Cut processed product and guardrail

Abstract

The present invention relates to a cut-processed product of a Zn-Al-Mg-based plated steel material having a parent steel material and a Zn-Al-Mg-based plating layer coated on the surface of the parent steel material, and a guardrail using the cut-processed product, the cut-processed product comprising a Zn-Al-Mg-based plated steel material, the cut end surface of the cut processed product is covered with a linear coating film formed by linearly flowing in components of the Zn-Al-Mg-based plating layer, and the coating rate of the linear coating film with respect to the cut end surface is 60-90%. The non-plated surface of the mother steel material and the linear coating film around the non-plated surface in the cut end surface of the cut processed product are coated with a repair coating film, the initial coating film resistance value in the repair coating film is 10-1000 Omega / cm < 2 >, and the coating film resistance value after immersion after the cut processed product is immersed in 5 mass% saline water for 3 hours is 5-50 Omega / cm < 2 >. And the film thickness of the repairing coating film is 10-100 [mu] m.

Description

Technical Field

[0001] The present disclosure relates to a cut-off product and a guardrail. Background Art

[0002] When the plated steel material is processed into a product shape, the plated steel material is cut, and the steel base of the steel material is exposed in a part of the cut section. The corrosion resistance of the cut end surface not covered by the plating layer is reduced, so it is necessary to improve the corrosion resistance of the cut end surface.

[0003] In order to improve the corrosion resistance of the cut end surface of plated steel materials, various processing methods and technologies have been studied. For example, there are known cut end surface antirust processing technologies such as an inclined end surface processing method (Patent Document 1, etc.) in which a larger portion of the end surface section is coated with a plating layer than in the past by shearing, a longitudinal shearing processing method (Patent Document 2, etc.), and a laser cutting method (Patent Document 3, etc.).

[0004] However, it is difficult to cover the entire surface of the cut section with a plating layer, and there is a problem that a partially exposed cut end surface may rust in the early stage of exposure.

[0005] Therefore, as a conventional anti-corrosion technology for cut end faces, a repair paint containing Zn-based metal powder is generally applied to the exposed steel surface of the cut end face (for example, Patent Document 4).

[0006] Patent Document 1: Japanese Patent Application Publication No. 2020-32437

[0007] Patent Document 2: Japanese Patent Application Publication No. 2017-192989

[0008] Patent Document 3: Japanese Patent Application Publication No. 2021-087988

[0009] Patent Document 4: Japanese Patent Application Publication No. 2017-122186 Summary of the invention

[0010] Problems to be solved by the invention

[0011] It is expected that by combining the above-mentioned rust-proofing technology of the cut end surface with repair coating, higher corrosion resistance can be imparted to the cut end surface.

[0012] However, in the cut end surface, the area of ​​the steel substrate that serves as the cathode is very small relative to the plating layer that serves as the anode, so the reduction reaction of water or oxygen is concentrated, causing cathodic peeling of the repair coating, so sufficient corrosion resistance cannot be maintained, especially for suppressing red rust in the early stage of corrosion.

[0013] In addition, cathodic peeling of the repair coating film occurred, and thus expected long-term corrosion resistance could not be obtained.

[0014] Therefore, an object of the present disclosure is to provide a cut product in which cathodic peeling of a repair coating is suppressed and which has excellent cut end surface corrosion resistance from the initial stage to the long term, and a guardrail using the same.

[0015] Means for solving problems

[0016] Means for solving the problem include the following.

[0017] <1> A cut-off product is a cut-off product of a Zn-Al-Mg-based plated steel material having a base steel material and a Zn-Al-Mg-based plated layer coated on the surface of the base steel material, wherein:

[0018] The cut end surface of the cut product is covered with a linear film formed by linear inflow of the components of the Zn-Al-Mg-based plating layer, and the coverage of the linear film with respect to the cut end surface is 60 to 90%.

[0019] The non-plated surface of the base steel material and the linear film around the non-plated surface in the cut end surface of the cut product are covered with a repair coating film.

[0020] The initial coating resistance value R1 in the repair coating is 10 to 1000 Ω / cm 2 , and the coating resistance value R2 after the cut product is immersed in 5 mass % salt water for 3 hours is 5 to 50 Ω / cm 2 ,

[0021] The repair coating film has a thickness of 10 μm or more.

[0022] <2> According to the above <1> In the cut-off product, the repair coating film contains Zn-based metal powder and a binder resin.

[0023] <3> According to the above <1> or <2> The cut product, wherein the maximum length of the linear film at the cut end surface of the cut product is 70 to 100% of the plate thickness of the cut product.

[0024] <4> According to the above <1> ~ <3> The cut product according to any one of the preceding claims, wherein an initial coating resistance value R1 in the repair coating is 300 to 500 Ω / cm 2 .

[0025] <5> According to the above <1> ~ <4> The cut product according to any one of the preceding claims, wherein the coating resistance value R2 after immersion in the repair coating is 10 to 45 Ω / cm 2 .

[0026] <6> According to the above <2> In the cut product, the Zn-based metal powder contains Zn and Al.

[0027] <7> According to the above <6> The cut product is characterized in that the content of Al in the Zn-based metal powder containing Zn and Al is 20 to 45% by mass relative to Zn.

