Hot-dipped aluminum-zinc steel plate with hot-rolled steel plate as base plate and manufacturing method thereof

Abstract

The invention discloses a hot-dip aluminum-zinc steel plate with a hot-rolled steel plate as a base plate and a manufacturing method thereof, and solves the technical problems of high production cost due to the adoption of a cold-rolled steel plate as a base plate as well as poor surface quality and low coating binding force due to the adoption of a hot-rolled pickled steel plate as a base plate in the existing hot-dip aluminum-zinc steel plate. According to the scheme, the hot-dipped aluminum-zinc steel plate with the base plate being a hot-rolled steel plate comprises 0.03%-0.18% of C, 0.001%-0.050% of Si, 0.10%-0.80% of Mn, smaller than or equal to 0.020% of P, smaller than or equal to 0.015% of S, 0.015%-0.050% of Alt and the balance Fe and inevitable impurity elements. The yield strength RP0.2 of the hot-dip aluminum-zinc steel plate with the thickness of 1.6-3.0 mm is 230-400 MPa, the percentage elongation after fracture A80mm is 18%-35%, and the hot-dip aluminum-zinc steel plate is qualified when d is equal to 0a in a 180-degree bending test; and the surface quality of the hot-dipped aluminum-zinc steel plate is above the FB level.

Description

Technical Field

[0001] The invention relates to a hot-dip aluminum-zinc steel plate, in particular to a hot-dip aluminum-zinc steel plate with a substrate of a hot-rolled steel plate and a manufacturing method thereof, belonging to the technical field of iron-based alloys. Background Art

[0002] Hot-dip aluminum-zinc steel plates are widely used in construction and electrical cabinets due to their excellent corrosion resistance and heat resistance. The characteristics of this use are thicker specifications, large usage, and price sensitivity. The thickness of the steel plates is between 1.6 and 3.0 mm.

[0003] The substrate of traditional hot-dip aluminum-zinc steel plates is made of cold-rolled steel plates, and its manufacturing process is: hot rolling-pickling-cold rolling-hot-dip. The advantages are good surface quality and excellent coating adhesion, and the disadvantage is high cost.

[0004] In the context of increasingly fierce market competition, hot-rolled steel plates are directly hot-dip galvanized after pickling. The cost is greatly reduced compared to hot-dip galvanizing of cold-rolled substrates, but the quality is poor, with quality problems such as missed plating and poor bonding between the coating and the substrate, which cannot meet the requirements of high-end applications.

[0005] The Chinese patent document with application publication number CN1542158A discloses a hot-dip aluminum-zinc alloy steel sheet and a method for manufacturing the same. It discloses a conventional aluminum-zinc alloy steel sheet and a manufacturing process, which uses a cold-rolled substrate. The aluminum-zinc alloy steel sheet produced by this technology has a high production cost.

[0006] The Chinese patent document with application publication number CN2690416Y discloses a hot-dip aluminum-zinc alloy steel sheet, which discloses a conventional aluminum-zinc alloy steel sheet using a cold-rolled substrate. The aluminum-zinc alloy steel sheet produced by this technology has a high production cost.

[0007] The Chinese patent document with application publication number CN105369136A discloses a hot-dip aluminum-zinc steel sheet and a method for manufacturing the same, and discloses a hot-dip aluminum-zinc production technology using a hot-rolled pickled sheet with a thickness specification of 1.5 to 3.5 mm as a substrate. The aluminum-zinc-coated steel sheet produced by this technology has problems with poor surface quality and coating adhesion.

[0008] The Chinese patent document with application publication number CN114645235A discloses a method for manufacturing a continuous hot-base aluminum-zinc coated steel sheet for an electric control cabinet, and discloses a hot-dip aluminum-zinc production technology using a hot-rolled pickled sheet as a substrate. The aluminum-zinc coated steel sheet produced by this technology has problems of poor surface quality and poor coating adhesion.

