JP2003183801A - Galvannealed steel sheet and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a galvannealed steel sheet which is cheap and exhibits a slidability better than that of a conventional one even after press working. <P>SOLUTION: This galvannealed steel sheet is prepared by hot-dip galvanizing the surface of a steel sheet, heating the resultant plating layer to be alloyed with the surface of the steel sheet, and subjecting thus plated steel sheet to temper rolling. The steel sheet has such characteristics that the iron content of an alloyed plating layer is 11-14 mass% or higher; the surface roughness (Ra) is 0.6 μm-1.0 μm; the number of mountaintops per inch (PPI) on the surface is 350 or less; the mountain-valley undulation value (Wca) is 0.4 μm or lower; the presence probability of mountain parts in the region upper than the position apart from the median by 2 μm in the direction of a mountaintop in the probability amplitude density distribution of surface roughness is 0.05 or lower; and the mountain density of which the mountain part area of the virtual horizontal cross section at the position is 10<SP>-5</SP>-10<SP>-3</SP>mm<SP>2</SP>is 3×10<SP>2</SP>/mm<SP>2</SP>or less. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alloyed hot dip galvanized steel sheet and a method for producing the same, and particularly to an alloyed hot dip galvanized steel sheet which is used as an anticorrosion surface-treated steel sheet for automobiles and has excellent slidability and a method thereof. Regarding manufacturing technology.

[0002]

2. Description of the Related Art Alloyed hot-dip galvanized steel sheet (hereinafter referred to as GA
Steel plate) is relatively inexpensive and has excellent corrosion resistance, and is therefore widely used as a steel plate for automobiles. In recent years, from the viewpoint of cost reduction, the integral molding of car bodies and the like has progressed, and it is required that the steel sheets used have better performance such as slidability, powdering resistance, and low temperature chipping resistance. It has become so.

As a conventional technique for improving slidability, it has been proposed to provide an Fe-based electroplating layer on the upper layer of a GA steel sheet, as disclosed in, for example, Japanese Patent Laid-Open No. 3-19145. However, although this technique improves the slidability, it has the drawback of increasing the manufacturing cost.

Further, Japanese Patent Publication No. 3-55544 discloses that the soft η phase and ζ phase, which are disadvantageous to the slidability of the alloyed plating layer, are reduced to a state close to a δ ₁ single phase advantageous to slidability. I suggest you do. However, in order to eliminate the above-mentioned soft phase, alloying work at high temperature for a long time is required, and a large amount of undesired r phase is separately generated. Therefore, the technique described in the Japanese Patent Publication No. 3-55544 is G
There is a problem that the powdering resistance of the steel sheet A is deteriorated.

Further, Japanese Patent Laid-Open No. 11-30281 discloses that the amount of Al-O in the surface layer of the alloyed plating, and the η phase and ζ.
It is proposed to regulate the amount of phases within a certain range to improve slidability. Then, specifically, to reduce the amount of Al-O, dipping the GA steel plate in an alkaline solution or surface grinding with a brush roll is performed, and to reduce the η phase and the ζ phase, dipping in an acid solution. Good things are disclosed. However, this technique is to perform another treatment twice after the galvannealing, which requires new equipment for performing the treatment, which causes an increase in manufacturing cost.

[0006]

In view of such circumstances, the present invention provides an alloyed hot-dip galvanized steel sheet which has better slidability and is cheaper than before even when press working, and a method for producing the same. The purpose is to do.

[0007]

In order to achieve the above-mentioned object, the inventor made many kinds of GA steel plates having various surface shapes changed, and conducted a sliding test using a die to evaluate their sliding properties. investigated. As a result, the surface shape of the alloyed plating layer in contact with the mold surface, that is, the surface roughness, the undulations of the valleys,
Furthermore, the present invention was completed based on the finding that the presence state of the ridges existing on the surface has a great influence on the sliding characteristics of the GA steel sheet.

That is, the present invention is a steel sheet having an alloyed hot-dip galvanized layer on the surface, wherein the iron content in the alloyed hot-dip galvanized layer is 11 to 14% by mass. The surface of the plating layer has a surface roughness (Ra) of 0.6 to 1.0 μm, a peak number per inch of length (PPI) of 350 or less, and a waviness value (W) of mountains and valleys.
ca) is 0.4 μm or less, and the existence probability of the mountain portion is 0.05 or less at the height closer to the peak direction of 2 μm from the median value in the probability amplitude density distribution of the surface roughness,
The hot-dip galvanized steel sheet is characterized in that the number of the peaks whose area at the height is 10 ⁻⁵ to 10 ⁻³ mm ² is 3 × 10 ² pieces / mm ² or less.

