A production method of high-elongation zinc-aluminum-magnesium plated steel strip

Abstract

This invention discloses a method for producing high-elongation zinc-aluminum-magnesium coated steel strip, including hot rolling, cold rolling, degreasing, annealing, hot-dip zinc-aluminum-magnesium coating, cooling, and finishing and straightening processes; comprising a substrate and a coating; the chemical composition of the substrate, by mass percentage, is: C: 0.008-0.06%, Si≤0.03%, Mn: 0.10-0.20%, P≤0.015%, S≤0.012%, Als: 0.020-0.060%, Ti: 0.030-0.070%, N≤0.0040%, with the remainder being Fe and unavoidable impurities; the chemical composition of the coating, by mass percentage, is: Al: 1.1-2.5%, Mg: 1.1-1.8%, with the balance being Zn and trace amounts of unavoidable impurities. This invention achieves grain coarsening through substrate composition optimization and process control, thereby obtaining high elongation while maintaining the inherent high corrosion resistance of the zinc-aluminum-magnesium coating.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, and particularly relates to a method for producing high elongation zinc-aluminum-magnesium coated steel strip. Background Technology

[0002] With the rapid development of photovoltaic power generation, high-end home appliances, and automobile manufacturing, the market demand for high-performance coated steel sheets is increasing. Zinc-aluminum-magnesium coated steel sheets have attracted widespread attention due to their excellent corrosion resistance, which can be 10-20 times that of ordinary galvanized sheets. In particular, the cut surfaces have self-healing anti-corrosion properties.

[0003] Currently, while conventional zinc-aluminum-magnesium coated steel sheets offer excellent corrosion resistance, they typically have high strength but relatively insufficient elongation. The elongation after fracture of ordinary zinc-aluminum-magnesium steel strips is generally between 10% and 17%, which is insufficient to meet the demands of deep drawing processes with extremely high formability requirements. Although existing technologies can improve elongation by using ultra-low carbon materials and high-temperature annealing processes, this method is costly, energy-intensive, and prone to deteriorating the surface quality of the coating.

[0004] Furthermore, high aluminum and magnesium content in zinc-aluminum-magnesium coatings can increase coating brittleness, making them prone to microcracks after bending. Meanwhile, defects such as zinc ash and zinc slag on the coating surface also affect its application in high-end fields. Therefore, developing a zinc-aluminum-magnesium coated steel strip that combines high elongation, excellent coating surface quality, and good processing performance is of significant practical importance. Summary of the Invention

[0005] The purpose of this invention is to provide a method for producing high-elongation zinc-aluminum-magnesium coated steel strip. By optimizing the substrate composition and controlling the process, grain coarsening is achieved, thereby obtaining high elongation while maintaining the inherent high corrosion resistance of the zinc-aluminum-magnesium coating.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] This invention discloses a method for producing high-elongation zinc-aluminum-magnesium coated steel strip, comprising hot rolling, cold rolling, degreasing, annealing, hot-dip zinc-aluminum-magnesium coating, cooling, and finishing and straightening processes; specifically:

[0008] Hot rolling process: The slab heating temperature is 1130~1200℃, the final rolling temperature is 900~970℃, and a higher coiling temperature of 740~800℃ is adopted to facilitate grain coarsening of hot-rolled plates and control of carbonitride precipitation morphology.

[0009] Cold rolling process: High cold rolling reduction rate is adopted and controlled at 70% to 90% to provide high energy storage for subsequent recrystallization annealing and promote recrystallization grain growth;

[0010] Annealing process: A relatively high annealing temperature of 800-860℃ is adopted, and the unit tension of the strip in the furnace is controlled at 4-7 N / mm² to promote full recrystallization and coarsening of grains, while developing a favorable {111} texture.

