Zinc-plated steel sheet with excellent press formability, chemical treatment properties, and appearance quality, and method for manufacturing the same.

Abstract

To provide a galvanized steel sheet excellent in press-moldability, chemical conversion treatability and appearance quality, and a method for manufacturing the galvanized steel sheet.SOLUTION: A galvanized steel sheet excellent in press-moldability, chemical conversion treatability and appearance quality includes an inorganic coating including Mn: 1.0 mg / m2 or more and 100 mg / m2 or less, P: 10.0 mg / m2 or more and 100 mg / m2 or less, 1.0×10-5 mol / m2 or more and 5.0×10-3 mol / m2 or less of the total [A] of the molar number of one kind or two kinds or more among Cl, S, F and Br derived from chloride, a sulfuric acid compound, fluoride and bromide and the remainder consisting of inevitable impurities on the galvanized surface of a hot-dip galvanized steel sheet.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a zinc-plated steel sheet with excellent press formability, chemical treatment properties, and appearance quality, and to a method for producing the same. [Background technology]

[0002] Zinc-plated steel sheets are used in automobile bodies and other components to improve corrosion resistance and appearance. In the automobile manufacturing process, automobile manufacturers produce automobile bodies by press-forming steel sheets. Therefore, zinc-plated steel sheets, which are formed into complex shapes for automobile bodies, require excellent press-formability, and coating technologies have been developed to impart high lubricity to the surface of the steel sheets.

[0003] Among these, phosphate-based coatings have been widely used as lubricating coatings because they exhibit excellent lubricity and allow for the relatively easy formation of a uniform and well-adhering coating by utilizing the chemical reaction between the plated surface and the treatment solution. For example, Patent Document 1 shows a galvanized steel sheet having a pre-phosphate coating mainly composed of zinc phosphate. In this process, surface preparation using a titanium colloid-containing aqueous solution or zinc phosphate colloid-containing water is necessary as a pretreatment to form a dense coating.

[0004] On the other hand, manganese phosphate coatings are known to be hard among phosphate coatings and have a high effect in suppressing galling of the plating onto the mold even when formed under high surface pressure, thus providing a high lubrication effect even in thin films. For example, Patent Documents 2 to 7 disclose a technology for improving the press formability of steel sheets by applying a phosphate-based inorganic lubricating coating mainly composed of manganese phosphate to the plated surface.

[0005] The electroplated steel sheet is shipped after being coated with rust preventive oil, and is painted after being press-formed and joined by an automobile manufacturer. In the painting process, first, an alkaline degreasing treatment is performed to remove the oil adhering to the steel sheet surface. At this time, if the steel sheet has been stored for a long time with oil coating and the rust preventive oil is strongly adsorbed to the steel sheet, or if a large amount of oil and metal ions are mixed into the liquid as the degreasing liquid is continuously used and the degreasing power weakens, the degreasing may not be sufficient, which may have an adverse effect on the subsequent chemical conversion treatment and the appearance after painting.

[0006] Specifically, when oil remains on the steel sheet surface even after degreasing, the formation reaction of the chemical conversion coating film is inhibited at this site, resulting in a non-uniform chemical conversion film, which causes unevenness in the appearance after painting. In particular, in the case of a steel sheet provided with a lubricating film for the purpose of improving press formability, including the above-mentioned phosphoric acid-based film, since the film itself may have the effect of enhancing the lubricating oil retention property, this problem is likely to occur, and improvement techniques have been demanded.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present invention overcomes the above problems and provides a zinc-based plated steel sheet excellent in press formability, chemical conversion treatment property, and appearance quality, and a method for producing the same.

