Surface-treated steel sheet

Abstract

To disclose a surface-treated steel plate with excellent weldability and corrosion resistance.SOLUTION: A surface-treated steel plate has an alloyed molten zinc plating steel plate, and a surface treatment layer provided on at least one main face of the alloyed molten zinc plating steel plate. The surface treatment layer has a double-layer constitution of an inner layer and an outer layer. The inner layer is a chemical conversion treatment layer in contact with the alloyed molten zinc plating steel plate, and an adhesion amount of the inner layer is 200 mg / m2 or more and 2000 mg / m2 or less. A ratio M1 / M2 of a maximum adhesion amount M1 and a minimum adhesion amount M2 of the inner layer is 2.0 or more and 50 or less. The outer layer contains binder resin and an anti-rust agent. When the outer layer does not contain the anti-rust agent, the adhesion amount of the outer layer is 1.0 g / m2 or more and 5.0 g / m2 or less. When the outer layer contains the anti-rust agent, the adhesion amount of the outer layer is 2.0 g / m2 or more and 20 g / m2.SELECTED DRAWING: None

Description

Technical Field

[0001] This application discloses a surface-treated steel sheet.

[0002] Surface-treated steel sheets are used as structural materials for automobiles and the like. A surface-treated steel sheet has, for example, a plated steel sheet and a surface treatment layer provided on at least one main surface of the plated steel sheet. In the prior art, a coating film is adopted as the surface treatment layer, and the weldability and corrosion resistance of the surface-treated steel sheet are improved by adjusting the types and contents of the components constituting the coating film.

[0003] For example, Patent Document 1 discloses a technique for improving the weldability and corrosion resistance of a surface-treated steel sheet having a coating film on at least one side of a plated steel sheet by containing a predetermined amount of a binder resin, non-oxide ceramic particles containing V, and doped zinc oxide particles in the coating film.

[0004] Further, Patent Document 2 discloses a technique for improving the weldability and corrosion resistance of a coated metal material having an organic film on the surface of a metal material by containing a predetermined resin having a urethane bond and predetermined conductive particles in the organic film.

[0005] Further, Patent Document 3 discloses a technique for improving the weldability and corrosion resistance of a coated metal plate having a coating layer on the surface of a metal plate by containing a predetermined amount of conductive particles having a predetermined particle size in the coating layer.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the prior art, in improving the weldability and corrosion resistance of surface-treated steel sheets, although the types and contents of the components constituting the surface treatment layer have been studied, improving the weldability and corrosion resistance of surface-treated steel sheets by devising other factors has not been sufficiently studied. In this regard, there is room for improvement in improving the weldability and corrosion resistance of surface-treated steel sheets.

Means for Solving the Problems

[0008] As one of the means for solving the above problems, the present application provides an alloying hot-dip galvanized steel sheet, a surface treatment layer provided on at least one main surface of the alloying hot-dip galvanized steel sheet, and a surface-treated steel sheet having the same, wherein the surface treatment layer has a two-layer structure of an inner layer and an outer layer, the inner layer is a chemical conversion treatment layer in contact with the alloying hot-dip galvanized steel sheet, the adhesion amount of the inner layer is 200 mg / m 2 or more and 2000 mg / m 2 or less, the maximum adhesion amount M1 and the minimum adhesion amount M2 of the inner layer satisfy the relationship of the following formula (1), the outer layer contains a binder resin and a rust preventive agent, the outer layer does not contain a conductive agent, the adhesion amount of the outer layer is 1.0 g / m 2 or more and 5.0 g / m 2 or less, a surface-treated steel sheet is disclosed.

[0009] As one of the means for solving the above problems, the present application provides an alloying hot-dip galvanized steel sheet, a surface treatment layer provided on at least one main surface of the alloying hot-dip galvanized steel sheet, A surface-treated steel sheet having The surface treatment layer has a two-layer structure of an inner layer and an outer layer, The inner layer is a chemical conversion treatment layer that contacts the alloyed hot-dip galvanized steel sheet, The coating amount of the inner layer is 200 mg / m 2 or more and 2000 mg / m 2 or less, The maximum coating amount M1 and the minimum coating amount M2 of the inner layer satisfy the relationship of the following formula (1), The outer layer contains a binder resin, a conductive agent, and a rust preventive agent, The coating amount of the outer layer is 2.0 g / m 2 or more and 20 g / m 2 or less, Surface-treated steel sheet is disclosed.

[0010] 2.0 ≦ M1 / M2 ≦ 50 ···(1)

[0011] In the surface-treated steel sheet of the present disclosure, The conductive agent may be doped oxide particles, an Si alloy containing 50% by mass or more of Si, an Si compound containing 50% by mass or more of Si, or a composite thereof, The content of the conductive agent in the outer layer may be 5 vol% or more and 30 vol% or less.

[0012] In the surface-treated steel sheet of the present disclosure, The doped oxide particles may be doped zinc oxide particles.

[0013] In the surface-treated steel sheet of the present disclosure, The Si alloy or the Si compound may be ferrosilicon containing 70% by mass or more of Si.

[0014] In the surface-treated steel sheet of the present disclosure, The rust preventive agent may be amorphous silica having a particle diameter of 0.5 μm or more and 10 μm or less, The content of the amorphous silica in the outer layer may be 5 vol% or more and 30 vol% or less.

Advantages of the Invention

[0015] In the surface-treated steel sheet of the present disclosure, the plated steel sheet as the base material is an alloyed hot-dip galvanized steel sheet, the adhesion amount of each of the inner layer and the outer layer of the surface treatment layer is within a predetermined range, and the inner layer of the surface treatment layer satisfies a predetermined distribution state (maximum adhesion amount M1 / minimum adhesion amount M2). Thereby, weldability and corrosion resistance are likely to be compatible in the surface-treated steel sheet.

Embodiments for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described. Note that these descriptions are merely illustrative of the embodiments of the present invention, and the present invention is not limited to the following embodiments.

