JP3508506B2 - Cold rolled steel sheet with excellent workability, rough surface resistance and ridging resistance - Google Patents

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 (including a surface-treated raw sheet; the same applies hereinafter) suitable for use in automobile steel sheets and the like, and particularly to workability such as deep drawability and rough skin resistance. And a cold-rolled steel sheet having excellent ridging resistance.

[0002]

2. Description of the Related Art Cold-rolled steel sheets used for automobile panels and the like are required to have deep drawability and have high r value (Rankford value) and high ductility (El) as mechanical properties. . Such a cold-rolled steel sheet for deep drawing is generally manufactured by hot rolling at a transformation point of Ar ₃ or higher, cold rolling to obtain a thin sheet having a final thickness, and recrystallization annealing.

By the way, in general, ferritic stainless steels such as 17% Cr stainless steel are described in "Journal of the Japan Institute of Metals,"
Vol.3, No.4, (1967), P.519 "and" Journal of Japan Institute of Metals, Vol.31, No.6, (1967), P.717 "," riding ". It is known that there is a property of causing a unique phenomenon called. This is a phenomenon in which when a thin plate is subjected to deformation such as tension or deep drawing, fine streaky wrinkles are generated along the rolling direction. The above ridging phenomenon was conventionally thought to be peculiar to stainless steel, but even in the case of general cold-rolled steel sheets, Ar _{3 is} aimed at energy saving in the hot rolling process and cost reduction by improving the yield. It has become known that it tends to occur when hot finish rolling is completed at a temperature below the transformation point. When such a ridging defect occurs, the surface smoothness and beauty of the stainless steel plate, automobile steel plate, and the like, which are as important as the mechanical properties, are impaired, which may be fatal to the product value. Further, it is known that in cold-rolled steel sheets, when it is attempted to secure workability such as r-value, the roughness of the surface of the steel sheet is significantly increased during press forming, resulting in an appearance defect called “texture”.

Conventionally, as means for suppressing the occurrence of ridging in deep drawing steel sheets, "iron and steel vol.77, No.8,
(1991) p.84 "and" Iron and Steel vol.78, No.4, (1992) p.12.
4 '', that is, prolonging the time between passes in the hot rough rolling, a proposal such as hot-rolled sheet annealing or pass-annealing, as a means for preventing skin roughness, A method of cooling immediately after finish rolling is known. However, there is no unified view on the main cause of ridging, and it is not known what kind of index should be used to optimize the manufacturing conditions. It has been difficult to stably achieve both ridging property, rough skin resistance, and deep drawing property. Furthermore, since there is no effective index that correlates with the ridging property, the above-mentioned conventional methods have a tendency to take excessive measures, and thus unnecessarily reduce productivity.

The rough surface is said to be caused by the coarsening of the crystal grain size after cold rolling and recrystallization annealing. However, in a specific situation, it is the current situation that the factors that determine the presence or absence of rough skin have not been grasped.

On the other hand, as for deep drawability, {11
It is said that it is preferable to form grains of 1} orientation, and conversely {10
0} is known as an azimuth that decreases the r value. So far, we have developed {111}, which is suitable for deep drawing,
Technological progress has been made in the direction of decreasing the {100} component, and the average r value is also sorted out exclusively by the ratio I of the X-ray inverse intensity.
It has been done at {111} / I {100}. Where X
The line measurement is, so to speak, average macroscopic information that does not include information on the distribution of crystal grains, and this I {111} /
Even if the r value can be evaluated by the index of I {100}, the high r
There was a problem that ridging resistance and skin roughening resistance, which must be compatible with the values, could not be evaluated.

[0007]

As described above, in the conventional cold-rolled steel sheet manufacturing technology, while satisfying energy saving, process saving, low cost, high productivity, etc., deep drawing workability, ridging resistance, It was not possible to manufacture a product excellent in any of the characteristics of rough skin resistance. As a basic cause, it is considered that the factors and indexes for properly controlling these materials were not clear. The object of the present invention is to solve the above-mentioned problems that the prior art had in an advantageous manner. In addition to excellent workability (especially deep drawability), both rough skin resistance and ridging resistance can be stably achieved. It is to provide a cold rolled steel sheet.

