An anti-aging aluminum killed deep drawing electroplated zinc product and its production method

Abstract

This invention discloses an anti-aging aluminum killed deep-drawing electro-galvanized product and its production method. It employs a low-carbon chemical composition design to meet the quality requirements of anti-aging aluminum killed deep-drawing electro-galvanized DC04 products. It can manufacture high-strength, low-cost, high-surface-quality anti-aging aluminum killed deep-drawing electro-galvanized DC04 products with processing performance meeting automotive component requirements, without the need for adding precious metals such as Ti and Nb. This is achieved by controlling the appropriate mass percentages of carbon and manganese and the matching relationship of nitrogen, supplemented by a suitable process flow. The product exhibits stable performance, high r-value, high elongation, and no tensile strain marks. It also solves the technical problems of traditional processes, such as long yield plateaus, narrow process windows, difficulty in controlling the solid solution C content, and large strength fluctuations. Furthermore, it overcomes the defect of tensile strain marks appearing during stamping and forming. Simultaneously, it improves the pass rate of high-grade outer sheet stamping and is easy to promote and apply industrially.

Description

Technical Field

[0001] This invention belongs to the field of metal processing technology, specifically relating to an anti-aging aluminum killed deep drawing electroplated zinc product and its production method. Background Technology

[0002] Low-carbon deep-drawing aluminum-killed steel sheet DC04 is primarily produced using a bell-type annealing furnace. However, bell-type annealing furnaces are prone to surface adhesion, uneven performance, and poor sheet shape, failing to meet the high surface quality requirements of electroplating for high-end automotive applications. According to EN 10152-2017, the aging period for low-carbon non-IF steel is three months, meaning that stamping within three months of production should not result in machining strain marks. Due to the short continuous annealing time, dissolved carbon remains in the crystal lattice after annealing; this can easily lead to machining strain marks caused by aging during subsequent processing. It is understood that there is currently no precedent in China for the continuous annealing production of aluminum-killed steel DC04; all high-end deep-drawing automotive steels utilize continuous annealing processes combined with IF steel composition design.

[0003] Because existing technologies cannot meet the high surface quality and deep-drawing requirements of electroplating for high-end automobiles, tensile strain marks appear, posing a technical problem that affects the surface quality of the outer panel. Therefore, there is an urgent need for a production method for anti-aging deep-drawing aluminum-killed steel DC04 electroplated zinc products that is suitable for industrial production, easy to control, and can reduce costs and increase efficiency for enterprises. Summary of the Invention

[0004] To overcome the shortcomings of the existing technology, the present invention aims to provide a manufacturing process for anti-aging aluminum killed deep drawing electro-galvanized DC04 products. This method adopts a smelting process of converter + RH + continuous casting billet + hot rolling + cold rolling + annealing + leveling + electroplating to produce aluminum killed deep drawing electro-galvanized DC04 products. This process ensures both the mechanical properties of aluminum killed deep drawing electro-galvanized DC04 and good anti-aging ability, making it easy for large-scale industrial production.

[0005] To achieve the above-mentioned objectives, this invention provides a composition design and process design for an anti-aging aluminum killed deep-drawing electroplated zinc DC04 product. The specific process steps are as follows: Raw materials: (steelmaking process) molten iron pretreatment → converter smelting → (LF+RH) refining → continuous casting → (hot continuous rolling process) billet heating → rough rolling → finish rolling → controlled cooling → hot rolling coiling → (cold rolling process) hot rolling coil uncoiling → pickling, cold continuous rolling → coiling → cold hardened coil uncoiling → continuous annealing → leveling → electroplating → finishing → surface and functional inspection.

[0006] The chemical composition of the anti-aging aluminum-killed deep-drawing electroplated zinc product, by mass percentage, is: C: 0.005-0.02%, Mn: 0.10-0.70%, Si≤0.02%, Al: 0.020-0.050%, Nb+V+Ti: not more than 0.01%, P not more than 0.015%, S not more than 0.015%, N not more than 0.0030%, O not more than 0.0030%. It does not contain strong carbon and nitrogen-binding elements such as Nb, V, and Ti, or precious elements such as Mo and Cr. The remainder is Fe and unavoidable impurities.