[0011] Hot-dip galvanizing process: Precisely control the temperature of the zinc pot to 430~470℃, so that the deviation from the temperature of the plating solution (420~460℃) is ≤10℃, reduce thermal shock, and ensure the adhesion of the coating; control the dew point of the atmosphere inside the furnace nose to -10~20℃;

[0012] Cooling process: Segmented cooling control is adopted. From 460℃ to 340℃, a slower cooling rate of 15-30℃ / s is used to reduce the internal stress of the coating; from 340℃ to 200℃, a faster cooling rate of 30-40℃ / s is used to suppress the excessive formation of brittle phases in the coating.

[0013] Finishing and straightening process: The finishing elongation is controlled at 0.1% to 0.9%, and the total straightening elongation is ≤0.3% to eliminate the yield plateau, improve the plate shape, and avoid excessive work hardening.

[0014] The zinc-aluminum-magnesium coated steel strip includes a substrate and a coating; wherein

[0015] The chemical composition of the substrate, by mass percentage, is as follows: C: 0.008–0.06%, Si ≤ 0.03%, Mn: 0.10–0.20%, P ≤ 0.015%, S ≤ 0.012%, Als: 0.020–0.060%, Ti: 0.030–0.070%, N ≤ 0.0040%, with the remainder being Fe and unavoidable impurities;

[0016] The chemical composition of the coating, by mass percentage, is: Al: 1.1-2.5%, Mg: 1.1-1.8%, with the balance being Zn and trace amounts of unavoidable impurities.

[0017] Furthermore, the chemical composition of the substrate, by mass percentage, is as follows: C: 0.008%, Si: 0.02%, Mn: 0.20%, P: 0.010%, S: 0.008%, Als: 0.045%, Ti: 0.050%, N: 0.0035%, with the remainder being Fe and unavoidable impurities.

[0018] Furthermore, the chemical composition of the coating, by mass percentage, is: Al: 2.2%, Mg: 1.5%, with the balance being Zn and trace impurities.

[0019] Furthermore, the specific steps include:

[0020] (1) Hot rolling process: slab heating temperature 1150℃, final rolling temperature 950℃, coiling temperature 760℃;

[0021] (2) Cold rolling process: cold rolling reduction rate of 85%, rolling thickness of 0.8 mm;

[0022] (3) Degreasing and cleaning process: the temperature of the bath solution is 60℃ and the free alkalinity of the alkaline solution in the degreasing bath is 70 points;

[0023] (4) Annealing process: Annealing temperature 830℃, furnace tension 5.5N / mm²;

[0024] (5) Hot-dip galvanizing process: zinc pot temperature 450℃, plating solution temperature 440℃, furnace nose dew point 5℃;

[0025] (6) Cooling process: 460-340℃ cooling rate 20℃ / s, 340-200℃ cooling rate 35℃ / s;

[0026] (7) Finishing and straightening: Finishing elongation rate 0.5%, straightening elongation rate 0.2%.

[0027] Furthermore, the specific steps include:

[0028] (1) Hot rolling process: slab heating temperature 1180℃, final rolling temperature 940℃, coiling temperature 780℃;

[0029] (2) Cold rolling process: cold rolling reduction rate of 80%, rolling thickness of 1.2mm;

[0030] (3) Degreasing and cleaning process: the temperature of the bath solution is 55℃ and the free alkalinity of the alkaline solution in the degreasing bath is 75 points;

[0031] (4) Annealing process: Annealing temperature 850℃, furnace tension 5.0N / mm²;

[0032] (5) Hot-dip galvanizing process: zinc pot temperature 440℃, plating solution temperature 435℃, furnace nose dew point 10℃;

[0033] (6) Cooling process: 460-340℃ cooling rate 25℃ / s, 340-200℃ cooling rate 32℃ / s;

[0034] (7) Finishing and straightening: Finishing elongation rate 0.7%, straightening elongation rate 0.25%.

[0035] Furthermore, the chemical composition of the substrate, by mass percentage, is: C: 0.05%, Si: 0.025%, Mn: 0.15%, P: 0.012%, S: 0.010%, Als: 0.035%, Ti: 0.045%, N: 0.0038%, with the remainder being Fe and unavoidable impurities; the chemical composition of the coating, by mass percentage, is: Al: 1.8%, Mg: 1.3%, with the balance being Zn and trace impurities.