[0028] <8> According to the above <6> The cut product, wherein the content of Al in the Zn-based metal powder containing Zn and Al is 28 to 34 mass % relative to Zn.

[0029] <9> According to the above <2> or <6> ~ <8> The cut-off product according to any one of the preceding claims, wherein the content of the Zn-based metal powder relative to the entire repair coating film is 60 to 80% by mass of the metal powder.

[0030] <10> According to the above <2> or <6> ~ <9> The cut product according to any one of the preceding claims, wherein the binder resin is at least one selected from the group consisting of a polystyrene resin and an epoxy resin.

[0031] <11> A guardrail having the above <1> ~ <10> The cut product according to any one of the above.

[0032] Effects of the Invention

[0033] According to the present disclosure, it is possible to provide a cut product in which cathodic peeling of a repair coating film is suppressed and which has excellent cut end surface corrosion resistance from the initial stage to the long term, and a guardrail using the same. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a simplified cross-sectional perspective view showing a cut product of the present disclosure.

[0035] Figure 2 This is a simplified cross-sectional view of the cut product of the present disclosure, in which the cut product is cut along a direction perpendicular to the cut end surface of the cut product and perpendicular to the plate thickness direction.

[0036] Figure 3 This is a simplified perspective view showing the state of a cut end surface when cutting by a conventional shearing method.

[0037] Figure 4 This is a schematic diagram for explaining a sample for measuring a coating film resistance value. DETAILED DESCRIPTION

[0038] Hereinafter, an example of the coated steel sheet of the present disclosure will be described.

[0039] In addition, in this specification, the numerical range expressed using "to" means a range including the numerical values ​​described before and after "to" as the lower limit and the upper limit.

[0040] In numerical ranges described in stages, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of another numerical range described in stages.

[0041] In the numerical range, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the Examples.

[0042] The term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes as long as the intended purpose of the process can be achieved.

[0043] “A combination of preferred embodiments” is a more preferred embodiment.

[0044] In this specification, the "Zn-Al-Mg-based plating layer" is also referred to as a "plating layer".

[0045] The "Zn-Al-Mg-based plated steel material" is also referred to as a "plated steel material".

[0046] The “non-plated surface” refers to the surface of the base steel material of the plated steel material that is not coated with the Zn—Al—Mg-based plating layer.

[0047] The cut-off product disclosed in the present disclosure is a cut-off product of a Zn—Al—Mg-based plated steel material having a base steel material and a Zn—Al—Mg-based plating layer coated on the surface of the base steel material.

[0048] The cut end surface of the cut product is covered with a linear film formed by linear inflow of the components of the Zn-Al-Mg-based plating layer, and the coverage of the linear film with respect to the cut end surface is 60 to 90%.

[0049] The non-plated surface of the base steel material and the linear film around the non-plated surface in the cut end surface of the cut product are covered with the repair coating film.

[0050] The initial resistance of the repair coating is 10 to 1000 Ω / cm 2 , and the coating resistance value after immersion of the cut product in 5 mass % salt water for 3 hours (hereinafter also referred to as "coating resistance value after salt water immersion") is 5 to 50 Ω / cm 2 .

[0051] Furthermore, the film thickness of the repair coating is 10 μm or more.

[0052] In the cut product of the present disclosure, the cut end surface of the cut product is coated with a linear film formed by linear inflow of components of the Zn-Al-Mg-based plating layer, and the non-plated surface of the base steel material is coated with a repair coating film.

[0053] The repair coating film having the above-mentioned properties can suppress cathodic peeling and suppress the reduction of corrosion resistance in the early stage of corrosion.

[0054] In addition, the sacrificial anodic corrosion protection effect of the components of the Zn-Al-Mg-based plating layer and the components of the repair coating film can maintain high corrosion resistance from the initial stage of corrosion to the long-term corrosion.

[0055] Therefore, the disclosed cut product can suppress cathodic peeling of the repair coating film and has excellent corrosion resistance of the cut end surface from the initial stage to the long term.

[0056] The cut product of the present disclosure will be described in detail.

[0057] (Coated Steel)

[0058] Plated steel is a steel material that can be cut.

[0059] The plated steel material is a Zn-Al-Mg plated steel material having a base steel material and a plated layer coated on the surface of the base steel material. Specifically, the plated steel material preferably has a plated layer on both sides of the base steel material.

[0060] The base steel is the steel material on which the coating is to be formed.

[0061] The parent steel material is not particularly limited. Examples of the parent steel material include steel plates of ultra-low C type (a structure mainly composed of ferrite), Al-k type (a structure containing pearlite in ferrite), dual-phase structure type (for example, a structure containing martensite in ferrite, a structure containing bainite in ferrite), processing-induced transformation type (a structure containing retained austenite in ferrite), and fine crystal type (a structure mainly composed of ferrite).

[0062] The plating layer is a Zn-Al-Mg plating layer, which is a plating layer containing at least zinc, aluminum, and magnesium. The Zn-Al-Mg plating layer has higher corrosion resistance than the Zn plating layer or the Al plating layer because it contains Al and Mg.

[0063] Examples of the plating layer include zinc-aluminum-magnesium-tin plating, zinc-aluminum-magnesium-silicon plating, zinc-aluminum-magnesium-tin-silicon plating, and other well-known Zn-Al-Mg plating layers, in addition to the zinc-aluminum-magnesium plating.

