High-surface-quality cold-rolled hot-dip aluminum-zinc-plated steel plate and manufacturing method thereof

Abstract

The invention relates to a high-surface-quality cold-rolled hot-dip aluminum-zinc-plated steel plate and a manufacturing method thereof. The technical problem that the surface of an existing cold-rolled hot-dip aluminum-zinc-plated steel plate with the thickness of 1.0-2.0 mm has the defect of waist creases is mainly solved. According to the technical scheme, a base plate of the high-surface-quality cold-rolled hot-dip aluminum-zinc-plated steel plate comprises the following chemical components in percentage by weight: 0.04%-0.08% of C, 0.001%-0.030% of Si, 0.35%-0.45% of Mn, less than or equal to 0.015% of P, less than or equal to 0.010% of S, 0.005%-0.015% of Ti, 0.01%-0.02% of Al, 0.0010%-0.0020% of N, and the balance of Fe and inevitable impurities, wherein [Ti-3. 42 (N-Al / 1.92)] / C is more than or equal to 0.5 and less than or equal to 2.0. The surface of the cold-rolled hot-dip aluminum-zinc-plated steel plate with the thickness of 1.0-2.0 mm is free of waist creases.

Description

Technical Field

[0001] The present invention relates to a cold-rolled hot-dip aluminum-zinc coated steel sheet, in particular to a high-surface-quality cold-rolled hot-dip aluminum-zinc coated steel sheet and a manufacturing method thereof, specifically, to a cold-rolled hot-dip aluminum-zinc coated steel sheet with a thickness of 1.0 to 2.0 mm and no waist folding defect on the surface for use in the home appliance industry, belonging to the technical field of iron-based alloys. Background Art

[0002] Hot-dip aluminum-zinc alloy steel sheets have been widely used in home appliances, construction and electrical cabinet industries due to their high corrosion resistance, high reflectivity, zinc-speckled surface and comprehensive excellent performance.

[0003] The thickness of cold-rolled hot-dip galvanized steel sheets used in the home appliance industry is 1.0-2.0 mm. After being processed and formed, the cold-rolled hot-dip galvanized steel sheets are usually used as outer panels. They belong to appearance parts and have increasingly higher requirements for surface quality. During the production process or use process, the cold-rolled hot-dip galvanized steel sheets with a thickness of 1.0-2.0 mm bend when passing through the turning roller, and the surface of the steel sheet is prone to waist folding defects, which cannot meet the high surface quality requirements of home appliance panels.

[0004] The Chinese patent document with application publication number CN103088354A discloses a control method for eliminating the waist-fold defect of steel strip, which mainly solves the technical problem of repairing the waist-fold defect by returning the steel strip to the uncoiler and re-processing it with an anti-wrinkle roller before the strip line in the entrance section runs; there is an aluminum-zinc coating on the surface of the cold-rolled hot-dip aluminum-zinc coating. If an anti-wrinkle roller is installed in the hot-dip aluminum-zinc coating unit, the surface of the liquid coating will be damaged. The waist-fold defect of the cold-rolled hot-dip aluminum-zinc coating cannot be solved by installing an anti-wrinkle roller equipment in the hot-dip aluminum-zinc coating unit.

[0005] The Chinese patent document with application publication number CN103084430A discloses a method and device for reducing the waist-fold defect of strip steel, solving the technical problem of waist-fold of existing pickling plate products; according to the initial position setting value of the deep bending roller and the working position setting value of the deep bending roller, the servo system of the hydraulic cylinder that controls the deep bending roller to move forward and backward adjusts the hydraulic cylinder to the set position, which can realize dynamic following control of the deep bending roller position, ensure that the deep bending roller and the strip steel always maintain the correct contact position, and reduce waist-fold defects; the surface of the cold-rolled hot-dip aluminum-zinc coated steel plate has an aluminum-zinc coating. If a deep bending roller is installed in the hot-dip aluminum-zinc coating unit, the surface of the liquid coating will be damaged, and the waist-fold defect of the cold-rolled hot-dip aluminum-zinc coated steel plate cannot be solved by installing a deep bending roller equipment in the hot-dip aluminum-zinc coating unit.

