JPH06212276A - Manufacturing method of cold-rolled steel sheet for deep drawing with excellent corrosion resistance - Google Patents

Abstract

(57) [Summary] [Purpose] To propose a technology for manufacturing cold-rolled steel sheets for automobiles, which has excellent deep drawability and corrosion resistance. [Structure] Mainly C: 0.005 wt% or less, Si: 1.0 wt%
% Or less, Mn: 2.0 wt% or less, Ni: 0.1 to 1.0 wt%, B:
0.0001 to 0.0050 wt%, Cu: 0.1 to 1.5 wt%, Al: 0.01 to
0.10 wt%, P: 0.01 to 0.15 wt% or less, S: 0.03 wt% or less, N: 0.01 wt% or less, O: 0.005 wt% or less, Ti: 0.01
Steel containing 0.10 wt% to 0.10 wt% and 0.001 to 0.050 wt% is treated by a conventional method and then subjected to recrystallization annealing in the temperature range of 700 to 950 ° C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a cold-rolled steel sheet suitable for use in automobile steel sheets and the like, which has excellent deep drawability and corrosion resistance.

[0002]

2. Description of the Related Art In recent years, steel sheets for automobiles have a tensile strength of 35 kgf /
A high-strength cold-rolled steel sheet having mm ² or more and excellent deep drawability has been demanded. The adoption of such high-tensile cold-rolled steel sheets has made it possible to reduce the gauge of automobile steel sheets. However, there is a tendency for corrosion resistance, especially pitting corrosion resistance, to decrease as the thickness of automobile steel plates decreases, and prevention of such corrosion is an important issue. For this reason, it has recently become necessary to develop a high-strength cold-rolled steel sheet having excellent deep drawability and corrosion resistance as an automobile steel sheet. On the other hand, for the purpose of cost reduction, attempts have been made to replace the members that have conventionally used surface-treated steel sheets with corrosion-resistant cold-rolled steel sheets. Furthermore, in order to further improve the corrosion resistance, surface treatment of the corrosion-resistant cold-rolled steel sheet is also under study. In order to meet such demands, it is necessary to develop a cold-rolled steel sheet that has deep drawability equivalent to that of conventional ones and at the same time has higher corrosion resistance.

By the way, conventionally, several methods have been proposed for producing a high-strength cold-rolled steel sheet having excellent deep drawability. For example, Japanese Examined Patent Publication No. 63-9579 discloses a method for producing a high-strength cold-rolled steel sheet having good surface properties by adding P and Cu in combination. However, even though this proposed technique can manufacture a high-strength cold-rolled steel sheet for deep drawing, no consideration is given to corrosion resistance.

[0004]

The problem of the above-mentioned prior art is that it is excellent in deep drawability but lacks consideration for corrosion resistance. The purpose of the present invention is to solve such problems. The purpose is to establish a technique capable of overcoming the point, and this object is achieved by devising the composition and manufacturing conditions of the steel described in detail below.

[0005]

[Means for Solving the Problems] As a result of intensive studies aimed at achieving the above-mentioned objects, the inventors have found that when the steel composition and manufacturing conditions are complied with, extremely excellent corrosion resistance and deep drawability are obtained. It has been found that a high-strength cold-rolled steel sheet having

The gist of the present invention is as follows. (1) C: 0.005 wt% or less, Si: 1.0 wt% or less, Mn:
2.0 wt% or less, Ni: 0.1 to 1.0 wt%, B: 0.0001
~ 0.0050wt%, Cu: 0.1-1.5wt%, Al: 0.01-0.10wt%
%, P: 0.01 to 0.15 wt% or less, S: 0.03 wt% or less,
N: 0.01 wt% or less, O: 0.005 wt% or less,
And Ti: 0.01-0.10wt%, Nb: 0.001-0.050wt%
Steel containing 1 or 2 of these, the balance of which is Fe and unavoidable impurities, is hot-rolled, then pickled and cold-rolled, followed by recrystallization annealing in the temperature range of 700 to 950 ° C. A method for manufacturing a cold-rolled steel sheet for deep drawing having excellent corrosion resistance, which is characterized by being applied (first invention). (2) In the method described in 1 above, the composition of the steel is
C: 0.005 wt% or less, Si: 1.0 wt% or less, Mn: 2.0
wt% or less, Ni: 0.1 to 1.0 wt%, B: 0.0001 to 0.
0050wt%, Cu: 0.1-1.5wt%, Al: 0.01-0.10wt%,
P: 0.01 to 0.15 wt% or less, S: 0.03 wt% or less,
N: 0.01 wt% or less, O: 0.005 wt% or less, and
Ti: 0.01 to 0.10 wt%, Nb: 0.001 to 0.050 wt%, containing 1 or 2 types, and Cr: 0.05 to 1.5 wt%,
Mo: Steel containing one or two of 0.05 to 1.5 wt% and the balance being Fe and unavoidable impurities is hot-rolled, then pickled and cold-rolled, and then 700-95.
A method for producing a cold-rolled steel sheet for deep drawing having excellent corrosion resistance, which comprises performing recrystallization annealing in a temperature range of 0 ° C (second invention). (3) A method for producing a cold-rolled steel sheet for deep drawing having excellent corrosion resistance, characterized by performing recrystallization annealing in a continuous hot-dip galvanizing line in the method described in 1 or 2 above (third invention).

