Surface-treated steel
A surface-treated steel material with a Zn-based plating layer and a film containing P, Si, and Mg forms a protective film on unplated areas, effectively preventing red rust through controlled elution, thereby improving corrosion resistance.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- NIPPON STEEL CORPORATION
- Filing Date
- 2024-11-22
- Publication Date
- 2026-06-03
Smart Images
Figure 2026090874000001 
Figure 2026090874000002 
Figure 2026090874000003
Abstract
Description
[Technical Field]
[0001] This invention relates to surface-treated steel materials. [Background technology]
[0002] Conventionally, plated steel sheets (zinc-plated steel sheets), in which a zinc-based plating layer is formed on the surface of a steel sheet, have been used in a wide range of applications such as automobiles, building materials, and home appliances. For example, in the building materials sector, research has long been conducted to improve the corrosion resistance of zinc-plated steel sheets in response to the need for longer lifespan of building materials. In this context, the inclusion of Al and Mg in the zinc-plated layer has been investigated as a way to improve corrosion resistance. For example, Patent Documents 1 to 3 disclose plated steel materials in which high corrosion resistance is achieved by including a certain amount of Al and Mg in addition to Zn in the plating layer.
[0003] Furthermore, to impart corrosion resistance and paint adhesion to the surface of such zinc-plated steel sheets, methods such as chromate treatment using a treatment solution mainly containing chromic acid, dichromate, or their salts, treatment using a chromium-free metal surface treatment agent, phosphate treatment, treatment with a silane coupling agent alone, and organic resin coating treatment are generally known and in practical use. These coatings can be given various functions by changing their film composition.
[0004] For example, Patent Document 4 describes a chromium-free surface-treated steel sheet that has excellent flatness and corrosion resistance after processing, as well as excellent adhesive bonding properties, even when alkaline-degreased by the user or exposed to a corrosive environment for a long period of time. The surface treatment composition (X) is applied to the surface of a zinc-plated steel sheet or an aluminum-plated steel sheet, and contains 1 to 400 parts by mass of an organic phosphoric acid compound (B) and 50 to 150 parts by mass of an inorganic phosphoric acid compound (C) per 100 parts by mass of solids of a titanium-containing aqueous solution (A) obtained by mixing at least one titanium compound selected from hydrolyzable titanium compounds, low condensates of hydrolyzable titanium compounds, titanium hydroxide, and low condensates of titanium hydroxide with hydrogen peroxide, and then dried to form a surface treatment film with a thickness of 0.01 to 1.0 μm, wherein a solvent-based organic resin (E), a non-chromium rust-preventive additive (F), and [M 2+ 1-x M 3+ x(OH)2][A n- A highly corrosion-resistant surface-treated steel sheet is disclosed, characterized by having an upper layer film with a film thickness of 0.1 to 3.0 μm formed by applying and drying a paint composition (Y) containing a solid lubricant (G) of ]x / n·zH2O.
[0005] Furthermore, Patent Document 5 discloses a chemically treated steel sheet having a chemical treatment coating containing an organic resin and using a molten Zn-Al-Mg alloy plated steel sheet as a base material, which is excellent in all aspects of weather resistance, water resistance, blackening resistance, coating adhesion, and anti-glare properties. Patent Document 5 discloses that by forming a phosphate coating on the surface of a molten Zn-Al-Mg alloy plated steel sheet, and then forming a chemical treatment coating on the phosphate coating, which is made by crosslinking an aqueous fluorine-containing resin prepared without the use of an emulsifier with an organic crosslinking agent and a group 4A metal compound, the weather resistance, water resistance, blackening resistance, coating adhesion, and anti-glare properties of the chemically treated steel sheet using a molten Zn-Al-Mg alloy plated steel sheet as a base material are all improved. [Prior art documents] [Patent Documents]
[0006] [Patent Document 1] Japanese Patent Publication No. 2006-193791 [Patent Document 2] International Publication No. 2011 / 001662 [Patent Document 3] Japanese Patent Publication No. 2021-172878 [Patent Document 4] Japanese Patent Publication No. 2012-77368 [Patent Document 5] Japanese Patent Publication No. 2012-77322 [Overview of the project] [Problems that the invention aims to solve]
[0007] When plated steel is used, it may be cut to a specified size. In this case, the cut surface (cut end surface) will not have a plated layer. Furthermore, even on plated surfaces, there may be areas where the plated layer is not formed (exposed steel material) due to unplated areas, peeling of the plated layer due to scratches, or cracking of the plated layer due to cutting, punching, bending, drawing, etc. In the plated steel materials described in Patent Documents 1 to 3, the plated portion exhibits excellent corrosion resistance, and in particular, when the plating layer contains Mg and Zn, after a certain period of time has elapsed since the start of exposure, the dissolution of the plating layer progresses to some extent, and a compound film containing the constituent elements of the plated portion is formed on the unplated portion, thereby suppressing the progression of corrosion even in the unplated portion. However, as a result of the inventors' investigations, it has been found that even with these plated steel materials, in the early stages of corrosion when the dissolution of the plating layer has not progressed much, red rust may occur on the cut end surface, unplated portion, or portion of the steel sheet that has been exposed due to scratches or processing after the plating layer has been formed (collectively referred to as the unplated portion).
[0008] Furthermore, even in the case of surface-treated steel materials having a coating, such as those described in Patent Documents 4 and 5, the coating is often not formed on unplated areas where the steel material is exposed due to cut surfaces (cut ends), scratches, punching, bending, drawing, etc. In such cases, there is a problem in that red rust is generated (rusting) in the early stages of corrosion. Therefore, there is a need for technological development that can suppress the formation of red rust on the non-plated parts.
[0009] In view of the above background, the present invention is premised on a surface-treated steel material typified by a surface-treated steel sheet having a plating layer containing Zn (Zn-based plating layer) and a film formed on the surface of the plating layer, and particularly provides a surface-treated steel material in which the formation of red rust in the non-plated part at the initial stage of corrosion is suppressed (having excellent red rust resistance). [Means for Solving the Problems]
[0010] The inventors of the present invention examined a method for suppressing the formation of red rust in the non-plated part of the surface-treated steel material. As a result, it was found that by containing a highly elutable chemical in the film and controlling the composition ratio of the elements in the film so that the eluted components form a precipitated film on the non-plated part, the formation (rusting) of red rust in the non-plated part can be suppressed. In addition, it was found that in order to increase the elution rate of the chemical, it is effective to form a concentrated part in which P and Si are concentrated in the film.