[0017] 1. First Embodiment The surface-treated steel sheet according to the first embodiment has an alloyed hot-dip galvanized steel sheet and a surface treatment layer provided on at least one main surface of the alloyed hot-dip galvanized steel sheet. The surface treatment layer has a two-layer structure of an inner layer and an outer layer. The inner layer is a chemical conversion treatment layer in contact with the alloyed hot-dip galvanized steel sheet. The adhesion amount of the inner layer is 200 mg / m 2 or more and 2000 mg / m 2 or less. The maximum adhesion amount M1 and the minimum adhesion amount M2 of the inner layer satisfy the relationship of the following formula (1). The outer layer contains a binder resin and a rust preventive agent. The outer layer does not contain a conductive agent. The adhesion amount of the outer layer is 1.0 g / m 2 or more and 5.0 g / m 2 or less.

[0018] 2.0 ≦ M1 / M2 ≦ 50 ···(1)

[0019] 1.1 Alloyed Hot-Dip Galvanized Steel Sheet The alloyed hot-dip galvanized steel sheet may have, for example, a base steel sheet and an alloyed hot-dip galvanized layer provided on at least one main surface of the base steel sheet. The "main surface" referred to in this application is the surface corresponding to the front or back side of the sheet. The alloyed hot-dip galvanized layer may be provided on only one main surface of the base steel sheet, or may be provided on both main surfaces. Further, the alloyed hot-dip galvanized layer may be provided over the entire main surface of the base steel sheet, or may be provided on a part of the main surface.

[0020] As the base steel sheet, those having various chemical compositions and metallographic structures can be adopted. The base steel sheet may be a plain steel sheet or a steel sheet containing additive elements such as chromium, and the chemical composition and metallographic structure of the base steel sheet may be adjusted in consideration of the intended mechanical properties, formability, etc. Further, the thickness of the base steel sheet is not particularly limited, and may be, for example, 0.2 mm or more and 6.0 mm or less.

[0021] The alloyed hot-dip galvanized layer may be a plating layer having a chemical composition known to those skilled in the art. For example, the alloyed hot-dip galvanized layer may contain additive elements such as Al in addition to Zn, and may also contain Fe, etc. derived from the alloying treatment. The adhesion amount of the alloyed hot-dip galvanized layer to the base steel sheet is not particularly limited and may be a general adhesion amount.

[0022] When manufacturing an alloyed hot-dip galvanized steel sheet, unevenness is formed on the plating surface during the alloying treatment of the plating. By adjusting the skin pass conditions after the alloying treatment, etc., the unevenness on the plating surface can be controlled within a predetermined range, and when a surface treatment layer is formed thereafter, the relationship of the above formula (1) is more likely to be satisfied. That is, the alloyed hot-dip galvanized steel sheet may have unevenness on the plating surface. Specifically, the arithmetic mean roughness Ra of the plating surface of the alloyed hot-dip galvanized steel sheet may be 0.4 μm or more or 0.6 μm or more, and may also be 2.0 μm or less or 3.0 μm or less. The arithmetic mean roughness Ra of the plating surface of the alloyed hot-dip galvanized steel sheet is measured in accordance with JIS B 0601:2013. The arithmetic mean roughness Ra is measured three times each in the rolling direction and the direction perpendicular to the rolling direction, and the average value thereof is obtained, and this is taken as the arithmetic mean roughness Ra of the plating surface.

[0023] 1.2 Surface treatment layer The surface treatment layer is provided on at least one main surface of the alloyed hot-dip galvanized steel sheet. The surface treatment layer may be provided only on one main surface of the alloyed hot-dip galvanized steel sheet, or may be provided on both main surfaces. Also, the surface treatment layer may be provided over the entire main surface of the alloyed hot-dip galvanized steel sheet, or may be provided on a part of the main surface. The surface treatment layer can be laminated on the plating surface among the surfaces of the above alloyed hot-dip galvanized steel sheet.

[0024] The surface treatment layer has a two-layer structure of an inner layer and an outer layer. The "inner layer" is a layer provided closer to the inside than the outer layer and is the layer in contact with the alloyed hot-dip galvanized steel sheet. The "outer layer" is a layer provided closer to the outside than the inner layer and is the layer in contact with the outer surface of the inner layer.

[0025] 1.2.1 Inner layer The inner layer is a chemical conversion treatment layer that contacts the alloyed hot-dip galvanized steel sheet. By providing a chemical conversion treatment layer as the inner layer on the surface of the alloyed hot-dip galvanized steel sheet and further providing the outer layer described below on the surface of the chemical conversion treatment layer, the adhesion of the outer layer to the steel sheet is improved, and the weldability and corrosion resistance are further improved. The chemical conversion treatment layer may be a layer that substantially does not contain chromium (chromate-free layer). Examples of the chromate-free treatment liquid used for the chemical conversion treatment include silica-based treatment liquids mainly composed of silicon compounds such as liquid-phase silica, gas-phase silica, and silicates, zircon-based treatment liquids mainly composed of zircon-based compounds, and mixtures thereof. The chemical conversion treatment layer may contain a binder resin. For example, the chemical conversion treatment layer may contain at least one of those exemplified as the binder resin that can form the outer layer described below, and may contain a polyester resin. The content of the binder resin and the content of components other than the binder resin (such as the above-mentioned silicon compounds) in the inner layer are not particularly limited. For example, the content of the binder resin in the inner layer may be 0 vol% or more and 50 vol% or less, and the content of components other than the binder resin may be 50 vol% or more and 100 vol% or less. The chemical conversion treatment layer as the inner layer may be an inorganic film containing an inorganic component as a binder.