[0008]

DISCLOSURE OF THE INVENTION In order to improve the ridging resistance and the surface roughening resistance of a cold-rolled steel sheet, the present inventors have proposed {10
Focusing on the 0} colony, repeated intensive research was conducted. as a result,
By controlling the presence of colonies in the cold-rolled steel sheet, it is possible to improve both deep drawability, resistance to ridging, and resistance to surface roughening, and that realization hinders productivity in the hot rolling process. We obtained the finding that it is possible without doing. The present invention has been completed based on the above findings, and its gist is as follows.

(1) C: 0.01 wt% or less, Si: 2.0 wt% or less, Mn: 3.0 wt% or less, P: 0.15 wt% or less, Al: 0.01 to
0.20 wt%, N: 0.01 wt% or less, the balance is composed of Fe and inevitable impurities, and the cross-sectional area ratio and average diameter of {100} -oriented colonies are as follows (1) and
A cold-rolled steel sheet having excellent workability, resistance to surface roughening, and resistance to ridging, which satisfies the expression (2). Note f / D ≧ 0.0005 (1) (2.8 −r) / 250 ≦ f / D ≦ (4.0 −r) / 250 (2) where f: {100} orientation colony cross-sectional area ratio D : Average diameter of colonies in {100} orientation (μm) r: Average r value (however, r ≧ 1.5)

(2) C: 0.01 wt% or less, Si: 2.0 wt% or less, Mn: 3.0 wt% or less, P: 0.15 wt% or less, Al: 0.01 to
0.20wt%, N: 0.01wt% or less, and Ti: 0.001〜
0.2 wt%, Nb: 0.001 to 0.2 wt% of 1 type or 2 types, the balance is composed of Fe and inevitable impurities, and the cross-sectional area ratio and average diameter of {100} -oriented colonies are as follows. A cold-rolled steel sheet having excellent workability, surface roughening resistance, and ridging resistance, which is characterized by satisfying the expressions (1) and (2). Note f / D ≧ 0.0005 (1) (2.8 −r) / 250 ≦ f / D ≦ (4.0 −r) / 250 (2) where f: {100} orientation colony cross-sectional area ratio D : Average diameter of colonies in {100} orientation (μm) r: Average r value (however, r ≧ 1.5)

(3) C: 0.01 wt% or less, Si: 2.0 wt% or less, Mn: 3.0 wt% or less, P: 0.15 wt% or less, Al: 0.01 to
0.20 wt%, N: 0.01 wt% or less, B: 0.0001 to 0.008 wt%
And the balance is composed of Fe and inevitable impurities, and the cross-sectional area ratio and average diameter of the {100} -oriented colonies satisfy the following formulas (1) and (2). Cold-rolled steel sheet with excellent heat resistance, resistance to surface roughening and resistance to ridging. Note f / D ≧ 0.0005 (1) (2.8 −r) / 250 ≦ f / D ≦ (4.0 −r) / 250 (2) where f: {100} orientation colony cross-sectional area ratio D : Average diameter of colonies in {100} orientation (μm) r: Average r value (however, r ≧ 1.5)

(4) C: 0.01 wt% or less, Si: 2.0 wt% or less, Mn: 3.0 wt% or less, P: 0.15 wt% or less, Al: 0.01 to
0.20 wt%, N: 0.01 wt% or less, B: 0.0001 to 0.008 wt%
And Ti: 0.001 to 0.2 wt%, Nb: 0.001 to 0.2
1% or 2% by weight, and the balance is composed of Fe and inevitable impurities, and the cross-sectional area ratio and average diameter of {100} -oriented colonies are expressed by the following formulas (1) and (2). A cold-rolled steel sheet excellent in workability, surface roughening resistance, and ridging resistance, which is characterized by being satisfied. Note f / D ≧ 0.0005 (1) (2.8 −r) / 250 ≦ f / D ≦ (4.0 −r) / 250 (2) where f: {100} orientation colony cross-sectional area ratio D : Average diameter of colonies in {100} orientation (μm) r: Average r value (however, r ≧ 1.5)

