Surface-treated steel sheet

Abstract

A surface-treated steel sheet including a steel sheet, a zinc-based plated layer, and a chemical conversion treatment layer that contains Si, C, O and P, and has a C concentration of 20.0 mass % or more, an O concentration of 15.0 mass % or more, a Si concentration of 10.0 mass % or more, and a P concentration of 0.10 mass % or more. When t is a thickness of the chemical conversion treatment layer, an area from a surface to a position of t/10 from the surface is a surface layer region, an area from the position of 9t/10 from the surface to an interface between the treatment layer and the plated layer is an interface side region, and a region sandwiched therebetween is an intermediate region. A maximum value of a P concentration of the surface layer region is 1.5 times to 5.0 times the average P concentration of an intermediate region.

Claims

1. A surface-treated steel sheet comprising: a steel sheet; a zinc-based plated layer formed on a surface of the steel sheet; and a chemical conversion treatment layer formed on a surface of the zinc-based plated layer, wherein the chemical conversion treatment layer contains Si, C, O and P, the chemical conversion treatment layer has an average C concentration across the entire chemical conversion treatment layer of 20.0 mass % or more, an average O concentration across the entire chemical conversion treatment layer of 15.0 mass % or more, an average Si concentration across the entire chemical conversion treatment layer of 10.0 mass % or more, and an average P concentration across the entire chemical conversion treatment layer of 0.10 mass % or more, when t is a thickness of the chemical conversion treatment layer, an area starting from a surface of the chemical conversion treatment layer and ending at a position of t/10 from the surface of the chemical conversion treatment layer in a thickness direction is a surface layer region, an area starting from the position of 9t/10 from the surface of the chemical conversion treatment layer in the thickness direction and ending at an interface between the chemical conversion treatment layer and the zinc-based plated layer is an interface side region, and a region sandwiched between the surface layer region and the interface side region is an intermediate region, a maximum value of a mass % P concentration of the surface layer region is 1.5 times to 5.0 times an average mass % P concentration of an intermediate region.

2. The surface-treated steel sheet according to claim 1, wherein Al is present in the interface side region, and an F content, on a mass basis, of the interface side region is 20% or more of an F content, on a mass basis, of the entire chemical conversion treatment layer.

3. The surface-treated steel sheet according to claim 2, wherein Sb is present in the interface side region.

4. The surface-treated steel sheet according to claim 3, wherein a surface of the zinc-based plated layer is regular spangle-finished.

5. The surface-treated steel sheet according to claim 2, wherein a surface of the zinc-based plated layer is regular spangle-finished.

6. The surface-treated steel sheet according to claim 1, wherein Sb is present in the interface side region.

7. The surface-treated steel sheet according to claim 6, wherein a surface of the zinc-based plated layer is regular spangle-finished.

8. The surface-treated steel sheet according to claim 1, wherein a surface of the zinc-based plated layer is regular spangle-finished.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a view showing an example of a cross section of a surface-treated steel sheet according to the present embodiment.

(2) FIG. 2 is a view illustrating a chemical conversion treatment layer of the surface-treated steel sheet according to the present embodiment.

(3) FIG. 3 is a diagram showing an example of a results of performing continuous point analysis using EDS for the chemical conversion treatment layer of the surface-treated steel sheet according to the present embodiment.

EMBODIMENT OF THE INVENTION

(4) Hereinafter, a surface-treated steel sheet according to an embodiment of the present invention (surface-treated steel sheet according to the present embodiment) will be described.

(5) As shown in FIG. 1, a surface-treated steel sheet 1 according to the present embodiment includes a steel sheet 11, a zinc-based plated layer 12 formed on a surface of the steel sheet 11, and a chemical conversion treatment layer 13 formed on a surface of the zinc-based plated layer 12.

(6) The chemical conversion treatment layer 13 contains Si, C, O and P, and has a C concentration of 20.0 mass % or more, an O concentration of 15.0 mass % or more, a Si concentration of 10.0 mass % or more, and a P concentration of 0.10 mass % or more. As shown in FIG. 2, when t is a thickness of the chemical conversion treatment layer 13, an area starting from a surface of the chemical conversion treatment layer 13 and ending at a position of t/10 from the surface of the chemical conversion treatment layer 13 in a thickness direction is a surface layer region 101, an area starting from the position of 9t/10 from the surface of the chemical conversion treatment layer 13 in the thickness direction and ending at an interface between the chemical conversion treatment layer 13 and the zinc-based plated layer 12 (at a position of t from the surface in the thickness direction) is an interface side region 102, and a region sandwiched between the surface layer region 101 and the interface side region 102 is the intermediate region 103, a maximum value of a P concentration of the surface layer region 101 is 1.5 to 5.0 times the average P concentration of an intermediate region 103.

(7) In FIG. 1, the zinc-based plated layer 12 and the chemical conversion treatment layer 13 (surface layer region 101+intermediate region 103+interface side region 102) are formed on one surface of the steel sheet 11, but may be formed on both surfaces of the steel sheet 11.

(8) <Steel Sheet (Base Steel Sheet)>

(9) The zinc-based plated layer 12 and the chemical conversion treatment layer 13 characterize the surface-treated steel sheet 1 according to the present embodiment. 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 G 3193: 2019 or a cold-rolled steel sheet described in JIS G 3141: 2017 may be used.

(10) <Zinc-Based Plated Layer>

(11) The zinc-based plated layer 12 of the surface-treated steel sheet 1 according to the present embodiment is a zinc-based plated layer formed on a surface of the steel sheet 11 and containing a zinc.

(12) [Chemical Composition]

(13) The chemical composition of the zinc-based plated layer 12 is not limited as long as it is a plated layer containing a zinc as a main component.

(14) However, a chemical composition of Al: 4.0% or more and less than 25.0%, Mg: 0% or more and less than 12.5%, Sn: 0% to 20%, Bi: 0% or more and less than 5.0%, In: 0% or more and less than 2.0%, Ca: 0% to 3.0%, Y: 0% to 0.5%, 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% to 5.0%, Sb: 0% or more and less than 0.5%, Sr: 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 remainder: Zn and impurities is preferable because a more significant effect of improving corrosion resistance is obtained.

(15) The reason why the above-mentioned chemical composition of the zinc-based plated layer (hereinafter, sometimes referred to simply as a plated layer) 12 is preferable will be described. Hereinafter, a numerical value range indicated by numerical values with the term to interposed therebetween essentially includes the numerical values at both ends as a lower limit and an upper limit, respectively. That is, for example, 0% to 20% represents 0% or more and 20% or less.

(16) Unless otherwise specified, % related to the chemical composition of the zinc-based plated layer represents mass %. [Al: 4.0% or more and less than 25.0%]

(17) Al is an element effective for improving corrosion resistance in the zinc-based plated layer. When Al is made to be contained in the chemical conversion treatment layer, it is preferable that the plated layer contains Al. For obtaining the above-described effect to a sufficient extent, the Al concentration is preferably 4.0% or more.

(18) On the other hand, if the Al concentration is 25.0% or more, the corrosion resistance of a cut end surface of the zinc-based plated layer decreases. For this reason, the Al concentration is preferably less than 25.0%.

(19) The zinc-based plated layer 12 may contain Al, with the remainder consisting of Zn and impurities. However, the following elements may be further contained. [Mg: 0% or more and less than 12.5%]

(20) Mg is an element having an effect of enhancing the corrosion resistance of the plated layer. For obtaining the above-described effect to a sufficient extent, the Mg concentration is preferably more than 1.0%.

(21) On the other hand, a Mg concentration of 12.5% or more does not lead to further enhancement of the corrosion resistance improving effect, and may deteriorate the workability of the plated layer. In addition, there is a manufacture-related problem such as an increase in amount of dross generated in a plating bath. For this reason, the Mg concentration is preferably less than 12.5%. [Sn: 0% to 20.0%] [Bi: 0% or more and less than 5.0%] [In: 0% or more and less than 2.0%]

(22) These elements contribute to improvement of corrosion resistance and sacrificial corrosion resistance. Therefore, one or more of these elements may be contained. For obtaining the above-described effect to a sufficient extent, the concentration of each of the elements is preferably 0.05% or more, or 0.1% or more.

(23) Of these, Sn is preferable because it is a low-melting-point metal and can be easily incorporated without impairing the properties of the plating bath.

(24) On the other hand, if 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 decreases. For this reason, it is preferable that the Sn concentration is 20.0% or less, the Bi concentration is less than 5.0%, and the In concentration is less than 2.0%. [Ca: 0% to 3.0%]

(25) Ca is an element which reduces the amount of formation of dross likely to be formed during operation, and contributes to improvement of plating manufacturability. Therefore, Ca may be contained. For obtaining this effect, the Ca concentration is preferably 0.1% or more.

