JP7339531B2 - Hot dip plated steel sheet - Google Patents

Description

The present invention relates to a hot dip plated steel sheet.

Hot-dip plated steel sheets are excellent in corrosion resistance, and among them, Zn-Al-Mg-based hot-dip plated steel sheets are particularly excellent in corrosion resistance. Such hot-dip plated steel sheets are widely used in various manufacturing industries such as building materials, home electric appliances, and automobile fields, and the amount of use thereof is increasing in recent years.

By the way, for the purpose of showing letters, patterns, design drawings, etc. on the surface of the hot-dip plated steel sheet, letters, patterns, designs, etc. It may appear on the surface of the hot-dip plating layer.

However, when a process such as printing or coating is performed on the hot-dip plated layer, there is a problem that the cost and time required for applying characters, designs, etc. are increased. Furthermore, when printing or painting characters or designs on the surface of the plating layer, not only does the metallic luster appearance that is highly popular with consumers be lost, but the coating itself deteriorates over time and the adhesion of the coating film deteriorates. Due to the problem of deterioration over time, the durability is poor, and characters and designs may disappear over time. In the case of stamping ink to reveal characters, designs, etc. on the surface of the plated layer, the cost and time can be relatively reduced, but there is a concern that the ink may reduce the corrosion resistance of the hot-dip plated layer. Furthermore, when the design, etc. is revealed by grinding the hot-dip plating layer, the durability of the design, etc. is excellent, but the thickness of the hot-dip plating layer at the grinding point is greatly reduced, which inevitably reduces the corrosion resistance, resulting in the deterioration of the plating properties. is concerned.

As shown in the following patent documents, various technical developments have been made for Zn-Al-Mg hot-dip plated steel sheets. Techniques for improving the durability of letters, designs, etc. on the surface of the plating layer. is not known.

Regarding Zn--Al--Mg hot-dip plated steel sheets, there are prior arts aimed at making the satin-like coating appearance seen in Zn--Al--Mg hot-dip plated steel sheets more beautiful.
For example, Patent Document 1 discloses a Zn-Al-Mg hot dip plated steel sheet having a fine texture and a satin-like appearance with many smooth glossy parts, that is, a large number of white parts per unit area, and a glossy A Zn-Al-Mg hot-dip plated steel sheet having a good satin-like appearance in which the ratio of the area of the part is large is described. In addition, Patent Document 1 describes that the unfavorable pear-skin state is a state in which irregular white portions and circular glossy portions are intermingled and scattered on the surface, presenting a surface appearance. there is
In addition, Patent Document 4 discloses a highly corrosion-resistant hot-dip galvanized steel sheet in which the ternary eutectic structure of Al/MgZn ₂ /Zn is refined to increase the glossiness of the coating layer as a whole and improve the appearance uniformity. Are listed.
However, no technique has been known in the past to improve the durability and prevent the corrosion resistance from deteriorating when characters or the like are displayed on the surface of the plating layer.

Japanese Patent No. 5043234 Japanese Patent No. 5141899 Japanese Patent No. 3600804 WO2013/002358

The present invention has been made in view of the above circumstances, and provides a hot-dip plated steel sheet that can display letters, designs, etc. on the surface of the plating layer, has excellent durability, and is also excellent in corrosion resistance. The challenge is to

The gist of the present invention is as follows.
[1] A steel plate and a hot-dip coating layer formed on the surface of the steel plate,
The hot dip plated layer has an average composition of Al: 0 to 90% by mass, Mg: 0 to 10% by mass, the balance being Zn and impurities,
A pattern portion arranged to have a predetermined shape and a non-pattern portion are formed on the hot-dip plating layer,
The pattern portion is arranged so as to have an intentional shape that is a combination of one or more of straight lines, curved lines, dots, figures, numbers, symbols, patterns, or characters,
The pattern portion and the non-pattern portion each include one or both of a first region or a second region defined by the following determination method,
A hot-dip plated steel sheet, wherein a difference between an area ratio of the first region in the pattern portion and an area ratio of the first region in the non-pattern portion is 30% or more in absolute value.
[Determining Method] Draw virtual grid lines on the surface of the hot-dip plated layer at intervals of 1 mm, and then draw circles S centered on the center of gravity G of each region 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 layers included in the circle S is 10 mm. The average value of the maximum diameter Rmax and the minimum diameter Rmin of the diameters R of the circles S in a plurality of regions is defined as a reference diameter Rave, and the region having the circle S with the diameter R less than the reference diameter Ra is defined as the first region. A region having a circle S whose R is equal to or greater than the reference diameter Rave is defined as a second region. The surface boundary line is a boundary between a high-brightness portion and a low-brightness portion on the surface of the plating layer.
[2] The hot dip plated layer has an average composition of 4 to 22% by mass of Al, 0 to 10% by mass of Mg, and the balance contains Zn and impurities. Hot dip plated steel sheet.
[3] The hot-dip plated steel sheet according to [1] or [2], wherein the hot-dip plated layer further contains Si: 0.0001 to 2% by mass in average composition.
[4] The hot-dip plated 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, and C in a total content of 0.001 to 2% by mass, the hot dip plated steel sheet according to any one of [1] to [3] .
[ 5 ] The hot-dip plated steel sheet according to any one of [1] to [ 4 ], wherein the total adhesion amount of the hot-dip plated layer on both sides of the steel sheet is 30 to 600 g/m ² .

