Surface-treated steel material

Abstract

Provided a surface-treated steel material having high corrosion resistance and a low sliding coefficient. A surface-treated steel material according to the present invention is obtained by arranging a steel material, a Zn-containing plating layer, and a coating, in this order. The coating contains trivalent Cr, an organosilicon compound, and fluorine (F), and the trivalent Cr concentration in the coating is 0.30-15.00 mass%.

Description

Surface-treated steel

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

[0002] Zinc-based plating layers, formed from zinc or zinc-containing alloys, are known to improve the corrosion resistance of steel materials. To further enhance the corrosion resistance and resistance to blackening 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 Documents 1 and 2 describe forming a film containing trivalent chromium (Cr) on the surface of a zinc-based plating layer. Patent Documents 1 and 2 also describe that the film containing trivalent Cr improved the corrosion resistance of flat plates and processed parts.

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

[0005] Patent documents 1 and 2 describe that the corrosion resistance of steel sheets having a zinc-based plating layer is improved by a coating containing trivalent chromium. However, according to the inventors' findings, the corrosion resistance of steel materials does not always improve even when a coating containing trivalent chromium is used. Furthermore, forming a coating containing trivalent chromium reduces sliding properties, and the plating layer that adheres to the mold may easily peel off during press working.

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

[0007] One aspect of the present invention for solving the above problems relates to the following surface-treated steel materials [1] to [8]. [1] A surface-treated steel material in which a steel material, a plating layer containing Zn, and a film are arranged in this order, wherein the film contains trivalent Cr, an organosilicon compound, and fluorine (F), and the concentration of trivalent Cr in the film is 0.30% by mass or more and 15.00% by mass or less. [2] The surface-treated steel material according to [1], wherein the concentration of F in the film is 5.00% by mass or more and 30.00% by mass or less. [3] The surface-treated steel material according to [1] or [2], wherein the concentration of F in the film is 6.50% by mass or more and 30.00% by mass or less. [4] The surface-treated steel material according to any one of [1] to [3], 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. [5] The surface-treated steel material according to any one of [1] to [4], wherein the coating contains Zr, P, or V. [6] The surface-treated steel material according to any one of [1] to [5], wherein the coating contains Co. [7] The surface-treated steel material according to any one of [1] to [6], wherein the coating has a film thickness of 0.05 μm or more and 1.00 μm or less. [8] The surface-treated steel material according to any one of [1] to [7], wherein the plating layer has an Al content of 1.0% by mass or more and 22.0% by mass or less, an Mg content of 1.5% by mass or more and 10.0% by mass or less, and the remainder consists of Zn and optionally added trace additives.

[0008] According to the present invention, a surface-treated steel material with 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. The type of steel used as the base material is not particularly limited and may be any type of steel, 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 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 mainly composed of Zn. Note that "mainly composed of Zn" means that the plating layer contains 50% by 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 it may be 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 acts as a passivator, improving the corrosion resistance of the plating layer and suppressing the generation of dross during manufacturing. By setting the Al content to 1.0% by mass or more, the corrosion resistance of the plating layer can be sufficiently improved and the generation of dross can 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 protection effect by Zn can be suppressed. Preferably, the Al content is 12.0% by mass or more and 20.0% by mass or less.

[0014] Furthermore, 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, preventing erosion by corrosive factors and improving the corrosion resistance of the plating layer. By setting the Mg content to 1.5% by mass or more, sufficient dense and uniform corrosion products can be generated, thereby sufficiently improving the corrosion resistance of the plating layer. By setting the Mg content to 10.0% by mass or less, the reduction in the sacrificial corrosion protection 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] Furthermore, when the plating layer contains Al, silicon (Si) may be included in a range of 0.005% to 2.0% by mass to improve adhesion between the steel material and the plating layer, thereby suppressing the growth of the Fe-Zn alloy layer and Fe-Al alloy layer at the interface between the steel material and the plating layer. In addition, when the plating layer contains Mg, Zn may be included to avoid adverse effects on appearance and corrosion resistance. １１ Mg ２ To suppress the formation and growth of phases, titanium (Ti), boron (B), Ti-B alloys, Ti-containing compounds, or B-containing compounds may be included. Preferably, the content of these compounds is in the range of 0.001% by mass or more and 0.1% by mass or less for Ti, and in the range of 0.0005% by mass or more and 0.045% by mass or less for B.