[0026] In the surface-treated steel sheet, the adhesion amount of the inner layer is 200 mg / m 2 or more and 2000 mg / m 2 or less. If the adhesion amount of the inner layer is too small, it is difficult to obtain the above-mentioned adhesion improvement effect, and the corrosion resistance is also likely to decrease. If the adhesion amount of the inner layer is too large, the weldability is likely to decrease. The adhesion amount of the inner layer may be 300 mg / m 2 or more or 500 mg / m 2 or more, and may also be 1500 mg / m 2 or less or 1000 mg / m 2 or less. Incidentally, the adhesion amount of the chemical conversion treatment layer in the surface-treated steel sheet can be measured by fluorescent X-ray and cross-sectional analysis. Specifically, a calibration curve board is prepared for each chemical conversion treatment. The chemical conversion treatment board and the calibration curve board are measured by fluorescent X-ray, and the adhesion amount of the prepared chemical conversion treatment board is calculated from the X-ray intensity of the contained elements and the X-ray intensity of the calibration curve board.

[0027] In the surface-treated steel sheet, the maximum adhesion amount M1 and the minimum adhesion amount M2 of the inner layer satisfy the relationship of the above formula (1). That is, the ratio M1 / M2 of M1 to M2 is 2.0 or more and 50 or less. If the ratio M1 / M2 is too small, the inner layer as a whole tends to be thick and the weldability tends to decrease. If the ratio M1 / M2 is too large, the adhesion unevenness of the inner layer becomes too large and the corrosion resistance tends to decrease. The ratio M1 / M2 may be 5.0 or more or 10 or more, and may also be 40 or less or 20 or less. The maximum adhesion amount M1 and the minimum adhesion amount M2 of the inner layer can vary depending on the unevenness of the plated surface as described above, and also on the state of the treatment liquid when forming the inner layer (such as the type and viscosity of the components constituting the chemical conversion treatment liquid, the wettability of the treatment liquid with respect to the steel sheet, etc.). In the surface-treated steel sheet, the maximum adhesion amount M1 and the minimum adhesion amount M2 of the inner layer are specified as follows. That is, in the steel sheet after inner layer coating and before outer layer coating, by using a micro XRF manufactured by EDAX, when measuring 50 points in a measurement range of 30 μφ, the average value of the top 5 points is taken as M1, the average value of the bottom 5 points is taken as M2, and the ratio M1 / M2 of M1 to M2 can be obtained. Alternatively, in the measurement of the adhesion amount after outer layer coating, by confirming the cross-section of the surface-treated steel sheet with an electron microscope or the like, the maximum thickness part of the chemical conversion treatment layer is taken as the part where the "maximum adhesion amount M1" is located, the minimum thickness part is taken as the part where the "minimum adhesion amount M2" is located, and by confirming the thickness ratio, it is also possible to obtain M1 / M2 (= maximum thickness / minimum thickness).

[0028] The thickness of the inner layer is not particularly limited as long as it satisfies the above adhesion amount and ratio M1 / M2. For example, the thickness of the inner layer may be 0.5 μm or more and 5.0 μm or less in the part where the maximum adhesion amount M1 is located, and may be 0.01 μm or more and 2.5 μm or less in the part where the minimum adhesion amount M2 is located.

[0029] 1.2.2 Outer layer In the surface-treated steel sheet according to the first embodiment, the outer layer contains a binder resin and a rust preventive agent. The outer layer can be configured as a coating film containing these components.

[0030] The binder resin contained in the outer layer may be, for example, at least one resin selected from polyester resins, urethane resins, and acrylic resins. When a polyester resin is employed as the binder resin, the polyester resin may have a glass transition temperature Tg of -20 to 70 °C and may have a number average molecular weight of 3,000 to 30,000. When a urethane resin is employed as the binder resin, the urethane resin may have a Tg of 0 to 50 °C and may have a number average molecular weight of 5,000 to 25,000. When an acrylic resin is employed as the binder resin, the acrylic resin may have a Tg of 0 to 50 °C and may have a number average molecular weight of 3,000 to 25,000. The binder resin may be cured by a curing agent. As the curing agent, for example, a melamine resin, an isocyanate resin, an epoxy resin, or the like may be employed. The content of the binder resin in the outer layer is not particularly limited and may be, for example, 50 vol% or more or 60 vol% or more, and may also be 90 vol% or less, 80 vol% or less, or 70 vol% or less.

[0031] The rust inhibitor contained in the outer layer may be an inorganic rust inhibitor or an organic rust inhibitor. The form of the rust inhibitor may be, for example, particulate. The rust inhibitor may be water-soluble or water-insoluble. When the rust inhibitor is water-soluble, for example, when the outer layer is exposed to a wet environment, the rust inhibitor in the outer layer dissolves and elutes in water, and a rust prevention function of suppressing the corrosion of the plating layer can be exhibited.

[0032] The content of the rust inhibitor in the outer layer may be appropriately adjusted according to the intended rust prevention effect. For example, the content of the rust inhibitor in the outer layer may be 0.5 vol% or more, 1 vol% or more, or 5 vol% or more, and may also be 50 vol% or less, 40 vol% or less, or 30 vol% or less.

[0033] The rust preventive agent may contain at least one of P and V, which are elements that exhibit a rust preventive function. Examples of rust preventive agents containing P include phosphoric acids such as orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, and tetraphosphoric acid; ammonium salts such as ammonium triphosphate and diammonium hydrogen phosphate; metal phosphates with metals such as Na, Mg, Al, K, Ca, Mn, Ni, Zn, and Fe; phosphonic acids such as aminotri(methylenephosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediaminetetra(methylenephosphonic acid), and diethylenetriaminepenta(methylenephosphonic acid) and their salts; organic phosphoric acids such as phytic acid and their salts, etc. Examples of rust preventive agents containing V include vanadium pentoxide, HVO3 metavanadic acid, ammonium metavanadate, VOCl3 vanadium oxytrichloride, V2O3 vanadium trioxide, vanadium dioxide, VOSO4 vanadium oxy sulfate, VO(OC(=CH2)CH2COCH3)3 vanadium oxyacetylacetonate, V(OC(=CH2)CH2COCH3)3 vanadium acetylacetonate, VCl3 vanadium trichloride, etc.

