Surface-treated steel material

Abstract

This surface-treated steel material has a steel material and a plating layer formed on at least a part of the surface of the steel material. The plating layer is a Zn-based plating layer containing 0.3 to 12.5% by mass of Mg. When a part of the surface of the steel material where the plating layer is not formed is defined as a non-plated part, MgO, Mg(OH) 2 , MgCO 3 , Mg 4 Al 2 (OH) 12 CO 3 ·3H 2 O, Mg 6 Al 2 (OH) 16 CO 3 ·4H 2 O, Zn 6 Al 2 (OH) 16 CO 3 ·4H 2 O, 4MgCO 3 ·Mg(OH) 2 ·5H 2 O, Zn 5 (CO 3 ) 2 (OH) 6 , Zn 5 (OH) 8 Cl 2 ·H 2 O, NaZn 4 (SO 4 )Cl(OH) 6 ·6H 2 O. One or more of these compounds are present.

Description

Technical Field

[0001] The present invention relates to a surface-treated steel material. This application 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 Art

[0002] Among the surface-treated steel materials with good corrosion resistance, the most commonly used one is a zinc (Zn)-based plated steel sheet. This zinc-based plated steel sheet is 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 for a long time to improve the corrosion resistance of zinc-based plated steel sheets due to the need for longer service life of building materials. Under such circumstances, it has been studied to improve the corrosion resistance by incorporating Al and Mg into the zinc-based plating layer. For example, Patent Documents 1 to 4 disclose plated steel materials containing a certain amount of Al and Mg and achieving high corrosion resistance.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0004] The plated steel materials disclosed in Patent Documents 1 to 4 are excellent in long-term flat surface corrosion resistance. However, when the plated steel materials are used, they may be cut into a predetermined size. At this time, no plating layer is formed on the cut surface (cut end face). Further, even on the surface where plating has been performed, there may be a portion where plating has not been performed, or the plating layer may peel off due to scratches, or the plating layer may crack due to cutting, punching, bending, drawing processing, etc., resulting in a portion where the plating layer is not formed (the steel sheet is exposed). As a result of investigations by the present inventors, it has been found that although the plated steel materials of Patent Documents 1 to 3 are excellent in the corrosion resistance of the plated portions, red rust may occur at the cut end faces, non-plated portions, or portions where the steel sheet is exposed due to scratches or processing after the plating layer has been formed (collectively referred to as non-plated portions) at the initial stage of corrosion. Therefore, there is a demand for the development of a technology capable of suppressing the generation of red rust in such non-plated portions.

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

Means for Solving the Problems

[0006] The present inventors have investigated the above problems. As a result, it has been found that the generation of red rust is suppressed by causing a compound containing a predetermined amount of Mg to exist on the surface of the steel sheet in a non-plated portion where no plating layer is formed.

[0007] The present invention has been made in view of the above findings. The gist of the present invention is as follows. [1] The surface-treated steel material according to 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 steel material. The plating layer is a Zn-based plating layer containing 0.3 to 12.5% by mass of Mg. When a part of the surface of the steel material where the plating layer is not formed is defined as a non-plated part, at least one of the following compounds A, B, C, D, E, F, G, H, I, and J exists in at least a part of the non-plated part. and the compound includes at least one selected from the group consisting of the compound D, the compound E, the compound F, the compound H, and the compound I, and at least one selected from the group consisting of the compound A, the compound B, the compound C, the compound G, and the compound J . 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. The surface-treated steel material described in [2][1] may contain 4.0 to 25.0% by mass of Al in the plating layer. The surface-treated steel material described in [3][1] or [2] may have 50% or more of the area ratio coated with the compound. 4 [1] to 3 Among the surface-treated steel materials described in any of the above, the compound may contain two or more selected from the group consisting of the compound B, the compound D, the compound G, the compound H, and the compound I. 5 [1] to 4 Among the surface-treated steel materials described in any of the above, the total composition ratio of one or two of the compound H and the compound I among the compounds may be 10% or more in molar ratio. [Advantages of the Invention]

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

[0009]