According to the present invention, the density of the boundary lines appearing on the surface of the hot dipping layer is compared with the first region included in the portion where the density of the boundary lines appearing on the surface of the hot dipping layer is relatively high. By dividing the first region into the second region included in the low target portion and setting the absolute value of 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 portion and the non-patterned portion can be distinguished with the naked eye by the difference in the density of the boundary lines. As a result, it is possible to provide a hot-dip plated steel sheet that is excellent in durability and corrosion resistance when characters, designs, etc. are displayed on the surface of the hot-dip plated layer.

FIG. 1 is a schematic diagram illustrating a method of determining the first region and the second region in the hot-dip plated steel sheet of the present embodiment. FIG. 2 is a schematic diagram explaining a method of determining the first region and the second region in the hot-dip plated steel sheet of the present embodiment. FIG. 1 is a schematic diagram showing a boundary line obtained by binarizing imaged data of the surface of a hot-dip plating layer of No. 1. FIG. FIG. 4 shows No. 1 of the embodiment. 1 is an enlarged photograph taken by a scanning electron microscope of the first region of Example 1. FIG. FIG. 5 shows No. 1 of the embodiment. 1 is an enlarged photograph of the second region of No. 1 by a scanning electron microscope. FIG. 6 is an enlarged plan view showing the surface of the hot-dip plated steel sheet that is an example of the present embodiment.

A hot-dip plated steel sheet that is an embodiment of the present invention will be described below.
The hot-dip plated steel sheet of the present embodiment includes a steel plate and a hot-dip plated layer formed on the surface of the steel plate, and the hot-dip plated layer has an average composition of Al: 0 to 90% by mass and Mg: 0 to 10% by mass. %, the remainder containing Zn and impurities, and a pattern portion and a non-pattern portion arranged to have a predetermined shape are formed in the hot-dip plating layer, and the pattern portion and the non-pattern portion are each: 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 It is a hot-dip plated steel sheet with a value of 30% or more.

The determination method is as follows. Virtual grid lines are drawn on the surface of the hot-dip plated layer at intervals of 1 mm, and then, for each of a plurality of regions partitioned by the virtual grid lines, a circle S centered on the center of gravity G of each region 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 layers included in the circle S is 10 mm. The average value of the maximum diameter Rmax and the minimum diameter Rmin of the diameters R of the circles S in a plurality of regions is defined as a reference diameter Rave, and the region having the circle S with the diameter R less than the reference diameter Ra is defined as the first region. A region having a circle S whose R is equal to or greater than the reference diameter Rave is defined as a second region.

The boundaries appearing in the hot-dip plated layer are, for example, grain boundaries appearing in the plated surface and boundaries between high-brightness portions and low-brightness portions of the plating surface.

The area included in the high-density portion of the crystal grain boundary appearing on the plated surface, or the area included in the low-density portion of the crystal grain boundary, is arranged so that it is shaped like a straight line or letter on the plated surface. Then, it is recognized that there are straight lines and characters on the plating surface.

Similarly, the area included in the part of the plated surface with a high density of light and dark boundaries, or the area included in the part with a low density of light and dark boundaries on the plated surface, should be shaped like a straight part or a letter on the plated surface. , it is recognized that there are straight lines or characters on the plating surface.

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

In the hot-dip plated steel sheet of the present embodiment, when virtual grid lines are drawn on the surface of the hot-dip plated layer at intervals of 1 mm, a plurality of regions partitioned by the virtual grid lines are hot-dip plated in the vicinity of each partitioned region. Depending on the density of the surface boundaries of the layer, it is divided into either the first region or the second region.

