Surface treated steel

Abstract

The surface-treated steel of this case comprises: steel, and a plating layer formed on at least a portion of the surface of the aforementioned steel; the aforementioned plating layer is a Zn-based plating layer containing 0.3 to 12.5% ​​by mass of Mg; the portion of the aforementioned surface of the steel where the aforementioned plating layer is not formed is defined as a non-plated portion, and at least a portion of the aforementioned non-plated portion contains: MgO, Mg(OH)₂, MgCO₃, Mg₄Al₂(OH)₁₂CO₃・3H₂O, Mg₆Al₂(OH)₁₆CO₃・4H₂O, Zn₆Al₂(OH)₁₆CO₃・4H₂O containing Mg, 4MgCO₃・Mg(OH)₂・5H₂O, Zn₅(CO₃)₂(OH)₆ containing Mg, Zn₅(OH)₈Cl₂・H₂O containing Mg, and NaZn₄(SO₄)₄ containing Mg. 4) One or more compounds in Cl(OH)6・6H2O.

Description

Surface-treated steel Field of the Invention The present invention relates to surface-treated steel. This case claims priority based on Japanese Patent Application No. 2023-116278 filed in Japan on July 14, 2023, and incorporates its content herein by reference. Background of the Invention Among surface-treated steels with good corrosion resistance, zinc (Zn)-based plated steel sheets are most commonly used. These zinc-based plated steel sheets are used in various manufacturing industries such as the automotive, home appliance, and building material fields. For example, in the building material field, research has been conducted to improve the corrosion resistance of zinc-based plated steel sheets since ancient times in view of the demand for longer service life of building materials. Among these, there has been a continuous review of adding Al and Mg to the zinc-based plating layer to improve corrosion resistance. For example, Patent Documents 1 to 4 disclose a plated steel sheet containing a certain amount of Al and Mg, which has achieved high corrosion resistance. [Prior Art Documents] [Patent Documents] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-193791 [Patent Document 2] International Publication No. 2011 / 001662 [Patent Document 3] Japanese Patent Application Laid-Open No. 2021-172878 [Patent Document 4] Japanese Patent Application Publication No. 2016-519220 Summary of the Invention Problems to be Solved by the Invention The plated steel sheets disclosed in the above Patent Documents 1 to 4 are excellent in long-term corrosion resistance of the planar part. However, when the plated steel sheet is used, it is sometimes cut into a predetermined size. At this time, no plating layer is formed on the cut surface (cut end face). Also, even on the surface where plating is applied, there may be unplated parts or damage, resulting in peeling of the plating layer, or cracks may occur in the plating layer due to cutting, punching, bending, stretching, or other processing, so there are parts where no plating layer is formed (exposing the steel sheet). As a result of investigations by the inventors of this case, it was found that in the plated steel sheets of Patent Documents 1 to 3, although the corrosion resistance of the plated part is excellent, in the initial stage of corrosion, red rust sometimes occurs in the non-plated parts such as the cut end face, unplated parts, or parts where the steel sheet is exposed due to damage or processing after the plating layer is formed (collectively referred to as non-plated parts). Therefore, there has been a continuous pursuit of technological development to suppress the generation of red rust in such non-plated parts. In view of the above background, the present invention is represented by a surface-treated steel sheet having a Zn-based plating layer containing Mg and is premised on this surface-treated steel. The object of the present invention is to provide a surface-treated steel that can suppress the generation of red rust in non-plated parts. Means for Solving the Problems The inventors of this case conducted investigations on the above problems. As a result, it was found that in non-plated parts where no plating layer is formed, by making a predetermined Mg-containing compound present on the surface of the steel sheet, the generation of red rust can be suppressed. The present invention has been completed in view of the above viewpoints. The gist of the present invention is as follows. [1] The surface-treated steel material of one aspect of the present invention has: a steel material, and a plating layer formed on at least a part of the surface of the aforementioned steel material; the aforementioned plating layer is a Zn-based plating layer containing 0.3 to 12.5% by mass of Mg; a part of the aforementioned surface of the aforementioned steel material where the aforementioned plating layer is not formed is defined as a non-plated part. At this time, one or more of the following compounds A, B, C, D, E, F, G, H, I, and J are present in at least a part of the aforementioned non-plated part: 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: NaZn containing Mg 4 (SO 4 )Cl(OH) 6 ・6H 2 O. [2] The surface-treated steel material as described in [1], wherein the plating layer may also contain 4.0 to 25.0% by mass of Al. [3] The surface-treated steel material as described in [1] or [2], wherein 50% or more by area ratio may be covered with the aforementioned compound. [4] The surface-treated steel material as described in any one of [1] to [3], wherein the aforementioned compound may also contain: one or more selected from the group consisting of the aforementioned Compound D, the aforementioned Compound E, the aforementioned Compound F, the aforementioned Compound H, and the aforementioned Compound I; and one or more selected from the group consisting of the aforementioned Compound A, the aforementioned Compound B, the aforementioned Compound C, the aforementioned Compound G, and the aforementioned Compound J. [5] The surface-treated steel material as described in any one of [1] to [4], wherein the aforementioned compound may also contain two or more selected from the group consisting of the aforementioned Compound B, the aforementioned Compound D, the aforementioned