Surface-treated steel material

Abstract

This surface-treated steel contains: a steel material; and a coating layer formed on at least part of a surface of the steel material, in which the coating layer is a Zn-coating layer containing 0.3 to 12.5 mass% of Mg, and when a portion of the surface of the steel material where the coating layer is not formed is defined as a non-coated portion, one or more compounds, among 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)Cl(OH)6·6H20 containing Mg, are present in at least part of the non-coated portion.

Description

TECHNICAL FIELD

[0001] The present invention relates to a surface-treated steel.

[0002] Priority is claimed on Japanese Patent Application No. 2023-116278, filed July 14, 2023, the content of which is incorporated herein by reference.BACKGROUND ART

[0003] A zinc (Zn)-coated steel sheet is the most used as a surface-treated steel having good corrosion resistance. This zinc-coated steel sheet is used in various manufacturing industries such as automobiles, home appliances, and building materials. For example, in the field of building materials, studies to enhance corrosion resistance of zinc-coated steel sheets have long been conducted in response to the demand for extending the service life of building materials.

[0004] Under such circumstances, it has been studied to enhance corrosion resistance by containing Al or Mg in a zinc-coating layer.

[0005] For example, Patent Documents 1 to 4 disclose coated steel materials, each containing a certain amount of Al and Mg to achieve high corrosion resistance.Citation ListPatent Document

[0006] Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2006-193791 Patent Document 2: PCT International Publication No. WO 2011 / 001662 Patent Document 3: Japanese Unexamined Patent Application, First Publication No. 2021-172878 Patent Document 4: Published Japanese Translation No. 2016-519220 of the PCT International Publication SUMMARY OF INVENTIONTechnical Problem

[0007] The coated steel materials disclosed in Patent Documents 1 to 4 are excellent in long-term flat portion corrosion resistance. However, the coated steel materials may be cut into a predetermined size in use. In this case, a coating layer is not formed on the cut surface (cut end surface). In addition, even on the coated surface, there may be bare spots or a portion where a coating layer is not formed (a steel sheet is exposed) due to peeling of the coating layer caused by defects or cracking of the coating layer caused by cutting, punching, bending, drawing, or the like.

[0008] As a result of examination by the present inventors, it has been found that in the coated steel materials of Patent Documents 1 to 3, although the corrosion resistance of a coated portion is excellent, red rust may occur on a cut end surface, bare spots, or a portion where a steel sheet is exposed by defects or processing after a coating layer is formed (collectively referred to as a non-coated portion) as described above in the initial stage of corrosion. Therefore, there is a demand for technology development that can suppress the occurrence of red rust in such a non-coated portion.

[0009] In consideration of the background as described above, an object of the present invention is to provide a surface-treated steel in which the occurrence of red rust in a non-coated portion is suppressed on the premise of a surface-treated steel represented by a surface-treated steel sheet having a Zn-coating layer containing Mg.Solution to Problem

[0010] The present inventors have studied the above problems. As a result, the present inventors have found that the occurrence of red rust is suppressed by allowing a predetermined Mg-containing compound to be present on a surface of a steel sheet in a non-coated portion where a coating layer is not formed.

[0011] The present invention has been made in view of the above findings. The gist of the present invention is as follows. [1] A surface-treated steel according to an aspect of the present invention containing: a steel material; and a coating layer formed on at least part of a surface of the steel material, in which the coating layer is a Zn-coating layer containing 0.3 to 12.5 mass% of Mg, and when a portion of the surface of the steel material where the coating layer is not formed is defined as a non-coated portion, one or more compounds of a compound A, a compound B, a compound C, a compound D, a compound E, a compound F, a compound G, a compound H, a compound I, and a compound J are present in at least part of the non-coated portion, the compounds A to J being as follows, 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 6 Al 2 (OH) 16 CO 3 ·4H 2 O containing Mg; Compound G: 4MgCO 3 ·Mg(OH) 2 ·5H 2 O; Compound H: Zn 5 (CO 3 ) 2 (OH) 6 containing Mg; Compound I: Zn 5 (OH) 8 Cl 2 ·H 2 O containing Mg; and Compound J: NaZn 4 (SO 4 )Cl(OH) 6 ·6H 2 O containing Mg. [2] In the surface-treated steel according to [1], the coating layer may contain 4.0 to 25.0 mass% of Al. [3] In the surface-treated steel according to [1] or [2], 50% or more, by area fraction, may be covered with the one or more compounds. [4] In the surface-treated steel according to any one of [1] to [3], the one or more compounds may include: 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; and 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. [5] In the surface-treated steel according to any one of [1] to [4], the one or more compounds may include two or more selected from the group consisting of the compound B, the compound D, the compound G, the compound H, and the compound 1. [6] In the surface-treated steel according to any one of [1] to [5], the total constituent ratio, by molar ratio, of either one or both of the compound H and the compound I among the one or more compounds may be 10% or more. Advantageous Effects of Invention

[0012] According to the above aspect of the present invention, it is possible to provide the surface-treated steel in which the occurrence of red rust in the non-coated portion is suppressed.BRIEF DESCRIPTION OF DRAWINGS

[0013] [FIG. 1] A schematic diagram illustrating an example of a surface-treated steel sheet that is one form of a surface-treated steel according to the present embodiment. [FIG. 2] A diagram illustrating an image of normalization of an XAFS spectrum. DESCRIPTION OF EMBODIMENTS

[0014] A surface-treated steel according to an embodiment of the present invention (a surface-treated steel according to the present embodiment) is described as an example of a surface-treated steel sheet.

[0015] As illustrated in FIG. 1, a surface-treated steel sheet (hereinafter, the surface-treated steel sheet according to the present embodiment) 1 that is an example of the surface-treated steel according to the present embodiment includes a steel sheet (base steel sheet) 11 and a coating layer 12 formed on at least part of one surface 101 of the steel sheet 11, and when a portion of the one surface 101 of the steel sheet 11 where the coating layer 12 is not formed is defined as a non-coated portion 41, a predetermined compound 31 containing Mg is present in at least a part of the non-coated portion 41 of the steel sheet 11.

[0016] In FIG. 1, in a surface 101, the surface that comes into contact with a coating bath and that has a coating layer formed thereon is a coated surface 103, and the surface that is exposed when cut to a predetermined size after being withdrawn from the coating bath is an end surface 102. The end surface 102 is oriented in a direction intersecting the coated surface 103, which is often substantially perpendicular to the coated surface 103.

[0017] The shape of the surface-treated steel according to the present embodiment is not limited to a steel sheet. For example, the shape may be a shape obtained by bending a steel sheet, a shape such as a steel pipe, a shape such as a steel bar or a steel wire, or a shape having a cross-sectional shape such as an H-shape or a T-shape.

[0018] Hereinafter, the surface-treated steel according to the present embodiment will be described in detail using a surface-treated steel sheet as an example.

[0019] In the following description, a numerical value range indicated by using "to" means a range including the numerical values described before and after "to" as a lower limit and an upper limit. However, a numerical range in which "more than" or "less than" is attached to the numerical values described before and after "to" means a range not including these numerical values as the lower limit or the upper limit.<Steel Sheet (Steel Material)>

[0020] The surface-treated steel sheet 1 according to the present embodiment is characterized by the coating layer 12 and the compound 31. Therefore, the steel sheet 11 is not particularly limited. Determination of the steel sheet 11 depends on an applied product, required strength, sheet thickness, and the like. For example, a hot-rolled steel sheet described in JIS G 3131:2018, JIS G 3113:2018, and the like, or a cold-rolled steel sheet described in JIS G 3141:2021, JIS G 3135:2018, and the like may be used. In addition, as described above, steel materials such as steel pipes, steel wires, and various members composed of steel other than steel sheets can be used.

[0021] The sheet thickness is not limited, but a preferable sheet thickness range is 1.0 to 9.0 mm.<Coating layer>

[0022] In the surface-treated steel sheet 1 according to the present embodiment, the coating layer 12 is formed on at least part of a surface of the steel sheet 11. This coating layer 12 is a Zn-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.

[0023] In the present embodiment, the Zn-coating layer is a coating layer in which the concentration of Zn is 50.0 mass% or more.

[0024] In the coating layer 12 of the surface-treated steel sheet 1 according to the present embodiment, Zn and Mg, or Zn, Mg, and Al often form an alloy in the coating layer, but the presence state of Zn, Mg, and Al is not limited.

