CA2963622C

CA2963622C - Steel sheet for crown cap, manufacturing method therefor, and crown cap

Info

Publication number: CA2963622C
Application number: CA2963622A
Authority: CA
Inventors: Takumi Tanaka; Tomonari HIRAGUCHI; Katsumi Kojima; Hiroki Nakamaru; Nobusuke Kariya
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2014-11-28
Filing date: 2015-11-19
Publication date: 2019-08-27
Anticipated expiration: 2035-11-19
Also published as: US20170335438A1; PH12017500676B1; KR20170070184A; JPWO2016084353A1; MX2017006871A; PH12017500676A1; BR112017010201A2; KR101975129B1; CN107109559B; TW201636433A; AU2015351836A1; JP5988012B1; BR112017010201B1; CN107109559A; TWI601830B; CO2017004922A2; WO2016084353A1; NZ730832A; AU2015351836B2; CA2963622A1

Abstract

Provided are: a steel sheet for a crown cap that has adequate strength and moldability even when used after being made thin; a manufacturing method therefor; and a crown cap. The steel sheet has a composition containing, in mass%, C: 0.010% to 0.025%, Si: not more than 0.10%, Mn: 0.05% to 0.50%, P: not more than0.050%, S: 0.005% to 0.050%, Al: 0.020% to 0.070%, and N: less than 0.0040%, the balance being obtained from Fe and unavoidable impurities. Regarding yield strength after heat treatment for fifteen minutes at 210°C, yield strength in the rolling direction is at least 550 MPa and yield strength in the rolling plane in a direction that is 45° from the rolling direction is not more than the mean of the yield strength in the rolling direction and the yield strength in the rolling plane in a direction that is 90° from the rolling direction.

Description

DESCRIPTION
Title of Invention: STEEL SHEET FOR CROWN CAP, MANUFACTURING
METHOD THEREFOR, AND CROWN CAP
Technical Field [0001]
The present invention relates to a steel sheet which is used as a material for a crown cap serving as a cap for a glass bottle, a method for manufacturing the same, and a crown cap.
Background Art

[0002]
Glass bottles have been widely used for a long time as containers for beverages, such as soft drinks and alcoholic drinks. A cap made of metal, which is referred to as a crown cap, is generally used for a narrow-mouthed glass bottle. In general, crown caps are manufactured by press forming by using a thin steel sheet as a material. A crown cap includes a disk-shaped portion which covers the mouth of a bottle and a pleated portion disposed in the periphery thereof, and by crimping the pleated portion around the mouth of the bottle, the bottle is hermetically sealed.

[0003]
The characteristics required for a thin steel sheet which is used as a material for crown caps include strength and formability. Bottles provided with a crown cap are often filled with contents that cause an internal pressure, such as beer or a carbonated beverage. The material is required to have a strength such that, even when the internal pressure is increased because of a change in temperature or the like, the sealing of the bottle is not broken by deformation of the crown cap. Furthermore, even if the strength of the material is sufficient, when the material has poor formability, there may be a case where the shape of pleats becomes non-uniform, and sufficient sealing performance cannot be obtained even when the pleated portion is crimped around the mouth of a bottle.

[0004]
As the thin steel sheet which is used as a material for crown caps, an SR (Single Reduced) steel sheet is mainly used. An SR steel sheet is produced by reducing the thickness of a steel sheet by cold rolling, and then annealing the steel sheet, followed by temper rolling. In existing techniques, since the thickness of the material for crown caps is 0.20 mm or more, it is possible to secure sufficient strength and formability by employing an SR sheet made from mild steel which is used for cans of food and drinks.

[0005]
However, in recent years, there has been an increased demand for a reduction in the thickness of the material for crown caps, as in steel sheets for cans, for the purpose of cost reduction. When the thickness of the material for crown caps is less than 0.20 mm, the strength of the existing SR steel sheet is insufficient. In order to ensure strength, it is conceivable to use a DR (Double Reduced) steel sheet which has been subjected to secondary cold rolling after annealing. However, when the secondary cold rolling reduction is increased, formability is degraded, resulting in poor sealing of bottles.

