Production method of 590MPa-grade zinc-aluminum-magnesium-plated dual-phase steel strip for automobile structure

Abstract

The invention discloses a production method of a 590MPa-grade zinc-aluminum-magnesium-plated dual-phase steel strip for an automobile structure. The production method comprises a smelting-continuous casting production process flow, a hot rolling production technological process; pickling and cold rolling; (4) continuous hot galvanizing and finishing process flow; the steel comprises the following chemical components in percentage by mass: 0.075%-0.120% of C, 0.15%-0.35% of S i, 1.85%-2.2% of Mn, less than or equal to 0.040% of P, less than or equal to 0.015% of S, 0.010%-0.060% of Al t, 0.15%-0.30% of Cr, 0.0008%-0.0025% of Ca and the balance of Fe and impurities. The 590MPa-grade zinc-aluminum-magnesium-plated dual-phase steel strip for the automobile structure has the characteristics of high strength, high strain hardening index, good strength and ductility matching, high corrosion resistance and the like, and meets the requirements of lightweight material selection of automobiles and differentiated application of users.

Description

Technical Field

[0001] The present invention belongs to the technical field of metallurgical sheets, and particularly relates to a production method of 590 MPa grade galvanized aluminum-magnesium dual-phase steel strip for automotive structures. Background Art

[0002] With the establishment of the goals of automotive lightweighting and energy conservation and consumption reduction, the production of low-cost high-strength steel has become the main focus of major steel enterprises. Galvanized aluminum-magnesium dual-phase steel strip, with its high strength and good corrosion resistance, has become one of the important materials for achieving automotive lightweighting, and has received extensive attention and application in the automotive manufacturing industry, especially showing significant advantages in the manufacturing of automotive structural parts and body panels. The galvanized aluminum-magnesium dual-phase steel strip for automotive structures is an advanced automotive steel material that combines high strength, good corrosion resistance, and excellent formability. Dual-phase steel is composed of ferrite and martensite, and has characteristics such as a low yield ratio, a high initial work hardening rate, and a good combination of strength and ductility. Through specific heat treatment processes, such as rapid cooling and induction heating, an ideal dual-phase structure can be obtained, thus meeting the requirements of automotive structures for high strength and good formability. On the basis of traditional hot-dip galvanized coatings, a ternary alloy high-corrosion-resistant steel plate is made by adding appropriate amounts of aluminum and magnesium elements. The magnesium and aluminum elements in the coating can form a stable protective film during the corrosion process, significantly improving the corrosion resistance of the steel plate. The zinc-aluminum-magnesium coating not only improves the overall corrosion resistance of the steel plate, but also particularly enhances the corrosion resistance at the cut, which is particularly important for automotive structural parts. With the continuous progress of technology and the reduction of costs, the application prospect of galvanized aluminum-magnesium dual-phase steel strip in automotive structures will be broader.

[0003] The 590 MPa grade galvanized aluminum-magnesium dual-phase steel is an advanced high-strength steel widely used in the automotive field, and is mainly applied to automotive high-strength structural parts, connectors, etc., such as cross and longitudinal beams, connecting plates, anti-collision bars, etc. Summary of the Invention

[0004] The purpose of the present invention is to provide a production method of 590 MPa grade galvanized aluminum-magnesium dual-phase steel strip for automotive structures. The 590 MPa grade galvanized aluminum-magnesium dual-phase steel strip for automotive structures of the present invention has characteristics such as high strength, a high strain hardening index, good strength and ductility matching, and high corrosion resistance, meeting the requirements of automotive lightweight material selection and user differentiated applications. The mechanical properties meet: yield strength Rp0.2: 340 - 460 MPa, tensile strength Rm ≥ 590 MPa, elongation A50 ≥ 20%, and strain hardening index n 90 ≥ 0.13.

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

[0006] A production method of 590 MPa grade galvanized aluminum-magnesium dual-phase steel strip for automotive structures of the present invention includes:

[0007] (1) Smelting - continuous casting production process flow: hot metal pretreatment - converter - LF refining - slab continuous casting; in the top and bottom combined blowing smelting of the converter, oxygen blowing is carried out for decarburization and temperature raising. During the tapping process of the converter, ferrosilicon, ferromanganese, ferrosilicon, and ferrochromium are added for deoxidation alloying, controlling the P and S components to prevent the molten steel from being overoxidized, and the tapping temperature ≥ 1600 °C; the LF secondary refining adopts the whole-process argon blowing process of LF, and adjusts to the target composition according to the molten steel composition; the superheat of the slab continuous casting is 15 - 40 °C, and the drawing speed is controlled at 0.8 - 2.0 m / min;

