JPH09296221A - Production of cold rolled steel sheet and galvanealed steel sheet excellent in uniformity of workability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve uniformity in the workability of a steel sheet by prescribing the contents of elements in a steel and executing coiling and recoiling after rough rolling. SOLUTION: In the case of >=0.004% S and Ti*=Ti-3.42N, it is effective for the uniformity of the workability of the steel to satisfy Ti*/S>=1 and <=0.15% Mn. Furthermore, after rough rolling, temporary coiling and recoiling are very effective for increasing the uniformity of its workability, but, for sufficiently showing the above effect, it is important that (the higher value between the solid solution C content L ((C-Ti*/8) before the coiling obtd. from Ti*/C>9 or from calculation and (C-0.8S×12/32)) satisfies L<0.0005. Moreover, it is important that the ratio of the amt. of S precipitated as MnS among the whole S content after the coiling following the hot rolling (S% as MnS/the whole 5%) satisfies <=0.2. By these conditions, the solid solution C can be reduced before the coiling after the finish rolling to prevent deterioration in the material of the product.

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, a hot-dip galvanized steel sheet, and a method for producing an alloyed hot-dip galvanized steel sheet, in which the workability in the coil is extremely small. Applications of the steel sheet produced by the present invention are automobiles, home appliances, building materials and the like, and when the high-strength steel sheet produced by the present invention is applied for automobiles, the sheet thickness can be reduced, It can improve fuel efficiency and contribute to global environmental problems, which have become a big problem in recent years.

[0002]

2. Description of the Related Art As disclosed in Japanese Patent Application Laid-Open No. 58-185752, ultra-low carbon steel sheets have excellent workability and are therefore widely used for applications such as automobiles. In addition, devices for further improving the workability have been devised by defining the components and the production method of the ultra-low carbon steel. For example, JP-A-3-130323 and JP-A-4
In JP-A-143228 and JP-A-4-116124, C, Mn and P in an ultra low carbon steel containing Ti are described.
It has been disclosed that excellent workability can be obtained by reducing the amount of the like. 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.

From the viewpoint of reducing variations in materials, Japanese Patent Laid-Open Nos. 3-170618 and 4-5.
There is one described in Japanese Patent No. 2229. However, in these inventions, it is necessary to increase the rolling reduction in the finish hot rolling or to increase the winding temperature after the hot rolling, so that a large load is applied to the hot rolling process. Therefore, the inventors of the present invention, as shown in Japanese Unexamined Patent Publication No. 8-3686, have Ti ₄ in the γ region.
By positively utilizing the precipitation of C ₂ S ₂ , most of the solid solution C was fixed before winding, and the technique of significantly improving the uniformity of workability was established. However, even with this method, Ti ₄ C
Precipitation of ₂ S ₂ is not perfect, and when high-temperature winding is performed, a small amount of solute C that remains in the center of the coil forms fine carbides, which causes the material to deteriorate rather than the end. There were cases.

The problem of deterioration of the quality of the end member is the same in the case of a good workability and high strength cold rolled steel sheet reinforced with P or Si. Japanese Patent Laid-Open No. 59-3182 discloses a technique relating to these steel plates.
7, JP-A-59-38337, JP-B-57
No. 575794 and Japanese Patent Application Laid-Open No. 61-276931, but none of them has been devised to improve the width of the coil and the yield at the end in the longitudinal direction. It is not a technique for positively utilizing Ti sulfide as in the present invention.

[0005]

In the Ti-added ultra-low carbon steel, C is precipitated as TiC by hot rolling after hot rolling to reduce the solid solution C, thereby ensuring the material after cold rolling and annealing. It was the usual way to do it.
This is the same when strengthening with P or Si. However, at the width end and the lengthwise end of the hot rolled coil, cooling during winding and after winding progresses remarkably rapidly, so that TiC precipitation is not sufficient and the material deteriorates in these portions. There was a problem that it would end up. In order to solve this problem, a technology has been developed to accelerate the precipitation of carbosulfide in the γ region, but it is difficult to completely remove the solid solution C before winding, and therefore high temperature winding is required. If this is done, the solid solution C slightly remaining in the center of the coil may form fine carbides and the material quality may deteriorate, and it is difficult to ensure extremely high workability over the entire length of the coil under any winding conditions. Met.

