Aluminum-zinc hot-dip plated steel sheet with yield strength of 280mpa and method for manufacturing the same

Abstract

This invention discloses a hot-dip galvanized steel sheet with a yield strength of 280MPa and its manufacturing method, mainly solving the technical problem of bending cracking in existing 280MPa-grade hot-dip galvanized steel sheets. The technical solution is a hot-dip galvanized steel sheet with a yield strength of 280MPa, wherein the chemical composition of the substrate by weight percentage is: C: 0.008%–0.012%, Si≤0.03%, Mn: 0.40%–0.60%, P: 0.03%–0.05%, S≤0.0050%, Nb: 0.005%–0.015%, Ti: 0.045%–0.055%, Al: 0.08%–0.10%, N: 0.0010%–0.0020%, and satisfies 16≤[Ti-3.42(N-Al / 1.92)] / C≤30, with the remainder being Fe and unavoidable inclusions. This steel sheet is mainly used in the home appliance industry.

Description

Technical Field

[0001] This invention relates to a cold-rolled hot-dip aluminized zinc-coated steel sheet, and more particularly to a hot-dip aluminized zinc-coated steel sheet with a yield strength of 280 MPa and its manufacturing method. Specifically, it relates to a hot-dip aluminized zinc-coated steel sheet with a thickness of 1.5 to 2.0 mm and a yield strength of 280 MPa for use in the home appliance industry; it belongs to the field of iron-based alloy technology. Background Technology

[0002] Due to its excellent corrosion resistance and attractive appearance, aluminized zinc steel sheet is widely used in various industries such as home appliances.

[0003] The aluminum-zinc coated products used in the home appliance industry are cold-rolled hot-dip aluminum-zinc coated steel sheets with a thickness of 1.5mm to 2.0mm and a yield strength of 200-300MPa.

[0004] With the continuous upgrading of home appliances, aluminized zinc-coated products for home appliances require products with higher yield strength. In order to meet the requirements of the home appliance industry, it is necessary to develop aluminized zinc-coated steel sheets with a yield strength of 280-360MPa and a steel plate efficiency index of ≤5MPa to avoid bending and cracking due to prolonged storage.

[0005] Chinese patent application CN105441795 A discloses a low-carbon cold-rolled steel sheet for LED lead frames and its production method, mainly solving the technical problems of uneven hardness, high surface roughness, and poor aging resistance of existing low-carbon cold-rolled steel sheets for LED lead frames. Its composition and weight percentage (wt%) are: C: 0.025%~0.05%, Si≤0.03%, Mn: 0.15%~0.25%, P≤0.020%, S≤0.010%, Alt: 0.025%~0.048%, B: 0.001%~0.0014%, N≤0.0035%, with the balance being Fe and unavoidable impurity elements. The yield strength Rel of the low-carbon cold-rolled steel sheet for LED lead frames is 200MPa~250MPa, the tensile strength Rm is 270MPa~340MPa, and the elongation after fracture A... 50mm The yield strength is ≥40%, the hardness is HRB40~52, the roughness is Ra≤0.5, and the aging index AI is 26-30. Both its yield strength and aging index do not meet the requirements for steel used in household appliances.

[0006] Chinese patent application CN112442577A discloses a cold-rolled steel sheet with excellent aging resistance for double-layer welded pipes and its manufacturing method, solving the technical problem of poor aging resistance in welded pipes made from cold-rolled steel sheets produced by continuous annealing when used for continuously brazed double-layer welded pipes. Its chemical composition by weight percentage is: C: 0.03–0.07%, Si ≤ 0.05%, Mn: 0.10–0.30%, P ≤ 0.025%, S ≤ 0.020%, Alt: 0.03–0.06%, N ≤ 0.003%, Cr: 0.05–0.15%, with the remainder being Fe and unavoidable inclusions. The aging index AI is 15–20. However, its aging index does not meet the requirements for steel used in household appliances.