The first region is a region included in a high-density portion 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 boundary lines appearing on the surface of the hot-dip plating layer is low. In the hot-dip plated layer, the locations where the first regions gather and the locations where the second regions gather have different densities of boundary lines, so the first regions and the second regions look different.

In order to make characters, figures, lines, dots, etc. visible on the surface of the hot-dip plating layer, it is necessary to be able to distinguish between the patterned parts that make up these characters, etc. and the other non-patterned parts. Just do it. For this 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 should be different.

Specifically, the absolute value of 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. This makes it possible to distinguish between the pattern portion and the non-pattern portion.

For example, when the pattern portion includes many first regions, many boundary lines appear in the pattern portion. In this case, the area ratio of the first region in the non-pattern portion is reduced. Since the area ratio of the first region is small in the non-pattern portion, the area ratio of the second region is relatively high. This makes it possible to distinguish with the naked eye a pattern portion in which many boundary lines are visible and a non-pattern portion in which few boundary lines are visible.

Also, when the pattern portion includes many second regions, the pattern portion appears to have fewer boundary lines. In this case, the area ratio of the second region in the non-pattern portion is decreased and the area ratio of the first region is increased. Since the non-pattern portion has a large area ratio of the first region, many boundary lines appear in the non-pattern portion. This makes it possible to distinguish with the naked eye a patterned portion in which few boundary lines appear and a non-patterned portion in which many boundary lines appear.

Thus, when the absolute value of 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, the appearance of the pattern portion and the non-pattern portion becomes different. Therefore, the pattern portion can be clearly identified. That is, in the visible light image of the surface of the plating layer, the difference in hue, brightness, saturation, etc. between the patterned portion and the non-patterned portion is large, so that the patterned portion and the non-patterned portion can be distinguished.

On the other hand, when the absolute value of 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 less than 30%, the difference in appearance between the pattern portion and the non-pattern portion disappears. cannot be clearly identified. That is, in a visible light image of the surface of the plating layer, the difference in hue, brightness, saturation, etc. between the patterned portion and the non-patterned portion becomes small, making it impossible to distinguish between the patterned portion and the non-patterned portion.

As described above, an example of the existence ratio of the first region in the pattern portion and the non-pattern portion was shown. If the value is 30% or more, it is not necessary to limit the existence ratio of the first region in each of the pattern portion and the non-pattern portion.

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

There are no particular restrictions on the material of the steel sheet that serves as the base of the hot-dip coating layer. Although the details will be described later, as the material, general steel can be used without any particular limitation, Al-killed steel or some high-alloy steel can also be used, and the shape is also not particularly limited. The hot-dip plating layer according to the present embodiment is formed by applying the hot-dip plating method, which will be described later, to the steel sheet.

Next, the chemical composition of the hot-dip plating layer will be explained.
The hot-dip plated layer contains, in average composition, Al: 0 to 90% by mass, Mg: 0 to 10% by mass, and Zn and impurities as the balance. More preferably, the average composition contains 4 to 22% by mass of Al, 1 to 10% by mass of Mg, and the balance of Zn and impurities. More preferably, the average composition contains 4 to 22% by mass of Al, 1 to 10% by mass of Mg, and the balance is Zn and impurities. Further, the hot-dip plated layer may contain Si: 0.0001 to 2% by mass in average composition. Furthermore, the hot-dip 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 Any one or two or more of these may be contained in a total amount of 0.001 to 2% by mass.

The content of Al is in the range of 0 to 90% by mass, preferably 4 to 22% by mass in terms of average composition. Al is preferably contained in order to ensure corrosion resistance. If the content of Al in the hot-dip plated layer is 4% by mass or more, the effect of improving the corrosion resistance is 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, the content 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, based on the average composition. Mg is preferably contained in order to improve corrosion resistance. If the content of Mg in the hot-dip plated layer is 1% by mass or more, the effect of improving the corrosion resistance is enhanced. If it exceeds 10% by mass, dross generation in the plating bath becomes significant, making it difficult to stably produce a hot-dip plated steel sheet. From the viewpoint of the balance between corrosion resistance and dross generation, the content is preferably 1.5 to 6% by mass. More preferably, it should be in the range of 2 to 5% by mass.

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

Further, the hot-dip plated layer may contain Si in the range of 0.0001 to 2% by mass.
Since Si may improve the adhesion of the hot-dip plating layer, it may be contained. By containing 0.0001% by mass or more of Si, the effect of improving adhesion is exhibited, so 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 content of Si is made 2% by mass or less. From the viewpoint of plating adhesion, it may be in the range of 0.0010 to 1% by mass, or in the range of 0.0100 to 0.8% by mass.