Compound G, the aforementioned Compound H, and the aforementioned Compound I. [6] The surface-treated steel material as described in any one of [1] to [5], wherein, among the aforementioned compounds, the total composition ratio of one or two of the aforementioned Compound H and the aforementioned Compound I may be 10% or more in terms of molar ratio. Advantageous Effects of the Invention According to the above aspect of the present invention, a surface-treated steel material capable of suppressing the generation of red rust in non-plated portions can be provided. Embodiments of the present invention Forms for implementing the invention Regarding the surface-treated steel material of an embodiment of the present invention (the surface-treated steel material of this embodiment), the surface-treated steel plate will be taken as an example for description. As shown in FIG. 1, an example of the surface-treated steel material of this embodiment, that is, the surface-treated steel plate 1 (hereinafter, the surface-treated steel plate of this embodiment) has: a steel plate 11 (base steel plate), and a plating layer 12 formed on at least a part of the surface 101 of the aforementioned steel plate 11; a part of the aforementioned surface 101 of the aforementioned steel plate 11 where the aforementioned plating layer 12 is not formed is defined as a non-plated part 41. At this time, a predetermined Mg-containing compound 31 exists in at least a part of the non-plated part 41 of the aforementioned steel plate 11. In FIG. 1, among the surface 101, the surface in contact with the plating bath and on which the plating layer is formed is the plating surface 103, and the surface exposed when cut into a predetermined size after being lifted from the plating bath is the end surface 102. The end surface 102 is in a direction intersecting the plating surface 103, and in most cases, it is substantially perpendicular to the plating surface 103. The shape of the surface-treated steel material of this embodiment is not limited to a steel plate. It can also be, for example: the shape after bending the steel plate, the shape of a steel pipe, the shape of a steel bar, a steel wire, or the shape of a steel section such as an H-shaped or T-shaped cross-sectional shape. Hereinafter, taking the surface-treated steel plate as an example, the surface-treated steel material of this embodiment will be described in detail. In the following description, the numerical range indicated by "~" means: a range including the numerical values described before and after "~" as the lower limit value and the upper limit value. However, the numerical range when the numerical values described before and after "~" are marked with "greater than" or "less than" means: a range not including these numerical values as the lower limit value or the upper limit value. <Steel plate (steel material)> The surface-treated steel plate 1 of this embodiment is characterized by the plating layer 12 and the compound 31. Therefore, there is no particular limitation on the steel plate 11. The steel plate 11 can be determined according to the products to be applied or the required strength, plate thickness, etc. For example, hot-rolled steel plates described in JIS G 3131:2018, JIS G 3113:2018, etc., and cold-rolled steel plates described in JIS G 3141:2021, JIS G 3135:2018, etc. can be used. As described above, steel materials such as steel pipes, steel wires, and various members made of steel other than steel plates can also be used. The plate thickness is not limited, but the appropriate plate thickness range is 1.0~9.0 mm. <Coating layer> In the surface-treated steel sheet 1 of the present embodiment, a coating layer 12 is formed on at least a part of the surface of the steel sheet 11. The coating layer 12 is a Zn-based coating layer containing 0.3 mass% or more and 12.5 mass% or less of Mg. The coating layer may further contain 4.0 mass% or more and 25.0 mass% or less of Al. In the present embodiment, the so-called Zn-based coating layer is a coating layer having a Zn concentration of 50.0 mass% or more. In the coating layer 12 of the surface-treated steel sheet 1 of the present embodiment, Zn and Mg, or Zn, Mg, and Al mostly form alloys in the coating layer, but the state of existence of Zn, Mg, and Al is not limited. Although the coating layer 12 can be formed on the entire plating surface 103 (front and back surfaces (for a cut plating steel sheet, mostly the surfaces other than the end faces)) of the steel sheet 11 (100% in terms of area ratio), there may be parts (non-plated parts 41) where the coating layer 12 is not formed due to non-plating, damage, etc. resulting in peeling. The area ratio of the non-plated part 41 should be 10% or less of the entire plating surface. The area ratio of the non-plated part 41 on the plating surface 103 can also be 0%. The coating layer 12 can also be formed on a part of the surface other than the plating surface 103 in the surface 101 (the end face 102 in Fig. 1), but if it is a surface-treated steel sheet cut into a predetermined size after forming the coating layer, the end face (cut end face) mostly does not form the coating layer. Regarding the area ratio of the non-plated part 41, it is sufficient that it is greater than 0% of the entire surface, which includes the surface other than the plating surface 103. In the surface-treated steel sheet 1 of the present embodiment, in addition to making the coating layer 12 a Zn-based coating layer 12 containing Mg, the specific treatment described later is performed, whereby the generation of red rust can be suppressed (the red rust resistance can be improved) even in the non-plated part 41. Although the reason is unknown, it is considered that due to the specific treatment, Mg contained in the Zn-based coating layer 12 dissolved by sacrificial corrosion generates the compound described later in the non-plated part 41. If the coating layer 12 is not a Zn-based coating layer containing Mg, the effect of forming the compound 31 cannot be obtained sufficiently. Also, even