[0007] Chinese Patent Application Publication No. CN 103510001 A discloses a cold-rolled steel sheet for double-layer welded pipes and its production method, mainly addressing the problem that existing technologies require annealing treatment when producing double-layer welded pipes from cold-rolled steel sheets, resulting in the aging of the cold-rolled steel sheets. The chemical composition by weight percentage is: C: 0.0010%–0.0035%, Si≤0.05%, Mn: 0.10%–0.25%, P≤0.020%, S≤0.015%, Ti: 0.04%–0.07%, N≤0.0035%, with the remainder being Fe and unavoidable inclusions. The yield strength of the cold-rolled steel sheet is 180–240 MPa. However, the yield strength of the product does not meet the requirements for steel used in household appliances.

[0008] Chinese patent application publication number CN 103938077 A discloses a cold-rolled steel sheet for double-layer welded pipes and its production method. The chemical composition (mass percentage) is: C≤0.008%, Mn 0.3~0.5%, Si≤0.01%, P≤0.015%, S0.012~0.018%, Als0.03~0.06%, Ti0.05~0.10%, N≤0.003%, with the balance being Fe and unavoidable impurities. The method controls the chemical composition content to manage compound precipitates and avoid aging. However, the product's yield strength does not meet the requirements for steel used in household appliances.

[0009] Existing hot-dip aluminized zinc-coated steel sheets have problems such as low yield strength, poor aging performance, and inability to meet the technical requirements of bending processing in the forming process of the home appliance industry. Summary of the Invention

[0010] The purpose of this invention is to provide a hot-dip aluminized zinc-coated steel sheet with a yield strength of 280MPa and its manufacturing method, mainly to solve the technical problem of bending cracking caused by the failure of existing 1.5-2.0mm thick, 280MPa grade hot-dip aluminized zinc-coated steel sheets to meet the forming requirements due to insufficient aging performance. The hot-dip aluminized zinc-coated steel sheet of this invention meets the forming and processing requirements of the home appliance industry for aluminized zinc-coated steel sheets.

[0011] The technical approach of this invention utilizes a low-carbon, medium-manganese, and high-aluminum composition, adds low-cost phosphorus and trace amounts of niobium-titanium alloying elements, and controls the steel plate microstructure through hot rolling, cold rolling annealing, and cooling to obtain a recrystallized ferrite microstructure. This achieves the material's high yield strength and low aging, thereby improving and eliminating the problem of bending cracks in the transverse and longitudinal directions of 1.5mm-2.0mm aluminized zinc-coated steel plates.

[0012] The technical solution adopted in this invention is a hot-dip aluminized zinc-coated steel sheet with a yield strength of 280MPa. The chemical composition of the substrate by weight percentage is as follows: C: 0.008%~0.012%, Si≤0.03%, Mn: 0.40%~0.60%, P: 0.03%~0.05%, S≤0.0050%, Nb: 0.005%~0.015%, Ti: 0.045%~0.055%, Al: 0.08%~0.10%, N: 0.0010%~0.0020%, and satisfies 16≤[Ti-3.42(N-Al / 1.92)] / C≤30, with the remainder being Fe and unavoidable inclusions.

[0013] The metallographic structure of the hot-dip aluminized zinc-coated steel sheet of this invention is recrystallized ferrite, with a ferrite grain size grade of 19.0 to 19.5; the yield strength R of the 1.5 to 2.0 mm thick hot-dip aluminized zinc-coated steel sheet is... P0.2 The tensile strength is 280–360 MPa, and the tensile strength R is... m The strength is 350–420 MPa, and the elongation after fracture is A. 80mm It ranges from 30% to 38%.

[0014] After applying an 8% tensile pre-strain to the hot-dip aluminized zinc-coated steel sheet of the present invention, it is subjected to isothermal heat treatment at 100°C for 60 minutes. The increase in yield stress and the 180° bending test of the hot-dip aluminized zinc-coated steel sheet before and after heat treatment are detected, with d=0a. The aging index AI value of the hot-dip aluminized zinc-coated steel sheet is ≤5MPa. The 180° bending test of the hot-dip aluminized zinc-coated steel sheet along the rolling direction is qualified with d=0a. The 180° bending test of the hot-dip aluminized zinc-coated steel sheet perpendicular to the rolling direction is qualified with d=0a.