Further, according to the present invention, the steel sheet is immersed in a hot dip galvanizing bath to form a hot dip galvanized layer on the surface of the steel sheet and heated to alloy the hot dip galvanized layer,
In the method for producing an alloyed hot-dip galvanized steel sheet which is temper-rolled, the Al concentration in the hot-dip galvanizing bath is set to 0.14.
5% by mass or less, a bath temperature of 450 to 465 ° C., a plate temperature when the steel sheet enters the hot dip galvanizing bath is 465 ° C. or less, and a heating temperature at the time of alloying is 510 ° C. or more. Further, the temper rolling is performed so that the surface roughness (Ra) is 0.3 to 0.8 μm, and the number of peaks per inch (PP).
I) is a method for producing an alloyed hot-dip galvanized steel sheet, which is performed by using a work roll having a surface of 400 to 600 and an elongation of 0.5 to 1.2%.

In the present invention, the area and density of the peaks in the unevenness of the alloyed plating layer surface of the galvannealed steel sheet are adapted to the slidability of the steel sheet. Even when this steel sheet is used as a material for automobile parts, the press formability becomes better than before. Moreover, since the conventional manufacturing process is not changed, the manufacturing cost can be kept low.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The embodiments of the present invention will be described in detail below along with the background of the invention.

First, an alloyed plating layer (hereinafter, simply
It is the iron content in the plating layer), but the value is large.
Since the plating layer will be harder and less likely to be deformed, sliding
At times, the frictional resistance with the mold surface is small, which is advantageous. this
Is produced on the surface of the plating layer during alloying with a high iron content.
Easy and soft ζ phase (Vickers hardness of about 200H
v. ) Is reduced, and relatively hard δ₁Phase (Vickers hard
This is because a large amount of about 300 Hv,) is generated. There
The inventors of the present invention have made extensive studies and found that the iron content in the plating layer is
It was found that the ratio is preferably 11 to 14% by mass. 11 quality
If the amount is less than%, the above δ ₁14 phases not fully produced
If the amount exceeds%, the plating layer will be powdered during press working.
This is because powdery peeling, which is called
This upper limit is preferably 13% by mass.

Further, when a GA steel sheet in which only the surface roughness of the plating layer (arithmetic mean roughness defined by JIS: symbol Ra) was changed was examined, the sliding properties thereof were such that Ra was 0.6.
It was found that when the thickness was in the range of up to 1.0 μm, it tended to be favorable. As shown in FIG. 1, this means that Ra is relatively small and flat (specifically, Ra 1.0 μm).
The following) is because the surface of the mold 1 is less likely to be caught at the mountain portion 2 on the surface of the plating layer, and the sliding resistance is reduced.
However, when Ra is reduced to less than 0.6 μm, the peaks are reduced, but at the same time, the recesses 3 are also reduced. As a result, the oil accumulation effect of the lubricating oil used during sliding (the lubricating oil blows out from the concave portion to the convex portion and reduces the frictional resistance with the surface of the mold 1) becomes small, and the slidability of the GA steel sheet deteriorates rather. To do. Therefore, in the present invention, the surface roughness (R
In the case of a), it is decided that the thickness is 0.6 to 1.0 μm.

Furthermore, the inventor has found that at many positions on the surface of the plating layer, the number of peaks per inch (symbol: PPI).
The abbreviation for Peak per inch) was measured and the relationship with the slidability of the steel sheet was investigated. As a result, it was found that the smaller the PPI, the better the slidability. Specifically, 350 or less are preferable. This is because, as shown in FIG. 2, when the PPI is large, the contact angle (θ in the figure) at the contact portion with the surface of the mold 1 becomes large, and the resistance to the mountain portion 2 becomes large, and the slidability is increased. Is considered to be deteriorated. On the other hand, P
When the PI is small, as shown in FIG. 2, the large peak portion 2 exists, the contact angle with the peak portion 2 becomes small, and the resistance is relatively suppressed.

Therefore, in the present invention, the PP on the surface of the plating layer is
We decided to limit I to 350 or less.