[0006] The Chinese patent application publication number CN105297052A discloses a method for controlling the anti-wrinkle roller of a pickling line, which mainly solves the technical problem of controlling waist-fold defects of different products. When the yield strength of the incoming material is less than 350MPa and the thickness is less than 2.0mm, the hot rolling coiling temperature factor is not considered, and the system controls the anti-wrinkle roller to automatically press down, and the pressure is controlled to 60% of the reference pressure; when the yield strength of the incoming material is less than 350MPa, the thickness is greater than or equal to 2.0mm and less than or equal to 5.0mm, the hot rolling coiling temperature factor is not considered, and the system controls the anti-wrinkle roller to automatically press down, and the pressure is controlled to 70% of the reference pressure; when the yield strength of the incoming material is less than 350MPa, the thickness is greater than 5.0mm, if the hot rolling coiling temperature is less than or equal to At 570 degrees Celsius, the system controls the anti-wrinkle roller to press down automatically, and the pressure is controlled to 70% of the reference pressure; above 570 degrees Celsius, the system controls the anti-wrinkle roller to press down automatically, and the pressure is controlled to 80% of the reference pressure; when the yield strength of the incoming material is greater than or equal to 350MPa and less than or equal to 450MPa, and the thickness is less than 2.5mm, the system controls the anti-wrinkle roller to press down automatically, and the pressure is controlled to 70% of the reference pressure; when the thickness is greater than or equal to 2.5mm, the anti-wrinkle roller is lifted; if the incoming material does not meet any of the above conditions, the anti-wrinkle roller is lifted and not put into use. There is an aluminum-zinc coating on the surface of the cold-rolled hot-dip aluminum-zinc steel sheet. If an anti-wrinkle roller is installed in the hot-dip aluminum-zinc unit, the surface of the liquid coating will be damaged. The waist fold defect of the cold-rolled hot-dip aluminum-zinc steel sheet cannot be solved by installing an anti-wrinkle roller in the hot-dip aluminum-zinc unit.

[0007] The Chinese patent application publication number CN106917041A discloses a thick cold-rolled hot-dip aluminum-zinc steel plate and its manufacturing method, which mainly solves the technical problems in the prior art that the manufacturing cost of cold-rolled hot-dip aluminum-zinc steel plates with a thickness of 1.8mm to 2.0mm is high and the manufacturing process has high requirements for the capacity of the cold rolling unit equipment. The present invention provides a thick cold-rolled hot-dip aluminum-zinc steel plate, whose chemical composition weight percentage is: C: 0.125% to 0.165%, Si≤0.045%, Mn: 0.1% to 0.4%, P≤0.03%, S≤0.025%, Alt: 0.010% to 0.060%, and the balance is Fe and unavoidable impurity elements. The cold-rolled hot-dip aluminum-zinc steel plate of the present invention is mainly used for the preparation of electrical cabinets, etc.; it reduces the cost of steel plates, but cannot eliminate the waist folding defect of cold-rolled hot-dip aluminum-zinc steel plates.

[0008] The Chinese patent application publication number CN108103429A discloses a production method for hot-dip aluminum-zinc-silicon steel sheet, which mainly solves the technical problems of low bonding strength between the hot-dip aluminum-zinc-silicon coating and the substrate of the hot-dip aluminum-zinc-silicon steel sheet in the prior art, and the aluminum-zinc layer falling off during the stamping process of the hot-dip aluminum-zinc-silicon steel sheet. The production method of the hot-dip aluminum-zinc-silicon steel sheet of the present invention is to perform hot-dip galvanizing and flattening on the substrate of the hot-dip aluminum-zinc-silicon steel sheet after annealing in a horizontal continuous annealing furnace, and obtain a finished steel sheet with a thickness of 1.0mm to 2.0mm by coiling, and the temperature of the zinc pot is 585-595℃; the coating weight of the hot-dip aluminum-zinc-silicon steel sheet is controlled to be 90-120g / m2; the flattening extension rate is 0-0.5%; it mainly solves the problem of coating bonding strength, and cannot eliminate the waist folding defect of the cold-rolled hot-dip aluminum-zinc-silicon steel sheet.

[0009] The Chinese patent application publication number CN103320689A discloses an aluminum-zinc deep-drawing steel and its manufacturing method, which mainly reduces the annealing speed to ensure the deep-drawing performance, resulting in the surface quality not meeting the requirements of home appliance plates and the technical problem of low output. Its composition weight percentage: C: 0.001-0.0025%, Si: 0.05-0.06%, Mn: 0.1-0.2%, P≤0.015%, S≤0.01%, Alt: 0.025-0.065%, Ti: 0.04-0.06%, N: ≤0.0040, the remainder is Fe and unavoidable impurity elements. Its focus is to meet the deep-drawing performance of the steel plate while increasing the speed and surface quality. The product yield strength is 127-200MPa. It mainly solves the problem of surface color difference of aluminum-zinc deep-drawing steel, but cannot eliminate the waist folding defect of cold-rolled hot-dip aluminum-zinc steel plate.

