JP2001329353A - Method for producing galvannealed steel sheet excellent in press-fprmability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive galvannealed steel sheet excellent in workability by restraining the generation and the growth of Γ phase and the remaining of ζ phase. SOLUTION: A steel sheet containing <=0.01% C, 0.005-0.10% Si, 0.05-0.5% Mn, 0.005-0.06% Al, <=0.025% P, 0.005-0.1% Ti and if necessary, 0.005-0.1% Nb and/or 0.0001-0.01% B, is used as the base material and plated layers containing δ1 phase, Γ1 phase and the Γ phase having <=1 mm thickness, are formed at 30-90 g/m2 coating surface density per one side surface. After annealing the basis sheet for plating, the galvanization is applied by dipping into galvanizing bath containing 0.1-0.2% Al having bath temperature of 490-550 deg.C at 490-600 deg.C inlet temperature and the cooling is performed to 400 deg.C steel sheet temperature at 5-15 deg.C/sec cooling speed, and after adjusting the coating surface density, the alloying treatment is applied at 450-550 deg.C for 5-60 sec.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a galvannealed steel sheet having excellent workability and a method for producing the same.

[0002]

2. Description of the Related Art Alloyed hot-dip galvanized steel sheets have high corrosion resistance,
Because it has excellent paintability, adhesion after painting, and weldability,
It is widely used as a rust-proof steel plate in various fields such as home appliances and automobile bodies. In such an application, since it is usually processed into a required shape by press molding and used, it is also important to have excellent workability in addition to corrosion resistance. For the galvannealed steel sheet, after reducing the steel sheet in a hot-dip galvanizing line, a bath temperature of 45% to which 0.13 to 0.15% by mass of Al is added to suppress excessive alloying treatment.
Inlet temperature 47 in hot dip galvanizing bath of 0-470 ° C
It is manufactured by immersion at 0 to 500 ° C. for hot-dip galvanizing, then adjusting the amount of coating with a gas wiping nozzle, and performing a heat alloying treatment. For the heating alloying treatment, generally, an alloying treatment furnace employing a burner heating method, a high-frequency induction heating method, a heating method using both of them, or the like is used.

When a heat alloying treatment is performed immediately after plating, the η-Zn phase disappears in the plating layer as the alloying reaction proceeds, and the ζ phase (FeZn ₁₃ ), δ ₁ phase (FeZn ₇ ), Γ ₁ phase ( Fe ₅ Zn ₂₁ ), Γ phase (Fe ₃ Zn ₁₀ ), and the like are sequentially generated. The workability of alloyed hot-dip galvanized steel sheet is greatly affected by this coating layer structure. Specifically, when a soft soft phase remains thick in the surface layer of the plating layer, the sliding resistance with the mold at the time of press molding increases, and a plate breakage or a flaking phenomenon in which the plating layer peels in a scale-like manner occurs. Conversely, when the ζ phase disappears and a hard and brittle Γ phase is formed thickly at the interface between the plating layer and the base steel sheet, a powdering phenomenon occurs in which the plating layer peels off in a powder form, and the powder of the peeled plating layer becomes gold. It accumulates in the mold and causes damage to the mold and the plating layer.

[0004] When the peeling of the plating layer due to the flaking phenomenon or the powdering phenomenon is remarkable, not only adversely affects the press forming operation, but also the corrosion proceeds from the peeled portion as a starting point, so that the corrosion resistance is reduced. For this reason, it is necessary to minimize the residual amount of the ζ phase and the generation amount of the Γ phase in an alloyed hot-dip galvanized steel sheet that is expected to be used for applications with high workability. However, in the conventional manufacturing method in which hot-alloying treatment is performed after hot-dip Zn plating, the relationship between hot-dip galvanizing conditions and hot-alloying conditions, and the formation and disappearance behavior of the ζ phase and the formation and growth behavior of the Γ phase are sufficiently clarified. Not. As a result, under conditions where the ζ phase disappears, the Γ phase is formed thicker,
Under the condition of suppressing the growth of the phase, the residual amount of the ζ phase tends to increase. As a result, it has been difficult to stably produce an alloyed hot-dip galvanized steel sheet having excellent workability. Further, the conventional production method has a drawback in that an alloying treatment furnace is required, so that the equipment burden is large and the energy cost is also high, so that an alloyed hot-dip galvanized steel sheet cannot be produced at low cost.

