JP6645031B2 - Manufacturing method of galvannealed steel sheet - Google Patents

Description

The present invention relates to a method for producing a galvannealed steel sheet.

  Alloyed hot-dip galvanized steel sheet, after hot-dip galvanized on the steel sheet surface, is heated and held at a temperature equal to or higher than the melting point of zinc to cause Zn and Fe to interdiffuse between the steel sheet and the plating, and This is a steel sheet on which a Zn-Fe alloy layer is formed. Such a steel sheet is excellent in terms of plating adhesion, plating corrosion resistance, weldability (for example, continuous spotting property) and the like, and thus is widely used as a steel sheet for automobiles in Japan and the world.

  In recent years, in order to manufacture hot-dip galvanized steel sheets for automobiles at lower cost, in the production of alloyed hot-dip galvanized steel sheets for automobiles, technological development for increasing the passing speed and constant speed has been promoted. The steel type that is the main target of the development is, for example, a steel sheet to which at least one or more of ultra-low carbon Nb and Ti are added. BACKGROUND ART Ultra-low carbon Nb and Ti-added steel sheets are widely used because they have high press formability and are useful for improving fuel efficiency by reducing the weight of a vehicle body and ensuring occupant safety in a collision.

  However, when the threading speed of the production line is increased, sediment called bottom dross deposited on the bottom of the zinc bath is rolled up in the bath and adheres to the steel plate, so that surface flaws due to dross are likely to occur. Become. Also, by increasing the passing speed of the production line, the alloying time after hot-dip galvanizing becomes insufficient, and there is a concern that unalloying between the steel sheet and the plating may occur.

  As a solution for suppressing the generation of bottom dross, for example, increasing the Al concentration in a zinc bath has been reported. However, when the Al concentration in the zinc bath is increased, the alloying time after the plating is prolonged due to the Fe-Al-based alloy layer generated at the interface between the steel sheet and the plating. If it is not sufficient, unalloying may occur. In addition, if the sheet passing speed is reduced in order to secure the alloying time after plating, productivity is lowered, which is not desirable. Therefore, for example, the following countermeasures have been proposed.

  For example, Patent Literature 1 below discloses a method of accelerating an alloying reaction by enriching P as an oxide on the surface layer of a steel sheet by adjusting a dew point in a reducing atmosphere during annealing before plating to a required range. Is disclosed. Patent Document 2 below discloses a method of controlling an oxide film thickness on a steel sheet surface by adjusting a combustion air ratio of a non-oxidizing furnace and an atmospheric dew point of a reducing furnace to promote alloying. I have. Patent Literature 3 below also discloses a method of using a non-oxidizing furnace and a reducing furnace to balance the amount of oxidation and reduction of iron to promote alloying. Further, in Patent Document 4 below, a steel sheet containing Si, Mn, and P is provided with a pre-plating containing at least one element selected from Ni, Co, Cu, and In. Discloses a method of promoting alloying.

  The technique disclosed in Patent Document 5 is to improve the surface appearance and plating adhesion of an alloyed hot-dip galvanized steel sheet by including a layered oxide of Si, Mn, or Al in a plating layer. It is.

JP 2012241121 A JP-A-5-306446 JP-A-4-232241 JP 2010-265525 A JP 2007-270176 A

  However, as a countermeasure against alloying delay and unalloying when the Al concentration in the bath is increased, the method for increasing the dew point in the annealing furnace disclosed in Patent Document 1 generates an extremely low carbon steel sheet. Due to the insufficient amount of the oxide, a sufficient alloying promoting effect could not be obtained. Further, in the method of sequentially performing oxidation and reduction disclosed in Patent Literatures 2 and 3, the operation range is narrow, and once the balance between oxidation and reduction is lost, unalloying occurs and iron oxide is transferred to the hearth roll. There is a concern that the pickup may cause defects such as plating surface flaws. In addition, the technique disclosed in Patent Document 4 requires a new pre-plating facility, which leads to a significant cost increase. Further, Patent Document 5 discloses that Cr, Ni, and Cu are added to steel to improve strength. However, the effect of Ni on the alloying speed, the amount of Ni added, and the Al concentration in the bath are disclosed. The relationship is not considered at all.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to prevent alloying processability from lowering even when the Al concentration in a bath is increased to suppress bottom dross. To provide a new and improved galvannealed steel sheet and a method for producing the galvannealed steel sheet.

