JPH10183254A - Production of cold rolled steel sheet for deep drawing excellent in ridging resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a cold rolled steel sheet in which the improvement of productivity in hot rolling and the reduction of surface defects are attained and excellent in ridging resistance. SOLUTION: A steel slab contg., by weight, <=0.03% C and <=0.005% N or furthermore contg. 0.0003 to 0.003% B and contg. one or two kinds of 0.003 to 0.08% Ti and 0.002 to 0.05% Nb so as to satisfy the inequality of Ti/48+Nb/93>=C/12+N/14 (where Ti, Nb, C and N: weight%) is formed into a continuously cast slab, and after that, this steel slab is subjected to heating and soaking treatment at 900 to 1100 deg.C, is subjected to rough rolling so as to regulate the draft in a final rough stand to >=30% and is subjected to finish rolling so as to regulate the rolling temp. to less than the Ar3 point to >=800 deg.C to form into a hot rolled sheet, which is thereafter subjected to cold rolling and continuous annealing.

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 for deep drawing used in automobiles and the like, and more particularly to a method for producing a cold-rolled steel sheet for deep drawing having excellent ridging resistance.

[0002]

2. Description of the Related Art Conventionally, a hot-rolled steel sheet, which is a raw material of a cold-rolled steel sheet, is prepared by heating and equalizing a steel slab having a predetermined composition to a high temperature of 1200 ° C. or higher, followed by rough rolling and a temperature range of ₃ points or more of Ar. It was manufactured by subjecting it to finish rolling. High temperature heating such a slab, since deformation resistance of the steel by utilizing the low towards the high temperature, to other to achieve reduction of the rolling force, the finish rolling end temperature steel temperature above Ar ₃ point of the heating The purpose is to compensate for the temperature drop in the subsequent rough rolling and finish rolling stages. When the finishing temperature of the hot-rolled steel sheet is equal to or lower than the Ar ₃ point, the material of the hot-rolled steel sheet and the material of the cold-rolled steel sheet using the same become poor. Generally, if the slab heating temperature is set high and the hot-rolling finishing temperature is set to _three or more Ar points, the crystal orientation of the hot-rolled steel sheet is randomized, and a good cold-rolled steel sheet made of the same can be obtained.

[0003] However, high-temperature heating of the slab shortens the life of the heating furnace, thereby increasing costs such as repair costs of the furnace. In addition, the oxide film formed on the surface of the slab and steel slab becomes thicker, and the scale becomes smaller. This also contributed to an increase in surface defects such as biting and a decrease in yield. Furthermore, since the rolling is performed in the austenite (γ) region, there is a problem that the load on the rolling roll increases and the roll life is shortened.

[0004] In response to such a problem, for example,
Japanese Patent No. 32696 discloses that hot rolling is performed using Ar. _ThreeHeat at low temperatures below the point
A method for producing a low-carbon cold-rolled steel sheet to be hot-rolled is disclosed.
You. This method uses Ar_ThreeAustena below 600 ° C
20% finish reduction in (γ + α) two phase region
By performing hot rolling to ％ 60%, Ar_ThreeAbove the point
Carbon that is comparable to the steel material finished and rolled in
The purpose is to obtain cold-rolled steel sheets. However, Ar_Three
If rolling is performed below the point, mechanical properties, especially ductility,
Remarkable deterioration of properties, and ridging
The problem that it was easy to do was left.

[0005] Ridging as used herein refers to the time when a product is processed.
Surface defects that occur, used on the outermost surface of processed products
Critical defects are often encountered in cold-rolled steel sheets for deep drawing.
Become. Also, Japanese Patent Application Laid-Open No. Hei 5-132718 discloses that C, N, S
And further, one or both of Ti and Nb
Was restricted to steels in relation to the amounts of C, N and S._Three~ Ar _Three
Rolling with a total reduction of 35% or more in a temperature range of + 100 ° C
After that, the average cooling during the γ → α transformation is suddenly increased at 10 ° C / sec or more.
Cool down, Ar_ThreeThe total draft in the temperature range below the point is 70% or more
Rolled at 600-750 ° C, pickled and cooled
Cold drawn steel sheet for deep drawing without ridging
A manufacturing method is disclosed. However, with this method,
Requires quenching after rolling, complicating the process, cooling equipment
There were problems in terms of cost and efficiency, such as installation of equipment.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, improves the productivity of hot rolling, reduces surface defects, and provides a method for producing a cold-rolled steel sheet having excellent ridging resistance. The purpose is to:

[0007]

SUMMARY OF THE INVENTION The present invention provides, in weight percent,
C: 0.003% or less, N: 0.005% or less, and T
One or two of i: 0.003 to 0.08% and Nb: 0.002 to 0.05% were obtained by the following formula (1): Ti / 48 + Nb / 93 ≧ C / 12 + N / 14 (1) , Ti, Nb, C, N:% by weight) to obtain a continuous cast slab, and then heat and soak the steel at 900 to 1100 ° C to obtain a final rough stand draft. Is subjected to a rough rolling of 30% or more and a finish rolling of a rolling temperature of 800 ° C. or more at an Ar ₃ point or less to form a hot-rolled sheet, and then subject the cold-rolled and continuous annealing to the hot-rolled sheet. This is a method for producing a cold-rolled steel sheet for deep drawing having excellent ridging resistance.

