such as low yield strength ratio, high work hardening ability, good weldability, no yield elongation, no room temperature aging, and high elongation. It can meet users' lightweight material selection requirements and is widely used in complex formed structural parts requiring certain strength. Mechanical properties meet: Yield strength R p0.2 250~340MPa, tensile strength R m ≥450MPa, yield strength ratio ≤0.65, elongation A 80 ≥27%, n≥0.16. Attached Figure Description

[0021] The present invention will be further described below with reference to the accompanying drawings.

[0022] Figure 1 This is a microstructure diagram of Embodiment 1 of the present invention. Detailed Implementation

[0023] The present invention will be described in detail below through specific embodiments. These embodiments are only intended to help understand the present invention and do not limit the scope of the present invention.

[0024] Example

[0025] According to the above steelmaking process requirements, the actual chemical composition of the slab is shown in Table 1.

[0026] Table 1 Chemical composition (wt%) of embodiments of the present invention

[0027]

[0028]

[0029] According to the above hot rolling process requirements, the hot rolling thickness is 2.8 to 4.8 mm, and the actual process is shown in Table 2.

[0030] Table 2 Hot rolling process of embodiments of the present invention

[0031]

[0032] According to the above cold rolling and annealing process requirements, the cold rolling thickness is 0.8 to 2.0 mm, and the actual process is shown in Table 3.

[0033] Table 3 Annealing process of embodiments of the present invention

[0034]

[0035] The mechanical properties of the steel strip in this embodiment of the invention were tested, and the test results are shown in Table 4.

[0036] Table 4 Mechanical properties of steel strip in embodiments of the present invention

[0037]

[0038]

[0039] As shown in Table 4, the mechanical properties of the cold-rolled duplex steel strip with a tensile strength of 450 MPa according to this invention are as follows: Yield strength R p0.2 284~301MPa, tensile strength R m 491~498MPa, elongation A 80 The yield strength is 29.5%–34.5%, the n-value is 0.19–0.21, and the yield strength ratio is 0.58–0.60. In summary, the yield strength ratio of the steel strip obtained by this process is suitable, and the product has been tested by users and found to have appropriate performance, making it suitable for widespread application.

[0040] 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 cold-rolled duplex steel strip with a tensile strength of 450 MPa, characterized in that: include: (1) Smelting-continuous casting production process: hot metal pretreatment—converter—LF refining—slab continuous casting; oxygen blowing for decarburization and heating is carried out in the top and bottom blowing smelting of the converter. During the tapping process of the converter, aluminum iron, manganese iron and silicon iron are added for deoxidation and alloying. The P and S composition is controlled to prevent the steel liquid from over-oxidation. The tapping temperature is ≥1620℃; the LF ladle refining adopts the LF full-process argon blowing process. After calcium treatment, the soft blowing time is ≥10min. The composition is adjusted to the target composition according to the steel liquid composition; the superheat of slab continuous casting is 15~35℃, and the casting speed is controlled at 1.0~1.8m / min; (2) Hot rolling production process: billet heating—rough rolling—finish rolling—coiling; billet time in the furnace is 160-260 min, furnace exit temperature is 1220-1280℃, rough rolling adopts 3+3 mode 2-stand rolling mill, finish rolling adopts 7-stand rolling mill, finish rolling start temperature is 960-1040℃, finish rolling end temperature is 860-905℃, hot rolled steel strip thickness is 2.8-4.8mm; cooling adopts laminar flow cooling equipment, coiling temperature is 560-610℃; (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 55-70% and a thickness of 0.8-2.0 mm. (4) Continuous annealing process: production speed 60~130m / min, after uncoiling the cold hardened steel strip, heat it to 790~840℃, slowly cool it to 660~690℃, then cool it to 270~300℃, over-aging temperature 260~300℃, after over-aging treatment, finally cool it to room temperature, and the elongation of the leveling machine is 0.4~0.8%; The chemical composition of the cold-rolled duplex steel strip by mass percentage is: C: 0.05-0.08%, Si: 0.1-0.35%, Mn: 1.10-1.40%, P≤0.020%, S≤0.010%, Alt: 0.010-0.050%, Ca: 0.0010-0.0030%, N≤0.0070%, with the remainder being Fe and impurities.

2. The method for producing cold-rolled duplex steel strip with a tensile strength of 450 MPa according to claim 1, characterized in that: The chemical composition of the cold-rolled duplex steel strip by mass percentage is C: 0.08%, Si: 0.33%, Mn: 1.35%, P: 0.010%, S: 0.001%, Alt: 0.036%, Ca: 0.0015%, N: 0.0046%, with the remainder being Fe and impurities.

3. The method for producing cold-rolled duplex steel strip with a tensile strength of 450 MPa according to claim 1, characterized in that: The chemical composition of the cold-rolled duplex steel strip by mass percentage is C: 0.07%, Si: 0.26%, Mn: 1.32%, P: 0.017%, S: 0.002%, Alt: 0.027%, Ca: 0.0022%, N: 0.0035%, with the remainder being Fe and impurities.

4. The method for producing cold-rolled duplex steel strip with a tensile strength of 450 MPa according to claim 1, characterized in that: The chemical composition of the cold-rolled duplex steel strip by mass percentage is C: 0.07%, Si: 0.23%, Mn: 1.23%, P: 0.015%, S: 0.006%, Alt: 0.043%, Ca: 0.0011%, N: 0.0056%, with the remainder being Fe and impurities.

5. The method for producing cold-rolled duplex steel strip with a tensile strength of 450 MPa according to claim 1, characterized in that: The chemical composition of the cold-rolled duplex steel strip by mass percentage is C: 0.06%, Si: 0.13%, Mn: 1.32%, P: 0.015%, S: 0.002%, Alt: 0.036%, Ca: 0.0011%, N: 0.0035%, with the remainder being Fe and impurities.

6. The method for producing cold-rolled duplex steel strip with a tensile strength of 450 MPa according to claim 1, characterized in that: The initial rolling temperature for finishing is 977–1028℃, the final rolling temperature for finishing is 866–900℃, and the coiling temperature is 565–600℃.

7. The method for producing cold-rolled duplex steel strip with a tensile strength of 450 MPa according to claim 1, characterized in that: The production speed is 75-124 m / min. After uncoiling the chilled hardened steel strip, it is heated to 801-826℃, slowly cooled to 664-681℃, and then rapidly cooled to 275-292℃. The over-aging temperature is 267-289℃. After the over-aging treatment, it is finally cooled to room temperature. The elongation of the leveling machine is 0.52-0.874%.

8. The method for producing cold-rolled duplex steel strip with a tensile strength of 450 MPa according to claim 1, characterized in that: Mechanical properties of cold-rolled duplex steel strip: Yield strength R p0.2 284~301MPa, tensile strength R m 491~498MPa, elongation A 80 : 29.5%~34.5%, n value 0.19~0.21, yield strength ratio 0.58~0.60.

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