[0036] Furthermore, the specific steps include:

[0037] (1) Hot rolling process: slab heating temperature 1160℃, final rolling temperature 960℃, coiling temperature 770℃;

[0038] (2) Cold rolling process: cold rolling reduction rate of 82%, rolling thickness of 1.0 mm;

[0039] (3) Degreasing and cleaning process: the temperature of the bath solution is 65℃ and the free alkalinity of the alkaline solution in the degreasing bath is 68 points;

[0040] (4) Annealing process: Annealing temperature 840℃, furnace tension 4.8N / mm²;

[0041] (5) Hot-dip galvanizing process: zinc pot temperature 445℃, plating solution temperature 438℃, furnace nose dew point 8℃;

[0042] (6) Cooling process: 460-340℃ cooling rate 22℃ / s, 340-200℃ cooling rate 38℃ / s;

[0043] (7) Finishing and straightening: Finishing elongation rate 0.6%, straightening elongation rate 0.22%.

[0044] Furthermore, the chemical composition of the substrate, by mass percentage, is: C: 0.035%, Si: 0.015%, Mn: 0.18%, P: 0.009%, S: 0.006%, Als: 0.050%, Ti: 0.055%, N: 0.0032%, with the remainder being Fe and unavoidable impurities; the chemical composition of the coating, by mass percentage, is: Al: 2.0%, Mg: 1.6%, with the balance being Zn and trace impurities.

[0045] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0046] High elongation: Through the synergistic process of "Ti microalloying (fixing C and N interstitial atoms) + high winding temperature + high cold rolling reduction + high annealing temperature + low tension", the matrix grains are effectively coarsened and a strong {111} recrystallization texture is developed, so that the elongation after fracture (A80) of the product can stably reach more than 30%, which is much higher than that of conventional zinc-aluminum-magnesium products (10%-17%), meeting the requirements of deep drawing.

[0047] Excellent corrosion resistance: It retains the inherent high corrosion resistance of zinc-aluminum-magnesium coating, and can withstand up to 3000 hours of neutral salt spray test without red rust.

[0048] Low cost and low energy consumption: The substrate uses low carbon components, which reduces the requirements for steelmaking raw materials; although the annealing temperature is relatively high, it is far lower than the annealing temperature required for producing ultra-low carbon IF steel, and the overall energy consumption and production cost are effectively controlled.

[0049] Excellent coating surface quality: By controlling the pot temperature, dew point and cooling process, surface defects (such as zinc ash and zinc dross) and microcracks in the coating are reduced, resulting in excellent product surface quality suitable for high-end applications such as subsequent color coating. Detailed Implementation

[0050] The present invention will be described in more detail below through specific embodiments. These embodiments are merely descriptions of the best mode of implementation and do not limit the scope of the invention in any way.

[0051] Example 1

[0052] The chemical composition and mass percentage of the high elongation zinc-aluminum-magnesium coated steel strip in this embodiment are as follows: C: 0.008%, Si: 0.02%, Mn: 0.20%, P: 0.010%, S: 0.008%, Als: 0.045%, Ti: 0.050%, N: 0.0035%, with the remainder being Fe and unavoidable impurities.

[0053] Coating composition: Al: 2.2%, Mg: 1.5%, balance is Zn and trace impurities.

[0054] The production method in this embodiment includes the following steps:

[0055] (1) Hot rolling process: slab heating temperature 1150℃, final rolling temperature 950℃, coiling temperature 760℃;

[0056] (2) Cold rolling process: cold rolling reduction rate of 85%, rolling thickness of 0.8 mm;

[0057] (3) Degreasing and cleaning process: the temperature of the bath solution is 60℃ and the free alkalinity of the alkaline solution in the degreasing bath is 70 points;

[0058] (4) Annealing process: Annealing temperature 830℃, furnace tension 5.5N / mm²;

[0059] (5) Hot-dip galvanizing process: zinc pot temperature 450℃, plating solution temperature 440℃, furnace nose dew point 5℃;

[0060] (6) Cooling process: 460-340℃ cooling rate 20℃ / s, 340-200℃ cooling rate 35℃ / s;

[0061] (7) Finishing and straightening: Finishing elongation rate 0.5%, straightening elongation rate 0.2%.