(26) On the other hand, if the Ca concentration is high, the corrosion resistance of a flat portion itself of the plated layer 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% or more and less than 0.5%] [Ce: 0% or more and less than 0.5%]

(27) Y, La and Ce are elements that contribute to improvement of corrosion resistance. For obtaining this effect, it is preferable that one or more of these elements are each contained at 0.05% or more, or 0.1% or more.

(28) On the other hand, if the concentration of these elements is excessively high, there is a concern that the viscosity of the plating bath increases, and thus the initial make-up of the plating bath itself is often difficult, and a steel having good plating 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% or more and less than 2.5%]

(29) Si is an element that contributes to improvement of corrosion resistance. In addition, Si is an element having an effect of enhancing adhesion between the steel sheet and the plated layer by suppressing a situation in which an alloy layer formed between a steel sheet surface and the plated layer in formation of the plated layer on the steel sheet has an excessively large thickness. For obtaining these effects, the Si concentration is preferably 0.1% or more. The Si concentration is more preferably 0.2% or more.

(30) On the other hand, if the Si concentration is 2.5% or more, an excessive amount of Si is precipitated in the plated layer, so that not only corrosion resistance decreases but also the workability of the plated layer is deteriorated. Therefore, the Si concentration is preferably less than 2.5%. The Si concentration is more preferably 1.5% or less. [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%]

(31) These elements contribute to improvement of corrosion resistance. For obtaining this effect, it is preferable that the concentration of at least one of the elements is 0.05% or more.

(32) On the other hand, if the concentration of these elements is excessively high, there is a concern that the viscosity of the plating bath increases, and thus the initial make-up of the plating bath itself is often difficult, and a steel having good plating 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%]

(33) Fe is mixed in the plated layer as an impurity in manufacture of the plated layer. Fe may be contained at up to about 5.0%, and as long as the content of Fe is in this range, there is little adverse impact on the effect of the surface-treated steel sheet according to the present embodiment. For this reason, the Fe concentration is preferably 5.0% or less. [B: 0% or more and less than 0.5%]

(34) B is an element that bonds to Zn, Al, Mg or the like to form various intermetallic compounds when contained in the plated layer. Such intermetallic compounds have an effect of improving LME. For obtaining this effect, the B concentration is preferably 0.05% or more.

(35) On the other hand, if the B concentration is excessively high, there is a concern that the melting point of plating significantly increases, and this plating operability is deteriorated, so that a surface-treated steel sheet having good plating properties cannot be obtained. For this reason, the B concentration is preferably less than 0.5%. [Sb: 0% or more and less than 0.5%]

(36) When the plated layer contains Sb, the external appearance of the plated layer changes, a spangle is formed, and improvement in metallic gloss is observed. For obtaining this effect, the Sb concentration is preferably 0.03% or more.

(37) On the other hand, if the Sb concentration is excessively high, there is a concern that the viscosity of the plating bath increases, and thus the initial make-up of the plating bath itself is often difficult, and a steel having good plating properties cannot be manufactured. For this reason, the Sb concentration is preferably less than 0.5%. [Sr: 0% or more and less than 0.5%] [Pb: 0% or more and less than 0.5%]

(38) Like Sb, Sr and Pb are elements that contribute to formation of a spangle. For obtaining this effect, it is preferable that the concentration of at least one of Sr and Pb is 0.05% or more.

(39) On the other hand, if the concentration of these elements is excessively high, there is a concern that the viscosity of the plating bath increases, and thus the initial make-up of the plating bath itself is often difficult, and a steel having good plating properties cannot be manufactured. For this reason, the concentration of each of the elements is preferably less than 0.5%.

(40) The thickness of the zinc-based plated layer 12 is not limited, and is preferably 10 g/m.sup.2 or more per one surface for improving corrosion resistance. On the other hand, a thickness of more than 200 g/m.sup.2 does not lead to further enhancement of corrosion resistance, and causes an economic disadvantage. For this reason, the thickness is preferably 200 g/m.sup.2 or less.

(41) [Spangle]

(42) From the viewpoint of designability, it is preferable that a spangle pattern is formed on a surface of the zinc-based plated layer 12 in the surface-treated steel sheet 1 according to the present embodiment.

(43) The spangle pattern generally includes a regular spangle and a minimized spangle, and from the viewpoint of designability, a regular spangle is more preferable. That is, it is preferable that surface of the zinc-based plated layer 12 in the surface-treated steel sheet 1 according to the present embodiment is regular spangle-finished.

(44) <Chemical Conversion Treatment Layer>

(45) The chemical conversion treatment layer 13 of the surface-treated steel sheet 1 according to the present embodiment contains Si, C, O and P. and has a C concentration of 20.0 mass % or more, an O concentration of 15.0 mass % or more, and a Si concentration of 10.0 mass % or more. That is, since the chemical conversion treatment layer 13 contains an inorganic component as a main component, excellent black deposit resistance is obtained. The upper limit of each of the C concentration, the O concentration and the Si concentration is not specified, and the C concentration is more than 40.0 mass % mainly when the main component is an organic component. For this reason, the C concentration is preferably 40.0 mass % or less. From the viewpoint of the powdering property of the chemical conversion treatment layer 13, it is preferable that the O concentration is 40.0 mass % or less, and the Si concentration is 25.0 mass % or less.

(46) The chemical conversion treatment layer 13 of the surface-treated steel sheet according to the present embodiment is obtained by applying a treatment solution containing an organosilicon compound such as a silane coupling agent and a P compound such as a phosphate on a plated layer containing a zinc under predetermined conditions and performing drying. Therefore, the chemical conversion treatment layer 13 of the surface-treated steel sheet according to the present embodiment contains Si, C, O and P.

(47) If P is not contained at 0.10 mass % or more, generally required corrosion resistance cannot be obtained. For this reason, the P concentration is 0.10 mass % or more. On the other hand, an excessively high P concentration is not preferable because powdering is likely to occur. If the P concentration of the treatment liquid is high, the amount of soluble components tends to be large, leading a decrease in corrosion resistance. For this reason, the P concentration of the chemical conversion treatment layer is preferably 5.0 mass % or less.

(48) A F compound (fluorine compound), a Zr compound (zirconium compound) and/or a V compound (vanadium compound) may be contained in the treatment solution so that the chemical conversion treatment layer 13 of the surface-treated steel sheet according to the present embodiment further contains F, Zr and/or V derived from these compounds. The chemical conversion treatment layer 13 may contain Al, Zn, Sb or the like eluted from the zinc-based plated layer.

(49) In the chemical conversion treatment layer 13, the solid content mass ratio between P derived from the phosphorus compound (W) and Si derived from the organosilicon compound (V) [(Ws)/(Vs)], is preferably 0.15 to 0.31. A solid content mass ratio [(Ws)/(Vs)] of less than 0.15 is not preferable because an effect of the phosphorus compound (W) as an elutability inhibitor cannot be obtained.

(50) On the other hand, a solid content mass ratio [(Ws)/(Vs)] of more than 0.31 is not preferable because the chemical conversion treatment layer is significantly dissolved in water. The solid content mass ratio [(Ws)/(Vs)] is more preferably 0.16 to 0.28, still more preferably 0.18 to 0.25.

(51) In the chemical conversion treatment layer 13 of the surface-treated steel sheet 1 according to the present embodiment, when t is a thickness of the chemical conversion treatment layer, an area starting from a surface of the chemical conversion treatment layer 13 and ending at a position of t/10 from the surface of the chemical conversion treatment layer 13 in a thickness direction is a surface layer region 101, an area starting from the position of 9t/10 from the surface of the chemical conversion treatment layer 13 in the thickness direction and ending at an interface between the chemical conversion treatment layer 13 and the zinc-based plated layer 12 is an interface side region 102, and a region sandwiched between the surface layer region and the interface side region is the intermediate region 103, a maximum value of a P concentration of the surface layer region 101 is 1.5 times to 5.0 times the average P concentration of an intermediate region 103.

(52) A surface that is unlikely to be stained with fingerprints can be formed by segregating P in a surface layer region of the chemical conversion treatment layer 13 to adjust surface free energy. (Fingerprint resistance is improved.)

(53) If the maximum value of the P concentration in the surface layer region 101 is less than 1.5 times the average P concentration of the intermediate region 103, fingerprint resistance becomes insufficient. Preferably, the maximum value of the P concentration in the surface layer region 101 is not less than 2.0 times the average P concentration in the intermediate region 103. In this case, fingerprint resistance can be further improved.