  Based on the recognition of the above-mentioned problems, the present inventors have conducted intensive studies on the alloying processability of a steel sheet with Ni added to steel, on the premise of a step of immersing the steel sheet in a zinc plating bath having a high Al concentration. . When a steel sheet that has undergone annealing reduction is immersed in a galvanizing bath, Al and Fe, which have a high affinity for the steel sheet, react with each other at an early stage to form an Fe-Al alloy layer. The thicker the Fe-Al alloy layer is, the lower the alloying speed is. In such a case, if the equipment capacity does not change, the speed of the production line for the galvannealed steel sheet must be reduced.

  The present inventors have found that when Ni is added to steel as a countermeasure for delaying alloying, the alloying speed of the Fe—Al-based alloy layer increases with an increase in the amount of Ni added. In order to investigate the cause, the initial interfacial alloy layer was identified in the galvannealed steel sheet. In addition to the Fe-Al alloy layer, the Ni-Al alloy layer was added to the galvannealed steel sheet. Was formed at the same time. Ni in the initial interface alloy layer is supplied from the steel, and the alloying is promoted by replacing a part of the Fe-Al-based alloy layer that delays the alloying rate with the Ni-Al alloy layer. It is estimated that

The present invention has been completed based on such new knowledge, and is a method for producing a galvannealed steel sheet described below.

The present invention comprises the following (1).

(1) As essential components, in mass%, C: less than 0.01%, Si: less than 0.08%, Mn: 0.05 to 1.5%, P: less than 0.06%, Ti: 0.004 to 0.1% and Nb: one or two of 0.004 to 0.1%, and Ni: 0.025 to 0.25%, and S, sol. A steel sheet containing Al, N, O, Mo, Cr, Cu, V and B, with the balance being Fe and impurities, and 0.20 to 0.5 mass% of Al, located on the surface of the steel sheet; And an alloyed hot-dip layer containing 0.0005 g / m ² or more and 0.0650 g / m ² or less per side, with the balance being Zn, Fe and impurities. The Ni content N _c (g / m ² ) per one side of the alloyed hot-dip galvanized steel sheet satisfying the formula (1) with respect to the Al content _Ac (mass%) of the alloyed hot-dip coating layer . It is a production method, wherein C: less than 0.01%, Si: less than 0.08%, Mn: 0.05 to 1.5%, P: less than 0.06%, Ti: 0 by mass% as essential components. 0.004 to 0.1% and Nb: one of two kinds of 0.004 to 0.1% or Species, and Ni: contained more _{N s%,} S as an optional component, sol. A step of heating and annealing a steel sheet containing Al, N, O, Mo, Cr, Cu, V, and B, the balance being Fe and impurities, at a continuous recrystallization temperature or higher in a continuous galvanizing facility; a _{b wt% (0.15 ≦ a b ≦ 0.20} ) immersing the molten galvanizing bath containing Al of the alloy without solidifying the plating film of the steel sheet was immersed in the galvanizing bath processing comprises a step of performing, Ni content _{N s} of the steel sheet (mass%), the relative Al concentration _{a b} in the molten zinc plating bath (wt%), satisfies the equation (2), Manufacturing method of galvannealed steel sheet.
N _c ≧ 0.6 × A _c ² −0.25 × A _c +0.033 Expression (1)
N _s ≧ 4.5 × A _b −0.65 Equation (2)

  As described above, according to the present invention, in the method for producing an alloyed hot-dip galvanized steel sheet, even when the Al concentration in the bath is increased in order to reduce bottom dross, an alloy equivalent to or higher than the zinc plating bath having a low Al concentration is used. The rate of conversion can be obtained. Thereby, the alloyed hot-dip galvanized steel sheet can be stably produced without increasing the alloying furnace capacity or reducing the line speed.