The present invention does not depend on the winding temperature,
An object of the present invention is to provide a method for producing a cold-rolled steel sheet, a hot-dip galvanized steel sheet, and an alloyed hot-dip galvanized steel sheet, in which deterioration of end material is extremely small in the width and the entire length in the longitudinal direction of the coil.

[0007]

In order to solve the above problems, the inventors of the present invention positively utilize S in ultra-low carbon steel and optimize the ratio of Ti content to S content. To determine the amount of Mn, and to perform rolling and unwinding after rough rolling to precipitate specific precipitates and obtain a high r-value cold-rolled steel sheet with excellent workability uniformity. did.

As a result, S ≧ 0.004% and Ti *
= Ti-3.42N, it has been found that Ti * / S ≧ 1 and Mn ≦ 0.15% are effective. In addition, after rough rolling, it is very effective to wind the coil once and rewind it in order to improve the uniformity of workability.
To maximize the effect of winding and rewinding, T
i * / C> 9 or the amount of dissolved C before winding obtained by calculation L ((C-Ti * / 8) and (C-0.8S × 12/3)
It has been found that it is very important that the larger value of 2) satisfies L <0.0005.

Further, after winding after hot rolling, the ratio of the amount of S precipitated as MnS in the total amount of S, K (= (S% a
It has been found that it is extremely important that (s MnS) / (total S%)) satisfies K ≦ 0.2 in order to obtain the uniformity of the material. 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 after rough rolling, it is once wound into a coil in the low temperature γ region and then unwound to introduce strain to Ti ₄
By accelerating the precipitation of C ₂ S ₂ , the solid solution C is sufficiently reduced before the winding of the finish hot rolling. As a result, even if the end of the coil 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 the deterioration of the material caused by the precipitation of fine carbides is reduced. Further, in the case of the steel of the present invention, most of C is fixed as Ti ₄ C ₂ S _{2 in} the hot rolling process before winding, so cold rolling having high workability over the entire length of the coil does not depend on the winding temperature. A steel plate can be obtained.

The present invention is constructed on the basis of the above findings, and the gist thereof is as follows. (1)% by weight, C: 0.0005 to 0.007%, S
i: 0.005 to 0.8%, Mn: 0.01 to 0.15
%, P: 0.2% or less, S: 0.004 to 0.02%,
Al: 0.005 to 0.1%, N: 0.007% or less, and when Ti is Ti * = Ti-3.42N, Ti * / S ≧ 1 and Ti * / C > 9, or the calculated amount L of solid solution C before winding (the larger value of (C-Ti * / 8) and (C-0.8S × 12/32)) is L <
The condition of 0.0005 is satisfied, and Ti: 0.01 to
Steel containing 0.1% in the range, the balance being iron and unavoidable impurities is heated at 1250 ° C. or lower and rough-rolled, then the rough bar is wound into a coil and unwound, and then the finishing temperature is reached. Finishing rolling of ≧ (Ar ₃ −100) ° C. is performed, and winding is performed in a temperature range of room temperature to 800 ° C., and the ratio of the amount of S precipitated as MnS in the total amount of K (= (S% as MnS))
/ (Total S%)) is set to K ≦ 0.2, and after pickling, the rolling reduction is ≧ 6.
A method for producing a cold-rolled steel sheet having excellent workability uniformity, which comprises cold rolling at 0% and annealing at a recrystallization temperature or higher.

(2) As a steel component, further, in% by weight,
B: 0.0001 to 0.0030% is contained, The manufacturing method of the cold-rolled steel sheet excellent in the uniformity of workability of the preceding clause (1) characterized by the above-mentioned. (3) Prior to finish rolling, the trailing end of the preceding material and the leading end of the following material are joined to be subjected to finishing rolling, and the workability is uniform as described in (1) or (2) above. Excellent cold rolled steel sheet manufacturing method.

(4) Instead of the annealing after cold rolling described in any one of (1) to (3) above, annealing is performed at a recrystallization temperature or higher in a continuous hot dip galvanizing line having an in-line annealing furnace. A method for producing a hot-dip galvanized steel sheet having excellent workability uniformity, which comprises subjecting the steel sheet to galvanizing and performing galvanizing during the cooling process. (5) After the zinc plating described in (4) above, further 40
A method for producing an alloyed hot-dip galvanized steel sheet excellent in uniformity of workability, which comprises performing an alloying treatment in a temperature range of 0 to 600 ° C.

