JPH0892656A - Method for manufacturing cold rolled steel sheet with excellent deep drawability - Google Patents

Abstract

(57) [Summary] [Objective] To propose a method for economically producing a cold-rolled steel sheet having a significantly excellent deep drawability with an r value of 3.0 or more. [Constitution] C: 0.0020 wt% or less, Si: 0.01 to 2.0 wt
%, Mn: 0.1 to 3.0 wt%, P: 0.01 to 0.1 wt%,
S: 0.003 wt% or less, Al: 0.01 to 0.06 wt%, N: 0.
0020wt% or less, Nb: 0.001 to 0.20wt%, B: 0.0004
˜0.0030 wt%, and the above C, N and S are Y =
A steel containing 1000 (wt% C + wt% S + wt% N) ≤ 60, with the balance being Fe and inevitable impurities, Ar ₃
In the temperature range of transformation point to 500 ℃, while performing lubrication, hot finish rolling with a total reduction of 50 to 95% is performed, then hot-rolled sheet recrystallization treatment is performed, and then reduction of 50 to 95% is performed. Cold-rolled sheet is re-rolled and annealed at 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 cold-rolled steel sheet suitable for use as a steel sheet for automobiles and the like, and to a method for producing a cold-rolled steel sheet having excellent formability, particularly deep drawability.

[0002]

2. Description of the Related Art In general, cold-rolled steel sheets used for automobile steel sheets are required to have good press workability. A recent trend in this press working is the complexity of integral molding and working. Therefore, a higher level of press workability has been required for cold rolled steel sheets used for this type of application.

By the way, as a general conventional manufacturing technique for cold-rolled steel sheet, for example, JP-A-59-226149 and JP-A-62 are available.
-192539, there is a method proposed. The technique disclosed in Japanese Patent Laid-Open No. 59-226149 described above is 0.002 wt% C-
0.02wt% Si-0.23wt% Mn-0.009wt% P-0.008wt% S-0.025
wt% Al-0.0021 wt% N-0.10 wt% Ti,
The average r value is 1.21 to 1.48. In addition, JP-A-62-192
The technology disclosed in Japanese Patent No. 539 is 0.008 wt% C-0.04 wt% Si-1.5.
3 wt% Mn-0.01 wt% P-0.004 wt% S-0.0068 wt% Ti-0.024
This is due to wt% Nb, and its average r value is about 1.41. However, there has been a problem that a material having an r value of such a level cannot meet the above-mentioned severe processing applications. Further, Japanese Patent Publication No. 44-17270 discloses that low carbon rimmed steel is cold rolled and annealed twice.
A technique for increasing the r value to 2.18 is disclosed. However, this method not only consumes a large amount of energy, but also has low productivity and is disadvantageous in terms of cost.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art in an advantageous manner, and to improve the productivity of cold-rolled steel sheet having remarkably excellent deep drawability. The purpose is to propose a manufacturing method without incurring a disadvantage in terms of cost. Further, a more specific object of the present invention is to propose a method for economically producing a cold-rolled steel sheet having an r value of 3.0 or more and having extremely excellent deep drawability.

[0005]

Under the recognition of the above problems, the present inventors have studied in detail the composition of steel and the manufacturing conditions. As a result, in particular C, N, S and
It was newly discovered that the above-mentioned problems can be solved by controlling the content of Nb and the like and also appropriately controlling the manufacturing conditions such as hot rolling conditions.

That is, the gist of the present invention is as follows. (1) C: 0.0020 wt% or less, Si: 0.01 to 2.
0 wt%, Mn: 0.1-3.0 wt%, P: 0.01-0.1 wt
%, S: 0.003 wt% or less, Al: 0.01 to 0.06 wt%,
N: 0.0020 wt% or less, Nb: 0.001 to 0.20 wt%, B:
0.0004 to 0.0030 wt%, and the above C, N and S
Contains Y = 10000 (wt% C + wt% S + wt% N) ≦ 60, and the balance is Fe and inevitable impurities, and lubricates the steel in the temperature range from Ar ₃ transformation point to 500 ° C. While performing hot finish rolling with a total reduction of 50 to 95%, followed by hot-rolled sheet recrystallization treatment, then cold rolling with a reduction of 50 to 95%, and then at 700 to 950 ℃. A method for producing a cold-rolled steel sheet having excellent deep drawability, which comprises performing cold-rolled sheet recrystallization annealing.

