JP5299346B2 - Cold-rolled steel sheet excellent in deep drawability and method for producing alloyed hot-dip galvanized steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for cooling a hot rolled steel sheet for sufficiently achieving crystal grain refining of the hot rolled steel sheet through the whole thickness and obtaining the deep drawability of an end product, in producing a cold rolled steel sheet and a galvannealed steel sheet for deep drawing. <P>SOLUTION: In producing the cold rolled steel sheet or the galvannealed steel sheet by hot rolling, cold rolling, and continuous annealing of a slab, finish rolling is completed in a stand which is located before the final stand by two stages or one stage in a hot rolling stand train in which hot rolling is continuously performed, and the steel sheet is cooled after the finish rolling before the final stand in a condition where finishing temperature (T) and cooling start time (t) satisfy the following formula: 40/(log[t(second)]+2)-20&le;T-Ar3(&deg;C)&le;60/(log[t(second)]+2). <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention relates to a cooling method, particularly in a hot rolling process, when producing an ultra-low carbon cold-rolled steel sheet and an galvannealed steel sheet excellent in deep drawability. The cold-rolled steel sheet and the galvannealed steel sheet according to the present invention are used for automobiles, household electrical appliances, buildings and the like.

  As a manufacturing method of an ultra-low carbon cold-rolled steel sheet excellent in deep drawability, various techniques have been studied since the metal structure and state of the hot-rolled steel sheet as the material are important. In particular, the refinement of the hot-rolled structure has a great influence on the texture formation during the subsequent cold rolling and continuous annealing, and is very useful for obtaining excellent deep drawability. Enormous research has been conducted, and many are used as actual manufacturing techniques. By the way, as one of such techniques, there is a technique for achieving fine graining by cooling in a short time after finish rolling. However, since various instruments are provided immediately after the final finishing stand, cooling in a short time is difficult.

  However, in recent years, for example, a technique for cooling between finishing stands such as Patent Document 1 has enabled cooling in a short time. And the technique of cooling between several stands in consideration of the cooling capability between stands like patent document 2 is also disclosed. Moreover, about the material improvement of the ultra-low carbon steel plate by such a short time cooling, the technique which prescribed | regulated finishing temperature, cooling start time, etc. like patent document 3 is disclosed. However, it cannot be said that the relevance with respect to these temperatures and times has been sufficiently studied, and there is no one that specifically defines the lower limit for the cooling start time.

Japanese Patent No. 3705233 JP 2009-241115 A JP 2009-114473 A

  Conventionally, attention has been paid to shorten the cooling start time after finish rolling as much as possible in order to prevent coarsening of the austenite structure after rolling. Further, since this coarsening is more likely to occur as the finishing temperature is higher, it has been defined in a temperature range of Ar3 to Ar3 + several tens of degrees Celsius considering Ar3 or more and temperature variation in the plate width direction. However, the coarsening of the structure is a phenomenon in which temperature and time are closely related, and there should be some relationship between the two. Furthermore, even in the case of finish rolling, even a thin steel plate with a thickness of about 3 to 4 mm has a rapid temperature gradient in the thickness direction due to heat removal due to contact with the rolling roll, and the temperature is recovered by reheating from the inside of the plate after rolling. If cooling is started before the material becomes uniform, the structure changes in the thickness direction according to this temperature gradient, which may hinder material improvement in the final cold-rolled steel sheet. It was confirmed while doing.

  The present invention, when producing a cold-rolled steel sheet and an alloyed hot-dip galvanized steel sheet excellent in deep drawability, the finishing temperature in the case of cooling in a short time after finish rolling in order to refine the hot-rolled steel sheet It is an object of the present invention to provide a method for producing a cold-rolled steel sheet and an alloyed hot-dip galvanized steel sheet that are excellent in deep drawability and have determined appropriate conditions and relations for the cooling start time.

  The inventors of the present invention diligently conducted research to achieve the above-described goal, and obtained the following unprecedented knowledge as described below.

