Surface-treated steel material

Abstract

This invention provides a surface-treated steel material having high corrosion resistance and a low sliding coefficient. The present invention relates to a surface-treated steel material in which a steel material, a plating layer containing Zn, and a film are arranged in this order. The film contains trivalent Cr and an organic silicon compound, and the trivalent Cr concentration in the film is 0.30 mass% to 15.0 mass%.

Description

Surface-treated steel

[0001] The present invention relates to a surface-treated steel material.

[0002] It is known that zinc-based plating layers formed from zinc or zinc-containing alloys improve the corrosion resistance of steel materials. To further improve the corrosion resistance and blackening resistance of the zinc-based plating layer, an inorganic coating is sometimes formed on the surface of the zinc-based plating layer.

[0003] For example, Patent Documents 1 and 2 describe the formation of a coating containing trivalent chromium on the surface of a zinc-based plating layer, and state that the coating containing trivalent chromium can improve the corrosion resistance of flat plates and processed parts.

[0004] International Publication No. 2023 / 121175 Special Publication No. 2024-505793

[0005] Patent Documents 1 and 2 describe that a coating containing trivalent chromium improves the corrosion resistance of a steel sheet having a zinc-based plating layer. However, according to the findings of the present inventors, the use of a coating containing trivalent chromium sometimes does not improve the corrosion resistance of the steel material. Furthermore, the formation of a coating containing trivalent chromium sometimes reduces the sliding properties, and the plating layer that has adhered to the mold is likely to peel off during press working.

[0006] In view of these circumstances, an object of the present invention is to provide a surface-treated steel material that has high corrosion resistance and a low sliding coefficient.

[0007] One aspect of the present invention for solving the above problems relates to the surface-treated steel materials of [1] to [7] below. [1] A surface-treated steel material comprising a steel material, a Zn-containing plating layer, and a coating, arranged in this order, wherein the coating contains trivalent Cr and an organosilicon compound, and the trivalent Cr concentration in the coating is 0.30 mass% or more and 15.0 mass% or less. [2] The surface-treated steel material according to [1], wherein the coating contains Zr. [3] The surface-treated steel material according to [1] or [2], wherein the mass concentration ratio (Cr / Si) of the trivalent Cr to the Si derived from the organosilicon compound in the coating is 0.020 or more and 0.850 or less. [4] The surface-treated steel material according to [1] to [3], wherein the coating contains at least one element selected from P and V. [5] The surface-treated steel material according to any one of [1] to [4], wherein the coating contains Co. [6] The surface-treated steel material according to any one of [1] to [5], wherein the coating has a thickness of 0.05 μm or more and 1.00 μm or less. [7] The surface-treated steel material according to any one of [1] to [6], wherein the plating layer has an Al content of 1.0 mass% or more and 22.0 mass% or less, an Mg content of 1.5 mass% or more and 10.0 mass% or less, and the balance consisting of Zn and optionally added trace additives.

[0008] According to the present invention, a surface-treated steel material having high corrosion resistance and a low coefficient of friction is provided.

[0009] An embodiment of the present invention will be described below.

[0010] 1. Surface-Treated Steel Material The surface-treated steel material according to this embodiment has a steel material, a plating layer, and a coating, arranged in this order.

[0011] 1-1. Steel Material The type of steel material used as the base steel material is not particularly limited, and may be any type, such as steel plate, steel bar, H-shaped steel, I-shaped steel, wire rod, construction hardware, steel pipe, etc. For example, any steel plate can be used, such as hot-rolled mild steel plate and steel strip described in JIS G 3131 (2018), hot-rolled steel plate and steel strip for automobiles described in JIS G 3113 (2018), cold-rolled steel plate and steel strip described in JIS G 3141 (2017), and various stainless steel plates (including austenitic, martensitic, ferritic, and ferrite-martensite dual-phase).

[0012] 1-2. Plating Layer The plating layer is a plating layer containing zinc (Zn). The plating layer is preferably a plating layer containing Zn as the main component. Incidentally, "containing Zn as the main component" means that the plating layer contains 50 mass% or more of Zn. The plating layer may be a plating layer manufactured by any method, such as electroplating, hot-dip plating, or vapor deposition plating. The plating layer may be a Zn plating layer, or a plating layer made of an alloy containing Zn (for example, an alloy such as Zn-Al, Zn-Mg, Zn-Ni, or Zn-Al-Mg).