[0010] During the production or use process, the cold-rolled hot-dip aluminum-zinc coated steel sheet with a thickness of 1.0 to 2.0 mm bends when passing through the turning roller, and waist fold defects are easily generated on the surface of the steel sheet, which cannot meet the high surface quality requirements of home appliance plates. Summary of the invention

[0011] The purpose of the present invention is to provide a high-surface-quality cold-rolled hot-dip aluminum-zinc steel plate and a method for manufacturing the same, mainly to solve the technical problem of waist-folding defects on the surface of the existing 1.0-2.0 mm thick cold-rolled hot-dip aluminum-zinc steel plate; the cold-rolled hot-dip aluminum-zinc steel plate of the present invention has high surface quality, and no waist-folding defects will be produced on the surface of the steel plate during production and use, thus meeting the use requirements of the home appliance industry.

[0012] The technical idea adopted by the present invention is that the base plate of the steel plate is designed with low carbon, low manganese and low nitrogen elements, and trace titanium alloy elements are added; the structure and performance of the steel plate are regulated by hot rolling process, cold rolling annealing and rapid cooling after plating to obtain fine recrystallized ferrite structure + free cementite, so as to achieve the purpose of no waist folding defects in the bending process of the steel plate, thereby realizing 1.0-2.0mm thick cold-rolled hot-dip aluminum-zinc steel plate to meet the high surface quality requirements of home appliance outer panels.

[0013] The technical solution adopted by the present invention is a high surface quality cold-rolled hot-dip aluminum-zinc coated steel plate, the chemical composition weight percentage of the substrate of which is: C: 0.04% ~ 0.08%, Si: 0.001% ~ 0.030%, Mn: 0.35% ~ 0.45%, P ≤ 0.015%, S ≤ 0.010%, Ti: 0.005% ~ 0.015%, Al: 0.01% ~ 0.02%, N: 0.0010% ~ 0.0020%, and satisfies 0.5 ≤ [Ti-3.42 (N-Al / 1.92)] / C ≤ 2.0, and the rest is Fe and unavoidable inclusions.

[0014] The metallographic structure of the cold-rolled hot-dip aluminum-zinc coated steel sheet of the present invention is recrystallized ferrite + free cementite, and the ferrite grain size grade is I9.5 to I10.0; the yield strength R of the cold-rolled hot-dip aluminum-zinc coated steel sheet with a thickness of 1.0 to 2.0 mm is P0.2 260~340MPa, tensile strength R m 360~420MPa, elongation after fracture A 80mm The weight of the zinc layer on one side of the cold-rolled hot-dip galvanized steel sheet is 60 to 80 g / m 2 ; There is no waist fold mark on the surface of cold-rolled hot-dip aluminum-zinc coated steel plate.

[0015] The cold-rolled hot-dip aluminum-zinc coated steel sheet of the present invention is mainly used in the household appliance industry.

[0016] The reasons why the chemical composition of the cold-rolled hot-dip galvanized steel sheet of the present invention is limited to the above range are as follows:

[0017] Carbon: Carbon is a relatively cheap and economical solid solution strengthening element. It forms titanium carbide with titanium microalloy elements in the steel matrix, which is beneficial to the control of grain size. This patent focuses on the influence of carbon content on strength, elongation and organization during design, and at the same time, it must achieve the purpose of grain refinement with titanium elements. With the increase of carbon content, the strength of the steel matrix increases, while titanium carbide tends to be coarse and the refinement effect is not obvious. The comprehensive setting of the C content range is set to 0.04-0.08%.

[0018] Silicon: Silicon contributes greatly to strength, but the heating process of the horizontal annealing furnace is an oxidizing atmosphere. The silicon element in the steel plate is easily oxidized, which is not conducive to the bonding strength of the aluminum-zinc coating. According to test results, silicon alloy is not added during the production process and is a residual element. The Si content is 0.001% to 0.030%.

[0019] Manganese: An important solid solution strengthening element. In order to ensure the comprehensive mechanical strength of steel, appropriate Mn is added to improve the strength of the steel plate. Excessive addition of manganese will result in excessive strength and cost and difficulty in forming. Too low manganese content will cause the Mn / S ratio to be too low, which will easily cause surface cracks on the slab and poor material manufacturability. The Mn content control range of the present invention is Mn: 0.35-0.45%.

