SURFACE-TREATED STEEL

Abstract

This surface-treated steel includes surface-treated steel comprising: a steel sheet; a plated layer including zinc formed on the steel sheet; and a film formed on the plated layer, wherein the film has a thickness of 100 nm or more and 1000 nm or less, wherein the film includes: an amorphous phase A containing Si, C, O, P, Zn, and V, and one or two or more kinds selected from the group consisting of Ti, Zr, and Al as constituent elements, wherein Zn/Si, which is a peak intensity ratio between Zn and Si, is 1.0 or more, and V/P, which is a mass ratio between V and P, is 0.050 to 1.000 when analysis is performed by EDS; and an amorphous phase B containing Si, O, and Zn, wherein the amorphous phase B has a Zn/Si ratio of less than 1.0, the Zn/Si ratio is a peak intensity ratio between Zn and Si when analysis is performed by EDS, a Zn content of the amorphous phase A is 10 mass % or less, and in a cross section in a thickness direction, a percentage of a length of an interface between the plated layer and the amorphous phase B to a length of an interface between the plated layer and the film is 30% or more.

Claims

1. A Surface-treated steel comprising: a steel sheet; a plated layer including zinc formed on the steel sheet; and a film formed on the plated layer, wherein the film has a thickness of 100 nm or more and 1000 nm or less, wherein the film includes: an amorphous phase A containing Si, C, O, P, Zn, and V, and one or two or more kinds selected from the group consisting of Ti, Zr, and Al as constituent elements, wherein Zn/Si, which is a peak intensity ratio between Zn and Si, is 1.0 or more, and V/P, which is a mass ratio between V and P, is 0.050 to 1.000 when analysis is performed by EDS; and an amorphous phase B containing Si, O, and Zn, wherein the amorphous phase B has a Zn/Si of less than 1.0, the Zn/Si is a peak intensity ratio between Zn and Si when analysis is performed by EDS, a Zn content of the amorphous phase A is 10 mass % or less, and in a cross section in a thickness direction, a percentage of a length of an interface between the plated layer and the amorphous phase B to a length of an interface between the plated layer and the film is 30% or more.

2. The surface-treated steel according to claim 1, wherein a chemical composition of the plated layer includes, by mass %, Al: 0.1% or more and less than 25.0%, Mg: 0% or more and less than 12.5%, Sn: 0% or more and 20% or less, Bi: 0% or more and less than 5.0%, In: 0% or more and less than 2.0%, Ca: 0% or more and 3.0% or less, Y: 0% or more and 0.5% or less, La: 0% or more and less than 0.5%, Ce: 0% or more and less than 0.5%, Si: 0% or more and less than 2.5%, Cr: 0% or more and less than 0.25%, Ti: 0% or more and less than 0.25%, Ni: 0% or more and less than 0.25%, Co: 0% or more and less than 0.25%, V: 0% or more and less than 0.25%, Nb: 0% or more and less than 0.25%, Cu: 0% or more and less than 0.25%, Mn: 0% or more and less than 0.25%, Fe: 0% or more and 5.0% or less, Sr: 0% or more and less than 0.5%, Sb: 0% or more and less than 0.5%, Pb: 0% or more and less than 0.5%, B: 0% or more and less than 0.5%, and the remainder: Zn and impurities.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0024] FIG. 1 is a view illustrating an example of a cross section of a surface-treated steel according to the present embodiment.

EMBODIMENTS OF THE INVENTION

[0025] Hereinafter, a surface-treated steel according to an embodiment of the present invention (surface-treated steel according to the present embodiment) is described.

[0026] As shown in FIG. 1, the surface-treated steel 1 according to the present embodiment includes a steel sheet 11, a plated layer 12 containing zinc formed on the steel sheet 11, and a film 13 formed on the plated layer 12.

[0027] The film 13 has an amorphous phase A131 having a predetermined constituent element and an amorphous phase B132 different from the amorphous phase A131.

[0028] In FIG. 1, the plated layer 12 and the film 13 are formed only on one surface of the steel sheet 11, but may be formed on both surfaces. Further, the plated layer 12 may be formed on at least a part of the steel sheet (surface), but may be formed on the entire surface. The film 13 may be formed on at least a part of the plated layer 12 (surface), but may be formed on the entire surface.

[0029] Hereinafter, the steel sheet 11, the plated layer 12, and the film 13 is described.

<Steel Sheet>

[0030] In the surface-treated steel 1 according to the present embodiment, excellent coating adhesion and corrosion resistance can be obtained by the plated layer 12 and the film 13. Therefore, the steel sheet 11 is not particularly limited. The steel sheet 11 may be determined according to a product to be applied, required strength, sheet thickness, and the like, and for example, a hot-rolled steel sheet described in JIS G3113: 2018 or JIS G3131: 2018, or a cold-rolled steel sheet described in JIS G3135: 2018 or JIS G3141: 2017 can be used.

<Plated Layer>

[0031] The plated layer 12 included in the surface-treated steel 1 according to the present embodiment is a zinc-based plated layer formed on the surface of the steel sheet 11 and containing zinc.