[0015] The hot-dip aluminized zinc-coated steel sheet of the present invention was subjected to natural aging for 12-14 months at room temperature, followed by aging performance testing and a 180° bending test with a bending mandrel diameter d=0a. After 12-14 months of natural aging, the aging index AI value of the hot-dip aluminized zinc-coated steel sheet was ≤5MPa. The 180° bending test of the hot-dip aluminized zinc-coated steel sheet along the rolling direction was qualified with d=0a. The 180° bending test of the hot-dip aluminized zinc-coated steel sheet perpendicular to the rolling direction was also qualified with d=0a.

[0016] The hot-dip aluminized zinc-coated steel sheet of this invention has excellent aging properties and good bending performance.

[0017] The reasons for limiting the chemical composition of the hot-dip aluminized zinc-coated steel sheet of the present invention to the above-mentioned range are as follows:

[0018] Carbon: Carbon is a relatively inexpensive and economical solid solution strengthening element, but it is also one of the elements that cause aging. It forms niobium carbide and titanium carbide with niobium and titanium microalloying elements in the steel matrix to strengthen the matrix. This patent focuses on the effect of carbon content on strength, elongation, and microstructure during the design process, while also meeting the requirements for aging. As the carbon content increases, the strength of the steel matrix increases, but the aging performance deteriorates. Through repeated experiments and screening, the carbon content range was comprehensively set at 0.008% to 0.012%.

[0019] Silicon: Silicon contributes significantly to strength, but the horizontal annealing furnace heating process is an oxidizing atmosphere, and the silicon element in the steel plate is easily oxidized, which is detrimental to the adhesion of the aluminum-zinc coating. Based on the test results, no silicon alloy is added during the production process, as it is a residual element, and the Si content is designed to be ≤0.03%.

[0020] Manganese: an important solid solution strengthening element. In order to ensure the comprehensive mechanical strength of steel, adding appropriate amounts of Mn can improve the strength of steel plates. Excessive addition of manganese will result in excessive strength and cost, while too low a manganese content will result in poor aging resistance of the material. The Mn content in this invention is controlled within the range of Mn: 0.40% to 0.60%.

[0021] Microalloying elements niobium and titanium: Nb and Ti are important trace elements in the substrate of hot-dip galvanized steel sheets. Adding trace amounts of niobium and titanium forms carbides with carbon in the steel, reducing carbon atom solid solution and improving the aging resistance of the steel sheet. Simultaneously, to achieve good bending performance in different directions after 12-14 months of natural aging, adding 0.005-0.015% niobium to the steel revealed good bending performance and more stable aging properties in both the transverse and longitudinal directions. More than 0.015% niobium leads to high costs, while less than 0.005% fails to meet the requirements for improving aging and bending performance in both the transverse and longitudinal directions. Adding low-cost titanium and trace amounts of niobium achieves the best balance between aging performance and economy in the steel sheet. Through extensive testing and considering low-cost requirements, the content of Nb in this invention is 0.005-0.015%, and Ti is 0.045%-0.055%. To ensure reliable aging resistance, the applicant has discovered through years of research that when the content of C, Ti, N and Al elements in hot-dip aluminized zinc steel sheet meets the following relationship: by weight percentage, 16≤[Ti-3.42(N-Al / 1.92)] / C≤30, the aging performance AI value of hot-dip aluminized zinc steel sheet is ≤5MPa.

[0022] Aluminum: The main purpose of adding Al to steel is deoxidation. To further control the aging properties of steel plates and fix the nitrogen content, an excess of aluminum is added to form AlN with nitrogen to improve aging properties. Studies have found that when the aluminum content is less than 0.08%, the stability of aging properties is insufficient, and when the aluminum content is greater than 0.10%, steelmaking becomes more difficult and costly. Therefore, the Al content is set at 0.08–0.10%.

