JPH083686A - Cold rolled steel sheet excellent in uniformity of workability and its production - Google Patents

Abstract

PURPOSE:To prevent the occurrence of material deterioration at the edges in the width and the longitudinal direction of a rolled coil and to improve rolling yield by adding Ti to an ultralow carbon steel and optimizing S content and Ti content in the steel, respectively. CONSTITUTION:This steel has a composition which consists of, by weight ratio, 0.0005 to 0.007% C, 0.03 to 0.15% Mn, 0.005 to 0.8% Si, 0.005 to 0.1% Al, <=0.2% P, 0.004 to 0.02% S, <=0.007% N, 0.01 to 0.1% Ti, and the balance Fe with inevitable impurities and satisfies the condition of Ti*/S=1.5 when Ti* represents (Ti-3.42N) and in which the proportion of the quantity of S precipitated in the form of MnS in the total S quantity, K=(S% as MnS)/(total S%), is regulated to <=0.2. Further, preferred quantity of precipitated C is 0.0003%. This steel is hot-rolled at heating temp. of <=1200 deg.C and at finishing temp. of >=(Ar3-100) deg.C, coiled at a temp. between room temp. and 800 deg.C, cold-rolled at 60% draft, and annealed at a temp. not lower than the recrystallization temp.

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 the same, in which the workability in the coil is extremely small. The applications of these steel sheets are automobiles, home appliances, building materials, etc. is there. Further, when the high-strength steel plate of the present invention is applied to an automobile, the plate thickness can be reduced, which leads to an improvement in fuel consumption and a global environmental problem that has become a serious problem in recent years. it can.

[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, 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 added.
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, and it is not the technique of positively utilizing the Ti sulfide as in the present invention. From the viewpoint of reducing variations in materials, JP-A-3-170618 and JP-A-4-5222 are used.
There is a technique described in Japanese Patent No. 9 publication. 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.

The effect of the present invention is similarly exhibited in a good workability high strength cold rolled steel sheet reinforced with P or Si. A technique relating to these steel sheets is disclosed in Japanese Patent Laid-Open No. 59-59
-31827, JP-A-59-38337,
JP-B-57-57945, JP-A-61-2769
No. 31, etc., but none of them has been devised to improve the yield of the coil in the width and end portions in the longitudinal direction, and the Ti sulfide as in the present invention is positively utilized. It is not a technique to do.

[0004]

Problems to be Solved by the Invention Addition of Ti or Ti,
In the case of Nb-added ultra-low carbon steel, it is a normal method to precipitate C as TiC or NbC by high temperature winding after hot rolling and reduce the solid solution C to secure the material after cold rolling and annealing. Was there. 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 proceeds remarkably rapidly, so precipitation of TiC and NbC is not sufficient, and the material in these portions is There was a problem of deterioration. 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.

It is an object of the present invention to provide a cold-rolled steel sheet, a hot-dip galvanized steel sheet, and a method for producing the same, in which deterioration of the material in the width and the longitudinal end portion of the coil is extremely small.

[0006]

In order to solve the above-mentioned problems, the inventors of the present invention positively utilize S in ultra-low carbon steel and optimize the ratio between the Ti amount and the S amount. In order to obtain a cold-rolled steel sheet excellent in uniformity of workability by precipitating a specific precipitate by defining the Mn content and further reducing fine precipitates.

As a result, S ≧ 0.004% and Ti *
= Ti-3.42N, it was found that Ti * / S ≧ 1.5 and Mn ≦ 0.15% are effective. Furthermore, after winding after hot rolling, the proportion of S precipitated as MnS in the total S is K = (S% as M
It has been found that it is extremely important that nS) / (total S%) satisfies K ≦ 0.2 in order to obtain the uniformity of the material. This is because the amount of MnS precipitated out of the total amount of S is reduced as much as possible, and Ti ₄ C ₂ S ₂ is positively precipitated, so that the solid solution C can be reduced before the hot rolling for finishing. Even if the end of the coil is rapidly cooled during winding after hot rolling, the solid solution C is sufficiently fixed before winding, so a large amount of solid solution C remains at the coil end, It is considered to be based on the mechanism that the deterioration of the material due to the precipitation of carbide is reduced.