[0008] (2) Hot rolling production process flow: billet heating - rough rolling - finish rolling - coiling; the billet stays in the furnace for 170 - 250 min, the furnace outlet temperature is 1200 - 1300 °C, the rough rolling adopts a 3 + 3 mode with 2 - stand roughing mills, the finish rolling adopts 7 - stand finishing mills, the finish rolling starting temperature is 960 - 1080 °C, the finish rolling final temperature is 850 - 930 °C, the thickness of the hot - rolled steel strip is 2.3 - 4.5 mm; cooling adopts laminar cooling equipment, and the coiling temperature is 540 - 600 °C;

[0009] (3) Pickling and cold rolling process flow: after the hot - rolled steel strip is pickled to remove the surface scale, it is cold - rolled by a 5 - stand cold rolling mill, the cold rolling reduction rate is 45 - 70%, and the thickness is 0.7 - 2.2 mm;

[0010] (4) Continuous hot - dip galvanizing and skin - pass rolling process flow: after the cold - rolled and hardened steel strip is uncoiled and welded for continuous production, the speed in the furnace area is 60 - 140 m / min, the soaking temperature is 780 - 830 °C, slowly cooled to 660 - 710 °C, quickly cooled to 420 - 470 °C, the temperature entering the zinc pot is 440 - 490 °C, the temperature at the top roll cooling tower top ≤ 250 °C, the skin - pass rolling elongation is 0.2% - 0.5%, and the tension leveling elongation ≤ 0.5%;

[0011] The chemical composition of the dual - phase steel in mass percentage is: C: 0.075 - 0.120%, Si: 0.15 - 0.35%, Mn: 1.85 - 2.2%, P ≤ 0.040%, S ≤ 0.015%, Alt: 0.010 - 0.060%, Cr: 0.15 - 0.30%, Ca: 0.0008 - 0.0025%, and the rest is Fe and impurities.

[0012] Further, the chemical composition of the dual - phase steel in mass percentage is C: 0.098%, Si: 0.30%, Mn: 2.00%, P: 0.023%, S: 0.007%, Alt: 0.035%, Cr: 0.19%, Ca: 0.0010%, and the rest is Fe and impurities.

[0013] Further, the mechanical properties of the dual - phase steel satisfy: yield strength Rp 0.2 : 398 - 433 MPa.

[0014] Furthermore, the mechanical properties of the duplex steel satisfy: the tensile strength R m : 647 - 670 MPa.

[0015] Furthermore, the mechanical properties of the duplex steel satisfy: the elongation A 50 : 22 - 25.5%.

[0016] Furthermore, the mechanical properties of the duplex steel satisfy: the strain hardening index n 90 : 0.17 - 0.18.

[0017] Furthermore, the duplex steel is applied to high-strength automotive structural parts and connectors: cross and longitudinal beams, connecting plates, anti-collision bars, anti-collision bars.

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

[0019] The 590 MPa grade galvanized aluminum-magnesium duplex steel of the present invention has characteristics such as high strength, high strain hardening index, good strength and ductility matching, and high corrosion resistance, meeting the requirements of automotive lightweight material selection and user differentiated applications. The mechanical properties are: the yield strength Rp 0.2 : 340 - 460 MPa, the tensile strength R m ≥590 MPa, the elongation A 50 ≥20%, the strain hardening index n 90 ≥0.13. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is the microstructure diagram of the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] The content of the present invention is described in detail below through specific embodiments. The embodiments are only helpful for understanding the present invention and do not limit the content of the present invention.

[0022] Embodiment

[0023] According to the above requirements of the steelmaking production process, the chemical composition of the actual slab is shown in Table 1.

[0024] Table 1 Chemical composition (wt%) of the embodiment of the present invention

[0025]

[0026] The hot-rolled thickness is 2.3 - 4.5 mm, and the actual process is shown in Table 2.

[0027] Table 2 Hot-rolling process of the embodiment of the present invention

[0028]

[0029] According to the requirements of cold rolling, hot dip galvanizing, and skin pass rolling processes, the cold rolling thickness is 0.7 - 2.2 mm, and the actual hot dip galvanizing and skin pass rolling processes are shown in Table 3.

[0030] Table 3 Hot Dip Galvanizing and Skin Pass Rolling Processes of the Embodiment of the Present Invention

[0031]

[0032]

[0033] The mechanical properties of the steel strip of the embodiment of the present invention were inspected, and the inspection results are shown in Table 4.