[0032] The chemical composition of the plated layer 12 is not limited as long as it is a zinc-based plated layer. However, when the chemical composition includes, by mass %, Al: 0.1% or more and less than 25.0%, Mg: 0% or more and less than 12.5%, Sn: 0% or more and 20% or less, Bi: 0% or more and less than 5.0%. In: 0% or more and less than 2.0%, Ca: 0% or more and 3.0% or less, Y: 0% or more and 0.5% or less. La: 0% or more and less than 0.5%, Ce: 0% or more and less than 0.5%, Si: 0% or more and less than 2.5%, Cr: 0% or more and less than 0.25%. Ti: 0% or more and less than 0.25%, Ni: 0% or more and less than 0.25%, Co: 0% or more and less than 0.25%, V: 0% or more and less than 0.25%, Nb: 0% or more and less than 0.25%, Cu: 0% or more and less than 0.25%, Mn: 0% or more and less than 0.25%, Fe: 0% or more and 5.0% or less, Sr: 0% or more and less than 0.5%, Sb: 0% or more and less than 0.5%, Pb: 0% or more and less than 0.5%, B: 0% or more and less than 0.5%, and the remainder: Zn and impurities, a more remarkable effect of improving corrosion resistance can be obtained, which is preferable.

[0033] The reason for the preferred chemical composition of the plated layer 12 is described. Hereinafter, the numerical range indicated by interposing to is based on including the numerical values at both ends as the lower limit value and the upper limit value. However, when it is described that the numerical value is less than or greater than the numerical value, the numerical value is not included as the lower limit value or the upper limit value.

[0034] In addition, unless otherwise specified, the % regarding the chemical composition of the plated layer is mass %. [0035] [Al: 0.1% or more and less than 25.0%]

[0036] Al is an element effective for improving corrosion resistance in the zinc-based plated layer. In the case of sufficiently obtaining the above effect, the Al content is preferably 0.1% or more.

[0037] On the other hand, when the Al content is 25.0% or more, the corrosion resistance of the cut end surface of the plated layer is deteriorated. Therefore, the Al content is preferably less than 25.0%.

[0038] The plated layer 12 may contain Al, and the remainder may be composed of Zn and impurities. However, the following elements may be further included as necessary.

[0039] Even in that case, the Zn content is preferably 50% or more. [0040] [Mg: 0% or more and less than 12.5%]

[0041] Mg is an element having an effect of enhancing the corrosion resistance of the plated layer. In the case of sufficiently obtaining the above effect, the Mg content is preferably more than 1.0%.

[0042] On the other hand, when the Mg content is 12.5% or more, the effect of improving corrosion resistance is saturated, and there is a case that the workability of the plated layer is deteriorated. In addition, a manufacturing problem arises, such as an increase in the amount of material in a plating bath generated. Therefore, the Mg content is preferably less than 12.5%. [0043] [Sn: 0% or more and 20% or less] [0044] [Bi: 0% or more and less than 5.0%] [0045] [In: 0% or more and less than 2.0%]

[0046] These elements are elements that contribute to improvement of corrosion resistance and sacrificial anticorrosive. Therefore, any one or more kinds of them may be contained. In the case of obtaining the above effect, the amount is preferably 0.05% or more.

[0047] Among them, Sn is preferable because it is a low melting point metal and can be easily contained without impairing the properties of the plating bath.

[0048] On the other hand, when the Sn content is more than 20%, the Bi content is 5.0% or more, or the In content is 2.0% or more, corrosion resistance is deteriorated. Therefore, it is preferable to set the Sn content to 20% or less, the Bi content to less than 5.0%, and the In content to less than 2.0%, respectively. [0049] [Ca: 0% or more and 3.0% or less]

[0050] Ca is an element that reduces the formation amount of dross that is likely to be formed during operation and contributes to improvement of plating manufacturability. Therefore, Ca may be contained. When this effect is obtained, the Ca content is preferably 0.1% or more.

[0051] On the other hand, when the content of Ca is high, the corrosion resistance itself of the flat portion of the plated layer tends to deteriorate, and the corrosion resistance around the welded portion may also deteriorate. Therefore, the Ca content is preferably 3.0% or less. [0052] [Y: 0% or more and 0.5% or less] [0053] [La: 0% or more and less than 0.5%] [0054] [Ce: 0% or more and less than 0.5%]

[0055] Y, La, and Ce are elements that contribute to improvement of corrosion resistance. In the case of obtaining this effect, it is preferable to contain 0.05% or more of each of one or more kinds of these.

[0056] On the other hand, when the amount of these elements is excessive, the viscosity of the plating bath increases, and the initial make-up of the plating bath itself is often difficult, and there is a concern that a steel having good plating properties cannot be manufactured. Therefore, the Y content is preferably 0.5% or less, the La content is preferably less than 0.5%, and the Ce content is preferably less than 0.5%. [0057] [Si: 0% or more and less than 2.5%]

[0058] Si is an element that contributes to improvement 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 sheet surface sheet and the plated layer to enhance adhesion between the steel sheet and the plated layer when the plated layer is formed on the steel sheet. When these effects are obtained, the Si content is preferably 0.1% or more. The Si content is more preferably 0.2% or more.

[0059] On the other hand, when the Si content is 2.5% or more, excessive Si is precipitated in the plated layer, and not only corrosion resistance is deteriorated but also workability of the plated layer is deteriorated. Therefore, the Si content is preferably less than 2.5%. The Si content is more preferably 1.5% or less. [0060] [Cr: 0% or more and less than 0.25%] [0061] [Ti: 0% or more and less than 0.25%] [0062] [Ni: 0% or more and less than 0.25%] [0063] [Co: 0% or more and less than 0.25%] [0064] [V: 0% or more and less than 0.25%] [0065] [Nb: 0% or more and less than 0.25%] [0066] [Cu: 0% or more and less than 0.25%] [0067] [Mn: 0% or more and less than 0.25%]

[0068] These elements are elements that contribute to improvement of corrosion resistance. When this effect is obtained, the amount of one or more of these elements is preferably 0.05% or more.