[0009] In the existing technology, the quality of hot-dip aluminum-zinc steel sheets using cold-rolled sheets as substrates can be guaranteed, but the cost is too high; although the cost of hot-dip aluminum-zinc steel sheets using heat-based pickling sheets as substrates can be reduced, there are quality defects and they can only be used in scenarios such as photovoltaic brackets that do not require high surface quality.

[0010] Manufacturing hot-dip galvanized steel sheets with low cost and high quality is a technical problem that the industry urgently needs to solve. Summary of the invention

[0011] The purpose of the present invention is to provide a hot-dip aluminum-zinc steel plate with a hot-rolled steel plate as the substrate and a manufacturing method thereof, so as to solve the technical problems that the existing hot-dip aluminum-zinc steel plate uses a cold-rolled steel plate as the substrate, has a high production cost, and uses a hot-rolled pickled steel plate as the substrate, has poor surface quality and low coating bonding strength.

[0012] The technical idea of ​​the present invention is that the hot-dip aluminum-zinc steel plate substrate adopts a hot-rolled steel plate, and the hot-rolled steel plate is ground and descaled to remove the surface iron oxide scale; and through the coordination of grinding and descaling, annealing, and hot-dip aluminum-zinc coating processes, a low-cost, high-surface-quality hot-dip aluminum-zinc steel plate is produced.

[0013] The technical solution adopted by the present invention is a hot-dip galvanized steel plate whose substrate is a hot-rolled steel plate, and the chemical composition weight percentage of the substrate is: C: 0.03%~0.18%, Si: 0.001%~0.050%, Mn: 0.10%~0.80%, P≤0.020%, S≤0.015%, Alt: 0.015%~0.050%, and the remainder is Fe and unavoidable impurity elements.

[0014] The metallographic structure of hot-dip aluminum-zinc steel sheet is ferrite + free cementite + pearlite, and the grain size level in the metallographic structure is 8 to 10.5; the single-sided coating weight of hot-dip aluminum-zinc steel sheet is 40 to 90g / m 2 ; Yield strength R of 1.6~3.0mm thick hot-dip galvanized steel sheet P0.2 230~400MPa, tensile strength R m 340~480MPa, elongation after fracture A 80 mm It is 18% to 35%, 180° bending test, d=0a is qualified, and the coating does not fall off; the surface quality of hot-dip galvanized steel plate is above FB grade.

[0015] The mechanical properties, surface quality and coating bonding strength of the hot-dip aluminum-zinc steel plate of the present invention meet the use requirements of high-end building roof panels and electrical cabinets.

[0016] A method for manufacturing a hot-dip galvanized steel sheet whose substrate is a hot-rolled steel sheet, the method comprising:

[0017] The steps of grinding and descaling a hot-rolled steel sheet with a thickness of 1.6 to 3.0 mm, annealing in a horizontal continuous annealing furnace, hot-dip galvanizing, cooling after plating, and coating a fingerprint-resistant film, and coiling to obtain a finished hot-dip galvanized steel sheet, wherein:

[0018] The chemical composition weight percentage of the hot-rolled steel plate is: C: 0.03% to 0.18%, Si: 0.001% to 0.050%, Mn: 0.10% to 0.80%, P≤0.020%, S≤0.015%, Alt: 0.015% to 0.050%, and the balance is Fe and unavoidable impurity elements; the yield strength of the hot-rolled steel plate is 240 to 410 MPa, the tensile strength is 350 to 490 MPa, and the elongation after fracture is A 80mm 20% to 35%;

[0019] The grinding and descaling step uses a grinding roller with a steel brush to grind and descale the surface of the hot-rolled steel plate, and the surface roughness of the hot-rolled steel plate after descaling is 0.7 to 1.4 μm;

[0020] The annealing step includes annealing the descaling hot-rolled steel plate in a horizontal continuous annealing furnace at a temperature of 630 to 650° C. for a time of 20 to 70 seconds;

[0021] In the hot-dip aluminum-zinc coating step, the weight percentage of the plating solution in the zinc pot is Al: 52-58%, Si: 1.3-1.8%, and the balance is Zn and inevitable impurity elements; the annealed hot-rolled steel sheet is put into the zinc pot for hot-dip aluminum-zinc coating, and the weight of the single-side zinc layer of the hot-dip aluminum-zinc steel sheet is controlled to be 40-90g / m 2 ;

[0022] The post-plating cooling step includes blowing air to cool the hot-dip aluminum-zinc steel sheet after it leaves the aluminum-zinc pot to room temperature.