[0008] The present invention also relates to a method of the present invention wherein C: 0.003% by weight.
Below, N: 0.005% or less, B: 0.0003 to 0.003%, Ti: 0.003 to 0.08% and Nb: 0.002 to 0.05%
One or two of the above are represented by the following formula (1): Ti / 48 + Nb / 93 ≧ C / 12 + N / 14 (1) (where Ti, Nb, C, N: wt%) After making the steel satisfactorily contained into a continuous cast slab, the slab is subjected to heating and soaking at 900 to 1100 ° C, and the rough rolling is performed so that the final rough stand draft is 30% or more. Ar ₃ points or less and finish rolling to 800 ° C. or more to form a hot-rolled sheet, and then subject the cold-rolled sheet to cold rolling and continuous annealing. This is a method for producing a rolled steel sheet.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limitation in the present invention will be described below. In the present invention, C of the continuous cast slab is 0.
003% or less and N should be 0.005% or less. In the present invention in which continuous annealing is performed, when the C and N contents exceed the above values, the non-aging property and the deep drawability deteriorate.

In the present invention, in addition to the above composition, T
One or two of i and Nb are added. Ti and Nb are added to fix solid solution C and solid solution N, precipitate as stable carbide or nitride, and form a texture advantageous for deep drawability. The amounts of Ti and Nb to be added are 0.003, respectively.
-0.08%, 0.003-0.05%. If it is less than 0.003%, the above effects cannot be expected. On the other hand, Ti is 0.08%,
Even if Nb is added in excess of 0.05%, improvement in mechanical properties in proportion to the added amount cannot be expected.

Further, Ti and Nb are within the above range and C,
Adjustment is made so as to satisfy the expression (1) in relation to the N amount.
Equation (1), Ti / 48 + Nb / 93 ≧ C / 12 + N / 14 (where,
If Ti, Nb, C, and N are not satisfied, the amounts of Ti and Nb for fixing solid solution C and solid solution N are insufficient, and the non-aging property and the deep drawability deteriorate. In addition to the above components, Mn
0.20% or less, Si is 0.1% or less, P is 0.03% or less, S is
It is preferably set to 0.015% or less. The other balance is substantially Fe.

The slab having the composition described above is subjected to heating and soaking at 900 to 1100 ° C. In the present invention, the heat soaking heat treatment of the slab, ductility by coarsening the precipitates generated during heating and soaking,
This is performed to improve drawability. If the heating temperature exceeds 1100 ° C., the precipitates become finer, and improvement in ductility and drawability cannot be obtained. On the other hand, when the temperature is lower than 900 ° C., the effect of reducing the amount of heat is remarkable, but the deformation resistance of the steel sharply increases, so that the rolling becomes difficult.

The slab that has been heated and soaked is formed into a hot-rolled sheet by hot rolling. Hot rolling is composed of two stages of rough rolling and finish rolling. Ridging is metallurgically caused by the fact that after hot rolling, a group of crystal orientations that are not easily divided even after a working-recrystallization process, for example, {100} orientation grains are stretched in the rolling direction and remain. Is what you do. The present inventors have newly found that the ridging is remarkable due to the grain growth following the recrystallization after the rough rolling, and the occurrence of the ridging can be prevented by suppressing the grain growth following the recrystallization after the rough rolling. Therefore, in the present invention, the final stand draft of the rough rolling is reduced by 30%.
Above. Thereby, grain growth after recrystallization is suppressed, and generation of ridging can be prevented. If it is less than 30%, the above effects cannot be expected.

When B is contained, the content is preferably at least 35%. The upper limit of the rolling reduction of the final stand in the rough rolling is determined mainly by the relationship between the steel type and the capacity of the rolling mill, and is about 40% for this steel type. In addition, rough rolling
to end at r ₃ points or more are preferable from the viewpoint of ridging prevention.

In the finish rolling, α of 800 ° C. or more at an Ar ₃ point or less
Zone rolling. By using the α region rolling, the deformation resistance is low and the rolling power can be reduced, which is more economical than when rolling is performed in the γ region at the same temperature. However, when the rolling temperature is lowered to less than 800 ° C., recrystallization after finish rolling becomes difficult, and the target mechanical properties cannot be secured. In addition,
When B is contained, it is necessary to ensure recrystallization after hot rolling.
The temperature is preferably set to 0 ° C. or higher.

