JPH08283909A - Cold rolled steel sheet with excellent workability uniformity and method for producing the same - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to provide a cold-rolled steel sheet which is made of Nb-added ultra-low carbon steel as a raw material and is extremely excellent in uniformity of the material in the longitudinal direction of the coil. [Structure] 1) Actively utilizing S, 2) Optimizing the ratio with the amounts of Nb and S, and 3) Reducing the amount of Mn to precipitate Nb-containing carbosulfide efficiently in the γ region. .
As a result, workability is ensured even if the winding temperature and the time therefor are not sufficiently secured at the end of the hot-rolled sheet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold-rolled steel sheet having very little variation in workability in a coil and a method for producing the cold-rolled steel sheet.

[0002]

2. Description of the Related Art As disclosed in Japanese Patent Application Laid-Open No. 58-185752, an ultra-low carbon steel sheet has excellent workability and is therefore widely used in applications such as automobiles. Further, by defining the composition and manufacturing method of the ultra-low carbon steel, measures have been taken to further improve the workability.

For example, Japanese Patent Laid-Open No. 3-130323,
JP-A-4-143228 and JP-A-4-116.
In Japanese Patent No. 124, C in ultra low carbon steel containing Ti,
It is disclosed that excellent workability can be obtained by reducing the amounts of Mn, P and the like as much as possible. However, in these inventions, there is no description from the viewpoint of improving the width of the coil and the yield at the end in the longitudinal direction, and it is not the technique of positively utilizing Nb carbosulfide as in the present invention. .

Further, from the viewpoint of reducing variations in materials, there are those disclosed in Japanese Patent Laid-Open Nos. 3-170618 and 4-52229. However, in these inventions, it is necessary to increase the rolling reduction in finishing hot rolling and to raise the winding temperature after hot rolling, which imposes a heavy load on the hot rolling process.

[0005]

In the Nb-added ultra-low carbon steel, C is precipitated as NbC by high temperature winding after hot rolling, and the solid solution C is reduced, so that the material after cold rolling and annealing is Ensuring was the usual method.
However, at the width end and the lengthwise end of the hot-rolled coil, the NbC precipitation is not sufficient because the cooling during and after winding progresses remarkably quickly, and the material deteriorates in these portions. There was a problem of being lost. Therefore, in practice, the ends of the hot-rolled sheet or the cold-rolled sheet are often cut off, which has been a cause of increasing the manufacturing cost of the ultra-low carbon steel.

An object of the present invention is to provide a cold-rolled steel sheet excellent in workability in which the deterioration of the material in the width and the end portion in the longitudinal direction of the coil is extremely small and a manufacturing method thereof.

[0007]

In order to solve the above-mentioned problems, the inventors of the present invention positively utilize S in ultra-low carbon steel and specify a specific carbide by defining the Mn content. In order to obtain a cold-rolled steel sheet which has been deposited and has excellent workability uniformity, the present inventors conducted extensive studies. As a result, S ≧ 0.00
It was found that 4% and Mn ≦ 0.15% are effective.

Furthermore, after winding after hot rolling, the proportion of S precipitated as MnS in all S is K = (S% as M
nS) / (total S%) satisfying K ≦ 0.2 is extremely important for obtaining the uniformity of the material, and in order for the material to be uniform, Nb-containing carbosulfide in the total amount of C Of the amount of C that precipitates as L = (C% as carbosulfide) / (total C
%) Has been found to be L ≧ 0.7.
This is considered to be based on the following mechanism.
That is, the amount of MnS precipitated out of the total amount of S is reduced as much as possible, and Nb-containing carbosulfide is positively precipitated to reduce the solid solution C before the hot rolling for finishing. As a result, even if the coil end is rapidly cooled during winding after hot rolling, a large amount of solid solution C remains at the coil end because the solid solution C is sufficiently fixed before winding. It is considered that deterioration of the material due to precipitation of fine carbide is reduced.