Further, in the case of the steel of the present invention, a large amount of C is fixed as Ti ₄ C ₂ S _{2 in} the hot rolling process before winding,
It is better to positively lower the coiling temperature for the purpose of avoiding the precipitation of fine carbides, rather than precipitating a slight amount of the solid solution C remaining as a fine precipitate by hot coiling before the coiling in hot rolling. It has also been found that a better and more uniform material may be obtained.

The present invention has been made on the basis of these findings, and the gist thereof is as follows. (1)% by weight, C: 0.0005 to 0.007%, M
n: 0.03 to 0.15%, Si: 0.005 to 0.8
%, Al: 0.005 to 0.1%, P: 0.2% or less,
S: 0.004 to 0.02%, N: 0.007% or less,
Ti: 0.01 to 0.1% and Ti * = Ti-3.42
When N is set, Ti is contained in a range that satisfies Ti * / S ≧ 1.5, the balance is iron and inevitable impurities, and the ratio of the amount of S precipitated as MnS in the total amount of K is K = (S%
As MnS) / (total S%) is K ≦ 0.2, which is a cold-rolled steel sheet excellent in uniformity of workability.

(2) Further, the cold-rolled steel sheet excellent in workability uniformity according to the above (1), characterized in that the amount of C precipitated as carbide is 0.0003% or less. (3) The cold rolled steel sheet having excellent workability uniformity according to (1) or (2), further containing Nb: 0.002 to 0.05%. (4) Any one of the above (1) to (3), further containing B: 0.0001 to 0.0030%.
The cold-rolled steel sheet having excellent uniformity of workability according to the item.

(5) A steel having the composition described in any one of (1) to (4) is hot-rolled at a heating temperature ≤1200 ° C and a finishing temperature ≥ (Ar ₃ -100) ° C, A method for producing a cold-rolled steel sheet excellent in uniformity of workability, which comprises winding in a temperature range from room temperature to 800 ° C., cold rolling with a rolling reduction ≧ 60%, and further annealing at a recrystallization temperature or higher. . (6) Heating temperature of steel having the component described in any one of (1) to (4) above ≦ 1200 ° C., finishing temperature ≧ (Ar ₃
After hot rolling at −100) ° C., winding in the temperature range from room temperature to 800 ° C., and then cold rolling at a rolling reduction ≧ 60%, re-rolling in a continuous hot dip galvanizing line with an in-line annealing furnace. A method for producing a hot-dip galvanized steel sheet having excellent workability uniformity, which comprises performing annealing at a crystallization temperature or higher and performing galvanization during a cooling process.

(7) 400 to 6 after galvanizing
The method for producing a hot-dip galvanized steel sheet excellent in uniformity of workability according to (6), wherein the alloying treatment is performed in a temperature range of 00 ° C.

[0013]

The cold-rolled steel sheet and the method for producing the same according to the present invention are based on an ultra-low carbon steel containing Ti or Nb, or a steel obtained by strengthening it with P or Si, based on the amount of S and Mn.
Amount, Ti amount and specific sulfide amount are limited, and by sufficiently precipitating C after hot rolling and before winding, a high-strength cold steel with excellent uniformity in workability in the longitudinal and width directions of the coil. It provides a rolled steel sheet. 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 carbide-forming elements such as Ti and Nb for fixing it must be increased, which leads to an increase in cost and the amount of solid solution C at the end of the hot-rolled coil. Since it remains or a large amount of fine carbides such as TiC and NbC are precipitated in the grains, the grain growth property is hindered and the workability is deteriorated. Therefore, the C content is 0.007%
The content is set below, but preferably 0.003% or less. On the other hand, from the viewpoint of vacuum degassing treatment cost, the lower limit of the C content is 0.0005%.

Since Si is effective as an inexpensive strengthening element, it is used depending on the intended strength level. However, when the amount exceeds 0.8%, YP rises sharply,
The elongation lowers and the plating properties are significantly impaired, so the upper limit is made 0.8%. For hot dip galvanizing, the Si 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 reasons of steelmaking costs.

Mn is one of the most important elements in the present invention.
One. That is, when the Mn amount exceeds 0.15%, M
The nS precipitation amount increases, and as a result, the Ti ₄ C ₂ S ₂ precipitation amount decreases. Therefore, even if high temperature winding is performed, the cooling rate is high at the end of the hot-rolled coil and the solid solution C Remains in a large amount, or a large number of fine carbides are deposited, which significantly deteriorates the material. Therefore, the Mn content is 0.15% or less, and more preferably less than 0.10%. On the other hand, M
Even if the amount of n is less than 0.03%, no special effect is obtained,
In addition, the steelmaking cost is increased, so the lower limit is made 0.03%.

