JPH10130780A - Cold rolled steel sheet reduced in inplane anisotropy and excellent in formability, and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cold rolled steel sheet reduced in inplane anisotropy and excellent in formability by adding specific amounts of Ti to a low C aluminum killed steel and specifying hot rolling, cold rolling rate, and conditions in annealing, etc., respectively. SOLUTION: A steel, having a composition consisting of, by weight, 0.02-0.06% C, <=0.5% Si, 0.05-2.0% Mn, <=0.10% P, <=0.02% S, 0.005-0.1% Al, <=0.01% N, Ti in an amount satisfying Ti-48×(N/14+S/32)>=0.02 and Ti<=0.1%, and the balance essentially Fe is used. This steel is hot-rolled at >=800 deg.C and coiled at <=750 deg.C. After acid pickling, cold rolling is performed at 70-95% rolling rate. The resultant steel sheet is heated at >=5 deg.C/sec temp.-rise rate up to a temp. between the recrystallization temp. and the Ac3 point and held at this temp. for <=5min. The steel sheet is cooled at >=5 deg.C/sec cooling rate down to 250-500 deg.C and subjected to overaging treatment in this temp. region for <=10min. The degree of elongation of annealed recrystallized grains in the cross section parallel to a rolling direction is regulated to >=1.5, and the index Δr of inplane anisotropy using r-value is regulated to <=0.1 absolute value.

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 having a small in-plane anisotropy and excellent formability and a method for producing the same, and more particularly, to a deep drawn shape such as a cylinder or a square tube. TECHNICAL FIELD The present invention relates to a cold-rolled steel sheet having a small in-plane anisotropy and being excellent in formability suitable for an automobile part and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Material properties required for steel sheets for automobiles are as follows.
In recent years, it has become increasingly sophisticated year by year. In particular, automobile parts such as fenders for automobile outer panels and oil pans for automobile engines are subjected to extremely severe press forming. Therefore, steel sheets for automobiles applied to these parts are required to have deep drawability and ductility. Further improvements are expected. Furthermore, recently, due to global environmental problems such as CO ₂ emission regulations, improvement in fuel efficiency has been demanded, while demand for improvement in collision safety has also increased. In order to meet such demands, not only the improvement of the engine efficiency and the improvement of the structure of the vehicle body, but also the reduction of the weight and strength of the vehicle body have been attempted. Speaking of steel plates for automobiles, tensile strength is 3
BACKGROUND ART High-strength cold-rolled steel sheets having a formability of 40 MPa or higher and having good formability have come to be widely used for various parts constituting a vehicle body of an automobile.

As a method for producing a high-strength cold-rolled steel sheet having excellent formability, a solid solution strengthening element such as Mn, P, or Si is added.
2. Description of the Related Art A method of manufacturing a very low carbon steel to which a carbonitride forming element such as Ti or Nb is added by a continuous annealing apparatus is well known.
For example, the invention disclosed in Japanese Patent Publication No. 59-42742 is an invention relating to an ultra-low carbon high strength cold rolled steel sheet to which Ti is added in a complex manner. However, these conventional cold-rolled steel sheets have a drawback that the anisotropy is large. The high-strength cold-rolled steel sheet is not only used for parts subjected to bending or light drawing, but may also be formed into a deep drawn shape such as a cylinder or a square tube. If the height of the ears is large when forming such a part, the thickness of the formed part fluctuates depending on the rolling direction, and there is a quality problem that sufficient uniformity as a part cannot be obtained, and the material yield is poor. Economic problems such as these will become apparent.

