JP2023090240A - Hot-dip galvanized steel sheet - Google Patents

Abstract

To provide a hot-dip galvanized steel sheet excellent in corrosion resistance and appearance quality.SOLUTION: A hot-dip galvanized steel sheet (1) includes a base material steel sheet (10) and a hot-dip galvanized layer (20) formed on the base material steel sheet (10). The hot-dip galvanized layer (20) has a chemical composition described in the specification. In a rectangular observation field area (50) including the surface (S) of the hot-dip galvanized layer (20) and having a L direction length of 120 μm and a H direction length of 96 μm, the length SL of the surface (S) and the shortest distance SD between one end part (P1) of the surface (S) and the other end part (P2) satisfy a formula (1), and in a cross section including the L direction and the H direction, the number of recessed parts formed on the surface (S) of the hot-dip galvanized layer (20) and satisfying formulae (2)-(4) described in the specification is 1.0 piece or more per 10 cm in the L direction, SL/SD≤α (1).SELECTED DRAWING: Figure 3

Description

The present disclosure relates to hot-dip galvanized steel sheets.

A hot-dip galvanized steel sheet having a hot-dip galvanized layer on the surface layer is applied to various fields such as automobiles, home appliances, and building materials. In recent years, particularly in the field of hot-dip galvanized steel sheets for building materials, there has been a demand for hot-dip galvanized steel sheets exhibiting excellent corrosion resistance on the assumption that they will be used in more severe environments. In this specification, the non-alloyed hot-dip galvanized steel sheet is also simply referred to as "hot-dip galvanized steel sheet". That is, hot-dip galvanized steel sheets in this specification do not include alloyed hot-dip galvanized steel sheets.

JP 2011-144429 A (Patent Document 1), JP 2014-118584 A (Patent Document 2), JP 2013-014794 A (Patent Document 3), and JP 2000-336467 A (Patent Document Document 4) proposes a hot-dip galvanized steel sheet with excellent corrosion resistance.

The hot-dip galvanized steel sheet disclosed in Patent Document 1 contains Mg: 1 to 10%, Al: 4 to 20%, and Si: 0.0001 to 0.5% by mass% on the surface of the steel sheet. , a hot-dip galvanized layer, the balance of which is Zn and impurities, and an Al--Fe--Si--Zn quaternary alloy layer at the coating/steel plate interface. Patent Document 1 describes that this hot-dip galvanized steel sheet has high corrosion resistance and high coating adhesion.

The hot-dip galvanized steel sheet disclosed in Patent Document 2 has, in mass %, C: 0.05 to 0.1%, Si: 0.10% or less, Mn: 0.30 to 0.70%, P: A steel sheet containing 0.040% or less, S: 0.010% or less, N: 0.005% or less, Al: 0.10% or less, the balance being Fe and impurities, and at least part of the surface of the steel sheet a hot-dip galvanized layer containing 0.3 to 0.6% Al formed in the steel plate and the hot-dip galvanized layer containing 0.12 to 0.22 g/m ² of Al, and and an intermetallic compound containing Fe ₂ Al ₅ with an average grain size of 1 μm or less, and a yield strength of 260 to 350 MPa. Patent Document 2 describes that this hot-dip galvanized steel sheet has excellent coating adhesion and spot weldability after press working, corrosion resistance after painting after press working, and excellent appearance after painting.

The hot-dip galvanized steel sheet disclosed in Patent Document 3 has a hot-dip galvanized layer on the surface of the steel sheet, in terms of mass %, Al: 4 to 22%, Mg: 1 to 6%, and the balance being Zn and impurities. A steel sheet having a non-recrystallized rate of 30% or more in the surface layer of the plating base sheet, and the average diameter of the ternary eutectic phase of Al/MgZn ₂ /Zn among the constituent phases of the plating layer is 10 to 100 μm. . Patent Document 3 describes that this hot-dip galvanized steel sheet has excellent appearance uniformity and exhibits high corrosion resistance regardless of the cleanliness uniformity of the base plate.

The hot-dip galvanized steel sheet disclosed in Patent Document 4 contains Mg: 0.1 to 3.0%, Al: 0.02 to 1.0%, and Fe: 2% or less in mass% on the surface of the steel sheet. A hot-dip galvanized layer with the balance being Zn and impurities, and an oxide layer containing Mg on the upper layer of the hot-dip galvanized layer. Patent Document 4 describes that this hot-dip galvanized steel sheet is excellent in corrosion resistance, plating adhesion and spot weldability.

JP 2011-144429 A JP 2014-118584 A JP 2013-014794 A JP-A-2000-336467

By the way, for example, hot-dip galvanized steel sheets for building materials have a great influence on the appearance of buildings. Therefore, hot-dip galvanized steel sheets are required to have a beautiful appearance in addition to excellent corrosion resistance. However, Patent Documents 1 and 4 do not consider the beauty of the appearance of hot-dip galvanized steel sheets. Further, a hot-dip galvanized steel sheet having excellent appearance quality may be obtained by techniques other than the techniques described in Patent Documents 2 and 3 above.

An object of the present disclosure is to provide a hot-dip galvanized steel sheet with excellent corrosion resistance and excellent appearance quality.

The hot-dip galvanized steel sheet according to the present disclosure is
a base material steel plate;
A hot-dip galvanized layer formed on the base steel plate,
The hot-dip galvanized layer is mass %,
Al: 0.1 to 60.0%,
Mg: 0-30.0%,
Si: 0 to 1.0%,
B: 0 to 0.50%,
Ca: 0-3.0%,
Y: 0 to 3.0%,
La: 0 to 3.0%,
Ce: 0 to 3.0%,
Cr: 0-0.5%,
Ti: 0 to 0.5%,
Ni: 0 to 0.5%,
Co: 0-0.5%,
V: 0 to 0.5%,
Nb: 0 to 0.5%,
Cu: 0-0.5%,
Mn: 0-0.5%,
Sr: 0-0.5%,
Sb: 0-0.5%,
Pb: 0 to 0.5%,
Sn: 0 to 2.0%,
Bi: 0 to 2.0%,
In: 0 to 2.0%,
Fe: 0 to 5.0%, and
Balance: having a chemical composition consisting of 35.0% or more of Zn and impurities,
When the rolling direction of the hot-dip galvanized steel sheet is defined as the L direction and the plate thickness direction of the hot-dip galvanized steel sheet is defined as the H direction,
In a rectangular observation field region including the surface of the hot-dip galvanized layer, the side of the hot-dip galvanized steel sheet extending in the L direction is 120 μm in length and the side extending in the H direction is 96 μm in length,
The length of the surface of the hot-dip galvanized layer is SL,
One end of the surface of the hot-dip galvanized layer is P1 point,
The other end of the surface of the hot-dip galvanized layer is P2 point,
When the shortest distance between the P1 point and the P2 point is defined as SD,
The SL and the SD satisfy the formula (1),
When the thickness of the hot-dip galvanized layer is defined as T μm,
In a cross section including the L direction and the H direction,
formed on the surface of the hot-dip galvanized layer,
The number of recesses that satisfies the formulas (2) to (4) for the length W μm in the L direction and the depth D μm in the H direction is 1.0 or more per 10 cm in the L direction.
SL/SD≦α (1)
D≦0.7×T (2)
D≤5.0 (3)
0.2×D≦W≦5.0×D (4)
Here, α in the formula (1) is 1.10 when the Mg content in the hot-dip galvanized layer is 0 to less than 0.5% by mass, and the Mg content in the hot-dip galvanized layer is 0. 0.5 to 30.0% by mass, it is 1.50.

The hot-dip galvanized steel sheet according to the present disclosure has excellent corrosion resistance and excellent appearance quality.

FIG. 1 is a schematic diagram showing a cross section of an example of a hot-dip galvanized steel sheet 1 including a surface S of a hot-dip galvanized layer 20. FIG. FIG. 2 is a schematic diagram showing a cross section of an example of the hot-dip galvanized steel sheet 1 having the hot-dip galvanized layer 20 having the chemical composition described above. FIG. 3 is a schematic diagram showing a cross section of an example of the hot-dip galvanized steel sheet 1 according to this embodiment. FIG. 4 is a schematic diagram showing a cross section of another example of the hot-dip galvanized steel sheet 1 according to this embodiment. FIG. 5 is an enlarged view of area 60 of FIG. FIG. 6 is a schematic diagram showing a cross section of another example of the hot-dip galvanized steel sheet 1 according to this embodiment. FIG. 7 is a side view showing an example of a hot dip galvanizing facility 100 used for conventional hot dip galvanizing treatment. FIG. 8 is a side view showing an example of a hot dip galvanizing facility 100 used for hot dip galvanizing treatment according to this embodiment. FIG. 9 is a side view showing another example of the hot dip galvanizing equipment 100 used for the hot dip galvanizing treatment according to this embodiment.

If the hot-dip galvanized layer formed on the surface layer of the hot-dip galvanized steel sheet contains an easily oxidizable element, the corrosion resistance of the hot-dip galvanized steel sheet is enhanced. Specifically, since Al is easily oxidized, the inclusion of Al in the hot-dip galvanized layer enhances the effect of sacrificial corrosion protection, and significantly enhances the corrosion resistance of the hot-dip galvanized steel sheet. Therefore, the present inventors thought that a hot-dip galvanized steel sheet containing Al in the hot-dip galvanized layer would provide excellent corrosion resistance. More specifically, if the hot-dip galvanized layer contains, by mass%, Al: 0.1 to 60.0% and Zn: 35.0% or more, the corrosion resistance of the hot-dip galvanized steel sheet can be improved. have a nature.

On the other hand, the hot-dip galvanized steel sheet having the hot-dip galvanized layer with the chemical composition described above sometimes has poor appearance quality. Therefore, the present inventors paid attention to the surface state of the hot-dip galvanized layer in order to improve the appearance quality of the hot-dip galvanized steel sheet. Specifically, the present inventors considered quantifying the unevenness of the surface of the hot-dip galvanized layer and investigating the relationship with appearance quality. Here, in the field of hot-dip galvanized steel sheets, generally, the unevenness of the surface of the hot-dip galvanized layer has been quantified mainly by a stylus-type roughness meter. Therefore, the present inventors evaluated the surface of the hot-dip galvanized layer having the chemical composition described above using a stylus-type roughness meter. As a result, in the hot-dip galvanized steel sheets having the hot-dip galvanized layer with the above-mentioned chemical composition, even if the unevenness of the surface of the hot-dip galvanized layer evaluated with a stylus type roughness meter is the same, the appearance quality is different. It turned out that there is a case.