Figure 1

Figure 2

[0010] The surface-treated steel material according to an embodiment of the present invention (the surface-treated steel material according to the present embodiment) will be described by taking a surface-treated steel plate as an example. ​​A surface-treated steel plate 1, which is an example of the surface-treated steel material according to this embodiment (hereinafter, the surface-treated steel plate according to this embodiment), as shown in FIG. 1, has a steel plate (base steel plate) 11 and a plating layer 12 formed on at least a part of the surface 101 of the steel plate 11. When a part of the surface 101 of the steel plate 11 where the plating layer 12 is not formed is defined as a non-plated part 41, a predetermined compound 31 containing Mg exists in at least a part of the non-plated part 41 of the 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 cutting to a predetermined size after being pulled out of the plating bath is the end face 102. The end face 102 is in a direction intersecting the plating surface 103 and is, in many cases, substantially perpendicular to the plating surface 103. The shape of the surface-treated steel material according to this embodiment is not limited to a steel plate. For example, it may be a shape obtained by bending a steel plate, a shape such as a steel pipe, a shape such as a steel bar or a steel wire, or a shape such as a structural steel with an H-shaped or T-shaped cross-sectional shape. Taking the surface-treated steel plate as an example of the surface-treated steel material according to this embodiment, it will be described in detail below. In the following description, the numerical range represented 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 in the case where "exceeding" or "less than" is attached to the numerical values described before and after "~" means a range not including these numerical values as the lower limit value or the upper limit value.

[0011] <Steel plate (steel material)> The surface-treated steel plate 1 according to this embodiment is characterized by the plating layer 12 and the compound 31. Therefore, the steel plate 11 is not particularly limited. The steel plate 11 may be determined according to the applied product, required strength, plate thickness, etc. For example, hot-rolled steel plates described in JIS G 3131:2018, JIS G 3113:2018, etc. or cold-rolled steel plates described in JIS G 3141:2021, JIS G 3135:2018, etc. can be used. Also, as described above, steel materials such as steel pipes, steel wires, and various members made of steel other than steel plates can be used. The plate thickness is not limited, but the preferable plate thickness range is 1.0 to 9.0 mm.

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

[0013] In the surface-treated steel sheet 1 according to this embodiment, by using the plating layer 12 as a Zn-based plating layer 12 containing Mg and performing the specific treatment described later, the generation of red rust is suppressed (the red rust resistance is improved) even in the non-plated portion 41. Although the cause is not necessarily clear, it is thought that by performing a specific treatment, Mg contained in the Zn-based plating layer 12 that dissolves by sacrificial corrosion generates a compound described later in the non-plated portion 41. When the plating layer 12 is not a Zn-based plating layer containing Mg, the formation effect of the compound 31 cannot be sufficiently obtained. Also, 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 obtained.

[0014] To obtain the above effects, the Mg concentration (content) contained in the Zn-based plating 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 compound containing Mg is not 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 deteriorates. Therefore, the Mg concentration is set to 12.5 mass% or less.

[0015] In the plating layer 12 (Zn-based plating layer), the concentration (content) of elements other than the above is not limited. However, when the chemical composition of the plating layer 12 is, by mass, Mg: 0.3 - 12.5%, Al: 0 - 25.0%, Sn: 0 - 20.0%, Bi: less than 0 - 5.0%, In: less than 0 - 2.0%, Ca: 0 - 3.0%, Y: 0 - 0.5%, La: less than 0 - 0.5%, Ce: less than 0 - 0.5%, Si: less than 0 - 2.5%, Cr: less than 0 - 0.25%, Ti: less than 0 - 0.25%, Ni: less than 0 - 0.25%, Co: less than 0 - 0.25%, V: less than 0 - 0.25%, Nb: less than 0 - 0.25%, Cu: less than 0 - 0.25%, Mn: less than 0 - 0.25%, Fe: 0 - 5.0%, Sr: less than 0 - 0.5%, Sb: less than 0 - 0.5%, Pb: less than 0 - 0.5%, B: less than 0 - 0.5%, and the balance: Zn and impurities, excellent corrosion resistance can be obtained for the surface-treated steel sheet 1 including the portion where the plating layer 12 is formed, which is preferable.

[0016] The reasons for the preferred chemical composition of the plating layer 12 will be described. Unless otherwise specified, the % regarding the concentration (content) of each element in the chemical composition of the plating layer 12 is mass%.

