Surface-treated steel

Abstract

To provide a surface-treated steel material that is excellent in corrosion resistance and conductivity.SOLUTION: A surface-treated steel material includes: a steel material; a plating layer including Zn or a Zn alloy; and a chemical treatment coating film. The chemical treatment coating film includes: an organosilicon compound including a siloxane bond; P; and F. When t represents a thickness of the chemical treatment coating film, a region 1 represents a range where a starting point is a position from a surface of the chemical treatment coating film to t×1 / 6 in a direction of the thickness and an end point is a position from the surface of the chemical treatment coating film to t×1 / 2 in the direction of the thickness, and a region 2 represents a range where a starting point is a position from the surface of the chemical treatment coating film to t×1 / 2 in the direction of the thickness and an end point is a position from the surface of the chemical treatment coating film to t×5 / 6 in the direction of the thickness, X2 / X1 that is a ratio of an average value X2 of ion counts of the Si in the region 2 to an average value X1 of ion counts of the Si in the region 1 is 1.05-1.50.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Conventionally, plated steel sheets (zinc-based plated steel sheets), in which a zinc-based plating layer is formed on the surface of steel sheets, have been used in a wide range of applications, including automobiles, building materials, and home appliances. Furthermore, for the purpose of imparting corrosion resistance, paint adhesion, etc. to the surface of such zinc-based plated steel sheet, 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 with a silane coupling agent alone, and organic resin coating treatment are generally known and in practical use.

[0003] As an example of a technique that mainly uses a silane coupling agent, Patent Document 1 discloses a chromate-free surface-treated metal material in which an aqueous metal surface treatment agent containing an organosilicon compound (W) obtained by blending two silane coupling agents with specific structures in a specific mass ratio and a specific inhibitor is applied to the surface of the metal material, and then dried to form a composite coating containing each component. Furthermore, Patent Document 2 discloses a surface-treated metal material that has been subjected to a chromate-free surface treatment that is excellent in each of the elements of corrosion resistance, heat resistance, fingerprint resistance, electrical conductivity, paintability, and resistance to black residue during processing, and a chromium-free metal surface treatment agent that is used to impart excellent corrosion resistance and alkali resistance to metal materials. Patent Document 3 also describes a chromate-free precoated metal sheet having an upper coating film (α) formed on at least one side of the metal sheet, wherein (1) a silane coupling agent (A) containing an amino group in the molecule and a silane coupling agent (B) containing a glycidyl group in the molecule are blended and reacted between the metal sheet and the upper coating film (α), and the silane coupling agent (A) has a cyclic siloxane bond and a chain siloxane bond in its structure, and the abundance ratio of the cyclic siloxane bond and the chain siloxane bond is 1090 to 1100 cm, which indicates a cyclic siloxane bond by FT-IR reflection method. -1 The absorbance (C1) and the linear siloxane bond at 1030-1040 cm -1 and (2) an inhibitor component (Y) containing at least one metal compound (E) selected from titanium compounds and zirconium compounds, a phosphate compound (J), and a fluorine compound (F), wherein the ratio of the absorbance (C1) of the metal compound (C) to the absorbance (C2) of the metal compound (C) [C1 / C2] is 0.4 to 2.5; and (3) an inhibitor component (Y) containing at least one metal compound (E) selected from titanium compounds and zirconium compounds, a phosphate compound (J), and a fluorine compound (F), provided that the fluorine compound (F) is not required when the metal compound (E) is a fluorometal complex compound (E'). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4776458 [Patent Document 2] Patent No. 5336002 [Patent Document 3] Patent No. 5933324 Summary of the Invention [Problem to be solved by the invention]

[0005] The technologies disclosed in Patent Documents 1 and 2 are excellent technologies that have been put to practical use as surface-treated steel sheets that have been subjected to chromate-free surface treatment, which has excellent corrosion resistance, heat resistance, fingerprint resistance, electrical conductivity, paintability, and resistance to black residue during processing. However, due to the increasing sophistication of customer needs in recent years, the corrosion resistance of plating (especially initial white rust resistance) of prior art may not be sufficient for practical use. That is, with the techniques described in Patent Documents 1 and 2, there is concern that white rust may occur in the plating layer when the test time exceeds the SST test that has been generally used up to now, or in processed areas that have lower corrosion resistance than flat areas.