(2) C: 0.0020 wt% or less, Si: 0.01 to
2.0 wt%, Mn: 0.1-3.0 wt%, P: 0.01-0.1 wt
%, S: 0.003 wt% or less, Al: 0.01 to 0.06 wt%,
N: 0.0020 wt% or less, Nb: 0.001 to 0.20 wt%, B:
0.0004 to 0.0030 wt%, and the above C, N and S
Contains Y = 10000 (wt% C + wt% S + wt% N) ≦ 60, and further contains Ni: 1.0 wt% or less, Cu: 1.0
Steel containing at least one wt% or less and Mo: 1.0 wt% or less, with the balance being Fe and inevitable impurities, is used in the temperature range of Ar ₃ transformation point to 500 ° C. While performing lubrication, hot finish rolling with a total reduction of 50 to 95% is performed, then hot-rolled sheet recrystallization treatment is performed, and then cold rolling with a reduction of 50 to 95% is performed, and then, 700 ~
A method for producing a cold-rolled steel sheet having excellent deep drawability, which comprises performing cold-rolled sheet recrystallization annealing at 950 ° C.

(3) C: 0.0020 wt% or less, Si: 0.01 to
2.0 wt%, Mn: 0.1-3.0 wt%, P: 0.01-0.1 wt
%, S: 0.003 wt% or less, Al: 0.01 to 0.06 wt%,
N: 0.0020 wt% or less, Nb: 0.001 to 0.20 wt%, B:
0.0004 to 0.0030 wt%, and the above C, N and S
Contains satisfies Y = 10000 (wt% C + wt% S + wt% N) ≦ 60, further Ti: containing 0.01～0.05Wt%, the balance being Fe and unavoidable impurities Steel, Ar ₃ transformation point ~
In the temperature range of 500 ℃, while applying lubrication, the total reduction ratio is 50 ~
95% hot finish rolling, then hot-rolled sheet recrystallization treatment, cold rolling with a reduction rate of 50-95%, and then cold-rolled sheet recrystallization annealing at 700-950 ° C. A method for producing a cold rolled steel sheet having excellent deep drawability, which is characterized in that

(4) C: 0.0020 wt% or less, Si: 0.01 to
2.0 wt%, Mn: 0.1-3.0 wt%, P: 0.01-0.1 wt
%, S: 0.003 wt% or less, Al: 0.01 to 0.06 wt%,
N: 0.0020 wt% or less, Nb: 0.001 to 0.20 wt%, B:
0.0004 to 0.0030 wt%, and the above C, N and S
Contains Y = 10000 (wt% C + wt% S + wt% N) ≦ 60, and further contains Ni: 1.0 wt% or less, Cu: 1.0
wt% or less and Mo: 1.0 wt% or less, and any one or more selected from, and Ti:
Steel containing 0.01 to 0.05 wt% and the balance Fe and unavoidable impurities is hot-finished at a total reduction of 50 to 95% while lubricating at a temperature range of Ar ₃ transformation point to 500 ° C. After rolling, and then hot-rolled sheet recrystallization treatment,
A method for producing a cold-rolled steel sheet having excellent deep drawability, which comprises performing cold rolling at 50 to 95% and then performing cold recrystallization annealing at 700 to 950 ° C.

(5) In the above inventions (1) to (4), C, N
And S are Y = 10000 (wt% C + wt% S + wt% N) <
It is preferable to satisfy 18.

(6) In the above inventions (1) to (5), the method of recrystallizing the hot-rolled sheet is as follows: rolling in a temperature range of the hot rolling end temperature to 400 ° C. and self-rolling annealing, or It is recommended to anneal in the temperature range of 700 to 950 ℃ after rolling.

[0012]

Next, the reason why the steel composition is limited to the above-mentioned essential constitution in the present invention will be explained. C: 0.0020 wt% or less; C is an element that adversely affects the deep drawability, so it is better to reduce it as much as possible. If the amount exceeds 0.0020 wt%, the effect becomes particularly remarkable, so the content is made 0.0020 wt% or less, preferably less than 0.0010 wt%.

Si: 0.01 to 2.0 wt%; Si is an element effective as a deoxidizing element in the steelmaking process and for strengthening the steel, and at least 0.01 wt% is required to obtain the desired strength.
% Must be added. However, the amount added is 2.0 wt%
If it exceeds 1.0, the workability deteriorates, so 0.01 to 2.0 wt%, preferably 0.01 to 0.1 wt%.