Further, the inventors of the present invention have previously found a method of reducing the material deterioration of the coil end by positively depositing Ti ₄ C ₂ S ₂ in the Ti-added ultra-low carbon steel. However, as a result of further diligent research, in Nb-added ultra-low carbon steel, N equivalent to Ti ₄ C ₂ S ₂ was obtained during hot rolling.
Precipitation of b-containing carbosulfide, that is, even in Nb-added ultra-low carbon steel, the amount of solute C is reduced by positively precipitating Nb-containing carbosulfide during hot rolling, and variation in material in the coil It has been newly found that the winding temperature is reduced and the winding temperature dependency is reduced. Further, in the present invention, since it is not necessary to add Ti, it has excellent powdering resistance,
The r-value anisotropy Δr defined as follows is also extremely small at 0.2 or less.

Δr = (r _L + r _C ) / 2−r _D r _L : r value in the rolling direction when the elongation is 15% r _C : r value in the direction perpendicular to the rolling direction when the elongation is 15% r _D : R value in the direction of 45 ° with respect to the rolling direction when the elongation is 15%, that is, the gist of the present invention is as follows.

(1) C: 0.0005 to 0.
007%, Mn: 0.01 to 0.15%, Si: 0.0
05-0.8%, Al: 0.005-0.1%, P:
0.2% or less, S: 0.004 to 0.02%, N: 0.
007% or less, containing Nb: 0.005-0.1%,
The balance consists of iron and unavoidable impurities, and the ratio of the amount of S precipitated as MnS in the total amount of S K = (S% a
s MnS) / (total S%) is K ≦ 0.2, and the ratio of the amount of C precipitated as Nb-containing carbosulfide in the total C amount L = (C% as carbosulfide) / (total C) %) Is L ≧ 0.
7. A cold-rolled steel sheet excellent in workability uniformity, which is No. 7.

(2) B: 0.0001 to 0.0030%
A cold-rolled steel sheet containing the above-described item (1), which is excellent in workability uniformity. (3) Heating temperature of steel having the components described in (1) or (2) above ≦ 1250 ° C., finishing temperature ≧ (Ar ₃ −100)
Uniformity of workability characterized by hot rolling at ℃, winding at room temperature to 800 ℃, cold rolling at a rolling reduction ≧ 60%, and annealing at recrystallization temperature or higher. Excellent cold rolled steel sheet manufacturing method.

(4) A steel having the composition described in (1) or (2) above is heated at a heating temperature of ≤1250 ° C and a finishing temperature of ≥ (Ar.
₃ -100) subjected to hot rolling ° C., coiling at a temperature range of 800 ° C. from room temperature, and then was subjected to rolling reduction ≧ 60% cold rolling, a continuous galvanizing line having a line within the annealing furnace A method for producing a hot-dip galvanized cold-rolled steel sheet having excellent workability uniformity, which comprises performing annealing at a recrystallization temperature or higher and galvanizing during a cooling process.

(5) A steel having the composition described in (1) or (2) 2 above is heated at a temperature of ≦ 1250 ° C. and a finishing temperature of ≧ (A
r ₃ -100) ° C hot rolling, room temperature to 800 ° C
, Then cold rolling with a rolling reduction of ≧ 60%, followed by annealing at a recrystallization temperature or higher in a continuous hot dip galvanizing line with an in-line annealing furnace, and galvanizing during the cooling process. A method for producing an alloyed hot-dip galvanized cold-rolled steel sheet having excellent workability uniformity, which comprises performing an alloying treatment in a temperature range of 400 to 600 ° C.

[0015]

The cold-rolled steel sheet and the method for producing the same according to the present invention limit the amounts of S, Mn, Nb and the amounts of specific sulfides and carbosulfides, and ensure that C is sufficiently added before winding after hot rolling. By precipitating, a cold-rolled steel sheet excellent in workability uniformity in the longitudinal direction and the width direction of the coil is provided. The reasons for the limitation will be described below.

First, the reasons for limiting the chemical components in the present invention will be described. As the amount of C increases, the amount of carbide-forming elements such as Nb for fixing it must be increased, resulting in high cost. Also, solid solution C remains at the end of the hot-rolled coil or NbC Since a large amount of fine carbides and the like precipitate in the grains, the grain growth property is hindered and the workability deteriorates. Therefore, the C content is 0.007% or less, preferably 0.003% or less. The lower limit is 0.0005% from the viewpoint of vacuum degassing treatment cost.