(54) On the other hand, if the maximum value of the P concentration in the surface layer region is more than 5.0 times the average P concentration in the intermediate region, a brittle phosphorus compound is formed on the surface, so that powdering occurs during press processing, which is not preferable as a steel sheet including a zinc-based plated layer.

(55) Further, in the chemical conversion treatment layer 13 of the surface-treated steel sheet 1 according to the present embodiment, it is preferable that Al is present in the interface side region 102, and the F content (concentration) of the interface side region 102 is 20% or more of the F content (concentration) of the entire chemical conversion treatment layer 13.

(56) The fact that Al is present in the interface side region 102 of the chemical conversion treatment layer 13 and F is concentrated in the above-described range indicates that Al and F form a complex salt. The complex salt is hardly soluble, and hardly permeable to corrosive factors from the outside. Thus, when such a complex salt is formed, the flat sheet corrosion resistance of the surface-treated steel sheet is improved, so that the generation of white rust is suppressed.

(57) When Al is not present in the interface side region 102 or the F content of the interface side region 102 is less than 20% of the F content of the entire chemical conversion treatment layer 13, the above-described effect cannot be obtained to a sufficient extent. The upper limit is not limited, but even if the F content of the interface region 102 is increased over a certain level, further enhancement of the effect is not obtained and economic efficiency is deteriorated because F that does not form a complex salt with Al increases in a case where the content of F becomes excessively high with respect to Al. Therefore, the content of F may be, for example, 60% or less.

(58) In addition, it is preferable that Sb is present (contained) in the interface side region 102 in the chemical conversion treatment layer 13 of the surface-treated steel sheet 1 according to the present embodiment. In this case, blackening of the surface-treated steel sheet can be suppressed (blackening resistance is improved). The mechanism thereof is unknown, but may be similar to a mechanism in which flush treatment with Co or the like contributes to prevention of blackening of the surface-treated steel sheet.

(59) For the surface-treated steel sheet according to the present embodiment, whether the chemical conversion treatment layer contains the elements of Si, C, O, P and F, the ratio of the maximum value of the P concentration of the surface layer region to the average P concentration of the intermediate region, the ratio of the F content of the surface layer region to the F content of the entire chemical conversion treatment layer, and the presence or absence of Al and Sb in the interface side region are determined by EDS linear analysis.

(60) Specifically, by a cryogenic focused ion beam (FIB) method, a test piece is cut out from a zinc-based plated steel sheet on which a chemical conversion treatment layer is formed, and a cross section structure of the obtained test piece is observed with a transmission electron microscope (TEM) at a magnification which allows the entire chemical conversion treatment layer to fall within the observed visual field. For identifying the constituent elements of each layer, line analysis is performed along the thickness direction by TEM-EDS (energy dispersive X-ray spectroscopy), and quantitative analysis of the chemical composition at each site is performed. The method of the line analysis is not particularly limited, and continuous point analysis with an interval of several nm between points may be performed, or an element map in an arbitrary region may be measured to determine the thickness-direction distribution of the element in terms of the average in a plane direction.

(61) The values of the C concentration, the O concentration, the Si concentration and the P concentration in the chemical conversion treatment layer are each determined as the average of the line analysis results for the entire chemical conversion treatment layer.

(62) As the maximum value of the P concentration of the surface layer region, the largest value among the concentrations obtained by performing line analysis of the surface layer region in the thickness direction is adopted.

(63) Each of the F content of the interface side region and the F content of the entire chemical conversion treatment layer is average F concentration of observed region (layer)volume of the region (layer), respectively. (The volume of the interface side region is 1/10 of that of the entire chemical conversion treatment layer.)

(64) In the interface side region, line analysis is performed in the thickness direction. It is determined that Al is present if the average Al concentration is 0.10 mass % or more, and it is determined that Sb is present if the maximum value of the Sb concentration is 0.01 mass % or more.

(65) The apparatus used for the analysis is not particularly limited, and for example, TEM (electrolysis emission transmission electron microscope: JEM-2100F manufactured by JEOL Ltd.) or EDS (JED-2300T manufactured by JEOL Ltd.) may be used.

(66) The thickness of the chemical conversion treatment layer 13 of the surface-treated steel sheet 1 according to the present embodiment is preferably 10 to 2000 nm. A thickness of less than 10 nm is not preferable because there is a possibility that a surface of the steel cannot be covered, and thus sufficient corrosion resistance cannot be obtained. On the other hand, a thickness of more than 2000 nm is not preferable because black deposit resistance during processing decreases. The thickness is more preferably 200 to 800 nm.

(67) The thickness of the chemical conversion treatment layer can be measured by observing a cross section using IEM.

(68) The interface between the plated layer and the chemical conversion treatment layer is identified by observation of the cross sectional with the TEM, and the thickness from this interface to the surface of the chemical conversion treatment layer is defined as a thickness of the chemical conversion treatment layer.

(69) <Manufacturing Method>

(70) Next, a preferred manufacturing method for the surface-treated steel sheet according to the present embodiment will be described.

(71) As long as the surface-treated steel sheet according to the present embodiment has the above-described characteristics, the effects thereof can be obtained regardless of a manufacturing method, the manufacturing method described below is preferable because it enables stable manufacture.

(72) That is, the surface-treated steel sheet according to the present embodiment can be manufactured by a manufacturing method including the following steps. (I) a plating step of forming a zinc-based plated layer on a surface of a steel (steel sheet) by immersing the steel in a plating bath containing Zn; (II) a step of applying a surface treatment metal agent (treatment solution) to a steel including a zinc-based plated layer; (III) a heating step of heating the steel sheet, to which the surface treatment metal agent is applied, to form a chemical conversion treatment layer containing Si, C. O and P; and (IV) a cooling step of cooling the steel sheet after the heating step.

(73) Hereinafter, preferred conditions for each step will be described.

(74) [Plating Step]

(75) There is no particular limitation on the plating step. The plating may be performed by a normal hot-dip galvanizing method so as to obtain sufficient plating adhesion.

(76) In addition, there is no particular limitation on the manufacturing method for the steel that is subjected to the plating step.

(77) The manufacturing method may be a manufacturing method for a zinc-plated steel sheet as specified in JIS G 3302: 2019 or a manufacturing method for a plated steel sheet as specified in JIS G 3323: 2019.

(78) Since the composition of the plating bath is substantially equal to the composition of the plated layer, the composition of the plating bath may be adjusted according to the composition of a desired zinc-based plated layer. For regular spangle-finishing a surface of the plated layer, it is preferable that the plating bath contains Sb at 0.03 to 0.15 mass %.

(79) [Application Step]

(80) In the application step, a surface treatment metal agent (treatment solution) is applied to the steel sheet after the plating step (steel sheet including a zinc-based plated layer) using a roll coater or the like.

(81) The surface treatment metal agent contains an organosilicon compound (V), which is a compound containing Si, C and O, as a film-forming component. The organosilicon compound is not particularly limited, and is obtained by, for example, blending a silane coupling agent (A) containing one amino group in the molecule and a silane coupling agent (B) containing one glycidyl group in the molecule at a solid content mass ratio [(A)/(B)] of 0.5 to 1.7.

(82) The blending ratio between the silane coupling agent (A) and the silane coupling agent (B) is preferably 0.5 to 1.7 in terms of a solid content ratio [(A)/(B)]. A solid content ratio [(A)/(B)] of less than 0.5 is not preferable because bath stability and black deposit resistance may be significantly deteriorated. On the other hand, a solid content ratio [(A)/(B)] of more than 1.7 is not preferable because water resistance may significantly decrease.

(83) The surface treatment metal agent contains a P compound (phosphorus compound) (W) as an inhibitor component. The phosphorus compound (W) is not particularly limited, and examples thereof include phosphoric acid, ammonium phosphate, potassium phosphate, and sodium phosphate.

(84) For the blending amount of the phosphorus compound (W), the solid content mass ratio between Si derived from the organosilicon compound (V) and P derived from the phosphorus compound (W), [(Ws)/(Vs)], is preferably 0.15 to 0.31. It is not preferable that the solid content mass ratio between Si derived from the organosilicon compound (V) and P derived from the phosphorus compound (W), [(Ws)/(Vs)], is less than 0.15 because good corrosion resistance cannot be obtained due to the shortage of the inhibitor component. On the other hand, a solid content mass ratio [(Ws)/(Vs)] of more than 0.31 is not preferable because the film (chemical conversion treatment layer) is significantly dissolved in water, so that good corrosion resistance cannot be obtained.