[0006] Furthermore, in Patent Document 3, it is necessary to include an organic resin as a film-forming component, which means that even if the coating has excellent corrosion resistance and coating adhesion, it has the problem of poor electrical conductivity.

[0007] The present invention aims to provide a surface-treated steel material having excellent corrosion resistance and electrical conductivity, based on the premise that the surface of the zinc-based plated steel material has a plating layer containing zinc or a zinc alloy on the surface of the steel material and a chemical conversion coating on the surface of the zinc-based plated steel material. [Means for solving the problem]

[0008] The corrosion resistance of surface-treated steel with a chemical conversion coating improves as the chemical conversion coating's barrier properties (ability to block the penetration of corrosion factors such as moisture and chloride ions) improve. Also, in areas where the chemical conversion coating is damaged by scratches or other factors, the greater the inhibitor effect, which prevents corrosion of the plating layer when moisture adheres and dissolves substances (mainly metal elements), the better the corrosion resistance, including white rust resistance. As described above, the chemical conversion coatings disclosed in Patent Documents 1 and 2 are coatings that have both barrier properties and inhibitor effects. However, in environments where higher white rust resistance than conventional coatings is required, these properties are insufficient, causing corrosion of the plating layer and early formation of white rust. In light of these circumstances, the present inventors investigated methods for improving the barrier properties and inhibitor effect of chemical conversion coatings, assuming that the inclusion of an organic resin is not essential for achieving excellent electrical conductivity. As a result, they discovered that the barrier properties can be improved by making the chemical conversion coating contain an organosilicon compound as a film-forming component and P and F as inhibitor components, and by concentrating Si at the interface between the chemical conversion coating and the plating layer.

[0009] The present invention has been made in light of the above findings. [1] A method for producing a steel material comprising: a plating layer containing Zn or a Zn alloy formed on the surface of the steel material; and a chemical conversion coating formed on the surface of the plating layer, wherein the chemical conversion coating contains an organosilicon compound having a siloxane bond, and P and F; and when a TOF-SIMS is used to measure the ion count distribution of Si and Zn from the surface of the chemical conversion coating in the thickness direction of the chemical conversion coating toward the interface between the chemical conversion coating and the plating layer, the method comprises determining the distance between the surface of the chemical conversion coating and the position where the measured ion count of Si first becomes equal to 20 times the measured ion count of Zn. a surface-treated steel material in which, when the thickness of the chemical conversion coating is t, a region 1 is defined as a range starting from a position t×1 / 6 from the surface of the chemical conversion coating in the thickness direction and ending at a position t×1 / 2 from the surface of the chemical conversion coating in the thickness direction, and a region 2 is defined as a range starting from the position t×1 / 2 from the surface of the chemical conversion coating in the thickness direction and ending at a position t×5 / 6 from the surface of the chemical conversion coating in the thickness direction, and X2 / X1 is a ratio of the average value X1 of the Si ion count in region 1 to the average value X2 of the Si ion count in region 2, which is 1.05 to 1.50. [2] The C3H6N on the surface of the chemical conversion coating measured using the TOF-SIMS + The ion counts of X3, CH4N + Ion counts of X4, NH4 +The surface-treated steel material according to [1], wherein X3 / X1 is 0.0025 to 0.0340, X4 / X1 is 0.080 to 0.110, and X5 / X1 is 0.0050 to 0.0120, where X5 is the ion count of the above. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a surface-treated steel material that is excellent in corrosion resistance and electrical conductivity. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram showing an example of a cross section of a surface-treated steel material according to an embodiment of the present invention. [Figure 2] This figure shows an example of the results of continuous measurement of Si ion count and Zn ion count using TOF-SIMS from the surface of a chemical conversion coating to a depth of 100 nm toward the plating layer, with the Zn ion count shown being 20 times larger. [Figure 3] This figure shows an example of the results of continuous measurement of Si ion count and Zn ion count using TOF-SIMS from the surface of a chemical conversion coating toward the plating layer to a depth of 100 nm, and also shows the difference in Si concentration behavior due to differences in PMT (maximum temperature reached). However, the Zn ion count shows a value 20 times higher. DETAILED DESCRIPTION OF THE INVENTION