Since Si is effective as an inexpensive strengthening element, it is used depending on the intended strength level. However, when the Si content exceeds 0.8%, YP rapidly rises,
The elongation is lowered and the plating property is significantly impaired, so the content is made 0.8% or less. For hot dip galvanizing, it is preferably 0.3% or less from the viewpoint of plating property. High strength (TS
350 MPa or more) is required, 0.1
% Or less is more preferable. The lower limit is 0.005% from the viewpoint of steelmaking cost.

Mn is one of the extremely important elements in the present invention. That is, when Mn exceeds 0.15%, M
Since the precipitation amount of nS increases, and as a result, the precipitation amount of Nb-containing carbosulfide decreases, even if high-temperature winding is performed, at the end of the hot-rolled coil, the cooling rate is high and the solid solution C Remains in a large amount and a large number of fine carbides precipitate, so that the material is significantly deteriorated. Therefore, Mn is preferably 0.15% or less, and more preferably less than 0.10%. On the other hand, even if Mn is less than 0.01%, no particular effect is obtained, which causes an increase in steelmaking cost.
%.

Like P, P is positively utilized as an inexpensive strengthening element depending on the intended strength level. However, if the P content exceeds 0.2%, it causes cracking during hot or cold working, the secondary workability is significantly deteriorated, and the alloying rate of the hot dip galvanization is significantly delayed, so the P content is 0.2%. Below. From the above viewpoint, it is more preferably 0.08% or less. When high strength is not required, 0.03% or less is more preferable.

S is an extremely important element in the present invention, and its addition amount is 0.004 to 0.02%. S
When the amount is less than 0.004%, the precipitation amount of Nb-containing carbosulfide is not sufficient, and when the coil is wound at a low temperature, solid solution C is generated at the end of the coil even when wound at a high temperature. A large amount remains, or fine precipitation of NbC hinders grain growth during annealing, resulting in significant deterioration of workability. If the amount of S exceeds 0.02%, hot cracking tends to occur, and more MnS precipitates than the precipitation of Nb-containing carbosulfide, causing the same problem, and the uniformity of workability cannot be ensured. In addition,
0.004 to 0.012% is a more preferable range.

Al is at least 0.005 as a deoxidizer.
% Needs to be added. However, the amount of Al is 0.
If it exceeds 1%, not only the cost is increased, but also inclusions are increased and the workability is deteriorated. As with C, N needs to increase the amount of Al, which is a nitride-forming element, as well as C, which increases the cost, and the increase in precipitates leads to deterioration in ductility, so the smaller the content, the better. Therefore, N
Is 0.007% or less. It is preferably 0.003% or less.

Nb is the most important element in the present invention, and it precipitates as Nb-containing carbosulfide and also makes the hot-rolled sheet finer to improve the deep drawability. Further, since Nb is added alone, the r-value anisotropy Δr is extremely small at 0.2 or less,
When hot dip galvanizing is applied, the powdering resistance is significantly improved. Therefore, Nb is added in the range of 0.005 to 0.1%. If Nb is less than 0.005%, Nb-containing carbosulfide cannot be precipitated before winding, and addition of an amount exceeding 0.1% not only saturates the effect of fixing C. Ductility deteriorates significantly. From the above viewpoint, Nb is more preferably in the range of 0.02 to 0.05%.

In order to secure the material at the coil end, the ratio K of the amount of S precipitated as MnS in the total amount of S is K.
= (S% as MnS) / (total S%) must be K ≦ 0.2. Furthermore, it is desirable that K <0.15. This (S% as MnS) is determined as follows. That is, the precipitate is electrolytically extracted with a solvent (for example, a nonaqueous solvent) that does not dissolve the sulfide. The obtained extraction residue is subjected to chemical analysis, and the Mn amount is measured (= X (g)). At this time, when the amount of electrolysis of the entire sample is Y (g), (S% as MnS) = X
/ Y × 32/55 × 100 (%).

The most important aspect of the present invention is to sufficiently precipitate Nb-containing carbosulfide during slab heating and hot rolling.
That is, the ratio of the amount of C precipitated as Nb-containing carbosulfide in the total amount of C, L = (C% as carbosulfide) / (total C
%) Must be L ≧ 0.7. Also, this Nb
The content of carbosulfide is basically obtained by replacing the Ti position of Ti ₄ C ₂ S ₂ with Nb, but the atomic ratio is 1 ≦ Nb.
The composition ratio may be in the range of / S ≦ 2, 1 ≦ Nb / C ≦ 2. This (C% as carbosulfide) is obtained as follows. That is, N, such as sulfuric acid and hydrogen peroxide
Precipitates are extracted by a method that dissolves small-sized carbides such as bC. The obtained residue is subjected to chemical analysis, and the amount of Nb is measured (= N (g)). At this time, when the extraction amount of the entire sample is Z (g), (C% as carbosulfide) = N / Z × 12/93 ×
It becomes 100 (%).

