JP2021085087A - Hot-dip metal coated steel sheet - Google Patents

Abstract

To provide a hot-dip metal coated steel sheet capable of intentionally expressing a character, a design and the like on the surface of a plated layer, excellent in those durability and excellent in corrosion resistance.SOLUTION: A hot-dip metal coated steel sheet includes a steel sheet and a hot-dip metal coated layer formed on the surface of the steel plate. The hot-dip metal coated layer including, in the average composition, Al:0-90 mass%, Mg:0-10 mass% and the remainder consisting of Zn and impurities has a pattern part arranged to be a predetermined shape and a non-pattern part; the pattern part and the non-pattern part include one or both of first and second regions, respectively; and the absolute value of a difference between the area ratio of the first region in the pattern part and that in the non-pattern part is 30% or more.SELECTED DRAWING: None

Description

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

The hot-dip galvanized steel sheet has excellent corrosion resistance, and among them, the Zn-Al-Mg-based hot-dip galvanized steel sheet has particularly excellent corrosion resistance. Such hot-dip galvanized steel sheets are widely used in various manufacturing industries such as building materials, home appliances, and automobile fields, and their amounts have been increasing in recent years.

By the way, for the purpose of displaying characters, patterns, design images, etc. on the surface of the hot-dip plating layer of the hot-dip plating steel plate, the hot-dip plating layer is subjected to processes such as printing and painting to produce characters, patterns, design images, etc. It may appear on the surface of the hot-dip plating layer.

However, when a process such as printing or painting is performed on the hot-dip plating layer, there is a problem that the cost and time for applying characters, designs, and the like increase. Furthermore, when characters, designs, etc. are displayed on the surface of the plating layer by printing or painting, not only the metallic luster appearance, which is highly favored by consumers, is lost, but also the coating film itself deteriorates over time and the coating film adheres. Due to the problem of sexual deterioration over time, the durability is inferior, and there is a risk that characters, designs, etc. will disappear over time. Further, when characters, designs, etc. are displayed on the surface of the plating layer by stamping the ink, although the cost and time can be relatively reduced, there is a concern that the ink may reduce the corrosion resistance of the hot-dip plating layer. Further, when the design or the like is revealed by grinding the hot-dip plating layer, the durability of the design or the like is excellent, but the thickness of the hot-dip galvanizing layer at the ground portion is significantly reduced, so that the corrosion resistance is inevitably lowered and the plating characteristics are lowered. Is a concern.

As shown in the following patent documents, various technological developments have been made for Zn-Al-Mg-based hot-dip galvanized steel sheets, but technologies for improving the durability of Zn-Al-Mg-based hot-dip galvanized steel sheets when characters or designs appear on the surface of the plating layer. Is not known.

Regarding the Zn-Al-Mg-based hot-dip galvanized steel sheet, there is a conventional technique for improving the satin-like plating appearance seen in the Zn-Al-Mg-based hot-dip galvanized steel sheet.
For example, Patent Document 1 describes a Zn-Al-Mg-based hot-dip galvanized steel sheet having a satin-like appearance with fine texture and many smooth glossy portions, that is, a large number of white portions per unit area and gloss. A Zn-Al-Mg-based hot-dip galvanized steel sheet having a good satin-like appearance in which the ratio of the area of the portion is large is described. Further, Patent Document 1 describes that an unfavorable satin finish is a state in which an amorphous white portion and a circular glossy portion are mixed to exhibit a surface appearance scattered on the surface. There is.
Further, Patent Document 4 describes a highly corrosion-resistant hot-dip galvanized steel sheet in which the glossiness of the plating layer is increased as a whole and the appearance uniformity is improved by refining the ternary eutectic structure of _{Al / MgZn 2 / Zn.} Are listed.
However, a technique for improving the durability and not lowering the corrosion resistance when characters or the like appear on the surface of the plating layer has not been known conventionally.

Japanese Patent No. 5043234 Japanese Patent No. 5141899 Japanese Patent No. 360804 International Publication No. 2013/002358

The present invention has been made in view of the above circumstances, and provides a hot-dip galvanized steel sheet capable of displaying characters, designs, etc. on the surface of a plating layer, having excellent durability thereof, and also having excellent corrosion resistance. That is the issue.

The gist of the present invention is as follows.
[1] A steel plate and a hot-dip galvanized layer formed on the surface of the steel plate are provided.
The hot-dip plating layer contains Al: 0 to 90% by mass and Mg: 0 to 10% by mass in average composition, and the balance contains Zn and impurities.
A patterned portion and a non-patterned portion arranged so as to have a predetermined shape are formed on the hot-dip plating layer.
The patterned portion and the non-patterned portion include one or both of the first region and the second region defined by the following determination method, respectively.
A galvanized steel sheet characterized in that the difference between the area ratio of the first region in the pattern portion and the area ratio of the first region in the non-pattern portion is 30% or more in absolute value.
[Determination Method] Virtual grid lines are drawn on the surface of the hot-dip plating layer at 1 mm intervals, and then a circle S centered on the center of gravity point G of each region is drawn for each of a plurality of regions partitioned by the virtual grid lines. .. The diameter R of the circle S is set so that the total length of the surface boundary lines of the hot-dip plating layer contained inside the circle S is 10 mm. The average value of the maximum diameter Rmax and the minimum diameter Rmin among the diameters R of the circles S of the plurality of regions is defined as the reference diameter Rave, and the region having the circle S whose diameter R is less than the reference diameter Rave is defined as the first region. The region having a circle S in which R is equal to or larger than the reference diameter Rave is defined as the second region.
[2] The method according to [1], wherein the hot-dip plating layer contains Al: 4 to 22% by mass and Mg: 0 to 10% by mass in an average composition, and the balance contains Zn and impurities. Hot-dip galvanized steel sheet.
[3] The hot-dip galvanized steel sheet according to [1] or [2], wherein the hot-dip galvanized layer further contains Si: 0.0001 to 2% by mass in an average composition.
[4] The hot-dip plating layer further has an average composition of Ni, Ti, Zr, Sr, Fe, Sb, Pb, Sn, Ca, Co, Mn, P, B, Bi, Cr, Sc, Y, REM. The hot-dip galvanized steel sheet according to any one of [1] to [3], which contains 0.001 to 2% by mass of any one or more of Hf and C in total.
[5] The pattern portion is arranged so as to have a shape obtained by any one of a straight portion, a curved portion, a dot portion, a figure, a number, a symbol, a pattern or a character, or a combination of two or more of them. The hot-dip galvanized steel sheet according to any one of [1] to [4].
[6] The hot-dip galvanized steel sheet according to any one of [1] to [5], wherein the pattern portion is intentionally formed.
[7] The hot-dip galvanized steel sheet according to any one of [1] to [6], wherein the amount of adhesion of the hot-dip galvanized layer is 30 to 600 g / m ^{2 in total on both sides of the steel sheet.}

