Surface-treated steel

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

Technical Field

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

Background Art

[0002] It is known that a zinc-based plating layer formed of zinc or an alloy containing zinc enhances the corrosion resistance of steel materials. In order to further improve the corrosion resistance and blackening resistance of the zinc-based plating layer, an inorganic film may be formed on the surface of the zinc-based plating layer.

[0003] For example, Patent Document 1 and Patent Document 2 describe that a film containing trivalent chromium is formed on the surface of a zinc-based plating layer. Patent Document 1 and Patent Document 2 describe that the flat corrosion resistance, the corrosion resistance of the processed part, etc. can be improved by the film containing trivalent chromium.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Patent Document 1 and Patent Document 2 describe that the corrosion resistance of a steel sheet having a zinc-based plating layer is improved by a film containing trivalent chromium. However, according to the findings of the present inventors, the corrosion resistance of steel materials may not be improved even when using a film containing trivalent chromium. In addition, when a film containing trivalent chromium is formed, the sliding property deteriorates, and during press working, the plating layer adhered to the die may be easily peeled off.

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

[0007] One aspect of the present invention for solving the above problems relates to the following surface-treated steel materials [1] to [7]. [1] A surface-treated steel material having a steel material, a plating layer containing Zn, and a coating arranged in this order, The aforementioned film contains trivalent Cr and an organosilicon compound. The concentration of trivalent Cr in the aforementioned film is 0.30% by mass or more and 15.0% by mass or less. Surface-treated steel. [2] The coating contains Zr, [1] Surface-treated steel materials [3] 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. Surface-treated steel materials as described in [1] or [2]. [4] The coating contains at least one element of P and V, Surface-treated steel materials as described in [1] to [3]. [5] The coating contains Co, Surface-treated steel materials as described in any of [1] to [4]. [6] The coating has a thickness of 0.05 μm or more and 1.00 μm or less. Surface-treated steel materials as described in any of [1] to [5]. [7] The plating layer is The Al content is 1.0% by mass or more and 22.0% by mass or less. The Mg content is 1.5% by mass or more and 10.0% by mass or less. The remainder consists of Zn and optionally added trace amounts of additives. Surface-treated steel materials as described in any of [1] to [6]. [Effects of the Invention]

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

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

[0010] 1. Surface-treated steel 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 materials The type of steel used as the base material is not particularly limited and can be any type, such as steel plates, steel bars, H-beams, I-beams, wire rods, building hardware, or steel pipes. For example, as steel plates, any type of steel plate can be used, including hot-rolled mild steel plates and strips as described in JIS G 3131 (2018), hot-rolled steel plates and strips for automobiles as described in JIS G 3113 (2018), cold-rolled steel plates and strips as described in JIS G 3141 (2017), and various types of stainless steel plates (including austenitic, martensitic, ferritic, and ferritic-martensitic duplex types).

[0012] 1-2. Plating layer The plating layer is a plating layer containing zinc (Zn). Preferably, the plating layer is a plating layer with Zn as the main component. Note that "with Zn as the main component" means that the plating layer contains 50% by mass or more of Zn. The plating layer may be 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, alloys such as Zn-Al, Zn-Mg, Zn-Ni, Zn-Al-Mg, etc.).

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

[0014] Also, the plating layer may 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 plating layer, prevents erosion by corrosion factors, and enhances the corrosion resistance of the plating layer. By setting the Mg content to 1.5% by mass or more, the above-mentioned dense and uniform corrosion products can be sufficiently generated to sufficiently enhance the corrosion resistance of the plating layer. By setting the Mg content to less than or equal to 10.0% by mass, a decrease in the sacrificial corrosion prevention effect by Zn can be suppressed, and the generation of dross can also be suppressed. 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] Also, when the plating layer contains Al, in order to improve the adhesion between the steel material and the plating layer, silicon (Si) that can suppress the growth of the Fe-Zn alloy layer and the Fe-Al alloy layer at the interface between the steel material and the plating layer may be contained in the range of 0.005% by mass or more and 2.0% by mass or less. Furthermore, when the plating layer contains Mg, Zn that has an adverse effect on appearance and corrosion resistance 11 In order to suppress the formation and growth of the Mg2 phase, it may contain titanium (Ti), boron (B), a Ti-B alloy, a Ti-containing compound, or a B-containing compound. The content of these compounds is preferably such that Ti is in the range of 0.001% by mass or more and 0.1% by mass or less, and B is in the range of 0.0005% by mass or more and 0.045% by mass or less.