[0025] The coating layer 12 may be formed over the entirety (100% in terms of area fraction) of the coated surfaces 103 (front and back surfaces (often surfaces other than end surfaces in a case of a coated steel sheet that has been cut)) of the steel sheet 11, but each coated surface 103 may have the non-coated portion 41 where the coating layer is not formed due to bare spots, peeling caused by defects, or the like. The area fraction of the non-coated portion 41 is preferably 10% or less of the entire coated surface. The area fraction of the non-coated portion 41 in the coated surface 103 may be 0%.

[0026] The coating layer 12 may also be formed on part of another surface (end surface 102 in FIG. 1) other than the coated surface 103 in the surface 101, but in a case of a surface-treated steel sheet cut to a predetermined size after formation of the coating layer, an end surface (cut end surface) often does not have a coating layer formed thereon. The area fraction of the non-coated portion 41 may be more than 0% of the entire surface including surfaces other than the coated surface 103.

[0027] In the surface-treated steel sheet 1 according to the present embodiment, the coating layer 12 is a Zn-coating layer 12 containing Mg, and a specific treatment described later is then performed. Thus, the occurrence of red rust is suppressed even in the non-coated portion 41 (red rust resistance is enhanced).

[0028] It is not necessarily clear why, but it is considered that, by performing the specific treatment, Mg contained in the Zn-coating layer 12 that dissolves due to sacrificial corrosion produces a compound described later in the non-coated portion 41.

[0029] In a case where the coating layer 12 is not a Zn-coating layer containing Mg, the effect of producing the compound 31 is not sufficiently obtained.

[0030] In addition, even though the steel sheet 11 contains Mg, the amount of Mg contained in the steel sheet 11 is very small, and Mg is less eluted from the steel sheet 11. Therefore, the same effect cannot be obtained.

[0031] In order to obtain the above effect, the Mg concentration (content) contained in the Zn-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%, an Mg-containing compound is not produced. Thus, the Mg concentration is set to 0.3 mass% or more. On the other hand, when the Mg concentration is more than 12.5 mass%, workability is deteriorated. Thus, the Mg concentration is set to 12.5 mass% or less.

[0032] In the coating layer 12 (Zn-coating layer), the concentration (content) of elements other than the above-described elements is not limited. However, it is preferable that the chemical composition of the coating layer 12, by mass%, is: 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 remainder: Zn and impurities, because excellent corrosion resistance of the surface-treated steel sheet 1, including at the portion where the coating layer 12 is formed, can be obtained.

[0033] The reason for the preferred chemical composition of the coating layer 12 will be described. Unless otherwise specified, % related to the concentration (content) of each element in the chemical composition of the coating layer 12 is mass%.[Mg: 0.3% to 12.5%]

[0034] For the formation of a Mg-containing compound, the Mg concentration is 0.3% or more. In addition, Mg is an element having an effect of enhancing the corrosion resistance of the coating layer 12. When the effect of enhancing corrosion resistance is obtained, the Mg concentration is preferably 0.5% or more. The Mg concentration is more preferably 1.0% or more, and still more preferably 3.0% or more.

[0035] On the other hand, when the Mg concentration is more than 12.5%, the effect of enhancing corrosion resistance is saturated, and the workability of the coating layer may be deteriorated. In addition, there is a manufacturing-related problem such as an increase in amount of dross generated in a coating bath. Therefore, the Mg concentration is set to 12.5% or less. The Mg concentration is more preferably 10.0% or less, and still more preferably 8.0% or less.[Al: 0% to 25.0%]

[0036] Al is an element effective for enhancing corrosion resistance in the coating layer (Zn-coating layer) 12. Therefore, the lower limit of the Al concentration is 0%, but Al may be contained. For obtaining the above-described effect to a sufficient extent, the Al concentration is preferably 2.0% or more or 4.0% or more. As necessary, the Al concentration may be 6.0% or more or 8.0% or more.

[0037] On the other hand, when the Al concentration is more than 25.0%, the sacrificial corrosion protection action of the coating layer 12 deteriorates. For this reason, the Al concentration is preferably 25.0% or less. As necessary, the Al concentration may be 20.0% or less, or 16.0% or less.[Sn: 0% to 20.0%][Bi: 0% to less than 5.0%][In: 0% to less than 2.0%]

[0038] These elements are elements that contribute to enhancement of corrosion resistance and sacrificial corrosion resistance. Therefore, the lower limit of the concentration of each element is 0%, but any one or more of these elements may be contained. In a case of obtaining the above-described effect, the concentration of each element is preferably 0.05% or more.

[0039] Among these, Sn is preferable because Sn is a low-melting-point metal and can be easily contained without impairing properties of the coating bath.

[0040] On the other hand, when the Sn concentration is more than 20.0%, the Bi concentration is 5.0% or more, or the In concentration is 2.0% or more, corrosion resistance deteriorates. For this reason, 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%.[Ca: 0% to 3.0%]

[0041] Ca is an element that reduces the formation amount of dross that is likely to be formed during operation and contributes to improvement of coating manufacturability. Therefore, the lower limit of the Ca concentration is 0%, but Ca may be contained. For obtaining this effect, the Ca concentration is preferably 0.1% or more.

[0042] On the other hand, when the Ca concentration is high, the corrosion resistance of a flat portion itself of the coating layer 12 tends to be deteriorated, and the corrosion resistance of the periphery of the weld may also be deteriorated. For this reason, the Ca concentration is preferably 3.0% or less.[Y: 0% to 0.5%][La: 0% to less than 0.5%][Ce: 0% to less than 0.5%]

[0043] Y, La, and Ce are elements that contribute to improvement of corrosion resistance. The lower limit of the concentration of each element is 0%, but for obtaining this effect, it is preferable that one or more of these elements are each contained in an amount of 0.05% or more.

[0044] On the other hand, when the concentration of each element is excessive, there is a concern that the viscosity of the coating bath increases, and it is thus difficult to perform initial make-up of coating bath itself, and a steel material having good coating properties cannot be manufactured. For this reason, 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%.[Si: 0% to less than 2.5%]

[0045] Si is an element that contributes to enhancement of corrosion resistance. In addition, Si is also an element having an effect of suppressing formation of an excessively thick alloy layer formed between the surface of the steel sheet 11 and the coating layer 12 to enhance adhesion between the steel sheet 11 and the coating layer 12 when the coating layer 12 is formed on the steel sheet 11. The lower limit of the Si concentration is 0%, but for obtaining these effects, the Si concentration is preferably 0.1% or more. The Si concentration is more preferably 0.2% or more.

[0046] On the other hand, when the Si concentration is 2.5% or more, an excessive amount of Si precipitates in the coating layer 12, and corrosion resistance thus deteriorates and the workability of the coating layer 12 deteriorates. Therefore, the Si concentration is preferably less than 2.5%. The Si concentration is more preferably 1.5% or less.[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%]

[0047] These elements are elements that contribute to enhancement of corrosion resistance. The lower limit of the concentration of each element is 0%, but to obtain this effect, it is preferable that the concentration of one or more of these elements is set to 0.05% or more.

[0048] On the other hand, when the concentration of each element is excessive, there is a concern that the viscosity of the coating bath increases, and it is thus difficult to perform initial make-up of coating bath itself, and a steel material having good coating properties cannot be manufactured. For this reason, the concentration of each of the elements is preferably less than 0.25%.[Fe: 0% to 5.0%]

[0049] Fe may be mixed into the coating layer 12 when the coating layer 12 is manufactured. Fe may be contained up to approximately 5.0%, but as long as the content of Fe is in this range, there is little adverse effect on the effect of the surface-treated steel sheet 1 according to the present embodiment. For this reason, the Fe concentration is preferably 5.0% or less. Fe is not necessarily contained. The lower limit of the Fe concentration is 0%.[Sr: 0% to less than 0.5%][Sb: 0% to less than 0.5%][Pb: 0% to less than 0.5%]

[0050] When Sr, Sb, and Pb are contained in the coating layer 12, the external appearance of the coating layer 12 changes, a spangle is formed, and improvement in metallic gloss is observed. The lower limit of the concentration of each element is 0%, but for obtaining this effect, the concentration of one or more of Sr, Sb, and Pb is preferably 0.05% or more, and more preferably 0.1% or more.