According to the present invention, the surface of the hot-dip plating layer is compared with the first region included in the portion where the density of the boundary line appearing on the surface of the hot-dip plating layer is relatively high and the density of the boundary line appearing on the surface of the hot-dip plating layer. By dividing into the second region included in the target low portion and setting the difference between the area ratio of the first region in the pattern portion and the area ratio of the first region in the non-pattern portion to 30% or more in absolute value, The pattern portion and the non-pattern portion can be discriminated with the naked eye by the difference in the density of the boundary line. As a result, when characters, designs, etc. appear on the surface of the hot-dip galvanized layer, it is possible to provide a hot-dip galvanized steel sheet having excellent durability and corrosion resistance.

FIG. 1 is a schematic view illustrating a method of determining a first region and a second region in the hot-dip galvanized steel sheet of the present embodiment. FIG. 2 is a schematic view illustrating a method of determining a first region and a second region in the hot-dip galvanized steel sheet of the present embodiment. FIG. 3 shows No. 3 of the embodiment. It is a schematic diagram which shows the boundary line obtained by performing the binarization process on the imaging data of the surface of the hot-dip plating layer of 1. FIG. 4 shows No. 4 of the embodiment. 1 is a magnified photograph of the first region of No. 1 by a scanning electron microscope. FIG. 5 shows No. 5 of the embodiment. It is a magnified photograph by a scanning electron microscope of the second region of 1. FIG. 6 is an enlarged plan view showing the surface of a hot-dip galvanized steel sheet which is an example of the present embodiment.

Hereinafter, the hot-dip galvanized steel sheet according to the embodiment of the present invention will be described.
The hot-dip galvanized steel sheet of the present embodiment includes a steel sheet and a hot-dip plating layer formed on the surface of the steel sheet, and the hot-dip plating layer has an average composition of Al: 0 to 90% by mass and Mg: 0 to 10 mass. % Is contained, the balance contains Zn and impurities, and a patterned portion and a non-patterned portion are formed in the hot-dip plating layer so as to have a predetermined shape, and the patterned portion and the non-patterned portion are respectively formed. The difference between the area ratio of the first region in the pattern portion and the area ratio of the second region in the non-pattern portion is absolute, including one or both of the first region and the second region defined by the following determination method. It is a hot-dip galvanized steel sheet having a value of 30% or more.

The determination method is as follows. Virtual grid lines are drawn on the surface of the hot-dip plating layer at 1 mm intervals, and then a circle S centered on the center of gravity point G of each region is drawn for each of a plurality of regions partitioned by the virtual grid lines. The diameter R of the circle S is set so that the total length of the surface boundary lines of the hot-dip plating layer contained inside the circle S is 10 mm. The average value of the maximum diameter Rmax and the minimum diameter Rmin among the diameters R of the circles S of a plurality of regions is defined as the reference diameter Rave, and the region having the circle S whose diameter R is less than the reference diameter Rave is defined as the first region. The region having a circle S in which R is equal to or larger than the reference diameter Rave is defined as the second region.

The boundary line appearing on the hot-dip plating layer can exemplify, for example, the grain boundaries appearing on the plating surface and the boundary between the high-brightness portion and the low-brightness portion of the plating surface.

The region included in the portion with high density of grain boundaries appearing on the plating surface or the region included in the portion with low density of grain boundaries is arranged so as to have a shape like a straight line portion or a character on the plating surface. Then, it is recognized that there are straight lines and characters on the plating surface.

Similarly, the region included in the portion of the plating surface where the boundary density between light and dark is high, or the region included in the portion where the boundary density between light and dark is low on the plating surface is shaped like a straight line or a character on the plating surface. When placed in, it is recognized that there are straight lines and letters on the plating surface.

Therefore, the present inventors have attempted to divide the surface of the hot-dip plating layer into a first region and a second region according to the density of the boundary line appearing on the plating surface.

In the hot-dip galvanized steel sheet of the present embodiment, when virtual grid lines are drawn on the surface of the hot-dip plating layer at 1 mm intervals, a plurality of regions partitioned by the virtual grid lines are melt-plated in the vicinity centered on each compartment region. It is divided into either a first region or a second region according to the density of the surface boundary line of the layer.

The first region is a region included in a portion having a high density of boundary lines appearing on the surface of the hot-dip plating layer. Further, the second region is a region included in a portion where the density of the boundary line appearing on the surface of the hot-dip plating layer is low. Since the density of the boundary line is different between the portion where the first region is gathered and the portion where the second region is gathered in the hot-dip plating layer, the first region and the second region look different.

In order to make characters, figures, lines, dots, etc. visible on the surface of the hot-dip plating layer, the patterned parts constituting these characters and other non-patterned parts should be distinguishable. Just do it. For that purpose, the area ratio of the first region in the pattern portion and the area ratio of the first region in the non-pattern portion may be different.