[0011] The present invention has been made in view of the above problems. The gist of the present invention is as follows. [1] A steel material, a plating layer containing Zn formed on at least a part of the surface of the steel material, and a film formed on the surface of the plating layer and containing P, Si, Al, and Mg. When the cross-section of the film is analyzed by TEM-EDS for the P content, Al content, Mg content, and Si content in mass%, the average value of P / Al, which is the ratio of the P content to the Al content, is 0.010 to 10.000, and the average value of Mg / Si, which is the ratio of the Mg content to the Si content, is 0.025 to 1.000. In the film, when the region where the P concentration is 1.0 mass% or more is defined as the P concentrated part and the region where the Si concentration is 1.0 mass% or more is defined as the Si concentrated part, the area ratio of the P concentrated part is 1.00 to 30.00%, the area ratio of the Si concentrated part is 1.00 to 30.00%, and the area ratio of the cracks present on the surface of the film is less than 0. I 0%. A surface-treated steel material characterized by the above. [2] The average value of (P + Al) / (Mg + Si), which is the ratio of the sum of the P content and the Al content to the sum of the Mg content and the Si content in mass%, is 0.025 to 5.000, and the surface-treated steel material according to [1] is characterized in that. [3] The surface-treated steel material according to [1] or [2] is characterized in that the glass transition temperature of the film is 40°C or lower. [4] When performing thin film X-ray diffraction on the surface, the specific intensity I1, which is the ratio of the maximum value to the minimum value of the detected intensity at 2θ of 9.25 to 10°, and the specific intensity I2, which is the ratio of the maximum value to the minimum value of the detected intensity at 2θ of 10 to 12°, one or both of them are 1.50 or more. The thin film X-ray diffraction is measured under the conditions that Cu-Kα line, which is a characteristic X-ray, is used as the X-ray, the output of the X-ray is 45 kV and 40 mA, and the incident angle of the X-ray is 0.5°. The surface-treated steel material according to any one of [1] to [3] is characterized in that. [5] When the area of the exposed surface is 50 cm 2 and it is naturally immersed in 150 mL of a test solution consisting of pure water at 40°C in a sealed state for 24 hours, the P concentration of the test solution after immersion is 0.100 mg / L -1 or more, and the Si concentration of the test solution is 0.100 mg / L -1 or more. The surface-treated steel material according to any one of [1] to [4] is characterized in that. [6] When the area of the exposed surface is 50 cm 2 and it is naturally immersed in 150 mL of a test solution consisting of pure water at 40°C in a sealed state for 24 hours, the Zn concentration of the test solution after immersion is 0.100 mg / L -1 or more. The surface-treated steel material according to any one of [1] to [5] is characterized in that. [7] The equivalent circle diameter of the P enrichment part is 1.0 to 20.0 μm, and the equivalent circle diameter of the Si enrichment part is 1.0 to 20.0 μm. The surface-treated steel material according to any one of [1] to [6] is characterized in that. [8] The surface-treated steel material according to any one of [1] to [7], characterized in that the average chemical composition of the plating layer contains 4.00% by mass or more and 70.00% by mass or less of Al and 0.3% by mass or more and 12.5% by mass or less of Mg. [9] The surface-treated steel material according to any one of [1] to [8], characterized in that the average thickness of the coating is 1.00 to 10.00 μm. [Effects of the Invention]
[0012] According to the present invention, it is possible to provide a surface-treated steel material in which the formation of red rust on unplated areas is suppressed. [Modes for carrying out the invention]
[0013] A surface-treated steel material according to one embodiment of the present invention (a surface-treated steel material according to this embodiment) will be described below.
[0014] The surface-treated steel material according to this embodiment comprises a steel material, a plating layer containing Zn formed on at least a portion of the surface of the steel material, and a film containing P, Si, Al, and Mg formed on the surface of the plating layer.
[0015] <Plating layer> The surface-treated steel material according to this embodiment has a plating layer containing Zn formed on at least a portion of the surface of the steel material. From the viewpoint of corrosion resistance, the plating layer preferably contains 20% by mass or more of Zn in its average chemical composition, more preferably 30% by mass or more, and even more preferably 50% by mass or more. The average chemical composition of the plating layer may consist of Zn and impurities, but may also contain 4.00% to 70.00% by mass of Al and 0.3% to 12.5% by mass of Mg. Furthermore, if necessary, it may also contain one or more of the following: Sn, Bi, In, Ca, Y, La, Ce, Si, Cr, Ti, Ni, Co, V, Nb, Cu, Mn, Fe, Sr, Sb, Pb, and B. For example, the average chemical composition of the plating layer, in mass%, is: Al: 4.00% or more, 70.00% or less; Mg: 0.3% or more, 12.5% or less; Sn: 0% or more, 20.0% or less; Bi: 0% or more, less than 5.0%; In: 0% or more, less than 2.0%; Ca: 0% or more, 3.0% or less; Y: 0% or more, 0.5% or less; La: 0% or more, less than 0.5%; Ce: 0% or more, less than 0.5%; Si: 0% or more, less than 2.5%; Cr: 0% or more, less than 0.25%; Ti: 0% The above includes less than 0.25%, Ni: 0% or more, less than 0.25%, Co: 0% or more, less than 0.25%, V: 0% or more, less than 0.25%, Nb: 0% or more, less than 0.25%, Cu: 0% or more, less than 0.25%, Mn: 0% or more, less than 0.25%, Fe: 0% or more, 5.0% or less, Sr: 0% or more, less than 0.5%, Sb: 0% or more, less than 0.5%, Pb: 0% or more, less than 0.5%, B: 0% or more, less than 0.5%, with the remainder being Zn and impurities. In this case, it is preferable because a more superior corrosion resistance can be obtained as a surface-treated steel sheet, including the portion where the plating layer is formed.
[0016] The reasons for the preferred chemical composition of the plating layer are explained below. Unless otherwise specified, the percentages for the concentration (content) of each element in the chemical composition of the plating layer are given in mass percentages.
[0017] [Al:4.00% or more, 70.00% or less] Al is an effective element for improving corrosion resistance in zinc-based plating layers. Therefore, it may be included. To obtain the above effect sufficiently, it is preferable to have an Al concentration of 4.00% or higher. On the other hand, if the Al concentration exceeds 70.00%, the sacrificial corrosion protection effect of the plating layer decreases. Therefore, it is preferable that the Al concentration be 70.00% or less. More preferably, the Al concentration is 50.00% or less.
[0018] [Mg: 0.3% or more, 12.5% or less] Mg is an element that enhances the corrosion resistance of the plating layer. To obtain the effect of improved corrosion resistance, it is preferable to have an Mg concentration of 0.3% or higher. It is more preferable to have an Mg concentration of 1.0% or higher, and even more preferable to have an Mg concentration of 3.0% or higher. On the other hand, if the Mg concentration exceeds 12.5%, the effect of improving corrosion resistance saturates, and the processability of the plating layer may decrease. In addition, manufacturing problems may arise, such as an increase in the amount of dross generated in the plating bath. For this reason, it is preferable to keep the Mg concentration at 12.5% or less.
[0019] [Sn: 0% or more, 20.0% or less] [Bi: 0% or more, less than 5.0%] [In: 0% or more, less than 2.0%] These elements contribute to improved corrosion resistance and sacrificial corrosion protection. Therefore, one or more of these elements may be included. To obtain the above effects, it is preferable that the concentration of each element be 0.1% or higher, and more preferably 0.2% or higher. Of these, Sn is preferred because it is a low-melting-point metal that can be easily incorporated without impairing the properties of the plating bath. On the other hand, if the Sn concentration exceeds 20.0%, the Bi concentration is 5.0% or higher, or the In concentration is 2.0% or higher, the corrosion resistance decreases. Therefore, it is preferable to keep the Sn concentration at 20.0% or lower, the Bi concentration at less than 5.0%, and the In concentration at less than 2.0%, respectively.