In embodiments, a graph plotting the steel in the Ni content N _s relative to the bath Al concentration A _b. In embodiments, relative to Al content A _c in the plating layer is a graph plotting the Ni content N _c in the plating layer per side.

  Hereinafter, the present invention will be described in detail.

(A) Chemical Composition of Steel Sheet as Base Material First, the steel components of the galvannealed steel sheet according to the present invention are as follows. In the following, “%” represents “% by mass” unless otherwise specified.

(C: less than 0.01%)
The steel component of the galvannealed steel sheet according to the present invention is an ultra-low carbon steel containing at least one of Ti and Nb, and the smaller the value of C, the better the workability. Therefore, the content of C is set to less than 0.01%. However, C is inevitably contained in steel, and lowering the content more than necessary increases the inclusions in the steel and adversely affects elongation. In addition, there is a manufacturing limit in reducing the C content. Therefore, the lower limit of the content of C is, for example, 0.0005%. The content of C is preferably less than 0.005%.

(Si: less than 0.08%)
Si is an element that increases the strength of steel. However, when the amount of Si in the steel increases, alloying of the plating layer is delayed. When Si is added to steel in an amount of 0.08% or more, a sufficient alloying promotion effect cannot be obtained even if the Ni concentration in the steel is adjusted to the range of the present invention. For this reason, the content of Si needs to be adjusted to less than 0.08%. More preferably, the content of Si is less than 0.06%. The content of Si is, for example, 0.005% or more.

(Mn: 0.05-1.5%)
Mn is an element having a solid solution strengthening effect when added. However, if the content of Mn is too large, the elongation is deteriorated and the yield point is unnecessarily increased due to fine precipitation of TiC or the like. In the ultra-low carbon steel containing at least one of Ti and Nb which are steel components of the galvannealed steel sheet according to the present invention, the Mn content is 1.5% in order to emphasize workability. The following is assumed. If the content of Mn is too low, the steel may become brittle, so the content of Mn is set to 0.05% or more. More preferably, the content of Mn is 0.2% or more.

(P: less than 0.06%)
P is an element capable of increasing the strength of the steel sheet without significantly impairing the workability of the steel sheet, particularly, the elongation. However, when the content of P is 0.06% or more, the alloying speed is reduced, and the effect of the present invention cannot be obtained even if a predetermined amount of Ni is added to steel. Therefore, the content of P is set to less than 0.06%. More preferably, the P content is less than 0.04%. The P content is, for example, 0.005% or more.

(Ti: 0.004-0.1%, Nb: 0.004-0.1%)
Ti and Nb are optional addition elements, and form carbide precipitates in the steel when added. Such precipitates can improve the strength of the steel sheet by precipitation strengthening. Therefore, Ti and Nb are added for the purpose of improving the strength.

  For example, when the content of Ti is less than 0.004% and the content of Nb is less than 0.004%, the amount of precipitates of Ti or Nb is small and the effect of improving the strength is small. And the lower limits of the contents of Nb are each 0.004%. On the other hand, when the content of either Ti or Nb exceeds 0.1%, the amount of precipitates becomes excessive, and the ductility of the steel sheet is significantly reduced. .1%. Each content of Ti and Nb is preferably 0.01% or more, and preferably 0.05% or less.