[0006]
Under the circumstances described above, in order to obtain a steel sheet having excellent strength and formability, the following techniques have been proposed.

[0007]
Patent Literature 1 discloses an ultrathin soft steel sheet for a container excellent in can strength and can formability, containing, in percent by weight, N: 0.0040 to 0.0300% and Al: 0.005 to 0.080%, characterized in that the 0.2% proof stress is 430 MPa or less, the total elongation is 15 to 40%, and the internal friction Q-1 is 0.0010 or more.

[0008]
Patent Literature 2 discloses a high-strength high-workability steel sheet for a can, containing, in percent by mass, C: 0.001 to 0.080%, Si: 0.003 to 0.100%, Mn: 0.10 to 0.80%, P: 0.001 to 0.100%, S: 0.001 to 0.020%, Al: 0.005 to 0.100%, N: 0.0050 to 0.0150%, and B: 0.0002 to 0.0050%, characterized by including, in area fraction, 0.01 to 1.00%
of crystal grains whose elongation rate is 5.0 or more in a cross section in the rolling direction.
Citation List Patent Literature

[0009]
PTL 1: Japanese Unexamined Patent Application Publication No. 2001-49383 PTL 2: Japanese Unexamined Patent Application Publication No. 2013-28842 Summary of Invention Technical Problem

[0010]
However, the existing techniques have the problems described below.

[0011]
The steel sheet described in Patent Literature 1 is soft and contains a large amount of N. Therefore, in order to obtain the required strength, it is necessary to increase the secondary cold rolling reduction. When the secondary cold rolling reduction is increased, anisotropy is also increased, and formability is impaired.

[0012]
The steel sheet described in Patent Literature 2 has a large N content as in the steel sheet described in Patent Literature 1. Therefore, it is difficult to achieve both strength and workability required for the material for crown caps.

[0013]
The present invention has been accomplished under the circumstances described above, and it is an object of the present invention to solve the problems of the existing techniques and to provide a steel sheet for a crown cap having sufficient strength and formability even when the thickness thereof is reduced for use, a manufacturing method therefor, and a crown cap.
Solution to Problem

[0014]
The present inventors have performed thorough studies in order to solve the problems described above. As a result, it has been found that by optimizing the steel composition, hot rolling conditions, annealing conditions, and secondary cold rolling conditions (DR conditions), it is possible to obtain a steel sheet for a crown cap having sufficient strength and formability.

[0015]
The present invention has been made on the basis of the finding described above, and the gist of the invention is as follows:

[1] A steel sheet for a crown cap comprising:
a composition containing, in percent by mass, C: 0.010%
to 0.025%, Si: 0.10% or less, Mn: 0.05% to 0.50%, P: 0.050%
or less, S: 0.005% to 0.050%, Al: 0.020% to 0.070%, N: less than 0.0040%, and the balance being Fe and inevitable impurities, regarding yield strength after heat treatment at 210 C
for 15 minutes, a yield strength in a rolling direction being 550 MPa or more, and a yield strength in a direction 45 from the rolling direction in a rolling plane being equal to or less than an average of the yield strength in the rolling direction and a yield strength in a direction 90 from the rolling direction in the rolling plane.
[2] A method for manufacturing the steel sheet for a crown cap according to [1], including:
a hot rolling step of hot rolling a slab and coiling the hot rolled steel sheet at a coiling temperature of 530 C to 590 C;
a primary cold rolling step of cold rolling the hot rolled steel sheet after the hot rolling step;
an annealing step of annealing the cold rolled steel sheet at an annealing temperature of 650 C to 720 C after the primary cold rolling step; and a secondary cold rolling step of performing secondary cold rolling with a rolling reduction of 25% to 40% after the annealing step.
[3] A crown cap formed of the steel sheet for a crown cap according to [1].
[4] A method for manufacturing a steel sheet for a crown cap including:
a hot rolling step of hot rolling a slab having a composition containing, in percent by mass, C: 0.010% to 0.025%, Si: 0.10% or less, Mn: 0.05% to 0.50%, P: 0.050% or less, S: 0.005% to 0.050%, Al: 0.020% to 0.070%, N: less than 0.0040%, and the balance being Fe and inevitable impurities, and coiling the hot rolled steel sheet at a coiling temperature of 530 C to 590 C;
a primary cold rolling step of cold rolling the hot rolled steel sheet after the hot rolling step;
an annealing step of annealing the cold rolled steel sheet at an annealing temperature of 650 C to 720 C after the primary cold rolling step; and a secondary cold rolling step of performing secondary cold rolling with a rolling reduction of 25% to 40% after the annealing step, the manufactured steel sheet having, regarding yield strength after heat treatment at 210 C for 15 minutes, a yield strength in a rolling direction is 550 MPa or more, and a yield strength in a direction 45 from the rolling direction in a rolling plane is equal to or less than the average of the yield strength in the rolling direction and a yield strength in a direction 90 from the rolling direction in the rolling plane.
Advantageous Effects of Invention

[0016]
According to the present invention, it is possible to obtain a steel sheet for a crown cap having sufficient strength and formability even when the thickness thereof is reduced for use. It is possible to achieve both strength and crown cap formability of a steel sheet, and a reduction in the thickness of a crown cap can be realized.
Description of Embodiments

[0017]
The present invention will be described in detail below.
Unless otherwise specified, "%" means percent by mass.

[0018]
A steel sheet of the present invention has a specific composition, and regarding yield strength after heat treatment at 210 C for 15 minutes, the yield strength in a rolling direction is 550 MPa or more, and the yield strength in a direction 45 from the rolling direction in a rolling plane is equal to or less than the average of the yield strength in the rolling direction and the yield strength in a direction 90 from the rolling direction in the rolling plane. As a result, it is possible to obtain a crown cap which has sufficient strength and formability and whose thickness can be reduced for use.

[0019]
Composition The composition of the present invention will be described.

[0020]
C: 0.010% to 0.025%
C is an element that contributes to achieving both strength and workability when its content is set in an optimum range. When the C content is less than 0.010%, the amount of strengthening due to solute C is small and, therefore, strength becomes insufficient. On the other hand, when the C content exceeds 0.025%, the shape of pleats of a formed crown cap becomes non-uniform, resulting in shape defects. Therefore, the C content is set to be 0.010% to 0.025%.

[0021]
Si: 0.10% or less When the Si content is excessively large, formability is adversely affected. Accordingly, the Si content exceeding 0.10% is not desirable. Therefore, the Si content is set to be 0.10% or less. From the viewpoint of improvement in the strength of the steel sheet, the Si content is preferably 0.02% to 0.10%.

[0022]
Mn: 0.05% to 0.50%
When the Mn content falls below 0.05%, even in the case where the S content is decreased, it becomes difficult to avoid hot brittleness, resulting in problems such as surface crack during continuous casting. On the other hand, the Mn content exceeding 0.50% adversely affects formability, similarly to Si. Therefore, the Mn content is set to be 0.05% to 0.50%.

[0023]
P: 0.050% or less When the P content exceeds 0.050%, steel is hardened, and corrosion resistance is decreased. Therefore, the P
content is set to be 0.050% or less.