[0020] Microalloying element titanium: Ti is an important trace element in the substrate of the anti-waist fold hot-dip aluminum-zinc steel plate. By adding a trace amount of titanium and carbon in steel to form carbides, the carbides play a role in refining the grains during the annealing process of the material. Through a large number of tests and studies, it is found that the fine grains have an obvious effect on the anti-waist fold defect on the surface of the hot-dip aluminum-zinc steel plate. Adding a large amount of titanium will lead to high costs and the material yield strength is too high and does not meet the requirements of the mechanical properties of the home appliance plate. Through a large number of tests and verifications, combined with the low cost requirements, the content of Ti added in the present invention is 0.005% to 0.015%. In order to ensure the reliability of the anti-waist fold performance of the aluminum-zinc steel plate surface, the applicant has found through years of research that when the content of C, Ti, N and Al elements in the hot-dip aluminum-zinc steel plate meets the following relationship: by weight percentage, 0.5≤[Ti-3.42(N-Al / 1.92)] / C≤2, the hot-dip aluminum-zinc steel plate will not have a surface waist fold.

[0021] Aluminum: The main purpose of adding Al to steel is deoxidation. Fixed nitrogen content in steel can give full play to the role of trace titanium in grain size refinement. By adding certain aluminum and nitrogen elements to form AlN, it is found through research that when the aluminum content is less than 0.01%, it is easy to cause insufficient titanium refinement effect. When the aluminum content is greater than 0.02%, it will increase the cost. Therefore, Al is set to 0.01~0.02%.

[0022] Nitrogen: N in the steel of the present invention is an impurity element. Too high a content of N is not conducive to the effect of trace titanium elements, so the content of N needs to be strictly controlled. The technical solution of the present invention sets the N content to 0.0010-0.0020%.

[0023] Sulfur: S in the steel of the present invention is an impurity element. Too high S will cause the precipitation of MnS in the steel, which is not conducive to continuous casting production and slab quality control. The technical solution of the present invention sets S≤0.010%.

[0024] Phosphorus: Phosphorus in steel is usually an impurity element. In order to ensure stable and reliable production with low cost, the P in this patent is ≤0.015%.

[0025] A method for manufacturing a high-surface-quality cold-rolled hot-dip aluminum-zinc coated steel sheet, the method comprising:

[0026] The molten steel is continuously cast to obtain a continuous casting slab, wherein the weight percentage of the chemical composition of the molten steel is: C: 0.04% to 0.08%, Si: 0.001% to 0.030%, Mn: 0.35% to 0.45%, P≤0.015%, S≤0.010%, Ti: 0.005% to 0.015%, Al: 0.01% to 0.02%, N: 0.0010% to 0.0020%, and 0.5≤[Ti-3.42(N-Al / 1.92)] / C≤2.0 is satisfied, and the rest is Fe and unavoidable inclusions;

[0027] The continuous casting slab is heated to 1150-1200° C. in a heating furnace and then hot rolled. The hot rolling is a two-stage rolling process, the rough rolling is 5-pass continuous rolling; the finishing rolling is 7-pass continuous rolling, the starting temperature of the finishing rolling is 980-1050° C.; the finishing temperature of the finishing rolling is 890-920° C., and the finishing rolling reduction rate is 90%-91.5%; the thickness of the steel plate after finishing rolling is 3.5-4.0 mm, the laminar cooling adopts the front-stage cooling, and the coiling temperature is 650-680° C. to obtain the hot-rolled steel coil;

[0028] After the hot-rolled steel coil is unrolled, it is pickled, cold rolled, annealed in a horizontal continuous annealing furnace, and hot-dip galvanized to obtain a finished cold-rolled hot-dip galvanized steel sheet with a thickness of 1.0 to 2.0 mm; the cold rolling reduction rate is 50% to 71%, the heating section temperature of the hardened strip steel after cold rolling in the horizontal continuous annealing furnace is 630 to 660° C., the annealing temperature of the soaking section is 781 to 799° C., the annealing time of the strip steel in the soaking section is 48 to 60 seconds, and the annealed strip steel is cooled to 590 to 600° C.; the annealed strip steel is put into a zinc pot for hot-dip galvanizing; the single-side zinc layer weight of the cold-rolled hot-dip galvanized steel sheet is controlled to be 60 to 80 g / m 2 The hot-dip galvanized steel strip is cooled after leaving the zinc pot at a cooling rate of 15 to 20°C / s, and the temperature of the hot-dip galvanized steel strip at the first turning roller after cooling is controlled to be 240 to 260°C.