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, the alloying rate of hot dip galvanization is significantly delayed, so the upper limit is 0.2%. From the above viewpoint, it is more preferably 0.08% or less. Further, 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 a high temperature, a large amount of solute C remains at the end of the coil, and fine precipitation of TiC and NbC hinders 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 precipitate than the precipitation of Ti ₄ C ₂ S ₂ , causing the same problem, resulting in uniform workability. Is not secured. The S content is 0.004 to 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 ≧
Set to 1.5. When Ti * / S is less than 1.5, Ti ₄ C ₂
Precipitation of S ₂ is not sufficient and a large amount of TiS and MnS are 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 2, and more preferably 3 or more when a further effect is desired.

Al is at least 0.005 as a deoxidizer.
% Must be added. However, if the amount of Al exceeds 0.1%, not only the cost will increase, but also inclusions will increase and the workability will deteriorate. As with C, N needs to increase the amount of nitride-forming elements such as Ti and Al as in the case of C, which increases the cost, and the increase of precipitates leads to deterioration of ductility, so the smaller the content of N, the better. Therefore, the N content is set to 0.007% or less, preferably 0.003% or less.

Ti is added in an amount of 0.01 to 0.1%. Ti
If the amount is less than 0.01%, Ti ₄ C ₂ S ₂ cannot be precipitated before winding, and even if the amount exceeds 0.1%, the effect of fixing C is saturated. It becomes difficult to secure the peeling resistance of the plated layer during press molding. From the viewpoint of sufficiently precipitating Ti ₄ C ₂ S ₂ , it is preferable to add Ti in an amount of more than 0.025%.

In order to secure the material at the coil ends, the ratio of the amount of S precipitated as MnS in the total amount of S, K
= (S% as MnS) / (total S%) must be K ≦ 0.2. Furthermore, 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 that does not dissolve the sulfide (for example, a nonaqueous solvent). 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 (%).

Nb has the effect of atomizing the hot rolled sheet and fixing C and improves the deep drawability, so it is added in an amount of 0.002 to 0.05% if necessary. If the added amount is less than 0.002%, the effect of improving the workability is slight. On the other hand, if Nb exceeds 0.05%, the effect of improving the deep drawability is saturated, and the ductility is significantly deteriorated. B strengthens the grain boundary and improves secondary workability, so 0.0001 to 0.0030% is added if necessary. B amount is 0.0
If less than 001%, the effect is poor, and 0.003%
Even if added excessively, its effect is saturated and ductility deteriorates.

The amount of C precipitated as carbide is 0.0003
%, The amount of fine precipitates increases, the growth of crystal grains during annealing is suppressed, and the r value decreases. Therefore, if necessary, the amount of C precipitated as carbides is set to 0.0003% or less. From such a viewpoint, the amount of C precipitated as carbide having a diameter of 10 nm or less is preferably 0.0001% or less, and the amount of C precipitated as carbide having a diameter of 20 nm or less is preferably 0.0002% or less. The amount of C precipitated as carbide (= C%) is determined by chemical analysis of all precipitates obtained by electrolytic extraction in a non-aqueous solvent,
Ti content analyzed as a compound of Ti (= T%)
Is calculated by subtracting the amount of Ti precipitated as TiN (= T1%) and the amount of Ti precipitated as Ti ₄ C ₂ S ₂ (= T2%). Further, when Nb is detected by the same chemical analysis, its amount (= N1%) is also added. Therefore, C = (T-T
1−T2) / 4 + 12/93 × N1. Where T
1 is given by T1 = total N% × 3.42, and T2 is T2 by analyzing the amount of S (= S) in the extraction residue.
= S × 3.

The 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 using iron ore as the raw material and by a blast furnace or a converter. Good. When scrap is used as all or part of the raw material, Cu, Cr, Ni, S
Elements such as n, Sb, Zn, Pb and Mo may be contained.

Next, the reasons for limitation regarding the manufacturing process 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) in which hot rolling is performed immediately after casting
Suitable for processes like.