Therefore, the present inventors believe that the beauty of the appearance of a hot-dip galvanized steel sheet is determined not only by the level of unevenness that can be measured by a stylus type roughness meter, but also by the level of unevenness that can be measured by a stylus type roughness meter. Furthermore, I thought that fine unevenness may also have an effect. That is, there is a possibility that the beauty of the appearance can be further improved by reducing finer irregularities than the irregularities that can be measured by a stylus-type roughness meter. Therefore, the present inventors have studied how to further reduce fine irregularities on the surface of the hot-dip galvanized layer. First, fine unevenness on the surface of the hot-dip galvanized layer was evaluated by observing a secondary electron image of the cross section of the hot-dip galvanized steel sheet using a scanning electron microscope (SEM). This point will be specifically described using schematic diagrams.

FIG. 1 is a schematic diagram showing a cross section of an example of a hot-dip galvanized steel sheet 1 including a surface S of a hot-dip galvanized layer 20. FIG. FIG. 1 is a schematic diagram showing the unevenness in an extreme manner for explaining the evaluation of fine unevenness by SEM observation. The horizontal direction of the observation field region 50 in FIG. 1 corresponds to the rolling direction of the hot-dip galvanized steel sheet 1, and the vertical direction of the observation field region 50 in FIG. In addition, in this specification, the rolling direction of the hot-dip galvanized steel sheet 1 is also called "L direction." Moreover, the board thickness direction of the hot-dip galvanized steel sheet 1 is also called "H direction." Here, in FIG. 1, the L-direction length of the observation visual field region 50 is 120 μm, and the H-direction length is 96 μm.

In FIG. 1, region 10 is the base steel plate and region 20 is the hot dip galvanized layer. A person skilled in the art can identify the base material steel sheet 10 and the hot-dip galvanized layer 20 in the observation field region 50 from the contrast. Referring to FIG. 1, surface S of hot-dip galvanized layer 20 in observation field region 50 is represented by a curved line. In FIG. 1, two points of intersection between the surface S of the hot-dip galvanized layer 20 and the observation field region 50 are defined as points P1 and P2. That is, the point P1 is defined as one end of the surface S in the observation visual field area 50 and the point P2 is defined as the other end of the surface S in the observation visual field area 50 . Furthermore, the dashed line A shown in FIG. 1 is a line segment connecting the points P1 and P2.

Both the surface S in the observation visual field region 50 and the dashed line A have one end at the point P1 and the other end at the point P2. Therefore, by comparing the length of the surface S in the observation visual field region 50 and the length of the dashed line A, fine unevenness of the surface S of the hot-dip galvanized layer 20 can be evaluated. Therefore, in this embodiment, the length of the surface S of the hot-dip galvanized layer 20 in the observation field region 50 is defined as SL. Furthermore, the length of the dashed line A in the observation visual field area 50, that is, the shortest distance between the points P1 and P2 is defined as SD. As described above, the base material steel sheet 10 and the hot-dip galvanized layer 20 can be identified from the contrast in the observation field region 50 . Therefore, SL and SD can be obtained as appropriate by performing image analysis on the observation visual field region 50 .

Here, it is defined as Fn1=SL/SD. Fn1 is an index of fine irregularities formed on the surface S of the hot-dip galvanized layer 20 in the observation field region 50 . Fn1 is a positive number equal to or greater than 1, and the closer Fn1 is to 1, the smaller the minute irregularities formed on the surface S of the hot-dip galvanized layer 20 are. Thus, with Fn1, it is possible to quantitatively evaluate the fine irregularities of the surface S of the hot-dip galvanized layer 20 .

Subsequently, the present inventors observed the cross section of the hot-dip galvanized steel sheet 1 having the hot-dip galvanized layer 20 having the above-described chemical composition with a secondary electron image using an SEM, and observed the surface S of the hot-dip galvanized layer 20. Fine unevenness was evaluated. As a result, the inventors of the present invention have found that the chemical composition of the hot-dip galvanized layer 20 remarkably increases Fn1 when Mg is contained in an amount of 0.5% by mass or more. Accordingly, the present inventors specifically measured the Fn1 of the surface S of the hot-dip galvanized layer 20 of the hot-dip galvanized steel sheet 1 having the hot-dip galvanized layer 20 containing 0.5% or more of Mg.

FIG. 2 is a schematic diagram showing a cross section of an example of the hot-dip galvanized steel sheet 1 having the hot-dip galvanized layer 20 having the chemical composition described above. FIG. 2 was created using a conventional hot-dip galvanized steel sheet 1 containing 0.5% by mass or more of Mg. 2, the horizontal direction is the rolling direction (L direction) of the hot-dip galvanized steel sheet 1, and the vertical direction is the plate thickness direction (H direction) of the hot-dip galvanized steel sheet 1, as in FIG. Also in FIG. 2, similarly to FIG. 1, the L-direction length of the observation visual field region 50 is 120 μm, and the H-direction length is 96 μm.

A large number of fine irregularities are formed on the surface S of the hot-dip galvanized layer 20 shown in FIG. Specifically, image analysis is performed on FIG. (=SL/SD) was obtained. As a result, Fn1 was 2.50 on the surface S of the hot-dip galvanized layer 20 shown in FIG.

In this way, the present inventors have found Fn1 that can sufficiently improve the appearance quality of the hot-dip galvanized steel sheet 1 having the hot-dip galvanized layer 20 containing 0.5% by mass or more of Mg in addition to the chemical composition described above. , examined in detail. As a result, in addition to the chemical composition described above, the hot-dip galvanized steel sheet 1 having the hot-dip galvanized layer 20 containing 0.5% by mass or more of Mg has excellent appearance quality if Fn1 is 1.50 or less. was found to have

Specifically, FIG. 3 is a schematic diagram showing a cross section of an example of the hot-dip galvanized steel sheet 1 according to this embodiment. FIG. 3 was created by the method described below. 3, the horizontal direction is the rolling direction (L direction) of the hot-dip galvanized steel sheet 1, and the vertical direction is the plate thickness direction (H direction) of the hot-dip galvanized steel sheet 1, as in FIGS. . Also in FIG. 3, similarly to FIGS. 1 and 2, the L-direction length of the observation visual field region 50 is 120 μm, and the H-direction length is 96 μm.

The surface S of the hot-dip galvanized layer 20 shown in FIG. 3 has greatly reduced fine irregularities as compared with FIG. Specifically, image analysis is performed on FIG. As a result of calculating (=SL/SD), Fn1 was 1.00. Thus, the surface S of the hot-dip galvanized layer 20 of the hot-dip galvanized steel sheet 1 according to the present embodiment shown in FIG. 3 is very smooth. As a result, the hot-dip galvanized steel sheet 1 according to the present embodiment has superior appearance quality as compared with the conventional hot-dip galvanized steel sheet 1 shown in FIG.

Similarly, the present inventors found that, in addition to the chemical composition described above, the hot-dip galvanized steel sheet 1 having the hot-dip galvanized layer 20 containing 0 to less than 0.5% by mass of Mg also has a surface S of Fn1 Various measurements were taken. As a result, in addition to the above chemical composition, the hot-dip galvanized steel sheet 1 having the hot-dip galvanized layer 20 containing 0 to less than 0.5% by mass of Mg is excellent if Fn1 is 1.10 or less. Detailed studies by the present inventors have revealed that it has good appearance quality.

Based on the above knowledge, on the surface S of the hot-dip galvanized layer 20 of the hot-dip galvanized steel sheet 1 according to the present embodiment, in the observation field region 50, Fn1 (=SL/SD) satisfies the following formula (1) .
SL/SD≦α (1)
Here, α in the formula (1) is 1.10 when the Mg content in the hot-dip galvanized layer 20 is 0 to less than 0.5% by mass, and the Mg content in the hot-dip galvanized layer 20 is 0. 0.5 to 30.0% by mass, it is 1.50.

That is, hot dip zinc having a hot dip galvanized layer 20 with a chemical composition containing Mg: 0 to 30.0%, Al: 0.1 to 60.0%, and Zn: 35.0% or more in mass % The plated steel sheet 1 has an Fn1 of 1.10 or less when the Mg content is 0 to less than 0.5%, and an Fn1 of 1.50 or less when the Mg content is 0.5 to 30.0%. Detailed studies by the present inventors have revealed that if there is, the quality of the appearance is excellent.

On the other hand, when Fn1 was reduced on the surface S of the hot-dip galvanized layer 20, there was a case where a dent was partially confirmed. Specifically, referring to FIG. 4, a depression (concave portion) is partially confirmed in the vicinity of the L-direction central portion of the observation visual field region 50 on the surface S of the hot-dip galvanized layer 20 . The reason for this is considered by the inventors as follows.

As described in the chemical composition above, the hot-dip galvanized layer 20 according to the present embodiment contains Al, which is an easily oxidizable element. Therefore, oxidized dross is likely to be formed in the hot-dip galvanizing bath, which is the raw material of the hot-dip galvanizing layer 20 according to the present embodiment. Note that Mg is more easily oxidized than Al. Therefore, it is considered that when the Mg content is 0.5% or more, a large amount of oxidized dross is formed and Fn1 becomes larger. Here, the oxidized dross in this specification means an oxide formed by reaction between elements contained in the hot-dip galvanizing bath and oxygen in the air.

Furthermore, in the process of manufacturing the hot-dip galvanized steel sheet 1, the base steel sheet 10 is immersed in a hot-dip galvanizing bath so that the surface of the base steel sheet 10 is coated with hot-dip galvanization. That is, when a hot-dip galvanizing bath containing Al is used, oxide dross floating on the surface of the hot-dip galvanizing bath tends to adhere to the surface of the base steel plate 10 along with the hot-dip galvanizing.

That is, the present inventors believe that the fine irregularities formed on the surface S of the hot-dip galvanized layer 20 having the chemical composition described above are formed by the remaining oxidized dross. Therefore, in the present embodiment, the formation of oxidized dross is greatly suppressed in the liquid surface of the hot-dip galvanizing bath in the vicinity of the threading line of the base steel sheet 10 . As a result, in the hot-dip galvanized steel sheet 1 according to the present embodiment, Fn1 can be reduced even with the hot-dip galvanized layer 20 having the chemical composition described above.

On the other hand, as a result of greatly suppressing the formation of oxidized dross in a part of the liquid surface of the hot-dip galvanizing bath, the amount of hot-dip galvanized coating may fluctuate. The area where the amount of hot-dip galvanization is partially reduced remains as a recess after the hot-dip galvanization solidifies. The present inventors believe that recesses are formed in the surface S of the hot-dip galvanized layer 20 in this way.