[0064] Examples of the plating layer include plating layers containing cobalt, molybdenum, tungsten, nickel, titanium, chromium, iron, magnesium, lead, bismuth, antimony, tin, copper, cadmium, arsenic, and the like as a different metal element or impurity.

[0065] In particular, from the viewpoint of corrosion resistance, the zinc-based coating is preferably a coating containing aluminum in addition to zinc and a coating containing aluminum and magnesium. That is, if a zinc alloy plated steel sheet is used as the raw material sheet, a better corrosion resistance can be obtained compared to a galvanized steel sheet, so it is preferred.

[0066] Specifically, as the plating layer, a plating layer containing, by mass ratio, Zn: 65.0%, Al: 5.0% to 25.0%, and Mg: 2.0% to 12.5% ​​can be exemplified.

[0067] More specifically, the plating layer may have the following chemical composition, which contains, by mass %, the following:

[0068] Zn: 65.0%,

[0069] Al: 5.0% to 25.0%,

[0070] Mg: 2.0% to 12.5%,

[0071] Sn: 0% to 20.0%,

[0072] Bi: 0% to 5.0%,

[0073] In: 0%~2.0%,

[0074] Ca: 0% to 3.00%,

[0075] Y: 0% to 0.5%,

[0076] La: 0% to 0.5%,

[0077] Ce: 0% to 0.5%,

[0078] Si: 0% to 2.5%,

[0079] Cr: 0% to 0.25%,

[0080] Ti: 0% to 0.25%,

[0081] Zr: 0% to 0.25%,

[0082] Mo: 0% to 0.25%,

[0083] W: 0%~0.25%,

[0084] Ag: 0% to 0.25%,

[0085] P: 0%~0.25%,

[0086] Ni: 0% to 0.25%,

[0087] Co: 0% to 0.25%,

[0088] V: 0%~0.25%,

[0089] Nb: 0% to 0.25%,

[0090] Cu: 0% to 0.25%,

[0091] Mn: 0% to 0.25%,

[0092] Li: 0% to 0.25%,

[0093] Na: 0% to 0.25%,

[0094] K: 0% to 0.25%,

[0095] Fe: 0% to 5.0%,

[0096] Sr: 0% to 0.5%,

[0097] Sb: 0% to 0.5%,

[0098] Pb: 0% to 0.5%,

[0099] B: 0% to 0.5%, and

[0100] Impurities.

[0101] The method for forming the plated layer is not particularly limited, and any method such as a known electroplating method, a hot dip plating method, a vapor deposition method, a dispersion plating method, and a vacuum plating method can be employed.

[0102] The coating weight is not particularly limited, but is preferably 15 g·m -2 Above 140g·m -2 Below, more preferably 30g·m -2 Above 90g·m -2 the following.

[0103] If the coating weight is 15 g·m -2 If the coating weight is 140 g·m -2 Below, the corrosion resistance is high and the blackening of the plating layer can be suppressed.

[0104] (Cut end surface of cut product)

[0105] -Linear membrane-

[0106] The cut product according to the present disclosure is coated with a linear film formed by linear inflow of components of the Zn-Al-Mg-based plating layer on the cut end surface. The linear film has a line width of, for example, about 10 to 100 μm.

[0107] For example, if a plated steel material is cut by laser cutting, the coating formed on the surface of the base steel material near the cut portion melts due to the heat of the laser. The melted coating component flows toward the cut end surface in a rainy manner and solidifies again. As a result, the cut end surface is covered with a linear film containing the coating component (see Figure 1 ).

[0108] On the other hand, if the plated steel is cut by the conventional shearing method, the plating formed near the cut portion on the surface of the base steel follows the shearing blade into the cut end face. As a result, the cut end face is covered with a strip of plating (see Figure 3 ).

[0109] in addition, Figure 1 101 denotes a cut product, 101C denotes a cut end surface, 10 denotes a plated steel material, 12 denotes a base steel material, 14 denotes a plating layer, 16 denotes a linear film, and 18 denotes a repair coating film.

[0110] Figure 3 In the figure, 201 indicates a cut product, 201C indicates a cut end surface, 20 indicates a plated steel material, 22 indicates a base steel material, 24 indicates a plating layer, and CD indicates a cutting direction.

[0111] -Linear film coverage-

[0112] The coverage of the linear film on the cut end surface is 60 to 90%.

[0113] If the coverage of the linear film is less than 60%, the coverage of the linear film on the cut end surface is too low, resulting in reduced corrosion resistance. On the other hand, if the plated steel material is cut, the plating layer on the surface of the plated steel material melts in a portion of the cut end surface, and the components of the melted plating layer flow into the cut end surface. However, it is difficult to make the components of the melted plating layer flow into the entire surface of the cut end surface.

[0114] Therefore, the coverage of the linear film is set to the above range. The coverage of the plating layer is preferably 70 to 90%.

[0115] The coverage of the linear film was measured by the following method.

[0116] The cut end surface of the cut workpiece to be measured is immersed in a solvent capable of dissolving the repair coating (ie, the binder resin) and cleaned with an ultrasonic cleaner for more than 1 minute to completely remove the repair coating.

[0117] Next, gold was vapor-deposited on the cut end surface to a thickness of about 10 nm to produce a sample.