(85) The solid content of the surface treatment metal agent is 3.0 to 15.0 mass %. If the solid content of the surface treatment metal agent is less than 3.0 mass %, corrosion resistance decreases. The reason for this is unknown, but may be that water remains in the chemical conversion treatment layer (film), so that the barrier property of the film is deteriorated. On the other hand, if the solid content of the surface treatment metal agent is more than 15.0 mass %, it is difficult to segregate P of the surface layer region. The reason for this is unknown, but may be that a compound contained in the surface treatment metal agent and containing Si, C and O suppresses movement of P in the surface treatment metal agent.

(86) It is preferable to use the surface treatment metal agent within 72 hours after the organosilicon compound (V), which is a compound containing Si, C and O, and the P compound (phosphorus compound) (W) are mixed. After more than 72 hours, the effect of segregating P in the surface layer region decreases. The reason for this is unknown, but may be that the organosilicon compound (V) and the P compound (phosphorus compound) (W) contained in the surface treatment metal agent react with each other, so that movement of P in the surface-treated metal agent is suppressed.

(87) For performing control so that a complex salt of Al and F is formed in the interface side region of the chemical conversion treatment layer, it is preferable that Al is contained in the zinc-based plated layer, and a fluorine compound (X) is contained in the surface treatment metal agent. When the fluorine compound is contained, Al on the plated surface is dissolved, and Al and F react with each other, so that a hardly soluble salt is formed in the interface side region of the chemical conversion treatment layer.

(88) Examples of the fluorine compound include hydrogen fluoride.

(89) For the blending amount of the fluorine compound (X), the concentration of F derived from the fluorine compound (X) contained in the surface treatment agent is preferably 0.03 to 4.50 mass %. If the blending amount of the fluorine compound (X) is less than 0.03 mass %, the amount of dissolution of Al on the plating surface is insufficient, so that a hardly soluble salt obtained by reaction between Al and F is not formed, and thus it is difficult to obtain the effect of improving corrosion resistance. If the blending amount of the fluorine compound (X) is more than 4.50 mass %, Al is excessively dissolved on the plated surface, so that the external appearance is deteriorated.

(90) For the blending amount of the fluorine compound (X), the solid content mass ratio between Si derived from the organosilicon compound (V) and F derived from the fluorine compound (X), [(Xs)/(Vs)], is preferably 0.01 to 0.30. If the solid content mass ratio between Si derived from the organosilicon compound (V) and F derived from the fluorine compound (X), [(Xs)/(Vs)], is less than 0.01, the effect of improving corrosion resistance cannot be obtained to a sufficient extent. On the other hand, a solid content mass ratio [(Xs)/(Vs)] of more than 0.30 is not preferable because the chemical conversion treatment layer is significantly dissolved in water.

(91) The surface treatment metal agent may contain a Zr compound (Y). The Zr compound (Y) is not particularly limited, and examples thereof include ammonium zirconium carbonate, hexafluorozirconium hydroacid, and ammonium zirconium hexafluoride.

(92) For the blending amount of the Zr compound (Y), the solid content mass ratio between Si derived from the organosilicon compound (V) and Zr derived from the Zr compound (Y), [(Ys)/(Vs)], is preferably 0.06 to 0.15. If the solid content mass ratio between Si derived from the organosilicon compound (V) and the Zr derived from the Zr compound (Y), [(Ys)/(Vs)], is less than 0.06, the effect of improving corrosion resistance is insufficient. On the other hand, a solid content mass ratio [(Ys)/(Vs)] of more than 0.15 does not lead to further enhancement of the effect of improving corrosion resistance.

(93) The surface treatment metal agent may contain a V compound (Z). The V compound (Z) is not particularly limited, and examples thereof include vanadium pentoxide V.sub.2O.sub.5, metavanadate 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 linvanadomolybdic acid. It is also possible to use compounds obtained by reducing a pentavalent vanadium compound to tetravalence to divalence with an organic compound having at least one functional group selected from the group consisting of a hydroxyl group, a carbonyl group, carboxylic acid, a primary to tertiary amino group, an amide group, a phosphoric acid group and a phosphonic acid group.

(94) For the blending amount of the V compound (Z), the solid content mass ratio between Si derived from the organosilicon compound (V) and V derived from the V compound (Z), [(Zs)/(Vs)], is preferably 0.05 to 0.17. If the solid content mass ratio between Si derived from the organosilicon compound (V) and V derived from the V compound (Z), [(Zs)/(Vs)], is less than 0.05, the effect of improving corrosion resistance cannot be obtained to a sufficient extent. On the other hand, a solid content mass ratio [(Zs)/(Vs)] of more than 0.17 is not preferable because bath stability is deteriorated.

(95) For performing control so that Sb is present in the interface side region of the chemical conversion treatment layer, it is preferable that Sb is contained in the zinc-based plated layer, hydrogen fluoride is contained in the surface treatment metal agent, and the pH of the surface treatment metal agent is set to 1 to 5. When hydrogen fluoride is contained in the surface treatment agent to set the pH of the surface treatment metal agent to 1 to 5, Sb in the zinc-based plated layer is eluted in the surface treatment metal agent, and moves to the interface side region of the chemical conversion treatment layer.

(96) For setting the pH to 1 to 5, a pH adjuster may be incorporated in the surface treatment metal agent. The pH adjuster is not particularly limited, and organic acids such as formic acid, acetic acid and lactic acid, ammonium salts, amines, and the like may be used.

(97) [Heating Step and Cooling Step]

(98) In the heating step, the steel sheet, to which a surface treatment metal agent is applied is heated and dried with a drying furnace or the like to form a chemical conversion treatment layer on a surface thereof.

(99) In the heating step, P can be segregated in the surface layer region of the chemical conversion treatment layer by heating the surface treatment metal agent at an appropriate temperature rising rate. The reason for this is unknown, but may be that in the process of forming the chemical conversion treatment layer, P moves to a chemical conversion treatment layer-non-formed portion due to poor compatibility between a film containing Si, O and C and P in the process of forming the chemical conversion treatment layer.

(100) For segregating P, it is necessary that the temperature rising rate be 10 to 150 C./sec until the temperature reaches 55 C., which is a temperature at which the surface treatment metal agent is dried to form the chemical conversion treatment layer, after application at room temperature. If the temperature rising rate is more than 150 C./sec, the movement of P becomes insufficient, so that the P concentration in the surface layer region cannot be sufficiently increased. On the other hand, if the temperature rising rate is less than 10 C./sec, the amount of movement of P increases, so that the P concentration of the surface layer region becomes excessive.

(101) In the heating step, a layer including a complex salt of Al and F can be formed by controlling the time until formation of the chemical conversion treatment layer immediately after application of the surface treatment metal agent to concentrate F in a region on the interface side with the plated layer in the chemical conversion treatment layer if the surface treatment metal agent contains hydrogen fluoride.

(102) The time from application of the surface treatment metal agent to formation of the chemical conversion treatment layer immediately is preferably 1.0 to 10.0 seconds. If the time until formation of the chemical conversion treatment layer is less than 1.0 seconds, a complex salt of Al and F is hardly formed, so that it is not possible to obtain F-concentrated layer sufficient for improving corrosion resistance. On the other hand, if the time until formation of the chemical conversion treatment layer is more than 10.0 seconds, the surface layer of the plated layer is excessively etched by hydrogen fluoride, resulting in deterioration of the external appearance of the steel sheet after chemical conversion treatment.

EXAMPLES

(103) A cold-rolled steel sheet having a sheet thickness of 0.8 mm and satisfying the provision of JIS G 3141: 2017 was immersed in a plating bath having a composition shown in Table 1, thereby obtaining a plated steel sheet whose thickness is shown in Table 8. In Table 1, for example, Zn-0.2% Al indicates a composition having Al of 0.2 mass % with the remainder of Zn and impurities. For a to g, a hot-dip plating method was applied, and for h, an electro plating method was applied.

(104) In addition, a silicon compound (silane coupling agent), a phosphorus compound (P compound), a fluorine compound (F compound), a zirconium compound (Zr compound) and a vanadium compound (V compound) shown in Tables 2 to 6 were mixed in proportions shown in Table 7, thereby preparing aqueous surface treatment metal agents.

(105) The surface treatment metal agent was applied to the plated steel sheet by a roll coater, and dried to by heating to 55 C. to form a chemical conversion treatment layer. Here, the combinations of the plated steel sheet, the surface treatment metal agent and the application and drying conditions were as shown in Tables 10-1 to 10-12.

(106) In this way, surface-treated steel sheets Nos. 1 to 171 were manufactured.