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

[0017] The types and amounts of elements contained in the plating layer are measured by inductively coupled plasma analysis (ICP analysis). Specifically, the coating is removed using a known coating remover at a location at least 30 mm away from the edge and towards the inner surface, and at least 30 mm away from the processed area if welding or bending has been performed. After cleaning the exposed surface, the plating layer is dissolved in hydrochloric acid. By performing ICP analysis on the solution in which the plating layer has been dissolved, the types and amounts of elements contained in the plating layer can be identified.

[0018] 1-3. The coating is a film formed by surface treatment on the surface of the plating layer.

[0019] In this embodiment, the coating contains trivalent Cr, an organosilicon compound, and fluorine (F).

[0020] The organosilicon compound forms a cross-linked structure within the film, improving its adhesion to the plating layer. In this embodiment, it is believed that the trivalent chromium dispersed in the film reacts or interacts with the organosilicon compound to form a denser film structure, thereby improving the barrier properties of the film and enhancing the corrosion resistance of the surface-treated steel material. 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 chromium in the coating is 0.30% by mass or more and 15.00% by mass or less. By setting the trivalent chromium concentration to 0.30% by mass or more, 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 chromium concentration to 15.00% by mass or less, the increase in the sliding coefficient due to the aggregation of trivalent chromium can be suppressed. From the viewpoint of balancing these factors, the concentration of trivalent chromium in the coating is preferably 0.50% by mass or more and 10.00% by mass or less, and more preferably 1.00% by mass or more and 3.50% by mass or less.

[0022] Fluorine enhances the water repellency of the coating. Therefore, fluorine is thought to improve the corrosion resistance of surface-treated steel materials.

[0023] The amount of fluorine in the coating is more preferably 5.00% by mass or more and 30.00% by mass or less, and even more preferably 6.50% by mass or more and 30.00% by mass or less, relative to the total mass of the coating. The higher the fluorine concentration, the greater the corrosion resistance of the surface-treated steel material. By setting the fluorine concentration to 30.0% by mass or less, the coating can be made moderately flexible, thereby improving the workability (bendability) of the surface-treated steel material.

[0024] Furthermore, the concentration of Si derived from the organosilicon compound is preferably 2.00% by mass or more and 30.00% by mass or less. By setting the Si concentration to 2.00% by mass or more, a siloxane bond network is formed throughout the entire film. A Si concentration of 10.00% by mass or more and 20.00% by mass or less is more preferable. The higher the Si concentration derived from the organosilicon compound, the higher the fingerprint resistance of the surface-treated steel material can be. On the other hand, if the Si concentration is 30.00% by mass or less, preferably 20.00% by mass or less, the film can be made moderately flexible, improving the workability (bendability) of the surface-treated steel material.

[0025] The coating preferably contains zirconium (Zr), phosphorus (P), or vanadium (V).

[0026] 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. In this embodiment, the combined use of trivalent Cr and zirconium significantly enhances the corrosion resistance improvement effect of zirconium. This is thought to be because both trivalent Cr and zirconium are incorporated into the bonding of the organosilicon compound, making the coating structure extremely dense. Zirconium also makes it less likely for the coating to peel off due to water.

[0027] The amount of zirconium in the coating is preferably 0.10% by mass or more and 20.00% by mass or less, and more preferably 1.00% by mass or more and 10.00% by mass or less, relative to the total mass of the coating. By setting the amount 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.

[0028] Furthermore, the mass concentration ratio (Cr / Si) of trivalent Cr to Si derived from organosilicon compounds in the coating is preferably 0.020 to 0.850. The higher the Cr / Si ratio, the easier it is to improve barrier properties due to a denser coating structure. The lower the Cr / Si ratio, the less Cr is present, and the less likely Cr aggregates are to form in the coating. This makes it less likely for Cr to be unevenly distributed in the coating, improving the sliding properties of the coating. Also, the lower the Cr / Si ratio, the relatively larger the amount of organosilicon compounds can be, which can improve the fingerprint resistance of the surface-treated steel material. From the viewpoint of balancing these factors, a Cr / Si ratio of 0.100 to 0.650 is more preferable.