[0034] The rust preventive agent may be a guanidino group-containing compound, a piguanidino group-containing compound, a thiocarbonyl group-containing compound, etc.

[0035] A rust preventive pigment can also be used as the rust preventive agent. Examples of rust preventive pigments include silica particles and the above-mentioned metal phosphate particles, etc. When a rust preventive pigment is used as the rust preventive agent, its particle size and content are not particularly limited. In particular, when the rust preventive agent is amorphous silica, especially when it has a particle size of 0.5 μm or more and 10 μm or less, a high effect can be expected. In this case, the content of amorphous silica in the outer layer may be, for example, 5 vol% or more and 30 vol% or less.

[0036] In the surface-treated steel sheet according to the first embodiment, the outer layer does not have to contain a conductive agent. "Not containing a conductive agent" means that a component intended to function as a conductive agent is not substantially contained. Specific examples of the conductive agent will be described later.

[0037] In the surface-treated steel sheet according to the first embodiment, the adhesion amount of the outer layer is 1.0 g / m 2 or more and 5.0 g / m 2 or less. If the adhesion amount of the outer layer is too small, the corrosion resistance is likely to decrease. If the adhesion amount of the outer layer is too large, the weldability is likely to decrease. In the surface-treated steel sheet according to the first embodiment, the adhesion amount of the outer layer may be 1.5 mg / m 2 or more or 2.0 mg / m 2 or more, and may also be 4.5 mg / m 2 or less or 4.0 mg / m 2 or less. Incidentally, the adhesion amount of the coating film in the surface-treated steel sheet can be measured by the gravimetric method or cross-sectional observation. As the measurement of the adhesion amount by the gravimetric method, after measuring the initial weight of the steel sheet cut into a predetermined size, a method of removing the coating film using a solvent capable of dissolving the binder resin or a dedicated chemical, or a method of removing the coating film by blast treatment using resin beads or alumina beads, is used to measure the weight of the steel sheet from which the coating film has been removed, and it is possible to calculate by obtaining these differences.

[0038] 1.2.3 Others The inner layer and the outer layer may contain other components other than the above-described components. Examples of other components include various additives. For example, pigments other than the above-described rust-preventive pigments (such as bright pigments for improving design), lubricants, defoaming agents, thickeners, and the like. The content of other components in the surface treatment layer is not particularly limited.

[0039] 2. Second Embodiment In addition to the above first embodiment, the surface-treated steel sheet of the present disclosure may have the following second embodiment. That is, the surface-treated steel sheet according to the second embodiment has an alloyed hot-dip galvanized steel sheet and a surface treatment layer provided on at least one main surface of the alloyed hot-dip galvanized steel sheet. The surface treatment layer has a two-layer structure of an inner layer and an outer layer. The inner layer is a chemical conversion treatment layer in contact with the alloyed hot-dip galvanized steel sheet. The adhesion amount of the inner layer is 200 mg / m 2 or more and 2000 mg / m 2The following holds. The maximum adhesion amount M1 and the minimum adhesion amount M2 of the inner layer satisfy the relationship of the following formula (1). The outer layer contains a binder resin, a conductive agent, and a rust preventive agent. The adhesion amount of the outer layer is 2.0 g / m 2 or more and 20 g / m 2 or less.

[0040] 2.0 ≤ M1 / M2 ≤ 50 ···(1)

[0041] The surface-treated steel sheet according to the second embodiment can have the same configuration as the surface-treated steel sheet according to the first embodiment, except that (I) the outer layer essentially contains a conductive agent in addition to the binder resin and the rust preventive agent (II) the adhesion amount of the outer layer is 2.0 to 20 g / m 2 or more.

[0042] 2.1 Conductive Agent The conductive agent has a function of improving the conductivity of the outer layer and improving the weldability of the surface-treated steel sheet. In the present application, for example, the volume resistivity is 1.0×10 3Those having a value of Ω / cm or less can serve as a conductive agent. Examples of the conductive agent include metals and metal compounds. Specifically, metals such as magnesium, aluminum, silicon, calcium, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, germanium, strontium, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, indium, tin; alloys such as magnesium, aluminum, silicon, phosphorus, calcium, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, germanium, arsenic, strontium, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, indium, tin, antimony, tellurium; or compounds such as oxides of the above-mentioned metal elements may be used. Among them, magnesium, aluminum, silicon, chromium, iron, nickel, zinc, tin, zinc-aluminum alloy, zinc-aluminum-magnesium alloy, zinc-aluminum-magnesium-silicon alloy, zinc-iron alloy, zinc-chromium alloy, zinc-nickel alloy, iron-nickel alloy, iron-chromium alloy, stainless steel, ferrosilicon, ferromanganese, ferrophosphor, zinc oxide, etc. are easily available. The content of the conductive agent in the outer layer is not particularly limited and may be appropriately determined in consideration of the desired weldability and corrosion resistance.

[0043] In particular, when the conductive agent is doped oxide particles, an Si alloy containing 50 mass% or more of Si, an Si compound containing 50 mass% or more of Si, or a composite thereof, it is easy to improve the conductivity (weldability) and the adhesion to the electrodeposition coating film for the outer layer. In this case, the content of the conductive agent in the outer layer may be 5 vol% or more and 30 vol% or less.

[0044] When the conductive agent is doped oxide particles, specific examples of the doped oxide particles include doped zinc oxide particles. Examples of the doped zinc oxide particles include those obtained by doping at least one doping element selected from the group consisting of Group 13 elements of the periodic table such as B, Al, Ga, and In, and Group 15 elements of the periodic table such as P and As into zinc oxide particles to improve conductivity. When the doping element is Al or Ga, it is easier to further improve the conductivity. The content of the doping element may be, for example, 0.05 atom% or more or 0.1 atom% or more with respect to the undoped zinc oxide particles, and may be 5 atom% or less.