[0013] For example, the plating layer may contain 1.0 mass% or more and 22.0 mass% or less of aluminum (Al). Al passivates the plating layer, improving its corrosion resistance and suppressing the generation of dross during production. By setting the Al content to 1.0 mass% or more, the corrosion resistance of the plating layer can be sufficiently improved and the generation of dross can also be sufficiently suppressed. By setting the Al content to 22.0 mass% or less, a decrease in the adhesion of the plating layer can be suppressed and a decrease in the sacrificial corrosion protection effect due to Zn can be suppressed. The Al content is preferably 12.0 mass% or more and 20.0 mass% or less.

[0014] The coating layer may also contain 1.5% by mass or more and 10.0% by mass or less of magnesium (Mg). Mg uniformly generates dense corrosion products on the surface of the coating layer, preventing erosion by corrosion factors and improving the corrosion resistance of the coating layer. By setting the Mg content to 1.5% by mass or more, the dense and uniform corrosion products can be sufficiently generated, thereby sufficiently improving the corrosion resistance of the coating layer. By setting the Mg content to 10.0% by mass or less, it is possible to suppress a decrease in the sacrificial corrosion protection effect caused by Zn and also to suppress the generation of dross. The Mg content is preferably 2.0% by mass or more and 8.5% by mass or less, and more preferably 4.0% by mass or more and 7.0% by mass or less.

[0015] When the plating layer contains Al, it may contain silicon (Si) in an amount of 0.005 mass % or more and 2.0 mass % or less, which can suppress the growth of an Fe—Zn alloy layer and an Fe—Al alloy layer at the interface between the steel material and the plating layer, in order to improve the adhesion between the steel material and the plating layer. Furthermore, when the plating layer contains Mg, it may contain Zn, which has a negative effect on the appearance and corrosion resistance. １１ Mg ２ To suppress the formation and growth of phases, titanium (Ti), boron (B), a Ti—B alloy, a Ti-containing compound, or a B-containing compound may be contained. The content of these compounds is preferably in the range of 0.001% by mass to 0.1% by mass for Ti, and in the range of 0.0005% by mass to 0.045% by mass for B.

[0016] The plating layer may also contain trace additives or unavoidable impurities added arbitrarily in addition to Zn as the balance. Trace additives are, for example, elements added to enhance the corrosion resistance of the plating layer. Trace additives may be elements such as Sn, Bi, In, Ca, Y, La, Ce, Si, Cr, Ti, Ni, Co, V, Nb, Cu, Mn, Fe, Sr, Sb, Pb, B, Li, Zr, Mo, W, Ag, and P. The content of these trace additives may be from the detection limit to 1% by mass.

[0017] 1-3. Coating The coating is a film formed by surface treatment on the surface of the plating layer.

[0018] In this embodiment, the coating contains trivalent chromium (Cr) and an organosilicon compound.

[0019] The organosilicon compound can be, for example, a molecule in which an organic functional group and a hydrolyzable functional group are bonded to a silicon molecule. The organic functional group is an organic reactive group such as an amino group, an epoxy group, a (meth)acryloyl group, a vinyl group, or a mercapto group, and the hydrolyzable functional group is a functional group such as an alkoxy group. The organic functional group may be bonded to the silicon molecule via an alkylene group or an oxyalkylene group.

[0020] The organosilicon compound forms a crosslinked structure in the coating, improving the adhesion of the coating to the plating layer. Furthermore, in this embodiment, the trivalent Cr dispersed in the coating reacts or interacts with the organosilicon compound to form a denser coating structure, which is thought to improve the barrier properties of the coating and thereby enhance the corrosion resistance of the surface-treated steel material. Furthermore, because trivalent Cr has low toxicity, it is thought that it will not cause problems such as adverse effects on the human body or environmental pollution.

