Surface-treated steel material

Abstract

This surface-treated steel material includes a steel material and a plating layer formed on at least part of the surface of the steel material. The plating layer is a Zn-based plating layer containing 0.3-12.5 mass% of Mg. One or more compounds from among MgO, Mg(OH)2, MgCO3, Mg4Al2(OH)12CO3･3H2O, Mg6Al2(OH)16CO3･4H2O, Mg-containing Zn6Al2(OH)16CO3･4H2O, 4MgCO3･Mg(OH)2･5H2O, Mg-containing Zn5(CO3)2(OH)6, Mg-containing Zn5(OH)8Cl2･H2O, and Mg-containing NaZn4(SO4)Cl(OH)6･6H2O is present on least part of a non-plated section, where the non-plated section is a portion of the surface of the steel material where the plating layer is not formed.

Description

Surface-treated steel

[0001] This application claims priority from Japanese Patent Application No. 2023-116278, filed on July 14, 2023, the contents of which are incorporated herein by reference.

[0002] Zinc (Zn)-plated steel sheets are the most widely used surface-treated steel materials with good corrosion resistance. These zinc-plated steel sheets are used in various manufacturing industries, including the automotive, home appliance, and building materials fields. For example, in the building materials field, research has long been conducted to improve the corrosion resistance of zinc-plated steel sheets in response to the need for longer life for building materials. In this context, studies have been conducted to improve corrosion resistance by incorporating Al and Mg into the zinc-plated layer. For example, Patent Documents 1 to 4 disclose plated steel materials that contain certain amounts of Al and Mg to achieve high corrosion resistance.

[0003] Japanese Patent Publication No. 2006-193791 International Publication No. 2011 / 001662 Japanese Patent Publication No. 2021-172878 Japanese Patent Publication No. 2016-519220

[0004] The plated steel materials disclosed in Patent Documents 1 to 4 above have excellent long-term flat corrosion resistance. However, when plated steel materials are used, they may be cut to a predetermined size. In this case, the cut surface (cut end surface) is left without a plating layer. Furthermore, even on plated surfaces, there may be unplated areas or areas where the plating layer is not formed (exposed steel sheet) due to scratches that cause the plating layer to peel off or cracks that occur during cutting, punching, bending, drawing, etc. As a result of research conducted by the present inventors, it was found that, although the plated steel materials disclosed in Patent Documents 1 to 3 have excellent corrosion resistance in the plated portions, red rust may form in the early stages of corrosion on the cut end surfaces, unplated areas, or areas where the steel sheet is exposed due to scratches or processing after the plating layer has been formed (collectively referred to as non-plated areas). Therefore, there is a need for technological development that can suppress the formation of red rust in such non-plated areas.

[0005] In consideration of the above-mentioned background, an object of the present invention is to provide a surface-treated steel material, typified by a surface-treated steel sheet having a Zn-based plating layer containing Mg, in which the formation of red rust in unplated portions is suppressed.

[0006] The present inventors have investigated the above-mentioned problems and have found that the formation of red rust can be suppressed by having a specified Mg-containing compound present on the surface of a steel sheet in a non-plated portion where no plating layer is formed.

[0007] The present invention has been made in light of the above findings. The gist of the present invention is as follows. [1] A surface-treated steel material according to one aspect of the present invention comprises a steel material and a plating layer formed on at least a portion of the surface of the steel material, the plating layer being a Zn-based plating layer containing 0.3 to 12.5 mass % of Mg, and when a portion of the surface of the steel material where the plating layer is not formed is defined as a non-plated portion, one or more compounds selected from the following compounds A, B, C, D, E, F, G, H, I, and J are present in at least a portion of the non-plated portion. Compound A: MgO, Compound B: Mg(OH) ２ , Compound C: MgCO ３ , Compound D: Mg ４ Al ２ (OH) １２ CO ３ ・3H ２ O, Compound E: Mg ６ Al ２ (OH) １６ CO ３ ・4H ２ O, Compound F: Zn containing Mg ６ Al ２ (OH) １６ CO ３ ・4H ２ O, Compound G: 4MgCO ３ Mg(OH) ２ ・5H ２ O, Compound H: Zn containing Mg ５ (CO ３ ) ２ (OH) ６ Compound I: Zn containing Mg５ (OH) ８ Cl ２ ・H ２ O, Compound J: NaZn containing Mg ４ (SO ４ )Cl(OH) ６ ・6H ２ O. [2] In the surface-treated steel material described in [1], the plating layer may contain 4.0 to 25.0 mass% Al. [3] In the surface-treated steel material described in [1] or [2], 50% or more of the surface area may be covered with the compound. [4] In the surface-treated steel material described in any of [1] to [3], the compound may include one or more compounds selected from the group consisting of Compound D, Compound E, Compound F, Compound H, and Compound I, and one or more compounds selected from the group consisting of Compound A, Compound B, Compound C, Compound G, and Compound J. [5] In the surface-treated steel material described in any of [1] to [4], the compound may include two or more compounds selected from the group consisting of Compound B, Compound D, Compound G, Compound H, and Compound I. [6] In the surface-treated steel material according to any one of [1] to [5], the total composition ratio of one or both of the compounds H and I may be 10% or more in terms of molar ratio.

[0008] According to the above aspect of the present invention, it is possible to provide a surface-treated steel material in which the formation of red rust in the non-plated portion is suppressed.