[0016] In addition, the inventor has noticed, in a cross-sectional view in the plate thickness direction of the GA steel plate, the waviness of the wavy surface formed by the peaks (also referred to as projections) and the valleys (also referred to as recesses) on the surface of the plating layer. However, the waviness was measured by the method specified in JIS B 0610, and the value of the centerline waviness (symbol: Wca) was evaluated. When the relationship between the Wca value and slidability was investigated, it was found that the Wca value was 0.4 μm or less.
It was found that the slidability was improved, and this was added to the requirements of the present invention. This has a Wca of 0.4 μm
If it exceeds, the frictional resistance with the mold increases and the slidability decreases, as in the case where Ra is large.

However, the iron content, surface roughness (Ra), peak number (PPI), and waviness (Wca value) of the plating layer described above completely affect the sliding property of the GA steel sheet. I thought that it would not be considered and repeated further research.

First, regarding the slidability between the GA steel plate and the mold, the inventors considered that the contact state between the tip of the ridge and the mold on the surface of the GA steel plate affects the slidability. .
Then, at the time of pressing, the steel plate is pressed by the mold with a certain amount of surface pressure, but at this time, the tip of the crest portion is crushed and the crushed crest portion tip comes into contact with the mold, The idea that the smaller the contact area is, the smaller the coefficient of friction between the die and the surface of the steel sheet and the better the slidability is. And, the plating layer of the GA steel plate has the above-mentioned iron content, and the plating layer surface has the above-mentioned surface roughness (Ra),
Waviness value (Wca), number of peaks per inch (P
If the range of (PI) is satisfied, it is possible that the surface of the steel sheet that comes into contact with the mold is a portion that is approximately 2 μm away from the median of the probability amplitude distribution of the surface roughness of the steel sheet in the peak direction. all right.

That is, it was found that the existence probability of peaks at a height of 2 μm closer to the peak direction from the median of the probability amplitude density distribution of surface roughness has a large correlation with the friction coefficient with the mold. Here, the probability amplitude distribution, when the uneven curve of the surface shape is cut by a straight line of a certain height, the number of intersections of the straight line and the uneven curve is taken as the frequency of that height, and the distribution of the frequency at each height Is a probability distribution. If the frequency with respect to height is represented in a histogram, a probability amplitude distribution curve as shown in FIG. 3 is obtained.
Then, as shown in FIG. 4, the existence probability of the mountain portion at a height of 2 μm closer to the peak direction from the median of the probability amplitude distribution is 2 μm from the median for a sample of a predetermined size.
It is obtained by dividing the sum total of the areas of the peaks (areas indicated by the shaded areas in FIG. 4) cut by the plane at a height closer to the m peak direction by the sample area (L × W). .

The inventor has conducted hot rolling in a normal rolling process,
Pickling and cold rolling are sequentially performed to produce a cold-rolled steel sheet having a thickness of 0.8 mm, and the steel sheet is recrystallized and annealed at an annealing temperature of 800 ° C., and then Al concentration is 0.135% by mass and bath temperature is 460
5 after immersing in hot dip galvanizing bath at ℃
A sample was cut out from the alloyed hot-dip galvanized steel sheet (GA steel sheet) obtained by alloying the plated layer by heating to 20 ° C. and further temper rolling. The surface shape of the sample was adjusted to each value by changing the surface shape and elongation of the work roll during temper rolling. Here, the surface roughness (R
a) is adjusted in the range of 0.6 to 1.0 μm, the number of peaks per inch of length (PPI) is adjusted to 350 or less, and the undulation value (Wca) of peaks and valleys is adjusted to 0.4 μm or less. The influence of the existence probability of the mountain portion on the slidability was investigated by changing the existence probability. The surface roughness (Ra), the number of peaks per inch (PPI), and the undulation value of mountains and valleys (Wca)
Respectively confirmed the value as follows. Ra measurement It was obtained by measuring the two-dimensional surface roughness with a measurement length of 2.5 mm and a cutoff of 0.8 mm (JIS B 060).
1). Measurement of PPI Two-dimensional surface roughness was measured with a measurement length of 2.5 mm and a cutoff of 0.8 mm to determine the number of peaks per inch. The reference level was 0.254 μm. Measurement of Wca It was determined with a measurement length of 24 mm and a cutoff of 0.8 to 8 mm (see JIS B 0610).