[0024]
S: 0.005% to 0.050%
S binds to Mn to form MnS in steel and precipitates a large amount of MnS, thereby degrading the hot ductility of steel. When the S content exceeds 0.050%, this effect becomes noticeable. On the other hand, in order to set the S content to be less than 0.005%, the desulfurization cost becomes excessively high. Therefore, the S content is set to be 0.005% to 0.050%

[0025]
Al: 0.020% to 0.070%
Al is an element that is added as a deoxidizer.
Furthermore, Al forms AlN with N in steel to decrease solute N in steel. When the Al content is less than 0.020%, the effect as a deoxidizer is insufficient, resulting in solidification defects. On the other hand, in the case where the extent of secondary cold rolling is large, a large Al content will cause a degradation in formability. When the Al content exceeds 0.070%, the shape of pleats becomes non-uniform during formation of a crown cap, resulting in shape defects. Therefore, the Al content is set to be 0.020% to 0.070%.

[0026]
N: less than 0.0040%
When the N content is 0.0040% or more, the steel sheet is hardened, and formability is degraded. Therefore, the N
content is set to be less than 0.0040%, and preferably 0.0035% or less.

[0027]
The balance other than the essential components described above includes iron and inevitable impurities.

[0028]
Mechanical properties Mechanical properties of a steel sheet for a crown cap according to the present invention will be described below.

[0029]
A steel sheet for a crown cap is required to have a strength such that the crown cap is not removed under the influence of an internal pressure of the bottle. For this reason, in existing techniques, the thickness of a steel sheet for a crown cap is 0.20 mm or more. However, there has been an increased demand for a reduction in the thickness. When the thickness is reduced to less than 0.20 mm, a larger strength than that of existing materials is required. In the case where the yield strength in a rolling direction of a steel sheet is less than 550 MPa, it is not possible to impart a sufficient strength to a crown cap whose thickness has been reduced, and the pressure resistance becomes insufficient. Therefore, the yield strength in the rolling direction is set to be 550 MPa or more.

[0030]
Furthermore, in general, in a DR steel sheet, the yield strength differs depending on the direction in the rolling plane. When the yield strength in a direction 45 from the rolling direction is more than the average of the yield strength in the rolling direction and the yield strength in a direction 90 from the rolling direction, formability is degraded. Therefore, in the present invention, the yield strength in a direction 45 from the rolling direction in a rolling plane is set to be equal to or less than the average of the yield strength in the rolling direction and the yield strength in a direction 90 from the rolling direction in the rolling plane. That is, the difference obtained by subtracting the yield strength in a direction 45 from the rolling direction in the rolling plane from the average of the yield strength in the rolling direction and the yield strength in a direction 90 from the rolling direction in the rolling plane is set to be 0 MPa or more, and preferably to 25 MPa.

[0031]
It is possible to manufacture a steel sheet having the yield strength described above by a manufacturing method which will be described later.
Furthermore, a crown cap is formed, often after a steel sheet has been subjected to baking finish and, therefore, it is necessary to evaluate the quality of the material after treatment corresponding to baking finish. Accordingly, in the present invention, the yield strength is measured after heat treatment corresponding to baking finish at 210 C for minutes, and the tensile testing method for metallic materials according to "JIS Z 2241" can be applied thereto.

[0032]
Method for manufacturing steel sheet for crown cap An example of a method for manufacturing a steel sheet for a crown cap according to the present invention will be described below.

[0033]
A method for manufacturing a steel sheet for a crown cap according to the present invention includes a hot rolling step in which a steel slab having the composition described above is subjected to hot rolling, followed by coiling at a coiling temperature of 530 C to 590 C; a primary cold rolling step in which cold rolling is performed after the hot rolling step; an annealing step in which annealing is performed at an annealing temperature of 650 C
to 720 C after the primary cold rolling step; and a secondary cold rolling step in which secondary cold rolling is performed with a rolling reduction of 25% to 40% after the annealing step. These steps will be described below.