if the steel sheet 11 contains Mg, since the amount of Mg contained in the steel sheet 11 is trace, and Mg dissolves less from the steel sheet 11, the same effect cannot be obtained. In order to obtain the above effect, the Mg concentration (content) contained in the Zn-based coating layer 12 is set to 0.3 mass% or more and 12.5 mass% or less. When the Mg concentration (content) is less than 0.3 mass%, a Mg-containing compound cannot be formed. Therefore, the Mg concentration is set to 0.3 mass% or more. On the other hand, when the Mg concentration is greater than 12.5 mass%, the workability will decrease. Therefore, the Mg concentration is set to 12.5 mass% or less. In the plating layer 12 (Zn-based plating layer), the concentrations (contents) of elements other than those described above are not limited. However, the chemical composition of the plating layer 12 is, by 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%, 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%, 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. Thus, including the part where the plating layer 12 is formed, excellent corrosion resistance can be obtained for the surface-treated steel sheet 1, and thus it is suitable. Explain the reasons for the suitable chemical composition of the plating layer 12. Unless otherwise specified, the % related to the concentration (content) of each element in the chemical composition of the plating layer 12 is mass%. [Mg: 0.3 to 12.5%] In order to form Mg-containing compounds, the Mg concentration is 0.3% or more. Mg is also an element that has the effect of improving the corrosion resistance of the plating layer 12. To obtain the effect of improving corrosion resistance, the Mg concentration is preferably set at 0.5% or more. The Mg concentration is more preferably set at 1.0% or more, and even more preferably 3.0% or more. On the other hand, when the Mg concentration is greater than 12.5%, in addition to the saturation of the effect of improving corrosion resistance, the workability of the plating layer may sometimes decrease. There may also be manufacturing problems such as an increase in the amount of scum generated in the plating bath. Therefore, the Mg concentration is set at 12.5% or less. The Mg concentration is more preferably 10.0% or less, and even more preferably 8.0% or less. [Al: 0 to 25.0%] Al is an effective element for improving corrosion resistance in the plating layer (Zn-based plating layer) 12. Therefore, although the lower limit of the Al concentration is 0%, Al can also be contained. To fully obtain the above effect, the Al concentration is preferably set at 2.0% or more or 4.0% or more. The Al concentration can also be set at 6.0% or more or 8.0% or more according to requirements. On the other hand, when the Al concentration is greater than 25.0%, the sacrificial corrosion protection effect of the plating layer 12 will decrease. Therefore, the Al concentration is preferably 25.0% or less. The Al concentration can also be set at 20.0% or less or 16.0% or less according to requirements. [Sn: 0 to 20.0%] [Bi: 0 to less than 5.0%] [In: 0 to less than 2.0%] These elements are elements that help improve corrosion resistance and sacrificial corrosion protection. Therefore, although the lower limit of the concentration of these elements is 0%, any one or more of them can also be contained. To obtain the above effects, the concentration should preferably be set to 0.05% or more respectively. Among these, Sn is suitable because it is a low-melting metal and can be easily contained without damaging the properties of the plating bath. On the other hand, when the Sn concentration is greater than 20.0%, the Bi concentration is 5.0% or more, or the In concentration is 2.0% or more, the corrosion resistance will decrease. Therefore, it is preferably set to: Sn concentration of 20% or less, Bi concentration of less than 5.0%, and In concentration of less than 2.0%. [Ca: 0 to 3.0%] The element Ca helps improve plating manufacturability by reducing the formation amount of scum that is easily formed during operation. Therefore, although the lower limit of the Ca concentration is 0%, Ca can also be contained. To obtain this effect, the Ca concentration should preferably be set to 0.1% or more. On the other hand, if the Ca concentration is high, the corrosion resistance of the planar part of the plating layer 12 itself tends to deteriorate, and the corrosion resistance around the welded part may sometimes deteriorate. Therefore, the Ca concentration should preferably be 3.0% or less. [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 help improve corrosion resistance. Although the lower limit of the concentration of these elements is 0%, to obtain this effect, one or more of them should preferably be contained at 0.05% or more respectively. On the other hand, when the concentration of these elements is excessive, the viscosity of the plating bath will increase, and it will mostly become difficult to build the plating bath itself, and it may be impossible to manufacture steel materials with good plating properties. Therefore, it is preferably set to: Y concentration of 0.5% or less, La concentration of less than 0.5%, and Ce concentration of less than 0.5%. [Si: 0 to less than 2.5%] Si is an element that helps improve corrosion resistance. Also, Si is an element that, when forming the plating layer 12 on the steel plate 11, inhibits the alloy layer formed between the surface of the steel plate 11 and the plating layer 12 from becoming too thick, and has the effect of improving the adhesion between the steel plate 11 and the plating layer 12. Although the lower limit of the Si concentration is 0%, to obtain these effects, the Si concentration should preferably be set to 0.1% or more. The Si concentration is more preferably 0.2% or more. On the other hand, when the Si concentration reaches 2.5% or more, an excessive amount of Si will precipitate in the plating layer 12, not only reducing the corrosion resistance but also reducing the workability of the