[0012] A surface-treated steel material according to one embodiment of the present invention (surface-treated steel material according to this embodiment) will be described. As shown in Fig. 1, the surface-treated steel material 1 according to this embodiment includes a steel material 11, a plating layer 12 containing Zn or a Zn alloy formed on the surface of the steel material 11, and a chemical conversion coating 13 formed on the surface of the plating layer 12. In Fig. 1, the plating layer 12 and the chemical conversion coating 13 are formed on only one surface of the steel material 11, but they may also be formed on the other surface. Furthermore, in the surface-treated steel material 1 according to this embodiment, when the ion count distribution of Si and Zn is measured using TOF-SIMS in the thickness direction of the chemical conversion coating from the surface of the chemical conversion coating toward the interface between the chemical conversion coating and the plating layer, when the distance between the surface of the chemical conversion coating and the position where the measured ion count of Si first becomes equal to 20 times the measured ion count of Zn, is defined as the thickness t of the chemical conversion coating, the distance from the surface of the chemical conversion coating in the thickness direction is t× When a range starting from a position t×1 / 6 in the thickness direction from the surface of the chemical conversion coating and ending at a position t×1 / 2 in the thickness direction from the surface of the chemical conversion coating is defined as region 1, and a range starting from the position t×1 / 2 in the thickness direction from the surface of the chemical conversion coating and ending at a position t×5 / 6 in the thickness direction from the surface of the chemical conversion coating is defined as region 2, X2 / X1, which is the ratio of the average value X2 of the Si ion count in region 2 to the average value X1 of the Si ion count in region 1, is 1.05 to 1.50.

[0013] The steel material 11, the plating layer 12, and the chemical conversion coating 13 will be described below.

[0014] [Steel] The surface-treated steel material 1 according to this embodiment has excellent corrosion resistance due to the plating layer 12 and the chemical conversion coating 13. Therefore, there are no particular limitations on the steel material 11. The steel material 11 may be determined depending on the product to which it is applied and the required strength, thickness, etc. For example, a hot-rolled steel sheet as specified in JIS G 3131:2018 or JIS G 3113:2018, or a cold-rolled steel sheet as specified in JIS G 3141:2021 or JIS G 3135:2018 can be used.

[0015] [Plating layer] The chemical composition of the plating layer 12 is not limited as long as it is a plating layer (zinc-based plating layer) containing 40 mass% or more of Zn, either alone or as a Zn alloy. For example, platings specified in JIS G 3313:2021, JIS G 3302:2019, JIS G 3323:2019, JIS G 3317:2019, or JIS G 3321:2019 can be used.

[0016] The coating weight of the plating layer 12 is not limited, but in order to improve corrosion resistance, it is set to 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 weight exceeds 200g / m, the corrosion resistance will saturate and it will be economically disadvantageous. 2 It is preferable that:

[0017] The type of the plated layer is not limited, and may be, for example, a hot-dip plated layer or an electroplated layer.

[0018] [Chemical conversion coating] <The chemical conversion coating contains an organosilicon compound having a siloxane bond, P, and F> The chemical conversion coating 13 provided on the surface-treated steel material 1 according to this embodiment is obtained by applying a treatment liquid (chemical conversion solution) containing a silane coupling agent, a phosphate compound, and a fluorine compound to a plating layer containing Zn (zinc) or a zinc alloy under specified conditions, followed by drying. Therefore, the chemical conversion coating 13 provided on the surface-treated steel material 1 according to this embodiment contains, as a film-forming component, a silicon compound having a siloxane bond (Si-O-Si bond: including cyclic siloxane bond and linear siloxane bond) derived from the silane coupling agent, and also contains P and F as inhibitor components. It is believed that P and F exist as inhibitors in the form of phosphate compounds and fluorine compounds. When a silicon compound is the film-forming component, the average Si concentration of the chemical conversion coating is, for example, 10 mass % or more. Furthermore, if necessary, the chemical conversion coating 13 may contain Zr or V derived from a Zr compound or a V compound. The chemical conversion coating 13 provided on the surface-treated steel material 1 according to this embodiment does not substantially contain organic resin.