[0029] 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.

[0030] Phosphorus enhances the adhesion of the coating to the plating layer, thereby improving the corrosion resistance of surface-treated steel materials.

[0031] Phosphorus is typically included in the coating as phosphoric acid or a salt thereof. Examples of phosphoric acid or salts thereof include phosphoric acids such as orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, and tetraphosphoric acid, or salts of these (for example, ammonium salts such as triammonium phosphate and diammonium hydrogen phosphate), aminotri(methylene phosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediaminetetra(methylene phosphonic acid), and diethylenetriaminepenta(methylene phosphonic acid), phosphonic acids 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, and Fe may also be used as the salts. One of these phosphoric acids or salts thereof may be used alone, or two or more of them may be used in combination.

[0032] The content of phosphorus in the coating is preferably 0.10% by mass or more and 25.00% by mass or less, more preferably 1.00% by mass or more and 15.00% by mass or less, based on the total mass of the coating. By setting the content 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.

[0033] Vanadium functions as an inhibitor to form a precipitation film or a passivation film, thereby further improving the corrosion resistance of the surface-treated steel material.

[0034] The content of vanadium in the coating is preferably 0.10% by mass or more and 20.00% by mass or less, more preferably 1.00% by mass or more and 10.00% by mass or less, based on the total mass of the coating. By setting the content within the above range, the corrosion resistance of the surface-treated steel material can be further improved.

[0035] Furthermore, the coating preferably contains cobalt (Co).

[0036] Cobalt can suppress discoloration of the plated steel sheet, and can particularly effectively suppress blackening. Cobalt may be divalent cobalt or trivalent cobalt.

[0037] The cobalt content in the film is preferably from 0.01% by mass to 10.00% by mass, and more preferably from 0.10% by mass to 5.00% by mass, relative to the total mass of the film. By setting the content within the above range, the blackening resistance of the surface-treated steel material can be effectively improved.

[0038] The film may further contain elements such as titanium (Ti), niobium (Nb), tantalum (Ta), and tungsten (W). In addition, the film may contain silica particles and the like. The content of these elements or additives in the film is preferably from 0.01% by mass to 3.00% by mass, and more preferably from 0.01% by mass to 2.00% by mass, relative to the total mass of the film.

[0039] The contents of fluorine (F) and other elements in the film are measured by inductively coupled plasma analysis (ICP analysis). Specifically, the film is scraped off with a scrubber at a position 30 mm or more away from the end toward the inner surface, and when processing such as welding or bending has been performed, at a position 30 mm or more away from the processed part. The range for scraping off the film can be, for example, 3 cm in width and 3 cm in length, but when the film is thin, the range may be expanded to obtain a sufficient sample amount. By performing ICP analysis on the scraped-off film, the type and amount of elements contained in the plating layer can be identified.

[0040] The valence of Cr is measured by X-ray photoelectron spectroscopy (XPS) on a film collected from the same range. XPS measurement is performed using mono-Al Kα (hν: 1486.6 eV) as the X-ray source. When the detected peak top position is 576 to 578 eV, it is determined as trivalent Cr, and when it is 579 to 580 eV, it is determined as hexavalent Cr.

[0041] For Si, measurement is performed by Fourier transform infrared spectroscopy (FT-IR) using the attenuated total reflection method (ATR) at 1100 to 1000 cm －１ (siloxane bond), 1500 to 1300 cm －１ (C-H bond, Si-CH ３ bending vibration of bond), 900 to 800 cm (Si-CH ３Confirm that an absorption peak is detected in all of the bond stretching vibrations). Further, confirm that this Si is derived from an organosilicon compound rather than silica or a silicone resin. Specifically, for a sample obtained by scraping the coating film with a scrubber, ２９ a peak at -40 to -80 ppm (T peak) indicating a silanol group having an Si-C bond (Tn structure), which is observed by solid-state nuclear magnetic resonance measurement targeting Si, and SiO ４ measure the peak area ratio (T peak / Q peak) between the peak at -90 to -120 ppm (Q peak) indicating (Qn structure). When this peak area ratio is 6 / 4 to 9 / 1, that is, when the T peak has a larger peak area than the Q peak specific to silica or silicone resin, it is determined that almost no silica or silicone resin is present in the coating film, and the detected Si is Si derived from an organosilicon compound.