[0020] [Ca: 0% or more, 3.0% or less] Ca is an element that reduces the amount of dross that tends to form during operation, thereby contributing to improved plating manufacturability. Therefore, it may be included. To obtain this effect, it is preferable to have a Ca concentration of 0.1% or higher. On the other hand, if the Ca concentration is high, the corrosion resistance of the flat parts of the plating layer tends to deteriorate, and the corrosion resistance around the weld may also deteriorate. For this reason, a Ca concentration of 3.0% or less is preferable.
[0021] [Y: 0% or more, 0.5% or less] [La: 0% or more, less than 0.5%] [Ce: 0% or more, less than 0.5%] Y, La, and Ce are elements that contribute to improved corrosion resistance. To achieve this effect, it is preferable to include at least 0.1% of each of these elements, and more preferably 0.2% or more. On the other hand, if the concentrations of these elements become excessive, the viscosity of the plating bath increases, often making it difficult to prepare the plating bath itself, and there are concerns that steel materials with good plating properties cannot be manufactured. For this reason, it is preferable to keep the Y concentration at 0.5% or less, the La concentration at less than 0.5%, and the Ce concentration at less than 0.5%.
[0022] [Si: 0% or more, less than 2.5%] Si is an element that contributes to improved corrosion resistance. Furthermore, when forming a plating layer on a steel sheet, Si has the effect of suppressing the formation of an excessively thick alloy layer between the steel sheet surface and the plating layer, thereby improving the adhesion between the steel sheet and the plating layer. To obtain these effects, it is preferable to have a Si concentration of 0.1% or higher. More preferably, the Si concentration is 0.2% or higher. On the other hand, if the Si concentration exceeds 2.5%, excess Si precipitates in the plating layer, reducing not only corrosion resistance but also the processability of the plating layer. Therefore, it is preferable to keep the Si concentration below 2.5%. More preferably, the Si concentration is 1.5% or less.
[0023] [Cr: 0% or more, less than 0.25%] [Ti: 0% or more, less than 0.25%] [Ni: 0% or more, less than 0.25%] [Co: 0% or more, less than 0.25%] [V: 0% or more, less than 0.25%] [Nb: 0% or more, less than 0.25%] [Cu: 0% or more, less than 0.25%] [Mn: 0% or greater, less than 0.25%] These elements contribute to improved corrosion resistance. To achieve this effect, it is preferable to have a concentration of 0.05% or more of one or more of these elements. On the other hand, if the concentrations of these elements become excessive, the viscosity of the plating bath increases, often making it difficult to prepare the plating bath itself, which raises concerns that steel materials with good plating properties cannot be manufactured. For this reason, it is preferable to keep the concentration of each element below 0.25%.
[0024] [Fe: 0% or more, 5.0% or less] Fe is incorporated into the plating layer during its manufacture. While it may be present in concentrations up to approximately 5.0%, within this range, the adverse effect on the surface-treated steel sheet according to this embodiment is small. Therefore, it is preferable to keep the Fe concentration below 5.0%.
[0025] [Sr: 0% or more, less than 0.5%] [Sb: 0% or more, less than 0.5%] [Pb: 0% or more, less than 0.5%] When Sr, Sb, and Pb are included in the plating layer, the appearance of the plating layer changes, spangles are formed, and an improvement in metallic luster is observed. To obtain this effect, it is preferable to have a concentration of 0.1% or more of one or more of Sr, Sb, and Pb, and more preferably 0.2% or more. On the other hand, if the concentrations of these elements become excessive, the viscosity of the plating bath increases, often making it difficult to prepare the plating bath itself, which raises concerns that steel materials with good plating properties cannot be manufactured. For this reason, it is preferable to keep the concentration of each element below 0.5%.
[0026] [B: 0% or more, less than 0.5%] B is an element that, when included in the plating layer, combines with Zn, Al, Mg, etc., to form various intermetallic compounds. These intermetallic compounds have the effect of improving LME (Laser Metal Efficiency). To obtain this effect, it is preferable to have a B concentration of 0.05% or more, more preferably 0.1% or more, and even more preferably 0.2% or more. On the other hand, if the concentration of B is excessive, the melting point of the plating will rise significantly, leading to concerns that the plating operation will deteriorate and surface-treated steel sheets with good plating properties cannot be obtained. For this reason, it is preferable to keep the concentration of B below 0.5%.
[0027] [Remainder: Zn and purines] In the chemical composition of the plating layer, elements other than those mentioned above may be Zn and impurities. Impurities are elements that are introduced during the manufacturing process. While the total concentration of impurities is usually 0.5% or less, a total concentration of 0.1% or less is preferable.
[0028] The chemical composition of the plating layer can be measured by the following method. First, an acid solution is obtained by stripping and dissolving the plating layer with an acid containing an inhibitor that suppresses corrosion of the base metal (steel plate) (for example, an acid made by adding 1% by mass of Hibilon (A-6) (manufactured by Sugimura Chemical Industry Co., Ltd.) to 10% by mass of hydrochloric acid). Next, the chemical composition (average chemical composition) of the plating layer can be obtained by measuring the obtained acid solution with ICP analysis.
[0029] The amount of plating layer to be applied is not limited, but to improve corrosion resistance, 10 g / m² per side is recommended. 2 It is preferable that the amount of adhesion is 450 g / m² per side. 2 Beyond this limit, corrosion resistance saturates, and it becomes economically disadvantageous. Therefore, the amount of adhesive applied per side is 450 g / m². 2 The following is preferable:
[0030] The amount of plating layer can be measured by the following method. A 30mm x 30mm sample is taken from a surface-treated steel sheet. The plating layer is then stripped and dissolved from this sample using an acid containing an inhibitor that suppresses corrosion of the base metal (for example, an acid made by adding 1% by mass of Hibilon (A-6) (manufactured by Sugimura Chemical Industry Co., Ltd.) to 10% by mass of hydrochloric acid). The weight change of the plated steel sheet after stripping and dissolving is measured, and the amount of adhesion is calculated from the results.
[0031] <coating> The surface-treated steel material according to this embodiment has a film formed on the surface of the plating layer. The inventors investigated a method to suppress the formation of red rust on unplated areas by incorporating a highly elutable agent into the coating, eluting the agent component in a corrosive environment, and forming a precipitated film on the unplated areas with the eluted component. As a result, we found that by adding P compounds, Al compounds, Mg compounds, and Si compounds as additives to a resin matrix coating, the components leached from the coating form a precipitated film on the unplated areas. This precipitated film then passivates the steel, dramatically improving the resistance to red rust in the unplated areas of surface-treated steel materials. The coating on the surface-treated steel material according to this embodiment is constructed based on the above findings. Specifically, the coating on the surface-treated steel material according to this embodiment is obtained by adding a P compound, an Al compound, an Mg compound, and a Si compound as additives to a resin-based coating. As a result, this coating contains P derived from the P compound, Al derived from the Al compound, Mg derived from the Mg compound, and Si derived from the Si compound. As the matrix resin, known organic resins such as polyester resin, polyurethane resin, epoxy resin, phenolic resin, acrylic resin, and polyolefin resin can be used. To further improve adhesion to the metal plate, it is preferable to use at least one resin (polyester resin, urethane resin, epoxy resin, acrylic resin, etc.) that has forced sites or polar functional groups in its molecular chain. The resin may be used alone or in combination of two or more types. The resin content is preferably more than 0% by mass, 1% or more by mass, and more preferably 5% or more by mass, relative to the film solids. This improves corrosion resistance. Alternatively, the resin content is preferably 85% by mass or less, more preferably 60% by mass or less, and even more preferably 40% by mass or less, relative to the film solids. By setting the resin content to 85% by mass or less, the corrosion resistance of the film can be improved while ensuring other performance requirements for the film.