[0009] 1 is a schematic diagram showing an example of a surface-treated steel sheet, which is one form of a surface-treated steel material according to the present embodiment; FIG. 2 is a diagram showing an image of normalization of an XAFS spectrum;

[0010] A surface-treated steel material according to one embodiment of the present invention (surface-treated steel material according to this embodiment) will be described using a surface-treated steel sheet as an example. As shown in FIG. 1 , a surface-treated steel sheet 1 (hereinafter, referred to as the surface-treated steel sheet according to this embodiment) is an example of a surface-treated steel material according to this embodiment. The surface-treated steel sheet 1 (hereinafter, referred to as the surface-treated steel sheet according to this embodiment) has a steel sheet (base steel sheet) 11 and a coating layer 12 formed on at least a portion of a surface 101 of the steel sheet 11. When the portion of the surface 101 of the steel sheet 11 on which the coating layer 12 is not formed is designated as a non-coated portion 41, a predetermined compound 31 containing Mg is present in at least a portion of the non-coated portion 41 of the steel sheet 11. In FIG. 1 , the surface of the surface 101 that comes into contact with the coating bath and on which the coating layer is formed is the coating surface 103, and the surface exposed when the steel sheet is cut to a predetermined size after being pulled out of the coating bath is the end surface 102. The end surface 102 is oriented in a direction intersecting the coating surface 103 and, in many cases, is substantially perpendicular to the coating surface 103. The shape of the surface-treated steel material according to this embodiment is not limited to a steel sheet. For example, the shape may be a shape obtained by bending a steel plate, a shape like a steel pipe, a shape like a steel bar or steel wire, or a shape like a steel section with an H-shaped or T-shaped cross section. The surface-treated steel material according to this embodiment will be described in detail below, taking a surface-treated steel plate as an example. In the following description, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. However, when the numerical values ​​written before and after "to" are followed by "greater than" or "less than," the numerical range does not include these numerical values ​​as the lower or upper limit.

[0011] <Steel Sheet (Steel Material)> The surface-treated steel sheet 1 according to this embodiment is characterized by the coating layer 12 and the compound 31. Therefore, the steel sheet 11 is not particularly limited. The steel sheet 11 may be determined based on the product to which it is applied, the required strength, thickness, etc. For example, a hot-rolled steel sheet as described in JIS G 3131:2018, JIS G 3113:2018, etc., or a cold-rolled steel sheet as described in JIS G 3141:2021, JIS G 3135:2018, etc., can be used. As described above, steel materials other than steel sheets, such as steel pipes, steel wires, and various steel components, can also be used. The thickness is not limited, but a preferred thickness range is 1.0 to 9.0 mm.

[0012] <Plated Layer> In the surface-treated steel sheet 1 according to this embodiment, a plated layer 12 is formed on at least a portion of the surface of the steel sheet 11. This plated layer 12 is a Zn-based plated layer containing 0.3 mass % to 12.5 mass % Mg. The plated layer may further contain 4.0 mass % to 25.0 mass % Al. In this embodiment, the Zn-based plated layer is a plated layer having a Zn concentration of 50.0 mass % or more. In the plated layer 12 of the surface-treated steel sheet 1 according to this embodiment, Zn and Mg, or Zn, Mg, and Al, often form an alloy in the plated layer, but the state of existence of Zn, Mg, and Al is not limited. The plated layer 12 may be formed on the entire plated surface 103 (front and back surfaces (in the case of a cut plated steel sheet, this is often the surface other than the end faces)) (100% by area), or there may be portions (non-plated portions 41) that are not formed due to non-plating or peeling due to scratches, etc. The area ratio of the non-plated portion 41 is preferably 10% or less of the entire plated surface. The area ratio of the non-plated portion 41 on the plated surface 103 may be 0%. The plating layer 12 may also be formed on a portion of the surface 101 other than the plated surface 103 (end surface 102 in FIG. 1 ). However, in the case of a surface-treated steel sheet that is cut to a predetermined size after forming the plating layer, the plating layer is often not formed on the end surface (cut end surface). The area ratio of the non-plated portion 41 may be more than 0% of the entire surface, including the surface other than the plated surface 103.

[0013] In the surface-treated steel sheet 1 according to this embodiment, the plating layer 12 is a Zn-based plating layer 12 containing Mg, and then a specific treatment described below is performed, thereby suppressing the formation of red rust even in the non-plated portion 41 (improving red rust resistance). The reason for this is not entirely clear, but it is believed that the specific treatment causes Mg contained in the Zn-based plating layer 12, which dissolves due to sacrificial corrosion protection, to form a compound described below in the non-plated portion 41. If the plating layer 12 is not a Zn-based plating layer containing Mg, the effect of forming the compound 31 cannot be fully achieved. Even if the steel sheet 11 contains Mg, the amount of Mg contained in the steel sheet 11 is very small, and the elution of Mg from the steel sheet 11 is small, so the same effect cannot be achieved.

[0014] To achieve the above effects, the Mg concentration (content) in the Zn-based plating layer 12 is set to 0.3 mass% or more and 12.5 mass% or less. If the Mg concentration (content) is less than 0.3 mass%, compounds containing Mg are not formed. Therefore, the Mg concentration is set to 0.3 mass% or more. On the other hand, if the Mg concentration is more than 12.5 mass%, workability decreases. Therefore, the Mg concentration is set to 12.5 mass% or less.

