Plated steel and solar power generation stand

Abstract

The plated steel material has a steel sheet, a plated layer formed on the steel sheet, and an oxide layer formed on the plated layer, the plated layer has a chemical composition containing, in mass%, Al: 1.0 to 60.0%, Mg: 1.0 to 15.0%, Si: 0 to 2.0%, Ca: 0 to 2.0%, and Fe: 0 to 2.0%, with the remainder being Zn and impurities, the oxide layer has a thickness of 5 nm or more, a ratio of a total of maximum intensities of Al and Mg in energy dispersive X-ray analysis of the oxide layer to a maximum intensity of Zn, that is, an (Al+Mg) / Zn intensity ratio, is 1.0 or more, and the oxide layer contains an amorphous structure.

Description

Technical Field

[0001] This disclosure relates to galvanized steel and solar power generation racks. Background Technology

[0002] Steel with a hot-dip Zn-coated layer containing Al and Mg on its surface (hot-dip Zn-Al-Mg series steel) exhibits excellent corrosion resistance. Therefore, hot-dip Zn-Al-Mg series steel is widely used as a material for structural components requiring corrosion resistance, such as building materials.

[0003] For example, Patent Document 1 discloses a coated steel sheet comprising: a steel sheet, a coating formed on at least a portion of the surface of the steel sheet, and an oxide layer formed on at least a portion of the surface of the coating. When measured using XPS at a position 5.0 nm away from the surface of the oxide layer in the thickness direction, the ratio of the maximum detection intensity of Mg to the maximum detection intensity of Mg oxide or hydroxide is 1Mg / 1Mg. Ox The value ranges from 0.00 to 1.20. Patent Document 1 discloses that, with the above configuration, the proportion of Mg contained in the coating existing in the form of oxide [MgO] or hydroxide [Mg(OH)2] can be increased, and the proportion of Al contained in the coating existing in the form of oxide [Al2O3] or hydroxide [Al(OH)3] can be decreased. As a result, the lubricity and chemical conversion treatability of the coating can be improved.

[0004] Existing technical documents Patent documents Patent Document 1: International Publication No. 2022 / 153840 Summary of the Invention

[0005] The problem that the invention aims to solve In recent years, water resistance has also been required for hot-dip Zn-Al-Mg steels. Water resistance refers to corrosion resistance when exposed to flowing water. In a flowing water environment, corrosion products adhering to the surface of the hot-dip galvanized coating are washed away, impairing their rust-preventing effect. Therefore, the water resistance of steel is evaluated using methods different from conventional corrosion resistance. For example, high water resistance is required for various building materials used outdoors, such as guardrails on roads, solar power generation platforms, or the walls of waterways frequently supplied with rainwater and industrial water.

[0006] In the prior art, there has been almost no research on water resistance. For example, the corrosion resistance of planar surfaces, which is well known as a conventional evaluation method, is mostly evaluated according to JASO M609-91, in which the corrosive solution is set to a non-flowing state.

[0007] Furthermore, the inventors of this invention conducted research and found that even commonly used hot-dip galvanized Zn-Al-Mg steels with high corrosion resistance do not necessarily have sufficient water corrosion resistance. For example, although Patent Document 1 specifies the ratio of each oxide in the oxide layer on the coating surface, the inventors of this invention found that even with this specification, corrosion may easily occur in a running water environment, meaning that the water corrosion resistance becomes insufficient.

[0008] This disclosure is made in view of the above-mentioned circumstances. The purpose of this disclosure is to provide coated steel with excellent resistance to water corrosion and a mounting platform for solar power generation.

[0009] Methods for solving problems The main points of this disclosure are as follows.

[0010] [1] One embodiment of the present invention comprises a plated steel material having: a steel sheet, a coating formed on the steel sheet, and an oxide layer formed on the coating. The coating has the following chemical composition: containing, by mass%,: Al: 1.0~60.0% Mg: 1.0–15.0% Si: 0~2.0%, Ca: 0–2.0%, and Fe: 0~2.0%, Further containing a total of 5.0% or less of one or more elements selected from the following: Ni: 0~1.000%, La: 0~0.500% Ce: 0~0.500% Sb: 0~0.500%, Pb: 0~0.500%, Sr: 0~0.500%, Bi: 0~0.500%, Sn: 0~1.000% Cu: 0~1.000%, Ti: 0~1.000%, Mn: 0~1.000%, Cr: 0~1.000% Nb: 0~1.000%, Zr: 0~1.000%, Mo: 0~1.000%, V: 0~1.000% In: 0~1.000%, Co: 0~1.000%, Ag: 0~1.000%, Li: 0~1.000%, B: 0~0.500% Y: 0~0.500%, and P: 0~0.500%, The remaining portion contains Zn and impurities. The thickness of the oxide layer is 5 nm or more. The ratio of the combined maximum intensity of Al and Mg in energy-dispersive X-ray analysis of the oxide layer to the maximum intensity of Zn, i.e., the (Al+Mg) / Zn intensity ratio, is greater than 1.0. The oxide layer contains an amorphous structure.