[0062] The product performance in this embodiment is as follows: yield strength 195MPa, tensile strength 315MPa, elongation after fracture A 80 35.5%, coating weight 150g / m², no red rust after 3000 hours of neutral salt spray test.

[0063] Example 2

[0064] The chemical composition and mass percentage of the high elongation zinc-aluminum-magnesium coated steel strip in this embodiment are as follows: C: 0.05%, Si: 0.025%, Mn: 0.15%, P: 0.012%, S: 0.010%, Als: 0.035%, Ti: 0.045%, N: 0.0038%, with the remainder being Fe and unavoidable impurities.

[0065] Coating composition: Al: 1.8%, Mg: 1.3%, balance is Zn and trace impurities.

[0066] The production method in this embodiment includes the following steps:

[0067] (1) Hot rolling process: slab heating temperature 1180℃, final rolling temperature 940℃, coiling temperature 780℃;

[0068] (2) Cold rolling process: cold rolling reduction rate of 80%, rolling thickness of 1.2mm;

[0069] (3) Degreasing and cleaning process: the temperature of the bath solution is 55℃ and the free alkalinity of the alkaline solution in the degreasing bath is 75 points;

[0070] (4) Annealing process: Annealing temperature 850℃, furnace tension 5.0N / mm²;

[0071] (5) Hot-dip galvanizing process: zinc pot temperature 440℃, plating solution temperature 435℃, furnace nose dew point 10℃;

[0072] (6) Cooling process: 460-340℃ cooling rate 25℃ / s, 340-200℃ cooling rate 32℃ / s;

[0073] (7) Finishing and straightening: Finishing elongation rate 0.7%, straightening elongation rate 0.25%.

[0074] The product performance in this embodiment is as follows: yield strength 210MPa, tensile strength 335MPa, elongation after fracture A 80 32.0%, coating weight 120g / m², no red rust after 2800 hours of neutral salt spray test.

[0075] Example 3

[0076] The chemical composition and mass percentage of the high elongation zinc-aluminum-magnesium coated steel strip in this embodiment are as follows: C: 0.035%, Si: 0.015%, Mn: 0.18%, P: 0.009%, S: 0.006%, Als: 0.050%, Ti: 0.055%, N: 0.0032%, with the remainder being Fe and unavoidable impurities.

[0077] Coating composition: Al: 2.0%, Mg: 1.6%, balance Zn and trace impurities.

[0078] The production method in this embodiment includes the following steps:

[0079] (1) Hot rolling process: slab heating temperature 1160℃, final rolling temperature 960℃, coiling temperature 770℃;

[0080] (2) Cold rolling process: cold rolling reduction rate of 82%, rolling thickness of 1.0 mm;

[0081] (3) Degreasing and cleaning process: the temperature of the bath solution is 65℃ and the free alkalinity of the alkaline solution in the degreasing bath is 68 points;

[0082] (4) Annealing process: Annealing temperature 840℃, furnace tension 4.8N / mm²;

[0083] (5) Hot-dip galvanizing process: zinc pot temperature 445℃, plating solution temperature 438℃, furnace nose dew point 8℃;

[0084] (6) Cooling process: 460-340℃ cooling rate 22℃ / s, 340-200℃ cooling rate 38℃ / s;

[0085] (7) Finishing and straightening: Finishing elongation rate 0.6%, straightening elongation rate 0.22%.

[0086] The product performance in this embodiment is as follows: yield strength 202MPa, tensile strength 325MPa, elongation after fracture A 80 33.8%, coating weight 180g / m², no red rust after 3200 hours of neutral salt spray test.