[0007]

The following is a description of experimental studies that have led to the present invention. C: 0.002 wt%, Si: 0.01 wt%, Mn: 0.2 wt%
%, P: 0.05 wt%, S: 0.005 wt%, Al: 0.04 wt%,
N: 0.002 wt%, Ti: 0.03 wt%, Nb: 0.003 wt%, B:
0.001 wt%, Cu: (0.01 and 0.30) wt%, Ni: 0.2 wt%
%, O: (0.002 to 0.010) wt% 12 seat bar composition
After heating to 50 ° C.-soaking, hot rolling was performed at a finishing temperature of 880 ° C. Then, after pickling-cold rolling, 850 ℃-
Recrystallization annealing was performed for 20 seconds. Figure 1 shows the effect of steel components, especially Cu and O, on corrosion resistance. The corrosion resistance is evaluated by immersing it in 0.5% NaCl corrosive solution for 8 hours,
Carry out a corrosion cycle of drying for 16 hours (number of cycles
30), and performed by measuring the maximum pitting depth after the corrosion test. As can be seen from the results shown in this figure, the corrosion resistance strongly depends on the steel components, especially Cu and O content.
It was revealed that the corrosion resistance of the (0.30 wt% Cu) steel was remarkably improved when O ≦ 0.005 wt%.

As a result of various studies based on the above experimental results, the present inventors determined the conditions of the present invention as follows. (1) Steel component composition; The reasons for limiting the composition of each component are explained below.

C: 0.005 wt% or less C is preferable because the smaller the content, the better the deep drawability. However, if the C content is 0.005 wt% or less, no adverse effect is exerted. Therefore, the content of C is limited to 0.005 wt% or less.

Si: 1.0 wt% or less Since Si has the effect of strengthening steel, Si is contained in a necessary amount according to the desired strength. If the amount exceeds 1.0 wt%, deep drawability and corrosion resistance are improved. 1.0 wt because it deteriorates
% Or less.

Mn: 2.0 wt% or less Mn has the action of strengthening steel, so it is contained in the required amount according to the desired strength, but if the amount exceeds 2.0 wt%, deep drawability and corrosion resistance deteriorate. 2.0 wt%
Limited to:

Ni: 0.1 to 1.0 wt% Ni is added to improve the surface properties of the steel sheet when Cu is added. If the added amount is less than 0.1 wt%, the effect of addition is poor,
On the other hand, if added in excess of 1.0 wt%, the deep drawability is adversely affected, so the range was limited to 0.1-1.5 wt%.

B: 0.0001 to 0.0050 wt% B is added to improve the secondary work embrittlement resistance of steel.
If the added amount is less than 0.0001 wt%, the effect of addition is poor, while if added over 0.0050 wt%, the deep drawability is adversely affected, so the range was limited to 0.0001 to 0.0050 wt%.

Cu: 0.1-1.5 wt% Cu is an element that plays an important role in the present invention.
It is added to improve the corrosion resistance. The amount added is 0.1
Less than wt% is less effective in improving corrosion resistance, while 1.5w
If added in excess of t%, the deep drawability will be adversely affected, so the range was limited to 0.1 to 1.5 wt%. In order to further exhibit the effect of improving the corrosion resistance, the Cu addition amount is 0.
It is preferable to limit it to 18 to 1.5 wt%.

Al: 0.01 to 0.10 wt% Al is contained for the purpose of deoxidizing and improving the yield of carbon / nitride forming elements. If the content is less than 0.01 wt%, the addition effect is small, while , 0.10 wt%, the deoxidizing effect and the above-mentioned yield improving effect saturate, so the range was limited to 0.01 to 0.10 wt%.

