JPH11131204A - High strength hot-dip galvanized steel sheet and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high strength hot-dip galvanized steel sheet good in surface appearance, high in strength, furthermore excellent in the uniformity of plated coating and moreover excellent in adhesion in the case of being used as automotive inner and outer plates, to produce a hot-dip galvannealed steel sheet free from the generation of unevenness in alloying and linear marks and to provide a method capable of stably producing these. SOLUTION: At the time of subjecting a high strength steel sheet in which the content of Si is regulated to, by weight, >=0.2% and/or the content of P is regulated to >=0.2% to hot-dip galvanizing, Mn series compd. is adhered thereto by 0.2 to 2000 mg/m<2> as the content of Mn, thereafter, it is annealed in a nonoxidizing atmosphere contg. hydrogen, is subsequently immersed in a hot-dip zinc bath at least contg. 0.05 to 0.30% Al to be plated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength hot-dip galvanized steel sheet and a high-strength galvannealed steel sheet using a high-strength steel sheet made of a high-Si content steel and / or a high-P content steel as a base steel sheet, and production thereof. More particularly, the present invention relates to a hot-dip galvanized steel sheet and an alloyed hot-dip galvanized steel sheet which are used as automobile inner and outer panels and have high strength and excellent uniformity and adhesion of a plating film, and methods for producing the same.

[0002]

2. Description of the Related Art In recent years, improvement in fuel efficiency of automobiles has been called for from the viewpoint of prevention of global warming, and high strength and thin materials have been strongly demanded from the viewpoint of weight reduction of vehicles and ensuring safety. on the other hand,
From the viewpoint of extending the life of a car body, alloyed hot-dip galvanized steel sheets have long been used as car body materials. Therefore,
Development of high-strength hot-dip galvanized steel sheets has been carried out to satisfy both of these characteristics.

[0003] Generally, Si, Mn,
Solid solution strengthening elements such as P are added. However, S
When a steel sheet containing i or P is used as a plating base plate, there is a problem that uneven alloying or non-plating due to surface non-uniformity before hot rolling occurs. Above all,
Since Si covers the steel sheet surface by selective oxidation during pre-plating annealing, the wettability with molten zinc deteriorates, causing non-plating and the occurrence of uneven streaks caused by red scale generated during hot rolling. The application of Si to the plate is particularly avoided. Further, Si and P also have a problem that the alloying speed is reduced. On the other hand, Mn does not have a significant adverse effect on the surface quality or alloying speed, but needs to be added in a large amount because of its low strengthening ability.

[0004] Problems of the Si-containing steel plate will be described below. (1) Wettability When using Si-containing steel as a plating base sheet,
However, since the steel sheet surface is selectively oxidized during the pre-plating annealing, the wettability with the molten zinc is deteriorated, and non-plating is caused.

[0005] (2) Scale-related uneven streaks [0005] In the case of Si-containing steel, streaks due to red scale generated during hot rolling are generated, so application of Si to an automobile outer panel is particularly avoided. Due to careful consideration such as descaling during hot rolling, even if the red scale is light enough to be difficult to distinguish after hot rolling, due to the difference in Si concentration during alloying treatment after hot-dip galvanizing Due to the non-uniformity of alloying, linear marks are formed on the surface of the steel sheet in the same manner as the red scale during hot rolling.

(3) Alloying rate In the case of Si-containing steel, Si is selectively oxidized on the steel sheet surface during CGL annealing, which impairs wettability with molten zinc. Even if non-plating does not occur, there is a problem that alloying is delayed due to inhibition of wettability.

Conventionally, as a base steel sheet of an alloyed hot-dip galvanized steel sheet for an automobile outer panel, although it has the above problems,
P-containing high-strength steel sheets are often used as those having a small adverse effect on the quality of automotive outer panels. However, there are quality or manufacturing problems as described below.

(1) Alloying Speed P-containing high-strength steel sheets have the problem that the alloying speed is significantly reduced by P. This is because Fe concentrates on the steel sheet surface during annealing, and when the steel sheet is immersed in the plating bath, it reacts with Al added in the plating bath and suppresses the Fe-Zn alloying reaction. Is generated thickly, and Fe
This is for strongly suppressing the -Zn reaction. Therefore,
A method has been adopted in which the line speed is reduced to secure the soaking time during alloying to complete the alloying. However, in this case, there is a problem that productivity is significantly reduced.