[0042] In the present embodiment, the total reflection method (ATR) is performed under the following measurement conditions. ・ATR crystal: diamond (or Ge) ・Measurement mode: ATR, 1 reflection ・Measurement wavenumber range: 4000 to 650 cm －１ ・Resolution: 4 cm －１ ・Number of integrations: 32 times ・Background: Acquire atmospheric background immediately before measurement ・Light source: Mid-infrared light source (glower) ・Detector: DTGS ・Sample pressing: The measurement is performed by bringing the sample into close contact with a constant load using an ATR head ・Measurement position: Any position 30 mm or more away from the end of the test piece

[0043] The coating may contain resin, but it is preferable to omit resin to reduce manufacturing costs. The presence or absence of resin is confirmed by both thermogravimetric analysis (TGA) showing no significant weight loss due to thermal decomposition in the 300°C to 500°C range, and time-of-flight secondary ion mass spectrometry (ToF-SIMS) showing no detection of polymer fragment ions specific to resin. Specifically, first, the weight change of the coating upon heating is measured by TGA. Generally, organic resins show significant weight loss due to thermal decomposition in the temperature range of approximately 300°C to 500°C. On the other hand, the inorganic skeleton portion of the components derived from the silane coupling agent does not decompose even when heated up to approximately 900°C. Note that the organic groups contained in the silane coupling agent can decompose in the 300°C to 500°C range, but the weight loss is smaller than that of the resin. Therefore, if no significant weight loss due to thermal decomposition is observed in the TGA measurement in the range of 300°C to 500°C, it can be initially determined that the film substantially does not contain resin components. Furthermore, secondary ions emitted from the film surface are analyzed by ToF-SIMS. If resin components are present, C ｘ H ｙ O ｚ － High molecular weight fragment ions such as those listed above are detected. On the other hand, while silane coupling agents also contain organic components, only fragments of low molecular weight origin are detected. Therefore, by confirming that resin-specific high molecular weight fragment ions are not detected in ToF-SIMS analysis, it is possible to confirm that the film does not contain resin components.

[0044] The film thickness is preferably 0.05 μm or more and 1.50 μm or less. The thinner the film thickness, the less likely the film is to peel off during processing, thereby improving the corrosion resistance of the processed area. From the above viewpoint, the film thickness 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.

[0045] The film thickness is measured by cutting a 40 μm × 10 μm test piece from the surface-treated steel material using the cryo-FIB method, cutting it in the thickness direction of the steel material (perpendicular to the surface of the steel plate) in a plan view. When cutting the test piece from the component, it should be cut at a location at least 30 mm away from bends and welds. The cut cross section is observed using a transmission electron microscope (TEM) at a magnification (100,000 to 1,000,000x) where the entire film and a portion of the plating layer are visible in the field of view. The acceleration voltage for this observation is 200 kV. The film observed at the topmost outer edge of the plating layer when observed with FE-TEM is identified as the film formed as described above. The boundary between the film and the plating layer can be easily identified from the observation image by a person skilled in the art. In this way, the distance from the boundary between the film and the plating layer to the surface of the film is measured as the film thickness. Measurements are taken at three different points parallel to the steel surface, with the measurement intervals varying by 10 μm each. The average value of these measurements is then taken as the film thickness.

[0046] 2. Method for manufacturing surface-treated steel The surface-treated steel described above can be manufactured by applying a treatment solution containing a trivalent chromium compound and an organosilicon compound to the surface of the plating layer of a plated steel having the steel material and the plating layer, and then drying the applied treatment solution.

[0047] In this embodiment, the treatment solution contains a fluoride in order to add fluorine to the formed film. The fluoride may be chromium fluoride, titanium fluoride, silver fluoride, zirconate fluoride, etc.

[0048] The amount of fluoride in the treatment solution is preferably 0.35% by mass or more and 30.00% by mass or less, more preferably 5.00% by mass or more and 30.00% by mass or less, and even more preferably 10.00% by mass or more and 25.00% by mass or less, based on the total mass of solids in the treatment solution, in terms of element F.

[0049] 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.

