JPH06184645A - Production of cold rolled steel sheet reduced in inplane ansotropy and having high r-value - Google Patents

Abstract

PURPOSE:To stably produce a cold rolled steel sheet excellent in workability, reduced in inplane anisotropy, and having high r-value on an industrial scale. CONSTITUTION:A hot steel slab which has a composition containing <=0.08% C, <=0.3% Si, 0.01-0.4% Mn, <=0.02% S, 0.01-0.08% sol.Al, and <=0.01% N or further containing specific amounts of B or containing, besides the above, one or more kinds among specific amounts of Ti, Nb, Zr, V, and Mo in the percentages satisfying inequality [C equivalent]-[Ti equivalent/4[<=0.0020 is successively subjected to working and heat treatment by means of a process including at least the following treatments as shown in a figure: (a) cooling down to a temp. in the region lower than the A3 point; (b) precipitation treatment consisting of holding at a temp. in the above region lower than the A3 point for 1-60min; (c) temp. rise up to a region between the A3 point and [A3 point +200 deg.C] to cause inverse transformation from alpha to gamma; (d) cooling from the gamma-phase temp. region; (e) cold rolling at 50-97% total draft; and (f) recrystallization treatment at 550-900 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a cold-rolled steel sheet having a small in-plane anisotropy and a high rank-order value (r value) and an excellent deep drawability.

[0002]

2. Description of the Related Art Cold rolled steel sheets are generally made of hot rolled steel sheets obtained by hot rolling, and are manufactured by cold rolling and recrystallization annealing. It is widely used in "fields where strong workability is required" such as the exterior materials of.

By the way, the workability of this cold-rolled steel sheet largely depends on the characteristics of the hot-rolled steel sheet as a raw material. For this reason, in recent years, in order to obtain a cold-rolled steel sheet having excellent deep drawability, studies on manufacturing conditions in the hot rolling stage have been actively conducted.

For example, in Japanese Patent Laid-Open No. 58-133325, an ultra-low carbon steel having a C content of 0.0045% or less (hereinafter,% representing a component ratio is% by weight) is used as a raw material, and hot rolling thereof is performed. A method for manufacturing a cold-rolled steel sheet having excellent deep drawability by defining the conditions is disclosed.

However, in this proposal, no study has been made on precipitates and microstructures that affect the workability of steel sheets,
Probably because of this, it was difficult to say that the characteristic values of the cold-rolled steel sheet obtained according to this method were as intended. That is, the above-mentioned method proposed in Japanese Patent Laid-Open No. 58-133325 is based on the state of precipitation of carbonitrides and sulfides from heating to finish rolling and austenite (hereinafter abbreviated as “γ”). It cannot be said that it was completed based on an examination focusing on the transformation behavior to ferrite (hereinafter abbreviated as “α”) and the change in processing α between finish rolling and winding. It was thought that this was the cause that did not lead to satisfactory results.

On the other hand, in order to obtain a "cold rolled steel sheet with good workability" having a small in-plane anisotropy and a high r value, a {111} texture is developed in α after recrystallization treatment. It is said that it is desirable to let them do. Where the {11
Since the 1} texture occurs near the α grain boundary, {11
1} In order to smoothly and stably develop the texture, it was necessary to reduce the α grain size generated by the transformation during hot rolling and increase the α grain boundary area.

Therefore, as an attempt to produce a "hot-rolled steel sheet having a small α grain size" which leads to the realization of a highly workable cold-rolled steel sheet, the steel is finish-rolled in the γ region and then rapidly cooled, whereby γ → α The results of a test for refining α-grains after transformation have also been reported {CAMP-ISIJ, Vol. 3 (199
0), pp. 785-786}.

Certainly, according to the above method, a relatively fine α
Although a hot-rolled steel sheet having a grain structure can be obtained, there was still a limit to the refinement of α grains. Therefore, for example, α
It has been difficult to obtain a uniform structure finely divided to have a particle size of less than 10 μm. Therefore, for a cold-rolled steel sheet made of this material, it is the maximum value of the in-plane anisotropy (r value r ₀ , r _45, r ₉₀ in each direction of 0 °, 45 °, 90 °). r _max
And the minimum value r _min ) has been made small, and a sufficiently high and uniform r value has not been stably provided.

It is considered that this is because the grain size of α-grains is ultimately greatly influenced by the size of γ-grains before transformation, and recently, in order to further refine the α-grains, the grain size before transformation has been increased. It has come to be said that the miniaturization of γ grains is essential.