[0016] Furthermore, the plating layer may contain trace amounts of optional additives and unavoidable impurities in addition to Zn. Trace amounts of additives are elements added, for example, to improve the corrosion resistance of the plating layer. Trace amounts of additives can include 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 amounts can be between the detection limit and 1% by mass.

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

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

[0019] Organosilicon compounds can be molecules in which an organic functional group and a hydrolyzable functional group are bonded to a silicon molecule. Organic functional groups are organic reactive groups such as amino groups, epoxy groups, (meth)acryloyl groups, vinyl groups, and mercapto groups, while hydrolyzable functional groups are functional groups such as alkoxy groups. The organic functional groups may be bonded to the silicon molecule via alkylene groups, oxyalkylene groups, etc.

[0020] Organosilicon compounds form cross-linked structures within the film, improving its adhesion to the plating layer. In this embodiment, trivalent chromium dispersed in the film reacts or interacts with the organosilicon compounds to form a denser film structure, which is thought to improve the barrier properties of the film and thus enhance the corrosion resistance of the surface-treated steel. Furthermore, since trivalent chromium has low toxicity, it is not expected to cause any problems such as adverse effects on human health or environmental pollution.

[0021] The concentration of trivalent Cr in the coating is between 0.30% by mass and 15.0% by mass. By setting the trivalent Cr concentration to 0.30% by mass or higher, the dense coating structure described above can be easily formed, and the corrosion resistance of the surface-treated steel can be improved by enhancing the barrier properties. By setting the trivalent Cr concentration to 15.0% by mass or lower, the improvement in the sliding coefficient due to the aggregation of trivalent Cr can be suppressed. From the viewpoint of balancing these factors, the concentration of trivalent Cr in the coating is preferably between 0.5% by mass and 10.0% by mass, and more preferably between 1.0% by mass and 3.5% by mass.

[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 higher the fingerprint resistance of the surface-treated steel material can be.

[0023] Zirconium enhances the corrosion resistance of surface-treated steel materials by forming a cross-linked structure within the coating, thereby improving the adhesion of the coating to the plating layer and increasing the density of the coating structure to improve barrier properties. Furthermore, zirconium can also make the coating structure more dense, making it less susceptible to peeling due to water.

[0024] The amount of zirconium in the coating 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, relative to the total mass of the coating. By setting it within the above 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 enhanced.

[0025] Furthermore, the mass concentration ratio (Cr / Si) of trivalent Cr to Si derived from organosilicon compounds in the coating is preferably between 0.020 and 0.850. A higher Cr / Si ratio is more likely to result in improved barrier properties due to a denser coating structure. A lower Cr / Si ratio results in a lower amount of Cr, making it less likely for Cr aggregates to form in the coating. This reduces the uneven distribution of Cr in the coating, improving the coating's sliding properties. Additionally, a lower Cr / Si ratio allows for a relatively higher amount of organosilicon compounds, thereby improving the fingerprint resistance of the surface-treated steel. From the viewpoint of balancing these factors, a Cr / Si ratio of 0.100 to 0.650 is more preferable.

[0026] Furthermore, the coating preferably contains phosphorus (P) or vanadium (V). These elements, like zirconium, enhance the corrosion resistance of the coating and can also make the coating structure denser, making it less susceptible to peeling due to water. The coating may contain phosphorus and vanadium individually, or both. From the viewpoint of more effectively utilizing the corrosion resistance-enhancing effect of these elements and the water resistance-enhancing effect due to the densification of the coating, it is preferable that the coating contains both phosphorus and vanadium.

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

[0028] Phosphorus is typically included in the coating as phosphoric acid or its salts. Examples of phosphoric acid or its salts include phosphoric acids or their salts (e.g., ammonium salts such as triammonium phosphate and diammonium hydrogen phosphate), such as orthophosphate, metaphosphate, pyrophosphate, triphosphate, and tetraphosphate; phosphonic acids or their salts (e.g., aminotri(methylenephosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediaminetetra(methylenephosphonic acid), and diethylenetriaminepenta(methylenephosphonic acid)); and organic phosphoric acids or their salts, such as phytic acid. In addition to ammonium salts, metal salts with Na, Mg, Al, K, Ca, Mn, Ni, Zn, and Fe may also be used. These phosphoric acids or their salts may be used individually or in combination of two or more.

[0029] The amount of phosphorus in the coating 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, relative to the total mass of the coating. By keeping it 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 enhanced.

[0030] Vanadium acts as an inhibitor, forming precipitated or passive films that further enhance the corrosion resistance of surface-treated steel materials.

[0031] The amount of vanadium in the coating 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, relative to the total mass of the coating. By keeping it within this range, the corrosion resistance of the surface-treated steel material can be further enhanced.