Means for Solving the Problems

[0009] The gist of the present invention is as follows. (1) On the zinc plating surface of a hot-dip galvanized steel sheet, An inorganic coating is applied, consisting of manganese phosphate, one or more salts from chlorides, sulfates, fluorides, and bromides, and residual unavoidable impurities, and the inorganic coating is, Mn: 1.0 mg / m 2 or more and 100 mg / m 2 or less, P: 10.0 mg / m 2 or more and 100 mg / m 2 or less, and further, the total number of moles [A] of one or more of Cl, S, F, and Br derived from chloride, sulfate, fluoride, and bromide is 1.0 × 10 -5 mol / m 2 or more and 5.0 × 10 -3 mol / m 2 or less, Something A zinc-based plated steel sheet excellent in press formability, chemical conversion treatment property, and appearance quality, characterized by the above. (2) In the inorganic film, the ratio [A] / [P] of the total number of moles [A] of the above and the number of moles [P] of P in the range from the outermost surface measured by an X-ray photoelectron spectrometer to 2 nm is 0.01 or more and 5.0 or less. The zinc-based plated steel sheet excellent in press formability, chemical conversion treatment property, and appearance quality according to (1). (3) Manganese ions or permanganate ions are 0.01 mol / L or more and 2.5 mol / L or less, phosphate ions are 0.6 mol / L or more and 3. mol / L or less, and further, not an acid but an alkali metal salt, ammonium salt, zinc salt of a compound One or more of chloride ions, sulfate ions, fluoride ions, and bromide ions added to the solution as are added, and the molar concentration [A L of their total and the molar concentration [P L of phosphate ions The ratio [A L / [P LA method for producing a zinc-plated steel sheet with excellent press formability, chemical conversion treatmentability, and appearance quality, characterized by contacting an aqueous solution containing ] such that ] is 0.2 or more and 1.5 or less, and containing residual unavoidable impurities, with the plated surface for a time of 0.1 seconds or more and 10 seconds or less, and then drying it to obtain the zinc-plated steel sheet described in (1) or (2). [Effects of the Invention]

[0010] The present invention makes it possible to provide zinc-plated steel sheets with excellent press formability, chemical treatment properties, and appearance quality. [Brief explanation of the drawing]

[0011] [Figure 1] This diagram illustrates the relationship between [A] in the coating, chemical treatment properties, and sliding properties. [Figure 2] This diagram illustrates the relationship between the [AS] / [PS] ratio in the coating, chemical treatment properties, and sliding properties. [Modes for carrying out the invention]

[0012] Details of the present invention are described below.

[0013] As a result of diligent research to solve the above-mentioned problems, we have found that by incorporating an appropriate amount of compounds containing halogen ions such as fluoride ions, chloride ions, and bromide ions, and oxoacid ions such as sulfate ions (hereinafter referred to as Ion Group A) into an inorganic lubricating film mainly composed of manganese phosphate, as described in Patent Document 2, etc., the chemical treatment properties can be improved without impairing the sliding properties.

[0014] The metal salts consisting of the aforementioned group A ions have higher solubility in alkaline aqueous solutions compared to manganese phosphate, which is the main component of the inorganic film. Therefore, it is believed that good chemical conversion treatment properties can be obtained when a portion of the film dissolves and detaches along with the rust-preventive oil during alkaline degreasing treatment.

[0015] Furthermore, a detailed investigation into the relationship between the surface condition of the inorganic film, chemical conversion treatment properties, and surface appearance after painting revealed that the higher the relative abundance of ions A relative to phosphate ions on the surface, the more uniform the crystal size of the formed chemical conversion film becomes, resulting in a more beautiful surface appearance after painting. This is thought to be because the presence of ions A on the surface accelerates the desorption reaction of rust-preventive oil. Even if there are areas where the degree of adsorption between the steel plate and rust-preventive oil is strong locally, the degreasing solution from the surrounding area penetrates further, allowing the rust-preventive oil to be removed from the entire surface, thus increasing the uniformity of degreasing and chemical conversion treatment properties.

[0016] Furthermore, since the degreasing process is performed after the steel plates are pressed and assembled, the removal of a portion of the inorganic lubricating film during the degreasing process does not impair the inherent properties of the lubricating film, such as improving the sliding properties of the steel plates during pressing. The embodiments of the present invention will now be described in detail.