At present, as a "means for refining γ grains" which have been studied and built up over many years, I) controlled rolling, II) large reduction rolling (for example, JP-A-62-253733, JP-A-63-145720). (Refer to Japanese Patent Publication No.) and the like are known. However, the following problems have been pointed out for each of these technologies.

That is, in the case of the controlled rolling technique, the γ grains produced by the hot working called "controlled rolling" cannot actually be further refined when it becomes fine to a certain extent. However, it is still difficult to obtain "a uniform fine structure in which the grain size of α transformed from the γ grains is about 20 μm".

On the other hand, in the structure refining technique by large reduction rolling, a large reduction with a reduction rate of 30% or more per pass in the γ non-recrystallization temperature range is applied to work hardening the γ grains “including a deformation zone within the grains”. γ ″, and then γ → α transformation is caused to achieve the refinement of the structure. However, in this method "γ →
The γ grain before α transformation ”is simply elongated by large reduction rolling and does not become a fine grain, so there is a limit to the refinement of the γ structure as a prerequisite for realizing a fine α structure. It has not been possible to realize a uniform fine structure having an α grain size of less than 20 μm, for example.

As described above, in order to develop the {111} texture necessary for improving the deep drawability of the cold rolled steel sheet, it is difficult to reduce the α grain size caused by the transformation during hot rolling in the prior art. Therefore, it is considered that this is a major obstacle in producing a high r-value cold-rolled steel sheet having a small in-plane anisotropy.

Therefore, the object of the present invention is to stably reveal the "ultrafine uniform structure" in the hot rolling stage, which was difficult to realize by the conventional method, and based on this, It was to establish means for stably manufacturing a high r-value cold-rolled steel sheet exhibiting excellent workability and having a small in-plane anisotropy on an industrial scale.

[0015]

Means for Solving the Problems The inventors of the present invention have obtained the following findings as a result of earnest studies from various viewpoints in order to achieve the above object.

A) First, a low carbon aluminum killed steel having a C content of 0.08% or less and an N content of 0.01% or less, or a low carbon containing one or more of Ti, Nb, Zr, V and Mo added thereto. Using continuous cast slabs or ingots of aluminum-killed steel (hereinafter collectively referred to as "hot steel slabs") as materials,
During the hot rolling, the α structure is exposed in advance by temperature adjustment, and a precipitation treatment is performed to rapidly precipitate carbonitrides and sulfides to purify the matrix. Then, subsequently, the structure is heated to reverse transform the α phase to the γ phase, or after rolling at a predetermined reduction rate, the temperature is raised to reverse transform the α phase to the γ phase, or Γ grain size of raw steel is 20
When it becomes 0 μm or more, if “raw steel before α is revealed” is once rolled in the γ temperature range to a predetermined reduction ratio and then subjected to thermomechanical treatment in the above process to reverse transform α into γ,
The γ structure that appears is an ultrafine structure that cannot be obtained by conventional controlled rolling.

B) Therefore, if this ultrafine uniform γ structure is cooled as it is, or if it is further rolled and then cooled, the α produced by transformation is extremely fine because it is based on the ultrafine γ structure. Thus, it is possible to obtain an “isotropic uniform fine structure far below the α grain size of 20 μm” which was extremely difficult to realize in the past.

C) When this "steel plate in which precipitates are coarse and α grain structure is refined" is cold-rolled and then recrystallized, {111} texture is sufficiently developed and in-plane anisotropy is small. A cold rolled steel sheet having a high r value can be stably obtained.

The present invention has been completed on the basis of the above findings and the like. "C: 0.08% or less, Si: 0.3%
Below, Mn: 0.01 to 0.4%, S: below 0.02%, so
l.Al: 0.01 to 0.08%, N: 0.01% or less, or B: 0.0001 to 0.0050%, or one or more of Ti, Nb, Zr, V and Mo. : In total
0.015 to 0.350% is also the formula [C equivalent]-[Ti equivalent / 4] ≤ 0.0020 A hot steel slab that contains Fe and unavoidable impurities with the balance satisfying the following conditions is cooled to at least a) below the A ₃ point (ie Ae ₃ point), b) above the A ₃ point performing deposition by keeping 1-60 minutes, c) the temperature to a temperature range of a ₃ point - [a _3-point + 200 ° C.] was raised, effect reverse transformation from α to gamma, d) the gamma phase temperature By cooling from the zone, e) cold rolling with a total reduction of 50 to 97%, f) recrystallization at a temperature of 550 to 900 ° C, and sequentially processing and heat treating in steps including , Which enables stable production of a high r-value cold-rolled steel sheet having a small in-plane anisotropy ”.

