JP5673708B2 - Alloyed hot-dip galvanized steel sheet with excellent surface appearance and plating adhesion - Google Patents

Description

  The present invention relates to an alloyed hot-dip galvanized steel sheet excellent in surface appearance and plating adhesion suitable for automobile outer plates and structural members.

Alloying hot dip galvanizing is applied for the purpose of corrosion protection of steel sheets, and is widely used for automobile outer plates and structural members. As a manufacturing method thereof, in a continuous hot dip galvanizing line (hereinafter referred to as CGL), after degreasing cleaning, annealing is performed by indirect heating with a radiant tube in a reducing atmosphere containing H ₂ and N ₂ , and a plating bath There is an all-reduction furnace method in which after cooling to near the temperature, it is immersed in a hot dip galvanizing bath, and after leaving the plating bath, it is reheated and alloyed.

About annealing before plating, in CGL with a non-oxidizing furnace, after degreasing and cleaning, heat in a non-oxidizing atmosphere in a non-oxidizing furnace, and then anneal in a reducing atmosphere containing H ₂ and N ₂ A non-oxidizing furnace method may also be performed.

  In recent years, in the automobile industry, the strength of steel materials to be used has been demanded for the purpose of reducing the weight of a vehicle body and improving the collision safety. However, generally, since the ductility is lowered when the strength of the steel material is increased, a steel material in which a large amount of elements such as Si and Mn is added to the steel to increase the strength without deteriorating the ductility is employed.

  In order to improve the anti-corrosion ability of the car body, it is required to galvanize these high-strength steel sheets, but in high-strength steel sheets, non-plating occurs when immersed in a hot-dip galvanizing bath. There's a problem. Since non-plating remains even after alloying, the surface appearance is inferior. Further, there is a problem that the plating adhesion is lowered even if non-plating does not occur.

  As the cause of non-plating and lowering of plating adhesion, oxidizable elements such as Si and Mn in steel added to increase the strength easily oxidize even in a reducing atmosphere for Fe. It has been considered that there is selective oxidation in the annealing process of CGL to form an external oxide film on the steel sheet surface.

  The external oxide film refers to an oxide film formed by oxidization of an easily oxidizable element in steel by outward diffusion to the steel sheet surface and oxidation. The external oxidation phenomenon occurs when the outward diffusion rate of the easily oxidizable element is faster than the rate at which oxygen in the annealing atmosphere diffuses inward into the steel.

  When the steel sheet comes out of the plating bath, if an external oxide film of an easily oxidizable element exists on the surface of the steel sheet, non-plating occurs due to poor wettability with molten zinc. Even when non-plating does not occur, if there is a lot of external oxide film remaining at the interface between the steel plate and the plating layer after plating, the plating layer peels off from the external oxide film during processing such as press molding. Decreases.

  As means for solving these problems, means for suppressing the selective oxidation of easily oxidizable elements and preventing the formation of an external oxide film on the steel sheet surface has been adopted in the annealing process of CGL.

  For example, in Patent Document 1, by giving specific electroplating before annealing, it takes time for the oxidizable elements to diffuse outward and reach the steel sheet surface, and to form an external oxide film on the steel sheet surface. A method of preventing is disclosed.

  Patent Document 2 discloses that a steel sheet is rolled up at a high temperature after hot rolling, a grain boundary oxide layer is formed immediately below the black skin on the steel sheet surface, and the outward diffusion of easily oxidizable elements is reduced during reduction annealing in a hot dip galvanizing line. A method for preventing the formation of an external oxide film on the surface of a steel sheet by inhibiting the field oxide layer is disclosed.

  In Non-Patent Document 1, heat treatment is performed on a hot-rolled steel sheet with black skin to form a grain boundary oxide layer, and by forming a solid solution Si, Mn-depleted region on the surface layer of the steel sheet, reduction in a hot dip galvanizing line A method for preventing the formation of an external oxide film on the surface of a steel sheet by reducing the amount of Si and Mn diffused outward during annealing is disclosed.

  Patent Document 3 discloses a method for preventing non-plating by subjecting a steel sheet to reduction annealing, pickling and removing an external oxide film of an easily oxidizable element formed on the steel sheet surface, and reheating and hot-dip galvanizing. It is disclosed.

