Method for improving yield ratio of 590MPa-grade dual-phase galvanized steel strip

Abstract

The invention discloses a method for improving the yield ratio of a 590MPa-grade dual-phase galvanized steel strip, which comprises the following steps: selecting a dual-phase steel strip meeting requirements as a base material, and the dual-phase steel strip comprises the following chemical components in percentage by weight: 0.05-0.15% of C, 0.1-0.5% of S i, 1.0-2.5% of Mn, less than or equal to 0.02% of P, less than or equal to 0.01% of S and the balance of Fe and impurities; a steel strip with good surface quality after hot rolling and acid rolling is subjected to the steps of heating treatment, slow cooling treatment, rapid cooling treatment, galvanization treatment and flattening treatment to produce the steel strip. The heating temperature is 800 to 840 DEG C; the slow cooling temperature is 650-700 DEG C; the rapid cooling temperature is 430-480 DEG C; the zinc pot entering temperature is 430-470 DEG C, and the time is 3-10 seconds; and the finishing elongation rate is 0.20%-0.30%. The purpose of the invention is to reduce the yield ratio while ensuring the strength of the steel strip by optimizing the galvanization process, thereby improving the forming performance of the steel strip.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal material processing, and particularly relates to a method for improving the yield ratio of 590 MPa grade dual-phase galvanized steel strip. Background Art

[0002] Dual-phase steel is an advanced high-strength steel composed of ferrite and martensite, which has high strength, good formability and welding performance, and is widely used in fields such as automobile manufacturing. However, the yield ratio (the ratio of yield strength to tensile strength) of dual-phase steel is relatively high, which to a certain extent limits its formability. Especially in the production process of galvanized steel strip, how to reduce the yield ratio while ensuring strength has become a technical problem in the industry.

[0003] At present, the methods for improving the yield ratio mainly include adjusting chemical composition, optimizing heat treatment process, etc., but these methods often have difficulty in taking into account both strength and formability. Therefore, it is of great significance to develop a method that can effectively improve the yield ratio of dual-phase galvanized steel strip. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for improving the yield ratio of 590 MPa grade dual-phase galvanized steel strip, which reduces the yield ratio while ensuring the strength of the steel strip by optimizing the galvanizing process, thereby improving its formability. The mechanical properties of the steel strip meet the technical requirements: yield strength 371 - 392 MPa, tensile strength 636 - 656 MPa, elongation at break 21 - 24.5%, strain hardening index n 90 0.17 - 0.19, yield ratio ≤ 0.60.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A method for improving the yield ratio of 590 MPa grade dual-phase galvanized steel strip of the present invention selects a dual-phase steel strip that meets the requirements as the base material, and its chemical composition by weight percentage is: C 0.05% - 0.15%, Si 0.1% - 0.5%, Mn 1.0% - 2.5%, P ≤ 0.02%, S ≤ 0.01%, and the balance is Fe and inevitable impurities; the steel strip with good surface quality after hot rolling and pickling rolling is produced through heat treatment, slow cooling treatment, rapid cooling treatment, galvanizing treatment and tempering treatment steps; wherein:

[0007] The heating temperature is 800 - 840 °C;

[0008] The slow cooling temperature is 650 - 700 °C;

[0009] The rapid cooling temperature is 430 - 480 °C;

[0010] The temperature when entering the zinc pot is 430 - 470 °C, and the galvanizing time is 3 - 10 seconds;

[0011] The skin pass elongation is 0.20 - 0.30%.

[0012] Furthermore, the mechanical properties meet the requirements: yield strength of 371 - 392 MPa, tensile strength of 636 - 656 MPa, elongation of 21 - 24.5%, strain hardening index n of 0.17 - 0.19, and yield ratio ≤ 0.60.

[0013] Furthermore, it specifically includes:

[0014] Select a dual - phase steel strip with qualified chemical composition as the base material;

[0015] Heat the steel strip to 820 °C and hold for 10 minutes;

[0016] Slowly cool it to 660 °C at a cooling rate of 5 °C / s;

[0017] Quickly cool it to 450 °C at a cooling rate of 30 °C / s;

[0018] Immerse the steel strip in zinc liquid at 460 °C for 5 seconds, and then cool it to room temperature at a cooling rate of 8 °C / s;

[0019] Perform skin pass treatment on the steel strip, and the skin pass elongation is 0.2462%.