[0034] Table 4 Mechanical Properties of the Steel Strip of the Embodiment of the Present Invention

[0035]

[0036] It can be seen from the data in Table 4 that the mechanical properties of the 590 MPa grade galvanized aluminum - magnesium dual - phase steel strip for automotive structures of the present invention are as follows: yield strength Rp 0.2 : 390 - 418 MPa, tensile strength R m : 622 - 665 MPa, elongation A 50 : 21 - 25.5%, strain hardening index n 90 : 0.17 - 0.18. The steel strip products obtained by the above - mentioned process are suitable in performance after being used by users and can be promoted for use.

[0037] The above - described embodiments are only descriptions of the preferred embodiments 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 producing a 590MPa grade galvanized aluminum-magnesium dual-phase steel strip for automobile structure, characterized in that: include: (1) Smelting-continuous casting production process: molten iron pretreatment-converter-LF refining-slab continuous casting; oxygen blowing decarburization and heating are carried out in the converter top and bottom combined blowing smelting, and aluminum iron, manganese iron, silicon iron and chromium iron are added in the converter steelmaking process for deoxidation and alloying, and the P and S components are controlled to prevent the molten steel from overoxidation. The steelmaking temperature is ≥1600℃; LF refining outside the furnace adopts the LF full-process argon blowing process to adjust the target composition according to the molten steel composition; the slab continuous casting superheat is 15-40℃, and the casting speed is controlled at 0.8-2.0m / min; (2) Hot rolling production process: heating of ingot - rough rolling - finishing rolling - coiling; ingot furnace time is 170-250 min, furnace temperature is 1200-1300°C, rough rolling is performed by 3+3 mode 2-stand rolling mill, finishing rolling is performed by 7-stand rolling mill, finishing rolling start temperature is 960-1080°C, finishing rolling final temperature is 850-930°C, hot rolled steel strip thickness is 2.3-4.5 mm; cooling is performed by laminar cooling equipment, coiling temperature is 540-600°C; (3) Pickling cold rolling process: After the hot-rolled steel strip is pickled to remove the surface iron oxide scale, it is cold-rolled in a 5-stand cold rolling mill with a cold rolling reduction rate of 45-70% and a thickness of 0.7-2.2 mm; (4) Continuous hot-dip galvanizing and skin-passing process: The cold-hardened steel strip is unrolled and then welded for continuous production, the furnace speed is 60-140m / min, the soaking temperature is 780-830℃, the temperature is slowly cooled to 660-710℃, the temperature is quickly cooled to 420-470℃, the temperature of the zinc pot is 440-490℃, the temperature of the top roller cooling tower is ≤250℃, the skin-pass elongation is 0.2%-0.5%, and the elongation of the straightening is ≤0.5%; The chemical composition of the dual-phase steel in mass percentage is: C: 0.075-0.120%, Si: 0.15-0.35%, Mn: 1.85-2.2%, P≤0.040%, S≤0.015%, Alt: 0.010-0.060%, Cr: 0.15-0.30%, Ca: 0.0008-0.0025%, and the rest is Fe and impurities.

2. The method for producing a 590MPa grade galvanized aluminum-magnesium dual-phase steel strip for automobile structure according to claim 1, characterized in that: The chemical composition of the dual-phase steel by mass percentage is C: 0.098%, Si: 0.30%, Mn: 2.00%, P: 0.023%, S: 0.007%, Alt: 0.035%, Cr: 0.19%, Ca: 0.0010%, and the rest is Fe and impurities.

3. The method for producing a 590MPa grade galvanized aluminum-magnesium dual-phase steel strip for automobile structure according to claim 1, characterized in that: The mechanical properties of the dual-phase steel meet the following requirements: yield strength Rp 0.2 :398-433MPa.

4. The method for producing a 590MPa grade galvanized aluminum-magnesium dual-phase steel strip for automobile structure according to claim 1, characterized in that: The mechanical properties of the dual-phase steel meet the following requirements: tensile strength R m :647-670MPa.

5. The method for producing a 590MPa grade galvanized aluminum-magnesium dual-phase steel strip for automobile structure according to claim 1, characterized in that: The mechanical properties of the dual-phase steel meet the following requirements: elongation A 50 :22-25.5%.

6. The method for producing a 590MPa grade galvanized aluminum-magnesium dual-phase steel strip for automobile structure according to claim 1, characterized in that: The mechanical properties of the dual-phase steel meet the following requirements: strain hardening index n 90 :0.17-0.

18.

7. The method for producing a 590MPa grade galvanized aluminum-magnesium dual-phase steel strip for automobile structure according to claim 1, characterized in that: The dual-phase steel is used in high-strength automotive structural parts and connecting parts: transverse and longitudinal beams, connecting plates, anti-collision bars, and anti-collision bars.

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