[0023] The reasons for the production process adopted by the present invention are as follows:

[0024] 1. Setting of grinding and descaling process

[0025] The surface roughness of the substrate of hot-dip galvanized steel sheet will affect the bonding strength between the coating and the substrate, as well as the size of the zinc spangles. The greater the roughness, the better the wettability of the plating solution, the better the bonding strength of the coating, and the larger the zinc spangles. If the roughness is less than 0.7μm, the bonding strength will be affected, and the brush roller descaling process will be difficult to achieve; if the roughness is greater than 1.4μm, the size of the zinc spangles will be too large, the surface will be unsightly, and the corrosion resistance of the large zinc spangle coating will also be affected. Taking all factors into consideration, the surface roughness of the hot-rolled steel sheet after descaling is 0.7~1.4μm.

[0026] Through a comparative study of the surfaces of hot-rolled steel plates descaled by grinding and hot-rolled steel plates descaled by pickling, it was found that after pickling, there is often a layer of carbon film covering the surface of the steel plate. This carbon film contaminant is graphitized and difficult to remove, which deteriorates the wettability of the plating solution and can cause local non-plating or poor coating adhesion on the steel plate, affecting the surface quality and bending performance of the hot-dip aluminum-zinc steel plate. Hot-rolled steel plates descaled by grinding avoid this problem.

[0027] 2. Setting of annealing temperature and annealing time

[0028] In order to make the steel plate reach the process temperature of aluminum-zinc plating before entering the zinc pot, a horizontal continuous annealing furnace is used to heat the steel plate. Since there is a cooling section between the heating section and the zinc pot, the cooling section will cause a certain temperature drop of the strip. In order to ensure that the temperature of the strip entering the zinc pot is stable and controllable and prevent the temperature of the zinc pot from fluctuating too much, causing zinc slag precipitation and affecting the surface quality, the annealing temperature of the continuous annealing furnace is higher than the aluminum-zinc liquid temperature. Taking all factors into consideration, the annealing temperature of the hot-rolled steel plate in the soaking section of the horizontal continuous annealing furnace is 630-650°C; at the same time, since the steel plate has not undergone cold rolling deformation, the grains of the steel plate are equiaxed. If the annealing time is too long, the grains will grow abnormally, affecting the mechanical properties. After repeated on-site experimental verification, the annealing time of the hot-rolled steel plate in the soaking section of the horizontal continuous annealing furnace is 20-70s.

[0029] The metallographic structure of the hot-dip aluminum-zinc steel sheet produced by the method of the present invention is ferrite + free cementite + pearlite, and the grain size level in the metallographic structure is 8 to 10.5; the single-side coating weight of the hot-dip aluminum-zinc steel sheet is 40 to 90 g / m 2 ; Yield strength R of 1.6~3.0mm thick hot-dip galvanized steel sheet P0.2 230~400MPa, tensile strength R m 340~480MPa, elongation after fracture A 80mm It is 18% to 35%, 180° bending test, d=0a is qualified, and the coating does not fall off; the surface quality of hot-dip galvanized steel plate is above FB grade.