[0011] [2] According to the coated steel described in [1] above, the chemical composition of the coating may also contain one or more of the following elements in mass percent: Si: 0.1–2.0% Ca: 0.1–2.0% Fe: 0.1–2.0%, Ni: 0.001~1.000% La: 0.010~0.500% Ce: 0.010~0.500% Sb: 0.001~0.500% Pb: 0.001~0.500%, Sr: 0.001~0.500%, Bi: 0.001~0.500% Sn: 0.050~1.000% Cu: 0.001~1.000%, Ti: 0.001~1.000% Mn: 0.001~1.000%, Cr: 0.001~1.000% Nb: 0.001~1.000% Zr: 0.001~1.000% Mo: 0.001~1.000%, V: 0.001~1.000% In: 0.001~1.000% Co: 0.001~1.000%, Ag: 0.001~1.000%, Li: 0.001~1.000% B: 0.001~0.500% Y: 0.010~0.500%, and P: 0.001~0.500%.

[0012] [3] According to the coated steel described in [1] or [2] above, it may also be that the chemical composition of the coating is: Al: 10.0–30.0% by mass Mg: 4.0–15.0% by mass The (Al+Mg) / Zn strength ratio of the oxide layer is 2.0 or higher.

[0013] [4] The plated steel according to any one of [1] to [3] above may also have the following chemical composition in the coating: Al: 15.0–30.0% by mass Mg: 4.0–15.0% by mass The (Al+Mg) / Zn strength ratio of the oxide layer is 3.0 or higher.

[0014] [5] In the plated steel according to any one of [1] to [4] above, no diffraction spots representing crystalline structure can be detected in the electron diffraction image obtained by analyzing the cross section of the oxide layer using electron diffraction.

[0015] [6] A solar power generation platform according to one embodiment of the present invention comprises the plated steel material described in any one of [1] to [5] above.

[0016] Invention Effects According to the above-described solution disclosed herein, it is possible to provide coated steel with excellent water corrosion resistance and a solar power generation platform. Attached Figure Description

[0017] Figure 1 This is an electron diffraction image of the cross-section of the oxide layer in the coated steel of this embodiment, obtained using TEM (transmission electron microscopy).

[0018] Figure 2 This is an electron diffraction image of the cross-section of the oxide layer in the coated steel of this embodiment, obtained using TEM (transmission electron microscopy).

[0019] Figure 3 This is a schematic diagram illustrating an example of a solar power generation platform according to this embodiment. Detailed Implementation

[0020] A coated steel material (hereinafter, sometimes referred to as the coated steel material of this embodiment) according to one embodiment of the present disclosure will be described. However, the present disclosure is not limited to the configuration disclosed in this embodiment, and various modifications can be made without departing from the spirit of the present disclosure.

[0021] The following provides a detailed description of each of the constituent elements of this disclosure.

[0022] Regarding the numerical ranges specified below with “~”, the lower and upper limits are included within these ranges. Values ​​expressed as “below” or “above” are not included within these ranges. In the following descriptions, “%” for chemical composition refers to “mass%” unless otherwise specified.

[0023] Hot-dip galvanized steel The coated steel of this embodiment comprises: a steel sheet, a coating formed on the steel sheet, and an oxide layer formed on the coating. Furthermore, in the coated steel of this embodiment, the thickness of the oxide layer is 5 nm or more, the ratio of the sum of the maximum intensity of Al and the maximum intensity of Mg in energy dispersive X-ray analysis of the oxide layer to the maximum intensity of Zn, i.e., the (Al+Mg) / Zn intensity ratio, is 1.0 or more, and the oxide layer contains an amorphous structure.

[0024] <Steel> The steel to be plated is described.

[0025] The steel used is primarily steel plates, but there are no particular restrictions on their size.

[0026] The steel sheet can be any steel sheet that can be used in a typical hot-dip galvanizing process. Specifically, it conforms to the requirement that steel sheets that can be used in processes such as continuous hot-dip galvanizing (CGL) production lines, where the molten metal is immersed and then solidified, are acceptable. As for the size of the steel sheet, for example, sheets with a thickness of 10 mm or less and a width of 2000 mm or less can be used, but the size of the steel sheet is not limited to these.

[0027] There are no particular restrictions on the type of steel used. For example, general steel, Al-killed steel, very low carbon steel, high carbon steel, various high-tensile steels, some high-alloy steels (steels containing corrosion-resistant strengthening elements such as Ni and Cr), bolt steel, steel wire for bridge cables, and various other steel plates can be used. More specifically, this includes, for example, cold-rolled steel sheets as specified in JIS G 3131, 3141:2017, steels contained in general structural rolled steels corresponding to so-called SS materials, so-called general steels contained in hot-rolled steel sheets as shown in JIS G 3193:2008, pre-plated steels such as JIS H8641, JIS G 3302, 3303, 3313, 3314, 3315, 3317, and 3321 that are thinly coated with various metals, JIS G 3136Al killed steel, very low carbon steel, high carbon steel, and various high-tensile steels described in JIS G 3113, 3134, and 3135.

[0028] <Oxide layer> The plated steel in this embodiment has an oxide layer on the coating. It should be noted that when the coating is located on both sides of the steel, the oxide layer can be provided on one side of the coating or on both sides.

[0029] The inventors of this invention have studied a method for improving the water corrosion resistance of coated steel (especially Zn-Al-Mg based coated steel). The results showed that water corrosion resistance is improved by including an amorphous structure in the oxide layer. Specifically, it was found that water corrosion resistance is improved when the ratio of the combined maximum intensity of Al and Mg in energy-dispersive X-ray analysis of the oxide layer to the maximum intensity of Zn, i.e., the (Al+Mg) / Zn intensity ratio, is 1.0 or higher.