(107) For the obtained surface-treated steel sheet, fingerprint resistance, powdering resistance, corrosion resistance, the external appearance and blackening resistance were evaluated in the following manner.

(108) <Fingerprint Resistance>

(109) Vaseline (registered trademark) was applied to a surface of the flat sheet test piece, and left standing for 10 minutes, the Vaseline (registered trademark) was then removed, and a color difference (E) before and after the application of the Vaseline (registered trademark) was measured using a spectrophotometric colorimeter (SC-T45 manufactured by Suga Test Instruments Co., Ltd.). Here, the evaluation criteria are as follows. A sample meeting +, or was rated as being excellent in fingerprint resistance. +: E0.5 : 0.52

(110) A flat sheet test piece was prepared, and subjected to contact bending in accordance with JIS Z 2248: 2014, and a cellophane tape peeling test was conducted on the contact bending part. Thereafter, the cellophane tape-peeled part was observed with a scanning electron microscope to evaluate the residual state of the chemical conversion treatment film. A sample meeting was rated as being excellent in powdering resistance, and a sample meeting was rated as being acceptable in practical use.

(111) <Evaluation Criteria>

(112) : Either cracking or peeling is not observed in the chemical conversion treatment film.

(113) : Cracking is observed, but peeling is not observed in the chemical conversion treatment film.

(114) x: Peeling of chemical conversion treatment film is recognized.

(115) <Corrosion Resistance (White Rust Resistance)>

(116) A flat sheet test piece was prepared, and a salt water spray test conforming to JIS Z 2371: 2015 was conducted on each test piece to evaluate the state of generation of white rust on the surface after 144 hours (ratio of the white rust generation area to the area of the test piece). A sample meeting was rated as having corrosion resistance sufficient for practical use, a sample meeting was rated as being excellent in corrosion resistance, and a sample meeting was rated as being further excellent in corrosion resistance.

(117) <Evaluation Criteria>

(118) =Rust is generated over less than 5% of the total area.

(119) =Rust is generated over 5% or more and less than 10% of the total area.

(120) =Rust is generated over 10% or more and less than 30% of the total area.

(121) x=Rust is generated over 30% or more of the total area.

(122) <External Appearance>

(123) The external appearance of the flat sheet test piece was visually evaluated on the basis of the following criteria. A sample meeting was rated as being excellent in external appearance.

(124) <Evaluation Criteria>

(125) : Whitening is not observed.

(126) : Local whitening is recognized.

(127) <Blackening Resistance>

(128) The test sheet was held in a wet box at a temperature of 70 C. and a relative humidity of 80% for 6 days, and then taken out, and a blackening state of the test sheet was visually evaluated.

(129) The evaluation criteria are as follows. A sample meeting was rated as being acceptable, and a sample meeting was rated as being particularly excellent in blackening resistance.

(130) =The area fraction of blackened portions is less than 1%.

(131) =The area fraction of blackened portions is 1% or more and less than 25%.

(132) =The area fraction of blackened portions is 25% or more and less than 50%.

(133) x=The area fraction of blackened portions is 50% or more.

(134) TABLE-US-00001 TABLE 1 Plating composition Spangle a Zn0.2% Al Minimized spangle b Zn0.2% Al0.08% Sb Regular spangle c Zn6.0% Al3.0% Mg None d Zn11.0% Al3.0% Mg0.2% Si None e Zn16.0% Al6.0% Mg0.2% Si None f Zn19.0% Al6.0% Mg1.5% None Sn0.5% Ca0.2% Si g Zn24.0% Al12.0% None Mg0.5% Ca1.2% Si h Zn None

(135) TABLE-US-00002 TABLE 2 Name A1 3-Aminopropyltrimethoxysilane A2 3-Aminopropyltriethoxysilane B1 3-Glycidoxypropyltrimethoxysilane B2 3-Glycidoxypropyltriethoxysilane

(136) TABLE-US-00003 TABLE 3 Name W1 Phosphoric acid W2 Ammonium phosphate

(137) TABLE-US-00004 TABLE 4 Name X1 Hydrogen fluoride

(138) TABLE-US-00005 TABLE 5 Name Y1 Ammonium zirconium carbonate Y2 Hexafluorozirconium hydroacid

(139) TABLE-US-00006 TABLE 6 Name Z1 Vanadium oxysulfate VOSO.sub.4 Z2 Vanadium oxyacetylacetonate VO(OC(CH.sub.2)CH.sub.2COCH.sub.3)

(140) TABLE-US-00007 TABLE 7 Organosilicon compound (V) F compound (X) F Silane concentration Zr coupling P compound (W) in treatment compound (Y) V Compound (Z) Solid agent Proportion Proportion Proportion solution Proportion Proportion content No. A B A/B Type Ws/Vs Type Xs/Vs mass % Type Ys/Vs Type Zs/Vs (mass %) pH ST1 A1 B1 1.0 W1 0.17 3.0 5.5 ST2 A1 B2 0.7 W2 0.20 6.7 8.5 ST3 A2 B1 1.3 W1 0.30 8.3 5.5 ST4 A2 B2 1.5 W2 0.16 11.5 7.8 ST5 A1 B1 1.3 W1 0.16 X1 0.02 0.11 5.6 5.2 ST6 A1 B2 1.4 W2 0.20 X1 0.28 1.90 6.8 8.2 ST7 A2 B1 0.6 W1 0.20 X1 0.25 1.97 7.9 5.3 ST8 A2 B2 0.7 W2 0.20 X1 0.15 1.53 10.2 8.0 ST9 A1 B1 0.8 W2 0.18 11.5 3.5 ST10 A1 B2 1.1 W1 0.27 12.8 3.4 ST11 A2 B1 1.3 W2 0.16 4.5 2.4 ST12 A2 B2 1.5 W1 0.16 4.5 4.5 ST13 A1 B1 1.0 W1 0.18 X1 0.04 0.14 3.6 2.3 ST14 A1 B2 1.0 W2 0.27 X1 0.04 0.22 5.5 1.5 ST15 A2 B1 0.9 W1 0.27 X1 0.05 0.43 8.6 4.8 ST16 A2 B2 0.9 W2 0.27 X1 0.28 1.87 6.7 3.5 ST17 A1 B1 0.8 W1 0.20 X1 0.04 0.30 Y1 0.10 7.7 1.3 ST18 A1 B2 0.6 W2 0.21 X1 0.04 0.29 Z2 0.07 7.3 2.8 ST19 A2 B1 1.6 W1 0.23 X1 0.05 0.50 Y1 0.14 Z1 0.06 10.1 4.9 ST20 A2 B2 1.3 W2 0.24 X1 0.28 3.38 Y2 0.07 Z2 0.16 12.1 3.4 ST21 A1 B1 1.5 W2 0.27 1.5 7.5 ST22 A2 B2 0.6 W2 0.25 1.8 7.7 ST23 A2 B1 1.1 W2 0.16 18.0 7.8 ST24 A2 B2 1.3 W1 0.28 23.0 5.3 ST25 A2 B1 1.2 W2 0.02 X1 0.02 0.14 3.1 6.3 ST26 A1 B2 1.3 W1 0.45 X1 0.28 2.30 14.0 6.4 ST27 A2 B1 1.2 W2 0.15 X1 0.02 0.01 3.1 6.3 ST28 A1 B2 1.3 W1 0.17 X1 0.28 4.80 14.0 6.4 ST29 A1 B1 1.1 W1 0.03 3.6 2.3 ST30 A2 B2 0.7 W2 0.12 6.7 3.5

(141) TABLE-US-00008 TABLE 8 Sheet Plating thickness Thickness No. (mm) Type (g/m.sup.2) Spangle O1 0.8 a 90 Minimized spangle O2 0.8 b 90 Regular spangle O3 0.8 c 90 None O4 0.8 d 90 None O5 0.8 e 90 None O6 0.8 f 90 None O7 0.8 g 90 None O8 0.8 h 30 None

(142) TABLE-US-00009 TABLE 9 Application Time until formation conditions Drying step of chemical conversion Film adhesion Temperature treatment layer after amount rising rate application No. (nm) ( C./sec) (sec) C1 20 30 2.1 C2 50 100 5.2 C3 80 140 8.5 C4 300 15 9.3 C5 450 50 7.1 C6 600 120 4.2 C7 750 145 1.5 C8 1000 20 7.8 C9 1500 80 5.0 C10 1800 130 2.5 C11 300 1 2.3 C12 450 3 4.5 C13 800 5 7.2 C14 900 7 8.1 C15 50 180 1.5 C16 250 200 2.8 C17 500 220 5.0 C18 750 250 9.7 C19 70 140 0.1 C20 400 100 0.8 C21 850 60 0.2 C22 1850 20 0.9 C23 70 140 11.0 C24 400 100 18.9 C25 850 60 13.8 C26 1850 20 25.5