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION First, the research results which are the basis of the present invention will be described. A sheet bar having the composition shown in Table 1 was heated to 950 ° C and uniformly soaked, and then the finish rolling temperature was set to 900 to 70.
The temperature was changed to 0 ° C., hot rolling was performed with a total reduction of 90% in 3 passes, and then coil winding treatment was performed at 700 ° C. for 1 hour. After that, cold rolling with a reduction rate of 75%, 760-880
Recrystallization annealing was performed at 20 ° C for 20 seconds. FIG. 1 shows the results of examining the relationship between the surface roughening resistance and the ridging resistance and f / D for the obtained cold rolled steel sheets having an average r value of about 2. Here, f is the cross-sectional area ratio of the {100} -oriented colonies, and D is the average diameter (μm) of the {100} -oriented colonies. Note that the orientation concentration in the colony is El
ectron Back Scattering Diffraction Patern is used to measure the crystal orientation of the steel sheet in the thickness section for each crystal grain, and the crystal grain group with an angle between adjacent crystal grains of 15 degrees or less is regarded as a colony, and the average crystal orientation of the colony is {100} direction ± 1
Those within 5 ° were treated as {100} -oriented colonies. When there were no crystal grains within an angle of 15 ° in the periphery, it was considered that a single grain formed a colony. The same applies to the following. In addition, the ridging evaluation index in the figure is a value obtained by giving 15% tensile strain to a JIS No. 5 tensile test piece and evaluating this by visual observation. If the ridging evaluation index is 2 or less, it can be said that the ridging level has no practical problem. From FIG. 1, when f / D is small, the rough skin resistance and the ridging resistance also decrease, and r≈2.
In order to avoid these defects, f / D should be 0.00
It turns out that it is necessary to make it 3 or more.

FIG. 2 shows a result obtained by arranging such relationships at various r-value levels. According to FIG. 2, the cold-rolled steel sheet has f / D of 0.0005 or more and the relationship with the average r value (where r ≧ 1.5) is (2.8−r) / 250 ≦ f /
By setting D, it can be said that workability, resistance to rough skin, and resistance to ridging can be made excellent. Also, the average r value has a certain degree of correlation with the absolute value of the {100} -oriented colonies, and when f / D becomes large, (4.0-r) / 250 <f / D cannot be achieved in reality. Therefore, f / D is (2.8 −r) / 250 ≦
The range should be f / D≤ (4.0-r) / 250. The average r value is represented by r in the following equation. r = (r _L + 2r _D + r _C ) / 4 Here, r _L , r _D , and r _C represent Rankford values in the rolling direction, the rolling 45 ° direction, and the rolling right-angle direction, respectively.

The reason why each constituent of the present invention is limited to the above range will be described below. 1) {100} orientation colony The {100} orientation colony is the most important requirement in the present invention and has excellent workability and rough surface resistance after cold rolling-annealing.
In order to improve ridging resistance, as described above,
Ratio of area ratio and average diameter of {100} -oriented colonies, f /
It is important to control D. The inventors have found that the steel sheet hot-rolled in the ferrite region (below the Ar ₃ transformation point) has rough surface resistance,
As a result of various examinations regarding ridging resistance, it was found that {100} orientation colonies (groups of crystal grains with an angle between adjacent crystal grains of 15 ° or less) are the factors that most affect these characteristics. Electron Back Scattering Diffrac
It was clarified by a study using tion Patern. It was found that controlling the size and fraction of colonies is the most effective for improving ridging resistance.

Specifically, f / D ≧ 0.00, where f is the cross-sectional area ratio f of {100} colonies and D is the diameter (μm).
In 05, the relationship with the average r value must be (2.8 −r) / 250 ≦ f / D ≦ (4.0 −r) / 250. The {100} colonies are also affected by the texture of the hot-rolled sheet, and the f / D is (2.8 −
If it is smaller than r) / 250, the ridging property is deteriorated. Thus, it can be said that {100} plays the role of a so-called precipitate, which inhibits the deformation of the {111} matrix suitable for deep drawing. Considering not only the area ratio but also the colony diameter. It is necessary to comprehensively control the distribution state.

Here, f / D is considered to represent the distribution of {100} colonies. That is, when f / D is large, coarse {100} colonies are sparsely distributed, and when f / D is small, minute {100} colonies are relatively densely distributed. Represents a state. In order to suppress the occurrence of ridging, sparse distribution of coarse colonies is not preferable, and f / D is large, specifically, f / D ≧ (2.8 −
r) / 250 is required. Here, f
It is presumed that the reason why / D is a function of the r value is that the higher the r value is, the less the deformation in the sheet thickness direction is during molding, so that the occurrence of ridging is suppressed even if f / D is small.
However, f / D cannot be reduced unnecessarily depending on the r value. As shown in FIGS. 1 and 2, when f / D is small, a steel sheet having a low r value tends to have rough skin. According to a further investigation by the present inventors, the r value is (2.8 −r) / 250 <especially when f / D <0.0005.
Even if it is high enough to satisfy 0.0005, rough skin will occur. This is because when f / D becomes smaller and the area where there is a balance between colony size and sparseness is exceeded, rough skin is likely to occur, and especially when f / D <0.0005, rough skin occurs due to improvement in workability due to improvement in r value. It is surmised that it may exceed the difficulty (estimated because it is difficult to reduce the thickness like ridging).