In the hot dip plated 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 may contain 0.001 to 2% by mass in total of one or more of Corrosion resistance can be further improved by containing these elements. REM is one or more of the rare earth elements with atomic numbers 57-71 in the periodic table.

The remainder of the chemical composition of the hot-dip layer is zinc and impurities. Impurities include those that are unavoidably contained in base metals such as zinc, and those that are contained by dissolving steel in the plating bath.

The average composition of the hot-dip plated layer can be measured by the following method. First, after removing the surface coating film with a coating remover that does not corrode the plating (for example, Neoriver SP-751 manufactured by Sansai Kako Co., Ltd.), the hot-dipped plating layer with hydrochloric acid containing an inhibitor (for example, Hibilon manufactured by Sugimura Chemical Industry Co., Ltd.) can be determined by dissolving and subjecting the resulting solution to inductively coupled plasma (ICP) emission spectrometry. Moreover, when the surface layer coating film is not provided, the operation for removing the surface layer coating film can be omitted.

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

The hot dip plated layer containing Al, Mg and Zn includes [Al phase] and [Al/Zn/ _MgZn2 ternary eutectic structure]. It has a form in which the [Al phase] is included in the [Al/Zn/ _MgZn2 ternary eutectic structure] matrix. Further, the [Al/Zn/ _MgZn2 ternary eutectic structure] matrix may contain [ _MgZn2 phase] and [Zn phase]. Further, when Si is added, [Mg ₂ Si phase] may be included in the matrix of [Al/Zn/MgZn ₂ ternary eutectic structure].

Here, the [Al/Zn/ _MgZn2 ternary eutectic structure] is a ternary eutectic structure of the Al phase, the Zn phase, and the intermetallic compound _MgZn2 phase. The Al phase that is formed corresponds to, for example, the "Al"phase" at high temperature in the Al-Zn-Mg ternary equilibrium diagram (an Al solid solution that dissolves Zn and contains a small amount of Mg). is. At room temperature, the Al″ phase at high temperatures usually appears separated into a fine Al phase and a fine Zn phase. is a Zn solid solution in which a small amount of Mg is dissolved in. The MgZn ₂ phase in the ternary eutectic structure is a metal that exists in the vicinity of Zn: about 84% by mass in the Zn-Mg binary system equilibrium diagram. As far as we can see from the phase diagram, each phase does not dissolve other additive elements, or even if they do, it is considered to be a very small amount, but the amount is clear in normal analysis. In this specification, the ternary eutectic structure consisting of these three phases is referred to as [Al/Zn/ _MgZn2 ternary eutectic structure].

In addition, [Al phase] is a phase that looks like an island with a clear boundary in the matrix of the ternary eutectic structure. (Al solid solution that dissolves Zn and contains a small amount of Mg). The Al″ phase at high temperature differs in the amount of solid-soluted Zn and Mg depending on the concentration of Al and Mg in the plating bath. It separates into phases, but the island-like shape seen at room temperature can be considered to be the remains of the Al″ phase at high temperature. It is thought that it is not dissolved, or even if it is dissolved, it is a very small amount, but it cannot be clearly distinguished by ordinary analysis. In this specification, the retained phase is referred to as [Al phase], which can be clearly distinguished from the Al phase forming the ternary eutectic structure by microscopic observation.

Further, the [Zn phase] is a phase that looks like an island with a clear boundary in the matrix of the ternary eutectic structure, and actually contains a small amount of Al and a small amount of Mg as a solid solution. There is also As far as the phase diagram is concerned, it is considered that this phase does not dissolve other additive elements or, if dissolved, 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. there is no problem either.

The [MgZn ₂ phase] is a phase that looks like islands with clear boundaries in the matrix of the ternary eutectic structure, and actually contains a small amount of Al as a solid solution. As far as the phase diagram is concerned, it is considered that this phase does not dissolve other additive elements or, if dissolved, 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 the [MgZn ₂ phase] depending on the production conditions, but it is contained in the plating layer under most production conditions.

The [Mg ₂ Si phase] is a phase that looks like an island with clear boundaries 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-dissolved, or even if they are solid-dissolved, the amount is extremely small. This [Mg ₂ Si phase] can be clearly distinguished in the plating by microscopic observation.