[0019] Figure 2 shows the results of continuous measurements of Si ion counts and Zn ion counts using TOF-SIMS from the surface of the chemical conversion coating toward the plating layer to a depth of 100 nm. Note that the Zn ion count shown in the graph is 20 times larger than the actual value. In this embodiment, as shown in FIG. 2 , when the ion count distributions of Si and Zn are measured using TOF-SIMS from the surface of the chemical conversion coating 13 in the thickness direction of the chemical conversion coating 13 toward the interface between the chemical conversion coating 13 and the plating layer 12, the position where the measured ion count of Si equals 20 times the measured ion count of Zn for the first time is identified, and this position is defined as the interface between the chemical conversion coating and the plating layer, with the distance between this position and the surface of the chemical conversion coating being defined as the thickness t of the chemical conversion coating.

[0020] 2, in this embodiment, region 1 refers to a range that starts at a position t×1 / 6 from the surface of the chemical conversion treatment coating 13 in the thickness direction and ends at a position t×1 / 2 from the surface of the chemical conversion treatment coating 13 in the thickness direction. Region 2 refers to a range that starts at the position t×1 / 2 from the surface of the chemical conversion treatment coating 13 in the thickness direction and ends at a position t×5 / 6 from the surface of the chemical conversion treatment coating 13 in the thickness direction.

[0021] <X2 / X1, which is the ratio of the average value X2 of the Si ion count in region 2 to the average value X1 of the Si ion count in region 1, is 1.05 to 1.50.> The present inventors conceived a coating design that improves white rust resistance by enhancing the barrier properties of a chemical conversion coating, based on the premise that the inclusion of an organic resin is not essential for achieving excellent conductivity. As a result, they discovered that in a chemical conversion coating that contains a silicon compound (mainly an SiOx skeleton with cyclic siloxane bonds or linear siloxane bonds) and has P and F as inhibitor components (thought to exist as phosphate compounds and fluorine compounds), the barrier properties can be improved by concentrating Si in the region of the chemical conversion coating 13 on the interface with the plating layer. Specifically, when X2 / X1, which is the ratio of the average Si ion count X2 in region 2 to the average Si ion count X1 in region 1, is 1.05 to 1.50, the barrier properties of the chemical conversion coating 13 are sufficiently improved. If X2 / X1 is less than 1.05, the concentration of Si is insufficient, the improvement in barrier properties is insufficient, and sufficient white rust resistance cannot be obtained. The reason why the barrier properties improve when X2 / X1 is 1.05 or more, that is, when Si is concentrated in region 2, is not clear, but it is thought that the concentration of Si increases the density of chemical conversion coating 13. On the other hand, if X2 / X1 exceeds 1.50, cracks will occur in the chemical conversion coating, and sufficient white rust resistance will not be obtained. The distribution of Si ion counts in the chemical conversion coating 13 can be confirmed by performing ion analysis in the depth direction using TOF-SIMS as described below.

[0022] <Preferably, the C3H6N on the surface of the chemical conversion coating measured using TOF-SIMS + The ion counts of X3, CH4N + Ion counts of X4, NH4 + When the ion count is X5, X3 / X1 is 0.0025 to 0.0340, X4 / X1 is 0.080 to 0.110, and X5 / X1 is 0.0050 to 0.0120. When a silane coupling agent is used to form a chemical conversion coating containing a silicon compound, an amine-containing silane coupling agent is often used in the film formation stage from the viewpoint of forming a network of SiOx skeletons. However, after the chemical conversion coating is formed, it is preferable that the number of amino groups in the chemical conversion coating is small, since amino groups have a low barrier function against substances that cause corrosion. Therefore, in the surface-treated steel material according to this embodiment, the ratio of C3H6N to the number of Si ions on the surface of the chemical conversion coating is + , CH4N + , NH4 + It is preferable to make the ratio of the number of ions of the ... Specifically, the C3H6N on the surface of the chemical conversion coating was measured using TOF-SIMS. + The ion counts of X3, CH4N + Ion counts of X4, NH4 + When the ion count of Si is designated as X5, it is preferable that the ratio of each of X3, X4, and X5 to the average value X1 of the Si ion count in the chemical conversion coating be within a predetermined range, with X3 / X1 being 0.0025 to 0.0340, X4 / X1 being 0.080 to 0.110, and X5 / X1 being 0.0050 to 0.0120. In this case, the barrier properties of the chemical conversion coating are further improved, and white rust resistance is further improved. C3H6N + , CH4N + , NH4 + The ion count can be confirmed by performing ion analysis on the surface of the chemical conversion coating using TOF-SIMS as described below.