[0023] Nitrogen: N in the steel of this invention is an impurity element. Excessive N content is detrimental to aging performance and therefore requires strict control of the N content. The technical solution of this invention sets the N content to 0.0010–0.0020%.

[0024] Sulfur: S in the steel of this invention is an impurity element. Excessive S will cause the precipitation of MnS in the steel, which is detrimental to stamping performance. The technical solution of this invention sets the S content to ≤0.0050%.

[0025] Phosphorus: P in steel is usually an impurity element, but the P content has a certain strengthening effect on the matrix, and P can also combine with C and Ti in steel to reduce the solid solution carbon content, which is beneficial to improving the aging properties of the steel matrix. Through repeated experiments, this invention has found that when the P content is in the range of 0.03% to 0.05% in the composition system of this patent, the optimal match between the mechanical properties and aging resistance of the material can be achieved.

[0026] A method for manufacturing hot-dip aluminized zinc-coated steel sheet with a yield strength of 280 MPa, the method comprising:

[0027] Molten steel is continuously cast to obtain a continuously cast slab. The chemical composition of the molten steel is as follows (weight percentage): C: 0.008%–0.012%, Si ≤ 0.03%, Mn: 0.40%–0.60%, P: 0.03%–0.05%, S ≤ 0.0050%, Nb: 0.005%–0.015%, Ti: 0.045%–0.055%, Al: 0.08%–0.10%, N: 0.0010%–0.0020%, and satisfies 16 ≤ [Ti - 3.42(N - Al / 1.92)] / C ≤ 30, with the remainder being Fe and unavoidable inclusions.

[0028] The continuously cast slab is heated to 1150-1200℃ in a heating furnace and then hot-rolled. The hot rolling is a two-stage rolling process: roughing is a 5-pass continuous rolling; finishing is a 7-pass continuous rolling. The finishing temperature starts at 990-1080℃ and ends at 900-940℃, with a finishing reduction rate of 90-92%. After finishing, the thickness of the hot-rolled steel plate is 3.8-4.1mm. Laminar flow cooling is used in the front-stage cooling, and the coiling temperature is 600-640℃ to obtain the hot-rolled steel coil.

[0029] After being recoiled, the hot-rolled steel coil undergoes pickling, cold rolling, annealing in a horizontal continuous annealing furnace, and hot-dip aluminized zinc coating to obtain a finished hot-dip aluminized zinc coated steel sheet with a thickness of 1.5–2.0 mm. The cold rolling reduction rate is 50%–62%. The strip in the hardened state after cold rolling is annealed in a horizontal continuous annealing furnace at a heating temperature of 630–660°C, with a soaking temperature of 731–769°C. The annealing time in the soaking zone is 50–70 seconds. The annealed strip is then cooled to 590–600°C and placed in an aluminum-zinc bath for hot-dip aluminized zinc coating.

[0030] The rationale for the production process adopted in this invention is as follows:

[0031] 1. Setting the heating temperature of continuously cast slabs

[0032] In the heating process of economic continuous casting slabs, a lower heating temperature is required. In order to prevent the austenite grain size from growing after the slab is heated and reducing the yield strength of the finished steel plate, the heating temperature is set at 1150-1200℃.

[0033] 2. Setting the finishing rolling temperature

[0034] The Fe-C phase diagram shows that the designed steel composition falls within the hypoeutectoid steel range. To avoid uneven microstructure and decreased aging properties caused by rolling in the two-phase region, the finishing rolling temperature for the hot rolling process is set at 900℃~940℃, based on the unit's production capacity.

[0035] 3. Setting of laminar flow cooling method and hot rolling coiling temperature

[0036] Rapid cooling during phase transformation can produce a fine-grained structure and improve strength. The design of the coiling temperature in this patent primarily considers that a lower coiling temperature can control ferrite grain growth and improve the strengthening effect. A coiling temperature below 600℃ fails to adequately precipitate titanium carbide and aluminum nitride during rolling, thus failing to control free carbon and nitrogen atoms in the steel, resulting in insufficient aging resistance and making the steel prone to bending and cracking due to aging issues after 12-14 months. A coiling temperature above 640℃ easily leads to excessively coarse grains, failing to meet the mechanical property requirements of 280MPa steel plates. Taking all factors into consideration, laminar cooling with front-stage cooling and a coiling temperature of 600℃~640℃ are used to obtain hot-rolled steel coils.