[0005] As a method of reducing the production cost of an alloyed hot-dip galvanized steel sheet, a hot-dip galvanizing bath is maintained at a high temperature.
A method is known in which the amount of heat required for the alloying treatment is applied from a hot-dip galvanizing bath to an original plate (Japanese Patent Laid-Open No. 52-48).
524, JP-A-8-60327). According to this method, no alloying furnace is required, and self-galvanizing for alloying up to the surface layer of the plating layer is possible only with the amount of heat given from the hot-dip galvanizing bath,
An alloyed hot-dip galvanized steel sheet can be manufactured at low cost.

[0006]

However, Japanese Patent Application Laid-Open No.
Japanese Patent No. 48524 discloses an alloying treatment for only the thin-plated side where the coating weight per side is less than 30 g / m ² , which is intended for differential thickness plated steel sheets, and the general-purpose plating weight per side is 30 g / m ^2. It is not suitable for alloying both surfaces of the above galvanized steel sheet. On the other hand, Japanese Unexamined Patent Publication No. Hei 8-60327 only introduces a method of self-galvanizing, and clarifies the effects of plating conditions on the formation and disappearance behavior of the ζ phase and the formation and growth behavior of the Γ phase. It has not been. Therefore, even with this method, it cannot be said that a technique for inexpensively producing an alloyed hot-dip galvanized steel sheet having excellent workability has been established.

[0007] The present invention has been devised to solve such a problem, and by comprehensively managing the composition of the original plate, the plating conditions, and the wiping and cooling conditions after plating, the present invention provides a method for reducing the phase. It is an object of the present invention to provide an inexpensive alloyed hot-dip galvanized steel sheet excellent in workability by suppressing generation and growth of and remaining ζ phase.

[0008]

The alloyed hot-dip galvanized steel sheet of the present invention has a C content of 0.01%.
% By mass, Si: 0.005 to 0.10% by mass, M
n: 0.05 to 0.5% by mass, Al: 0.005 to 0.
06 mass%, P: 0.025 mass% or less, Ti: 0.0
The base material is a steel sheet containing 0.5 to 0.1% by mass, and the balance is substantially Fe. The plating layer composed of a δ ₁ phase, a Γ ₁ phase, and a Γ phase having a thickness of 1 μm or less is 30 to 90 g per side. / M
It is characterized by being formed with a plating adhesion amount of ² .
The steel sheet further contains Nb: 0.005 to 0.1% by mass and B:
One or two of 0.0001 to 0.01% by mass can be contained. This galvannealed steel sheet has the following properties:
0.01 mass% or less, Si: 0.005 to 0.10 mass%, Mn: 0.05 to 0.5 mass%, Al: 0.005
0.06% by mass, P: 0.025% by mass or less, Ti:
0.005 to 0.1% by mass, and if necessary Nb:
0.005 to 0.1% by mass and B: 0.0001 to 0.
1% by mass, and the balance is substantially Fe
After passing a steel sheet having the composition of
Al: bath temperature 490-550 containing 0.1-0.2% by mass
Inlet temperature 490-600 in hot dip galvanizing bath
C. and hot-dip galvanized, followed by gas wiping to adjust the coating weight per side to 30 to 90 g / m ² , and a cooling rate of 5 to 1 until the steel sheet temperature reaches 400 ° C.
Manufactured by cooling at 5 ° C / sec. In the case of alloying treatment, after adjusting the coating weight, 450 to 550 ° C
For 5 to 60 seconds.

[0009]

[Action] Referring to the equilibrium diagram of the Fe-Zn system (FIG. 1),
Since the peritectic point of the ζ phase is about 530 ° C., thermodynamically, the ζ phase does not exist stably at a temperature higher than this peritectic point.
That is, when the bath temperature of the hot-dip galvanizing bath and the inlet temperature of the original plate are set to be higher than the peritectic point, it can be seen that the formation of the ζ phase is suppressed. Further, from the results of the research by the present inventors, it has been found that the peritectic point decreases to about 490 ° C. when 0.1 to 0.2% by mass of Al is added to the hot-dip galvanizing bath.

