Surface-treated steel sheet

Abstract

This surface-treated steel sheet has a base material steel sheet, a plating layer, a first coating, and a second coating. The plating layer has a Zn concentration of 40%-100% and a Mg concentration of 0% or more and less than 4.0%. The following items satisfy a predetermined relationship: the maximum concentration of Ti, the maximum concentration of Zr, and the maximum concentration of V in the interval from a first interface to the center of the the first coating film in the thickness direction of the first interface and a second interface; the average concentration of C in the central section of the first coating; the average concentration of C in the central section of the second coating; the maximum concentration of Mg in a border area of the first coating; the average concentration of Mg in the central section of the first coating; the maximum concentration of F in the border area of the first coating; the average concentration of F in the central section of the first coating; the average concentration of Si in the central section of the first coating; the average concentration of Zn in the central section of the first coating; and the average concentration of Zn in the central section of the second coating.

Description

Surface-treated steel sheet

[0001] The present invention relates to a surface-treated steel sheet. This application claims priority based on Japanese Patent Application No. 2022-161691 filed on October 6, 2022, and Japanese Patent Application No. 2022-161692 filed on October 6, 2022, the contents of which are incorporated herein by reference.

[0002] Conventionally, plated steel sheets (zinc-plated steel sheets) having a plating layer mainly composed of zinc formed on the surface of the steel sheet have been used in a wide range of applications, such as automobiles, building materials, and home appliances. Furthermore, for the purpose of imparting corrosion resistance, paint adhesion, and the like to the surface of such zinc-plated steel sheets, methods such as chromate treatment using a treatment solution containing chromic acid, dichromic acid, or a salt thereof as a main component, treatment using a metal surface treatment agent that does not contain chromium, phosphate treatment, treatment using a silane coupling agent alone, and organic resin coating treatment are commonly known and in practical use.

[0003] In recent years, in response to various legal restrictions on hexavalent chromium compounds, which may have adverse effects on the environment and human health, development of chromium-free metal surface treatment agents has been promoted. Examples of chromium-free metal surface treatment agents include technologies using oxides or hydroxides of Group 4 metals such as Ti and Zr. For example, Patent Document 1 discloses a chromate-free chemically treated steel sheet having a zinc-plated or zinc-alloy-plated steel sheet as a substrate, in which a chemical conversion coating containing a valve metal oxide or hydroxide and a fluoride, both of which exhibit high insulation resistance, is formed on the surface of the substrate. Patent Document 2 also discloses a hot-dip zinc alloy-plated steel sheet with excellent corrosion resistance, in which a chemical conversion coating containing one or more of a valve metal hydroxide, oxide, oxyacid, oxyacid acid salt, and fluoride as the main components is formed on a Mg-containing zinc alloy plating layer via an interfacial reaction layer containing one or more compounds selected from magnesium fluoride, magnesium phosphate, and a composite compound of magnesium and a valve metal oxyacid acid salt. In Patent Document 2, a zinc alloy plating layer containing Mg is used as a base, and an interfacial reaction layer containing Mg is formed, thereby achieving high white rust resistance (corrosion resistance). Also, Patent Document 3 discloses a hot-dip zinc alloy-plated steel sheet with excellent corrosion resistance, in which a composite chemical conversion coating of Ti and V is formed on a Zn-Al alloy plating layer via an interfacial reaction layer of Al-F. In Patent Document 3, a zinc alloy plating layer containing Al is used as a base, and an Al-F reaction layer is formed, thereby achieving high white rust resistance.

[0004] Japanese Patent Publication No. 2002-194558 Japanese Patent Publication No. 2007-23309 Japanese Patent Publication No. 2003-306777

[0005] The technologies disclosed in Patent Documents 1 to 3 are excellent technologies that have been put to practical use as surface-treated steel sheets that have undergone chromate-free surface treatments with excellent corrosion resistance. To improve the corrosion resistance of chromate-free treatments, technologies for forming a reaction layer containing metal elements contained in the plating layer have been used, as described in Patent Documents 2 and 3. However, due to the recent increasing sophistication of customer needs, it has become clear that these prior art technologies may not provide sufficient corrosion resistance. For example, with zinc-plated steel sheets using plating that does not contain Mg or Al, it is difficult to form the reaction layer described in Patent Documents 2 or 3, resulting in insufficient corrosion resistance in flat (planar) and processed areas. Furthermore, even in the case of galvanized steel sheets using plating containing Mg and Al in the plating layer, when a chemical conversion coating (film) is formed in a continuous hot-dip galvanized steel sheet production line, from the viewpoint of productivity, the time from applying a chemical conversion treatment solution to the surface of a zinc-based plated steel sheet to drying to form a chemical conversion coating is very short, within 5 seconds. Therefore, since the Zn phase of the zinc alloy plating contains only trace amounts of Mg and Al, it is difficult to form the reaction layer on the Zn phase of the plating, resulting in insufficient corrosion resistance. For these reasons, there is a demand for surface-treated steel sheets that have excellent corrosion resistance (white rust resistance) in both processed and flat areas. Furthermore, it is preferable that the surface-treated steel sheets have excellent lubricity so that they can be easily processed into complex shapes.

[0006] The present invention aims to provide a surface-treated steel sheet having excellent corrosion resistance and lubricity, based on the premise that the surface-treated steel sheet has a chromate-free coating on the surface of a zinc-based plated steel material having a plating layer containing zinc or a zinc alloy on the surface of the steel material.

[0007] The corrosion resistance of surface-treated steel materials having a coating improves with increasing barrier properties (i.e., the ability to prevent the penetration of corrosion factors such as moisture and chloride ions) of the coating. Furthermore, in areas where the coating is damaged due to scratches or other defects, the greater the inhibitor effect (the ability of substances (mainly metal elements) in the coating to dissolve and prevent corrosion of the plating layer when moisture adheres) is increased, the better the corrosion resistance, including white rust resistance, improves. As described above, the chemical conversion coatings disclosed in Patent Documents 1 to 3 possess both barrier and inhibitor properties. However, in environments requiring higher white rust resistance than conventional coatings, these properties are insufficient, raising concerns that the plating layer may corrode and white rust may occur prematurely. In light of these circumstances, the present inventors investigated methods for improving the barrier properties and inhibitor effect of coatings. As a result, they found that when a coating is formed on the surface of a zinc plating layer or zinc alloy plating layer in a short time, the barrier properties of the coating can be improved and the corrosion resistance can be dramatically increased by forming multiple locations where specific elements are concentrated, in addition to controlling the concentration of each element from near the interface between the Zn phase of the zinc plating layer or zinc alloy plating layer and the coating to the surface of the coating.