[0118] For the cut end surface of the sample, the element distribution of Zn, Al and Mg in the analysis components of the base steel, the coating, carbon and oxygen is measured by electron probe microanalysis (EPMA) from the direction perpendicular to the plate thickness. Then, the ratio of the area where any one of Zn, Al and Mg is detected relative to the cut section is calculated as the coverage of the linear film.

[0119] Here, in the element distribution measurement of the coating composition using EPMA, the composition of the coating and the composition of the base steel can be identified by judging whether any one of the coating components of Zn, Al and Mg is present at 1 atm% or more in the EPMA quantitative analysis. Then, the area where it can be confirmed that any one of the coating components of Zn, Al and Mg is present at 1 atm% or more in the EPMA quantitative analysis is regarded as the area covered with the linear film.

[0120] This operation was performed three times, and the average value was calculated.

[0121] The measurement conditions of EPMA were set as follows: measurement area = cut section width (ie, plate thickness) × 10 mm, acceleration voltage = 25 kV, and electron beam diameter = 10 μm.

[0122] -Maximum length of linear membrane-

[0123] The maximum length of the linear film is preferably 70 to 100% of the thickness of the cut product.

[0124] If the maximum length of the linear film is 70% or more, there is no bias at one end of the cut end surface in the plate thickness direction, and the cut end surface is covered with the linear film from one end to the other end in the plate thickness direction. Therefore, the corrosion resistance is easily improved.

[0125] Therefore, the maximum length of the linear film is preferably within the above range. The maximum length of the linear film is more preferably 90 to 100%.

[0126] The maximum length of the linear film can be measured by the following method.

[0127] The cut end surface of the cut workpiece to be measured is immersed in a solvent capable of dissolving the repair coating (ie, the binder resin) and cleaned with an ultrasonic cleaner for more than 1 minute to completely remove the repair coating.

[0128] Next, gold was vapor-deposited on the cut end surface to a thickness of about 10 nm to prepare a sample with the cut end surface as an observation surface.

[0129] For the observed surface of the sample, the element distribution of Zn, Al and Mg in the coating composition was determined by electron probe microanalysis (EPMA). Then, the length of the longest linear region among the linear regions where any one of Zn, Al and Mg was detected was measured. The length of the linear region is the length along the plate thickness direction of the sample (refer to Figure 1 Then, the ratio of the length of the longest linear region to the thickness of the sample plate is calculated.

[0130] This operation was performed three times, and the average value was calculated.

[0131] In addition, in addition to the above, the method for measuring the maximum length of the linear film is defined as the same method as the method for measuring the coverage of the linear film.

[0132] -Repair coating-

[0133] The non-plated surface of the base steel material and the linear film around the non-plated surface in the cut end surface of the cut product according to the present disclosure are covered with a repair coating film (see Figure 1 and Figure 2 ).

[0134] Specifically, for example, the repair coating can be applied to the linear film from the edge of the linear film (i.e., the boundary between the non-plated surface of the base steel and the linear film) to at least 100 μm. The repair coating is preferably applied to cover the entire cut end surface.

[0135] in addition, Figure 2 This is a simplified cross-sectional view of a cut product cut along a direction perpendicular to the cut end surface of the cut product and perpendicular to the plate thickness direction.

[0136] Figure 2 In the figure, 101C indicates the cut end surface of the cut product, 12 indicates the base steel material of the plated steel material, 16 indicates the linear film, and 18 indicates the repair coating film.

[0137] The formation state of the repair coating film can be confirmed by the following method.

[0138] The cut workpiece to be measured is cut in a direction perpendicular to the cut end surface and perpendicular to the plate thickness direction.

[0139] Next, the steel plate to be measured is embedded with an embedding resin mixed with an embedding curing agent in a specified ratio, and the embedded sample is mechanically polished to expose the cut surface after cutting the processed part, thereby producing a sample with the cut surface as the observation surface.

[0140] The observation surface of the sample is observed at a magnification of 50 to 100 using a SEM (Scanning Electron Microscope) equipped with an EDS (Energy Dispersive X-ray Spectrometer). In addition, the element distribution of Zn, Al, and Mg is measured in the coating composition. Then, the edge of the linear film is determined by detecting the area of ​​any one of Zn, Al, and Mg. Then, the distance between the edge of the linear film and the edge of the repair coating is calculated from the SEM observation image. Among them, the distance between the edge of the linear film and the edge of the repair coating is the distance along the surface of the linear film.

[0141] By this operation, the formation state of the repair coating film can be confirmed.

[0142] The measurement conditions of EDS were set as follows: measurement area = cutting section width (ie, plate thickness) × 200 μm in cutting direction, acceleration voltage = 15 V, and electron beam diameter = 10 μm.

[0143] --Composition of repair coating--

[0144] The repair coating contains a component having a sacrificial anodic corrosion protection effect.

[0145] Specifically, the repair coating film preferably contains Zn-based metal powder and a binder resin. The repair coating film may contain other additives as necessary.

[0146] The Zn-based metal powder is a metal powder containing Zn.

[0147] The Zn-based metal powder may be a metal powder containing Zn alone, or may be a metal powder containing Zn and a metal other than Zn.