[0051] On the other hand, when the concentration of each element is excessive, there is a concern that the viscosity of the coating bath increases, and it is thus difficult to perform initial make-up of coating bath itself, and a steel material having good coating properties cannot be manufactured. For this reason, the concentration of each of the elements is preferably less than 0.5%.[B: 0% to less than 0.5%]

[0052] B is an element that combines with Zn, Al, Mg, or the like when contained in the coating layer 12 and forms various intermetallic compounds. Such intermetallic compounds have an effect of improving LME. The lower limit of the B concentration is 0%, but for obtaining this effect, the B concentration is preferably 0.05% or more, and more preferably 0.1% or more.

[0053] On the other hand, when the B concentration is excessively high, there is a concern that the melting point of coating significantly increases, the operability of coating deteriorates, and the surface-treated steel sheet 1 having good coating properties thus cannot be obtained. For this reason, the B concentration is preferably less than 0.5%.[Remainder: Zn and Impurities]

[0054] In the chemical composition of the coating layer 12, elements other than the above-described elements may be Zn and impurities. The concentration of Zn in the coating layer 12 is 50.0% or more, but is preferably 62.5% or more, more preferably 70.0% or more, still more preferably 85.0% or more. In the present embodiment, the Zn-coating layer means that the concentration of Zn in the coating layer 12 is 50.0% or more.

[0055] The impurities are elements mixed from a raw material or the like mainly in a manufacturing process. The concentration of the impurities is usually 0.5% or less in total, but preferably 0.1% or less in total. For various reasons such as reduction in raw material cost, raw materials having a relatively large content of elements other than the above-described elements including Zn may be intentionally used. Therefore, in the present embodiment, these elements (elements other than the above-described elements including Zn) are all regarded as impurity elements regardless of mixing or intentional addition of these elements. Therefore, the total concentration of these elements is preferably 0.5% or less.

[0056] The adhesion amount of the coating layer 12 is not limited, and is preferably 10 g / m 2< or more per one surface for enhancing corrosion resistance. As necessary, the adhesion amount may be 20 g / m 2< or more, 40 g / m 2< or more, or 60 g / m 2< or more per one surface for further enhancing corrosion resistance. On the other hand, even though the adhesion amount is more than 400 g / m 2< per one surface, corrosion resistance is saturated and it is economically disadvantageous. Therefore, the adhesion amount per one surface is preferably 400 g / m 2< or less. As necessary, the adhesion amount may be 350 g / m 2< or less, 300 g / m 2< or less, or 250 g / m 2< or less per one surface for further improving economic efficiency.

[0057] The chemical composition of the coating layer 12 can be measured by the following method.

[0058] First, an acid solution is obtained in which the coating layer 12 is peeled off and dissolved with an acid containing an inhibitor that suppresses corrosion of a base metal (steel sheet 11) (for example, an acid obtained by adding 1% of HIBIRON (A-6) (manufactured by Sugimura Chemical Industrial Co., Ltd.) to 10% hydrochloric acid). Next, the obtained acid solution is measured by ICP analysis, and the chemical composition of the coating layer 12 can be thus obtained.

[0059] For the adhesion amount of the coating layer 12, before and after the coating layer 12 is peeled off and dissolved with the acid containing an inhibitor, the mass (weight) change of a sample (sample collected from the surface-treated steel sheet 1) is measured using the above-described method, and the adhesion amount is calculated from the result.<Compound>

[0060] In the surface-treated steel sheet 1 according to the present embodiment, the compound 31 containing Mg is present in at least part of the non-coated portion 41 on the surface 101(coated surface 103 and end surface 102) of the steel sheet 11. This compound contains one or more selected from the following (substantially consisting of one or more selected from the following, but acceptable to contain a small amount 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 6 A 12 (OH) 16 CO 3 ·4H 2 O containing Mg Compound G: 4MgCO 3 ·Mg(OH) 2 ·5H 2 O Compound H: Zn 5 (CO 3 ) 2 (OH) 6 containing Mg Compound I: Zn 5 (OH) 8 Cl 2 ·H 2 O containing Mg Compound J: NaZn 4 (SO 4 )Cl(OH) 6 ·6H 2 O containing Mg

[0061] Here, the description "containing Mg" means that Mg is not contained in the chemical formula, but some of the elements in the chemical formula are substituted with Mg or Mg enters into the compound, resulting in the inclusion of Mg in the compound. The specific Mg concentration (Mg content) of each compound including the compound F, the compound H, the compound I, and the compound J with the description "containing Mg" is according to the preparation procedure of a reagent described later. The Mg concentrations (Mg contents) of the compound F, the compound H, the compound I, and the compound J prepared by the preparation procedure of the reagent described later are all 0.1% or more, by mass%. The amount of Mg in each of these compounds can be easily measured by a known ICP optical emission spectrometry test.

[0062] The presence of these compounds enhances corrosion resistance in the non-coated portion 41 and suppresses the formation of red rust. It is not necessarily clear why, but when the present inventors conducted electrochemical measurements on an end surface, it was found that, in a case where these compounds are present, the current value is reduced on both the cathode side and the anode side (particularly significantly on the anode side) as compared with a case where these compounds are absent. From this, it is considered that the presence of these compounds causes a physical protection effect (inhibition of cathode reaction), and a passivation effect (inhibition of anode reaction) caused by an increase in pH in the vicinity of the surface, which occurs when these Mg-containing compounds dissolve in moisture present in the environment.

[0063] Even though compounds contain Mg, when the compounds are other than the above-described compounds, the above action cannot be obtained, and the desired effect thus cannot be achieved.

[0064] The compound preferably contains one or more selected from the following group a and one or more selected from the following group b.

[0065] Group a: the group consisting of compound D, compound E, compound F, compound H, and compound I,

[0066] Group b: the group consisting of compound A, compound B, compound C, compound G, and compound J.

[0067] The compounds of the group a are compounds with a significant effect on enhancing red rust resistance by a physical protective action (inhibition of cathode reaction) due to the presence of these compounds, and the compounds of the group b are compounds having a significant effect on enhancing red rust resistance by a passivation action (inhibition of anode reaction) due to an increase in pH in the vicinity of the surface caused when these Mg-containing compounds dissolve in moisture present in the environment.

[0068] By containing the compounds of both the group a and the group b, a more excellent red rust suppressing effect can be obtained as compared with a case of containing only the compounds of one group due to a synergistic effect.

[0069] In addition, from the viewpoint of enhancing corrosion resistance, the compound preferably 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 1. It may be substantially consisting of two or more selected from the above-described group.

[0070] In addition, among the compounds, the total constituent ratio of one or two of the compound H and the compound I is preferably 10% or more in terms of the amount-of-substance ratio (molar ratio).

[0071] In addition, although the presence of the above-described compounds provides the corrosion resistance enhancing effect (red rust resistance enhancing effect), in order to obtain a sufficient effect over the entirety of the surface-treated steel sheet 1, it is preferable that 50% or more, by area fraction, of the non-coated portion 41 where the coating layer 12 is not formed is covered with the above-described compounds. The covered area fraction may be 100%.

[0072] The identification of the compounds present in the non-coated portion 41 is obtained by performing X-ray absorption fine structure analysis (hereinafter, referred to as XAFS analysis) and performing fitting processing of an XAFS spectrum.

[0073] Specifically, the identification is obtained by the following method.

[0074] First, for example, a sample having a sheet thickness × 7 mm × 7 mm including the non-coated portion 41 to be measured is cut out and collected from the surface-treated steel sheet 1. The non-coated portion 41 (for example, a range of 1.0 mm × 1.2 mm) in the sample is subjected to the XAFS analysis to obtain an XAFS spectrum. The compounds are identified by fitting the obtained spectra by linear combination of spectra of standard samples of the respective compounds using Athena (analysis software).

[0075] Measurement conditions for the XAFS analysis are as follows. · Measurement on K absorption edge of Mg · Measurement atmosphere: in high vacuum · Measurement temperature: room temperature · Energy range: 1250 eV to 1540 eV (step: 0.2 eV) · The incident X-ray intensity I 0 is determined from the sample current of the Au mesh. · The detected X-ray intensity I is determined 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 measurement of the sample. · In order to improve S / N ratio, three measurements are performed and the average value of spectra is used for the analysis.

