JPH07107179B2 - Manufacturing method of cold rolled steel sheet for ultra deep drawing - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a cold-rolled steel sheet having excellent deep drawability, which is useful for use in steel sheets for automobiles and the like.

(Prior Art) Cold-rolled steel sheets used for automobile panels and the like are required to have excellent deep drawability. In order to improve the deep drawability, high Rankford value (r value) and high ductility (El) are required as mechanical properties of the steel sheet.

By the way, in the conventional assembly of automobile bodies, a large number of stamped parts are spot-welded, respectively, but recently, there has been an increasing demand to reduce the number of parts and the number of welds by enlarging and integrating some of these parts. Came.

For example, an oil pan of an automobile is currently completed by welding due to its complicated shape, but there is a strong demand for integral molding by an automobile manufacturer. On the other hand, vehicle designs are becoming more complex to meet the diversifying needs, and the number of parts that are difficult to form using conventional steel sheets is increasing. In order to meet these requirements, a cold rolled steel sheet having a deep drawability that is far superior to the conventional one has been required.

Conventionally, various methods have been proposed for improving deep drawability. By the way, it is known that the deep drawability of a steel sheet is closely related to its texture, and a higher value is obtained as the number of {222} orientations increases and as the number of {200} orientations decreases. As a conventional method for obtaining this high value, for example, Japanese Patent Publication No. 44-17
No. 268 Public Relations, Japanese Patent Publication No. 17269/44 or Japanese Patent Publication No.
A so-called two-stage cold rolling method has been proposed, in which cold rolling is performed twice in a low carbon rimmed steel sheet as disclosed in Japanese Patent No. 172270.

According to this two-stage cold rolling method, the final product has many {222} oriented grains and few {200} oriented grains. This is because the temporary cold rolling-annealing treatment increases {222} oriented grains and decreases {200} oriented grains as compared with the hot rolled steel sheet before cold rolling, so that cold rolling-annealing is performed again. And the {222} oriented grains are further increased, while the {200} oriented grains are further reduced, so that a steel sheet having a high value can be manufactured.

On the other hand, in JP-A-56-62926, C: 0.008%, Si:
0.57%, Mn: 0.35%, Al: 0.43%, Nb: 0.061% steel,
We propose a technique to obtain = 4.7 by performing box-type annealing at 950 ° C for 1 hr after normal hot rolling-cold rolling.

(Problems to be Solved by the Invention) Among the above-mentioned techniques, the former two-stage cold rolling method is superior in that it improves deep drawability, but one cold rolling-annealing step is required as compared with the conventional step. I have to do many times,
Therefore, there is a drawback that the energy and cost required become enormous.

Further, the latter of the above-mentioned conventional techniques utilizes the formation mechanism of the transformation texture, so the recrystallization annealing temperature is set to Ar.
_The temperature must be raised to ₃ transformation points or higher, and therefore, energy cost is increased and equipment and technical difficulties due to high-temperature annealing are higher than those in recrystallization annealing in which the Ar ₃ transformation point is lower than that. In addition, there is a problem that a large amount of Si or Al must be added, which deteriorates the surface properties of the steel sheet.

The object of the present invention is to overcome the above problems in the case of performing cold rolling twice and the above problems in dealing with only the component composition, mainly by adopting a novel method involving the entanglement of hot rolling conditions and component compositions. The present invention proposes a manufacturing method that can advantageously improve the deep drawability of a steel sheet.

(Means for Solving the Problems) The research results that form the basis of this invention will be described. C: 0.001
~ 0.008wt% (simply indicated as% below), Si: 0.01%, Mn: 0.10
~ 0.35%, P: 0.008 ~ 0.018%, Si: 0.002 ~ 0.02%, N: 0.001
~ 0.008%, Ti: 0.01 ~ 0.20%, Nb: 0 ~ 0.008% of the composition of the steel is heated at 1150 ℃ -after soaking, rough rolling is completed in the range of 950 ℃ ~ Ar ₃ transformation point Rolling reduction of 90% was performed. At this time, the hot rolling finish temperature was kept constant at 700 ° C by adjusting the finish rolling start temperature. Continue to 7
A winding self-annealing treatment was performed at 00 ° C for 1 hr. The finish rolling was lubrication rolling. Further, the obtained hot-rolled sheet was pickled, cold-rolled at a rolling reduction of 75%, and then recrystallized at 830 ° C for 40 seconds.