[0023] Analysis by TOF-SIMS is carried out as follows. First, the sputtering rate is confirmed for a known oxide film thickness formed on a silicon substrate. Then, using an analysis sample, the number of ions of all mass numbers is counted for each sputtering time, and this value is taken as the total ion count. The analysis depth is calculated from the product of the sputtering time and the sputtering rate confirmed above. The ion count is defined as the number obtained by dividing the ion count of the ion of interest by the total ion count. The measurement equipment and conditions are as follows: Equipment: ION-TOF TOF-SIMS.5 Irradiation ions: Bi1 + Accelerating voltage: 30 kV Sputtering time: 2 seconds Measurement area: 100μm x 100μm Sputter ion gun: O2 +

[0024] Whether or not a chemical conversion coating contains P and F can be determined by examining the surface-treated steel with an X-ray fluorescence analyzer to confirm the presence of P and F, respectively. Other elements such as Zr and V can also be analyzed in the same way. If the detected intensity of each element is three or more times higher than when measured on plated steel without a chemical conversion coating, it is determined that the element is contained in the chemical conversion coating.

[0025] Whether or not the chemical conversion coating 13 contains an organosilicon compound having a siloxane bond can be determined by FT-IR as follows. Specifically, when measured by FT-IR, the siloxane bond is indicated by a wavelength of 1030 to 1200 cm -1 If an absorbance peak is observed (e.g., 800 cm -1 ~2300cm -1 If an absorbance of 10 times or more of the baseline between the two is obtained, it is judged to have siloxane bonds. In FT-IR, the measurement conditions are, for example, as follows. Measurement method: Diffuse reflectance or ATR method Resolution: 4cm -1 Number of times accumulated: 128 Measurement atmosphere: air

[0026] The coating weight of the chemical conversion coating is 100 to 2000 mg / m 2 Preferably, the coating amount is 100 mg / m 2 If the amount is less than 2000 mg / m, sufficient effect may not be obtained. 2If it exceeds this value, the film thickness becomes too thick and there is a risk of the chemical conversion coating peeling off.

[0027] [Manufacturing method] Next, a preferred method for producing the surface-treated steel material according to this embodiment will be described. The surface-treated steel material according to this embodiment can obtain the effects as long as it has the above characteristics regardless of the manufacturing method, but the manufacturing method described below is preferred because it can be manufactured stably.

[0028] That is, the surface-treated steel material according to this embodiment can be produced by a production method including the following steps. (I) a plating process of forming a plating layer containing Zn or a Zn alloy on the surface of a steel material such as a steel sheet; (II) a coating step of coating a steel material having a plating layer with a chemical conversion treatment solution; (III) A drying-cooling process in which the steel material coated with the chemical conversion treatment solution is heated to dry it and then cooled to form a chemical conversion coating. Preferable conditions for each step will be explained.

[0029] <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 is electroplated to form a plating layer on the surface. The method for forming the plating layer is not particularly limited; it may be performed by a conventional method that ensures sufficient plating adhesion. The steel sheet to be subjected to the plating step and its manufacturing method are not limited. For example, the steel sheet to be immersed in the plating bath may be a hot-rolled steel sheet as specified in JIS G 3131:2018 or JIS G 3113:2018 or a cold-rolled steel sheet as specified in JIS G 3141:2021 or JIS G 3135:2018. The composition of the plating bath may be adjusted depending on the chemical composition of the plating layer to be obtained. After the steel material is pulled out of the plating bath, the coating weight of the plating layer can be adjusted by wiping, if necessary.

[0030] <Coating process> In the coating step, a chemical conversion treatment liquid (surface treatment metal agent) containing a silane coupling agent, a phosphate compound, and a fluorine compound is applied to a steel material having a plating layer containing Zn or a Zn alloy. In the coating step, the method for coating the surface-treating metal agent is not limited, and for example, it can be coated using a roll coater, a bar coater, a sprayer, or the like.