[0030] The reason why the coating's water resistance is improved by including amorphous structures in the oxide layer is not clear, but the inventors of the present invention consider the reasons as follows.

[0031] First, if the structure in the oxide layer becomes amorphous, the number of crystal boundaries decreases. It is believed that since crystal boundaries are generally easily corroded, their presence is reduced by amorphizing the structure, thereby improving water corrosion resistance.

[0032] Furthermore, it is preferable that the oxide layer does not contain crystalline structures. That is, it is preferable that all oxides constituting the oxide layer are amorphous. However, the surface portion of the oxide layer, in particular, has a significant impact on water corrosion resistance. Therefore, it is sufficient that the surface portion of the oxide layer is amorphous. It should be noted that the term "surface portion" here refers to the region from the outermost surface of the oxide layer to a depth of 100 nm.

[0033] Whether the structure contained in the oxide layer is amorphous or crystalline can be confirmed by electron diffraction images of the cross section of the oxide layer obtained using TEM (transmission electron microscopy). If it is an amorphous structure, a halo pattern can be identified. In the case of crystalline structure (metallic phase), diffraction spots (crystal diffraction spots) indicating crystalline structure can be identified around the halo pattern.

[0034] Figure 1 , Figure 2 This is an electron diffraction image of the cross-section of the oxide layer in the coated steel of this embodiment, obtained using TEM (transmission electron microscopy). Figure 1 In the case of the electron diffraction pattern shown, since only the halo pattern was identified, it can be concluded that the structure contained in the oxide layer is amorphous. Furthermore, in Figure 2 In the case of the electron diffraction pattern shown, since crystalline diffraction spots were identified around the halo pattern, it can be known that the oxide layer simultaneously contains both amorphous structure and metallic phase. In this embodiment, it could be... Figure 1 , Figure 2 Any pattern in the electron diffraction pattern is acceptable. That is, the halo pattern can be identified in the electron diffraction image.

[0035] The following describes the method for identifying the tissue contained in the oxide layer.

[0036] In this embodiment, a 10 μm square analytical sample is first collected from the coated steel in a cross-section containing an oxide layer along the thickness direction of the plate, and the sample is thinned to a thickness of 50 to 100 nm.

[0037] Next, using a TEM ("JEM-2100F", manufactured by Nippon Electron Ltd.) with an electron beam probe diameter set to 3 nm, five electron diffraction patterns were obtained by measuring five points every 2 μm along the direction of the plate surface on the sample surface corresponding to the oxide layer. If even one halo pattern appeared in the obtained electron diffraction pattern, it was determined that the oxide layer contained an amorphous structure. It should be noted that the accelerating voltage for observation using the TEM was set to 200 kV. In addition, when the sample used for analysis also included the coating, the coating was excluded from the measurement, and only the oxide layer was measured.

[0038] In addition, the ratio of the sum of the maximum intensities of Al and Mg in energy dispersive X-ray analysis of the oxide layer to the maximum intensity of Zn, i.e., the (Al+Mg) / Zn intensity ratio, is set to 1.0 or higher.

[0039] Al and Mg are elements that more readily form passive coatings compared to Zn. That is, a higher content of Al and Mg in the oxide layer results in a greater improvement in corrosion resistance. Furthermore, Al oxides tend to be amorphous. On the other hand, Zn oxides tend to be crystalline; therefore, by increasing the content of Al and Mg in the oxide layer compared to Zn, an amorphous oxide layer can be easily obtained. From this perspective, the (Al+Mg) / Zn strength ratio is 1.0 or higher. Preferably, it is 2.0 or higher, more preferably 3.0 or higher. It should be noted that there is no particular upper limit to the (Al+Mg) / Zn strength ratio, but it can be 6.0 or lower.

[0040] The (Al+Mg) / Zn strength ratio can be determined using the following method.

[0041] First, 10 μm square analytical samples were collected from the coated steel, including a cross-section of the oxide layer along the thickness direction of the plate. These samples were then thinned to a thickness of 50–100 nm. Next, using a transmission electron microscope (TEM-EDS) equipped with an energy-dispersive X-ray analyzer (EDS; “JED-2300Tx2”, manufactured by Nippon Electronics Corporation), the electron probe diameter was set to 3 nm, the irradiation current (set value) was set to 1.0 nA, and the cross-section of the oxide layer was observed. EDS analysis was performed at 5 points every 2 μm along the plate surface. It should be noted that the observation position using the TEM was set to half the thickness of the oxide layer cross-section, the accelerating voltage was set to 200 kV, and the electron irradiation time was set to a maximum peak intensity of 2000 counts or more in the spectrum obtained by EDS measurement.

[0042] Next, based on the obtained X-ray analysis results, the maximum intensity (cps) of Zn, Al, and Mg was determined, and the ratio of the sum of the maximum intensities of Al and Mg to the maximum intensity of Zn was calculated. The intensity ratios were calculated for each of the five points obtained, and their average was taken as the "(Al+Mg) / Zn intensity ratio" in this embodiment. It should be noted that in the obtained X-ray analysis results, Zn showed a peak in the range of 1.01±0.1 eV, Al showed a peak in the range of 1.49±0.1 eV, and Mg showed a peak in the range of 1.25±0.1 eV. By analyzing the peaks in these ranges, the maximum intensity (cps) of Zn, Al, and Mg could be determined.