[0029] The reasons for the production process adopted by the present invention are as follows:

[0030] 1. Setting of heating temperature of continuous casting slab

[0031] In the heating process of economical continuous casting slab, a lower heating temperature is required. In order to prevent the austenite grain size from growing after the slab is heated and reduce the yield strength of the finished steel plate, the heating temperature is set at 1150-1200℃.

[0032] 2. Setting of finishing temperature

[0033] In order to avoid the coarse grains on the surface of the material caused by two-phase rolling, which will cause surface waist fold defects due to coarse grains after annealing of the aluminum-zinc steel plate, the finishing temperature needs to be controlled above the phase change point. According to the production capacity of the unit, the hot rolling process sets the finishing temperature to 890-920℃.

[0034] 3. Setting of laminar cooling method and hot rolling coiling temperature

[0035] Rapid cooling during the phase change process can obtain fine grain structure, which is designed as front-end cooling. The design of the coiling temperature of this patent is based on the premise of adding trace titanium to give full play to its grain refinement effect. The coiling temperature is less than 650℃, which cannot fully precipitate titanium carbide during the rolling and coiling process, thereby achieving grain refinement to solve the waist folding defect on the surface of aluminum-zinc steel plates. The coiling temperature is greater than 680℃, which is easy to cause coarse titanium carbide precipitates. Taking all factors into consideration, laminar cooling adopts front-end cooling, and the coiling temperature is 650-680℃ to obtain hot-rolled steel coils.

[0036] 4. Setting of cold rolling reduction rate

[0037] The present invention provides a cold rolling process for the above-mentioned high surface quality cold-rolled hot-dip aluminum-zinc coated steel sheet. After the above-mentioned hot-rolled steel coil is unrolled and pickled to remove the surface iron oxide, it is cold-rolled multiple times on a cold rolling mill or a reciprocating single-stand rolling mill. Due to the limitation of the deformation capacity of the unit, this patent adopts a low compression ratio method to produce a substrate for thick-gauge aluminum-zinc coated products, and the cold rolling reduction rate is set to 50% to 71%.

[0038] 5. Setting of heating section temperature, annealing temperature and annealing time of strip in horizontal continuous annealing furnace

[0039] In order to obtain a steel plate with recrystallized ferrite + free cementite structure and obtain the target yield strength of the strip, this patent is based on the cold rolling reduction rate of 50% to 71% low compression ratio. It is found that the use of a soaking temperature lower than 781°C will lead to unstable annealing and poor material properties, and the soaking section temperature higher than 799°C will lead to excessive grain growth and surface waist folding defects. Therefore, the strip is set at a heating section temperature of 630 to 660°C in the horizontal continuous annealing furnace, the annealing temperature of the soaking section is 781 to 799°C, the annealing time of the strip in the soaking section is 48 to 60s, the annealed strip is cooled to 590 to 600°C, and put into the zinc pot for hot-dip aluminum-zinc plating.

[0040] 6. Temperature setting of the first turning roller for cooling hot-dip galvanized steel strip after plating

[0041] The steel plate is cooled quickly after leaving the zinc pot, and the steel strip will bend at the first turning roller during cooling after plating. Through continuous experiments, it is found that when the temperature of the steel strip at the first turning roller during cooling after plating is higher than 290 degrees, the material will be too soft, resulting in waist fold defects on the surface when bending. Combined with the actual cooling capacity, the hot-dip aluminum-zinc strip is cooled after leaving the zinc pot, and the cooling rate is 15-20℃ / s. The temperature of the hot-dip aluminum-zinc strip at the first turning roller during cooling after plating is set to 240-260℃.

[0042] The metallographic structure of the hot-rolled steel plate produced by the method of the present invention is ferrite + a small amount of pearlite, and the grain size of the ferrite in the metallographic structure is 9.0 to 10; the yield strength R of the 3.5 to 4.0 mm thick hot-rolled steel plate is P0.2 255~338MPa, tensile strength R m 377~420MPa, elongation after fracture A 80mm It is 30% to 38%.

[0043] The metallographic structure of the cold-rolled hot-dip aluminum-zinc coated steel sheet produced by the method of the present invention is recrystallized ferrite, and the ferrite grain size grade is I9.5 to I10.0; the yield strength R of the 1.0 to 2.0 mm thick cold-rolled hot-dip aluminum-zinc coated steel sheet is P0.2 260~340MPa, tensile strength R m 360~420MPa, elongation after fracture A 80mm The weight of the zinc layer on one side of the cold-rolled hot-dip galvanized steel sheet is 60 to 80 g / m 2 ; There is no waist fold mark on the surface of cold-rolled hot-dip aluminum-zinc coated steel plate.