Fig. 1 shows the effect of steel components on the values of hot-rolled and cold-rolled sheets. The value is strongly dependent on the steel composition and is 1.2 (C / 12 + N
/ 14 + S / 32) <(Ti / 48 + Nb / 93) and the addition of Nb = 0.008% significantly improved.

Also, C: 0.002%, Si: 0.01%, Mn: 0.15%, P: 0.012%, S: 0.
Steel with a composition of 015%, N: 0.002%, Ti: 0.065%, Nb: 0.007% is heated at 1150 ° C-after soaking, the same rough rolling as above is performed, and then the total rolling reduction is 90%. It was rolled. At this time, the rough rolling end temperature (RDT) was changed to 1050 to 880 ° C by adjusting the rough rolling start temperature. In the finish rolling, the hot rolling finish temperature was kept constant at 700 ° C by adjusting the finish rolling start temperature. Subsequently, a self-annealing treatment at 700 ° C. for 1 hr was performed. The finish rolling was lubrication rolling. Further, the obtained hot-rolled sheet was pickled, cold-rolled at a rolling reduction of 75%, and then recrystallized at 830 ° C for 40 seconds.

FIG. 2 shows the effect of the rough rolling end temperature on the values of the hot-rolled sheet and the cold-rolled sheet. Values strongly depend on RDT, RDT ≤ 95
It was remarkably improved by setting the temperature to 0 ° C.

Also, C: 0.002%, Si: 0.01%, Mn: 0.14%, P: 0.012%, S: 0.
Steel with the composition of 009%, N: 0.002%, Ti: 0.067%, Nb: 0.007% is heated at 1150 ° C-After soaking, rough rolling is performed in the same manner as above, and then the total reduction rate is 90%. It was rolled. At this time, the hot rolling finish temperature was changed from 680 ° C to 750 ° C by adjusting the rough rolling start temperature. Also, continue to 650
The coil was annealed for 1 hr in the temperature range of ℃ to 750 ℃.
The finish rolling was lubrication rolling. Furthermore, after the obtained hot-rolled sheet was pickled, it was cold-rolled at a rolling reduction of 75%, and then 830
Recrystallization annealing was performed at -40 ° C for 40 seconds.

Fig. 3 shows the effect of the winding temperature on the values of the hot-rolled sheet and the cold-rolled sheet. The value strongly depends on (FDT)-(CT) and was significantly improved by setting (FDT)-(CT) ≤ 100 ° C.

As a result of repeated studies based on the above experimental results, the inventors can manufacture a cold-rolled steel sheet excellent in deep drawability by regulating the composition and manufacturing conditions of steel as follows. I found that. The main points are: 1.C: 0.008% or less, Si: 0.5% or less, Mn: 1.0% or less, P: 0.15%
Below, S: 0.02% or less, Al: 0.010 to 0.10%, N: 0.008% or less, Ti: 0.035 to 0.20% and Nb: 0.001 to 0.015% and the amount of C, N, S and Ti and Nb Steel that has a relationship of 1.2 (C / 12 + N / 14 + S / 32) <(Ti / 48 + Nb / 93) with the additive amount is hot-rolled in a temperature range of 950 ° C or lower and Ar ₃ transformation point or higher, and then Ar Finishing rolling is performed at a reduction ratio of 80% or more while lubricating in the temperature range of 600 ° C or more below ₃ transformation points, and then the hot rolling finishing temperature (FDT) and coiling temperature (CT) are (FDT) It is characterized in that it is wound under the condition satisfying the relations of − (CT) ≦ 100 ° C. and (CT) ≧ 600 ° C., then cold rolled at a reduction rate of 50 to 95%, and then recrystallized annealing is performed. , Method for manufacturing cold rolled steel sheet for ultra deep drawing, 2.C: 0.008% or less, Si: 0.5% or less, Mn: 1.0% or less, P: 0.15%
Or less, S: 0.02% or less, Al: 0.010 to 0.10%, N: 0.008% or less, Ti: 0.035 to 0.20%, N
b: 0.001 to 0.015% and B: 0.0001 to 0.0010%, and the amount of C, N, S and the amount of Ti and Nb added are 1.2 (C / 12 + N / 14 + S / 32) <(Ti / 48 + Nb / 93) After steel is hot-roughly rolled in a temperature range of 950 ° C or below and above Ar ₃ transformation point, it is rolled at a temperature range of 600 ° C or above below Ar ₃ transformation point and reduced by 80% or more. Under the condition that the hot rolling finish temperature (FDT) and the coiling temperature (CT) satisfy the relations of (FDT)-(CT) ≤ 100 ° C and (CT) ≥ 600 ° C. Winding, then cold rolling at a reduction rate of 50 to 95%, followed by recrystallization annealing, a method for producing a cold rolled steel sheet for ultra deep drawing, 3.C: 0.008% or less, Si : 0.5% or less, Mn: 1.0% or less, P: 0.15%
Below, S: 0.02% or below, Al: 0.010 to 0.10%, N: 0.008% or below, Ti: 0.035 to 0.20%,
And Nb: 0.001 to 0.015% and the amount of C, N, S and the amount of Ti and Nb added are 1.2 (C / 12 + N / 14 + S / 32) <(Ti / 48 + Nb / 93) Steel is hot-roughly rolled in a temperature range of 950 ° C or lower and Ar ₃ transformation point or higher, and then finish rolled at a rolling reduction of 80% or more while lubricating it in a temperature range of Ar ₃ transformation point or higher and 500 ° C or higher. Performed, then subjected to cold rolling at a reduction rate of 50 to 95% after recrystallization annealing, followed by performing recrystallization annealing,
Manufacturing method of cold rolled steel sheet for ultra deep drawing, 4.C: 0.008% or less, Si: 0.5% or less, Mn: 1.0% or less, P: 0.15%
Or less, S: 0.02% or less, Al: 0.010 to 0.10%, N: 0.008% or less, Ti: 0.035 to 0.20%, N
b: 0.001 to 0.015% and B: 0.0001 to 0.0010%, and the amount of C, N, S and the amount of Ti and Nb added are 1.2 (C / 12 + N / 14 + S / 32) <(Ti / 48 + Nb / 93), the steel is hot-roughly rolled in the temperature range of 950 ° C or lower and the Ar ₃ transformation point or higher, and then rolled by 80% or more while being lubricated in the Ar ₃ transformation point or the 500 ° C or higher temperature range. Characterized by performing finish rolling at a rate, then, after performing recrystallization annealing, cold rolling at a reduction rate of 50 to 95%, and subsequently performing recrystallization annealing.
It is a method for manufacturing a cold rolled steel sheet for ultra deep drawing.