(Ni: 4.5 x Al mass% in hot-dip galvanizing bath-0.65% or more)
Ni in the steel elutes at the same time as Fe when immersed in the plating bath, and a part of the eluted Ni reacts quickly with Al in the bath to form a Ni-Al alloy layer. The formed Ni-Al-based alloy layer replaces a part of the Fe-Al-based alloy layer formed by the reaction between Fe in steel and Al in the bath, and contributes to promoting alloying. As the Al concentration in the bath increases, the formation amount of the Fe-Al-based alloy layer increases, so that the alloying is delayed. However, Ni in the steel is delayed by forming the Ni-Al-based alloy layer. The effect can be offset. The content _{N s} required for offsetting the delay effect Ni (mass%), relative to the bath Al concentration _{A b} (mass%), satisfies the following expression (2).
N _s ≧ 4.5 × A _b −0.65 Equation (2)

For example, if you set the bath Al concentration _{A b} 0.15% to 0.20%, the lower limit of the content of _{N s} of Ni, for example, a 0.025%. Further, the upper limit of the Ni content is set to 0.25% in consideration of an increase in steelmaking cost. The content of Ni is more preferably 0.05% to 0.20%.

Here, equation (2), in the examples described below, if the relative bath Al concentration A _b of the test No serving as the invention example was plotted in steel Ni content N _s, defined in equation (2) The range is set based on the fact that the range of alloying OK and NG can be clearly distinguished with the straight line as a boundary. Incidentally, the graph plotting the steel in the Ni content N _s relative to the bath Al concentration A _b of the test No as the present invention example shown in FIG.

The steel of the galvannealed steel sheet according to the present invention is made of S, sol. Elements such as Al, N, O, Mo, Cr, Cu , V, and B may be contained in small amounts.

(B) Chemical Composition of Plating Layer to be Film Next, the components of the plating layer of the galvannealed steel sheet according to the present invention will be described.

(Al: 0.20 to 0.50%)
The content of Al in the galvanized layer to be a film is 0.20 to 0.50%. When the content of Al is less than 0.20%, the effect of suppressing the development of the alloy layer in the plating bath becomes insufficient, so that it is difficult to control the amount of plating applied. Therefore, the lower limit of the Al content is 0.20%. Further, a preferred lower limit of the Al content is 0.25%. On the other hand, when the content of Al exceeds 0.50%, the alloying speed is reduced even when the concentration of Ni in the steel is set to the above range, so that the content of Al is 0.50% or less. I do. The Al content is preferably 0.45% or less.

(Ni: 0.0005g / ^{m 2} or more, with respect to Al content _{A c} in the plating layer ^{_{(mass%), 0.6 × A c 2}} -0.25 × A c +0.033 higher)
The lower limit of the Ni content in steel necessary for promoting alloying is 0.0025%, and the contained Ni in steel causes interdiffusion with the plating film simultaneously with Fe during alloying. Therefore, a predetermined amount of Ni is contained in the film. When the content of Ni is less than 0.0005 g / m ² per one side, the effect of promoting alloying is not exhibited, so the content of Ni in the plating layer is 0.0005 g / m ² or more per side. The content of Ni in the plating layer needs to be higher as the Al concentration in the bath increases. Therefore, the Ni content N _c (g / m ² ) in the plating layer per one side should satisfy the following expression (1) with respect to the Al content A _c (mass%) of the plating layer. Controlled.
N _c ≧ 0.6 × A _c ² −0.25 × A _c +0.033 Expression (1)

Here, equation (1) is, in the embodiment described below, with respect to Al content A _c in the plating layer of the test No serving as the invention example, plotting the Ni content N _c in the plating layer per side In this case, the setting was made based on the fact that the range of alloying OK and NG can be clearly distinguished using the curve defined by the equation (1) as a boundary. Incidentally, with respect to Al content A _c in the plating layer of the test No made as Working Example illustrates a graph plotting the Ni content N _c in the plating layer per side in FIG.

  In addition, it is preferable that the content of Fe in the plating layer is 8 to 14%. As conventionally known, when the content of Fe in the plating layer is less than 8%, the η phase may locally remain in the surface layer portion of the alloy layer, and the slidability is reduced, and It is not preferable because a king or a plate break may easily occur. When the content of Fe in the plating layer exceeds 14%, when the steel sheet is subjected to bending, the alloyed hot-dip galvanized layer undergoes compression deformation inside the bent portion, and the amount of powdering peeling increases. I do. Therefore, the content of Fe in the plating layer is preferably from 8 to 14%, more preferably from 9 to 13%.