[0037] 4. Setting the cold rolling reduction rate

[0038] This invention provides a cold rolling process for the aforementioned age-resistant galvanized steel sheet. After recoiling the hot-rolled steel coil with the above-mentioned composition and pickling to remove surface iron oxide scale, it undergoes multiple cold rolling processes on a continuous cold rolling mill or a reciprocating single-stand mill. Due to limitations in the mill's deformation capacity, this patent employs a low compression ratio method to produce substrates for thick-gauge galvanized products, setting the cold rolling reduction rate to 50%–62%.

[0039] 5. Setting the heating temperature, annealing temperature, and annealing time of the strip in the horizontal continuous annealing furnace.

[0040] To obtain steel plates with recrystallized ferrite microstructure and achieve the target yield strength of the strip, this patent, based on a low compression ratio of 50-62% during cold rolling, found that lower annealing temperatures and isothermal treatment for a certain time are beneficial for improving matrix strength and aging resistance. However, a soaking temperature below 730℃ leads to insufficient annealing and deterioration of material properties, while a soaking temperature above 779℃ causes carbide decomposition, resulting in an aging index (AI) value below ≤5MPa, which easily leads to bending cracks due to natural aging within 12-14 months. Therefore, the heating temperature of the strip in the horizontal continuous annealing furnace is set at 630-660℃, the soaking temperature at 731-769℃, and the annealing time in the soaking section at 50-70s. The annealed strip is then cooled to 590-600℃ and hot-dip galvanized in an aluminum-zinc bath.

[0041] The hot-rolled steel sheet produced by the method of this invention has a ferrite microstructure with a ferrite grain size of 10.0–11. The yield strength R of the 3.8–4.1 mm thick hot-rolled steel sheet is... P0.2 The tensile strength is 275–368 MPa, and the tensile strength R is... m The strength is 387–450 MPa, and the elongation after fracture is A. 80mm It ranges from 31% to 40%.

[0042] The metallographic structure of the hot-dip aluminized zinc-coated steel sheet produced by the method of this invention is recrystallized ferrite, with a ferrite grain size grade of 19.0 to 19.5; the yield strength R of the 1.5 to 2.0 mm thick hot-dip aluminized zinc-coated steel sheet is... P0.2 The tensile strength is 280–360 MPa, and the tensile strength R is... m The strength is 350–420 MPa, and the elongation after fracture is A. 80mm It ranges from 30% to 38%.

[0043] After applying an 8% tensile pre-strain to the hot-dip aluminized zinc-coated steel sheet produced by the method of this invention, it is subjected to isothermal heat treatment at 100°C for 60 minutes. The increase in yield stress and the 180° bending test of the hot-dip aluminized zinc-coated steel sheet before and after heat treatment are detected, with d=0a. The aging index AI value of the hot-dip aluminized zinc-coated steel sheet is ≤5MPa. The 180° bending test of the hot-dip aluminized zinc-coated steel sheet along the rolling direction is qualified with d=0a. The 180° bending test of the hot-dip aluminized zinc-coated steel sheet perpendicular to the rolling direction is qualified with d=0a.

[0044] The hot-dip aluminized zinc steel sheet produced by the method of this invention, after 12-14 months of natural aging, has an aging index AI value ≤5MPa; the hot-dip aluminized zinc steel sheet undergoes a 180° bending test along the rolling direction, with d=0a passing; the hot-dip aluminized zinc steel sheet undergoes a 180° bending test perpendicular to the rolling direction, with d=0a passing, thus meeting the requirements of the home appliance industry for the forming and processing of aluminized zinc steel sheets.