[0020] Furthermore, it specifically includes:

[0021] Select a dual - phase steel strip with qualified chemical composition as the base material;

[0022] Heat the steel strip to 830 °C and hold for 10 minutes;

[0023] Slowly cool it to 680 °C at a cooling rate of 5 °C / s;

[0024] Quickly cool it to 470 °C at a cooling rate of 30 °C / s;

[0025] Immerse the steel strip in zinc liquid at 450 °C for 5 seconds, and then cool it to room temperature at a cooling rate of 8 °C / s;

[0026] Perform skin pass treatment on the steel strip, and the skin pass elongation is 0.2533%.

[0027] Furthermore, it specifically includes:

[0028] Select a dual - phase steel strip with qualified chemical composition as the base material;

[0029] Heat the steel strip to 840 °C and hold for 10 minutes;

[0030] Slowly cool it to 700 °C at a cooling rate of 5 °C / s;

[0031] Quickly cool to 480°C at a cooling rate of 30°C / s;

[0032] Immerse the steel strip in zinc liquid at 460°C for 5 seconds of galvanizing time, and then cool to room temperature at a cooling rate of 8°C / s;

[0033] Perform skin pass rolling on the steel strip, and the skin pass elongation is 0.2509%.

[0034] Furthermore, the finished thickness of the steel strip is 1.0 mm.

[0035] Furthermore, the finished thickness of the steel strip is 1.2 mm.

[0036] Furthermore, the finished thickness of the steel strip is 1.5 mm.

[0037] Compared with the prior art, the beneficial technical effects of the present invention:

[0038] Reduce the yield ratio: By optimizing the galvanizing process, the present invention can significantly reduce the yield ratio of the dual-phase galvanized steel strip, thereby improving its formability.

[0039] Maintain high strength: While reducing the yield ratio, the present invention can maintain the high strength of the steel strip, meeting the requirements of industries such as automobiles and household appliances for material strength. Specific embodiments

[0040] The following details the content of the present invention through specific embodiments. The embodiments are intended to help understand the present invention without limiting the content of the present invention.

[0041] Example 1

[0042] Select a dual-phase steel strip with qualified chemical composition as the base material.

[0043] Heat the steel strip to 820°C and hold for 10 minutes.

[0044] Slowly cool to 660°C at a cooling rate of 5°C / s.

[0045] Quickly cool to 450°C at a cooling rate of 30°C / s.

[0046] Immerse the steel strip in zinc liquid at 460°C for 5 seconds of galvanizing time, and then cool to room temperature at a cooling rate of 8°C / s.

[0047] Perform skin pass rolling on the steel strip, and the skin pass elongation is 0.2462%.

[0048] Example 2

[0049] Select a dual-phase steel strip with qualified chemical composition as the base material.

[0050] Heat the steel strip to 830 °C and hold for 10 minutes.

[0051] Slowly cool it to 680 °C at a cooling rate of 5 °C / s.

[0052] Quickly cool it to 470 °C at a cooling rate of 30 °C / s.

[0053] Immerse the steel strip in zinc liquid at 450 °C for 5 seconds of galvanizing time, and then cool it to room temperature at a cooling rate of 8 °C / s.

[0054] Perform skin pass treatment on the steel strip, and the skin pass elongation is 0.2533%.

[0055] Example 3

[0056] Select a dual-phase steel strip with a chemical composition meeting the requirements as the base material.

[0057] Heat the steel strip to 840 °C and hold for 10 minutes.

[0058] Slowly cool it to 700 °C at a cooling rate of 5 °C / s.

[0059] Quickly cool it to 480 °C at a cooling rate of 30 °C / s.

[0060] Immerse the steel strip in zinc liquid at 460 °C for 5 seconds of galvanizing time, and then cool it to room temperature at a cooling rate of 8 °C / s.