[0017] The inorganic coating on the base hot-dip galvanized surface contains manganese at a concentration of 1.0 mg / m². 2 More than 100mg / m 2 The following range is used for manganese content: 1.0 mg / m³ 2 Below this level, sufficient adhesion of the plating to the mold cannot be adequately suppressed, and therefore sufficient moldability cannot be ensured. Manganese content of 100 mg / m³ 2 Beyond a certain point, the effect of suppressing plating adhesion saturates, and the chemical conversion treatment performance also deteriorates in the present invention.

[0018] Furthermore, the coating contains phosphorus at 10.0 mg / m². 2 More than 100mg / m 2 It contains phosphorus within the following range: 10.0 mg / m³ 2 Below this level, sufficient compatibility with the rust-preventive oil during machining and sliding cannot be achieved, and adequate formability cannot be ensured. 2 Beyond a certain point, the affinity effect with the rust-preventive oil saturates, and the chemical conversion treatment properties also deteriorate in this invention.

[0019] The appropriate amount of ion group A to be contained in the film is determined by the sum of the moles of ion group A contained in the film per unit area, as shown in Figure 1, where [A] is 1.0 × 10⁻⁶. -5 mol / m 2 The above 5.0 × 10 -3 mol / m 2 The following conditions ensure good sliding properties while improving chemical treatment properties: [A] content is 1.0 × 10 -5 mol / m 2 If the value is less than the limit, no improvement in chemical treatment properties can be obtained. Conversely, if the value exceeds the limit, it becomes difficult to continuously form a hard manganese phosphate film that ensures sliding properties, and the press formability deteriorates.

[0020] Furthermore, regarding the relative abundance of ion group A in the outermost layer of the inorganic film, as shown in Figure 2, increasing this ratio is preferable because it increases the uniformity of the degreasing and chemical conversion treatment reactions, as described above, and makes the size of the chemical conversion film crystals more uniform. To achieve this, the total number of moles of one or more types of ion group A present in the outermost layer of the inorganic film [A S ] and the number of moles of P present in the outermost layer [P S ] ratio [A S ] / [P S ] is 0.01 or greater. On the other hand, this is [A S ] / [P S If the value becomes too large, the sliding performance tends to be slightly inferior, so the upper limit should be 5.0 or less.

[0021] Here, the outermost layer of the inorganic film is defined as the average value obtained by removing impurities and dirt attached to the surface by Ar sputtering using an X-ray photoelectron spectroscopy analyzer (e.g., ULVAC-PHI PHI5800), and measuring the atomic concentration at three equally spaced points from the point where the atomic concentration of C is 10% or less toward the steel plate, at 1 nm intervals from 1 nm to 2 nm in the depth direction. Atomic concentration is a value obtained by dividing the area intensity obtained by removing the background from the peaks of each element detected from the measurement site using an X-ray photoelectron spectroscopy analyzer by the relative sensitivity coefficient set for each instrument, and can be calculated using analysis software.

[0022] Furthermore, even if the above-mentioned coating contains unavoidable impurities in addition to the components contained in the hot-dip galvanizing, it will not affect the properties of the steel sheet such as sliding properties or chemical conversion treatment properties. Examples of unavoidable impurities include Li, Be, C, F, Na, Mg, Al, Si, Cl, K, Ca, Ni, Mo, V, W, Ti, Fe, Rb, Sr, Y, Zn, Nb, Cs, Ba, Cr, Cd, Pb, Sn, As, and lanthanides.

[0023] A hot-dip galvanized steel sheet that forms an inorganic film can be any hot-rolled or cold-rolled steel sheet with a metal film containing 50% or more Zn by mass on its surface. The plating composition may be pure Zn, or it may contain Zn as the main component, along with one or more alloying elements and impurity elements such as Fe, Ni, Co, Al, Pb, Sn, Sb, Cu, Ti, Si, B, P, N, S, O, etc. In particular, a so-called alloyed hot-dip galvanized steel sheet, which is produced by immersing the steel sheet in a Zn plating bath containing a small amount of Al and then heat-treating it to contain about 5-20% Fe in the plating phase relative to the total mass of the plating, is excellent in corrosion resistance after painting and spot weldability, and is suitable as an automotive steel sheet for use in the present invention.