[0021] The trivalent Cr concentration in the coating is 0.30% by mass or more and 15.0% by mass or less. By setting the trivalent Cr concentration to 0.30% by mass or more, it becomes easier to form the dense coating structure, and the corrosion resistance of the surface-treated steel material can be increased by improving the barrier properties. By setting the trivalent Cr concentration to 15.0% by mass or less, it is possible to suppress an increase in the sliding coefficient due to aggregation of trivalent Cr. From the viewpoint of balancing these, the trivalent Cr concentration in the coating is preferably 0.5% by mass or more and 10.0% by mass or less, and more preferably 1.0% by mass or more and 3.5% by mass or less.

[0022] The concentration of Si derived from the organosilicon compound is preferably 2.0% by mass or more and 30.0% by mass or less, more preferably 10.0% by mass or more and 20.0% by mass or less, and even more preferably 12.0% by mass or more and 20.0% by mass or less. The higher the concentration of Si derived from the organosilicon compound, the more the fingerprint resistance of the surface-treated steel material can be improved.

[0023] Zirconium forms a cross-linked structure in the coating, which improves the adhesion of the coating to the plating layer and also makes the coating structure denser, improving the barrier properties and further increasing the corrosion resistance of the surface-treated steel material. Zirconium also makes the coating structure denser, making the coating less susceptible to peeling due to water.

[0024] The amount of zirconium in the coating is preferably 0.1 mass % or more and 20.0 mass % or less, and more preferably 1.0 mass % or more and 10.0 mass % or less, relative to the total mass of the coating. By setting the amount within this range, the adhesion between the plating layer and the coating can be further improved, and the corrosion resistance of the surface-treated steel material can be further improved.

[0025] Furthermore, the mass concentration ratio (Cr / Si) of trivalent Cr to Si derived from the organosilicon compound in the coating is preferably 0.020 or more and 0.850 or less. The larger the Cr / Si, the more likely it is that a denser coating structure will result in improved barrier properties. The smaller the Cr / Si, the less Cr there is, and the less likely Cr aggregates are to form in the coating. This makes it difficult for Cr to be unevenly distributed in the coating, improving the sliding properties of the coating. Furthermore, the smaller the Cr / Si, the relatively larger the amount of organosilicon compound can be, thereby improving the fingerprint resistance of the surface-treated steel material. From the viewpoint of achieving a balance between these factors, it is more preferable that Cr / Si be 0.100 or more and 0.650 or less.

[0026] The coating preferably contains phosphorus (P) or vanadium (V). These elements, like zirconium, not only enhance the corrosion resistance of the coating, but also densify the coating structure, making it less susceptible to peeling due to water. The coating may contain either phosphorus or vanadium alone, or may contain both. From the viewpoint of more effectively achieving the effects of these elements in improving corrosion resistance and the effects of densifying the coating in improving water resistance, the coating preferably contains both phosphorus and vanadium.

[0027] Phosphorus improves the adhesion of the coating to the plating layer, thereby improving the corrosion resistance of the surface-treated steel material.

[0028] Phosphorus is typically contained in the coating as phosphoric acid or its salt. Examples of phosphoric acid or its salt include phosphoric acids such as orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, and tetraphosphoric acid, or their salts (e.g., ammonium salts such as triammonium phosphate and diammonium hydrogen phosphate), phosphonic acids such as aminotri(methylenephosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediaminetetra(methylenephosphonic acid), and diethylenetriaminepenta(methylenephosphonic acid), or their salts, and organic phosphoric acids such as phytic acid or their salts. In addition to ammonium salts, metal salts with Na, Mg, Al, K, Ca, Mn, Ni, Zn, Fe, and the like may also be used. These phosphoric acids or their salts may be used alone or in combination of two or more.

[0029] The amount of phosphorus in the coating is preferably 0.1 mass % or more and 25.0 mass % or less, and more preferably 1.0 mass % or more and 15.0 mass % or less, relative to the total mass of the coating. By setting the amount within this range, the adhesion between the plating layer and the coating can be further improved, and the corrosion resistance of the surface-treated steel material can be further improved.

[0030] Vanadium functions as an inhibitor and forms a precipitate film or a passive film, thereby further improving the corrosion resistance of the surface-treated steel material.

[0031] The amount of vanadium in the coating is preferably 0.1 mass % or more and 20.0 mass % or less, and more preferably 1.0 mass % or more and 10.0 mass % or less, relative to the total mass of the coating. By setting the amount within this range, the corrosion resistance of the surface-treated steel material can be further improved.