[0015] The concentrations (contents) of elements other than those mentioned above in the plating layer 12 (Zn-based plating layer) are not limited. However, if the chemical composition of the plating layer 12 is, in mass %, Mg: 0.3 to 12.5%, Al: 0 to 25.0%, Sn: 0 to 20.0%, Bi: 0 to less than 5.0%, In: 0 to less than 2.0%, Ca: 0 to 3.0%, Y: 0 to 0.5%, La: 0 to less than 0.5%, Ce: 0 to less than 0.5%, Si: 0 to less than 2.5%, Cr: 0 to less than 0.25%, Ti: 0 to less than 0.25%, Ni: 0 to less than 0.25%, and Co: 0 to 0. 0.25%, V: 0 to less than 0.25%, Nb: 0 to less than 0.25%, Cu: 0 to less than 0.25%, Mn: 0 to less than 0.25%, Fe: 0 to 5.0%, Sr: 0 to less than 0.5%, Sb: 0 to less than 0.5%, Pb: 0 to less than 0.5%, B: 0 to less than 0.5%, and the balance: Zn and impurities, this is preferable because it provides excellent corrosion resistance as a surface-treated steel sheet 1, including the portion where the plating layer 12 is formed.

[0016] The following describes the reasons for the preferred chemical composition of the plating layer 12. Unless otherwise specified, the percentages for the concentration (content) of each element in the chemical composition of the plating layer 12 are mass percentages.

[0017] [Mg: 0.3 to 12.5%] To form Mg-containing compounds, the Mg concentration is 0.3% or more. Mg is also an element that has the effect of enhancing the corrosion resistance of the coating layer 12. To obtain the effect of improving corrosion resistance, the Mg concentration is preferably 0.5% or more. The Mg concentration is more preferably 1.0% or more, and even more preferably 3.0% or more. On the other hand, if the Mg concentration exceeds 12.5%, the effect of improving corrosion resistance saturates and the workability of the coating layer may deteriorate. Furthermore, manufacturing problems such as an increase in the amount of dross generated in the coating bath may occur. Therefore, the Mg concentration is set to 12.5% ​​or less. The Mg concentration is more preferably 10.0% or less, and even more preferably 8.0% or less.

[0018] [Al: 0 to 25.0%] Al is an element effective in improving the corrosion resistance of the plating layer (Zn-based plating layer) 12. Therefore, although the lower limit of the Al concentration is 0%, Al may be contained. To fully obtain the above effect, the Al concentration is preferably 2.0% or more or 4.0% or more. If necessary, the Al concentration may be 6.0% or more or 8.0% or more. On the other hand, if the Al concentration exceeds 25.0%, the sacrificial corrosion protection effect of the plating layer 12 decreases. Therefore, the Al concentration is preferably 25.0% or less. If necessary, the Al concentration may be 20.0% or less or 16.0% or less.

[0019] [Sn: 0 to 20.0%] [Bi: 0 to less than 5.0%] [In: 0 to less than 2.0%] These elements contribute to improving corrosion resistance and sacrificial corrosion protection. Therefore, although the lower limit of the concentration of these elements is 0%, one or more of them may be contained. To obtain the above effects, it is preferable to set the concentration of each to 0.05% or more. Of these, Sn is preferred because it is a low-melting-point metal and can be easily added without impairing the properties of the plating bath. On the other hand, if the Sn concentration exceeds 20.0%, the Bi concentration is 5.0% or more, or the In concentration is 2.0% or more, corrosion resistance decreases. Therefore, it is preferable to set the Sn concentration to 20% or less, the Bi concentration to less than 5.0%, and the In concentration to less than 2.0%, respectively.

[0020] [Ca: 0 to 3.0%] Ca is an element that reduces the amount of dross that tends to form during operation and contributes to improving plating manufacturability. Therefore, although the lower limit of the Ca concentration is 0%, Ca may be contained. To obtain this effect, the Ca concentration is preferably 0.1% or more. On the other hand, if the Ca concentration is high, the corrosion resistance of the flat portions of the plating layer 12 tends to deteriorate, and the corrosion resistance around the weld may also deteriorate. Therefore, the Ca concentration is preferably 3.0% or less.

[0021] [Y: 0 to 0.5%] [La: 0 to less than 0.5%] [Ce: 0 to less than 0.5%] Y, La, and Ce are elements that contribute to improving corrosion resistance. Although the lower limit of the concentration of these elements is 0%, to obtain this effect, it is preferable to contain at least one of them at 0.05% or more. On the other hand, excessive concentrations of these elements increase the viscosity of the coating bath, often making preparation of the coating bath itself difficult, raising concerns that steel products with good coating properties may not be produced. Therefore, it is preferable to set the Y concentration to 0.5% or less, the La concentration to less than 0.5%, and the Ce concentration to less than 0.5%.

[0022] [Si: 0 to less than 2.5%] Si is an element that contributes to improving corrosion resistance. Furthermore, when forming the plating layer 12 on the steel sheet 11, Si also has the effect of preventing the alloy layer formed between the surface of the steel sheet 11 and the plating layer 12 from becoming excessively thick, thereby improving the adhesion between the steel sheet 11 and the plating layer 12. While the lower limit of the Si concentration is 0%, to obtain these effects, the Si concentration is preferably 0.1% or more. The Si concentration is more preferably 0.2% or more. On the other hand, if the Si concentration is 2.5% or more, excessive Si precipitates in the plating layer 12, which not only reduces the corrosion resistance but also reduces the workability of the plating layer 12. Therefore, the Si concentration is preferably less than 2.5%. The Si concentration is more preferably 1.5% or less.