(2) Unevenness in alloying at coil tip / tail end In P-containing steel, alloying unevenness due to a change in conditions during hot rolling tends to occur. That is, the alloying speed at the leading and trailing ends of the cold-rolled coil is particularly slow, and alloying may not be performed by any means. This phenomenon occurs at the tip of the hot rolled coil.
It is presumed that this is caused by the special thermal history of the tail end. For this reason, since several tens of meters of the coil tip / tail end are not alloyed, this part is cut off and discarded, which causes a decrease in yield.

Also, in order to alloy the tip and tail ends,
The operator also adjusts the alloying processing conditions during operation, but since the alloying processing is performed while aiming at the part where alloying is particularly slow, excessive alloying processing is applied to the center part of the coil, Poor powdering properties may be caused.

(3) Unevenness in streak-like alloying In general, in P-containing steel, P in the steel tends to concentrate at the grain boundaries of the steel. The alloying reaction rate of the field is significantly reduced. For this reason, fine streaks occur on the surface after the alloying treatment, and the surface appearance is impaired, and the streaks adversely affect the chemical conversion treatment property, the paintability, and the like.

(4) Linear mark In the P-containing steel, P concentrates on the surface of the steel plate during annealing, and when the steel plate is immersed in the plating bath, it reacts with Al added in the plating bath to form Fe- F to suppress Zn alloying reaction
The e-Al alloy is formed thickly. This reaction is sensitive to bath composition, and slight fluctuations in Al concentration in the bath cause Fe-
The production amount of the Al alloy fluctuates greatly. Therefore, if there is a portion where the Al distribution in the plating bath is locally high or low, in the case of P-containing steel, partial alloying unevenness may occur, and a linear mark may be generated.

(5) Stability of production conditions Since steel sheets inserted into a hot-dip galvanizing line are diversified, alloying conditions differ depending on each steel sheet. During the operation, the operator sets the alloying conditions for each steel type.However, at the joints of steel types with greatly different conditions, it takes time to change the setting of the conditions, resulting in over-alloy and insufficient alloying, resulting in low yield. In addition to the decrease, stable production cannot be performed. For example, when a P-containing steel is connected after an IF alloy that is relatively fast to alloy, a portion not alloyed occurs at the tip of the P-containing steel in several tens of meters, and conversely, after the P-containing steel, If the IF steel is connected, a portion of the tip of the IF steel that causes poor powdering due to over-alloying is generated by several tens of meters, so that there is a portion to be cut off and discarded.

Conventionally, as a method of improving the wettability or a method of accelerating the alloying reaction, a method of pre-plating a metal or alloy such as Ni or Fe on the surface of a steel sheet prior to hot-dip plating (for example, see Japanese Unexamined Patent Publication No. -110859, etc., hereinafter referred to as prior art).

[0015]

However, in the prior art, since pre-plating is performed by electrolytic treatment as pre-treatment, there is a problem that equipment cost for pre-plating increases.

The present invention has been made in view of such circumstances, and when used as an automobile inner and outer panel, has a good surface appearance, high strength, and excellent plating film uniformity.
It is another object of the present invention to provide a high-strength hot-dip galvanized steel sheet having excellent adhesion and a high-strength hot-dip galvanized steel sheet that does not cause alloying unevenness or linear marks. Another object of the present invention is to provide a manufacturing method capable of stably manufacturing them.

[0017]

In order to solve the above-mentioned problems, the first invention is directed to a method for manufacturing a semiconductor device having a Si content of 0.2% or more and / or a P content of 0.02% or more in weight%. When performing hot-dip galvanizing on a certain high-strength steel sheet, 0.2 to 2000 mg / m ^{2 of} a Mn-based compound is attached as an Mn amount, and then annealed in a non-oxidizing atmosphere containing hydrogen. A method for producing a high-strength hot-dip galvanized steel sheet having excellent coating uniformity and adhesion, characterized by immersing in a hot-dip zinc bath containing 0.30% Al and performing plating.

According to a second aspect of the present invention, in the manufacturing method of the first aspect, the hot-dip galvanizing is performed by performing a preheating step in a weakly oxidizing atmosphere. Provided is a method for manufacturing a hot-dip galvanized steel sheet.

