TWI396773B - Hot-dipped galvanized steel sheet - Google Patents

Description

Hot-dip galvanized steel sheet Field of invention

The present invention relates to a hot-dip galvanized steel sheet.

Background of the invention

The alloyed hot-dip galvanized steel sheet (GA) having high spot welding continuous spotting property and corrosion resistance after coating is widely used for automotive steel sheets and the like. In the alloyed hot-dip galvanized steel sheet, when the degree of alloying is high at the time of press forming (called Γ phase, Fe is in the range of 20% to 28% of the body-centered cubic system of Zn and Fe). When the intermetallic compound (Fe ₃ Zn ₁₀ ) is a large amount, the plating layer is hard, and it is pulverized and peeled into a powder form at the time of press molding, and there is a problem of pulverization. In addition, when the degree of alloying is low (referred to as the ζ phase, Fe is in the range of 5.5 to 6.2% by mass of Fe and the monoclinic intermetallic compound (FeZn ₁₃ ) of Fe), causing plating. Adhesion to the mold causes peeling of the plating layer due to sliding on the surface under high surface pressure, and there is a problem that the plating layer called peeling is damaged. However, due to the optimization of the plating structure and the advancement of the press technology, alloyed hot-dip galvanized steel sheets which are not currently having major problems are being used. In order to improve the powdering resistance, the basic means is to suppress the formation of the Γ phase at the interface between the plating and the substrate. Further, in order to improve the peeling resistance, the basic means is to suppress the formation of the ζ phase on the plating surface layer.

Patent Document 1 discloses an alloyed hot-dip galvanized steel sheet having a Γ phase at an interface between a plating and a substrate of 1.0 μm or less, and a plating surface layer having an η phase and containing 0.003% or less by mass of Fe. The hexagonal Zn phase is in contact with the plating layer in which the above ζ phase is absent.

Patent Document 2 discloses an alloyed hot-dip galvanized steel sheet having a Γ phase thickness of 0.5 μm or less and having a plating layer in which no η or ζ phase is present on the plating surface layer.

Patent Document 3 discloses an alloyed hot-dip galvanized steel sheet having a plating layer on its surface and a surface roughness of Rmax ≦ 8 μm.

Patent Document 4 discloses an alloyed hot-dip galvanized steel sheet in which the surface coverage ratio of the ζ phase and the X-ray diffraction intensity ratio of the ζ phase and the other phase are set within a specific range.

On the other hand, there is a series of techniques for improving the formability of the press by providing a lubricating film on the surface layer of the galvanized steel sheet without performing the control of the plating layer as described above.

Patent Document 5 discloses a galvanized steel sheet in which a plating surface layer is coated with a film I and a film II, and the film I has an anti-adhesive function, and is Mn, Mo, Co, Ni, Ca, Cr, V, W, One or two or more kinds of metal oxides/hydroxides of Ti, Al, and Zn are mainly used, and the film II has a sliding lubricating function, and one or two kinds of oxyacids of P and B are mainly used, and The two film layers are thickened at the interface side by the film I, and the film II is obliquely covered in a state where the surface side is thick.

Patent Document 6 discloses an alloyed hot-dip galvanized steel sheet having a flat portion on the surface of the iron-zinc alloy plating and having an oxide film mainly composed of an oxide of Zn at the flat portion thereof, the oxide of the Zn The film thickness is 8 nm or more and 200 nm or less, and the interface width is 25 nm or more and 500 nm or less.

Patent Document 7 discloses a galvanized steel sheet in which a crystalline phosphate film is formed on the surface layer.

Prior technical literature Patent literature

Patent Document 1: Japanese Patent Publication No. 01-068456

Patent Document 2: Japanese Patent Publication No. 04-013855

Patent Document 3: Japanese Patent Publication No. 03-191045

Patent Document 4: Japanese Patent Publication No. 08-092714

Patent Document 5: Japanese Patent Publication No. 04-176878

Patent Document 6: JP-A-2003-171751

Patent Document 7: JP-A-2007-217784

However, in the alloyed hot-dip galvanized steel sheets of Patent Documents 1 and 2, the η and ζ phases are not present in the plating surface layer, and the thickness of the ruthenium phase is also small. Therefore, the plating layer is formed substantially in a single phase of a hexagonal intermetallic compound (FeZn ₇ ) in which Zn and Fe are 7 to 11.4% by mass of Fe, which is called δ ₁ . Therefore, it is an idealized plating structure for suppressing both pulverization and flaking, but the slidability at the time of press molding is inferior to those of the patent documents 5 to 7 in which the lubricating film is adhered to the surface layer of the galvanized steel sheet.

Further, the alloyed hot-dip galvanized steel sheet of Patent Document 3 has a ζ phase in the plating surface layer and a certain degree of roughness on the plating surface for the purpose of making up for the reduction of the flaking property. However, its effect is limited. The alloyed hot-dip galvanized steel sheet of Patent Document 4 has a ruthenium phase for the purpose of improving chemical conversion treatment and cationic electrocoating characteristics. However, the alloyed hot-dip galvanized steel sheet of Patent Document 4 does not have an ideal plating structure from the viewpoint of achieving both powdering and peeling. Further, the alloyed hot-dip galvanized steel sheet of Patent Document 4 is inferior to the techniques of Patent Documents 5, 6, and 7 in terms of slidability at the time of press molding.

On the other hand, the alloyed hot-dip galvanized steel sheet of Patent Document 5 in which the lubricating film is adhered to the surface layer of the galvanized steel sheet exhibits excellent slidability regardless of the presence or absence of the ruthenium phase in the plating surface. As a result, cracks are not easily generated even when a large blank holding force (BHF) is applied during press molding, but a large blanking force must be applied to suppress wrinkles. That is, although the lower limit of the blanking force generated by the crack increases, the lower limit of the necessary blanking force also increases in order to eliminate wrinkles. Therefore, the range of the blanking force which does not occur in wrinkles or cracks, that is, the press forming range is substantially equal to the related art.

The alloyed hot-dip galvanized steel sheets of Patent Documents 6 and 7 exhibit good slidability at the time of press molding regardless of the presence or absence of a ζ phase in the plating surface layer. However, the effect is inferior to the technique of Patent Document 5. In addition, the range of forming of the press machine is approximately the same as that of the related art.