(143) TABLE-US-00010 TABLE 10-1 Manufacture conditions Time (h) until application/drying Conditions for Base Surface after preparation application/drying sheet treatment of surface of surface Analysis under metal treatment metal treatment metal Si content C content O content P content No. test agent agent agent (mass %) (mass %) (mass %) (mass %) 1 O2 ST1 58 C1 12.3 36.0 22.1 2.1 2 O2 ST2 48 C2 11.5 29.9 19.0 2.0 3 O2 ST3 68 C3 17.2 22.8 22.9 2.6 4 O2 ST4 131 C4 15.7 29.8 18.7 3.2 5 O2 ST1 34 C5 14.1 21.8 21.9 2.9 6 O2 ST2 147 C6 13.0 26.0 29.5 2.3 7 O2 ST3 84 C7 11.4 29.6 24.1 2.8 8 O2 ST4 46 C8 11.3 26.6 27.6 2.0 9 O2 ST1 6 C9 12.4 27.1 33.7 2.4 10 O2 ST2 20 C10 16.6 35.8 19.4 3.1 11 O1 ST3 21 C1 11.3 34.1 29.9 2.4 12 O3 ST4 21 C2 11.7 26.5 34.8 2.5 13 O4 ST1 22 C3 13.7 34.1 27.1 2.5 14 O5 ST2 55 C4 11.0 25.4 26.4 2.6 15 O6 ST3 65 C5 12.4 27.5 30.0 1.9 16 O7 ST4 31 C6 13.8 28.4 25.2 3.0 17 O1 ST1 41 C11 17.2 30.2 25.7 4.1 18 O2 ST2 5 C12 10.1 20.5 22.1 2.1 19 O3 ST3 59 C13 11.7 27.2 18.8 2.8 20 O4 ST4 69 C14 10.6 23.2 20.2 2.0 21 O5 ST1 37 C11 14.1 27.1 25.0 2.3 22 O6 ST2 35 C12 15.9 25.5 22.4 2.9 23 O7 ST3 14 C13 16.3 32.4 30.0 2.9 24 O2 ST4 60 C14 15.8 20.7 27.3 2.8 25 O1 ST1 218 C15 17.1 25.5 18.5 4.2 26 O2 ST2 215 C16 12.2 22.1 33.7 2.4 27 O3 ST3 229 C17 19.8 32.3 31.1 3.2 28 O4 ST4 215 C18 12.7 25.5 19.0 2.6 29 O5 ST1 75 C15 11.5 33.3 32.7 1.9 30 O6 ST2 178 C16 14.5 29.3 31.9 3.5 31 O7 ST3 147 C17 19.3 24.1 27.5 3.6 32 O2 ST4 110 C18 17.2 26.7 18.3 4.0 33 O2 ST5 7 C1 12.2 21.9 23.7 2.7 34 O2 ST6 19 C2 12.0 21.1 18.5 2.2 35 O2 ST7 67 C3 11.3 28.3 27.8 2.1 36 O2 ST8 158 C4 17.5 29.9 26.9 3.5 37 O2 ST5 27 C5 12.4 23.5 28.7 1.9 38 O2 ST6 43 C6 13.6 32.2 21.1 2.3 39 O2 ST7 43 C7 10.9 24.1 33.6 2.3 40 O2 ST8 29 C8 10.9 30.2 33.4 2.4 41 O2 ST5 61 C9 13.8 24.5 28.7 3.3 42 O2 ST6 33 C10 11.8 25.8 23.0 2.3 43 O1 ST7 67 C1 19.9 33.8 20.1 4.0 44 O3 ST8 8 C2 17.9 25.6 25.5 2.8 45 O4 ST5 65 C3 17.3 28.7 19.2 3.3 46 O5 ST6 4 C4 10.3 22.7 30.8 1.7 47 O6 ST7 48 C5 17.4 20.9 19.4 3.0 48 O7 ST8 29 C6 12.5 23.5 20.6 2.0

(144) TABLE-US-00011 TABLE 10-2 Manufacture conditions Time (h) until application/drying Conditions for Base Surface after preparation application/drying sheet treatment of surface of surface Analysis under metal treatment metal treatment metal Si content C content O content P content No. test agent agent agent (mass %) (mass %) (mass %) (mass %) 49 O1 ST5 70 C19 10.0 35.5 22.6 2.3 50 O2 ST6 12 C20 11.2 27.1 32.5 2.4 51 O3 ST7 118 C21 11.2 24.5 25.8 2.7 52 O4 ST8 24 C22 18.6 26.1 26.3 2.8 53 O5 ST5 31 C19 15.5 30.9 20.6 3.0 54 O6 ST6 71 C20 13.3 34.4 30.5 2.3 55 O7 ST7 202 C21 17.6 25.0 30.6 3.3 56 O2 ST8 69 C22 11.1 28.3 24.3 2.0 57 O1 ST5 34 C23 16.6 24.5 24.4 3.3 58 O2 ST6 20 C24 19.6 22.3 23.3 3.5 59 O3 ST7 38 C25 11.2 33.9 23.9 1.9 60 O4 ST8 52 C26 14.0 25.6 30.7 2.4 61 O5 ST5 65 C23 15.9 36.8 18.9 3.8 62 O6 ST6 29 C24 15.6 23.1 17.6 2.7 63 O7 ST7 149 C25 17.9 25.9 20.9 4.3 64 O2 ST8 45 C26 10.9 34.8 24.4 1.7 65 O2 ST9 180 C1 12.3 32.8 30.1 2.8 66 O2 ST10 26 C2 19.9 35.0 32.8 4.3 67 O2 ST11 45 C3 11.6 22.5 27.3 2.8 68 O2 ST12 5 C4 15.5 36.5 25.6 2.9 69 O2 ST9 20 C5 11.7 20.8 30.8 1.9 70 O2 ST10 209 C6 19.2 33.2 30.4 3.8 71 O2 ST11 37 C7 15.4 31.4 22.5 2.7 72 O2 ST12 27 C8 17.9 24.3 20.7 4.2 73 O2 ST9 57 C9 15.6 28.3 23.9 2.4 74 O2 ST10 113 C10 16.6 36.0 25.0 2.6 75 O2 ST11 39 C1 10.7 31.2 25.1 2.4 76 O2 ST12 52 C2 19.0 22.1 21.5 3.4 77 O2 ST9 47 C3 18.3 20.1 21.8 3.0 78 O2 ST10 40 C4 14.0 24.0 19.6 2.5 79 O2 ST11 20 C5 13.2 32.9 23.9 2.4 80 O2 ST12 29 C6 11.5 25.8 24.5 2.1 81 O2 ST13 111 C1 12.2 25.7 20.7 2.4 82 O2 ST14 47 C2 19.1 28.3 22.8 3.4 83 O2 ST15 38 C3 18.7 22.2 27.6 4.6 84 O2 ST16 223 C4 11.7 27.2 30.7 2.6 85 O2 ST13 12 C5 12.0 22.9 28.7 2.5 86 O2 ST14 67 C6 13.7 29.0 26.3 2.3 87 O2 ST15 202 C7 17.8 31.2 32.0 4.2 88 O2 ST16 1 C8 15.6 26.9 21.6 3.2 89 O2 ST13 67 C9 14.4 35.6 34.2 3.2 90 O2 ST14 31 C10 14.4 22.1 33.2 2.4 91 O2 ST15 51 C1 11.1 27.4 29.0 1.9 92 O2 ST16 61 C2 13.1 20.3 30.3 2.0 93 O2 ST13 48 C3 15.9 32.3 33.9 2.7 94 O2 ST14 3 C4 19.4 35.3 19.3 4.6 95 O2 ST15 16 C5 15.0 32.6 30.1 2.8 96 O2 ST16 28 C6 16.2 29.3 34.5 3.2

