JPH07110976B2 - Manufacturing method of cold-rolled steel sheet for deep drawing with small in-plane anisotropy - Google Patents

Description

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

(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, conventionally, assembling an automobile body has been performed by spot-welding a large number of stamped parts, but recently, there has been a demand to reduce the number of parts and the number of welds by enlarging some of these parts and integrating them. Is increasing.

For example, automobile oil pans are currently completed by welding due to their complicated shape, but there is a strong demand for integral molding by automobile manufacturers. on the other hand,
In order to meet diversifying needs, vehicle designs have become more complex, which has increased the number of parts that are difficult to form using conventional steel sheets. In order to meet these requirements, a cold-rolled steel sheet having deep drawability that is far superior to the conventional one is required.

By the way, the in-plane anisotropy of the r-value is very important for performing such ultra-deep drawing.
r _max −r _min ≦ 0.5 is required.

Conventionally, various methods have been proposed for improving the deep drawability, for example, Japanese Patent Publication Nos. 44-17268 and 44-172.
Japanese Patent No. 69 and Japanese Patent No. 44-17270 disclose a method for manufacturing a cold rolled steel sheet having a value increased to 2.18 by subjecting a low carbon rimmed steel to cold rolling and annealing twice. However, with such a value, it cannot be said that the deep drawing property is sufficient. Also "Iron and Steel, (1971), S280"
Then, C: 0.008wt% (simply indicated by% below), Mn: 0.31%,
P: 0.012%, S: 0.015%, N: 0.0057%, Al: 0.036%, Ti:
Steel with a composition of 0.20%, primary cold rolling rate: 50%, intermediate annealing: 80
It has been shown that a steel sheet for ultra-deep drawing of = 3.1 can be produced by treating under the conditions of 0 ° C-10 hours, secondary cold rolling rate: 80%, and final annealing: 800 ° C-10 hours. However, since the total cold rolling reduction of the above method is as high as 90%, it is not possible to secure the plate thickness (0.6 mm or more) of the normally used cold rolled steel plate. Moreover, nothing is suggested regarding the in-plane anisotropy of the r value.

(Problems to be Solved by the Invention) The present invention was developed in view of the above-mentioned current situation,
By optimizing the steel composition and cold rolling-annealing conditions,
It is an object of the present invention to propose a method capable of producing a cold-rolled steel sheet having a deep drawability and a small in-plane anisotropy, which are far superior to the conventional ones.

(Means for Solving the Problems) As a result of intensive studies to achieve the above-mentioned object, the inventors have succeeded in controlling the manufacturing conditions as described below to thereby obtain an ultra-thin aperture having a small in-plane anisotropy. It was found that a cold-rolled steel sheet for automobiles can be obtained.

That is, the present invention is one of the following compositions, C: 0.005 wt% or less, Si: 0.1 wt% or less, Mn: 1.0 wt% or less, P: 0.1 wt% or less, S: 0.05 wt% or less, Al : 0.01 to 0.10 wt% and N: 0.005 wt% or less, and 1 or 2 selected from Ti: more than 0.02 to 0.15 wt% and Nb: 0.001 to 0.05 wt% with the balance being Fe. And composition consisting of unavoidable impurities, C: 0.005 wt% or less, Si: 0.1 wt% or less, Mn: 1.0 wt% or less, P: 0.1 wt% or less, S: 0.05 wt% or less, Al: 0.01 to 0.10 wt% And N: 0.005 wt% or less and B: 0.0001 to 0.0020 wt% with the balance Fe and inevitable impurities, C: 0.005 wt% or less, Si: 0.1 wt% or less, Mn: 1.0 wt% or less, P: 0.1 wt% or less, S: 0.05 wt% or less, Al: 0.01 to 0.10 wt% and N: 0.005 wt% or less, and Ti: more than 0.02 to 0.15 wt% and Nb: 0.001 to 0.05 One or two selected from wt% and B: 0.0001-0.0020wt% After hot rolling, steel containing the balance of Fe and unavoidable impurities is first cold-rolled at a reduction rate of 30% or more, and then recrystallized at a temperature of (recrystallization temperature + 80 ° C). Intermediate annealing in the temperature range of, followed by secondary cold rolling with a reduction rate of 30% or more and a total reduction rate of 78% or more, followed by a temperature of 50 ° C or more and 920 ° C or less higher than that of intermediate annealing. It is a method for producing a cold-rolled steel sheet for deep drawing having a small in-plane anisotropy, which comprises performing final annealing in a zone.