As described above, the related art is excellent in terms of both pulverization and peeling, or slidability at the time of press molding, but the range of the blank holder force that can be used may not be expanded. Therefore, a high press formability is required, and even a range of the blank holding force which is not generated by wrinkles and cracks, that is, the press forming range is expanded.

The present invention employs the following means for solving the above problems.

(1) A first aspect of the present invention is a hot-dip galvanized steel sheet comprising a steel sheet and a plating layer attached to a surface of the steel sheet, mainly composed of Zn, and having an adhesion amount of 20 g/m. ² or more and 100 g/m ² or less; the plating layer contains an amorphous film on the surface layer, the amorphous film containing an inorganic oxyacid salt and a metal-based oxide, the metal-based oxide containing Zn; the plating layer having a ζ phase and δ ₁ phase; the plating layer contains 8% by mass or more and 13% by mass or less of Fe; the Zn contained in the metal oxide is present until the outermost layer of the amorphous film; the background spacing of the ζ phase is 0.126 nm, and the background is subtracted The X-ray diffraction intensity after subtraction of the interplanar spacing of 0.127 nm of the δ ₁ phase is subtracted from the background X-ray diffraction intensity, and the obtained value of the X-ray diffraction intensity ratio I is 0.06 or more and 0.35 or less.

(2) In the hot-dip galvanized steel sheet according to the above (1), the plating layer may have a Γ phase having an average thickness of 1.5 μm or less.

(3) In the hot-dip galvanized steel sheet according to the above (1), the plating layer may contain 0.10 g/m ² or more and 0.25 g/m ² or less of Al.

(4) In the hot-dip galvanized steel sheet according to the above (1), the plating layer may contain Ni of more than 0 and 0.40 g/m ² or less.

(5) In the hot-dip galvanized steel sheet according to the above (4), the plating layer may contain 0.15 g/m ² or more and 0.45 g/m ² or less of Al.

(6) In the hot-dip galvanized steel sheet according to any one of the above aspects, the inorganic oxyacid salt may contain one or more of P or B.

(7) In the hot-dip galvanized steel sheet according to any one of the above aspects, the metal-based oxide may further contain an oxide of one or more of Mn and Al.

(8) The hot-dip galvanized steel sheet according to any one of the above-mentioned (1), wherein the total amount of P and B in the inorganic oxyacid salt is 1 mg/m ² or more and 250 mg/m ² or less; Among the metal-based oxides containing Zn, the total amount of Mn, Mo, Co, Ni, Ca, V, W, Ti, and Ce may be 1 mg/m ² or more and 250 mg/m ² or less.

(9) In the hot-dip galvanized steel sheet according to any one of the above aspects (1) to (5), the Zn present in the amorphous film may be formed as a main component of a compound containing phosphorus oxyacid and zinc. .

According to the structure described in the above (1), the amorphous film contains a component containing an anti-adhesive function and a non-polar oxyacid salt having a sliding lubricating function and a metal-based oxide. Further, regarding the plating structure, a certain amount of ζ phase remains in the surface layer. Therefore, by utilizing the synergistic effect of the lubricative film and the plating structure, it is possible to provide a hot-dip galvanized steel sheet having excellent lubricity and chemical conversion treatability and having a press forming range wider than that of the related art. As a result, in terms of press forming of a steel sheet for an automobile body, the yield is improved, and it can be produced more efficiently than the related art. In addition, the design freedom of the mold is wide, and a widely designed press forming can be performed. As a result, the value of the car's goods will increase.

Further, according to the structure described in the above (2), it is possible to provide a hot-dip galvanized steel sheet having good pulverization properties.

Further, according to the configuration described in the above (3), it is possible to provide a hot-dip galvanized steel sheet which is easy to obtain the plating structure described in (1) and which has a wide press forming range.

Further, according to the configurations described in the above (4) and (5), it is possible to provide a hot-dip galvanized steel sheet which can further suppress the formation of the ruthenium phase in the plating layer, and the press molding range can be further widened.

Further, according to the structures described in the above (6), (7), and (8), it is possible to provide a hot-dip galvanized steel sheet, and the plating structure described in (1) can be further easily obtained, and the press forming range can be further widened. .

Further, according to the configuration described in the above (9), it is possible to provide a hot-dip galvanized steel sheet which has a wider lubricity and a wider range of press forming.

Simple illustration

Fig. ₁ is a schematic diagram showing the background subtraction method at the time of obtaining the I value by using the X-ray diffraction intensity I of the ζ phase and the δ ₁ phase in the plating layer from the X-ray diffraction analysis result of the hot-dip galvanized steel sheet.

Fig. 2A is a schematic view showing the results of depth analysis obtained by the Auger electron spectroscopy method for the lubricative film of the plated steel sheet according to the first embodiment of the present invention.

Fig. 2B is a schematic view showing the results of depth analysis obtained by the Auger electron spectroscopy method for the lubricative film of the plated steel sheet according to the second embodiment of the present invention.

Fig. 3 is an SEM image showing a measurement region of the depth analysis of the lubricative film in a white line frame.

Fig. 4 is a spectrum of the 3s energy level of Zn and the 2p energy level of P when the state of the surface layer of the film is analyzed by X-ray photoelectron spectroscopy in the depth direction.

Fig. 5 is a spectrum of 2p energy level of Zn at the time of state analysis of the surface layer of the film by X-ray photoelectron spectroscopy.

Fig. 6 is a schematic view showing the structure of a hot-dip galvanized steel sheet.

Figure 7 is a graph showing the ratio of the ζ phase to the δ ₁ phase in the plating layer. The X-ray diffraction intensity ratio I of the δ ₁ phase is the horizontal axis, and the lower limit (β) of the blanking force generated by the crack is divided by The numerical value obtained by the lower limit (α) of the necessary blanking force for eliminating wrinkles is the vertical axis, and the examples of the examples and comparative examples of Table 3 are summarized.

Figure 8 is a graph showing the ratio of the ζ phase to the δ ₁ phase in the coating. The X-ray diffraction intensity ratio I of the δ ₁ phase is the horizontal axis, and the lower limit (β) of the blanking force generated by the crack is divided by The numerical value obtained by the lower limit (α) of the necessary blanking force for eliminating wrinkles is the vertical axis, and the examples of the examples and comparative examples of Table 4 are summarized.

