JP5436009B2 - High strength galvannealed steel sheet with excellent plating adhesion and method for producing the same - Google Patents

Description

  The present invention is a high strength alloy having a tensile strength of 980 MPa or more, which is mainly used as a steel plate for structural members for automobiles, particularly as a material for parts requiring corrosion resistance, such as side members, side sills, cross members, and pillar lower reinforcement members. The present invention relates to a galvannealed steel sheet.

  In recent years, high strength steel sheets for automobiles have been demanded from the viewpoint of improving fuel efficiency by reducing vehicle weight, and alloyed hot-dip galvanized steel sheets used as materials for parts requiring corrosion resistance are no exception. The alloyed hot-dip galvanized steel sheet is obtained by alloying a hot-dip galvanized layer with a Zn-Fe alloy mainly for the purpose of improving corrosion resistance, post-coating corrosion resistance and weldability with respect to the hot-dip galvanized steel sheet.

  As with hot-dip galvanized steel sheets, the phenomenon that the coating layer peels off in powder or lump form during press forming (called “powdering”) is a problem, but with increasing strength, Strong press forming is performed, and the load applied to the surface of the plating layer during the forming process is increased, so that powdering is a more serious problem.

The powdering in the alloyed hot-dip galvanized steel sheet is caused by the formation of a particularly hard and brittle Γ phase such as Fe ₃ Zn ₁₀ . When the Γ phase is formed, the plating adhesion is lowered and the plating layer is easily peeled off, so that powdering is likely to occur. For this reason, suppressing excessive progress of the Fe—Zn alloying reaction and suppressing the formation of the Γ phase is a guideline for producing an alloyed hot-dip galvanized steel sheet having excellent plating adhesion.

  Conventionally, various techniques have been proposed from this viewpoint. For example, in Patent Document 1, the average Fe content in the plating layer is suppressed to 7 to 11% by weight, the amounts of ζ phase, δ1 phase, and Γ phase are adjusted to suppress the formation of Γ phase. It is disclosed that the powdering resistance and the flaking resistance are improved by keeping the degree low. However, if the average Fe amount in the plating layer is kept low, Zn and Fe concentrations are continuously distributed in the interface region of the plating layer, so the formation of the Γ phase in that region is not necessarily suppressed, and sufficient plating is performed. Adhesiveness, and thus sufficient powdering resistance, is not obtained.

  Further, in Patent Document 2, the effective Al concentration in the plating bath is defined, and the Γ phase is divided by locally forming a concentrated Al portion at the plating layer-ground steel plate interface, and the Γ layer cracks. It is described that plating adhesion is improved by suppressing the progress of. However, with this measure, it cannot be said that the powdering resistance at the time of molding is sufficient with respect to the recent increase in strength.

  In addition, as a technique for improving the powdering resistance, Patent Document 3 discloses that the coil winding temperature at the time of hot rolling is high and the cooling rate is slowed down, so that the grain boundary under the scale, which is directly under the plating layer, It is described that an oxide is grown to improve plating adhesion during press working. However, when 0.1% or more of Mn, which plays an important role in increasing the strength, is contained, Mn oxide is excessively formed on the surface, and there is a concern about non-plating.

  Patent Document 4 discloses an alloyed hot-dip galvanized steel sheet using a ground steel sheet mainly composed of ferrite-martensite DP steel, and a concentrated layer of Al, that is, atoms over a depth of 300 mm or more from the surface of the plated layer. The anti-powdering property is improved so that a region of Al% / Zn% of 0.10 or more exists at several%. However, this technique is intended to increase the hardness of the surface layer 300 の of the plating layer by concentrating Al, and the plating adhesion is not fundamentally improved.