[0007] A method for producing the above-mentioned anti-aging aluminum killed deep-drawing electro-galvanized product further includes controlling the process parameters in the continuous casting process as follows: platform temperature 1560±5℃, tundish temperature 1540℃~1550℃, ensuring that the superheat of the continuous casting billet is controlled to be less than 25℃ during production, casting speed 0.8~1.0 / min, reducing liquid surface fluctuations and controlling the depth of oscillation marks; the output is a rectangular continuous casting billet.

[0008] In the above technical solution, further, in the hot rolling process, the low-temperature heating is ≤1200℃, the preheating section is 880±20℃, the heating section is 1100±20℃, and the soaking section is 1180±20℃, with a heating time of 2.5-3 hours. This ensures uniform heating of the slab, high temperature control accuracy, and overall slab temperature difference controlled within ±30℃. To guarantee the surface quality of the steel, the furnace atmosphere (weak oxidizing atmosphere) is strictly controlled during heating, maintaining the final rolling temperature between 890 and 930℃. A reduction ratio distribution system is adopted, with a large reduction ratio in the intermediate mills and a small reduction ratio in the end mills. Finishing mills F1-F7 are equipped with automatic thickness control (AGC) devices to effectively control the strip thickness accuracy. Low-temperature heating and high-pressure descaling water ensure minimal primary iron oxide scale formation, improving product surface quality.

[0009] In the above technical solution, furthermore, in the high-temperature coiling process, the material is conventionally water-cooled to the coiling temperature and then coiled, followed by slow cooling storage in a warehouse, with the coiling temperature controlled between 710 and 750°C. High-temperature coiling combined with slow cooling storage in the warehouse allows AlN to precipitate as large particles at the grain boundaries, rather than being dissolved within the grain boundaries. This reduces the pinning effect on the grain boundaries, promoting the formation of coarse grains and ensuring the deep-drawing performance of the material. Furthermore, it reduces the solid solution of N, ensuring the material's resistance to aging.

[0010] In the above technical solution, further, in the pickling and cold rolling processes, the acid solution temperature is controlled at 65-75℃, the free acid concentration in the No. 1 pickling tank is controlled at 50-80g / L, the free acid concentration in the No. 2 pickling tank is controlled at 80-120g / L, and the free acid concentration in the No. 3 pickling tank is controlled at 120-160g / L; the pickling speed is 80-220m / min; the total cold rolling reduction rate is controlled at ≥75%; the five-stand full six-roll cold continuous rolling is carried out, and the reduction is distributed according to 30%, 22%, 20%, 16%, and 12%.

[0011] Furthermore, in the above technical solution, during the continuous annealing process, the annealing temperature is controlled at 830–850℃, and the annealing speed is controlled at 100–180 m / min. High-temperature annealing ensures the precipitation of Fe3C at the grain boundaries, reduces the solid solution of C, and is beneficial to deep drawing performance and aging.

[0012] In the above technical solution, further, in the cooling process, the temperature is first slowly cooled to 680℃ at a cooling rate of 9-11℃ / s; then rapidly cooled to 420℃ at a cooling rate of 25-40℃ / s; aged at 410-430℃ for 400-1000s; and finally cooled to 160-180℃.

[0013] In the above technical solution, further, in the leveling process, the smoothing elongation rate of the leveling machine is controlled to be 0.6-1.1%.

[0014] In the above technical solution, furthermore, in the alkaline washing, brushing, electrolytic degreasing and rinsing processes, the temperature of the degreasing solution is controlled at 45-75℃, and the pH of the degreasing solution is ≥9.5.