The method of manufacturing a cold rolled steel sheet according to the present invention is
Based on the ultra-low carbon steel with i added, or the one strengthened with P or Si, the S content, Mn content, Ti content, and
By limiting the amount of specific sulfides, and further performing rough rolling and winding and unwinding, C is sufficiently precipitated before winding after hot rolling, and the workability in the longitudinal and width directions of the coil is uniform. A cold rolled steel sheet having excellent properties is provided. The reasons for the limitation will be described below.

First, the reasons for limiting the chemical components will be described. As the amount of C increases, the amount of Ti, which is a carbide-forming element for fixing it, must be increased, which increases the cost, and solid solution C remains at the end of the hot-rolled coil. Or, since a large amount of fine carbides are precipitated in the grains, the grain growth property is hindered and the workability is deteriorated, so 0.007% is made the upper limit. From this point of view, 0.
003% or less is preferable. Further, the lower limit of the amount of C is set to 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, if the amount exceeds 0.8%, YP sharply increases,
0.8% as the elongation decreases and the plating properties are significantly impaired.
Is the upper limit. For hot-dip galvanizing, the content is preferably 0.3% or less from the viewpoint of plating properties. If high strength (350 MPa or more in TS) is not required, 0.1% or less is more preferable. The lower limit of the amount of Si is 0.005% for the reason of steelmaking cost.

Mn is one of the most important elements in the present invention.
One. That is, when Mn exceeds 0.15%, Mn
Since the amount of precipitation of S increases and the amount of precipitation of Ti ₄ C ₂ S ₂ decreases as a result, even if high-temperature winding is performed, the cooling rate is high at the end of the hot-rolled coil and solid solution C is generated. A large amount remains, or a large number of fine carbides are deposited to significantly deteriorate the material. Therefore, the upper limit of the amount of Mn is preferably 0.15%, more preferably less than 0.10%. On the other hand, if the Mn content is less than 0.01%, hot cracking is induced and the steelmaking cost is increased, so the lower limit is 0.01.
%.

Similar to Si, P is also positively utilized as an inexpensive strengthening element depending on the target strength level. However, if the amount of P exceeds 0.2%, it causes cracking during hot or cold working, and the secondary workability is significantly deteriorated. Further, since the alloying rate of hot dip galvanization is significantly delayed, the upper limit of the P content is set to 0.2%. From the above viewpoints, the content 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%. When the amount of S is less than 0.004%, the amount of precipitation of Ti ₄ C ₂ S ₂ is not sufficient, and of course when winding at low temperature,
Even if wound at high temperature, solid solution C is generated at the end of the coil.
Remains in a large amount, or fine precipitation of TiC or NbC impedes grain growth during annealing, resulting in significant deterioration of workability. On the other hand, if the amount of S exceeds 0.02%, hot cracking tends to occur, and more MnS and TiS are precipitated than the precipitation of Ti ₄ C ₂ S _2. Therefore, the same problem occurs and the workability is not uniform. Not secured. From this viewpoint, the S amount is 0.0
04-0.012% is a more preferable range.

By the way, S has an important relationship with the amount of Ti, and when Ti * = Ti-3.42N, Ti * / S
≧ 1. When Ti * / S is less than 1, precipitation of Ti ₄ C ₂ S ₂ is not sufficient and a large amount of TiS or MnS is precipitated, so that it becomes difficult to precipitate C before winding after hot rolling. Therefore, at the end of the hot-rolled coil, a large amount of solid solution C remains or fine carbide precipitates even if the coiling temperature is increased, resulting in extreme deterioration of the material. Ti * / S is preferably more than 1.2, and is 1.5 or more when a further effect is desired.

Al is at least 0.005 as a deoxidizer.
% Must be added. However, if it exceeds 0.1%, not only the cost is increased, but also inclusions are increased and the workability is deteriorated. N is the same as C
Since it is necessary to increase the amount of nitride forming elements such as i and Al, the cost becomes high, and the ductility is deteriorated due to the increase of precipitates. Therefore, the upper limit of the N amount is set to 0.
007%. More preferably, it is 0.003% or less.