Mn: 0.1-3.0 wt%; Mn is an element effective as a deoxidizing element in the steelmaking process and for strengthening the steel, and at least 0.1 wt% is required to obtain the desired strength.
% Must be added. However, the amount added is 3.0 wt%
If it exceeds 0.1%, the workability is deteriorated, so 0.1 to 3.0 wt% is preferable, and 0.1 to 0.15 wt% is preferable.

P: 0.01-0.1 wt%; P acts to strengthen the steel, and to obtain the desired strength, it should be at least 0.
It is necessary to add it in an amount of 01 wt%, but if the addition amount exceeds 0.1 wt%, the workability deteriorates, so it is added in the range of 0.01 to 0.1 wt%, preferably 0.01 to 0.02 wt%.

S: 0.003 wt% or less; S deteriorates deep drawability, so it is necessary to reduce it as much as possible. S amount
If it exceeds 0.003 wt%, its adverse effects will increase, so
It is 0.003 wt% or less, preferably 0.0010 wt% or less.

Al: 0.01 to 0.06 wt%; Al is added for the purpose of deoxidizing action in the steelmaking process and for improving the yield of carbonitride forming elements, but if the addition amount is less than 0.01 wt% There is no effect, on the other hand, even if it exceeds 0.06 wt%, the effect is saturated, so 0.01 to 0.06 wt%, preferably 0.01 to
0.035 wt%

N: 0.0020 wt% or less; N deteriorates the deep drawability, so it is necessary to reduce it as much as possible. 0.0020wt
If it exceeds%, the adverse effect will be particularly large, so 0.00
It is 20 wt% or less, preferably 0.0010 wt% or less.

Nb: 0.001 to 0.20 wt%; Nb precipitates and fixes solid solution C as a carbide, refines the structure before hot finish rolling, and preferentially crystal grains of {111} orientation after hot-rolled sheet annealing. In the cold rolled sheet after recrystallization annealing,
It is an element that preferentially forms crystal grains in the {111} orientation, which is advantageous for deep drawability. If the addition amount is less than 0.001 wt%, its effect is small, and even if it exceeds 0.20 wt%, no further improvement of the effect is seen, so the addition amount of Nb is 0.001 to 0.20 wt%.
%, Preferably 0.001 to 0.030 wt%.

B: 0.0004 to 0.0030 wt%; B is an element effective for improving the secondary work embrittlement resistance. B amount is 0.00
Addition of less than 04 wt% has no effect, while 0.0030 wt%
%, The deep drawability will deteriorate.
The amount is 0.0030 wt%, preferably 0.0004 to 0.0025 wt%.

Y = 10000 (wt% C + wt% S + wt% N) ≦ 60; C, S and N all have an adverse effect on the r value, and controlling the sum of them is extremely important for improving press workability. is there. If the total sum is set to 10,000 (wt% C + wt% S + wt% N) and is 60 or less, preferably 50 or less, more preferably less than 18, the r value is remarkably improved.

Ni: 1.0 wt% or less, Cu: 1.0 wt% or less, M
o: 1.0 wt% or less; all of these elements are added as necessary in order to obtain the desired strength.
If it is added in excess of 1.0 wt%, the deep drawability will decrease. Therefore, the addition amounts of Ni, Cu and Mo are all 1.0 wt% or less, preferably 0.01 to 0.5 wt%.

Ti: 0.01 to 0.05 wt%; Ti is an element that precipitates and fixes the solid solution C and N in steel and preferentially forms crystal grains in the {111} orientation, which is advantageous for deep drawability. The amount added is
If the amount is less than 0.01% by weight, the effect is small, and if the amount exceeds 0.05% by weight, the effect is not further improved. Therefore,
The amount of Ti added is 0.01 to 0.05 wt%, preferably 0.010 to 0.04.
5 wt%