The height and direction of the ear are closely related to the in-plane anisotropy Δr of the r value, and the smaller the absolute value of Δr, the smaller the height of the ear. Specifically, assuming that the Rankford values in the 0 °, 45 °, and 90 ° directions with respect to the rolling direction are r ₀ , r ₄₅ , and r ₉₀ , respectively, Δr becomes Δr = (r
₀₋₂ × r ₄₅ + r ₉₀ ) / 2. If the direction of ear generation is r ₉₀ ≧ r ₀ > r ₄₅ (V-shaped distribution), the directions are 0 ° and 90 ° from the rolling direction, and r ₄₅ > r ₉₀
If ≧ r ₀ (reverse V-shaped distribution), the direction is 45 ° from the rolling direction. The in-plane anisotropy of the r value is due to the texture, and when the {110} <100> orientation is strong, r
_It shows anisotropy of V-shaped distribution of ₉₀ ≧ r ₀ > r ₄₅ , {100}
When the <110> orientation is strong, an inverted V-shaped distribution of r ₄₅ > r ₉₀ ≧ r ₀ is exhibited.

Therefore, as a measure for improving the anisotropy of such a high-strength cold-rolled steel sheet, Japanese Patent Application Laid-Open No. 62-287018 discloses a method in which a steel containing Ti and Nb is added in a temperature range where recrystallization in the austenite range does not occur. There is disclosed an invention in which anisotropy is reduced by hot rolling, immediately winding at a low temperature, fixing solid solution C and solid solution N during hot rolling, and performing cold rolling and recrystallization annealing. Also, JP-A-62-161919 discloses that
A hot-rolled steel sheet having a low anisotropy by precipitating appropriate AlN by lowering the slab heating temperature and raising the winding temperature by hot rolling is cold-rolled at a high cold-rolling rate of 85 to 93%. Then, an invention of manufacturing a thin steel sheet having small anisotropy by recrystallization annealing is disclosed. In addition,
-3732 and JP-B-8-14003,
Based on a low carbon aluminum killed steel component system, Ti or Nb is added and N is fixed as these nitrides to suppress the precipitation of AlN during annealing and control the size of TiC precipitates. There is disclosed an invention for reducing the performance.

[0006]

However, the invention described in Japanese Patent Application Laid-Open No. 62-287018 discloses a method for improving the anisotropy of a high-strength cold-rolled steel sheet in a component system based on an ultra-low carbon steel. However, in order to reduce interstitial solid solution elements such as C and N, secondary refining such as RH must be performed, and there is a problem that steelmaking costs are increased.
Further, the invention described in Japanese Patent Application Laid-Open No. 62-161919 requires a high cold rolling ratio of 85% or more to improve anisotropy, so that the load of cold rolling increases. is there. Further, the inventions described in JP-B-57-3732 and JP-B-8-14003 are based on the premise of box annealing that requires a long time, and have a problem that the production amount per unit time is low.

According to the present invention, in order to improve the in-plane anisotropy of the r value, the precipitate size, distribution and precipitation time of the precipitates are optimized, and the {110} <100> orientation or An object of the present invention is to provide a cold-rolled steel sheet having small in-plane anisotropy and excellent formability by suppressing generation of the {100} <110> orientation, and a method for producing the same.

[0008]

Means for Solving the Problems The inventors of the present invention considered the difference between the r-value planes of cold-rolled steel sheets in view of the production by an industrial-scale continuous annealing equipment or a continuous hot-dip galvanizing equipment which is currently usually employed. As a result of intensive studies to improve the anisotropy, there is a strong correlation between the elongation degree of recrystallized grains and the Δr value of a steel sheet obtained by adding Ti or Nb to a low carbon aluminum killed steel as shown in FIG. Was found. In addition, the present inventors have newly found that a steel sheet having an Δr value ≦ ± 0.1 can be manufactured by limiting the slab reheating temperature, hot rolling conditions, cold rolling ratio, annealing conditions, and the like.