[0024] There are no particular restrictions on the amount of plating applied, but considering the corrosion resistance required for automotive steel sheets, the total sum of all components constituting the plating should be 20 g / m². 2 The above is preferable. If the amount of plating is too much, there will be a lot of peeling of the plating during steel sheet processing, and it may remain in the mold and cause indentation defects, so the upper limit is 100g / m 2 It is preferable that this is the case. Furthermore, the present invention is not affected in any way by the properties of the steel sheet that serves as the base material for hot-dip galvanizing, and there are no restrictions on the strength class, composition, or microstructure. In addition, there are no restrictions on the raw materials used in manufacturing the steel sheet or the method of manufacturing the steel sheet.

[0025] The method for producing this coating involves contacting a solution containing manganese ions or permanganate ions and phosphoric acid, and also containing one or more of the following ions—chloride ions, sulfate ions, fluoride ions, and bromide ions—added to the aqueous solution as a salt such as an alkali metal salt, ammonium salt, or zinc compound, rather than an acid, with the plated surface and then drying it.

[0026] The oxoate ions and halogen ions mentioned above are strong acids or acids with very strong plating etching power. If they are mixed into the processing solution in their acidic form, the dissolution reaction on the surface of the steel sheet may proceed excessively when the solution comes into contact with the steel sheet, potentially causing a defect in appearance. Therefore, they must be added to the processing solution as salts.

[0027] Preferred types of salts include alkali metal salts, ammonium salts, and zinc compounds. The cations and ion group A compounds contained in these salts have high solubility in aqueous solutions, so they do not adversely affect the chemical conversion treatment improvement effect, nor do they adversely affect other steel sheet properties such as sliding properties and corrosion resistance.

[0028] The composition of the treatment solution used can be adjusted to achieve an appropriate film state by considering the method and contact time of contacting the plated surface with a solution containing manganese ions or permanganate ions, phosphoric acid, and ions A, but preferably the molar concentration of phosphorus [P L [A] is 0.6 mol / L or more and 3.0 mol / L or less, and the total molar concentration of one or more ions from group A is [A L ] and the ratio of the molar concentration of phosphorus [A L ] / [P L It is desirable to set the value of [ ] to 0.2 or more and 1.5 or less, and to contact it with the plated surface for a time of 0.1 seconds or more and 10 seconds or less, and then dry it.

[0029] In this invention, the inorganic film mainly composed of manganese phosphate formed on the plated surface is formed by a mechanism in which sparingly soluble phosphate compounds precipitate by utilizing the increase in pH that occurs when the plated surface is dissolved by contact with an acidic solution containing phosphoric acid. On the other hand, since ion group A cannot form sparingly soluble compounds on its own in response to pH changes, it is necessary to incorporate ion group A along with the formation of phosphate compounds. Therefore, in order to ensure that ion group A exists in an appropriate state within the inorganic film, it is necessary to control the formation rate of the phosphate compounds and the concentration of ion group A in the solution.

[0030] [P L If the concentration is less than 0.6 mol / L, the film formation rate is slow, and as the phosphate compound forms over time, group A ions are released, preventing sufficient incorporation of group A ions into the film. If it exceeds 3.0 mol / L, the amount of film formed becomes too large, resulting in an excessive amount of phosphate film in typical film formation processes, making it impossible to guarantee the effectiveness of the chemical conversion treatment.

[0031] Also, ...A L ] / [P L If the value is less than 0.2, the required amount of ion group A cannot be incorporated into the film, and a sufficient improvement in chemical conversion treatment performance cannot be obtained. Conversely, if it exceeds 1.5, sludge adheres to the plated surface due to overdissolution by ion group A, causing the surface to discolor.