[0050] Examples of trivalent chromium compounds include chromium nitrate, chromium sulfate, chromium phosphate, chromium fluoride, chromium acetate, chromium oxalate, and chromium chloride. These trivalent chromium compounds may be used individually or in combination of two or more.

[0051] The amount of trivalent chromium compound in the treatment solution is preferably 0.30% by mass or more and 15.00% 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 element.

[0052] 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.

[0053] The amount of trivalent chromium compounds and organosilicon compounds in the treatment solution is preferably 2.00% by mass or more and 30.00% by mass or less, and more preferably 10.00% by mass or more and 20.00% by mass or less, relative to the total mass of solids in the treatment solution, in terms of Si element.

[0054] Furthermore, the concentration ratio of trivalent chromium compounds and organosilicon compounds in the treatment solution is preferably such that the concentration ratio of trivalent Cr to Si element (Cr / Si) is 0.020 or more and 0.850 or less, and more preferably 0.100 or more and 0.650 or less.

[0055] The treatment solution may contain a zirconium compound.

[0056] 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.

[0057] The amount of zirconium compound in the treatment solution is preferably 0.10% by mass or more and 20.00% by mass or less, and more preferably 1.00% by mass or more and 10.00% by mass or less, based on the total mass of solids in the treatment solution, in terms of Zr element.

[0058] The treatment solution may contain phosphoric acid or vanadium compounds.

[0059] 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.

[0060] The amount of phosphoric acid in the treatment solution is preferably 0.10% by mass or more and 25.00% by mass or less, and more preferably 1.00% by mass or more and 15.00% by mass or less, based on the total mass of solids in the treatment solution, in terms of element P.

[0061] 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 to divalent to tetravalent with a reducing agent, as well as divalent to 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.

[0062] 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 element V.

[0063] The processing solution may contain a cobalt compound.

[0064] Examples of cobalt compounds include cobalt salts such as cobalt nitrate, cobalt sulfate, and cobalt carbonate.

[0065] The amount of cobalt compound in the treatment solution is preferably 0.01% by mass or more and 10.00% by mass or less, and more preferably 0.10% by mass or more and 5.00% by mass or less, based on the total mass of solids in the treatment solution, in terms of Co element.

[0066] 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 fluoride) or as another type of fluoride.

[0067] Furthermore, the treatment solution may contain rheology control agents or other inorganic compounds.

[0068] The processing solution may contain resin, but it is preferable that it does not contain resin in order to reduce manufacturing costs. The amount of resin in the processing solution is preferably 0.00% by mass or more and 0.50% by mass or less, and more preferably 0.00% by mass or more and 0.10% by mass or less, relative to the total mass of solids in the processing solution.

[0069] The treatment solution is preferably applied to the surface of the plating layer by methods such as roll coating, bar coating, and spraying.

[0070] 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).

[0071] 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, structural steel, supports, and beams for greenhouses or agricultural greenhouses, transport components, sound barriers, soundproof walls, sound-absorbing walls, snow barriers, guardrails, railings, protective fences, supports, components for railway vehicles, components for overhead lines, components for electrical equipment, components for safety and environmental applications, structural components, solar panel mounting frames, and air conditioner outdoor units.

[0072] 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.

[0073] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0074] 1. Preparation of materials 1-1. Plated steel sheets Three types of plated steel sheets, A1 to A3 below, were prepared by plating 1.2 mm thick steel sheets with zinc-based plating baths of different compositions. The basis weight of the plating layer was 150 g / m² per side for all of them. ２ The following were determined: • 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 sheet • A3: Hot-dip Zn-19 mass%Al-6 mass%Mg-0.2 mass%Si plated steel sheet