[0032] However, in order to obtain a sufficient improvement in red rust resistance, it is necessary to control the composition of the coating so that the P content, Si content, Al content, and Mg content in the coating satisfy a predetermined relationship. Specifically, the average value of P / Al, which is the ratio of P content to Al content by mass%, in the coating is set to 0.010 to 10.000, and the average value of Mg / Si, which is the ratio of Mg content to Si content, is set to 0.025 to 1.000. If the average P / Al value is less than 0.010, the amount of additive chemicals leached from the coating will be small, resulting in insufficient improvement in the rust resistance of the unplated areas. On the other hand, if the average P / Al value exceeds 10.000, the amount of additive chemicals leached from the coating will be too large, degrading the corrosion resistance of the flat surfaces. Furthermore, if the average Mg / Si value is less than 0.025, the additive chemicals leached from the coating will not easily form a compound film on the unplated areas, resulting in insufficient improvement in the rust resistance of the unplated areas. On the other hand, if the average Mg / Si value exceeds 1.000, the amount of additive chemicals leached from the coating becomes too large, degrading the corrosion resistance of the flat surfaces.
[0033] Furthermore, it is preferable that the average value of (P+Al) / (Mg+Si), which is the ratio of the sum of the P content and Al content to the sum of the Mg content and Si content in the film, is between 0.025 and 5.000 by mass. In this case, the Mg and Al dissolved from the film are formed as a compound in the unplated areas, further improving the resistance to red rust in the unplated areas.
[0034] In the coating, the ranges for P content, Al content, Mg content, and Si content are not limited, but it is preferable that the P content is 0.100 to 10.000 mass%, the Al content is 0.100 to 10.000 mass%, the Mg content is 0.100 to 10.000 mass%, and the Si content is 0.100 to 10.000 mass% when calculated as the concentration in the coating.
[0035] [Measurement method] The P, Si, Al, and Mg content of the coating can be measured by quantitative analysis using an energy dispersive X-ray spectroscopy (EDS) (TEM-EDS) attached to a transmission electron microscope (TEM). Specifically, test specimens are cut from surface-treated steel with a coating using the cryo-FIB (Focused Ion Beam) method, and the cross-sectional structure of the cut specimens is observed using a TEM. For example, a transmission electron microscope such as the JEM-2100F (manufactured by JEOL Ltd.) can be used, an EDS measuring device such as the JED-2300T (manufactured by JEOL Ltd.) can be used, and a FIB device such as the NB5000 (manufactured by Hitachi High-Tech Corporation) can be used. In the FIB method, the processing position is determined by SEM observation, but before SEM observation, Au is deposited as an electron irradiation protective film to form a protective film composed of carbon. After SEM observation, processing is performed using the FIB method under acceleration voltage conditions of 40-5kV. A Cu mesh is used for sample holding. To identify the components of the coating, quantitative analysis of P, Al, Mg, and Si is performed using TEM-EDS at five or more points in the center of the coating's thickness direction (any point between 3 / 8 and 5 / 8 of the thickness from the surface is acceptable). The arithmetic mean of the mass percentage content at each point is adopted as the P, Si, Al, and Mg content of the coating. Additionally, the arithmetic mean of the P / Al ratio (mass ratio) of the five points is taken as the average P / Al value, and the arithmetic mean of the Mg / Si ratio (mass ratio) is taken as the average Mg / Si value. Similarly, the average (P+Al) / (Mg+Si) can also be calculated. Observation and EDS analysis are performed under conditions of an acceleration voltage of 200kV and a probe diameter of 1nmΦ.
[0036] In the coating of the surface-treated steel material according to this embodiment, thin-film X-ray diffraction (thin-film XRD) is performed on the surface under conditions of a shallow incident angle of X-rays, and the ratio of the maximum value to the minimum value of the detected intensity (cps) when 2θ is 9.25 to 10° (maximum value / minimum value) is defined as specific intensity I1, and the ratio of the maximum value to the minimum value of the detected intensity (cps) when 2θ is 10 to 12° (maximum value / minimum value) is defined as specific intensity I2. It is preferable that one or both of I1 and I2 are 1.50 or higher. A value of I1 of 1.50 or higher means that the P compound contains a certain amount or more of aluminum phosphate (AlPO4), and a value of I2 of 1.50 or higher means that the P compound contains aluminum dihydrogen triphosphate dihydrate (AlH2P3O 10 This means that it contains a certain amount of (2H2O). These compounds have the effect of suppressing the dissolution of steel, so when either or both of I1 and I2 are 1.50 or higher, the formation of red rust in the unplated areas is suppressed (red rust resistance is improved).
[0037] [Measurement method] The maximum and minimum values of the detection intensity (cps) at a predetermined diffraction angle, used to determine the specific intensities I1 and I2, are measured by thin-film X-ray diffraction. Specifically, a surface-treated steel sample is cut into approximately 2 cm squares. Thin-film XRD is performed on the surface of this sample using characteristic X-rays, Cu-Kα rays, with an X-ray output of 45 kV and 40 mA, and an incident X-ray angle of 0.5°, to determine the minimum and maximum X-ray intensities within a predetermined diffraction angle range. However, for measurement, the measurement range is 2θ = 5 to 60°, the step size is 0.02°, and the time per step is 1 second.
[0038] (P enriched part, Si enriched part) In the coating of the surface-treated steel material according to this embodiment, when the region with a P concentration of 1.0% by mass or more is defined as a P-enriched region and the region with a Si concentration of 1.0% by mass or more is defined as a Si-enriched region, the area ratio of the P-enriched region is 1.00 to 30.00%, and the area ratio of the Si-enriched region is 1.00 to 30.00%. The presence of concentrated areas increases the elution of additives, improving the resistance to red rust in the unplated areas. If the area ratio of the P-enriched area is less than 1.00%, or if the area ratio of the Si-enriched area is less than 1.00%, the resistance to red rust in the unplated area will not be sufficiently improved. On the other hand, from the viewpoint of elution, a larger area ratio of P-enriched areas and Si-enriched areas is preferable. However, if the area ratio of the P-enriched area exceeds 30.00%, or the area ratio of the Si-enriched area exceeds 30.00%, there is a risk that the corrosion resistance (corrosion resistance of flat areas) in areas other than the unplated areas (locations where the plating layer or film exists) will decrease. The reason why the presence of concentrated areas increases elution is not clear, but it is presumed that an increase in the area ratio of concentrated areas reduces the resin ratio of the coating, thereby reducing the protective properties of the coating. Furthermore, when the region with an Al concentration of 1.0% by mass or more is defined as the Al-enriched region, and the region with an Mg concentration of 1.0% by mass or more is defined as the Mg-enriched region, it is preferable that the Al-enriched region exists in the P-enriched region and the Mg-enriched region exists in the Si-enriched region.