[0032] The time from when the above-mentioned treatment solution comes into contact with the steel plate surface until it dries should be between 0.1 seconds and 10 seconds. If it is less than 0.1 seconds, a sufficient phosphoric acid film cannot be formed, and sliding properties cannot be guaranteed. On the other hand, if it exceeds 10 seconds, the plating surface will be over-dissolved by group A ions, causing sludge to adhere to the plating surface and discoloration of the surface.

[0033] Furthermore, methods for bringing the steel plate into contact with the above-mentioned treatment liquid include methods such as immersing the steel plate in the treatment liquid and then homogenizing the amount of liquid applied using a ringer roll or gas wiping, or roll coating.

[0034] Furthermore, rinsing with water is not necessarily required after contact between the treatment solution and the steel plate. If rinsing is performed, the method is not specifically defined, but it can be done by immersion or spraying. In this case, excessive rinsing with water can damage the inorganic film surface. S ] / [P S Since there is a risk of the [condition] decreasing, it is important to adjust the rinsing time, water temperature, water pressure, etc. as appropriate.

[0035] The drying of the processing liquid or moisture is performed using a blower, hot air furnace, induction heater, etc. It is sufficient that the moisture is removed within a specified time, and there are no specific requirements for the drying temperature, but from an economic standpoint, it is preferable to keep it below 200°C.

[0036] The content of each element and ion in the film can be measured using ICP emission spectrometry or the like by dissolving the film in chromic acid. For oxoacid ions, the molar concentration in the film can be obtained by measuring the content of chlorine, sulfur, and other halogen ions, which are elements that make up oxoacids, using the above method. Alternatively, the amount of elements present on the film surface may be quantitatively evaluated using fluorescent X-rays with a calibration curve created using ICP emission spectrometry or the like. The type of oxoacid can be identified by the presence of chlorine and sulfur on the film surface and within the film using photoelectron spectroscopy (XPS) or the like. Before performing the above analysis, the sample should be ultrasonically cleaned with hexane or ethanol to remove oil and dirt from the surface. [Examples]

[0037] The present invention will be described non-limitingly using examples. For the galvanized steel sheets to which the inorganic coating was applied, alloyed hot-dip galvanized steel sheets (AS, Fe: 10 mass%, Al: 0.2 mass%, remainder Zn) and hot-dip galvanized steel sheets (GI) were used. The treatment solution under the conditions shown in Table 1 was applied using a roll coater, and then dried in a hot-air drying oven at 50°C to form the coating.

[0038] [Table 1]

[0039] <Chemical treatment properties> The sample consisted of plated steel sheets coated with the above-mentioned inorganic lubricating film, to which rust-preventive oil (Nippon Parkerizing Co., Ltd. Knoxrust 550HN) was applied to one side at a rate of 2.0 g / m². 2 The sample was treated. To degrade the degreasing ability, the sample was immersed for 90 seconds in Fine Cleaner 4380 (40°C, manufactured by Nippon Parkerizing Co., Ltd.), a degreasing solution containing 5 g / L of the above-mentioned rust-preventive oil and 100 ppm each of iron and zinc. Subsequently, it was immersed for 30 seconds in the surface conditioning agent Percolene Z (manufactured by Nippon Parkerizing Co., Ltd.), and then for 90 seconds in PB-3080 (manufactured by Nippon Parkerizing Co., Ltd., liquid temperature 43°C). The chemical conversion treatment film was evaluated by SEM observation (secondary electron beam imaging), with ◎ and ○ according to the evaluation criteria below being considered as passing. Evaluation criteria: ◎: A dense chemical conversion film with a crystal size of 1-10 μm is formed. ○: Although there is some variation in crystal size, a 1-10 μm thick chemical conversion film is formed densely and without transparency. △: The chemical conversion film is formed without transparency, but there are crystals larger than 10 μm in size. ×: The chemical conversion coating is not partially formed.