Detailed description of the preferred embodiment

In order to solve the above-described problems of the related art, the inventors of the present invention have focused on the technique of attaching a lubricating film to the surface layer of the galvanized steel sheet shown in Patent Document 5. In terms of related technologies, it is considered that the film having the anti-adhesive function is concentrated on the interface side with the plating layer, and the film having the sliding lubrication function is inclined on the surface side of the film surface, that is, in a state where the surface side of the plating layer becomes thicker. It is used to obtain the appropriate requirements for a wide range of press forming load. In addition, when the related art is applied to alloyed hot-dip galvanized steel sheets, since the sliding property is not affected by the use of this technique even when the plating structure is unfavorable for sliding properties, it is considered that the plating structure does not affect the sliding property. . However, the inventors of the present invention are not limited to the concept of the related art, but are capable of expanding the range of the forming range of the pressable machine in the range of the blanking force which does not cause wrinkles and cracks. The coating structure and the film structure were studied. As a result, it has been found that by using the synergistic effect of the lubricative film and the plating structure in which a specific amount of the ζ phase remains in the surface layer, the range in which the blanking force can be used can be expanded, that is, the press forming range can be obtained. Anti-adhesive function and composition with sliding lubrication function.

In the suitable film structure of the related art, since the sliding lubricating component is thickened on the plating surface, and the sliding interface exists between the sliding lubricating component and the anti-adhesive component, even in the case of processing under low surface pressure, the height is high. Lubrication effect. Therefore, there is a disadvantage that wrinkles are easily generated. This disadvantage is eliminated by distributing both the sliding lubricating component and the anti-adhesive component into the lubricating film. However, as described in Patent Document 5, when the processing is performed at a high surface pressure as such a countermeasure, the boundary pressure at which the scratch occurs is lowered, and cracking at the time of pressing is disadvantageous, which causes the above problem. Therefore, in order to form a film that is stronger than the related art, the same anti-adhesive function can be reviewed. As a result, it has been found that a specific amount of the ruthenium phase having a relatively high reactivity remains in the plating surface layer, and a large amount of Zn is mixed into the lubricative film by the Zn dissolution reaction derived from the plating surface layer, and is present until the outermost layer. Zn is used to increase the boundary pressure generated by the scratch and to raise the lower limit (β) of the blanking force at which the crack occurs in the press. It has been found that it is compatible with the lower limit (α) of the blank holder force necessary for eliminating wrinkles described later, and the initial purpose of expanding the load range of the press molding can be achieved. Here, it was found that Zn which is the outermost layer of the coating is formed by further forming a compound containing a compound containing phosphorus oxyacid and zinc as a main component to obtain suitable lubricity. On the other hand, since the ζ phase remains too much, the slidability is impaired, and conversely, cracks may occur. Therefore, it is important that only an appropriate amount of ruthenium layer remains.

Further, as a result of repeated review, it has been found that a specific amount of the ruthenium phase remains in the surface of the plating, and it is preferable to use a heating curve of "cooling by cooling or gas-water cooling after rapid heating at a high temperature". In addition, it has been found that the component having the anti-adhesive function and the component having the sliding lubricating function and the Zn are contained in the mixed state in the film, and in order to allow Zn to exist in the outermost layer in the film, it is preferable to use the inorganic oxyacid salt and The treatment liquid of the metal-based oxide is subjected to a film formation treatment. Further, it has been found that it is effective to perform film formation treatment by roll coating in addition to moderately controlling the concentration in the treatment liquid and the temperature of the sheet before the treatment.

Hereinafter, embodiments of the present invention will be described in detail.

First, the structural requirements of the plated steel sheet according to the first embodiment of the present invention will be described in detail. The plating layer of this embodiment contains Zn as a main component and contains Fe having a content of 8 mass% or more and 13 mass% or less. In addition, "mainly Zn" means that Zn is contained in an amount of 50% by mass or more.

When the Fe content of the plating layer is less than 8% by mass, the corrosion resistance after coating is poor due to the unalloyed alloy, and the slidability is poor due to the ζ phase, which causes peeling during processing. On the other hand, when the Fe content exceeds 13% by mass, the Γ phase becomes thick and the powdering property is deteriorated. In order to satisfy the peeling property, the powdering property, and the corrosion resistance after coating, the Fe content is preferably 8.5 mass% or more and 12.5% by mass or less, and preferably 9 mass% or more and 12 mass% or less.

When it is used as a steel sheet for automobiles, the plating layer is preferably 20 g/m ² or more and 100 g/m ² or less per one side. When the plating layer is less than 20 g/m ² , the corrosion resistance may be insufficient, and 30 g/m ² or more is a suitable embodiment. When the plating layer exceeds 100 g/m ² , the continuous dot resistance at the time of spot welding is lowered, and 70 g/m ² or less is a suitable embodiment.

In order to ensure good powdering properties, the thickness of the ruthenium phase is preferably 1.5 μm or less on average. A suitable thickness of the Γ phase is 1 μm or less, and the most suitable thickness of the T phase is 0.8 μm or less.

When the plating layer is 20 g/m ² or more and 100 g/m ² or less, the alloying is appropriately performed, and the total Al concentration in the plating bath is preferably in the range of 0.11% by mass or more and 0.15% by mass or less. If the total Al concentration in the plating bath is less than 0.11% by mass, the alloying of the plating layer cannot be controlled, and the plating layer becomes an excessive alloy. When the total Al concentration in the plating bath is more than 0.15% by mass, the alloying of the plating layer is delayed, and the production efficiency is lowered. In this case, the amount of Al in the plating layer, that is, the total amount of the separator in the initial alloying and the amount of Al from the plating bath falls within the range of 0.10 g/m ² or more and 0.25 g/m ² or less. The Al of the plating layer is desirably controlled within the range of 0.13 g/m ² or more and 0.22 g/m ² or less, and preferably 0.15 g/m ² or more and 0.20 g/m ² or less.