The present invention has been made on the basis of the above findings. The gist of the present invention is as follows: (1) C: 0.02 to 0.06% by weight, Si ≦
0.5%, Mn: 0.05 to 2.0%, P ≦ 0.10
%, S ≦ 0.02%, Al: 0.005 to 0.1%, N
≦ 0.01%, and further, Ti is added to Ti-48 ×
(N / 14 + S / 32) ≧ 0.02 and Ti ≦ 0.1
%, The balance being Fe and unavoidable impurities, the elongation of the recrystallized annealing grains in a section parallel to the rolling direction being 1.4 or more, and a surface using the Rankford value. A cold-rolled steel sheet having a small in-plane anisotropy and an excellent formability, wherein the index Δr of the in-plane anisotropy is 0.1 or less. (2) The cold-rolled steel sheet having a small in-plane anisotropy and an excellent formability according to the above (1), further comprising Nb ≦ 0.1% by weight.

(3) C: 0.02 to 0.0% by weight
6%, Si ≦ 0.5%, Mn: 0.05-2.0%, P
≦ 0.10%, S ≦ 0.02%, Al: 0.005
0.1%, N ≦ 0.01%.
i−48 × (N / 14 + S / 32) ≧ 0.02 and T
i ≦ 0.1% is contained within the range satisfying the condition, and the balance is F
e, and a steel consisting of unavoidable impurities is hot-rolled in a temperature range of 800 ° C. or more, then wound at 750 ° C. or less, pickled, and subjected to cold rolling at a rolling ratio of 70% or more and 95% or less. And further, at a heating rate of 5 ° C./s or more, at a recrystallization temperature or more,
Ac is heated to a temperature range of ₃ points or less, maintained at the temperature range for 5 minutes or less, cooled at a cooling rate of 5 ° C./s or more to a temperature range of 250 to 500 ° C., and cooled to a temperature range of 10 minutes or less at the temperature range. The aging treatment is characterized in that the degree of elongation of the recrystallized annealing grains in a section parallel to the rolling direction is 1.4 or more, and the index Δr of in-plane anisotropy using the Rankford value is 0. A method for producing a cold-rolled steel sheet having a small in-plane anisotropy of 1 or less and excellent in formability.

[0011] (4) The steel may further contain N
b) 0.1% and the hot-rolling end temperature is not lower than the Ar ₃ transformation point temperature. This is a method for producing a rolled steel sheet. However, the elongation here is a value to be measured by the method shown in JIS G 0552. The present invention is also applicable to hot-dip galvanized steel sheets.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
First, the reasons for limiting the chemical components of the present invention will be described.
If C exceeds 0.06%, the elongation of the recrystallized grains becomes small. 0.02
%, The Δr value becomes too large, so that 0.02
% Or more. Si is a solid solution strengthening element, and 0.5%
If added in an excessive amount, solid solution hardening becomes remarkable and becomes unsuitable for processing. In the case of hot-dip galvanizing, the content is preferably 0.1% or less for the adhesion of hot-dip galvanizing.

Mn is contained in an amount of 0.1 to prevent red embrittlement of steel.
More than 05% is required. Further, if added in excess of 2.0%, the ductility decreases, so the content is made 2.0% or less. In addition, A of Mn
If leverage effect of lowering the c _3-point it is necessary to ensure the temperature of recrystallization annealing is preferably 1.0% or less. P is a strong solid solution strengthening element and is added according to the required strength level. However, if the addition exceeds 0.10%, the weldability is adversely affected.
0%.

If S is too large, it not only causes cracking during hot rolling, but also causes deterioration of the average r value. Therefore, the content of S should be reduced as much as possible. Al is 0.005 for deoxidation of molten steel.
However, if added in a large amount, not only increases nonmetallic inclusions and deteriorates ductility, but also increases cost, so the upper limit is set to 0.1%. N is an element unfavorable for the average r value like C, so N is set to 0.01% or less.