On the other hand, f / D is (4.0-r) / 250 or less. That is, increasing f / D means that {10
0} means that the colony area ratio becomes high, and the absolute amount of {100} influences the workability rather than the fraction, and in reality, the average r value cannot be set to that value. ) / 250 was set as the upper limit of f / D.

2) Steel Composition In the present invention, the steel composition is also an important requirement, and the reasons for limitation thereof will be described below. C: 0.01 wt% or less C is preferably as small as possible from the viewpoint of improving deep drawability, but if the content is 0.01 wt% or less, it does not exert a bad influence so much, so it is made 0.01 wt% or less.

Si: 2.0 wt% or less Si has the effect of strengthening steel and is added in a required amount according to the desired strength. However, if the added amount exceeds 2.0 wt%, deep drawability deteriorates. 2.0 wt% or less.

Mn: 3.0 wt% or less Mn has a function of strengthening steel and is added in a required amount according to desired strength. However, if the added amount exceeds 3.0 wt%, deep drawability deteriorates. 3.0 wt% or less.

P: 0.15 wt% or less P has the action of strengthening steel and is added in the required amount according to the desired strength. However, if the added amount exceeds 0.15 wt%, deep drawability deteriorates. 0.15wt% or less.

S: 0.05 wt% or less S is preferable because the smaller the content, the better the deep drawability. However, if the S content is 0.05 wt% or less, there is no significant adverse effect, so S is set to 0.05 wt% or less.

Al: 0.01 to 0.20 wt% Al has a deoxidizing effect and is added to improve the yield of carbonitride forming elements, but if its content is less than 0.01 wt%, it has no effect. On the other hand, even if added over 0.20 wt%, the deoxidizing effect is saturated, so 0.01 to 0.20 wt% is set.

N: 0.01 wt% or less N is preferably as small as possible in order to improve the deep drawability, but if the content is 0.01 wt% or less, it does not exert a bad influence so much, so it is made 0.01 wt% or less. .

Ti: 0.001 to 0.2 wt% Ti has the effect of preventing solid solution C in steel from being precipitated and fixed as carbides and reducing it, and preventing deterioration of deep drawability due to solid solution C. If the addition amount is less than 0.001 wt%, there is no addition effect,
On the other hand, even if added in excess of 0.2 wt%, no further effect will be obtained, rather causing deterioration of deep drawability, so 0.001 to 0.
2 wt%

Nb: 0.001 to 0.2 wt% Nb has the effect of precipitating and fixing the solid solution C in the steel as carbides and reducing it, and preventing the deterioration of deep drawability due to the solid solution C. If the addition amount is less than 0.001 wt%, there is no addition effect,
On the other hand, even if added in excess of 0.2 wt%, no further effect can be obtained, which leads to deterioration of deep drawability.
0.2 wt%

B: 0.0001 to 0.0080 wt% B is added to improve the secondary work embrittlement resistance of steel, but if the amount of addition is less than 0.0001 wt%, there is no effect.
On the other hand, if it is added in excess of 0.0080 wt%, it leads to deterioration of deep drawability, so 0.0001 to 0.0080 wt% is set.

Next, a method for manufacturing a cold rolled steel sheet according to the present invention will be described. As a material for hot rolling, in addition to a material obtained by reheating a continuous casting slab, a material immediately after continuous casting without being lowered to a temperature below the Ar ₃ transformation point or for heat treatment may be used for energy saving. From the viewpoint of energy saving, the slab heating is preferably performed at a temperature of 1200 ° C. or lower, and more preferably 1100 ° C. or lower. Further, in order to randomize the crystal grains in the colony, it is important to repeat working and recrystallization during rolling in the ferrite region, so it is preferable to set the rough rolling temperature to the Ar ₃ transformation point or lower, and to finish It is preferable to perform high-pressure draft rolling in a high temperature region during rolling.