[0045] When the conductive agent is an Si alloy or an Si compound, specific examples of the Si alloy or the Si compound include ferrosilicon containing 70 mass% or more of Si. By including ferrosilicon as a conductive agent in the outer layer, it is easy to improve the corrosion resistance along with the conductivity of the outer layer. In particular, ferrosilicon containing 70 mass% or more of Si is excellent in corrosion resistance and moldability.

[0046] The conductive agent may be, for example, in the form of particles. When the conductive agent is in the form of particles, its average particle size is not particularly limited, and an appropriate size may be selected in consideration of the thickness of the outer layer and the like. If the particle size of the conductive agent is too small compared to the thickness of the outer layer, the conductivity is likely to decrease. On the other hand, if the particle size of the conductive agent is too large compared to the thickness of the outer layer, the conductive agent is likely to fall off from the coating film. In this regard, the particle size of the conductive agent may be 1 / 10 or more or 1 / 5 or more of the thickness of the outer layer, and may also be 2 times or less. The average particle size of the conductive agent may be, for example, 0.1 μm or more, 0.3 μm or more, 0.5 μm or more, or 1.0 μm or more, and may also be 20 μm or less, 10 μm or less, 8.0 μm or less, 6.0 μm or less, 5.0 μm or less, 4.0 μm or less, or 2.5 μm or less. Note that the "average particle size" refers to the average primary particle size when the particles present in the outer layer exist as primary particles, and the average secondary particle size when they exist in an aggregated state. The average particle size is measured as follows. That is, the surface-treated steel sheet with the outer layer formed is cut, its cross-section is exposed and then polished, and the polished cross-section thus obtained is observed with a scanning electron microscope to obtain an observation image. Several particles present in the field of view of the observation image are arbitrarily selected, the equivalent circle diameter of each particle is determined, and the average value thereof is taken as the average particle size. Whether the particles in the observation image are the conductive agent can be easily determined by performing elemental analysis or the like.

[0047] 2.2 Adhesion amount of the outer layer In the surface-treated steel sheet according to the second embodiment, the adhesion amount of the outer layer is 2.0 g / m 2 or more and 20 g / m 2 or less. In the second embodiment, since the conductive agent is essentially contained in the outer layer, excellent weldability can be ensured even if the adhesion amount of the outer layer is increased. On the other hand, if the adhesion amount of the outer layer is made too thin, it becomes difficult to ensure corrosion resistance. In the surface-treated steel sheet according to the second embodiment, the adhesion amount of the outer layer may be 3.5 g / m 2 or more or 5.0 g / m 2 or more, and may also be 15 g / m 2 or less or 10 g / m 2 or less.

[0048] 3. Manufacturing method of surface-treated steel sheet The above surface-treated steel sheet can be manufactured, for example, by the following method. That is, the manufacturing method of the surface-treated steel sheet is obtaining an alloyed hot-dip galvanized steel sheet, forming an inner layer by performing a chemical conversion treatment on at least one main surface of the alloyed hot-dip galvanized steel sheet, and forming an outer layer by applying a paint containing a binder resin, a rust preventive agent, and optionally a conductive agent to the surface of the inner layer, may be included.

[0049] 3.1 Production of alloyed hot-dip galvanized steel sheet The alloyed hot-dip galvanized steel sheet can be obtained, for example, by obtaining a slab by continuous casting, performing hot rolling on the slab to obtain a hot-rolled sheet, winding up the hot-rolled sheet, performing cold rolling on the hot-rolled sheet to obtain a cold-rolled sheet, annealing the cold-rolled sheet, performing plating and alloying treatment on the annealed sheet, and controlling the unevenness of the plating surface by skin pass. The continuous casting conditions, hot rolling conditions, winding-up conditions, cold rolling conditions, annealing conditions, and plating conditions may be conventional well-known general conditions. On the other hand, unevenness is formed on the surface of the plating during the alloying treatment of the plating. In the manufacturing method of the present disclosure, by controlling the skin pass after the alloying treatment to control the roughness of the plating surface, it becomes easier to control the maximum adhesion amount M1 and the minimum adhesion amount M2 of the chemical conversion treatment layer described later so as to satisfy the above formula (1). For example, the skin pass conditions may be controlled so that the arithmetic mean roughness Ra of the plating surface of the alloyed hot-dip galvanized steel sheet is 0.2 μm or more and 1.5 μm or less.

[0050] 3.2 Chemical conversion treatment In the manufacturing method of the present disclosure, a chemical conversion treatment layer is formed as an inner layer by subjecting at least one main surface of the alloyed hot-dip galvanized steel sheet obtained as described above to a chemical conversion treatment. The chemical conversion treatment can be performed by applying various treatment liquids as described above to the steel sheet surface and drying. Here, the wettability of the treatment liquid with respect to the steel sheet changes depending on the material (solvent, additive, etc. in the treatment liquid) when forming the chemical conversion treatment layer. In this regard, even if the components contained in the inner layer after drying have the same composition, depending on the wettability of the treatment liquid with respect to the steel sheet during the chemical conversion treatment, the ratio M1 / M2 may or may not satisfy the relationship of the above formula (1). That is, in the manufacturing method of the present disclosure, in addition to controlling the roughness of the plating surface as described above, it is preferable to control the wettability of the treatment liquid with respect to the steel sheet during the chemical conversion treatment so that the ratio M1 / M2 satisfies the relationship of formula (1).

[0051] 3.3 Formation of the coating film In the manufacturing method of the present disclosure, a coating film is formed as an outer layer by applying a paint containing a binder resin, a rust preventive agent, and optionally a conductive agent to the surface of the inner layer formed as described above and drying. Here, it is advisable to adjust the coating amount of the paint and the like so that the adhesion amount of the outer layer is within the range described above.

Examples

[0052] Hereinafter, the present invention will be further described while showing examples, but the present invention is not limited to the following examples. The present invention can adopt various conditions as long as it does not deviate from the gist of the present invention and achieves the object of the present invention.