  That is, by investigating various combinations of finishing temperature and cooling start time, as a condition for obtaining a metal structure of a hot-rolled steel sheet that is preferable for the material of the cold-rolled steel sheet, that is, a uniform fine grain structure in the thickness direction, the relationship between the two Is found.

  The present invention has been constructed on the basis of such ideas and new findings, and the gist thereof is as follows.

(1) In mass%,
C: 0.0010 to 0.0025%,
Si: 0.01 to 0.1%,
Mn: 0.05 to 0.15%,
P: 0.001 to 0.015%,
S: 0.001 to 0.01%,
Al: 0.005 to 0.05%,
N: 0.001 to 0.003%
A slab having a composition comprising at least one of Ti and Nb in a range of Ti: 0.01 to 0.05% and Nb: 0.005 to 0.02%, the balance being Fe and inevitable impurities When producing a cold-rolled steel sheet by performing hot rolling, cold rolling, and continuous annealing, finishing is performed at a stand that is two or one stage prior to the last stand in the hot rolling stand row where hot rolling is continuously performed. When cooling between the end of rolling and the final stand, cooling is started under the condition that the finishing temperature (T) and the cooling start time (t) satisfy the following formula (1), and the exit side at the final stand The manufacturing method of the cold-rolled steel plate excellent in deep drawability characterized by winding temperature at 650-750 degreeC below temperature (Ar3 transformation point-30 degreeC).
40 / (log [t (seconds)] + 2) -20 ≦ T-Ar3 (° C.) ≦ 60 / (log [t (seconds)] + 2) (1)
However, 0.1 ≦ t (seconds) ≦ 0.7

  (2) Furthermore, the manufacturing method of the cold-rolled steel plate excellent in the deep drawability of the said (1) term | claim characterized by the said slab containing mass% and B: 0.0002-0.0010%.

  (3) Even if the metal structure of the hot-rolled steel sheet has a fine grain uniformly in the total thickness or a coarse grain region exists in the surface layer part, the coarse grain region is 20% or less in total in the front and back as the plate thickness ratio. The manufacturing method of the cold-rolled steel plate excellent in the deep drawability of the said (1) or (2) term characterized by the above-mentioned.

(4) By mass%
C: 0.0010 to 0.0025%,
Si: 0.01 to 0.1%,
Mn: 0.05 to 0.15%,
P: 0.001 to 0.015%,
S: 0.001 to 0.01%,
Al: 0.005 to 0.05%,
N: 0.001 to 0.003%
A slab having a composition comprising at least one of Ti and Nb in a range of Ti: 0.01 to 0.05% and Nb: 0.005 to 0.02%, the balance being Fe and inevitable impurities , Hot rolling, cold rolling, continuous annealing, hot dip galvanizing, alloying heat treatment, to produce an alloyed hot dip galvanized steel sheet, the last in a hot rolling stand row in which hot rolling is continuously performed When finishing rolling is completed at the stand two or one stage before the stand and then cooled to the final stand, the finishing temperature (T) and the cooling start time (t) satisfy the following formula (1). The alloyed hot-dip galvanized steel sheet excellent in deep drawability, characterized in that cooling is started under conditions, the outlet temperature in the final stand is (Ar3 transformation point −30 ° C.) or less, and winding is performed at 650 to 750 ° C. How to make .
40 / (log [t (seconds)] + 2) -20 ≦ T-Ar3 (° C.) ≦ 60 / (log [t (seconds)] + 2) (1)
However, 0.1 ≦ t (seconds) ≦ 0.7

  (5) Further, the slab is mass% and contains B: 0.0002 to 0.0010%. Production method.

  (6) Even if the metal structure of the hot-rolled steel sheet has a fine grain uniformly in the total thickness, or a coarse grain region exists in the surface layer part, the coarse grain region is 20% or less in total in the front and back as the plate thickness ratio. The manufacturing method of the galvannealed steel plate excellent in the deep drawability of the said (4) or (5) term characterized by the above-mentioned.