[0031] The silane coupling agent is contained as a film-forming component. For example, a Si compound obtained by blending a silane coupling agent (A) containing one amino group in the molecule with a silane coupling agent (B) containing one glycidyl group in the molecule at a solid concentration ratio (A) / (B) of 0.5 to 1.7 may be used as the silane coupling agent.

[0032] Examples of fluorine compounds contained in the chemical conversion treatment solution include hydrofluoric acid (HF), fluoroboric acid (BF4H), hydrosilicic acid (HSiF6), fluorozirconic acid (H2ZrF6), and hydrofluoric titanic acid (H2TiF6). One or more compounds may be used. Among these, hydrofluoric acid is more preferred. When hydrofluoric acid is used, better corrosion resistance and paintability can be obtained.

[0033] The phosphate compounds contained in the chemical conversion treatment solution remain in the chemical conversion coating as an inhibitor component, P. This inhibitor component, P, improves the corrosion resistance of the chemical conversion coating. In this embodiment, the phosphate compound contained in the chemical conversion treatment solution is not particularly limited, but examples thereof include phosphoric acid, ammonium phosphate, potassium phosphate, and sodium phosphate. Among these, phosphoric acid is more preferable. When phosphoric acid is used, better corrosion resistance can be obtained.

[0034] When a Zr compound is contained in the chemical conversion treatment solution, examples of the Zr compound include ammonium zirconium carbonate, hexafluorozirconic acid, and ammonium hexafluorozirconium. When a V compound is contained, examples of the V compound include vanadium pentoxide VO, metavanadate HVO, ammonium metavanadate, sodium metavanadate, vanadium oxytrichloride VOCl, vanadium trioxide VO, vanadium dioxide VO, vanadium oxysulfate VOSO, vanadium oxyacetylacetonate VO(OC(=CH)CHCOCH)), vanadium acetylacetonate V(OC(=CH)CHCOCH), vanadium trichloride VCl, and vanadomolybdic acid. It is also possible to use a pentavalent vanadium compound reduced to a tetravalent or divalent vanadium compound 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, primary to tertiary amino groups, an amide group, a phosphate group, and a phosphonate group.

[0035] Regarding application, when a surface treatment metal agent is applied to a steel material using, for example, a roll coater, it is preferable that the temperature of the steel material when it enters the roll coater (hereinafter referred to as "sheet temperature at the time of application") be 40°C or higher in order to speed up the reaction between the steel material and the chemical conversion treatment agent and to keep the time it takes for the steel material to reach its maximum temperature to be 7 seconds or less. On the other hand, if the sheet temperature during application exceeds 80°C, depending on the composition of the surface treatment metal agent, the water in the aqueous surface treatment agent may evaporate too rapidly, resulting in the phenomenon of small bubble-like blisters or holes, known as popping. Therefore, the sheet temperature during application is preferably 40°C or higher and 80°C or lower, more preferably 45°C or higher and 60°C or lower.

[0036] <Drying-cooling process> In the drying-cooling process, the steel material coated with the chemical conversion treatment solution is heated, dried, and baked. After drying, it is cooled to room temperature (for example, about 15 to 25°C). This forms a chemical conversion coating on the surface of the plating layer. When obtaining the surface-treated steel material according to this embodiment, the PMT (Peak Metal Temperature: the highest temperature that the steel material can reach) is set to 155 to 200°C in the drying-cooling process. As shown in Figure 3, the higher the PMT, the larger the X2 / X1. When the PMT is less than 155° C., the ratio X2 / X1 is less than 1.05. On the other hand, when the PMT is more than 200° C., the coating (chemical conversion coating) dries out and the ratio X2 / X1 exceeds 1.50. Furthermore, the time from application of the chemical conversion treatment solution until it reaches the PMT (heat-up time) is set to 7 seconds or less. If the time from application to reaching the PMT exceeds 7 seconds, the coating will not dry uniformly in the thickness direction, resulting in an X2 / X1 ratio of less than 1.05.

[0037] When X3 / X1, X4 / X1, or X5 / X1 in the chemical conversion coating is to be reduced, it is preferable to set the PMT to 160°C or higher.