[0008] [Amendment based on Rule 91 19.01.2024] The present invention has been made in light of the above findings. The gist of the present invention is as follows. [1] A surface-treated steel sheet according to one aspect of the present invention is a surface-treated steel sheet having: a base steel sheet; a plating layer formed on a surface of the base steel sheet; a first coating formed on the surface of the plating layer; and a second coating formed on the surface of the first coating and having a thickness of 0.6 μm or more, wherein the plating layer has a Zn concentration of 40 mass% or more and 100 mass% or less, and a Mg concentration of 0 mass% or more and less than 4.0 mass%, and when the concentrations of C, O, F, Mg, Al, Si, P, Ti, V, Zn, and Zr are continuously measured by linear analysis in a thickness direction from the plating layer toward the surface of the surface-treated steel sheet, the position where the Zn concentration becomes 35.0 mass% or less is defined as a first interface, which is an interface between the plating layer and the first coating, and a region including the first interface and located between a range of 10 nm from the first interface toward the plating layer and a range of 15 nm from the first interface toward the first coating in the thickness direction is defined as a boundary region, When the position where the Zn concentration becomes 3.0 mass % or less for the first time is defined as the second interface between the first coating and the second coating, and the range from the center between the first interface and the second interface in the thickness direction to a position 10 nm toward the second interface is defined as the central part of the first coating, and when the region of the second coating between positions 400 nm and 410 nm from the second interface in the thickness direction is defined as the central part of the second coating, one or more of the following formulas (1) to (3) and formulas (4) to (15) are satisfied:Dti≧5.0 (1) Dzr≧5.0 (2) Dv≧5.0 (3) Dti+Dzr+Dv≦25.0 (4) B1c<10.0 (5) B2c≧40.0 (6) 5.0 / M≦Amg≦25.0 (7) 0.5≦B1mg≦5.0 (8) 15.0 / M≦Af≦40.0 (9) 0.5≦B1f≦15.0 (10) Amg / B1mg≧2.0 (11) Af / B1f≧2.0 (12) B1si<5.0 (13) B1zn≧0.5 (14) B2zn<3.0 (15) wherein Dti is the maximum Ti concentration, in mass %, of the first coating from the first interface to the center in the thickness direction between the first interface and the second interface; Dzr is the maximum Zr concentration, in mass %, of the first coating from the first interface to the center in the thickness direction between the first interface and the second interface; Dv is the maximum V concentration, in mass %, of the first coating from the first interface to the center in the thickness direction between the first interface and the second interface; B1c is the average C concentration, in mass %, of the central portion of the first coating; B2c is the average C concentration, in mass %, of the central portion of the second coating; Amg is the maximum Mg concentration, in mass %, of the boundary region of the first coating; B1mg is the average Mg concentration, in mass %, of the central portion of the first coating; and Af is the maximum F concentration, in mass %, of the boundary region of the first coating. [2] The surface-treated steel sheet according to [1] may further satisfy the following formula (16):

[0045] B1f is the average concentration of F in the central portion of the first coating, B1si is the average concentration of Si in the central portion of the first coating, B1zn is the average concentration of Zn in the central portion of the first coating, B2zn is the average concentration of Zn in the central portion of the second coating, and M is a constant that is 1 when the Mg concentration of the plating layer is 0 mass% or more and less than 1.0 mass%, and is 2 when the Mg concentration of the plating layer is 1.0 mass% or more and less than 4.0 mass%.0≦Cmg<5.0 (16) Here, Cmg is the Mg concentration in mass % at a position 10 nm toward the coating layer from the first interface in the thickness direction of the coating layer. [3] The surface-treated steel sheet according to [1] or [2] may further satisfy the following formulas (17) to (19): 5.0≦Aal≦20.0 (17) 0.2≦B1al≦5.0 (18) Aal / B1al≧5.0 (19) Here, Aal is the maximum concentration of Al in mass % in the boundary region, and B1al is the average concentration of Al in mass % in the central portion of the first coating. [4] The surface-treated steel sheet according to any of [1] to [3] may further satisfy the following formulas (20) to (21): 10.0≦Ap≦25.0 (20) 0.5≦B1p≦8.0 (21) where Ap is the maximum concentration of P in the boundary region, and B1p is the average concentration of P in mass% in the central portion of the first coating. [5] The surface-treated steel sheet according to any one of [1] to [4] may further satisfy the following formula (22): 1.0≦B1zn≦30.0 (22) [6] The surface-treated steel sheet according to any one of [1] to [5] may further satisfy the following formula (23): X2si / Y2si≧1.1 (23) where X2si is the maximum concentration of Si in mass% in a region from the surface of the second coating to 100 nm toward the second interface, and Y2si is the average concentration of Si in mass% in a region of the second coating from the surface to 300 to 310 nm toward the second interface. [7] The surface-treated steel sheet according to any one of [1] to [6] may further satisfy the following formula (24): Af / B1f≧2.5 (24).

[0009] According to the above aspect of the present invention, it is possible to provide a surface-treated steel sheet having excellent corrosion resistance and lubricity.

[0010] 1 is a schematic diagram showing an example of a cross section of a surface-treated steel sheet according to an embodiment of the present invention, and FIG. 2 is a diagram showing an example of an elemental analysis result in the thickness direction obtained using an FE-TEM equipped with an energy dispersive X-ray analyzer.

[0011] A surface-treated steel sheet according to one embodiment of the present invention (surface-treated steel sheet according to the present embodiment) will be described. In the following description, the numerical ranges defined by "to" are included as lower and upper limits, respectively. On the other hand, values ​​indicated as "greater than" or "less than" are not included in the numerical range. Furthermore, all ratios (e.g., A mg / B mg, which is the ratio of A mg to B mg described below) are dimensionless. As shown in FIG. 1 , the surface-treated steel sheet 1 according to the present embodiment includes a base steel sheet 10, a plating layer 20 formed on the surface of the base steel sheet 10, a first coating 30 formed on the surface of the plating layer 20, and a second coating 40 formed on the surface of the first coating 30. In the surface-treated steel sheet 1 according to the present embodiment, the plating layer 20 is a zinc plating layer or zinc alloy plating layer containing 0 mass % or more and less than 4.0 mass % Mg (i.e., a Mg concentration of 0 mass % or more and less than 4.0 mass %). In the present embodiment, when the concentrations (concentration distributions) of C, O, F, Mg, Al, Si, P, Ti, V, Zn, and Zr are continuously measured by linear analysis in the thickness direction from the plating layer toward the surface of the coated steel sheet, the position where the Zn concentration first becomes 35.0 mass% or less is defined as a first interface 25, which is the interface between the plating layer 20 and the first coating 30. A region including the first interface 25 and extending from the first interface 25 in the thickness direction to a range of 10 nm toward the plating layer 20 and a range of 15 nm toward the first coating 30 is defined as a boundary region A. In other words, boundary region A is a 25-nm region in the thickness direction spanning both the plating layer 20 and the first coating 30 across the interface. The position where the Zn concentration first becomes 3.0 mass% or less as a result of the linear analysis is defined as a second interface 35, which is the interface between the first coating 30 and the second coating 40. The plating layer 20, the first coating 30, and the second coating 40 may be formed on one side or both sides of the base steel sheet 10. The first coating 30 and the second coating 40 are, for example, chemical conversion coatings.