[0148] The metal powder containing Zn and a metal other than Zn may be a mixed metal powder of a metal powder containing Zn alone and a metal powder containing a metal other than Zn alone, or may be an alloy metal powder containing Zn and a metal other than Zn.

[0149] Examples of metals other than Zn include Al, Si, Mg, Co, Ti, V, Cr, Mn, Fe, Co, Ni, and stainless steel.

[0150] Among them, Al is preferred as a metal other than Zn. That is, it is preferred that the Zn-based metal powder contains Zn and Al. This is because if Al is contained in the metal powder, Zn6Al2(OH)2+, which is considered to have excellent corrosion resistance for the steel plate of the base material, is easily generated by Zn and Al. 16 CO3·4H2O, so the corrosion resistance is improved.

[0151] Among them, the content of Al in the Zn-based metal powder containing Zn and Al is preferably 20 to 45% by mass, more preferably 25 to 35% by mass, and particularly preferably 28 to 34% by mass relative to Zn.

[0152] When the Al content is 20 mass % or more, an excessive decrease in the coating film resistance values ​​of R1 and R2 in the initial stage and after salt water immersion can be suppressed, thereby improving the corrosion resistance.

[0153] When the Al content is 45 mass % or less, an excessive increase in the coating film resistance value R2 after immersion in salt water can be suppressed, and cathodic peeling of the repair coating film becomes less likely to occur.

[0154] The total content of Zn and Al in the Zn-based metal powder containing Zn and Al is preferably 90 mass % or more, more preferably 95 mass % or more, and particularly preferably 100 mass % based on the Zn-based metal powder.

[0155] That is, the total content of metals other than Zn and Al (particularly V content) is preferably 10 mass % or less, more preferably 5 mass % or less, and particularly preferably 0 mass % based on the Zn-based metal powder.

[0156] The average particle size of the Zn-based metal powder is preferably 1 to 20 μm, more preferably 1 to 10 μm. When the average particle size of the Zn-based metal powder is within the above range, corrosion resistance is improved.

[0157] The “average particle size” refers to a particle size at which the accumulation from the smaller diameter side reaches 50% in a particle size distribution based on the number determined by a dynamic light scattering method.

[0158] Regarding the particle size of the Zn-based metal powder, the repair coating film (ie, the binder resin) is dissolved with a solvent, the Zn-based metal powder is recovered by centrifugal separation, and then the particle size is measured.

[0159] The content of the Zn-based metal powder is preferably 60 to 80% by mass, more preferably 65 to 75% by mass, based on the entire repair coating film.

[0160] When the content of the Zn-based metal powder is 60 mass % or more, an excessive increase in the resistance value of the coating film in the initial stage and after immersion in salt water can be suppressed, and cathodic peeling of the repair coating film becomes less likely to occur.

[0161] When the content of the Zn-based metal powder is 80 mass % or less, an excessive decrease in the resistance value of the coating film in the initial stage and after immersion in salt water can be suppressed, thereby improving the corrosion resistance.

[0162] Therefore, the content of the Zn-based metal powder is preferably within the above range.

[0163] Examples of the binder resin include well-known resins such as polystyrene resins, polyester resins, epoxy resins, polyurethane resins, polyolefin resins, acrylic resins, and phenolic resins.

[0164] Among them, as a binder resin, at least one selected from polystyrene resin and epoxy resin is preferred. If these resins are used, it is easy to control the coating film resistance value after salt water immersion within a preferred range, and it is easy to improve corrosion resistance.

[0165] The binder resin may be a cross-linked resin or a non-cross-linked resin, but a cross-linked resin is preferred from the viewpoint of improving corrosion resistance.

[0166] As the crosslinking agent for forming the crosslinked resin, known crosslinking agents such as melamine, isocyanate, silane compound, zirconium compound, titanium compound, etc. can be used depending on the type of the resin to be crosslinked.

[0167] The content of the binder resin is preferably 20 to 40% by mass, more preferably 25 to 35% by mass, based on the repair coating film.

[0168] When the content of the binder resin is 20% by mass or more, an excessive decrease in the resistance value of the coating film in the initial stage and after immersion in salt water can be suppressed, thereby improving the corrosion resistance.

[0169] When the content of the binder resin is 40% by mass or less, an excessive increase in the resistance value of the coating film in the initial stage and after immersion in salt water can be suppressed, and cathodic peeling of the repair coating film becomes less likely to occur.

[0170] Therefore, the content of the binder resin is preferably within the above range.

[0171] Other additives in the repair coating include pigments (MgO, Al2O 3、 Precipitated barium sulfate, barium carbonate, calcium carbonate, carbon, magnesium carbonate, etc.), dispersants, defoamers, preservatives, thickeners, film-forming aids, etc.

[0172] --Film thickness of repair coating--

[0173] If the repair coating is too thin, the corrosion resistance is reduced. There is no particular upper limit on the thickness of the repair coating, but if the thickness becomes too thick, not only the coating cost per cut end face increases, but also the drying time after the repair coating is applied is prolonged.

[0174] Therefore, the film thickness of the repair coating film is 10 μm or more. The film thickness of the repair coating film is preferably 10 to 100 μm, and more preferably 20 to 30 μm.

[0175] The film thickness of the repair coating can be measured by the following method.