Specifically, the difference between the area ratio of the first region in the pattern portion and the area ratio of the first region in the non-pattern portion is preferably 30% or more in absolute value. This makes it possible to distinguish between the patterned portion and the non-patterned portion.

For example, when the pattern portion includes a large number of first regions, many boundary lines can be seen in the pattern portion. In this case, the area ratio of the first region in the non-patterned portion is reduced. Since the area ratio of the first region is small in the non-patterned portion, the area ratio of the second region is relatively high, so that the non-patterned portion looks like having few boundary lines. This makes it possible to visually distinguish between a pattern portion in which a large number of boundary lines can be seen and a non-pattern portion in which a small number of boundary lines can be seen.

Further, when the pattern portion includes a large amount of the second region, the pattern portion seems to have few boundary lines. In this case, the area ratio of the second region in the non-patterned portion is reduced, and the area ratio of the first region is increased. Since the non-patterned portion has a large area ratio of the first region, many boundary lines can be seen in the non-patterned portion. This makes it possible to visually distinguish between a pattern portion in which the boundary line appears to be small and a non-pattern portion in which the boundary line appears to be large.

As described above, when the difference between the area ratio of the first region in the patterned portion and the area ratio of the first region in the non-patterned portion is 30% or more in absolute value, the appearance of the patterned portion and the non-patterned portion becomes different. Therefore, the pattern portion can be clearly identified. That is, in the visible light image on the surface of the plating layer, the difference in hue, lightness, saturation, etc. between the patterned portion and the non-patterned portion becomes large, so that the patterned portion and the non-patterned portion can be distinguished.

On the other hand, when the difference between the area ratio of the first region in the pattern portion and the area ratio of the first region in the non-patterned portion is less than 30% in absolute value, the difference in appearance between the patterned portion and the non-patterned portion disappears, and the pattern portion Can no longer be clearly identified. That is, in the visible light image on the surface of the plating layer, the difference in hue, lightness, saturation, etc. between the patterned portion and the non-patterned portion becomes small, so that the patterned portion and the non-patterned portion cannot be distinguished.

As described above, an example of the existence ratio of the first region in the patterned portion and the non-patterned portion is shown, but the difference between the area ratio of the first region in the patterned portion and the area ratio of the first region in the non-patterned portion is absolute. If the value is 30% or more, it is not necessary to limit the abundance ratio of the first region in each of the patterned portion and the non-patterned portion.

Hereinafter, embodiments of the present invention will be described with respect to the hot-dip galvanized steel sheet.

The material of the steel sheet used as the base of the hot-dip plating layer is not particularly limited. Although the details will be described later, general steel or the like can be used as the material without particular limitation, Al killed steel or some high alloy steel can also be applied, and the shape is not particularly limited. By applying the hot-dip plating method described later to the steel sheet, the hot-dip plating layer according to the present embodiment is formed.

Next, the chemical composition of the hot-dip galvanized layer will be described.
The hot-dip plating layer contains Al: 0 to 90% by mass and Mg: 0 to 10% by mass in average composition, and contains Zn and impurities as the balance. More preferably, the average composition contains Al: 4 to 22% by mass, Mg: 1 to 10% by mass, and Zn and impurities as the balance. More preferably, the average composition contains Al: 4 to 22% by mass and Mg: 1 to 10% by mass, and the balance is Zn and impurities. Further, the hot-dip plating layer may contain Si: 0.0001 to 2% by mass in an average composition. Further, the melt-plated layer has an average composition of Ni, Ti, Zr, Sr, Fe, Sb, Pb, Sn, Ca, Co, Mn, P, B, Bi, Cr, Sc, Y, REM, Hf, C. A total of 0.001 to 2% by mass of any one or more of the above may be contained.

The Al content is in the range of 0 to 90% by mass, preferably 4 to 22% by mass in average composition. Al may be contained in order to ensure corrosion resistance. When the Al content in the hot-dip plating layer is 4% by mass or more, the effect of improving the corrosion resistance is further enhanced. If it is 90% or less, the plating layer can be stably formed. If it exceeds 22% by mass, the effect of improving corrosion resistance is saturated. From the viewpoint of corrosion resistance, it is preferably 5 to 18% by mass. More preferably, it is 6 to 16% by mass.

The content of Mg is in the range of 0 to 10% by mass, preferably 1 to 10% by mass in average composition. Mg is preferably contained in order to improve the corrosion resistance. When the Mg content in the hot-dip plating layer is 1% by mass or more, the effect of improving the corrosion resistance is further enhanced. If it exceeds 10% by mass, dross is significantly generated in the plating bath, and it becomes difficult to stably produce a hot-dip galvanized steel sheet. From the viewpoint of the balance between corrosion resistance and dross generation, it is preferably 1.5 to 6% by mass. More preferably, it is in the range of 2 to 5% by mass.

Al and Mg may be 0%, respectively. That is, the hot-dip galvanizing layer of the hot-dip galvanized steel sheet of the present embodiment is not limited to the Zn-Al-Mg-based hot-dip galvanizing layer, and may be a Zn-Al-based hot-dip galvanizing layer. It may be an alloyed hot-dip galvanized layer.

Further, the hot-dip plating layer may contain Si in the range of 0.0001 to 2% by mass.
Si may be contained because it may improve the adhesion of the hot-dip galvanized layer. Since the effect of improving the adhesion is exhibited by containing 0.0001% by mass or more of Si, it is preferable to contain 0.0001% by mass or more of Si. On the other hand, even if the content exceeds 2% by mass, the effect of improving the plating adhesion is saturated, so the Si content is set to 2% by mass or less. From the viewpoint of plating adhesion, the range may be 0.0010 to 1% by mass, or 0.0100 to 0.8% by mass.