[0069] On the other hand, when the amount of these elements is excessive, the viscosity of the plating bath increases, and the initial make-up of the plating bath itself is often difficult, and there is a concern that a steel having good plating properties cannot be manufactured. Therefore, the amount of each element is preferably less than 0.25%. [0070] [Fe: 0% or more and 5.0% or less]

[0071] Fe is mixed into the plated layer as an impurity when the plated layer is manufactured. Fe may be contained up to about 5.0%, but if the content is in this range, the adverse effect on the effect of the surface-treated steel according to the present embodiment is small. Therefore, the Fe content is preferably 5.0% or less. [0072] [Sr: 0% or more and less than 0.5%] [0073] [Sb: 0% or more and less than 0.5%] [0074] [Pb: 0% or more and less than 0.5%]

[0075] When Sr, Sb, and Pb are contained in the plated layer, the external appearance of the plated layer changes, a spangle is formed, and improvement in metallic gloss is confirmed. When this effect is obtained, the amount of one or more kinds of Sr, Sb, and Pb is preferably 0.05% or more.

[0076] On the other hand, when the amount of these elements is excessive, the viscosity of the plating bath increases, and the initial make-up of the plating bath itself is often difficult, and there is a concern that a steel having good plating properties cannot be manufactured. Therefore, the amount of each element is preferably less than 0.5%. [0077] [B: 0% or more and less than 0.5%]

[0078] B is an element that forms various intermetallic compounds by combining with Zn, Al, Mg, or the like when contained in the plated layer. This intermetallic compound has an effect of improving LME. When this effect is obtained, the B content is preferably 0.05% or more. The B content is more preferably 0.1% or more.

[0079] On the other hand, when the B content is excessive, there is a concern that the melting point of plating is significantly increased, plating operability is deteriorated, and a surface-treated steel having good plating properties cannot be obtained. Therefore, the B content is preferably less than 0.5%.

[0080] The adhesion amount of the plated layer 12 is not limited, but is preferably 10 g/m.sup.2 or more per at least one surface for improving corrosion resistance. On the other hand, even when the adhesion amount exceeds 200 g/m.sup.2 per one surface, corrosion resistance is saturated and it is economically disadvantageous. Therefore, the adhesion amount is preferably 200 g/m.sup.2 or less.

<Film>

[0081] As shown in FIG. 1, the film 13 included in the surface-treated steel 1 according to the present embodiment has the amorphous phase A131 and the amorphous phase B132. The amorphous phase B132 is mainly formed on a part of the film 13 on the interface side with the plated layer 12, and contributes to improvement of adhesion of the film 13.

Amorphous Phase A

[0082] The film 13 included in the surface-treated steel 1 according to the present embodiment is obtained by coating a treatment solution containing a Si compound such as a silane coupling agent, a P compound such as a phosphate, a V compound, and one or more kinds of compounds selected from the group consisting of Ti, Zr, and Al, which are valve metals, onto a plated layer containing zinc under predetermined conditions and drying the treatment solution. The amorphous phase A131 is a layer that occupies a main part of the film 13, and contains, as constituent elements, Si, C, and O derived from a silane coupling agent, P derived from a P compound, V derived from a V compound, one or more kinds selected from the group consisting of Ti, Zr, and Al that are valve metals, and Zn eluted from the plated layer.

[0083] Si, C, and O (mainly present as a silicon compound) are elements constituting a matrix of the film 13.

[0084] V and P (mainly present as compounds) are inhibitors, and when V and P are not contained, sufficient corrosion resistance cannot be obtained.

[0085] In the surface-treated steel 1 according to the present embodiment, it is necessary that the amorphous phase A131 contains P and V, and V/P, which is the ratio of the contents of V and P in mass %, is set to 0.050 to 1.000.

[0086] When VIP is less than 0.050, a synergistic effect of P and V cannot be obtained, sufficient corrosion resistance cannot be obtained, and coating adhesion is also deteriorated. In addition, when V/P exceeds 1.000, the elution amount from the film 13 increases, and coating adhesion is deteriorated.

[0087] Ti, Zr, and/or Al (valve metal) are elements whose oxides are stable, and when contained in the film, passivate the surface of the film 13 to improve corrosion resistance. When the film 13 does not contain these elements, sufficient corrosion resistance cannot be obtained.

[0088] As described later, the valve metal also contributes to the formation of the amorphous phase B. Therefore, if the valve metal is not contained, sufficient coating adhesion cannot be obtained.

[0089] As described later, in the surface-treated steel 1 according to the present embodiment, a layer having a SiOZn bond (amorphous phase B) obtained by hydrogen bonding between Zn eluted from the plated layer 12 and Si in the film 13 is formed in the vicinity of the interface between the film 13 and the plated layer 12, thereby improving the adhesion of the film 13.

[0090] However, Zn reacts with the inhibitor to form and precipitate zinc phosphate. Therefore, when the elution amount of Zn from the plated layer is excessive and the amount of Zn exceeds 10 mass % in the amorphous phase A, P present as an inhibitor in the film 13 decreases and corrosion resistance decreases. Therefore, the amount of Zn in the amorphous phase A131 is set to 10 mass % or less.