[0034]
Hot rolling step Molten steel is adjusted so as to have the chemical composition described above by a known method using a converter or the like, and is formed into a slab by a continuous casting method. Subsequently, the steel slab is subjected to rough rolling. Although the rough rolling method is not particularly limited, the slab heating temperature is preferably 1,200 C or higher. Then, finish rolling is performed. The finish rolling temperature is preferably 850 C or higher from the standpoint of stability of the rolling load. The term "finish rolling temperature"
refers to the temperature of the sheet when it enters the last stand of a finish rolling mill. On the other hand, when the finish rolling temperature is increased more than necessary, manufacturing of a thin steel sheet may become difficult in some cases. That is, when the thickness of the sheet is small, since the decrease in the temperature of the sheet during rolling is large, it is difficult to perform finish rolling while maintaining the high temperature of the sheet, thus being uncontrollable. Therefore, the finishing temperature is preferably 850 C to 900 C.
When the coiling temperature in the hot rolling step is lower than 530 C, in order to perform an operation without impairing efficiency, it is necessary to decrease the finish rolling temperature accordingly, which is inappropriate. On the other hand, when the coiling temperature exceeds 590 C, the amount of AIN which precipitates after coiling becomes excessively large, leading to a decrease in the grain size after annealing, resulting in a degradation in formability.
Therefore, the coiling temperature is set to be 530 C to 590 C, and preferably 540 C to 580 C.

[0035]
Primary cold rolling step It is preferable to remove surface scale before the primary cold rolling step. The method for removing surface scale is not particularly limited, and various common methods, such as pickling and physical removal, can be used.
Surface scale can be suitably removed by pickling. The picking conditions are not particularly limited, and pickling may be performed in the usual manner.

[0036]
The rolling reduction in the primary cold rolling is preferably 85% or more in order to manufacture an ultrathin material. However, when the rolling reduction is increased excessively, the load on the rolling machine becomes excessively large, and it may become difficult to perform rolling in some cases. Therefore, the rolling reduction is preferably set to be 94% or less.

[0037]
Annealing step When the annealing temperature is higher than 720 C, trouble during passing of the sheet, such as heat buckling, is likely to occur during continuous annealing, which is not desirable. When the annealing temperature is lower than 650 C, recrystallization becomes imperfect, resulting in non-uniform quality of the material. Therefore, the annealing temperature is set to be 650 C to 720 C.
Furthermore, the soaking period in the annealing step is not particularly limited, but is preferably 10 seconds or more in order to surely obtain a recrystallization structure, and is preferably 50 seconds or less in order to prevent excessive grain growth.

[0038]
Secondary cold rolling (DR rolling) step The strength of the annealed steel sheet is increased by secondary cold rolling. When the rolling reduction in the secondary cold rolling is less than 25%, it is not possible to obtain strength sufficient to ensure the pressure resistance of a crown cap. Furthermore, when the rolling reduction in the secondary cold rolling exceeds 40%, the difference of the yield strength in a direction 45 from the rolling direction in the rolling plane from the average of the yield strength in the rolling direction and the yield strength in a direction 900 from the rolling direction in the rolling plane is positively increased, resulting in a degradation in formability. Therefore, the rolling reduction in the secondary cold rolling is set to be 25% to 40%.

[0039]
A high-strength steel sheet according to the present invention is obtained by the method described above. Even when the resulting steel sheet is subjected to surface treatment, such as plating or chemical conversion treatment, the advantageous effects of the present invention are not impaired.
EXAMPLES

[0040]
Steels having the compositions shown Table 1 and containing the balance being Fe and inevitable impurities were refined by a converter, and steel slabs were obtained by continuous casting. The resulting steel slabs were each heated to 1,250 C, then hot-rolled at a rolling start temperature of 1,150 C and at a finish rolling temperature of 860 C, and coiled at the coiling temperature shown in Table 2. Next, after scale was removed by pickling, primary cold rolling was performed with the primary cold rolling reduction shown in Table 2, annealing was performed in a continuous annealing furnace at the annealing temperature shown in Table 2, and secondary cold rolling (DR rolling) was performed with the secondary cold rolling reduction shown in Table 2 to obtain steel sheets (levels 1 to 9) with a thickness of 0.15 to 0.18 mm. The resulting steel sheets were Cr-plated on both surfaces with a coating weight of 100 mg/m2 per surface and, thereby, tin-free steel sheets were obtained.