[0012] The X-ray analysis is performed using a field emission-transmission electron microscope (FE-TEM) equipped with an energy dispersive X-ray analyzer, for example, under the following conditions: A test piece is cut out from the surface-treated steel sheet on which a coating has been formed by a cryo-focused ion beam (FIB) method, and the cross-sectional structure of the cut out test piece is observed with a transmission electron microscope (TEM) at a magnification (100,000 to 1,000,000 times) that allows the entire coating and part of the Zn phase of the plating layer to be seen in the field of view. To identify the constituent elements of each layer, elemental analysis of the entire field of view in the thickness direction is performed by line analysis using TEM-EDS (Energy Dispersive X-ray Spectroscopy), and the concentrations of C, O, F, Mg, Al, Si, P, Ti, V, Zn, and Zr are continuously measured at each position from the plating layer to the surface of the coated steel sheet. The acceleration voltage during observation and EDS analysis is 200 kV. When observed with an FE-TEM, the plating layer is clearly different from the coating, so that a position that is clearly different from the coating can be determined to be the plating layer by observation with the FE-TEM. The starting point of the line analysis may be, for example, any position in the plating layer observed with the FE-TEM. Furthermore, even if the coating layer cannot be sufficiently identified by FE-TEM observation, if, for example, the Zn concentration is 85 mass % or more and the Mg concentration and Al concentration are both 1.0 mass % or less at the start point of the EDS line analysis, then the start point is certainly the coating layer, and there is no need to repeat the FE-TEM observation or the EDS line analysis. The end point of the line analysis is the surface of the coating (the surface of the coated steel sheet).

[0013] Line analysis is also possible with EPMA, but since EPMA does not allow observation at a higher magnification than TEM, it may not be possible to analyze with high precision the concentration distribution of each element in the coating of the surface-treated steel sheet according to this embodiment. Therefore, in this embodiment, line analysis is performed using an FE-TEM equipped with an energy dispersive X-ray analyzer.

[0014] The base steel sheet 10, the plating layer 20, the first coating 30, and the second coating 40 will be described below.

[0015] <Base Steel Sheet> The surface-treated steel sheet according to this embodiment has excellent corrosion resistance due to the plating layer and coating. Therefore, the base steel sheet is not particularly limited. The base steel sheet may be determined depending on the product to which it is applied, the required strength, plate thickness, etc. For example, hot-rolled mild steel sheets and steel strips, or hot-rolled steel sheets and steel strips for automotive structures (sometimes collectively referred to as hot-rolled steel sheets) described in JIS G 3131:2018 or JIS G 3113:2018, or cold-rolled steel sheets and steel strips, or automotive workable cold-rolled high-tensile steel sheets and steel strips (sometimes collectively referred to as cold-rolled steel sheets) described in JIS G 3141:2021 or JIS G 3135:2018, may be used.

[0016] <Plated Layer> The chemical composition of the plated layer provided on the surface-treated steel sheet according to this embodiment has a zinc (Zn) concentration (content) of 40 mass% or more and 100 mass% or less, and a Mg concentration (content) of 0 mass% or more and less than 4.0 mass%. The plated layer is a zinc plated layer or a zinc alloy plated layer. The contents of elements other than Zn and Mg are not limited, and may be, for example, in mass %, Al: 0% or more and less than 25.0%, Sn: 0% or more and less than 20%, Bi: 0% or more and less than 5.0%, In: 0% or more and less than 2.0%, Ca: 0% or more and less than 3.0%, Y: 0% or more and less than 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%, The plating layer may have the following composition: Mn: 0% or more but less than 0.25%, Fe: 0% or more but less than 5.0%, Sr: 0% or more but less than 0.5%, Sb: 0% or more but less than 0.5%, Pb: 0% or more but less than 0.5%, B: 0% or more but less than 0.5%, and the balance: impurities. All elements other than Zn, including Mg and Al, are optional, with their lower limits set to 0%. In other words, the chemical composition of the plating layer may consist only of Zn and impurities. If necessary, the Mg concentration may be 0.1% or more, 0.5% or more, or 1.0% or more, and the Mg concentration may be 3.5% or less, 3.0% or less, or 2.5% or less. If necessary, the Al concentration may be 0.1% or more, 0.2% or more, 1.0% or more, or 4.0% or more, and the Al concentration may be 21.0% or less, 17.0% or less, or 12.0% or less. If necessary, the Zn concentration may be 50% or more, 60% or more, 70% or more, 80% or more, or 85% or more, or may be less than 100%, less than 99%, less than 97%, or less than 95%. The total concentration of impurities is preferably less than 1.0%.

[0017] The chemical composition of the plating layer can be determined by dissolving the plating layer in, for example, a 10% HCl aqueous solution containing an inhibitor that suppresses corrosion of the base steel (base steel sheet) (for example, IBIT manufactured by Asahi Chemical Industry Co., Ltd.), and then performing composition analysis by ICP atomic emission spectrometry.

[0018] The coating weight of the plating layer is not limited, but in order to improve corrosion resistance, it is recommended to use 10 g / m per side. ２ On the other hand, the amount of adhesion per side is preferably 200 g / m or more. ２ If the coating amount exceeds 200 g / m, the corrosion resistance will be saturated and it will be economically disadvantageous. ２ It is preferable that:

[0019] The type of the plated layer is not limited, and may be, for example, a hot-dip plated layer or an electroplated layer.

[0020] <First Coating> In the surface-treated steel sheet according to this embodiment, the first coating is present on the coating layer (the surface opposite to the base steel sheet), i.e., between the coating layer and the second coating. The first coating is also referred to as a primer coating or underlayer coating. In this embodiment, the central portion B1 of the first coating refers to a region starting from the center of the interface between the coating layer and the first coating (first interface) and the interface between the first coating and the second coating (second interface) in the thickness direction, and ending at a position 10 nm toward the second interface. As described below, the first coating is a coating formed by applying a chemical conversion treatment solution containing an aqueous solution containing any of Ti, Zr, and V, Mg, and F, to which phosphoric acid and nitric acid have been added, and then drying the solution. The first coating contains any of Ti, Zr, and V, Mg, and F, and may also contain P and Si.