Further, regarding the ratio of the ζ phase to the δ ₁ phase in the plating layer, the X-ray diffraction intensity ratio I of the ζ phase and the δ ₁ phase is

I=ζ(d=0.126nm)/δ ₁ (d=0.127nm)‧‧‧(1)

In the case of the formula, the X-ray diffraction intensity ratio I is set in the range of 0.06 or more and 0.35 or less. Further, ζ (d = 0.126 nm) in the above formula represents the X-ray diffraction intensity value of the ζ phase in the interplanar spacing d = 0.126 nm. Further, δ ₁ (d = 0.127 nm) represents an X-ray diffraction intensity value of the δ ₁ phase in the interplanar spacing d = 0.127 nm. Since the ζ phase has a larger amount of zinc than the δ ₁ phase, if I is small, the amount of zinc in the plating layer is small, and as a result, the adhesion to the mold is reduced, and the sliding becomes good. When the X-ray diffraction intensity ratio I is less than 0.06, the slidability is too good, and the lower limit (α) of the blank holder force necessary for eliminating wrinkles is increased, and on the other hand, the plating surface is dissolved and mixed. The amount of Zn in the amorphous film containing the inorganic oxyacid salt and the metal-based oxide is insufficient, and the boundary of the blanking force causing the crack is lowered, so that the moldable range is narrowed. If the X-ray diffraction intensity ratio I is more than 0.35, the slidability will be insufficient, although the lower limit (α) of the blanking force necessary to eliminate the wrinkles will be lowered, but the lower limit of the blanking force at which the crack is generated (β) ) will fall lower than it, so the formable range is also narrowed in this case. More preferably, the X-ray diffraction intensity ratio is in the range of 0.10 or more and 0.35 or less, and most preferably in the range of 0.15 or more and 0.30 or less.

Further, both the X-ray diffraction intensity ζ (d = 0.126 nm) and the X-ray diffraction intensity δ ₁ (d = 0.127 nm) are values obtained by subtracting the background. The method of deducting the background is shown in Figure 1. The horizontal axis of Fig. 1 represents the incident angle of X-rays, and the vertical axis represents the diffraction intensity.

In Fig. 1, K1 represents a line corresponding to the background of the peak 19 of the δ ₁ phase, and K2 represents a line corresponding to the background of the peak 20 of the ζ phase. Further, L represents a line of the intensity δ ₁ (d = 0.127 nm) after subtracting the background from the δ ₁ phase, and M represents a line of the intensity ζ (d = 0.126 nm) after the background subtraction of the ζ phase.

Next, the structural requirements of the plated steel sheet according to the second embodiment of the present invention will be described in detail. Coating system to this embodiment of Zn as a main component, having a content ratio of Al ² less than 8 mass%, 13 mass% of Fe and 0.15g / m ² or more 0.45g / m, and more than 0g / m ² and in Ni of 0.40 g/m ² or less.

In the second embodiment, the plating is performed by a method in which a small amount of Ni is pre-plated on the surface of the steel sheet, and the Al concentration in the plating bath is higher than that in the hot-dip galvanizing bath in the first embodiment. method. The purpose is to further suppress the formation of the ζ phase. According to the state diagram of the Zn-Al-Fe ternary alloy, when the concentration of Al in the plating bath is high, the ζ phase is not easily formed, and the δ ₁ phase is easily formed. Here, if only the Al concentration in the plating bath is increased, since the Fe-Al separator is formed more at the interface of the substrate, the alloying is delayed and the production efficiency is lowered. In order to prevent this phenomenon, by pre-plating a small amount of Ni on the surface of the steel sheet, and pre-plating Ni in the vicinity of the steel sheet interface during bath immersion, it reacts with Al in the bath, which lowers the Al concentration near the interface and controls the Fe-Al formed at the interface. There will not be too many isolation layers. On the other hand, since a high concentration of Al exists in the adhered plating layer, it is difficult to form a ruthenium phase during alloying.

Ni in the plating layer is set to be more than 0 g/m ² and 0.40 g/m ² or less is caused by an appropriate range of pre-plated Ni. It is suitable that the amount of adhesion of the pre-plated Ni is 0.10 g/m ² or more and 0.50 g/m ² or less. By immersing it in a hot-dip galvanizing bath, a part will melt|dissolve in a plating bath and it will lose, and the amount of Ni remaining in a plating layer is more than 0 g/m<^2> , suitably 0.07g/m<^2> or more and 0.40g/m<^2> or less. range. Further, when the pre-plated Ni is 0.10 g/m ² or more, the occurrence of non-plating is suppressed. When the pre-plated Ni exceeds 0.50 g/m ² , the reaction with Al in the bath is intense, and the formation of the separator becomes uneven, which impairs the appearance after alloying.

The Al in the plating layer is specified to be 0.15 g/m ² or more and 0.45 g/m ² or less, which is caused by an appropriate range of the Al concentration in the plating bath. When the pre-plated Ni is 0.10 g/m ² or more and 0.50 g/m ² or less, the Al concentration in the plating bath is preferably in the range of 0.16 mass% or more and 0.20 mass% or less. When the Al concentration in the plating bath is less than 0.16 mass%, the alloying cannot be controlled and the alloying is excessive. When the Al concentration in the plating bath is more than 0.20% by mass, the alloying is delayed and the production efficiency is lowered. Here, when the plating layer is 20 g/m ² or more and 100 g/m ² or less, Al in the plating layer, that is, the separator in the initial alloying and the total amount of Al from the plating bath fall at 0.15 g/m ² or more and 0.45 g/ The range below m ² .

Further, in the case of the second embodiment, as compared with the case of the first embodiment, the Al concentration in the plating bath can be increased as described above, and since the ζ phase is difficult to be formed and the δ ₁ phase is easily generated, the X can be controlled. The ray intensity ratio I is further lowered.

Next, the structural requirements for the lubricating film will be described in detail. In the first embodiment and the second embodiment, the lubricating film formed on the surface of the plating is an amorphous film composed of an inorganic oxyacid salt and a metal oxide.

In the inorganic oxyacid salt, as the type of the inorganic oxyacid salt which can be applied to the first and second embodiments, an oxo acid containing P in the film composition, and the like can be suitably used. In addition to these, boric acid containing B and an oxo acid and salts thereof can be suitably used. These may be used singly or in combination. When used in combination, it is suitable to contain an oxo acid containing P. Further, an oxide colloid composed of Si, Al, Ti or the like may be contained. It is considered that these main systems function as lubricating functions, and the lubricating machine can be caused by rolling of particles that are damaged when the press is processed.