[0017] [Mg: 0.3~12.5%] For the formation of 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 plating layer 12. When obtaining the effect of improving corrosion resistance, it is preferable to set the Mg concentration to 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, when the Mg concentration exceeds 12.5%, the effect of improving corrosion resistance saturates, and the workability of the plating layer may decrease. In addition, manufacturing problems such as an increase in the amount of dross generated in the plating bath 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: 0~25.0%] Al is an element effective for improving the corrosion resistance in the plating layer (Zn-based plating layer) 12. Therefore, the lower limit of the Al concentration is 0%, but Al may be contained. When sufficiently obtaining the above effect, it is preferable to set the Al concentration to 2.0% or more or 4.0% or more. If necessary, the Al concentration may be set to 6.0% or more or 8.0% or more. On the other hand, when the Al concentration exceeds 25.0%, the sacrificial corrosion prevention effect of the plating layer 12 decreases. Therefore, the Al concentration is preferably 25.0% or less. If necessary, the Al concentration may be set to 20.0% or less or 16.0% or less.

[0019] [Sn: 0~20.0%] [Bi: 0~less than 5.0%] [In: 0~less than 2.0%] These elements contribute to improving corrosion resistance and sacrificial anticorrosion properties. Therefore, the lower limit of the concentration of these elements is 0%, but one or more of them may be contained. When obtaining the above effects, it is preferable that the concentration is 0.05% or more for each. Among these, Sn is preferable because it is a low melting point metal and can be easily contained without impairing the properties of the plating bath. On the other hand, when the Sn concentration exceeds 20.0%, the Bi concentration is 5.0% or more, or the In concentration is 2.0% or more, the corrosion resistance decreases. Therefore, it is preferable that the Sn concentration is 20% or less, the Bi concentration is less than 5.0%, and the In concentration is less than 2.0% respectively.

[0020] [Ca: 0 to 3.0%] Ca is an element that reduces the amount of dross that is easily formed during operation and contributes to improving plating productivity. Therefore, the lower limit of the Ca concentration is 0%, but Ca may be contained. When obtaining this effect, it is preferable that the Ca concentration is 0.1% or more. On the other hand, when the Ca concentration is high, the corrosion resistance of the flat part of the plating layer 12 itself tends to deteriorate, and the corrosion resistance around the welded part may also deteriorate. Therefore, it is preferable that the Ca concentration is 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. The lower limit of the concentration of these elements is 0%, but when obtaining this effect, it is preferable that one or more of them contain 0.05% or more respectively. On the other hand, when the concentration of these elements becomes excessive, the viscosity of the plating bath increases, and it often becomes difficult to form the plating bath itself, and there is a concern that a steel material with good plating properties cannot be manufactured. Therefore, it is preferable that the Y concentration is 0.5% or less, the La concentration is less than 0.5%, and the Ce concentration is less than 0.5%.

[0022] [Si: 0 to less than 2.5%] Si is an element that contributes to the improvement of corrosion resistance. Also, when forming the plating layer 12 on the steel sheet 11, Si is an element that has the effect of suppressing the formation of an overly thick alloy layer formed between the surface of the steel sheet 11 and the plating layer 12, and enhancing the adhesion between the steel sheet 11 and the plating layer 12. The lower limit of the Si concentration is 0%, but when obtaining these effects, it is preferable to set the Si concentration to 0.1% or more. The Si concentration is more preferably 0.2% or more. On the other hand, when the Si concentration becomes 2.5% or more, excessive Si precipitates in the plating layer 12, not only reducing the corrosion resistance but also deteriorating the workability of the plating layer 12. Therefore, it is preferable to set the Si concentration to 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 are elements that contribute to the improvement of corrosion resistance. The lower limit of the concentration of these elements is 0%, but when obtaining 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, when the concentration of these elements becomes excessive, the viscosity of the plating bath increases, and it often becomes difficult to prepare the plating bath itself, and there is a concern that steel materials with good plating properties cannot be manufactured. Therefore, it is preferable to set the concentration of each element to less than 0.25%.

[0024] [Fe: 0 to 5.0%] When manufacturing the plating layer 12, Fe may be mixed into the plating layer 12. It may be contained up to about 5.0%. However, if it is within this range, the adverse effect on the effect of the surface-treated steel sheet 1 according to the present embodiment is small. Therefore, it is preferable that the Fe concentration is 5.0% or less. The inclusion of Fe is not essential. 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, and Pb are contained in the plating layer 12, the appearance of the plating layer 12 changes, spangles are formed, and an improvement in metallic luster is confirmed. The lower limit of the concentration of these elements is 0%, but when obtaining this effect, it is preferable that the concentration of one or more of Sr, Sb, and Pb is 0.05% or more, and more preferably 0.1% or more. On the other hand, when the concentration of these elements becomes excessive, the viscosity of the plating bath increases, and it often becomes difficult to form the plating bath itself, and there is a concern that a steel material with good plating properties cannot be manufactured. Therefore, it is preferable that the concentration of each element is less than 0.5%.