According to a third aspect of the present invention, there is provided a method of manufacturing a high-strength galvannealed steel sheet, wherein the hot-dip galvanizing is performed by the hot-dip galvanizing method according to the first or second aspect of the present invention, and then a heat treatment for alloying the plated layer is performed. Provide a way.

According to a fourth aspect of the present invention, there is provided a high-strength steel sheet having a Si content of 0.2% or more and / or a P content of 0.02% or more by weight, and at least one surface of the steel sheet. 0.2 to 2000 mg in terms of the amount of Mn formed
/ M ² , a high-strength molten zinc excellent in uniformity and adhesion of a film, comprising: a Mn-based compound layer having an amount of / m ² ; and a galvanized layer formed on the surface of the Mn-based compound layer. Provide plated steel sheets.

According to a fifth aspect, in the high-strength galvanized steel sheet of the fourth aspect, the Mn-based compound layer has a Mn-based compound uniformly dispersed therein, and a fine ζ phase is formed immediately above these compounds. Provided is a high-strength hot-dip galvanized steel sheet excellent in uniformity and adhesion of a film, characterized by being uniformly formed.

According to a sixth aspect of the present invention, there is provided a high-strength alloyed steel sheet manufactured by subjecting a hot-dip galvanized sheet according to the method for manufacturing a high-strength hot-dip galvanized steel sheet of the first or second invention to a heat treatment for alloying a plated layer. Provide hot-dip galvanized steel sheet.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described specifically. In the present invention, when hot-dip galvanizing is performed on a high-strength steel sheet having a Si content of 0.2% or more and / or a P content of 0.02% or more by weight, M
0.2 to 2000 mg / m ^{2 in} terms of the Mn amount of the n-based compound
After the adhesion, when the steel sheet is annealed in a non-oxidizing atmosphere containing hydrogen, the surface of the steel sheet contains a Mn-based compound or a metal Mn in addition thereto.
An Mn-based compound layer having an amount of g / m ² is formed. afterwards,
When plating is performed by immersing in a molten zinc bath containing at least 0.05 to 0.30% Al, F
e-Zn crystals (ζ phase) are finely and uniformly generated, and a hot-dip galvanized steel sheet excellent in film uniformity and adhesion can be obtained. In this case, Mn-based compounds are uniformly dispersed in the Mn-based compound layer, and a fine 分散 phase is uniformly generated immediately above these compounds. Furthermore, when the alloying heat treatment of the plating layer is performed thereafter, the alloying reaction proceeds from the fine and uniformly generated Fe—Zn crystal (ζ phase) as a starting point, so that a delay in alloying can be suppressed.

Here, the reason why the Si content is specified to be 0.2% or more and / or the P content is specified to be 0.02% or more is to obtain a steel sheet having a high strength level in which these contents are the object of the present invention. Because it is the minimum amount required for

The Mn compound is 0.2 to 20 in terms of Mn.
The was decided to 200 mg / m ² adhered has less effect of improving wettability or alloying promotion by Mn-based compound is less than 0.2 mg / m ² as the amount of Mn, whereas, Mn
This is because the effect is saturated even if the amount exceeds 2000 mg / m ² .

The amount of Al contained in the molten zinc bath is adjusted to 0.05
０．３0.30% is defined as that Fe is less than 0.05%.
-Since the amount of the generated Al alloy is small, the effect of suppressing the Fe-Zn reaction is small, the powdering resistance is deteriorated, and 0.30%
Is exceeded, the amount of Fe—Al alloy produced is too large.
This is because the effect of suppressing the e-Zn reaction is too large and alloying cannot be performed.

Next, the effect of the Mn compound in the present invention will be described with reference to FIGS. FIG. 1 shows a case where the steel containing Si is plated by a normal method.
FIG. 3 shows the case where the Mn-based compound of the present invention is adhered and galvanized on the same Si-containing steel (the present invention), FIG. 3 shows the case where the P-containing steel is plated by a normal method, and FIG.
FIG. 4 shows the surface state after annealing and the state of the initial alloy phase after plating in the case where the Mn-based compound is adhered and galvanized in the contained steel (the present invention).