FIG. 1 is a schematic view showing an example of the cold-rolled steel sheet manufacturing process according to the present invention. Hereinafter, the reason why the component composition of the material steel and the working / heat treatment conditions are limited as described above in the present invention will be specifically described together with the action and effect.

[0021]

[Action]

<Ingredient composition of raw steel> C C is an element that adversely affects the deep drawability of the steel sheet,
The smaller the content, the better. In particular, when the C content exceeds 0.08%, the deep drawability deteriorates remarkably, so the content was limited to 0.08% or less.

Si Since Si is also an element that adversely affects the deep drawability of the steel sheet, it is preferable that the content of Si is as small as possible. In particular, if the Si content exceeds 0.3%, not only the deep drawability will deteriorate significantly, but also the scale properties will deteriorate and the product quality will be impaired, so the content is limited to 0.3% or less. did.

Mn Mn has an effect of improving the toughness of the steel sheet, but if the content is less than 0.01%, the effect due to the above effect is not sufficient and hot brittleness occurs, while 0.4% Since the deep drawability deteriorates remarkably if it is contained in excess, Mn content was set to 0.01 to 0.4%.

The lower S S is, the more the deep drawability of the steel sheet is improved.
Since the adverse effect is not so remarkable when it is reduced to about 02%, the S content is set to 0.02% or less.

Sol.Al Al is added for deoxidation and improving the yield of carbonitride and sulfide forming elements, but if the content is less than 0.01% in sol.Al, the above-mentioned effects are obtained. Is not obtained sufficiently, while 0.08
%, The effect becomes saturated and it becomes uneconomical, so the Al content was defined as 0.01 to 0.08% in terms of sol.Al content.

The lower the N 2 N content is, the smaller the amount of carbonitride forming element added is, which is preferable. In particular, its content is 0.01
%, The addition of carbonitride-forming elements inevitably reduces the r-value of the steel sheet, so the N content is 0.01%.
The following was set.

Ti, Nb, Zr, V and Mo These components form carbonitrides or sulfides to reduce the solid solution C, N and S, and the precipitates make the crystal grains finer appropriately. If necessary, they are added individually or in combination. However, the total content of these
If it is less than 0.015%, the desired effect due to the above-mentioned action cannot be obtained. On the other hand, if the total content is more than 0.350%, the strength becomes too high and it becomes unsuitable as a steel sheet for working, and it is economically disadvantageous. Becomes Therefore, the total content of these components was set to 0.015 to 0.350%.

The formula "[C equivalent]-[Ti equivalent / 4] ≤
0.0020 "means that solid solution C, N and S are 0.0020% or less,
It shows the relationship for precipitating the remaining C, N, and S as carbonitrides and sulfides.
When the value of "equivalent / 4]" exceeds 0.0020, the amount of solid solution C, N and S increases, so that the {111} recrystallization texture does not develop and the deep drawability of the steel sheet deteriorates.

[0029] B B is added as necessary so has the effect of preventing to become "vertical cracks" problem drawing part, the desired effect due to the content of the working is less than 0.0001% On the other hand, if the content exceeds 0.0050%, the effect is saturated and it is economically disadvantageous. Therefore, the B content is set to 0.0001 to 0.0050%.

<Working / Heat Treatment Conditions> The raw material billet having the above-mentioned composition used for hot rolling may be one produced by continuous casting (usually thick slab or thin slab) or separated from an ingot. It may be manufactured by ingot rolling. Further, the raw steel billet may be subjected to hot rolling after heating the cold billet after continuous casting or slabbing to a predetermined temperature. It is also possible to employ a method in which a steel slab sent from the line at a high temperature is used as it is, or is subjected to hot rolling with some auxiliary heating. Note that FIG. 2 is a schematic view showing another example of the “cold rolled steel sheet manufacturing process according to the present invention” when the reheating rolling or the direct feeding rolling is adopted.

In the present invention, such hot steel pieces are sequentially processed and heat-treated under the above-mentioned conditions, and the processing conditions at this time are specified for the following reasons.