0.01 to 0.1% of Ti is added. T
If the amount of i is less than 0.01%, Ti_FourC _TwoS_TwoBefore winding
Cannot be deposited on the
Even if added, not only the effect of fixing C is saturated,
It is difficult to secure the peeling resistance of the plating layer during molding
become. Ti_FourC_TwoS_TwoOf sufficient precipitation
Therefore, it is preferable to add more than 0.025% of Ti.
Yes.

In order to precipitate all the solid solution C as carbosulfide during hot rolling, especially during winding and unwinding after rough rolling, T
It is important to satisfy the relationship i * / C> 9.
However, even if this relationship is not satisfied, if the amount of solute C at the time of winding after finish rolling is less than 5 ppm, that is, the amount of solute C before winding L ((C-Ti * / 8 )
And (C−0.8S × 12/32, whichever is larger) is L
If the relationship <0.0005 is satisfied, a sufficient effect can be obtained. In the formula of C−0.8S × 12/32, 0.8 is a coefficient that represents the amount of S that did not become MnS, and 12/32 is the amount of S that is necessary to combine C with 1: 1. It is a coefficient.

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 after winding after hot rolling is K (= (S% as MnS) /
(Total S%) must be K ≦ 0.2. Further, from this viewpoint, it is desirable that K <0.15. This (S% as MnS) is obtained 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 to measure the Mn amount (= X
(G)). At this time, assuming that the amount of electrolysis of the entire sample is Y (g), (S% as MnS) = X / Y
It becomes x32 / 55x100 (%).

B strengthens the grain boundaries and improves the secondary workability, so it is added in a range of 0.0001 to 0.0030% as required. If the addition amount of B is less than 0.0001%, its effect is poor, and even if it exceeds 0.003%, its effect is saturated and ductility deteriorates. Raw materials for obtaining the above components are not particularly limited, but scraps may be used as raw materials other than the method of preparing the components by iron ore as a raw material, blast furnace and converter, and this may be melted in an electric furnace. . When scrap is used as all or part of the raw material, Cu, Cr, Ni, Sn, Sb, Zn, P
Elements such as b and Mo may be contained.

Next, the reasons for limitation regarding the manufacturing process will be described. The slab to be subjected to hot rolling is not particularly limited. That is, it may be a continuous cast slab or a thin slab caster. In addition, continuous casting-direct rolling (CC-D
Also applicable to processes like R).

The heating temperature in hot rolling is Ti ₄ C ₂
In order to increase the amount of S ₂ deposited as much as possible, it is essential to set the temperature to 1250 ° C. or lower. From this viewpoint, preferably 1
200 ° C or lower is preferable. Also, more preferably 1150
C or lower is good. After the rough rolling is finished, the rough bar is once wound into a coil. At this time, heating and holding may be performed at 1100 ° C. or lower, or isothermal holding may be performed in a coil box or the like. It may also be kept in the atmosphere. From the viewpoint of surface properties, it may be held in an inert gas atmosphere. The introduction of strain by winding and unwinding and the retention in the low temperature γ region significantly promote the precipitation of Ti ₄ C ₂ S ₂ ,
Material deterioration of the width end and the lengthwise end of the hot-rolled coil is significantly reduced, and the thickness accuracy of the hot-rolled sheet is improved.

The rewound coil is left as it is (Ar ₃ -1
Finish rolling may be performed at a finishing temperature of 00) ° C. or higher,
A rough bar may be joined and continuous hot rolling may be performed. By joining the rough bars and performing finish rolling continuously,
Since the portion corresponding to the coil end portion at the time of winding, which causes deterioration of the material, is reduced, the yield is improved and the plate thickness accuracy of the hot rolled plate is also improved.