plating layer 12. Accordingly, the Si concentration should preferably be set to less than 2.5%. The Si concentration is more preferably 1.5% or less. [Cr: 0 ~ less than 0.25%] [Ti: 0 ~ less than 0.25%] [Ni: 0 ~ less than 0.25%] [Co: 0 ~ less than 0.25%] [V: 0 ~ less than 0.25%] [Nb: 0 ~ less than 0.25%] [Cu: 0 ~ less than 0.25% ~] These elements are elements that help improve corrosion resistance. Although the lower limit of concentration of such elements is 0%, if the effect is to be obtained, the concentration of more than 1 species of such elements shall be set to more than 0.05%. On the other hand, when the concentration of these elements is excessive, the viscosity of the coating bath will be improved, and the construction of the coating bath itself will mostly become difficult, fearing that it is not possible to produce steel in good condition of the coating properties. Therefore, the concentration of each element should be set to be less than 0.25%. [Fe: 0~5.0%] Fe is sometimes mixed into the coating layer 12 in the manufacture of the coating layer 12 . Sometimes it will contain to about 5.0%, but if this ranges, the degree of adverse effect on the effect of the surface-treated steel plate 1 of the present embodiment is small. Therefore, the Fe concentration should be set below 5.0%. No need to contain Fe. The lower limit of Fe concentration is 0%. [Sr: 0 ~ less than 0.5%] [Sb: 0 ~ less than 0.5%] [Pb: 0 ~ less than 0.5%] When Sr, Sb, and Pb are contained in the coating layer 12, the appearance of the coating layer 12 changes and zinc flowers will form. Although the lower limit of concentration of these elements is 0%, if the effect is to be obtained, the concentration of more than 1 species of Sr, Sb, and Pb should be set to 0.05% or more, rather than 0.1% or more. On the other hand, when the concentration of these elements is excessive, the viscosity of the coating bath will be improved, and the construction of the coating bath itself will mostly become difficult, fearing that it is not possible to produce steel in good condition of the coating properties. Therefore, the concentration of each element should be set to less than 0.5% respectively. [B: 0~less than 0.5%] When this element B is contained in the coating layer 12, it combines with Zn, Al, Mg, etc. to produce various intermetallic compounds. The intermetallic compounds had the effect of improving LME. Although the lower limit of B concentration is 0%, if the effect is to be obtained, the B concentration should be set to more than 0.05%, rather than to more than 0.1%. On the other hand, when the concentration of B is too high, the coating melting point will be significantly improved, the plating operability will deteriorate, and it is feared that surface-treated steel plates with good plating properties condition cannot be obtained1. Therefore, the B concentration should be set to less than 0.5%. [Remaining portion: Zn and impurities] In the chemical composition of the plating layer 12, it suffices that, other than the above elements, there are Zn and impurities. 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 the present embodiment, the so-called Zn-based plating layer means that the Zn concentration in the plating layer 12 is 50.0% or more. The so-called impurities are mainly elements mixed in from raw materials and the like during the manufacturing process. Usually, the total concentration of impurities is 0.5% or less, preferably 0.1% or less. For various reasons such as reducing raw material costs, sometimes raw materials and the like with a relatively large content of elements other than the above-mentioned elements including Zn are deliberately used. Thus, in the present embodiment, regardless of the mixing or deliberate addition of such elements (elements other than the above-mentioned elements including Zn), these elements are regarded as impurity elements. Therefore, the total concentration of these elements is preferably set to 0.5% or less. The adhesion amount of the plating layer 12 is not limited, however, in order to improve the corrosion resistance, it is preferably 10 g / m per single side. 2 Above. As needed, in order to further improve the corrosion resistance, it may also be set to 20 g / m per single side. 2 Above, 40 g / m 2 Above or 60 g / m 2 Above. On the other hand, even if the adhesion amount is greater than 400 g / m per single side 2 and the corrosion resistance has reached saturation, it is also not beneficial in terms of economy. Therefore, the adhesion amount per single side is preferably 400 g / m 2 Or less. As needed, in order to further improve the economy, it may also be set to 350 g / m per single side 2 Or less, 300 g / m 2 Or less or 250 g / m 2 Or less. The chemical composition of the plating layer 12 can be measured by the following method. First, an acid containing an inhibitor that can suppress the corrosion of the base iron (steel plate 11) (for example, an acid obtained by adding 1% of HIBIRON (A-6) (manufactured by Sugimura Chemical Industry Co., Ltd.) to 10% hydrochloric acid) is used to strip and dissolve the plating layer 12 to obtain an acid solution. Then, the obtained acid solution is measured by ICP analysis, whereby the chemical composition of the plating layer 12 can be obtained. Regarding the adhesion amount of the plating layer 12, the method described above was used to measure the change in the mass (weight) of the sample (a sample taken from the surface-treated steel sheet 1) before and after the plating layer 12 was stripped and dissolved through an acid containing an inhibitor, and the adhesion amount was calculated from the results. <Compound> Regarding the surface-treated steel sheet 1 of the present embodiment, a compound 31 containing Mg is present in at least a part of the non-plated portion 41 on the surface 101 (the plating surface 103 and the end surface 102) of the steel sheet 11. The compound contains one or more selected from the following (substantially composed of one or more selected from the following, but allowing the inclusion of 