[0044] Compared with the prior art, the present invention has the following positive effects: 1. After the steel plate of the present invention is bent by the cooling turning roller after plating, there is no waist fold defect on the surface, and no waist fold defect occurs during the production process of the cold-rolled hot-dip aluminum-zinc steel plate or in the use of the user. 2. The cold-rolled hot-dip aluminum-zinc steel plate of the present invention has high surface quality, and the high surface quality without waist fold is achieved through the coordinated design of components and process, and the implementation is simple and easy; it overcomes the deficiency of damaging the surface of the liquid coating layer by installing anti-wrinkle rollers or deep bending roller equipment to solve the waist fold defect. 3. The method of the present invention is based on new research and understanding of titanium elements. By adding 0.005-0.015% titanium elements to the substrate of the cold-rolled hot-dip aluminum-zinc steel plate, the hot rolling and cold rolling process parameters are coordinated to control the waist fold of the aluminum-zinc steel plate at a low cost. 4. The method of the present invention effectively solves the problems of insufficient compression ratio and limited rolling capacity of the existing cold rolling mill, thereby solving the problem of substandard material performance caused by coarse grains after annealing of the cold-rolled steel plate, and can achieve stable production of cold-rolled substrates with a low compression ratio of 50-71%. 5. The method of the present invention has strong operability and is easy to implement in corresponding hot rolling and cold rolling structure control methods; it can be achieved by adjusting the process parameters of the finishing temperature, coiling temperature and annealing temperature of the cold rolling annealing furnace during the hot rolling process. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a metallographic structure photograph of the hot-rolled steel plate of Example 4 of the present invention.

[0046] Figure 2 This is a metallographic structure photograph of the cold-rolled hot-dip aluminum-zinc coated steel sheet according to Example 4 of the present invention. DETAILED DESCRIPTION

[0047] The present invention is further described below in conjunction with Examples 1-6, as shown in Tables 1-6.

[0048] Table 1 shows the chemical composition (by weight percentage) of the substrate of the cold-rolled hot-dip aluminum-zinc coated steel sheet according to the embodiment of the present invention, with the remainder being Fe and unavoidable impurities.

[0049] Table 1 Chemical composition of the substrate of the cold-rolled hot-dip aluminum-zinc coated steel sheet according to the embodiment of the present invention, unit: weight percentage.

[0050]

[0051] The contents of C, Ti, N and Al elements in the substrate of the cold-rolled hot-dip aluminum-zinc-coated steel sheet of the present invention simultaneously satisfy the following relationships: in terms of weight percentage, 0.5≤[Ti-3.42(N-Al / 1.92)] / C≤2.0; in Examples 1-6, [Ti-3.42(N-Al / 1.92)] / C are 0.51, 0.82, 0.65, 1.57, 0.68 and 0.70, respectively.

[0052] Molten steel with required chemical composition is obtained by converter smelting, and the molten steel is continuously cast to obtain continuous casting slabs. The thickness of the continuous casting slabs is 210-230 mm, the width is 800-1300 mm, and the length is 5000-10000 mm.

[0053] The continuously cast slab is sent to a heating furnace for reheating, and after being removed from the furnace and dephosphorized, it is sent to a continuous hot rolling mill for rolling; the rolling is controlled by a rough rolling mill and a finishing rolling mill, and the laminar cooling adopts front-stage cooling, and then coiling is performed to produce hot-rolled steel coils, and the thickness of the hot-rolled steel plate is 3.5-4.0 mm; the hot rolling process control is shown in Table 2.

[0054] Table 2 Hot rolling process control parameters of the embodiment of the present invention

[0055]

[0056] The hot rolled steel sheet obtained by the above method is shown in Figure 1 The metallographic structure of the hot-rolled steel plate is ferrite + a small amount of pearlite, and the grain size of the ferrite in the metallographic structure is 9.0 to 10; the yield strength R of the 3.5 to 4.0 mm thick hot-rolled steel plate is P0.2 255~338MPa, tensile strength R m 377~420MPa, elongation after fracture A 80mm It is 30% to 38%.