[0026] [B: 0 to less than 0.5%] B is an element that combines with Zn, Al, Mg, etc. when contained in the plating layer 12 to form various intermetallic compounds. This intermetallic compound has the effect of improving the LME. The lower limit of the B concentration is 0%, but when obtaining this effect, it is preferable that the B concentration is 0.05% or more, and more preferably 0.1% or more. On the other hand, when the B concentration becomes excessive, the melting point of the plating significantly increases, and there is a concern that the plating operability deteriorates and a surface-treated steel sheet 1 with good plating properties cannot be obtained. Therefore, it is preferable that the B concentration is less than 0.5%.

[0027] [Balance: Zn and impurities] The chemical composition of the plating layer 12 may contain Zn and impurities other than the above-mentioned elements. The concentration of Zn 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, the Zn-based plating layer means that the concentration of Zn in the plating layer 12 is 50.0% or more. Impurities are elements that are mixed in from raw materials during the manufacturing process. The total concentration of impurities is usually 0.5% or less, but it is preferable if the total concentration is 0.1% or less. For various reasons such as reducing raw material costs, raw materials containing relatively large amounts of elements other than the above elements, including Zn, may be used intentionally. Therefore, in this embodiment, these elements (elements other than the above elements, including Zn) are all considered to be impurity elements, regardless of whether they are mixed in or intentionally added. For this reason, it is preferable that the total concentration of these elements is 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 It is preferable that the thickness is 20 g / m2 or more per side in order to further improve the corrosion resistance, if necessary. 2 More than 40g / m 2 or more than 60g / m 2 On the other hand, the adhesion amount may be 400 g / m 2 If the coating weight exceeds 400g / m, the corrosion resistance will be saturated and it will be economically disadvantageous. 2 It is preferable that the thickness is 350 g / m or less per side in order to further improve the economic efficiency, if necessary. 2 Below 300g / m 2 or less than 250g / 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, an acid solution for peeling and dissolving the plating layer 12 is obtained by using an acid containing an inhibitor for suppressing the corrosion of the subway (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). Next, the chemical composition of the plating layer 12 can be obtained by measuring the obtained acid solution by ICP analysis.

[0030] The adhesion amount of the plating layer 12 is calculated from the results of measuring the mass (weight) change of samples (samples collected from the surface-treated steel plate 1) before and after peeling and dissolving the plating layer 12 with an acid containing an inhibitor using the method described above.

[0031] <Compound> In the surface-treated steel plate 1 according to the present embodiment, a compound 31 containing Mg is present in at least a part of the non-plated portion 41 of the surface 101 (plating surface 103, end face 102) of the steel plate 11. This compound contains one or more selected from the following (substantially consisting of one or more selected from the following, but it is allowed 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 (CO3 ) 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 Here, the description of "containing Mg" means that although Mg is not included in the chemical formula, a part of the elements in the chemical formula is replaced by Mg, or Mg has penetrated into the compound, and the compound contains Mg as a whole. The specific Mg concentration (Mg content) of each compound including Compound F, Compound H, Compound I, and Compound J with the description of "containing Mg" is determined by the preparation procedure of the reagent described later. The Mg concentrations (Mg contents) of Compound F, Compound H, Compound I, and Compound J prepared by the preparation procedure of the reagent described later are all 0.1% or more in mass%. The Mg amount of these compounds can be easily measured by a known ICP emission spectroscopic test. The presence of these compounds improves the corrosion resistance in the non-plated part 41 and suppresses the formation of red rust. Although the reason is not necessarily clear, when the present inventors performed electrochemical measurement on the end face, it was found that when these compounds are present, the current value is suppressed on both the cathode side and the anode side (especially largely on the anode side) compared with the case where these compounds are not present. From this, it is considered to be due to the physical protection effect (cathode reaction suppression) caused by the presence of these compounds and the passivation effect (anode reaction suppression) caused by the increase in the pH near the surface when the compounds containing these Mg dissolve in the moisture in the environment.