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: NaZn containing Mg 4 (SO 4 )Cl(OH) 6 ・6H 2 O Herein, the description of "~ containing Mg" means that although Mg is not contained in the chemical formula, a part of the elements in the chemical formula is replaced by Mg, or Mg penetrates into the compound and contains Mg in the form of the compound. Regarding Compound F, Compound H, Compound I, and Compound J with the description of "~ containing Mg", the specific Mg concentration (Mg content) of each compound including them depends on the production steps of the reagents described later. The Mg concentration (Mg content) of Compound F, Compound H, Compound I, and Compound J obtained by the production steps of the reagents described later is 0.1% or more by mass. The Mg amount of these compounds can be easily measured by a known ICP emission spectroscopic analysis test. In the non-plated portion 41, the corrosion resistance is improved and the formation of red rust is suppressed due to the presence of these compounds. Although the reason is unknown, after the inventors of the present case performed electrochemical measurement on the end face, it was found that compared with the case where these compounds do not exist, when these compounds exist, the current value can be suppressed on both the cathode side and the anode side (especially the suppression on the anode side is larger). From this, it can be considered that the reason is due to the physical protection effect (suppressing the cathode reaction) brought about by the presence of these compounds; or, when these Mg-containing compounds dissolve in the moisture in the environment, the passivation effect (suppressing the anode reaction) caused by the increase in pH near the surface occurs. Even for a compound containing Mg, if it is a compound other than the above, the above effects cannot be obtained, and thus the target effect cannot be achieved. The compound preferably contains: one or more selected from Group a below, and one or more 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 compounds with a significant effect as follows: the physical protection effect (inhibiting the cathodic reaction) brought about by these compounds enhances the red rust resistance; the compounds in Group b are compounds with a significant effect as follows: the passivation effect (anodic reaction inhibition) brought about by the increase in pH near the surface when these Mg-containing compounds dissolve in the moisture in the environment enhances the red rust resistance. By simultaneously containing the compounds in Group a and Group b, a better red rust inhibition effect than when only one group of compounds is contained is obtained through an additive effect. Furthermore, from the viewpoint of enhancing the corrosion resistance, the compound preferably contains two or more selected from the group consisting of Compound B, Compound D, Compound G, Compound H, and Compound I. It may also be substantially composed of two or more selected from the above group. Among the compounds, the total composition ratio of one or both of Compound H and Compound I in terms of the molar ratio (mole ratio) is preferably 10% or more. Moreover, although the above compounds can obtain the effect of enhancing the corrosion resistance (the effect of enhancing the red rust resistance), if a sufficient effect is to be obtained on the entire surface-treated steel sheet 1, in the non-plated portion 41 where the plating layer 12 is not formed, it is preferably that 50% or more is covered by the above compound in terms of the area ratio. The covered area ratio can also be 100%. For the identification of the compound present in the non-plated portion 41, it can be obtained by performing X-ray Absorption Fine Structure analysis (hereinafter referred to as XAFS analysis) and performing fitting processing on the XAFS spectrum. Specifically, it is obtained by the following method. First, a sample with a thickness of, for example, 7 mm × 7 mm is cut out from the surface-treated steel sheet 1, and the sample covers, for example, the non-plated portion 41 to be measured. XAFS is obtained by performing XAFS analysis on the non-plated portion 41 (for example, in the range of 1.0 mm × 1.2 mm) in the sample. For the obtained spectrum, Athena (analysis software) is used and fitting is performed with a linear combination of the standard sample spectra of each compound, thereby identifying the compound. The measurement conditions during XAFS analysis are set as follows. - Measure the K absorption edge of Mg - Measurement gas environment: High vacuum - Measurement temperature: Room temperature - Energy range: 1250 eV to 1540 eV (step: 0.2 eV) - Incident X-ray intensity I 0 is obtained from the sample current of the Au mesh. - The X-ray intensity I is measured by the fluorescence yield method (SDD detector) and the total electron yield method (sample current method). - Before measuring the sample, the Au4f peak position of XPS is measured for energy calibration. - To improve the S / N ratio, three measurements are performed, and the average value of the spectrum is used for analysis. Also, the fitting is performed based on the following criteria. - Regarding energy, calibration is performed based on the Au4f peak position of XPS. - As shown in Figure 2, the overall intensity is normalized in such a way that the background is subtracted and the intensity difference between the pre-edge and the post-edge reaches 1. - The spectrum obtained from the sample is fitted with a linear combination of the standard sample spectra of each compound. The appropriateness of the fitting is confirmed using the R factor. If the R factor is 5% or less in the region up to 1300 to 1380 eV, it is judged to be appropriate. If the R factor is greater than 5%, it is judged that fitting cannot be performed. The inability to fit with the standard samples of compounds A to J means that it is impossible to determine the presence of at least one of compounds A to J. The R factor is calculated by the following