[0053] 1. Manufacture of surface-treated steel sheet 1.1 Preparation of alloyed hot-dip galvanized steel sheet Five types of zinc-based plated steel sheets and cold-rolled steel sheets described below were prepared, immersed in an aqueous solution (2.5 mass%, 40 °C) of an aqueous alkaline degreasing agent (FC-301 manufactured by Nippon Parkerizing Co., Ltd.) for 2 minutes to degrease the surface, and then washed with water and dried to obtain a base metal plate for surface treatment.

[0054] GA: Galvanized Alloyed Steel Sheet (thickness 0.8 mm, 10 mass% Fe, coating weight 45 g / m2) ZL: Electroplated Zn-10 mass% Ni Alloy Coated Steel Sheet (thickness 0.8 mm, coating weight 40 g / m2) GI: Galvanized Steel Sheet (thickness 0.8 mm, coating weight 60 g / m2) EG: Electrogalvanized Steel Sheet (thickness 0.8 mm, coating weight 40 g / m2) CR: Cold Rolled Steel Sheet (thickness 0.8 mm, no coating)

[0055] In addition, for GA, by changing the conditions of the skin pass after plating, the following four types of GA steel sheets were produced. Needless to say, the skin pass was performed on the entire surface of the plated steel sheet, and by adjusting conditions such as the reduction ratio of the skin pass, the ratio of the portion leveled in a planar shape and the portion with unevenness remaining without being reduced or with a small amount of reduction was changed. When observing the cross-section of the plated steel sheet, the portion of the plated surface that is substantially parallel to the interface between the plating and the base metal steel sheet was determined as the "planar portion" described below.

[0056] GA1: The area ratio of the portion flattened into a planar portion by the skin pass is 40% or more and less than 60% GA2: The area ratio of the portion flattened into a planar portion by the skin pass is 20% or more and less than 40% GA3: The area ratio of the portion flattened into a planar portion by the skin pass is 60% or more and less than 85% GA4: The area ratio of the portion flattened into a planar portion by the skin pass is 85% or more

[0057] 1.2 Formation of the Inner Layer (Conversion Coating Layer) Next, the following three types of treatment liquids for conversion coating were prepared. While changing the bar coating number so that the coating amounts shown in Tables 2 and 3 were obtained, the treatment liquids were applied onto the above metal plates, and then dried while setting the temperature reaching the metal plate surface in the hot air furnace to 70 °C and air-dried, thereby forming a conversion coating layer on the surface of the metal plates.

[0058] Treatment liquid for chemical conversion treatment composed of Zr compound, silane coupling agent, silica fine particles, and polyester resin with Nv of 10% S2: Treatment liquid for chemical conversion treatment with the same composition as S1, to which water is added and Nv is adjusted to 5% S3: Treatment liquid for chemical conversion treatment with the same composition as S1, to which a surfactant is added to improve wettability with a metal plate and Nv is 10%

[0059] 1.3 Formation of outer layer (coating film) Next, in order to form a coating film having the composition (vol%) shown in Table 1, each component was mixed so as to have the same solid content concentration as in Table 1, and a paint composition for forming a coating film was prepared. While changing the bar coater number and dilution ratio so that the coating amount shown in Tables 2 and 3 was obtained, this composition was applied onto the chemical conversion treatment layer with a bar coater and dried using an oven under the condition that the maximum reaching temperature was 200 °C, thereby forming a coating film as the outer layer. The components contained in the paint composition are shown below.

[0060] (Rust preventive pigment) Si: Silica (amorphous silica with an oil absorption of 100 to 1000 ml / 100 g, a specific surface area of 200 to 1000 m 2 / g, and an average particle size of 1 to 30 μm) (Silomasque 02 manufactured by Fuji Silysia) PA: Aluminum tripolyphosphate (average particle size of 1 to 2 μm) PM: Magnesium phosphate (average particle size of 1 to 2 μm)

[0061] (Conductive pigment) FeSi: Ferrosilicon particles (average particle size of 3 to 7 μm) SUS: SUS particles (average particle size of 3 to 7 μm) ZnO: Doped zinc oxide particles (23-Kt manufactured by Hakusuitech Co., Ltd. (average particle size = 0.5 μm))

[0062] (Binder resin) B1: A resin obtained by blending melamine (Cymel 325 manufactured by Mitsui Cytec Co., Ltd.) with a polyester resin (Vylon 200 manufactured by Toyobo Co., Ltd.) at a solid content ratio of 70:30 was used. B2: Water-based epoxy resin (0434AN manufactured by ADEKA Corporation)

[0063] 2. Performance evaluation test 2.1 Spot weldability The surface-treated steel sheet prepared as described above was subjected to a continuous dotting test for spot welding using a CF-type Cr-Cu electrode with a tip diameter of 5 mm and an R of 40, at a pressing force of 1.96 kN, a welding current of 8 kA, and a conduction time of 12 cycles / 50 Hz. The number of dots just before the nugget diameter fell below 3√t (t is the plate thickness) was determined. The superiority or inferiority of the spot weldability was evaluated using the following evaluation points. In such a welding test, when it was "4", "5", or "6", it was judged that the weldability was excellent. The results are shown in Tables 2 and 3. 1: No nugget is generated and no welding can be done at all, or the number of dots is less than 10 dots 2: The number of dots is 10 or more and less than 50 dots 3: The number of dots is 50 or more and less than 200 dots 4: The number of dots is 200 or more and less than 1000 dots 5: The number of dots is 1000 or more and less than 2000 dots 6: The number of dots is 2000 or more

[0064] 2.2 Corrosion resistance test The end face of the surface-treated steel sheet prepared as described above was sealed with sealing tape, and a cycle corrosion test under the following cycle conditions was carried out for 30 cycles.