  As detailed above, according to the present invention, the hot-rolled sheet is refined using the inter-stand cooling technique, and when deep-drawing of the cold-rolled steel sheet and the galvannealed steel sheet after cold-rolling annealing is improved, Appropriate finish rolling temperature and cooling start time can be selected. The refinement of the hot-rolled structure under such hot-rolling conditions is caused by, for example, the annealing temperature caused by the recrystallization delay during cold-rolling annealing, which occurs when the refinement is achieved by adding alloy elements or increasing the amount thereof. Since there are no harmful effects such as high temperature of steel and a decrease in annealing speed, not only as a technology to produce excellent deep drawability, but also to improve productivity such as increasing production efficiency during annealing and to reduce alloying elements Therefore, it can be said that the present invention is an industrially valuable invention.

It is a figure showing the structure | tissue of the hot rolled sheet obtained by finish rolling temperature and cooling start time. It is a microscope picture showing the example of the metal structure of a hot rolled sheet.

  First, the experiment that led to the completion of the present invention will be described.

  The present inventors used a 250 mm-thick slab having a component of 0.0019C-0.05Si-0.09Mn-0.038Ti by mass%, and after reheating this slab to 1200 ° C., hot rolling After finishing rolling in the hot-rolled stand row, in which the thickness is 3.5 mm or more at the Ar3 temperature or higher (Ar3: 895 ° C.) in the stand that is two or one stage before the final stand, A series of hot rolling was performed by cooling to 855 ° C. as the final stand exit side temperature using a cooling device installed in the above, and then winding at 700 ° C. after cooling in a normal cooling zone. In this case, the finishing temperature (T) and the cooling start time (t) are changed by changing the entry side temperature of the finish rolling, the sheet passing speed of the steel sheet, and the position of the cooling device between the stands. The metal structure of hot rolled steel sheet was investigated. The result is shown in FIG.

  In FIG. 1, the symbol ◎ is the condition that a fine grain structure with a grain size number of 7.5 or more is formed over the entire thickness according to ASTM, and the symbol Δ is a coarse grain less than 7.0 in the total thickness This is the condition that was formed. The mark “◯” and the mark “X” are the conditions under which a fine grain region of 7.5 or more inside the plate thickness but a coarse grain region of 7.0 or less was formed in the surface layer portion. However, here, the circles indicate that the coarse-grained area is 20% or less in total in terms of the plate thickness ratio, whereas the X marks exceed 20%. According to FIG. 1, it is clear that the region of the four conditions is defined by the finishing temperature and the cooling start time.

  Here, the structure having a coarse-grained region in the surface layer portion of the circle mark or the x mark is not clearly identified in the technology for cooling immediately after finishing hot rolling represented by conventional inter-stand cooling, but this It is considered that the conditions for forming such a structure are limited to a very short time region after finish rolling. In other words, because this experiment used continuous hot rolling of the actual machine, the plate passing speed was as fast as 600 mpm or more, and the cooling device was brought closer to the stand for actually finishing and rolling within 1 m. It is considered that the cooling start time was obtained and the existence of a specific tissue was clarified.

  In addition, although the typical metal structure of said 4 conditions was shown in FIG. 2, especially the structure | tissue in which the surface layer part is a coarse grain is separated clearly in the place where a fine grain part and a coarse grain part have plate thickness. It is a feature. And if this coarse-grained region is present in a total thickness of more than 20% as a sheet thickness ratio, even if the inside of the sheet thickness is 7.5 or more fine grains, There was no improvement in characteristics, particularly deep drawability. That is, the unique mixed structure clarified by the present invention, as well as the thickness ratio, is that cooling is started in a short time after finish rolling including inter-stand cooling, and the hot-rolled steel sheet is finely granulated. It became clear that the structure should be considered for improving the material after annealing, especially deep drawability.

  Next, the reason for limiting the steel composition in the present invention will be further described. Here,% regarding the composition means mass%.