formula. Here, d' in the formula represents the fitting data (the spectral data after linearly combining the spectra of each compound), and d represents the measurement data. R factor = Σ(d' - d) 2 / Σd 2When the sum of the composition ratios of each compound is defined as 100%, a compound with a composition ratio of 1% or more is determined to be "present". At this time, the spectrum obtained from the sample is approximated by a linear combination of spectra obtained by multiplying the standard sample spectra of each compound by coefficients (that is, when A, B,..., J are the spectra of compounds A, B,..., J, and a, b,..., j are the coefficients, the spectrum of the sample = aA + bB +... jJ and a + b +... j = 100% for approximation). Each of the coefficients is defined as the composition ratio of each compound. The units of a, b, c,..., j are the molar ratios of compounds A, B, C,..., J, respectively. When performing the above fitting, the standard samples of each compound are reagents commercially available or prepared based on the following criteria. - Compound A (MgO): (commercially available reagent) manufactured by Fuji Film Wako Pure Chemical Corporation, product name: Magnesium Oxide - Compound B (Mg(OH) 2 ): (commercially available reagent) manufactured by Kanto Chemical Co., Inc., product name: Magnesium Hydroxide - Compound C (MgCO 3 ): Production steps: Weigh and mix monoethylene glycol (purity 99.9%, 950 g) and distilled water (50 g) in a 1 L screw cap vial. Add NaCl to make the concentration reach 1 mol / kg. In a three-neck round-bottom flask containing the monoethylene glycol + water + NaCl solution (250 g), add 10.0 ± 0.1 g of 4MgCO 3 ·Mg(OH) 2 ·5H 2 O. At this time, use a reflux condenser. Open the mixture to the atmosphere and stir it for 3 days under continuous CO 2 bubbling (20 - 50 mL / min). When stirring, use a thermostat and keep the temperature at 150 ± 5 °C. After stirring, filter the precipitate by suction and dry it. - Compound D (Mg 4 Al 2 (OH) 12 CO 3 ·3H 2 O): Production steps: Prepare 0.20 M MgCl 2-0.1M AlCl 3 solution (where the amount of MgCl 2 is set within the range of 0.019M to 0.020M MgCl 2 ) is dropped into 0.1M Na 2 CO 3 and adjusted to pH 10, then left for 24 hours, after which, suction filtration is carried out and it is dried. ・Compound E (Mg 6 Al 2 (OH) 16 CO 3 ・4H 2 O): (commercially available reagent) manufactured by Fuji Film and Wako Pure Chemical Industries, Ltd., product name: Hydrotalcite ・Compound F (Zn containing Mg 6 Al 2 (OH) 16 CO 3 ・4H 2 O): Production steps: 0.2M ZnCl 2 -0.1M AlCl 3 -0.050M MgCl 2 solution (where the amount of MgCl 2 is set within the range of 0.045M to 0.055M MgCl 2 ) is dropped into 0.1M Na 2 CO 3 and adjusted to pH 10, then left for 24 hours, after which, suction filtration is carried out and it is dried. ・Compound G (4MgCO 3 ・Mg(OH) 2 ・5H 2 O): (Commercially available reagent) Manufactured by Kanto Chemical Co., Inc., Product name: Magnesium carbonate hydroxide, Compound H (Zn containing Mg 5 (CO 3 ) 2 (OH) 6 ): Production steps: Add 0.1M Na 2 CO 3 dropwise into 0.1M ZnCl 2 -0.050M MgCl 2 solution (where the amount of MgCl 2 is determined to be in the range of 0.045M to 0.055M MgCl 2 ) and adjust to pH 10, then leave for 24 hours, and then perform suction filtration and dry it. Compound I (Zn containing Mg 5 (OH) 8 Cl 2 ・H 2 O): Production steps: Add 0.1M NaOH dropwise into 0.1M ZnCl 2 -0.050M MgCl 2 solution (where the amount of MgCl 2 is determined to be in the range of 0.045M to 0.055M MgCl 2 ) and adjust to pH 10, then leave for 24 hours, and then perform suction filtration and dry it. Compound J (NaZn containing Mg 4 (SO 4 )Cl(OH) 6 ・6H 2O): Manufacturing steps: In 0.5 M ZnSO 4 -0.10 M MgCl 2 (where the amount of MgCl 2 is defined as 0.09 M to 0.011 M MgCl 2 within the range of)-In 30 mL of 1.4 M NaCl solution, add 1 g of ZnO powder, and drop in 0.1 M NaOH to adjust the pH to 10, then stir for 120 hours. After that, perform suction filtration and dry it. Also, the compound coating rate (coating area rate) in the non-plated portion 41 is obtained by the following method. For the portion where the plating layer 12 is not formed (non-plated portion 41), perform Mg distribution analysis through μ-XRF (micro-X-Ray Fluorescence), and measure the intensity of the μ-XRF spectrum. The area ratio of the region where the Mg concentration is 0.5 atomic% or more with respect to the area of the non-plated portion 41 where the plating layer 12 is not formed is defined as the "compound coating rate". At this time, μ-XRF is set to the following measurement conditions. Measurement gas environment: Vacuum Acceleration voltage: 15 kV Current value: 50 μA Tube target: Rh tube target Scanning speed: 4.00 mmS -1 Multi-functional measuring instrument: 30 μm <Manufacturing method> Regarding the surface-treated steel sheet 1 of this embodiment, regardless of the manufacturing method, if it has the above characteristics, the effects can be obtained. However, it can be manufactured through a manufacturing method including the following steps. (I) Plating step: On the surface of the steel sheet 11 (base material steel sheet), form a Zn-based plating layer 12 containing Mg; (II) Processing step: For the steel sheet (plated steel sheet) on which the plating layer 12 (Zn-based plating layer) is formed, perform cutting and / or blanking to make the plated steel sheet into an arbitrary shape; and (III) Compound formation step: Form a predetermined compound containing Mg in the non-plated portion 41 of the end face and / or the plating surface. Appropriate conditions will be described for each step. [Plating Step] In the plating step, a steel material such as a steel plate is immersed in a plating bath containing Mg and Zn, or electroplated, whereby a plating layer 12 is formed on the surface. The formation conditions of the plating layer 12 are not particularly limited. It can be carried out by a usual method to obtain sufficient plating adhesion. Also, the steel material supplied to the plating step or its manufacturing method is not