[0043] The thickness of the oxide layer is 5 nm or more. If the thickness of the oxide layer is too small, sufficient water corrosion resistance may not be obtained. Therefore, the thickness of the oxide layer is 5 nm or more. Preferably, it is 10 nm or more, more preferably 15 nm or more, and even more preferably 20 nm or more. It should be noted that there is no particular upper limit to the thickness of the oxide layer, but it is, for example, 50 nm or less.

[0044] The thickness of the oxide layer was determined by the following method.

[0045] Using transmission electron microscopy (TEM-EDS) images obtained in the same manner as the determination of the (Al+Mg) / Zn intensity ratio described above, the thickness of the oxide layer was measured at 5 points with a 1 nm spacing in the cross-section of the oxide layer, and the average value of these points was defined as the “thickness of the oxide layer”.

[0046] <Coating> The plated steel of this embodiment has a coating on the steel. The coating can be formed on one side of the steel or on both sides.

[0047] The preferred coating thickness is 15–250 g / m² per single side. 2 .

[0048] (The structure of the coating) In the clad steel sheet of this embodiment, the cladding structure is not particularly limited. Depending on the chemical composition of the coating of the clad steel sheet of this embodiment, the cladding structure may include, for example, (Al-Zn) dendrites, lamellar structures of (Al-Zn) phase / MgZn2 phase, lamellar structures of Zn phase / MgZn2 phase, ternary eutectic structures of Zn / Al / MgZn2, MgZn2 phase, dendritic or amorphous Zn phase, Mg2Si phase and / or other intermetallic compound phases.

[0049] (Chemical composition of the coating) The chemical composition of the coating on the plated steel according to this embodiment will be described. Hereinafter, all "%" in chemical composition refers to "mass %".

[0050] Al: 1.0~60.0% Al is an effective element in coatings containing aluminum (Al), zinc (Zn), and magnesium (Mg) to ensure corrosion resistance. To fully achieve the above-mentioned effect, the Al content is set to 1.0% or more. The Al content is preferably 5.0% or more, and more preferably 10.0% or more.

[0051] On the other hand, if the Al content exceeds 60.0%, the corrosion resistance and the corrosion resistance of the cut end face of the coating decrease. Furthermore, there is a possibility of increased Al oxide formation, leading to increased crystallinity of the oxide layer. Therefore, the Al content is set to 60.0% or less. The Al content is preferably 50.0% or less, and more preferably 40.0% or less.

[0052] Mg: 1.0–15.0% Mg is an element that improves the corrosion resistance of the coating. To fully achieve the above effect, the Mg content is set to 1.0% or more. The Mg content is preferably 4.0% or more, and more preferably 5.0% or more.

[0053] On the other hand, if the Mg content exceeds 15.0%, the corrosion resistance decreases. Additionally, it leads to manufacturing problems such as increased slag production in the plating bath. Therefore, the Mg content is set to 15.0% or less. Preferably, the Mg content is 11.0% or less.

[0054] Si: 0~2.0% Si is an element that forms compounds with Mg, contributing to improved corrosion resistance of coatings. Additionally, Si also has the effect of preventing excessively thick alloy layers from forming between the steel sheet and the coating during coating formation, thus improving the adhesion between them. Therefore, it may be included. While the presence of Si is not strictly necessary, with a lower limit of 0%, it is preferable to set the Si content to 0.1% or higher to achieve the aforementioned effects.

[0055] On the other hand, if the Si content is set to exceed 2.0%, the corrosion resistance after coating will decrease due to excessive Si crystallization in the coating or insufficient formation of lamellar structures. Furthermore, the processability of the coating will decrease. Therefore, the Si content is set to 2.0% or less. More preferably, the Si content is 1.5% or less.

[0056] Ca: 0–2.0% If the coating contains Ca, the amount of slag that is easily formed during the plating operation will decrease with the increase of Mg content, thus improving the plating manufacturability. Therefore, it is permissible to include Ca. Ca is not necessarily required, with a lower limit of 0%, but to achieve the above-mentioned effects, it is preferable to set the Ca content to 0.1% or more.

[0057] On the other hand, if the Ca content becomes excessive, there is a tendency for corrosion resistance to decrease. Therefore, the Ca content is set to 2.0% or less. Preferably, the Ca content is 1.0% or less.

[0058] Fe: 0~2.0% During the manufacturing of the coating, Fe may be introduced into the coating as an impurity from the steel sheet or the like used as the coating substrate. Sometimes it may contain up to 2.0%, but if it is within this range, the adverse effect on the properties of the coated steel sheet of this embodiment is small. Therefore, it is preferable to set the Fe content to 2.0% or less. More preferably, the Fe content is 1.5% or less, and even more preferably 1.0% or less.

[0059] On the other hand, to completely prevent Fe contamination, which would incur significant costs, the Fe content could also be set at 0.1% or higher.