In the present invention, the steel may further contain sb: 0.001 to 0.02%.

Hereinafter, the research results which are the basis of the present invention will be described.

C: 0.002%, Si: 0.01%, Mn: 0.11%, P: 0.010%, S: 0.01
1%, Al: 0.05%, N: 0.002%, Ti: 0.032% and Nb: 0.00
A steel slab containing 8% and the balance being Fe is hot-rolled to a plate thickness of 6 mm, and then the primary cold rolling reduction rate is 66%.
Intermediate annealing, secondary cold rolling reduction: 66%, final annealing: 870 ℃ -20s
Each treatment was performed. At this time, the intermediate annealing temperature was variously changed, and the r value after the final annealing was measured. The recrystallization temperature of this steel type was about 720 ° C.

Figure 1 shows the results of an examination of the effect of the intermediate annealing temperature on the values after the final annealing and r _max -r _min .

As is clear from the figure, the value after the final annealing and its in-plane anisotropy (r _max −r _min ) strongly depend on the intermediate annealing temperature, and the intermediate annealing temperature is between the recrystallization temperature and the (recrystallization temperature +80 ℃)
In the case of, ≧ 2.8 and r _max −r _min ≦ 0.5 were obtained.

(Working) Based on the results of a large number of experiments in which the component composition range, the final rolling reduction, etc. were variously changed according to the above-mentioned experiments, the scope of the present invention was limited as follows.

(1) Steel composition In this invention, steel composition is important, C: 0.005% or less, Si: 0.1% or less, Mn: 1.0% or less, P: 0.1%
Below, S: 0.05% or less, Al: 0.01 to 0.10% and N: 0.005%
The following must be included and one or two selected from Ti: 0.01 to 0.15% and Nb: 0.001 to 0.05%, and / or B: 0.0001 to 0.0020% must be contained. If necessary, Sb: 0.001
It is also possible to contain 0.02%.

The reasons for limitation of each component are shown below.

C: 0.005% or less C is preferably as small as possible for improving deep drawability, but if the content is 0.005% or less, it does not exert a bad influence so much, so it is limited to 0.005% or less.

Si: 0.1% or less Si has the effect of strengthening steel and is added in the required amount according to the desired strength, but if the addition amount exceeds 0.1%, it will adversely affect the deep drawability, so 0.1% or less. Limited

Mn: 1.0% or less Mn also has the action of strengthening steel, similar to Si, and is added in the required amount according to the desired strength, but if the addition amount exceeds 1.0%, it also adversely affects the deep drawability, so Limited to 1.0% or less.

P: 0.1% or less P, like Si and Mn, acts to strengthen the steel and is added in the required amount according to the desired strength, but if the addition amount exceeds 0.1%, deep drawability is adversely affected. , 0.1% or less.

Si: 0.05% or less S is preferably reduced as much as possible because the smaller the content, the better the deep drawability. However, if the content of S is 0.05% or less, it does not exert a bad influence so much, so it is limited to 0.05% or less.

Al: 0.010 to 0.10% Al is added as a deoxidizing agent and for improving the yield of carbonitride forming elements described later, but if the content is less than 0.010%, its addition effect is poor, while 0.10% Even if added in excess of%, the effect reaches saturation, so 0.010-0.10
It was limited to the range of%.

N: 0.005% or less N is preferably reduced as much as possible because the smaller the content, the better the deep drawability. However, if the content is 0.005% or less, it does not exert a bad influence so much, so it is limited to 0.005% or less.

Ti: more than 0.02 to 0.15% Ti is a carbonitride forming element and is added to reduce the solid solution (C, N) in steel and preferentially form the {111} orientation, which is advantageous for deep drawability. To be done. However, the addition amount is 0.02%
In the following, the effect of addition is poor, and even if added in excess of 0.15%, no further effect is obtained, and rather it leads to deterioration of the steel sheet surface properties and ductility, so it was limited to a range of more than 0.02 to 0.15%.

Nb: 0.001 to 0.05% Nb is a carbide forming element, which reduces the solid solution C in the steel and promotes the refinement of the structure of the hot rolled sheet, preferentially the {111} orientation that is advantageous for deep drawability. Added to form However, if the addition amount is less than 0.001%, its effect is poor, while if it is added in excess of 0.05%, no further effect can be obtained, and rather it leads to deterioration of ductility.
It was limited to the range of 001-0.05%.