(Operation) Hereinafter, the present invention will be described in detail.

(1) Steel composition In this invention, steel composition is important, C: 0.008% or less, Si: 0.5% or less, Mn: 1.0% or less, P: 0.15% or less, S: 0.02% or less, Al: 0.010 ~ 0.10%, N: 0.008% or less, Ti: 0.035 ~ 0.20%, N
b: 0.001 to 0.015%, and the amount of C, N, S and the amounts of Ti and Nb added satisfy the relationship of 1.2 (C / 12 + N / 14 + S / 32) <(Ti / 48 + Nb / 93). There must be. In addition, B: 0.0001 for improving the secondary work embrittlement resistance and value anisotropy.
~ 0.0010% must be added.

If the steel composition does not satisfy the above conditions, excellent deep drawability cannot be obtained. The reasons for limiting each component will be described below.

(A) C: 0.008% or less, and the smaller the content of C, the better the deep drawability is, but it is preferable. However, if the content of C is 0.008% or less, there is no significant adverse effect, so the content is limited to 0.008% or less.

(B) Si: 0.5% or less, Si has the effect of strengthening the steel, and is added in the required amount according to the desired strength. However, if the added amount exceeds 0.5%, the deep drawability is adversely affected. % Or less.

(C) Mn: 1.0% or less, Mn has an action of strengthening steel and is added in a required amount according to desired strength. However, if the added amount exceeds 1.0%, deep drawability is adversely affected. % Or less.

(D) P: 0.15% 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%, deep drawability is adversely affected. % Or less.

(E) S: 0.02% or less, and the smaller the content of S is, the better the deep drawability is, but it is preferable. However, if the content of S is 0.02% or less, there is no significant adverse effect, so the content is limited to 0.02% or less.

(F) Al: 0.010 to 0.10%, Al is deoxidized and added as necessary to improve the retention of carbonitride forming elements, but if 0.010% or less, there is no addition effect, while 0.10% is added. Even if added in excess, no further deoxidizing effect can be obtained, so the content was limited to 0.010 to 0.10%.

(G) N: 0.008% or less, and the smaller the content of N, the better the deep drawability, which is preferable. However, if the content of N is 0.008% or less, there is no significant adverse effect, so the content is limited to 0.008% or less.