Japanese Patent No. 2695259 JP-A-8-269667 Japanese Patent Laid-Open No. 9-31620 JP 2008-127637 A

  As described above, in the prior art, the galvannealed steel sheet using a high-strength steel sheet as the base steel sheet cannot be said to have sufficient plating adhesion and powdering resistance. This invention is made | formed in view of this problem, and it aims at providing the high intensity | strength galvannealed steel plate excellent in plating adhesiveness and powdering resistance.

  The present inventor has a limit in improving the adhesion of plating only by adjusting the average value of Fe amount and Al amount of the entire plating layer. We have investigated measures to improve the adhesion of the plating layer. By controlling the Al concentration in the interface region between the plating layer and the ground steel plate, we can suppress the formation of the Γ phase in the interface region. As a result, the present inventors have found that the plating adhesion and thus the powdering resistance can be improved without causing deterioration of chemical conversion properties and non-plating, thereby completing the present invention.

That is, the high-strength galvannealed steel sheet of the present invention is a base steel sheet coated with an alloyed galvanized layer, and the base steel sheet has a chemical composition of mass%,
C: 0.1 to 0.3%
Si: 0.2% or less,
Mn: 1.0-4.0%,
P: 0.1% or less,
S: 0.01% or less,
Al: 0.01 to 3.0%
A plating layer, wherein the balance consists of Fe and inevitable impurities, and the ratio [Zn] / [Fe] of the local Zn content and Fe content in the thickness direction is 0.5 or more and 5.0 or less, The average value (average Al concentration) of the Al amount in the interface region with the ground steel plate is 1.5% or more.

  The steel sheet further has a chemical composition of Nb: 0.005-0.5%, Ti: 0.005-0.5%, Cu: 0.003-0.5%, Ni: 0.003-l . 0%, Mo: 0.01 to 1.0%, B: 0.0001 to 0.1%, Ca: 0.0005 to 0.005%, Mg: 0.0005 to 0.01%, V: 0 One or more of 0.003 to 1.0% may be included.

  This high-strength alloyed hot-dip galvanized steel sheet is obtained by coating a ground steel sheet formed of a high-strength steel sheet of a predetermined component with an alloyed hot-dip galvanized layer, and easily generates a Γ phase, [Zn] / Since the average Al concentration in the interface region with [Fe] of 0.5 to 5.0 is 1.5% or more, generation of a Γ phase in the interface region, which causes peeling, can be suppressed. The adhesion of the alloyed hot dip galvanized layer can be improved, and powdering of the alloyed hot dip galvanized layer can be prevented even when the steel plate is strengthened with increased strength.

  Moreover, the method for producing a high-strength galvannealed steel sheet according to the present invention comprises subjecting the base steel sheet to hot dip galvanization, and further performing an alloying treatment for alloying the coated hot dip galvanized layer, As the alloying treatment, a treatment is performed at an alloying treatment temperature of 450 ° C. to 500 ° C. for 10 to 30 seconds, and subsequently at 200 to 300 ° C. for 10 minutes or more.

  According to this manufacturing method, the alloying process performed after the hot dip galvanizing process is divided into two stages, the alloying is performed at a relatively low temperature and in a short time as the first stage alloying process, and subsequently as the second stage alloying process, Since heating is performed at 200 to 300 ° C. for 10 minutes or more, the Al concentration distribution in the plate thickness direction (steel plate surface vertical direction) can be controlled in the interface region between the plating layer and the ground steel plate, from the alloying temperature to room temperature. In the cooling process, an Al concentrated layer can be left in the interface region. Thereby, the formation of a Γ phase in the interface region can be suppressed, the adhesion of the plating layer can be improved, and an alloyed hot-dip galvanized steel sheet having excellent powdering resistance during press forming can be provided.

  According to the high-strength galvannealed steel sheet of the present invention, since the average Al concentration in the interface region between the high-strength ground steel sheet and the galvannealed layer is 1.5% or more, a hard and brittle Γ phase Can be prevented from being generated in the interface region, and thereby, it is possible to provide excellent plating adhesion to a high-strength ground steel plate, and thus powdering resistance. For this reason, even under strong processing on high-strength steel sheets, it is possible to suppress powdering, prevent die squeezing of press-formed products, prevent deterioration of corrosion resistance of the plating peeling part, and suppress the generation of scratches by the peeled plating pieces. it can.