[0010] Based on such a premise, the present inventors have
The effects of plating conditions, wiping and cooling conditions after hot-dip plating, and the composition of the original plate on the formation and disappearance of the ζ phase and the formation and growth of the Γ phase were investigated. As a result, A
l: Using a hot-dip galvanizing bath containing 0.1 to 0.2% by mass, setting the bath temperature and inlet temperature to 490 ° C. or higher of the peritectic point of the ζ phase to suppress the formation of the ζ phase and alloying It has been found that when using ultra-low carbon Ti-added steel or Ti-Nb composite-added steel having a high processing speed for a plating base sheet, the alloying treatment reaction proceeds to the surface layer of the plating layer in the cooling process after hot-dip plating. The alloyed hot-dip galvanized steel sheet obtained in this way can be manufactured at low cost because no alloying treatment furnace is required, and because the entire plating layer is alloyed, both the flaking resistance and the powdering resistance are reduced. Satisfies quality characteristics. After the adjustment of the amount of plating, 450-550 ° C ×
When the alloying treatment is performed for 5 to 60 seconds, an alloyed hot-dip galvanized steel sheet in which the alloying reaction has appropriately progressed while suppressing the formation of the ζ phase is obtained. The resulting alloyed hot-dip galvanized layer does not grow thick in the 成長 phase, despite the high Fe concentration as compared to the unalloyed galvanized layer. When this alloyed hot-dip galvanized steel sheet is pressed, a large number of fine cracks are generated in the alloyed hot-dip galvanized layer at the time of working, and the binding force of the original plate for plating is reduced. Therefore, workability such as drawing workability is improved without lowering powdering resistance.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An ultra-low carbon Ti-added steel or a Ti-Nb composite-added steel having a high degree of cleanliness and a high alloying treatment speed is used as a base plate for plating. Ultra-low carbon Ti-added steel or Ti-
Nb composite added steel is excellent in drawability and is a steel material that is frequently used as a member with a high degree of workability. The ultra-low carbon Ti-added steel used in the present invention has a C content of 0.01% by mass or less,
i: 0.005 to 0.10% by mass, Mn: 0.05 to
0.5% by mass, Al: 0.005 to 0.06% by mass,
P: 0.025% by mass or less, Ti: 0.005 to 0.1
% By mass. The ultra low carbon Ti-Nb composite added steel has the same amount of C, Si, Mn, Al, P, T as the ultra low carbon Ti added steel.
In the composition including i, Nb is adjusted to 0.005 to 0.1% by mass. Ultra-low carbon Ti-added steel and ultra-low carbon Ti-N
b 0.0001 to 0.01 mass% of B
Can be included.

C in steel has an effect of delaying the alloying treatment reaction of the galvanized layer and suppressing self-galvanizing. In addition, since the drawability deteriorates, the upper limit of the C content is set to 0.01% by mass in the present invention. S
Although i and Mn are effective in improving the strength of the steel sheet, they are easily oxidizable elements and cause non-plating.
0.005 to 0.10 mass%, Mn: 0.05 to 0.5
It was set in the range of mass%. Al fixes solid solution N and exhibits the effect of preventing aging. However, the effect is saturated even when 0.06% by mass or more is added, so Al: 0.005 to 0.06% by mass.
Was set in the range. Ti and Nb are alloy components that fix solid solution C and N and improve draw formability, but the effect is saturated even when added in an amount of 0.1% by mass or more. .1% by mass. B is effective for preventing embrittlement of the steel sheet, but the effect is saturated even when added in an amount of 0.01% by mass or more. Therefore, B is set in the range of 0.0001 to 0.01% by mass. Although P is effective in improving the strength of the steel sheet, it significantly lowers the alloying treatment speed.
It was regulated to 025% by mass or less.

Extremely low carbon T adjusted to a predetermined component / composition
The i-added steel or the Ti-Nb composite added steel is annealed in a gas reduction furnace and then introduced into a hot-dip galvanizing bath containing 0.1 to 0.2% by mass of Al. This hot dip galvanizing bath is
The peritectic point was lowered to 490 ° C. by the addition of Al. When the Al content is less than 0.1% by mass, the peritectic point is
The temperature does not drop to 0 ° C., the alloying treatment speed increases, and the Γ phase grows easily. Conversely, an amount of A exceeding 0.2% by mass
When l is added, the alloying treatment speed is reduced, self-galvanizing cannot be performed, and the energy cost required for the alloying treatment in a manufacturing process including the alloying treatment increases.

In the hot-dip galvanizing bath, the lower limit of the bath temperature is set to 490 ° C. in order to suppress the formation of the Δ phase and to impart the calorie necessary for the alloying reaction to the steel sheet. However, when the bath temperature exceeds 550 ° C., the Δ phase grows thick, and the energy cost required for maintaining the hot-dip galvanizing bath at a high temperature also increases. In addition, the inlet temperature of the original plate for plating is set at 490 to 600 ° C. in order to suppress the bath temperature fluctuation and suppress the growth of the Δ phase. The coating weight per side of the hot-dip galvanized metal adhering to the original plate pulled up from the hot-dip galvanizing bath is adjusted to 30 to 90 g / m ² . Alloying reaction does not proceed sufficiently even under the conditions specified in the present invention the amount of plating deposition is too large, since the eta-Zn phase remains in the plating layer surface, the coating weight 90 g / m ² or less by gas wiping It is necessary to In the gas wiping method used for adjusting the amount of plating, the lower limit of squeezing is 30 g / m ² .