B: 0.0001 to 0.0020% B effectively contributes to the improvement of secondary work embrittlement resistance, but if the addition amount is less than 0.0001%, the addition effect is poor, while 0.00
If it exceeds 20%, the deep drawability will deteriorate, so 0.0001 to 0.00
Limited to 20% range.

Sb: 0.001% to 0.02% Sb effectively contributes to prevention of nitrification during box annealing. However, if the addition amount is less than 0.001%, the effect is not
If it exceeds 0.020%, the surface property of the steel sheet deteriorates, so when it is added, it is necessary to add it in the range of 0.001 to 0.02%.

(2) Cold rolling-annealing step The cold rolling-annealing step is the most important in the present invention. After the primary cold rolling is performed at a rolling rate of 30% or more, the recrystallization temperature-
Intermediate annealing is performed in the temperature range of (recrystallization temperature + 80 ° C), and then secondary cold rolling is performed at a reduction rate of 30% or more and a total reduction rate of 78% or more, and then 50% higher than the intermediate annealing temperature. It is necessary to perform final annealing in the temperature range that is higher than ℃ and lower than 920 ℃.

If the reduction ratio of primary cold rolling or secondary cold rolling is less than 30%, an appropriate rolling texture is not formed during cold rolling, so that {111} orientation, which is advantageous for deep drawability, is formed after intermediate annealing or final annealing. It gets harder. As a result, the {111} orientation is not preferentially formed and the deep drawability deteriorates.

Fig. 2 shows the relationship between the total rolling reduction and the value. As is clear from the figure, if the total rolling reduction is less than 78%, strong {111} orientation is not formed after the final annealing, As a result, a super deep drawability of ≧ 2.8 cannot be secured.

The annealing conditions may be either continuous annealing or box annealing for both the intermediate annealing and the final annealing. The intermediate annealing needs to be performed in the temperature range of recrystallization temperature to (recrystallization temperature + 80 ° C). The reason is that when intermediate annealing is performed in a temperature range lower than the recrystallization temperature, a large number of {111} orientations are formed after the intermediate annealing, resulting in poor deep drawability after secondary cold rolling-final annealing.
On the other hand, when intermediate annealing is performed in a temperature range higher than (recrystallization temperature + 80 ° C), the recrystallized grains become too large, and as a result, many {111} orientations are formed after the secondary cold rolling-final annealing. This is because not only the deep drawability is poor, but also the in-plane anisotropy is large. Therefore, the intermediate annealing temperature is limited to the range of recrystallization temperature to (recrystallization temperature + 80 ° C).

The final annealing must be performed at a temperature range higher than that of the intermediate annealing by 50 ° C or more in order to secure excellent deep drawability and ductility. However, if annealing is performed in a temperature range higher than 920 ° C, the crystal orientation becomes random due to α-γ transformation,
Deep drawability deteriorates.

The cold-rolled steel sheet after the final annealing can be temper-rolled at 5% or less. Further, hot dip galvanizing and electrogalvanizing can be applied to the steel sheet of the present invention.

(Example) After hot-rolling steel slabs having various compositions shown in Table 1, primary cold rolling-intermediate annealing-2 secondary cold rolling-under various conditions shown in Table 2.
Final annealing was performed.

The results of examining the material properties of the obtained product plate are also shown in Table 2.

The tensile properties were measured using JIS No. 5 tensile test pieces. Also, the value was measured by the 3-point method after 15% tensile prestrain, and was measured in the L direction (rolling direction) and the D direction (45 directions in the rolling direction).
° direction) and C direction (90 ° rolling direction) average value = (r _L + 2r _D + r _C ) / 4. The in-plane anisotropy of the r value is 10 in the rolling direction.
It was determined as the difference (r _max −r _min ) between the maximum value r _max and the minimum value r _min of the values measured every °.

As is clear from the table, all the cold-rolled steel sheets obtained according to the present invention had extremely excellent deep drawability and in-plane anisotropy as compared with the comparative examples.

In addition, the same steel grade was used, and after secondary cold rolling under the treatment conditions shown in Table 3, final annealing was simultaneously performed in a continuous hot-dip galvanizing line, and the results of examining the material properties of hot-dip galvanized steel sheets were shown in Table 3. Shown in. The types of plating are Zn plating and alloyed Zn plating.