In the hot-dip plating layer, the average composition is Ni, Ti, Zr, Sr, Fe, Sb, Pb, Sn, Ca, Co, Mn, P, B, Bi, Cr, Sc, Y, REM, Hf, C. 1 type or 2 or more types of the above may be contained in a total amount of 0.001 to 2% by mass. By containing these elements, the corrosion resistance can be further improved. REM is one or more rare earth elements having atomic numbers 57 to 71 in the periodic table.

The rest of the chemical composition of the hot-dip plating layer is zinc and impurities. Impurities include those that are inevitably contained in zinc and other bullions, and those that are contained by melting steel in a plating bath.

The average composition of the hot-dip plating layer can be measured by the following method. First, the surface coating is removed with a coating remover that does not erode the plating (for example, Neo River SP-751 manufactured by Sansai Kako), and then a hot-dip plating layer is used with hydrochloric acid containing an inhibitor (for example, Hiviron manufactured by Sugimura Chemical Industrial). Can be determined by dissolving the solution and subjecting the obtained solution to inductively coupled plasma (ICP) emission spectroscopic analysis. Further, when the surface layer coating film is not provided, the work of removing the surface layer coating film can be omitted.

Next, the structure of the hot-dip plating layer will be described. The structure described below is a structure when the hot-dip plating layer has an average composition and contains Al: 4 to 22% by mass, Mg: 1 to 10% by mass, and Si in 0 to 2% by mass.

The hot-dip galvanizing layer containing Al, Mg and Zn contains [Al phase] and [ternary eutectic structure of _{Al / Zn / MgZn 2].} It has a form in which [Al phase] is included in the substrate of [Al / Zn / MgZn _{2 ternary eutectic structure]. Further, [MgZn 2} phase] and [Zn phase] may be contained in the base material of [Al / Zn / MgZn _{2 ternary eutectic structure].} Further, when Si is added _{, [Mg 2} Si phase] may be contained in the base material of _{[Al / Zn / MgZn 2 ternary eutectic structure].}

Here, the [ternary eutectic structure of Al / Zn / MgZn ₂ ] is a ternary eutectic structure of the Al phase, the Zn phase and the metal compound MgZn ₂ phase, and this ternary eutectic structure is defined. The Al phase formed corresponds to, for example, the "Al" phase at high temperature in the ternary equilibrium diagram of Al-Zn-Mg (an Al solid solution that dissolves Zn and contains a small amount of Mg). Is. The Al ″ phase at high temperature usually appears as a fine Al phase and a fine Zn phase at room temperature. Further, the Zn phase in the ternary eutectic structure dissolves a small amount of Al as a solid solution, and in some cases, Is a Zn solid solution in which a smaller amount of Mg is dissolved. The MgZn _two phase in the ternary eutectic structure is a metal existing in the vicinity of Zn: about 84% by mass in the binary system equilibrium state diagram of Zn—Mg. It is an intercompound phase. As far as the state diagram is concerned, it is considered that other additive elements are not dissolved in each phase, or even if they are dissolved, the amount is very small, but the amount is clear by ordinary analysis. In this specification, the ternary eutectic structure consisting of these three phases is referred to as [Al / Zn / MgZn ₂ ternary eutectic structure].

The [Al phase] is a phase that looks like an island with a clear boundary in the base of the ternary eutectic structure, for example, at a high temperature in the ternary equilibrium state diagram of Al-Zn-Mg. It corresponds to the "Al" phase "(Al solid solution that dissolves Zn in a solid solution and contains a small amount of Mg). The amount of Zn and Mg that dissolve in the Al "phase at high temperature differs depending on the concentration of Al and Mg in the plating bath. The Al" phase at this high temperature is usually fine Al phase and fine Zn at room temperature. Although separated into phases, the island-like shape seen at room temperature can be seen as retaining the skeleton of the Al ″ phase at high temperature. As far as the state diagram is concerned, other additive elements are dissolved in this phase. It is considered that the amount is very small even if it is not plated or is dissolved in solid solution, but it cannot be clearly distinguished by ordinary analysis. The retained phase is referred to as [Al phase] in the present specification. This [Al phase] can be clearly distinguished from the Al phase forming the ternary eutectic structure by microscopic observation.

The [Zn phase] is a phase that looks like an island with a clear boundary in the substrate of the ternary eutectic structure, and actually contains a small amount of Al and a small amount of Mg in a solid solution. There is also. As far as the phase diagram is concerned, it is considered that other additive elements are not solid-solved in this phase, or even if they are solid-solved, the amount is extremely small. This [Zn phase] can be clearly distinguished from the Zn phase forming the ternary eutectic structure by microscopic observation. The plating layer of the present invention may contain [Zn phase] depending on the manufacturing conditions, but since the experiment showed almost no effect on the improvement of corrosion resistance of the processed portion, the plating layer contained [Zn phase]. There is no particular problem.

Further, the [MgZn _2- phase] is a phase that looks like an island with a clear boundary in the base material of the ternary eutectic structure, and in reality, a small amount of Al may be dissolved as a solid solution. As far as the phase diagram is concerned, it is considered that other additive elements are not solid-solved in this phase, or even if they are solid-solved, the amount is extremely small. This [MgZn ₂ phase] can be clearly distinguished from the _{MgZn 2} phase forming the ternary eutectic structure by microscopic observation. The plating layer of the present invention _{may not contain [MgZn 2-} phase] depending on the production conditions, but it is contained in the plating layer under most production conditions.

Further, the [Mg ₂ Si phase] is a phase that looks like an island with a clear boundary in the solidified structure of the plating layer when Si is added. As far as the phase diagram is concerned, it is considered that Zn, Al and other additive elements are not solid-solved, or even if they are solid-solved, they are in a very small amount. This [Mg ₂ Si phase] can be clearly distinguished by microscopic observation during plating.

Next, the patterned portion, the non-patterned portion, the first region and the second region on the surface layer of the hot-dip plating layer will be described.