The existence probability of the mountain portion was determined by using a surface shape analyzer (SAS-2010) manufactured by Meishing Machinery Co., Ltd. and a tip diameter of 2 μ
Measurement area 2 mm x 1 mm = 2 mm ² using a stylus of m
About 2mm (2000p
oints) for 1 m at 10 μm intervals in the y direction
m (100) was measured. Based on this measurement data, the probability amplitude density distribution of the surface roughness is obtained, and the plane that is 2 μm closer to the median in this probability amplitude density distribution is taken as the boundary surface, and the portion with a height higher than that (convex higher than the plane is projected. (Part) and a part having a height less than that are shown in black and white.

An example of the binarization map is shown in FIG. In the binarized map shown in FIG. 5, a black portion indicates a portion higher than the height of the boundary surface, and a white portion indicates a portion lower than the boundary surface.
Then, from this binarized map, the existence probability of the mountain portion, that is, the area of the black portion (mm ² ) / 2 in the image analysis device
The value of (mm ² ) was determined. Note that FIG. 5A is an example in which the mountain existence probability is 0.061, and FIG. 5B is an example in which the mountain existence probability is 0.048.

Furthermore, for each sample, 1.5 g / m ^{2 of} rust preventive oil was applied, and a flat plate was slid under the conditions of a surface pressure of 9.8 MPa and a sliding distance of 100 mm and a sliding speed of 500 mm / min. A test was conducted to determine the friction coefficient.

FIG. 6 shows the relationship between the friction coefficient and the existence probability of the peak portion (the area ratio of the black portion in FIG. 5) in the plane cross section at a height closer to the peak of 2 μm from the median in the probability amplitude distribution. Show. From FIG. 6, when the existence probability of the peak portion at a height closer to the peak of 2 μm from the median in the probability amplitude distribution is 0.05 or less, the friction coefficient decreases, and
It can be seen that 130 or less can be secured.

From the above, according to the present invention, the probability of existence of peaks in a flat section at a height of 2 μm closer to the peak direction from the median value of the probability amplitude density distribution of surface roughness is 0.0.
It must be 5 or less.

Further, as a result of further examination, as described above, the probability of existence of peaks at a height of 2 μm closer to the crest direction than the median in the probability amplitude density distribution of surface roughness is 0.05 or less. Furthermore, it was found that the slidability is further improved by reducing the number of the peaks having a small area, that is, the number of black portions having a small area in FIG. It is presumed that this is because, if there are many small ridges, the small ridges produce a file-like effect and increase the frictional resistance with the die surface, as shown in FIG. It was also found that the number of peaks having an area of 10 ⁻⁵ to 10 ⁻³ mm ² affects the coefficient of friction with the die surface. FIG. 8 shows the relationship between the number of peaks having an area of 10 ⁻⁵ to 10 ⁻³ mm ² and the friction coefficient. Area is 10 ^-5 to 10 ^-3 mm
^It can be seen that the coefficient of friction is further reduced by setting the number of the crests of ² to 300 / mm ² or less.

Therefore, in the present invention, the area of the mountain portion is
Is 10^-Five-10^-3mm²The number of mountain parts is 3 × 10²Pieces / m
m²Must be: Where 3 × 10²Pieces / mm
²The ridges whose number is specified below are
Area when cut with 10 ^-Five-10^-3mm²In the range of
The reason for setting a certain mountain part is that the area is 10^-Fivemm²Less than a mountain
Part, the contact area with the mold is too small even if it exists
This is because it does not affect the frictional resistance with the mold surface.
Also, the area is 10^-3mm²As the super mountain part existed
Also, if it is within the range of existence probability mentioned above, the friction coefficient with the mold
Is not increased.

The number of peaks having an area of 10 ^-5 to 10 ^-3 mm ² at a height closer to the peak of 2 μm from the median in the probability amplitude density distribution of surface roughness is binarized as described above. The map was measured using an image analyzer.

Next, a method of manufacturing the GA steel sheet according to the present invention described above will be described.

As is conventional, it is manufactured through a step of plating a steel sheet with molten zinc, a step of alloying the plating, and a step of temper rolling the steel sheet after alloying. However,
In each process, various operating conditions and devices are taken into consideration in order to obtain the GA steel sheet according to the present invention.

First, as the conditions for hot dip galvanizing, it is necessary to make appropriate the Al concentration of the zinc bath, the bath temperature, and the temperature of the steel sheet to be introduced into the bath (hereinafter referred to as the entry sheet temperature). That is, the surface of the GA steel plate is made smooth and the low surface roughness (R
a), low PPI, and reduction in the number of peaks. As a result of the study, it has been found that for that purpose, it is effective to lower the Al concentration, the bath temperature and the entry plate temperature in the hot dip galvanizing bath (hereinafter referred to as the plating bath).

