Production method of 500MPa-grade galvanized dual-phase steel strip for automobile bracket

Abstract

The invention discloses a production method of a 500MPa-grade galvanized dual-phase steel strip for an automobile bracket. The 500MPa-grade galvanized dual-phase steel strip comprises the following chemical components in percentage by mass: 0.05-0.08% of C, less than or equal to 0.25% of S , 1.5-1.8% of Mn, less than or equal to 0.020% of P, less than or equal to 0.015% of S, 0.015-0.060% of Alt, 0.01-0.25% of Cr, 0.0010-0.0030% of Ca and the balance of Fe. The production method specifically comprises the following steps: a smelting-continuous casting production process flow; a hot rolling production technological process; pickling and cold rolling; and carrying out continuous hot galvanizing and finishing processes. The 500MPa-grade galvanized dual-phase steel for the automobile bracket has the characteristics of low yield ratio, high work hardening capacity, good corrosion resistance, welding performance, no yield elongation, no room-temperature aging, high elongation and the like, and can meet the requirements of users on light-weight and high-corrosion-resistance material selection.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgical plates, and in particular relates to a production method of a 500MPa-grade galvanized dual-phase steel strip for an automobile bracket. Background Art

[0002] Competition in the automotive industry is becoming increasingly fierce. New energy vehicles are constantly impacting the traditional market. People's demands for safety, environmental protection, comfort and energy saving in modern cars are constantly increasing. The design of the entire vehicle must be aimed at energy conservation and emission reduction, low carbon and environmental protection, and lightweight while ensuring safety performance. Therefore, there is an increasingly strong demand for automotive steel in terms of high strength, high plasticity, collision energy absorption performance, etc. At the same time, it is also required that steel has good stamping and forming properties in order to produce high-precision and high-strength automotive parts.

[0003] Galvanized duplex steel is a new generation of advanced high-strength steel widely used in the field of automobile plates. It is mainly composed of ferrite and martensite dispersed in the matrix in an island shape. It has the advantages of low yield strength ratio, high work hardening ability, good corrosion resistance, welding performance, no yield extension, no room temperature aging, high elongation, anti-collision energy absorption, etc., and is widely used in automobile structural parts, reinforcement parts and anti-collision parts. Due to its good strength-toughness matching, weldability and corrosion resistance, 500MPa grade galvanized duplex steel is widely used in automobile bracket structural parts that require certain strength requirements, playing a bridging and supporting role.

[0004] At present, the composition design of the 500MPa grade hot-dip galvanized duplex steel plate produced by Anhui University of Technology (500MPa grade high work hardening rate hot-dip galvanized duplex steel plate and its preparation method, application number 201910462743.3) is C: 0.02-0.05%, Mn: 0.80-1.20%, Mo: 0.30-0.50%, Nb: 0.025-0.040%, and the coiling temperature is 700-730°C. Different from the composition and process design of the present invention, higher Mo and Nb increase the alloy cost, and the high coiling temperature has higher requirements on the rolling rhythm; the 500MPa grade galvanized duplex steel produced by Bengang Plate Co., Ltd. (a 500MPa grade galvanized duplex steel and its production method, application number 202311 737228.4) In the composition design, B: 0.0015-0.0020%, the coiling temperature is 450-550°C, which are different from the composition and process design of the present invention. A high B content may increase the risk of corner cracking of the ingot, and a low coiling temperature has an adverse effect on the metallographic banded structure of the product; in the composition design of the 500MPa-class galvanized duplex steel for passenger cars produced by Wuhan Iron and Steel Co., Ltd. (a 500MPa-class galvanized duplex steel for passenger cars and a production method, application number 201510968625.1), Mo: 0.01-0.30% or Cr: 0.02-0.9%, Nb: 0.001-0.03%, high Mo, Cr, and Nb contents affect the alloy cost and surface quality, which is different from the chemical composition design of the present invention. Summary of the invention