[0021] In the first coating (first coating according to the present embodiment) provided on the surface-treated steel sheet according to the present embodiment, in the region from the first interface to the center between the first and second interfaces, where Dti (unit: mass %) is the maximum concentration of Ti in mass %, Dzr (unit: mass %) is the maximum concentration of Zr in mass %, and Dv (unit: mass %) is the maximum concentration of V in mass %, one or more selected from Dti, Dzr, and Dv are 5.0% or more, and the total of one or more is 25.0% or less. In this case, the barrier properties of the coating are enhanced. Since increasing each value leads to the coating becoming brittle and the barrier properties decreasing, the total of Dti, Dzr, and Dv is preferably 20.0% or less. That is, the surface-treated steel sheet according to the present embodiment satisfies one or more of formulas (1) to (3) and formula (4). Dti≧5.0 (1) Dzr≧5.0 (2) Dv≧5.0 (3) Dti+Dzr+Dv≦25.0 (4)

[0022] In the first coating according to this embodiment, the average carbon concentration B1c (unit: mass %) at the center B1 of the first coating is less than 10.0%. If B1c is 10.0% or more, the barrier properties of the coating are reduced, resulting in poor corrosion resistance. Furthermore, the first coating is substantially free of organic resin (1 mass % or less). There is no simple measurement method for confirming that the organic resin content is 1 mass % or less through analysis of the first coating. However, increasing the amount of organic resin in the surface treatment solution increases the carbon concentration in the coating. Therefore, in this embodiment, B1c is set to less than 10.0% as an indicator of an organic resin content of 1 mass % or less. That is, the surface-treated steel sheet according to this embodiment satisfies the following formula (5): B1c<10.0 (5) To obtain excellent corrosion resistance, it is more preferable that B1c be 6.0% or less, 4.5% or less, or 3.0% or less. Since there is no lower limit for B1c, the lower limit for Bc is 0%. If necessary, B1c may be set to 0.5% or more, 1.0% or more, or 1.5% or more.

[0023] Furthermore, in the first coating according to this embodiment, the maximum Mg concentration Amg (unit: mass%) in the boundary region A is 2.5 to 25.0%, the average Mg concentration B1mg (unit: mass%) in the central portion B1 of the first coating is 0.5 to 5.0%, and the ratio of Amg to B1mg, Amg / B1mg, is 2.0 or greater. In other words, Mg is concentrated near the first interface. By containing a predetermined amount of Mg and concentrating Mg near the first interface, the barrier properties of the coating are improved, resulting in improved corrosion resistance. If Amg is less than 2.5%, B1mg is less than 0.5%, or Amg / B1mg is less than 2.0, the corrosion resistance improvement effect is insufficient. However, if the Mg concentration of the plating layer is less than 1.0 mass%, an Amg of less than 5.0% is insufficient. This is thought to be because, due to the large volume fraction of Zn in the coating structure, it is necessary to form a stronger Mg-enriched layer than a coating layer containing more Mg in order to suppress the occurrence of white rust. Therefore, when the Mg concentration of the coating layer is 0% by mass or more but less than 1.0% by mass, Amg is 5.0 to 25.0%. On the other hand, if Amg exceeds 25.0%, the adhesion between the coating layer and the first coating decreases, resulting in a decrease in corrosion resistance. If B1mg exceeds 5.0%, no Mg-enriched portion is formed, resulting in a decrease in corrosion resistance. That is, the surface-treated steel sheet according to this embodiment satisfies the following formulas (7), (8), and (11). 5.0 / M≦Amg≦25.0 (7) 0.5≦B1mg≦5.0 (8) Amg / B1mg≧2.0 (11) Here, M is a constant that is 1 (i.e., M=1) when the Mg concentration in the chemical composition of the plating layer is 0% or more and less than 1.0% by mass, and is 2 (i.e., M=2) when the Mg concentration is 1.0% or more and less than 4.0% by mass. If necessary, Amg may be set to 20.0% or less, 15.0% or less, 12.0% or less, 10.0% or less, or 8.0% or less. In particular, only when the Mg concentration in the chemical composition of the plating layer is 1.0% or more and less than 4.0% by mass, the upper limit of Amg may be limited; for example, Amg may be set to 12.0% or less, 10.0% or less, 8.0% or less, or 6.0% or less. Furthermore, B1mg may be set to 4.0% or less, 3.0% or less, or 2.0% or less, as required.There is no particular need to set an upper limit for A mg / B mg, but A mg / B mg may be 20.0 or less, 15.0 or less, or 10.0 or less. If necessary, A mg / B mg may be 2.5 or more, 3.5 or more, or 4.5 or more.

[0024] F also enhances the barrier properties of the coating. Like Mg, it is contained in a predetermined amount in the first coating and then concentrated near the first interface. Specifically, in the first coating, the maximum F concentration Af (unit: mass %) in the boundary region A is 7.5 to 40.0%, the average F concentration B1f (unit: mass %) in the central portion B1 of the first coating is 0.5 to 15.0%, and the ratio of Af to B1f, Af / B1f, is 2.0 or greater. Preferably, Af / B1f is 2.5 or greater. If Af is less than 7.5%, B1f is less than 0.5%, or Af / B1f is less than 2.0, the corrosion resistance improvement effect is insufficient. However, if the Mg concentration in the plating layer is less than 1.0 mass%, the effect is not obtained if Af is less than 15.0%. This is thought to be because, due to the large volume fraction of Zn in the coating structure, it is necessary to form a stronger F-enriched layer than a coating layer containing more Mg in order to suppress the occurrence of white rust. Therefore, when the Mg concentration of the coating layer is 0% by mass or more but less than 1.0% by mass, Af is 15.0 to 40.0%. On the other hand, if Af exceeds 40.0%, excess F impairs barrier properties and reduces corrosion resistance. If B1f exceeds 15.0%, no F-enriched portion is formed, and excellent corrosion resistance cannot be obtained. That is, the surface-treated steel sheet according to this embodiment satisfies the following formulas (9), (10), and (12). 15.0 / M≦Af≦40.0 (9) 0.5≦B1f≦15.0 (10) Af / B1f≧2.0 (12) Here, M is a constant that is 1 (i.e., M=1) when the Mg concentration in the chemical composition of the plating layer is 0% or more and less than 1.0%, and is 2 (i.e., M=2) when the Mg concentration is 1.0% or more and less than 4.0%. Preferably, the following formula (24) is satisfied: Af / B1f≧2.5 (24) If necessary, Af may be set to 38.0% or less, 35.0% or less, 30.0% or less, 25.0% or less, or 20.0% or less. In particular, only when the Mg concentration in the chemical composition of the plating layer is 1.0 mass% or more and less than 4.0 mass%, the upper limit of Af may be limited, and for example, Af may be set to 25.0% or less, 20.0% or less, 16.0% or less, or 12.0% or less.Furthermore, B1f may be set to 12.0% or less, 10.0% or less, or 7.5% or less, as needed. There is no need to particularly set an upper limit for Af / B1f, but Af / B1f may be set to 50.0 or less, 30.0 or less, 20.0 or less, or 10.0 or less, as needed. Af / B1f may be set to 3.0 or more, 3.5 or more, or 4.5 or more.

[0025] In the first coating according to this embodiment, B1si (unit: mass %), which is the average concentration of Si in the central portion B1 of the coating, is less than 5.0%. If B1si is 5.0% or more, a coating with barrier properties will not be formed and corrosion resistance will decrease. From the viewpoint of improving corrosion resistance, B1si is more preferably 2.0% or less. That is, in the first coating according to this embodiment, when the average concentration of Si in the central portion B1 of the first coating is Bsi (unit: mass %), the following formula (13) is satisfied: B1si<5.0 (13) If necessary, B1si may be set to 1.5% or less, 1.0% or less, or 0.5% or less. Although the lower limit of B1si is 0%, B1si may be set to 0.1% or more.