B strengthens the grain boundary and improves the secondary workability, so 0.0001 to 0.0030% is added if necessary. If it is added in an amount of less than 0.0001%, the effect is poor, and if it is added in excess of 0.0030%, the effect is saturated and the ductility deteriorates. The raw material for obtaining the above-mentioned components is not particularly limited, but scrap iron may be used as a raw material other than a method of adjusting the components by a blast furnace and a converter using iron ore as a raw material, and this may be melted in an electric furnace. . When scrap is used as all or part of the raw material, Cu, Cr, N
Elements such as i, Sn, Sb, Zn, Pb and Mo may be contained.

Next, the reasons for limitation regarding the manufacturing process of the present invention will be described. The slab used for hot rolling is not particularly limited. That is, it may be a continuous cast slab or a thin slab caster. Further, continuous casting-direct rolling (CC
-DR).

It is essential that the heating temperature in the hot rolling is 1250 ° C. or lower in order to increase the precipitation amount of Nb-containing carbosulfide. From this viewpoint, the temperature is preferably less than 1200 ° C, and more preferably less than 1150 ° C. The finishing temperature in hot rolling needs to be (Ar ₃ -100) ° C or higher in order to secure press formability. Further, in the hot rolling, bar finishing may be performed after the rough rolling is completed and continuous hot rolling may be performed.

The present invention is characterized in that workability can be secured even when the winding temperature is low. That is, in the present invention, the precipitation of C is sufficiently completed as Nb-containing carbosulfide during the process of hot rolling to the cooling after hot rolling, and the material is remarkably formed even at high temperature winding. There is no improvement.
Therefore, the winding may be carried out at a temperature suitable for the operation, and is carried out in the range of room temperature to 800 ° C. Winding at less than room temperature requires not only excessive equipment but also no particular effect. Further, if it exceeds 800 ° C, the crystal grains of the hot-rolled sheet become coarse, or the oxide scale on the surface becomes thick, and the cost of pickling increases, so 800 ° C is the upper limit. In the case of the steel of the present invention,
When the coiling temperature is high, a small amount of the solid solution C that remains may be precipitated as fine carbide, or the compound of P may be precipitated.
The material tends to deteriorate rather. Therefore, the winding is 6
It is preferable to carry out at a temperature of 50 ° C. or lower. To completely avoid the precipitation of these harmful compounds, it is often preferred to wind at temperatures below 500 ° C. Furthermore, in order to shorten the time it takes for the temperature to drop to near room temperature after winding,
It is preferable to wind at 100 ° C or lower. It goes without saying that such low temperature winding can reduce the manufacturing cost.

The rolling reduction of cold rolling is 60% or more from the viewpoint of ensuring deep drawability. The annealing temperature in continuous annealing is higher than the recrystallization temperature in order to secure workability. The recrystallization annealing temperature in the continuous hot-dip galvanizing line is also set to the recrystallization temperature or higher for the same reason. The hot dip galvanizing is 420 to 500 from the viewpoint of plating property and plating adhesion.
℃ is good. If the temperature of the subsequent alloying treatment is too low, not only the alloying reaction will be too slow to impair the productivity but also the corrosion resistance and weldability will be poor, and if it is too high, the plating peeling resistance will be deteriorated. To do. In order to obtain a plated layer with more excellent adhesion, it is preferable to carry out alloying in the range of 480 to 550 ° C.

The heating rate in the continuous annealing or continuous hot dip galvanizing line is not particularly limited, and may be a normal rate or ultra-rapid heating at 1000 ° C./s or more. In addition to hot dip galvanizing, various surface treatments such as electroplating may be performed.