limited. If it is a surface-treated steel plate, for example, hot-rolled steel plates described in JIS G 3113:2018 and JIS G 3131:2018 or cold-rolled steel plates described in JIS G 3141:2021 and JIS G 3135:2018 can be used as the steel plates immersed in the plating bath. Also, steel materials such as steel pipes, steel wires, and various members made of steel other than steel plates can be used. The plating bath composition can be adjusted according to the chemical composition of the desired plating layer 12. After lifting the steel material from the plating bath, the adhesion amount of the plating layer 12 can be adjusted by wiping as required. [Processing Step] In the processing step, cutting and / or punching are performed to form the plated steel plate into an arbitrary shape. Once cutting or punching is performed, an end face without the plating layer 12 is formed at the cut portion. The same end face is also formed at the punched portion. In the processing step, bending processing, drawing processing, etc. can also be further performed to change the shape. At this time, a non-plated portion 41 may be generated on the plating surface. [Compound Formation Step] In the compound formation step, a predetermined compound containing Mg is formed in the non-plated portion 41 (end face and / or non-plated portion 41 on the plating surface) where the plating layer 12 is not formed. To form the compound, for the steel plate after the processing step, the following solution is brought into contact with the plating layer 12 and the non-plated portion 41 where the plating layer 12 is not formed, and contacted for 1 to 20 minutes; the solution contains: Cl - : 1.0 to 100.0 mM, SO 4 2- : 0.1 to 10.0 mM, Na + : 1.0 to 100.0 mM, CO 3 2- : 1.0 to 100.0 mM, with a pH of 4.5 to 7.0 and a liquid temperature of 25 to 60 °C. After the above contact, in an inert gas environment such as nitrogen or argon, and in a gas environment with a temperature of 40 to 60 °C and a relative humidity of 20 to 40%, the steel plate is sufficiently dried for 5 to 20 minutes. If Cl in the solution - 、SO 4 2- 、 Na + 、 CO 3 2- If the concentrations of, and the solution pH are outside the above ranges, the adhesion between the compound formed in the non-plated portion 41 and the steel plate 11 (substrate) will deteriorate, and it will be impossible to sufficiently form the predetermined compound in the non-plated portion 41. Also, if the contact time is shorter than the above range, the compound will not be able to sufficiently form the predetermined compound in the non-plated portion 41. If the contact time is greater than 20 minutes, the plated portion may be corroded and the corrosion resistance of the plated portion will decrease. Also, when the temperature of the solution is less than 25°C or greater than 60°C, the predetermined compound formed in the non-plated portion will be insufficient. Also, when the dry gas environment is other than an inert gas environment such as nitrogen or argon, red rust may sometimes occur in the non-plated portion. When the drying temperature is less than 40°C or greater than 60°C, the predetermined compound formed in the non-plated portion may be insufficient; or, when it is greater than 60°C, since drying progresses rapidly, the compound may sometimes not remain in the non-plated portion. As a result, the predetermined compound may sometimes not be formed and red rust may occur in the non-plated portion. When the relative humidity is less than 20% or greater than 40%, the predetermined compound formed in the non-plated portion will be insufficient. As a result, the predetermined compound may sometimes not be formed and red rust may occur in the non-plated portion. When the drying time is less than 5 minutes or greater than 20 minutes, the predetermined compound formed in the non-plated portion will be insufficient. As a result, the predetermined compound may sometimes not be formed and red rust may occur in the non-plated portion. [Examples] A hot-rolled steel plate with a thickness of 4.5 mm that meets JIS G 3131:2018 was prepared as the steel material. The steel plate was subjected to hot-dip plating to form a Zn-based plating layer having the chemical compositions described in Tables 1 to 6. The impurity concentration (content) in the plating layer was 0.1% or less. Also, regarding the coating weight of the plating layer, both the front and back sides of the plated surface were set to 135 g / m 2 。 The plated steel sheet (surface-treated steel sheet) obtained by cutting with an electric shearing machine is formed with an end face having: a portion with a plating layer and a portion without a plating layer (exposed steel sheet). A non-plated portion is not formed on the plating surface. Among the plated steel sheets, for sample numbers 1-1 to 1-107 and 2-1 to 2-22, since a Mg-containing compound is formed on the end face, the solutions shown in Tables 7 to 12 are brought into contact with the end face. Thereafter, it is dried in a nitrogen gas environment and in the gas environments described in Tables 13 to 18. On the other hand, for sample numbers 2-23 to 2-27, a compound is expected to be formed by any of the following methods. - Compound formation method 1: Immersion in 5 mass% NaCl aqueous solution (pH: 5 to 6, solution temperature: 30 °C) for 20 minutes - Compound formation method 2: Immersion in 5 mass% NaCl aqueous solution (pH: 5 to 6, solution temperature: 25 °C) for 72 hours - Compound formation method 3: 28.6 g of magnesium ethoxide is diluted with pure water to 200 cc and further diluted with ethylene glycol monoethyl ether to 1 L to obtain a plating bath. Using this plating bath, coating is performed by the lifting method and dried, and then heat treatment is carried out at 100 to 400 °C - Compound formation method 4: Using a molten salt and the molten salt is MgCl 2 : 60 mol%, NaCl: 20 mol%, KCl: 20 mol% and heated to 500 °C to melt, in an H 2 O partial pressure of 16 mmHg gas environment, the current density is set to 20 A / dm 2 and the energization time is set