As shown in FIG. 1, when the Si-containing steel is galvanized by a usual method, the selectively oxidized Si
The oxide causes non-plating.

As shown in FIG. 2, when the Mn-based compound is deposited according to the present invention and then galvanized, the Mn-based compound or the Mn-based compound containing metal Mn in addition to the Mn-based compound is added to the outermost surface of the steel sheet during annealing. A layer is formed and no plating occurs because it is wet with the molten zinc. After hot-dip galvanizing, a Fe—Zn crystal (ζ phase) is formed on the Mn compound layer.
Are finely and uniformly generated. After that, when the alloying heat treatment of the plating layer is performed, fine and uniform Fe
Since the alloying reaction proceeds starting from the -Zn crystal (ζ phase), alloying is promoted. High Si content in steel, S
Even when the selected oxide of i is formed thickly, the Mn-based compound is formed independently of this, and serves as a starting point of the ζ phase nucleation. Therefore, even when the steel type changes or the amount of Mn attached changes, a constant Fe-Zn alloying reaction proceeds irrespective of these fluctuation factors, resulting in excellent operation stability.

Further, as shown in FIG. 3, when the P-containing steel is galvanized by the usual method, a thick Fe-Al alloy layer is formed due to the concentrated P on the surface, and the Fe-Zn reaction suppressing effect is obtained. Becomes larger. Therefore, in the initial alloy phase, a coarse ζ phase is sparsely formed, and the other part is a strong Fe-
Since it is covered with the Al alloy suppressing layer, there is no starting point for causing the Fe-Zn reaction, and the alloying speed is very slow.

As shown in FIG. 4, even in the case of P-containing steel,
When zinc plating is performed after the Mn-based compound is adhered according to the present invention, a layer containing metal Mn or a Mn-based compound is formed on the outermost surface of the steel sheet during annealing, and the generation of the Fe-Al layer is reduced. On the Mn-containing layer, Fe
-Zn crystals (ζ phase) are finely and uniformly generated. Furthermore, when the alloying heat treatment of the plating layer is performed thereafter, the alloying reaction proceeds from the finely and uniformly generated Fe—Zn crystal (ζ phase) as a starting point, thereby promoting the alloying. P in steel
Even when the content or the Al concentration in the bath is high and the Fe-Al alloy is thick and easy to form, the Mn-based compound is formed independently of this, and fine and uniform nuclei of the ζ phase are generated. Therefore, even when the steel type is changed, the P content in the steel is changed, the Al concentration in the bath is changed, or the Mn amount in the compound layer is changed, the F value is constant regardless of these fluctuation factors.
Since the e-Zn alloying reaction proceeds, the operation stability is also excellent.

When producing the hot-dip galvanized steel sheet of the present invention as described above, the annealing after the Mn-based compound is attached must be performed in a non-oxidizing atmosphere containing hydrogen. This is to reduce the steel sheet with hydrogen.

When the hot dip galvanizing is performed according to the method of the present invention, it is more effective to perform the preheating step in a weakly oxidizing atmosphere. That is, by preheating in a weakly oxidizing atmosphere after attaching the Mn-based compound,
Since the Mn-based compound is oxidized and decomposition and scattering of the Mn-based compound can be suppressed, the Mn-based compound layer can be effectively formed.

The steel sheet targeted by the present invention may be a high-strength steel sheet containing 0.2% or more of Si and / or 0.02% or more of P, and other components are not particularly limited. In addition to Fe and inevitable impurities, C, S, M
One or more of g, Cr, Ni, Cu, Ta, Al and the like may be contained. Also, to manufacture IF steel,
Nb and Ti may be added. In the case of a steel sheet based on IF steel, several ppm of B may be added in order to prevent embrittlement of secondary workability.

The Mn compound used in the present invention is obtained by dissolving inorganic salts such as manganese nitrate and manganese sulfate in water or an organic solvent, or by mixing them. Further, a surfactant may be added for the purpose of increasing the adhesion of the solution of these chemicals to the steel sheet. Further, for the purpose of increasing the adhesion of the solution of these chemicals to the steel sheet, an organic resin may be dissolved in the solution and used as a binder. In addition, after adding the Mn-based compound to the lubricating oil during cold rolling or the rust-preventive oil after rolling, without degreasing, the steel sheet can be charged into an annealing furnace having a preheating furnace of a direct heating system. . However, when this method is adopted for an all-radiant tube type annealing furnace, it is not preferable because oil remains as dirt and affects the plating property and the surface appearance after alloying treatment. According to Mn-
The adverse effect can be reduced because the S-based compound is uniformly dispersed and the fine ζ phase is uniformly formed immediately above the precipitate. The effect of the present invention does not change even if alkaline electrolytic degreasing is performed before the Mn-based compound is attached.