In order to improve the ridging resistance, it is necessary to randomize the colonies formed on the hot rolled sheet in the ferrite region. Therefore, it is important to randomize and disperse the crystals in the colony. According to the experiments by the inventors, the crystal grains in the colony can be randomized and dispersed by repeating the working and recrystallization twice or more during the hot rolling in the ferrite region. In order to repeat working and recrystallization twice or more during such ferrite region rolling, it is effective to perform at least one pass of rough rolling in the ferrite region, for example. If such rough rolling is performed, processing and recrystallization are performed between the rough rolling and finish rolling, and after finishing rolling, respectively, and processing and recrystallization can be repeated twice or more in the ferrite region. As a result, {100} colonies are dispersed, and if the same {100} colony abundance f is obtained, f / D becomes large. However, the abundance f itself of {100} is
Since it also decreases due to the presence of solute carbon and precipitates in the hot rolled sheet, it is necessary to consider changes in the average r value due to it. For example, there are changes in the amount and morphology of precipitates in the hot rolling stage, and changes in the amount of solute carbon due to the holding time before finish rolling. It is also necessary to consider that when the purity of the steel component is high, grain growth is likely to occur and the structure before finish rolling changes. As mentioned above,
By repeating rolling and recrystallization in the ferrite region twice or more, colonies are dispersed and ridging is eliminated.

The winding is preferably carried out at a temperature of 550 ° C. or higher in order to recrystallize the hot rolled sheet in the winding stage after finish rolling. This step is also useful for randomizing the crystal grains in the colony by rolling-recrystallization. At this time, it is not necessary to completely recrystallize the hot rolled sheet,
Even if it is partially recrystallized, the effect is obtained. Further, subsequently to this, the hot rolled sheet may be annealed. Note that strong reduction in the latter stage of finish rolling that promotes recrystallization of the hot rolled sheet is an effective means for improving ridging resistance. Lubrication rolling during finish rolling is effective for making the rolling structure uniform and reducing the rolling load.

The cold rolling step is indispensable for obtaining a high r value, and the cold rolling reduction is preferably in the range of 50 to 95%. It is necessary to perform recrystallization annealing on the cold rolled steel strip that has undergone the cold rolling process. For the annealing, either equipment of a continuous annealing furnace and a continuous hot dip galvanizing line may be used.
The annealing temperature is preferably in the range of 700 to 920 ° C. The annealed steel strip may be subjected to temper rolling of 10% or less in order to correct the shape and adjust the surface roughness. The cold-rolled steel sheet of the present invention can be used as it is, but it can also be applied as an original plate of a surface-treated steel sheet for processing. The surface treatment may be any of zinc plating (including alloy system), tin plating, enamel and the like. The steel sheet of the present invention may be subjected to a special treatment after annealing or galvanizing to improve chemical conversion treatment property, weldability, press formability, corrosion resistance and the like.

[0033]

Example A steel slab having the composition shown in Table 1 was heated and uniformly soaked at 1050 ° C., and then, under the hot rolling conditions shown in Table 2, a hot rolled steel strip having a plate thickness of 3.5 mm was formed. Subsequently, cold rolling was performed to obtain a cold-rolled steel strip having a plate thickness of 0.8 mm, and recrystallization annealing was performed at the temperature shown in Table 2.
Cross section 1 of the obtained cold rolled steel sheet cut in the rolling direction
The cross-sectional area ratio and size of {100} colonies were investigated by image analysis using EBSD for the orientation of each grain over a region of mm ² or more, and the following material properties were measured. JIS No. 5 tensile test piece is used for tensile properties, and r value is 15
% After applying a tensile pre-strain, measurement was performed by the three-point method, and the average of the r values in the rolling direction, the rolling direction of 45 ° and the rolling direction of 90 ° was r = (r _L + 2r _D + R _C ) /
4 (where r _L , r _D , and r _C are Rankford values in the rolling direction, rolling 45 ° direction, and rolling right-angle direction, respectively)
Sought by. The ridging resistance was determined by using the ridging evaluation index, and 15% tensile strain was applied to a steel plate processed into a JIS No. 5 tensile test piece and evaluated visually.
A ridging evaluation index of 2 or less is a ridging level with no practical problems. The rough skin resistance was evaluated visually by performing a hydraulic bulge test (120 mmφ). The results are also shown in Table 2. From Table 1 and Table 2, it can be seen that the cold-rolled steel sheet according to the present invention has excellent ridging resistance and deep drawability as compared with the comparative example.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

As described above, according to the present invention,
By controlling the component composition and the fraction and size of {100} colonies within a predetermined range, it is possible to achieve both stable ridging resistance, rough skin resistance, and deep drawing resistance without excessively reducing productivity. did it.