(H) Ti: 0.035 to 0.20%, Ti is a carbonitride forming element, reduces solid solution (C, N) in steel, and preferentially forms {111} surroundings advantageous for deep drawability. However, if the addition amount is 0.035% or less, there is no effect, and if it is added over 0.20%, no further effect can be expected, and conversely it leads to deterioration of the surface quality. Limited to%.

(I) Nb: 0.001 to 0.015%, Nb is a carbide-forming element, which has the effect of reducing the solid solution C in steel and is also effective in refining the microstructure before finishing hot rolling. That is, even if there is no solid solution (C, N) in the steel, if the structure before finish rolling is coarse, the
1} orientation is less likely to be formed. On the other hand, if the microstructure before finish rolling is fine, strain is likely to be accumulated and {111} orientation is formed on the hot-rolled sheet. Furthermore, it was also clarified that solute Nb has the effect of accumulating strain during rolling.
If the content is less than 0.001%, there is no effect, while 0.015%
%, No further effect can be expected and the recrystallization temperature increases, so the content was limited to 0.001 to 0.015%.

(J) B: 0.0001 to 0.0010%, B is effective for improving the secondary work embrittlement resistance and also for improving the anisotropy of the value. That is, when Nb and B coexist, the crystal grains become finer than the Nb-added material, and as a result, the anisotropy (Δr) of the value of the hot-rolled sheet decreases. When such a hot rolled sheet having a small Δr value is used as a cold rolled base material, the Δr value of the cold rolled sheet also becomes small. If the addition amount is less than 0.0001%, there is no effect, while
If it exceeds 0.0010%, the deep drawability will deteriorate, so 0.0001 to 0.
Limited to 0010%.

(K) 1.2 (C / 12 + N / 14 + S / 32) <(Ti / 48 + Nb / 93) When solid solution (C, N) does not exist before finish rolling, {111} orientation is preferential after hot rolling-annealing And the deep drawability of the hot rolled sheet is improved. In this invention, 1.2 (C / 12 + N / 14
+ S / 32) <(Ti / 48 + Nb / 93) and it was found that solid solution (C, N) does not exist before finish rolling by adding Ti and Nb in an equivalent amount or more with respect to C and N. . At that time, it was clarified that the value of the hot rolled sheet was improved.
And when the value of such a hot rolled sheet is high, it found out that the value after cold rolling-annealing improves markedly.

(2) Regarding the hot rolling process, the hot rolling process is important in the present invention. After the hot rough rolling is completed in the temperature range of 950 ° C. or lower and the Ar ₃ transformation point or higher, A
while lubricating alms at r ₃ transformation point 600 ° C. or higher temperature region, after the rolling reduction is subjected to finish rolling of 80% or more, hot rolling finishing temperature (FDT) and the coiling temperature (CT) is (FDT) − (CT) ≦ 100
℃ and (CT) ≧ 600 ℃ or more, after winding under the conditions that satisfy the relation of 950 ℃ or less, or after hot rough rolling in the temperature range of 950 ℃ or less Ar ₃ transformation point or more, 500 ℃ or less Ar ₃ transformation point It is necessary to perform recrystallization annealing after rolling at a rolling reduction of 80% or more while applying lubrication in the temperature range of.

When the rough rolling is completed in the temperature range of 950 ° C or higher, the structure after rough rolling, that is, before finish rolling becomes coarse, so that the strain introduced during finish rolling is less likely to be accumulated, resulting in {111}. Azimuth is less likely to be formed. In addition, when finished in a temperature range below the Ar ₃ transformation point, the {100} orientation is formed during rough rolling, and the deep drawability deteriorates.
On the other hand, when rough rolling is completed in a temperature range of 950 ° C. or lower and Ar ₃ transformation point or higher, the structure before finish rolling becomes finer, so that strain introduced during finish rolling tends to be accumulated, resulting in { The 111} orientation is preferentially formed, and the deep drawability is improved. Note that the rolling reduction during rough rolling is due to the refinement of the structure.
50% or more is desirable.

Further, when the finish rolling is finished in the temperature range of the Ar ₃ transformation point or higher, the texture becomes random due to the γ → α transformation, and excellent deep drawability cannot be obtained. On the other hand, even by lowering the finishing temperature to 500 ° C. or less, can not be expected even more deep drawability improving, only the rolling load increases, following the rolling temperature Ar ₃ transformation point 500
It was set to ℃ or higher.

Also, if the total reduction ratio during finish rolling is not more than 80%,
Since the {111} orientation is not formed during rolling, the deep drawability is poor.