[0087] Comparative Example 1

[0088] Compared with Example 1, the substrate composition of Comparative Example 1 does not contain Ti, while other components and process conditions are the same as in Example 1.

[0089] Comparative Example 1 Product Performance: Yield strength 285MPa, tensile strength 380MPa, elongation after fracture A 80 18.5%.

[0090] Comparative Example 2

[0091] Compared with Example 1, the hot rolling temperature of Comparative Example 2 was 680°C, and other process conditions were the same as those of Example 1.

[0092] Comparative Example 2 Product Performance: Yield strength 265MPa, tensile strength 365MPa, elongation after fracture A 80 20.3%.

[0093] The results of the above embodiments demonstrate that, through composition optimization and process control, the present invention successfully prepared zinc-aluminum-magnesium coated steel strip with high elongation, and its elongation after fracture A 80 All reach over 30%, far exceeding that of conventional zinc-aluminum-magnesium steel strips (usually 10%-17%), while maintaining the high corrosion resistance of the zinc-aluminum-magnesium coating.

[0094] 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-elongation zinc-aluminum-magnesium coated steel strip, characterized in that, This includes hot rolling, cold rolling, degreasing, annealing, hot-dip galvanizing (Aluminum-Magnesium), cooling, and finishing and straightening processes; specifically: Hot rolling process: The slab heating temperature is 1130~1200℃, the final rolling temperature is 900~970℃, and a higher coiling temperature of 740~800℃ is adopted to facilitate grain coarsening of hot-rolled plates and control of carbonitride precipitation morphology. Cold rolling process: High cold rolling reduction rate is adopted and controlled at 70% to 90% to provide high energy storage for subsequent recrystallization annealing and promote recrystallization grain growth; Annealing process: A relatively high annealing temperature of 800-860℃ is adopted, and the unit tension of the strip in the furnace is controlled at 4-7 N / mm² to promote full recrystallization and coarsening of grains, while developing a favorable {111} texture. Hot-dip galvanizing process: Precisely control the temperature of the zinc pot to 430~470℃, so that the deviation from the temperature of the plating solution (420~460℃) is ≤10℃, reduce thermal shock, and ensure the adhesion of the coating; control the dew point of the atmosphere inside the furnace nose to -10~20℃; Cooling process: Segmented cooling control is adopted. From 460℃ to 340℃, a slower cooling rate of 15-30℃ / s is used to reduce the internal stress of the coating; from 340℃ to 200℃, a faster cooling rate of 30-40℃ / s is used to suppress the excessive formation of brittle phases in the coating. Finishing and straightening process: The finishing elongation is controlled at 0.1% to 0.9%, and the total straightening elongation is ≤0.3% to eliminate the yield plateau, improve the plate shape, and avoid excessive work hardening. The zinc-aluminum-magnesium coated steel strip includes a substrate and a coating. The chemical composition of the substrate, by mass percentage, is as follows: C: 0.008–0.06%, Si ≤ 0.03%, Mn: 0.10–0.20%, P ≤ 0.015%, S ≤ 0.012%, Als: 0.020–0.060%, Ti: 0.030–0.070%, N ≤ 0.0040%, with the remainder being Fe and unavoidable impurities; The chemical composition of the coating, by mass percentage, is: Al: 1.1-2.5%, Mg: 1.1-1.8%, with the balance being Zn and trace amounts of unavoidable impurities.

2. The method for producing high elongation zinc-aluminum-magnesium coated steel strip according to claim 1, characterized in that, The chemical composition of the substrate, by mass percentage, is: C: 0.008%, Si: 0.02%, Mn: 0.20%, P: 0.010%, S: 0.008%, Als: 0.045%, Ti: 0.050%, N: 0.0035%, the remainder being Fe and unavoidable impurities.

3. The method for producing high-elongation zinc-aluminum-magnesium coated steel strip according to claim 2, characterized in that, The chemical composition of the coating, by mass percentage, is: Al: 2.2%, Mg: 1.5%, with the balance being Zn and trace impurities.