[0041]
Characteristics evaluation was made on the steel sheets thus obtained by the methods described below.

[0042]
Yield strength After conducting heat treatment corresponding to baking finish at 210 C for 15 minutes, a tensile test was carried out. The tensile test was performed, using a JIS No. 5 tensile test piece, in accordance with "JIS Z 2241" to measure the yield strength in the rolling direction, the yield strength in a direction 45 from the rolling direction in the rolling plane, and the yield strength in a direction 90 from the rolling direction in the rolling plane.

[0043]
Crown cap formability Using each of the resulting steel sheets, a crown cap was formed, and crown cap formability was evaluated. A
circular blank with a diameter of 37 mm was used and formed by press working into a size (outside diameter: 32.1 mm, height: 6.5 mm, number of pleats: 21) of a type 3 crown cap according to "JIS S 9017" (withdrawn standard). The evaluation was visually performed. The case where the pleats all had a uniform size was evaluated to be very good CO), the case where the pleats had a substantially uniform size was evaluated to be good (D), and the case where the pleats had a non-uniform size was evaluated to be poor (x).
Note that, in the visual determination, the case where the maximum value of pleat width (breadth) was 1.5 times or more the minimum value was determined to be non-uniform.

[0044]
Pressure test using formed crown cap Crown caps were formed by the same method as that described above. A vinyl chloride liner was formed inside each of the crown caps. A commercially available beer bottle was closed with the crown cap, and the internal pressure at which the crown cap was removed was measured by using a Secure Seal Tester manufactured by Glassline Corporation.
The case where the pressure resistance was equal to or more than that of the existing crown cap was evaluated to be good (D), and the case where the pressure resistance did not reach that of the existing crown cap was evaluated to be poor (x).

[0045]
The results thus obtained are shown in Table 3.

[0046]

[Table 1]
(mass%) Si Mn P S Al Level 1 0.019 0.01 0.22 0.015 0.010 0.057 0.0034 Level 2 0.025 0.01 0.30 0.019 0.013 0.035 0.0029 Level 3 0.011 0.02 0.25 0.016 0.020 0.031 0.0030 Level 4 0.020 0.01 0.48 0.021 0.015 0.046 0.0031 Level 5 0.022 0.03 0.41 0.018 0.019 0.069 0.0027 Level 6 0.019 0.01 0.28 0.020 0.020 0.061 0.0038 Level 7 0.009 0.02 0.24 0.012 0.010 0.040 0.0030 Level 8 0.015 0.01 0.35 0.013 0.015 0.046 0.0032 Level 9 0.021 0.03 0.40 0.021 0.011 0.031 0.0033

[0047]

[Table 2]
Hot rolling PrimarySecondary.
Thickness i cold rolling Thickness coiling cold rolling temperature of hot-rolled t: emprature of finished Remarks reduction reduction sheet (mm) ( C) (%) sheet (mm) ( C) (%) Example of Level 1 570 2.5 90 680 30 0.18 present invention Example of Level 2 540 2.5 88 660 40 0.18 present invention Example of Level 3 580 2.8 90 700 35 0.18 present invention Example of Level 4 530 2.5 92 650 25 0.15 present invention Example of Level 5 590 2.5 90 690 30 0.18 present invention Example of Level 6 550 2.8 90 720 35 0.18 present invention Level 7 560 2.5 88 650 40 0.18 Comparative example Level 8 570 2.8 90 640 35 0.18 Comparative example Level 9 560 2.5 92 670 20 0.16 Comparative example

[0048]