The adhesion of the Mn-based compound to the surface of the steel sheet can be performed by spraying or applying these solutions onto the steel sheet and then drying, or spraying the solution on a preheated steel sheet. However, since the main purpose is to form a Mn-based compound layer on the surface of the steel sheet during annealing, it is only necessary that metal Mn or a Mn-based compound adhere to the steel sheet surface during annealing.
The method of adhesion is not limited to the above solution coating method, and may be performed by any means such as an electroplating method, an electroless plating method, and a vapor deposition method. However, in view of capital investment, a relatively simple solution coating method and an electroless plating method are preferred. Although the non-uniformity of Mn distribution at the time of initial deposition is alleviated to some extent by the chemical reaction in the annealing furnace, it goes without saying that it is better to distribute Mn uniformly at the time of initial deposition.

For annealing the steel sheet, a radiant tube type annealing furnace which is generally used can be used. In the case of performing preheating in a weakly oxidizing atmosphere, for example, an annealing furnace of a direct flame heating method may be used. Considering the efficiency of Mn deposition and the efficiency of the hot-dip galvanizing apparatus as a whole, the direct heating method, which can increase the rate of temperature rise, is preferable.

In the hot-dip galvanized or alloyed hot-dip galvanized layer of the coated steel sheet of the present invention, in addition to Zn, Fe and Al as main elements, A
s, Bi, Cd, Ce, Co, Cr, In, La, L
i, Mg, Mn, Ni, O, P, Pb, S, Sb, S
One, two or more of n, Ti, Zr and the like may be contained, and even if they are contained, the effect of the present invention is not impaired.

In the alloying treatment step, a method such as a gas heating method, an induction heating method, a direct current heating method or the like can be adopted, but the effect of the present invention is not changed by the difference in the alloying furnace heating method.

Since the present invention is mainly applied to automotive outer panels, the base steel sheet is mainly a cold-rolled steel sheet. The effect of the present invention can be obtained also in the case of a base of a hot-rolled steel sheet. Further, the present invention can be applied not only to automobile parts but also to applications such as building materials, electric appliances, and home appliances.

[0041]

EXAMPLES Cold-rolled steel sheets of the six components shown in Table 1 were used as test materials. Of these, A is T used as a comparative material.
This is an i-IF steel, and B to F are high-strength steel sheets containing Si and / or P targeted in the present invention. Manganese sulfate (MnSO ₄ ) is used for these steel sheets BF.
Of 3 g / L, 30 g / L, 300 g / L, manganese nitrate (Mn (NO ₃ ) ₂ ), manganese chloride (MnCl
₂ ), an aqueous solution containing 30 g / L of manganese bromide (MnBr ₂ ) was prepared and applied with a fixed amount by a bar coater.
It was instantaneously dried at 150 ° C. by a drying furnace of an induction heating system.

[0042]

[Table 1]

These steel sheets were annealed and plated using a hot-dip galvanizing simulator. The annealing condition is 85
The test was performed at 0 ° C. for 30 seconds in 10% H ₂ —N ₂ (dew point −40 ° C.). During annealing, some of them are 500
A condition for performing a weak oxidation pretreatment at 30 ° C. for 30 seconds was added.

The hot-dip galvanizing was performed using a galvanizing bath containing 460 ° C. containing 0.12% of Al at an intruding plate temperature of 460 ° C. and an immersion time of 3 seconds. After plating, the amount of zinc deposited was adjusted to 60 g / m ² per one side with a N ₂ gas wiper.

The sample after plating was evaluated for the occurrence of non-plating, the observation of the initial alloy phase morphology, and the evaluation of plating adhesion by a 0T bending test.
0,475,500,525,550,575,600
The alloying process was performed at 20 ° C. for 20 seconds, and the alloying speed was compared based on the temperature at which alloying up to the surface layer was possible. The alloying temperature was adjusted so that the iron content in the film was 10% ± 0.5%, and the occurrence of alloying unevenness was observed using a sample subjected to an alloying treatment for 20 seconds. .