[0045] Compared with existing technologies, this invention has the following positive effects: 1. The method of this invention is a low-cost production method for hot-dip aluminized zinc-coated steel sheets with a yield strength of 280MPa, achieving high strength and aging resistance of the material. It solves the technical problem of preventing cracking of aluminized zinc-coated steel sheets under 12-14 months of natural aging conditions when bent at 180 degrees (d=0a). 2. By adding trace amounts of niobium, the hot-dip aluminized zinc-coated steel sheet of this invention can achieve uniformity in bending performance in different bending directions in the transverse and longitudinal directions, ensuring that the user's use is not limited by direction. 3. This invention uses a substrate produced by a 50-62% low compression ratio cold rolling process. The low compression ratio results in low energy consumption and low cost. 4. The hot rolling and cold rolling microstructure control methods in this invention are highly operable and easy to implement, requiring only control of the temperature during hot rolling and the process parameters of the annealing furnace. 5. The method of this invention combines artificial aging with the actual bending performance after natural aging to explore the correspondence between the current bending performance and the bending performance of the material in the next 12-14 months. This allows for online evaluation of the product's performance in the next 12-14 months, providing reliability for the use of the material. Attached Figure Description

[0046] Figure 1 This is a metallographic photograph of the hot-rolled steel plate of Example 4 of the present invention.

[0047] Figure 2 This is a metallographic photograph of the hot-dip aluminized zinc-coated steel sheet of Embodiment 4 of the present invention. Detailed Implementation

[0048] The present invention will be further described below with reference to Examples 1-6, as shown in Tables 1-5.

[0049] Table 1 shows the chemical composition (by weight percentage) of the substrate of the hot-dip aluminized zinc-coated steel sheet in the embodiments of the present invention, with the balance being Fe and unavoidable impurities.

[0050] Table 1 Chemical composition of the substrate of hot-dip aluminized zinc-coated steel sheet according to the embodiments of the present invention, unit: weight percentage.

[0051]

[0052] The C, Ti, N, and Al content in the substrate of the hot-dip aluminized zinc-coated steel sheet of the present invention simultaneously satisfies the following relationship: by weight percentage, 16 ≤ [Ti-3.42(N-Al / 1.92)] / C ≤ 30; in Examples 1-6, [Ti-3.42(N-Al / 1.92)] / C are 24.0, 27.6, 19.0, 27.0, 19.3, and 16.8, respectively.

[0053] The steel is smelted in a converter to obtain molten steel with the required chemical composition. The molten steel is then continuously cast to obtain continuously cast slabs with a thickness of 210mm to 230mm, a width of 800mm to 1300mm, and a length of 5000mm to 10000mm.

[0054] The continuously cast slab is sent to a heating furnace for reheating, and after descaling, it is sent to a continuous hot rolling mill for rolling. The rolling is controlled by the roughing mill and the finishing mill. Laminar flow cooling is used for front-end cooling, and then the slab is coiled to produce hot-rolled steel coils. The thickness of the hot-rolled steel plate is 3.8 to 4.1 mm. The hot rolling process control is shown in Table 2.

[0055] Table 2 Hot rolling process control parameters of the present invention embodiments

[0056]

[0057]

[0058] For hot-rolled steel sheets obtained using the above method, see [link to relevant documentation]. Figure 1 The metallographic structure of hot-rolled steel sheet is ferrite, with a ferrite grain size of 10.0–11. The yield strength R of 3.8–4.1 mm thick hot-rolled steel sheet is... P0.2 The tensile strength is 275–368 MPa, and the tensile strength R is... m The strength is 387–450 MPa, and the elongation after fracture is A. 80mm It ranges from 31% to 40%.

[0059] The hot-rolled steel plate obtained by the present invention was subjected to tensile testing in accordance with GB / T228.1-2010 Metallic Materials - Tensile Testing - Part 1: Test Method at Room Temperature. The mechanical properties of the hot-rolled steel plate are shown in Table 3.