[0075] 1-2. Surface Treatment Solution A surface treatment solution was prepared by mixing the following materials in the ratios shown in Table 1. In order to suppress gelation due to the rapid reaction of methyltriethoxysilane, a beaker containing pure water and chromium nitrate nonahydrate was placed in a bath containing ice, and then methyltriethoxysilane was added dropwise while stirring to prepare the treatment solution. The trivalent chromium compound and cobalt compound were in hydrate form, and the amount of each hydrate used is shown in Table 1. Two types of trivalent chromium compounds were prepared, and one of them was used. • Trivalent chromium compounds: (Type B1) Chromium fluoride tetrahydrate (manufactured by Sigma-Aldrich) (Type B2) Chromium nitrate nonahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) • Organosilicon compounds: Methyltrimethoxysilane (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) • Zirconium compounds: Zirconate fluoride (manufactured by Sigma-Aldrich) • Phosphorus compounds: Phosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) • Vanadium compounds: Vanadium pentoxide (manufactured by Tokyo Chemical Industries, Ltd.) • Cobalt compounds: Cobalt nitrate hexahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0076]

[0077] 2. Surface Treatment: A silicate-based alkaline degreasing agent (Fine Cleaner 4336, manufactured by Nippon Parkerizing Co., Ltd.) was sprayed onto the surface of each plated steel sheet at a concentration of 20 g / L and a temperature of 60°C for 2 minutes. After rinsing with pure water for 30 seconds and drying, the surface of each plated steel sheet was degreased.

[0078] 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 piece 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.

[0079] 3. Measurement 3-1. Test specimens were cut from the steel sheet with the formed film (surface-treated steel sheet) 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 1,000,000 times) where the entire film and a portion of the plating layer were within the field of view. The acceleration voltage was 200 kV. The film observed at the topmost outer edge of the plating layer during FE-TEM observation was identified as the formed film. In this way, the distance from the boundary between the film and the plating layer to the film surface was measured as the film thickness. The film thickness was measured at three points parallel to the steel surface, with measurement intervals varying by 10 μm, and the average value was taken as the film thickness.

[0080] 3-2. Amount of elements in the coating For all samples, the coating was scraped off with a scrubber in a 3 cm wide and 3 cm long area at a distance of 30 mm or more from the edge of the plated steel sheet. The concentrations of Cr, Si, F, P, V, Zr, Co, Zn, Al, Mg, and O were calculated from the scraped coating by ICP analysis. The Cr / Si ratio was calculated by converting the ICP results to a mass ratio.

[0081] Furthermore, the Cr content in the coating was investigated using X-ray photoelectron spectroscopy (XPS) on coatings collected from the same area. XPS measurements were performed using mono-Al Kα (hν: 1486.6 eV) as the X-ray source. If the detected peak top position was between 576 and 578 eV, it was determined to be trivalent Cr; if it was between 579 and 580 eV, it was determined to be hexavalent Cr.

[0082] Furthermore, the Si contained in the coating was confirmed to originate from organosilicon compounds using a Fourier transform infrared spectrophotometer (FT-IR). Total internal reflection (ATR) was used at 1100–1000 cm⁻¹. －１ (Siloxane bond), 900-800 cm (Si-CH ３ Since absorption peaks were detected in all of the bond stretching vibrations, it was determined that the Si originated from an organosilicon compound. These peaks were not detected in surface-treated steel sheet 6.

[0083] The Total Internal Reflection (ATR) method was performed under the following measurement conditions: • ATR crystal: Diamond (or Ge) • Measurement mode: ATR single reflection • Measurement wavenumber range: 4000–650 cm －１ ・Resolution: 4cm －１ • Number of cumulative measurements: 32 • Background: Atmospheric background acquired immediately before measurement • Light source: Mid-infrared light source (Glover) • Detector: DTGS • Sample contact: Measurement performed with constant pressure using an ATR head • Measurement position: Any point at least 30 mm away from the edge of the test piece

[0084] Table 2 shows the type of plated steel sheet, the type of treatment solution, the amount of each element, the concentration of trivalent Cr, F, 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 trivalent Cr and Si concentrations in the film are those in the film formed with anhydrous materials. A "-" in the table indicates that the component is not present or cannot be calculated.

[0085]

[0086] 4. Evaluation 4-1. Planar Corrosion Resistance The corrosion resistance of the planar surfaces of the 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 end face, 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%.

[0087] 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 rate of white rust reached 10%. Scores from SS to A were considered acceptable.

[0088] <Evaluation Criteria> Score SS: Over 330 cycles S: Over 280 cycles and 330 cycles or less A: Over 160 cycles and 280 cycles or less B+: Over 120 cycles and 160 cycles or less B: 120 cycles or less

[0089] 4-2. Corrosion Resistance of Processed Areas The corrosion resistance of the processed areas of the 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 thickness of 7 mm using an Erichsen extrusion apparatus. 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.