The heating temperature in hot rolling is Ti ₄ C ₂
In order to increase the precipitation amount of S ₂ as much as possible, it is essential to set the temperature to 1200 ° C or lower. From this viewpoint, it is preferably 1150 ° C. or lower. The finishing temperature in hot rolling is
In order to secure press formability, it is necessary to set the temperature to (Ar ₃ -100) ° C or higher. 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 if the coiling 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. There is nothing to do. 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. Also, 8
If the temperature exceeds 00 ° C, the crystal grains of the hot-rolled sheet become coarse and the oxide scale on the surface becomes thick, which causes an increase in pickling cost. Therefore, the upper limit is 800 ° C. In the case of the steel of the present invention, when the coiling temperature is high, the slightly remaining solid solution C is precipitated as fine carbide or the compound of P is precipitated, and the material tends to be rather deteriorated. Therefore, the winding is preferably performed at a temperature of 650 ° C or lower. To completely avoid the precipitation of these harmful compounds, it is more preferable to wind at a temperature of 500 ° C. or lower. Furthermore, in order to shorten the time taken for the temperature to drop to around room temperature after winding, 100
It is preferable to wind it at a temperature of not more than ° C. 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 50 from the viewpoint of plating property and plating adhesion.
0 ° C is good. If the alloying treatment temperature after that 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. It is preferable to carry out. In order to obtain a plated layer with better adhesion, 480-550
It is preferable to carry out alloying in the range of ° 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) Table 1, Table 2 (continued-1 of Table 1), Table 3
(Continued-2 of Table 1) and Table 4 (Continued-3 of Table 1)
Ti-added ultra-low carbon steel having the chemical composition shown in T and T
i, Nb-added ultra-low carbon steel was tapped in a converter and made into a slab by a continuous casting machine, and then Table 5 and Table 7 (continued in Table 5-
2), Table 10 (continued from Table 5-5) and Table 13 (Table 5)
(8) Hot rolling is performed under the conditions shown in 8),
Then, the coil was wound at various winding temperatures. A sample was cut out from the center of the 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 shown in Table 5, Table 8 (continuation-3 of Table 5), Table 11 (continuation-6 of Table 5) and Table 14 (continuation-9 of Table 5). After that, Table 6 (continued from Table 5-1), Table 9 (Table 5
Continuation-4), Table 12 (Continuation-7 in Table 5) and Table 15 (Continuation-10 in Table 5) were subjected to temper rolling at a reduction rate and subjected to a tensile test. Here, the tensile test and the measurement of the average Rankford value (hereinafter referred to as r value) were performed using JIS No. 5 test pieces. 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 by

R = (r _L + 2r _D + r _C ) / 4 The test results are summarized in Table 6, Table 9, Table 12 and Table 15.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

[Table 3]

[0036]

[Table 4]

[0037]

[Table 5]

[0038]

[Table 6]

[0039]

[Table 7]

[0040]

[Table 8]

[0041]

[Table 9]

[0042]

[Table 10]

[0043]

[Table 11]

[0044]

[Table 12]

[0045]

[Table 13]

[0046]

[Table 14]

[0047]

[Table 15]

As is clear from Tables 5 to 15, it is understood that the steels having the components of the present invention can obtain excellent materials by being wound at a temperature of 800 ° C. or lower. In particular, the coiling temperature becomes low, and the amount of C precipitated as carbides is 0.
If it is less than 0003%, an extremely excellent material can be obtained. On the other hand, it was revealed that the comparative steel was inferior in material quality at low temperature winding.

Example 2 Tables 16 and 18 (Table 16)
No. 2 of the steel Nos. 1 to 4 manufactured under the conditions shown in (2). 1, 2, 3, 6, 11, 12, 13, 1
4, 21, 24, 25, 28, 33, 35, 38, 39
Cold rolled steel sheet (after hot rolling to 4 mm thick, cold rolling 0.8 m
Material thickness in the longitudinal direction of the cold-rolled coil was investigated by using (thickness of m).

The test results are shown in Table 17 (continued from Table 16-1).
And Table 19 (continued from Table 16-3).

[0051]

[Table 16]

[0052]

[Table 17]

[0053]

[Table 18]

[0054]

[Table 19]

As is clear from Tables 16 to 19, 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 remarkably deteriorated toward the coil end, and in the case of low temperature winding, the material was inferior in the entire length of the coil. It is clear that this tendency becomes more prominent toward the edges.