[0038] Once the drying temperature (maximum temperature) is reached, there is no need to hold the temperature. After the chemical conversion coating is dried, the surface-treated steel material is cooled to room temperature. The cooling conditions are not limited. [Example]

[0039] 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 plate No. 1 was produced by electroplating, and Nos. 2 to 8 by hot-dip galvanizing. In Table 1, for example, Zn-0.2%Al indicates a composition containing 0.2 mass% Al with the remainder consisting of Zn and impurities, Zn-6.0%Al-3.0%Mg indicates a composition containing 6.0 mass% Al and 3.0 mass% Mg with the remainder consisting of Zn and impurities, and the same applies to the other compositions.

[0040] The substrate of the plated steel sheet was a cold-rolled steel sheet satisfying JIS G 3141:2021. The plated steel sheet is treated with a silicon compound obtained by blending 3-aminopropyltrimethoxysilane (A1) or 3-aminopropyltriethoxysilane (A2) as a silane coupling agent (A) containing one amino group with 3-glycidoxypropyltrimethoxysilane as a silane coupling agent (B) containing one glycidyl group in the molecule in a blending ratio (A) / (B) of 0.5 to 2.0 (as shown in Table 2A) in terms of solid content mass ratio, derived from phosphoric acid. The chemical conversion treatment solution used was phosphoric acid, with a ratio (P / S) of 0.2 between the solid mass of phosphorus (P) and the solid mass of silicon (Si) derived from silicon compounds; hydrofluoric acid, with a ratio (F / S) of 0.075 between the solid mass of fluorine (F) derived from hydrofluoric acid and the solid mass of silicon (Si) derived from silicon compounds; and vanadium oxysulfate, with a ratio (V / Si) of 0.075 between the solid mass of vanadium (V) derived from vanadium oxysulfate and the solid mass of silicon (Si) derived from silicon compounds. Anatase-type titanium dioxide (particle size distribution: 5-200 nm) was added to some of the chemical conversion treatment solutions. The chemical conversion treatment solution was applied using a roll coater in a room at 15°C, with the plate temperature controlled with hot air during application. After applying the chemical conversion treatment solution, hot air was blown onto the steel sheet through a punched metal (a steel sheet with multiple through holes) to heat the steel sheet to the dry sheet temperature (PMT) shown in Table 2A at an average heating rate of 8 to 43°C / second. The heating time (the time from application to reaching the PMT) was as shown in Table 2B. The steel was then cooled to 20°C by air-cooling (by blowing air through a punched metal) or by water-cooling. This resulted in surface-treated steel products Nos. 1 to 34. Nos. 33 and 34 are surface-treated steel products produced by adding a photocatalyst to the chemical conversion treatment solution.

[0041] In addition, a treatment solution containing 3-aminopropyltrimethoxysilane (A1) as a silane coupling agent (A) containing one amino group and 3-glycidoxypropyltrimethoxysilane as a silane coupling agent (B) containing one glycidyl group in the molecule in a compounding ratio (A) / (B) of 0.5 in terms of solid mass ratio, with the other components being the same as above, was added with polyurethane resin to obtain No. 35 surface-treated steel material having a coating containing polyurethane resin with a weight 0.25 times that of No. 2.

[0042] [Table 1]

[0043] The obtained surface-treated steel materials were examined using the method described above to determine whether the chemical conversion coating contained an organosilicon compound having a siloxane bond, P, and F. The results showed that in all examples, the chemical conversion coating contained an organosilicon compound having a siloxane bond, P, and F.

[0044] Furthermore, the obtained surface-treated steel material was measured using TOF-SIMS by the above-mentioned method, and X2 / X1, which is the ratio of the average value X2 of the Si ion count in region 2 to the average value X1 of the Si ion count in region 1, and the Si + The average ion count of C3H6N on the surface of the chemical conversion coating + Ion counts of CH4N + Ion counts of NH4 + The ion count ratios X3 / X1, X4 / X1, and X5 / X1 were calculated. The results are shown in Table 2B.

[0045] Furthermore, the white rust resistance and electrical conductivity of the flat portion and processed portion were evaluated by the following methods, and the results are shown in Table 2B.