Next, manufacturing conditions will be described. -The hot-rolled slab may be manufactured by an ordinary continuous casting method or ingot making method. Further, there is no particular need to determine the hot rough rolling process of this slab, for example, a recast continuous casting slab, after continuous casting, immediately or without heat treatment without lowering the temperature below the Ar ₃ transformation point. What has been done may be rolled. At that time, the slab heating temperature is preferably in the range of 1100 to 1200 ° C. from the viewpoint of making the austenite structure uniform. In hot finish rolling, a particularly important condition is to lubricate in the temperature range of Ar ₃ to 500 ° C,
Rolling with a total reduction of 50 to 95%. That is, when the finish rolling is performed at a temperature higher than Ar ₃ , the crystal orientation becomes random due to the γ-α transformation, and {111} on the hot rolled sheet.
The texture is not formed, and the r value of the cold rolled steel sheet decreases. On the other hand, even if finish rolling is carried out at less than 500 ° C, the r value is not improved, and only the rolling load is unnecessarily increased. Therefore, the hot finishing rolling temperature range is Ar ₃ to 500 ° C. Should be done in. In addition, the reduction ratio of hot finish rolling is 50
%, The {111} texture is not formed on the hot-rolled sheet, while if it exceeds 95%, an unfavorable texture is formed at the r value. Therefore, the reduction ratio of hot finish rolling is 50 to 50%. 95
Must be set to%. Further, if the hot finish rolling is a non-lubricating rolling, it is not preferable for deep drawability due to shear deformation due to frictional force between the roll and the steel sheet.
Since the crystal grains of 0} orientation are formed in the surface layer of the steel sheet and the improvement of the r value cannot be expected, the hot finish rolling is performed by lubrication rolling, preferably lubrication rolling having a friction coefficient of 0.15 or less.

Re-crystallization treatment of hot-rolled sheet Since the steel sheet that has been subjected to hot finish rolling has a worked structure, this steel sheet is subjected to re-crystallization treatment and {111}
It is necessary to form oriented crystal grains. Preferable recrystallization conditions are a heat treatment at 700 to 950 ° C. for 20 seconds or more, or a self-annealing treatment for winding at a rolling end temperature to 400 ° C.

[Cold rolling] If the cold rolling reduction is less than 50%, a sufficient r value cannot be obtained, while if it exceeds 95%, the r value rather decreases. Therefore, the reduction of cold rolling must be 50 to 95%.

Recrystallization annealing of cold-rolled sheet Since the steel sheet as cold rolled has a work structure,
By subjecting this to recrystallization annealing at 700 to 950 ° C,
It is possible to develop a {111} recrystallized texture and obtain a high r value. If the annealing temperature is lower than 700 ° C, the recrystallization structure is undeveloped, and if it exceeds 950 ° C, the crystal orientation becomes random due to the γ-α transformation in the cooling process, and only a low r value can be obtained.

[0028]

EXAMPLE A steel slab having the composition shown in Table 1 was reheated,
After hot rough rolling, hold at high temperature under various conditions, and then hot finish rolling with different rolling temperature, reduction rate and lubrication condition, and then perform hot-rolled sheet recrystallization treatment, cold rolling and cold rolled sheet re-rolling. A cold-rolled steel sheet having a plate thickness of 0.7 mm was manufactured through the process of crystal annealing. Table 2 shows each of these manufacturing conditions. The lubricant used for lubrication rolling was a mineral oil-based lubricant, with a friction coefficient of 0.15.
Met. Examining the material properties of these test materials,
The results are also shown in Table 2. Here, the r value is J
After using IS5 tensile test piece and pre-straining 15%, 3
Measured by the point method, the r values in the rolling direction, the direction of 45 ° with respect to the rolling direction, and the direction of 90 ° with respect to the rolling direction are defined as r _L , r _D, and r _C , respectively, and their average value r Was determined by r = (r _L + 2r _D + r _C ) / 4.

[0029]

[Table 1]

[0030]

[Table 2]

From Table 2, it can be seen that all the cold-rolled steel sheets produced by the method of the present invention have excellent deep drawability with an r value of 3.0 or more. On the other hand, the comparative example is inferior in the r value characteristic.

[0032]

As described above, according to the manufacturing method of the present invention, it is possible to provide a cold rolled steel sheet having excellent deep drawability. Furthermore, the present invention can provide a cold-rolled steel sheet having an r value of 3.0 or more as deep drawability.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location C22C 38/16 (72) Inventor Kazuhiro Seto 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Steel Research and Development Headquarters Steel Research Laboratory (72) Inventor Takashi Sakata 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Kawasaki Steel Co., Ltd. Steel Research and Development Division Steel Research Laboratory (72) Inventor Toshiyuki Kato 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Japan Kawasaki Steel Co., Ltd.