[0032] The coating preferably contains cobalt (Co).

[0033] Cobalt can effectively prevent discoloration of the plated steel sheet, particularly blackening. The cobalt may be divalent cobalt or trivalent cobalt.

[0034] The amount of cobalt in the coating is preferably 0.01 mass % or more and 10.0 mass % or less, and more preferably 0.1 mass % or more and 5.0 mass % or less, relative to the total mass of the coating. By setting the amount within this range, the blackening resistance of the surface-treated steel material can be effectively improved.

[0035] The coating may contain atoms such as titanium (Ti), niobium (Nb), tantalum (Ta), and tungsten (W). The coating may also contain silica particles, fluorides, and the like. The amount of these atoms or additives in the coating is preferably 0.01% by mass or more and 3.0% by mass or less, and more preferably 0.01% by mass or more and 2.0% by mass or less, relative to the total mass of the coating.

[0036] The amounts of these elements in the coating can be measured by X-ray photoelectron spectroscopy (XPS), which is performed using a mono-Al Kα (hν: 1486.6 eV) X-ray source at an acceleration voltage of 1 kV.

[0037] For Cr, if the detected peak top position is 576 to 578 eV, it is determined to be trivalent Cr, and if it is 579 to 580 eV, it is determined to be hexavalent Cr.

[0038] Regarding Si, it can be confirmed by Fourier transform infrared spectrophotometer (FT-IR) whether it is Si derived from an organosilicon compound. －１ (siloxane bond), 1500-1300 cm －１ (C-H bond, Si-CH ３ bond bending vibration), 900-800 cm (Si-CH ３ When an absorption peak is detected in any of the bands (stretching vibration of bond), the Si is determined to be Si derived from an organosilicon compound.

[0039] The thickness of the coating is preferably 0.05 μm or more and 1.50 μm or less. The thinner the thickness, the less likely the coating will peel off during processing, and the corrosion resistance of the processed portion can be improved. From the above viewpoint, the thickness of the coating is preferably 0.05 μm or more and 1.00 μm or less, and more preferably 0.10 μm or more and 0.80 μm or less.

[0040] 2. Method for Producing Surface-Treated Steel Material The above-described surface-treated steel material can be produced by applying a treatment solution containing a trivalent Cr compound and an organosilicon compound to the surface of the plating layer of a plated steel material having the above steel material and the above plating layer, and then drying the applied treatment solution.

[0041] The solvent for the treatment liquid is preferably an aqueous medium from the viewpoint of explosion prevention during the production of surface-treated steel materials. The aqueous medium is a liquid medium containing water as the main component, such as water or a mixture of water and a water-soluble organic solvent. The content of the liquid medium can be appropriately determined within a range of solid concentration suitable for application of the treatment liquid.

[0042] Examples of trivalent Cr compounds include chromium nitrate, chromium sulfate, chromium phosphate, chromium fluoride, chromium acetate, chromium oxalate, chromium chloride, etc. These trivalent Cr compounds may be used alone or in combination of two or more.

[0043] The amount of trivalent Cr compounds in the treatment solution, calculated as trivalent Cr atoms, is 0.30 mass % or more and 15.0 mass % or less, preferably 0.30 mass % or more and 7.50 mass % or less, and more preferably 0.30 mass % or more and 3.50 mass % or less, relative to the total mass of the solids in the treatment solution (components that make up the coating, excluding the solvent component, from among the components in the treatment solution).

[0044] Examples of organosilicon compounds include methyltriethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, trimethylmethoxysilane, dimethyldiethoxysilane, trimethylethoxysilane, 3-aminopropyltrimethoxysilane, n-methyl-3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltris(2-methoxyethoxy)silane, n-aminoethyl-3-aminopropyltrimethoxysilane, n-aminoethyl-3-aminopropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3- Examples of suitable silanes include mercaptopropylmethyldimethoxysilane, vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(2-methoxyethoxy)silane, vinyltriacetoxysilane, 3-(3,4-epoxycyclohexylethyltrimethoxy)silane, γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, 3-ureidopropyltriethoxysilane, 3-chloropropyltrimethoxysilane, 3-anilidopropyltrimethoxysilane, 3-(4,5-dihydroimidazolepropyltriethoxy)silane, n-phenyl-3-aminopropyltrimethoxysilane, heptadecafluorodecyltrimethoxysilane, tridecafluorooctyltrimethoxysilane, trifluoropropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, and p-styryltrimethoxysilane. These organosilicon compounds may be used alone or in combination of two or more.