[0026] The inclusion of Zn in the first coating improves corrosion resistance. In the first coating according to this embodiment, if B1zn (unit: mass %), which is the average Zn concentration in the central portion B1 of the first coating, is less than 0.5%, the effect of improving corrosion resistance due to Zn is not sufficiently obtained. Therefore, in the first coating according to this embodiment, B1zn is 0.5% or more. That is, the surface-treated steel sheet according to this embodiment satisfies the following formula (14): B1zn≧0.5 (14) B1Zn is preferably 1.0% or more. On the other hand, if B1zn exceeds 30.0%, corrosion resistance is slightly reduced, so B1zn is preferably 30.0% or less. If necessary, B1zn may be 25.0% or less, 21.0% or less, or 18.0% or less, or 1.0% or more, 2.0% or more, 3.5% or more, or 5.0% or more.

[0027] In the surface-treated steel sheet according to this embodiment, it is preferable that the maximum Al concentration in mass % (Aal) (unit: mass %) in the boundary region A is 5.0 to 20.0%, the average Al concentration in mass % (B1al) (unit: mass %) in the central portion B1 of the first coating is 0.2 to 5.0%, and the ratio of Aal to B1al (Aal / B1al) is 5.0 or more. That is, the surface-treated steel sheet according to this embodiment preferably satisfies the following formulas (17) to (19): 5.0≦Aal≦20.0 (17) 0.2≦B1al≦5.0 (18) Aal / B1al≧5.0 (19) In this case, corrosion resistance (white rust resistance) is improved. Although there is no upper limit for Aal, Aal may be set to 20.0% or less or 15.0% or less, taking into account the Al concentration in the coating layer. Aal may be 0.5% or more, 1.0% or more, 3.0% or more, 7.0% or more, or 10.0% or more. Bal may be 3.0% or less, 2.0% or less, or 1.0% or less, and Bal may be 0.1% or more, or 0.3% or more. There is no need to particularly set an upper limit for Aal / Bal, but Aal / Bal may be 80.0 or less, 60.0 or less, or 30.0 or less. If necessary, Aal / Bal may be 7.0 or more, 10.0 or more, or 15.0 or more.

[0028] Furthermore, it is preferable that Ap (unit: mass%), which is the maximum concentration of P in terms of mass %, in the boundary region A, is 10.0 to 25.0%, and B1p (unit: mass%), which is the average concentration of P in the central portion B1 of the first coating, is 0.5 to 8.0%. That is, it is preferable that the surface-treated steel sheet according to this embodiment satisfies the following formulas (20) and (21): 10.0≦Ap≦25.0 (20) 0.5≦B1p≦8.0 (21) In this case, corrosion resistance is improved.

[0029] The amount of the first coating is 150 to 800 mg / m ２ Preferably, the coating amount is 150 mg / m ２ If the coating amount is less than 800 mg / m, the corrosion resistance may decrease. ２ If it exceeds 10 ...

[0030] Furthermore, it is preferable that Cmg, which is the Mg concentration in mass %, at a position in boundary region A closest to the coating layer (a position 10 nm from the first interface toward the coating layer in the thickness direction) is 0% or more and less than 5.0%. That is, it is preferable that the surface-treated steel sheet according to this embodiment satisfies the following formula (16): 0≦Cmg<5.0 (16) In this case, cracks in the coating due to processing are reduced, and therefore the corrosion resistance of the processed portion is improved.

[0031] <Second Coating> The second coating (second coating according to the present embodiment) provided in the surface-treated steel sheet according to the present embodiment is present on the surface of the first coating (the surface opposite to the plating layer). The second coating may also be called a resin coating, an organic resin coating, or a coating. The second coating may also be called an upper coating. In the surface-treated steel sheet according to the present embodiment, the region of the second coating between positions 400 nm and 410 nm from the second interface in the thickness direction is referred to as the central portion B2 of the second coating. In the second coating according to the present embodiment, the average carbon concentration B2c (unit: mass %) in the central portion B2 of the second coating is 40.0% or more. That is, the surface-treated steel sheet according to the present embodiment satisfies the following formula (6): B2c ≧ 40.0 (6) If B2c is less than 40.0%, corrosion resistance and lubricity cannot be obtained. If necessary, B2c may be 45.0% or more, 50.0% or more, or 55.0% or more. There is no upper limit to B2c, but from the viewpoint of lubricity, B2c may be 90.0% or less, 85.0% or less, 80.0% or less, or 75.0% or less.

[0032] In the second coating according to this embodiment, the amount of Zn diffused from the coating layer is small, and the average Zn concentration B2zn (unit: mass%) in the central portion B2 of the second coating is less than 3.0%. That is, the surface-treated steel sheet according to this embodiment satisfies the following formula (15): B2zn<3.0 (15)

[0033] Furthermore, in the second coating, when the maximum Si concentration in the region from the surface to a depth of 100 nm toward the second interface is X2si (unit: mass %) and the average Si concentration in the region from the surface of the second coating to a depth of 300 to 310 nm toward the second interface is Y2si (unit: mass %), the ratio of X2si to Y2si, X2si / Y2si, is preferably 1.1 or greater. Increasing the Si concentration near the surface of the second coating (i.e., near the surface of the surface-treated steel sheet), enhances the barrier properties of the coating, improving corrosion resistance, and increases surface hardness, improving lubricity. That is, the surface-treated steel sheet according to this embodiment preferably satisfies the following formula (23): X2si / Y2si≧1.1 (23) There is no need to set an upper limit for X2si / Y2si, but X2si / Y2si may be 10.0 or less, 5.0 or less, 3.0 or less, 2.0 or less, or 1.5 or less. X2si / Y2si may be set to 1.2 or more, or 1.3 or more.

[0034] The thickness (film thickness) of the second coating is 0.6 μm or more. If the film thickness is less than 0.6 μm, the target corrosion resistance and lubricity will not be achieved. Preferably, it is 0.7 μm or more or 0.8 μm or more, more preferably 1.0 μm or more. There is no upper limit, but if it exceeds 5.0 μm, costs will increase, which is not preferable. Therefore, the thickness of the second coating may be 5.0 μm or less, and may be 4.0 μm or less, 3.0 μm or less, or 2.0 μm or less, as necessary.

[0035] The above-mentioned B1c, B2c, Amg, B1mg, Af, B1f, B1si, Cmg, Aal, B1al, Ap, B1p, B1zn, B2zn, X2si, Y2si, Dti, Dzr, Dv, etc. are determined from the results of measurement by linear analysis using the above-mentioned FE-TEM equipped with an energy dispersive X-ray analyzer.