Amorphous Phase B

[0091] The amorphous phase B132 is a layer having a SiOZn bond formed by a covalent bond by a dehydration condensation reaction between Zn eluted from the plated layer 12 and Si of a silane coupling agent contained in a treatment solution for forming a film when the film 13 is formed. Therefore, the amorphous phase B132 contains Si, O, and Zn. On the other hand, the amorphous phase B132 contains a large amount of SiOZn bonds, but since Zn not bonded to Si preferentially forms an ionic bond with P in the amorphous phase A131, Zn/Si, which is the peak intensity ratio between Zn and Si, is smaller (Zn/Si is less than 1.0) than that of the amorphous phase A in which Zn/Si is 1.0 or more. The reason why the amorphous phase B is produced is unknown, but it is considered that the valve metal serves as a catalyst for the dehydration condensation reaction of the silane coupling agent.

[0092] The presence of the amorphous phase B132 at the interface between the film 13 and the plated layer 12 in the film 13 improves the adhesion of the film 13. Therefore, in the surface-treated steel 1 according to the present embodiment, the amorphous phase B132 is formed on the interface side of the film 13 with the plated layer 12. The amorphous phase B132 may be formed intermittently or continuously. When the effect of improving the adhesion is sufficiently obtained, a percentage of the length of the interface between the plated layer 12 and the amorphous phase B132 to the length of the interface between the plated layer 12 and the film 13 needs to be 30% or more when viewed in the cross section in the thickness direction. That is, a percentage of the length of the interface between the plated layer 12 and the amorphous phase A131 to the length of the interface between the plated layer 12 and the film 13 is 70% or less. The percentage of the length of the interface between the plated layer 12 and the amorphous phase B132 to the length of the interface between the plated layer 12 and the film 13 may be 100%, or may be 70% or less from the viewpoint of a heterogeneous reaction field.

[0093] The reason why the adhesion is improved by the presence of the amorphous phase B is not clear, but it is considered that the SiOZn bond of the amorphous phase B is formed by a dehydration condensation reaction between Zn (zinc) on the surface of the plated layer and a silane coupling agent contained in a treatment solution for forming a film.

[0094] It is considered that the percentage of the length of the interface between the plated layer 12 and the amorphous phase B132 to the length of the interface between the plated layer 12 and the film 13 is also affected by the thickness of the oxide film on the plating surface.

[0095] The identification of the amorphous phase A and the amorphous phase B in the film 13 and the contents, peak intensity ratios, and mass ratios of the constituent elements contained in the amorphous phase A and the amorphous phase B can be measured using energy dispersive X-ray spectroscopy (EDS).

[0096] Specifically, using a focused ion beam apparatus (R B) FB2000 A (manufactured by Hitachi, Ltd.) or a device equivalent thereto, a thin film sample for TEM observation is prepared from the measurement object position by the FIB-p sampling method. The outermost surface of the sample is subjected to W deposition for protection. A Cu mesh is used as a mesh.

[0097] Using a field emission transmission electron microscope HF-2000 (manufactured by Hitachi, Ltd.), the microstructure of the obtained sample is observed in a field of view at a magnification of 50,000 times at an acceleration voltage of 200 kV, and an element analysis is performed using an attached EDS analyzer delta plus level 2 (manufactured by Kevex) at an acceleration voltage of 200 kV.

[0098] Quantitative evaluation is performed for Si, C, O, P, V, Zn, Ti, Zr, and Al by a semi-quantitative method. The amount of the element at the measurement position is determined, and the peak intensity ratio and the mass ratio (ratio of the amount in mass %) of the element are also calculated.

[0099] The amorphous phase A is defined as the portion where the peak intensity ratio of Zn to Si, Zn/Si, is 1.0 or more as a result of the measurement and is determined to be amorphous by electron diffraction of TEM, and the amorphous phase B is defined as the portion where the peak intensity ratio between Zn and Si, Zn/Si, is less than 1.0 and which is determined to be amorphous by electron beam diffraction of TEM.

[0100] When the amount of Si, C, O, P, Zn, V, Ti, Zr, and Al is 0.5 mass % or more in each of the amorphous phase A and the amorphous phase B, it is determined that the amorphous phase A and the amorphous phase B contain the target element (element of 0.5 mass % or more).

[0101] In the measurement, a thicker than the measurement point size is selected, and a point analysis is performed on the center portion of each phase. For each of the phases considered to be the amorphous phase A and the amorphous phase B, measurement is performed at three or more points, and the average value thereof is adopted as the amount in the phase.

[0102] In addition, the length (percentage) of the interface between the plated layer and the amorphous phase B in the length of the interface between the plated layer and the film is determined by observing the interface between the plated layer and the film in the range of 10 m or more as the interface length using the field emission transmission electron microscope described above, and measuring the length of the interface between the plated layer and the amorphous phase B among them. (It is calculated by [the length of the interface between the plated layer and the amorphous phase B]/[the length of the interface between the plated layer and the film]100.)

Film Thickness

[0103] The thickness of the film 13 (including the amorphous phase A131 and the amorphous phase B132) is 100 nm or more and 1000 nm or less.

[0104] When the thickness of the film 13 is less than 100 nm, corrosion resistance and coating adhesion are deteriorated. On the other hand, when the thickness of the film 13 exceeds 1000 nm, although corrosion resistance is good, the amount of the inhibitor component eluted from the film 13 increases, and coating adhesion is deteriorated.

[0105] The film thickness is measured with an electromagnetic film thickness meter. Specifically, 10 arbitrary points are measured using an electromagnetic film thickness meter, and the average value thereof is taken as the film thickness.

[0106] Next, a preferred method for manufacturing the surface-treated steel according to the present embodiment is described.

[0107] The surface-treated steel according to the present embodiment can obtain the effect as long as it has the above characteristics regardless of the manufacturing method, but the following manufacturing method is preferable because it can be stably manufactured.