[0023] [Cr: 0 to less than 0.25%] [Ti: 0 to less than 0.25%] [Ni: 0 to less than 0.25%] [Co: 0 to less than 0.25%] [V: 0 to less than 0.25%] [Nb: 0 to less than 0.25%] [Cu: 0 to less than 0.25%] [Mn: 0 to less than 0.25%] These elements contribute to improving corrosion resistance. Although the lower limit of the concentration of these elements is 0%, to obtain this effect, it is preferable to set the concentration of one or more of these elements to 0.05% or more. On the other hand, excessive concentrations of these elements increase the viscosity of the coating bath, often making the preparation of the coating bath itself difficult, raising concerns that steel products with good coating properties may not be produced. Therefore, it is preferable to set the concentration of each element to less than 0.25%.

[0024] [Fe: 0 to 5.0%] Fe may be mixed into the plating layer 12 during production of the plating layer 12. Although it may be contained up to about 5.0%, within this range, the adverse effect on the effects of the surface-treated steel sheet 1 according to this embodiment is small. Therefore, it is preferable that the Fe concentration be 5.0% or less. The inclusion of Fe is not essential, and the lower limit of the Fe concentration is 0%.

[0025] [Sr: 0% to less than 0.5%] [Sb: 0% to less than 0.5%] [Pb: 0% to less than 0.5%] When Sr, Sb, or Pb is contained in the plating layer 12, the appearance of the plating layer 12 changes, spangles are formed, and improved metallic luster is confirmed. The lower limit of the concentration of these elements is 0%, but to achieve this effect, the concentration of one or more of Sr, Sb, and Pb is preferably 0.05% or more, and more preferably 0.1% or more. On the other hand, excessive concentrations of these elements increase the viscosity of the plating bath, often making the preparation of the plating bath itself difficult, raising concerns that steel products with good plating properties cannot be produced. Therefore, it is preferable to set the concentration of each element to less than 0.5%.

[0026] [B: 0 to less than 0.5%] When contained in the coating layer 12, B combines with Zn, Al, Mg, etc. to form various intermetallic compounds. These intermetallic compounds have the effect of improving LME. The lower limit of the B concentration is 0%, but to obtain this effect, the B concentration is preferably 0.05% or more, and more preferably 0.1% or more. On the other hand, if the B concentration is excessive, the melting point of the coating will rise significantly, which may deteriorate the coating operability and prevent the production of a surface-treated steel sheet 1 with good coating properties. Therefore, the B concentration is preferably less than 0.5%.

[0027] [Remainder: Zn and Impurities] The chemical composition of the plating layer 12 may consist of Zn and impurities other than the above-mentioned elements. The Zn concentration in the plating layer 12 is 50.0% or more, preferably 62.5% or more, more preferably 70.0% or more, and even more preferably 85.0% or more. In this embodiment, a Zn-based plating layer means that the Zn concentration in the plating layer 12 is 50.0% or more. Impurities are elements that are mainly mixed in from raw materials during the manufacturing process. The total concentration of impurities is usually 0.5% or less, but a total concentration of 0.1% or less is preferable. For various reasons, such as reducing raw material costs, raw materials containing relatively high amounts of elements other than the above-mentioned elements, including Zn, may be used intentionally. Therefore, in this embodiment, these elements (elements other than the above-mentioned elements, including Zn) are all considered impurity elements, regardless of whether they are mixed in or intentionally added. Therefore, the total concentration of these elements is preferably 0.5% or less.

[0028] The coating weight of the plating layer 12 is not limited, but is set to 10 g / m per side to improve corrosion resistance. ２ If necessary, the coating weight is 20 g / m per side to further improve corrosion resistance. ２ Above, 40g / m ２ or more than 60 g / m ２ On the other hand, the amount of adhesion may be 400 g / m per side. ２ If the coating weight exceeds 400 g / m, the corrosion resistance will be saturated and it will be economically disadvantageous. ２ If necessary, the thickness is 350 g / m per side for further improvement in economy. ２ Below, 300g / m ２ or less than 250 g / m ２ The following may also be used.

[0029] The chemical composition of the plating layer 12 can be measured by the following method. First, the plating layer 12 is stripped and dissolved using an acid containing an inhibitor that suppresses corrosion of the base steel (steel sheet 11) (for example, an acid obtained by adding 1% Hibilon (A-6) (manufactured by Sugimura Chemical Industry Co., Ltd.) to 10% hydrochloric acid) to obtain an acid solution. Next, the obtained acid solution is measured by ICP analysis to obtain the chemical composition of the plating layer 12.

[0030] The deposition amount of the plating layer 12 is determined by measuring the change in mass (weight) of a sample (sample taken from the surface-treated steel sheet 1) before and after peeling and dissolving the plating layer 12 with an acid containing an inhibitor using the method described above, and calculating the deposition amount from the results.