( A ) The temperature of the hot steel slab below A ₃ points (Ae ₃ points)
Reason for cooling to the temperature range The reason why the hot steel billet is cooled to a temperature range below the A ₃ point is that the method of the present invention has “a reverse transformation from α phase to γ phase” as a main requirement. This is because it is necessary to generate the α phase. The temperature after cooling at this time is not particularly limited as long as it is a temperature of less than A ₃ point, but in terms of practical operability, a region of a temperature as high as possible near less than A ₃ point { A ₃ points to [A ₃ points-200
C]} is preferable.

However, when the γ grain size of the continuously cast or ingot cast steel slab is 200 μm or more, the hot steel slab is cooled as it is to a temperature range below the A ₃ point, and α is obtained after rolling. → Even if the γ reverse transformation is caused, the desired uniform ultrafine structure may not be obtained.

However, even in such a case, as shown in FIG. 2, before the hot steel slab is cooled as it is or after it is once inserted into the heating furnace, the rolling of the final pass is performed in the temperature range of A ₃ point or more and at the final stage. By rolling with a pass reduction of 30% or more, the γ grains are recrystallized and refined (γ grain size: 200 μm
Since the processing strain can be introduced into the γ grains, the precipitation sites of the α grains can be increased, and the α grains can be refined in the subsequent cooling process.

Preferably, the rolling reduction in the final pass is 45% or more. If the rolling reduction in the final pass is less than 30%, not only the γ grains will not be recrystallized into fine grains but also the processing strain will be small, so that the α grains will not be fined in the next cooling step. Further, when the temperature of the rolling in the final pass is lower than the A ₃ point, the α phase is mixed and the working strain is concentrated in the soft α phase, and the working strain is not accumulated in the γ phase. The α grains generated by α transformation are not refined. It is preferable that this rolling is carried out for one or more passes, and the final pass is performed under the above conditions.
For the rolling before the final pass, it is not necessary to particularly limit the conditions, and ordinary rolling may be used.

(B) A ₁ to 60 minutes in a temperature range of less than ₃ points
Reason for carrying out the precipitation treatment by holding it The purpose of the precipitation treatment is to precipitate C, N and S in the steel as carbonitrides or sulfides to improve the deep drawability.
For that purpose, the temperature may be maintained in the temperature range of less than A ₃ .
Because the α phase has a lower solubility than the γ phase,
This is because precipitation proceeds rapidly. The holding time at this time may be 1 to 60 minutes. This is because if the holding time is less than 1 minute, the amount of precipitation will be small, and if it is longer than 60 minutes, the precipitation will be saturated, resulting in an increase in manufacturing cost.

In the present invention, the means for holding the "steel plate after being cooled to a temperature range of A ₃ point or less" in the rolling line in the above temperature range is not particularly limited, but, for example, a recently developed "coil box" is used. Can be used.
Further, the steel plate may be rapidly cooled in order to attain a predetermined precipitation treatment temperature. By quenching, the manufacturing time can be shortened, and the α grains can be made finer to improve the deep drawability.

(C) Temperature of A ₃ point to [A ₃ point + 200 ° C.]
Reason for heating up to the temperature range As described above, when the hot steel billet is once cooled to a temperature range below the A ₃ point to generate the α phase and then heated to the A ₃ point or higher, the α → γ reverse transformation causes It is possible to make the γ grains finer. That is, the reason why the temperature is raised to the temperature range of A ₃ point or higher is
It is to sufficiently exert the characteristic action and effect of the method according to the present invention, that is, "very fine γ grains are generated by reverse transformation from work-hardened α". In this case, the upper limit of the temperature rise is [A ₃ point + 200 ° C.] because the grain growth of γ occurs when the temperature rises above this temperature and finally the desired uniform ultrafine structure steel sheet is obtained. Due to disappearance.

If rolling is performed in a temperature range of less than the A ₃ point prior to this temperature rise, strain is accumulated in α and the reverse transformation nuclei to γ are increased by this rolling. It is possible to further reduce the size of the γ grains as compared with the case. Therefore, it may be heated after performing rolling in the temperature range of A less than ₃ points.

From the temperature range below A ₃ point, A ₃ point ~
The heating rate when raising the temperature to the temperature range of [A ₃ point + 200 ° C.] is preferably 0.1 ° C./sec or more. As a result, a large number of γ nuclei can be generated from α, the γ grain growth after the reverse transformation can be suppressed, and the processing strain in the temperature range of A ₃ point or lower can be released prior to the α → γ reverse transformation. Therefore, it is possible to realize a desired fine γ grain. As a means for raising the temperature, any method such as "utilization of processing heat" or "active heating from the outside (electric heating)" or a combination of both may be adopted.