Next, the patterned portion, the non-patterned portion, the first region, and the second region in 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 are formed so as to have a predetermined shape. It is preferable that the pattern portion is arranged so as to form any one of linear portions, curved portions, dot portions, figures, numerals, symbols, patterns, or characters, or a combination of two or more of these. . Also, the non-pattern portion is a region other than the pattern portion. Moreover, even if the shape of the pattern portion is partially missing, such as missing dots, it is permissible as long as it can be recognized as a whole. Also, the non-pattern portion may have a shape that borders the boundary of the pattern portion.

If any one of straight lines, curved lines, dots, figures, numbers, symbols, patterns or characters, or a combination of two or more of these is arranged on the surface of the hot-dip plating layer, these can be used as the pattern area, and the other area can be used as the non-pattern area. The boundary between the patterned portion and the non-patterned portion can be recognized with the naked eye. The boundary between the patterned portion and the non-patterned portion may be grasped from an enlarged image using an optical microscope or a magnifying glass.

The pattern portion is preferably formed to have a size that allows the existence of the pattern portion to be determined with the naked eye, under a magnifying glass, or under a microscope. Moreover, the non-pattern portion is a region that occupies most of the hot-dip plated layer (the surface of the hot-dip plated layer), and the pattern portion may be arranged in the non-pattern portion. The pattern portion is arranged in a predetermined shape within the non-pattern portion. Specifically, in the non-pattern portion, the pattern portion includes any one of linear portions, curved portions, graphics, dot portions, graphics, numerals, symbols, patterns, or characters, or a combination of two or more of these. It is arranged so that it becomes a shape. By adjusting the shape of the pattern portion, any one or more of the straight line portion, curved portion, figure, dot portion, figure, number, symbol, pattern or letter on the surface of the hot-dip plating layer A shape that combines the For example, on the surface of the hot-dip plated layer, a string of characters, a string of numbers, a symbol, a mark, a diagram, a design image, or a combination of these, etc., formed of a pattern portion appears. This shape is a shape intentionally or artificially formed by a manufacturing method to be described later, and is not naturally formed.

Thus, 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 each include one or two of the first region and the second region.

The first region is a region included in a high-density portion 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 boundary lines appearing on the surface of the hot-dip plating layer is low. The location where the first regions are concentrated and the location where the second regions are concentrated in the hot-dip plated layer can be identified because the density of the boundary line is different.

Next, a method for determining the first area and the second area 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 plated layer at intervals of 1 mm. In FIG. 1, the virtual grid lines are indicated by dashed-dotted lines. Note that FIG. 1 does not show a boundary line where the hot-dip plating layer appears. Next, a plurality of regions M partitioned by virtual grid lines 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, for each of a plurality of regions M partitioned by the virtual grid lines K, the center of gravity G of each region is set. Next, a circle S centered on the center of gravity 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 layers included inside the circle S is 10 mm.

A circle S corresponding to an arbitrary region M is shown in FIGS. 2(a) and 2(b). 2(a) and 2(b) show boundary lines appearing on the surface of the hot-dip plating layer. The boundary lines shown in FIGS. 2(a) and 2(b) both have a total length of 10 mm. In this embodiment, the diameter of the circle S is adjusted so that the total length of the boundary lines L included in the circle S is 10 mm. Therefore, as shown in FIG. 2A, when there are many boundary lines L in and around the area M, the diameter R of the circle S is relatively small. On the other hand, as shown in FIG. 2B, when there are relatively few boundary lines L in and around the region M, the diameter R of the circle S is relatively large. A circle S is 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 of the circles S in the plurality of regions M is defined as a 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. A region having a circle S whose R is equal to or greater than the reference diameter Rave is defined as a second region. The first area is an area included in a portion where many boundary lines L exist, as shown in FIG. 2(a). It becomes a region included in a portion that exists in a small amount.

The boundary line appearing in the hot-dip plating layer can be exemplified by, for example, the grain boundary 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 plated surface.

The pattern portion includes a plurality of regions partitioned by virtual grid lines, and each region is classified as either a first region or a second region. The non-pattern portion also includes a plurality of regions partitioned by virtual grid lines, and each region is classified as either a first region or a second region. That is, the pattern portion may include either the first region or the second region, or may include both the first region and the second region. Similarly, the non-pattern portion may include 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 area fraction of each of the first region and the second region can be obtained. As the area fraction of the first region increases, the pattern portion includes a relatively large number of boundary lines. On the other hand, when the area fraction of the second region in the pattern portion is high, the pattern portion includes relatively few boundary lines. Thus, the appearance of the pattern portion depends on the area ratios of the first region and the second region.