[0176] The cut workpiece to be measured is cut in a direction perpendicular to the cut end surface and perpendicular to the plate thickness direction.

[0177] Next, the cut processed part to be measured is embedded with an embedding resin mixed with an embedding curing agent in a specified ratio, and the embedded sample is mechanically polished to expose the cut surface after the cut processed part is cut, thereby producing a sample with the surface in the orthogonal direction of the cut end surface as the observation surface.

[0178] The observation surface of the sample was observed by SEM (Scanning Electron Microscope) at a magnification of 50 to 100, and the film thickness of the repair coating film formed at any position on the non-plated surface of the base steel material was measured.

[0179] The film thickness measurement was carried out using three embedded samples, and the average value of the three measured values ​​was calculated.

[0180] --Repair coating film resistance value--

[0181] If the initial coating resistance R1 in the repair coating is less than 10Ω / cm 2 , the metal powder in the repair coating is slowly oxidized, and the sacrificial anode corrosion protection of the repair coating loses its activity at an early stage, so the corrosion resistance is reduced.

[0182] If the initial coating resistance R1 in the repair coating is higher than 1000Ω / cm 2 , the sacrificial anode corrosion protection of the repair coating will not work at all, and red rust will sometimes be generated in the steel substrate under the repair coating due to the influence of water film in the atmosphere, thereby reducing the corrosion resistance.

[0183] Therefore, the initial coating resistance value R1 in the repair coating is set to 10 to 1000 Ω / cm 2 .

[0184] In addition, the initial coating resistance value R1 in the repair coating indicates the coating resistance value when the proportion of the total amount of metal powder in the repair coating that is not corroded is 80% or more. As long as the proportion of the total amount of metal powder in the repair coating that is not corroded is 80% or more, the coating resistance value R1 in this state is 10 to 1000Ω / cm 2 From the above viewpoint, the initial coating film resistance value R1 is preferably 300 to 500 Ω / cm 2 .

[0185] As long as the proportion of the total amount of metal powder in the coating that has not been corroded is 80% or more, the initial coating resistance value R1 represents the coating resistance value in any state of storing the cut product in a non-corrosive environment or using the cut product in a corrosive environment.

[0186] Specifically, the coating resistance value in the repair coating of the cut product stored in a non-corrosive environment from the time the cut product is made to the time the cut product is put to use (for example, until the cut product is installed as a beam as a guardrail) is equivalent to the "initial coating resistance value R1".

[0187] Furthermore, as long as the proportion of the total amount of metal powder in the repair coating that is not corroded is 80% or more, the coating resistance value in the repair coating of the cut product used as a guardrail beam in a corrosive environment is also equivalent to the "initial coating resistance value R1".

[0188] The corrosion ratio of the total amount of metal powder is the sum of the oxidation ratio and the hydrogen oxidation ratio of the metal powder. The corrosion ratio of the metal powder can be measured by analyzing the cross-sectional image of the repaired coating film. Specifically, it is as follows.

[0189] In the cut end surface of the cut workpiece to be measured, the central region where the repaired coating film was removed within a range of 10 mm from the end was cut in a direction perpendicular to the cut end surface and parallel to the plate thickness direction.

[0190] Next, the cut processed part to be measured is embedded with an embedding resin mixed with an embedding curing agent in a specified ratio, and the embedded sample is mechanically polished to expose the cut surface after the cut processed part and the repair coating, thereby producing a sample with the surface in the orthogonal direction of the cut end surface as the observation surface.

[0191] The observation surface of the sample was subjected to mapping analysis using a SEM (Scanning Electron Microscope) equipped with an EDS (Energy Dispersive X-ray Spectroscopy). The observation magnification was set to a magnification that allowed the entire repair coating to be observed in the film thickness direction from the interface between the repair coating and the base steel material to the coating surface, and to a field of view that allowed the interface between the repair coating and the base steel material to be observed at a depth of 100 μm or more.

[0192] This field of view observation was performed at three locations per one embedded sample and at nine locations in total per three embedded samples, and the corrosion ratio of the metal powder in each field of view was calculated.

[0193] The corrosion ratio (%) of the metal powder can be calculated as "(the number of corroded metal powders / the total number of metal powders)×100" in the field of view.

[0194] Corroded metal powder can be identified by mapping analysis using an SEM equipped with EDS, based on the coincidence of detection positions of metal elements such as Zn and oxygen.

[0195] However, the corroded metal powder does not contain additives such as MgO and Al2O3 that were initially added to the coating in an oxidized state. The proportion of all corroded metal powders excluding these additives is calculated as follows.

[0196] First, after calculating the corrosion rate of the metal powder by visual field observation, the ratio of the additives (MgO, Al2O3, etc.) added to the paint material as the raw material is subtracted. Specifically, the ratio (%) of the additives (MgO, Al2O3, etc.) initially added in all the metal particles contained in the paint material is subtracted from the corrosion rate (%) of the metal powder obtained by visual field observation.

[0197] That is, the corrosion ratio (%) of the metal powder can be calculated as "(the number of corroded metal powders - the number of additives) / the total number of metal powders × 100" in the field of view.

[0198] In this way, the measured value of the additive ratio is subtracted from the measured value of the corrosion ratio in the above-mentioned 9 viewing fields, and the average value of the obtained ratios is calculated.