JP-A-3-28359 JP-A-9-41110 JP 2003-277902 A

Yoshitsugu Suzuki, Surface Technology, Vol.55, No.1, p.48 (2004)

  However, in the technique disclosed in Patent Document 1, a new plating facility must be provided in front of the CGL annealing furnace, or a plating process must be performed in advance in the electroplating line, resulting in a significant cost increase. In Patent Document 2, since the coiling temperature is increased, the ductility of the steel sheet is lowered, and the intended characteristics cannot be obtained. Further, if the grain boundary oxide layer is excessively formed, the grain boundary may be embrittled. In Non-Patent Document 1, it is necessary to newly provide a process for heating a hot-rolled steel sheet, resulting in a decrease in productivity and an increase in cost. Further, if the grain boundary oxide layer is excessively formed, the grain boundary may be embrittled. Furthermore, since the solute Si and Mn concentrations in the steel sheet surface layer are lowered, the material is different between the steel sheet surface layer and the inside of the steel sheet, and cracking may occur during press processing based on the interface of the different materials. In Patent Document 3, it is necessary to pass the pickling line after the reduction annealing, which increases the number of processes and leads to an increase in cost.

  An object of the present invention is to solve the problems of the prior art as described above, and to provide an alloyed hot-dip galvanized steel sheet excellent in surface appearance and plating adhesion.

  In order to solve the above problem, the present inventors have made intensive studies, and as a result, even under conditions where an external oxide film is formed during reduction annealing, the crystal grains of the steel sheet surface layer in contact with the plating layer should be made fine. In addition to suppressing non-plating, the present inventors have found that plating adhesion during processing is greatly improved. According to the present invention, since there is no need to introduce new equipment or add a new process, there is no risk of an increase in cost or a decrease in productivity. Further, since it is not necessary to form a grain boundary oxide layer on the steel sheet surface layer, there is no fear of grain boundary embrittlement. Furthermore, since the solute Si and Mn concentrations in the surface layer of the steel plate do not decrease, the solute Si concentration in the surface layer of the steel plate can be kept as high as the inside of the steel plate, and the material in the thickness direction is constant. There is no worry of cracking even during strong processing.

  Although the details of the reason why the non-plating is suppressed or the plating adhesion is improved are not clear, the inventors have found that the steel plate having the above structure suppresses the non-plating and is excellent in the plating adhesion.

The present invention has been completed based on the above findings, and the gist thereof is as follows.
(1) The steel plate base material is mass%,
C: 0.001-0.3%
Si: 0.1-3.0%
Mn: 0.5-3.0%
Al: 0.001 to 0.1%,
P: 0.0001-0.3%
S: 0.0001-0.1%,
N: 0.0001~0.1%,
further,
Ti: 0.001-0.2%,
Nb: 0.001 to 0.2% of one or two types,
On the surface of the steel sheet, the balance of which is Fe and inevitable impurities,
Fe: 5.0-20.0%,
Al: contains 0.01-1.0%,
The balance is an alloyed hot-dip galvanized steel sheet having a plating layer made of Zn and inevitable impurities,
The steel grain base material in contact with the plating layer has a crystal grain size of 10 μm or less , measured by glow discharge optical emission spectrometry (GDS), and the Si strength of the steel sheet base material (I _Si ) and the average Si strength inside the steel sheet base material (I _bulk ratio) state, and are the minimum value of 0.8 or more I _Si / I _bulk, the plating bath of 10 to 50 m / min relative to the steel plate, as the flow velocity at the location of 10~50cm in the depth direction from the bath surface of the plating bath galvannealed steel sheet excellent in surface appearance and coating adhesion, characterized in Rukoto produced giving the jet.
However, when the steel sheet was analyzed from the outermost layer to a depth of 3.6 μm with I _Si : GDS, the Si emission intensity at each measurement depth,
I _bulk : average value of I _Si when the depth from the outermost layer of the steel sheet is between 3.2 and 3.6 μm ,
It is.
(2) The galvannealed steel sheet excellent in surface appearance and plating adhesion as described in (1) above, wherein the steel sheet base material further contains Mo: 0.001 to 1.0% by mass.
(3) Surface appearance and plating adhesion according to (1) or (2) above, wherein the steel sheet base material further contains 0.001 to 5.0% in total of one or more of Cr, Ni, and Cu in mass%. Alloyed hot-dip galvanized steel sheet with excellent properties.
(4) The steel sheet base material is further described in any one of the above (1) to (3), in which the content is 0.001 to 0.5% in total of one or more of V, Zr, Hf, and Ta in mass%. Alloyed hot-dip galvanized steel sheet with excellent surface appearance and plating adhesion.
(5) The steel sheet base material according to any one of (1) to (4) above, further containing 0.0001 to 0.1% in total of one or more of Ca, Mg, Y, La, and Ce in mass%. An alloyed hot-dip galvanized steel sheet excellent in surface appearance and plating adhesion described in 1.
(6) The steel plate base material is further mass%, and contains B: 0.0001 to 0.005%. Alloyed hot dip galvanizing excellent in surface appearance and plating adhesion according to any one of (1) to (5) above steel sheet.