Furthermore, if lubrication rolling is not performed during finish rolling, additional shearing force acts on the steel sheet surface layer due to the frictional force between the roll and the steel sheet, resulting in unfavorable deep drawability on the steel sheet surface layer portion. Since the orientation is preferentially formed, the deep drawability deteriorates. Therefore, lubrication rolling is necessary.

In the case of the self-annealing material for winding that is not subjected to recrystallization annealing after rolling, CT ≧ 600 ° C. because recrystallization is not completed unless the winding temperature is 600 ° C. or higher. Further, in order to improve the additional drawability, it is advantageous that the rolling temperature is low and the winding temperature is high. Therefore, it is necessary to perform the rolling under the condition that the hot rolling finish temperature (FDT) and the coiling temperature (CT) satisfy (FDT) − (CT) ≦ 100 ° C. Incidentally, for those subjected to recrystallization annealing after hot rolling, winding self-annealing is not necessary,
The hot rolling end temperature may be 500 ° C. or higher, and the winding temperature may be low.

Recrystallization annealing after hot rolling may be either continuous annealing or box annealing. The annealing temperature is preferably in the range of 550 to 950 ° C. The heating rate may be in the range of 10 ° C / hr to 50 ° C / s.

(3) Regarding the cold rolling step, this step is indispensable for obtaining a high value, and it is indispensable to set the cold reduction rate to 50 to 95%. When the cold rolling reduction is less than 50% or more than 95%, excellent deep drawability cannot be obtained.

(4) Regarding the annealing step The cold rolled steel strip that has undergone the cold rolling step needs to be subjected to recrystallization annealing. The annealing method may be either a box annealing method or a continuous annealing method, but the heating temperature is in the range of recrystallization temperature (about 600 ° C) to 950 ° C.

The steel strip after annealing is used for shape correction and surface roughness adjustment.
You may add temper rolling of 10% or less.

The cold-rolled steel sheet obtained by the present invention can also be applied to an original plate of a surface-treated steel sheet for working. Surface treatments include zinc plating (including alloys), tin plating, enamel and the like.

(Example) After heating and soaking the steel slab having the composition shown in Table 1 at 1150 ° C., under the conditions shown in Table 2, rough rolling, finish rolling, pickling, cold rolling, and further 830 ° C.
It was annealed for -40s.

The material properties after cold rolling-annealing are also shown in Table 2. The tensile properties were measured using JIS No. 5 tensile test pieces, and the values were measured by the 3-point method after applying a 15% tensile prestrain.
Direction (rolling direction), D direction (45 ° rolling direction) and C direction (90 ° rolling direction) average value and anisotropy = (r _L + 2r _D + r _C ) / 4, Δr = (r _L It was calculated as −2r _D + r _C ) / 2. Further, as the evaluation of the secondary processing brittleness resistance,
A cylindrical sample processed with a limiting drawing ratio of 3.8 was cooled to −50 ° C., and then a pressure test was conducted to evaluate whether or not brittle cracking occurred.

It can be seen that the cold rolled steel sheet produced according to the present invention has excellent deep drawability and secondary work embrittlement resistance as compared with the comparative example.

In addition, a steel slab having the composition shown in Table 1 was heated at 1150 ° C.
After soaking, rough rolling was performed under the conditions shown in Table 3, then finish rolling, followed by pickling, and then No. 11 to No. 8
Rapid heating annealing at 30 ℃ -60s, and for Nos. 16-20,
Box-shaped annealing was performed at 750 ° C for 5 hours, followed by pickling, cold rolling, and then annealing at 830 ° C for 40 seconds.

Table 3 also shows the material properties of the cold rolled sheet after cold rolling and annealing.

It was confirmed that the cold-rolled steel sheet manufactured according to the present invention has good deep drawability and secondary work embrittlement resistance.

(Effects of the Invention) According to the present invention, it is possible to manufacture a cold-rolled sheet having a deep drawability that is far superior to conventional ones without causing an increase in manufacturing cost.