[0030] Compared with the prior art, the present invention has the following positive effects: 1. The hot-dip aluminum-zinc substrate of the present invention adopts a hot-rolled steel plate that has been descaled by grinding, and through reasonable process control, a hot-dip aluminum-zinc steel plate of the same quality as that manufactured by a cold-rolled substrate is obtained, and the manufacturing cost is low; compared with the existing hot-dip aluminum-zinc steel plate process manufactured by a cold-rolled substrate, the cold rolling process is saved, and the manufacturing process is simple. 2. Compared with the existing hot-dip aluminum-zinc steel plate process manufactured by a hot pickled substrate, the surface quality and coating bonding strength of the method of the present invention are significantly improved, and the hot-rolled plate adopts an acid-free descaling method, which is green and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1This is a scanning electron microscope photograph of the cross section of the hot-dip galvanized steel plate coating according to Example 1 of the present invention. DETAILED DESCRIPTION

[0032] The present invention is further described below in conjunction with Examples 1 to 6, as shown in Tables 1 to 4.

[0033] Table 1 shows the chemical composition (by weight percentage) of the hot-rolled steel sheets according to the embodiments of the present invention, with the remainder being Fe and unavoidable impurities.

[0034] Table 1 Chemical composition of the steel of the present invention, unit: weight percentage.

[0035]

[0036] The hot-rolled steel plate with a thickness of 1.6 to 3.0 mm is subjected to grinding and descaling, annealing in a horizontal continuous annealing furnace, hot-dip galvanizing, cooling after plating, and coating with a fingerprint-resistant film, and the finished hot-dip galvanized steel plate is obtained by coiling; the grinding and descaling step uses a grinding roller with a steel brush to grind and descale the surface of the hot-rolled steel plate, and the surface roughness of the hot-rolled steel plate after descaling is 0.7 to 1.4 μm; the annealing step includes annealing the hot-rolled steel plate after descaling in the soaking section of the horizontal continuous annealing furnace at a temperature of 630 to 650°C and an annealing time of 20 to 70 seconds. The mechanical properties of the hot-rolled steel plate are shown in Table 2; the descaling and annealing process control parameters are shown in Table 3.

[0037] Table 2 Mechanical properties of hot-rolled steel sheets according to the present invention

[0038]

[0039] Table 3 Descaling and annealing process control parameters of the present invention

[0040]

[0041] The hot-dip aluminum-zinc steel plate coating obtained by the above method is shown in Figure 1 The alloy layer connected to the steel plate substrate and the aluminum-zinc coating are Figure 1 It is clearly visible that the coating thickness is uniform and the alloy layer is tightly bonded to the steel substrate.

[0042] The metallographic structure of hot-dip aluminum-zinc steel sheet is ferrite + free cementite + pearlite, and the grain size level in the metallographic structure is 8 to 10.5; the single-sided coating weight of hot-dip aluminum-zinc steel sheet is 40 to 90g / m 2 ; Yield strength R of 1.6~3.0mm thick hot-dip galvanized steel sheet P0.2 230~400MPa, tensile strength R m 340~480MPa, elongation after fracture A 80 mmIt is 18% to 35%, 180° bending test, d=0a is qualified, and the coating does not fall off; the surface quality of hot-dip galvanized steel plate is above FB.

[0043] The hot-dip aluminum-zinc steel sheet obtained by the present invention is subjected to a tensile test according to "GB / T228.1-2010 Tensile Test of Metal Materials Part 1: Room Temperature Test Method"; its surface quality is determined according to the provisions of "GB / T 14978-2008 Continuous Hot-dip Aluminum-Zinc Alloy Coated Steel Sheet and Steel Strip". If at least one surface of the steel sheet has no defects such as small zinc particles, black spots, zinc fluctuations, etc., it is determined to be a higher-grade surface of FB, otherwise it is determined to be a common-grade surface of FA. According to "GB / T 232-2010 "Metallic Material Bending Test Method", a 180° bending test is carried out, d=0a, to test the coating bonding strength. If no coating peeling occurs on the outer surface of the sample after the bending test, it is qualified, otherwise it is deemed unqualified. The mechanical properties and surface quality parameters of the hot-dip aluminum-zinc steel sheet are shown in Table 4.