  The alloyed hot-dip galvanized steel sheet of the present invention can prevent non-plating and decrease in plating adhesion even when the steel sheet base material contains a large amount of easily oxidizable elements. Moreover, since the Si concentration in the surface layer of the steel sheet is as high as the inside of the steel sheet, the material change in the thickness direction is small and there is no risk of cracking even during strong processing.

The cross-sectional schematic diagram of the crystal grain of the steel plate base material which touches a plating layer. Data obtained by calculating I _Si / I _bulk from GDS measurement results.

  In the present invention (1), the crystal grain size of the steel sheet base material in contact with the plating layer is limited to 10 μm or less because the effect of suppressing non-plating and the effect of improving the plating adhesion appears by making it 10 μm or less. It is. From the viewpoint of plating adhesion during strong processing, the thickness is preferably 8 μm or less, and more preferably 5 μm or less. The crystal grains of the steel sheet base material in contact with the plating layer refer to crystal grains immediately below the plating layer, as shown in the schematic cross-sectional view of FIG.

  In order to reduce the crystal grain size of the steel plate base material in contact with the plating layer to 10 μm or less, it is necessary to contain a specific amount of Ti or Nb in the steel plate base material as described in the present invention (1). The effects of Ti and Nb include the effect of pinning grain boundaries by forming fine carbonitrides, and the effect of solid solution Ti and Nb suppressing grain boundary movement. To refine.

  A method for further enhancing the effect of containing Ti or Nb is not particularly limited, but there are the following methods. That is, (i) the finishing temperature during hot rolling is 900 ° C. or less, (ii) the coiling temperature is 600 ° C. or less after hot rolling, (iii) the sheeting speed in the hot dipping line is 150 m. However, all have the effect of refining the crystal grains of the steel plate base material.

  The following method may be used to measure the crystal grain size of the steel plate base material in contact with the plating layer. A steel plate is cut out to a size of 10 mm × 10 mm, subjected to cross-section polishing using an argon ion irradiation-type cross-section polishing apparatus, and then a cross-sectional backscattered electron microscope (FE-SEM) is used to observe a cross-section backscattered electron image. A backscattered electron image is taken at an acceleration voltage of 5 kV and a magnification of 10,000 times, and the average of the major axis and minor axis of the grain is taken as the grain size of one grain, and the average grain size of the grain in contact with the plating / steel interface is obtained. At least 5 fields of view were taken for each sample, and all average values were taken as the crystal grain size of the steel plate base material in contact with the plating layer.

  By setting the crystal grain size of the steel plate base material in contact with the plating layer to 10 μm or less, non-plating is suppressed and the plating adhesion is improved as follows. The non-plating is considered to be a phenomenon that occurs due to the presence of an external oxide film on the surface of the steel plate base material, which inhibits the reaction between the steel plate and molten zinc, resulting in a region that cannot react during immersion of molten zinc. Since the grain boundary has a remarkably fast diffusion rate of the element compared to the inside of the grain, the reactivity of the steel sheet and molten zinc is improved by reducing the crystal grain size on the steel sheet surface as in the present invention, and external oxidation is applied to the steel sheet surface. It is considered that non-plating was suppressed regardless of whether or not a film was present.