Further, the metal-based oxide is an oxide or hydroxide of Zn, Al, Ni, Mn, Mo, Co, Ni, Ca, V, W, Ti, Ce or the like. These are added to the reaction liquid, and are components which are dissolved in the reaction liquid from the molten plating layer by Zn, Al, and Ni, and are mixed into the lubricating film. These Zn, in particular, are important as a component for strengthening the function of preventing adhesion between the mold and the plating layer. The fact that these components are mixed into the lubricative film can be judged by elemental analysis of the depth direction obtained by the analysis of the electrons. The fact that Zn is on the outermost layer of the film can be confirmed by the analysis of Zn by spectroscopic analysis or X-ray photoelectron spectroscopy without using sputtering to perform elemental analysis on the surface of the sample.

Further, the appropriate amount of the inorganic oxyacid salt is a total amount of P and B, and the appropriate amount of the metal-based oxide is Zn, Al, Ni, Mn, Mo, Co, Ni, Ca, V, W, The total of Ti and Ce is preferably 1 mg/m ² or more and 250 mg/m ² or less. When the respective components are less than 1 mg/m ² , there is no effect, and when it exceeds 250 mg/m ² , the chemical conversion treatability is adversely affected. Suitably, any one of the components is in the range of 3 mg/m ² or more and 150 mg/m ² or less.

Further, among the lubricating films, a major feature different from the related art is an inorganic oxyacid salt and a Zn-containing metal-based oxide, and Zn oxide is present in the film up to the outermost layer.

The suitable technique in the above Patent Document 5 is a technique in which the P-containing component of the sliding lubricating function is thickened toward the surface layer in the film, and the Mn-containing component having the anti-adhesive function is obliquely coated at the base interface, and the glow discharge spectroscopic is disclosed. The result of the analysis.

On the other hand, the results of the depth analysis corresponding to the Auger electron spectroscopic analysis of the first embodiment and the second embodiment are shown in FIGS. 2A and 2B. The analysis results of Patent Document 5 and the analysis results of the first and second embodiments are compared. First, the technique of Patent Document 5 is known, that is, the related art has a peak in which the P-containing component and the Mn-containing component have significantly different positions. Further, it was found that Zn exists only in the inner layer of the lubricating film. On the other hand, the Zn in the lubricative film is more overwhelming than the related art, and the presence of Zn can be confirmed even in the outermost layer of the lubricating film.

That is, the hot-dip galvanized steel sheet according to the present embodiment is different from the related art, and Zn is present in the lubricating film up to the outermost layer. The adoption of such a film structure leads to an expansion of the press forming range.

Further, Zn in the lubricating film may be formed as a main component (50% or more) of a compound (salt) containing phosphorus oxyacid and Zn. In other words, the Zn of the outermost layer can also form a form in which a compound (salt) containing phosphorus oxyacid and zinc is present mainly (50% or more). The state of Zn in the film was identified by X-ray photoelectron spectroscopy. Using an X-ray photoelectron spectroscopy device (PHI5600) manufactured by ULVAC-PHI Co., Ltd., an analysis region Φ 0.8 mm, an Ar pressure of 10 ^-2 Pa, and an acceleration voltage of 4 kV were performed for 2 nm (SiO ₂ conversion) sputtering per minute, while changing the sputtering time. The results of spectroscopic analysis using an electrostatic hemispherical analyzer using Al kα ray as an X-ray source are shown in Figs. 4 and 5 . Figure 4 shows the 2p spectrum of P and the 3s spectrum of Zn from the outermost layer up to a depth of 18 nm. The horizontal axis represents the binding energy (eV). Here, it is known that the compound body containing phosphorus oxyacid and zinc from the outermost layer to the depth of 2 nm is substantially the same as the compound containing phosphorus oxyacid and zinc and zinc zinc ‧ metal zinc at a depth of 4 nm, from a depth of 6 nm to 18 nm zinc oxide and metal zinc are the main components. Figure 5 is a 2p spectrum of Zn of the same sample. The horizontal axis represents the binding energy (eV). It is still known that the main body of the compound containing phosphorus oxyacid and zinc is from the outermost layer to the depth of 2 nm, and the phosphorus-containing oxyacid is substantially the same as the zinc compound and the zinc oxide ‧ metal zinc, and the zinc oxide is from 6 nm to 18 nm in depth. Metal zinc is the main body.

Next, the manufacturing conditions of the plated steel sheet according to an embodiment of the present invention will first be described on the conditions of the plating layer.

In the present embodiment, a specific amount of the ζ phase remains in the plating layer, and the thickness of the Γ phase is set to 1.5 μm or less, preferably 1 μm or less, and most preferably 0.8 μm or less.

Therefore, in the first aspect, the total Al concentration in the plating bath is set to be 0.11% by mass or more and 0.15% by mass or less. On the basis of the alloying, an induction heater or the like is used for rapid cooling at a high temperature to cool or gas. A heating curve for cooling, such as cooling. The maximum temperature of the alloying is higher than the peritectic temperature of the ζ phase, and it is effective to set it below the peritectic temperature when it is cooled. The peritectic temperature of the ζ phase becomes 530 ° C in the state diagram of the Zn-Fe-binary alloy, and it is difficult to form the primary crystal form if it reaches a ζ phase of 500 ° C or more in the Al-containing bath.

Further, from the viewpoint of suppressing the growth of the Γ phase, it is suitable to shorten the isothermal holding time as much as possible and to perform cooling immediately after heating. Specifically, the alloying temperature is 470 ° C or higher and 600 ° C or lower, preferably 500 ° C or higher and 530 ° C or lower, and the isothermal temperature is maintained within 25 seconds, preferably within 5 seconds, and the cooling rate at the time of cooling is 25 ° C / Below sec, it is preferably 4 ° C / sec or more and 8 ° C / sec or less, and it is preferably cooled up to about 350 ° C.