The hot rolled sheet is pickled after being wound around a coil. The pickling is performed to remove the surface scale of the hot-rolled sheet, and the pickling solution and the processing conditions may be generally known methods. The hot rolled sheet treated by the method of the present invention has a thin oxide layer, good pickling properties, and little loss due to pickling. The hot-rolled sheet is subjected to cold rolling to a predetermined thickness after pickling, and then to continuous annealing to obtain a product.

In the cold rolling, a predetermined product thickness may be obtained.
In the present invention, the conditions of the cold rolling are not particularly specified. However, in order to improve the properties after annealing, it is desirable that the rolling reduction of the cold rolling is 60% or more. The continuous annealing after the cold rolling is desirably performed in a temperature range of 600 ° C to 900 ° C. The cold-rolled steel sheet of the present invention is mainly used for deep drawing, but has a zinc plating property, a tin plating property,
It is needless to say that it has excellent surface treatment properties such as enamelness and can be applied as various surface-treated original sheets subjected to surface treatment such as zinc plating, tin plating, and enamel.

[0018]

EXAMPLES Steel having the composition shown in Table 1 was melted by a converter,
After a slab was formed by continuous casting, hot rolling was performed under the rolling conditions shown in Tables 2 and 3 to obtain a hot-rolled sheet. These hot-rolled sheets were pickled with a hydrochloric acid solution and cold-rolled under the rolling conditions shown in Tables 2 and 3 to obtain cold-rolled sheets having a thickness of 0.7 to 1.2 mm. Next, these cold-rolled sheets were annealed under continuous annealing conditions shown in Tables 2 and 3.

[0019]

[Table 1]

The tensile properties of these annealed sheets were examined using JIS No. 5 test pieces. In addition, the ridging property was measured on JIS No. 5 test pieces cut from the rolling direction of these annealed sheets.
After a tensile prestrain of 15% was added, the surface irregularities were visually evaluated. In the evaluation, 1 was evaluated as good and 5 was evaluated as inferior and 1 to 5 was evaluated. Tables 2 and 3 show these results. Evaluation 1,
The occurrence of gilding in No. 2 is of such a degree that there is no practical problem.

[0021]

[Table 2]

[0022]

[Table 3]

From Tables 2 and 3, the steel sheet of the present invention manufactured within the scope of the present invention has an elongation value of 48% or more, an r value of 1.9 or more, excellent tensile properties, drawability, and ridging properties. The evaluation was 1 or 2, and the occurrence of ridging was of a practically acceptable level. On the other hand, in the steel sheet of the comparative example out of the range of the present invention, the elongation value and the r value are low, or ridging occurs.

Test No. 5 and Test No. 16 with low finishing rolling temperature
Has a low r value. Test No. 7, Test No. 1 with high heating temperature
In 8, ridging has occurred. In Test No. 9 and Test No. 20, where the rolling reduction of the final stand in the rough rolling was low, the r value was low and ridging occurred. In tests No. 10, No. 11, No. 21 and No. 22 in which the steel composition was out of the range of the present invention, the r value was low.

[0025]

According to the present invention, since a complicated process and special equipment are not required, a cold-rolled steel sheet having improved hot rolling productivity and excellent ridging resistance can be manufactured at low cost. Since the heating is performed at a lower temperature, an industrially remarkable effect of reducing surface defects such as biting of the surface scale can be expected.

Claims (2)

[Claims] 1. The method according to claim 1, wherein the content of C is 0.003% or less, N is 0.005% or less, and one or two of Ti: 0.003 to 0.08% and Nb: 0.002 to 0.05% are represented by the following ( 1) After making a steel containing the steel satisfying the formula into a continuous cast slab, the slab is heated and soaked at 900 to 1100 ° C., and the rough rolling is performed to reduce the final rough stand rolling reduction to 30% or more. A hot-rolled sheet obtained by subjecting a hot-rolled sheet to finish rolling in which the rolling temperature is Ar ₃ points or less and 800 ° C. or higher, and then subjecting the hot-rolled sheet to cold rolling and continuous annealing, which is excellent in ridging resistance. Manufacturing method of cold-rolled steel sheet for deep drawing. Note Ti / 48 + Nb / 93 ≧ C / 12 + N / 14 (1) where, Ti, Nb, C, N: wt% 2. The composition according to claim 2, wherein C: 0.003% or less, N: 0.005% or less, B: 0.0003 to 0.003%, and Ti: 0.003 to 0.08% by weight.
% And Nb: A continuous cast slab containing steel containing one or two of 0.002 to 0.05% so as to satisfy the following formula (1), and then heating the slab at 900 to 1100 ° C. After performing soaking heat treatment and performing rough rolling in which the final rough stand draft is 30% or more and finish rolling in which the rolling temperature is 800 ° C. or more at _three points or less, a hot rolled sheet is obtained. Cold rolling,
A method for producing a cold-rolled steel sheet for deep drawing excellent in ridging resistance, characterized by performing continuous annealing. Note Ti / 48 + Nb / 93 ≧ C / 12 + N / 14 (1) where, Ti, Nb, C, N: wt%