  C is an extremely important element that determines the workability of the product, and it is better that the texture formed by subsequent cold rolling and continuous annealing becomes more favorable for deep drawability as the amount of solid solution C in the hot rolled steel sheet decreases. Are known. Accordingly, it is preferable to reduce the amount to less than 0.0010%, but not only the load at the steel making stage is increased, but the hot-rolled sheet structure tends to be coarse columnar crystallization along the temperature gradient in the thickness direction during water cooling. Even with inter-stand cooling as in the invention, it becomes difficult to obtain a fine grain structure, and as a result, deep drawability deteriorates. On the other hand, if it exceeds 0.0025%, the amount of Ti or Nb added later will increase, leading to an increase in the recrystallization temperature during continuous annealing and degrading deep drawability, so this is the upper limit.

  Si is preferably not added to give excellent deep drawability, and the upper limit is 0.1%. On the other hand, excessively lowering increases the load in the steelmaking stage, so 0.01% is made the lower limit.

  Since Mn is preferably not added in order to give excellent deep drawability, the upper limit is made 0.15%. However, if it is less than 0.05%, the fixing of S becomes insufficient and causes cracking in hot rolling, so this is the lower limit.

  P is also preferably not added in order to give better deep drawability, so 0.015% is made the upper limit. On the other hand, since lower than 0.001% is not preferable because the removal P cost is extremely increased, this is the lower limit.

  If S exceeds 0.01%, it causes hot cracking and deteriorates workability, so 0.01% is made the upper limit. However, if less than 0.001%, the desulfurization cost is extremely increased, which is not preferable.

  Al is used for deoxidation preparation and fixation of N when Ti is not added, but if it is less than 0.005%, its effect is insufficient. On the other hand, if the Al content exceeds 0.05%, the cost is increased or the surface properties are deteriorated, so the upper limit is made 0.05%.

  N should be less in steels that provide deep drawability, so 0.003% is the upper limit. On the other hand, since it is not preferable to lower the cost extremely, 0.001% is made the lower limit.

  Ti is one of the important elements for ensuring deep drawability. That is, it is added to fix the solute C and N. Therefore, 0.01% is made the lower limit. On the other hand, if added over 0.05%, the amount of precipitated carbonitride increases and the amount of solid solution Ti increases, so the recrystallization temperature increases, so this is the upper limit.

  Nb is also an important element for securing deep drawability like Ti, so one or more of Ti and Nb may be added. That is, Nb is added to fix solute C and N. Therefore, Nb has a lower limit of 0.005%. On the other hand, excessive addition causes an increase in recrystallization temperature over Ti. Therefore, the upper limit is made 0.02%.

  B is preferably added because it is effective in preventing secondary work embrittlement. At that time, if it is less than 0.0002%, a sufficient effect cannot be obtained. On the other hand, if it exceeds 0.0010%, not only the effect is saturated but also the recrystallization temperature is increased in the same manner as Ti and Nb.

  You may contain 1% or less of Cu, Sn, Zn, Mo, W, Cr, and Ni in the steel which has these as a main component in total.

  Next, the reasons for limiting the manufacturing conditions will be described.

  The slab used for hot rolling is not particularly limited. That is, what was manufactured with the continuous casting slab, the thin slab caster, etc. should just be used. It is also compatible with processes such as continuous casting-direct rolling (CC-DR) in which hot rolling is performed immediately after casting.

In the present invention, the most important hot rolling condition is that the slab is reheated and then reduced to a thickness of 30 to 60 mm by rough rolling. In a series of steps in which the steel sheet is cooled and wound in a coil shape, the rolling is completed at a stand that is two or one stage before the final stand, and then cooled until the final stand exit side. In this case, the finish rolling temperature (T) and the cooling start time (t) are set to satisfy the following expression based on the previous experiment.
T-Ar3 (° C.) ≧ 40 / (log [t (seconds)] + 2) −20 (2)
T-Ar3 (° C.) ≦ 60 / (log [t (seconds)] + 2) (3)
Here, the above formula (2) is the condition that the boundary between x and ◯ in FIG. 1, that is, the coarse grain region existing in the surface layer portion in the metal structure of the hot-rolled steel sheet is 20% or less in total as the sheet thickness ratio. The above equation (3) is the condition that the boundary between ◎ and Δ in FIG. 1, that is, the condition that the crystal grain size is as fine as 7.5 or more over the entire thickness. Therefore, the following formula (1), which combines the above formulas (2) and (3), represents the conditions for defining the areas of ◎ and ◯ in FIG.
40 / (log [t (seconds)] + 2) -20 ≦ T-Ar3 (° C.) ≦ 60 / (log [t (seconds)] + 2) (1)