[0039] Furthermore, it is preferable that the equivalent circular diameter of the P-enriched area is 1.0 to 20.0 μm, and the equivalent circular diameter of the Si-enriched area is 1.0 to 20.0 μm. If the equivalent circular diameter of the P-enriched or Si-enriched areas is less than 1.0 μm, there is a concern that cracks will easily occur in the coating, leading to a deterioration in the corrosion resistance of the flat surfaces. On the other hand, if it exceeds 20.0 μm, there is a concern that the perimeter length of each enriched area will decrease, reducing the amount of added chemicals that can be eluted.
[0040] [Measurement method] The area ratio and size (equivalent circle diameter) of the P-enriched and Si-enriched regions are measured using SEM-EDS. Specifically, a 20mm square sample is cut from a surface-treated steel material with a coating, and gold with a thickness of approximately 100nm is deposited onto the surface of the coating. This surface was examined using a scanning electron microscope (SEM) at a magnification of 1000x, covering an area of 8000 μm. 2The above areas are observed using secondary electron imaging. When elemental mapping is performed using SEM-EDS with the analytical elements being C, O, Si, and P, regions with a P content of 1.0 mass% or more are identified as P-enriched regions, and regions with a Si content of 1.0 mass% or more are identified as Si-enriched regions, and their area ratios are calculated. Furthermore, the equivalent circle diameters of the P-enriched and Si-enriched regions are determined by measuring the equivalent circle diameters (equivalent diameters) of the regions with a P content of 1.0 mass% or more and the Si content of 1.0 mass% or more observed during the elemental mapping described above, and taking the average value of these values as the equivalent circle diameters of the P-enriched and Si-enriched regions. The above measurements were performed at three locations at least 5 mm apart from each other, and the average of the three measurements was used as the area ratio and equivalent circle diameter of the P-enriched and Si-enriched areas. To determine the presence or absence of Al-enriched or Mg-enriched areas, the same measurement can be performed by adding Al and Mg to the target element during the measurement.
[0041] The presence of cracks on the surface of the coating increases the surface area, which is desirable from the viewpoint of drug elution, and therefore, is desirable in terms of corrosion resistance of unplated parts such as end faces. On the other hand, the presence of cracks may reduce the corrosion resistance (corrosion resistance of flat parts) in the areas where the plating layer or coating exists. In the surface-treated steel material according to this embodiment, the elution properties are enhanced by the P-enriched and Si-enriched portions. Therefore, from the viewpoint of achieving compatibility with the corrosion resistance of the flat surface, it is preferable to have a crack area ratio of 0.10% or less, or less than 0.10%, on the surface of the coating.
[0042] [Measurement method] The area ratio of cracks on the surface of the coating is determined by the following method. A 20mm square sample is cut from a surface-treated steel material with a coating, and gold approximately 100nm thick is deposited onto the surface of the coating. This surface was examined using a scanning electron microscope (SEM) at a magnification of 1000x, covering an area of 8000 μm. 2The above area is observed using a secondary electron image. Since cracks appear darker relative to the film, the secondary electron image is binarized to determine the area of the crack-like portion with lower brightness relative to the film. The ratio of this area to the observation field of view is defined as the crack area ratio. Here, the crack area ratio is measured using the image processing software "ImageJ". Specifically, the secondary electron image is imported into ImageJ, and the image is binarized using the "Threshold" setting in "Adjust" under "Image" so that cracks are displayed in white and areas other than cracks are displayed in black. After binarization, the "Measure" function under "Analyze" is used, and the "Area fraction" of the white area in "Results" is read to determine the crack area ratio. Perform the above measurements at three locations at least 5 mm apart from each other, and use the average of these measurements as the crack area ratio.
[0043] (Glass transition temperature) In the surface-treated steel material according to this embodiment, it is preferable that the glass transition temperature of the coating is 40°C or lower. The lower the glass transition temperature of the resin that forms the base (matrix) of the coating, the higher the elution rate of the additive. A higher elution rate improves resistance to red rust in the unplated areas. The reason why the elution rate of the additive increases with lower glass transition temperatures is not clear, but it is presumed that a lower glass transition temperature makes the resin softer and allows the additive to move more easily at low temperatures, resulting in a larger amount of eluted additive. When the glass transition temperature is greater than 40°C, the effect of increasing the elution rate of the added agent is small. On the other hand, there is no lower limit to the glass transition temperature, but for resins commonly used in coatings, the glass transition temperature is at least around -100°C, and often above -50°C.
[0044] [Measurement method] The glass transition temperature of the coating is determined using a differential scanning calorimetry (DSC). For the measurement, the measurement temperature is set to 250 to -50°C, and the temperature at which the baseline shifts is defined as the glass transition temperature. If the coating contains two or more types of resin, the baseline will shift at two different positions, and the highest temperature among these shifts will be considered the glass transition temperature of the coating.
[0045] (elution rate) As described above, the surface-treated steel material according to this embodiment has excellent resistance to red rust, as the additives contained in the coating are easily leached out. Specifically, when measuring the dissolution rate, it is preferable that it falls within the following range.
[0046] In other words, the exposed surface area is 50 cm². 2 When the test solution, consisting of 150 mL of pure water at 40°C, was immersed in a sealed container for 24 hours, the phosphorus concentration in the test solution after immersion was 0.100 mgL. -1 The above is the result, and the Si concentration of the test solution is 0.100 mgL. -1 The above, and / or the area of the exposed surface is 50 cm². 2 When the sample was immersed in 150 mL of a test solution consisting of pure water at 40°C in a sealed state for 24 hours, the Zn concentration of the test solution after immersion was 0.100 mg / L. -1 The above is preferable. The elution of P and Si is from the additive agent, and the elution of Zn is from the plating layer. In addition to the elution of P and Si from the additive agent, the elution of Zn from the plating layer can further improve the resistance to red rust in the unplated areas. If the above conditions are met, even in environments with high temperature and humidity, where water exposure is prolonged and dissolved chemical components are likely to leak out of the system, a compound film derived from the added chemical can be formed on the non-plated parts, providing resistance to red rust.
[0047] [Measurement method] The elution rate is determined by the following method. A sample containing the coating was cut from the surface-treated steel material, and the exposed surface area of the coated portion of the sample was 50 cm². 2 Seal all surfaces except the exposed ones with tape. The container is immersed in 150 mL of a test solution consisting of pure water at a temperature of 40°C, ensuring that the exposed surface does not come into contact with the container. The container is then sealed with a lid and left in this sealed state for 24 hours. After 24 hours, the concentrations (contents) of P, Si, and Zn in the test solution are measured by ICP analysis.
[0048] (thickness) The average thickness of the coating on the surface-treated steel material according to this embodiment is preferably 1.00 to 10.00 μm. If the average thickness of the coating is less than 1.00 μm, there is a concern that the amount of additive chemicals leached out will be insufficient. On the other hand, if it exceeds 10.00 μm, the effect of improving the resistance to red rust in the unplated area will saturate, while manufacturing costs will increase. Furthermore, there is a concern that it will become difficult to ensure a sufficient amount of zinc leached from the plating layer.