[0046] <Flat surface corrosion resistance (white rust resistance) I> The flat test specimens were subjected to a salt spray test in accordance with JIS Z 2371:2015 for up to 190 hours, and 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 as follows: S and AA were considered to have sufficient corrosion resistance. (Corrosion resistance evaluation criteria) S: 1% or less AA: More than 1%, less than 3% A: More than 3%, less than 5% B: More than 5%, less than 10% C: More than 10%

[0047] <Flat surface corrosion resistance (white rust resistance) II> The flat test specimens were subjected to a salt spray test in accordance with JIS Z 2371:2015 for up to 240 hours, and corrosion resistance was evaluated based on the occurrence of white rust (area ratio) on the test specimens after the test. The corrosion resistance evaluation criteria are shown below. S and AA were considered to have sufficient corrosion resistance. (Corrosion resistance evaluation criteria) S: 1% or less AA: More than 1%, less than 3% A: More than 3%, less than 5% B: More than 5%, less than 10% C: More than 10%

[0048] <Corrosion resistance of processed parts (white rust resistance)> The center of a 70mm x 150mm rectangular test piece (flat plate) was subjected to an Erichsen test (7mm extrusion), and then a salt spray test according to JIS Z 2371:2015 was conducted for 72 hours, and the occurrence of white rust in the extruded part was observed. The evaluation criteria were the same as for the flat part corrosion resistance, and a rating of S, AA, A, or B was considered to indicate sufficient corrosion resistance. (Corrosion resistance evaluation criteria) S: 1% or less AA: More than 1%, less than 3% A: More than 3%, less than 5% B: More than 5%, less than 10% C: More than 10%

[0049] <Conductivity> Using JIS C 2550-4:2011 A method, the total area of ​​10 contact electrodes is 1000mm 2 The interlaminar resistance coefficient was measured under the following conditions. If it was A or higher, it was determined that the conductivity was sufficient. (Evaluation criteria for conductivity) A: Interlayer resistance coefficient is 300 Ω mm 2 less than B: Interlayer resistance coefficient is 300 Ω mm 2 End

[0050] [Table 2A]

[0051] [Table 2B]

[0052] As can be seen from Tables 1 to 2B, Nos. 1 to 14, which are examples of the present invention, exhibited sufficient corrosion resistance (white rust resistance) even in a 240-hour salt spray test, and also had excellent corrosion resistance in the processed areas and sufficient conductivity. On the other hand, in Comparative Examples Nos. 15 to 34, the X2 / X1 ratio was outside the range of the present invention, and the corrosion resistance in a severe environment was insufficient. Furthermore, Comparative Example No. 35 contained a polyurethane resin, and although it had excellent corrosion resistance, it had poor conductivity. [Explanation of symbols]

[0053] 1: Surface-treated steel 11: Steel material 12: Plating layer 13: Chemical conversion coating

Claims

1. Steel and a plating layer containing Zn or a Zn alloy formed on a surface of the steel material; a chemical conversion coating formed on the surface of the plating layer; and the chemical conversion coating contains an organosilicon compound having a siloxane bond, P, and F; When a TOF-SIMS is used to measure the ion count distributions of Si and Zn from the surface of the chemical conversion coating in the thickness direction of the chemical conversion coating toward the interface between the chemical conversion coating and the plating layer, the distance between the surface of the chemical conversion coating and the position where the measured ion count of Si first becomes equal to 20 times the measured ion count of Zn is defined as the thickness t of the chemical conversion coating, where Region 1 is a range starting from a position t×1 / 6 from the surface of the chemical conversion coating in the thickness direction and ending from a position t×1 / 2 from the surface of the chemical conversion coating in the thickness direction, and Region 2 is a range starting from the position t×1 / 2 from the surface of the chemical conversion coating in the thickness direction and ending from a position t×5 / 6 from the surface of the chemical conversion coating in the thickness direction, and X2 / X1 is a ratio of the average value X2 of the Si ion count in Region 2 to the average value X1 of the Si ion count in Region 1, and is 1.05 to 1.

50. Surface treated steel.

2. C on the surface of the chemical conversion coating measured using the TOF-SIMS ３ H ６ N ＋ The ion count of X3, CH ４ N ＋ The ion count of X4, NH4 ＋ When the ion count of the above is X5, X3 / X1 is 0.0025 to 0.0340, X4 / X1 is 0.080 to 0.110, and X5 / X1 is 0.0050 to 0.0120. The surface-treated steel material according to claim 1.

Images