On the other hand, even in the non-pattern portion, the area fraction of each of the first region and the second region can be obtained. As with the patterned portion, the appearance of the non-patterned portion depends on the area fractions 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-pattern portion is 30% or more in absolute value, the pattern portion and the non-pattern portion can be distinguished. Become. When the difference in 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-pattern portion is small, and the appearance of the pattern portion and the non-pattern portion are similar. It becomes an appearance, and it becomes difficult to identify the pattern portion. The larger the difference in the 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 to the naked eye or under a magnifying glass or microscope. Being identifiable under a magnifying glass or a microscope means, for example, that the shape formed by the pattern portion is identifiable in a field of view of 50 times or less. With a field of view of 50 times or less, the patterned portion and the non-patterned portion can be distinguished from each other by the difference in appearance. The patterned portion and the non-patterned portion are preferably distinguishable by a factor of 20 or less, more preferably by a factor of 10 or less, and more preferably by a factor of 5 or less.

The hot-dip plated 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 plated layer. Here, the types of the chemical conversion treatment film layer and the coating film layer are not particularly limited, and known chemical conversion treatment film layers and coating film layers can be used.

Next, a method for manufacturing the hot-dip plated steel sheet of the present embodiment will be described.
The hot-dip plated steel sheet of the present embodiment is hot-dip plated on a steel sheet manufactured through steelmaking, casting, and hot rolling. When manufacturing the steel sheet, pickling, hot-rolled sheet annealing, cold rolling, and cold-rolled sheet annealing may be further performed. Hot-dip plating may be a continuous hot-dip plating method in which a steel sheet is continuously passed through a hot-dip plating bath, or a hot-dip plating method in which a steel material processed into a predetermined shape or the steel sheet itself is immersed in a hot-dip plating bath and then pulled out. It's okay.

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

The temperature of the hot-dip plating bath varies depending on the composition, but is preferably in the range of 400-500° C., for example. This is because a desired hot-dip plating layer can be formed if the temperature of the hot-dip plating bath is within this range.
Also, the adhesion amount of the hot-dip coating layer may be adjusted by gas wiping or the like on the steel sheet pulled up from the hot-dip coating bath. It is preferable to adjust the coating weight of the hot-dip plating layer so that the total coating weight 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 plated steel sheet is lowered, which is not preferable. If the coating amount exceeds 600 g/m ² , the molten metal that adheres to the steel sheet will drip, making it impossible to smoothen the surface of the hot-dip plated layer, which is not preferable.

A non-oxidizing gas having a temperature higher than the final solidification temperature of the coating is locally sprayed onto the molten metal by a gas nozzle on the steel plate or steel immediately after being pulled out of the hot dip coating bath. Nitrogen or argon may be used as the non-oxidizing gas. In addition, although the optimum temperature range differs depending on the composition, it is advisable to blow 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. . Furthermore, the temperature of the non-oxidizing gas is preferably higher than the final solidification temperature. For example, in a plating composition of Al: 11% and Mg: 3%, when the temperature of the molten metal is 330 to 340°C, non-oxidizing gas having a gas temperature higher than the final solidification temperature should be blown. The cooling rate of the molten metal slows down in the periphery where the non-oxidizing gas is blown, which causes the boundaries or grain boundaries appearing on the surface to become coarse. Therefore, by adjusting the blowing amount and range of the non-oxidizing gas, the size of the boundaries or grain boundaries appearing on the surface can be arbitrarily adjusted. Thereby, 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 forming a chemical conversion treatment layer on the surface of the hot-dip plated layer, the hot-dip plated steel sheet after forming the hot-dip plated layer is subjected to the chemical conversion treatment. The type of chemical conversion treatment is not particularly limited, and known chemical conversion treatments can be used.
In addition, when forming a coating film layer on the surface of the hot-dip plating layer or the surface of the chemical conversion treatment layer, after forming the hot-dip plating layer or after forming the chemical conversion treatment layer, the coating is applied to the hot-dip plated steel sheet. process. The type of coating treatment is not particularly limited, and known coating treatments can be used.