In the second aspect, after the surface of the steel sheet is pre-plated with Ni in a range of 0.10/m ² or more and 0.50 g/m ² , the total Al concentration in the plating bath is set to be 0.16 mass% or more and 0.20 mass% or less. In the case of alloying, an induction heater or the like is used, and after heating at a high temperature, the heating curve is cooled by cooling or gas-water cooling. Since the Al concentration in the bath is high, the alloying temperature is also set to be higher than 510 ° C to 560 ° C, and the isothermal temperature is maintained for 3 seconds, and the cooling rate at the time of cooling is 2 ° C / sec or more and 4 ° C / sec or less is cooled until 450. Around °C, and spray cooling is preferred. Furthermore, according to the second aspect, the ζ phase can be reduced even if the Γ phase is the same thickness as compared with the first aspect. Thus, the range of presses that are not generated by both wrinkles and cracks is wide.

In any of the aspects, it is important to adopt a heating curve for cooling by cooling or gas-water cooling after rapid heating at a high temperature. On the other hand, if the heating curve is maintained isothermally after low-temperature heating, there is a case where the ζ phase does not remain and the Γ phase is thickened, or the Γ phase is thin and the ζ phase is excessive, and it is difficult to obtain a balance between the two, which is not suitable.

Next, the manufacturing conditions of the lubricating film of the plated steel sheet according to the present embodiment will be described. In the present embodiment, the lubricating film is present in the lubricating film in a state in which the inorganic oxyacid salt and the metal-based oxide are mixed. In the film structure, a treatment liquid containing a component of an inorganic oxyacid salt and a metal oxide is used, and the concentration of the plate and the plate temperature of the hot-dip galvanized steel sheet are appropriately controlled, and a roll coating treatment is suitably performed. achieve. Furthermore, the roll coating process can also be reversed.

As the component which forms an inorganic oxyacid salt, P-containing oxyacid (phosphoric acid, phosphorous acid, hypophosphite, etc.), boric acid, etc., and these salts can be used suitably. An oxide colloid composed of Si, Al, Ti or the like may be added in addition to these. It is preferable to use a component of a metal oxide to use, for example, an inorganic salt such as Mn-based manganese sulfate or manganese nitrate or permanganate. In addition to this, an oxide/hydroxide of Zn, Al, Ni, Mo, Co, Ni, Ca, V, W, Ti, and Ce may be contained, and the metal nitrate or carbonate may be used to form the components. Ammonium salts, sulfates, and the like. Further, in order to improve the liquid stability of the treatment liquid, sulfuric acid, nitric acid or the like may be added as needed.

The total concentration of the treatment liquid is set in the range of 5 g/l or more and 30 g/l or less. Here, the total concentration means the total concentration of elements other than oxygen such as P, B, Zn, or Mn. The production efficiency of the lubricating film of less than 5 g/l is poor, and the speed of the plate has to be lowered. When it exceeds 30 g/l, the lubricating film tends to form an excessively inclined structure. The temperature of the treatment liquid is suitably from 10 to 50 °C. The sheet temperature of the hot-dip galvanized steel sheet before the film formation treatment is preferably 30 ° C or more and 70 ° C or less. This is advantageous in that it dissolves Zn when it comes into contact with the treatment liquid, and is advantageous for film formation and drying after the film formation treatment. These effects are less than 30 °C. If it exceeds 70 ° C, the dissolution of Zn will be excessive and the film will become brittle.

In the film, in particular, in order to form the main surface of the Zn containing phosphorus oxyacid and zinc, it is suitable to increase the concentration of the P-containing oxyacid in the treatment liquid, to lower the drying temperature of the film as much as possible, and to shorten the drying. time. The P-containing oxyacid monomer is 10 g/l or more, the drying temperature is 60 ° C or less, and the drying time is 5 seconds or less. If the conditions are not met, the amount of zinc oxide formed increases.

The steel sheet used in the present embodiment is not particularly limited, and if it is considered to be used for a good press molding, it is preferable to use an extremely low carbon steel sheet excellent in deep extensibility and ductility. For example, a steel sheet in which Ti or Nb is added and a solid solution C is reduced is suitable, and a steel sheet having a high strength by adding P, Mn, Si, B or the like as needed is not problematic in the effect of the present invention. It is inevitable that it contains impurity elements such as Cr, Cu, Ni, and Sn.

In the plated steel sheet according to the embodiment of the present invention, the lubricative film is multiplied by the plating structure in which the surface layer has a specific amount of ruthenium phase, and the range of the blank holder force which can be used as compared with the steel sheet according to the related art can be used. The machine forming range is expanded, and the lubricious film mixture contains components having anti-adhesive functions and components having a sliding lubricating function. Thereby, it is obtained that the lower limit (β) of the blanking force generated by the crack is divided by the lower limit (α) of the blanking force necessary for eliminating the wrinkles, and the value obtained exceeds 1.21, further suitably 1.25, which is particularly suitable. It is 1.27, the most suitable one is the 1.30 steel plate.

Example 1

Next, the present invention will be described by way of non-limiting examples.

(1) Test materials

The composition of the test steel plate is shown in Table 1. A cold rolled material having a thickness of 0.7 mm was used.

(2) Plating conditions

After the test material was degreased, it was heated to 800 ° C in a 4% H ₂ -N ₂ atmosphere for 60 s, and then air-cooled to 470 ° C, and then immersed in a hot-dip galvanizing bath at 460 ° C for 3 s, and the amount of plating was adjusted by wiping. The conditions shown in Table 2 below were heated and alloyed, and then air-cooled to 350 ° C, and then spray-cooled and taken out.

(3) Analysis of plating

The amount of Zn, Fe, and Al in the plating layer was measured by dissolving a plating layer of hydrochloric acid containing 0.6% of an inhibitor added to hexamethylenetetramine manufactured by Kokusai Co., Ltd., and then measuring by ICP emission spectrometry. These totals are used as the total adhesion amount. Such _a ζ phase [delta] relative to the X-ray diffraction intensity ratio of the above formula I the value of the system will use the results obtained from X-ray diffraction using the method of FIG. 1 in relation to the coating phase of ζ phase [delta] ₁ ratio Calculated after deducting the background. The thickness of the ruthenium layer is etched by a nitric acid etching solution (nital, alcohol + nitric acid), and then observed near the interface of the substrate by an optical microscope. The sample system was N=3, and 10 sufficiently separated average fields of view were observed for each sample to measure the thickness, and the average of the whole was taken as the thickness of the Γ phase.

(4) Film treatment conditions

A treatment liquid containing the components shown in Table 2 was used. The plated steel sheet was preheated to a specified temperature and then treated by the following method.