[0057] The hot-rolled steel plate obtained by the present invention was subjected to a tensile test according to "GB / T228.1-2010 Tensile test of metallic materials Part 1: Room temperature test method", and the mechanical properties of the hot-rolled steel plate are shown in Table 3.

[0058] Table 3 Mechanical properties of hot-rolled steel sheets according to the present invention

[0059]

[0060] After the hot-rolled steel coil is unrolled, it is pickled, cold rolled, annealed in a horizontal continuous annealing furnace, and hot-dip galvanized to obtain a finished cold-rolled hot-dip galvanized steel sheet with a thickness of 1.0 to 2.0 mm; the cold rolling reduction rate is 50% to 71%, the heating section temperature of the hardened strip steel after cold rolling in the horizontal continuous annealing furnace is 630 to 660° C., the annealing temperature of the soaking section is 781 to 799° C., the annealing time of the strip steel in the soaking section is 48 to 60 seconds, and the annealed strip steel is cooled to 590 to 600° C.; the annealed strip steel is put into a zinc pot for hot-dip galvanizing; the single-side zinc layer weight of the cold-rolled hot-dip galvanized steel sheet is controlled to be 60 to 80 g / m 2; After the hot-dip galvanized steel strip is discharged from the zinc pot, it is cooled at a cooling rate of 15-20℃ / s. The temperature of the hot-dip galvanized steel strip at the first turning roller after cooling is controlled to be 240-260℃; the cold-rolled hot-dip galvanized steel sheet is not leveled. The cold rolling and annealing process parameters are shown in Table 4; the cooling parameters of the cold-rolled hot-dip galvanized steel strip after it is discharged from the zinc pot are shown in Table 5.

[0061] Table 4 Cold rolling and annealing control parameters of the embodiment of the present invention

[0062]

[0063] Table 5 Cooling control parameters of cold-rolled hot-dip aluminum-zinc coated steel strip after exiting the zinc pot according to the embodiment of the present invention

[0064]

[0065] The cold-rolled hot-dip aluminum-zinc coated steel sheet obtained by the above method is shown in Figure 2 The metallographic structure of the cold-rolled hot-dip aluminum-zinc coated steel sheet is recrystallized ferrite, and the ferrite grain size is I9.5 to I10.0; the yield strength R of the 1.0 to 2.0 mm thick cold-rolled hot-dip aluminum-zinc coated steel sheet is P0.2 260~340MPa, tensile strength R m 360~420MPa, elongation after fracture A 80mm The weight of the zinc layer on one side of the cold-rolled hot-dip galvanized steel sheet is 60 to 80 g / m 2 ; There is no waist fold mark on the surface of cold-rolled hot-dip aluminum-zinc coated steel plate.

[0066] The cold-rolled hot-dip aluminum-zinc steel sheet obtained by the present invention was subjected to a tensile test according to "GB / T228.1-2010 Metallic Material Tensile Test Part 1: Room Temperature Test Method". The mechanical properties and coating properties of the cold-rolled hot-dip aluminum-zinc steel sheet are shown in Table 6.

[0067] Table 6 Mechanical properties and coating parameters of cold-rolled hot-dip aluminum-zinc steel sheets according to the present invention

[0068]

[0069] As shown in Table 6, the cold-rolled hot-dip aluminum-zinc coated steel sheet of the embodiment has no waist fold marks on the surface; the cold-rolled hot-dip aluminum-zinc coated steel sheet of the present invention does not produce waist fold marks on the steel sheet surface during production and use. The method of the present invention achieves the manufacture of aluminum-zinc coated steel sheets with high surface and no waist fold marks by designing the composition of microalloys and regulating the organization and performance by hot rolling control and annealing process technology.

[0070] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. A high surface quality cold-rolled hot-dip aluminum-zinc coated steel sheet, the chemical composition weight percentage of the substrate of which is C: 0.04% to 0.08%, Si: 0.001% to 0.030%, Mn: 0.35% to 0.45%, P≤0.015%, S≤0.010%, Ti: 0.005% to 0.015%, Al: 0.01% to 0.02%, N: 0.0010% to 0.0020%, and satisfies 0.5≤[Ti-3.42(N-Al / 1.92)] / C≤2.0, and the rest is Fe and unavoidable inclusions; the yield strength R of the 1.0 to 2.0 mm thick cold-rolled hot-dip aluminum-zinc coated steel sheet P0.2 260~340MPa, tensile strength R m 360~420MPa, elongation after fracture A 80mm The weight of the zinc layer on one side of the cold-rolled hot-dip galvanized steel sheet is 60 to 80 g / m 2 ; There is no waist fold mark on the surface of cold-rolled hot-dip aluminum-zinc coated steel plate.