[0060] Table 3 Mechanical properties of hot-rolled steel plates according to embodiments of the present invention

[0061]

[0062] After being recoiled, the hot-rolled steel coil undergoes pickling, cold rolling, annealing in a horizontal continuous annealing furnace, and hot-dip aluminizing and zinc coating to obtain a finished hot-dip aluminized and zinc-coated steel sheet with a thickness of 1.5–2.0 mm. The cold rolling reduction rate is 50%–62%. The strip in the hardened state after cold rolling is annealed in a horizontal continuous annealing furnace at a heating temperature of 630–660℃, with a soaking temperature of 731–769℃ and an annealing time of 50–70 seconds in the soaking zone. The annealed strip is then cooled to 590–600℃ and placed in an aluminum-zinc bath for hot-dip aluminizing and zinc coating. The cold rolling and annealing process parameters are shown in Table 4.

[0063] Table 4. Cold rolling and annealing process control parameters in embodiments of the present invention.

[0064]

[0065] For hot-dip aluminized zinc-coated steel sheets obtained using the above method, see [link to relevant documentation]. Figure 2 The metallographic structure of hot-dip aluminized zinc-coated steel sheet is recrystallized ferrite, with a ferrite grain size grade of 19.0 to 19.5; the yield strength R of 1.5 to 2.0 mm thick hot-dip aluminized zinc-coated steel sheet is... P0.2 The tensile strength is 280–360 MPa, and the tensile strength R is... m The strength is 350–420 MPa, and the elongation after fracture is A. 80mm It ranges from 30% to 38%.

[0066] The cold-rolled hot-dip aluminized zinc-coated steel sheet obtained by this invention was subjected to tensile tests according to GB / T228.1~2010 Metallic Materials - Tensile Testing - Part 1: Test Method at Room Temperature. After applying an 8% tensile pre-strain, the hot-dip aluminized zinc-coated steel sheet was subjected to isothermal heat treatment at 100℃ for 60 minutes. The increase in yield stress and the 180° bending test were detected before and after heat treatment, with d=0a. The mechanical properties and aging index of the steel sheet are shown in Table 5.

[0067] For the hot-dip aluminized zinc-coated steel sheets of Examples 1-6, after natural aging for 12 months, 12 months, 13 months, 13 months, 14 months and 14 months respectively, the hot-dip aluminized zinc-coated steel sheets along the rolling direction were subjected to a 180° bending test, and d=0a was qualified. The hot-dip aluminized zinc-coated steel sheets perpendicular to the rolling direction were subjected to a 180° bending test, and d=0a was qualified.

[0068] Table 5 Mechanical properties of hot-dip aluminized zinc-coated steel sheets according to embodiments of the present invention

[0069]

[0070] As shown in Table 5, the yield strength of the hot-dip aluminized zinc-coated steel sheet in Example 4 was 350 MPa, the tensile strength was 415 MPa, the elongation was 35.9%, and the aging index AI value was 1 MPa. After 13 months of natural aging, the hot-dip aluminized zinc-coated steel sheet passed the 180° bending test along the rolling direction (d=0a). The hot-dip aluminized zinc-coated steel sheet passed the 180° bending test perpendicular to the rolling direction (d=0a). This invention achieves the manufacture of high-strength, age-resistant aluminized zinc-coated steel sheet through micro-alloying composition design and hot rolling control and annealing process technology.

[0071] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A hot-dip aluminized zinc-coated steel sheet with a yield strength of 280 MPa, wherein the chemical composition of the substrate by weight percentage is: C: 0.008%–0.012%, Si ≤ 0.03%, Mn: 0.40%–0.60%, P: 0.03%–0.05%, S ≤ 0.0050%, Nb: 0.005%–0.015%, Ti: 0.045%–0.055%, Al: 0.08%–0.10%, N: 0.0010%–0.0020%, and satisfies 16 ≤ [Ti - 3.42(N - Al / 1.92)] / C ≤ 30, with the remainder being Fe and unavoidable inclusions; the yield strength R of the 1.5–2.0 mm thick hot-dip aluminized zinc-coated steel sheet is... P0.2 The tensile strength is 280–360 MPa, and the tensile strength R is... m The strength is 350–420 MPa, and the elongation after fracture is A. 80 mm The percentage is 30% to 38%; after 12 to 14 months of natural aging at room temperature, the aging index AI value of the hot-dip aluminized zinc steel sheet is ≤5 MPa; the 180° bending test of the hot-dip aluminized zinc steel sheet along the rolling direction is qualified with d=0a; the 180° bending test of the hot-dip aluminized zinc steel sheet perpendicular to the rolling direction is qualified with d=0a.