Here, even if recesses are formed on the surface S of the hot-dip galvanized layer 20, if the size of the recesses is small and the number of recesses is not too large, the appearance quality of the hot-dip galvanized steel sheet 1 is large. have no effect. Therefore, in this embodiment, first, the size of the recess formed on the surface S of the hot-dip galvanized layer 20 is defined as follows. When the thickness of the hot-dip galvanized layer 20 is defined as T μm, in a cross section including the rolling direction (L direction) of the hot-dip galvanized steel sheet 1 and the plate thickness direction (H direction) of the hot-dip galvanized steel sheet 1, hot-dip zinc It is formed on the surface S of the plating layer 20, and the length W μm in the L direction and the depth D μm in the H direction satisfy Expressions (2) to (4).
D≦0.7×T (2)
D≤5.0 (3)
0.2×D≦W≦5.0×D (4)

The number of recesses defined as above is 1.0 or more per 10 cm in the L direction. Note that if the number of concave portions is too large, Fn1 exceeds the above range. Therefore, in the hot-dip galvanized steel sheet 1 according to the present embodiment, Fn1 satisfies the formula (1), and the size of the concave portion satisfies the formulas (2) to (4). As a result, the hot-dip galvanized layer 20 has a chemical composition containing Mg: 0 to 30.0%, Al: 0.1 to 60.0%, and Zn: 35.0% or more by mass%. Even if it is, it is possible to obtain a hot-dip galvanized steel sheet 1 having excellent appearance quality.

The gist of the hot-dip galvanized steel sheet 1 according to the present embodiment completed based on the above knowledge is as follows.

[1]
A hot-dip galvanized steel sheet,
a base material steel plate;
A hot-dip galvanized layer formed on the base steel plate,
The hot-dip galvanized layer is mass %,
Al: 0.1 to 60.0%,
Mg: 0-30.0%,
Si: 0 to 1.0%,
B: 0 to 0.50%,
Ca: 0-3.0%,
Y: 0 to 3.0%,
La: 0 to 3.0%,
Ce: 0 to 3.0%,
Cr: 0-0.5%,
Ti: 0 to 0.5%,
Ni: 0 to 0.5%,
Co: 0-0.5%,
V: 0 to 0.5%,
Nb: 0 to 0.5%,
Cu: 0-0.5%,
Mn: 0-0.5%,
Sr: 0-0.5%,
Sb: 0-0.5%,
Pb: 0 to 0.5%,
Sn: 0 to 2.0%,
Bi: 0 to 2.0%,
In: 0 to 2.0%,
Fe: 0 to 5.0%, and
Balance: having a chemical composition consisting of 35.0% or more of Zn and impurities,
When the rolling direction of the hot-dip galvanized steel sheet is defined as the L direction and the plate thickness direction of the hot-dip galvanized steel sheet is defined as the H direction,
In a rectangular observation field region including the surface of the hot-dip galvanized layer, the side of the hot-dip galvanized steel sheet extending in the L direction is 120 μm in length and the side extending in the H direction is 96 μm in length,
The length of the surface of the hot-dip galvanized layer is SL,
One end of the surface of the hot-dip galvanized layer is P1 point,
The other end of the surface of the hot-dip galvanized layer is P2 point,
When the shortest distance between the P1 point and the P2 point is defined as SD,
The SL and the SD satisfy the formula (1),
When the thickness of the hot-dip galvanized layer is defined as T μm,
In a cross section including the L direction and the H direction,
formed on the surface of the hot-dip galvanized layer,
The length W μm in the L direction and the depth D μm in the H direction satisfy the formulas (2) to (4), and the number of recesses satisfying the formulas (2) to (4) is 1.0 or more per 10 cm in the L direction.
Hot-dip galvanized steel sheet.
SL/SD≦α (1)
D≦0.7×T (2)
D≤5.0 (3)
0.2×D≦W≦5.0×D (4)
Here, α in the formula (1) is 1.10 when the Mg content in the hot-dip galvanized layer is 0 to less than 0.5% by mass, and the Mg content in the hot-dip galvanized layer is 0. 0.5 to 30.0% by mass, it is 1.50.

[2]
The hot-dip galvanized steel sheet according to [1],
The chemical composition of the hot-dip galvanized layer contains one or more elements selected from Groups 1 to 8,
Hot-dip galvanized steel sheet.
Group 1: Mg: 0.1 to 30.0%,
Second group: Si: 0.1 to 1.0%,
Group 3: B: 0.01-0.50%,
Group 4: Ca, Y, La, and Ce: 0.1-3.0%,
Group 5: Cr, Ti, Ni, Co, V, Nb, Cu, and Mn: 0.1 to 0.5%,
Group 6: Sr, Sb, and Pb: 0.1 to 0.5%,
Group 7: Sn, Bi, and In: 0.1 to 2.0%,
Group 8: Fe: 0.1 to 5.0%

The hot-dip galvanized steel sheet 1 according to this embodiment will be described in detail below. In this specification, "%" regarding the content of elements means "% by mass" unless otherwise specified.

[About hot-dip galvanized steel sheets]
A hot-dip galvanized steel sheet 1 according to this embodiment includes a base steel sheet 10 and a hot-dip galvanized layer 20 formed on the base steel sheet 10 . The base material steel sheet 10 and the hot-dip galvanized layer 20 will be described in detail below.

[About the base material steel plate]
The base material steel plate 10 according to this embodiment is not particularly limited. That is, in the present embodiment, the base material steel sheet 10 is a known material applied to the hot-dip galvanized steel sheet 1 according to the mechanical properties (for example, tensile strength, workability, etc.) required for the hot-dip galvanized steel sheet 1 to be manufactured. steel plate should be used. For example, the base material steel plate 10 may be a steel plate for building materials, a steel plate for automobile exterior panels, or a steel plate for electrical equipment. Moreover, the base material steel plate 10 may be a hot-rolled steel plate or a cold-rolled steel plate.

[About hot-dip galvanized layer]
The hot-dip galvanized layer 20 according to this embodiment is formed on the surface of the base steel plate 10 . The hot-dip galvanized layer 20 is formed by solidifying after hot-dip galvanizing adheres on the base material steel plate 10 .

[About the chemical composition of the hot-dip galvanized layer]
The chemical composition of the hot-dip galvanized layer 20 according to this embodiment contains the following elements.

Al: 0.1-60.0%
Aluminum (Al) is an easily oxidizable element and enhances the corrosion resistance of the hot-dip galvanized layer 20 by sacrificial corrosion protection. If the Al content is too low, this effect cannot be sufficiently obtained even if the content of other elements is within the range of the present embodiment. On the other hand, if the Al content is too high, even if the content of other elements is within the range of the present embodiment, the corrosion resistance after welding may be extremely lowered. Therefore, the Al content is 0.1-60.0%. The lower limit of the Al content is preferably 0.1%, more preferably 1.0%, still more preferably 5.0%, still more preferably 7.0%, still more preferably 10.0%. %. A preferable upper limit of the Al content is 55.0%, more preferably 50.0%, and still more preferably 45.0%.

The rest of the chemical composition of the hot-dip galvanized layer 20 according to this embodiment consists of Zn and impurities. Here, the impurities are those that are mixed from the raw material when the hot-dip galvanizing treatment is performed, are not intentionally included, and do not adversely affect the hot-dip galvanized steel sheet 1 according to the present embodiment. Means what is allowed in the range.

[Regarding arbitrary elements]
The chemical composition of the hot-dip galvanized layer 20 according to this embodiment may further contain one or more elements selected from the following first to eighth groups. The first to eighth groups will be described below.
Group 1:
Mg: 0-30.0%
Second group:
Si: 0-1.0%
Third group:
B: 0-0.50%
Fourth group:
Ca: 0-3.0%
Y: 0-3.0%
La: 0-3.0%
Ce: 0-3.0%
Group 5:
Cr: 0-0.5%
Ti: 0-0.5%
Ni: 0-0.5%
Co: 0-0.5%
V: 0-0.5%
Nb: 0-0.5%
Cu: 0-0.5%
Mn: 0-0.5%
Group 6:
Sr: 0-0.5%
Sb: 0-0.5%
Pb: 0-0.5%
Group 7:
Sn: 0-2.0%
Bi: 0-2.0%
In: 0-2.0%
Group 8:
Fe: 0-5.0%

[Group 1 (Mg)]
The chemical composition of the hot-dip galvanized layer 20 according to the present embodiment may further contain Mg instead of part of Zn.

Mg: 0-30.0%
Magnesium (Mg) is an optional element and may not be contained. That is, the Mg content may be 0%. Mg is an easily oxidizable element and enhances the corrosion resistance of the hot-dip galvanized layer 20 by sacrificial corrosion protection. As long as the Mg content is even small, the above effect can be obtained to some extent. On the other hand, if the Mg content is too high, the viscosity of the hot-dip galvanizing bath increases and the appearance quality of the hot-dip galvanized steel sheet 1 deteriorates even if the content of other elements is within the range of the present embodiment. Therefore, the Mg content is 0-30.0%. In addition, if the Mg content is 0.5% or more, the corrosion resistance of the hot-dip galvanized steel sheet 1 is further enhanced. On the other hand, in this case, oxidized dross is more likely to be formed on the surface S of the hot-dip galvanized layer 20, and Fn1 (=SL/SD) is likely to increase. A preferable lower limit of the Mg content is more than 0%, more preferably 0.1%, more preferably 0.5%, more preferably 1.0%, more preferably 2.0% is. A preferable upper limit of the Mg content is 25.0%, more preferably 20.0%, and still more preferably 15.0%.

[Second group (Si)]
The chemical composition of the hot-dip galvanized layer 20 according to the present embodiment may further contain Si instead of part of Zn.

Si: 0-1.0%
Silicon (Si) is an optional element and may not be contained. That is, the Si content may be 0%. Si enhances the corrosion resistance of the hot-dip galvanized steel sheet 1 . If even a small amount of Si is contained, the above effect can be obtained to some extent. On the other hand, if the Si content is too high, the viscosity of the hot-dip galvanizing bath increases and the appearance quality of the hot-dip galvanized steel sheet 1 deteriorates even if the contents of other elements are within the ranges of the present embodiment. Therefore, the Si content is 0-1.0%. A preferable lower limit of the Si content is more than 0%, more preferably 0.1%, still more preferably 0.2%, still more preferably 0.3%. A preferable upper limit of the Si content is 0.9%, more preferably 0.8%, and still more preferably 0.7%.

[Third group (B)]
The chemical composition of the hot-dip galvanized layer 20 according to the present embodiment may further contain B instead of part of Zn.

B: 0-0.50%
Boron (B) is an optional element and may not be contained. That is, the B content may be 0%. B suppresses hot dip cracking of the hot-dip galvanized steel sheet 1 after welding. If B is contained even in a small amount, the above effect can be obtained to some extent. On the other hand, if the B content is too high, the melting point of the hot-dip galvanizing bath may increase even if the contents of other elements are within the ranges of the present embodiment, making hot-dip galvanizing treatment difficult. Therefore, the B content is 0-0.50%. The lower limit of the B content is preferably over 0%, more preferably 0.01%, and still more preferably 0.02%. A preferable upper limit of the B content is 0.45%, more preferably 0.40%.