[0015] Ti is one of the most important additive elements in the present invention. Ti forms precipitates as TiN, TiS, Ti ₄ C ₂ S _2, etc. in the austenite temperature range, but in order to reduce the Δr value, TiC deposited in a lower temperature range than the precipitate temperature range of the precipitates is effective. Use.
During continuous annealing under specific conditions, the {110} <100> orientation and the {100} <110> orientation, which are unfavorable for the in-plane anisotropy of the r value during recrystallization, grow and nucleate. If TiC is finely precipitated, the growth in these orientations can be suppressed. In order to effectively precipitate TiC during recrystallization, the amount of Ti added is Ti-
48 × (N / 14 + S / 32) ≧ 0.02. On the other hand, if added in excess of 0.1%, not only the effect of reducing the in-plane anisotropy of the r value is saturated, but also the surface properties and the chemical conversion property deteriorate, so the upper limit of Ti is 0.1%. The following is assumed. In hot-dip galvanizing applications, the addition of more than 0.06% of Ti deteriorates the adhesion of hot-dip galvanizing and causes powdering during press molding.

Nb is added as necessary to precipitate NbC effective for reducing the Δr value similarly to TiC. However, the addition of more than 0.1% saturates the effect of reducing the in-plane anisotropy of the r value, so the upper limit is made 0.1%. When Nb is added in excess of 0.03%, the recrystallization temperature during annealing rises significantly. Therefore, if it is necessary to lower the recrystallization temperature, it is preferably set to 0.03% or less. In the present invention, the other components are Fe, but the inclusion of unavoidable impurities mixed from the smelting raw material such as scrap is allowed.

Next, the reasons for limiting the production method of the present invention will be described.
In the present invention, the additive element is added to molten steel in the form of a simple substance or a master alloy.
By adding and casting to achieve the target component content.
The slab obtained in this way is sent directly to a hot rolling mill as
Or after reheating in a heating furnace after cooling to room temperature
Hot rolling may be performed. There are no particular restrictions on the reheating temperature
However, if the temperature is lower than 1200 ° C., Ti _FourC_TwoS_TwoIs
Precipitate precipitates do not form a solid solution again, and Ti used during annealing
Since the amount of C decreases, the reheating temperature should be 1200 ° C or more.
desirable.

The hot rolling step needs to be completed in a temperature range in which the final rolling final pass temperature (FT) is 800 ° C. or higher. If the rolling temperature falls below 800 ° C. during hot rolling, the α-rolling occurs near the surface layer of the hot-rolled sheet, the grain size near the surface layer becomes coarse, and the material variation in the sheet thickness direction becomes remarkable. This is because the surface quality is reduced. However, when Nb is added, recrystallization in the α phase is suppressed, so that the {110} <100> orientation and the {10}
Since the orientation in which the 0｝ <110> orientation is easily generated remains in the hot-rolled sheet stage, it is necessary to end the hot rolling in a temperature range of Ar ₃ or more.

When the winding temperature after the finish rolling is higher than 750 ° C., C solid-dissolved in the hot-rolled sheet coarsely precipitates as precipitates such as TiC and NbC and reduces the Δr value during annealing. Effective for solid solution C or fine TiC, NbC
Therefore, the winding temperature is limited to 750 ° C. or less. In the cold rolling process after pickling, the rolling reduction is 70% or more,
% Cold rolling. If the rolling reduction is less than 70%, recrystallization is not sufficiently performed in the subsequent annealing step, so that ductility is deteriorated. In addition, even if cold rolling is performed at a rolling ratio of more than 95%, the in-plane anisotropy is rather increased. Therefore, the rolling reduction in the cold rolling process is set to 70% or more and 95% or less.

The annealing step in the present invention is based on continuous annealing. Performing continuous annealing under specific conditions is not preferable for in-plane anisotropy of r value during recrystallization {110}
Grain growth in the <100> orientation and the {100} <110> orientation occurs. At this time, the grain growth can be suppressed by finely depositing TiC. If the rate of temperature rise is less than 5 ° C./s, unfavorable in-plane anisotropy {110} <100> orientation and {100} <11
Since the crystal grains having the <0> orientation generate nuclei, the heating rate is limited to 5 ° C./s or more.