[0090] <Evaluation Criteria> Score: More than 21 cycles A: More than 15 cycles and 21 cycles or less B+: More than 10 cycles and 15 cycles or less B: 10 cycles or less

[0091] 4-3. Fingerprint Resistance The fingerprint resistance of the surface-treated steel sheets was evaluated. More specifically, the increase or decrease in L value (ΔL) before and after the 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.

[0092] <Evaluation Criteria> Score S: ΔL is less than 0.5 A: ΔL is 0.5 or more and less than 1.0

[0093] 4-4. Sliding Properties The sliding properties of the 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.

[0094] <Evaluation Criteria> Score S: Sliding coefficient less than 0.5 A: Sliding coefficient of 0.5 or more and less than 0.7 B: Sliding coefficient of 0.7 or more

[0095] 4-5. The blackening resistance of the surface-treated steel sheets obtained 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.

[0096] <Evaluation Criteria> Score S: ΔL* value is 0 or greater and less than 10 A: ΔL* value is 10 or greater and less than 15

[0097] The evaluation results for each surface-treated steel sheet are shown in Table 3.

[0098]

[0099] As shown in Tables 1 to 3, surface-treated steel materials having a coating containing trivalent Cr, organosilicon compounds, and fluorine (F), 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.

[0100] Furthermore, in the surface-treated steel sheet 4, which does not contain trivalent Cr or Zr, the area rate of white rust reached 10% after 116 cycles in the planar corrosion resistance test, and after 7 cycles in the processed area corrosion resistance test. In contrast, in the surface-treated steel sheet 22, which does not contain trivalent Cr but contains Zr, the area rate of white rust reached 10% after 138 cycles in the planar corrosion resistance test, and after 12 cycles in the processed area corrosion resistance test. Thus, Zr alone can improve the corrosion resistance of surface-treated steel sheets.

[0101] Furthermore, in the surface-treated steel sheet 1 containing trivalent Cr but not Zr, the area rate of white rust reached 10% after 201 cycles in the planar corrosion resistance test, and after 18 cycles in the processed area corrosion resistance test. In contrast, in the surface-treated steel sheet 10 containing both trivalent Cr and Zr, the area rate of white rust reached 10% after 317 cycles in the planar corrosion resistance test, and after 29 cycles in the processed area corrosion resistance test.

[0102] These results show that the degree of improvement in corrosion resistance due to Zr when trivalent Cr is included (comparison between surface-treated steel sheet 1 and surface-treated steel sheet 22) is significantly higher than the degree of improvement due to Zr when trivalent Cr is not included (comparison between surface-treated steel sheet 4 and surface-treated steel sheet 22).

[0103] On the other hand, surface-treated steel sheet 2, with a trivalent Cr concentration of less than 0.30 mass%, exhibited lower corrosion resistance on its flat surface and processed areas compared to other surface-treated steel sheets. This is thought to be because a dense film structure was not formed by trivalent Cr, resulting in insufficient barrier properties. Furthermore, surface-treated steel sheet 3, with a trivalent Cr concentration exceeding 15.00 mass%, had a higher coefficient of friction than other surface-treated steel sheets. This is thought to be due to the aggregation and uneven distribution of trivalent Cr.

[0104] This application claims priority to Japanese Patent Application No. 2025-057059, filed on 28 March 2025. The matters set forth in the original specifications and claims of these applications are incorporated herein by reference.

[0105] 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 comprising a steel material, a plating layer containing Zn, and a coating, arranged in this order, wherein the coating contains trivalent Cr, an organosilicon compound, and fluorine (F), and the concentration of trivalent Cr in the coating is 0.30% by mass or more and 15.00% by mass or less.

2. The surface-treated steel material according to claim 1, wherein the concentration of F in the coating is 5.00% by mass or more and 30.00% by mass or less.

3. The surface-treated steel material according to claim 1, wherein the concentration of F in the coating is 6.50% by mass or more and 30.00% by mass or less.

4. 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.

5. The surface-treated steel material according to claim 1, wherein the coating comprises Zr, P, or V.

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

7. 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.

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

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