In addition, the amount of the plating layer to be applied may be a generally used amount, or may be ²⁰ to 70 g / m ² per one surface.

(C) CGL Manufacturing Conditions Next, the manufacturing conditions of the galvannealed steel sheet according to the present invention will be described.

(Annealing conditions: above the recrystallization temperature of the base material)
The base material is heated in a reducing atmosphere at a temperature higher than the recrystallization temperature. Here, the heating temperature in annealing is preferably not less than the recrystallization temperature of steel to which at least one or more of ultra-low carbon Ti and Nb is added and not more than 850 ° C, and is preferably in the range of not less than 780 ° C and not more than 830 ° C. More preferred. After the reduction treatment, the steel sheet is cooled to a temperature range suitable for hot-dip galvanizing. The atmosphere at the time of annealing may contain, for example, 3% to 8% by volume of H ₂ and maintain a reducing atmosphere for general Fe whose balance is N ₂ .

(Al concentration in plating bath: 0.15 to 0.20%)
The Al concentration in the plating bath is 0.15 to 0.20%. When the Al concentration in the plating bath is less than 0.15%, bottom dross may be generated depending on the distribution of the Al concentration in the bath and temperature fluctuations in the bath, and a dross defect is generated by the generated bottom dross. there's a possibility that. Further, when the Al concentration in the bath exceeds 0.20%, the content of Ni in the steel necessary for promoting alloying needs to be increased, which leads to an increase in manufacturing cost. Is more preferably 0.18%.

Regarding the immersion time in the plating bath, if it is 1 s or longer, the performance and operability are not particularly hindered. In addition, the plating conditions other than the above-mentioned conditions may be conditions in a generally adopted range. For example, the plating bath temperature is 450 to 470 ° C., and the penetration plate temperature is 450 to 480 ° C. If there is, there is no particular problem. Even if the plating bath contains, for example, Fe, Pb, Cd, Sb, Cr, Ni, W, Ti, Mg, and Si as components other than Al at 0.1% or less, the present invention It does not affect the performance of the invention. The coating weight of the plating is adjusted by wiping or the like after being lifted from the plating bath, and may be, for example, in the range of 25 to 70 g / m ² per one surface generally used as a product. In addition, the surface temperature of the steel sheet decreases due to heat removed by wiping. Here, when the surface temperature of the steel sheet falls to 420 ° C. or lower, the plating film solidifies, and it becomes necessary to re-input energy at the time of raising the temperature of alloying, which may cause a delay in alloying. Preferably, it is inserted into an alloying furnace. Further, if the plating film once solidifies before the alloying treatment, it is not preferable because the alloying promoting effect of the present invention is lost.

(D) Alloying treatment The alloying treatment temperature may be in the range of 480 to 530 ° C, more preferably in the range of 490 to 520 ° C. When the alloying treatment temperature is lower than 480 ° C., the heating time for achieving a predetermined degree of alloying increases, so that the lower limit of the alloying treatment temperature is preferably 480 ° C. The lower limit of the alloying temperature is more preferably 490 ° C.

On the other hand, when the alloying temperature exceeds 530 ° C., even if the same degree of alloying can be achieved, a hard alloy layer such as Γ phase and Γ ₁ phase is easily formed under the plating. Is preferably 530 ° C. or lower. Further, the upper limit of the alloying temperature is more preferably 520 ° C. or lower. As a heating means in the alloying treatment, any known means such as radiation heating, high-frequency induction heating, and electric heating may be used.