[0036] <Manufacturing Method> Next, a preferred manufacturing method of the surface-treated steel sheet according to this embodiment will be described. The surface-treated steel sheet according to this embodiment can obtain the effects as long as it has the above-mentioned characteristics regardless of the manufacturing method, but the manufacturing method described below is preferred because it can be manufactured stably.

[0037] That is, the surface-treated steel sheet according to this embodiment can be produced by a production method including the following steps: (I) a plating step of forming a plating layer containing zinc or a zinc alloy on the surface of a steel sheet, (II) a first coating formation step of applying a chemical conversion treatment solution to the steel sheet having the plating layer, and heating and drying the solution to form a first coating, and (III) a second coating formation step of applying a chemical conversion treatment solution to the surface of the steel sheet having the plating layer and the first coating, and heating and drying the solution to form a second coating.

[0038] [Plating Process] In the plating process, a steel material such as a steel sheet is immersed in a plating bath containing Zn or a Zn alloy, or electroplated, to form a plating layer on the surface. The method for forming the plating layer is not particularly limited. A conventional method may be used so long as sufficient plating adhesion is obtained. The steel sheet subjected to the plating process and its manufacturing method are also not limited. Examples of steel sheets that can be immersed in the plating bath include hot-rolled mild steel sheets and steel strips described in JIS G 3131:2018 or JIS G 3113:2018, hot-rolled steel sheets and steel strips for automotive structures, cold-rolled steel sheets and steel strips described in JIS G 3141:2021 or JIS G 3135:2018, and workable cold-rolled high-tensile steel sheets and steel strips for automobiles. The composition of the plating bath can be adjusted according to the chemical composition of the desired plating layer. After the steel material is pulled out of the coating bath, the coating weight of the coating layer can be adjusted by wiping, if necessary. When Cmg is set to 0% or more and less than 5.0%, the Mg concentration in the coating layer is preferably set to 0% by mass or more and 3.0% by mass or less. When Aal / B1al is set to 5.0 or more, the Al concentration in the coating layer is preferably set to 0.1% by mass or more.

[0039] [First Coating Formation Process] In this process, a treatment liquid (chemical conversion treatment liquid) is applied to a steel sheet having a plating layer, and then heated and dried to form a first coating. When forming the first coating according to this embodiment, the chemical conversion treatment liquid is an aqueous solution containing any one of Ti, Zr, or V, Mg, and F, and optionally Si, to which phosphoric acid and nitric acid are further added. Applying such a treatment liquid makes it possible to concentrate specific elements at the interface between the plating layer and the chemical conversion treatment coating. Specifically, the concentrations of each element and the concentrations of phosphoric acid and nitric acid in the treatment liquid are set as follows. Here, the concentrations of phosphoric acid and nitric acid do not include the concentrations of phosphates, nitrates, etc. By simultaneously including phosphoric acid and nitric acid within the above-mentioned ranges, dissolution of the plating proceeds and specific substances are concentrated at the interface between the coating and the plating, thereby significantly improving adhesion. One or more of Ti, V, Zr: 5.0 to 20.0 g / L Mg: 0.7 to 7.0 g / L F: 14.4 to 46.1 g / L P: 6.8 to 32.9 g / L Si: 0.0 to 0.4 g / L Phosphoric acid: 10.0 to 80.0 g / L Nitric acid: 5.0 to 40.0 g / L When Ap and B1p are to be set within the specified ranges, it is preferable that the P concentration in the chemical conversion treatment solution be 10.0 g / L or higher.

[0040] Furthermore, when B1zn is set to 1.0 to 30.0% to improve corrosion resistance, it is preferable to control the contact time between the treatment solution and the plated steel sheet when applying the chemical conversion treatment solution using a roll coater, thereby setting the Zn concentration in the treatment solution to 0.5 to 5.0 g / L by mass. The Zn concentration can be adjusted by immersing the plated steel sheet in the treatment solution or by adding Zn powder. To increase B1zn, Zn powder or a Zn compound may be added to the chemical conversion treatment solution. Even when Zn powder or a Zn compound is not added to the chemical conversion treatment solution, Zn diffuses from the plating layer, so B1zn often does not reach 0%.

[0041] Examples of magnesium that can be contained in the chemical conversion treatment solution include magnesium fluoride, magnesium nitrate, magnesium sulfate, magnesium chloride, and magnesium acetate.

[0042] The F contained in the chemical conversion treatment solution is a fluorine compound, such as hydrofluoric acid HF or fluoroboric acid BF. ４ H, hydrosilicofluoric acid H ２ SiF ６ , fluorozirconium chloride H ２ ZrF ６ , Titanium Hydrofluoric Acid H ２ TiF ６ Examples of compounds include the following. The compound may be one type or a combination of two or more types. Among these, hydrofluoric acid is more preferred. When hydrofluoric acid is used, better corrosion resistance and paintability can be obtained.

[0043] When Zr is contained in the chemical conversion treatment solution, examples of Zr compounds include ammonium zirconium carbonate, hexafluorozirconic acid, and ammonium zirconium hexafluorooxide. When V is contained, examples of V compounds include vanadium pentoxide V. ２ O ５ , metavanadate HVO ３ , ammonium metavanadate, sodium metavanadate, vanadium oxytrichloride VOCl ３ , vanadium trioxide V ２ O ３ , vanadium dioxide VO ２ , vanadium oxysulfate VOSO ４ , vanadium oxyacetylacetonate VO(OC(=CH ２ ) CH ２ COCH ３ )) ２ , vanadium acetylacetonate V(OC(=CH ２ ) CH ２ COCH ３ )) ３ , vanadium trichloride VCl ３Examples of suitable vanadium compounds include phosphovanadomolybdic acid and phosphonic acid. It is also possible to use a pentavalent vanadium compound reduced to a tetravalent or divalent vanadium using an organic compound having at least one functional group selected from the group consisting of a hydroxyl group, a carbonyl group, a carboxyl group, a primary to tertiary amino group, an amide group, a phosphate group, and a phosphonic acid group. When titanium is contained, examples of suitable titanium compounds include ammonium hexafluorotitanate, titanium hydrofluoric acid, and titanium nitrate.

[0044] There are no limitations on the method for applying the chemical conversion treatment solution, and it can be applied using, for example, a roll coater, a bar coater, a sprayer, or the like.

[0045] After the chemical conversion treatment liquid is applied, it is heated to the maximum heating temperature (maximum reached temperature (PMT)) within 5 seconds after application and dried. The average heating rate until it reaches (PMT - 10°C) is preferably 5 to 50°C / s. When Aal / B1al is to be 5.0 or more, it is preferable to use two-stage heating, with the heating rate in the latter half being faster than the heating rate in the first half. Specifically, if the time from the start of heating until it reaches a temperature (PMT - 10°C) 10°C lower than the maximum heating temperature (PMT) is defined as t, it is preferable that the average heating rate V2 in the latter half from the start of heating to 0.5t to 1.0t is 1.25 times or more the average heating rate V1 in the first half from the start of heating to 0.5t, that is, V2 / V1 ≧ 1.25. Furthermore, when two-stage heating is used to make Aal / B1al 5.0 or more, it is preferable that the heating rate V1 in the first half is 5°C / s or more. Furthermore, if the furnace time for heating and drying is long, F tends to concentrate near the interface, resulting in a large Af / B1f. For example, if the furnace time is 15 seconds or longer, Af / B1f can be made 2.5 or higher. Furthermore, when heating, it is preferable to spray the solution onto the steel sheet through a punched metal (a steel sheet having multiple through holes).