4. The method for producing high-elongation zinc-aluminum-magnesium coated steel strip according to claim 3, characterized in that, Specifically, the following steps are included: (1) Hot rolling process: slab heating temperature 1150℃, final rolling temperature 950℃, coiling temperature 760℃; (2) Cold rolling process: cold rolling reduction rate of 85%, rolling thickness of 0.8 mm; (3) Degreasing and cleaning process: the temperature of the bath solution is 60℃ and the free alkalinity of the alkaline solution in the degreasing bath is 70 points; (4) Annealing process: Annealing temperature 830℃, furnace tension 5.5N / mm²; (5) Hot-dip galvanizing process: zinc pot temperature 450℃, plating solution temperature 440℃, furnace nose dew point 5℃; (6) Cooling process: 460-340℃ cooling rate 20℃ / s, 340-200℃ cooling rate 35℃ / s; (7) Finishing and straightening: Finishing elongation rate 0.5%, straightening elongation rate 0.2%.

5. The method for producing high-elongation zinc-aluminum-magnesium coated steel strip according to claim 1, characterized in that, Specifically, the following steps are included: (1) Hot rolling process: slab heating temperature 1180℃, final rolling temperature 940℃, coiling temperature 780℃; (2) Cold rolling process: cold rolling reduction rate of 80%, rolling thickness of 1.2mm; (3) Degreasing and cleaning process: the temperature of the bath solution is 55℃ and the free alkalinity of the alkaline solution in the degreasing bath is 75 points; (4) Annealing process: Annealing temperature 850℃, furnace tension 5.0N / mm²; (5) Hot-dip galvanizing process: zinc pot temperature 440℃, plating solution temperature 435℃, furnace nose dew point 10℃; (6) Cooling process: 460-340℃ cooling rate 25℃ / s, 340-200℃ cooling rate 32℃ / s; (7) Finishing and straightening: Finishing elongation rate 0.7%, straightening elongation rate 0.25%.

6. The method for producing high-elongation zinc-aluminum-magnesium coated steel strip according to claim 5, characterized in that, The chemical composition of the substrate, by mass percentage, is: C: 0.05%, Si: 0.025%, Mn: 0.15%, P: 0.012%, S: 0.010%, Al: 0.035%, Ti: 0.045%, N: 0.0038%, with the remainder being Fe and unavoidable impurities; the chemical composition of the coating, by mass percentage, is: Al: 1.8%, Mg: 1.3%, with the balance being Zn and trace impurities.

7. The method for producing high elongation zinc-aluminum-magnesium coated steel strip according to claim 1, characterized in that, Specifically, the following steps are included: (1) Hot rolling process: slab heating temperature 1160℃, final rolling temperature 960℃, coiling temperature 770℃; (2) Cold rolling process: cold rolling reduction rate of 82%, rolling thickness of 1.0 mm; (3) Degreasing and cleaning process: the temperature of the bath solution is 65℃ and the free alkalinity of the alkaline solution in the degreasing bath is 68 points; (4) Annealing process: Annealing temperature 840℃, furnace tension 4.8N / mm²; (5) Hot-dip galvanizing process: zinc pot temperature 445℃, plating solution temperature 438℃, furnace nose dew point 8℃; (6) Cooling process: 460-340℃ cooling rate 22℃ / s, 340-200℃ cooling rate 38℃ / s; (7) Finishing and straightening: Finishing elongation rate 0.6%, straightening elongation rate 0.22%.

8. The method for producing high elongation zinc-aluminum-magnesium coated steel strip according to claim 1, characterized in that, The chemical composition of the substrate, by mass percentage, is: C: 0.035%, Si: 0.015%, Mn: 0.18%, P: 0.009%, S: 0.006%, Als: 0.050%, Ti: 0.055%, N: 0.0032%, with the remainder being Fe and unavoidable impurities; the chemical composition of the coating, by mass percentage, is: Al: 2.0%, Mg: 1.6%, with the balance being Zn and trace impurities.