[0031] <Compounds> In the surface-treated steel sheet 1 according to this embodiment, a compound 31 containing Mg is present in at least a portion of the non-plated portion 41 of the surface 101 (plated surface 103, end surface 102) of the steel sheet 11. This compound contains one or more compounds selected from the following (consisting essentially of one or more compounds selected from the following, but it is permissible to contain trace amounts of other compounds): Compound A: MgO Compound B: Mg(OH) ２ Compound C: MgCO ３ Compound D: Mg ４ Al ２ (OH) １２ CO ３ ・3H ２ O Compound E: Mg ６ Al ２ (OH) １６ CO ３ ・4H ２ O Compound F: Zn containing Mg ６ Al ２ (OH) １６ CO ３ ・4H ２ O Compound G: 4MgCO ３ Mg(OH) ２ ・5H ２ O Compound H: Zn containing Mg ５ (CO ３ ) ２ (OH) ６ Compound I: Zn containing Mg ５ (OH)８ Cl ２ ・H ２ O Compound J: Mg-containing NaZn ４ (SO ４ )Cl(OH) ６ ・6H ２ Here, the phrase "contains Mg" means that although the chemical formula does not contain Mg, some of the elements in the chemical formula are substituted with Mg, or Mg has penetrated the compound, and the compound contains Mg. The specific Mg concentration (Mg content) of each compound, including Compound F, Compound H, Compound I, and Compound J, which are described as "contains Mg," depends on the reagent preparation procedure described below. The Mg concentration (Mg content) of Compound F, Compound H, Compound I, and Compound J prepared according to the reagent preparation procedure described below is 0.1% by mass or more. The Mg content of these compounds can be easily measured using known ICP atomic emission spectroscopy. The presence of these compounds improves corrosion resistance and suppresses the formation of red rust in the non-plated portion 41. Although the cause is not entirely clear, the inventors performed electrochemical measurements on the end surface and found that when these compounds were present, the current value was suppressed on both the cathode and anode sides (especially the anode side) compared to when these compounds were not present. This suggests that the presence of these compounds acts as a physical protector (suppressing the cathodic reaction) and that the presence of these compounds acts as a passivator (suppressing the anodic reaction) due to the increase in pH near the surface that occurs when these Mg-containing compounds dissolve in environmental moisture.

[0032] Even if the compound contains Mg, compounds other than those listed above do not provide the above-mentioned effect, and therefore the desired effect cannot be achieved. The compound preferably contains one or more compounds selected from the following group a and one or more compounds selected from group b. Group a: A group consisting of Compound D, Compound E, Compound F, Compound H, and Compound I; Group b: A group consisting of Compound A, Compound B, Compound C, Compound G, and Compound J. The compounds in group a are highly effective in improving red rust resistance due to the physical protective effect (cathode reaction inhibition) provided by the presence of these compounds, while the compounds in group b are highly effective in improving red rust resistance due to the passivation effect (anodic reaction inhibition) caused by the increase in pH near the surface that occurs when these Mg-containing compounds dissolve in moisture in the environment. By simultaneously containing compounds from groups a and b, a synergistic effect is achieved, resulting in a more excellent red rust inhibition effect than when only compounds from one group are included.

[0033] From the viewpoint of improving corrosion resistance, the compound preferably contains two or more compounds selected from the group consisting of compound B, compound D, compound G, compound H, and compound I. The compound may essentially consist of two or more compounds selected from the above group. Furthermore, it is preferable that the total composition ratio of one or both of compound H and compound I among the compounds is 10% or more in terms of substance ratio (molar ratio).

[0034] Furthermore, although the presence of the above compounds provides an effect of improving corrosion resistance (effect of improving red rust resistance), in order to obtain a sufficient effect for the entire surface-treated steel sheet 1, it is preferable that 50% or more in terms of area ratio of the non-plated portion 41 where the plating layer 12 is not formed is covered with the above compounds. The covered area ratio may be 100%.

[0035] The compounds present in the non-plated portion 41 are identified by X-ray absorption fine structure analysis (hereinafter referred to as XAFS analysis) and fitting of the XAFS spectrum. Specifically, the compounds are obtained by the following method. First, a sample, for example, measuring the sheet thickness x 7 mm x 7 mm, including the non-plated portion 41 to be measured is cut out from the surface-treated steel sheet 1. XAFS analysis is performed on the non-plated portion 41 of the sample (for example, a range of 1.0 mm x 1.2 mm) to obtain an XAFS spectrum. The obtained spectrum is then fitted with a linear combination of the spectra of standard samples of each compound using Athena (analysis software), thereby identifying the compounds. The measurement conditions for the XAFS analysis are as follows:・Measurement of Mg K absorption edge ・Measurement atmosphere: High vacuum ・Measurement temperature: Room temperature ・Energy range: 1250 eV to 1540 eV (step: 0.2 eV) ・Incident X-ray intensity I ０is calculated from the sample current of the Au mesh. The detected X-ray intensity I is calculated using the fluorescence yield method (SDD detector) and the total electron yield method (sample current method). For energy correction, the XPS Au4f peak position is measured before measuring the sample. To improve the signal-to-noise ratio, three measurements are performed, and the average spectrum is used for analysis. Fitting is performed as follows: Energy is corrected based on the XPS Au4f peak position. As shown in Figure 2, the background is subtracted and the overall intensity is normalized so that the difference in intensity between the pre-edge and post-edge is 1. The spectrum obtained from the sample is fitted with a linear combination of the spectra of standard samples of each compound. The R-factor is used to confirm the validity of the fitting; an R-factor of 5% or less in the 1300-1380 eV region is considered valid, while an R-factor of more than 5% is considered unfit. The fact that fitting using standard samples of compounds A to J was not possible means that it cannot be determined that at least one of compounds A to J is present. The R factor is calculated using the following formula. Here, d' in the formula represents fitting data (spectral data obtained by linearly combining the spectra of each compound), and d represents measurement data. R factor = Σ(d' - d) ２ / Σd ２ When the sum of the constituent ratios of each compound is taken as 100%, compounds with a constituent ratio of 1% or more are judged to be "present." In this case, the spectrum obtained from the sample is approximated by a linear combination of spectra obtained by multiplying the spectra of standard samples of each compound by coefficients (i.e., when A, B, ..., J are the spectra of compounds A, B, ..., J, and a, b, ..., j are coefficients, the sample spectrum is approximated so that aA + bB + ..., jJ, and a + b + ..., j = 100%). Each of these coefficients is taken as the constituent ratio of each compound. The units of a, b, c, ..., j are the molar ratios of compounds A, B, C, ..., J, respectively.