[0005] The purpose of the present invention is to provide a production method of a 500MPa grade galvanized dual-phase steel strip for automobile brackets. The 500MPa grade galvanized dual-phase steel for automobile brackets of the present invention has the characteristics of low yield strength ratio, high work hardening ability, good corrosion resistance, welding performance, no yield extension, no room temperature aging, high elongation, etc., which can meet the user's lightweight and high corrosion resistance material selection requirements, and is widely used in automobile bracket structural parts that require certain strength requirements. The mechanical properties meet the following requirements: yield strength R p0.2 : 300-380MPa, tensile strength R m ≥500MPa, yield strength ratio ≤0.7, elongation A 80 ≥24%, n≥0.15.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The present invention discloses a production method of a 500MPa grade galvanized dual-phase steel strip for automobile brackets, wherein the mass percentage of the chemical components is C: 0.05-0.08%, Si≤0.25%, Mn: 1.5-1.8%, P≤0.020%, S≤0.015%, Alt: 0.015-0.060%, Cr: 0.01-0.25%, Ca: 0.0010-0.0030%, and the rest is Fe and unavoidable impurities; the production method is specifically as follows:

[0008] (1) Smelting-continuous casting production process: molten iron pretreatment-converter-LF refining-slab continuous casting; oxygen blowing and decarburization are carried out during the top and bottom combined blowing smelting in the converter, and aluminum iron, manganese iron, silicon iron and chromium iron are added during 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 20-40℃, and the casting speed is controlled at 1.0-1.8m / min;

[0009] (2) Hot rolling production process: heating of ingot - rough rolling - finishing rolling - coiling; ingot furnace time is 160-280min, furnace temperature is 1210-1270℃, rough rolling adopts 3+3 mode 2-stand rolling mill, finishing rolling adopts 7-stand rolling mill, finishing rolling start temperature is 950-1050℃, finishing rolling final temperature is 860-910℃, hot rolled steel strip thickness is 2.5-4.8mm; cooling adopts laminar cooling equipment, coiling temperature is 540-610℃;

[0010] (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 50-75% and a thickness of 0.7-2.0 mm;

[0011] (4) Continuous hot-dip galvanizing and skin-passing process: The cold-hardened steel strip is unrolled and welded for continuous production. The furnace speed is 70-120 m / min, the average temperature is 790-830°C, and it is slowly cooled to 670-710°C, then cooled to 440-465°C, the temperature of entering the zinc pot is 440-470°C, the temperature of the top roller cooling tower is 190-230°C, the skin-passing elongation is 0.2-0.6%, and the straightening elongation is ≤0.4%.

[0012] Furthermore, the mass percentage of its chemical composition is C: 0.06-0.08%, Si 2-0.20%, Mn: 1.55-1.70%, P 0.008-0.018%, S 0.001-0.006%, Alt: 0.030-0.043%, Cr: 0.05-0.25%, Ca: 0.0010-0.0025%, and the rest is Fe and unavoidable impurities.

[0013] Furthermore, the hot-rolled thickness is 4.0 mm.

[0014] Furthermore, the cold-rolled thickness is 1.4 mm.

[0015] Furthermore, the mechanical properties of the steel strip meet the following requirements: yield strength R p0.2 : 344-364MPa, tensile strength R m : 504-553MPa, yield strength ratio: 0.66-0.68, elongation A 80 :26.5-28.0%, n: 0.15-0.16.

[0016] Compared with the prior art, the beneficial technical effects of the present invention are:

[0017] The 500MPa grade galvanized dual-phase steel strip of the present invention has the characteristics of low yield strength ratio, high work hardening ability, good corrosion resistance, welding performance, no yield extension, no room temperature aging, high elongation, etc., which can meet the user's lightweight and high corrosion resistance material selection requirements, and is widely used in automobile bracket structural parts that require certain strength requirements. Mechanical properties: yield strength R p0.2 : 300-380MPa, tensile strength R m ≥500MPa, yield strength ratio ≤0.7, elongation A 80 ≥24%, n≥0.15. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will be further described below in conjunction with the accompanying drawings.

[0019] Figure 1 The microstructure diagram of the embodiment of the present invention. DETAILED DESCRIPTION

[0020] The present invention is described in detail below through specific examples. The examples are only intended to help understand the present invention but are not intended to limit the present invention.

[0021] Example

[0022] According to the above steelmaking production process requirements, the actual slab chemical composition is shown in Table 1.

[0023] Table 1 Chemical composition of the present invention (wt%)

[0024]

[0025] According to the above hot rolling process requirements, the typical hot rolling thickness is 4.0 mm, and the actual process is shown in Table 2.