RC: After roller coating, dry (plate temperature 50 ° C)

Dip: After immersion treatment, wash with water and dry (plate temperature 50 ° C)

EC: After electrolytic treatment, wash and dry (plate temperature 50 ° C)

(5) Analysis of the film

After the film was dissolved in a chromic acid aqueous solution, each element was quantitatively analyzed by ICP emission spectrometry. Here, the amount of the inorganic oxyacid salt shown in Table 3 means the total amount of P and B, and the amount of the metal-based oxide means the total amount of Mn, Zn, Al, Ce, and Ti.

The film structure is selected from the flat portion where the unevenness of the plating surface as shown in Fig. 3 is not strong, and is about 3 μm × 3 μm, and is sputtered at a sputtering rate of about 10 nm/min per 0.1 min by Auger electron spectroscopy. Elemental analysis was performed, and depth analysis was performed at a total of about 10 nm on the surface layer. As shown in Fig. 2A and Fig. 2B, P, Mn, and Zn are contained in a mixed state in which no intentional segregation is present, and the case where Zn is present until the surface layer of the film is classified into a class A. On the other hand, as shown in Fig. 5 of Patent Document 5, the P-containing component and the Mn-containing component have peaks at significantly different positions, P is on the surface layer side, Mn has a peak on the inner layer side, and there is no Zn on the surface layer of the film. Classified as Class B.

The Zn system on the outermost layer of the film was obtained by X-ray photoelectron spectroscopy to obtain spectra corresponding to the fourth and fifth images, to investigate whether or not Zn was present up to the outermost layer of the film, and the Zn-based phosphorus-containing oxyacid and zinc in the outermost layer. The compound body (P-Zn) is also a zinc oxide host (ZnO).

(6) Coefficient of friction

The film formed by the film formation treatment was cut out to have a width of 17 mm and a length of 300 mm, and coated with 1 g/m ² of NOX-RUST 550HN (manufactured by Pakasing), and subjected to an elongation test at a tensile speed of 500 mm/min. The load of the press was changed at 200 to 800 kgf (1.96 × 10 ³ to 7.84 × 10 ³ N) to determine the drawing load, and the slope was obtained from the curve with the load of the press as the horizontal axis, and 1/2 times as the coefficient of friction.

(7) Wrinkles and cracks

The sample after the film formation treatment was punched with a hole of 90 mm Φ , and a cylindrical forming test was performed with a hole diameter of 50 mm (4R) and a die diameter of 54 mm (4R). The blank load is changed between 3 and 7 tons (2.94 × 10 ⁴ to 6.93 × 10 ⁴ N), and the lower limit load (α) of the wrinkle elimination and the lower limit load (β) of the crack generation are obtained.

(8) Chemical conversion treatment

The commercially available chemical conversion treatment liquid (SD5000: Nippon Paint) was subjected to degreasing and surface conditioning after the film formation treatment, and then subjected to chemical conversion treatment. It is preferable to form a film uniformly by SEM observation, and it is common to have a region where no film is formed within an area ratio of 10%.

(9) Comparative material

The comparative material system was not subjected to film formation treatment (in Table 3, 32 and 33 in the number column), and Fe-Zn plating (Fe 80%) with 3 g/m ² was added instead of the film formation processor (Table 3). , 34 of the number column).

The performance evaluation results are shown in Table 3. However, in Table 3, the numbered columns 1 to 24 are related to the plated steel sheets of the present invention, and the 25 to 34 series are related to the comparative examples. Further, X-ray diffraction intensity _{with. 1} such a coating on the ζ phase ratio of the δ ₁ phase ratio I ζ phase [delta] is the abscissa, BHF limit of generating cracks (beta]) divided by The numerical values obtained by the lower limit (α) of the necessary blanking force for eliminating wrinkles are plotted on the vertical axis, and the examples and comparative examples of Table 3 are summarized in Fig. 7.

Any of the plated steel sheets according to the present invention has a low friction coefficient and excellent slidability, and is also excellent in chemical conversion treatability. Further, the formable range between the wrinkle generation limit and the crack generation limit is wider as compared with the prior art.

On the other hand, in the comparative examples 25, 26, 27, and 29, since the film structure of the lubricating film was B type, the wrinkle generation limit was high, and the moldable range was narrower than that of the present inventors. Further, in Comparative Examples 28, 30, and 31, the film structure was Class A, but the amount of the film was too large, the chemical conversion treatment property was poor, or the plating structure did not satisfy the X-ray winding of the ζ phase and the δ ₁ phase in the plating layer of the present invention described above. The correlation of the incident intensity ratio I is such that the range of crack generation is low and the formable range is narrower than that of the present invention.

Example 2

Next, a description will be given of a second embodiment in which the plating method is different from that of the above-described first embodiment.

(1) Test materials

The composition of the test steel plate is shown in Table 1. A cold rolled material having a thickness of 0.7 mm was used.

(2) Plating conditions

After degreasing and pickling the test material, pre-plated Ni was electroplated using a Watt bath. Thereafter, the mixture was heated to 470 ° C in a 4% H ₂ -N ₂ atmosphere, and the state was kept immersed in a hot-dip galvanizing bath at 460 ° C for 3 s, and the amount of plating was adjusted by wiping. The conditions shown in Table 4 below were heated and alloyed, and then air-cooled to 450 ° C, and then spray-cooled and taken out.

(3) Analysis of plating

The adhesion amount of Zn, Fe, Al, and Ni in the plating layer was measured by dissolving a plating layer of hydrochloric acid to which 0.6% of hexamethylenetetramine was added, and the ICP emission spectrometry was used. These totals are used as the total adhesion amount. Others were carried out in the same manner as in Example 1.

(4) Film treatment conditions and film analysis

This was carried out in the same manner as in Example 1.

(5) Performance evaluation test

The coefficient of friction, wrinkles, crack generation limit, and chemical conversion treatability were evaluated in the same manner as in Example 1.

The performance evaluation results are shown in Table 4. However, in Table 4, the numbered columns 35 to 50 are related to the plated steel sheets of the present invention, and 51 to 57 are the plated steel sheets of the comparative examples. Further, X-ray diffraction intensity _{with. 1} such a coating on the ζ phase ratio of the δ ₁ phase ratio I ζ phase [delta] is the abscissa, BHF limit of generating cracks (beta]) divided by The numerical values obtained by the lower limit (α) of the necessary blanking force for eliminating wrinkles are plotted on the vertical axis, and the examples and comparative examples of Table 4 are summarized in Fig. 8.