In the hot-dip plated steel sheet of the present embodiment, the surface of the hot-dip plated layer is divided into a first region in which the density of the boundary lines appearing on the surface of the hot-dip plated layer is relatively high, and a boundary line that appears on the surface of the hot-dip plated layer. It is divided into a second region that exists in a relatively low density portion, and 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, It becomes possible to discriminate pattern parts and non-pattern parts. The formed patterned portion and non-patterned portion are not formed by printing or painting, and thus have high durability. Moreover, 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 plating layer. Furthermore, the patterned portion and the non-patterned portion are not formed by grinding the surface of the hot-dip plating layer. Therefore, there is no difference between the thickness of the hot-dip plated layer in the pattern portion and the thickness of the hot-dip plated layer in the non-pattern portion. Therefore, the hot-dip plated steel sheet of the present embodiment has excellent corrosion resistance.

According to the present embodiment, it is possible to provide a hot-dip plated steel sheet having high durability in a pattern portion formed into a predetermined shape and having suitable plating properties such as corrosion resistance. In particular, in this embodiment, when the temperature of the molten metal pulled up from the plating bath is in the range of (final solidification temperature -5) ° C. to (final solidification temperature +5) ° C., the surface of the hot dip plated layer is covered with a non-oxidizing gas. By locally spraying with a gas nozzle, the size of the boundary or grain boundary appearing on the surface of the hot-dip plated layer after solidification is arbitrarily adjusted, and the range of the patterned portion or non-patterned portion is intentionally or artificially The pattern portion is arranged so as to have any one of linear portions, curved portions, dot portions, figures, numerals, symbols, patterns or letters, or a combination of two or more of these. can. As a result, various designs, trademarks, and other identification marks can be displayed on the surface of the hot-dip plated layer without printing, painting, or grinding, and the identifiability of the source of the steel sheet and design can be improved. . In addition, the pattern portion can provide the hot-dip plated steel sheet with information necessary for process control, inventory control, and the like, and arbitrary information requested by the consumer. This can also contribute to the improvement of the productivity of the hot-dip plated steel sheet.

Next, examples of the present invention will be described. After the steel sheet was degreased and washed with water, it was subjected to reduction annealing, immersion in a plating bath, control of the coating amount, and cooling. 1 to 32 Zn-Al-Mg system hot-dip plated steel sheets were produced. When the steel sheet is lifted from the plating bath, when the temperature of the molten metal is in the range of (final solidification temperature - 5) ° C to (final solidification temperature + 5) ° C, non-oxidizing gas is added to the molten metal on the surface of the steel plate. A kind of nitrogen gas was blown from a gas nozzle in a heated state. The nitrogen gas blowing conditions were as shown in Table 1. All the gas temperatures shown in Table 1 were equal to or higher than the final solidification temperature. After that, the molten metal was completely solidified by cooling. By blowing nitrogen gas, it was controlled so that a square pattern with a side of 50 mm appeared. However, no. For No. 30, nitrogen gas was blown from a 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.

Also, a Zn-Al-Mg hot-dip plated steel sheet was produced in the same manner as described above. After that, a square pattern with a side of 50 mm was printed on the surface of the hot-dip plated layer by an inkjet method. This result is No. 33 in Table 2.

Further, a Zn-Al-Mg hot-dip plated steel sheet was produced in the same manner as described above. After that, the surface of the hot-dip plated layer was ground to form a square pattern with a side of 50 mm. This result is No. 34 in Table 2.

The area ratios of the first region and the second region included in the patterned portion and the non-patterned portion of the obtained hot-dip plated steel sheet were determined. First, the boundary between the patterned portion and the non-patterned portion was specified by observing the surface of the hot-dip plated layer with the naked eye. When it was difficult to identify the boundary with the naked eye, a magnifying glass or a magnified image of an optical microscope was used. In an example where it was difficult to determine the boundary, the boundary was set based on the nitrogen gas blowing range, 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 (indicated as pattern portion in Table 2) and other regions (indicated as non-pattern portion in Table 2) was obtained by the following determination method.
As shown in FIG. 1, virtual grid lines K were drawn on the surface of the hot-dip plated layer at intervals of 1 mm. Note that FIG. 1 does not show a boundary line where the hot-dip plating layer appears. Next, a plurality of regions M partitioned by virtual grid lines K were set. The shape of each region M was a square with a side of 1 mm. Next, for each of a plurality of regions M partitioned by the virtual grid lines K, the center of gravity G of each region was set. Then, a circle S centered on the center of gravity G was drawn. The diameter R of the circle S was adjusted so that the total length of 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 of the circles S in the plurality of regions M is defined as a 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. A region having a circle S whose R is equal to or greater than the reference diameter Rave was defined as a second region.