[0040] <Sliding properties> After the coating treatment, the sample was cut to a width of 17 mm and a length of 300 mm, and 1 g / m² of Knoxrust 550HN (manufactured by Nippon Parkerizing Co., Ltd.) was applied. 2 After oiling, a draw bead test was performed at a tensile speed of 500 mm / min. The pull-out load was measured while varying the clamping load from 200 to 800 kgf (1.96 × 10³ to 7.84 × 10³ N). The slope was determined from a plot with the clamping load on the horizontal axis, and this was multiplied by 1 / 2 to obtain the coefficient of friction. ◎ and ○ according to the evaluation criteria below were considered passing grades. Evaluation criteria: ◎: Friction coefficient less than 0.15 ○: Friction coefficient is less than 0.20 △: Friction coefficient is 0.20 or higher and less than 0.30 ×: Friction coefficient greater than 0.30

[0041] <Exterior Evaluation> The appearance of galvanized steel sheets after coating was visually evaluated for unevenness. The observation area was 210 mm x 300 mm, and the evaluation was conducted according to the following criteria, with a circle (○) indicating a pass. Evaluation criteria: ○: No visible inconsistencies exist. △: Clearly visible irregularities cover less than 50% of the area. ×: Clearly visible irregularities cover 50% or more of the area.

[0042] As shown in Table 1, for samples (levels 1 to 31) manufactured under conditions within the scope of the present invention, we were able to obtain galvanized steel sheets with good chemical treatment properties, excellent sliding properties, and a good appearance.

[0043] Of these, levels 8 and 17 met the passing level for chemical conversion treatment, but the inorganic film surface [A S ] / [P S Because the ] was slightly low, some unevenness was observed in the crystal size of the chemical conversion coating.

[0044] On the other hand, in comparative examples levels 32 to 34, the total amount of element A in the coating was less than the range of the present invention, and sufficient chemical conversion treatment properties could not be obtained. Also, in level 35, the total amount of element A in the coating was more than the range of the present invention, and sufficient sliding properties could not be obtained.

[0045] At levels 36 and 37, the amount of P or Mn in the coating was less than the range of the present invention, and sufficient sliding properties could not be obtained. At levels 38 and 39, sulfuric acid and hydrochloric acid, which are strong acids, were added to the treatment solution, resulting in uneven appearance due to uneven treatment.

Claims

1. The zinc-plated surface of a hot-dip galvanized steel sheet is coated with an inorganic film consisting of manganese phosphate, one or more salts from chlorides, sulfates, fluorides, and bromides, and residual unavoidable impurities, wherein the inorganic film has a Mn content of 1.0 mg / m². 2 More than 100mg / m 2 Below, P: 10.0mg / m 2 More than 100mg / m 2 Furthermore, the sum of the moles of one or more of the following elements derived from chlorides, sulfates, fluorides, and bromides [A] is 1.0 × 10⁻⁶ -5 mol / m 2 The above 5.0 x 10 -3 mol / m 2 A zinc-plated steel sheet characterized by having excellent press formability, chemical treatment properties, and appearance quality.

2. The zinc-plated steel sheet according to claim 1, characterized in that, in the inorganic film, the ratio [A] / [P] of the sum of the number of moles [A] in the range from the outermost layer to 2 nm, as measured by an X-ray photoelectron spectroscopy analyzer, to the number of moles of P [P] is 0.01 or more and 5.0 or less.

3. Manganese ions or permanganate ions are in a concentration of 0.01 mol / L or more and 2.5 mol / L or less, phosphate ions are in a concentration of 0.6 mol / L or more and 3.0 mol / L or less, and chloride ions, sulfate ions, fluoride ions, bromide ions, which are added to the solution as salts of an alkali metal salt, an ammonium salt, or a zinc compound rather than an acid, one or more of these are contained such that the molar concentration [A L of the sum of these and the molar concentration [P L of phosphate ions have a ratio [A L / [P L of 0.2 or more and 1.5 or less. An aqueous solution containing inevitable impurities is brought into contact with the plating surface for a time of 0.1 seconds or more and 10 seconds or less and then dried to obtain the zinc-plated steel sheet according to claim 1 or 2, a method for manufacturing a zinc-based plated steel sheet excellent in press formability, chemical conversion treatment properties, and appearance quality.

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