P: 0.01 to 0.15 wt% or less P is an element which plays an important role in the present invention,
Since it has the effect of strengthening steel and the effect of improving corrosion resistance, the necessary amount is added. The addition amount is 0.01wt
If it is less than%, it has little effect on improving the corrosion resistance, while it is 0.
If it exceeds 15 wt%, the deep drawability will be adversely affected.
The range is limited to 0.15 wt%. In addition, in order to expect the effect of improving the corrosion resistance due to the addition of P, the addition amount of P is preferably in the range of 0.03 to 0.15 wt%.

S: 0.03 wt% or less S is preferable because the smaller the content, the better the deep drawability and corrosion resistance. However, up to 0.03 wt% does not have a bad effect, so a content of 0.03 wt% or less was allowed. In order to further improve the corrosion resistance, the S content is preferably 0.0035 wt% or less.

N: 0.01 wt% or less N decreases the more the deep drawability is improved, but if the N content is 0.01 wt% or less, it does not have a bad influence. Therefore, the N content is 0.01 wt% or less. Is acceptable.

O: 0.005 wt% or less O is an element that plays the most important role in the present invention, and this O must be 0.005 wt% or less in order to improve the corrosion resistance. Furthermore, the effect of reducing O is
As shown in FIG. 1, it is effective only for the Cu-added steel, and the Cu-free steel has almost no O-reducing effect on the corrosion resistance. Although the details of the action of O are not clear,
It is considered that the reduction of O may reduce fine oxides which are the starting point of pitting corrosion, or change the surface condition of the steel sheet, and change the surface properties that are advantageous for corrosion resistance, particularly pitting corrosion resistance.
This O content is 0.003 wt% to improve the corrosion resistance.
The following is more preferable.

Ti: 0.01 to 0.10 wt% Ti is a carbon / nitride forming element, and is a solid solution (C,
N) is precipitated and fixed as (TiC, TiN), and is added to form a {111} orientation that is advantageous for deep drawability. If the added amount is less than 0.01 wt%, the effect is poor, while if added over 0.1 wt%, the effect is saturated, and in some cases it may lead to deterioration of the surface properties. Limited to wt%.

Nb: 0.001 to 0.05 wt% Nb is a carbide forming element. In order to precipitate and fix solid solution C in steel as NbC, preferentially forming {111} orientation advantageous to deep drawability. Is added. The amount added is 0.00
If it is less than 1 wt%, its effect is poor, while 0.05 wt%
If added in excess of 0.001 to 0.05, ductility will deteriorate.
Limited to wt%.

Cr: 0.05 to 1.5 wt% Cr is added to improve the corrosion resistance, but if the added amount is less than 0.05 wt%, the addition effect is poor, while 1.
Addition in excess of 5 wt% adversely affects deep drawability, so the amount was limited to 0.05 to 1.5 wt%.

Mo: 0.05 to 1.5 wt% Mo is added to improve the corrosion resistance, but if the added amount is less than 0.05 wt%, the effect of addition is poor, while 1.5 wt%
%, It adversely affects the deep drawability, so it was limited to 0.05 to 1.5 wt%.

(2) Hot rolling conditions In the present invention, hot rolling conditions are also important. From the viewpoint of energy saving, a desirable hot rolling condition is to perform rough rolling after subjecting the continuously cast slab to reheating or continuous casting without immediately lowering the temperature below the Ar ₃ transformation point or after heat retention. This finishing temperature of hot rolling is preferred that the deep drawability performed at Ar ₃ transformation point or more of the temperature, or at a low temperature thermal extension of less than Ar ₃ transformation point from the viewpoint of energy saving. In addition,
The hot rolling coiling temperature is preferably in the range of 300 to 850 ° C., and it is preferable to set the coiling temperature to 500 ° C. or higher in order to promote precipitation and improve the deep drawability by coarsening.

(3) Cold rolling conditions In order to obtain a high r value, a cold rolling reduction of 60% or more is preferable. A more preferable cold rolling reduction is 70% or more.