  The plating adhesion is considered to depend on whether or not an external oxide film remains at the interface between the plating layer and the steel sheet, or whether or not cracks are generated and propagated in the plating layer during processing. When the crystal grain size of the steel sheet base material in contact with the plating layer is made finer as in the present invention, (I) as described above, the reactivity between the steel sheet and the molten zinc is improved, so that the interface between the plating layer and the steel sheet is externally applied. Plating adhesion is improved by two points: no oxide film remains, and (II) the crystal grains are fine, which suppresses the generation of cracks from the steel sheet during processing and reduces cracks in the plating layer. I think that.

In the present invention (1), the Si intensity (I _Si ) of the steel sheet base material measured by GDS is the Si emission intensity at each measurement depth when the steel sheet is analyzed from the outermost layer to a depth of 3.6 μm by GDS. It is. The average Si strength (I _bulk ) inside the steel plate base material is the average value of I _Si when the depth from the outermost surface layer of the steel plate is between 3.2 μm and 3.6 μm. In the present invention (1), the value obtained by dividing the Si strength (I _Si ) of the steel plate base metal by the average Si strength (I _bulk ) inside the steel plate base material, and the minimum value of I _Si / I _bulk was limited to 0.8 or more. This is because an effect of suppressing cracking of the steel sheet surface layer during strong processing appears when the value is 0.8 or more.

The following method may be used to measure the minimum value of I _Si / I _bulk . That is, the steel plate is cut into a size of 20 mm × 30 mm and immersed in a solution of 0.2% inhibitor added to a 10% HCl aqueous solution to dissolve and remove only the plating layer. After that, GDS is analyzed from the outermost layer of the steel sheet to a depth of 3.6μm, and I _Si / I _bulk is calculated. Fig. 2 shows an example of data showing the relationship between I _Si / I _bulk obtained by measurement under conditions where the sputtering rate is 40 nm / sec in terms of SiO ₂ and the photomultiplier sensitivity is 650 V, and the depth from the outermost layer. Shown in The value of the position indicated by 3 in the figure is the minimum value of I _Si / I _bulk .

The reason why the surface layer cracking of the steel sheet during strong working is suppressed by setting the minimum value of I _Si / I _bulk to 0.8 or more is considered as follows. When the Si concentration differs between the steel sheet surface layer and the inside, materials such as strength and ductility differ between the surface layer and the inside of the steel sheet. At the time of strong working, the lower the strength in the steel sheet surface layer and inside, the main deformation will be, so it is considered that stress concentrates on the boundary with different Si concentration and cracks occur. If the minimum value of I _Si / I _bulk is 0.8 or more, the difference in Si concentration between the steel sheet surface layer and the inside is low, and the variation in material in the thickness direction is small. Conceivable.

In order to set the minimum value of I _Si / I _bulk to 0.8 or more, in the continuous hot dip galvanizing line, the atmosphere should be in an appropriate range so that Si in the steel plate base metal is more easily oxidized during recrystallization annealing. Need to control. The higher the H ₂ concentration in the atmosphere and the lower the dew point, the easier the external oxidation of Si in the steel plate base metal, so in an atmosphere with an O ₂ concentration of 10 ppm or less, the H ₂ concentration is 5% or more and the dew point is- Must be 40 ° C or less.

In general, it has been considered that when Si in a steel sheet base metal is externally oxidized during recrystallization annealing, non-plating is likely to occur during immersion in the plating bath. However, in the present invention, as described above, by refining the crystal grains of the steel plate base material, plating is possible even if an external oxide film is present on the surface of the steel plate, so the minimum value of I _Si / I _bulk Has made it possible to provide an alloyed hot-dip galvanized steel sheet having a value of 0.8 or more.

  In addition to the above method, the present inventors have found that it is effective to remove scum adhering to the steel plate on the plating bath surface in the plating bath in order to prevent non-plating more stably. . The scum is an oxide film of Zn or Al and floats on the surface of the plating bath. The present inventors have found that when a large amount of an external oxide film is present on the surface of the steel plate, scum is likely to adhere when the steel plate is immersed in a bath, and thus non-plating is likely to occur. Moreover, even if scum adhered once, it discovered that a scum could be removed by giving a jet with respect to a steel plate in a bath, and non-plating could be prevented. The scum can be easily removed by controlling the jet flow velocity from 10m / min to 50m / min and applying a plating bath at a position 10cm to 50cm downward from the bath surface, and stable non-plating. Can be prevented.