[0045] The amount of the organosilicon compound in the treatment liquid is preferably 2.0% by mass or more and 30.0% by mass or less, and more preferably 10.0% by mass or more and 20.0% by mass or less, in terms of Si atoms, relative to the total mass of the solids in the treatment liquid.

[0046] Furthermore, the concentration ratio of the trivalent Cr compound and the organosilicon compound in the treatment solution, in terms of the concentration ratio of trivalent Cr to Si atoms (Cr / Si), is preferably 0.020 or more and 0.850 or less, and more preferably 0.100 or more and 0.650 or less.

[0047] The treatment liquid may contain a zirconium compound.

[0048] Examples of the zirconium compound include zirconium normal propylate, zirconium normal butylate, zirconium tetraacetylacetonate, zirconium monoacetylacetonate, zirconium bisacetylacetonate, zirconium monoethylacetoacetate, zirconium acetylacetonate bisethylacetoacetate, zirconium acetate, zirconium monostearate, fluorozirconic acid, zirconium carbonate, zirconium ammonium carbonate, zirconium potassium carbonate, and zirconium sodium carbonate, etc. These zirconium compounds may be used alone or in combination of two or more.

[0049] The amount of the zirconium compound in the treatment liquid is preferably 0.1 mass % or more and 20.0 mass % or less, and more preferably 1.0 mass % or more and 10.0 mass % or less, in terms of Zr atoms, relative to the total mass of the solid content in the treatment liquid.

[0050] The treatment liquid may contain phosphoric acid and a vanadium compound.

[0051] Examples of phosphoric acid include phosphoric acids such as orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, and tetraphosphoric acid, or salts thereof (e.g., ammonium salts such as triammonium phosphate and diammonium hydrogen phosphate), phosphonic acids such as aminotri(methylenephosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediaminetetra(methylenephosphonic acid), and diethylenetriaminepenta(methylenephosphonic acid), or salts thereof, and organic phosphoric acids such as phytic acid or salts thereof. In addition to ammonium salts, metal salts with Na, Mg, Al, K, Ca, Mn, Ni, Zn, Fe, and the like may also be used. These phosphoric acids or salts thereof may be used alone or in combination of two or more.

[0052] The amount of phosphoric acid in the treatment liquid is preferably 0.1% by mass or more and 25.0% by mass or less, and more preferably 1.0% by mass or more and 15.0% by mass or less, in terms of P atoms, relative to the total mass of the solids in the treatment liquid.

[0053] Examples of vanadium compounds include vanadium compounds obtained by reducing pentavalent vanadium compounds such as vanadium pentoxide, metavanadic acid, ammonium metavanadate, sodium metavanadate, and vanadium oxytrichloride with a reducing agent to divalent to tetravalent vanadium compounds, as well as divalent to tetravalent vanadium compounds such as vanadium trioxide, vanadium dioxide, vanadium oxysulfate, vanadium oxyoxalate, vanadium oxyacetylacetonate, vanadium acetylacetonate, vanadium trichloride, vanadium phosphomolybdic acid, vanadium sulfate, vanadium dichloride, and vanadium oxide. These vanadium compounds may be used alone or in combination of two or more.

[0054] The amount of the vanadium compound in the treatment liquid is preferably 0.1% by mass or more and 20.0% by mass or less, and more preferably 1.0% by mass or more and 10.0% by mass or less, in terms of vanadium atoms, relative to the total mass of the solid content in the treatment liquid.

[0055] The treatment liquid may contain a cobalt compound.

[0056] Examples of cobalt compounds include cobalt nitrate, cobalt sulfate, and cobalt carbonate.