On the surface layer of the hot-dip plating layer of the present embodiment, a patterned portion and a non-patterned portion arranged so as to have a predetermined shape are formed. The pattern portion is preferably arranged so as to have a shape obtained by any one of a straight line portion, a curved portion, a dot portion, a figure, a number, a symbol, a pattern or a character, or a combination of two or more of these. .. The non-patterned portion is an area other than the patterned portion. Further, the shape of the pattern portion is acceptable as long as it can be recognized as a whole even if a part of the pattern portion is missing such as missing dots. Further, the non-patterned portion may have a shape that borders the boundary of the patterned portion.

When any one of straight lines, curved lines, dots, figures, numbers, symbols, patterns or letters, or a combination of two or more of them is arranged on the surface of the hot-dip plating layer, these Area can be a pattern part, and the other area can be a non-pattern part. The boundary between the patterned portion and the non-patterned portion can be grasped with the naked eye. The boundary between the patterned portion and the non-patterned portion may be grasped from a magnified image obtained by an optical microscope or a magnifying glass.

The pattern portion may be formed in a size that allows the presence of the pattern portion to be discriminated with the naked eye, under a magnifying glass, or under a microscope. Further, the non-patterned portion is a region that occupies most of the hot-dip plating layer (the surface of the hot-dip plating layer), and the patterned portion may be arranged in the non-patterned portion. The pattern portion is arranged in a predetermined shape in the non-pattern portion. Specifically, in the non-patterned part, the pattern part is a straight line part, a curved part, a figure, a dot part, a figure, a number, a symbol, a pattern or a character, or a combination of two or more of them. It is arranged so as to have a curved shape. By adjusting the shape of the pattern part, one of straight lines, curved lines, figures, dots, figures, numbers, symbols, patterns or letters, or two or more of them, can be placed on the surface of the hot-dip plating layer. The combined shape of is shown. For example, on the surface of the hot-dip plating layer, a character string composed of a pattern portion, a numerical string, a symbol, a mark, a line diagram, a design drawing, a combination thereof, or the like appears. This shape is a shape intentionally or artificially formed by a manufacturing method described later, and is not naturally formed.

As described above, the patterned portion and the non-patterned portion are regions formed on the surface of the hot-dip plating layer. The patterned portion and the non-patterned portion include one or two of the first region or the second region, respectively.

The first region is a region included in a portion having a high density of boundary lines appearing on the surface of the hot-dip plating layer. Further, the second region is a region included in a portion where the density of the boundary line appearing on the surface of the hot-dip plating layer is low. In the hot-dip plating layer, the place where the first region is gathered and the place where the second region is gathered are identifiable because the density of the boundary line is different.

Next, a method of determining the first region and the second region will be described with reference to FIG.
As shown in FIG. 1, virtual grid lines K are drawn on the surface of the hot-dip plating layer at 1 mm intervals. In FIG. 1, the virtual grid line is shown by a long-dotted chain line. Note that FIG. 1 does not show the boundary line where the hot-dip galvanized layer appears. Next, a plurality of regions M partitioned by the virtual grid line K are set. The shape of each region M is a square with a side of 1 mm. The area set here becomes either the first area or the second area. Next, the center of gravity point G of each region is set for each of the plurality of regions M partitioned by the virtual grid line K. Next, a circle S centered on the center of gravity point G is drawn. The diameter R of the circle S is set so that the total length of the surface boundary lines of the hot-dip plating layer contained inside the circle S is 10 mm.

2 (a) and 2 (b) show a circle S corresponding to an arbitrary region M. 2 (a) and 2 (b) show the boundary line appearing on the surface of the hot-dip galvanized layer. The boundary lines shown in FIGS. 2 (a) and 2 (b) have a total length of 10 mm. In the present embodiment, the diameter of the circle S is adjusted so that the total length of the boundary line L included in the circle S is 10 mm. Therefore, as shown in FIG. 2A, when a large number of boundary lines L exist in the region M and its vicinity, the diameter R of the circle S becomes relatively small. On the other hand, as shown in FIG. 2B, when the boundary line L is relatively small in the region M and its vicinity, the diameter R of the circle S is relatively large. Circles S are drawn for all regions and the diameter R of each circle S is determined.

Then, the average value of the maximum diameter Rmax and the minimum diameter Rmin among the circles S of the plurality of regions M is set as the reference diameter Rave, and the region having the circle S whose diameter R is less than the reference diameter Rave is set as the first region. The region having a circle S in which R is equal to or larger than the reference diameter Rave is defined as the second region. The first region is a region included in a portion where a large number of boundary lines L are present as shown in FIG. 2 (a), while the second region has a boundary line L as shown in FIG. 2 (b). It is an area included in the part that exists less.

The boundary line appearing on the hot-dip plating layer can exemplify, for example, the grain boundaries appearing on the plating surface and the boundary between the high-brightness portion and the low-brightness portion of the plating surface. The boundary between the high-brightness portion and the low-brightness portion may be a boundary line obtained by binarizing the imaging of the plating surface.

The pattern portion includes a plurality of regions partitioned by virtual grid lines, and each region is classified into either a first region or a second region. Further, the non-patterned portion also includes a plurality of regions partitioned by virtual grid lines, and each region is classified into either a first region or a second region. That is, the pattern portion may include only either the first region or the second region, or may include both the first region and the second region. Similarly, the non-patterned portion may include only either the first region or the second region, or may include both the first region and the second region.

Here, in the pattern portion, the surface integral of each of the first region and the second region can be obtained. Then, when the surface integral of the first region becomes high, the pattern portion includes a relatively large number of boundary lines. On the other hand, when the surface integral of the second region in the pattern portion becomes high, the pattern portion includes a relatively small number of boundary lines. As described above, the appearance of the pattern portion depends on the area ratio of the first region and the second region.

On the other hand, even in the non-patterned portion, the surface integral of each of the first region and the second region can be obtained. Similar to the patterned portion, the appearance of the non-patterned portion depends on the surface integral of the first region and the second region.