  The final stand outlet temperature after inter-stand cooling is (Ar3-30) ° C. or less. If this temperature is high, this is the temperature in the cooling zone (runout table) usually installed in the hot rolling line. This is because the fine-grained structure is coarsened during the passage through the free running zone until the subsequent cooling. The cooling speed in the inter-stand cooling is not particularly specified, but the passing time from the cooling start after rolling to the final stand exit side is 2 times longer than the final stand if the stand interval of the normal hot rolling stand row is about 5 m. Even when the rolling is finished at the stand before the stage and the cooling is started immediately, if the plate passing speed of the steel plate is 600 mpm or more, it is 1 s or less, so that the average cold speed is 50 ° C./s or more. However, in fact, when rolling is completed at the stand before the second stage, there is a region that cannot be cooled even between the stands, such as the part passing the stand one stage before, so the cooling speed in the cooling zone between the stands Needs to be larger. For example, if the cooling rate in the cooling zone is set to 150 ° C./s or more, the temperature change of the present invention can be stably achieved.

  In addition, although other rolling conditions are not specifically limited, it is preferable that the upper limit of the rolling reduction of finishing final rolling shall be 30% or less from a shape and plate | board stability.

  The hot-rolled steel sheet that passed through the final stand after finishing rolling and cooling between the stands in a series of finishing stand rows is still sufficiently high in the normal cooling zone (runout table) because the steel sheet temperature is still sufficiently high. In the present invention, the winding temperature is set to 650 to 750 ° C. This is because when the temperature is lower than 650 ° C., solid-drawn C and N remain, so that the deep drawability is deteriorated. On the other hand, when the temperature exceeds 750 ° C., the structure becomes coarse during winding and the effect of refining is lost. It is.

  Next, subsequent manufacturing conditions following hot rolling will be described. Cold rolling may be performed under normal conditions, and the rolling rate is set to 60% or more for the purpose of ensuring deep drawability after annealing. If the rolling reduction exceeds 95%, workability deteriorates, so this is the upper limit.

  The annealing temperature of the continuous annealing line may be a normal condition, and is 650 ° C. or more and Ac3 transformation point or less. When the annealing temperature is less than 650 ° C., recrystallization is not completed, and the workability is deteriorated. On the other hand, when the annealing temperature exceeds the Ac3 transformation point, the workability is lowered due to the transformation. When producing an alloyed hot-dip galvanized steel sheet, there is no difference not only in the Sendzimir method including the annealing step but also in the method of producing Ni by pre-Ni plating on the annealed plate.

  Further, temper rolling after annealing or after plating may be performed under normal conditions, and is performed with the upper limit of 1% from the adjustment of the surface and shape.

  Each process after hot rolling as described above, that is, cold-rolled steel sheet manufacturing process, pickling-cold rolling-annealing-temper rolling, galvannealed steel sheet manufacturing process, pickling- Cold rolling, annealing, galvanizing, alloying treatment, and temper rolling may be independent processes or may be partially continuous processes. From the viewpoint of production efficiency, it is ideal that everything is continuous.

  Next, the present invention will be described with reference to examples.