[Group 4 (Ca, Y, La, and Ce)]
The chemical composition of the hot-dip galvanized layer 20 according to the present embodiment may further contain one or more selected from the group consisting of Ca, Y, La, and Ce, instead of part of Zn. All of these elements are optional elements and enhance the corrosion resistance of the hot-dip galvanized steel sheet 1 .

Ca: 0-3.0%
Calcium (Ca) is an optional element and may not be contained. That is, the Ca content may be 0%. Ca forms an intermetallic compound with Al and Zn in the hot-dip galvanized layer 20 . As a result, the corrosion resistance of the hot-dip galvanized steel sheet 1 is enhanced. As long as even a little Ca is contained, the above effect can be obtained to some extent. On the other hand, if the Ca content is too high, even if the contents of other elements are within the ranges of the present embodiment, oxidized dross is likely to be formed, and the appearance quality of the hot-dip galvanized steel sheet 1 is deteriorated. Therefore, the Ca content is 0-3.0%. The lower limit of the Ca content is preferably over 0%, more preferably 0.1%, still more preferably 0.2%, still more preferably 0.3%. A preferable upper limit of the Ca content is 2.8%, more preferably 2.5%, and still more preferably 2.0%.

Y: 0-3.0%
Yttrium (Y) is an optional element and may not be contained. That is, the Y content may be 0%. Like Ca, Y forms an intermetallic compound with Al and Zn in the hot-dip galvanized layer 20 . As a result, the corrosion resistance of the hot-dip galvanized steel sheet 1 is enhanced. If Y is contained even in a small amount, the above effect can be obtained to some extent. On the other hand, if the Y content is too high, even if the contents of other elements are within the ranges of the present embodiment, oxidized dross is likely to be formed, and the appearance quality of the hot-dip galvanized steel sheet 1 is deteriorated. Therefore, the Y content is 0-3.0%. The lower limit of the Y content is preferably over 0%, more preferably 0.1%, still more preferably 0.2%, still more preferably 0.3%. A preferable upper limit of the Y content is 2.8%, more preferably 2.5%, and still more preferably 2.0%.

La: 0-3.0%
Lanthanum (La) is an optional element and may not be contained. That is, the La content may be 0%. La, like Ca, forms an intermetallic compound with Al and Zn in the hot-dip galvanized layer 20 . As a result, the corrosion resistance of the hot-dip galvanized steel sheet 1 is enhanced. The above effect can be obtained to some extent if even a small amount of La is contained. On the other hand, if the La content is too high, oxidized dross is likely to be formed even if the contents of other elements are within the ranges of the present embodiment, and the appearance quality of the hot-dip galvanized steel sheet 1 deteriorates. Therefore, the La content is 0-3.0%. The lower limit of the La content is preferably over 0%, more preferably 0.1%, still more preferably 0.2%, still more preferably 0.3%. A preferable upper limit of the La content is 2.8%, more preferably 2.5%, and still more preferably 2.0%.

Ce: 0-3.0%
Selenium (Ce) is an optional element and may not be contained. That is, the Ce content may be 0%. Ce, like Ca, forms an intermetallic compound with Al and Zn in the hot-dip galvanized layer 20 . As a result, the corrosion resistance of the hot-dip galvanized steel sheet 1 is enhanced. If even a little Ce is contained, the above effect can be obtained to some extent. On the other hand, if the Ce content is too high, oxidized dross is likely to be formed even if the contents of other elements are within the ranges of the present embodiment, and the appearance quality of the hot-dip galvanized steel sheet 1 deteriorates. Therefore, the Ce content is 0-3.0%. A preferable lower limit of the Ce content is more than 0%, more preferably 0.1%, still more preferably 0.2%, still more preferably 0.3%. A preferable upper limit of the Ce content is 2.8%, more preferably 2.5%, and still more preferably 2.0%.

[Group 5 (Cr, Ti, Ni, Co, V, Nb, Cu, and Mn)]
The chemical composition of the hot-dip galvanized layer 20 according to the present embodiment further includes one or more selected from the group consisting of Cr, Ti, Ni, Co, V, Nb, Cu, and Mn instead of part of Zn. may contain. All of these elements are optional elements and improve the appearance quality of the hot-dip galvanized steel sheet 1 .

Cr: 0-0.5%
Chromium (Cr) is an optional element and may not be contained. That is, the Cr content may be 0%. Cr enhances the appearance quality of the hot-dip galvanized steel sheet 1 . Cr also forms an intermetallic compound with Al in the hot-dip galvanized layer 20 . As a result, the corrosion resistance of the hot-dip galvanized steel sheet 1 is enhanced. If even a little Cr is contained, the above effect can be obtained to some extent. On the other hand, if the Cr content is too high, the viscosity of the hot-dip galvanizing bath increases and the appearance quality of the hot-dip galvanized steel sheet 1 deteriorates even if the contents of other elements are within the ranges of the present embodiment. Therefore, the Cr content is 0-0.5%. A preferable lower limit of the Cr content is over 0%, more preferably 0.05%, and still more preferably 0.1%. A preferable upper limit of the Cr content is less than 0.5%, more preferably 0.4%.

Ti: 0-0.5%
Titanium (Ti) is an optional element and may not be contained. That is, the Ti content may be 0%. Ti enhances the appearance quality of the hot-dip galvanized steel sheet 1 . Ti further forms an intermetallic compound with Al in the hot-dip galvanized layer 20 . As a result, the corrosion resistance of the hot-dip galvanized steel sheet 1 is enhanced. If even a little Ti is contained, the above effect can be obtained to some extent. On the other hand, if the Ti content is too high, the viscosity of the hot-dip galvanizing bath increases and the appearance quality of the hot-dip galvanized steel sheet 1 deteriorates even if the contents of other elements are within the ranges of the present embodiment. Therefore, the Ti content is 0-0.5%. The lower limit of the Ti content is preferably over 0%, more preferably 0.05%, still more preferably 0.1%. A preferable upper limit of the Ti content is less than 0.5%, more preferably 0.4%.

Ni: 0-0.5%
Nickel (Ni) is an optional element and may not be contained. That is, the Ni content may be 0%. Ni enhances the appearance quality of the hot-dip galvanized steel sheet 1 . Ni also forms an intermetallic compound with Al in the hot-dip galvanized layer 20 . As a result, the corrosion resistance of the hot-dip galvanized steel sheet 1 is enhanced. If even a little Ni is contained, the above effect can be obtained to some extent. On the other hand, if the Ni content is too high, the viscosity of the hot-dip galvanizing bath increases and the appearance quality of the hot-dip galvanized steel sheet 1 deteriorates, even if the contents of other elements are within the ranges of the present embodiment. Therefore, the Ni content is 0-0.5%. A preferable lower limit of the Ni content is more than 0%, more preferably 0.05%, and still more preferably 0.1%. A preferable upper limit of the Ni content is less than 0.5%, more preferably 0.4%.

Co: 0-0.5%
Cobalt (Co) is an optional element and may not be contained. That is, the Co content may be 0%. Co enhances the appearance quality of the hot-dip galvanized steel sheet 1 . Co also forms an intermetallic compound with Al in the hot-dip galvanized layer 20 . As a result, the corrosion resistance of the hot-dip galvanized steel sheet 1 is enhanced. As long as even a small amount of Co is contained, the above effect can be obtained to some extent. On the other hand, if the Co content is too high, the viscosity of the hot-dip galvanizing bath increases and the appearance quality of the hot-dip galvanized steel sheet 1 deteriorates even if the contents of other elements are within the ranges of the present embodiment. Therefore, the Co content is 0-0.5%. The lower limit of the Co content is preferably over 0%, more preferably 0.05%, still more preferably 0.1%. A preferable upper limit of the Co content is less than 0.5%, more preferably 0.4%.

V: 0-0.5%
Vanadium (V) is an optional element and may not be contained. That is, the V content may be 0%. V enhances the appearance quality of the hot-dip galvanized steel sheet 1 . V further forms an intermetallic compound with Al in the hot-dip galvanized layer 20 . As a result, the corrosion resistance of the hot-dip galvanized steel sheet 1 is enhanced. If V is contained even in a small amount, the above effect can be obtained to some extent. On the other hand, if the V content is too high, the viscosity of the hot-dip galvanizing bath increases and the appearance quality of the hot-dip galvanized steel sheet 1 deteriorates even if the contents of other elements are within the ranges of the present embodiment. Therefore, the V content is 0-0.5%. A preferable lower limit of the V content is more than 0%, more preferably 0.05%, and still more preferably 0.1%. A preferable upper limit of the V content is less than 0.5%, more preferably 0.4%.

Nb: 0-0.5%
Niobium (Nb) is an optional element and may not be contained. That is, the Nb content may be 0%. Nb enhances the appearance quality of the hot-dip galvanized steel sheet 1 . Nb further forms an intermetallic compound with Al in the hot-dip galvanized layer 20 . As a result, the corrosion resistance of the hot-dip galvanized steel sheet 1 is enhanced. If even a small amount of Nb is contained, the above effect can be obtained to some extent. On the other hand, if the Nb content is too high, the viscosity of the hot-dip galvanizing bath increases and the appearance quality of the hot-dip galvanized steel sheet 1 deteriorates even if the contents of other elements are within the ranges of the present embodiment. Therefore, the Nb content is 0-0.5%. A preferable lower limit of the Nb content is more than 0%, more preferably 0.05%, and still more preferably 0.1%. A preferable upper limit of the Nb content is less than 0.5%, more preferably 0.4%.

Cu: 0-0.5%
Copper (Cu) is an optional element and may not be contained. That is, the Cu content may be 0%. Cu enhances the appearance quality of the hot-dip galvanized steel sheet 1 . Cu also forms an intermetallic compound with Al in the hot-dip galvanized layer 20 . As a result, the corrosion resistance of the hot-dip galvanized steel sheet 1 is enhanced. If even a small amount of Cu is contained, the above effect can be obtained to some extent. On the other hand, if the Cu content is too high, the viscosity of the hot-dip galvanizing bath increases and the appearance quality of the hot-dip galvanized steel sheet 1 deteriorates even if the contents of other elements are within the ranges of the present embodiment. Therefore, the Cu content is 0-0.5%. A preferable lower limit of the Cu content is more than 0%, more preferably 0.05%, and still more preferably 0.1%. A preferable upper limit of the Cu content is less than 0.5%, more preferably 0.4%.

Mn: 0-0.5%
Manganese (Mn) is an optional element and may not be contained. That is, the Mn content may be 0%. Mn enhances the appearance quality of the hot-dip galvanized steel sheet 1 . Mn also forms an intermetallic compound with Al in the hot-dip galvanized layer 20 . As a result, the corrosion resistance of the hot-dip galvanized steel sheet 1 is enhanced. If even a small amount of Mn is contained, the above effect can be obtained to some extent. On the other hand, if the Mn content is too high, the viscosity of the hot-dip galvanizing bath increases and the appearance quality of the hot-dip galvanized steel sheet 1 deteriorates even if the contents of other elements are within the ranges of the present embodiment. Therefore, the Mn content is 0-0.5%. A preferable lower limit of the Mn content is more than 0%, more preferably 0.05%, and still more preferably 0.1%. A preferable upper limit of the Mn content is less than 0.5%, more preferably 0.4%.