[0015] In the above technical solution, furthermore, the electroplating process adopts gravity electroplating of zinc, the electroplating solution is zinc sulfate solution, the concentration of zinc sulfate in the electroplating solution is 100-120 g / L, the pH value is 1.3-1.8, the temperature of the electroplating solution is 50-60℃, and the running speed of the steel plate in the electroplating tank is 80-140 m / min; the target thickness of the zinc layer can be controlled according to user requirements, ranging from 10-90 g / m. 2 The zinc plating amount in each electroplating tank is evenly distributed according to the thickness to ensure uniform zinc layer and reduce energy consumption.

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

[0017] ① The chemical composition is designed using low-carbon (aluminum-killed steel). By controlling the C content, stable interstitial carbon atoms are generated, and large AlN particles precipitate at the grain boundaries, reducing N solid solution and ultimately achieving stable aging performance, which is easy to control. The product has stable performance, high r-value, high elongation, and no tensile strain marks, improving the pass rate of high-grade outer plate stamping.

[0018] ② Reasonable composition design and production process ensure surface quality. The finished steel has a uniform microstructure of ferrite and trace cementite. Through high-temperature annealing, the supersaturated solid solution C combines with Fe to precipitate trace amounts of Fe3C at the grain boundaries, and the grains contain trace amounts of interstitial solid solution C. N atoms fully combine with Al (excess) to form AlN. Under the slow cooling of hot-rolled high-temperature coiling, AlN precipitates as large-sized aluminum nitride particles at the grain boundaries, inhibiting the formation of solid solution AlN, ensuring the plasticity of the product, and also inhibiting solid solution N atoms. This reduces the C / N atom ratio in the grains, ensuring stable room-temperature aging, inhibiting the formation of yield plateaus, and suppressing the existence of tensile strain marks. The non-metallic inclusions and gas content meet the surface quality requirements of high-end automotive products. Attached Figure Description

[0019] Figure 1 Metallographic microstructure of the anti-aging aluminum killed deep drawing electroplated zinc product prepared for the example;

[0020] Figure 2 This is a schematic diagram of temperature control in the annealing cooling process of an embodiment. Detailed Implementation

[0021] The present invention will be further described below with reference to specific embodiments, but this does not limit the invention in any way. To avoid redundancy, unless otherwise specified, all raw materials used in the following embodiments are commercially available and of industrial grade; all methods used are conventional methods unless otherwise specified. The chemical composition testing standard is GB / T 223: Metallic materials, tensile testing—Part 1: Tensile testing at room temperature—and GB / T 228.1.

[0022] The example uses anti-aging aluminum killed deep drawing electro-galvanized DC04 with a thickness of 0.80 mm for automotive outer panels. Its chemical composition and mass percentage are shown in Table 1.

[0023] Table 1. Chemical composition of steel in the examples.

[0024]

[0025] The chemical composition (wt%) of the above-mentioned anti-aging aluminum-killed deep-drawing electroplated zinc products meets the requirements: C: 0.005-0.02%, Mn: 0.10-0.70%, Si≤0.02%, Al: 0.020-0.050%, Nb+V+Ti: not greater than 0.01%, P not greater than 0.015%, S not greater than 0.015%, N not greater than 0.0030%, O not greater than 0.0030%. No strong carbon and nitrogen-binding elements such as Nb, V, and Ti, or precious elements such as Mo and Cr are added. The remainder is Fe and unavoidable impurities.

[0026] Example

[0027] A production method for anti-aging aluminum killed deep-drawing electro-galvanized products includes steelmaking, continuous casting, slab heating, hot rolling, laminar flow cooling, pickling, continuous annealing, and leveling processes. The specific process steps and parameters are as follows:

[0028] Continuous casting: Platform temperature 1560±5℃, tundish temperature 1540℃~1550℃, ensuring the superheat of the continuously cast billet is controlled to be less than 25℃ during production, casting speed 0.8~1.0 / min, reducing liquid level fluctuations and controlling oscillation mark depth. The output is a rectangular continuously cast billet.