[0036] For the fitting, the following commercially available reagents or reagents prepared as follows are used as standard samples for each compound: Compound A (MgO): (commercially available reagent) manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name: magnesium oxide Compound B (Mg(OH) ２ ): (Commercially available reagent) Kanto Chemical Co., Ltd., product name: Magnesium hydroxide Compound C (MgCO ３ Preparation procedure: Monoethylene glycol (purity 99.9%, 950 g) and distilled water (50 g) are weighed and mixed in a 1 L screw-cap bottle. NaCl is added to a concentration of 1 mol / kg. 4MgCO 3 is added to a three-necked round flask containing monoethylene glycol + water + NaCl solution (250 g). ３ Mg(OH) ２ ・5H ２ Add 10.0±0.1 g of CO using a reflux condenser. Release the mixture to atmospheric pressure and add 10.0±0.1 g of CO using a reflux condenser. ２ The mixture is stirred for 3 days under bubbling (20 to 50 mL / min). During stirring, a thermostat is used to maintain the temperature at 150±5°C. After stirring, the precipitate is suction filtered and dried. Compound D (Mg ４ Al ２ (OH) １２ CO ３ ・3H ２ O): Preparation procedure: 0.20M MgCl ２ -0.1M AlCl ３ solution (except MgCl ２ The amount of MgCl is 0.019M to 0.020M. ２ ) to 0.1M Na ２ CO ３ The mixture is then adjusted to pH 10, left to stand for 24 hours, and then suction filtered and dried. ６ Al ２ (OH) １６ CO ３ ・4H ２ O): (Commercially available reagent) manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name: Hydrotalcite; Compound F (Zn containing Mg) ６ Al ２ (OH) １６ CO３ ・4H ２ O): Preparation procedure: 0.2M ZnCl ２ -0.1M AlCl ３ -0.050M MgCl ２ solution (except MgCl ２ The amount of MgCl is 0.045M to 0.055M. ２ ) to 0.1M Na ２ CO ３ The mixture is then adjusted to pH 10, left to stand for 24 hours, and then suction filtered and dried. Compound G (4MgCO ３ Mg(OH) ２ ・5H ２ O): (Commercially available reagent) manufactured by Kanto Chemical Co., Ltd., product name: magnesium hydroxide carbonate; Compound H (Zn containing Mg) ５ (CO ３ ) ２ (OH) ６ ): Preparation procedure: 0.1M ZnCl2-0.050M MgCl ２ solution (except MgCl ２ The amount of MgCl is 0.045M to 0.055M. ２ ) with 0.1M Na ２ CO ３ The mixture is then adjusted to pH 10, left to stand for 24 hours, and then suction filtered and dried. Compound I (Zn containing Mg) ５ (OH) ８ Cl ２ ・H ２ O): Preparation procedure: 0.1M ZnCl ２ -0.050M MgCl ２ solution (except MgCl ２ The amount of MgCl is 0.045M to 0.055M. ２ The pH of the compound J (NaZn containing Mg) is adjusted to 10 by adding 0.1 M NaOH dropwise, and the mixture is left for 24 hours, and then the mixture is suction filtered and dried. ４ (SO ４ )Cl(OH) ６ ・6H ２ O): Preparation procedure: 0.5M ZnSO ４ -0.10M MgCl ２(However, MgCl ２ The amount of MgCl is 0.09M to 0.011M. ２ 1 g of ZnO powder is added to 30 mL of 1.4 M NaCl solution, and 0.1 M NaOH is added dropwise to adjust the pH to 10. The mixture is stirred for 120 hours, and then suction filtered and dried.

[0037] The compound coverage (coverage area ratio) in the non-plated portion 41 is determined by the following method. Mg mapping analysis is performed on the portion (non-plated portion 41) where the plating layer 12 is not formed using μ-XRF (micro-X-ray fluorescence), the intensity of the μ-XRF spectrum is measured, and the ratio of the area of ​​the region where the Mg concentration is 0.5 atomic % or more to the area of ​​the non-plated portion 41 where the plating layer 12 is not formed is defined as the "compound coverage ratio." At this time, the μ-XRF measurement conditions are as follows: Measurement atmosphere: vacuum Acceleration voltage: 15 kV Current value: 50 μA Tube: Rh tube Scan speed: 4.00 mmS －１ Polymeter: 30 μm

[0038] <Manufacturing Method> The surface-treated steel sheet 1 according to this embodiment can achieve the effects as long as it has the above-mentioned characteristics regardless of the manufacturing method, but can be manufactured by a manufacturing method including the following steps: (I) a plating step of forming a Zn-based plating layer 12 containing Mg on the surface of a steel sheet 11 (base steel sheet), (II) a processing step of cutting and / or punching the steel sheet (plated steel sheet) on which the plating layer 12 (Zn-based plating layer) has been formed to form the plated steel sheet into a desired shape, and (III) a compound formation step of forming a predetermined compound containing Mg on the end surface and / or the non-plated portion 41 of the plated surface. Preferred conditions for each step will be described.