Specifically, when the Al concentration in the plating bath is high, a large amount of Fe-Al alloy that suppresses alloying is formed during plating, and the local alloy is present at the grain boundary of the steel sheet where Fe diffusion is fast. As a result, the unevenness of the plated surface becomes large, and it becomes difficult to set both the surface roughness (Ra) and the number of peaks per inch (PPI) within the above range. Therefore, in the present invention, the Al concentration is limited to 0.145 mass% or less, preferably 0.140 mass% or less. It should be noted that Al is contained in the plating bath in order to secure the powdering resistance of the GA steel plate, but for this purpose, it is preferably 0.130 mass% or more.

When the bath temperature and the entrance plate temperature are increased, the PPI on the plating surface is likely to increase similarly. This is also considered to be related to the Fe-Al alloy formed during plating, and as a low bath temperature and a low entry plate temperature, F at the grain boundary of the steel plate is considered.
It is desirable to reduce the diffusion rate of e. Therefore, as a result of repeated studies, it was found that the plate temperature should be 450 to 465 ° C and the approach plate temperature should be 465 ° C or less.

Furthermore, in alloying after plating, it is desirable to reduce the appearance of the ζ phase which adversely affects the slidability. Therefore, in the present invention, it is preferable to alloy at a high temperature at which the ζ phase becomes unstable, and it is decided to alloy at a temperature of 510 ° C. or higher. If the heating temperature during alloying is less than 510 ° C., the Fe content cannot be in the range of 11 to 14% while the ζ phase is sufficiently reduced. In the present invention, in order to suppress the iron content of the plating layer as described above to 11 to 14% by mass, at a temperature of 510 ° C. or higher, a holding time of about 10 to 20 seconds may be used. May be changed as appropriate.

In addition, G which has been cooled to room temperature after alloying
It is necessary to temper-roll A steel sheet.

In the present invention, this temper rolling is performed with low Ra and high P.
It is characterized by rolling with PI work rolls. As a result of the investigation, specifically, Ra was 0.3 to 0.8 μm for the GA steel plate manufactured under the above-mentioned plating conditions and alloying conditions.
Then, if a work roll having a surface shape of PPI of 400 to 600 is used and temper rolling is performed with the elongation rate of the steel sheet being 0.5 to 1.2%, Ra, PPI of the GA steel sheet surface,
It was found that the existence state of the mountain portion can be set within the above range. That is, in this temper rolling, fine irregularities formed by alloying are eliminated by a relatively flat roll.

The waviness value (Wca) of the steel plate surface can be set to 0.4 μm or less by using a steel plate having a Wca of 0.4 μm or less as a steel plate to be plated. In order to set the Wca of the original plate to 0.40 μm or less, the rolling conditions at the time of producing the original plate may be appropriately selected, for example, by reducing the waviness value of the work roll used during cold rolling.

[0038]

[Example] Hot rolling, pickling and cold rolling were sequentially performed in a normal rolling process to produce a cold rolled steel sheet having a sheet thickness of 0.8 mm.
Continuously hot dip galvanizing line (CGL)
Then, recrystallization annealing was performed at an annealing temperature of 800 ° C., and then hot dip galvanizing and alloying were performed under the conditions shown in Table 1.
Here, the Al concentration in the plating bath was 0.135% by mass, and the steel No. Only 13 is 0.150 mass% for comparison
And Further, the alloyed steel sheet was temper-rolled under the rolling conditions shown in Table 1. Samples for various tests were taken from the obtained galvannealed steel sheet, and the iron content in the plated layer, the surface shape of the steel sheet, and the slidability were investigated.

[0039]

[Table 1]

The iron content in the plating layer is
Was dissolved and analyzed by wet analysis. Also, the under
The numbers given by the line are outside the conditions of the present invention.
is there. Surface roughness is measured by surface roughness Ra (μm) and length
Number of peaks per inch PPI, center line waviness value Wca
(Μm), median value of the probability amplitude density distribution of surface roughness
The existence of the mountain part at a height closer to the peak of 2 μm
Rate, the area at this height is 10^-Five-10^-3mm²And
The number of the above-mentioned mountain parts per unit area (pieces / mm ^Two)
I investigated. For these survey methods, see above.
It is Ri. For the slidability investigation, use the same method as the above sliding test.
The coefficient of friction with the mold is calculated by the method, and the coefficient of friction exceeds 0.130.
X, 0.125 to 0.130 o, 0.125 or less
Was evaluated as ⊚. Table 2 shows the survey results of surface shape and slidability
Show the result.