[Group 6 (Sr, Sb, and Pb)]
The chemical composition of the hot-dip galvanized layer 20 according to the present embodiment may further contain one or more selected from the group consisting of Sr, Sb, and Pb instead of part of Zn. All of these elements are optional elements and improve the appearance quality of the hot-dip galvanized steel sheet 1 .

Sr: 0-0.5%
Strontium (Sr) is an optional element and may not be contained. That is, the Sr content may be 0%. Sr enhances the metallic luster of the hot-dip galvanized layer 20 and enhances the appearance quality of the hot-dip galvanized steel sheet 1 . As long as Sr is contained even in a small amount, the above effect can be obtained to some extent. On the other hand, if the Sr content is too high, oxidized dross is likely to be formed even if the contents of other elements are within the ranges of the present embodiment, and the appearance quality of the hot-dip galvanized steel sheet 1 is deteriorated. Therefore, the Sr content is 0-0.5%. A preferable lower limit of the Sr content is more than 0%, more preferably 0.05%, and still more preferably 0.1%. A preferable upper limit of the Sr content is less than 0.5%, more preferably 0.4%.

Sb: 0-0.5%
Antimony (Sb) is an optional element and may not be contained. That is, the Sb content may be 0%. Sb enhances the metallic luster of the hot-dip galvanized layer 20 and enhances the appearance quality of the hot-dip galvanized steel sheet 1 . The above effect can be obtained to some extent if even a small amount of Sb is contained. On the other hand, if the Sb content is too high, even if the contents of other elements are within the ranges of the present embodiment, oxidized dross is likely to be formed, and the appearance quality of the hot-dip galvanized steel sheet 1 is deteriorated. Therefore, the Sb content is 0-0.5%. A preferable lower limit of the Sb content is more than 0%, more preferably 0.05%, and still more preferably 0.1%. A preferable upper limit of the Sb content is less than 0.5%, more preferably 0.4%.

Pb: 0-0.5%
Lead (Pb) is an optional element and may not be contained. That is, the Pb content may be 0%. Pb enhances the metallic luster of the hot-dip galvanized layer 20 and enhances the appearance quality of the hot-dip galvanized steel sheet 1 . If even a small amount of Pb is contained, the above effect can be obtained to some extent. On the other hand, if the Pb content is too high, even if the content of other elements is within the range of the present embodiment, oxidized dross is likely to be formed, and the appearance quality of the hot-dip galvanized steel sheet 1 is deteriorated. Therefore, the Pb content is 0-0.5%. A preferable lower limit of the Pb content is over 0%, more preferably 0.05%, and still more preferably 0.1%. A preferable upper limit of the Pb content is less than 0.5%, more preferably 0.4%.

[Seventh group (Sn, Bi, and In)]
The chemical composition of the hot-dip galvanized layer 20 according to the present embodiment may further contain one or more selected from the group consisting of Sn, Bi, and In instead of part of Zn. All of these elements are optional elements and enhance the corrosion resistance of the hot-dip galvanized steel sheet 1 .

Sn: 0-2.0%
Tin (Sn) is an optional element and may not be contained. That is, the Sn content may be 0%. Sn forms an intermetallic compound with Mg in the hot-dip galvanized layer 20 . As a result, the corrosion resistance of the hot-dip galvanized steel sheet 1 is enhanced. If even a small amount of Sn is contained, the above effect can be obtained to some extent. On the other hand, if the Sn content is too high, the viscosity of the hot-dip galvanizing bath increases and the appearance quality of the hot-dip galvanized steel sheet 1 deteriorates even if the contents of other elements are within the ranges of the present embodiment. Therefore, the Sn content is 0-2.0%. The lower limit of the Sn content is preferably over 0%, more preferably 0.1%, still more preferably 0.2%, still more preferably 0.3%. A preferable upper limit of the Sn content is 1.9%, more preferably 1.8%, and still more preferably 1.7%.

Bi: 0-2.0%
Bismuth (Bi) is an optional element and may not be contained. That is, the Bi content may be 0%. Bi forms an intermetallic compound with Mg in the hot-dip galvanized layer 20 . As a result, the corrosion resistance of the hot-dip galvanized steel sheet 1 is enhanced. If even a small amount of Bi is contained, the above effect can be obtained to some extent. On the other hand, if the Bi content is too high, the viscosity of the hot-dip galvanizing bath increases and the appearance quality of the hot-dip galvanized steel sheet 1 deteriorates even if the contents of other elements are within the ranges of the present embodiment. Therefore, the Bi content is 0-2.0%. A preferable lower limit of the Bi content is more than 0%, more preferably 0.1%, still more preferably 0.2%, still more preferably 0.3%. A preferable upper limit of the Bi content is 1.9%, more preferably 1.8%, and still more preferably 1.7%.

In: 0-2.0%
Indium (In) is an optional element and may not be contained. That is, the In content may be 0%. In forms an intermetallic compound with Mg in the hot-dip galvanized layer 20 . As a result, the corrosion resistance of the hot-dip galvanized steel sheet 1 is enhanced. If even a small amount of In is contained, the above effect can be obtained to some extent. On the other hand, if the In content is too high, the viscosity of the hot-dip galvanizing bath increases and the appearance quality of the hot-dip galvanized steel sheet 1 deteriorates even if the contents of other elements are within the ranges of the present embodiment. Therefore, the In content is 0-2.0%. The lower limit of the In content is preferably over 0%, more preferably 0.1%, still more preferably 0.2%, still more preferably 0.3%. A preferable upper limit of the In content is 1.9%, more preferably 1.8%, and still more preferably 1.7%.

[Eighth group (Fe)]
The chemical composition of the hot-dip galvanized layer 20 according to the present embodiment may further contain Fe instead of part of Zn.

Fe: 0-5.0%
Iron (Fe) is an optional element and may not be contained. That is, the Fe content may be 0%. Fe increases the hardness of the hot-dip galvanized layer 20 and enhances the workability of the hot-dip galvanized steel sheet 1 . If even a little Fe is contained, the above effects can be obtained to some extent. On the other hand, if the Fe content is too high, the hardness of the hot-dip galvanized layer 20 becomes too high even if the content of other elements is within the range of the present embodiment, and the workability of the hot-dip galvanized steel sheet 1 is rather deteriorated. descend. Therefore, the Fe content is 0-5.0%. A preferable lower limit of the Fe content is more than 0%, more preferably 0.05%, still more preferably 0.1%, still more preferably 0.5%. A preferable upper limit of the Fe content is 4.5%, more preferably 4.0%, and still more preferably 3.5%.

As described above, the chemical composition of the hot-dip galvanized layer 20 according to the present embodiment essentially contains Al, the first group (Mg), the second group (Si), the third group (B), the fourth group ( Ca, Y, La, and Ce), fifth group (Cr, Ti, Ni, Co, V, Nb, Cu, and Mn), sixth group (Sr, Sb, and Pb), seventh group (Sn, Bi, and In) and one or more elements of group 8 (Fe) are optionally contained, and the balance is Zn and impurities. Here, if the Zn content is too low, the mechanical properties required for the hot-dip galvanized steel sheet 1 may not be obtained. Therefore, the Zn content is 35.0% or more. A preferable lower limit of the Zn content is 37.0%, more preferably 39.0%. Although the upper limit of the Zn content is not particularly limited, it is substantially 99.9%.

In this embodiment, the chemical composition of the hot-dip galvanized layer 20 can be obtained by the following method. The hot-dip galvanized layer 20 is dissolved using inhibitor-containing hydrochloric acid. As the inhibitor, for example, the product name IBIT manufactured by Asahi Chemical Industry Co., Ltd. can be used. The solution is subjected to elemental analysis using an inductively coupled plasma (ICP) emission spectrometer. The chemical composition of the hot-dip galvanized layer 20 can be obtained by the above method.

[Regarding formula (1)]
The hot-dip galvanized layer 20 according to the present embodiment includes the surface S of the hot-dip galvanized layer 20, the length of the side extending in the L direction of the hot-dip galvanized steel sheet 1 is 120 μm, and the length of the side extending in the H direction is In the rectangular observation field region 50 of 96 μm, the length of the surface S of the hot-dip galvanized layer 20 is SL, one end of the surface S of the hot-dip galvanized layer 20 is P1, and the surface S of the hot-dip galvanized layer 20 is is defined as point P2, and the shortest distance between point P1 and point P2 is defined as SD, SL and SD satisfy equation (1).
SL/SD≦α (1)
Here, α in the formula (1) is 1.10 when the Mg content in the hot-dip galvanized layer 20 is 0 to less than 0.5% by mass, and the Mg content in the hot-dip galvanized layer 20 is 0. 0.5 to 30.0% by mass, it is 1.50.

As described above, Fn1 (=SL/SD) is an index of fine unevenness formed on surface S of hot-dip galvanized layer 20 in observation field region 50 . Fn1 is a positive number equal to or greater than 1, and the closer Fn1 is to 1, the smaller the minute irregularities formed on the surface S of the hot-dip galvanized layer 20 are. Specifically, the hot-dip galvanized layer 20 having a chemical composition containing Mg: 0 to less than 0.5%, Al: 0.1 to 60.0%, and Zn: 35.0% or more in mass% The hot-dip galvanized steel sheet 1 having the hot-dip galvanized layer 20 having the chemical composition of the hot-dip galvanized steel sheet 1 has excellent appearance quality if Fn1 is 1.10 or less. Furthermore, it has a hot-dip galvanized layer 20 with a chemical composition containing Mg: 0.5 to 30.0%, Al: 0.1 to 60.0%, and Zn: 35.0% or more in mass%. The hot-dip galvanized steel sheet 1 having the hot-dip galvanized layer 20 having the chemical composition of the hot-dip galvanized steel sheet 1 has excellent appearance quality if Fn1 is 1.50 or less.

As described above, Al is an easily oxidizable element, and oxidized dross is likely to be formed in a hot-dip galvanizing bath containing Al. Since Mg is an element that is more easily oxidized than Al, oxidized dross is more likely to adhere to the surface S of the hot-dip galvanized layer 20 containing 0.5% by mass or more of Mg. As a result, Fn1 tends to increase on the surface S of the hot-dip galvanized layer 20 . Therefore, in the hot-dip galvanized steel sheet 1 according to the present embodiment, the upper limit of Fn1 is defined depending on whether the Mg content is 0 to less than 0.5% or 0.5 to 30.0%. As a result, the appearance quality is superior to that of the conventional hot-dip galvanized steel sheet 1 when the Mg content is 0 to 30.0%.