[0049] [Measurement method] The average thickness of the coating is determined by the following method. Prepare a test specimen in the same manner as for measuring the P, Si, Al, and Mg content of the coating, and measure the coating thickness at three points using TEM-EDS, ensuring that the entire coating is visible in the thickness direction. Furthermore, this measurement is performed in a total of three fields of view, and the average of the nine points (3 points x 3 fields of view) is taken as the average thickness of the coating. To measure the thickness, the phosphorus (P) content is measured by EDS analysis at 10 nm intervals from the plating layer toward the surface of the surface-treated steel. The point where the P content first exceeds 1 mass% is determined to be the interface between the film and the plating layer, and the distance from this interface to the surface of the film (surface of the surface-treated steel) is defined as the film thickness. Observation and EDS analysis are performed under conditions of an acceleration voltage of 200 kV and a probe diameter of 1 nmΦ, and the EDS analysis is performed under conditions of analyzing elements Zn, Al, Mg, O, C, P, and Si.
[0050] [Manufacturing method] The surface-treated steel sheet according to this embodiment can achieve the above-described effects regardless of the manufacturing method, as long as it possesses the above-described characteristics, but it can be manufactured by a manufacturing method that includes the following steps. (I) A plating process to obtain a plated steel sheet by forming a plating layer containing Zn on the surface of a steel material (base steel material), (II) Preparation of the treatment solution, which will form a film after application and drying, (III) A coating formation step in which a coating is formed by applying the treatment solution prepared in the treatment solution preparation step to the steel material after the plating process (plated steel material) and drying it, thereby obtaining surface-treated steel material. The preferred conditions for each process will be explained.
[0051] (Plating process) In the plating process, a plating layer is formed on the surface of a steel material, such as a steel plate, by immersing it in a plating bath containing zinc or by electroplating. The conditions for forming the plating layer are not particularly limited. It is acceptable to use a conventional method to ensure sufficient plating adhesion. Furthermore, there are no limitations on the steel materials used in the plating process or their manufacturing methods. In the case of surface-treated steel sheets, for example, hot-rolled steel sheets (hot-rolled steel sheets) as described in JIS G 3131:2018, JIS G 3113:2018, etc., or cold-rolled steel sheets (cold-rolled steel sheets) as described in JIS G 3141:2021, JIS G 3135:2018, etc., can be used as the steel sheets immersed in the plating bath. In addition, steel materials other than steel sheets, such as steel pipes, steel wires, and various components made of steel, can also be used. The composition of the plating bath should be adjusted according to the chemical composition of the plating layer to be obtained. After removing the steel material from the plating bath, the amount of plating layer can be adjusted by wiping as needed.
[0052] After the plating process and before the treatment solution preparation process, the surface of the surface-treated steel material may be degreased with a degreasing agent.
[0053] (Preparation of processing solution) In the processing solution preparation step, P compound, Al compound, Si compound, and Mg compound are mixed separately in powder form, with the P compound and Al compound, and the Si compound and Mg compound, using a mortar and pestle. Then, the mixture of P compound and Al compound, and the mixture of Si compound and Mg compound are mixed into a water-based paint containing a resin that will form the film matrix, and the mixture is stirred at 25-40°C for 0.50-1.00 hours to obtain the processing solution. By pre-mixing the P compound with the Al compound, and the Si compound with the Mg compound in powder form, and keeping the stirring time relatively short, it becomes easier to form P-enriched and Si-enriched regions of a predetermined size and area ratio. On the other hand, if the stirring time is too short, the added chemicals remain aggregated when the film is formed, resulting in poor corrosion resistance on flat surfaces.
[0054] The P compound is a compound containing P, and may contain one or more selected from, for example, inorganic phosphoric acid, organic phosphoric acid, and salts thereof. The inorganic phosphoric acid, organic phosphoric acid, and salts thereof are not particularly limited and any compound can be used. For example, as the inorganic phosphoric acid, it is preferable to use one or more selected from phosphoric acid, monophosphate, dicaphosphate, tertiary phosphate, pyrophosphate, pyrophosphate, tripolyphosphate, tripolyphosphate, phosphorous acid, phosphite, hypophosphorous acid, and hypophosphite. As the organic phosphoric acid, it is preferable to use phosphonic acid (phosphonic acid compound). If the P compound is a salt, the salt is preferably a salt of an element from Group 1 to Group 13 of the periodic table, more preferably a metal salt, and preferably one or more selected from alkali metal salts and alkaline earth metal salts. The added Al compound is not limited, but it is preferably one or more selected from aluminum sulfate, aluminum carbonate, aluminum chloride, aluminum oxide, aluminum hydroxide, condensed aluminum phosphate, and aluminum metaphosphate. The added Mg compound is not limited, but it is preferably one or more selected from magnesium fluoride, magnesium nitrate, magnesium sulfate, magnesium chloride, magnesium acetate, magnesium hydroxide, magnesium silicate, basic magnesium carbonate, and magnesium phosphate. The added Si compound is not limited, but it is preferably one or more selected from silica, sodium silicate, potassium silicate, magnesium silicate, and silane coupling.
[0055] (Film formation process) In the film formation process, the treatment solution prepared in the treatment solution preparation process is applied to the plated steel sheet and dried to form a film, thereby obtaining a surface-treated steel material. The application method is not limited. For example, it can be applied using a roll coater, bar coater, spray, etc. After applying the treatment solution, heat and dry it. It is preferable to heat the surface-treated steel material so that the heating temperature (maximum temperature reached: PMT) is between 60 and 120°C, and to hold it at the maximum temperature for 1.0 to 10.0 seconds. If the heating temperature is below 60°C, the drying of the treatment solution will be insufficient, and the corrosion resistance of the flat surface will deteriorate. On the other hand, if the heating temperature is above 120°C, the formation of concentrated areas tends to be insufficient, and cracks are more likely to occur in the coating. When heating, it is preferable to spray the material onto the steel plate through perforated metal (a steel plate with multiple through-holes). This forms a film on the surface of the plated steel material. (A surface-treated steel material according to this embodiment is obtained.) [Examples]
[0056] For the steel material, we prepared hot-rolled steel sheets with a thickness of 4.5 mm that satisfy JIS G 3131:2018. A hot-dip galvanizing process was performed on this steel sheet to form a plating layer. The composition of the plating layer is shown in Table 1. In Table 1, for example, Zn-0.18%Al indicates that it contains 0.18% Al, with the remainder being Zn and impurities, and Zn-55.00%Al-1.6%Si indicates that it contains 55.00% Al and 1.6% Si, with the remainder being Zn and impurities. The same applies to the others. The concentration (content) of impurities in the plating layers C1 to C8 was 0.3% or less in all cases. The amount of plating layer attached was 135 g / m² on both the front and back surfaces of the plated surface. 2 That's what I decided. The obtained plated steel sheet (surface-treated steel sheet) was cut with an electric shear to form an end face having a portion with a plated layer and a portion without a plated layer (where the steel sheet is exposed). No unplated areas were formed on the plated surface. After plating, the surface of the obtained surface-treated steel sheet was degreased using the degreasing agent Surf Cleaner 4336LA1+LB.