[0199] Then, the average value (%) of the obtained ratios was subtracted from 100%, and the obtained value (=100-average value of the obtained ratios) was defined as "the ratio of the non-corroded parts in the total amount of metal powder in the repair coating film".

[0200] In addition, regarding additives such as MgO and Al2O3 contained in the paint in an oxidized state, the increase in oxides in the repaired coating film due to the oxides brought by the additives in the paint can be calculated to identify the corroded metal powder.

[0201] On the other hand, if the coating resistance R2 after the repair coating is immersed in salt water is less than 5Ω / cm 2 , the metal powder in the repair coating is rapidly consumed in a corrosive environment, and the sacrificial anode corrosion protection of the repair coating loses its activity at an early stage, thereby reducing the corrosion resistance.

[0202] If the coating resistance R2 after the repair coating is immersed in salt water is higher than 50Ω / cm 2In a corrosive environment, the oxygen reduction reaction is concentrated on the exposed portion of the steel substrate directly below the repair coating. Due to the change to an alkaline environment, it becomes difficult for intermolecular forces such as hydrogen bonds to function, resulting in cathodic peeling of the repair coating, resulting in reduced corrosion resistance.

[0203] The coating film resistance value R2 after salt water immersion is preferably 10 to 45 Ω / cm 2 , more preferably 25 to 40 Ω / cm 2 .

[0204] Here, the coating resistance value after immersion in salt water in the repair coating is the coating resistance value after immersion of the cut workpiece in 5 mass % salt water for 3 hours. More specifically, it is the coating resistance value after at least the cut end surface of the cut workpiece is immersed in 5 mass % salt water at a liquid temperature of 25°C for 3 hours.

[0205] The initial coating resistance value and the coating resistance value after the salt water immersion in the repair coating can be adjusted according to, for example, the film thickness of the repair coating and the type and amount of the metal powder.

[0206] The coating film resistance value can be measured by the following method.

[0207] The cut processed product to be measured is cut into 10 mm squares to obtain a cut piece with a cut end face formed with a repair coating. The cut end face of the obtained cut piece is used as the measurement face, and a lead wire is connected to the portion other than the measurement face by a method that does not hinder conduction, such as spot welding or soldering. Only a fixed area of ​​the cut end face to be measured is exposed, and the other portions are insulated and sealed, thereby obtaining a sample of the repair coating (refer to Figure 4 ).

[0208] The coating film resistance value was measured by measuring the AC impedance of the repair coating film on the exposed cut end surface of the obtained sample.

[0209] This operation was performed twice, and the average value of the coating film resistance was calculated.

[0210] in addition, Figure 4 In the figure, 400 indicates a sample, 402 indicates a cut piece of a cut product, 404 indicates a wire, 404A indicates a connecting portion of the wire, 406 indicates an insulating seal, and 408 indicates a repair coating film on an exposed cut end surface.

[0211] (Application of cutting processed products)

[0212] The cut processed products disclosed herein are suitable for use in guardrails (specifically guardrail components, especially guardrail beams), steel sections for plastic greenhouses or agricultural greenhouses, pillars, beams, sound insulation walls, soundproof walls, components for electrical equipment, components for safe environments, structural components, steel plates used in solar racks, etc.

[0213] The cut-off processed product of the present disclosure can be used by subjecting the plated steel material to cutting processing and then subjecting it to processing such as press forming according to the above-mentioned use.

[0214] Example

[0215] Hereinafter, the present disclosure will be described in more detail by listing examples, but these examples do not limit the present disclosure.

[0216] (Preparation of plated steel sheet)

[0217] The following types of plated steel materials were prepared.

[0218] Zn-6%Al-3%Mg: Zn-Al-Mg plated steel sheet (sheet thickness = 4.5 mm, coating composition = Al: 6 mass%, Mg: 3 mass%, balance: Zn, single-sided coating weight = 120 g / m 2 )

[0219] Zn-11%Al-3%Mg: Zn-Al-Mg plated steel sheet (sheet thickness = 4.5 mm, coating composition = Al: 11 mass%, Mg: 3 mass%, balance: Zn, single-sided coating weight = 120 g / m 2 )

[0220] Zn-19%Al-6%Mg: Zn-Al-Mg plated steel sheet (sheet thickness = 4.5 mm, coating composition = Al: 19 mass%, Mg: 6 mass%, balance: Zn, single-sided coating weight = 120 g / m 2 )

[0221] Zn: Hot-dip galvanized steel sheet (sheet thickness = 4.5 mm, single-sided coating weight = 120 g / m 2 )

[0222] (Paint for repair)

[0223] Repair coatings having the compositions shown in Table 1 were prepared.

[0224] (Example)

[0225] According to the conditions in Table 2, the plated steel sheet was cut by laser cutting or conventional shearing to obtain a Figure 1 or Figure 3 In the laser cutting method, the gas flow rate and gas pressure ejected from the laser nozzle were adjusted, and the coverage of the linear film on the cut end surface and the maximum length of the linear film were shown in Table 2. In the shearing method, the clearance between the shear blade and the die was adjusted, and the coverage of the coating on the cut end surface was shown in Table 2.

[0226] Next, under the conditions shown in Table 2, a repair coating was applied on the non-plated surface of the base steel material of the plated steel sheet and the linear film or plating layer around the non-plated surface in the cut end surface of the sample to form a repair coating film.