(Example 3) Samples 2 and 11 of Tables 1 to 4
The effects of hot rolling heating temperature on the material properties after cold rolling and annealing were investigated using Nos. 22 and 34 (exposed steel slabs).
That is, the slab was heated to 1000 to 1300 ° C. in an actual machine, and hot rolling was performed at a finishing temperature of 940 ° C. so that the plate thickness became 4.0 mm. The average cooling rate on the run-out table was 20 ° C / s, after which the coil was wound at 690 ° 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 1, pickled, cold-rolled to 0.8 mm, and subsequently subjected to heat treatment equivalent to continuous annealing in a laboratory. The annealing conditions were annealing temperature: 790 ° C., soaking: 50 s, cooling rate: 60 ° C./s up to room temperature. Then, temper rolling was performed at a rolling reduction of 1.0%, and the steel was subjected to a tensile test.

The test results are summarized in Tables 20 and 21 (continued from Table 20).

[0058]

[Table 20]

[0059]

[Table 21]

As is clear from Tables 20 and 21,
The steel manufactured according to the scope of the present invention is excellent not only in the central portion of the hot rolled coil but also in the end portion thereof after the cold rolling and annealing. On the other hand, the heating temperature is 120
When the temperature was higher than 0 ° C, the material after cold rolling annealing was significantly deteriorated at the coil end. (Example 4) Steel Nos. In Tables 1 to 4 5, 10, 11,
12, 22, 24, 41, 42 were hot-rolled under the conditions shown in Table 22, followed by pickling with an actual machine, cold-rolling with a reduction rate of 80%, and continuous in-line annealing method. It was passed through a hot dip galvanizing line. Table 22 shows the plating conditions at this time. Similarly, after performing temper rolling at the rolling rate shown in Table 22, mechanical properties and plating adhesion were evaluated. The obtained results are shown in Table 23 (continued from Table 22).

Here, the adhesion of the plating was determined by determining the peeling condition of the zinc coating after the adhesive tape was adhered to the bent portion after peeling the zinc coating at 180 ° C. and peeling it off. 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

[0062]

[Table 22]

[0063]

[Table 23]

As is clear from Tables 22 and 23,
The galvannealed steel sheet produced according to the scope of the present invention exhibits excellent properties regardless of the coil position. On the other hand, in the comparative steel, the workability varied greatly depending on the coil portion.

[0065]

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, and the conventional cutting method has been adopted. The former coil end can be made into a 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.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication C23C 2/06 2/28 (72) Inventor Kazuo Koyama 20-1 Shintomi, Futtsu-shi, Chiba Made in Shinnihon (72) Inventor Manabu Takahashi 20-1 Shintomi, Futtsu City, Chiba Nippon Steel Co., Ltd. Technical Development Headquarters

Claims (7)

[Claims] 1. C: 0.0005-0.00, by weight.
7%, Mn: 0.03 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, Ti: 0.01 to 0.1% and Ti * = Ti-
When it is 3.42 N, it is contained in a range that satisfies Ti * / S ≧ 1.5, the balance is composed 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 MnS) / (total S%) is K ≦ 0.2, which is a cold-rolled steel sheet excellent in workability uniformity. 2. The cold-rolled steel sheet excellent in workability uniformity according to claim 1, wherein the amount of C precipitated as carbide is 0.0003% or less. 3. Nb: 0.002 to 0.05%
The cold-rolled steel sheet having excellent workability uniformity according to claim 1 or 2, further comprising: 4. B: 0.0001 to 0.003
The cold-rolled steel sheet having excellent workability uniformity according to any one of claims 1 to 3, wherein the cold-rolled steel sheet contains 0%. 5. A steel having the composition according to any one of claims 1 to 4 is used for heating temperature ≦ 1200 ° C. and finishing temperature ≧ (Ar
₃ -100) subjected to hot rolling ° C., winding, a rolling reduction ≧ 60% cold rolling performed in a temperature range of 800 ° C. from room temperature,
A method for producing a cold-rolled steel sheet having excellent workability uniformity, which is characterized by annealing at a recrystallization temperature or higher. 6. A steel having the composition according to any one of claims 1 to 4 for heating temperature ≦ 1200 ° C. and finishing temperature ≧ (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 steel sheet having excellent workability uniformity, which comprises performing annealing at a recrystallization temperature or higher and galvanizing during a cooling process. 7. 400 to 600 after galvanizing
The method for producing a hot-dip galvanized steel sheet excellent in workability uniformity according to claim 6, wherein the alloying treatment is performed in a temperature range of ° C.