  The reason why each element in the steel plate base material is limited in the present invention (1) will be described.

  The C content in the steel sheet base metal is limited to the range of 0.001 to 0.3% by mass%, and the lower limit necessary to ensure the strength is 0.001%. Addition exceeding 0.3% This is to cause deterioration.

  The reason why the Si content in the steel plate base material is limited to the range of 0.1 to 3.0% by mass is that the lower limit necessary for securing the strength is 0.1%, and addition exceeding 3.0% This is to cause deterioration.

  The Mn content in the steel plate base metal is limited to the range of 0.5 to 3.0% by mass%, the lower limit necessary to ensure strength is 0.5%, and addition over 3.0% adversely affects ductility It is for exerting.

  The reason why the Al content in the steel sheet base metal is limited to the range of 0.001 to 3.0% by mass% is that it is disadvantageous in terms of cost if it is less than 0.001%. It is for worsening.

  The reason why the P content in the steel plate base material is limited to the range of 0.0001 to 0.3% by mass% is that it is disadvantageous in terms of cost if it is less than 0.0001%. It is for worsening.

  The reason why the S content in the steel sheet base metal is limited to the range of 0.0001 to 0.1% by mass% is that it is disadvantageous in terms of cost if it is less than 0.0001%. It is for worsening.

  The reason why the N content in the base of the steel plate is limited to the range of 0.0001 to 0.1% by mass% is that it is disadvantageous in terms of cost if it is less than 0.0001%, and if it exceeds 0.1%, workability This is because of a decrease.

  The content of Ti and Nb in the steel plate base material is mass%, and Ti: 0.001 to 0.2%, Nb: 0.001 to 0.2% is limited to one or two, Ti: 0.001% or more , Nb: 0.001% or more of the inclusion of one or two kinds of crystal grains of the steel plate base metal, the effect of suppressing non-plating and the effect of improving the plating adhesion, Ti: Inclusion of one or two of more than 0.2% and Nb: more than 0.2% not only saturates the effect of suppressing non-plating and the effect of improving plating adhesion, but also lowers the ductility of the steel plate base material. Because. From the viewpoint of plating adhesion, it is preferably Ti: 0.005 to 0.1%, Nb: 0.005 to 0.1%, or more preferably Ti: 0.01 to 0.06%, Nb: 0.01 to 0.06% It is to be 1 type or 2 types.

  Next, the reason why the structure of the plating layer is limited in the present invention (1) will be described.

  The reason why the Fe content in the plating layer is limited to the range of 5.0 to 20.0% by mass% is that spot weldability is poor at 5.0% or less, and when it exceeds 20.0%, the adhesion of the plating layer itself This is because the plating layer breaks or falls off during processing and adheres to the mold, causing defects during molding.

  The reason why the Al content in the plating layer is limited to the range of 0.01 to 1.0% by mass is that if it is less than 0.01%, dross generation is remarkable and a good appearance cannot be obtained. If Al is added in excess, the alloying reaction is remarkably suppressed, and it becomes difficult to form an alloyed hot-dip galvanized layer.

  In order to measure the content of Fe and Al in the plating layer, a method of dissolving the plating layer with an acid and chemically analyzing the solution may be used. For example, an alloyed hot-dip galvanized steel sheet cut to 30 mm × 40 mm is obtained by dissolving only the plating layer with 5% HCl aqueous solution with inhibitor added while suppressing elution of the steel sheet base material, and the solution is obtained by ICP light emission. A method of quantifying the contents of Fe and Al from the obtained signal intensity and a calibration curve created from a solution having a known concentration may be used. In addition, taking into account measurement variations between samples, an average value obtained by measuring at least three samples cut out from the same alloyed hot-dip galvanized steel sheet may be employed.