The heat processing diagram in the alloying process of this invention is shown. The emission spectroscopic analysis results in the vicinity of the interface region of the high-strength galvannealed steel sheets of the inventive example (Sample No. A1) and the comparative example (Sample No. A3) are shown. The position in the plate thickness direction (horizontal axis) and Al It is a graph which shows the relationship with a density | concentration.

  First, the ground steel plate of the high-strength galvannealed steel plate according to the present invention (embodiment) will be described. This base steel plate has a chemical composition of mass% (hereinafter simply referred to as “%”) C: 0.1 to 0.3%, Si: 0.2% or less, Mn: 1.0 to 4.0. %, P: 0.1% or less, S: 0.01% or less, Al: 0.01 to 3.0%, with the balance being Fe and inevitable impurities. Hereinafter, the reason for component limitation will be described.

C: 0.1 to 0.3%
C is an essential element for ensuring the strength of the steel sheet, and if it is less than 0.1%, the strength is insufficient. On the other hand, when the C content is excessive, weldability deteriorates. For this reason, the lower limit of the C content is 0.10%, preferably 0.12%, and the upper limit is 0.30%, more preferably 0.25%.

Si: 0.2% or less Si is a substitutional solid solution strengthening element that greatly hardens the material. However, if added in a large amount, an oxide film is formed on the surface, and the alloying rate of hot dip galvanizing is remarkably slowed, resulting in uneven plating and non-plating. For this reason, the upper limit is limited to 0.2%.

Mn: 1.0-4.0%
Mn is an element effective for securing the strength of the steel sheet. If it is less than 1.0% strength improving effect is shortage. On the other hand, when it is contained in a large amount, segregation becomes prominent, workability is lowered, weldability is further deteriorated, and plating property is lowered due to generation of oxide on the steel sheet surface. For this reason, the lower limit of the amount of Mn is set to 1.0%, preferably 1.5%, and the upper limit is set to 4.0%, preferably 3.0%.

P: 0.1% or less P is an element that promotes grain boundary destruction by grain boundary segregation, and the smaller the better. In the present invention, the upper limit is limited to 0.1%, preferably 0.05%.

S: 0.01%
If S is excessively contained, sulfide inclusions increase and the strength of the steel sheet deteriorates. For this reason, the upper limit is limited to 0.01%, preferably 0.005%.

Al: 0.01 to 3.0%
Al is an element necessary for deoxidation. In order to effectively exhibit such an effect, 0.01% or more, preferably 0.5% or more is added. However, if added excessively, ductility is reduced and steel becomes brittle, so the upper limit is made 3.0%, preferably 2.5%.

The ground steel plate according to the embodiment includes the above components as basic components, and the balance is composed of Fe and inevitable impurities, but Nb: 0.005-0.5%, Ti: 0.005-0. 5%, Cu: 0.003-0.5%, Ni: 0.003-l. 0%, Mo: 0.01 to 1.0%, B: 0.0001 to 0.1%, Ca: 0.0005 to 0.005%, Mg: 0.0005 to 0.01%, V: 0 One or two or more of 0.003 to 1.0% can be added to the basic component. For example, the following compositions (1) to (5) can be obtained.
(1) The basic component contains one or two of Nb and Ti.
(2) One or two of Cu and Ni are included in the basic component or the component (1).
(3) One or two of Mo and B are included in the basic component and the component (1) or (2) above.
(4) The basic component, (1), (2) or (3) above contains one or two of Ca and Mg.
(5) V is included in the basic component, (1), (2), (3) or (4) above.