[0032] Furthermore, the coating preferably contains cobalt (Co).

[0033] Cobalt can suppress discoloration of plated steel sheets, and is particularly effective in suppressing blackening. The cobalt can be either divalent or trivalent cobalt.

[0034] The amount of cobalt in the coating 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, relative to the total mass of the coating. By keeping it within this range, the resistance to blackening of the surface-treated steel material can be effectively enhanced.

[0035] The coating may contain atoms such as titanium (Ti), niobium (Nb), tantalum (Ta), and tungsten (W). The coating may also contain silica particles or fluorides. The amount of these atoms or additives in the coating is preferably 0.01% to 3.0% by mass, and more preferably 0.01% to 2.0% by mass, 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). XPS measurements are 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 is located at 576-578 eV, it is determined to be trivalent Cr; if it is located at 579-580 eV, it is determined to be hexavalent Cr.

[0038] Regarding silicon, it is possible to confirm whether or not it is silicon derived from organosilicon compounds using a Fourier transform infrared spectrophotometer (FT-IR). Total internal reflection (ATR) is used at 1100-1000 cm⁻¹. -1 (Siloxane bond), 1500-1300 cm -1 When absorption peaks are detected in both the (bending vibration of CH bond and Si-CH3 bond) and the 900-800 cm (stretching vibration of Si-CH3 bond) range, the Si is determined to be derived from an organosilicon compound.

[0039] The coating preferably has a thickness of 0.05 μm or more and 1.50 μm or less. The thinner the coating, the less likely it is to peel off during processing, thereby improving the corrosion resistance of the processed area. From the above viewpoint, the coating preferably has a thickness of 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 manufacturing surface-treated steel materials The surface-treated steel material described above can be manufactured 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-mentioned steel material and the above-mentioned plating layer, and then drying the applied treatment solution.

[0041] The solvent in the treatment solution is preferably an aqueous medium from the viewpoint of explosion prevention during the manufacturing of surface-treated steel materials. The aqueous medium is a liquid medium mainly composed of water, 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 content concentrations suitable for application of the treatment solution.

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

[0043] The amount of trivalent Cr compound in the treatment solution is preferably 0.30% by mass or more and 15.0% by mass or less, based on the total mass of the solids in the treatment solution (components constituting the film, excluding solvent components), and more preferably 0.30% by mass or more and 7.50% by mass or less, and more preferably 0.30% by mass or more and 3.50% by mass or less, based on the amount of trivalent Cr atoms.

[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- These 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-isocyanatetopropyltriethoxysilane, and p-styryltrimethoxysilane. These organosilicon compounds may be used individually or in combination of two or more.

[0045] The amount of organosilicon compounds in the treatment solution 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, relative to the total mass of solids in the treatment solution, in terms of Si atoms.

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

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

[0048] Examples of zirconium compounds include zirconium n-propylate, zirconium n-butyrate, zirconium tetraacetylacetonate, zirconium monoacetylacetonate, zirconium bisacetylacetonate, zirconium monoethylacetoacetate, zirconium acetylacetonate bisethylacetoacetate, zirconium acetate, zirconium monostearate, zirconate fluoride, zirconium carbonate, ammonium zirconium carbonate, potassium zirconium carbonate, and sodium zirconium carbonate. These zirconium compounds may be used individually or in combination of two or more.

[0049] The amount of zirconium compound in the treatment solution 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, based on the total mass of solids in the treatment solution, in terms of Zr atoms.

[0050] The treatment solution may contain phosphoric acid or vanadium compounds.

[0051] Examples of phosphoric acids include phosphoric acids such as orthophosphate, metaphosphate, pyrophosphate, triphosphate, and tetraphosphate, 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, as well as 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, and Fe may also be used. These phosphoric acids or their salts may be used individually or in combination of two or more.

[0052] The amount of phosphoric acid in the treatment solution 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, relative to the total mass of solids in the treatment solution, in terms of P atoms.

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

[0054] The amount of vanadium compound in the treatment solution 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, relative to the total mass of solids in the treatment solution, in terms of V atoms.

[0055] The processing solution may contain a cobalt compound.

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

[0057] The amount of cobalt compound in the treatment solution 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, relative to the total mass of solids in the treatment solution, in terms of Co atoms.

[0058] The treatment solution 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 treatment film to the Zn-based plating layer. Examples of etching agents include fluorides. The fluoride may be included in the treatment solution as a zirconium fluoride (such as zirconic acid fluoride) or as another type of fluoride.