Then, when the difference between the area ratio of the first region in the pattern portion and the area ratio of the first region in the non-patterned portion is 30% or more in absolute value, the pattern portion and the non-pattern portion can be distinguished. Become. When the difference in the area ratio is less than 30%, the difference between the area ratio of the first region in the pattern portion and the area ratio of the first region in the non-patterned portion is small, and the appearances of the patterned portion and the non-patterned portion are similar. It becomes an appearance and it becomes difficult to identify the pattern part. The larger the difference in area ratio, the better, more preferably 40% or more, and even more preferably 60% or more.

The patterned portion and the non-patterned portion may be distinguishable with the naked eye, and may be distinguishable under a magnifying glass or a microscope. Distinguishable under a magnifying glass or a microscope means that, for example, the shape composed of the pattern portion can be identified in a field of view of 50 times or less. If the field of view is 50 times or less, the patterned portion and the non-patterned portion can be identified by the difference in appearance. The patterned portion and the non-patterned portion can be distinguished by preferably 20 times or less, more preferably 10 times or less, and more preferably 5 times or less.

The hot-dip galvanized steel sheet according to the present embodiment may have a chemical conversion treatment film layer or a coating film layer on the surface of the hot-dip plating layer. Here, the type of the chemical conversion-treated film layer or the coating film layer is not particularly limited, and a known chemical conversion-treated film layer or coating film layer can be used.

Next, a method for manufacturing the hot-dip galvanized steel sheet of the present embodiment will be described.
In the hot-dip galvanized steel sheet of the present embodiment, hot-dip plating is performed on a steel sheet manufactured through steelmaking, casting, and hot rolling. When producing a steel sheet, pickling, hot-rolled sheet annealing, cold rolling, and cold-rolled sheet annealing may be further performed. The hot-dip galvanizing method may be a continuous hot-dip galvanizing method in which a steel sheet is continuously passed through a hot-dip galvanizing bath. But it may be.

The hot-dip plating bath preferably contains Al: 0 to 90% by mass and Mg: 0 to 10% by mass, and contains Zn and impurities as the balance. Further, the hot-dip plating bath may contain Al: 4 to 22% by mass and Mg: 1 to 10% by mass, and the balance may contain Zn and impurities. Further, the hot-dip plating bath may contain Si: 0.0001 to 2% by mass. Furthermore, the hot-dip plating bath is any one of Ni, Ti, Zr, Sr, Fe, Sb, Pb, Sn, Ca, Co, Mn, P, B, Bi, Cr, Sc, Y, REM, Hf, and C. One type or two or more types may be contained in a total amount of 0.001 to 2% by mass. The average composition of the hot-dip galvanized layer of the present embodiment is almost the same as the composition of the hot-dip galvanized bath.

The temperature of the hot-dip plating bath varies depending on the composition, but is preferably in the range of 400 to 500 ° C., for example. This is because if the temperature of the hot-dip plating bath is within this range, a desired hot-dip plating layer can be formed.
Further, the amount of adhesion of the hot-dip galvanized layer may be adjusted by means such as gas wiping with respect to the steel sheet pulled up from the hot-dip galvanized bath. The amount of adhesion of the hot-dip plating layer is preferably adjusted so that the total amount of adhesion on both sides of the steel sheet is in ^{the range of 30 to 600 g / m 2.} If the adhesion amount is ^{less than 30 g / m 2} , the corrosion resistance of the hot-dip galvanized steel sheet is lowered, which is not preferable. If the amount of adhesion exceeds 600 g / m ^2, the molten metal adhering to the steel sheet will hang down and the surface of the hot-dip plating layer cannot be smoothed, which is not preferable.

A non-oxidizing gas having a temperature equal to or higher than the final solidification temperature of plating is locally sprayed onto the molten metal by a gas nozzle on the steel sheet or steel material immediately after being pulled up from the hot-dip plating bath. Nitrogen or argon may be used as the non-oxidizing gas. Although the optimum temperature range differs depending on the composition, it is preferable to spray the non-oxidizing gas when the temperature of the molten metal is in the range of (final solidification temperature -5) ° C to (final solidification temperature + 5) ° C. .. Further, the temperature of the non-oxidizing gas is preferably equal to or higher than the final solidification temperature. For example, in a plating composition of Al: 11% and Mg: 3%, it is preferable to spray a non-oxidizing gas having a gas temperature equal to or higher than the final solidification temperature when the temperature of the molten metal is 330 to 340 ° C. In the vicinity where the non-oxidizing gas is blown, the cooling rate of the molten metal is reduced, which results in coarse boundaries or grain boundaries appearing on the surface. Therefore, by adjusting the spray amount and range of the non-oxidizing gas, the size of the boundary or grain boundary appearing on the surface can be arbitrarily adjusted. As a result, the shapes of the patterned portion and the non-patterned portion can be arbitrarily adjusted, and the patterned portion and the non-patterned portion can be discriminated with the naked eye.

When a chemical conversion treatment layer is formed on the surface of the hot-dip plating layer, the hot-dip galvanized steel sheet after the hot-dip plating layer is formed is subjected to chemical conversion treatment. The type of chemical conversion treatment is not particularly limited, and a known chemical conversion treatment can be used.
When a coating film layer is formed on the surface of the hot-dip plating layer or the surface of the chemical conversion treatment layer, the hot-dip galvanized steel sheet after the hot-dip plating layer is formed or the chemical conversion treatment layer is formed is coated. Perform processing. The type of coating treatment is not particularly limited, and a known coating treatment can be used.