Hereinafter, the reasons for limiting the above-mentioned characteristic improving elements will be described below.
Nb and Ti are elements that refine crystal grains and are effective elements for improving the strength of the steel sheet without impairing toughness. In order to effectively exhibit these effects, the lower limit is preferably 0.005%, more preferably 0.03%. However, even if contained excessively, the effect is not only saturated but also disadvantageous in terms of cost. Therefore, the upper limit is preferably 0.5%, more preferably 0.3%.

  Cu and Ni are both solid solution strengthening elements and contribute to improving the strength of the steel sheet. Further, the presence of Cu and Ni can improve the corrosion resistance of the steel sheet itself. In order to fully exhibit these effects, the lower limit is preferably 0.003%, more preferably 0.01%. However, since the plated steel sheet itself is excellent in corrosion resistance, its effect is saturated even if it is excessively contained, and the cost is disadvantageous, so the upper limit of Cu is preferably 0.5%, more preferably 0.4. %. Similarly, if Ni is excessively contained, the effect is saturated and disadvantageous in terms of cost. Therefore, the upper limit of Ni is preferably 1.0%, more preferably 0.8%.

  Both Mo and B are effective elements for improving the hardenability of the steel sheet. Mo has the effect of suppressing hydrogen penetration and improving delayed fracture characteristics, and further has the effect of strengthening grain boundaries and suppressing the occurrence of hydrogen embrittlement. In order to effectively exhibit these effects, the lower limit of Mo is preferably 0.01%. However, if it is contained excessively, not only will the effect be saturated, but there will also be problems such as an increase in cost due to excessive addition of expensive alloy elements, and in addition, the strength of the hot rolled sheet becomes very high and rolling becomes difficult. For this reason, the upper limit of the amount of Mo is preferably 1.0%, more preferably 0.5%, and more preferably 0.3%. On the other hand, B also has the effect of strengthening grain boundaries and improving delayed fracture resistance. In order to sufficiently exhibit these effects, the lower limit of B is preferably 0.0001%, more preferably 0.00015%. However, since the hot workability deteriorates if contained excessively, the upper limit is preferably 0.01%, more preferably 0.005%.

  Both Ca and Mg are effective elements for controlling the form of sulfide in steel and improving workability. Moreover, the rise of the hydrogen ion concentration of the interface atmosphere accompanying corrosion on the steel sheet surface is suppressed. In order to fully exhibit these effects, it is preferable to contain 0.0005% or more of each. On the other hand, since processability will deteriorate if it is contained excessively, the preferable upper limit is made Ca: 0.005% and Mg: 0.01%.

  V contributes to the formation of protective rust, and in particular, the formation of protective rust is promoted by the combined addition of Ti and V. V is an element effective for increasing the strength of steel sheets and making them finer. Further, like Ti, it combines with C and N in steel to form fine carbonitrides and has a high tensile strength exceeding 980 MPa. It works effectively as a hydrogen trap site that causes hydrogen embrittlement, which is a concern with high-strength steel sheets. In order to exhibit these effects effectively, the lower limit is preferably 0.003, more preferably 0.01%. However, if it is added excessively, the amount of precipitates increases and the workability is lowered. Therefore, the upper limit is preferably 1.0%, more preferably 0.5%.

  The structure of the base steel sheet is not particularly limited, and the tensile strength may be 980 MPa or more, preferably 1180 MPa or more. An appropriate structure form such as a steel plate can be adopted.

  Next, the Al concentration distribution in the interface region between the galvannealed layer and the ground steel plate will be described. When hot-dip galvanizing is applied to the base steel plate, the Al-Fe alloyed layer is formed by containing Al in the galvanizing bath in an amount of about 0.2% or less, and the formation of a Γ phase that reduces plating adhesion is suppressed. That is widely known. This is considered to suppress the formation of the Γ phase by preferentially Al-Fe alloying, but also by the fact that Al is contained in the Fe-Zn alloy system by our study, It has been found that the formation of the Γ phase is suppressed. Therefore, in order to improve the plating adhesion of the plating layer, it is effective to increase the Al concentration in the interface region between the plating layer and the ground steel plate and suppress the formation of the Γ phase in the interface region.