[0057] The amount of the cobalt compound in the treatment liquid is preferably 0.01% by mass or more and 10.0% by mass or less, and more preferably 0.1% by mass or more and 5.0% by mass or less, in terms of Co atoms, relative to the total mass of the solid content in the treatment liquid.

[0058] The treatment liquid may contain an etching agent. The etching agent activates the surface of the Zn-based plating layer and contributes to improving the adhesion of the chemical conversion coating to the Zn-based plating layer. Examples of the etching agent include fluorides. The fluoride may be contained in the treatment liquid as a zirconium fluoride (such as fluorozirconic acid) or as another fluoride.

[0059] The treatment liquid may also contain a rheology control agent or other inorganic compounds.

[0060] The treatment liquid is preferably applied to the surface of the plating layer by a method such as roll coating, bar coating, or spraying.

[0061] The treatment solution applied to the surface of the plating layer is preferably dried (baked) at a temperature higher than 50°C and lower than 250°C, more preferably at a temperature of 70°C or higher and 150°C or lower, and even more preferably at a temperature higher than 100°C and lower than 140°C. If the drying temperature is higher than 50°C, the solvent can be sufficiently volatilized. If the drying temperature is lower than 250°C, decomposition of the coating components (particularly the organic chain) can be suppressed.

[0062] The surface-treated steel material is useful in a variety of applications, such as exterior and interior building materials. For example, the surface-treated steel material can be suitably used in a variety of applications, such as roofing materials and exterior materials for buildings, steel pipes and shaped steel beams, supports, and beams for greenhouses or agricultural greenhouses, transport components, sound insulation walls, soundproof walls, sound-absorbing walls, snow barriers, guardrails, balustrades, protective fences, supports, railway vehicle components, overhead line components, electrical equipment components, environmental safety components, structural components, solar mounting frames, and air conditioner outdoor units.

[0063] Furthermore, the surface-treated steel material can also be effectively used in applications where surface-treated steel materials have traditionally been used, such as enclosure applications for sound insulation walls, windbreaks, and switchboards.

[0064] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0065] 1. Preparation of Materials 1-1. Plated Steel Sheets Three types of plated steel sheets, designated A1 to A3 below, were prepared by plating 1.2 mm thick steel sheets in zinc-based plating baths with different compositions. The coating weight of each steel sheet was 150 g / m² per side. ２ A1: Hot-dip Zn-0.5% by mass Al-1% by mass Mg plated steel sheet A2: Hot-dip Zn-11% by mass Al-3% by mass Mg-0.2% by mass Si plated steel sheet A3: Hot-dip Zn-19% by mass Al-6% by mass Mg-0.2% by mass Si plated steel sheet

[0066] 1-2. Surface Treatment Solution A surface treatment solution was prepared by blending the following materials in the ratios shown in Table 1. The trivalent chromium compound and cobalt compound were hydrates, and Table 1 lists the amounts of each hydrate blended. Trivalent chromium compound: Chromium nitrate nonahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Organosilicon compound: Methyltrimethoxysilane (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Zirconium compound: Fluorozirconate (manufactured by Sigma-Aldrich) Phosphorus compound: Phosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Vanadium compound: Vanadium pentoxide (manufactured by Tokyo Chemical Industry Co., Ltd.) Cobalt compound: Cobalt nitrate hexahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Titanium compound: Titanium oxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0067]

[0068] 2. Surface Treatment The surface of each plated steel sheet was degreased by spraying a silicate-based alkaline degreasing agent (Fine Cleaner 4336, manufactured by Nippon Parkerizing Co., Ltd.) at a concentration of 20 g / L at a temperature of 60°C for 2 minutes, rinsing with pure water for 30 seconds, and then drying.

[0069] Each surface treatment solution was applied to the surface of a degreased plated steel sheet using a bar coater to a desired film thickness, then left to stand for 3 seconds and baked to form a coating from the treatment solution. Baking was performed by placing the test piece in an oven at 120°C for 30 seconds. By baking, the pure water contained in the surface treatment solution and the water in the hydrate of the trivalent chromium compound and the hydrate of the cobalt compound volatilized, forming a coating.