(145) TABLE-US-00012 TABLE 10-3 Manufacture conditions Time (h) until application/drying Conditions for Base after preparation application/drying sheet Surface of surface of surface Analysis under treatment treatment metal treatment metal Si content C content O content P content No. test metal agent agent agent (mass %) (mass %) (mass %) (mass %) 97 O1 ST9 29 C1 18.0 21.1 32.2 2.7 98 O3 ST10 76 C2 19.5 25.3 25.3 4.1 99 O4 ST11 211 C3 19.6 25.9 21.3 4.1 100 O5 ST12 35 C4 12.3 21.3 33.4 2.7 101 O6 ST9 36 C5 10.3 28.9 24.4 1.7 102 O7 ST10 9 C6 14.4 24.2 31.8 3.5 103 O1 ST11 33 C7 15.7 22.4 29.1 3.5 104 O3 ST12 41 C8 11.7 22.0 19.1 2.5 105 O4 ST13 60 C9 10.0 29.0 19.0 2.4 106 O5 ST14 92 C10 16.1 20.9 33.1 3.2 107 O6 ST15 16 C1 10.2 33.9 32.7 1.9 108 O7 ST16 12 C2 18.9 36.9 23.9 4.1 109 O1 ST13 64 C3 18.5 21.9 30.3 3.4 110 O3 ST14 0 C4 14.7 35.9 20.8 2.9 111 O4 ST15 149 C5 14.3 26.0 28.9 2.7 112 O5 ST16 57 C6 15.2 31.3 33.2 3.4 113 O2 ST17 25 C1 15.5 36.5 30.4 3.1 114 O2 ST18 62 C2 11.0 22.2 30.8 2.5 115 O2 ST19 64 C3 10.8 26.1 27.8 2.0 116 O2 ST20 51 C4 13.8 36.5 28.1 3.1 117 O2 ST17 22 C5 19.6 20.5 23.8 4.1 118 O2 ST18 11 C6 10.7 34.1 23.7 1.9 119 O2 ST19 64 C7 18.6 28.5 32.7 3.0 120 O2 ST20 41 C8 11.3 27.2 30.7 2.3 121 O2 ST17 26 C1 11.5 26.2 22.4 2.5 122 O2 ST18 57 C2 18.3 24.8 23.1 3.5

(146) TABLE-US-00013 TABLE 10-4 Manufacture conditions Time (h) until application/drying Conditions for Base after preparation application/drying sheet Surface of surface of surface Analysis under treatment treatment metal treatment metal Si content C content O content P content No. test metal agent agent agent (mass %) (mass %) (mass %) (mass %) 129 O1 ST21 93 C1 14.2 20.5 25.2 2.1 130 O2 ST22 39 C2 19.6 21.3 27.2 3.7 131 O3 ST21 218 C3 18.0 26.1 29.1 3.0 132 O4 ST22 48 C4 19.1 30.6 26.3 4.6 133 O5 ST21 170 C5 18.8 29.3 26.8 3.7 134 O6 ST22 62 C6 18.4 31.8 29.9 3.8 135 O7 ST21 18 C7 19.5 21.2 26.5 3.3 136 O2 ST22 41 C8 12.7 20.3 18.2 2.5 137 O1 ST23 90 C9 14.0 31.0 21.2 3.2 138 O2 ST24 103 C10 10.2 30.0 32.1 1.9 139 O3 ST23 100 C1 15.4 22.1 23.9 2.7 140 O4 ST24 168 C2 15.3 22.9 18.4 3.0 141 O5 ST23 173 C3 16.6 24.6 30.8 3.2 142 O6 ST24 125 C4 16.0 22.8 17.7 3.7 143 O7 ST23 193 C5 12.4 25.0 31.8 2.1 144 O2 ST24 208 C6 10.9 35.8 17.6 2.3 145 O1 ST25 192 C7 11.5 20.5 17.8 0.05 146 O2 ST25 27 C8 10.2 35.7 25.5 0.04 147 O3 ST25 22 C9 10.7 28.5 22.3 0.08 148 O4 ST25 27 C10 15.5 27.2 31.7 0.02 149 O5 ST26 63 C1 19.6 22.4 28.7 10.3 150 O6 ST26 83 C2 11.3 26.5 15.5 10.9 151 O7 ST26 39 C3 10.7 25.2 16.7 11.5 152 O1 ST26 47 C4 12.3 31.9 28.8 9.8 153 O1 ST27 29 C5 16.0 25.2 22.7 3.3 154 O2 ST27 24 C6 13.2 26.5 31.8 3.1 155 O3 ST27 27 C7 19.5 28.9 27.7 4.5 156 O4 ST27 70 C8 17.4 21.6 34.8 2.8 157 O5 ST28 53 C9 19.0 32.5 26.1 3.3 158 O6 ST28 27 C10 12.7 28.5 26.0 2.7 159 O7 ST28 49 C1 10.4 25.0 20.4 2.1 160 O1 ST28 34 C2 16.9 25.8 24.7 3.7 161 O8 ST5 67 C4 17.3 30.2 27.2 2.3 162 O8 ST6 41 C3 16.9 33.5 34.5 3.5 163 O8 ST7 22 C2 10.5 25.0 26.3 3.5 164 O8 ST8 163 C1 21.3 25.7 18.7 4.7 165 O1 ST29 150 C1 11.5 25.7 29.1 0.08 166 O2 ST30 190 C2 12.3 23.2 29.9 0.09 167 O3 ST29 204 C3 11.1 20.8 26.5 0.07 168 O4 ST30 96 C4 13.2 31.5 18.2 0.08 169 O5 ST29 88 C1 13.3 30.7 32.1 0.09 170 O6 ST30 178 C2 10.5 29.3 17.3 0.07 171 O7 ST29 156 C3 10.3 30.8 26.0 0.09

(147) TABLE-US-00014 TABLE 10-5 Analysis Maximum value Proportion of of P concentration Presence F content of Presence of surface layer or absence interface or absence region/average of Al in side region of Sb in P concentration interface (interface interface of intermediate side side region/ side No. region region total) region 1 4.8 Present 0 None 2 3.8 Present 0 None 3 4.4 Present 0 None 4 1.5 Present 0 None 5 3.3 Present 0 None 6 1.6 Present 0 None 7 1.9 Present 0 None 8 3.0 Present 0 None 9 2.4 Present 0 None 10 3.4 Present 0 None 11 2.3 Present 0 None 12 4.5 Present 0 None 13 3.0 Present 0 None 14 4.7 Present 0 None 15 2.1 Present 0 None 16 4.5 Present 0 None 17 8.3 Present 0 None 18 6.4 Present 0 None 19 5.1 Present 0 None 20 8.1 Present 0 None 21 9.9 Present 0 None 22 9.7 Present 0 None 23 9.7 Present 0 None 24 7.9 Present 0 None 25 0.9 Present 0 None 26 0.6 Present 0 None 27 1.2 Present 0 None 28 1.3 Present 0 None 29 1.1 Present 0 None 30 1.0 Present 0 None 31 1.2 Present 0 None 32 0.5 Present 0 None 33 4.8 Present 25 None 34 3.5 Present 22 None 35 3.2 Present 28 None 36 1.7 Present 30 None 37 4.6 Present 21 None 38 2.6 Present 38 None 39 4.7 Present 45 None 40 3.6 Present 25 None 41 2.6 Present 30 None 42 4.1 Present 37 None 43 2.1 Present 39 None 44 2.4 Present 40 None 45 3.3 Present 25 None 46 3.2 Present 28 None 47 2.3 Present 30 None 48 2.8 Present 23 None

(148) TABLE-US-00015 TABLE 10-6 Analysis Maximum value Proportion of of P concentration Presence F content of Presence of surface layer or absence interface or absence region/average of Al in side region of Sb in P concentration interface (interface interface of intermediate side side region/ side No. region region total) region 49 3.0 Present 5 None 50 4.7 Present 7 None 51 1.8 Present 1 None 52 3.0 Present 15 None 53 4.7 Present 13 None 54 2.3 Present 8 None 55 1.6 Present 9 None 56 2.2 Present 2 None 57 4.6 Present 35 None 58 4.2 Present 38 None 59 3.6 Present 28 None 60 2.1 Present 25 None 61 3.4 Present 47 None 62 3.3 Present 23 None 63 2.0 Present 40 None 64 2.9 Present 27 None 65 1.6 Present 0 None 66 2.1 Present 0 None 67 4.5 Present 0 None 68 2.7 Present 0 None 69 2.5 Present 0 None 70 1.7 Present 0 None 71 4.1 Present 0 Present 72 2.5 Present 0 Present 73 2.8 Present 0 Present 74 1.6 Present 0 Present 75 4.6 Present 0 Present 76 3.5 Present 0 Present 77 4.1 Present 0 Present 78 2.9 Present 0 Present 79 2.8 Present 0 Present 80 4.1 Present 0 Present 81 1.9 Present 25 Present 82 4.0 Present 29 Present 83 4.5 Present 37 Present 84 1.7 Present 43 Present 85 3.5 Present 50 Present 86 4.6 Present 25 Present 87 1.6 Present 25 Present 88 3.7 Present 26 Present 89 3.2 Present 40 Present 90 3.8 Present 38 Present 91 2.4 Present 38 Present 92 4.1 Present 31 Present 93 4.6 Present 37 Present 94 4.1 Present 42 Present 95 3.3 Present 41 Present 96 2.1 Present 40 Present