[0044] Table 4 Mechanical properties and surface quality grades of hot-dip galvanized steel sheets according to the present invention

[0045]

[0046] The surfaces of the hot-dip aluminum-zinc steel plates in Examples 1-6 of the present invention have no defects such as zinc slag, and the surface quality grade is FB, which is a relatively high grade; in the 180° bending test, d=0a, all are qualified, and there is no coating shedding on the surface of the hot-dip aluminum-zinc steel plates and no cracking on the substrate; the surface quality and bending performance can meet the requirements for use in high-end building roof panels and electrical cabinets.

[0047] 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 hot-dip galvanized steel sheet whose substrate is a hot-rolled steel sheet, wherein the chemical composition weight percentage of the substrate is: C: 0.03% to 0.18%, Si: 0.001% to 0.050%, Mn: 0.10% to 0.80%, P≤0.020%, S≤0.015%, Alt: 0.015% to 0.050%, and the balance is Fe and unavoidable impurity elements; the yield strength R of the 1.6 to 3.0 mm thick hot-dip galvanized steel sheet P0.2 230~400MPa, tensile strength R m 340~480MPa, elongation after fracture A 80mm It is 18% to 35%, 180° bending test, d=0a is qualified; the surface quality of hot-dip galvanized steel plate is above FB grade.

2. The substrate according to claim 1 is a hot-dip galvanized steel sheet of a hot-rolled steel sheet, characterized in that: The metallographic structure of the hot-dip aluminum-zinc steel sheet is ferrite + free cementite + pearlite, and the grain size level in the metallographic structure is 8 to 10.5; the single-side coating weight of the hot-dip aluminum-zinc steel sheet is 40 to 90 g / m 2 .

3. A method for manufacturing a hot-dip galvanized steel sheet whose substrate is a hot-rolled steel sheet, characterized in that: The method includes: The steps of grinding and descaling a hot-rolled steel sheet with a thickness of 1.6 to 3.0 mm, annealing in a horizontal continuous annealing furnace, hot-dip galvanizing, cooling after plating, and coating a fingerprint-resistant film, and coiling to obtain a finished hot-dip galvanized steel sheet, wherein: The chemical composition weight percentage of the hot-rolled steel plate is: C: 0.03% to 0.18%, Si: 0.001% to 0.050%, Mn: 0.10% to 0.80%, P≤0.020%, S≤0.015%, Alt: 0.015% to 0.050%, and the balance is Fe and unavoidable impurity elements; the yield strength of the hot-rolled steel plate is 240 to 410 MPa, the tensile strength is 350 to 490 MPa, and the elongation after fracture is A 80mm 20% to 35%; The grinding and descaling step uses a grinding roller with a steel brush to grind and descale the surface of the hot-rolled steel plate, and the surface roughness of the hot-rolled steel plate after descaling is 0.7 to 1.4 μm; The annealing step includes annealing the descaling hot-rolled steel plate in a horizontal continuous annealing furnace at a temperature of 630 to 650° C. for a time of 20 to 70 seconds; In the hot-dip aluminum-zinc coating step, the weight percentage of the plating solution in the zinc pot is Al: 52-58%, Si: 1.3-1.8%, and the balance is Zn and inevitable impurity elements; the annealed hot-rolled steel sheet is put into the zinc pot for hot-dip aluminum-zinc coating, and the weight of the single-side zinc layer of the hot-dip aluminum-zinc steel sheet is controlled to be 40-90g / m 2 ; The post-plating cooling step includes blowing air to cool the hot-dip aluminum-zinc steel sheet after it leaves the aluminum-zinc pot to room temperature.

4. The method for manufacturing a hot-dip galvanized steel sheet whose substrate is a hot-rolled steel sheet according to claim 3, characterized in that: The metallographic structure of the hot-dip aluminum-zinc steel sheet is ferrite+free cementite+pearlite, and the grain size level in the metallographic structure is 8 to 10.5; Yield strength R of 1.6~3.0mm thick hot-dip galvanized steel sheet P0.2 230~400MPa, tensile strength R m 340~480MPa, elongation after fracture A 80mm It is 18% to 35%, 180° bending test, d=0a is qualified; the surface quality of hot-dip galvanized steel plate is above FB grade.

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