Any of the plated steel sheets according to the present invention has a low friction coefficient and excellent slidability, and is also excellent in chemical conversion treatability. Further, compared with the comparative example (related art), the formable range between the wrinkle generation limit and the crack generation limit is wide. Further, compared with the plated steel sheet of the present invention relating to Table 3 (Example 1), it was found that the moldable range was wide.

Industry availability

In the present invention, the anti-adhesive function and the sliding lubricating functional component are present in the lubricative film in a state in which the fully lubricative film is mixed until the outermost layer, and Zn is present in the outermost layer. On this basis, a certain amount of ζ phase remains in the surface layer of the plating layer. By utilizing the synergistic effect of the lubricating film and the plating layer, the range of press forming of the hot-dip galvanized steel sheet can be expanded. As a result, the yield is improved in the press forming of the steel sheet for automobile body, and it can be produced more efficiently than the related art. In addition, the design freedom of the mold is wide, and a widely designed press forming can be performed, resulting in an increase in the commercial value of the automobile. Therefore, the value of its industrial use is extremely significant.

1. . . Hot-dip galvanized steel sheet

2. . . Steel plate

3. . . Plating

4. . . Amorphous film (lubricating film)

K1. . . Display the background line corresponding to the peak 19 of the δ ₁ phase

K2. . . Display the background line equivalent to the peak 20 of the prime phase

L. . . A line showing the intensity δ ₁ (d = 0127 nm) after subtracting the background from the δ ₁ phase

M. . . Line showing the intensity ζ (d=0126nm) after subtracting the background from the ζ phase

Fig. ₁ is a schematic diagram showing the background subtraction method at the time of obtaining the I value by using the X-ray diffraction intensity I of the ζ phase and the δ ₁ phase in the plating layer from the X-ray diffraction analysis result of the hot-dip galvanized steel sheet.

Fig. 2A is a schematic view showing the results of depth analysis obtained by the Auger electron spectroscopy method for the lubricative film of the plated steel sheet according to the first embodiment of the present invention.

Fig. 2B is a schematic view showing the results of depth analysis obtained by the Auger electron spectroscopy method for the lubricative film of the plated steel sheet according to the second embodiment of the present invention.

Fig. 3 is an SEM image showing a measurement region of the depth analysis of the lubricative film in a white line frame.

Fig. 4 is a spectrum of the 3s energy level of Zn and the 2p energy level of P when the state of the surface layer of the film is analyzed by X-ray photoelectron spectroscopy in the depth direction.

Fig. 5 is a spectrum of 2p energy level of Zn at the time of state analysis of the surface layer of the film by X-ray photoelectron spectroscopy.

Fig. 6 is a schematic view showing the structure of a hot-dip galvanized steel sheet.

Figure 7 is a graph showing the ratio of the ζ phase to the δ ₁ phase in the plating layer. The X-ray diffraction intensity ratio I of the δ ₁ phase is the horizontal axis, and the lower limit (β) of the blanking force generated by the crack is divided by The numerical value obtained by the lower limit (α) of the necessary blanking force for eliminating wrinkles is the vertical axis, and the examples of the examples and comparative examples of Table 3 are summarized.

Figure 8 is a graph showing the ratio of the ζ phase to the δ ₁ phase in the coating. The X-ray diffraction intensity ratio I of the δ ₁ phase is the horizontal axis, and the lower limit (β) of the blanking force generated by the crack is divided by The numerical value obtained by the lower limit (α) of the necessary blanking force for eliminating wrinkles is the vertical axis, and the examples of the examples and comparative examples of Table 4 are summarized.

1. . . Hot-dip galvanized steel sheet

2. . . Steel plate

3. . . Plating

4. . . Amorphous film (lubricating film)

Claims (9)

A hot-dip galvanized steel sheet comprising a steel sheet and a plating layer, the plating layer being attached to the surface of the steel sheet, having Zn as a main component and having an adhesion amount of 20 g/m ² or more and 100 g/m ² or less, characterized in that: The plating layer contains an amorphous film on the surface layer, the amorphous film containing an inorganic oxyacid salt and a metal-based oxide; the plating layer has a ζ phase and a δ ₁ phase; and the plating layer contains 8% by mass or more and 13% by mass or less of Fe. The Zn of the metal oxide is present until the outermost layer of the amorphous film; the X-ray diffraction intensity after the background subtraction of the background spacing of the ζ phase is 0.126 nm divided by the interplanar spacing of the δ ₁ phase The X-ray diffraction intensity after the background is subtracted from 0.127 nm, and the obtained value of the X-ray diffraction intensity ratio I is 0.06 or more and 0.35 or less. The hot-dip galvanized steel sheet according to the first aspect of the invention, wherein the plating layer has a Γ phase having an average thickness of 1.5 μm or less. The hot-dip galvanized steel sheet according to the first aspect of the invention, wherein the plating layer contains 0.10 g/m ² or more and 0.25 g/m ² or less of Al. The hot-dip galvanized steel sheet according to the first aspect of the invention, wherein the plating layer contains Ni which is more than 0 and is 0.40 g/m ² or less. The hot-dip galvanized steel sheet according to the fourth aspect of the invention, wherein the plating layer contains 0.15 g/m ² or more and 0.45 g/m ² or less of Al. The hot-dip galvanized steel sheet according to any one of the items 1 to 5, wherein the inorganic oxyacid salt contains one or more of P or B. The hot-dip galvanized steel sheet according to any one of the first aspect, wherein the metal-based oxide further contains an oxide of one or more of Mn and Al. The hot-dip galvanized steel sheet according to any one of the items 1 to 5, wherein the amount of P and B in the inorganic oxyacid salt is 1 mg/m ² or more and 250 mg/m ² or less; The amount of Mn, Mo, Co, Ni, Ca, V, W, Ti, and Ce among the metal-based oxides is 1 mg/m ² or more and 250 mg/m ² or less in total. The hot-dip galvanized steel sheet according to any one of the first to fifth aspects of the present invention, wherein the Zn based on the amorphous film is formed as a main component of a compound containing phosphorus oxyacid and zinc.