[0065] (Cycle conditions) Salt spray (SST, 5% NaCl, 35°C atmosphere) for 2 hours, drying (60°C) for 2 hours, and wetting (50°C, 98% RH) for 4 hours were taken as one cycle and carried out.

[0066] After that, the corrosion situation from the flat part was observed, and the following evaluation scores were given. In such a corrosion resistance test, when it was "3", "4", or "5", it was judged that the corrosion resistance was excellent. The results are shown in Tables 2 and 3. 1: The area ratio of white rust generation from the evaluation surface is 50% or more, or the generation of red rust from the evaluation surface is confirmed 2: The area ratio of white rust generation from the evaluation surface is 10% or more and less than 50% 3: The white rust occurrence area ratio from the evaluation surface is 5% or more and less than 10% 4: The white rust occurrence area ratio from the evaluation surface is 1% or more and less than 5% 5: The white rust occurrence area ratio from the evaluation surface is less than 1%

[0067]

Table 1

[0068]

Table 2

[0069]

Table 3

[0070] The following can be understood from the results shown in Table 2.

[0071] For No.1, 2, 8, and 14, the adhesion amount of the inner layer (chemical conversion treatment layer) in the surface-treated steel sheet was too small, resulting in a decrease in the corrosion resistance of the surface-treated steel sheet.

[0072] For No.7, 13, and 19, the adhesion amount of the inner layer (chemical conversion treatment layer) in the surface-treated steel sheet was too large, resulting in a decrease in the weldability of the surface-treated steel sheet.

[0073] For No.1, 2, 8, and 9, the ratio M1 / M2 of the maximum adhesion amount M1 to the minimum adhesion amount M2 of the inner layer (chemical conversion treatment layer) in the surface-treated steel sheet was too large, so in some parts the inner layer became too thin, resulting in a decrease in the corrosion resistance of the surface-treated steel sheet.

[0074] For No.7, 13, 19, 22 to 31, the ratio M1 / M2 of the maximum adhesion amount M1 to the minimum adhesion amount M2 of the inner layer (chemical conversion treatment layer) in the surface-treated steel sheet was too small, so the inner layer became too thick overall, resulting in a decrease in the weldability of the surface-treated steel sheet.

[0075] Regarding No.32, since the coating amount of the outer layer coating film was too small, the corrosion resistance of the surface-treated steel sheet decreased.

[0076] Regarding No.35, since the coating amount of the outer layer coating film was too large, the weldability of the surface-treated steel sheet decreased.

[0077] Regarding No.24 to 31, since plating steel sheets other than alloyed hot-dip galvanized steel sheets were used as the plating steel sheets for the base material, there were no appropriate irregularities on the plating surface. Despite controlling the coating amount of the inner layer within the predetermined range, M1 / M2 became too small. As a result, it was difficult to achieve both good weldability and corrosion resistance of the surface-treated steel sheet.

[0078] Also, for some examples, although alloyed hot-dip galvanized steel sheets were used as the plating steel sheets for the base material, the skin pass conditions were not appropriate and the irregularities on the plating surface were not controlled to an appropriate state, or the wetting property of the treatment liquid constituting the inner layer was not appropriate. Despite controlling the coating amount of the inner layer within the predetermined range, M1 / M2 could not be controlled within the predetermined range. As a result, it was difficult to achieve both good weldability and corrosion resistance of the surface-treated steel sheet.

[0079] On the other hand, regarding No.3 to 6, 10 to 12, 15 to 18, 20, 21, 33, 34, 36 to 39, alloyed hot-dip galvanized steel sheets with appropriate rolling reduction conditions in the skin pass were used as the plating steel sheets for the base material, and treatment liquids with appropriate wetting properties were used as the treatment liquids constituting the inner layer. As a result, the coating amount of the inner layer and M1 / M2 were controlled within the predetermined ranges, and the coating amount of the outer layer was controlled within the predetermined range. Therefore, it was possible to achieve both excellent weldability and corrosion resistance.

[0080] Also, the following can be understood from the results shown in Table 3.

[0081] Regarding No.44 and 45, since the coating amount of the outer layer was too small, the corrosion resistance of the surface-treated steel sheet decreased.

[0082] For No.50, the adhesion amount of the outer layer was too large, resulting in a decrease in the weldability of the surface-treated steel sheet.

[0083] For No.62, 63, and 66, the adhesion amount of the inner layer was too small, resulting in a decrease in the corrosion resistance of the surface-treated steel sheet.

[0084] For No.64, the adhesion amount of the inner layer was too large, resulting in a decrease in the weldability of the surface-treated steel sheet.

[0085] For No.62, 63, and 65, the ratio M1 / M2 of the maximum adhesion amount M1 to the minimum adhesion amount M2 of the inner layer was too large. As a result, the inner layer became too thin in some parts, leading to a decrease in the corrosion resistance of the surface-treated steel sheet.

[0086] For No.64, 67 - 70, the ratio M1 / M2 of the maximum adhesion amount M1 to the minimum adhesion amount M2 of the inner layer (chemical conversion treatment layer) in the surface-treated steel sheet was too small. As a result, the inner layer became too thick overall, leading to a decrease in the weldability of the surface-treated steel sheet.

[0087] For No.67 - 70, since a plating steel sheet other than an alloyed hot-dip galvanized steel sheet was adopted as the base plating steel sheet, there were no appropriate irregularities on the plating surface. Although the adhesion amount of the inner layer was controlled within a predetermined range, M1 / M2 became too small. As a result, it was difficult to achieve both good weldability and corrosion resistance of the surface-treated steel sheet.

[0088] Also, for some examples, although an alloyed hot-dip galvanized steel sheet was adopted as the base plating steel sheet, because a treatment liquid with inappropriate wettability was used for the inner layer, M1 / M2 could not be controlled within a predetermined range despite controlling the adhesion amount of the inner layer within a predetermined range. As a result, it was difficult to achieve both good weldability and corrosion resistance of the surface-treated steel sheet.