[0108] That is, the surface-treated steel according to the present embodiment can be manufactured by a manufacturing method including the following steps: [0109] (I) a plating step of forming a plated layer on a surface of a steel (steel sheet) by immersing the steel in a plating bath containing Zn or by electro plating in an aqueous solution or molten salt containing Zn; [0110] (II) a coating step of coating a surface treatment solution for metal (treatment solution) to a steel having a plated layer; and [0111] (III) a heating step of heating the steel coated with the surface treatment solution for metal to form a film containing Si, C, O, P, Zn, and V, and one or more kinds selected from the group consisting of Ti, Al, and Zr.

[0112] Preferred conditions for each step are described.

Plating Step

[0113] The plating step is not particularly limited. The plating may be performed by a normal method so that sufficient plating adhesion can be obtained.

[0114] The method for manufacturing the steel to be subjected to the plating step is also not limited.

[0115] For example, a method for manufacturing a zinc-based plated steel sheet prescribed in JIS G3302: 2019 may be used, or a method for manufacturing a plated steel sheet prescribed in JIS G3323: 2019 or JIS G3313: 2017 may be used.

[0116] The composition of the plating bath may also be adjusted according to the composition of the plated layer to be obtained.

[0117] After the cooling, it is desirable to avoid excessive oxidation of the surface, adhesion of oil, and the like until the coating step, and to control the plating surface state so as not to repel the chemical agent.

Coating Step

[0118] In the coating step, a surface treatment solution for metal containing a Si compound, a P compound, a V compound, and a compound of Ti, Zr, and/or Al is coated to a steel such as a steel sheet having a plated layer containing Zn. The Si compound, the P compound, the V compound, and the Ti compound, the Zr compound, and/or the Al compound are contained in order to be a constituent element of the film. The P compound also has an effect of eluting Zn of the plated layer by an etching reaction, and contributes to the production of the amorphous phase B by combination with the valve metal.

[0119] In the coating step, the method for coating the surface treatment solution for metal is not limited. For example, it can be coated using a roll coater, a bar coater, a spray, or the like.

[0120] The film thickness can be changed by changing the coating amount according to the rotation speed or the peripheral speed ratio between the pick-up roll and the applicator roll.

[0121] In the present embodiment, the Si compound contained in the surface treatment solution for metal is preferably a silane coupling agent containing an isocyanate group, an amino group, an epoxy group, or the like in the molecule for forming the amorphous phase B, and among them, an isocyanate group is more preferable.

[0122] The concentration of the Si compound in the surface treatment solution for metal is desirably 5 to 20 mass %.

[0123] In the present embodiment, the P compound contained in the surface treatment solution for metal is not particularly limited, and examples thereof include phosphoric acid, ammonium phosphate, potassium phosphate, and sodium phosphate. Among them, phosphoric acid is more preferable. When phosphoric acid is used, more excellent corrosion resistance can be obtained. The concentration of the P compound in the surface treatment solution for metal is desirably 1 to 5 mass %.

[0124] Examples of the V compound contained in the surface treatment solution for metal include vanadium pentoxide V.sub.2O.sub.5, metavanadic acid HVO.sub.3, ammonium metavanadate, sodium metavanadate, vanadium oxytrichloride VOCl.sub.3, vanadium trioxide V.sub.2O.sub.3, vanadium dioxide VO.sub.2, vanadium oxysulfate VOSO.sub.4, vanadium oxyacetylacetonate VO(OC(CH.sub.2)CH.sub.2COCH.sub.3).sub.2, vanadium acetylacetonate V(OC(CH.sub.2)CH.sub.2COCH.sub.3).sub.3, vanadium trichloride VCl.sub.3, and phosphovanadomolybdic acid. In addition, a pentavalent vanadium compound reduced to tetravalent to divalent one with an organic compound having at least one functional group selected from the group consisting of a hydroxyl group, a carboxylic acid, a carboxyl group, a primary to tertiary amino group, an amide group, a phosphoric acid group, and a phosphonic acid group can also be used. The concentration of the V compound in the surface treatment solution for metal is desirably 0.0001 to 4.0 mass %.

[0125] Examples of the Ti compound, the Zr compound, and the Al compound include titanium nitrate, zirconium nitrate, and aluminum nitrate.

Heating Step

[0126] In the heating step, the steel coated with the surface treatment solution for metal is heated, dried, and baked to form a film. As for the heating temperature (drying temperature), the peak metal temperature is preferably 60 to 200 C., and more preferably 80 to 150 C. It is not preferable that the peak metal temperature is lower than 60 C. because the solvent of the surface treatment solution for metal is not completely volatilized. On the other hand, when the peak metal temperature exceeds 200 C., the solvent drying effect by heating is saturated, which is not economical, and therefore, it is not preferable.

[0127] In the heating step, the method for heating the surface treatment solution for metal is not limited. For example, heating can be performed using IH, a hot blast furnace, or the like, and drying can be performed.

[0128] In addition, when the time from the coating of the surface treatment solution for metal (treatment solution) at room temperature (at the time of completion of coating) to the reaching of the peak metal temperature is long, the elution amount of Zn from the plated layer increases, and thus the time from the coating of the surface treatment solution for metal (treatment solution) to the reaching of the peak metal temperature is preferably 10.0 seconds or less, and more preferably 4.0 seconds or less.

[0129] The surface-treated steel after reaching the peak metal temperature is cooled to around room temperature. The cooling conditions are not particularly limited, but gas cooling, mist cooling using a liquid, and liquid submersion cooling can be considered.

