Production method of high-strength galvanized stamping steel for automobiles

Abstract

The invention discloses a production method of galvanized stamping steel for a high-strength automobile. The production method comprises the following steps: a steelmaking process; a hot rolling process; pickling and rolling; a hot galvanizing process; the steel for galvanization stamping comprises the following chemical components: 0.02 to 0.05 weight percent of C, less than or equal to 0.01 weight percent of Si, 0.20 to 0.30 weight percent of Mn, less than or equal to 0.020 weight percent of P, less than or equal to 0.010 weight percent of S, 0.020 to 0.050 weight percent of Alt, less than or equal to 0.0045 weight percent of N and the balance of Fe and inevitable impurities. The mechanical properties of the produced high-strength galvanized stamping steel strip meet the requirements of users: the yield strength is greater than or equal to 230MPa, the tensile strength is greater than or equal to 330MPa, and the percentage elongation after fracture A50mm is greater than or equal to 30.5%.

Description

Technical Field

[0001] This invention belongs to the field of material forming technology, and in particular relates to a method for producing high-strength galvanized stamping steel for automobiles. Background Technology

[0002] Galvanized stamping steel is widely used in the automotive industry and equipment manufacturing sector due to its excellent stamping performance. As the automotive industry and customers increasingly prioritize reducing vehicle weight, improving safety, lowering energy consumption, and minimizing environmental pollution, galvanized stamping steel has become a key material in automobile manufacturing. Furthermore, using higher-strength materials while maintaining part strength and rigidity can reduce the risk of wrinkling during forming and allow for appropriate reduction in sheet thickness, thus achieving vehicle body lightweighting. Customer feedback indicates that traditional DC51D+Z steel sheets exhibit wrinkling during use; investigation revealed that the wrinkled sheets were all low-strength steel sheets. To adapt to market development and meet customer needs, and considering the production situation of the manufacturing unit, product composition has been optimized. Through reasonable control of smelting, hot rolling, pickling, and hot-dip galvanizing processes, high-strength galvanized stamping steel for automobiles has been developed. Summary of the Invention

[0003] The purpose of this invention is to provide a method for producing high-strength galvanized stamping steel for automobiles. The mechanical properties of the produced high-strength galvanized stamping steel strip all meet the user requirements: yield strength ≥ 230 MPa, tensile strength ≥ 330 MPa, and elongation after fracture A. 50 mm ≥ 30.5%.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] This invention discloses a method for producing high-strength galvanized stamping steel for automobiles, comprising:

[0006] Steelmaking process: molten iron—converter smelting—RH refining—slab continuous casting;

[0007] Hot rolling process: including slab heating → high-pressure water descaling → width-fixing press → E1R1 roughing mill rolling → E2R2 roughing mill rolling → flying shear → high-pressure water descaling → F1-F7 finishing mill rolling → dense laminar flow cooling → coiling; wherein, the slab is heated in the heating furnace at a controlled temperature of 1190-1210℃; heating time of 180-240min; homogenization temperature of 1190-1220℃; homogenization time of 30-60min; furnace exit temperature of 1170-1200℃; in the hot rolling stage, the finishing rolling temperature is controlled within the range of 870-930℃, the coiling temperature within the range of 630-700℃, and a dispersed cooling method is selected;

[0008] Pickling and rolling process: pickling and uncoiling → welding → tension leveling → pickling → rinsing → drying → edge trimming → continuous rolling mill cold rolling → slitting → coiling; the reduction rate of steel strip during the pickling and rolling stage is 67-82%;

[0009] Hot-dip galvanizing process: hot-dip galvanizing uncoiling → welding → inlet looper → cleaning → annealing furnace → zinc pot → post-galvanizing cooling → water quenching → intermediate looper → finishing machine → straightening machine → roller coating machine → dryer → air cooling device → outlet looper → edge trimming → surface inspection → oiling → sampling → coiling; wherein, the heating and soaking zone outlet temperature of the annealing process is controlled at 730-770℃, and the elongation of the finishing machine is 1.10-1.30%;

[0010] The chemical composition of the galvanized stamping steel is as follows: C: 0.02-0.05wt%, Si≤0.01wt%, Mn: 0.20-0.30wt%, P≤0.020wt%, S≤0.010wt%, Alt: 0.020-0.050wt%, N≤0.0045wt%, with the remainder being Fe and unavoidable impurities.

[0011] Furthermore, the thickness of the cast billet is 230 mm.

[0012] Furthermore, the internal microstructure of the galvanized stamping steel is ferrite.

[0013] Furthermore, the mechanical properties of the high-strength galvanized stamping steel for automobiles all meet the following requirements: yield strength ≥ 230 MPa, tensile strength ≥ 330 MPa, and elongation after fracture A. 50 mm ≥ 30.5%.

[0014] Furthermore, the chemical composition of the galvanized stamping steel is as follows: C: 0.028wt%, Si: 0.005wt%, Mn: 0.23wt%, P: 0.010wt%, S: 0.006wt%, Alt: 0.034wt%, N: 0.0013wt%, with the remainder being Fe and unavoidable impurities.