If the holding time at the annealing temperature exceeds 5 minutes, {110} <10 is not preferable for in-plane anisotropy.
The holding time at the annealing temperature is limited to 5 minutes or less since TiC and NbC, which suppress the crystal grain growth in the 0> and {100} <110> directions, grow coarsely and lose the effect of suppressing the crystal grain growth. I do. The annealing temperature is A
c If the temperature is higher than ₃ points, annealing occurs in the γ region or α + γ two-phase region, causing coarsening of crystal grains, which not only deteriorates strength and ductility but also reduces in-plane anisotropy. Since the formation of the recrystallized texture is significantly inhibited, the Ac point is set to ₃ or less. If the temperature is lower than the recrystallization temperature, not only recrystallization does not occur but ductility is deteriorated, but also the formation of a recrystallized texture with small in-plane anisotropy does not occur.

The cooling rate after annealing (primary cooling rate) is 5
If the temperature is lower than ℃ / s, TiC and NbC grow coarsely and the effect of suppressing the growth of crystal grains is lost, and the {110} <100> orientation and {100} <110> orientation which are not preferable for in-plane anisotropy. Therefore, the primary cooling rate is limited to 5 ° C./s or more. The overaging treatment does not affect the in-plane anisotropy, but the ductility is improved by precipitating solute C present in supersaturation as cementite. Overage for less than a minute. However, when the temperature exceeds 500 ° C., the amount of precipitated cementite is small, so that solid solution C remains and ductility cannot be obtained. On the other hand, if the temperature is lower than 250 ° C., in order to sufficiently precipitate cementite, it is necessary to significantly increase the overaging time, which is not realistic. Further, even if the overaging treatment is performed for more than 10 minutes at the above-mentioned processing temperature, the effect of the overaging is saturated.
The following is assumed.

In the present invention, when forming a deep drawn part such as a cylinder or a square tube, if the height of the ear is large, the thickness of the formed part varies depending on the rolling direction, and sufficient uniformity as a part is obtained. Since the quality problem that the material cannot be obtained and the economic problem such as a poor material yield become apparent, the in-plane anisotropy index Δr using the r value needs to be 0.1 or less. Further, in order to set the index Δr to 0.1 or less, it is necessary that the degree of extension of the annealing recrystallized grains in a section parallel to the rolling direction is 1.4 or more.

[0024]

The present invention will be further described below with reference to examples. (Example 1) Steels of A to O having the chemical components shown in Table 1 were tapped in a blast furnace using iron ore as a raw material, melted in a converter, continuously cast, and heated at a temperature of 1230 ° C. After reheating and rolling at a finish rolling temperature of 850 ° C. to 900 ° C. to 6.0 mm as shown in Table 2, each was wound at a temperature shown in Table 2. After pickling, cold rolling is performed to 0.8 mm (rolling ratio 86.7%), and a continuous annealing line (maximum heating temperature 760)
７780 ° C., skin pass rolling ratio 0.8%).
However, for steels C and E, hot-dip galvanizing line after cold rolling (maximum heating temperature 770-780 ° C, hot-dip galvanizing 460 ° C, alloying treatment 520 ° C × 20 seconds, skin pass rolling ratio 0.8%) I passed through. However, the indication of the chemical composition is% by weight and nitrogen N is ppm by weight. The tensile test of the annealed plate obtained in this way, the test material,
First, it was processed into a No. 5 test piece described in JIS Z 2201, and the test was performed according to the test method described in JIS Z 2241.