[0032] Even for compounds containing Mg, the above effects cannot be obtained for compounds other than the above, so the intended effects cannot be obtained. The compound preferably contains one or more selected from the following group a and one or more selected from the following 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 that have a great effect on improving rust resistance due to the physical protection effect (cathode reaction suppression) caused by the presence of these compounds. The compounds in Group b are compounds that have a great effect on improving rust resistance due to the passivation effect (anode reaction suppression) caused by the increase in pH near the surface when these Mg-containing compounds dissolve in moisture in the environment. By simultaneously containing the compounds of Group a and Group b, a more excellent rust suppression effect can be obtained due to the synergistic effect compared to the case of containing only the compounds of one group.

[0033] Also, from the perspective of improving corrosion resistance, it is preferable that the compound contains two or more selected from the group consisting of Compound B, Compound D, Compound G, Compound H, and Compound I. Substantially, it may consist of two or more selected from the above group. Moreover, among the compounds, it is preferable that the total composition ratio of one or two of Compound H and Compound I is 10% or more in terms of the amount-of-substance ratio (molar ratio).

[0034] Also, although the effect of improving corrosion resistance (effect of improving rust resistance) can be obtained by the presence of the above compound, when a sufficient effect is obtained for the entire surface-treated steel sheet 1, it is preferable that 50% or more of the non-plated part 41 where the plating layer 12 is not formed is covered with the above compound. The covered area ratio may be 100%.

[0035] Regarding the identification of the compound present in the non-plated part 41, it is obtained by performing X-ray Absorption Fine Structure (XAFS) analysis (hereinafter referred to as XAFS analysis) and performing fitting processing of the XAFS spectrum. Specifically, it is obtained by the following method. First, from the surface-treated steel sheet 1, for example, a sample with a thickness of, for example, plate thickness × 7 mm × 7 mm including the non-plated part 41 to be measured is cut out and collected. XAFS analysis is performed on the non-plated part 41 (for example, in the range of 1.0 mm × 1.2 mm) in the sample to obtain an XAFS spectrum. Regarding the obtained spectrum, identification of the compound is performed by fitting with a linear combination of the spectra of standard samples of each compound using Athena (analysis software). The measurement conditions for XAFS analysis are as follows. · Measure the K absorption edge of Mg · Measurement atmosphere: 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. · Detected X-ray intensity I is obtained by the fluorescence yield method (SDD detector) and the total electron yield method (sample current method). · For energy correction, the Au4f peak position of XPS is measured before measuring the sample. · For improving the S / N ratio, three measurements are performed, and the average value of the spectra is used for analysis. Also, fitting is performed as follows. · Regarding energy, correction is performed based on the Au4f peak position of XPS. · As shown in Figure 2, subtract the background and normalize the overall intensity so that the intensity difference between the pre-edge and the post-edge becomes 1. · Fit the spectrum obtained from the sample with a linear combination of the spectra of standard samples of each compound. To confirm the validity of fitting, the R factor is used. If the R factor is 5% or less in the region from 1300 to 1380 eV, it is judged to be valid. If the R factor exceeds 5%, it is judged that fitting could not be performed. The fact that fitting could not be performed for the standard samples of Compounds A to J means that it cannot be determined that at least one of Compounds A to J is present. The R factor is calculated by the following formula. Here, d' in the formula represents the fitting data (spectral data when the spectra of each compound are linearly combined), and d represents the measurement data. R factor = Σ(d’―d) 2 / Σd 2 · When the sum of the composition ratios of each compound is 100%, a compound with a composition ratio of 1% or more is judged to be "present". At that time, the spectrum obtained from the sample is approximated by a linear combination of the spectra of the standard samples of each compound multiplied 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 approximation is made so that a + b +... j = 100%). Each of these coefficients is taken 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.