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

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

[Identification]
Visual evaluation was performed based on the following criteria for the test plates having the square pattern portions in the initial state immediately after production and in the aging state after being exposed to the outdoors for 6 months. In both the initial state and the aged state, ⊚ to △ were regarded as acceptable.

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

[Corrosion resistance]
A test plate was cut into a size of 150×70 mm and subjected to 30 cycles of accelerated corrosion test CCT according to JASO-M609. A to △ was regarded as a pass.

⊚: No rust occurred, and both the patterned portion and the non-patterned portion maintained a beautiful design appearance.
◯: No rust occurred, but a very slight change in design appearance was observed between the patterned portion and the non-patterned portion.
Δ: The design appearance 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 remarkably deteriorated and cannot be visually distinguished.

As shown in Table 2, No. 1 to No. The 29 Zn-Al-Mg system hot-dip plated steel sheets of the present invention example were excellent in both identifiability and corrosion resistance. In FIG. The observation result of the pattern portion of No. 1 by a scanning electron microscope is shown in FIG. 1 shows observation results of the non-patterned portion of No. 1 with a scanning electron microscope. The area ratio of the first region in the pattern portion is significantly different from that in the non-pattern portion, and it can be seen that the pattern portion and the non-pattern portion can be distinguished.

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 from the gas nozzle, so the first region in the pattern part and the area ratio of the first region in the non-pattern portion was less than 30%, and the distinguishability of the pattern portion was lowered.
Also, No. 31 and no. In No. 32, the composition of the hot-dip plated layer was outside the scope of the present invention, and the distinguishability was lowered after being exposed to the outdoors for 6 months.

On the other hand, No. 1 printed with a square pattern portion by an inkjet method. In No. 33, the pattern portion became thin due to exposure to the outdoors for 6 months, and the designability deteriorated.
In addition, No. 1, which had a grid pattern formed by grinding, was used. In No. 34, the thickness of the plated layer at the ground portion decreased, and the corrosion resistance at the ground portion decreased.
In addition, No. The plating layers 1-6 and 10-34 contained an Al phase and a ternary eutectic structure of Al/Zn/ _MgZn2 .

FIG. 6 shows the surface of a hot-dip plated steel sheet in which character strings (alphabet letters) are represented by pattern portions.
ADVANTAGE OF THE INVENTION According to this invention, the pattern part which consists of a character and a mark can be arbitrarily shown now on the surface of a hot-dip plated steel plate.

Claims (5)

A steel plate and a hot dip plated layer formed on the surface of the steel plate,
The hot dip plated layer has an average composition of Al: 0 to 90% by mass, Mg: 0 to 10% by mass, the balance being Zn and impurities,
A pattern portion arranged to have a predetermined shape and a non-pattern portion are formed on the hot-dip plating layer,
The pattern portion is arranged so as to have an intentional shape that is a combination of one or more of straight lines, curved lines, dots, figures, numbers, symbols, patterns, or characters,
The pattern portion and the non-pattern portion each include one or both of a first region or a second region defined by the following determination method,
A hot-dip plated steel sheet, wherein a difference between an area ratio of the first region in the pattern portion and an area ratio of the first region in the non-pattern portion is 30% or more in absolute value.
[Determining Method] Draw virtual grid lines on the surface of the hot-dip plated layer at intervals of 1 mm, and then draw circles S centered on the center of gravity G of each region 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 layers included in the circle S is 10 mm. The average value of the maximum diameter Rmax and the minimum diameter Rmin of the diameters R of the circles S in a plurality of regions is defined as a reference diameter Rave, and the region having the circle S with the diameter R less than the reference diameter Ra is defined as the first region. A region having a circle S whose R is equal to or greater than the reference diameter Rave is defined as a second region. The surface boundary line is a boundary between a high-brightness portion and a low-brightness portion on the surface of the plating layer. The hot dip plated steel sheet according to claim 1, wherein the hot dip plated layer contains, in average composition, Al: 4 to 22 mass%, Mg: 0 to 10 mass%, and the balance containing Zn and impurities. . 3. The hot dip plated steel sheet according to claim 1, wherein the hot dip plated layer further contains Si: 0.0001 to 2 mass % in average composition. The hot-dip plated 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, 4. The hot dip plated steel sheet according to any one of claims 1 to 3, characterized by containing 0.001 to 2% by mass of any one or more of C in total. The hot-dip plated steel sheet according to any one of claims 1 to 4, wherein the total amount of adhesion of the hot-dip plated layer on both sides of the steel sheet is 30 to 600 g/m ² .

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