[0227] The film thickness of the repair coating is shown in Table 2. Table 2 also shows the initial coating resistance and the coating resistance after immersion in salt water (i.e., the coating resistance after immersion of the cut product in 5 mass % salt water for 3 hours).

[0228] Through these operations, samples of cut products were obtained.

[0229] (evaluate)

[0230] The following evaluations were performed on the cut end surfaces of the obtained cut product samples.

[0231] - Cathodic disbonding resistance -

[0232] The combined cyclic corrosion test according to CCT-JASO M609 was carried out for 30 cycles.

[0233] Then, a tape ("CELLULOSE TAPE (registered trademark)", manufactured by Nichban Co., Ltd.) was attached to the repair coating film-forming surface of the cut end surface of the cut product sample and then peeled off.

[0234] Then, the peeled tape was observed, and the ratio of the area of ​​the repaired coating film peeled by the tape (hereinafter referred to as "peeled area ratio") to the area of ​​the repaired coating film attached to the tape was calculated and evaluated according to the following criteria.

[0235] A: Peeling area rate is 0%

[0236] B: The peeling area ratio is more than 0% and less than 5%

[0237] D: The peeling area rate exceeds 5%

[0238] -Long-term corrosion resistance 1-

[0239] The combined cyclic corrosion test according to CCT-JASO M609 was carried out for 120 cycles.

[0240] The red rust occurrence area on the cut end surface of the cut product sample was measured and evaluated according to the following criteria. In addition, "A" and "B" were passed.

[0241] A: Red rust area rate is 0%

[0242] B: Red rust area ratio is more than 0% and less than 5%

[0243] C: Red rust area ratio is more than 5% and less than 20%

[0244] D: Red rust area rate exceeds 20%

[0245] B or above is qualified

[0246] -Long-term corrosion resistance 2-

[0247] The combined cyclic corrosion test according to CCT-JASO M609 was carried out for 180 cycles.

[0248] The red rust occurrence area on the cut end surface of the cut product sample was measured and evaluated according to the following criteria. In addition, "A" and "B" were passed.

[0249] A: Red rust area rate is 0%

[0250] B: Red rust area ratio is more than 0% and less than 20%

[0251] D: Red rust area rate exceeds 20%

[0252] B or above is qualified

[0253] Table 1

[0254]

[0255] Table 2

[0256]

[0257] From the above results, it is understood that in the disclosed examples, cathodic peeling of the repair coating film is suppressed compared with the comparative examples, and the corrosion resistance of the cut end surface is excellent from the initial stage to the long term.

[0258] The symbols are explained as follows.

[0259] 10: Plated steel

[0260] 12: Parent steel

[0261] 14: Plating

[0262] 16: Linear membrane

[0263] 18: Repair coating

[0264] 101: Cutting processed products

[0265] 101C: Cut off the end face

[0266] In addition, the entire disclosure of Japanese Patent Application No. 2022-157063 is incorporated into this specification by reference.

[0267] All documents, patent applications, and technical specifications described in this specification are incorporated herein by reference to the same extent as if each individual document, patent application, or technical specification was specifically and individually indicated to be incorporated by reference.

Claims

1. A cut product, which is a cut product of a Zn-Al-Mg-based plated steel material having a base steel material and a Zn-Al-Mg-based plated layer coated on the surface of the base steel material, wherein: The cut end surface of the cut product is covered with a linear film formed by linear inflow of the components of the Zn-Al-Mg-based plating layer, and the coverage of the linear film with respect to the cut end surface is 60 to 90%. The non-plated surface of the base steel material and the linear film around the non-plated surface in the cut end surface of the cut product are covered with a repair coating film. The initial coating resistance value R1 in the repair coating is 10 to 1000 Ω / cm 2 , and the coating resistance value R2 after the cut product is immersed in 5 mass % salt water for 3 hours is 5 to 50 Ω / cm 2 , The repair coating film has a thickness of 10 μm or more.

2. The cut product according to claim 1, wherein: The repair coating film contains Zn-based metal powder and a binder resin.

3. The cut product according to claim 1, wherein: The maximum length of the linear film on the cut end surface of the cut product is 70 to 100% of the plate thickness of the cut product.

4. The cut product according to claim 1, wherein The initial coating resistance value R1 in the repair coating is 300 to 500 Ω / cm 2 .

5. The cut product according to claim 1, wherein The coating resistance value R2 of the repair coating after immersion is 25 to 40 Ω / cm 2 .

6. The cut product according to claim 2, wherein: The Zn-based metal powder contains Zn and Al.

7. The cut product according to claim 6, wherein: The content of Al in the Zn-based metal powder containing Zn and Al is 20 to 45% by mass relative to Zn.

8. The cut product according to claim 6, wherein: The content of Al in the Zn-based metal powder containing Zn and Al is 28 to 34 mass % relative to Zn.

9. The cut product according to claim 2, wherein: The content of the Zn-based metal powder relative to the entire repair coating film is 60 to 80% by mass of the metal powder.

10. The cut product according to claim 2, wherein: The binder resin is at least one selected from polystyrene resin and epoxy resin. 11 . A guardrail comprising the cut product according to claim 1 .

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