In addition, Table 4 shows the results of examining the material properties of the plated steel sheet obtained by performing electroplating on the electrogalvanizing line after the final annealing under the treatment conditions shown in Table 4. The types of plating are Zn plating, Zn-Ni plating and Zn-Fe plating.

As is clear from Tables 3 and 4, according to the present invention, a surface-treated steel sheet having extremely excellent deep drawability and tensile rigidity can be manufactured.

(Effects of the Invention) Thus, according to the present invention, it is possible to obtain a cold-rolled steel sheet having deep drawability and in-plane anisotropy, which are far superior to the conventional ones, and it is possible to obtain a large-sized panel or a super-difficult-to-work product which has been considered difficult in the past. Integral molding of oil pans is also possible. Further, it can be applied to various surface-treated steel sheets, which is extremely significant industrially.

[Brief description of drawings]

FIG. 1 is a graph showing the influence of the intermediate annealing temperature on the value and in-plane anisotropy, and FIG. 2 is a graph showing the relationship between the total rolling reduction and the value in cold rolling.

Continuation of front page (56) References JP-A-63-69922 (JP, A) JP-B-52-50723 (JP, B2)

Claims (4)

[Claims] 1. C: 0.005 wt% or less, Si: 0.1 wt% or less, Mn: 1.0 wt% or less, P: 0.1 wt% or less, S: 0.05 wt% or less, Al: 0.01 to 0.10 wt% and N: Steel containing 0.005 wt% or less, and containing 1 or 2 selected from Ti: more than 0.02 to 0.15 wt% and Nb: 0.001 to 0.05 wt%, with the balance Fe and inevitable impurities, After hot rolling, primary cold rolling was performed at a reduction rate of 30% or more, and then intermediate annealing was performed in the temperature range of recrystallization temperature to (recrystallization temperature + 80 ° C), and subsequently,
Secondary cold rolling with a reduction rate of 30% or more and a total reduction rate of 78% or more, then 50 ° C or more higher than that of intermediate annealing,
A method for producing a cold-rolled steel sheet for deep drawing having a small in-plane anisotropy, which comprises performing final annealing in a temperature range of 920 ° C or lower. 2. C: 0.005 wt% or less, Si: 0.1 wt% or less, Mn: 1.0 wt% or less, P: 0.1 wt% or less, S: 0.05 wt% or less, Al: 0.01 to 0.10 wt% and N: Steel containing 0.005 wt% or less and B: 0.0001 to 0.0020 wt% with the balance Fe and unavoidable impurities was subjected to primary cold rolling with a reduction ratio of 30% or more after hot rolling. After that, an intermediate annealing is performed in the temperature range of recrystallization temperature to (recrystallization temperature + 80 ° C), and then secondary cold rolling is performed with a reduction rate of 30% or more and a total reduction rate of 78% or more. A method for producing a deep-drawn cold-rolled steel sheet having a small in-plane anisotropy, which comprises performing final annealing in a temperature range higher than annealing by 50 ° C. or more and 920 ° C. or less. 3. C: 0.005 wt% or less, Si: 0.1 wt% or less, Mn: 1.0 wt% or less, P: 0.1 wt% or less, S: 0.05 wt% or less, Al: 0.01 to 0.10 wt% and N: Includes 0.005 wt% or less and Ti: more than 0.02 to 0.15 wt% and one or two selected from Nb: 0.001 to 0.05 wt% and B: 0.0001 to 0.0020 wt% with the balance being After hot rolling, steel consisting of Fe and unavoidable impurities is subjected to primary cold rolling at a reduction rate of 30% or more, and then subjected to intermediate annealing in the temperature range of recrystallization temperature to (recrystallization temperature + 80 ° C). Then, perform secondary cold rolling with a reduction rate of 30% or more and a total reduction rate of 78% or more, and then perform final annealing in a temperature range of 50 ° C or more higher than the intermediate annealing and 920 ° C or less. A method for producing a cold-rolled steel sheet for deep drawing, which has a small in-plane anisotropy. 4. The method for producing a cold-rolled steel sheet for deep drawing according to claim 1, 2 or 3, further comprising Sb: 0.001 to 0.02 wt% in the steel and having a small in-plane anisotropy.