When the alloying treatment is performed after the adjustment of the plating adhesion amount, the alloying reaction is appropriately advanced by heating the original plating plate at 450 to 550 ° C. for 5 to 60 seconds. Galvanized layer be plated being processed alloying disappeared eta-Zn phase by processing conditions until coating weight adjustment, which is the plating layer surface to [delta] ₁ phase grew tissue. Therefore, even when heated to 450 to 550 ° C., no ζ phase is generated. However, if the heating temperature is less than 450 ° C. or the heating time is shorter than 5 seconds, the alloying reaction does not proceed sufficiently.
At a heating temperature exceeding 50 ° C. or a long heating time exceeding 60 seconds, growth of the Δ phase is observed.

[0016] The steel sheet of which the coating weight has been adjusted by gas wiping is 5 to 15 until the steel sheet temperature reaches 400 ° C.
It is cooled at a cooling rate of ° C./sec. At a high cooling rate exceeding 15 ° C./sec, the alloying treatment reaction does not proceed sufficiently,
The η-Zn phase tends to remain on the surface of the plating layer. Conversely 5
At a cooling rate of less than ° C./sec, the Γ phase grows easily.
The steel sheet subjected to the alloying treatment is also cooled under the same conditions.
In this case, when the cooling rate exceeds 15 ° C./sec, the effect of suppressing the 成長 phase growth is saturated, and conversely, when the cooling rate is less than 5 ° C./sec, the Γ phase tends to grow. When the temperature of the steel sheet is lower than 400 ° C., the effect of the cooling rate on the progress of the alloying treatment reaction can be almost ignored. Therefore, the steel sheet is cooled at an appropriate cooling rate in a temperature range of 400 ° C. or less.

[0017]

Example 1 An ultra-low carbon Ti-added steel and a Ti-Nb composite-added steel having the compositions shown in Table 1 were melted and subjected to hot rolling, pickling, and cold rolling to a sheet thickness of 0.7 mm and a sheet width. A 1000 mm cold-rolled steel sheet was manufactured.

[0018]

This cold-rolled steel sheet was used as a plating base sheet, and was subjected to 800 reduction by a gas reduction annealing furnace maintained in an atmosphere of 50% by volume H ₂ -N _2.
After heating to 40 ° C. for 40 seconds, the mixture was fed into a hot-dip plating bath at a line speed of 100 m / min. The hot-dip plating conditions were selected from the ranges shown in Table 2, and specifically, the conditions in Table 3 were employed.

[0020]

[0021]

A test piece was cut out from each of the manufactured galvannealed steel sheets, the layer configuration of the plating layer was observed, and the test piece was subjected to a powdering resistance test and a flaking resistance test. Layer configuration of plating layer: 10 m width using scanning electron microscope
The surface structure and the cross-sectional structure of a test piece having a length of 20 mm and a length of 20 mm were observed at a magnification of 5000 times, and the presence or absence of an η-Zn phase,
The phase thickness was measured. The observations were classified as follows. η-Zn residual: layer structure in which η-Zn phase remains without alloying to the surface layer of the plating layer ζ + δ ₁ + Γ ₁ : layer structure in which ζ phase remains and Γ phase is not observed δ ₁ + Γ ₁ : ζ phase Is not observed, and the layer structure in which the thickness of the Γ phase is 1 μm or less δ ₁ + Γ ₁ + Γ: The ζ phase is not observed, and the thickness of the Γ phase is 1 μm.
Layer structure above

Powdering resistance test: width 20 mm, length 50 m so that an arc having a diameter of plate thickness x 6 is formed on the test surface.
After bending the m test piece by 180 degrees, the test piece was bent back into a flat plate shape. After attaching the pressure-sensitive adhesive tape to the portion subjected to the bending / unbending, the pressure-sensitive adhesive tape was peeled off, and the amount of the plating layer adhered to the pressure-sensitive adhesive tape was visually observed. The observations were classified as follows. If the score is 3 or more, it can be said that there is no problem in the quality characteristics. Powdering score 1: A large amount of plating layer peeled off at the time of bending / returning. 点 Rating 2: A large amount of plating layer adhered to pressure-sensitive adhesive tape. 評 Rating 3: Medium-sized plating layer on pressure-sensitive adhesive tape. Adhesion 〃 Rating 4: Small amount of plating layer adhered to pressure-sensitive adhesive tape 評 Rating 5: Plating layer did not adhere to pressure-sensitive adhesive tape