The finishing temperature in finish rolling needs to be (Ar ₃ -100) ° C. or higher in order to secure press formability. The present invention has a feature that workability can be secured even if the winding temperature after hot rolling is low. That is, according to the present invention, most of C is precipitated as Ti ₄ C ₂ S _{2 in} the process from the heating of hot rolling to the cooling after hot rolling, and the material is greatly improved even at high temperature winding. There is no such thing. 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 below room temperature only requires excessive equipment and has no particular effect. Also, 8
If the coiling temperature exceeds 00 ° C, the crystal grains of the hot-rolled sheet become coarse, the oxide scale on the surface becomes thick, and the pickling cost rises. Therefore, the upper limit is 800 ° C. From this point of view, and in order to prevent the deterioration of the material due to the precipitation of the P compound, the winding is preferably performed at a temperature of 650 ° C. or less. In order to completely avoid the precipitation of harmful compounds, it is more preferable to wind at a temperature of 500 ° C or lower. Furthermore, in order to reduce the time it takes for the temperature to drop to near room temperature after winding,
It is preferable to wind it at 00 ° C. or less. 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.
For the same reason, the recrystallization annealing temperature in the continuous hot dip galvanizing line is also set to the recrystallization temperature or higher. Hot dip galvanizing
From the viewpoint of plating properties and plating adhesion, 420-500 ° C
It is better to apply at the temperature of. 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 the weldability will be poor, and if it is too high, the plating peeling resistance will be deteriorated. It is preferable to carry out in the range of. In order to obtain a plating layer having more excellent adhesion, alloying is preferably performed 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 applied.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below with reference to Examples. [Example 1] Ti-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. After heating and coiling after the rough rolling and immediately rewinding, hot rolling is performed so that the finishing temperature is 926 ° C. and the plate thickness is 3 mm, and cooling is performed at a run-out table at a cooling rate of 25 ° C./s. The coil was wound at various winding temperatures shown in Tables 3 and 4 (continued from Table 3). A sample was cut out from the center of the coil in the longitudinal direction, and the following processing 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. The annealing conditions were as follows: annealing temperature: 790 ° C., soaking: 50 s, cooling rate: about 60 ° C./s up to room temperature. Then, temper rolling was performed at a rolling reduction of 0.8%, and the steel was subjected to a tensile test. Here, the tensile test and the measurement of the average Rank Ford value (hereinafter, r value) are based on JIS.
It carried out using the No. 5 test piece of Z2201 description. In addition,
The r value was evaluated at an elongation of 15%, and the values in the rolling direction (L direction), the direction perpendicular to the rolling direction (C direction), and the 45 ° direction (D direction) with respect to the rolling direction were measured. It was calculated. The test results are summarized in Tables 3 and 4.

R = (rL + 2rD + rC) / 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 steels having the components of the present invention can obtain extremely excellent materials at any coiling temperature as long as the temperature is 800 ° C. or lower. On the other hand, it was revealed that the material was inferior when the comparative steel J was wound at a high temperature and the other comparative steels were taken at a low winding temperature. [Example 2] Steels A, B, E, H, J used in Example 1
The material characteristics in the longitudinal direction of N cold rolled coils were investigated. The test results are summarized in Table 5.

[0038]

[Table 5]

As is apparent from Table 5, 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 comparative steel J, the material at the center of the coil is lower than that at the end, and in the other comparative steels, the material is significantly deteriorated toward the end of the coil. The material became inferior. It is clear that this tendency becomes more pronounced at the ends.

[Example 3] Steels B and D in Tables 1 and 2
The slabs of E, G, H and N are heated at 1250 ° C., after the rough rolling is finished, they are wound into a coil and immediately rewound, and then finish rolling is performed so that the finishing temperature is 915 ° C. and the plate thickness is 3 mm. After cooling at a cooling rate of 20 ° C./s on a run-out table, coiling at 400 ° C., heating at 1250 ° C., and hot rolling at a finishing temperature of 915 ° C. and a plate thickness of 3 mm , Cooling rate at run-out table 20
After cooling at 0 ° C / s, the sample was cut out from the central portion in the longitudinal direction of the coil wound at 400 ° C. 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: 810 ° C., soaking: 6
0s, cooling rate: from annealing temperature to 640 ° C, about 5 ° C /
s, about 70 ° C / s from 640 ° C to room temperature. Then, temper rolling was performed at a reduction rate of 0.7%, and test pieces were sampled from each position of 10 m from the front end, 10 m from the center and 10 m from the end of the sample, and the same test as in Example 1 was performed. It was
The results are summarized in Table 6.