[0089] On the other hand, for Nos. 40 to 43, 46 to 49, and 51 to 61, alloyed hot-dip galvanized steel sheets with appropriate rolling reduction conditions in the skin pass were adopted as the base plating steel sheets, and those with wettability controlled to an appropriate state were adopted as the treatment liquid constituting the inner layer. As a result of controlling the adhesion amount of the inner layer and M1 / M2 within a predetermined range and the adhesion amount of the outer layer within a predetermined range, excellent weldability and corrosion resistance could be achieved simultaneously.

[0090] From the results shown in Tables 2 and 3, it can be said that the surface-treated steel sheets satisfying the following requirement (A) or (B) have excellent weldability and corrosion resistance.

[0091] (A) A surface-treated steel sheet having: an alloyed hot-dip galvanized steel sheet, and a surface treatment layer provided on at least one main surface of the alloyed hot-dip galvanized steel sheet, wherein the surface treatment layer has a two-layer structure of an inner layer and an outer layer, the inner layer is a chemical conversion treatment layer in contact with the alloyed hot-dip galvanized steel sheet, the adhesion amount of the inner layer is 200 mg / m 2 or more and 2000 mg / m 2 or less, the maximum adhesion amount M1 and the minimum adhesion amount M2 of the inner layer satisfy the relationship of the following formula (1), the outer layer contains a binder resin and a rust preventive agent, the outer layer does not contain a conductive agent, the adhesion amount of the outer layer is 1.0 g / m 2 or more and 5.0 g / m 2 or less, a surface-treated steel sheet. 2.0 ≦ M1 / M2 ≦ 50 ···(1)

[0092] (B) A surface-treated steel sheet having: an alloyed hot-dip galvanized steel sheet, and a surface treatment layer provided on at least one main surface of the alloyed hot-dip galvanized steel sheet, wherein the surface treatment layer has a two-layer structure of an inner layer and an outer layer, The inner layer is a chemical conversion treatment layer that contacts the alloyed hot-dip galvanized steel sheet, the adhesion amount of the inner layer is 200 mg / m 2 or more and 2000 mg / m 2 or less, the maximum adhesion amount M1 and the minimum adhesion amount M2 of the inner layer satisfy the relationship of the following formula (1), the outer layer contains a binder resin, a conductive agent, and a rust preventive agent, the adhesion amount of the outer layer is 2.0 g / m 2 or more and 20 g / m 2 or less, Surface-treated steel sheet. 2.0 ≦ M1 / M2 ≦ 50 ···(1)

Claims

1. An alloyed hot-dip galvanized steel sheet, and at least one main surface of the alloyed hot-dip galvanized steel sheet, a surface treatment layer provided on the surface of the alloyed hot-dip galvanized steel sheet layer, A surface-treated steel sheet having The surface treatment layer has a two-layer structure of an inner layer and an outer layer, The inner layer is a chemical conversion treatment layer in contact with the alloyed hot-dip galvanized steel sheet, The adhesion amount of the inner layer is 200 mg / m ２ or more and 2000 mg / m ２ or less, and The maximum adhesion amount M1 and the minimum adhesion amount M2 of the inner layer satisfy the relationship of the following formula (1), The outer layer contains a binder resin and a rust preventive agent, The outer layer does not contain a conductive agent having a volume resistivity of 1.0×10 3 Ω / cm or less, The adhesion amount of the outer layer is 1.0 g / m ２ or more and 5.0 g / m ２ or less, Surface-treated steel sheet. 2.0 ≦ M1 / M2 ≦ 50... (1) Here, M1 / M2 is obtained by observing the cross-section of the surface-treated steel sheet with an electron microscope, taking the maximum thickness portion of the chemical conversion treatment layer as the portion of "maximum adhesion amount M1" and the minimum thickness portion as the portion of "minimum adhesion amount M2", and calculating the maximum thickness / minimum thickness from the thickness ratio.

2. An alloyed hot-dip galvanized steel sheet, and at least one main surface of the alloyed hot-dip galvanized steel sheet, a surface treatment layer provided on the surface of the alloyed hot-dip galvanized steel sheet layer, A surface-treated steel sheet having The surface treatment layer has a two-layer structure of an inner layer and an outer layer, The inner layer is a chemical conversion treatment layer in contact with the alloyed hot-dip galvanized steel sheet, The adhesion amount of the inner layer is 200 mg / m ２ or more and 2000 mg / m ２ or less, and The maximum adhesion amount M1 and the minimum adhesion amount M2 of the inner layer satisfy the relationship of the following formula (1), The outer layer contains a binder resin, a conductive agent, and a rust preventive agent, The adhesion amount of the outer layer is 2.0 g / m ２ or more and 20 g / m ２ or less, Surface-treated steel sheet. 2.0 ≦ M1 / M2 ≦ 50... (1) Here, M1 / M2 is obtained by observing the cross-section of the surface-treated steel sheet with an electron microscope, taking the maximum thickness portion of the chemical conversion treatment layer as the portion of "maximum adhesion amount M1" and the minimum thickness portion as the portion of "minimum adhesion amount M2", and calculating the maximum thickness / minimum thickness from the thickness ratio.

3. The conductive agent is a doped oxide particle, a Si alloy containing 50% by mass or more of Si, a Si compound containing 50% by mass or more of Si, or a composite thereof, The content of the conductive agent in the outer layer is 5 vol% or more and 30 vol% or less, The surface-treated steel sheet according to claim 2.

4. The doped oxide particles are doped zinc oxide particles, The surface-treated steel sheet according to claim 3.

5. The Si alloy or the Si compound is ferrosilicon containing 70% by mass or more of Si, The surface-treated steel sheet according to claim 3 or 4.

6. The rust preventive agent is amorphous silica having a particle diameter of 0.5 μm or more and 10 μm or less, and the content of the amorphous silica in the outer layer is 5 vol% or more and 30 vol% or less. The surface-treated steel sheet according to any one of claims 1 to 5.

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