[0026] Table 2 Hot rolling process of the embodiment of the present invention

[0027]

[0028] According to the above cold rolling, hot dip galvanizing and skin-passing process requirements, the typical cold rolling thickness is 1.4mm, and the actual hot dip galvanizing and skin-passing process is shown in Table 3.

[0029] Table 3 Hot-dip galvanizing and skin-passing process of the embodiment of the present invention

[0030]

[0031] The mechanical properties of the steel strip according to the embodiment of the present invention were tested, and the test results are shown in Table 4.

[0032] Table 4 Mechanical properties of the steel strip in the embodiment of the present invention

[0033]

[0034] From the data in Table 4, it can be seen that the mechanical properties of the 500MPa grade galvanized dual-phase steel strip for automobile brackets of the present invention are as follows: yield strength R p0.2 : 344-364MPa, tensile strength R m : 504-553MPa, yield strength ratio: 0.66-0.68, elongation A 80 : 26.5-28.0%, n: 0.15-0.16. The steel strip product obtained by the above process has been used by users in the inner plate structural parts of the bracket in the auxiliary frame, and has suitable performance and can be promoted for use.

[0035] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for producing a 500MPa grade galvanized dual-phase steel strip for automobile brackets, characterized in that: The mass percentage of its chemical composition is C: 0.05-0.08%, Si≤0.25%, Mn: 1.5-1.8%, P≤0.020%, S≤0.015%, Alt: 0.015-0.060%, Cr: 0.01-0.25%, Ca: 0.0010-0.0030%, and the rest is Fe and unavoidable impurities; the production method is as follows: (1) Smelting-continuous casting production process: molten iron pretreatment-converter-LF refining-slab continuous casting; oxygen blowing and decarburization are carried out during the top and bottom combined blowing smelting in the converter, and aluminum iron, manganese iron, silicon iron and chromium iron are added during 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 20-40℃, and the casting speed is controlled at 1.0-1.8m / min; (2) Hot rolling production process: heating of ingot - rough rolling - finishing rolling - coiling; ingot furnace time is 160-280min, furnace temperature is 1210-1270℃, rough rolling adopts 3+3 mode 2-stand rolling mill, finishing rolling adopts 7-stand rolling mill, finishing rolling start temperature is 950-1050℃, finishing rolling final temperature is 860-910℃, hot rolled steel strip thickness is 2.5-4.8mm; cooling adopts laminar cooling equipment, coiling temperature is 540-610℃; (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 50-75% and a thickness of 0.7-2.0 mm; (4) Continuous hot-dip galvanizing and skin-passing process: The cold-hardened steel strip is unrolled and welded for continuous production. The furnace speed is 70-120 m / min, the average temperature is 790-830°C, and it is slowly cooled to 670-710°C, then cooled to 440-465°C, the temperature of entering the zinc pot is 440-470°C, the temperature of the top roller cooling tower is 190-230°C, the skin-passing elongation is 0.2-0.6%, and the straightening elongation is ≤0.4%.

2. The method for producing a 500MPa grade galvanized dual-phase steel strip for automobile brackets according to claim 1, characterized in that: The mass percentage of its chemical composition is C: 0.06-0.08%, Si 2-0.20%, Mn: 1.55-1.70%, P 0.008-0.018%, S 0.001-0.006%, Alt: 0.030-0.043%, Cr: 0.05-0.25%, Ca: 0.0010-0.0025%, and the rest is Fe and unavoidable impurities.

3. The method for producing a 500MPa grade galvanized dual-phase steel strip for automobile bracket according to claim 1, characterized in that: Hot rolled thickness 4.0mm.

4. The method for producing a 500MPa grade galvanized dual-phase steel strip for automobile bracket according to claim 3, characterized in that: Cold rolled thickness 1.4mm.

5. The method for producing a 500MPa grade galvanized dual-phase steel strip for automobile bracket according to claim 1, characterized in that: The mechanical properties of the steel strip meet the following requirements: yield strength R p0.2 : 344-364MPa, tensile strength R m : 504-553MPa, yield strength ratio: 0.66-0.68, elongation A 80 :26.5-28.0%, n: 0.15-0.16.

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