[0046] [Second Coating Formation Process] In this process, a chemical conversion treatment solution is applied to the surface of the steel sheet on which the first coating has been formed, and then heated and dried to form a second coating. In this process, a treatment solution containing 70.0% or more of an organic resin is used so that the B2c is 40.0% or more. The organic resin is, for example, a urethane resin. Furthermore, to improve lubricity, 2.0 to 10.0% of colloidal silica is added. Furthermore, 0.1 to 2.0% of wax may be added.

[0047] There are no limitations on the method for applying the chemical conversion treatment solution, and it can be applied using, for example, a roll coater, a bar coater, a sprayer, or the like.

[0048] After the treatment liquid is applied, it is heated and dried. The PMT is set to 100 to 250°C. To increase the Si concentration at the outermost surface, it is preferable to set the PMT to 160°C or higher and the heating rate up to the PMT to 8°C / sec or less. In this case, the colloidal silica contained in the treatment liquid is concentrated at the outermost surface of the coating, increasing the Si concentration at the outermost surface.

[0049] A metal sheet (plated steel sheet) having a plating layer composition shown in Table 1 was prepared. The coating weight of the plating layer was 70 g / m ２ Metal sheet No. 1 was produced by electroplating, Nos. 2 to 8 by hot-dip galvanizing, and No. 4 by heat treatment (alloying treatment) after hot-dip galvanizing. In Table 1, for example, 99.6% Zn-0.2% Al indicates a composition containing 99.6% Zn and 0.2% Al, and the same applies to other compositions. The remainder of the plating layer composition is impurities. The base material of the plated steel sheet was a cold-rolled steel sheet that satisfied JIS G3141:2021.

[0050]

[0051] Chemical conversion treatment solutions having the compositions shown in Tables 4-1, 4-2, and 5 were applied to these plated steel sheets. However, for No. 49 and No. 118, the chemical conversion treatment solution contained 1.1 wt. % polyurethane resin as the organic resin component. The element concentrations in the chemical conversion treatment solutions were as shown in Tables 2-1, 2-2, and 3, (NH ４ ) ２ TiF６ , (NH ４ ) ２ ZrF ６ , V ２ O ５ , MgHPO ４ ・3H ２ O, H ３ P.O. ４ , N.H. ４ F, HNO ３ , Ca(NO ３ ) ２ ・4H ２ O.C. ５ H １２ O ３ The chemical conversion treatment solution was adjusted by mixing Si (vinyltrimethoxysilane) as needed. The chemical conversion treatment solution was applied using a roll coater. After applying the chemical conversion treatment solution, hot air was blown onto the steel plate through a punched metal (a steel plate having a plurality of through holes) within 5 seconds, and the steel plate was heated to the dry plate temperature (PMT) shown in Tables 4-1, 4-2, and 5 under the conditions shown in Tables 4-1, 4-2, and 5, and then cooled to 20°C by air cooling by blowing air through the punched metal or by water cooling, thereby forming a first coating (chemical conversion treatment coating). The deposition amount of the first coating for No. 41 was 600 mg / m ２ , No. 42 is 800 mg / m ２ and the others are 400 mg / m ２ It was decided.

[0052] Thereafter, a treatment solution containing 600 g / L of a water-dispersed urethane resin (ADEKA BONTITAR HUX-830), 100 g / L of colloidal silica, and 10 g / L of a polyethylene wax emulsion (Hitec E, manufactured by Toho Chemical Industry Co., Ltd.) was applied to the first coating using a roll coater, and the coating was heated to 160°C (drying temperature) at an average heating rate of 16°C / sec. After heating, the coating was air-cooled to obtain surface-treated steel sheets Nos. 1 to 51 and 101 to 120, each having a second coating containing a urethane resin. On the other hand, Nos. 52 and 53 were not subjected to the above treatment, and no second coating was formed.

[0053]

[0054]

[0055]

[0056]

[0057]

[0058]

[0059] Test specimens were cut out from the prepared chemical conversion treated steel sheets using a cooled FIB (Focused Ion Beam) processing method, and the cross-sectional structure of the cut out test specimens was observed using a field emission transmission electron microscope (FE-TEM) equipped with an energy dispersive X-ray analyzer at a magnification that allowed the entire first chemical conversion coating and the plating layer to be included in the observation field. ２ Since a Zn phase and a Zn phase were present, the Zn phase was identified by contrast (the relatively bright portion of the dark-field image was determined to be the Zn phase). EDS analysis confirmed that the Zn phase had a Zn concentration of 85% by mass or more and both Mg and Al concentrations of 1.0% by mass or less, and the concentration distribution of C, O, F, Mg, Al, Si, P, Ti, V, Zn, and Zr from the location confirmed to be a coating layer to the surface of the surface-treated steel sheet (the surface of the second chemical conversion coating) was measured using an energy dispersive X-ray analyzer. The results are shown in Tables 6-1 to 9. Also, Figure 2 shows the depth profile element distribution measurement results for Example Test No. 41.

[0060]

[0061]

[0062]

[0063]

[0064]

[0065]

[0066] The corrosion resistance of the flat surface, the corrosion resistance of the processed portion, and the lubricity of the prepared chemical conversion treated steel sheets were evaluated as follows. The results are shown in Tables 10-1, 10-2, and 11.

[0067] <Corrosion Resistance of Flat Surface> A neutral salt spray test conforming to JIS Z 2371:2015 was conducted on flat test specimens (rectangular test specimens measuring 70 mm x 150 mm) at a salt concentration of 70 g ± 5 g / L for 120, 240, and 360 hours, and the corrosion resistance was evaluated based on the occurrence of white rust (area ratio) on the test specimens after the test. The evaluation criteria for corrosion resistance are shown below. If there was SS after 240 hours, it was determined that the specimen had sufficient corrosion resistance. (Evaluation Criteria for Corrosion Resistance) SS: 5% or less S: More than 5% and 10% or less A: More than 10% and 30% or less B: More than 30% and 50% or less C: More than 50%

[0068] <Corrosion resistance of processed parts (white rust resistance)> The center of a flat test piece (a rectangular test piece of 70 mm x 150 mm) was subjected to an Erichsen test (7 mm extrusion), and then a salt spray test according to JIS Z 2371:2015 was performed for 72 hours, and the occurrence of white rust in the extruded part was observed. The evaluation criteria were the same as for the corrosion resistance of the flat part, and if it was SS or S, it was determined that the material had sufficient corrosion resistance. (Evaluation criteria for corrosion resistance) SS: 5% or less S: More than 5% and 10% or less A: More than 10% and 30% or less B: More than 30% and 50% or less C: More than 50%