(149) TABLE-US-00016 TABLE 10-7 Analysis Maximum value Proportion of of P concentration Presence F content of Presence of surface layer or absence interface or absence region/average of Al in side region of Sb in P concentration interface (interface interface of intermediate side side region/ side No. region region total) region 97 3.6 Present 0 None 98 1.8 Present 0 None 99 1.6 Present 0 None 100 4.3 Present 0 None 101 3.8 Present 0 None 102 4.4 Present 0 None 103 4.6 Present 0 None 104 3.1 Present 0 None 105 2.4 Present 0 None 106 1.9 Present 0 None 107 3.9 Present 0 None 108 2.5 Present 0 None 109 3.7 Present 0 None 110 2.8 Present 0 None 111 1.9 Present 0 None 112 4.1 Present 0 None 113 2.5 Present 28 Present 114 2.1 Present 30 Present 115 4.5 Present 33 Present 116 4.3 Present 33 Present 117 3.7 Present 37 Present 118 3.4 Present 21 Present 119 3.3 Present 28 Present 120 2.8 Present 40 Present 121 3.1 Present 45 Present 122 4.6 Present 30 Present

(150) TABLE-US-00017 TABLE 10-8 Analysis Maximum value Proportion of of P concentration Presence F content of Presence of surface layer or absence interface or absence region/average of Al in side region of Sb in P concentration interface (interface interface of intermediate side side region/ side No. region region total) region 129 1.9 Present 0 None 130 2.9 Present 0 None 131 1.8 Present 0 None 132 2.3 Present 0 None 133 1.5 Present 0 None 134 4.3 Present 0 None 135 4.2 Present 0 None 136 4.1 Present 0 None 137 0.8 Present 0 None 138 0.7 Present 0 None 139 1.3 Present 0 None 140 1.1 Present: 0 None 141 1.1 Present 0 None 142 1.2 Present 0 None 143 0.5 Present 0 None 144 0.4 Present 0 None 145 1.8 Present 0 None 146 2.5 Present 0 None 147 3.5 Present 0 None 148 3.5 Present 0 None 149 4.8 Present 0 None 150 1.6 Present 0 None 151 2.4 Present 0 None 152 4.9 Present 0 None 153 2.4 Present 11 None 154 2.1 Present 7 None 155 3.1 Present 5 None 156 2.2 Present 8 None 157 4.6 Present 50 None 158 3.0 Present 45 None 159 3.2 Present 48 None 160 3.0 Present 38 None 161 4.7 None 11 None 162 3.4 None 5 None 163 3.3 None 5 None 164 1.8 None 8 None 165 1.5 Present 0 None 166 1.7 Present 0.0 None 167 1.6 Present 0 None 168 1.5 Present 0 None 169 1.5 Present 0 None 170 1.7 Present 0 None 171 1.5 Present 0 None

(151) TABLE-US-00018 TABLE 10-9 Quality characteristics Fingerprint Powdering Corrosion External Blackening No. resistance resistance resistance appearance resistance Category 1 Inventive Example 2 Inventive Example 3 Inventive Example 4 Inventive Example 5 Inventive Example 6 Inventive Example 7 Inventive Example 8 Inventive Example 9 Inventive Example 10 Inventive Example 11 Inventive Example 12 Inventive Example 13 Inventive Example 14 Inventive Example 15 Inventive Example 16 Inventive Example 17 + X Comparative Example 18 + X Comparative Example 19 + X Comparative Example 20 + X Comparative Example 21 + X Comparative Example 22 + X Comparative Example 23 + X Comparative Example 24 + X Comparative Example 25 X Comparative Example 26 X Comparative Example 27 X Comparative Example 28 X Comparative Example 29 X Comparative Example 30 X Comparative Example 31 X Comparative Example 32 X Comparative Example 33 Inventive Example 34 Inventive Example 35 Inventive Example 36 Inventive Example 37 Inventive Example 38 Inventive Example 39 Inventive Example 40 Inventive Example 41 Inventive Example 42 Inventive Example 43 Inventive Example 44 Inventive Example 45 Inventive Example 46 Inventive Example 47 Inventive Example 48 Inventive Example

(152) TABLE-US-00019 TABLE 10-10 Quality characteristics Fingerprint Powdering Corrosion External Blackening No. resistance resistance resistance appearance resistance Category 49 Inventive Example 50 Inventive Example 51 Inventive Example 52 Inventive Example 53 Inventive Example 54 Inventive Example 55 Inventive Example 56 Inventive Example 57 Inventive Example 58 Inventive Example 59 Inventive Example 60 Inventive Example 61 Inventive Example 62 Inventive Example 63 Inventive Example 64 Inventive Example 65 Inventive Example 66 Inventive Example 67 Inventive Example 68 Inventive Example 69 Inventive Example 70 Inventive Example 71 Inventive Example 72 Inventive Example 73 Inventive Example 74 Inventive Example 75 Inventive Example 76 Inventive Example 77 Inventive Example 78 Inventive Example 79 Inventive Example 80 Inventive Example 81 Inventive Example 82 Inventive Example 83 Inventive Example 84 Inventive Example 85 Inventive Example 86 Inventive Example 87 Inventive Example 88 Inventive Example 89 Inventive Example 90 Inventive Example 91 Inventive Example 92 Inventive Example 93 Inventive Example 94 Inventive Example 95 Inventive Example 96 Inventive Example

(153) TABLE-US-00020 TABLE 10-11 Quality characteristics Fingerprint Powdering Corrosion External Blackening No. resistance resistance resistance appearance resistance Category 97 Inventive Example 98 Inventive Example 99 Inventive Example 100 Inventive Example 101 Inventive Example 102 Inventive Example 103 Inventive Example 104 Inventive Example 105 Inventive Example 106 Inventive Example 107 Inventive Example 108 Inventive Example 109 Inventive Example 110 Inventive Example 111 Inventive Example 112 Inventive Example 113 Inventive Example 114 Inventive Example 115 Inventive Example 116 Inventive Example 117 Inventive Example 118 Inventive Example 119 Inventive Example 120 Inventive Example 121 Inventive Example 122 Inventive Example

(154) TABLE-US-00021 TABLE 10-12 Quality characteristics Fingerprint Powdering Corrosion External Blackening No. resistance resistance resistance appearance resistance Category 129 Inventive Example 130 Inventive Example 131 Inventive Example 132 Inventive Example 133 Inventive Example 134 Inventive Example 135 Inventive Example 136 Inventive Example 137 X Comparative Example 138 X Comparative Example 139 X Comparative Example 140 X Comparative Example 141 X Comparative Example 142 X Comparative Example 143 X Comparative Example 144 X Comparative Example 145 X Comparative Example 146 X Comparative Example 147 X Comparative Example 148 X Comparative Example 149 Inventive Example 150 Inventive Example 151 Inventive Example 152 Inventive Example 153 Inventive Example 154 Inventive Example 155 Inventive Example 156 Inventive Example 157 Inventive Example 158 Inventive Example 159 Inventive Example 160 Inventive Example 161 Inventive Example 162 Inventive Example 163 Inventive Example 164 Inventive Example 165 X Comparative Example 166 X Comparative Example 167 X Comparative Example 168 X Comparative Example 169 X Comparative Example 170 X Comparative Example 171 X Comparative Example

(155) As is apparent from Tables 1 to 10 to 12, Invention Examples Nos, 1 to 16, 33 to 122, 129 to 136 and 149 to 164 in which the chemical conversion treatment layer contains predetermined amounts of Si, C, O and P and the maximum value of the P concentration of the surface layer region is 1.5 times to 5.0 times the average P concentration of the intermediate region were excellent in the fingerprint resistance while having sufficient powdering resistance and corrosion resistance.

(156) On the other hand, Comparative Examples Nos. 17 to 32, 137 to 148 and 165 to 171 were poor in any of fingerprint resistance, powdering resistance and corrosion resistance.

(157) Among the inventive examples, those in which Al is present in the interface side region and the F content of the interface side region is 20% or more of the F content of the entire chemical conversion treatment layer were further excellent in corrosion resistance.

(158) When Sb was present in the interface side region, further excellent blackening resistance was exhibited.

BRIEF DESCRIPTION OF THE REFERENCE SYMBOLS

(159) 1 Surface-treated steel sheet 11 Steel sheet 12 Plated layer 13 Chemical conversion treatment layer 101 Surface layer region 102 Interface side region 103 Intermediate region