(D) Reason for cooling from the γ-phase temperature range The steel rapidly heated to the γ-phase temperature range to cause reverse transformation is made into an isotropic and uniform ultrafine α-structure by the subsequent cooling,
Further, although cold rolling is performed, it is preferable to perform rolling with a total reduction of 50% or less in the γ phase temperature region prior to the cooling. This is because when rolling is performed in the γ-phase temperature range, the processing strain is accumulated in the γ grains generated by the reverse transformation, and the α-containing structure generated by subsequent cooling is further refined, so that its characteristics are further improved. Is. In this case, it is desirable that the rolling in the γ phase temperature range is stopped at a total reduction of 50% or less (preferably 30% or less) as described above. This is because γ is recrystallized and grain-grown when the total rolling reduction exceeds 50%, and α generated by subsequent cooling is not sufficiently miniaturized. Then, the steel which has been subjected to the above-described thermomechanical treatment and cooled into a plate material is cooled by an arbitrary means to obtain a fine α of 8 or more in ASTM grain size number.
Grains are obtained.

The cooling from the γ phase temperature range is from A ₃ point
It is desirable to cool the temperature range of [A ₃ points-100 ° C] at a cooling rate of 5 ° C / s or more. This makes it possible to generate a large number of α nuclei from fine γ and suppress the growth of α grains, so that fine α grains can be obtained. By refining the α grains before rolling in the next step, the area of the α grain boundaries can be increased, and the {111} recrystallized texture that is generated from the α grain boundaries and is favorable for improving the r value is sufficiently developed. Can be made.

By the way, "rolling explained in the item (a)"
Also, there is no restriction on where in the hot rolling line the "rolling heat treatment described in (c) and (e) above" is performed, but the former is performed in the rough rolling process and the latter is performed in the finish rolling process. Is advantageous in terms of equipment. At that time, the hot rolling winding temperature does not matter.

(E) Reason for carrying out cold rolling The purpose of cold rolling is to develop a rolling texture and to improve the r value and minimize the in-plane anisotropy in the subsequent recrystallization annealing step. To develop a {111} texture. For that purpose, the final plate thickness may be processed at a total reduction ratio of 50 to 97%. When the rolling reduction is less than 50% or more than 97%, the {111} texture does not develop even if recrystallization annealing is performed.

(F) Reason for performing recrystallization annealing Recrystallization annealing is an essential step for controlling the texture of α and producing a cold-rolled steel sheet excellent in deep drawability. For that purpose, annealing is performed in the temperature range of 550 to 900 ° C., and α
It is desirable to recrystallize. At temperatures lower than 550 ° C., recrystallization does not sufficiently occur even in batch annealing, which is annealing for a long time, and at temperatures above 900 ° C., γ-formation remarkably progresses, making it difficult to control a predetermined recrystallization texture of α. The method for carrying out the recrystallization annealing is not particularly limited, and for example, it can be carried out by a normal continuous annealing process, a batch annealing process or the like. During the skin pass reduction performed after the recrystallization annealing, a reduction of less than 10% may be supplementarily added.

Next, the present invention will be described more specifically by way of examples.

EXAMPLE 50 Aluminized steel having the chemical composition shown in Table 1 was used.
It was melted in a kg vacuum melting furnace and cast into slabs of 20 mm and 100 mm thickness. Subsequently, these slabs were hot-rolled under the conditions shown in Table 2, cooled and wound. Then, after pickling the hot rolled steel sheet after winding, after performing cold rolling,
"Continuous annealing at 800 ℃ x 2min (treatment a)" or "75
Recrystallization treatment was carried out by batch annealing (treatment B) at 0 ° C. × 5 hr.

Test pieces were taken from the cold-rolled steel sheet thus obtained, and the "yield strength (YP)", "elongation (El)" and "r value" were investigated. The results are shown in Table 3.

[0048]

[Table 1]

[0049]

[Table 2]

[0050]

[Table 3]

As is clear from the results shown in Table 3, the hot-rolled steel sheet manufactured according to the conditions specified in the present invention exhibits excellent r value and elongation, and has extremely small in-plane anisotropy. I understand. Further, it is clear that all the steel sheets according to the present invention have a low yield point and are very excellent in workability.

On the other hand, when the manufacturing conditions do not comply with the regulations of the present invention, the α structure is not sufficiently refined, resulting in poor properties of the obtained steel sheet.