When the hot-dip galvanized layer 20 has a chemical composition containing, by mass%, Mg: 0 to less than 0.5%, Al: 0.1 to 60.0%, and Zn: 35.0% or more, The upper limit of Fn1 is preferably 1.09, more preferably 1.08, still more preferably 1.07, still more preferably 1.05, still more preferably 1.04. As described above, the lower limit of Fn1 is 1.00 regardless of the Mg content.

When the hot-dip galvanized layer 20 has a chemical composition containing Mg: 0.5 to 30.0%, Al: 0.1 to 60.0%, and Zn: 35.0% or more by mass % , Fn1 is preferably 1.45, more preferably 1.40, still more preferably 1.35, still more preferably 1.30, still more preferably 1.25.

In this embodiment, Fn1 can be obtained by the following method. A test piece for microstructure observation is produced from the plate width central portion of the hot-dip galvanized steel sheet 1 according to the present embodiment. The microstructure observation is performed on the observation plane including the rolling direction (L direction) and the plate thickness direction (H direction) at the width center of the hot-dip galvanized steel sheet 1 . The size of the test piece for microstructure observation is not particularly limited as long as it is 5 mm in the L direction and an observation surface including the surface S of the hot-dip galvanized layer 20 can be obtained.

A secondary electron image (SEM image) is observed on the observation surface using an SEM. The size of the observation visual field area 50 is 120 μm in the L direction and 96 μm in the H direction. Also, the number of observation fields of view is not particularly limited, but is, for example, five fields of view. A person skilled in the art can identify the base material steel sheet 10 and the hot-dip galvanized layer 20 from the contrast in each observation field region 50 . That is, in each observation field region 50, the base material steel plate 10, the hot dip galvanized layer 20, the surface S of the hot dip galvanized layer 20, one end P1 point of the surface S, and the other end P2 point of the surface S is identified from the contrast. Furthermore, image analysis is performed for each observation field region 50 to obtain the length SL (μm) of the surface S and the shortest distance SD (μm) between the points P1 and P2. The image analysis method is not particularly limited, and may be a known method. Fn1 (=SL/SD) can be obtained from the obtained SL (μm) and SD (μm).

[Regarding concave part]
In the hot-dip galvanized steel sheet 1 according to the present embodiment, when the thickness of the hot-dip galvanized layer 20 is defined as T μm, a cross section including the rolling direction (L direction) and the plate thickness direction (H direction) of the hot-dip galvanized steel sheet 1 , the number of recesses formed on the surface S of the hot-dip galvanized layer 20 and having a length W μm in the L direction and a depth D μm in the H direction satisfying the formulas (2) to (4) is It is 1.0 or more per 10 cm.
D≦0.7×T (2)
D≤5.0 (3)
0.2×D≦W≦5.0×D (4)

As described above, even if recesses are formed on the surface S of the hot-dip galvanized layer 20, if the size of the recesses satisfies the formulas (2) to (4), Fn1 (=SL/SD) is α or less. As long as it is, it does not greatly affect the appearance quality. Therefore, in the present embodiment, by allowing the formation of recesses on the surface S of the hot-dip galvanized layer 20, the fine unevenness of the surface S is reduced. As used herein, the term “recess” means a recess in the surface layer of the hot-dip galvanized layer 20 where the thickness of the hot-dip galvanized layer 20 is locally reduced.

Here, the size of the recess will be specifically described with reference to the drawings. FIG. 5 is an enlarged view of area 60 of FIG. In FIG. 5, recesses are formed on the surface S of the hot-dip galvanized layer 20 . Referring to FIG. 5, a line segment parallel to the L direction and in contact with the bottom of the recess is defined as L1. Referring to FIG. 5, the surface S changes in the direction of gradually separating from the line segment L1, starting from the bottom. Furthermore, the surface S has an inflection point in the right direction from the bottom, which forms an upwardly convex shape. Similarly, the surface S also has an inflection point in the leftward direction from the bottom that forms an upwardly convex shape. Of these two inflection points, the one closer to the line segment L1 is defined as the upper end of the recess. A line segment passing through the upper end of the recess defined in this way and parallel to the L direction is defined as L2.

Referring to FIG. 5, line segments passing through the intersection of L2 and surface S and parallel to the H direction are defined as H1 and H2. The distance between the line segment L1 and the line segment L2 thus defined is defined as the size of the recess in the L direction. Similarly, the distance between the line segment H1 and the line segment H2 is defined as the size of the recess in the H direction. 4 and 5, the depth D μm in the H direction is 1.7 μm, and the length W μm in the L direction is 4.9 μm. Moreover, the thickness T μm of the hot-dip galvanized layer 20 shown in FIGS. 4 and 5 is 12 μm. The thickness of the hot-dip galvanized layer 20 can be obtained by a method described later.

Therefore, in the recesses shown in FIGS. 4 and 5, the depth D μm in the H direction is 0.7 times (0.7 × T μm = 8.4 μm) or less than the thickness T μm of the hot-dip galvanized layer 20, and the formula (2) is satisfied. In addition, the depth D μm in the H direction is 5.0 μm or less, satisfying Expression (3). Furthermore, the length W μm in the L direction is 0.2 times (0.2×D μm=0.34 μm) or more the depth D μm in the H direction, and five times (5.5 μm) the depth D μm in the H direction. 0×D μm=8.5 μm) and satisfies the formula (4).

The number of concave portions is 1.0 or more per 10 cm in the L direction. That is, when a cross section including the L direction and the H direction is observed, depending on the length of the observation visual field region 50 in the L direction, there may be cases where no concave portion is observed. In the observation visual field region 50 for obtaining Fn1 described above, the length in the L direction is 120 μm. Therefore, when the above observation field of view area 50 is used as a reference, it means that a concave portion is confirmed in one or more of the 833 fields of view. Also, the size of the field of view for confirming the concave portion is not particularly limited. However, according to the observation of the secondary electron image using the SEM for obtaining the above-mentioned Fn1, it is possible to simultaneously confirm the recesses, which is preferable.

Further, even if recesses are formed on the surface S of the hot-dip galvanized layer 20, if the size of the recesses is small and the number of recesses is not too large, the appearance quality of the hot-dip galvanized steel sheet 1 is greatly affected. do not give However, if the number of concave portions is too large, the above Fn1 exceeds α. Therefore, the upper limit of the number of concave portions is not particularly limited. The upper limit of the number of concave portions is, for example, 10000 per 10 cm in the L direction.

[About the thickness of the hot-dip galvanized layer]
The thickness T μm of the hot-dip galvanized layer 20 according to this embodiment is not particularly limited. The thickness T μm of the hot-dip galvanized layer 20 according to this embodiment is preferably 3.0 to 35.0 μm. In addition, the hot-dip galvanized layer 20 according to the present embodiment is arranged on both sides of the hot-dip galvanized steel sheet 1 respectively. In this specification, the thickness T μm of the hot-dip galvanized layer 20 means the thickness of the hot-dip galvanized layer 20 formed on one surface of the hot-dip galvanized steel sheet 1 . The thickness T μm of the hot-dip galvanized layer 20 is appropriately adjusted for the purpose of obtaining desired properties. The hot-dip galvanized steel sheet 1 according to this embodiment can obtain excellent appearance quality regardless of the thickness T μm of the hot-dip galvanized layer 20 .

The thickness of the hot-dip galvanized layer 20 can be obtained by a magnetic thickness test based on JIS H0401 (2013). Specifically, the hot-dip galvanized layer 20 is brought into contact with a probe of an eddy current phase type film thickness measuring device. The phase difference between the high-frequency magnetic field at the input side of the probe and the eddy currents excited thereby on the hot-dip galvanized layer 20 is measured. This retardation is converted into the thickness (μm) of the hot-dip galvanized layer 20 to obtain the thickness T μm of the hot-dip galvanized layer 20 .

[About other configurations]
The hot-dip galvanized steel sheet 1 according to this embodiment may have any configuration other than the base material steel sheet 10 and the hot-dip galvanized layer 20 . For example, the hot-dip galvanized layer 20 may have a conversion coating. Hereinafter, the case of having a chemical conversion coating will be described in detail with reference to the drawings.

FIG. 6 is a schematic diagram showing a cross section of another example of the hot-dip galvanized steel sheet 1 according to this embodiment. In FIG. 6, similarly to FIGS. 1 to 4, the horizontal direction is the rolling direction (L direction) of the hot-dip galvanized steel sheet 1, and the vertical direction is the plate thickness direction (H direction) of the hot-dip galvanized steel sheet 1. . Also in FIG. 6, similarly to FIGS. 1 to 4, the L-direction length of the observation visual field region 50 is 120 μm, and the H-direction length is 96 μm.

The hot-dip galvanized steel sheet 1 shown in FIG. 6 has a chemical conversion coating 30 in addition to the configuration of the hot-dip galvanized steel sheet 1 shown in FIGS. Specifically, the hot-dip galvanized steel sheet 1 shown in FIG. When the chemical conversion coating 30 is formed on the hot-dip galvanized layer 20, the corrosion resistance of the hot-dip galvanized steel sheet 1 is further enhanced.

In this embodiment, the type of chemical conversion coating 30 is not particularly limited. Conversion coating 30 is, for example, a chromium conversion coating. Conversion coating 30 may also be a phosphate conversion coating, an oxalate conversion coating, or a borate conversion coating. The thickness of the chemical conversion coating 30 is not particularly limited, and is, for example, 1 to 10 μm. In addition, in the hot-dip galvanized steel sheet 1 according to the present embodiment, the surface S of the hot-dip galvanized layer 20, one end P1 point of the surface S, and the other end P2 point of the surface S are above the chemical coating 30. It can be identified from the contrast even if it is formed in the That is, in the present embodiment, even if the chemical conversion coating 30 is formed on the hot-dip galvanized layer 20, the length SL of the surface S of the hot-dip galvanized layer 20 and the shortest distance SD between the points P1 and P2 can be determined by image analysis.

[Production method]
An example of a method for manufacturing the hot-dip galvanized steel sheet 1 according to this embodiment will be described. The manufacturing method described below is an example for manufacturing the hot-dip galvanized steel sheet 1 according to the present embodiment. That is, the hot-dip galvanized steel sheet 1 having the configuration described above may be manufactured by a manufacturing method other than the manufacturing method described below. However, the manufacturing method described below is a preferable example of the manufacturing method of the hot-dip galvanized steel sheet 1 according to the present embodiment.

The manufacturing method of the present embodiment includes a preparation step of preparing the base steel plate 10 and a hot dip galvanizing treatment step of forming the hot dip galvanized layer 20 on the base steel plate 10 . Each step will be described below.

[Preparation process]
In the preparation step, the base material steel plate 10 is prepared. As described above, the base material steel plate 10 may be a hot-rolled steel plate or a cold-rolled steel plate. Further, the chemical composition of the base steel sheet 10 is not particularly limited as long as the properties required for the base steel sheet 10 of the hot-dip galvanized steel sheet 1 are obtained.