Examples

[0130] As a plated steel sheet for forming a film on a surface, a hot-dip galvanized steel sheet which is a zinc-plated steel sheet prescribed in JIS G3302: 2019 and in which a plating adhesion amount is represented by 708 was prepared.

[0131] As shown in Table 1, any one of the following kinds of treatment solutions A to S was coated to the plated steel sheet using a roll coater.

(Treatment Solution A)

[0132] An aqueous solution prepared by dissolving 75 mg of vanadyl acetylacetonate, 3 g of diammonium hydrogen phosphate, and 1 g of titanium nitrate in 100 mL of a solution prepared with a mixture of ethanol and 0.05% aqueous ammonia at a ratio of 1:1 so that the mass ratio of 3-isocyanate propyltriethoxysilane is 10% and left to stand for 3 hours as a base liquid.

(Treatment Solution B)

[0133] An aqueous solution prepared by dissolving 70 mg of vanadyl acetylacetonate, 2 g of diammonium hydrogen phosphate, and 1 g of titanium nitrate in 100 mL of a solution prepared with a mixture of ethanol and 0.05% aqueous ammonia at a ratio of 1:1 so that the mass ratio of 3-isocyanate propyltriethoxysilane is 10% and left to stand for 3 hours as a base liquid.

(Treatment Solution C)

[0134] An aqueous solution prepared by dissolving 70 mg of vanadyl acetylacetonate, 1 g of diammonium hydrogen phosphate, and 1 g of titanium nitrate in 100 mL of a solution prepared with a mixture of ethanol and 0.05% aqueous ammonia at a ratio of 1:1 so that the mass ratio of 3-isocyanate propyltriethoxysilane is 10% and left to stand for 3 hours as a base liquid.

(Treatment Solution D)

[0135] An aqueous solution prepared by dissolving 100 mg of vanadyl acetylacetonate, 1 g of diammonium hydrogen phosphate, and 1 g of titanium nitrate in 100 mL of a solution prepared with a mixture of ethanol and 0.05% aqueous ammonia at a ratio of 1:1 so that the mass ratio of 3-isocyanate propyltriethoxysilane is 10% and left to stand for 3 hours as a base liquid.

(Treatment Solution E)

[0136] An aqueous solution prepared by dissolving 170 mg of vanadyl acetylacetonate, 1 g of diammonium hydrogen phosphate, and 1 g of titanium nitrate in 100 mL of a solution prepared with a mixture of ethanol and 0.05% aqueous ammonia at a ratio of 1:1 so that the mass ratio of 3-isocyanate propyltriethoxysilane is 10% and left to stand for 3 hours as a base liquid.

(Treatment Solution F)

[0137] An aqueous solution prepared by dissolving 1.7 g of vanadyl acetylacetonate, 1 g of diammonium hydrogen phosphate, and 1 g of titanium nitrate in 100 mL of a solution prepared with a mixture of ethanol and 0.05% aqueous ammonia at a ratio of 1:1 so that the mass ratio of 3-isocyanate propyltriethoxysilane is 10% and left to stand for 3 hours as a base liquid.

(Treatment Solution G)

[0138] An aqueous solution prepared by dissolving 9.0 g of vanadyl acetylacetonate, 1 g of diammonium hydrogen phosphate, and 1 g of titanium nitrate in 100 mL of a solution prepared with a mixture of ethanol and 0.05% aqueous ammonia at a ratio of 1:1 so that the mass ratio of 3-isocyanate propyltriethoxysilane is 10% and left to stand for 3 hours as a base liquid.

(Treatment Solution H)

[0139] An aqueous solution prepared by dissolving 1 g of diammonium hydrogen phosphate and 1 g of titanium nitrate in 100 mL of a solution prepared with a mixture of ethanol and 0.05% aqueous ammonia at a ratio of 1:1 so that the mass ratio of 3-isocyanate propyltriethoxysilane is 10% and left to stand for 3 hours as a base liquid.

(Treatment Solution I)

[0140] An aqueous solution prepared by dissolving 170 mg of vanadyl acetylacetonate and 1 g of titanium nitrate in 100 mL of a solution prepared with a mixture of ethanol and 0.05% aqueous ammonia at a ratio of 1:1 so that the mass ratio of 3-isocyanate propyltriethoxysilane is 10% and left to stand for 3 hours as a base liquid.

(Treatment Solution J)

[0141] An aqueous solution prepared by dissolving 170 mg of vanadyl acetylacetonate and 1 g of diammonium hydrogen phosphate in 100 ml of a solution prepared with a mixture of ethanol and 0.05% aqueous ammonia at a ratio of 1:1 so that the mass ratio of 3-isocyanate propyltriethoxysilane is 10% and left to stand for 3 hours as a base liquid.

(Treatment Solution K)

[0142] An aqueous solution prepared by dissolving 170 mg of vanadyl acetylacetonate, 1 g of diammonium hydrogen phosphate, and 1 g of zirconium nitrate in 100 mL of a solution prepared with a mixture of ethanol and 0.05% aqueous ammonia at a ratio of 1:1 so that the mass ratio of 3-isocyanate propyltriethoxysilane is 10% and left to stand for 3 hours as a base liquid.

(Treatment Solution L)

[0143] An aqueous solution prepared by dissolving 170 mg of vanadyl acetylacetonate, 1 g of diammonium hydrogen phosphate, and 1 g of aluminum nitrate in 100 mL of a solution prepared with a mixture of ethanol and 0.05% aqueous ammonia at a ratio of 1:1 so that the mass ratio of 3-isocyanate propyltriethoxysilane is 10% and left to stand for 3 hours as a base liquid.