[0070] 3. Measurement 3-1. Film Thickness Test pieces were cut out from the steel sheet (surface-treated steel sheet) on which a film had been formed using the cryo-FIB method, and the cross-sectional structure of the cut-out test piece was observed with a transmission electron microscope (TEM) at a magnification (100,000 to 1,000,000 times) such that the entire film and a portion of the plating layer were visible within the observation field. The acceleration voltage was 200 kV. The film observed at the top of the outermost part of the plating layer when observed with the FE-TEM was identified as the film formed above. The film thickness of the film identified in this way was measured. The film thickness was determined by measuring one point at a time at three locations, with measurement intervals of 1 mm each, and averaging the measurements.

[0071] 3-2. Amount of Elements in the Coating The amount of elements contained in the coating was measured by elemental analysis using energy dispersive X-ray spectroscopy (EDS) and electron diffraction analysis of the area observed with TEM. For Nos. 1 to 18 and Nos. 20 to 22, elemental analysis was performed in an area 0.5 μm wide and 0.5 μm long in the center of the coating, and the concentrations of Cr, Si, P, V, Zr, Co, Ti, Zn, Al, Mg, and O were calculated. For No. 19, the same analysis was performed in an area 0.1 μm wide and 0.1 μm long. Cr / Si was calculated as a mass ratio from the TEM / EDS results.

[0072] The Cr contained in the coating was investigated by X-ray photoelectron spectroscopy (XPS). XPS measurements were performed using a mono-Al Kα X-ray source (hν: 1486.6 eV) at an acceleration voltage of 1 kV. When the detected peak top position was 576 to 578 eV, it was determined to be trivalent Cr, and when it was 579 to 580 eV, it was determined to be hexavalent Cr.

[0073] Furthermore, it was confirmed by Fourier transform infrared spectroscopy (FT-IR) that the Si contained in the coating was derived from an organic silicon compound. －１ (siloxane bond), 1500-1300 cm －１ (C-H bond, Si-CH ３ bond bending vibration), 900-800 cm (Si-CH ３ Since absorption peaks were detected in both the SiO2 and SiO2 bands (bond stretching vibrations), it was determined that the Si originated from an organosilicon compound.

[0074] For the surface-treated steel sheets on which a coating was formed using each treatment solution, the type of plated steel sheet, the type of treatment solution, the amount of each element, the trivalent Cr concentration and Si concentration in the coating, the Cr / Si mass ratio, and the coating thickness are shown in Table 2. The trivalent Cr concentration and Si concentration in the coating are the concentrations in the coating formed from anhydrous products.

[0075]

[0076] 4. Evaluation 4-1. Plane Corrosion Resistance The corrosion resistance of the plane portion of the obtained surface-treated steel sheets was evaluated. More specifically, test specimens (70 mm wide x 150 mm long) were cut out from each surface-treated steel sheet, and the end faces were sealed. After that, one cycle (8 hours in total) of salt spraying, drying, and wetting processes was repeated until the area ratio of white rust occurred reached 10%.

[0077] In the salt spray process, a 5% NaCl aqueous solution at 35°C was sprayed onto the test piece for 2 hours. In the drying process, the test piece was left in an environment with a temperature of 60°C and a relative humidity of 30% for 4 hours. In the wetting process, the test piece was left in an environment with a temperature of 50°C and a relative humidity of 95% for 2 hours. The test piece was evaluated according to the following criteria based on the number of cycles until the area ratio of white rust reached 10%. A rating of SS to A was considered a pass.

[0078] <Evaluation criteria> Rating SS: Over 300 cycles S: Over 250 cycles and 300 cycles or less A: Over 100 cycles and 250 cycles or less B: 100 cycles or less

[0079] 4-2. Corrosion resistance of processed portion The corrosion resistance of the processed portion of the obtained surface-treated steel sheets was evaluated. More specifically, test pieces (50 mm wide x 50 mm long) cut from each surface-treated steel sheet were extruded to a length of 7 mm using an Erichsen apparatus. The obtained extruded samples were subjected to the same test as for the evaluation of flat surface corrosion resistance described above, and the test pieces were evaluated according to the following criteria based on the number of cycles until the area ratio of white rust occurred reached 10%. A rating of S and a rating of A were considered to be pass.