[0031]

EXAMPLES The present invention will be described in detail below with reference to examples. (Example 1) Nb-added ultra-low carbon steel having the chemical composition shown in Tables 1 and 2 (continued from Table 1) was tapped in a converter and made into a slab by a continuous casting machine, and then at 1140 ° C. It was heated and hot-rolled so that the finishing temperature was 925 ° C. and the plate thickness was 4.0 mm. Run out table
The average cooling rate for each of the samples was about 30 ° C./s, and thereafter, the coil was wound at various winding temperatures as shown in Tables 3 and 4 (continued from Table 3). A sample was cut out from the center of the hot rolled coil in the longitudinal direction, and the following treatment was performed. That is, after pickling in the laboratory, cold rolling was performed to 0.8 mm and heat treatment equivalent to continuous annealing was performed. Annealing conditions are: annealing temperature: (shown in Tables 3 and 4), soaking: 60
s, cooling rate: about 5 ° C / s from annealing temperature to 680 ° C,
From 680 ° C. to room temperature, it was set to about 65 ° C./s. afterwards,
Temper rolling was performed at a rolling reduction of 0.7%, and the tensile test was performed. Tensile test and average Rank Ford value (r value below)
Was measured using a JIS No. 5 test piece. Note that r
The value was evaluated at an elongation of 15% and was 4 with respect to the rolling direction (L direction), the direction perpendicular to the rolling direction (C direction), and the rolling direction.
The value in the 5 ° direction (D direction) was measured and calculated by the following formula.

R = (r _L + 2r _D + r _C ) / 4 The test results are summarized in Tables 3 and 4.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

[Table 3]

[0036]

[Table 4]

As is clear from Tables 3 and 4, it is understood that the steel having the components of the present invention can obtain an excellent material by being wound at a temperature of 800 ° C. or lower. Especially M
When the amount of N is low and Nb is sufficiently added to C, and the annealing temperature is high, the coiling temperature is low and the amount of C precipitated as fine carbide is small, resulting in an extremely excellent material. . On the other hand, it is clear that the comparative steels are inferior in material at low temperature coiling.

(Example 2) Steels B, C, D, G, H, J, L, N of Tables 1 and 2 produced under the same conditions as in Example 1
The tip (inner circumference) of the R and T hot rolled coils in the longitudinal direction (10 m from the tip), the center, and the end (outer circumference) (10 m from the extreme end)
A hot-rolled sheet was cut out from. The total length of the hot rolled coil was about 240 m. Then, using cold-rolled, annealed, and temper-rolled cold-rolled steel sheet (4 mm thick by hot rolling and then 0.8 mm thick by cold rolling) under the same conditions as in Example 1, the material properties in the longitudinal direction of the cold rolled coil were measured. investigated.

The test results are summarized in Tables 5 and 6 (continued from Table 5).

[0040]

[Table 5]

[0041]

[Table 6]

As is clear from Tables 5 and 6, the steel manufactured according to the scope of the present invention exhibits excellent characteristics not only in the central portion of the coil but also in the end portion 10m thereof. On the other hand, in the case of the comparative steel, the material was significantly deteriorated at the coil end, and in the case of low temperature winding, the material was deteriorated over the entire length of the coil. It is clear that this tendency becomes more prominent toward the edges.

(Example 3) The effects of hot rolling heating temperature on the material properties after cold rolling and annealing were investigated using steels C and Q (steel slabs produced in actual equipment) shown in Tables 1 and 2. That is, the slab was heated to 1100 to 1350 ° C. in an actual machine, and hot rolling was performed so that the finishing temperature was 940 ° C. and the plate thickness was 4.0 mm. The average cooling rate at the runout table is about 40
C / s, and then coiled at 620 ° C. The total length of the coil was about 200 m. A sample was cut out from the same coil from the same position as in Example 2, pickled, cold-rolled to 0.8 mm, and subsequently subjected to heat treatment equivalent to continuous annealing in a laboratory. Annealing conditions are: annealing temperature: 810 ° C., soaking: 50 s, cooling rate: about 6 up to room temperature.
0 ° C./s. Then, temper rolling was performed at a rolling reduction of 0.8%, and the steel was subjected to a tensile test.

The test results are summarized in Table 7.