[0039] [Plating Process] In the plating process, a steel material such as a steel sheet is immersed in a plating bath containing Mg and Zn or electroplated to form a plating layer 12 on the surface. The conditions for forming the plating layer 12 are not particularly limited. A conventional method may be used to obtain sufficient plating adhesion. Furthermore, the steel material subjected to the plating process and its manufacturing method are not particularly limited. In the case of a surface-treated steel sheet, the steel sheet to be immersed in the plating bath may be, for example, a hot-rolled steel sheet as described in JIS G 3113:2018 or JIS G 3131:2018 or a cold-rolled steel sheet as described in JIS G 3141:2021 or JIS G 3135:2018. Steel materials other than steel sheets, such as steel pipes, steel wires, and various steel components, may also be used. The composition of the plating bath may be adjusted according to the chemical composition of the desired plating layer 12. After the steel material is pulled out of the plating bath, the coating weight of the plating layer 12 can be adjusted by wiping, if necessary.

[0040] [Processing Step] In the processing step, the plated steel sheet is cut and / or punched to form a desired shape. When cutting or punching is performed, an end surface without the plating layer 12 is formed at the cut portion. An end surface is also formed at the punched portion. In the processing step, the shape may be further changed by bending, drawing, or the like. In this case, an unplated portion 41 may be formed on the plated surface.

[0041] [Compound Forming Step] In the compound forming step, a predetermined compound containing Mg is formed in the non-plated portion 41 (non-plated portion 41 on the end face and / or plated surface) where the plated layer 12 is not formed. － :1.0-100.0mM, SO ４ ２－ :0.1-10.0mM, Na ＋ :1.0-100.0mM, CO ３ ２－The plating layer 12 and the non-plated portion 41 where the plating layer 12 is not formed are brought into contact with a solution containing 1.0 to 100.0 mM of Cl, having a pH of 4.5 to 7.0 and a temperature of 25 to 60°C for 1 to 20 minutes. After the contact, the steel sheet is thoroughly dried for 5 to 20 minutes in an inert atmosphere such as nitrogen gas or argon gas at a temperature of 40 to 60°C and a relative humidity of 20 to 40%. － , S.O. ４ ２－ , Na ＋ , CO ３ ２－ If the concentration of the solution or the pH of the solution is outside the above range, adhesion between the compound formed in the non-plated portion 41 and the steel sheet 11 (base material) will be poor, and the specified compound will not be sufficiently formed in the non-plated portion 41. Furthermore, if the contact time is shorter than the above range, the specified compound will not be sufficiently formed in the non-plated portion 41. If the contact time exceeds 20 minutes, corrosion of the plated portion will progress, and the corrosion resistance of the plated portion may decrease. Furthermore, if the solution temperature is below 25°C or above 60°C, the specified compound will not be sufficiently formed in the non-plated portion. Furthermore, if the drying atmosphere is other than an inert atmosphere such as nitrogen gas or argon gas, red rust may occur in the non-plated portion. If the drying temperature is below 40°C or above 60°C, the specified compound may not be sufficiently formed in the non-plated portion, and if the drying temperature is above 60°C, drying may proceed too quickly and the compound may not remain in the non-plated portion. As a result, the specified compound may not be formed, and red rust may occur in the non-plated portion. If the relative humidity is below 20% or above 40%, the specified compound will not be sufficiently formed in the non-plated portion. As a result, the specified compounds are not formed, and red rust may occur in the non-plated parts. If the drying time is less than 5 minutes or more than 20 minutes, the specified compounds are not sufficiently formed in the non-plated parts. As a result, the specified compounds are not formed, and red rust may occur in the non-plated parts.

[0042] As the steel material, a hot-rolled steel sheet with a thickness of 4.5 mm that satisfied JIS G 3131:2018 was prepared. This steel sheet was subjected to hot-dip galvanizing to form a Zn-based coating layer having the chemical composition shown in Tables 1 to 6. The concentration (content) of impurities in the coating layer was 0.1% or less. The coating weight of the coating layer was 135 g / m on both the front and back surfaces of the coating surface. ２ It was decided.

[0043] The obtained plated steel sheets (surface-treated steel sheets) were cut with an electric shear to form end faces having portions with a plated layer and portions without a plated layer (where the steel sheet was exposed). No non-plated portions were formed on the plated surface. Of these plated steel sheets, for sample numbers 1-1 to 1-107 and 2-1 to 2-22, the end faces were contacted with the solutions shown in Tables 7 to 12 in order to form compounds containing Mg on the end faces. The end faces were then dried in a nitrogen gas atmosphere or in the atmospheres shown in Tables 13 to 18. Meanwhile, for sample numbers 2-23 to 2-27, compounds were formed by one of the following methods. Compound formation method 1: Immersed in a 5 mass% NaCl aqueous solution (pH: 5-6, solution temperature: 30°C) for 20 minutes. Compound formation method 2: Immersed in a 5 mass% NaCl aqueous solution (pH: 5-6, solution temperature: 25°C) for 72 hours. Compound formation method 3: After diluting 28.6 g of magnesium ethoxide with pure water to 200 cc, the solution was further diluted to 1 L with ethylene glycol monoethyl ether. The solution was applied by the pull-up method, dried, and then heat-treated at 100-400°C. Compound formation method 4: MgCl ２ 60 mol% of HCl, 20 mol% of NaCl, and 20 mol% of KCl, and the molten salt was heated and dissolved at 500°C. ２ In an atmosphere with a partial pressure of O of 16 mmHg, the current density was 20 A / dm 2 , and conduction time is set to 5 seconds, and cathodic electrolysis is performed. Compound formation method 5: Mg ２＋ 0.3 g / L and NO ３ － In an aqueous solution containing 0.5 g / L of HCl and having a pH of 7.0, the current density was 50 A / dm ２ , and conduct cathodic electrolysis for 5 seconds.