[0076] Fitting is also performed as follows. · The energy is corrected based on the Au4f peak position of XPS. · As illustrated in FIG. 2, the background subtraction is performed to normalize the overall intensity such that the intensity difference between the pre-edge and the post-edge is 1. · The spectrum obtained from the sample is fitted with a linear combination of the spectra of the standard samples of the individual compounds.

[0077] The R factor is used for validation of fitting, and it is determined that when the R factor is 5% or less in the region of 1300 to 1380 eV, the fitting is determined to be valid, whereas when the R factor is more than 5%, the fitting is determined to be invalid. Invalid fitting of the compounds A to J with the standard samples means that it cannot be determined whether at least one compound among the compounds A to J is present. The R factor is calculated by the following equation. Here, d' in the equation represents fitting data (spectrum data obtained by linearly combining the spectra of the individual compounds), and d represents measurement data. R factor = Σ d ′ − d 2 / Σd 2 · When the sum of the constituent ratios of the individual compounds is 100%, a compound having a constituent ratio of 1% or more is determined as "present". In this case, the spectrum obtained from the sample is approximated by a linear combination of spectra obtained by multiplying the spectrum of the standard sample of each compound by a coefficient (that is, when A, B,..., and J are spectra of compounds A, B,..., and J, and a, b,..., and j are coefficients, approximation is performed so that spectrum of the sample = aA + bB +...jJ and a + b +...j = 100%). Each coefficient is defined as the constituent ratio of each compound. The units of a, b, c, ···, and j are molar ratios of the compounds A, B, C, ···, and J, respectively.

[0078] When the above-described fitting is performed, as the standard samples of the individual compounds, the following commercially available reagents or reagents prepared in the following manner are used. · 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: Monoethylene glycol (purity 99.9%, 950 g) and distilled water (50 g) are weighed into a 1 L screw-cap bottle and mixed. NaCl is added so that the concentration is 1 mol / kg. To a 3-necked round flask charged with a monoethylene glycol + water +NaCl solution (250 g), 10.0±0.1 g of 4MgCO 3 ·Mg(OH) 2 ·5H 2 O is added. In this case, a reflux cooler is used. This mixture is exposed to atmospheric pressure and stirred for 3 days under continuous CO 2 bubbling (20 to 50 mL / min). During stirring, the temperature is maintained at 150±5°C using a thermostat. After stirring, the precipitate is filtered with suction and dried. · Compound D (Mg 4 Al 2 (OH) 12 CO 3 ·3H 2 O): Preparation procedure: A 0.20 M MgCl 2 -0.1 M AlCl 3 solution (provided that the amount of MgCl 2 is within the range of 0.019 M to 0.020 M MgCl 2 ) is added dropwise to 0.1 M Na 2 CO 3 , the pH is adjusted to 10, the mixture is left to stand for 24 hours, and then subjected to suction filtration and drying. · 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 6 Al 2 (OH) 16 CO 3 ·4H 2 O containing Mg): Preparation procedure: A 0.2 M ZnCl 2 -0.1 M AlCl 3 -0.050 M MgCl 2 solution (provided that the amount of MgCl 2 is within the range of 0.045 M to 0.055 M MgCl 2 ) is added dropwise to 0.1 M Na 2 CO 3 , the pH is adjusted to 10, and the mixture is left to stand for 24 hours, and then subjected to suction filtration and drying. · 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 5 (CO 3 ) 2 (OH) 6 containing Mg): Preparation procedure: 0.1 M Na 2 CO 3 is added dropwise to a 0.1 M ZnCl2-0.050 M MgCl 2 solution (provided that the amount of MgCl 2 is within the range of 0.045 M to 0.055 M MgCl 2 ), the pH is adjusted to 10, and the mixture is left to stand for 24 hours, and then subjected to suction filtration and drying. · Compound I (Zn 5 (OH) 8 Cl 2 ·H 2 O) containing Mg): Preparation procedure: 0.1 M NaOH is added dropwise to a 0.1 M ZnCl 2 -0.050 M MgCl 2 solution (provided that the amount of MgCl 2 is within the range of 0.045 M to 0.055 M MgCl 2 ), the pH is adjusted to 10, and the mixture is left to stand for 24 hours, and then subjected to suction filtration and drying. · Compound J (NaZn 4 (SO 4 )Cl(OH) 6 ·6H 2 O containing Mg): Preparation procedure: To 30 mL of a 0.5 M ZnSO 4 -0.10 M MgCl 2 (provided that the amount of MgCl 2 is within the range of 0.09 M to 0.011 M MgCl 2 )-1.4 M NaCl solution, 1 g of ZnO powder is added, and 0.1 M NaOH is added dropwise, the pH is adjusted to 10, and the mixture is then stirred for 120 hours, and subsequently subjected to suction filtration and drying.

[0079] In addition, the coverage (coverage area fraction) of the compound in the non-coated portion 41 is determined by the following method.

[0080] The portion where the coating layer 12 is not formed (non-coated portion 41) is subjected to mapping analysis of Mg with micro-X-Ray fluorescence (µ-XRF) to measure the intensity of the µ-XRF spectrum, and the ratio of the area of the region where the concentration of Mg is 0.5 atom% or more to the area of the non-coated portion 41 where the coating layer 12 is not formed is defined as the "coverage of the compound".

[0081] In this case, µ-XRF has the following measurement conditions. Measurement atmosphere: vacuum Acceleration voltage: 15 kV Current value: 50 µA Tube: Rh target X-ray tube Scan speed: 4.00 mmS -1< Polymeter: 30 µm <Manufacturing Method>

[0082] An effect of the surface-treated steel sheet 1 according to the present embodiment can be obtained regardless of the manufacturing method as long as the surface-treated steel sheet 1 has the above-described characteristics, but the surface-treated steel sheet 1 can be manufactured by a manufacturing method including the following steps: (I) a coating step of forming a Zn-coating layer 12 containing Mg on a surface of a steel sheet 11 (base steel sheet); (II) a processing step of cutting and / or punching the steel sheet (coated steel sheet) on which the coating layer 12 (Zn-coating layer) is formed to form the coated steel sheet into any shape; and (III) a compound forming step of forming a predetermined Mg-containing compound on the non-coated portion 41 of the end surface and / or the coated surface.

[0083] Preferred conditions for each step are described.[Coating Step]

[0084] In the coating step, a steel material such as a steel sheet is immersed in a coating bath containing Mg and Zn, or electro coating is performed to form a coating layer 12 on the surface. The formation conditions of the coating layer 12 are not particularly limited. The coating may be performed by a normal method so that sufficient coating adhesion can be obtained.

[0085] In addition, the steel material to be subjected to the coating step and the manufacturing method thereof are not limited. For the surface-treated steel sheet, as the steel sheet to be immersed in the coating bath, for example, a hot-rolled steel sheet described in JIS G 3113:2018 or JIS G 3131:2018, or a cold-rolled steel sheet described in JIS G 3141:2021 or JIS G 3135:2018 can be used. In addition, steel materials such as steel pipes, steel wires, and various members composed of steel other than steel sheets can be used.

[0086] The composition of the coating bath may be adjusted according to the chemical composition of the coating layer 12 to be obtained.

[0087] After the steel material is pulled up from the coating bath, the adhesion amount of the coating layer 12 can be adjusted by wiping as necessary.[Processing Step]

[0088] In the processing step, the coated steel sheet is cut and / or punched into any shape. When cutting or punching is performed, an end surface on which the coating layer 12 is not formed is formed at the cut portion. An end surface is similarly formed in the punching portion.

[0089] In the processing step, bending, drawing, or the like may be further performed to change the shape. In this case, the non-coated portion 41 may be generated in the coated surface.[Compound Forming Step]

[0090] In the compound forming step, the predetermined Mg-containing compound is formed in the non-coated portion 41 (non-coated portion 41 in the end surface and / or the coated surface) where the coating layer 12 is not formed.

[0091] In order to form the compound, the steel sheet after the processing step is brought into contact, for 1 to 20 minutes, with a solution having a pH of 4.5 to 7.0 and a liquid temperature of 25°C to 60°C and containing Cl -< : 1.0 to 100.0 mM, SO 4 2-< : 0.1 to 10.0 mM, Na +< : 1.0 to 100.0 mM, and CO 3 2-< : 1.0 to 100.0 mM, on the coating layer 12 and the non-coated portion 41 where the coating layer 12 is not formed.