2. The hot-dip aluminized zinc-coated steel sheet with a yield strength of 280 MPa as described in claim 1, characterized in that, The metallographic structure of the hot-dip aluminized zinc-coated steel sheet is recrystallized ferrite, and the ferrite grain size is grade I9.0 to I9.

5.

3. The hot-dip aluminized zinc-coated steel sheet with a yield strength of 280 MPa as described in claim 1, characterized in that, After applying an 8% tensile pre-strain to the hot-dip aluminized zinc-coated steel sheet, it is subjected to a heat treatment at 100℃ for 60 minutes isothermally. The increase in yield stress and the 180° bending test of the hot-dip aluminized zinc-coated steel sheet before and after heat treatment are detected, with d=0a. The aging index AI value of the hot-dip aluminized zinc-coated steel sheet is ≤5 MPa. The 180° bending test of the hot-dip aluminized zinc-coated steel sheet along the rolling direction is qualified with d=0a. The 180° bending test of the hot-dip aluminized zinc-coated steel sheet perpendicular to the rolling direction is qualified with d=0a.

4. The method for manufacturing hot-dip aluminized zinc-coated steel sheet with a yield strength of 280 MPa as described in any one of claims 1-3, characterized in that, The method includes: Molten steel is continuously cast to obtain a continuously cast slab. The chemical composition of the molten steel is as follows (weight percentage): C: 0.008%~0.012%, Si≤0.03%, Mn: 0.40%~0.60%, P: 0.03%~0.05%, S≤0.0050%, Nb: 0.005%~0.015%, Ti: 0.045%~0.055%, Al: 0.08%~0.10%, N: 0.0010%~0.0020%, and satisfies 16≤[Ti-3.42(N-Al / 1.92)] / C≤30, with the remainder being Fe and unavoidable inclusions. The continuously cast slab is heated to 1150-1200℃ in a heating furnace and then hot-rolled. The hot rolling is a two-stage rolling process: roughing is a 5-pass continuous rolling; finishing is a 7-pass continuous rolling. The finishing temperature starts at 990-1080℃ and ends at 900-940℃, with a finishing reduction rate of 90-92%. After finishing, the thickness of the hot-rolled steel plate is 3.8-4.1 mm. Laminar flow cooling is performed using front-stage cooling, and the coiling temperature is 600-640℃ to obtain the hot-rolled steel coil. After being recoiled, the hot-rolled steel coil undergoes pickling, cold rolling, annealing in a horizontal continuous annealing furnace, and hot-dip aluminized zinc coating to obtain a finished hot-dip aluminized zinc coated steel sheet with a thickness of 1.5–2.0 mm. The cold rolling reduction rate is 50%–62%. The strip in the hardened state after cold rolling is annealed in a horizontal continuous annealing furnace at a heating temperature of 630–660℃, with a soaking temperature of 731–769℃. The annealing time in the soaking zone is 50–70 seconds. The annealed strip is then cooled to 590–600℃ and placed in an aluminum-zinc bath for hot-dip aluminized zinc coating.

5. The method for manufacturing hot-dip aluminized zinc-coated steel sheet with a yield strength of 280 MPa as described in claim 4, characterized in that, The metallographic structure of the hot-rolled steel sheet is ferrite, and the grain size of the ferrite in the metallographic structure is 10.0 to 11. The yield strength R of the 3.8 to 4.1 mm thick hot-rolled steel sheet is... P0.2 The tensile strength is 275–368 MPa, and the tensile strength R is... m The strength is 387–450 MPa, and the elongation after fracture is A. 80 mm It ranges from 31% to 40%.

Images