The plating adhesion amount is not particularly limited, but is preferably 5 g / m ² or more in terms of single-sided adhesion from the viewpoint of corrosion resistance. Further, from the viewpoint of ensuring plating adhesion, it is desirable that the amount of adhesion on one side does not exceed 100 g / m ² . On the hot dip galvanized steel sheet of the present invention, for the purpose of improving paintability and weldability, it is possible to apply upper layer plating and various treatments such as chromate treatment, non-chromate treatment, phosphate treatment, lubricity improvement treatment. Even if the weldability improving process is performed, it does not depart from the present invention.

  In the present invention (2), the Mo content in the steel sheet base metal is limited to the range of 0.001 to 1.0% by mass%, Mo is a strengthening element, and the addition of 0.001% or more adds strength of the steel sheet -It contributes to the improvement of the ductility balance. However, addition exceeding 1.0% may worsen the strength-ductility balance and increase the cost, so the upper limit is preferably made 1.0%.

  In the present invention (3), the total content of one or more of Cr, Ni, and Cu in the steel plate base metal is limited to a range of 0.001 to 5.0% by mass%, Cr, Ni This is because Cu is a strengthening element, and the strength is further increased by the addition of 0.001% or more in total. However, if the total addition exceeds 5.0%, the ductility may be adversely affected, and the cost is increased, which is economically disadvantageous. Therefore, the upper limit is preferably set to 5.0%.

  In the present invention (4), the total content of one or more of V, Zr, Hf, Ta in the steel plate base material is limited to a range of 0.001 to 5.0% by mass%, 0.001 This is because when these elements are added in an amount of more than 0.5%, these elements form fine carbides, nitrides or carbonitrides and the strength of the steel sheet is further increased. This is because there is a risk of inviting.

  In the present invention (5), the total content of one or more of Ca, Mg, Y, La, Ce in the steel plate base metal is limited to a range of 0.0001 to 0.1% by mass%. This is because these elements are effective elements for inclusion control and deoxidation, and their effects appear when added in an amount of 0.001% or more. Since addition exceeding 0.1% may reduce weldability, the upper limit is preferably made 0.1%.

  In the present invention (6), the content of B in the steel plate base metal is limited to the range of 0.0001 to 0.005 mass%, the effect of strengthening the grain boundaries and increasing the strength of the steel plate by adding 0.0001% or more This is because, when it exceeds 0.005%, the workability deteriorates.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to the examples.

  A slab having the composition shown in Table 1 was heated at 1200 ° C., and then finish hot-rolled and wound up under the conditions shown in Table 2 to obtain a hot-rolled steel strip having a thickness of 4 mm. After pickling, cold rolling was performed to obtain a cold rolled steel strip having a thickness of 1.0 mm, and then alloyed hot dip galvanizing was performed using an in-line annealing CGL. The plate passing speed was 150 m / min. Under the conditions shown in Table 3, after annealing at 800 ° C. for 60 seconds and cooling to 485 ° C., immerse in a plating bath with a composition of Zn-0.13 mass% Al-0.03 mass% Fe with a bath temperature of 460 ° C. for 3 seconds. And then alloyed at 460 to 580 ° C. for 5 seconds to 2 minutes. The jet conditions of the plating bath are as shown in Table 4. The jet was provided by a liquid metal pump installed in the plating bath.

As described above, the crystal grain size of the steel plate base material in contact with the plating layer was taken with a backscattered electron image of FE-SEM acceleration voltage of 5 kV and magnification of 10,000 times for the cross section polished with the argon ion irradiation type cross section polishing equipment. Measured from the photograph taken. Further, the minimum value of I _Si / I _bulk was measured using GDS on a steel sheet in which only the plating layer was dissolved and removed with a 10% HCl aqueous solution to which 0.2% of an inhibitor was added, under a photomultiplicity sensitivity of 650V.

  The surface appearance was evaluated by visually judging the occurrence of non-plating. No unplating, fine unplating with a diameter of 0.5 mm or less occurred, ○ with acceptable appearance, △ with unplating with a diameter of 2 mm or less, unplating with a diameter exceeding 2 mm What occurred was set as x, and ◎ and ○ were set as acceptable levels.