[0041]

[Table 6]

From this, in the case of H and N whose components are out of the range of the present invention, the absolute value of the r value is low regardless of the presence or absence of coil winding and rewinding after rough rolling, and the end material is further deteriorated. However, in the examples of the present invention for steels B, D, E, and G, the quality of the end member is rather improved, and the absolute value of the r value is higher than that in the case where winding and unwinding are not performed. [Example 4] Steels B, E, F, H, K and M in Table 1 were hot-rolled under the same conditions as in Example 1 (winding temperature:
(590 ° C.), followed by pickling with an actual machine, cold rolling with a reduction rate of 80%, and passing through a continuous hot dip galvanizing line with an in-line annealing method. At this time, the maximum heating temperature is 820 ° C
After heating in between, cooling was performed, conventional hot dip galvanizing was performed at 470 ° C. (Al concentration in the bath was 0.12%), and further heating was performed and alloying treatment was performed at 550 ° C. for about 15 seconds. further,
After 0.7% temper rolling, the mechanical properties and plating adhesion were evaluated. The results obtained are summarized in Table 7.

Here, the plating adhesion was determined by 180 adhesion bending, the peeling condition of the zinc coating was adhered to the bent portion after the adhesive tape was adhered, and then peeled off to determine the amount of the peeled plating adhered to the tape. The evaluation was based on the following five levels. 1: Large peeling, 2: During peeling, 3: Small peeling, 4: Small amount of peeling,
5: No peeling

[0044]

[Table 7]

As is clear from Table 7, 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 variation depending on the coil portion was large.

[0046]

As described above, according to the present invention, the coiling temperature after hot rolling can be lowered and a material having excellent uniformity in the longitudinal and width directions of the coil can be obtained. The truncated coil end can be the product. Further, when the high-strength steel sheet of the present invention is applied to an automobile, the sheet thickness can be reduced, which leads to an improvement in fuel consumption and can contribute to a global environmental problem that has become a serious problem in recent years. , Its value is great.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical indication // C22C 38/00 301 C22C 38/00 301T 38/14 38/14

Claims (5)

[Claims] 1. By weight%, C: 0.0005 to 0.007%, Si: 0.005 to 0.8%, Mn: 0.01 to 0.15%, P: 0.2% or less, S: 0.004 to 0.02%, Al: 0.005 to 0.1%, N: 0.007% or less, and when Ti is Ti * = Ti-3.42N, Ti * / S ≧ 1 and Ti * / C> 9, or the larger of calculated amount L of solid solution C before winding ((C-Ti * / 8) and (C-0.8S × 12/32)) Value) is L <
The condition of 0.0005 is satisfied, and Ti: 0.01 to
Steel containing 0.1% in the range, the balance being iron and unavoidable impurities is heated at 1250 ° C. or lower and rough-rolled, then the rough bar is wound into a coil and unwound, and then the finishing temperature is reached. Finishing rolling of ≧ (Ar ₃ −100) ° C. is performed, and winding is performed in a temperature range of room temperature to 800 ° C., and the ratio of the amount of S precipitated as MnS in the total amount of K (= (S% as MnS))
/ (Total S%)) is set to K ≦ 0.2, and after pickling, the rolling reduction is ≧ 6.
A method for producing a cold-rolled steel sheet having excellent workability uniformity, which comprises cold rolling at 0% and annealing at a recrystallization temperature or higher. 2. A cold rolled steel sheet excellent in workability uniformity according to claim 1, further comprising B: 0.0001 to 0.0030% by weight as a steel component. Production method. 3. The excellent workability uniformity according to claim 1 or 2, wherein the trailing end portion of the preceding material and the leading end portion of the following material are joined to each other for finishing rolling before the finishing rolling. Cold rolled steel sheet manufacturing method. 4. Instead of annealing after cold rolling according to any one of claims 1 to 3, annealing is performed at a recrystallization temperature or higher in a continuous hot dip galvanizing line having an in-line annealing furnace,
A method for producing a hot-dip galvanized steel sheet having excellent workability uniformity, which comprises performing galvanization during a cooling process. 5. Production of a galvannealed steel sheet excellent in workability uniformity, which is characterized by further performing an alloying treatment in a temperature range of 400 to 600 ° C. after the galvanizing according to claim 4. Method.