[0015] Furthermore, the chemical composition of the galvanized stamping steel is as follows: C: 0.023wt%, Si: 0.006wt%, Mn: 0.25wt%, P: 0.012wt%, S: 0.006wt%, Alt: 0.033wt%, N: 0.0015wt%, with the remainder being Fe and unavoidable impurities.

[0016] Furthermore, the chemical composition of the galvanized stamping steel is as follows: C: 0.026wt%, Si: 0.006wt%, Mn: 0.26wt%, P: 0.011wt%, S: 0.005wt%, Alt: 0.028wt%, N: 0.0016wt%, with the remainder being Fe and unavoidable impurities.

[0017] Furthermore, the chemical composition of the galvanized stamping steel is as follows: C: 0.028wt%, Si: 0.006wt%, Mn: 0.24wt%, P: 0.013wt%, S: 0.006wt%, Alt: 0.030wt%, N: 0.0016wt%, with the remainder being Fe and unavoidable impurities.

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

[0019] To ensure the produced DC51D+Z steel strip possesses high strength and good stamping formability, this invention optimizes the composition design and reduces alloy costs; it also optimizes metallurgical process parameters and precisely controls hot rolling, pickling, and hot-dip galvanizing annealing processes, enabling the steel strip to achieve high strength and excellent stamping formability, preventing wrinkling of parts during stamping. Furthermore, the dense and uniform galvanized layer exhibits excellent corrosion resistance, significantly extending the service life of automotive components. The product's mechanical properties all meet the following requirements: yield strength ≥ 230 MPa, tensile strength ≥ 330 MPa, and elongation after fracture A… 50 mm ≥ 30.5%. Attached Figure Description

[0020] The present invention will be further described below with reference to the accompanying drawings.

[0021] Figure 1 The metallographic structure of the finished product in Example 1. Detailed Implementation

[0022] To address users' actual needs for high-strength galvanized stamping steel for automobiles, this invention provides a method for producing such steel that meets user requirements. The method includes:

[0023] 1. Smelting process

[0024] 1.1 Desulfurization pretreatment: KR hot metal desulfurization technology is adopted. It is required that the sulfur content at the end point after deep desulfurization is within 0.005%. KR desulfurization is carried out by mechanical stirring. After desulfurization, the desulfurization slag is completely removed. The area of ​​hot metal slag removal is required to be greater than 95% to prevent high sulfur slag from being added into the converter and causing sulfur reversion.

[0025] 1.2 Converter Smelting: After desulfurization pretreatment, molten iron is smelted in a converter. The phosphorus content of the molten iron entering the converter is ≤0.018%. Oxygen blowing is used for decarburization and temperature rise, and the P and S content is controlled to prevent over-oxidation of the molten steel. The final temperature of the converter is controlled above 1660℃. Steel must be tapped using a reusable ladle, and the temperature drop at tapping must be less than 70℃. During the tapping process, quicklime and modifiers are added to modify the top slag.

[0026] 1.3 Refining: The RH refining furnace performs decarburization treatment based on the composition and temperature of the molten steel. After decarburization, deoxidizer and aluminum are added according to the oxygen content. After circulating for more than 4 minutes, alloys such as ferromanganese are added to adjust the composition. The pure degassing time is guaranteed to be more than 6 minutes to ensure the uniformity of the temperature and composition of the molten steel, and at the same time, it is conducive to the flotation of inclusions in the molten steel, thereby improving the cleanliness of the molten steel.

[0027] 1.4 Continuous Casting: Continuous casting is a protective process to prevent secondary oxidation of the molten steel and to avoid secondary oxidation of the steel quality. A constant casting speed is adopted, controlled at 1.0-1.8 m / min, and the superheat is controlled appropriately during casting, maintaining a superheat of approximately 20-45℃ to promote the flotation of inclusions and enabling multi-furnace casting.

[0028] 2. Hot rolling process

[0029] The billet is heated by a walking beam furnace (heating process is shown in Table 1). The roughing rolling adopts a double-stand R1 and R2 reciprocating rolling process with a 3+5 roughing mode. The finishing rolling adopts a continuous rolling process of F1-F7 with a finishing rolling temperature of 870-930℃ to ensure rolling in the single-phase austenite region. The coiling temperature is 630-700℃, and low-temperature coiling is used to improve the strength of the steel strip. The specific hot rolling process is shown in Table 2.

[0030] Table 1 Heating Regime for Cast Billets

[0031]

[0032] Table 2 Rolling Process

[0033]

[0034] 3. Pickling and rolling process

[0035] The reduction rate of steel strip during the pickling and rolling stage ranges from 67% to 82%.

[0036] 4. Hot-dip galvanizing process

[0037] Annealing is performed in a vertical continuous annealing furnace, with a reducing atmosphere and a nitrogen-hydrogen mixed protective atmosphere used for cooling. The temperature range of the heating and soaking sections is 730-770℃ to ensure complete recrystallization of the grains. See Table 3 for the specific hot-dip galvanizing process.

[0038] Table 3 Hot-dip galvanizing process

[0039]

[0040] 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.

[0041] Example

[0042] 1. Based on the above steelmaking process requirements, the actual chemical composition (mass percentage) of the slab is shown in Table 4 below.