[0092] After the above contacting, the steel sheet is sufficiently dried in an inert atmosphere such as nitrogen gas or argon gas at a temperature of 40°C to 60°C and a relative humidity of 20% to 40% for 5 to 20 minutes.

[0093] When the concentrations of Cl -< , SO 4 2-< , Na +< , and CO 3 2-< in the solution or the pH of the solution are outside the above-described ranges, the adhesion between the compound to be formed in the non-coated portion 41 and the steel sheet 11 (base material) deteriorates, and the predetermined compound is not sufficiently formed in the non-coated portion 41. In addition, when the contact time is shorter than the above-described range, the predetermined compound is not sufficiently formed in the non-coated portion 41. When the contact time is more than 20 minutes, corrosion of the coated portion may proceed, leading to deterioration of corrosion resistance of the coated portion

[0094] In addition, when the temperature of the solution is lower than 25°C or higher than 60°C, the formation of the predetermined compound in the non-coated portion is insufficient.

[0095] In addition, in a case where the dry atmosphere is other than an inert atmosphere such as nitrogen gas or argon gas, red rust may occur in the non-coated portion.

[0096] When the drying temperature is lower than 40°C or higher than 60°C, the formation of the predetermined compound in the non-coated portion may be insufficient, and when the drying temperature is higher than 60°C, the compound may not remain in the non-coated portion because the drying proceeds rapidly. As a result, the predetermined compound is not formed, and red rust may occur in the non-coated portion.

[0097] When the relative humidity is less than 20% or more than 40%, the formation of the predetermined compound in the non-coated portion is insufficient. As a result, the predetermined compound is not formed, and red rust may occur in the non-coated portion.

[0098] When the drying time is shorter than 5 minutes or longer than 20 minutes, the formation of the predetermined compound in the non-coated portion is insufficient. As a result, the predetermined compound is not formed, and red rust may occur in the non-coated portion.Examples

[0099] As a steel material, a hot-rolled steel sheet having a sheet thickness of 4.5 mm satisfying JIS G 3131:2018 was prepared.

[0100] This steel sheet was subjected to hot-dip coating to form a Zn-coating layer having a chemical composition described in Tables 1 to 6. The concentration (amount) of impurities in the coating layer was 0.1% or less.

[0101] In addition, the adhesion amount of the coating layer was 135 g / m 2< on each of the front and back surfaces, which are the coated surfaces.

[0102] The obtained coated steel sheet (surface-treated steel sheet) was cut with an electric shear to form an end surface having a portion including the coating layer and a portion including no coating layer (the steel sheet was exposed). The non-coated portion was not formed in the coated surface.

[0103] For sample Nos. 1-1 to 1-107 and 2-1 to 2-22 of the coated steel sheet, solutions illustrated in Tables 7 to 12 were brought into contact with the end surfaces in order to form an Mg-containing compound in the end surfaces. Thereafter, drying was performed in an atmosphere described in Tables 13 to 18 in a nitrogen gas atmosphere.

[0104] On the other hand, for sample Nos. 2-23 to 2-27, the formation of compounds was attempted by any of the following methods. · Compound forming method 1: immersion in a 5 mass% NaCl aqueous solution (pH: 5 to 6, solution temperature: 30°C) for 20 minutes · Compound forming method 2: immersion in a 5 mass% NaCl aqueous solution (pH: 5 to 6, solution temperature: 25°C) for 72 hours · Compound forming method 3: 28.6 g of magnesium ethoxide is diluted with pure water to 200 cc, and then applied by a pulling method using a bath diluted to 1 L with ethylene glycol monoethyl ether, dried, and then heat-treated at 100°C to 400°C. · Compound forming method 4: By using a molten salt containing 60 mol% of MgCl 2 , 20 mol% of NaCl, and 20 mol% of KCl and dissolved by heating to 500°C, a cathode electrolysis treatment was performed at a current density of 20 A / dm 2< and an energizing time of 5 seconds in an atmosphere with a partial pressure of H 2 O of 16 mmHg. ·Compound forming method 5: In an aqueous solution containing 0.3 g / L of Mg 2+< and 0.5 g / L of NO 3 -< and having a pH of 7.0, a cathode electrolysis treatment was performed at a current density of 50 A / dm 2< and an energizing time of 5 seconds.

[0105] On the surface-treated steel sheet after the compound forming step, the compound present in the end surface was identified and the coverage on the end surface was measured in the same manner as described above. When a plurality of compounds were present, the presence ratio thereof was also determined.

[0106] Although not illustrated in the table, the thickness of each compound was set to about 10 nm to 30 µm by changing the time for bringing the steel sheet into contact with the solution. In addition, "ND" in the table, which means that the compounds are not detected, indicates that none of the compounds A to J were detected. More specifically, in the fitting of the compounds A to J with the standard samples, the R factor is more than 5% in the region of 1300 to 1380 eV, the fitting of the compounds A to J with the standard samples was invalid, which means that it cannot be determined whether at least one compound among the compounds A to J is present.

[0107] The XAFS analysis was performed on beamline BL1N2 at the AICHI SR center.

[0108] The results are indicated in Tables 19 to 24.

[0109] In addition, the surface-treated steel sheet after contact with the solution and drying was subjected to an exposure test to determine the area fraction of red rust in the end surface after 50 days.

[0110] The exposure conditions were as follows.

[0111] The steel sheet sample was inclined 30° from the horizontal so that the processed cut end surface was positioned upward, and was placed facing south to conduct an atmospheric exposure test. After the exposure, the sample was evaluated as follows by the ratio of the area where red rust has occurred to the area where no coating 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%

[0112] Those having a red rust area fraction of SS, S, AA, or A after 50 days of exposure were determined to have excellent red rust resistance.

[0113] The case where the ratio of the area where red rust has occurred was more than 100% is a case where red rust has occurred not only in the portion where the coating layer is not formed but also in the surrounding area.

[0114] In addition, in order to evaluate corrosion resistance under conditions severer than atmospheric exposure, a test of 30 cycles was performed according to 8.1 (neutral salt water spray cycle test method) of JIS H8502:1999, and evaluation was performed as follows by the ratio of the area where red rust has occurred to the area where no coating layer was formed in the sample. 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%