[0069] <Lubricity> Using HEIDON-14 (manufactured by Shinto Scientific Co., Ltd.), a stainless steel ball with a diameter of 10 mm was used as a slider and slid across the surface of the flat test piece at a load of 1.0 N and a sliding speed of 150 mm / min, and the dynamic friction coefficient μ was calculated from the resulting stress to evaluate the lubricity. The lubricity evaluation criteria are as follows: S and AA were judged to have sufficient lubricity. (Lubricity Evaluation Criteria) S: 0.1 or less AA: more than 0.1% and 0.2% or less A: more than 0.2% and 0.5% or less B: more than 0.5%

[0070]

[0071]

[0072]

[0073] As can be seen from Tables 1 to 11, examples of the invention that had a zinc plating layer or zinc alloy plating layer containing a predetermined amount of Mg, a first coating, and a second coating, and in which Ti, V, Zr, C, Mg, F, and Si were present at predetermined concentrations and concentrated in predetermined regions from the plating layer to the second coating, exhibited excellent corrosion resistance and lubricity. On the other hand, comparative examples (Nos. 24 to 40, 44 to 50, 52, 53, and 107 to 119) that did not have a second coating or in which the concentrations or concentrated states of Ti, V, Zr, C, Mg, F, and Si were outside the ranges of the invention were inferior in one or more of corrosion resistance and lubricity.

[0074] INDUSTRIAL APPLICABILITY The present invention can provide a surface-treated steel sheet having excellent corrosion resistance and lubricity, and has high industrial applicability.

[0075] REFERENCE SIGNS LIST 1 Surface-treated steel sheet 10 Steel sheet (base steel sheet) 20 Plated layer (zinc plated layer or zinc alloy plated layer) 25 First interface 30 First coating 35 Second interface 40 Second coating A Boundary region B1 Central portion of first coating B2 Central portion of second coating

Claims

1. A base steel plate; A plating layer formed on a surface of the base steel sheet; A first coating formed on a surface of the plating layer; a second coating formed on the surface of the first coating and having a thickness of 0.6 μm or more; A surface-treated steel sheet having The Zn concentration of the plating layer is 40 mass% or more and 100 mass% or less, and the Mg concentration is 0 mass% or more and less than 4.0 mass%, When the concentrations of C, O, F, Mg, Al, Si, P, Ti, V, Zn and Zr were continuously measured by linear analysis in the thickness direction from the plating layer toward the surface of the coated steel sheet, a position where the Zn concentration first becomes 35.0 mass% or less is defined as a first interface, which is an interface between the plating layer and the first coating; a boundary region is a region including the first interface, the boundary region being located between a range of 10 nm from the first interface on the plating layer side and a range of 15 nm on the first coating side in the thickness direction, a second interface between the first coating and the second coating is defined as a position where the Zn concentration becomes 3.0 mass % or less for the first time, and a range of 10 nm from a center between the first interface and the second interface in the thickness direction toward the second interface is defined as a central part of the first coating, When a region of the second coating between a position 400 nm and a position 410 nm away from the second interface in the thickness direction is defined as a central portion of the second coating, One or more of the following formulas (1) to (3) and formulas (4) to (15) are satisfied: A surface-treated steel sheet comprising: Dt i ≧ 5.0 (1) Dzr≧5.0 (2) Dv≧5.0 (3) Dti+Dzr+Dv≦25.0 (4) B1c<10.0 (5) B2c≧40.0 (6) 5.0 / M≦Amg≦25.0 (7) 0.5≦B1mg≦5.0 (8) 15.0 / M≦Af≦40.0 (9) 0.5≦B1f≦15.0 (10) Amg / B1mg≧2.0 (11) Af / B1f≧2.0 (12) B1si<5.0 (13) B1zn≧0.5 (14) B2zn<3.0 (15) Here, Dti is a maximum Ti concentration in mass % from the first interface to a center in the thickness direction between the first interface and the second interface of the first coating, Dzr is a maximum concentration of Zr in mass % from the first interface to a center between the first interface and the second interface in the thickness direction of the first coating, Dv is a maximum concentration of V in mass % from the first interface to a center in the thickness direction between the first interface and the second interface of the first coating, B1c is an average concentration of C in mass% in the central portion of the first coating, B2c is an average concentration of C in mass% in the central portion of the second coating, A mg is the maximum concentration in mass % of Mg in the boundary region of the first coating; B1mg is an average concentration of Mg in mass% in the central portion of the first coating, Af is the maximum concentration of F in mass % in the boundary region of the first coating; B1f is the average concentration of F in mass% in the central portion of the first coating, B1si is an average concentration of Si in mass% in the central portion of the first coating, B1zn is an average concentration of Zn in the central portion of the first coating, in mass %, B2zn is an average concentration of Zn in mass% in the central portion of the second coating, The M is a constant that is 1 when the Mg concentration of the plating layer is 0 mass % or more and less than 1.0 mass %, and is 2 when the Mg concentration of the plating layer is 1.0 mass % or more and less than 4.0 mass %.

2. Furthermore, the following formula (16) is satisfied: The surface-treated steel sheet according to claim 1 . 0≦Cmg<5.0 (16) Here, Cmg is the Mg concentration in mass % at a position 10 nm away from the first interface toward the plating layer in the thickness direction of the plating layer.

3. Furthermore, the following formulas (17) to (19) are satisfied: The surface-treated steel sheet according to claim 1 or 2. 5.0≦Aal≦20.0 (17) 0.2≦B1al≦5.0 (18) Aal / B1al≧5.0 (19) where Aal is the maximum concentration of Al in wt.% in the boundary region, The B1al is the average concentration of Al in mass % in the central portion of the first coating.

4. Furthermore, the following formulas (20) to (21) are satisfied: The surface-treated steel sheet according to claim 1 or 2. 10.0≦Ap≦25.0 (20) 0.5≦B1p≦8.0 (21) where Ap is the maximum concentration of P in the boundary region, The B1p is the average concentration of P in mass % in the central portion of the first coating.

5. Furthermore, the following formula (22) is satisfied: The surface-treated steel sheet according to claim 1 or 2. 1.0≦B1zn≦30.0 (22)

6. Furthermore, the following formula (23) is satisfied: The surface-treated steel sheet according to claim 1 or 2. X2si / Y2si≧1.1 (23) Here, X2si is the maximum concentration, in mass %, of Si in a region extending from the surface of the second coating to a region extending 100 nm toward the second interface, The Y2si is the average concentration of Si in mass % in a region of the second coating from the surface toward the second interface, the region being 300 to 310 nm long.

7. Furthermore, the following formula (24) is satisfied: The surface-treated steel sheet according to claim 1 or 2. Af / B1f≧2.5 (24)