In the hot-dip galvanized steel sheet of the present embodiment, the surface of the hot-dip plating layer is composed of a first region existing in a portion where the density of the boundary line appearing on the surface of the hot-dip plating layer is relatively high and a boundary line appearing on the surface of the hot-dip plating layer. By dividing it into a second region existing in a portion having a relatively low density and setting the difference between the area ratio of the first region in the pattern portion and the area ratio of the first region in the non-pattern portion to 30% or more. The patterned part and the non-patterned part can be distinguished. The formed patterned portion and non-patterned portion are not formed by printing or painting, and therefore have high durability. Further, since the patterned portion and the non-patterned portion are not formed by printing or painting, there is no influence on the corrosion resistance of the hot-dip galvanized layer. Further, the patterned portion and the non-patterned portion are not formed by grinding or the like on the surface of the hot-dip galvanized layer. Therefore, there is no difference between the thickness of the hot-dip plating layer in the patterned portion and the thickness of the hot-dip plating layer in the non-patterned portion. Therefore, the hot-dip galvanized steel sheet of the present embodiment has excellent corrosion resistance.

According to the present embodiment, it is possible to provide a hot-dip galvanized steel sheet having high durability and suitable plating characteristics such as corrosion resistance of a pattern portion formed into a predetermined shape. In particular, in the present embodiment, when the temperature of the molten metal after being pulled up from the plating bath is in the range of (final solidification temperature −5) ° C. to (final solidification temperature + 5) ° C., a non-oxidizing gas is applied to the surface of the molten plating layer. By locally spraying with a gas nozzle, the size of the boundary or crystal grain boundary appearing on the surface of the melt-plated layer after solidification can be arbitrarily adjusted to intentionally or artificially adjust the range of the patterned or non-patterned portion. The pattern part can be made into a shape, and the pattern part is arranged so as to have a shape in which any one of a straight part, a curved part, a dot part, a figure, a number, a symbol, a pattern or a character, or two or more kinds of these are combined. it can. As a result, various designs, trademarks, and other identification marks can be displayed on the surface of the hot-dip plating layer without printing, painting, or grinding, and the distinctiveness and design of the source of the steel sheet can be improved. .. Further, the pattern unit can add information necessary for process control, inventory control, etc., and arbitrary information required by the consumer to the hot-dip galvanized steel sheet. This can also contribute to the improvement of the productivity of the hot-dip galvanized steel sheet.

Next, examples of the present invention will be described. After degreasing and washing the steel sheet with water, reduction annealing, plating bath immersion, adhesion amount control, and cooling were performed to obtain the No. 1 shown in Table 2. The Zn-Al-Mg-based hot-dip galvanized steel sheets of 1-32 were manufactured. When the temperature of the molten metal is in the range of (final solidification temperature -5) ° C to (final solidification temperature +5) ° C when the steel plate is pulled up from the plating bath, the molten metal on the surface of the steel plate is exposed to non-oxidizing gas. A kind of nitrogen gas was sprayed from a gas nozzle in a heated state. The conditions for spraying nitrogen gas were as shown in Table 1. The gas temperatures shown in Table 1 were all equal to or higher than the final solidification temperature. After that, it was cooled to completely solidify the molten metal. By spraying nitrogen gas, it was controlled so that a square pattern having a side of 50 mm appeared. However, No. For No. 30, nitrogen gas was blown by the gas nozzle when the temperature of the molten metal was higher than the range of (final solidification temperature −5) ° C. to (final solidification temperature + 5) ° C.

Further, a Zn-Al-Mg-based hot-dip galvanized steel sheet was produced in the same manner as described above. Then, a square pattern having a side of 50 mm was printed on the surface of the hot-dip galvanized layer by an inkjet method. This result is referred to as No. It is shown in Table 2 as 33.

Further, a Zn-Al-Mg-based hot-dip galvanized steel sheet was produced in the same manner as described above. Then, the surface of the hot-dip galvanized layer was ground to form a square pattern having a side of 50 mm. This result is referred to as No. It is shown in Table 2 as 34.

With respect to the obtained galvanized steel sheet, the area ratios of the first region and the second region included in the patterned portion and the non-patterned portion were determined. First, the boundary between the patterned portion and the non-patterned portion was identified by visually observing the surface of the hot-dip galvanized layer. When it was difficult to identify the boundary with the naked eye, a magnified image of a magnifying glass or an optical microscope was used. In the case where it is difficult to determine the boundary, the boundary was set based on the blowing range of nitrogen gas, and the area ratios of the first region and the second region were evaluated.

Next, the area ratio of each region included in the square pattern (denoted as the pattern portion in Table 2) and the other regions (denoted as the non-pattern portion in Table 2) was determined by the following determination method.
As shown in FIG. 1, virtual grid lines K were drawn on the surface of the hot-dip plating layer at 1 mm intervals. Note that FIG. 1 does not show the boundary line where the hot-dip galvanized layer appears. Next, a plurality of regions M partitioned by the virtual grid line K were set. The shape of each region M was a square with a side of 1 mm. Next, the center of gravity point G of each region was set for each of the plurality of regions M partitioned by the virtual grid line K. Next, a circle S centered on the center of gravity point G was drawn. The diameter R of the circle S was adjusted so that the total length of the boundary lines appearing on the surface of the hot-dip plating layer was 10 mm.

Then, the average value of the maximum diameter Rmax and the minimum diameter Rmin among the circles S of the plurality of regions M is set as the reference diameter Rave, and the region having the circle S whose diameter R is less than the reference diameter Rave is set as the first region. The region having a circle S in which R is equal to or larger than the reference diameter Rave was defined as the second region.

The boundary line appearing on the hot-dip plating layer was defined as the boundary between the high-brightness portion and the low-brightness portion of the plating surface. This boundary was defined as the boundary line obtained by binarizing the brightness value in the imaging data of the plating surface. FIG. 3 shows an example of the boundary line after the binarization treatment on the surface of the hot-dip plating layer.

Then, the area ratios of the first region and the second region in the square pattern and the other portions were obtained, respectively, and the absolute value of the difference in the area ratios of the first region was obtained.