[0115] In a case where the area fraction of red rust after 30 cycles in the neutral salt spray test was SS, S, AA, A, or B, it was determined that red rust resistance was further excellent. [Table 1]Sample No.Chemical composition of coating layer (mass%)MgAlOther elementsZn and impurities1-10.30.00.099.71-23.04.00.093.01-33.04.00.093.01-43.04.00.093.01-53.04.00.093.01-63.04.00.093.01-73.04.00.093.01-83.04.00.093.01-90.34.00.095.71-100.34.00.095.71-110.34.00.095.71-123.04.0Sn:1.0%92.01-133.04.0Bi: 1.0%92.01-143.04.0In: 1.0%92.01-153.04.0Ca:1.0%92.01-163.04.0Y:0.1%92.91-173.04.0La:0.1%92.91-183.04.0Ce:0.1%92.91-193.04.0Si:0.1%92.91-203.04.0Cr:0.10%92.91-213.04.0Ti:0.10%92.91-223.04.0Ni:0.10%92.91-233.04.0Co:0.10%92.91-243.04.0V:0.10%92.91-253.04.0Nb:0.10%92.91-263.04.0Cu:0.10%92.91-273.04.0Mn:0.10%92.91-283.04.0Fe:0.1%92.91-293.04.0Sr:0.1%92.91-303.04.0Sb:0.1%92.91-313.04.0Pb:0.1%92.91-323.04.0B:0.1%92.9 [Table 2] Sample No.Chemical composition of coating layer (mass%)MgAlOther elementsZn and impurities1-333.06.00.091.01-343.06.00.091.01-353.06.00.091.01-363.06.00.091.01-372.57.00.090.51-382.57.00.090.51-392.57.00.090.51-403.07.00.090.01-413.07.00.090.01-423.010.00.087.01-433.010.00.087.01-443.010.00.087.01-453.010.00.087.01-463.010.50.086.51-473.012.50.084.51-483.012.50.084.51-493.011.00.086.01-503.011.00.086.01-513.011.00.086.01-523.011.00.086.01-533.011.00.086.01-543.011.00.086.01-553.011.00.086.0 [Table 3] Sample No.Chemical composition of coating layer (mass%)MgAlOther elementsZn and impurities1-563.011.00.086.01-572.511.00.086.51-582.511.00.086.51-592.511.00.086.51-602.511.00.086.51-612.511.00.086.51-623.012.00.085.01-633.012.00.085.01-643.012.00.085.01-653.012.00.085.01-663.012.00.085.01-673.010.00.087.01-683.010.00.087.01-693.012.50.084.51-703.012.50.084.51-713.011.00.086.01-723.011.00.086.01-733.011.00.086.01-743.011.00.086.01-753.011.00.086.0 [Table 4] Sample No.Chemical composition of coating layer (mass%)MgAlOther elementsZn and impurities1-766.013.00.081.01-776.013.00.081.01-786.013.00.081.01-796.018.00.076.01-806.018.00.076.01-816.018.00.076.01-8212.525.00.062.51-836.012.00.082.01-846.013.00.081.01-856.018.00.076.01-862.05.00.093.01-872.05.00.093.01-885.05.00.090.01-895.05.00.090.01-905.05.00.090.01-9112.54.00.083.51-923.00.00.097.0 [Table 5] Sample No.Chemical composition of coating layer (mass%)MgAlOther elementsZn and impurities1-934.00.00.096.01-942.02.00.096.01-952.02.00.096.01-962.02.00.096.01-975.02.00.093.01-985.02.00.093.01-995.02.00.093.01-10012.50.00.087.51-1012.02.00.096.01-1025.02.00.093.01-1035.02.00.093.01-1045.02.00.093.01-1052.00.00.098.01-1064.00.00.096.01-1070.50.00.099.5 [Table 6] Sample No.Chemical composition of coating layer (mass%)MgAlOther elementsZn and impurities2-10.16.00.093.92-20.26.00.093.82-33.010.00.087.02-43.010.00.087.02-53.010.00.087.02-63.010.00.087.02-73.010.00.087.02-83.010.00.087.02-93.010.00.087.02-103.010.00.087.02-113.010.00.087.02-123.010.00.087.02-133.010.00.087.02-143.010.00.087.02-153.010.00.087.02-163.010.00.087.02-173.010.00.087.02-183.010.00.087.02-193.010.00.087.02-203.010.00.087.02-213.010.00.087.02-223.010.00.087.02-233.010.00.087.02-243.010.00.087.02-253.010.00.087.02-263.010.00.087.02-273.010.00.087.0 [Table 7] Sample No.Compound forming stepSolutionCl -< concentration (mM)SO 4 2-< concentration (mM)Na +< concentration (mM)CO 3 2-< concentration (mM)Zn(OH) 2 addition amount (mM)pH1-11.00.11.01.010.06.51-21.00.11.01.010.06.51-310.00.110.01.010.05.51-450.00.150.010.010.05.51-51.01.01.010.010.06.11-610.01.010.010.010.06.31-750.01.050.010.010.04.51-81.01.01.010.010.07.01-910.01.010.010.010.06.21-1050.01.050.010.010.06.81-11100.010.0100.010.010.06.91-121.00.25.01.010.05.51-131.00.25.01.010.06.51-141.00.25.01.010.05.51-151.00.25.01.010.05.51-161.00.25.01.010.06.11-171.00.25.01.010.06.31-181.00.25.01.010.04.51-191.00.25.01.010.07.01-201.00.25.01.010.06.21-211.00.25.01.010.06.81-221.00.25.01.010.06.51-231.00.25.01.010.05.51-241.00.25.01.010.05.51-251.00.25.01.010.06.11-261.00.25.01.010.06.31-271.00.25.01.010.04.51-281.00.25.01.010.07.01-291.00.25.01.010.06.21-301.00.25.01.010.06.81-311.00.25.01.010.06.91-321.00.25.01.010.06.5 [Table 8] Sample No.Compound forming stepSolutionCl -< concentration (mM)SO 4 2-< concentration (mM)Na +< concentration (mM)CO 3 2-< concentration (mM)Zn(OH) 2 addition amount (mM)pH1-331.00.11.010.010.06.51-3410.00.110.010.010.06.51-3510.05.010.010.010.06.51-36100.05.0100.010.010.06.51-371.00.11.010.010.05.51-381.05.01.010.010.05.51-39100.05.0100.010.010.06.11-40100.00.1100.010.010.06.31-4150.05.050.010.010.04.51-421.00.11.010.010.07.01-4310.00.110.010.010.06.21-44100.00.1100.010.010.06.81-451.05.01.010.010.06.91-461.00.11.010.010.06.51-4750.00.150.010.010.04.51-48100.00.1100.010.010.04.51-4910.00.110.030.010.04.51-5050.00.150.030.010.04.51-5150.00.150.030.010.04.51-5250.00.150.010.095.06.51-53100.00.1100.010.095.06.51-541.05.01.010.095.06.51-5550.05.050.010.080.06.5 [Table 9] Sample No.Compound forming stepSolutionCl -< concentration (mM)SO 4 2-< concentration (mM)Na +< concentration (mM)CO 3 2-< concentration (mM)Zn(OH) 2 addition amount (mM)pH1-56100.05.0100.010.080.06.51-5710.00.110.010.055.04.51-5850.00.150.010.095.04.51-59100.00.1100.010.095.04.51-6010.05.010.010.065.04.51-6150.05.050.010.065.04.51-621.00.11.010.095.05.51-6310.00.110.010.095.05.51-6450.00.150.010.095.05.51-651.05.01.010.080.05.51-6610.05.010.010.080.05.51-6750.00.150.010.055.05.51-6810.05.010.010.095.05.51-6910.00.110.010.095.05.51-701.05.01.010.095.05.51-711.00.11.030.095.04.51-72100.00.1100.030.095.04.51-731.00.11.030.065.04.51-7410.00.110.030.065.06.81-751.00.11.030.080.06.8 [Table 10] Sample No.Compound forming stepSolutionCl -< concentration (mM)SO 4 2-< concentration (mM)Na +< concentration (mM)CO 3 2-< concentration (mM)Zn(OH) 2 addition amount (mM)pH1-761.00.11.030.065.06.81-7710.00.110.0100.065.06.81-7850.00.150.0100.065.06.01-791.00.11.0100.065.06.01-8010.00.110.0100.010.06.01-8150.00.150.0100.065.06.01-821.00.11.0100.065.06.81-831.00.11.030.065.06.01-8410.00.110.0100.065.06.01-851.00.11.0100.065.06.11-861.00.11.030.095.04.51-871.00.11.0100.010.04.51-881.00.11.0100.055.04.51-891.00.11.030.080.04.51-901.00.11.030.010.04.51-9110.05.010.010.065.07.01-921.00.25.01.010.05.0 [Table 11] Sample No.Compound forming stepSolutionCl -< concentration (mM)SO 4 2-< concentration (mM)Na +< concentration (mM)CO 3 2-< concentration (mM)Zn(OH) 2 addition amount (mM)pH1-931.00.11.010.010.06.91-941.00.11.030.095.04.51-951.00.11.0100.010.04.51-961.00.11.0100.010.04.51-971.00.11.030.055.04.51-981.00.11.030.080.04.51-9910.05.010.010.010.04.51-10010.05.010.010.065.07.01-1011.00.11.030.095.04.51-1021.00.11.0100.055.04.51-1031.00.11.030.065.04.51-1041.00.11.0100.065.06.11-1051.00.11.0100.010.06.11-1065.05.05.0100.010.06.11-10710.01.010.010.010.06.2 [Table 12] Sample No.Compound forming stepSolutionCl -< concentration (mM)SO 4 2-< concentration (mM)Na +< concentration (mM)CO 3 2-< concentration (mM)Zn(OH) 2 addition amount (mM)pH2-11.00.11.010.010.05.02-21.00.11.010.010.05.02-30.510.010.010.010.05.52-4200.010.010.010.010.05.52-510.0-10.010.010.05.52-610.050.010.010.010.05.52-710.010.00.110.010.05.52-810.010.0300.010.010.05.52-910.010.010.00.310.05.52-1010.010.010.0200.010.05.52-1110.010.010.010.010.04.02-1210.010.010.010.010.07.22-1310.010.010.010.010.05.52-1410.010.010.010.010.05.52-1510.010.010.010.010.05.52-1610.010.010.010.010.05.52-1710.010.010.010.010.05.52-1810.010.010.010.010.05.52-1910.010.010.010.010.05.52-2010.010.010.010.010.05.52-2110.010.010.010.010.05.52-2210.010.010.010.00.35.52-23Compound forming method 12-24Compound forming method 22-25Compound forming method 32-26Compound forming method 42-27Compound forming method 5 [Table 13] Sample No.Compound forming stepSolutionContactDryingLiquid temperature (°C)Contact time (min)AtmosphereAtmospheric temperature (°C)Atmospheric relative humidity (%)Drying time (min)1-1251Nitrogen gas404051-2251Nitrogen gas404051-3251Nitrogen gas404051-4251Nitrogen gas404051-5251Nitrogen gas404051-6251Nitrogen gas404051-7251Nitrogen gas404051-8251Nitrogen gas404051-9251Nitrogen gas404051-10251Nitrogen gas404051-11251Nitrogen gas404051-12305Nitrogen gas5030101-13305Nitrogen gas5030101-14305Nitrogen gas5030101-15305Nitrogen gas5030101-16305Nitrogen gas5030101-17305Nitrogen gas5030101-18305Nitrogen gas5030101-19305Nitrogen gas5030101-20305Nitrogen gas5030101-21305Nitrogen gas5030101-22305Nitrogen gas5030101-23305Nitrogen gas5030101-24305Nitrogen gas5030101-25305Nitrogen gas5030101-26305Nitrogen gas5030101-27305Nitrogen gas5030101-28305Nitrogen gas5030101-29305Nitrogen gas5030101-30305Nitrogen gas5030101-31305Nitrogen gas5030101-32305Nitrogen gas503010 [Table 14] Sample No.Compound forming stepSolutionContactDryingLiquid temperature (°C)Contact time (min)AtmosphereAtmospheric temperature (°C)Atmospheric relative humidity (%)Drying time (min)1-334010Nitrogen gas6020101-344010Nitrogen gas6020201-354010Nitrogen gas6020201-364010Nitrogen gas6020201-374010Nitrogen gas6020201-384010Nitrogen