[Hot-dip galvanizing process]
In the hot-dip galvanizing process, the prepared base steel sheet 10 is hot-dip galvanized to form a hot-dip galvanized layer 20 on the surface of the base steel sheet 10 . The hot-dip galvanizing equipment used in the hot-dip galvanizing process and the manufacturing method using the equipment will be specifically described below with reference to the drawings.

FIG. 7 is a side view showing an example of a hot dip galvanizing facility 100 used for conventional hot dip galvanizing treatment. Referring to FIG. 7 , in hot-dip galvanizing facility 100 , base steel plate 10 is transported and immersed in hot-dip galvanizing bath 120 stored in hot-dip galvanizing pot 110 . A sink roll 130 is arranged inside the molten zinc pot 110 . The sink roll 130 has a rotating shaft parallel to the width direction of the base steel plate 10 . The advancing direction of the base steel plate 10 is changed to above the hot-dip galvanizing equipment 100 by the sink roll 130 .

In the hot-dip galvanizing equipment 100 , a gas wiping device 140 is arranged above the hot-dip galvanizing bath 120 . The gas wiping device 140 includes a pair of gas injection devices and blows gas onto the base material steel plate 10 . In this way, part of the hot-dip galvanized coating on both surfaces of the base steel plate 10 is scraped off, and the amount of hot-dip galvanized coating on the surface of the base steel plate 10 is adjusted.

In the hot-dip galvanizing equipment 100 , a top roll 150 is further arranged above the gas wiping device 140 . The top roll 150 has a rotating shaft parallel to the width direction of the base steel plate 10 . The advancing direction of the base steel plate 10 is changed to the horizontal direction by the top roll 150 . The hot-dip galvanization on the surface of the base steel sheet 10 is solidified between the gas wiping device 140 and the top roll 150 as its temperature drops. Thus, the hot-dip galvanized layer 20 is formed on the surface of the base steel plate 10 . In order to form the hot-dip galvanizing layer 20 having the chemical composition described above, the chemical composition of the hot-dip galvanizing bath 120 should be adjusted to the chemical composition described above.

On the other hand, in such a conventional hot-dip galvanizing treatment, oxidized dross adheres to the surface of the hot-dip galvanized layer 20, forming fine irregularities. In particular, when the hot-dip galvanizing bath 120 having the above-described chemical composition is used to form the hot-dip galvanizing layer 20 having the above-described chemical composition, the oxidized dross in the hot-dip galvanizing bath 120 contains easily oxidizable elements. is easily formed. In this case, the oxide dross floating on the surface of the hot-dip galvanizing bath 120 adheres to the base material steel plate 10 together with the hot-dip galvanizing. As a result, oxidized dross remains on the surface layer of the hot-dip galvanized layer 20 , and fine irregularities are likely to be formed on the surface S of the hot-dip galvanized layer 20 . Therefore, in the present embodiment, adhesion of oxidized dross to the base material steel sheet 10 together with hot-dip galvanization is suppressed, and fine unevenness on the surface S of the hot-dip galvanized layer 20 is reduced. This point will be specifically described with reference to the drawings.

FIG. 8 is a side view showing an example of a hot dip galvanizing facility 100 used for hot dip galvanizing treatment according to this embodiment. 7 and 8, in the hot dip galvanizing equipment 100 used for the hot dip galvanizing treatment according to the present embodiment shown in FIG. 8, in addition to the configuration of the hot dip galvanizing equipment 100 shown in FIG. A housing 200 is arranged so as to cover the wiping device 140 .

The housing 200 has an open bottom surface and an opening for the base steel plate 10 to pass through on the top surface. Further, the housing 200 has a lower end placed in the hot-dip galvanizing bath 120 and an upper end that is the same as or above the gas wiping device 140 . In this way, although the housing 200 is not sealed, a portion of the liquid surface of the hot-dip galvanizing bath 120 and a portion of the space above the hot-dip galvanizing bath 120 including the gas wiping device 140 are exposed to the atmosphere. shield from

Further inside the housing 200 , as shown in FIG. 8 , the gas wiping device 140 blows gas onto the base steel plate 10 to adjust the amount of hot-dip galvanization. Therefore, in this embodiment, inert gas such as nitrogen gas is used instead of air as the gas injected from the gas wiping device 140 . That is, the gas inside housing 200 is replaced by the gas jetted from gas wiping device 140 .

Specifically, in this embodiment, the oxygen concentration inside the housing 200 is reduced to less than 1000 ppm by volume. In this case, the formation of oxidized dross is suppressed on the liquid surface of the hot-dip galvanizing bath 120 inside the housing 200 . Therefore, it is possible to sufficiently reduce the oxidation dross that adheres to the base material steel plate 10 along with the hot-dip galvanization. As a result, on the surface S of the hot-dip galvanized layer 20 of the manufactured hot-dip galvanized steel sheet 1, fine unevenness can be reduced, and Fn1 (=SL/SD) can be 1.50 or less. It should be noted that the oxygen concentration inside the housing 200 is preferably as low as possible.

On the other hand, as described above, the gas wiping device 140 scrapes off the hot-dip galvanized surface of the base steel plate 10 by blowing gas onto the base steel plate 10 to adjust the amount of hot-dip galvanized coating. As described above, the interior of the housing 200 is not hermetically sealed, but the gas inside is shielded to some extent from the outside air. Therefore, the gas injected from the gas wiping device 140 may increase the internal pressure of the housing 200 . In particular, when the amount of hot-dip galvanized coating on the surface of the base steel sheet 10 is reduced, the amount of gas injected from the gas wiping device 140 increases, and the internal pressure of the housing 200 tends to increase.

Here, as a result of the increase in the internal pressure of the housing 200, the trajectory of the gas jetted from the gas wiping device 140 becomes unstable, and the adhesion amount of hot-dip galvanization may become unstable. In this case, in the produced hot-dip galvanized steel sheet 1, areas where the amount of hot-dip galvanized coating is locally reduced occur. As a result, in the produced hot-dip galvanized steel sheet 1 , recesses are formed in the surface S of the hot-dip galvanized layer 20 . As described above, even if recesses are formed on the surface S of the hot-dip galvanized layer 20, if the sizes of the recesses satisfy formulas (2) to (4), the appearance quality is not significantly affected. However, it is preferable to suppress the increase in the internal pressure of the housing 200 . In this case, on the surface S of the hot-dip galvanized layer 20 of the manufactured hot-dip galvanized steel sheet 1, the recesses formed are smaller and less in number.

Here, the method for suppressing the increase in the internal pressure of housing 200 is not particularly limited. For example, it may be implemented by adjusting the size of an opening provided on the upper surface of housing 200 through which base steel plate 10 passes. Alternatively, the housing 200 may be provided with movable ventilation holes. A method for adjusting the internal pressure of the housing 200 by providing a movable ventilation hole will be specifically described with reference to the drawings.

FIG. 9 is a side view showing another example of the hot dip galvanizing equipment 100 used for the hot dip galvanizing treatment according to this embodiment. 8 and 9, in the hot dip galvanizing equipment 100 used for the hot dip galvanizing treatment according to the present embodiment shown in FIG. 9, in addition to the configuration of the hot dip galvanizing equipment 100 shown in FIG. A ventilation hole 210 with a movable lid is arranged in the body 200 . Ventilation hole 210A shown in FIG. 9 shows a state in which ventilation hole 210 is not open. A vent hole 210B shown in FIG. 9 shows a state in which the vent hole 210 is open.

As shown in FIG. 9, vent 210 has a movable lid. Therefore, when the internal pressure of the housing 200 increases, the movable lid moves to open the ventilation holes 210 (see the ventilation holes 210B in FIG. 9). Furthermore, when the internal pressure of the housing 200 drops below a certain level, the dead weight of the movable lid closes the ventilation hole 210 (see ventilation hole 210A in FIG. 9). Thus, according to the configuration shown in FIG. 9, even when the internal pressure of housing 200 increases, the increase in internal pressure of housing 200 can be suppressed.

As described above, in the hot-dip galvanizing process according to the present embodiment, the oxygen concentration in the housing 200 shown in FIG. 8 is reduced to less than 1000 ppm by volume. As a result, the manufactured hot-dip galvanized steel sheet 1 can reduce fine unevenness on the surface S of the hot-dip galvanized layer 20 and make Fn1 (=SL/SD) α or less. On the other hand, in this case, since the internal pressure of the housing 200 is somewhat increased, on the surface S of the hot-dip galvanized layer 20, 1.0/10 cm or more of recesses satisfying the formulas (2) to (4) are formed. be.

[Other manufacturing methods]
The method for manufacturing the hot-dip galvanized steel sheet 1 according to the present embodiment may include manufacturing processes other than the manufacturing processes described above. For example, the method for manufacturing the hot-dip galvanized steel sheet 1 according to the present embodiment may include a Ni pre-plating process before the hot-dip galvanizing process. In the Ni pre-plating step, the base steel plate 10 is plated with Ni to form a Ni-plated layer on the surface of the base steel plate 10 .

The method for manufacturing the hot-dip galvanized steel sheet 1 according to the present embodiment may further include a chemical conversion treatment step after the hot-dip galvanizing treatment step. In the chemical conversion treatment step, the produced hot-dip galvanized steel sheet 1 is subjected to chemical conversion treatment to form a chemical conversion coating 30 on the hot-dip galvanized layer 20 . When a chemical conversion treatment step is included, the method of chemical conversion treatment is not particularly limited, and a well-known method may be used. For example, when forming a chrome conversion coating as the conversion coating 30, the following method can be used.

First, a chromium conversion treatment solution is prepared. Chromium conversion treatment solutions contain, for example, trivalent chromium ions. Trivalent chromium ions can be included, for example, by dissolving chromium(III) chloride and chromium(III) sulfate. A commercially available chromate treatment solution may be used as the chromium conversion treatment solution. The hot-dip galvanized steel sheet 1 manufactured by the above-described method is immersed in a chromium conversion treatment solution to perform chromium conversion treatment. A chromium conversion coating can be formed by the above method.

The method for manufacturing the hot-dip galvanized steel sheet 1 according to the present embodiment may further include a temper rolling step after the hot-dip galvanizing step. In the temper rolling step, the manufactured hot-dip galvanized steel sheet 1 is subjected to temper rolling. When carrying out the above-described chemical conversion treatment process, the adhesion of the chemical conversion coating can be enhanced by carrying out the temper rolling process before the chemical conversion treatment process. The method of manufacturing the hot-dip galvanized steel sheet 1 may further include other manufacturing steps. However, the manufacturing method described above is an example of a manufacturing method for obtaining the hot-dip galvanized steel sheet 1 according to the present embodiment. Therefore, the manufacturing method of the hot-dip galvanized steel sheet 1 according to this embodiment is not limited to the manufacturing method described above.