[Identity]
The test plates provided with the square pattern portion, which were in the initial state immediately after production and in the aged state where they were exposed outdoors for 6 months, were visually evaluated based on the following criteria. In both the initial state and the time-lapse state, ◎ to △ were accepted.

⊚: The pattern part can be visually recognized even from 5 m away.
◯: The pattern portion cannot be visually recognized from 5 m ahead, but the visibility is high from 3 m ahead.
Δ: The pattern portion cannot be visually recognized from 3 m ahead, but the visibility is high from 1 m ahead.
X: The pattern part cannot be visually recognized from 1 m ahead.

[Corrosion resistance]
The test plate was cut to a size of 150 × 70 mm, and a corrosion acceleration test CCT conforming to JASO-M609 was tested for 30 cycles, and then the rust generation state was investigated and evaluated based on the following criteria. ◎ ~ △ were accepted.

⊚: No rust is generated, and both the patterned part and the non-patterned part maintain a beautiful design appearance.
◯: No rust was generated, but a slight change in the design appearance was observed in the patterned part and the non-patterned part.
Δ: The appearance of the design is slightly impaired, but the patterned portion and the non-patterned portion can be visually distinguished.
X: The appearance quality of the patterned portion and the non-patterned portion is significantly deteriorated and cannot be visually distinguished.

As shown in Table 2, No. 1-No. The Zn-Al-Mg-based hot-dip galvanized steel sheet of the 29th example of the present invention was excellent in both discriminative property and corrosion resistance. In FIG. 4, No. The observation result of the pattern part of No. 1 by the scanning electron microscope is shown, and FIG. The observation result by the scanning electron microscope of the non-pattern part of 1 is shown. It can be seen that the area ratio of the first region of the patterned portion is significantly different from that of the non-patterned portion, and the patterned portion and the non-patterned portion can be distinguished from each other.

No. Regarding 30, when the temperature of the molten metal was higher than the range of (final solidification temperature -5) ° C. to (final solidification temperature +5) ° C., nitrogen gas was blown by the gas nozzle, so that the first region in the pattern portion. The difference between the area ratio of the non-patterned portion and the area ratio of the first region in the non-patterned portion was less than 30%, and the distinctiveness of the patterned portion was lowered.
In addition, No. 31 and No. In No. 32, the composition of the hot-dip plating layer was out of the scope of the present invention, and the distinctiveness after outdoor exposure for 6 months was deteriorated.

On the other hand, No. 1 in which a square pattern portion was printed by an inkjet method. In No. 33, the pattern portion was thinned by outdoor exposure for 6 months, and the design was deteriorated.
In addition, No. 1 in which a grid-like pattern was formed by grinding. In No. 34, the thickness of the plating layer at the ground portion was reduced, and the corrosion resistance at the ground portion was reduced.
In addition, No. The plating layers 1 to 6 and 10 to 34 contained an Al phase and a ternary eutectic structure of _{Al / Zn / MgZn 2.}

FIG. 6 shows the surface of a hot-dip galvanized steel sheet in which a character string (alphabet) is represented by a pattern portion.
According to the present invention, a pattern portion composed of characters and marks can be arbitrarily represented on the surface of a hot-dip galvanized steel sheet.

Claims (7)

A steel plate and a hot-dip galvanized layer formed on the surface of the steel plate are provided.
The hot-dip plating layer contains Al: 0 to 90% by mass and Mg: 0 to 10% by mass in average composition, and the balance contains Zn and impurities.
A patterned portion and a non-patterned portion arranged so as to have a predetermined shape are formed on the hot-dip plating layer.
The patterned portion and the non-patterned portion include one or both of the first region and the second region defined by the following determination method, respectively.
A galvanized steel sheet characterized in that the difference between the area ratio of the first region in the pattern portion and the area ratio of the first region in the non-pattern portion is 30% or more in absolute value.
[Determination Method] Virtual grid lines are drawn on the surface of the hot-dip plating layer at 1 mm intervals, and then a circle S centered on the center of gravity point G of each region is drawn for each of a plurality of regions partitioned by the virtual grid lines. .. The diameter R of the circle S is set so that the total length of the surface boundary lines of the hot-dip plating layer contained inside the circle S is 10 mm. The average value of the maximum diameter Rmax and the minimum diameter Rmin among the diameters R of the circles S of the plurality of regions is defined as the reference diameter Rave, and the region having the circle S whose diameter R is less than the reference diameter Rave is defined as the first region. The region having a circle S in which R is equal to or larger than the reference diameter Rave is defined as the second region. The hot-dip galvanized steel sheet according to claim 1, wherein the hot-dip galvanized layer contains Al: 4 to 22% by mass and Mg: 0 to 10% by mass in an average composition, and the balance contains Zn and impurities. .. The hot-dip galvanized steel sheet according to claim 1 or 2, wherein the hot-dip galvanized layer further contains Si: 0.0001 to 2% by mass in an average composition. The hot-dip plating layer further has an average composition of Ni, Ti, Zr, Sr, Fe, Sb, Pb, Sn, Ca, Co, Mn, P, B, Bi, Cr, Sc, Y, REM, Hf, The hot-dip galvanized steel sheet according to any one of claims 1 to 3, wherein the hot-dip galvanized steel sheet contains any one or more of C in a total amount of 0.001 to 2% by mass. The pattern portion is arranged so as to have a shape obtained by any one of a straight line portion, a curved portion, a dot portion, a figure, a number, a symbol, a pattern or a character, or a combination of two or more of them. The hot-dip galvanized steel sheet according to any one of claims 1 to 4, which is characteristic. The hot-dip galvanized steel sheet according to any one of claims 1 to 5, wherein the pattern portion is intentionally formed. The hot-dip galvanized steel sheet according to any one of claims 1 to 6, wherein the amount of adhesion of the hot-dip galvanized layer is 30 to 600 g / m ^{2 in total on both sides of the steel sheet.}

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