[0029] Low-temperature heating ≤1200℃, preheating section 880±20℃, heating section 1100±20℃, soaking section 1180±20℃, heating time 2.5 hours to 3 hours. The slab is heated uniformly with high temperature control accuracy; the overall temperature difference of the slab can be controlled within ±30℃. To ensure the surface quality of the steel, the furnace atmosphere (weak oxidizing atmosphere) is strictly controlled during heating, maintaining the final rolling temperature between 890 and 930℃. A reduction ratio distribution system is adopted, with a larger reduction ratio in the intermediate mills and a smaller reduction ratio in the end mills. Finishing mills F1 to F7 are equipped with automatic thickness control (AGC) devices to effectively control the strip thickness accuracy.

[0030] High-temperature coiling, conventional water cooling to the coiling temperature and then coiling, slow cooling storage in the warehouse, controlling the coiling temperature at 710~750℃;

[0031] Pickling and cold rolling are performed. The acid solution temperature is controlled at 65-75℃, the free acid concentration in acid bath #1 is controlled at 50-80g / L, the free acid concentration in acid bath #2 is controlled at 80-120g / L, and the free acid concentration in acid bath #3 is controlled at 120-160g / L; the pickling speed is 80-220m / min; the total cold rolling reduction rate is controlled at ≥75%; five-stand full six-roll cold continuous rolling is performed, with the reduction amount allocated at 30%, 22%, 20%, 16%, and 12%.

[0032] Perform continuous annealing, controlling the annealing temperature at 830–850℃ and the annealing speed at 100–180 m / min;

[0033] The cooling process is as follows: first, slowly cool to 680℃ at a cooling rate of 9-11℃ / s; then rapidly cool to 440-470℃ at a cooling rate of 30℃ / s; perform an aging treatment at 400-440℃ for 400-1000s; finally, cool to 170℃.

[0034] The surface is leveled on a leveling machine, and the finishing elongation is controlled to be 0.6-1.1%.

[0035] Perform routine alkaline washing, brushing, electrolytic degreasing and rinsing. The temperature of the degreasing solution is controlled at 45-75℃ and the pH of the degreasing solution is ≥9.5.

[0036] Gravity electroplating is used for zinc plating. The plating solution is zinc sulfate solution with a concentration of 100–120 g / L, a pH value of 1.3–1.8, and a temperature of 50–60℃. The running speed of the steel plate in the electroplating tank is 80–140 m / min. The target zinc layer thickness can be controlled according to user requirements, ranging from 10–90 g / m. 2 .

[0037] Table 2 Process control parameters for each example steel

[0038]

[0039] Table 3. Performance test results of steel in each example.

[0040]

[0041] The anti-aging aluminum killed deep-drawing electro-zinc products described in the above embodiments employ a low-carbon chemical composition design, meeting the quality requirements of anti-aging aluminum killed deep-drawing electro-zinc DC04 products. They can manufacture high-strength, low-cost, high-surface-quality anti-aging aluminum killed deep-drawing electro-zinc DC04 products with processing performance meeting automotive component requirements, without the need for adding precious metals such as Ti and Nb. This is achieved by controlling the appropriate mass percentages of carbon and manganese and the matching relationship of nitrogen, supplemented by suitable process flows. The products exhibit stable performance, high r-value, high elongation, and no tensile strain marks. They also solve the technical problems of long yield plates, narrow process windows, difficulty in controlling solid solution C content, and large strength fluctuations inherent in traditional processes. Furthermore, they overcome the defect of tensile strain marks appearing during stamping and forming. Simultaneously, they improve the pass rate of high-grade outer sheet stamping and are easy to promote and apply industrially.

[0042] The performance test results of the example steel show that it has no yield plateau in yield strength, and the aging time is 4 months, which exceeds the requirement of ≥3 months. There are no tensile strain marks after stamping. Other performance indicators also meet the standard requirements for high-depth drawing automotive steel.