(E) Post-treatment The surface of the steel sheet after plating may be untreated, but may be subjected to a known post-treatment such as a chromic acid treatment, a phosphate treatment, and a resin film application treatment. Further, a rust-preventive oil may be applied to the surface of the steel sheet after plating. As the rust preventive oil to be applied, a commercially available general rust preventive oil may be used, or a highly lubricating rust preventive oil containing S or Ca which is an extreme pressure additive may be used.

  Hereinafter, the alloyed hot-dip galvanized steel sheet according to the present invention will be described more specifically with reference to examples. The examples described below are merely examples of the galvannealed steel sheet according to the present invention, and the present invention is not limited to the examples described below.

  Table 1 shows the component contents of the test materials used in this example. In Table 1, the unit of the content of each component is “% by mass”, and the balance is Fe. Steel containing these components was melted and cast in a laboratory to produce a slab having a thickness of 30 mm. The produced slab was kept at 1250 ° C. for 1 hour in the atmosphere, and subjected to rough rolling and finish rolling. Finish rolling was performed at 950 ° C., and the film was wound at 650 ° C. in the air. The hot rolled finished thickness was 3.0 mm. After pickling the hot-rolled sheet, cold rolling was performed to a sheet thickness of 0.8 mm to prepare a test material.

  This test material was plated under the following conditions using a vertical hot-dip Zn plating apparatus.

First, a 0.8 mm thick steel plate was degreased and washed with a 75 ° C. NaOH solution, and annealed at 800 ° C. × 30 s in an atmosphere in which the atmosphere gas was N ₂ + 5% by volume H ₂ and the dew point was −40 ° C. . After annealing, the steel sheet was cooled at a temperature of about 15 ° C./s to near the bath temperature, and the Al concentration in the bath was 0.13 to 0.23% by mass, and the bath temperature was 455 ° C. Dipped for 5 seconds. Thereafter, the amount of plating on one side was adjusted to 50 g / m ² by a wiping method. Further, the plated steel sheet was subjected to an alloying treatment using various heat patterns using an electric heating device. An air cooling system was used for cooling.

1) Sampling of sample piece A sample piece of 25 mmφ was sampled from the sample after the alloying treatment, and the plating layer was coated with a 10% HCl aqueous solution containing 0.5% by volume inhibitor (trade name: “Ibit 710N” manufactured by Asahi Chemical Co., Ltd.). Dissolved. The solution was analyzed by the ICP method, and the composition of the plating layer was analyzed. The amount of Ni in the film, which is closely related to the alloying processability, is represented by the amount of one-sided adhesion per 1 m ² , and the amount of Al in the film is represented by the Al concentration (% by mass) in the film. did.

2) Alloying treatment property The alloying treatment property was determined by GA (Galvanizing) when a test material of steel type 1 was plated in a low Al concentration bath (Al concentration: 0.135 mass%, Fe saturated bath) (Test No. 1). Annealing) was evaluated based on the alloying time of the material. Specifically, after the test material of each steel type was plated in a high Al bath (0.15% by mass or more of Al concentration, Fe saturated bath), the metallic luster of the GA material disappeared when heat treatment was performed. The point in time was determined to be alloying completed. The time until the completion of the alloying was measured to determine the alloying time of the GA material. Further, the alloying time of the GA material of each test No. Pass / fail was determined by comparison with the alloying time of GA material No. 1. The judgment conditions are shown below.
◎: alloying completion time is shortened ○: alloying completion time is equivalent ×: alloying completion time is extended

  When the alloying was completed, the Fe concentration in the film was approximately 10% by mass. The allowable range of the Fe concentration in the film at the time of completion of alloying varies depending on the alloying temperature. , The Fe concentration in the film does not exactly match. The Al concentration in the coating and the Ni content in the coating were measured by analyzing a sample in which the Fe content in the coating was around 10% by mass.

  Table 2 shows the evaluation results.

Further, a graph plotting the steel in the Ni content N _s relative to the bath Al concentration A _b of the test No as the present invention example shown in FIG. 1, Al in the plating layer of the test No made as Working Example relative to the content a _c, shows a graph plotting the Ni content N _c in the plating layer per side in FIG. Equations (1) and (2) were derived from these graphs.