[0057] [Table 1]
[0058] Furthermore, a treatment solution was prepared to form a protective film. First, the P compound, Al compound, Mg compound, and Si compound listed in Tables 2 to 5 were used to prepare the resin that would serve as the film matrix, as shown in Table 6. Five different compounds were prepared as P compounds. All of the P compounds used were commercially available. Their chemical formulas are also listed in Table 2. Five different compounds were prepared as Al compounds. All of the Al-containing compounds used were commercially available. Their chemical formulas are also listed in Table 3. Five different Mg compounds were prepared. All of the Mg-containing compounds used were commercially available. Their chemical formulas are also listed in Table 4. Four types of Si compounds were prepared. All of the Si-containing compounds used were commercially available. Their chemical formulas are also listed in Table 5. Six different types of resin were prepared. All of the resins used were commercially available.
[0059] [Table 2]
[0060] [Table 3]
[0061] [Table 4]
[0062] [Table 5]
[0063] [Table 6]
[0064] The P, Al, Mg, and Si compounds listed in Tables 2 to 5 were mixed separately in powder form, with the P and Al compounds, and the Si and Mg compounds, using a mortar and pestle. Then, the mixtures of the P and Al compounds, and the Si and Mg compounds, were mixed with a water-based paint containing the resin shown in Table 6, which would form the film matrix. The mixtures were stirred at 25°C for the time indicated in Table 7 to obtain the treatment solution. At this time, deionized water was added to adjust the solid content concentration of the treatment solution to 20% by mass. Conditions where the same reagent is listed, such as P4 and A4, mean that the reagent at the listed concentration was added twice. These treatment solutions were applied to the degreased surface-treated steel sheets obtained above, to achieve the dry film thicknesses shown in Tables 11 and 12. Then, the sheets were dried in an induction heating furnace to the values shown in Tables 7 and 8 for the maximum temperature and holding time, and subsequently air-cooled.
[0065] (Film-forming component) The obtained surface-treated steel sheets were quantitatively analyzed using an energy-dispersive X-ray spectroscopy (EDS) (TEM-EDS) attached to a transmission electron microscope (TEM) to determine the P / Al (mass ratio), Mg / Si (mass ratio), and (P+Al) / (Mg+Si) ratios of the coating. Specifically, test specimens were cut from surface-treated steel materials with a coating using the cryo-FIB (Focused Ion Beam) method, and the cross-sectional structure of the cut specimens was observed using a TEM. A JEM-2100F transmission electron microscope (manufactured by JEOL Ltd.), a JED-2300T EDS measurement device (manufactured by JEOL Ltd.), and an NB5000 FIB device (manufactured by Hitachi High-Tech Corporation) were used. For FIB cutting, the processing position was determined by SEM observation, but before SEM observation, a protective film of Au (gold) was deposited as an electron irradiation protective film, forming a protective film composed of carbon. After SEM observation, processing was performed using the FIB method under acceleration voltage conditions of 40-5kV. A Cu mesh was used for sample holding. To identify the components of the film, quantitative analysis of P, Al, Mg, and Si was performed using TEM-EDS at five points each, centered in the thickness direction of the film (3 / 8 to 5 / 8 of the thickness from the surface). The arithmetic mean of the mass percent content at each point was adopted as the P, Si, Al, and Mg content of the film. Furthermore, the arithmetic mean of P / Al and Mg / Si at the five points were taken as the average P / Al and Mg / Si values, respectively. Additionally, the arithmetic mean of (P+Al) / (Mg+Si) at the five points was taken as the average (P+Al) / (Mg+Si) value. Observation and EDS analysis were performed under conditions of an acceleration voltage of 200kV and a probe diameter of 1nmΦ. The results are shown in Tables 9 and 10.
[0066] (Area ratio and size of P-enriched and Si-enriched regions) The area ratio and size of the P-enriched and Si-enriched regions were measured using SEM-EDS. Specifically, a 20mm square sample was cut from a surface-treated steel material with a coating, and gold approximately 100nm thick was deposited onto the surface of the coating. This surface was examined using a scanning electron microscope (SEM) at a magnification of 1000x, covering an area of 8000 μm. 2 The above areas were observed using secondary electron imaging. When elemental mapping was performed using SEM-EDS with the analytical elements being C, O, Si, and P, regions with a P content of 1.0 mass% or more were identified as P-enriched regions, and regions with a Si content of 1.0 mass% or more were identified as Si-enriched regions, and their area ratios were calculated. Furthermore, the size of the P-enriched and Si-enriched regions was determined by measuring the equivalent circle diameter of the regions with a P content of 1.0 mass% or more and the Si content of 1.0 mass% or more observed during the elemental mapping, and taking the average value of these measurements as the size of the P-enriched and Si-enriched regions. The above measurements were performed at three locations separated by at least 5 mm from each other, and the average of the three measurements was used as the area ratio and size of the P-enriched and Si-enriched regions. The results are shown in Tables 9 and 10.
[0067] (Percentage of cracks on the surface of the coating) The area ratio of cracks on the surface of the coating was determined by the following method. A 20mm square sample was cut from a surface-treated steel material with a coating, and gold approximately 100nm thick was deposited onto the surface of the coating. This surface was examined using a scanning electron microscope (SEM) at a magnification of 1000x, covering an area of 8000 μm. 2 The above areas were observed using secondary electron imaging. Since cracks appear darker relative to the film, the secondary electron imaging was binarized to determine the area of the crack-like portion with lower brightness relative to the film. The ratio of this area to the observation field of view was defined as the crack area ratio. Here, the crack area ratio was measured using the image processing software "ImageJ". Specifically, the secondary electron imaging was imported into ImageJ, and the image was binarized using the "Threshold" setting in "Adjust" under "Image" so that cracks were displayed in white and areas other than cracks in black. After binarization, the "Measure" function under "Analyze" was used, and the "Area fraction" of the white area in "Results" was read to determine the crack area ratio. The above measurements were performed at three locations at least 5 mm apart from each other, and the average of these measurements was used as the crack area ratio. The results are shown in Tables 9 and 10.
[0068] (Specific intensity of X-ray diffraction peaks) To determine the specific intensities I1 and I2, the maximum and minimum intensities (cps) at predetermined diffraction angles were measured using X-ray diffraction. Specifically, surface-treated steel material was cut into approximately 2 cm squares, and X-ray diffraction (thin-film XRD) was performed on this sample using Cu-Kα rays, which are characteristic X-rays, with an X-ray output of 45 kV and 40 mA, and an X-ray incidence angle of 0.5°. The minimum and maximum values of the X-ray intensity within a predetermined diffraction angle range were then determined. However, for the measurement, the measurement range was set to 2θ = 5 to 60°, the step size to 0.02°, and the time per step to 1 second. The results are shown in Tables 9 and 10.