[0036] In the above fitting, the standard samples of each compound use the following commercially available reagents or reagents prepared in the following manner. · Compound A (MgO): (Commercially available reagent) Manufactured by FUJIFILM 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 ): Preparation procedure: Weigh 950 g of monoethylene glycol (purity 99.9%) and 50 g of distilled water into a 1 L screw-cap bottle and mix them. Add NaCl so that the concentration becomes 1 mol / kg. Into a three-necked round-bottom flask containing 250 g of the monoethylene glycol + water + NaCl solution, add 10.0 ± 0.1 g of 4MgCO 3 ·Mg(OH) 2 ·5H 2 O. At this time, use a reflux condenser. Open this mixture to atmospheric pressure and stir it for 3 days under continuous CO 2 bubbling (20 - 50 mL / min). During stirring, use a thermostat to 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): Preparation procedure: A 0.20M MgCl 2 -0.1M AlCl 3 solution (however, the amount of MgCl 2 is within the range of 0.019M - 0.020M MgCl 2 ) is added dropwise to 0.1M Na 2 CO 3 , adjusted to pH 10, then left standing for 24 hours, and then filtered by suction and dried. ·Compound E (Mg 6 Al 2 (OH) 16 CO 3 ·4H 2 O): (Commercially available reagent) Manufactured by Fujifilm Wako Pure Chemical Corporation, product name: Hydrotalcite ·Compound F (Zn containing Mg 6 Al 2 (OH) 16 CO 3 ·4H 2 O): Preparation procedure: A 0.2M ZnCl 2 -0.1M AlCl 3 -0.050M MgCl 2 solution (however, the amount of MgCl 2The amount is in the range of 0.045M to 0.055M MgCl 2 is added dropwise to 0.1M Na 2 CO 3 After adjusting the pH to 10, it is left standing for 24 hours, then suction filtered and 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 ): Preparation procedure: 0.1M ZnCl2 - 0.050M MgCl 2 solution (however, the amount of MgCl 2 is in the range of 0.045M to 0.055M MgCl 2 ) is added dropwise with 0.1M Na 2 CO 3 After adjusting the pH to 10, it is left standing for 24 hours, 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 (however, the amount of MgCl 2 is in the range of 0.045M to 0.055M MgCl 2 ) is added dropwise with 0.1M NaOH, after adjusting the pH to 10, it is left standing for 24 hours, then suction filtered and dried. ·Compound J (NaZn containing Mg 4 (SO 4 )Cl(OH) 6 ·6H 2 O): Preparation procedure: 0.5M ZnSO 4 -0.10M MgCl 2 (however, the amount of MgCl 2 is in the range of 0.09M to 0.011M MgCl2 It is within the range of... 30 mL of 1.4 M NaCl solution is added with 1 g of ZnO powder, 0.1 M NaOH is added dropwise, adjusted to pH 10, stirred for 120 hours, then suction filtered and dried.

[0037] Also, the coating rate (coated area ratio) of the compound in the non-plated part 41 is determined by the following method. For the part where the plating layer 12 is not formed (non-plated part 41), perform Mg mapping analysis by μ-XRF (micro-X-Ray Fluorescence), measure the intensity of the μ-XRF spectrum, and for the area of the non-plated part 41 where the plating layer 12 is not formed, 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 part 41 is defined as the "coating rate of the compound". At that time, the μ-XRF shall be under the following measurement conditions. Measurement atmosphere: Vacuum Acceleration voltage: 15 kV Current value: 50 μA X-ray tube: Rh X-ray tube Scan speed: 4.00 mmS -1 Collimator: 30 μm

[0038] <Manufacturing method> The surface-treated steel sheet 1 according to this embodiment can obtain the above effects as long as it has the above characteristics regardless of the manufacturing method, but it 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 the steel sheet 11 (base steel sheet); (II) A processing step of making the plated steel sheet into an arbitrary shape by cutting and / or punching the plated steel sheet with the plating layer 12 (Zn-based plating layer) formed; (III) A compound formation step of forming a predetermined compound containing Mg on the non-plated part 41 of the end face and / or the plated surface. For each step, the preferred conditions will be described.

[0039] [Plating step] In the plating process, a plating layer 12 is formed on the surface by immersing a steel material such as a steel sheet in a plating bath containing Mg and Zn or by performing electroplating. The formation conditions of the plating layer 12 are not particularly limited. It may be carried out by a normal method so as to obtain sufficient plating adhesion. In addition, the steel material used in the plating process and its manufacturing method are not limited. In the case of a surface-treated steel sheet, as the steel sheet to be immersed in the plating bath, for example, hot-rolled steel sheets described in JIS G 3113:2018 or JIS G 3131:2018, or cold-rolled steel sheets described in JIS G 3141:2021 or JIS G 3135:2018 can be used. Further, steel materials such as steel pipes, steel wires, and various members made of steel other than steel sheets can be used. The composition of the plating bath may be adjusted according to the chemical composition of the desired plating layer 12. After pulling the steel material out of the plating bath, if necessary, the adhesion amount of the plating layer 12 can be adjusted by wiping.