[0059] Furthermore, the treatment solution may contain rheology control agents or other inorganic compounds.

[0060] The treatment solution is preferably applied to the surface of the plating layer by methods such as roll coating, bar coating, and spraying.

[0061] The drying (baking) of the treatment solution applied to the surface of the plating layer is preferably carried out at a temperature higher than 50°C but lower than 250°C, more preferably at a temperature between 70°C and 150°C, and even more preferably at a temperature higher than 100°C but lower than 140°C. Raising the drying temperature above 50°C allows for sufficient volatilization of the solvent. Lowering the drying temperature below 250°C can suppress the decomposition of film components (especially organic chains).

[0062] 3.Applications The above-mentioned surface-treated steel is useful in a variety of applications, such as exterior and interior building materials. For example, the above-mentioned surface-treated steel can be suitably used in a variety of applications, such as roofing materials and exterior materials for buildings, steel pipes and structural steel for greenhouses or agricultural greenhouses, supports and beams, transport components, sound barriers, soundproof walls, sound-absorbing walls, snow barriers, guardrails, railings, protective fences, supports, railway vehicle components, overhead line components, electrical equipment components, safety and environmental components, structural components, solar panel mounting frames, and air conditioner outdoor units.

[0063] Furthermore, the above-mentioned surface-treated steel material can be effectively used in applications where surface-treated steel material has traditionally been used, such as sound barriers, windbreaks, and enclosures for power distribution panels. [Examples]

[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. Prepare the materials 1-1. Plated steel sheet Three types of plated steel sheets, A1 to A3, were prepared by plating 1.2 mm thick steel sheets with zinc-based plating baths of different compositions. The weight of the plating layer was 150 g / m² per side for all three types. 2 That's what I decided. A1: Hot-dip Zn-0.5 mass%Al-1 mass%Mg plated steel sheet ·A2: Hot dip Zn-11 mass%Al-3 mass%Mg-0.2 mass%Si plated steel plate A3: Hot-dip Zn-19 mass% Al-6 mass% Mg-0.2 mass% Si plated steel sheet

[0066] 1-2. Surface treatment solution The following materials were mixed in the proportions shown in Table 1 to prepare a surface treatment solution. The trivalent chromium compound and cobalt compound were in hydrate form, and the amount of each hydrate used is listed in Table 1. • Trivalent chromium compound: Chromium nitrate xahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) • Organosilicon compound: Methyltrimethoxysilane (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) • Zirconium compound: Zirconate fluoride (manufactured by Sigma-Aldrich) • Phosphorus compounds: 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] [Table 1]

[0068] 2. Surface treatment Each plated steel sheet was sprayed with a silicate-based alkaline degreasing agent (Fine Cleaner 4336, manufactured by Nippon Parkerizing Co., Ltd.) at a concentration of 20 g / L and a temperature of 60°C for 2 minutes, then rinsed with pure water for 30 seconds and dried to degrease the surface of each plated steel sheet.

[0069] Each surface treatment solution was applied to the surface of a degreased plated steel sheet using a bar coater to achieve the desired film thickness. After standing for 3 seconds, the sheet was baked to form a film using the treatment solution. The baking process involved placing the test specimen in a 120°C oven for 30 seconds. During baking, the pure water contained in the surface treatment solution, as well as the water in the trivalent chromium compound hydrate and cobalt compound hydrate, evaporates, forming the film.

[0070] 3. Measurement 3-1. Film Thickness Test specimens were cut from coated steel sheets (surface-treated steel sheets) using the cryo-FIB method. The cross-sectional structure of the cut specimens was observed using a transmission electron microscope (TEM) at a magnification (100,000 to 1,000,000x) where the entire coating and a portion of the plating layer were visible in the field of view. The acceleration voltage was 200kV. The coating observed at the topmost outer layer of the plating layer during FE-TEM observation was identified as the coating formed as described above. The film thickness of the identified coating was measured. The film thickness was measured at three locations with a 1mm interval between measurements, and the average value was used to determine the film thickness.

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

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

[0073] Furthermore, the Si contained in the coating was confirmed to originate from organosilicon compounds using Fourier transform infrared spectrophotometer (FT-IR). Total internal reflection (ATR) was used at 1100-1000 cm⁻¹. -1 (Siloxane bond), 1500-1300 cm -1 Since absorption peaks were detected in both the (bending vibration of CH bond and Si-CH3 bond) and the 900-800 cm (stretching vibration of Si-CH3 bond) ranges, it was determined that the Si originated from an organosilicon compound.