[0060] The coating of the plated steel in this embodiment has the chemical composition described above, with the remainder being Zn and impurities. The coating of the plated steel in this embodiment may further include, for example, one or more elements selected from Ni, La, Ce, Sb, Pb, Sr, Bi, Sn, Cu, Ti, Mn, Cr, Nb, Zr, Mo, V, In, Co, Ag, Li, B, Y, and P, in a range of up to 5.000% to replace a portion of Zn. These elements may not necessarily be included, therefore the lower limit for each element's content is 0%. More preferably, the total content of these elements is 3.000% or less.

[0061] La: 0~0.500% Ce: 0~0.500% Y: 0~0.500% La, Ce, and Y are elements that contribute to improving the corrosion resistance of the coating. Therefore, it is permissible to contain any one or more of La, Ce, and Y. It is not necessary to contain any one of La, Ce, and Y, with a lower limit of 0%, but to obtain the above-mentioned effect, the content of each of La, Ce, and Y is preferably 0.010% or more.

[0062] On the other hand, if the contents of La, Ce, and Y exceed 0.500%, the viscosity of the plating bath usually increases, making it difficult to build up the plating bath itself and thus impossible to produce coated steel sheets with good plating properties. Therefore, the contents of La, Ce, and Y are each set to 0.500% or less.

[0063] Sb: 0~0.500% Pb: 0~0.500% Sr: 0~0.500% Bi: 0~0.500% Sb, Pb, Sr, and Bi contribute to improved corrosion resistance. To achieve this effect fully, it is preferable to set the content of any one of Sb, Pb, Sr, and Bi to 0.001% or more. More preferably, the content of Sb, Pb, Sr, and Bi is 0.005% or more, and even more preferably 0.050% or more.

[0064] On the other hand, if the content of any one of Sb, Pb, Sr, and Bi exceeds 0.500%, the corrosion resistance may deteriorate. Therefore, the contents of Sb, Pb, Sr, and Bi are each set to 0.500% or less. The contents of Sb, Pb, Sr, and Bi are preferably 0.300% or less, and more preferably 0.200% or less.

[0065] Sn: 0~1.000% Sn is an element that increases the dissolution rate of Mg in coatings containing Zn, Al, and Mg. If the Mg dissolution rate increases, the corrosion resistance of the planar portion may deteriorate. Therefore, the upper limit for Sn content is 1.000% or less. Sn content is preferably 0.500% or less. On the other hand, Sn is an element that contributes to improving corrosion resistance. To fully obtain this effect, it is preferable to set the Sn content to 0.050% or more. Sn content is more preferably 0.100% or more.

[0066] Cu: 0~1.000% Ti: 0~1.000% Cr: 0~1.000% Nb: 0~1.000% Ni: 0~1.000% Mn: 0~1.000% Mo: 0~1.000% V: 0~1.000% In: 0~1.000% Co: 0~1.000% Cu, Ti, Cr, Nb, Ni, Mn, Mo, V, In, and Co contribute to improved corrosion resistance. To fully achieve this effect, it is preferable to set the content of any one of the above elements to 0.001% or more. More preferably, the content of each of the above elements is 0.005% or more, and even more preferably 0.050% or more.

[0067] On the other hand, if the content of any one of the above elements exceeds 1.000%, the resistance to red rust may deteriorate. Therefore, the content of each of the above elements is 1.000% or less. The content of each of the above elements is preferably 0.300% or less, more preferably 0.200% or less.

[0068] Zr: 0~1.000% Ag: 0~1.000% Li: 0~1.000% Zr, Ag, and Li are elements that improve the corrosion resistance of the coating. To achieve this effect sufficiently, it is preferable that the content of any one of Zr, Ag, and Li is 0.001% or more. More preferably, the content of Zr, Ag, and Li is 0.005% or more, and even more preferably 0.020% or more.

[0069] On the other hand, excessive amounts of Zr, Ag, and Li may degrade corrosion resistance. If the content of any one of Zr, Ag, and Li exceeds 1.000%, the resistance to red rust deteriorates significantly. Therefore, the contents of Zr, Ag, and Li are each 1.000% or less. Preferably, the contents of Zr, Ag, and Li are each 0.500% or less, more preferably 0.100% or less.

[0070] B: 0~0.500% P: 0~0.500% B and P are elements that improve appearance. To fully achieve this effect, it is preferable that the content of either B or P is 0.001% or more. More preferably, the content of B and P is 0.005% or more, and even more preferably 0.020% or more.

[0071] On the other hand, if the content of B and P is too high, the corrosion resistance may deteriorate. If the content of either B or P exceeds 0.500%, the corrosion resistance will deteriorate significantly. Therefore, the content of B and P is 1.000% or less. The content of B and P is preferably 0.500% or less, more preferably 0.100% or less.

[0072] In this embodiment, impurities may include substances mixed in from the manufacturing environment, etc., and / or elements that do not adversely affect the properties of the plated steel of this embodiment.

[0073] The chemical composition of the coating was determined by the following method.

[0074] First, a rectangular sample of 50 mm × 50 mm, containing the total thickness of the coating, is collected from the coating. The coating is dissolved in 10% HCl containing 0.04% vol% of Ibit 710 (manufactured by Asahi Chemicals), an inhibitor that inhibits corrosion of the base metal (steel sheet), to obtain an acid solution. It should be noted that the sample is collected from areas of the coating whose structure has not been affected by processing or heat treatment (e.g., areas avoiding machining or welding). Next, the chemical composition of the coating is determined by ICP analysis of the obtained acid solution. There are no particular limitations on the type of acid used, as long as it can dissolve the coating. It should be noted that the chemical composition of the coating in this embodiment is set as the average of measurements taken from three samples.