[0040] [Processing step] In the processing step, the plated steel sheet is made into an arbitrary shape by cutting and / or punching. When cutting or punching is performed, an end face where the plating layer 12 is not formed is formed at the cut portion. Similarly, an end face is formed at the punched portion. In the processing step, further, bending, drawing, etc. may be performed to change the shape. In this case, a non-plated portion 41 may occur on the plated surface.

[0041] [Compound formation step] In the compound formation step, a predetermined compound containing Mg is formed on the non-plated portion 41 (the end face and / or the non-plated portion 41 on the plated surface) where the plating layer 12 is not formed. For the formation of the compound, the steel sheet after the processing step is treated with 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-A solution containing 1.0 to 100.0 mM, having a pH of 4.5 to 7.0 and a solution temperature of 25 to 60°C, is brought into contact with the plating layer 12 and the non-plated portion 41 where the plating layer 12 is not formed for 1 to 20 minutes. After the above contact, in an inert atmosphere such as nitrogen gas or argon gas, in an atmosphere 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. Cl in the solution - , SO 4 2- , Na + , CO 3 2- If the concentration of, the pH of the solution is outside the above range, the adhesion between the compound formed on the non-plated portion 41 and the steel plate 11 (substrate) deteriorates, and a predetermined compound is not sufficiently formed on the non-plated portion 41. Also, if the contact time is shorter than the above range, a predetermined compound is not sufficiently formed on the non-plated portion 41. If the contact time exceeds 20 minutes, corrosion of the plated portion may progress and the corrosion resistance of the plated portion may decrease. Also, if the temperature of the solution is less than 25°C or exceeds 60°C, the formation of a predetermined compound on the non-plated portion becomes insufficient. Also, if the drying atmosphere is other than an inert atmosphere such as nitrogen gas or argon gas, red rust may occur on the non-plated portion. If the drying temperature is less than 40°C or exceeds 60°C, the formation of a predetermined compound on the non-plated portion may be insufficient, or if it exceeds 60°C, drying may proceed rapidly and no compound may remain on the non-plated portion. As a result, a predetermined compound may not be formed and red rust may occur on the non-plated portion. If the relative humidity is less than 20% or exceeds 40%, the formation of a predetermined compound on the non-plated portion becomes insufficient. As a result, a predetermined compound may not be formed and red rust may occur on the non-plated portion. If the drying time is less than 5 minutes or exceeds 20 minutes, the formation of a predetermined compound on the non-plated portion becomes insufficient. As a result, a predetermined compound may not be formed and red rust may occur on the non-plated portion.

Example

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

[0043] The obtained plated steel sheet (surface-treated steel sheet) was cut with an electric shear to form an end face having a portion with a plating layer and a portion without a plating layer (where the steel sheet was exposed). No non-plated portion was formed on the plated surface. Among this plated steel sheet, for sample numbers 1-1 to 1-107 and 2-1 to 2-22, in order to form a compound containing Mg on the end face, the solutions shown in Tables 7 to 12 were brought into contact with the end face. Then, it was dried in the atmospheres described in Tables 13 to 18 in a nitrogen gas atmosphere. On the other hand, for sample numbers 2-23 to 2-27, compound formation was attempted by any of the following methods. · Compound formation method 1: Immersion in a 5 mass% NaCl aqueous solution (pH: 5 to 6, solution temperature: 30 °C) for 20 minutes · Compound formation method 2: Immersion in a 5 mass% NaCl aqueous solution (pH: 5 to 6, solution temperature: 25 °C) for 72 hours · Compound formation method 3: Dilute 28.6 g of magnesium ethoxide with pure water to 200 cc, and then further dilute it to 1 L with ethylene glycol monoethyl ether. Apply it by the pulling-up method using this bath, dry it, and then perform heat treatment at 100 to 400 °C. · Compound formation method 4: MgCl 2 is 60 mol%, NaCl is 20 mol%, KCl is 20 mol%, and using a molten salt heated and dissolved at 500 °C, in an atmosphere where the partial pressure of H 2 O is 16 mmHg, perform cathodic electrolysis treatment with a current density of 20 A / dm 2 and an energization time of 5 seconds. · Compound formation method 5: Mg 2+ is 0.3 g / L and NO 3- In an aqueous solution containing 0.5 g / L and having a pH of 7.0, with a current density of 50 A / dm 2 and a energization time of 5 seconds, cathodic electrolysis treatment was carried out

[0044] For the surface-treated steel sheet after the compound formation step, identification of the compound present on the end face and measurement of the coverage rate on the end face were carried out in the above-described manner. When there were multiple compounds, their abundance ratios were also determined. Although not shown in the table, the thickness of the compound was set to about 10 nm to 30 μm by changing the contact time between the steel sheet and the solution. Also, the fact that no compound was detected in the table indicates that none of the compounds A to J were detected. More specifically, in the fitting with the standard samples of compounds A to J, the R factor exceeded 5% in the region up to 1300 to 1380 eV, the fitting with the standard samples of compounds A to J could not be performed, and it was not possible to determine that at least one of the compounds A to J was present.