[0061] Perform skin pass treatment on the steel strip, and the skin pass elongation is 0.2509%.

[0062] Conduct mechanical property tests on the steel strips of the embodiments of the present invention, and the test results are shown in Table 1 below.

[0063] Table 1

[0064]

[0065] The above-described embodiments are only descriptions of the preferred modes of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for improving the yield ratio of 590 MPa grade dual-phase galvanized steel strip, characterized in that: Select a dual-phase steel strip that meets the requirements as the base material. Its chemical composition by weight percentage is: C 0.05%-0.15%, Si 0.1%-0.5%, Mn 1.0%-2.5%, P≤0.02%, S≤0.01%, and the balance is Fe and inevitable impurities; produce the steel strip through the steps of heat treatment, slow cooling treatment, rapid cooling treatment, galvanizing treatment, and skin pass treatment for the steel strip with good surface quality after hot rolling and pickling rolling; where: The heating temperature is 800-840°C; The slow cooling temperature is 650-700°C; The rapid cooling temperature is 430-480°C; The temperature when entering the galvanizing pot is 430-470°C, and the galvanizing time is 3-10 seconds; The skin pass elongation is 0.20-0.30%.

2. The method for improving the yield ratio of a 590 MPa grade dual-phase galvanized steel strip according to claim 1, characterized in that: The mechanical properties meet: yield strength 371-392 MPa, tensile strength 636-656 MPa, elongation 21-24.5%, strain hardening index n90 0.17-0.19, yield ratio ≤0.

60.

3. The method for improving the yield ratio of the 590 MPa grade dual-phase galvanized steel strip according to claim 1, characterized in that: Specifically include: Select a dual-phase steel strip with a chemical composition that meets the requirements as the base material; Heat the steel strip to 820°C and hold for 10 minutes; Slowly cool to 660°C at a cooling rate of 5°C / s; Rapidly cool to 450°C at a cooling rate of 30°C / s; Immerse the steel strip in zinc liquid at 460°C, the galvanizing time is 5 seconds, and then cool to room temperature at a cooling rate of 8°C / s; Perform skin pass treatment on the steel strip, and the skin pass elongation is 0.2462%.

4. The method for improving the yield ratio of a 590 MPa grade dual-phase galvanized steel strip according to claim 1, characterized in that: Specifically include: Select a dual-phase steel strip with a chemical composition that meets the requirements as the base material; Heat the steel strip to 830°C and hold for 10 minutes; Slowly cool to 680°C at a cooling rate of 5°C / s; Rapidly cool to 470°C at a cooling rate of 30°C / s; Immerse the steel strip in zinc liquid at 450°C, the galvanizing time is 5 seconds, and then cool to room temperature at a cooling rate of 8°C / s; Perform skin pass treatment on the steel strip, and the skin pass elongation is 0.2533%.

5. The method for improving the yield ratio of a 590 MPa grade dual-phase galvanized steel strip according to claim 1, characterized in that: Specifically include: Select a dual-phase steel strip with a chemical composition that meets the requirements as the base material; Heat the steel strip to 840°C and hold for 10 minutes; Slowly cool to 700°C at a cooling rate of 5°C / s; Rapidly cool to 480°C at a cooling rate of 30°C / s; Immerse the steel strip in zinc liquid at 460°C, the galvanizing time is 5 seconds, and then cool to room temperature at a cooling rate of 8°C / s; Perform skin pass treatment on the steel strip, and the skin pass elongation is 0.2509%.

6. The method for improving the yield ratio of the 590 MPa grade dual-phase galvanized steel strip according to claim 3, characterized in that: The finished thickness of the steel strip is 1.0 mm.

7. The method for improving the yield ratio of the 590 MPa grade dual-phase galvanized steel strip according to claim 4, characterized in that: The finished thickness of the steel strip is 1.2 mm.

8. The method for improving the yield ratio of the 590 MPa grade dual-phase galvanized steel strip according to claim 5, characterized in that: The finished thickness of the steel strip is 1.5 mm.

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