Flaking resistance test: width 25 mm, length 2
A 50 mm test piece was coated with a rust-preventive oil, sandwiched in a mold as shown in FIG. 2, and subjected to a draw bead test. Next, a pressure-sensitive adhesive tape was attached to the test piece, and after peeling off, the amount of the plating layer adhered to the pressure-sensitive adhesive tape was measured by a chemical analysis method. When the adhesion amount of the plating layer is 5 g / m ² or less, it can be said that the flaking resistance is good and there is no problem in the quality characteristics.
As can be seen from the results of the investigations in Tables 4 to 7, none of the alloyed hot-dip galvanized steel sheets obtained under the conditions specified in the present invention had a ζ phase formed, and the Γ phase had a thickness of 1 μm or less. Met. In addition, both the powdering resistance test and the flaking resistance test showed good test results, indicating that the workability was excellent.

[0025]

[0026]

[0027]

[0028]

[0029]

[Comparative Example 1] In order to investigate the effect of each condition on workability, a hot-dip galvanized alloy was used under hot-dip galvanizing conditions (Table 8) out of the range specified in the present invention using plated steel sheets of steel types A to D. A steel plate was manufactured.

[0030]

A test piece was cut out from each of the manufactured alloyed hot-dip galvanized steel sheets, the layer configuration of the plating layer was observed in the same manner as in the example, and the powdering resistance and the flaking resistance were investigated. As can be seen from the survey results in Table 9, A
In Test Nos. 109 to 126 in which the l concentration, bath temperature, inlet temperature, and cooling rate are out of the ranges specified in the present invention, {the powdering resistance decreases due to the thick growth of the phase, or}
Since the flaking resistance was reduced due to the remaining phase, the workability was poor in all cases. In addition, Al concentration, cooling rate,
In the test numbers 127 to 133 in which the coating weight exceeds the range specified in the present invention, the alloying treatment reaction did not proceed to the surface layer of the plating layer, and the η-Zn phase remained. Not tested for King test.

[0032]

Example 2 The same cold-rolled steel sheet as in Example 1 was used as an original plate and heated at 800 ° C. for 40 seconds in a gas reduction annealing furnace maintained in an atmosphere of 50% by volume of H ₂ -N _2.
It was sent to the hot-dip plating bath at 00 m / min. The hot-dip plating conditions were selected from the ranges listed in Table 10, and specifically, Table 1
Condition 1 was employed.

[0033]

[0034]

For each of the alloyed hot-dip galvanized steel sheets manufactured, the layer structure of the plated layer and the powdering resistance were examined in the same manner as in Example 1, and the drawability was examined by the following draw-forming test. Drawing forming test: A cylindrical drawing test was performed under the following conditions, and the maximum formable wrinkle pressing force was measured. Blank diameter: 70mm Die radius: 35mm Die shoulder radius: 2.5mm Punch diameter: 33mm Punch shoulder radius: 5mm Molding height: 20mm Molding speed: 60mm / min Lubricating oil: Rustproof oil applied

[0036] As seen in 12 findings table, galvannealed steel sheets obtained under the conditions specified in the present invention are all turned plating layer with no ζ phase [delta] ₁ + gamma _1-phase And the maximum wrinkle holding force that can be formed is as large as 8 to 10 kN,
The powdering resistance was also 3 or more. That is, it can be seen that this galvannealed steel sheet has sufficient properties to withstand drawing.

[0037]

[0038]

COMPARATIVE EXAMPLE 2 In order to investigate the influence of plating conditions and / or alloying treatment conditions on drawability, hot-dip plating conditions (Table 1) were used that were out of the range specified in the present invention by using plating original sheets of steel types A to D. 13) An alloyed hot-dip galvanized steel sheet was manufactured.