[0053]

[Summary of Effects] As described above, according to the present invention, it is possible to stably manufacture a cold-rolled steel sheet having a small in-plane anisotropy and a high r value. Be done.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a cold-rolled steel sheet manufacturing process according to the present invention.

FIG. 2 is a schematic view showing another example of the cold-rolled steel sheet manufacturing process according to the present invention.

Claims (4)

[Claims] 1. A weight ratio of C: 0.08% or less, Si: 0.3% or less, Mn: 0.01 to
0.4%, S: 0.02% or less, sol.Al: 0.01 to 0.08%,
N: In-plane anisotropic, characterized by sequentially processing and heat treating a hot steel slab containing 0.01% or less and the balance Fe and unavoidable impurities in a step including at least the treatments a) to f) below. A method for producing a high r-value cold-rolled steel sheet having low properties. cooled to a temperature range below a) A _3-point, b) performs the A precipitation treatment to hold 1-60 minutes at a temperature range of less than ₃ points, c) the temperature of the A ₃ point - [A ₃ point + 200 ° C.] Temperature is raised to a temperature range to cause the reverse transformation of ferrite to austenite, d) cooling from the austenite phase temperature range, e) cold rolling with a total reduction of 50 to 97%, f ) A recrystallization treatment is performed at a temperature of 550 to 900 ° C. 2. A weight ratio of C: 0.08% or less, Si: 0.3% or less, Mn: 0.01 to
0.4%, S: 0.02% or less, sol.Al: 0.01 to 0.08%,
N: 0.01% or less B: 0.0001 to 0.0050%, the balance being Fe and inevitable impurities, hot steel slabs are sequentially processed and heat treated in a process including at least the following a) to f). A method for producing a high r-value cold-rolled steel sheet having small in-plane anisotropy. cooled to a temperature range below a) A _3-point, b) performs the A precipitation treatment to hold 1-60 minutes at a temperature range of less than ₃ points, c) the temperature of the A ₃ point - [A ₃ point + 200 ° C.] Temperature is raised to a temperature range to cause the reverse transformation of ferrite to austenite, d) cooling from the austenite phase temperature range, e) cold rolling with a total reduction of 50 to 97%, f ) A recrystallization treatment is performed at a temperature of 550 to 900 ° C. 3. By weight ratio, C: 0.08% or less, Si: 0.3% or less, Mn: 0.01 to
0.4%, S: 0.02% or less, sol.Al: 0.01 to 0.08%,
N: 0.01% or less is contained and Ti, Nb, Zr,
One or more types of V and Mo: 0.015 to 0.350% in total is also represented by the formula [C equivalent]-[Ti equivalent / 4] ≤ 0.0020. A hot steel slab that contains Fe and unavoidable impurities with the balance satisfying the following conditions, characterized by sequentially processing and heat treating in a step including at least the following treatments a) to f). A method for manufacturing a small high r-value cold rolled steel sheet. cooled to a temperature range below a) A _3-point, b) performs the A precipitation treatment to hold 1-60 minutes at a temperature range of less than ₃ points, c) the temperature of the A ₃ point - [A ₃ point + 200 ° C.] Temperature is raised to a temperature range to cause the reverse transformation of ferrite to austenite, d) cooling from the austenite phase temperature range, e) cold rolling with a total reduction of 50 to 97%, f ) A recrystallization treatment is performed at a temperature of 550 to 900 ° C. 4. By weight ratio, C: 0.08% or less, Si: 0.3% or less, Mn: 0.01 to
0.4%, S: 0.02% or less, sol.Al: 0.01 to 0.08%,
N: 0.01% or less B: 0.0001 to 0.0050%, Ti, Nb,
One or more types of Zr, V and Mo: 0.015 to 0.350% in total is also represented by the formula [C equivalent]-[Ti equivalent / 4] ≤0.0020. A hot steel slab that contains Fe and unavoidable impurities with the balance satisfying the following conditions, characterized by sequentially processing and heat treating in a step including at least the following treatments a) to f). A method for manufacturing a small high r-value cold rolled steel sheet. cooled to a temperature range below a) A _3-point, b) performs the A precipitation treatment to hold 1-60 minutes at a temperature range of less than ₃ points, c) the temperature of the A ₃ point - [A ₃ point + 200 ° C.] Temperature is raised to a temperature range to cause the reverse transformation of ferrite to austenite, d) cooling from the austenite phase temperature range, e) cold rolling with a total reduction of 50 to 97%, f ) A recrystallization treatment is performed at a temperature of 550 to 900 ° C.