[0075] [Manufacturing method for coated steel] Next, a preferred manufacturing method for the plated steel of this embodiment will be described. The effect of the plated steel sheet of this embodiment is independent of the manufacturing method, and can be obtained as long as it has the above-described characteristics. However, the following method can stably manufacture the plated steel of this embodiment, and is therefore preferred.

[0076] Specifically, the plated steel of this embodiment can be manufactured by a manufacturing method including the following steps (I) to (III).

[0077] (I) Annealing process for reducing annealing steel plates (II) A plating process in which a steel sheet is immersed in a plating bath containing Al, Mg, and Zn to prepare a plating base plate. (III) A controlled cooling process in which the above-mentioned plating base plate is cooled in a N2 atmosphere with a dew point of 0°C or higher within a temperature range from the bath temperature to the controlled cooling temperature at an average cooling rate of 7°C / second or less. The following explains the optimal conditions for each process.

[0078] First, prepare the steel (base steel) to form the coating. Preferred steels are as described above, such as general steel, high-tensile steel, low-carbon steel, etc.

[0079] When using pre-plated steel as the steel material, a pre-plating layer is formed on the steel surface before the annealing process. Examples of pre-plating layers include Ni pre-plating layers. By setting a pre-plating layer on the steel surface, the amorphization of the coating formed in subsequent processes can be promoted. The plating method can be hot-dip galvanizing, electroplating, displacement plating, or vapor deposition (PVD, etc.). Furthermore, the pre-plating layer can also be alloyed by heating. When a pre-plating layer is set on the steel surface, the steel with the pre-plating layer is used as the base material for hot-dip galvanizing.

[0080] In the preparation of pre-coatings, electroplating is suitable because it allows for the formation of a relatively thin coating. Alternatively, vapor deposition (PVD) can also be used.

[0081] The amount of pre-plated layer applied by electroplating can be adjusted by controlling the cumulative energizing time. When forming a Ni pre-plated layer, the amount of pre-plated layer is preferably, for example, 0.1 to 2.5 g / m². 2 .

[0082] Annealing process Before the plating process, the steel obtained by known methods can also be subjected to reduction annealing. Examples of steel include hot-rolled steel sheets or cold-rolled steel sheets. Regarding the annealing conditions, known conditions can be used, such as heating to 750–900°C in a 5% H₂-N₂ atmosphere with a dew point above -10°C and holding for 30–240 seconds.

[0083] <Plating Process> After annealing, the steel sheet used as the base material for plating is immersed in a plating bath. The composition of the plating bath is adjusted according to the chemical composition of the plating layer as described above. The bath temperature is preferably set between 420 and 700°C. If the bath temperature is too low, the plating layer may begin to solidify during the plating process. Therefore, a higher bath temperature is preferred, but if it is too high, manufacturing costs will increase. Therefore, the bath temperature is preferably set within the range of 420 to 700°C.

[0084] <Controlled Cooling Process> In the controlled cooling process, the original plated substrate after the plating process is wiped with a gas such as N2 to adjust the plating adhesion, and then cooled under specified conditions.

[0085] Specifically, the substrate being plated, retrieved from the plating bath, is cooled to below a controlled cooling temperature. At this point, the substrate reaches the same temperature as the plating bath. The controlled cooling temperature is the temperature at which the slowly cooling, high-dew-point atmosphere changes to a rapidly cooling, low-dew-point atmosphere, and is between 300°C and 330°C. During the controlled cooling process, the average cooling rate from the bath temperature to the controlled cooling temperature is set to 7°C / second or less, and the dew point of the atmosphere during cooling from the bath temperature to the controlled cooling temperature is set to 0°C or higher. Examples of gases used in the cooling process include N2 and Ar.

[0086] If the average cooling rate from the bath temperature to the controlled cooling temperature is reduced, the coating on the steel is cooled slowly while remaining in a molten state, thus the surface layer of the coating tends to become amorphous. If the surface layer of the coating becomes amorphous, the oxide layer formed thereon can also contain amorphous structures. Here, the surface layer of the coating refers to the peripheral region of the interface between the oxide layer and the coating. In addition, by slowly cooling from the bath temperature to the controlled cooling temperature, the thickness of the oxide layer formed on the coating can be increased, resulting in improved water corrosion resistance. Furthermore, by slowly cooling from the bath temperature to the controlled cooling temperature, the content of Al and Mg in the oxide layer can be higher than that of Zn, increasing the (Al+Mg) / Zn strength ratio. On the other hand, if the average cooling rate from the bath temperature to the controlled cooling temperature exceeds 7°C / second, the coating solidifies from the surface, and a crystalline metal layer may form on the coating surface. In that case, a large amount of crystalline oxide may also form in the oxide layer formed on the coating. Therefore, the average cooling rate from the bath temperature to the controlled cooling temperature is set to 7°C / second or less. From the viewpoint of forming an oxide layer of sufficient thickness, the average cooling rate from the bath temperature to the controlled cooling temperature is preferably 4°C / second or less, more preferably 2°C / second or less. The lower limit of the average cooling rate from the bath temperature to the controlled cooling temperature is not particularly limited, but from the viewpoint of manufacturing cost, it can be set to 1.5°C / second or more.