[0043] For anyone skilled in the art, many possible variations and modifications can be made to the technical solutions of this invention, or equivalent embodiments can be modified based on the disclosed technical content, without departing from the scope of the technical solutions of this invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of this invention without departing from the content of the technical solutions of this invention should still fall within the protection scope of the technical solutions of this invention.

Claims

1. A method for producing anti-aging aluminum killed deep-drawing electroplated zinc products, characterized in that, The process parameters for continuous casting are controlled as follows: platform temperature 1560±5℃, tundish temperature 1540℃~1550℃, and the superheat of the continuous casting billet is controlled to be less than 25℃ during production. The casting speed is 0.8~1.0m / min to reduce liquid surface fluctuation and control the depth of oscillation marks. The output is a rectangular continuous casting billet. In the hot rolling process, the low-temperature heating is ≤1200℃, the preheating section is 880±20℃, the heating section is 1100±20℃, and the soaking section is 1180±20℃. The heating time is 2.5~3h, and the overall temperature difference of the slab is controlled within ±30℃. During heating, the atmosphere in the furnace is controlled to be a weakly oxidizing atmosphere, and the final rolling temperature is controlled to be 890℃~930℃. A reduction ratio distribution system with a large reduction ratio in the intermediate mills and a small reduction ratio in the end mills is adopted. The finishing mills F1~F7 are equipped with automatic thickness control devices (AGC) to effectively control the thickness accuracy of the strip. In the high-temperature winding process, the winding temperature is conventionally cooled to the winding temperature and then wound up. The winding is then slowly cooled and stored in the warehouse, with the winding temperature controlled at 710℃~750℃. In the pickling and cold rolling processes, the acid solution temperature is 65℃~75℃, the free acid concentration in pickling tank #1 is 50~80g / L, the free acid concentration in pickling tank #2 is 80~120g / L, and the free acid concentration in pickling tank #3 is 120~160g / L; the pickling speed is 80~220m / min; the total reduction rate in cold rolling is controlled to be ≥75%; five-stand full six-roll cold continuous rolling is carried out, and the reduction is allocated according to 30%, 22%, 20%, 16%, and 12%; In the continuous annealing process, the annealing temperature is controlled at 830℃~850℃ and the annealing speed is 100~180m / min; In the cooling process, the temperature is first slowly cooled to 680℃ at a rate of 9–11℃ / s; then rapidly cooled to 420℃ at a rate of 25–40℃ / s; aged at 410℃–430℃ for 400–1000s; and finally cooled to 160℃–180℃. In the leveling process, the finishing elongation rate of the leveling machine is controlled to be 0.6% to 1.1%; During the alkaline washing, brushing, electrolytic degreasing and rinsing processes, the temperature of the degreasing solution is controlled at 45℃~75℃, and the pH of the degreasing solution is ≥9.

5. The electroplating process employs gravity electroplating of zinc. The electroplating solution is zinc sulfate solution with a zinc sulfate concentration of 100–120 g / L, a pH value of 1.3–1.8, and a solution temperature of 50℃–60℃. The running speed of the steel plate in the electroplating bath is 80–140 m / min. The target zinc layer thickness is controlled within the range of 10–90 g / m. 2 ; The chemical composition (mass percentage) of the anti-aging aluminum-killed deep-drawing electroplated zinc product is as follows: C: 0.005%–0.02%, Mn: 0.10%–0.70%, Si ≤ 0.02%, Al: 0.020%–0.050%, Nb+V+Ti: Not more than 0.01%, P not more than 0.015%, S not more than 0.015%, N not more than 0.0030%, O not more than 0.0030%, the remainder being Fe and unavoidable impurities; The aging-resistant aluminum-killed deep-drawing electroplated zinc product has a yield strength of 140–210 MPa, a tensile strength ≥270 MPa, and an elongation of A. 80 ≥38%, n 90 Value ≥ 0.18, r 90 Value ≥ 1.6, delivery time ≥ 3 months.

Images