[0069] (Glass transition temperature) The glass transition temperature of the coating was determined using differential scanning calorimetry (DSC). For the measurements, the measurement temperature was set to 250 to -50°C, and the temperature at which the baseline shifted was defined as the glass transition temperature. When the coating contains two or more types of resin, the baseline shifts at two different positions, and the highest temperature among these shifts was defined as the glass transition temperature of the coating. The results are shown in Tables 9 and 10.
[0070] (elution rate) The elution rate was determined using the following method. A sample containing the coating was cut from the surface-treated steel material, and the exposed surface area of the coated portion of the sample was 50 cm². 2 To achieve this, the areas other than the exposed surface were sealed with tape. The container was immersed naturally in 150 mL of a test solution consisting of pure water at a temperature of 40°C, with the lid closed to prevent contact between the exposed surface and the container, and left in a sealed state for 24 hours. After 24 hours, the concentrations (contents) of P, Si, and Zn in the test solution were measured by ICP analysis. The results are shown in Tables 11 and 12.
[0071] (thickness) The average thickness of the coating was determined by the following method. Test specimens were prepared in the same manner as for measuring the P, Si, Al, and Mg content of the coating. Using TEM-EDS, the coating thickness was measured at three points in a field of view that included the entire coating in the thickness direction. Furthermore, this measurement was performed in a total of three fields of view, and the average of the nine points (3 points x 3 fields of view) was taken as the average thickness of the coating. To measure the thickness, the phosphorus (P) content was measured by EDS analysis at 10 nm intervals from the plating layer toward the surface of the surface-treated steel. The point where the P content first exceeded 1 mass% was determined to be the interface between the film and the plating layer, and the distance from this interface to the surface of the film (surface of the surface-treated steel) was defined as the film thickness. Observation and EDS analysis were performed under conditions of an acceleration voltage of 200 kV and a probe diameter of 1 nmΦ. The EDS analysis was performed using Zn, Al, Mg, O, C, P, and Si as the analytical elements. The results are shown in Tables 11 and 12.
[0072] <Performance evaluation details> (Performance 1: End face corrosion resistance) Exposure tests were conducted on plated steel materials, and the area percentage of red rust on the end face after 100 days was determined. The exposure conditions were as follows: The plated steel sample was tilted 30° from the horizontal so that the treated cut end face was facing downwards, and the atmospheric exposure test was conducted facing south. After exposure, the sample was evaluated as follows based on the ratio of the area where red rust was formed to the area where the plating layer was not formed. A rating of SS, S, AA, or A indicated excellent corrosion resistance at the end face. A rating of B indicated that the area where red rust was formed exceeded 100%, meaning that red rust was formed not only in the areas where the plating layer was not formed, but also in the surrounding areas. SS: 50% or less S: More than 60%, less than 70% AA: More than 70%, less than 80% A: More than 80%, less than 100% B: More than 100%, less than 115% The results are shown in Tables 11 and 12.
[0073] (Performance 2: Corrosion resistance of flat surfaces) The evaluation of the corrosion resistance of the flat surface was performed as follows: The obtained plated steel material was cut into 100 mm x 50 mm pieces, and a salt spray test in accordance with JIS Z 2371 (2015) was conducted for up to 96 hours. The corrosion resistance of the flat surface was evaluated by the corrosion loss of the test piece after the test. The evaluation criteria for the corrosion resistance of the flat surface are shown below. "S", "AA", and "A" were considered acceptable. S: 0.020 (g / m³) 2 / hr) or less AA: More than 0.020~0.028(g / m 2 / hr) or less A: More than 0.028~0.10(g / m 2 / hr) or less B: More than 0.10~0.50(g / m 2 / hr) or less C: 0.50 (g / m³) 2 / hr) super The results are shown in Tables 11 and 12.
[0074] [Table 7]
[0075] [Table 8]
[0076] [Table 9]
[0077] [Table 10]
[0078] [Table 11]
[0079] [Table 12]
[0080] As can be seen from Tables 1 to 12, surface-treated steel sheets having a predetermined coating on the plating layer exhibited excellent resistance to red rust on the edge surfaces. On the other hand, when the required film was not formed on the plating layer, the red rust resistance of the end face was poor.
Claims
1. Steel materials, A plating layer containing Zn is formed on at least a portion of the surface of the steel material, A film containing P, Si, Al, and Mg is formed on the surface of the aforementioned plating layer, It has, When the cross-section of the aforementioned film was analyzed using TEM-EDS to determine the P content, Al content, Mg content, and Si content in mass%, The average value of P / Al, which is the ratio of the P content to the Al content, is between 0.010 and 10.
000. The average value of Mg / Si, which is the ratio of Mg content to Si content, is between 0.025 and 1.
000. In the aforementioned coating, when a region with a P concentration of 1.0% by mass or more is defined as a P-enriched region, and a region with a Si concentration of 1.0% by mass or more is defined as a Si-enriched region, The area ratio of the P-enriched area is 1.00 to 30.00%, and the area ratio of the Si-enriched area is 1.00 to 30.00%. The area ratio of cracks present on the surface of the aforementioned coating is less than 0.10%. A surface-treated steel material characterized by the following features.
2. The average value of (P + Al) / (Mg + Si), which is the ratio of the sum of the P content and Al content to the sum of the Mg content and Si content in mass%, is between 0.025 and 5.
000. The surface-treated steel material according to claim 1, characterized in that...
3. The glass transition temperature of the aforementioned film is 40°C or lower. A surface-treated steel material according to claim 1 or 2, characterized in that...
4. When thin-film X-ray diffraction is performed on the surface, 1.50 or greater if one or both of the specific intensity I1, which is the ratio of the maximum value to the minimum value of the detection intensity when 2θ is 9.25 to 10°, and the specific intensity I2, which is the ratio of the maximum value to the minimum value of the detection intensity when 2θ is 10 to 12°, The thin-film X-ray diffraction described above is performed using Cu-Kα rays, which are characteristic X-rays, as the X-rays, with the X-ray output being 45 kV and 40 mA, and the incident angle of the X-rays being 0.5°. The surface-treated steel material according to claim 1, characterized in that...
5. The exposed surface area is 50 cm². ２ When immersed in a sealed state for 24 hours in 150 mL of a test solution consisting of pure water at 40°C, The P concentration of the test solution after immersion is 0.100 mg / L. －１ The above is true, and the Si concentration of the test solution is 0.100 mg / L. －１ That's all. The surface-treated steel material according to claim 1, characterized in that...
6. The exposed surface area is 50 cm². ２ When immersed in a sealed state for 24 hours in 150 mL of a test solution consisting of pure water at 40°C, The Zn concentration of the test solution after immersion is 0.100 mg / L. －１ That's all. The surface-treated steel material according to claim 1, characterized in that...
7. The equivalent circular diameter of the P-enriched portion is 1.0 to 20.0 μm, and the equivalent circular diameter of the Si-enriched portion is 1.0 to 20.0 μm. The surface-treated steel material according to claim 1, characterized in that...
8. The average chemical composition of the aforementioned plating layer is 4.00% by mass or more and 70.00% by mass or less of Al, Mg in an amount of 0.3% by mass or more and 12.5% by mass or less, including, The surface-treated steel material according to claim 1, characterized in that...
9. The average thickness of the aforementioned film is 1.00 to 10.00 μm. The surface-treated steel material according to claim 1, characterized in that...