to 5 seconds to perform cathodic electrolysis treatment. - Compound formation method 5: In an aqueous solution containing Mg 2+ : 0.3 g / L and NO 3- : 0.5 g / L and pH: 7.0, the current density is set to 50 A / dm 2 and the energization time is 5 seconds to perform cathodic electrolysis treatment For the surface-treated steel sheet after the compound formation step, according to the above criteria, the compounds present on the end face are identified and the coating rate in the end face is measured. When multiple compounds are present, their existence ratios are also determined. Regarding the compound thickness, although not listed in the table, it was made to be around 10 nm to 30 μm by changing the contact time between the steel sheet and the solution. Also, in the table, the compound was not detected, which means that none of the compounds A to J were detected. More specifically, when fitting through the standard samples of compounds A to J, in the region up to 1300 to 1380 eV, the R factor is greater than 5%, and fitting cannot be performed through the standard samples of compounds A to J, meaning that the existence of at least one of the compounds A to J cannot be determined. The XAFS analysis was carried out using the beamline BL1N2 of the Aichi SR Center. The results are shown in Tables 19 to 24. Also, for the surface-treated steel sheet after contacting the solution and drying, an exposure test was performed, and the red rust area ratio in the end face after 50 days was calculated. The exposure conditions are as described below. The atmospheric exposure test was carried out with the processed cut end face as the upper part, setting the steel sheet sample to be inclined 30° from the horizontal and facing south. After exposure, the ratio of the area where red rust occurred in the sample to the area where no plating layer was formed was evaluated as follows. SS: 70% or less; S: greater than 70% and 80% or less; AA: greater than 80% and 90% or less; A: greater than 90% and 100% or less; B: greater than 100% and 115% or less; C: greater than 115%. When the red rust area ratio after 50 days of exposure is SS, S, AA, or A, it is judged that the red rust resistance is excellent. When the ratio of the area where red rust occurred is greater than 100%, it is the following situation: red rust occurs not only in the part where no plating layer was formed, but also around it. Also, for the corrosion resistance evaluation under conditions more severe than exposure to the atmosphere, a test of 30 cycles was carried out in accordance with 8.1 (Neutral Salt Spray Cycle Test Method) of JIS H8502:1999, and the ratio of the area where red rust occurred in the sample to the area where no plating layer was formed was evaluated as follows. SS: 70% or less; S: greater than 70% and 80% or less; AA: greater than 80% and 90% or less; A: greater than 90% and 100% or less; B: greater than 100% and 115% or less; C: greater than 115%. When the red rust area ratio after 30 cycles in the neutral salt spray test is SS, S, AA, A, or B, it is judged that the red rust resistance is even more excellent. [Table 1] [Table 2] [Table 3] [Table 4] [Table 5] [Table 6] [Table 7] [Table 8] [Table 9] [Table 10] [Table 11] [Table 12] [Table 13] [Table 14] [Table 15] [Table 16] [Table 17] [Table 18] [Table 19] [Table 20] [Table 21] [Table 22] [Table 23] [Table 24] It can be understood from Tables 1 to 24 that when the surface-treated steel plate has a predetermined compound at the end face, the red rust resistance of the end face is excellent. It is also understood that the red rust resistance can be even more excellent depending on the type, ratio, coating rate, combination, etc. of the compound. On the other hand, when the predetermined compound is not formed on the end face, the red rust resistance of the end face is poor. Sample numbers 2-23 to 2-27 applied formation methods 1 to 5 of the compound, and no Mg-containing compound was formed in the non-plated part, and only Zn-based compounds were formed. Industrial Applicability According to the present invention, a surface-treated steel material capable of suppressing the generation of red rust in the non-plated part can be provided, so the industrial applicability is high. 1: Surface-treated steel plate (surface-treated steel material) 11: Steel plate 12: Coating layer (Zn-based coating layer) 31: Compound 41: Non-plated part 101: Surface 102: End face 103: Plated surface FIG. 1 is a schematic diagram showing an example of a surface-treated steel plate, which is a form of the surface-treated steel material of the present embodiment. FIG. 2 is a diagram showing an image of the normalization of the XAFS spectrum. (None)

Claims

1. A surface-treated steel, characterized by comprising: a steel, and a plating layer formed on at least a portion of the surface of the steel; the plating layer being a Zn-based plating layer containing 0.3 to 12.5% ​​by mass of Mg; a portion of the aforementioned surface of the steel where the plating layer is not formed is defined as a non-plated portion, wherein at least a portion of the non-plated portion contains one or more compounds selected from the group consisting of compound A, compound B, compound C, compound D, compound E, compound F, compound G, compound H, compound I, and compound J; the aforementioned compounds comprising: 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; and compound J is present; wherein at least 50% of the non-plated portion is covered by the aforementioned compounds in terms of area ratio; compound A: MgO, Compound B: Mg(OH)2, Compound C: MgCO3, Compound D: Mg4Al2(OH)12CO3・3H2O, Compound E: Mg6Al2(OH)16CO3・4H2O, Compound F: Zn6Al2(OH)16CO3・4H2O containing Mg, Compound G: 4MgCO3・Mg(OH)2・5H2O, Compound H: Zn5(CO3)2(OH)6 containing Mg, Compound I: Zn5(OH)8Cl2・H2O containing Mg, Compound J: NaZn4(SO4)Cl(OH)6・6H2O containing Mg.

2. As in request item 1, the surface-treated steel, wherein, The aforementioned coating contains 4.0 to 25.0% by mass of Al.

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