[0087] Furthermore, if the dew point of the atmosphere from the bath temperature to the controlled cooling temperature is below 0°C, the thickness of the oxide layer may not be sufficiently ensured. Additionally, if the cooling process is performed in an atmospheric atmosphere, water vapor in the atmosphere may promote crystal nucleation, causing the coating to solidify from the surface and form a crystalline metallic layer. Therefore, the dew point of the atmosphere from the bath temperature to the controlled cooling temperature is set to above 0°C. There is no particular upper limit to the dew point of the atmosphere from the bath temperature to the controlled cooling temperature, but from a manufacturing cost perspective, it can be set below 40°C. The atmospheric gas can be N2, Ar, etc.

[0088] In the temperature range below the controlled cooling temperature, the average cooling rate is set to 15°C / second or higher, and the dew point of the atmosphere is set to -30°C or lower to cool the substrate. To maintain the amorphous oxide layer formed in the temperature range from the bath temperature to the controlled cooling temperature, the substrate is quenched at a low dew point in the temperature range below the controlled cooling temperature. Therefore, in the temperature range below the controlled cooling temperature, the average cooling rate is set to 15°C / second or higher. The upper limit of the average cooling rate in the temperature range below the controlled cooling temperature is not particularly limited, but from a manufacturing cost perspective, it can be set to 80°C / second or lower. Furthermore, by setting the dew point of the atmosphere in the temperature range below the controlled cooling temperature to a low dew point of -30°C or lower, oxide growth can be suppressed, and the phase transition from an amorphous structure to a crystalline structure can be suppressed by quenching. The dew point of the atmosphere in the temperature range below the controlled cooling temperature is preferably -40°C or lower. The lower limit of the dew point of the atmosphere in the temperature range below the controlled cooling temperature is not particularly limited, but from a manufacturing cost perspective, it can be set to -70°C or higher. For low dew points and sudden cooling, it is sufficient to apply the solution up to 70°C.

[0089] The coated steel of this embodiment can be stably manufactured using the methods described above.

[0090] [Solar power generation platform] The plated steel of this embodiment has excellent water corrosion resistance, and is therefore used, for example, for solar power generation racks. Figure 3 This is a perspective view showing an example of a solar power generation platform 10.

[0091] The solar power generation platform 10, for example, has multiple pillars 11 and multiple support members 12. The galvanized steel of this embodiment can be suitably used for the pillars 11 and support members 12. The solar power generation platform 10 has excellent durability because it meets the characteristics of the coating and oxide layer in the galvanized steel of this embodiment.

[0092] Furthermore, the galvanized steel of this embodiment can also be applied to the foundation structure 20 for mounting the solar power generation platform 10. The foundation structure 20 may be constructed with concrete or the like as a foundation, but in that case, the galvanized steel of this embodiment can be embedded in the concrete or similar foundation.

[0093] Example The effects of one aspect of the present invention will be illustrated more specifically through embodiments. However, the conditions in the embodiments are merely examples of conditions adopted to confirm the feasibility and effects of the present invention. The present invention is not limited to this single example of conditions. Various conditions may be adopted by the present invention as long as they do not depart from the spirit and purpose of the invention.

[0094] As the base material for annealing and plating, a cold-rolled steel sheet (0.05%C-0.1%Si-0.2%Mn) with a thickness of 2.3mm was prepared.

[0095] After the base steel is cut into 100mm×200mm (×plate thickness), an intermittent hot-dip galvanizing test device is used, followed by annealing and hot-dip galvanizing.

[0096] Before immersion in the plating bath, the base steel is subjected to a heat reduction treatment at 600°C in a furnace with an oxygen concentration of less than 20 ppm and an atmosphere of N2-5% H2. Afterward, the base steel is air-cooled with N2 gas, and after the plate temperature reaches the bath temperature +20°C during immersion, it is immersed in the plating bath at the bath temperature shown in Table 1 for about 3 seconds.

[0097] Next, the coating is applied to the surface of the base steel by lifting it up. During lifting, N2 wiping gas is used to control the amount of coating applied.

[0098] Next, various coated steels are manufactured by cooling the coating under various conditions. The chemical composition of the coating is as shown in Table 2. The manufacturing conditions are set as shown in Table 1. It should be noted that the plate temperature during manufacturing is measured using a thermocouple spot-welded to the center of the original coated plate.

[0099] The EDS analysis results and crystallinity evaluation results of the oxide layer are shown in Table 3. Furthermore, the water corrosion resistance of the coated steel was evaluated, and the results are shown in Table 3.

[0100] The chemical composition of the coating and the analysis and evaluation of the oxide layer were performed using the methods described above. It should be noted that for some base steels, a Ni pre-plating layer is formed before the plating process. The Ni adhesion amount of the Ni pre-plating layer is as shown in Table 1. The composition of the pre-plated Ni is included in the chemical composition of the coating disclosed in Table 2.

[0101] The evaluation of water corrosion resistance is carried out through the following methods.

[0102] The obtained coated steel is cut into test pieces with dimensions of 200mm × 100mm (× steel thickness). The test pieces are then placed on a platform at a 45° angle relative to the horizontal plane.