  In order to evaluate the plating adhesion at the time of processing to which compressive stress was applied, a tape was applied to the inside of the bent portion after the 60 ° V bending test, and the tape was peeled off. The plating adhesion was evaluated from the peeled state of the plating layer peeled off with the tape. ◎ indicates that there is almost no plating peeling (less than 3 mm peeling width), ○ indicates slight peeling that does not interfere with practical use (peeling width 3 mm or more and less than 7 mm), and △ indicates that a considerable amount of peeling is observed (peeling width 7 mm or more) Less than 10 mm) and x were those with severe peeling (peeling width 10 mm or more), and ◎ and ○ were acceptable.

In order to evaluate the presence or absence of cracks in the steel sheet surface during processing, the presence or absence of cracks in the steel sheet surface of the steel sheet after the bead pull-out test was confirmed. A pull-out test was performed with a radius of curvature of the bead tip of 2 mm, a pressing load of 3.9 × 10 ³ N, and a pulling speed of 200 mm / min. The cross section parallel to the drawing direction of the steel plate after the test was observed, and the presence or absence of cracks in the steel plate base material along the drawing direction was confirmed. The thing without a crack was set as the pass.

The evaluation results are shown in Table 5. From Table 5, in all of the inventive examples, the surface appearance, plating adhesion, and evaluation of steel plate cracking after bead drawing satisfy the acceptable level. The comparative examples that do not satisfy the scope of the present invention have low surface appearance, plating adhesion, and evaluation of steel plate cracking after bead drawing.

1 Plating layer
2 Crystal grain of steel plate base material in contact with plating layer
3 Minimum value of I _Si / I _bulk

Claims (6)

Steel plate base material is mass%,
C: 0.001-0.3%
Si: 0.1-3.0%
Mn: 0.5-3.0%
Al: 0.001 to 0.1%,
P: 0.0001-0.3%
S: 0.0001-0.1%,
N: 0.0001~0.1%,
further,
Ti: 0.001-0.2%,
Nb: 0.001 to 0.2% of one or two types,
On the surface of the steel sheet, the balance of which is Fe and inevitable impurities,
Fe: 5.0-20.0%,
Al: contains 0.01-1.0%,
The balance is an alloyed hot-dip galvanized steel sheet having a plating layer made of Zn and inevitable impurities,
The steel grain base material in contact with the plating layer has a crystal grain size of 10 μm or less , measured by glow discharge optical emission spectrometry (GDS), and the Si strength of the steel sheet base material (I _Si ) and the average Si strength inside the steel sheet base material (I _bulk ratio) state, and are the minimum value of 0.8 or more I _Si / I _bulk, the plating bath of 10 to 50 m / min relative to the steel plate, as the flow velocity at the location of 10~50cm in the depth direction from the bath surface of the plating bath galvannealed steel sheet excellent in surface appearance and coating adhesion, characterized in Rukoto produced giving the jet.
However, when the steel sheet was analyzed from the outermost layer to a depth of 3.6 μm with I _Si : GDS, the Si emission intensity at each measurement depth,
I _bulk : average value of I _Si when the depth from the outermost layer of the steel sheet is between 3.2 and 3.6 μm ,
It is.   2. The galvannealed steel sheet excellent in surface appearance and plating adhesion according to claim 1, wherein the steel sheet base material further contains Mo: 0.001 to 1.0% by mass.   The steel sheet base material is further alloyed with excellent surface appearance and plating adhesion according to claim 1 or 2 containing, in mass%, one or more of Cr, Ni, and Cu in a total amount of 0.001 to 5.0%. Hot dip galvanized steel sheet.   The steel sheet base material further comprises, in mass%, one or more of V, Zr, Hf, Ta, and 0.001 to 0.5% in total, and the surface appearance according to any one of claims 1 to 3 and Alloyed hot-dip galvanized steel sheet with excellent plating adhesion.   The steel sheet base material according to any one of claims 1 to 4, further comprising 0.0001 to 0.1% in total of one or more of Ca, Mg, Y, La, and Ce in mass%. Alloyed hot-dip galvanized steel sheet with excellent appearance and plating adhesion.   6. The galvannealed steel sheet excellent in surface appearance and plating adhesion according to any one of claims 1 to 5, wherein the steel sheet base material further contains B: 0.0001 to 0.005% by mass%.

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