[Brief description of drawings]

FIG. 1 is a graph showing the effect of f / D on ridging resistance and rough skin resistance.

[Fig. 2] Ridging resistance, rough skin resistance and average r value, f / D
It is a graph which shows the relationship with.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Obara 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Works Ltd. Technical Research Laboratory (58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 38 / 00-38/60 C21D 9/46

Claims (4)

(57) [Claims] 1. C: 0.01 wt% or less, Si: 2.0 wt% or less, M
n: 3.0 wt% or less, P: 0.15 wt% or less, Al: 0.01 to 0.20w
t%, N: 0.01 wt% or less, the balance is composed of Fe and inevitable impurities, and the cross-sectional area ratio and average diameter of {100} -oriented colonies are expressed by the following formulas (1) and (2). A cold-rolled steel sheet excellent in workability, resistance to surface roughening and resistance to ridging, which is satisfied. Note f / D ≧ 0.0005 (1) (2.8 −r) / 250 ≦ f / D ≦ (4.0 −r) / 250 (2) where, f: {100} orientation colony cross-sectional area ratio D : Average diameter of colonies in {100} orientation (μm) r: Average r value (however, r ≧ 1.5) 2. C: 0.01 wt% or less, Si: 2.0 wt% or less, M
n: 3.0 wt% or less, P: 0.15 wt% or less, Al: 0.01 to 0.20w
t%, N: 0.01 wt% or less, and Ti: 0.001 to 0.2 w
t%, Nb: 0.001 to 0.2 wt% of 1 type or 2 types, the balance is composed of Fe and inevitable impurities, and the cross-sectional area ratio and average diameter of {100} oriented colonies are as follows. A cold-rolled steel sheet having excellent workability, surface roughening resistance and ridging resistance, which is characterized by satisfying the expressions (1) and (2). Note f / D ≧ 0.0005 (1) (2.8 −r) / 250 ≦ f / D ≦ (4.0 −r) / 250 (2) where, f: {100} orientation colony cross-sectional area ratio D : Average diameter of colonies in {100} orientation (μm) r: Average r value (however, r ≧ 1.5) 3. C: 0.01 wt% or less, Si: 2.0 wt% or less, M
n: 3.0 wt% or less, P: 0.15 wt% or less, Al: 0.01 to 0.20w
t%, N: 0.01 wt% or less, B: 0.0001 to 0.008 wt%, the balance consisting of Fe and inevitable impurities, and the cross-sectional area ratio and average diameter of {100} -oriented colonies are as follows. A cold-rolled steel sheet having excellent workability, surface roughening resistance, and ridging resistance, which is characterized by satisfying the expressions (1) and (2). Note f / D ≧ 0.0005 (1) (2.8 −r) / 250 ≦ f / D ≦ (4.0 −r) / 250 (2) where, f: {100} orientation colony cross-sectional area ratio D : Average diameter of colonies in {100} orientation (μm) r: Average r value (however, r ≧ 1.5) 4. C: 0.01 wt% or less, Si: 2.0 wt% or less, M
n: 3.0 wt% or less, P: 0.15 wt% or less, Al: 0.01 to 0.20w
t%, N: 0.01 wt% or less, B: 0.0001 to 0.008 wt% included, Ti: 0.001 to 0.2 wt%, Nb: 0.001 to 0.2 wt%
1 or 2 of the above, and the balance is composed of Fe and inevitable impurities, and the cross-sectional area ratio and average diameter of the {100} -oriented colonies satisfy the following equations (1) and (2). A cold-rolled steel sheet with excellent workability, surface roughening resistance, and ridging resistance. Note f / D ≧ 0.0005 (1) (2.8 −r) / 250 ≦ f / D ≦ (4.0 −r) / 250 (2) where, f: {100} orientation colony cross-sectional area ratio D : Average diameter of colonies in {100} orientation (μm) r: Average r value (however, r ≧ 1.5)