[Table 3]
Yield Average of yield strength Yield strength strength in in rolling direction and in direction 450 0_0 Crown Pressure rolling yield strength in direction from rolling (MP --cap -- resistance -- Remarks a) direction 900 from rolling direction direction (MPa) formability (MPa) (MPa) C) 0 Example of Level 1 610 632 619 13 0 0 present invention Example of Level 2 628 650 640 10 0 0 present invention Example of Level 3 621 645 630 15 0 0 present invention Example of Level 4 579 602 592 10 0 0 present invention Example of Level 5 604 622 616 6 0 0 present invention Example of Level 6 617 643 631 12 0 0 present invention Level 7 545 563 556 7 0 x Comparative example Level 8 625 644 652 -8 x x Comparative example Level 9 543 557 555 2 x x Comparative example [ 0 0 4 9 ]
As shown in Table 3, in the steel sheets of levels 1 to 6 which are examples of the present invention, the yield strength in the rolling direction is 550 MPa, the yield strength in a direction 45 from the rolling direction in the rolling plane is equal to or less than the average of the yield strength in the rolling direction and the yield strength in a direction 90 from the rolling direction in the rolling plane, and both the crown cap formability and the pressure resistance are satisfactory.
[0050]
On the other hand, in the steel sheet of level 7 which is a comparative example, since the C content is excessively low, the yield strength in the rolling direction is less than 550 MPa, and the pressure resistance is insufficient.
In the steel sheet of level 8 which is a comparative example, since the annealing temperature is excessively low, the yield strength in a direction 450 from the rolling direction exceeds the average of the yield strength in the rolling direction and the yield strength in a direction 90 from the rolling direction in the rolling plane, and the crown cap formability is poor. Since the shape of the crown cap is poor, sealing performance is insufficient, and the pressure resistance is low. In the steel sheet of level 9 which is a comparative example, since the secondary cold rolling reduction is excessively small, the yield strength in the rolling direction is less than 550 MPa, the crown cap formability is poor, and the pressure resistance is insufficient.

Claims

1. A steel sheet for a crown cap comprising, in percent by mass, C: 0.010% to 0.025%, Si: 0.10% or less, Mn: 0.05% to 0.50%, P: 0.050% or less, S: 0.005% to 0.050%, Al: 0.020% to 0.070%, N: less than 0.0040%, and a balance being Fe and inevitable impurities, the steel sheet having, after heat treatment at 210°C for 15 minutes:
a yield strength in a rolling direction being 550 MPa or more, and a yield strength in a direction 45° from the rolling direction in a rolling plane being equal to or less than an average of the yield strength in the rolling direction and a yield strength in a direction 900 from the rolling direction in the rolling plane.

2. A crown cap comprising the steel sheet for a crown cap as defined in claim 1.

3. A method for manufacturing a steel sheet for a crown cap comprising:
a hot rolling step of hot rolling a slab having a composition containing, in percent by mass, C: 0.010% to 0.025%, Si: 0.10% or less, Mn: 0.05% to 0.50%, P: 0.050% or less, S: 0.005% to 0.050%, Al: 0.020% to 0.070%, N: less than 0.0040%, and the balance being Fe and inevitable impurities, and coiling the hot rolled steel sheet at a coiling temperature of 530°C to 590°C;
a primary cold rolling step of cold rolling the hot rolled steel sheet after the hot rolling step;
an annealing step of annealing the cold rolled steel sheet at an annealing temperature of 650°C to 720°C after the primary cold rolling step; and a secondary cold rolling step of performing secondary cold rolling with a rolling reduction of 25% to 40% after the annealing step, the manufactured steel sheet having, after heat treatment at 210°C for minutes, a yield strength in a rolling direction being 550 MPa or more, and a yield strength in a direction 45° from the rolling direction in a rolling plane being equal to or less than an average of the yield strength in the rolling direction and a yield strength in a direction 90° from the rolling direction in the rolling plane.