[0103] Next, droplets of liquid (Cl) were added to the surface of the test piece (evaluation surface) at a flow rate of 2 mL / min. - Concentration: 10 ppm, SO4 2- Concentration: 20 ppm), evaluating the number of days for the formation of white and red rust. Droplets were added 10 mm above the evaluation surface. The test environment was set to atmospheric conditions, with the temperature maintained at 25°C.

[0104] The corrosion resistance of flowing water is evaluated based on the number of days since white and red rust forms, using the following evaluation criteria.

[0105] Evaluation Criteria AAA: White rust lasts for more than 7 days, and red rust lasts for more than 120 days. AA: <1> White rust lasting more than 7 days, and red rust lasting more than 30 days but less than 120 days, or <2> White rust lasts 5-7 days, while red rust lasts more than 60 days. A: White rust takes 5-7 days, and red rust takes 30-60 days. B: <1> Red rust less than 30 days, or <2> White rust less than 5 days Steel coated with an evaluation result of A to AAA is considered to have excellent water corrosion resistance. Conversely, an evaluation of B is considered when the number of days for white rust to form is less than 30 days, or when the number of days for red rust to form is less than 5 days, regardless of the number of days for red rust to form. Such coated steel is considered to have poor water corrosion resistance. It should be noted that, according to the above evaluation method, coated steel with high water corrosion resistance can be judged to have high corrosion resistance on its flat surfaces as well.

[0106] The results are shown in Table 3.

[0107] [Table 1] [Table 2] [Table 3] As can be seen from Tables 1 to 3, the invention examples No. 1 to 31 exhibit excellent water corrosion resistance. In contrast, the comparative examples No. 32 to 41 show reduced water corrosion resistance because the chemical composition of the coating or the cooling conditions of the controlled cooling process deviate from the preferred range.

[0108] Industrial availability The Zn-Al-Mg hot-dip galvanized steel components disclosed herein have excellent corrosion resistance and adhesion of the chemical conversion treatment layer. Even when the chemical conversion treatment layer is formed, the conductivity with the welding electrode is also excellent, resulting in a superior appearance where defects are not easily noticeable. Therefore, they have high industrial applicability.

[0109] Symbol Explanation 10 Solar power generation platform 11 pillars 12 Supporting components 20 Basic Structures

Claims

1. A type of plated steel, comprising: steel plate The coating formed on the steel plate, and An oxide layer formed on the coating, The coating has the following chemical composition: containing, by mass%,: Al：1.0～60.0%、 Mg: 1.0–15.0% Si: 0~2.0%, Ca: 0–2.0%, and Fe: 0~2.0%, Further containing a total of less than 5.000% of one or more elements selected from the following: Ni: 0~1.000%, La: 0~0.500% Ce: 0~0.500% Sb: 0~0.500%, Pb: 0~0.500%, Sr：0～0.500%、 Bi: 0~0.500%, Sn: 0~1.000% Cu: 0~1.000%, Ti: 0~1.000%, Mn: 0~1.000%, Cr：0～1.000%、 Nb: 0~1.000%, Zr：0～1.000%、 Mo: 0~1.000%, V：0～1.000%、 In: 0~1.000%, Co: 0~1.000%, Ag: 0~1.000%, Li: 0~1.000%, B：0～0.500%、 Y: 0~0.500%, and P：0～0.500%， The remaining portion consists of Zn and impurities. The thickness of the oxide layer is 5 nm or more. The ratio of the combined maximum intensity of Al and Mg in energy-dispersive X-ray analysis of the oxide layer to the maximum intensity of Zn, i.e., the (Al+Mg) / Zn intensity ratio, is greater than 1.

0. The oxide layer contains an amorphous structure.

2. The plated steel according to claim 1, characterized in that, The chemical composition of the coating, expressed as a percentage by mass, contains one or more of the following elements: Si: 0.1–2.0% Ca: 0.1–2.0% Fe: 0.1–2.0%, Ni: 0.001~1.000% La: 0.010~0.500% Ce: 0.010~0.500% Sb: 0.001~0.500% Pb: 0.001~0.500%, Sr：0.001～0.500%、 Bi: 0.001~0.500% Sn: 0.050~1.000% Cu: 0.001~1.000%, Ti: 0.001~1.000% Mn: 0.001~1.000%, Cr：0.001～1.000%、 Nb: 0.001~1.000% Zr：0.001～1.000%、 Mo: 0.001~1.000%, V：0.001～1.000%、 In: 0.001~1.000% Co: 0.001~1.000%, Ag: 0.001~1.000%, Li: 0.001~1.000% B：0.001～0.500%、 Y: 0.010~0.500%, and P：0.001～0.500%。 3. The plated steel according to claim 1 or 2, wherein the chemical composition of the coating is as follows: Al：10.0～30.0%、 Mg: 4.0–15.0%, The (Al+Mg) / Zn strength ratio of the oxide layer is 2.0 or higher.

4. The plated steel according to any one of claims 1 to 3, wherein the chemical composition of the coating is as follows: Al：15.0～30.0%、 Mg: 4.0–15.0%, The (Al+Mg) / Zn strength ratio of the oxide layer is 3.0 or higher.

5. The plated steel according to any one of claims 1 to 4, wherein no diffraction spots representing crystalline structure are detected in the electron diffraction image obtained by analyzing the cross section of the oxide layer using electron diffraction.

6. A solar power generation platform comprising the plated steel material as described in any one of claims 1 to 5.

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