[0041]

[Table 2]

From Tables 1 and 2, steel No. as an example of the invention is shown.
It can be seen that Nos. 1, 3, 5, 7, and 8 have a friction coefficient of ⊚ or ∘, and exhibit good slidability. On the other hand, Steel No. In Nos. 2, 6 and 9, the surface shape of the work roll used during temper rolling was too large Ra or too small PPI, so the probability of existence of ridges or Ra of the obtained steel sheet was large, and the friction coefficient was It is getting bigger. Also, steel N
o. In No. 4, the alloying temperature was too low, so the iron content in the plating layer did not satisfy the range of the present invention, and the friction coefficient was large.
Further, steel No. No. 10 had a large PPI of the steel sheet because the plating bath temperature was too high. In No. 11, since the plating bath temperature and the entry plate temperature are high, the PPI and the peak density of the steel plate are large. No. 12 has a high plating bath temperature and a high entry plate temperature, and a low alloying temperature, so that PPI, mountain existence probability,
The peak density is high, and the friction coefficient is high in both cases. In addition, steel No. In No. 13, since the Al concentration in the plating bath is too high, both Ra and PPI are large and the friction coefficient is large.

[0043]

As described above, according to the present invention, an alloyed hot-dip galvanized steel sheet having good press formability can be provided even when it is used as a material for automobile parts having a complicated structure. Moreover, in the conventional manufacturing process, the manufacturing cost can be kept low because the manufacturing can be performed by slightly changing the plating conditions and the temper rolling conditions.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the influence of the surface roughness of a GA steel sheet on the slidability of the steel sheet.

FIG. 2 is a diagram for explaining the effect of PPI on the surface of a GA steel plate on the slidability of the steel plate.

FIG. 3 is a diagram illustrating a probability amplitude density distribution of surface roughness of a GA steel plate.

FIG. 4 is a diagram for explaining the existence probability of peaks at a height closer to the peak of 2 μm from the median in the probability amplitude density distribution of surface roughness.

5 is a probability amplitude density distribution of surface roughness of a GA steel plate, which is a map of the steel plate surface binarized based on a position 2 μm away from the median in the peak direction. FIG.

FIG. 6 is a graph showing a relationship between a mountain portion existence probability and a friction coefficient.

FIG. 7 is a diagram for explaining the influence of the number of minute peaks on the surface of a GA steel plate on the slidability of the steel plate.

FIG. 8 is a graph showing the relationship between the number of peaks in a minute peak and the coefficient of friction.

[Explanation of symbols]

1 mold 2 Yamabe 3 recess

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Claims (2)

[Claims] 1. A steel sheet having an alloyed hot-dip galvanized layer on the surface, wherein the iron content in the alloyed hot-dip galvanized layer is 11 to 14% by mass, and the surface of the alloyed hot-dip galvanized layer is , The surface roughness (Ra) is 0.6 to 1.0 μm, and the number of peaks (PPI) per inch is 350.
The undulation value (Wca) of ridges and valleys is 0.4 μm or less, and the existence probability of ridges at a height 2 μm closer to the peak direction from the median value of the probability amplitude density distribution of surface roughness is 0. No more than 05, and the number of the peaks having an area at the height of 10 ⁻⁵ to 10 ⁻³ mm ² is 3 ×
An alloyed hot-dip galvanized steel sheet characterized by being 10 ² pieces / mm ² or less. 2. A steel sheet is dipped in a hot dip galvanizing bath to form a hot dip galvanized layer on the surface of the steel sheet, which is then heated to alloy the hot-dip galvanized layer, followed by temper rolling. In the method for producing a hot-dip galvanized steel sheet, the Al concentration in the hot-dip galvanizing bath is 0.145% by mass.
Hereinafter, the bath temperature is 450 to 465 ° C., the plate temperature when the steel plate enters the hot dip galvanizing bath is 465 ° C. or less, and the heating temperature at the time of alloying is 510 ° C. or more,
Further, the temper rolling has a surface roughness (Ra) of 0.3 to
Using a work roll having a surface of 0.8 μm and a peak number per inch (PPI) of 400 to 600,
A method for producing an alloyed hot-dip galvanized steel sheet, which is performed at an elongation of 0.5 to 1.2%.