<Example 1>
The steel of the present invention shown in Table 1 is melted and hot-rolled at a slab heating temperature of 1200 ° C., and is 4.0 mm thick at a finishing temperature of 940 ° C. at the last two stands from the last stand in the finishing stand row. Finish rolling so as to form a belt, and then start cooling at a cooling start time of 0.1 s that satisfies the formula (1) using the cooling equipment between the stands, so that the final stand outlet temperature becomes 855 ° C. Then, it was further cooled in a normal cooling zone (runout table) and wound at a winding temperature of 750 ° C. This was pickled and then cold rolled to form a 0.7 mm thick cold rolled sheet. Next, after annealing this at a heating temperature of 750 ° C. in a continuous annealing line, temper rolling was performed at a temper rolling rate of 0.4% to obtain a cold-rolled steel sheet.

The results are shown in Table 2. Here, the hot rolled sheet crystal grain size is an ASTM grain size number measured from a cross-sectional structure obtained by taking a sample for microstructural observation from a hot rolled steel sheet as an intermediate product. The column of material properties is the tensile properties of the cold-rolled steel sheet, and the average r value and Δr value were investigated as an index of deep drawability. Here, the average r value and Δr value are the respective r values (r−L, r−C, R in the L direction parallel to the rolling direction, the C direction in the perpendicular direction, and the uniform elongation region in the X direction in the 45 ° direction. r−X) was calculated using the following equations (4) and (5).
Average r value = {(r−L) + (r−C) + 2 × (r−X)} / 4 (4)
Δr value = {(r−L) + (r−C) −2x (r−X)} / 2 (5)
According to Table 2, the steel A to G hot rolled sheets of the conditions of the present invention have a fine grain size of 7.5 or more, and are uniform throughout (the thickness ratio of the coarse grain region is 0%) or coarse. Since the plate thickness ratio of the grain region is 20% or less, the average r value of the cold rolled steel sheet is as high as 2.0 or more, the Δr value is as low as 0.6 or less, and a cold rolled steel sheet excellent in deep drawability is obtained. Has been obtained. On the other hand, the amount of C is low and the steel H outside the present invention has a grain size of 6.9 and is coarse, and the average r value is low. The amount B is high steel K, C content and the Ti content is high steel I, Nb amount is high steel J is the grain size of the hot-rolled sheet is at 7.5 number higher and fine, Ya recrystallization during annealing As a result of subsequent insufficient grain growth, the elongation and average r value were low, the Δr value was high, and the deep drawability was poor.

<Example 2>
Using the slabs of steel A (Ar3: 905 ° C) and steel B (Ar3: 900 ° C) in Table 1, hot rolling is performed at a slab heating temperature of 1200 ° C, and the two stands before the last stand in the finishing stand row The finish rolling was finished so as to obtain a steel strip of 3.5 mm thickness at various finishing temperatures shown in Table 3, and then cooling was started at various cooling start times using cooling equipment between the stands. The product was cooled to the outlet temperature, then further cooled in a normal cooling zone (runout table) and wound at various winding temperatures. This was pickled and then cold-rolled to obtain a cold-rolled sheet having a thickness of 0.65 mm. Subsequently, this was annealed at a heating temperature of 770 ° C. in a continuous annealing line, and then subjected to temper rolling at a temper rolling rate of 0.4% to obtain a cold-rolled steel sheet. Further, for steel B, this cold-rolled steel sheet was used as a raw material, Ni was pre-plated, heated, immersed in a zinc bath, wiped, and then alloyed at 530 ° C. for 12 seconds, and again 0.4% Temper rolling was performed at a temper rolling ratio to obtain an alloyed hot-dip galvanized steel sheet.

The results are shown in Table 4. The hot rolled sheets of the present invention conditions A1, A4 and B2, B3 are fine grains having a grain size number of 7.5 or more, and the coarse grain region existing in the surface layer portion is 10% or less on the front and back sides in terms of the plate thickness ratio. Both the obtained cold rolled steel sheet of steel A and the galvannealed steel sheet of steel B show a high average r value and a low Δr value. On the other hand, A5 and B5, which are the conditions of x in FIG. 1, are fine grains with a grain size of 7.5 or more inside the thickness of the hot-rolled sheet, but the coarse grain region existing in the surface layer portion is the plate thickness. The ratio of the front and back surfaces was over 20%, and the average r value as the final material was not so high, and the Δr value was high. On the other hand, A6 and B6, which are the conditions of Δ in FIG. 1, are coarse grains with a total grain thickness of 7.0 or less in the total thickness, and the average r value of the final material is still not high, and the Δr value Was expensive.