  The generation of the Γ phase in the interface region is considered as follows. In the region mainly composed of Fe on the ground steel plate side near the plating layer-ground steel plate interface, the α phase is relatively more stable than the room temperature at the alloying treatment temperature (about 500 ° C.). Is considered to be formed in the cooling process after alloying. However, when the alloying treatment temperature is high, Al atoms diffuse from the Al concentrated layer formed at the plating layer-ground steel plate interface during hot dip galvanization, so that sufficient Al is Zn in the interface region during cooling. -Will not be present in the Fe alloy. For this reason, formation of a Γ phase inevitably occurs in the interface region under conventional alloying conditions. The galvanizing bath usually contains about 0.15% or less of Al. Even when Al is contained at this level, the Al contained in the plating bath is preferentially alloyed with Fe over Zn at the stage of hot dip galvanizing. Therefore, the Al concentrated layer is formed at the interface between the plating layer and the ground steel plate after the plating and before the alloying treatment is performed.

  Therefore, in the present invention, in order to prevent Al atoms from diffusing from the interface region during the alloying process, firstly, a first stage alloying process is performed that is held at a relatively low temperature for a short time. However, in such a low temperature and short time holding, the alloying of Zn—Fe in the plating layer is insufficient. For this reason, in order to promote the alloying of Zn—Fe in the plating layer, after the first-stage alloying treatment, heating for about 10 minutes or more is performed at 250 to 300 ° C., in which Al atom diffusion hardly occurs. A second-stage alloying process is performed. By performing the alloying process in two stages in this way, sufficient alloying can be performed while suppressing the diffusion of Al. As a result, even after alloying treatment, an Al concentrated layer can be preserved in the interface region between the plating layer and the ground steel plate, thereby suppressing the formation of a Γ phase in the interface region, and adhesion of the plating during forming processing. Can be improved.

  In the interface region between the plating layer and the ground steel plate, atoms such as Fe, Zn, Al and the like are in a mutually diffused state, and the two layers are not joined with a certain interface as a boundary. Therefore, in the present invention, the interface region in the thickness direction where the Γ phase is formed during cooling is defined by the Zn (Fe) concentration (%) ratio, that is, [Zn] / [Fe], and [Zn] / [Fe]. The range where [Fe] was 0.5 to 5.0 was defined as the interface region. In order to suppress the formation of the Γ phase, it is necessary to set the average Al concentration in the interface region having [Zn] / [Fe] of 0.5 to 5.0 to 1.5% or more, as will be apparent from Examples described later. There is. When the Al content of the ground steel plate is 1.5% or more, a certain amount of Al exists in the interface region between the plating layer and the ground steel plate, so that the desired Al concentration is easily secured in each part of the interface region.

  Next, the manufacturing method of the said high intensity | strength galvannealed steel plate is demonstrated. The basic concept of the alloying treatment has already been explained, but here it will be explained mainly in terms of manufacturing conditions.

About manufacture of a base steel plate, according to a conventional method, the steel slab of the said composition is cast, the slab is hot-rolled and cold-rolled, and it winds up to the coil of desired plate | board thickness. The hot rolling conditions are not particularly limited, and for example, the heating temperature may be about 1100 to 1300 ° C, the finish rolling temperature may be about 800 to 950 ° C, and the winding temperature may be about 500 to 700 ° C. When the coil winding temperature is high, the steel plate scale becomes thick and the pickling property is lowered. Moreover, the conditions of the cold rolling are not particularly limited, but may be performed, for example, at a cold rolling rate of about 30 to 60%.

After cold rolling, annealing is performed to adjust the structure. Although the heat treatment process varies depending on the steel material structure, for example, it is held at about 700 to 900 ° C. for about 10 to 600 seconds. In order to suppress excessive oxidation of the surface due to heating, it is desirable to heat in a reducing atmosphere of approximately 10% H ₂ as is generally done.