Table 2 shows the results of evaluating the plating quality of the hot-dip galvanized steel sheet and the alloyed hot-dip galvanized steel sheet manufactured as described above, together with the manufacturing conditions. The evaluation items and evaluation criteria for plating quality shown in Table 2 are as follows.

^* 1. No plating (visual judgment) ○: good ×: no plating is observed

^* 2. Initial alloy phase (SEM observation) ：: Fine ζ phase is uniformly formed ×: ζ phase is sparsely formed B: Outburst structure

^* 3. Plating adhesion ○: good ×: plating peeling occurred

^* 4. Alloying speed ●: too fast ○: good ×: very slow

^* 5. Alloy unevenness (visual judgment) ○: good ×: streaks are observed

[0052]

[Table 2]

As shown in Table 2, in the examples of the present invention, good results were obtained for all the plating quality evaluation items, whereas in the comparative example having no attached matter, any of the above plating quality evaluation items was not satisfied. Was inferior.

[0054]

As described above, according to the present invention,
When used as an automobile inner and outer panel, the surface appearance is good,
Provided are a high-strength hot-dip galvanized steel sheet having high strength, excellent uniformity of a plating film, and excellent adhesion, and a high-strength galvannealed steel sheet that does not cause uneven alloying or linear marks. Further, a manufacturing method capable of stably manufacturing them is provided.

[Brief description of the drawings]

FIG. 1 is a view showing a state of a steel sheet surface after annealing and a state of an initial alloy phase after plating in a case where a Si-containing steel is plated by an ordinary method.

FIG. 2 is a view showing a state of a steel sheet surface after annealing and a state of an initial alloy phase after plating when a Mn-based compound is adhered and galvanized according to the present invention in a Si-containing steel.

FIG. 3 is a view showing a state of a steel sheet surface after annealing and a state of an initial alloy phase after plating when P-containing steel is plated by a normal method.

FIG. 4 is a view showing a state of a steel sheet surface after annealing and a state of an initial alloy phase after plating in a case where a P-containing steel is galvanized by adhering a Mn-based compound according to the present invention.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Masaru Sagiyama 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd.

Claims (6)

[Claims] When hot-dip galvanizing is performed on a high-strength steel sheet having a Si content of 0.2% or more and / or a P content of 0.02% or more by weight, a Mn-based compound is changed to Mn. After being deposited in an amount of 0.2 to 2000 mg / m ² , annealing is performed in a non-oxidizing atmosphere containing hydrogen, and then immersed in a molten zinc bath containing at least 0.05 to 0.30% Al to perform plating. A method for producing a high-strength hot-dip galvanized steel sheet having excellent coating uniformity and adhesion. 2. The high-strength hot-dip galvanizing method according to claim 1, wherein the preheating step is performed in a weakly oxidizing atmosphere when hot-dip galvanizing is performed. Steel plate manufacturing method. 3. A method for producing a high-strength alloyed hot-dip galvanized steel sheet, comprising, after galvanizing according to the method of claim 1 or 2, further performing an alloying heat treatment on the plated layer. 4. A high-strength steel sheet having a Si content of 0.2% or more and / or a P content of 0.02% or more in weight%, and formed on at least one surface of the steel sheet. Characterized by comprising a Mn-based compound layer in an amount of 0.2 to 2000 mg / m ² in terms of Mn amount, and a zinc plating layer formed on the surface of the Mn-based compound layer. High-strength galvanized steel sheet with excellent uniformity and adhesion. 5. The high-strength hot-dip galvanized steel sheet according to claim 4, wherein the Mn-based compound layer has a Mn-based compound uniformly dispersed therein, and a fine ζ phase is uniformly generated immediately above these compounds. High strength hot-dip galvanized steel sheet with excellent coating uniformity and adhesion. 6. A high-strength galvannealed steel sheet produced by subjecting a galvanized steel sheet to hot-dip galvanizing according to the method for manufacturing a high-strength hot-dip galvanized steel sheet according to claim 1 or 2 and then performing a heat treatment for alloying the plated layer. steel sheet.