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

[0046] Also, an exposure test was carried out on the surface-treated steel sheet after contact with the solution and drying, and the area ratio of red rust on the end face after 50 days was determined. The exposure conditions were as follows. The steel sheet sample was inclined 30° from the horizontal so that the treated cut end face was on top, installed facing south, and an atmospheric exposure test was carried out. After exposure, the sample was evaluated 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% and 80% or less AA: More than 80% and 90% or less A: More than 90% and 100% or less B: More than 100% and 115% or less C: More than 115% It was determined that those with a red rust area ratio of SS, S, AA, or A after 50 days of exposure had excellent red rust resistance. When the ratio of the area where red rust has occurred exceeds 100%, it means that red rust has occurred not only in the part where the plating layer is not formed but also around it.

[0047] Also, for the corrosion resistance evaluation under conditions more severe than exposure in the atmosphere, a 30-cycle test was conducted in accordance with 8.1 (Neutral Salt Spray Cycle Test Method) of JIS H8502:1999. Among the samples, the evaluation was carried out as follows based on the ratio of the area where red rust has occurred to the area where the plating layer is not formed. SS: 70% or less S: More than 70% and 80% or less AA: More than 80% and 90% or less A: More than 90% and 100% or less B: More than 100% and 115% or less C: More 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 was judged that the red rust resistance is further excellent.

[0048]

Table 1

[0049]

Table 2

[0050]

Table 3

[0051]

Table 4

[0052]

Table 5

[0053]

Table 6

[0054]

Table 7

[0055]

Table 8

[0056]

Table 9

[0057]

Table 10

[0058]

Table 11

[0059]

Table 12

[0060]

Table 13

[0061]

Table 14

[0062]

Table 15

[0063]

Table 16

[0064]

Table 17

[0065]

Table 18

[0066]

Table 19

[0067]

Table 20

[0068]

Table 21

[0069]

Table 22

[0070]

Table 23

[0071]

Table 24

[0072] As can be seen from Tables 1 to 24, in the case of the surface-treated steel sheet having a predetermined compound on the end face, the end face had excellent rust resistance. Further, it was found that the rust resistance may be further improved depending on the type, ratio, coverage rate, combination, etc. of the compound. On the other hand, when no predetermined compound was formed on the end face, the rust resistance of the end face was poor. In sample numbers 2-23 to 2-27 to which compound formation methods 1 to 5 were applied, no Mg-containing compound was formed in the non-plated part, and only a Zn-based compound was formed.

Industrial Applicability

[0073] According to the present invention, it is possible to provide a surface-treated steel material in which the generation of red rust in the non-plated part is suppressed, so the industrial applicability is high.

Explanation of Signs

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

Claims

1. Steel and A plating layer formed on at least a part of a surface of the steel material; having The plating layer is a Zn-based plating layer containing 0.3 to 12.5 mass % of Mg, When a portion of the surface of the steel material on which 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 part of the non-plated portion. A surface-treated steel material characterized by: 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 plating layer contains 4.0 to 25.0 mass% Al; 2. The surface-treated steel material according to claim 1 .

3. An area ratio of the non-plated portion is 50% or more, and the non-plated portion is covered with the compound.

3. The surface-treated steel material according to claim 1 or 2.

4. The compound is one or more selected from the group consisting of the compound D, the compound E, the compound F, the compound H, and the compound I; one or more selected from the group consisting of the compound A, the compound B, the compound C, the compound G, and the compound J; Including, 3. The surface-treated steel material according to claim 1 or 2.

5. The compound includes two or more selected from the group consisting of the compound B, the compound D, the compound G, the compound H, and the compound I.

3. The surface-treated steel material according to claim 1 or 2.

6. Among the compounds, the total composition ratio of one or two of the compounds H and I is 10% or more in terms of molar ratio.

3. The surface-treated steel material according to claim 1 or 2.

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