After the annealing, the steel sheet is cooled to a plating bath temperature (about 400 to 460 ° C.) and immersed in the plating bath for about 1 to 5 seconds to perform a hot dip galvanizing treatment. If the steel plate temperature at the time of penetration of the plating bath is too higher than the plating bath temperature, Fe elution from the steel plate to the plating bath increases, causing an increase in the amount of dross generated and reducing productivity. The plating bath component may be a normal one, for example, Al: 0.13-0.15%, including eluted Fe (about 0.02-0.06%), with the balance being Zn and inevitable impurities Can be mentioned. The plating adhesion amount is not particularly limited, but is preferably about 25 to 200 g / m ² (thickness: 4 to 30 μm) from the viewpoint of corrosion resistance and adhesion.

  An alloying process is performed within 1 to 30 seconds after the hot dip galvanizing process. As described above, in the alloying process, as shown in FIG. 1, first-stage alloying process 1 is first performed, and then second-stage alloying process 2 is performed. In the first-stage alloying treatment 1, the heating temperature T1 is set to 450 to 500 ° C., which is relatively lower than usual, and the holding time t1 is set to a relatively short time of 10 to 30 seconds. In the subsequent second-stage alloying treatment 2, the heating temperature T2 is set to 200 to 300 ° C., and the holding time t2 is set to 10 minutes or more. In the second-stage alloying process 2, when the heating temperature exceeds 300 ° C., alloying proceeds too much, the plating layer becomes hard, and powdering tends to occur. On the other hand, if the temperature is lower than 200 ° C., the effect of promoting alloying becomes insufficient. As for the heating time, if it is less than 10 minutes, the effect is insufficient. 10 minutes or more, preferably 30 minutes or more. The treatment may be performed for a longer time, for example, 60 minutes or longer. However, the effect of improving the adhesion is saturated, and the shorter the heat treatment time, the better the productivity. Therefore, it is usually performed in about 15 to 30 minutes. The treatment atmosphere is preferably a nitrogen atmosphere of 99% or more, more preferably a reducing atmosphere containing about 5 to 10% by volume of hydrogen and the balance being nitrogen. The heating method for alloying is not particularly limited, and conventional means such as gas heating and induction heater heating can be employed. After the alloying treatment, it is cooled to room temperature at a cooling rate of about 1 ° C./S or more.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not construed as being limited to such examples, and appropriate modifications are made within a range that can meet the gist of the description before and after. Can be implemented.

The steel having the composition shown in Table 1 was melted and the slab was heated at 1150 to 1250 ° C. for 30 minutes, then hot rolled at a finishing temperature of 850 ° C. and cooled at 40 ° C./s after the end of rolling. It wound up at 550 degreeC. After pickling, cold rolling is performed at a cold rolling rate of 50%, annealing is performed at 800 ° C. for 60 seconds, and subsequently the steel sheet cooled to a plating bath temperature (460 ° C.) is added to a plating bath having the following composition. Hot dip galvanizing was performed by immersing in 0.0 second, followed by alloying treatment under the conditions shown in Table 2 (T1, t1, T2, and t2 are as shown in FIG. 1). The atmosphere during alloying was a nitrogen gas atmosphere.
-Plating bath composition Al: 0.14%, Fe: 0.02%, balance Zn and inevitable impurities (less than 0.1%)

  A tensile test piece was taken from the galvannealed steel sheet produced as described above, and the tensile strength was measured. In addition, a component analysis test piece was collected, and the element distribution along the plate thickness direction was measured using a Marcus type high-frequency glow discharge optical emission spectrometer (GD-OES). The average Al concentration in the interface region where Zn] / [Fe] was 0.5 to 5.0 was determined. An example of the result of the emission spectroscopic analysis (sample Nos. A1 and A3 in Table 2) is shown in FIG. Further, Table 2 also shows the value of the average Al concentration in the interface region.