(Treatment Solution M)

[0144] An aqueous solution prepared by dissolving 170 mg of vanadyl acetylacetonate, 1 g of diammonium hydrogen phosphate, and 0.5 g each of titanium nitrate and zirconium nitrate in 100 ml, of a solution prepared with a mixture of ethanol and 0.05% aqueous ammonia at a ratio of 1:1 so that the mass ratio of 3-isocyanate propyltriethoxysilane is 10% and left to stand for 3 hours as a base liquid.

(Treatment Solution N)

[0145] An aqueous solution prepared by dissolving 170 mg of vanadyl acetylacetonate, 1 g of diammonium hydrogen phosphate, and 0.5 g each of titanium nitrate and aluminum nitrate in 100 mL of a solution prepared with a mixture of ethanol and 0.05% aqueous ammonia at a ratio of 1:1 so that the mass ratio of 3-isocyanate propyltriethoxysilane is 10% and left to stand for 3 hours as a base liquid.

(Treatment Solution O)

[0146] An aqueous solution prepared by dissolving 170 mg of vanadyl acetylacetonate, 1 g of diammonium hydrogen phosphate, and 0.5 g each of zirconium nitrate and aluminum nitrate in 100 mL of a solution prepared with a mixture of ethanol and 0.05% aqueous ammonia at a ratio of 1:1 so that the mass ratio of 3-isocyanate propyltriethoxysilane is 10% and left to stand for 3 hours as a base liquid.

(Treatment Solution P)

[0147] An aqueous solution prepared by dissolving 84 mg of vanadyl acetylacetonate, 1 g of diammonium hydrogen phosphate and 1 g of titanium nitrate in 100 mL of a solution prepared with a mixture of ethanol and 0.05% aqueous ammonia at a ratio of 1:1 so that the mass ratio of 3-isocyanate propyltriethoxysilane is 10% and left to stand for 3 hours as a base liquid.

(Treatment Solution Q)

[0148] An aqueous solution prepared by dissolving 1.6 g of vanadyl acetylacetonate, 1 g of diammonium hydrogen phosphate, and 1 g of titanium nitrate in 100 mL of a solution prepared with a mixture of ethanol and 0.05% aqueous ammonia at a ratio of 1:1 so that the mass ratio of 3-isocyanate propyltriethoxysilane is 10% and left to stand for 3 hours as a base liquid.

(Treatment Solution R)

[0149] An aqueous solution prepared by dissolving 1.3 g of vanadyl acetylacetonate, 1 g of diammonium hydrogen phosphate, and 1 g of titanium nitrate in 100 mL of a solution prepared with a mixture of ethanol and 0.05% aqueous ammonia at a ratio of 1:1 so that the mass ratio of 3-isocyanate propyltriethoxysilane is 10% and left to stand for 3 hours as a base liquid.

(Treatment Solution S)

[0150] An aqueous solution prepared by dissolving 170 mg of vanadyl acetylacetonate, 1 g of diammonium hydrogen phosphate and 1 g of titanium nitrate in 100 mL of a solution prepared with a mixture of ethanol and 0.05% aqueous ammonia at a ratio of 1:1 so that the mass ratio of 3-isocyanate propyltriethoxysilane is 3% and the mass ratio of silica sol (ST-NXS manufactured by Nissan Chemical Corporation) is 7%, and left to stand for 3 hours as a base liquid.

[0151] After the surface treatment solution for metal was coated to the steel sheet at room temperature (20 C.), the steel sheet was left as necessary, and then heated to the peak metal temperature in a hot air drying furnace so that the time from the completion of coating to the attainment of the peak metal temperature was the value shown in Table 1. The average heating rate is the average heating rate from the completion of coating to the reaching of the peak metal temperature, which is calculated including the standing time.

[0152] Thereafter, air cooling was performed to room temperature.

[0153] As a result, surface-treated steels Nos. 1 to 30 were obtained.

TABLE-US-00001 TABLE 1 Manufacture conditions Heating Average Time from completion of Coating heating coating at room temperature Kind of rate Peak metal (20 C.) to reaching treatment C./ temperature peak metal temperature No. solution seconds C. seconds 1 A 20 90 3.5 2 B 20 90 3.5 3 C 20 90 3.5 4 D 20 90 3.5 5 E 20 90 3.5 6 F 20 90 3.5 7 G 20 90 3.5 8 E 100 90 0.7 9 E 10 90 7.0 10 E 5 90 14.0 11 H 20 90 3.5 12 I 20 90 3.5 13 J 20 90 3.5 14 K 20 90 3.5 15 L 50 150 2.6 16 M 30 140 4.0 17 N 30 140 4.0 18 O 20 90 3.5 19 E 20 90 3.5 20 E 20 90 3.5 21 E 20 120 5.0 22 E 20 120 5.0 23 E 20 90 3.5 24 E 20 90 3.5 25 P 20 90 3.5 26 Q 20 90 3.5 27 E 7 90 10.5 28 L 50 150 2.6 29 R 20 90 3.5 30 S 20 90 3.5

[0154] With respect to the obtained surface-treated steel, the amorphous phase A and the amorphous phase B were identified by the above-described method (Zn/Si and whether it is amorphous or not), and the thickness of the film, the elemental analysis of the amorphous phase A and the amorphous phase B. and the percentage of the length of the interface between the plated layer and the amorphous phase B to the length of the interface between the plated layer and the film were determined.