Hereinafter, the hot-dip galvanized steel sheet according to the present embodiment will be described more specifically by way of examples. It should be noted that the conditions shown in Examples are examples for confirming the feasibility and effects of the present embodiment. Therefore, the hot-dip galvanized steel sheet 1 according to the present embodiment is not limited by the examples described below.

Steel sheet SPCC specified in JIS G3141 (2017) (chemical composition is C: 0.15% or less, Mn: 0.60% or less, P: 0.100% or less, S: 0.050% or less, balance: Fe and impurities) was used as a base material steel sheet to produce a hot-dip galvanized steel sheet. Specifically, after degreasing an SPCC having a thickness of 0.8 mm, it was heated at 800° C. for 60 seconds in an N ₂ —H ₂ atmosphere.

After the heated SPCC was cooled to about 490° C., hot-dip galvanizing treatment was performed using hot-dip galvanizing equipment as shown in FIG. The chemical composition of the hot-dip galvanizing bath was as shown in Table 1. "-" in Table 1 indicates that the content of the corresponding element was at the impurity level.

Table 2 shows the hot-dip galvanizing bath used for each test number. The hot-dip galvanizing baths were all heated to 490°C before use. The thickness of the hot-dip galvanized layer was adjusted by adjusting the amount of gas injected from the gas wiping device for the base material steel sheet of each test number. Further, the oxygen concentration inside the housing 200 shown in FIG. 9 was measured by an oxygen concentration sensor (not shown). Table 2 shows the average oxygen concentration inside the housing 200 for each test number as “oxygen concentration (ppm)”. The average oxygen concentration inside the housing 200 in each test number was adjusted by controlling the size of the housing 200 and the size of the opening of the housing 200 .

After that, the base material steel plate of each test number was cooled to room temperature at an average cooling rate of 20° C./sec or less. A hot-dip galvanized steel sheet of each test number was manufactured through the above steps. The hot-dip galvanized steel sheets of each test number produced had excellent corrosion resistance.

[Thickness of hot-dip galvanized layer]
For the hot-dip galvanized steel sheets of each test number, the thickness T (μm) of the hot-dip galvanized layer was measured by the method described above. The obtained thickness of the hot-dip galvanized layer for each test number is shown in Table 2 as "plated layer thickness T (μm)". In all of the hot-dip galvanized steel sheets of test numbers 1 to 24, the thickness T of the hot-dip galvanized layer was within the range of 3.0 to 35.0 μm.

[Evaluation of fine irregularities on the surface of the hot-dip galvanized layer]
For the hot-dip galvanized steel sheet of each test number, a test piece for microstructure observation was prepared from the central part of the sheet width. With respect to the observation surface of the test piece of each test number, a cross section including the L direction and the H direction and including the surface of the hot-dip galvanized layer was observed as a secondary electron image using an SEM. Each observation field region had a length in the L direction of 120 μm and a length in the H direction of 96 μm. Image analysis is performed on the obtained observation field region, the surface length SL (μm) of the hot-dip galvanized layer, the shortest distance SD (μm) between both ends P1 and P2 points on the surface of the hot-dip galvanized layer ), and Fn1 (=SL/SD) obtained from SL and SD. Table 2 shows the obtained Fn1 for each test number.

[Observation of recesses on hot-dip galvanized layer surface]
Concavities on the surface of the hot-dip galvanized layer were observed for each test number of the hot-dip galvanized steel sheet. Specifically, a test piece having a cross section of 1 m in the L direction, including the L direction and the H direction, and including the surface of the hot-dip galvanized layer was produced. Using an optical microscope, the test piece was observed while being moved in the L direction to confirm the presence or absence of recesses. As a result, concave portions were confirmed for test numbers 1 to 18. Therefore, regions containing concave portions among the test pieces of test numbers 1 to 18 were observed with secondary electron images using SEM in the same manner as in the evaluation of fine unevenness described above. All of the concave portions included in test numbers 1 to 18 satisfied formulas (2) to (4). From the number of recesses confirmed in the 1 m test piece, the density of the number of recesses per 10 cm in the L direction was determined. Table 2 shows the obtained number density of the concave portions as "the number of concave portions (pieces/10 cm)".

[Appearance quality]
The hot-dip galvanized steel sheets of each test number were observed with the naked eye to evaluate appearance quality. Specifically, when it was judged to have excellent appearance quality as a result of observation with the naked eye, it was evaluated as "E" (excellent). On the other hand, when it was determined that the appearance quality was not excellent as a result of observation with the naked eye, it was evaluated as "NA" (Not Acceptable). The excellent appearance quality was determined by comprehensively evaluating the appearance of the hot-dip galvanized steel sheet by visually confirming the presence or absence of luster, the presence or absence of discoloration, and the presence or absence of defects. The evaluation results are shown in the "appearance quality" column of Table 2.

[Test results]
The hot-dip galvanized steel sheets of test numbers 1 and 7 had a Mg content of less than 0.5% in the hot-dip galvanizing bath. Furthermore, the oxygen concentration inside the housing was less than 1000 ppm. As a result, on the surface of the hot-dip galvanized layer, Fn1 was 1.10 or less, that is, α or less. Furthermore, the number of concave portions was 1.0 or more per 10 cm in the L direction. As a result, the hot-dip galvanized steel sheets of test numbers 1 and 7 had excellent appearance quality.

The hot-dip galvanized steel sheets of test numbers 2-6 and 8-12 had a Mg content of 0.5% or more in the hot-dip galvanizing bath. Furthermore, the oxygen concentration inside the housing was less than 1000 ppm. As a result, on the surface of the hot-dip galvanized layer, Fn1 was 1.50 or less, that is, α or less. Furthermore, the number of concave portions was 1.0 or more per 10 cm in the L direction. As a result, the hot-dip galvanized steel sheets of test numbers 2 to 6 and 8 to 12 had excellent appearance quality.

On the other hand, the hot-dip galvanized steel sheets of test numbers 13 and 19 had a Mg content of less than 0.5% in the hot-dip galvanizing bath. Furthermore, the oxygen concentration inside the housing was 1000 ppm or higher. As a result, Fn1 exceeded 1.10, that is, exceeded α on the surface of the hot-dip galvanized layer. Furthermore, the number of concave portions was less than 1.0 per 10 cm in the L direction. As a result, the hot-dip galvanized steel sheets of test numbers 13 and 19 did not have excellent appearance quality.

The hot-dip galvanized steel sheets of test numbers 14-18 and 20-24 had a Mg content of 0.5% or more in the hot-dip galvanizing bath. Furthermore, the oxygen concentration inside the housing was 1000 ppm or higher. As a result, Fn1 exceeded 1.50, that is, exceeded α on the surface of the hot-dip galvanized layer. Furthermore, the number of concave portions was less than 1.0 per 10 cm in the L direction. As a result, the hot-dip galvanized steel sheets of test numbers 14-18 and 20-24 did not have excellent appearance quality.

The embodiments of the present disclosure have been described above. However, the above-described embodiments are merely examples for implementing the present disclosure. Therefore, the present disclosure is not limited to the above-described embodiments, and the above-described embodiments can be modified as appropriate without departing from the scope of the present disclosure.

1 hot-dip galvanized steel plate 10 base steel plate 20 hot-dip galvanized layer S surface of hot-dip galvanized layer 50 observation field region P1 one end of the surface of the hot-dip galvanized layer in the observation field region P2 hot-dip galvanized layer in the observation field region 30 chemical coating 100 hot dip galvanizing equipment 120 hot dip galvanizing bath 140 gas wiping device 200 housing 210 ventilation hole

Claims (2)

A hot-dip galvanized steel sheet,
a base material steel plate;
A hot-dip galvanized layer formed on the base steel plate,
The hot-dip galvanized layer is mass %,
Al: 0.1 to 60.0%,
Mg: 0-30.0%,
Si: 0 to 1.0%,
B: 0 to 0.50%,
Ca: 0-3.0%,
Y: 0 to 3.0%,
La: 0 to 3.0%,
Ce: 0 to 3.0%,
Cr: 0-0.5%,
Ti: 0 to 0.5%,
Ni: 0 to 0.5%,
Co: 0-0.5%,
V: 0 to 0.5%,
Nb: 0 to 0.5%,
Cu: 0-0.5%,
Mn: 0-0.5%,
Sr: 0-0.5%,
Sb: 0-0.5%,
Pb: 0 to 0.5%,
Sn: 0 to 2.0%,
Bi: 0 to 2.0%,
In: 0 to 2.0%,
Fe: 0 to 5.0%, and
Balance: having a chemical composition consisting of 35.0% or more of Zn and impurities,
When the rolling direction of the hot-dip galvanized steel sheet is defined as the L direction and the plate thickness direction of the hot-dip galvanized steel sheet is defined as the H direction,
In a rectangular observation field region including the surface of the hot-dip galvanized layer, the side of the hot-dip galvanized steel sheet extending in the L direction is 120 μm in length and the side extending in the H direction is 96 μm in length,
The length of the surface of the hot-dip galvanized layer is SL,
One end of the surface of the hot-dip galvanized layer is P1 point,
The other end of the surface of the hot-dip galvanized layer is P2 point,
When the shortest distance between the P1 point and the P2 point is defined as SD,
The SL and the SD satisfy the formula (1),
When the thickness of the hot-dip galvanized layer is defined as T μm,
In a cross section including the L direction and the H direction,
formed on the surface of the hot-dip galvanized layer,
The length W μm in the L direction and the depth D μm in the H direction satisfy the formulas (2) to (4), and the number of recesses satisfying the formulas (2) to (4) is 1.0 or more per 10 cm in the L direction.
Hot-dip galvanized steel sheet.
SL/SD≦α (1)
D≦0.7×T (2)
D≤5.0 (3)
0.2×D≦W≦5.0×D (4)
Here, α in the formula (1) is 1.10 when the Mg content in the hot-dip galvanized layer is 0 to less than 0.5% by mass, and the Mg content in the hot-dip galvanized layer is 0. 0.5 to 30.0% by mass, it is 1.50. The hot-dip galvanized steel sheet according to claim 1,
The chemical composition of the hot-dip galvanized layer contains one or more elements selected from Groups 1 to 8,
Hot-dip galvanized steel sheet.
Group 1: Mg: 0.1 to 30.0%,
Second group: Si: 0.1 to 1.0%,
Group 3: B: 0.01-0.50%,
Group 4: Ca, Y, La, and Ce: 0.1-3.0%,
Group 5: Cr, Ti, Ni, Co, V, Nb, Cu, and Mn: 0.1 to 0.5%,
Group 6: Sr, Sb, and Pb: 0.1 to 0.5%,
Group 7: Sn, Bi, and In: 0.1 to 2.0%,
Group 8: Fe: 0.1 to 5.0%

Images