[0039]

A test specimen was cut out from each of the manufactured alloyed hot-dip galvanized steel sheets, the layer configuration of the plating layer was observed as in Example 2, and the powdering resistance and drawing workability were examined. As can be seen from the survey results in Table 14, in Test Nos. 25 to 28 in which the bath temperature and inlet temperature during hot-dip plating were out of the ranges specified in the present invention, a ζ phase remained on the surface of the plating layer even after the heat alloying treatment. It remained and the maximum formable wrinkle holding force was 3 kN or less. In Test Nos. 29 to 33 in which the heating temperature, the holding time, and the cooling rate during the heat alloying treatment were out of the ranges specified in the present invention, the powdering resistance was 2 or less. That is, as is clear from the comparison with Table 12, the alloyed hot-dip galvanized steel sheets listed in Table 14 were inferior in drawability.

[0041]

[0042]

As described above, in the present invention, the residual composition of the ζ phase and the growth of the Γ phase are suppressed by comprehensively controlling the composition of the original plate, the plating conditions, the wiping conditions and the cooling conditions. The resulting galvannealed steel sheet is manufactured. Further, since the hot dip galvanized layer can be alloyed up to the surface layer without performing the alloying treatment after the hot dip galvanizing, an alloyed hot dip galvanized steel sheet excellent in workability is provided at low cost. On the other hand, in the case of alloying treatment,
By appropriately adjusting the alloying reaction, fine cracks generated in the hot-dip layer at the time of processing the hot-dip coated steel sheet can be controlled, so that the workability is further improved.

[Brief description of the drawings]

FIG. 1. Part of the Fe—Zn binary phase diagram

FIG. 2 is an explanatory diagram of a draw bead test.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Atsushi Ando 5 Ishizu Nishimachi, Sakai City, Osaka Prefecture F-term in Nisshin Steel Co., Ltd. Technical Research Laboratory 4K027 AA02 AA23 AB02 AB28 AB37 AB38 AB42 AC73 AE02 AE03 AE12 AE18 AE23 AE27

Claims (5)

[Claims] 1. C: 0.01 mass% or less, Si: 0.0
05 to 0.10% by mass, Mn: 0.05 to 0.5% by mass, Al: 0.005 to 0.06% by mass, P: 0.02
A steel sheet containing 5% by mass or less, Ti: 0.005 to 0.1% by mass, and the balance substantially having a composition of Fe;
An alloyed hot-dip galvanized steel sheet in which a plating layer composed of δ ₁ phase, Γ ₁ phase, and Γ phase having a thickness of 1 μm or less is formed with a coating weight of 30 to 90 g / m ² per side. 2. The galvannealed steel sheet according to claim 1, wherein the steel sheet further contains one or two of Nb: 0.005 to 0.1% by mass and B: 0.0001 to 0.01% by mass. . 3. C: 0.01 mass% or less, Si: 0.0
05 to 0.10% by mass, Mn: 0.05 to 0.5% by mass, Al: 0.005 to 0.06% by mass, P: 0.02
After passing a steel sheet containing 5% by mass or less and 0.005 to 0.1% by mass of Ti and substantially the composition of Fe in the remainder through a gas reduction furnace and annealing, Al: 0.1 to 0% Immersion in a hot-dip galvanizing bath containing 0.2% by mass at a bath temperature of 490 to 550 ° C. at an inlet temperature of 490 to 600 ° C. to perform hot-dip galvanizing, followed by gas wiping to obtain a coating weight of 30 to 90 g / m per side. ^{2. A} method for producing an alloyed hot-dip galvanized steel sheet excellent in workability, wherein the steel sheet is cooled to a temperature of 400 ° C. at a cooling rate of 5 to 15 ° C./sec. 4. C: 0.01 mass% or less, Si: 0.0
05 to 0.10% by mass, Mn: 0.05 to 0.5% by mass, Al: 0.005 to 0.06% by mass, P: 0.02
After passing a steel sheet containing 5% by mass or less and 0.005 to 0.1% by mass of Ti and substantially the composition of Fe in the remainder through a gas reduction furnace and annealing, Al: 0.1 to 0% Immersion in a hot-dip galvanizing bath containing 0.2% by mass at a bath temperature of 490 to 550 ° C. at an inlet temperature of 490 to 600 ° C. to perform hot-dip galvanizing, followed by gas wiping to obtain a coating weight of 30 to 90 g / m per side. Adjust to ² and 5 to 450-550 ° C
After performing the alloying treatment of heating for ~ 60 seconds, the steel sheet temperature becomes 4
A method for producing an alloyed hot-dip galvanized steel sheet having excellent workability, comprising cooling at a cooling rate of 5 to 15 ° C./sec until the temperature reaches 00 ° C. 5. The method according to claim 3, further comprising using a steel sheet containing one or two of Nb: 0.005 to 0.1% by mass and B: 0.0001 to 0.01% by mass. .