2. The high surface quality cold-rolled hot-dip aluminum-zinc coated steel sheet according to claim 1, characterized in that: The metallographic structure of the cold-rolled hot-dip aluminum-zinc coated steel sheet is recrystallized ferrite, and the ferrite grain size grade is I9.5 to I10.

0.

3. The high surface quality cold-rolled hot-dip aluminum-zinc coated steel sheet according to claim 1, characterized in that: The cold-rolled hot-dip aluminum-zinc coated steel sheet has no waist-folding defect on the surface of the steel sheet during use.

4. A method for manufacturing a high surface quality cold-rolled hot-dip aluminum-zinc coated steel sheet, characterized in that: The method comprises the following steps: The molten steel is continuously cast to obtain a continuous casting slab, wherein the weight percentage of the chemical composition of the molten steel is: C: 0.04% to 0.08%, Si: 0.001% to 0.030%, Mn: 0.35% to 0.45%, P≤0.015%, S≤0.010%, Ti: 0.005% to 0.015%, Al: 0.01% to 0.02%, N: 0.0010% to 0.0020%, and 0.5≤[Ti-3.42(N-Al / 1.92)] / C≤2.0 is satisfied, and the rest is Fe and unavoidable inclusions; The continuous casting slab is heated to 1150-1200° C. in a heating furnace and then hot rolled. The hot rolling is a two-stage rolling process, the rough rolling is 5 passes of continuous rolling; the finishing rolling is 7 passes of continuous rolling, the starting temperature of the finishing rolling is 980-1050° C.; the ending temperature of the finishing rolling is 890-920° C., and the finishing rolling reduction rate is 90%-91.5%; after finishing rolling, the thickness of the hot rolled steel plate is controlled to be 3.5-4.0 mm, the laminar cooling adopts the front stage cooling, and the coiling temperature is 650-680° C. to obtain the hot rolled steel coil; After the hot-rolled steel coil is unrolled, it is pickled, cold rolled, annealed in a horizontal continuous annealing furnace, and hot-dip galvanized to obtain a finished cold-rolled hot-dip galvanized steel sheet with a thickness of 1.0 to 2.0 mm; the cold rolling reduction rate is 50% to 71%, the heating section temperature of the hardened strip steel after cold rolling in the horizontal continuous annealing furnace is 630 to 660° C., the annealing temperature of the soaking section is 781 to 799° C., the annealing time of the strip steel in the soaking section is 48 to 60 seconds, and the annealed strip steel is cooled to 590 to 600° C.; the annealed strip steel is put into a zinc pot for hot-dip galvanizing; the single-side zinc layer weight of the cold-rolled hot-dip galvanized steel sheet is controlled to be 60 to 80 g / m 2 The hot-dip galvanized steel strip is cooled after exiting the zinc pot, and the cooling rate is 15-20°C / s. The temperature of the hot-dip galvanized steel strip at the first turning roller after cooling is controlled to be 240-260°C. There is no waist fold mark on the surface of the cold-rolled hot-dip galvanized steel plate.

5. The method for manufacturing a high surface quality cold-rolled hot-dip aluminum-zinc coated steel sheet according to claim 4, characterized in that: The metallographic structure of the hot-rolled steel plate is ferrite + a small amount of pearlite, and the grain size of the ferrite in the metallographic structure is 9.0 to 10; the yield strength R of the 3.5 to 4.0 mm thick hot-rolled steel plate is P0.2 255~338MPa, tensile strength R m 377~420MPa, elongation after fracture A 80mm It is 30% to 38%.

6. The method for manufacturing a high surface quality cold-rolled hot-dip aluminum-zinc coated steel sheet according to claim 4, characterized in that: The metallographic structure of the cold-rolled hot-dip aluminum-zinc coated steel sheet is recrystallized ferrite, and the ferrite grain size grade is I9.5 to I10.0; the yield strength R of the 1.0 to 2.0 mm thick cold-rolled hot-dip aluminum-zinc coated steel sheet is P0.2 260~340MPa, tensile strength R m 360~420MPa, elongation after fracture A 80mm It is 30% to 37%.

7. The method for manufacturing a high surface quality cold-rolled hot-dip aluminum-zinc coated steel sheet according to claim 4, characterized in that: The cold-rolled hot-dip aluminum-zinc coated steel sheet does not produce waist-less folding defects on the surface of the steel sheet during the production process.

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