(4) Annealing Conditions In the present invention, the annealing conditions are important, and it is necessary to anneal in the temperature range of 700 ° C. to 950 ° C. in order to obtain excellent deep drawability. Excellent deep drawability cannot be obtained at annealing temperatures below 700 ° C. On the other hand, if annealing is performed in a temperature range exceeding 950 ° C, the texture becomes random due to α → γ transformation, resulting in poor deep drawability. Therefore, the annealing temperature is limited to 700 ° C to 950 ° C. Preferably 800 ° C
~ 950 ° C. In the present invention, a continuous annealing line or a continuous hot dip galvanizing line is suitable as the annealing process. The reason for this is that since the annealing time in the above line is short, Cu does not concentrate on the surface of the steel sheet and the surface treatability becomes good. As the above continuous hot-dip galvanizing method, non-alloyed hot-dip galvanizing and alloyed hot-dip galvanizing are well suited. The steel sheet of the present invention may be subjected to a special treatment after annealing or galvanizing to improve chemical conversion treatment property, weldability, press formability, corrosion resistance and the like.

[0027]

EXAMPLE A steel slab having the chemical composition shown in Table 1 was heated and soaked at 1250 ° C., rough-rolled and then finish-rolled. The obtained hot-rolled sheet was pickled, cold-rolled at a reduction rate of 75% to a sheet thickness of 0.8 mm, and then 850 ° C-at a continuous annealing line.
Recrystallization annealing was performed for 20 seconds. The test materials thus obtained were tested for tensile properties. The tensile properties were measured using JIS No. 5 tensile test pieces. In addition, the r value was measured by the three-point method after applying a 15% tensile prestrain.
The average values in the direction (rolling direction), the D direction (45 ° direction to the rolling direction) and the C direction (90 ° direction to the rolling direction) were determined as r = (r _l + 2r _D + r _C ) / 4. We also tested corrosion resistance,
This was evaluated by the same method as described above. The material properties of the final product are shown in Table 2. It can be seen that the cold rolled steel sheet suitable for the present invention has excellent deep drawability and corrosion resistance.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

As described above, according to the present invention, Cu
It is possible to manufacture a cold-rolled steel sheet for deep drawing that has better corrosion resistance than before by controlling C and O, especially by controlling the annealing conditions.

[Brief description of drawings]

FIG. 1 is a graph showing the influence of Cu and O contents on corrosion resistance.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical indication C22C 38/54 38/58 (72) Inventor Susumu Sato 1 Kawasaki-cho, Chuo-ku, Chiba-shi Chiba Prefecture Kawasaki (72) Inventor Toshiyuki Kato 1 Kawasaki-machi, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Co., Ltd.

Claims (3)

[Claims] 1. C: 0.005 wt% or less, Si: 1.0 wt% or less, Mn: 2.0 wt% or less, Ni: 0.1 to 1.0 wt%, B: 0.0001 to 0.0050 wt%, Cu: 0.1 to 1.5 wt%, Al: 0.01 to 0.10 wt%, P: 0.01 to 0.15 wt% or less, S: 0.03 wt% or less, N: 0.01 wt% or less, O: 0.005 wt% or less, and Ti: 0.01 to 0.10 wt%, Nb: Steel containing 1 or 2 of 0.001 to 0.050 wt% and the balance being Fe and unavoidable impurities, hot-rolled, pickled and cold-rolled, and then kept at a temperature of 700 to 950 ° C. A method for producing a cold-rolled steel sheet for deep drawing having excellent corrosion resistance, which comprises performing recrystallization annealing in a range. 2. C: 0.005 wt% or less, Si: 1.0 wt% or less, Mn: 2.0 wt% or less, Ni: 0.1 to 1.0 wt%, B: 0.0001 to 0.0050 wt%, Cu: 0.1 to 1.5 wt%, Al: 0.01 to 0.10 wt%, P: 0.01 to 0.15 wt% or less, S: 0.03 wt% or less, N: 0.01 wt% or less, O: 0.005 wt% or less, and Ti: 0.01 to 0.10 wt%, Nb: 0.001 to 0.050 wt%, containing 1 or 2 types, Cr: 0.05 to 1.5 wt%, Mo: 0.05 to 1.5 wt%, containing 1 or 2 types, the balance being Fe and unavoidable Cold-rolled steel sheet for deep drawing with excellent corrosion resistance, characterized in that steel made of impurities is hot-rolled, then pickled and cold-rolled, followed by recrystallization annealing in the temperature range of 700 to 950 ° C. Manufacturing method. 3. The method according to claim 1, wherein the recrystallization annealing is performed in a continuous hot-dip galvanizing line, wherein the cold-rolled steel sheet for deep drawing has excellent corrosion resistance.