[0155] The results are shown in Table 2.

TABLE-US-00002 TABLE 2 Amorphous phase B Percentage Corrosion of resistance interface White Coating between rust adhesion Amorphous phase A film and generation Residual Zn Absent/ plated Film area area: content Valve metal intermittently layer Thickness fraction fraction No. Si C O P V mass % V/P Ti Zr Al present % nm % % Remarks 1 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 0.015 .circle-solid. Intermittent 60 400 30 60 Comparative Examples 2 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 0.021 .circle-solid. Intermittent 60 400 25 70 Comparative Examples 3 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 0.043 .circle-solid. Intermittent 65 400 20 75 Comparative Exaniples 4 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 0.061 .circle-solid. Intermittent 60 400 2 98 Inventive Examples 5 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 0.100 .circle-solid. Intermittent 60 400 2 90 Inventive Examples 6 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 1.000 .circle-solid. Intermittent 50 400 2 80 Inventive Examples 7 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 5.500 .circle-solid. Intermittent 60 400 2 60 Comparative Examples 8 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 2 0.100 .circle-solid. Intermittent 60 400 2 98 Inventive Examples 9 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 10 0.100 .circle-solid. Intermittent 60 400 5 95 Inventive Examples 10 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 20 0.100 .circle-solid. Intermittent 70 400 20 100 Comparative Examples 11 .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 0.000 .circle-solid. Intermittent. 55 400 20 60 Comparative Examples 12 .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 .circle-solid. Intermittent 55 400 50 100 Comparative Examples 13 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 0.100 Absent 0 400 60 30 Comparative Examples 14 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 0.100 .circle-solid. Intermittent 60 400 2 98 Inventive Examples 15 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 0.100 .circle-solid. Intermittent 40 400 5 98 Inventive Examples 16 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 0.100 .circle-solid. .circle-solid. Intermittent 60 400 2 98 Inventive Examples 17 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 0.100 .circle-solid. .circle-solid. Intermittent 50 400 3 98 Inventive Examples 18 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 0.100 .circle-solid. .circle-solid. Intermittent 50 400 3 98 Inventive Examples 19 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 0.100 .circle-solid. Intermittent 40 50 40 60 Comparative Examples 20 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 0.100 .circle-solid. Intermittent 50 100 5 95 Inventive Examples 21 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 0.100 .circle-solid. Intermittent 55 200 3 100 Inventive Examples 22 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 0.100 .circle-solid. Intermittent 65 800 2 98 Inventive Examples 23 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 0.100 .circle-solid. Intermittent 70 1000 1 90 Inventive Examples 24 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 0.100 .circle-solid. Intermittent 75 1500 1 60 Comparative Examples 25 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 0.051 .circle-solid. Intermittent 60 400 5 98 Inventive Examples 26 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 1.100 .circle-solid. Intermittent 60 400 2 75 Comparative Examples 27 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 12 0.100 .circle-solid. Intermittent 70 400 20 100 Comparative Examples 28 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 0.100 .circle-solid. Intermittent 30 400 5 98 Inventive Examples 29 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 0.800 .circle-solid. Intermittent 55 400 2 85 Inventive Examples 30 .circle-solid. .circle-solid. .circle-solid. .circle-solid. .circle-solid. 5 0.100 .circle-solid. Intermittent 23 400 30 60 Comparative Examples .circle-solid. of each element indicates that it is contained (the content is 0.5 mass % or more).

[0156] In addition, the corrosion resistance and coating adhesion of the obtained surface-treated steel were evaluated by the following method.

Corrosion Resistance

[0157] A flat sheet test piece was prepared, and each test piece was subjected to a salt water spray test in accordance with JIS Z 2371:2015 to evaluate the state of white rust generation on the surface after 120 hours (percentage of the area where white rust was generated in the area of the test piece).

[0158] When the white rust generation area fraction was 5% or less, it was judged that corrosion resistance was excellent.

Coating Adhesion

[0159] A flat sheet test piece was prepared, and a white coating (Amilac #1000) was coated so that the film thickness after drying was 20 m. This test piece was immersed in boiling water for 30 minutes, and then stretch forming is performed to a height of 7 mm with a punch stretch forming apparatus (Erichsen Test), and a tape peeling test was performed to confirm the coating film residual ratio.

[0160] When the residual area fraction of the coating film was 80% or more, it was judged that the coating adhesion was excellent.

[0161] As can be seen from Tables 1 and 2, in Nos. 4 to 6, 8, 9, 14 to 18, 20 to 23, 25, 28, and 29 containing a predetermined amount of Si, C, O, P, Zn, and V, and one or two or more kinds selected from the group consisting of Ti, Zr, and Al, and having a length percentage of an interface with the amorphous phase B of 30% or more, excellent corrosion resistance and coating adhesion are obtained.

[0162] On the other hand, Comparative Examples Nos. 1 to 3, 7, 10 to 13, 19, 24, 26, 27, and 30 that do not satisfy one or more of the requirements of the present invention are inferior in any one or both of corrosion resistance and coating adhesion.

Field of Industrial Application

[0163] According to the present invention, it is possible to provide a surface-treated steel having excellent coating adhesion and excellent corrosion resistance. The surface-treated steel has high industrial applicability.

BRIEF DESCRIPTION OF THE REFERENCE SYMBOLS

[0164] 1 Surface-treated steel [0165] 11 Steel sheet [0166] 12 Plated layer [0167] 13 Film [0168] 131 Amorphous phase A [0169] 132 Amorphous phase B