[0074] Table 2 shows the type of plated steel sheet, the type of treatment solution, the amount of each element, the concentration of trivalent Cr and Si in the film, the Cr / Si mass ratio, and the film thickness for surface-treated steel sheets coated with each treatment solution. Note that the concentration of trivalent Cr and Si in the film is the concentration in the film formed with anhydrous materials.

[0075] [Table 2]

[0076] 4. Evaluation 4-1. Corrosion resistance of flat surfaces The corrosion resistance of the flat surfaces of the obtained surface-treated steel sheets was evaluated. More specifically, test pieces (70 mm wide x 150 mm long) cut from each surface-treated steel sheet were sealed at the edges, and then subjected to a salt spray process, a drying process, and a wetting process for one cycle (totaling 8 hours). This cycle was repeated until the area rate of white rust occurrence reached 10%.

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

[0078] <Evaluation Criteria> Rating SS: Over 300 cycles S: Over 250 cycles and under 300 cycles A: More than 100 cycles and less than or equal to 250 cycles B: Less than 100 cycles

[0079] 4-2. Corrosion resistance of machined parts The corrosion resistance of the processed areas 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 7 mm using an Erichsen extruder. The same test as the evaluation of planar corrosion resistance described above was performed on the obtained extruded samples, and the test pieces were evaluated according to the following criteria based on the number of cycles until the area rate of white rust reached 10%. Scores of S and A were considered acceptable.

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

[0081] 4-3. Fingerprint resistance The fingerprint resistance of the obtained surface-treated steel sheets was evaluated. More specifically, the increase or decrease in L value (ΔL) before and after application of petroleum jelly was measured using a colorimeter on test pieces (50 mm wide x 50 mm long) cut from each surface-treated steel sheet. Both S and A scores were considered acceptable.

[0082] <Evaluation Criteria> Score S: ΔL is less than 0.5 A: ΔL is between 0.5 and 1.0 (inclusive).

[0083] 4-4. Sliding properties The sliding properties of the obtained surface-treated steel sheets were evaluated. More specifically, test pieces (17 mm wide x 300 mm long) cut from each surface-treated steel sheet were subjected to a drawbead testing machine with a pressing load of 2.0 to 5.5 kN and a pulling speed of 500 mm / min, sliding for 200 mm. The load when sliding at each pressing load was measured as the pulling load, and the slope of the line plotted with the pressing load on the x-axis and the pulling load on the y-axis was calculated as the sliding coefficient. The sliding properties were evaluated according to the following sliding coefficient criteria. A score of A was considered a passing grade.

[0084] <Evaluation Criteria> Rating S: Sliding coefficient less than 0.5 A: The sliding coefficient is 0.5 or more and less than 0.7. B: Sliding coefficient is 0.7 or higher

[0085] 4-5. Resistance to blackening The blackening resistance 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 placed in a constant temperature chamber at 70°C and 80% humidity for 144 hours, and the lightness (L* value) of the test pieces was measured before and after the test. Lightness was measured using a colorimeter (Konica Minolta, Inc., CR-400) with a diffuse illumination vertical 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 score of S and a score of A were considered acceptable.

[0086] <Evaluation Criteria> Rating S: ΔL* value is between 6 and 10. A: The ΔL* value is between 10 and 15 (inclusive).

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

[0088] [Table 3]

[0089] As shown in Tables 1 to 3, surface-treated steel materials having a coating containing trivalent Cr and organosilicon compounds, wherein the concentration of trivalent Cr in the coating is 0.30% by mass or more and 15.0% by mass or less, exhibited high corrosion resistance and a low coefficient of friction.

[0090] This application claims priority to Japanese Patent Application No. 2024-085064, filed on 24 May 2024. The matters set forth in the original specification and claims of said application are incorporated herein by reference. [Industrial applicability]

[0091] The surface-treated steel materials described above have high corrosion resistance and a low coefficient of friction. Therefore, they are useful in various applications where these characteristics are required.

Claims

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

2. The amount of Zr in the coating is 0.1% by mass or more and 20.0% by mass or less, relative to the total mass of the coating. The surface-treated steel material according to claim 1.

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

4. The aforementioned coating contains P or V, The surface-treated steel material according to claim 1.

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

6. The aforementioned film has a thickness of 0.05 μm or more and 1.00 μm or less. The surface-treated steel material according to claim 1.

7. The aforementioned plating layer is The Al content is 1.0% by mass or more and 22.0% by mass or less. The Mg content is 1.5% by mass or more and 10.0% by mass or less. The remainder consists of Zn and optionally added trace amounts of additives. A surface-treated steel material according to any one of claims 1 to 6.

Images