Claims (6)

% By mass
C: 0.0010 to 0.0025%,
Si: 0.01 to 0.1%,
Mn: 0.05 to 0.15%,
P: 0.001 to 0.015%,
S: 0.001 to 0.01%,
Al: 0.005 to 0.05%,
N: 0.001 to 0.003%
A slab having a composition comprising at least one of Ti and Nb in a range of Ti: 0.01 to 0.05% and Nb: 0.005 to 0.02%, the balance being Fe and inevitable impurities When producing a cold-rolled steel sheet by performing hot rolling, cold rolling, and continuous annealing, finishing is performed at a stand that is two or one stage prior to the last stand in the hot rolling stand row where hot rolling is continuously performed. When cooling between the end of rolling and the final stand, cooling is started under the condition that the finishing temperature (T) and the cooling start time (t) satisfy the following formula (1), and the exit side at the final stand The manufacturing method of the cold-rolled steel plate excellent in deep drawability characterized by winding temperature at 650-750 degreeC below temperature (Ar3 transformation point-30 degreeC).
40 / (log [t (seconds)] + 2) -20 ≦ T-Ar3 (° C.) ≦ 60 / (log [t (seconds)] + 2) (1)
However, 0.1 ≦ t (seconds) ≦ 0.7 Furthermore, the slab is mass%,
B: 0.0002 to 0.0010%
The manufacturing method of the cold-rolled steel plate excellent in the deep drawability of Claim 1 characterized by the above-mentioned.   Even in the case where there is a coarse grain region in the entire thickness of the metal structure of the hot-rolled steel sheet, or a coarse grain region in the surface layer part, the coarse grain region is 20% or less in total in the front and back sides as a sheet thickness ratio. The manufacturing method of the cold-rolled steel plate excellent in the deep drawability of Claim 1 or 2. % By mass
C: 0.0010 to 0.0025%,
Si: 0.01 to 0.1%,
Mn: 0.05 to 0.15%,
P: 0.001 to 0.015%,
S: 0.001 to 0.01%,
Al: 0.005 to 0.05%,
N: 0.001 to 0.003%
A slab having a composition comprising at least one of Ti and Nb in a range of Ti: 0.01 to 0.05% and Nb: 0.005 to 0.02%, the balance being Fe and inevitable impurities , Hot rolling, cold rolling, continuous annealing, hot dip galvanizing, alloying heat treatment, to produce an alloyed hot dip galvanized steel sheet, the last in a hot rolling stand row in which hot rolling is continuously performed When finishing rolling is completed at the stand two or one stage before the stand and then cooled to the final stand, the finishing temperature (T) and the cooling start time (t) satisfy the following formula (1). The alloyed hot-dip galvanized steel sheet excellent in deep drawability, characterized in that cooling is started under conditions, the outlet temperature in the final stand is (Ar3 transformation point −30 ° C.) or less, and winding is performed at 650 to 750 ° C. How to make .
40 / (log [t (seconds)] + 2) -20 ≦ T-Ar3 (° C.) ≦ 60 / (log [t (seconds)] + 2) (1)
However, 0.1 ≦ t (seconds) ≦ 0.7 Furthermore, the slab is mass%,
B: 0.0002 to 0.0010%
The manufacturing method of the galvannealed steel plate excellent in the deep drawability of Claim 4 characterized by the above-mentioned.   Even in the case where there is a coarse grain region in the entire thickness of the metal structure of the hot-rolled steel sheet, or a coarse grain region in the surface layer part, the coarse grain region is 20% or less in total in the front and back sides as a sheet thickness ratio. The manufacturing method of the galvannealed steel plate excellent in the deep drawability of Claim 4 or 5.