gas6020201-394010Nitrogen gas6020201-404010Nitrogen gas6020201-414010Nitrogen gas6020201-424010Nitrogen gas6020201-434010Nitrogen gas6020201-444010Nitrogen gas6020201-454010Nitrogen gas6020201-464010Nitrogen gas6020201-474010Nitrogen gas6020201-484010Nitrogen gas6020201-494010Nitrogen gas6020201-504010Nitrogen gas6020201-514010Nitrogen gas6020201-525015Nitrogen gas6020101-535015Nitrogen gas6020101-545015Nitrogen gas6020101-555015Nitrogen gas602010 [Table 15] Sample No.Compound forming stepSolutionContactDryingLiquid temperature (°C)Contact time (min)AtmosphereAtmospheric temperature (°C)Atmospheric relative humidity (%)Drying time (min)1-565015Nitrogen gas6020101-575015Nitrogen gas6020101-585015Nitrogen gas6020101-595015Nitrogen gas6020101-605015Nitrogen gas6020101-615015Nitrogen gas6020101-625015Nitrogen gas6020101-635015Nitrogen gas6020101-645015Nitrogen gas6020101-655015Nitrogen gas6020101-665015Nitrogen gas6020101-675015Nitrogen gas6020101-685015Nitrogen gas6020101-695015Nitrogen gas6020101-705015Nitrogen gas6020101-715015Nitrogen gas6020101-725015Nitrogen gas6020101-735015Nitrogen gas6020101-745015Nitrogen gas6020101-755015Nitrogen gas602010 [Table 16] Sample No.Compound forming stepSolutionContactDryingLiquid temperature (°C)Contact time (min)AtmosphereAtmospheric temperature (°C)Atmospheric relative humidity (%)Drying time (min)1-766015Nitrogen gas6020101-776015Nitrogen gas6020101-786015Nitrogen gas6020101-796015Nitrogen gas6020101-806015Nitrogen gas6020101-816015Nitrogen gas6020101-826015Nitrogen gas6020101-836020Nitrogen gas6020101-846020Nitrogen gas6020101-856020Nitrogen gas6020101-86301Nitrogen gas5030101-87301Nitrogen gas5030101-88301Nitrogen gas5030101-89301Nitrogen gas5030101-90301Nitrogen gas5030101-91301Nitrogen gas5030101-92405Nitrogen gas503010 [Table 17] Compound forming stepSample No.SolutionContactDryingLiquid temperature (°C)Contact time (min)AtmosphereAtmospheric temperature (°C)Atmospheric relative humidity (%)Drying time (min)1-934010Nitrogen gas5030101-94305Nitrogen gas5030101-95305Nitrogen gas5030101-96305Nitrogen gas5030101-97305Nitrogen gas5030101-98305Nitrogen gas5030101-99305Nitrogen gas5030101-1003020Nitrogen gas5030101-101301Nitrogen gas5030101-102301Nitrogen gas5030101-103301Nitrogen gas5030101-104301Nitrogen gas5030101-105301Nitrogen gas5030101-106301Nitrogen gas5030101-107301Nitrogen gas503010 [Table 18] Sample No.Compound forming stepSolutionContactDryingLiquid temperature (°C)Contact time (min)AtmosphereAtmospheric temperature (°C)Atmospheric relative humidity (%)Drying time (min)2-1301Nitrogen gas5030102-2301Nitrogen gas5030102-3301Nitrogen gas5030102-4301Nitrogen gas5030102-5301Nitrogen gas5030102-6301Nitrogen gas5030102-7301Nitrogen gas5030102-8301Nitrogen gas5030102-9301Nitrogen gas5030102-10301Nitrogen gas5030102-11301Nitrogen gas5030102-12301Nitrogen gas5030102-13201Nitrogen gas5030102-14300.4Nitrogen gas5030102-15301Air5030102-16301Nitrogen gas2030102-17301Nitrogen gas5050102-18301Nitrogen gas503032-19301Nitrogen gas2030102-20301Nitrogen gas5050102-21301Nitrogen gas503032-22301Nitrogen gas5030102-23Compound forming method 12-24Compound forming method 22-25Compound forming method 32-26Compound forming method 42-27Compound forming method 5 [Table 19] Sample No.CompoundsEvaluation of red rust resistanceRemarksTypesRatio of compound (amount-of-substance ratio)Coverage (%)Exposure 50 daysJASO 30 cycles1-1AA:100%41ABInvention Example1-2AA:100%39ABInvention Example1-3BB:100%29ABInvention Example1-4CC:100%28ABInvention Example1-5DD:100%27ABInvention Example1-6EE:100%26ABInvention Example1-7FF:100%29ABInvention Example1-8GG:100%28ABInvention Example1-9HH:100%28ABInvention Example1-10II:100%28ABInvention Example1-11JJ:100%26ABInvention Example1-12AA:100%51AAAInvention Example1-13AA:100%52AAAInvention Example1-14AA:100%53AAAInvention Example1-15AA:100%55AAAInvention Example1-16AA:100%57AAAInvention Example1-17AA:100%51AAAInvention Example1-18AA:100%56AAAInvention Example1-19AA:100%59AAAInvention Example1-20AA:100%58AAAInvention Example1-21AA:100%51AAAInvention Example1-22AA:100%51AAAInvention Example1-23AA: 100%51AAAInvention Example1-24AA: 100%52AAAInvention Example1-25AA:100%53AAAInvention Example1-26AA:100%54AAAInvention Example1-27AA:100%55AAAInvention Example1-28AA:100%58AAAInvention Example1-29AA:100%51AAAInvention Example1-30AA:100%52AAAInvention Example1-31AA:100%50AAAInvention Example1-32AA:100%51AAAInvention Example [Table 20] Sample No.CompoundsEvaluation of red rust resistanceRemarksTypesRatio of compound (amount-of-substance ratio)Coverage (%)Exposure 50 daysJASO 30 cycles1-33A·BA:50%61AAAInvention ExampleB:50%1-34A·CA:50%62AAAInvention ExampleC:50%1-35A·GA:50%64AAAInvention ExampleG:50%1-36A·JA:50%62AAAInvention ExampleJ:50%1-37B·CB:50%63AAAInvention ExampleC:50%1-38B·GB:50%67AAAInvention ExampleG:50%1-39B·JB:50%65AAAInvention ExampleJ:50%1-40C·GC:50%66AAAInvention ExampleG:50%1-41C·JC:50%65AAAInvention ExampleJ:50%1-42D·ED:50%59AAAInvention ExampleE:50%1-43D·FD:50%58AAAInvention ExampleF:50%1-44D·HD:50%57SAInvention ExampleH:50%1-45D·ID:50%61SAInvention ExampleI:50%1-46E·FE:50%62AAAInvention ExampleF:50%1-47E·HE:50%60AAAInvention ExampleH:50%1-48E·IE:50%63AAAInvention ExampleI:50%1-49F·HF:50%61AAAInvention ExampleH:50%1-50F·IF:50%60AAAInvention ExampleI:50%1-51G·JG:50%61AAAInvention ExampleJ:50%1-52A·DA:50%62SAAInvention ExampleD:50%1-53A·EA:50%60SAAInvention ExampleE:50%1-54A·FA:50%6SAAInvention ExampleF:50%1-55A·HA:50%69SAAInvention ExampleH:50% [Table 21] Sample No.CompoundsEvaluation of red rust resistanceRemarksTypesRatio of compound (amount-of-substance ratio)Coverage (%)Exposure 50 daysJASO 30 cycles1-56A·IA:50%60SAAInvention Example1:50%1-57B·DB:50%64SSSInvention ExampleD:50%1-58B·EB:50%65SAAInvention ExampleE:50%1-59B·FB:50%67SAAInvention ExampleF:50%1-60B·HB:50%61SSSSInvention ExampleH:50%1-61B·IB:50%62SSSSInvention ExampleI:50%1-62C·DC:50%63SAAInvention ExampleD:50%1-63C·EC:50%64SAAInvention ExampleE:50%1-64C·FC:50%65SAAInvention ExampleF:50%1-65C·HC:50%66SAAInvention ExampleH:50%1-66C·IC:50%60SAAInvention Example1:50%1-67D·GD:50%60SSSInvention ExampleG:50%1-68D·JD:50%60SAAInvention ExampleJ:50%1-69E·GE:50%61SAAInvention ExampleG:50%1-70E·JE:50%61SAAInvention ExampleJ:50%1-71F·GF:50%62SAAInvention ExampleG:50%1-72F·JF:50%63SAAInvention ExampleJ:50%1-73G·HG:50%64SSSSInvention ExampleH:50%1-74G·IG:50%66SSSSInvention ExampleI:50%1-75I·JI:50%65SAAInvention ExampleJ:50% [Table 22] Sample No.CompoundsEvaluation of red rust resistanceRemarksTypesRatio of compound (amount-of-substance ratio)Coverage (%)Exposure 50 daysJASO 30 cyclesB:33%1-76B·D·ID:34%61SSSSInvention ExampleI:34%B:33%1-77B·G·IG:34%60SSSSInvention Example1:34%B:33%1-78B·H·IH:34%60SSSSInvention ExampleI:34%D:33%1-79D·G·IG:34%62SSSSInvention ExampleI:34%1-80D·H·ID:33%61SAAInvention ExampleH:34%I:34%G:33%1-81G·H·IH:34%63SSSSInvention ExampleI:34%B·D·G·H·IB:25%D:25%1-82G:25%64SSSSInvention ExampleH:25%I:25%B:33%1-83B·D·HD:34%65SSSSInvention ExampleH:34%B:33%1-84B·G·HG:34%66SSSSInvention ExampleH:34%D:33%1-85D·G·HG:34%61SSSSInvention ExampleH:34%1-86C·FC:50%31AAAInvention ExampleF:50%1-87B·GB:50%32AAInvention ExampleG:50%1-88D·GD:50%39SSInvention ExampleG:50%1-89C·IC:50%38AAAAInvention ExampleI:50%1-90D·ID:50%37AAAInvention ExampleI:50%1-91B·HB:50%38SSSInvention ExampleH:50%1-92AA:100%51AAAInvention Example [Table 23] Sample No.CompoundsEvaluation of red rust resistanceRemarksTypesRatio of compound (amount-of-substance ratio)Coverage (%)Exposure 50 daysJASO 30 cycles1-93A·BA:50%61AAAInvention ExampleB:50%1-94C·FC:50%51AAAAInvention ExampleF:50%1-95B·GB:50%51AAAInvention ExampleG:50%1-96HH: 100%52AAAInvention Example1-97D·GD:50%53SSInvention ExampleG:50%1-98C·IC:50%61AAAAInvention ExampleI:50%1-99D·ID:50%62AAAInvention ExampleI:50%1-100B·HB:50%59SSSInvention ExampleH:50%1-101C·FC:50%29AAAInvention ExampleF:50%1-102D·GD:50%30AASInvention ExampleG:50%1-103C·IC:50%31AAAInvention ExampleI:50%D:33%1-104D·G·HG:34%32SSSInvention ExampleH:34%1-105B·GB:50%34AAAInvention ExampleG:50%1-106B·HB:50%31AAAInvention ExampleG:50%1-107HH:100%28ABInvention Example [Table 24] Sample No.CompoundsEvaluation of red rust resistanceRemarksTypesRatio of compound (amount-of-substance ratio)Coverage (%)Exposure 50 daysJASO 30 cycles2-1ND--BCComparative Example2-2ND--BCComparative Example2-3ND--CCComparative Example2-4ND--CCComparative Example2-5ND--CCComparative Example2-6ND--CCComparative Example2-7ND--CCComparative Example2-8ND--CCComparative Example2-9ND--CCComparative Example2-10ND--CCComparative Example2-11ND--CCComparative Example2-12ND--CCComparative Example2-13ND--CCComparative Example2-14ND--CCComparative Example2-15ND--CCComparative Example2-16ND--CCComparative Example2-17ND--CCComparative Example2-18ND--CCComparative Example2-19ND--CCComparative Example2-20ND--CCComparative Example2-21ND--CCComparative Example2-22ND--CCComparative Example2-23ND--CCComparative Example2-24ND--CCComparative Example2-25ND--CCComparative Example2-26ND--CCComparative Example2-27ND--CCComparative Example