Claims (4)

[Claims] 1. C: 0.0020 wt% or less, Si: 0.01 to 2.0
wt%, Mn: 0.1 to 3.0 wt%, P: 0.01 to 0.1 wt%, S: 0.003 wt% or less, Al: 0.01 to 0.06 wt%, N: 0.0020 wt% or less, Nb: 0.001 to 0.20 wt%, B : 0.0004 to 0.0030 wt%, and the above C, N and S satisfy Y = 10000 (wt% C + wt% S + wt% N) ≦ 60, and the balance is steel containing Fe and inevitable impurities, In the temperature range of Ar ₃ transformation point to 500 ℃, while performing lubrication, hot finish rolling with a total reduction of 50 to 95%, followed by hot-rolled sheet recrystallization treatment, then reduction of 50 to A method for producing a cold-rolled steel sheet having excellent deep drawability, which comprises performing cold rolling at 95% and then performing cold-rolled sheet recrystallization annealing at 700 to 950 ° C. 2. C: 0.0020 wt% or less, Si: 0.01 to 2.0
wt%, Mn: 0.1 to 3.0 wt%, P: 0.01 to 0.1 wt%, S: 0.003 wt% or less, Al: 0.01 to 0.06 wt%, N: 0.0020 wt% or less, Nb: 0.001 to 0.20 wt%, B : 0.0004 to 0.0030 wt%, and the above C, N and S satisfy Y = 10000 (wt% C + wt% S + wt% N) ≦ 60, and further contain Ni: 1.0 wt% or less, Cu: 1.0 wt % Or less and Mo: 1.0 wt% or less, and a steel containing one or more selected from the group consisting of Fe and unavoidable impurities in the balance, in the temperature range from the Ar ₃ transformation point to 500 ° C. , While performing lubrication, hot finish rolling with a total reduction of 50 to 95%, then hot-rolled sheet recrystallization treatment, and then reduction of 50
A method for producing a cold-rolled steel sheet having excellent deep drawability, which comprises performing cold rolling at 95% to 95% and then performing recrystallization annealing at 700 to 950 ° C. 3. C: 0.0020 wt% or less, Si: 0.01 to 2.0
wt%, Mn: 0.1 to 3.0 wt%, P: 0.01 to 0.1 wt%, S: 0.003 wt% or less, Al: 0.01 to 0.06 wt%, N: 0.0020 wt% or less, Nb: 0.001 to 0.20 wt%, B : 0.0004 to 0.0030 wt%, and the above C, N and S satisfy Y = 10000 (wt% C + wt% S + wt% N) ≦ 60, and further contain Ti: 0.01 to 0.05 wt%, The balance is steel consisting of Fe and unavoidable impurities, and is subjected to hot finish rolling with a total reduction of 50 to 95% while lubricating in the temperature range of Ar ₃ transformation point to 500 ℃, and then hot rolled sheet. After performing recrystallization treatment,
Cold rolling with a reduction rate of 50 to 95%, then 700 to 950
A method for producing a cold-rolled steel sheet having excellent deep drawability, which comprises performing cold-rolled sheet recrystallization annealing at 0 ° C. 4. C: 0.0020 wt% or less, Si: 0.01 to 2.0
wt%, Mn: 0.1 to 3.0 wt%, P: 0.01 to 0.1 wt%, S: 0.003 wt% or less, Al: 0.01 to 0.06 wt%, N: 0.0020 wt% or less, Nb: 0.001 to 0.20 wt%, B : 0.0004 to 0.0030 wt%, and the above C, N and S satisfy Y = 10000 (wt% C + wt% S + wt% N) ≦ 60, and further contain Ni: 1.0 wt% or less, Cu: 1.0 wt % Or less and Mo: 1.0 wt% or less, and any one or two or more selected, Ti: 0.01 to 0.05 wt% and the balance Fe and unavoidable impurities. In the temperature range of Ar ₃ transformation point to 500 ° C, while performing lubrication, hot finish rolling with a total reduction of 50 to 95% is performed, and then hot-rolled sheet recrystallization treatment is performed.
Cold rolling with a reduction rate of 50 to 95%, then 700 to 950
A method for producing a cold-rolled steel sheet having excellent deep drawability, which comprises performing cold-rolled sheet recrystallization annealing at 0 ° C.