[0043] Table 4. Chemical composition (wt.%) of examples

[0044]

[0045]

[0046] 2. According to the above hot rolling process requirements, the hot rolling thickness is 3.5-3.8mm. The actual process is shown in Table 5.

[0047] Table 5 Hot Rolling Process

[0048]

[0049] 3. According to the above hot-dip galvanizing process requirements, the finished product thickness is 0.7-0.8mm. The actual process is shown in Table 6.

[0050] Table 6 Hot-dip galvanizing process

[0051]

[0052] 4. The room temperature tensile mechanical properties of representative steel strip products obtained through the above process are shown in Table 7. The test methods refer to GB / T 228.1. The microstructure of the finished product is equiaxed ferrite, and the microstructure morphology is shown in Table 7. Figure 1 .

[0053] Table 7. Tensile mechanical properties of finished products at room temperature

[0054]

[0055] In summary, the products obtained through the above process meet the performance requirements after performance testing, have suitable strength, and can be widely used.

[0056] 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 high-strength galvanized stamping steel for automobiles, characterized in that, include: Steelmaking process: molten iron—converter smelting—RH refining—slab continuous casting; Hot rolling process: including slab heating → high-pressure water descaling → width-fixing press → E1R1 roughing mill rolling → E2R2 roughing mill rolling → flying shear → high-pressure water descaling → F1-F7 finishing mill rolling → dense laminar flow cooling → coiling; wherein, the slab is heated in the heating furnace at a controlled temperature of 1190-1210℃; heating time of 180-240min; homogenization temperature of 1190-1220℃; homogenization time of 30-60min; furnace exit temperature of 1170-1200℃; in the hot rolling stage, the finishing rolling temperature is controlled within the range of 870-930℃, the coiling temperature within the range of 630-700℃, and a dispersed cooling method is selected; Pickling and rolling process: pickling and uncoiling → welding → tension leveling → pickling → rinsing → drying → edge trimming → continuous rolling mill cold rolling → slitting → coiling; the reduction rate of steel strip during the pickling and rolling stage is 67-82%; Hot-dip galvanizing process: hot-dip galvanizing uncoiling → welding → inlet looper → cleaning → annealing furnace → zinc pot → post-galvanizing cooling → water quenching → intermediate looper → finishing machine → straightening machine → roller coating machine → dryer → air cooling device → outlet looper → edge trimming → surface inspection → oiling → sampling → coiling; wherein, the heating and soaking zone outlet temperature of the annealing process is controlled at 730-770℃, and the elongation of the finishing machine is 1.10-1.30%; The chemical composition of the galvanized stamping steel is as follows: C: 0.02-0.05wt%, Si≤0.01wt%, Mn: 0.20-0.30wt%, P≤0.020wt%, S≤0.010wt%, Alt: 0.020-0.050wt%, N≤0.0045wt%, with the remainder being Fe and unavoidable impurities.

2. The method for producing high-strength galvanized stamping steel for automobiles according to claim 1, characterized in that, The thickness of the cast billet is 230mm.

3. The method for producing high-strength galvanized stamping steel for automobiles according to claim 1, characterized in that, The internal microstructure of the galvanized stamping steel is ferrite.

4. The method for producing high-strength galvanized stamping steel for automobiles according to claim 1, characterized in that, The mechanical properties of the high-strength galvanized stamping steel for automobiles all meet the following requirements: yield strength ≥ 230 MPa, tensile strength ≥ 330 MPa, and elongation after fracture A. 50 mm ≥ 30.5%.

5. The method for producing high-strength galvanized stamping steel for automobiles according to claim 1, characterized in that, The chemical composition of the galvanized stamping steel is as follows: C: 0.028wt%, Si: 0.005wt%, Mn: 0.23wt%, P: 0.010wt%, S: 0.006wt%, Alt: 0.034wt%, N: 0.0013wt%, with the remainder being Fe and unavoidable impurities.

6. The method for producing high-strength galvanized stamping steel for automobiles according to claim 1, characterized in that, The chemical composition of the galvanized stamping steel is as follows: C: 0.023wt%, Si: 0.006wt%, Mn: 0.25wt%, P: 0.012wt%, S: 0.006wt%, Alt: 0.033wt%, N: 0.0015wt%, with the remainder being Fe and unavoidable impurities.

7. The method for producing high-strength galvanized stamping steel for automobiles according to claim 1, characterized in that, The chemical composition of the galvanized stamping steel is as follows: C: 0.026wt%, Si: 0.006wt%, Mn: 0.26wt%, P: 0.011wt%, S: 0.005wt%, Alt: 0.028wt%, N: 0.0016wt%, with the remainder being Fe and unavoidable impurities.

8. The method for producing high-strength galvanized stamping steel for automobiles according to claim 1, characterized in that, The chemical composition of the galvanized stamping steel is as follows: C: 0.028wt%, Si: 0.006wt%, Mn: 0.24wt%, P: 0.013wt%, S: 0.006wt%, Alt: 0.030wt%, N: 0.0016wt%, with the remainder being Fe and unavoidable impurities.

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