[0025]

[Table 1]

Table 2 shows the test results. However, the symbols in the table are FT: finish rolling end temperature, CT: winding temperature, ST: annealing temperature, YP: yield strength, TS: tensile strength, El: elongation at break, r: average Rankford value, Δ
r: Absolute value of in-plane anisotropy index, e: Extensibility of crystal grains. According to the present invention, there are 11 steels A to K, each having a degree of elongation of annealed recrystallized grains of 1. in a section parallel to the rolling direction.
A cold rolled steel sheet having an in-plane anisotropy index of not less than 4 and an in-plane anisotropy index r using an r value of 0.1 or less and having excellent formability is obtained. Steels other than the above are outside the scope of the present invention for the following reasons. Steel N has a Ti-48 (N / 14 + S
/32)=0.015] In addition, since steel L, M, and O have a higher winding temperature than the range of the present invention, C in solid solution in the hot-rolled sheet is changed to TiC, NbC, or the like. Precipitates are coarsely precipitated and solid solution C or fine TiC and NbC effective for reducing the Δr value during annealing cannot be secured, and the elongation of the recrystallized annealing grains in a cross section parallel to the rolling direction is reduced. 1.4
And the index Δr of in-plane anisotropy using the r value is not more than 0.
It is more than one.

[0027]

[Table 2]

(Example 2) Among the slabs having the chemical compositions shown in Table 1, steels A, B, C, D, E and F were cold rolled and annealed under conditions different from the production conditions performed in Example 1. Boards were manufactured. First, it was reheated to various temperatures in a heating furnace, rolled to 2.0 to 10.0 mm, and wound.
After the pickling, cold rolling was performed to 0.8 mm, and the sheet was passed through a continuous annealing line (skin pass rolling reduction 0.8%). However,
For steels C-3, C-4 and E-3, after cold rolling,
Hot-dip galvanizing line (hot-dip galvanizing 460 ° C, alloying treatment 520 ° C x 20 seconds, skin pass rolling rate 0.8%)
Passed through. Table 3 shows details of the manufacturing conditions.
However, the symbols in the table are SRT: slab heating temperature, F
T: Finish rolling end temperature, CT: Winding temperature, CR: Cold rolling reduction, ST: Annealing temperature, YP: Yield strength, TS: Tensile strength, El: Elongation at break, r: Average Rankford value, Δ
r: Absolute value of in-plane anisotropy, e: Elongation degree of crystal grains.

A tensile test was performed in the same manner as in Example 1. Table 3 shows the test results. The symbols in the table are
This is the same as Table 1 in the first embodiment. The steel of the present invention is steel A-2,
A-1, A-2, A-3, B-1, B-2, B-3, B
-4, B-5, C-3, D-1, D-2, D-3, E-
1, the in-plane anisotropy index of the in-plane anisotropy Δr using the r value is 0.1 or less, the elongation of the recrystallized annealing grains in a cross section parallel to the rolling direction is 1.4 or more. A cold rolled steel sheet having low formability and excellent formability has been obtained.

The comparative steels are outside the scope of the present invention for the following reasons. In steels B-6 and E-2, the finish temperature of the finish rolling is lower than the lower limit of the range of the present invention, and thus the elongation of crystal grains is out of the range of the present invention, and therefore, the in-plane anisotropy Δr Values are outside the scope of the invention. Steel C-4, F-1
Is T because the winding temperature exceeds the upper limit of the range of the present invention.
Precipitation of iC does not act effectively, and the elongation of the crystal grains is out of the range of the present invention, and therefore, the in-plane anisotropy Δr value is out of the range of the present invention. For steels A-4, C-2, and E-3, since the rolling reduction in cold rolling is lower than the lower limit of the range of the present invention,
In addition to the low driving force for recrystallization, the formation of a rolling texture is not sufficient, and thus the in-plane anisotropy Δr value is out of the range of the present invention. Since the annealing temperature of steel C-1 has not reached the recrystallization temperature, recrystallization does not sufficiently occur and not only does not have sufficient ductility, but also TiC precipitation is not sufficient, and therefore, the in-plane anisotropy Δr value Is outside the scope of the present invention.

[0031]

[Table 3]

[0032]

As described above, the present invention provides a cold-rolled steel sheet having a small in-plane anisotropy and excellent formability, and a method for producing the same. The invention is expected to greatly improve the moldability of automobile parts and the like formed into a deep drawing shape such as a rectangular cylinder, and has high industrial value.