[0044] For the surface-treated steel sheet after the compound formation process, the compounds present on the edge surface were identified and the coverage rate on the edge surface was measured as described above. When multiple compounds were present, their abundance ratios were also determined. Although not shown in the table, the thickness of the compounds was adjusted to approximately 10 nm to 30 μm by varying the time the steel sheet was in contact with the solution. In addition, "no compound detected" in the table indicates that none of compounds A to J were detected. More specifically, fitting using standard samples of compounds A to J resulted in an R factor of over 5% in the region from 1300 to 1380 eV, meaning that fitting using standard samples of compounds A to J was not possible and it was not possible to determine the presence of at least one of compounds A to J.

[0045] XAFS analysis was carried out at beamline BL1N2 of the Aichi SR Center. The results are shown in Tables 19 to 24.

[0046] In addition, an exposure test was conducted on the surface-treated steel sheets after contact with the solution and drying, and the area ratio of red rust on the edge surface after 50 days was determined. The exposure conditions were as follows. The steel sheet samples were tilted 30° from horizontal so that the treated cut edge surface was at the top and placed facing south to conduct the atmospheric exposure test. After exposure, the samples were evaluated as follows based on the ratio of the area where red rust occurred to the area where the plating layer was not formed: SS: 70% or less S: More than 70% to 80% AA: More than 80% to 90% A: More than 90% to 100% B: More than 100% to 115% C: More than 115%. Samples with a red rust area ratio of SS, S, AA, or A after 50 days of exposure were determined to have excellent red rust resistance. Samples with a red rust area ratio of more than 100% were those where red rust occurred not only in areas where the plating layer was not formed but also in the surrounding areas.

[0047] Furthermore, to evaluate corrosion resistance under conditions more severe than atmospheric exposure, a 30-cycle test was conducted in accordance with JIS H8502:1999, Section 8.1 (Neutral salt spray cycle test method), and the sample was rated as follows based on the ratio of the area where red rust occurred to the area where no plating layer was formed: SS: 70% or less S: More than 70% to 80% AA: More than 80% to 90% A: More than 90% to 100% B: More than 100% to 115% C: More than 115% If the red rust area ratio after 30 cycles in the neutral salt spray test was SS, S, AA, A, or B, it was determined that the sample had even better red rust resistance.

[0048]

[0049]

[0050]

[0051]

[0052]

[0053]

[0054]

[0055]

[0056]

[0057]

[0058]

[0059]

[0060]

[0061]

[0062]

[0063]

[0064]

[0065]

[0066]

[0067]

[0068]

[0069]

[0070]

[0071]

[0072] As can be seen from Tables 1 to 24, surface-treated steel sheets having predetermined compounds on the end faces had excellent red rust resistance on the end faces. It was also found that the red rust resistance could be further improved depending on the type, ratio, coverage, and combination of compounds. On the other hand, when the predetermined compounds were not formed on the end faces, the red rust resistance of the end faces was poor. In sample numbers 2-23 to 2-27, which were subjected to compound formation methods 1 to 5, no Mg-containing compounds were formed in the non-plated portions, and only Zn-based compounds were formed.

[0073] According to the present invention, a surface-treated steel material can be provided in which the formation of red rust in non-plated portions is suppressed, and therefore the present invention has high industrial applicability.

[0074] REFERENCE SIGNS LIST 1 Surface-treated steel sheet (surface-treated steel material) 11 Steel sheet 12 Plated layer (Zn-based plated layer) 31 Compound 41 Non-plated portion 101 Surface 102 End face 103 Plated surface

Claims

1. A surface-treated steel material comprising: a steel material; and a plating layer formed on at least a portion of the surface of the steel material, the plating layer being a Zn-based plating layer containing 0.3 to 12.5 mass% Mg, and when the portion of the surface of the steel material where the plating layer is not formed is defined as a non-plated portion, at least a portion of the non-plated portion contains one or more of the following compounds A, B, C, D, E, F, G, H, I, and J. Compound A: MgO, Compound B: Mg(OH) ２ , Compound C: MgCO ３ , Compound D: Mg ４ A ２ (OH) １２ CO ３ ・3H ２ O, Compound E: Mg ６ A ２ (OH) １６ CO ３ ・4H ２ O, Compound F: Zn containing Mg ６ A ２ (OH) １６ CO ３ ・4H ２ O, Compound G: 4MgCO ３ Mg(OH) ２ ・5H ２ O, Compound H: Zn containing Mg ５ (CO ３ ) ２ (OH) ６ Compound I: Zn containing Mg ５ (OH) ８ C ２ ・H ２ O, Compound J: NaZn containing Mg ４ (SO ４ )Cl(OH) ６ ・6H ２ O.

2. The surface-treated steel material according to claim 1, characterized in that the plating layer contains 4.0 to 25.0 mass % Al.

3. The surface-treated steel material according to claim 1 or 2, characterized in that 50% or more of the area of ​​the non-plated portion is covered with the compound.

4. The surface-treated steel material according to any one of claims 1 to 3, characterized in that the compound comprises one or more selected from the group consisting of compound D, compound E, compound F, compound H, and compound I, and one or more selected from the group consisting of compound A, compound B, compound C, compound G, and compound J.

5. The surface-treated steel material according to any one of claims 1 to 4, characterized in that the compound includes two or more compounds selected from the group consisting of compound B, compound D, compound G, compound H, and compound I.

6. The surface-treated steel material according to any one of claims 1 to 5, characterized in that, among the compounds, the total composition ratio of one or two of the compounds H and I is 10% or more in molar ratio.

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