[Brief description of drawings]

FIG. 1 is a graph showing the effect of steel components on the values of hot-rolled sheet and cold-rolled sheet, and FIG. 2 is a graph showing the effect of rough rolling end temperature on the values of hot-rolled sheet and cold-rolled sheet. The figure is a graph showing the influence of the winding temperature on the values of the hot-rolled sheet and the cold-rolled sheet.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kozo Kadoyama 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Technical Research Headquarters (56) References JP 63-145720 (JP, A) JP 63 -121623 (JP, A) JP-A-63-86819 (JP, A) JP-A-63-76848 (JP, A) Actually opened 61-119621 (JP, U)

Claims (4)

[Claims] 1. C: 0.008 wt% or less, Si: 0.5 wt% or less, Mn: 1.0 wt% or less, P: 0.15 wt% or less, S: 0.02 wt% or less, Al: 0.010 to 0.10 wt%, N: 0.008 wt% or less, Ti: 0.035 to 0.20 wt% and Nb: 0.001 to
A steel containing 0.015 wt% and in which the amounts of C, N, S and the amounts of Ti and Nb added were 1.2 (C / 12 + N / 14 + S / 32) <(Ti / 48 + Nb / 93) ° C. after rough hot rolling at Ar ₃ transformation point or higher temperature region below with performing lubricated with Ar ₃ transformation point 600 ° C. or higher temperature range, performs finish rolling at 80% or higher reduction rate, then heat Winding under the condition that the final finishing temperature (FDT) and the winding temperature (CT) satisfy the relations of (FDT)-(CT) ≤ 100 ° C and (CT) ≥ 600 ° C, and then reduce by 50 to 95%. Method for producing a cold-rolled steel sheet for ultra deep drawing, which comprises performing cold rolling at a constant rate and then performing recrystallization annealing. 2. C: 0.008 wt% or less, Si: 0.5 wt% or less, Mn: 1.0 wt% or less, P: 0.15 wt% or less, S: 0.02 wt% or less, Al: 0.010 to 0.10 wt%, N: 0.008 wt% or less, Ti: 0.035 to 0.20 wt%, Nb: 0.001 to 0.015 wt% and B: 0.0001 to 0.0010 wt%, and the amount of C, N, S and the addition amount of Ti and Nb are 1.2. Steel that has a relationship of (C / 12 + N / 14 + S / 32) <(Ti / 48 + Nb / 93) is hot-roughly rolled in a temperature range of 950 ° C or lower and Ar ₃ transformation point or higher, and then Ar ₃ transformation point or lower 600 ° C. While rolling in the above temperature range, finish rolling is performed at a reduction ratio of 80% or more, and then the hot rolling finish temperature (FDT) and the coiling temperature (CT) are (FDT)-(CT) ≤ 100 ℃ and (CT) ≧ 600 ℃ under the conditions that satisfy the relationship, then cold rolling at a reduction rate of 50 ~ 95%, followed by recrystallization annealing, characterized by ultra deep drawing cold. Manufacturing method of rolled steel sheet. 3. C: 0.008 wt% or less, Si: 0.5 wt% or less, Mn: 1.0 wt% or less, P: 0.15 wt% or less, S: 0.02 wt% or less, Al: 0.010 to 0.10 wt%, N: 0.008 wt% or less, Ti: 0.035 to 0.20 wt%, and Nb: 0.001 to 0.015 wt%, and the amount of C, N, S and Ti
Steel with a relationship of 1.2 (C / 12 + N / 14 + S / 32) <(Ti / 48 + Nb / 93) with Nb addition amount was subjected to hot rough rolling in the temperature range below 950 ° C and above the Ar ₃ transformation point. After that, finish rolling at a reduction rate of 80% or more while performing lubrication in a temperature range of 500 ° C or less below the Ar ₃ transformation point, and then cold rolling at a reduction rate of 50 to 95% after recrystallization annealing. Characterized by performing recrystallization annealing subsequently,
Manufacturing method of cold rolled steel sheet for ultra deep drawing. 4. C: 0.008 wt% or less, Si: 0.5 wt% or less, Mn: 1.0 wt% or less, P: 0.15 wt% or less, S: 0.02 wt% or less, Al: 0.010 to 0.10 wt%, N: 0.008 wt% or less, Ti: 0.035 to 0.20 wt%, Nb: 0.001 to 0.015 wt% and B: 0.0001 to 0.0010 wt%, and the amount of C, N, S and the addition amount of Ti and Nb are 1.2. Steel that has a relationship of (C / 12 + N / 14 + S / 32) <(Ti / 48 + Nb / 93) is hot-roughly rolled in a temperature range of 950 ° C or less and Ar ₃ transformation point or higher, and then 500 ° C or less of Ar ₃ transformation point. While performing lubrication in the above temperature range, finish rolling at a reduction rate of 80% or more, then cold rolling at a reduction rate of 50 to 95% after recrystallization annealing, and then perform recrystallization annealing. Characterized by,
Manufacturing method of cold rolled steel sheet for ultra deep drawing.