[0045]

[Table 7]

As is apparent from Table 7, the steel manufactured according to the scope of the present invention is excellent in the material after cold rolling and annealing not only in the central portion of the hot rolled coil but also in the end portion thereof. . On the other hand, when the heating temperature was higher than 1250 ° C, the material after cold rolling and annealing significantly deteriorated at the coil end. (Example 4) Steels B, D, G, J, L in Tables 1 and 2
Hot rolling was performed using N, R, and T under the same conditions as in Example 1 (winding temperature: 730 ° C.), followed by pickling with an actual machine, and cold rolling with a reduction rate of 80%. The plate was passed through an internal annealing galvanizing line. At this time, after heating at a maximum heating temperature of 800 ° C., cooling is carried out, conventional hot dip galvanizing is performed at 470 ° C. (Al concentration in the bath is 0.12%), further heating is performed, and alloying treatment is performed at 560 ° C. for about 12 seconds. went. Furthermore, 0.8% temper rolling is applied to obtain mechanical properties,
The plating adhesion was evaluated.

The results obtained are summarized in Table 8. Here, the plating adhesiveness was determined by determining the peeling condition of the zinc coating by adhering an adhesive tape to the bent portion, peeling the adhesive tape off, and peeling off the zinc film. The evaluation was made into the following 5 grades. 1: Large peeling, 2: During peeling, 3: Small peeling, 4: Small amount of peeling,
5: No peeling

[0048]

[Table 8]

As is apparent from Table 8, the alloyed hot-dip galvanized steel sheet produced according to the scope of the present invention exhibits excellent characteristics regardless of the coil portion. On the other hand, in the comparative steel, the workability varied greatly depending on the coil portion.

[0050]

As described above, according to the present invention, the coiling temperature after hot rolling can be lowered, and moreover, a material excellent in the longitudinal direction and the width direction of the coil can be uniformly obtained. The former coil end can be made into a product. Further, when the high-strength cold-rolled steel sheet included in the present invention is applied to an automobile, it is possible to reduce the sheet thickness, which leads to an improvement in fuel consumption and also to a global environmental problem which has become a big problem in recent years. Its value is great because it can contribute.

Claims (5)

[Claims] 1. C: 0.0005-0.00, by weight.
7%, Mn: 0.01 to 0.15%, Si: 0.005
~ 0.8%, Al: 0.005-0.1%, P: 0.2
% Or less, S: 0.004 to 0.02%, N: 0.007
% Or less, Nb: 0.005 to 0.1%, the balance consisting of iron and unavoidable impurities, and the ratio of the amount of S precipitated as MnS in the total amount of S K = (S% as M
nS) / (total S%) is K ≦ 0.2, and the ratio of the amount of C precipitated as Nb-containing carbosulfide in the total amount of C is L =
(C% as carbosulfide) / (total C%) is L ≧ 0.7, which is a cold-rolled steel sheet excellent in uniformity of workability. 2. A cold-rolled steel sheet having excellent workability uniformity according to claim 1, which contains B: 0.0001 to 0.0030%. 3. A steel having the composition according to claim 1 or 2 is heated at a temperature of ≦ 1250 ° C. and a finishing temperature of ≧ (Ar ₃ −10).
0) ° C. hot rolling, coiling in the temperature range from room temperature to 800 ° C., then cold rolling with a rolling reduction ≧ 60%, and further annealing at a recrystallization temperature or higher. A method for producing a cold rolled steel sheet having excellent uniformity. 4. A steel having the composition according to claim 1 or 2 is heated at a temperature of ≦ 1250 ° C. and a finishing temperature of ≧ (Ar ₃ −10).
0) ℃ hot rolled, rolled in the temperature range from room temperature to 800 ℃, then cold rolled with a rolling reduction ≧ 60%, then recrystallized in a continuous hot dip galvanizing line with an in-line annealing furnace A method for producing a hot-dip galvanized cold-rolled steel sheet excellent in workability uniformity, which comprises performing annealing at a temperature or higher and performing galvanization during a cooling process. 5. A steel having the composition according to claim 1 or 2 is heated at a temperature of ≦ 1250 ° C. and a finishing temperature of ≧ (Ar ₃ −10).
0) ℃ hot rolled, rolled in the temperature range from room temperature to 800 ℃, then cold rolled with a rolling reduction ≧ 60%, then recrystallized in a continuous hot dip galvanizing line with an in-line annealing furnace An alloyed hot-dip galvanized plate with excellent workability, characterized by being annealed at a temperature above the temperature, galvanized during the cooling process, and then alloyed at a temperature range of 400 to 600 ° C. Manufacturing method of rolled steel sheet.