[0080] <Evaluation criteria> Rating S: More than 15 cycles A: More than 9 cycles and 15 cycles or less B: 9 cycles or less

[0081] 4-3. Fingerprint Resistance The obtained surface-treated steel sheets were evaluated for fingerprint resistance. More specifically, test pieces (50 mm wide x 50 mm long) cut out from each surface-treated steel sheet were measured using a color difference meter to measure the increase or decrease in L value (ΔL) before and after applying Vaseline. Both a rating of S and a rating of A were considered to be passing.

[0082] <Evaluation criteria> Rating S: ΔL is less than 0.5 A: ΔL is 0.5 or more and less than 1.0

[0083] 4-4. Sliding Properties The sliding properties of the obtained surface-treated steel sheets were evaluated. More specifically, test pieces (width 17 mm × length 300 mm) cut out from each surface-treated steel sheet were slid for 200 mm using a drawbead tester with a pressing load of 2.0 to 5.5 kN and a pull-out speed of 500 mm / min. The load when sliding at each pressing load was measured as a pull-out load, and the slope of the line plotted with the pressing load on the x-axis and the pull-out load on the y-axis was calculated as a sliding coefficient, and the sliding properties were evaluated according to the sliding coefficient criteria below. A rating of A was considered a pass.

[0084] <Evaluation criteria> Rating S: Sliding coefficient less than 0.5 A: Sliding coefficient is 0.5 or more and less than 0.7 B: Sliding coefficient is 0.7 or more

[0085] 4-5. Blackening Resistance The obtained surface-treated steel sheets were evaluated for blackening resistance. More specifically, test pieces (50 mm wide x 50 mm long) cut out from each surface-treated steel sheet were left to stand in a thermostatic chamber at a temperature of 70°C and a humidity of 80% for 144 hours, and the lightness (L* value) of the test pieces was measured before and after the test. The lightness was measured using a color difference meter (CR-400, manufactured by Konica Minolta, Inc.) using a diffuse illumination and vertical light receiving method including specular reflection light in accordance with JIS Z8722:2009. The illumination diameter during measurement was 11 mmφ, and the measurement diameter was 8 mmφ. Based on the change in lightness (ΔL* value) before and after the test, the blackening resistance was evaluated according to the following criteria. Both a rating of S and a rating of A were considered passing.

[0086] <Evaluation criteria> Rating S: ΔL* value is 6 or more and less than 10 A: ΔL* value is 10 or more and less than 15

[0087] The evaluation results of each surface-treated steel sheet are shown in Table 3.

[0088]

[0089] As shown in Tables 1 to 3, surface-treated steel materials having a coating containing trivalent Cr and an organosilicon compound, in which the trivalent Cr concentration in the coating was 0.30 mass % or more and 15.0 mass % or less, had high corrosion resistance and a low sliding coefficient.

[0090] This application claims priority from Japanese Patent Application No. 2024-085064, filed May 24, 2024. The subject matter described in the specification and claims of that application as originally filed is incorporated herein by reference.

[0091] The surface-treated steel material has high corrosion resistance and a low coefficient of friction, making it useful in a variety of applications where these are required.

Claims

1. A surface-treated steel material comprising a steel material, a Zn-containing plating layer, and a coating, arranged in this order, wherein the coating contains trivalent Cr and an organosilicon compound, and the concentration of the trivalent Cr in the coating is 0.30 mass% or more and 15.0 mass% or less.

2. The surface-treated steel material according to claim 1, wherein the coating contains Zr.

3. The surface-treated steel material according to claim 1, wherein the mass concentration ratio (Cr / Si) of the trivalent Cr to the Si derived from the organosilicon compound in the coating is 0.020 or more and 0.850 or less.

4. The surface-treated steel material according to claim 1, wherein the coating contains phosphorus or vanadium.

5. The surface-treated steel material according to claim 1, wherein the coating contains Co.

6. The surface-treated steel material according to claim 1, wherein the coating has a thickness of 0.05 μm or more and 1.00 μm or less.

7. The surface-treated steel material according to any one of claims 1 to 6, wherein the plating layer has an Al content of 1.0 mass% or more and 22.0 mass% or less, an Mg content of 1.5 mass% or more and 10.0 mass% or less, and the balance consisting of Zn and optionally added trace additives.

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