In addition, in order to evaluate the powdering resistance at the time of press forming, a test piece was taken from each sample steel plate, and a cross cut (total of 100 squares) was made in a 10 × 10 mm area at intervals of 1 mm in length and width. Was bent with a bending radius of 5 mm, the cross cut portion was peeled off with tape, the number of peeled masses was counted, and the formability was evaluated based on the number. Those having a count number of 0 to 5 are particularly excellent in plating adhesion, “◎”, those having a count number of 6 to 20 are excellent in plating adhesion, “O”, and those having a count number of 21 to 50 Were evaluated as “△”, with a slight inferior plating adhesion, and “×” with a poor adhesion in the plating of 51-100. These evaluation results are also shown in Table 2.

  From sample Nos. A1 to A6 in Table 2 and FIG. 2, sample No. A5 that is not subjected to the second-stage alloying treatment and sample No. A6 in which the same processing conditions are inappropriate have a reduced Al concentration in the interface region. Plating adhesion decreased. Further, in the case where the second-stage alloying treatment was not performed as in sample No. A5 and the alloying treatment temperature was set lower than usual, the appearance was visually observed, and Zn-Fe alloying was not observed. In some cases, sufficient characteristics as an galvannealed steel sheet cannot be obtained. Further, even if the second-stage alloying treatment is appropriately performed, the predetermined average Al concentration is not ensured in the interface region even for sample Nos. A3 and A4 that are not suitable for the first-stage alloying treatment. Decreased. On the other hand, in sample Nos. A1 and A2 subjected to appropriate first and second stage alloying treatments, the average Al concentration in the interface region satisfies the conditions of the present invention, and excellent plating adhesion can be obtained. confirmed. Further, not only the steel type A but also other compositions such as steel types B and C, even if the composition is the same, the alloying treatment conditions satisfy the conditions of the present invention (Sample Nos. B1, B2, C1, C2 and D1 to K1) were sufficiently plated with Zn-Fe alloy as compared with unsatisfactory samples (samples B3, B4, B5, C3, and D2 to K2), and high plating adhesion was obtained.

Claims (3)

An alloyed hot-dip galvanized steel sheet in which a base steel sheet is coated with an alloyed hot-dip galvanized layer,
The base steel plate has a chemical composition of mass%,
C: 0.1 to 0.3%
Si: 0.2% or less,
Mn: 1.0-4.0%,
P: 0.1% or less,
S: 0.01% or less,
Al: 0.01 to 3.0%
And the balance consists of Fe and inevitable impurities,
The ratio [Zn] / [Fe] of the local Zn content and Fe content in the plate thickness direction is 0.5 or more and 5.0 or less, and the average value of the Al content in the interface region between the plating layer and the ground steel plate is A high-strength galvannealed steel sheet of 1.5% or more.   The high-strength galvannealed steel sheet according to claim 1, wherein the base steel sheet further has a chemical composition of Nb: 0.005-0.5%, Ti: 0.005-0.5%, Cu: 0.003-0.5%, Ni: 0.003-l. 0%, Mo: 0.01 to 1.0%, B: 0.0001 to 0.1%, Ca: 0.0005 to 0.005%, Mg: 0.0005 to 0.01%, V: 0 A high-strength galvannealed steel sheet containing one or more of 0.003 to 1.0%. A method for producing an alloyed hot-dip galvanized steel sheet, which is obtained by subjecting the ground steel sheet according to claim 1 or 2 to hot-dip galvanizing and further alloying the coated hot-dip galvanized layer.
The said alloying process is a manufacturing method of the high intensity | strength galvannealed steel plate which hold | maintains for 10 to 30 seconds at the alloying process temperature of 450 to 500 degreeC, and hold | maintains at 200 to 300 degreeC for 10 minutes or more continuously.

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