[Brief description of the drawings]

FIG. 1 is a diagram showing the results of preliminary experiments leading to the present invention in the relationship between the elongation e of recrystallized grains after annealing in a cross section parallel to the rolling direction and the in-plane anisotropy Δr value.

FIG. 2 shows the elongation e and the in-plane anisotropy Δ of the recrystallized grains after annealing in a cross section parallel to the rolling direction in Examples of the present invention.
It is a figure which shows the relationship of r value and the range of this invention.

[Procedure amendment]

[Submission date] November 1, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 1

[Correction method] Change

[Correction contents]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Claim 3

[Correction method] Change

[Correction contents]

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction contents]

The present invention has been made on the basis of the above findings, and the gist thereof is as follows: (1) In terms of% by weight, C = 0.02 to 0.06%, and Si ≦
0.5%, Mn = 0.05-2.0%, P ≦ 0.10
%, S ≦ 0.02%, Al = 0.005 to 0.1%, N
≦ 0.01%, and further, Ti is added to Ti-48 ×
(N / 14 + S / 32) ≧ 0.02 and Ti ≦ 0.1
%, The balance being Fe and unavoidable impurities, the elongation of the recrystallized annealing grains in a section parallel to the rolling direction being 1.4 or more, and a surface using the Rankford value. A cold-rolled steel sheet having small in-plane anisotropy and excellent formability, wherein the absolute value of the index Δr of in-plane anisotropy is 0.1 or less. (2) Further, in weight%, Nb ≦
The cold-rolled steel sheet according to the above (1), which has a small in-plane anisotropy and excellent formability, comprising 0.1%.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction contents]

(3) C = 0.02 to 0.0% by weight
6%, Si ≦ 0.5%, Mn = 0.05-2.0%, P
≦ 0.10%, S ≦ 0.02%, Al = 0.005
0.1%, N ≦ 0.01%.
i−48 × (N / 14 + S / 32) ≧ 0.02 and T
i ≦ 0.1% is contained within the range satisfying the condition, and the balance is F
e, and a steel consisting of unavoidable impurities is hot-rolled in a temperature range of 800 ° C. or more, then wound at 750 ° C. or less, pickled, and subjected to cold rolling at a rolling ratio of 70% or more and 95% or less. And further, at a heating rate of 5 ° C./s or more, at a recrystallization temperature or more,
Ac is heated to a temperature range of ₃ points or less, maintained at the temperature range for 5 minutes or less, cooled to a temperature range of 250 to 500 ° C. at a cooling rate of 5 ° C./s or more, and cooled to a temperature range of 10 minutes or less at the temperature range. The aging treatment is performed, wherein the elongation of the recrystallized grains in a section parallel to the rolling direction is 1.4 or more, and the absolute value of the in-plane anisotropy index Δr using the Rankford value Is 0.
A method for producing a cold-rolled steel sheet having a small in-plane anisotropy of 1 or less and excellent in formability.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0023

[Correction method] Change

[Correction contents]

In the present invention, when forming a deep drawn part such as a cylinder or a square tube, if the height of the ear is large, the thickness of the formed part varies depending on the rolling direction, and sufficient uniformity as a part is obtained. Since the quality problem that the material cannot be obtained and the economic problem such as poor material yield become apparent, the absolute value of the in-plane anisotropy index Δr using the r value needs to be 0.1 or less. is there. Furthermore, in order to set the absolute value of the index Δr to 0.1 or less, the elongation of the recrystallized annealing grains in a cross section parallel to the rolling direction needs to be 1.4 or more.