[0116] As can be seen from Tables 1 to 24, the surface-treated steel sheet having the predetermined compound in the end surface had an excellent red rust resistance of the end surface. In addition, it was found that the red rust resistance may be further excellent depending on the types, ratios, coverages, combinations, and the like of the compounds.

[0117] On the other hand, when the predetermined compound was not formed in the end surface, the red rust resistance of the end surface was poor. In the sample Nos. 2-23 to 2-27 to which the compound forming methods 1 to 5 were applied, the Mg-containing compound was not formed in the non-coated portion, and only the Zn-based compound was formed.INDUSTRIAL APPLICABILITY

[0118] According to the present invention, it is possible to provide the surface-treated steel in which the occurrence of red rust in the non-coated portion is suppressed, and industrial applicability is thus high.REFERENCE SIGNS LIST

[0119] 1 Surface-treated steel sheet (surface-treated steel) 11 Steel sheet 12 Coating layer (Zn-coating layer) 31 Compounds 41 non-coated portion 101 Surface 102 End surface 103 Coated surface

Claims

1. A surface-treated steel comprising: a steel material; and a coating layer formed on at least part of a surface of the steel material, wherein the coating layer is a Zn-coating layer containing 0.3 to 12.5 mass% of Mg, and when a portion of the surface of the steel material where the coating layer is not formed is defined as a non-coated portion, one or more compounds of a compound A, a compound B, a compound C, a compound D, a compound E, a compound F, a compound G, a compound H, a compound I, and a compound J are present in at least part of the non-coated portion, the compounds A to J being as follows, 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; and Compound J: NaZn4(SO4)Cl(OH)6·6H2O containing Mg.

2. The surface-treated steel according to claim 1, wherein the coating layer contains 4.0 to 25.0 mass% of Al.

3. The surface-treated steel according to claim 1 or 2, wherein 50% or more, by area fraction, of the non-coated portion is covered with the one or more compounds.

4. The surface-treated steel according to any one of claims 1 to 3, wherein the compounds include: 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; and 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.

5. The surface-treated steel according to any one of claims 1 to 4, wherein the compounds include 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.

6. The surface-treated steel according to any one of claims 1 to 5, wherein a total constituent ratio, by molar ratio, of either one or both of the compound H and the compound I among the one or more compounds is 10% or more.

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