  In addition, the test No. In No. 30, an alloying treatment was performed after the plating film was once solidified before being inserted into the alloying furnace.

  Here, the test No. Sample No. 1 had bottom dross due to low Al concentration in the bath. On the other hand, Test No. in which the Al concentration in the bath was 0.15% by mass. In Nos. 2 to 30, bottom dross did not occur.

  Further, as can be seen from the results in Table 2, in the examples of the present invention, despite the Al concentration in the bath of 0.15% by mass or more, Test No. An alloying completion time equal to or shorter than 1 could be realized. On the other hand, Test No. In 2, 4, 6, 9, 12, 15, and 18, the Ni concentration in the steel was lower than the Al concentration in the bath, so that alloying was delayed, and the alloying processability was reduced.

  Test No. In No. 19, since the Ni content in the steel was higher than the range of the present invention, the steelmaking cost was too high. Test No. In No. 26, since the Si content in the steel was higher than the range of the present invention, alloying was delayed, and the alloying processability was reduced. Test No. In No. 29, since the P content in the steel was higher than the range of the present invention, alloying was delayed, and the alloying processability was reduced.

  Test No. In No. 30, since the plating film was once solidified before being inserted into the alloying furnace, the effect of promoting alloying according to the present invention was not obtained, alloying was delayed, and the alloying processability was reduced.

  Therefore, according to the present invention, it was possible to obtain an alloying processability equal to or higher than that when the Al concentration in the hot-dip galvanizing bath is low, while suppressing bottom dross.

  As described above, the preferred embodiments of the present invention have been described in detail, but the present invention is not limited to such examples. It is obvious that those skilled in the art to which the present invention pertains can conceive various changes or modifications within the scope of the technical idea described in the claims. It is understood that these also belong to the technical scope of the present invention.

Claims (1)

C: less than 0.01%, Si: less than 0.08%, Mn: 0.05 to 1.5%, P: less than 0.06%, Ti: 0.004 to 0.1 by mass% as essential components % And Nb: one or two of 0.004 to 0.1%, and Ni: 0.025 to 0.25%, and S, sol. A steel sheet containing Al, N, O, Mo, Cr, Cu, V and B, with the balance being Fe and impurities;
It is located on the surface of the steel plate and contains 0.20 to 0.5% by mass of Al, and 0.0005 g / m ² or more and 0.0650 g / m ² or less of Ni per side, with the balance being Zn, Fe and An alloyed hot-dip layer made of impurities,
The Ni content N _c (g / m ² ) per side of the alloyed hot-dip layer satisfies the formula (1) with respect to the Al content A _c (% by mass) of the alloyed hot-dip layer. A method for producing a galvannealed steel sheet ,
C: less than 0.01%, Si: less than 0.08%, Mn: 0.05 to 1.5%, P: less than 0.06%, Ti: 0.004 to 0.1 by mass% as essential components % and Nb: from 0.004 to 0.1% of two one or two of, and Ni: contained more _{N s%,} S as an optional component, sol. A step of heating and annealing a steel sheet containing Al, N, O, Mo, Cr, Cu, V, and B, and the balance being Fe and impurities, at a recrystallization temperature or higher in a continuous galvanizing facility;
Immersing the steel sheet _{A b} wt% galvanizing bath containing Al of _{(0.15 ≦ A b ≦ 0.20)} ,
Performing an alloying treatment without solidifying the plating film of the steel sheet immersed in the hot-dip galvanizing bath,
The steel sheet of the Ni content N _{s (wt%),} the relative Al concentration A _b in the molten zinc plating bath _(wt%), satisfies the equation (2), a manufacturing method of the galvannealed steel sheet.
N _c ≧ 0.6 × A _c ² −0.25 × A _c +0.033 Expression (1)
N _s ≧ 4.5 × A _b −0.65 Equation (2)