[Procedure amendment 6]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction contents]

Table 2 shows the test results. However, the symbols in the table are FT: finish rolling end temperature, CT: winding temperature, ST: annealing temperature, YP: yield strength, TS: tensile strength, E1: elongation at break, r: average Rankford value, Δ
r: Absolute value of in-plane anisotropy index, e: Extensibility of crystal grains. According to the present invention, there are 11 steels A to K, each having a degree of elongation of annealed recrystallized grains of 1. in a section parallel to the rolling direction.
4 or more, and the index Δr of in- plane anisotropy using the r value
Cold-rolled steel sheet is obtained which pair value and excellent small formability plane anisotropy of 0.1 or less. Steels other than the above are outside the scope of the present invention for the following reasons. Steel N has a content of Ti-48 (N / 1
4 + S / 32) = 0.015] and steel L, M, O
Is because, because the winding temperature is higher than the range of the present invention, C solid-dissolved in the hot-rolled sheet is coarsely precipitated as precipitates such as TiC and NbC to reduce the Δr value during annealing. Effective solid solution C or fine TiC and NbC could not be secured, the degree of elongation of the annealing recrystallized grains in a section parallel to the rolling direction was less than 1.4, and in-plane anisotropy using r value Is greater than 0.1.

[Procedure amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0029

[Correction method] Change

[Correction contents]

A tensile test was performed in the same manner as in Example 1. Table 3 shows the test results. The symbols in the table are
This is the same as Table 1 in the first embodiment. The steel of the present invention is steel A-2,
A-1, A-2, A-3, B-1, B-2, B-3, B
-4, B-5, C-3, D-1, D-2, D-3, E-
1, the elongation of the annealing recrystallized grains in a cross section parallel to the rolling direction is 1.4 or more, and the absolute value of the in-plane anisotropy index Δr using the r value is 0.1 or less. A cold rolled steel sheet having small internal anisotropy and excellent formability has been obtained.

Claims (4)

[Claims] C .: 0.02 to 0.06%, Si ≦ 0.5%, Mn: 0.05 to 2.0%, P ≦ 0.10%, S ≦ 0. 02%, Al: 0.005 to 0.1%, N ≦ 0.01%, and Ti is further converted to Ti-48 × (N / 14 + S
/ 32) ≧ 0.02 and Ti ≦ 0.1% in the range that satisfies the conditions, the balance being Fe and unavoidable impurities, and the elongation of the recrystallized annealing grains in a cross section parallel to the rolling direction. Is 1.4 or more, and the Rankford value (r value)
A cold-rolled steel sheet having small in-plane anisotropy and excellent in formability, characterized in that the index Δr of in-plane anisotropy using is 0.1 or less. 2. The cold-rolled steel sheet according to claim 1, further comprising Nb ≦ 0.1% by weight in terms of in-plane anisotropy and excellent formability. 3. In% by weight, C: 0.02 to 0.06%, Si ≦ 0.5%, Mn: 0.05 to 2.0%, P ≦ 0.10%, S ≦ 0. 02%, Al: 0.005 to 0.1%, N ≦ 0.01%, and Ti is further converted to Ti-48 × (N / 14 + S
/32)≧0.02, and a steel containing Ti in a range satisfying the condition of 0.1% or less, with the balance being Fe and unavoidable impurities, after hot rolling in a temperature range of 800 ° C. or more,
It is wound up at 750 ° C. or less, pickled, cold rolled at a rolling ratio of 70% or more and 95% or less, and further heated at a rate of 5%.
After heating to a temperature range of not less than the recrystallization temperature and not more than ₃ points of Ac at a temperature of not less than 5 ° C. and holding at the temperature range of not more than 5 minutes, a cooling rate of 5 ° C.
/ S is cooled to a temperature range of 250 to 500 ° C. at a temperature of not less than 250 ° C., and an overaging treatment is performed in the temperature range for 10 minutes or less. A method for producing a cold-rolled steel sheet having a small in-plane anisotropy and an excellent formability, wherein the index Δr of the in-plane anisotropy using the Rankford value is not more than 1.4. 4. The steel according to claim 1, further comprising: Nb ≦
0.1% and the hot rolling end temperature is Ar
4. The method for producing a cold-rolled steel sheet having a small in-plane anisotropy and an excellent formability according to claim 3, wherein the temperature is _three or more transformation points.