KR102259719B1 - Steel sheet, method of manufacturing same, crown cap, and drawing and redrawing(drd) can - Google Patents

Abstract

In mass%, C: more than 0.0060% and 0.0100% or less, Si: 0.05% or less, Mn: 0.05% or more and 0.60% or less, P: 0.050% or less, S: 0.050% or less, Al: 0.020% or more and 0.050% or less, and N : A ferrite phase containing 0.0070% or more and 0.0140% or less, the balance being the component composition of Fe and unavoidable impurities, and a standard deviation of the ferrite grain size in the region from a depth of 1/4 of the plate thickness to the center of the plate thickness of 7.0 µm or less A steel sheet provided with sufficient strength and excellent formability even if the thickness is reduced by setting a structure having a phase and yield strength of 560 MPa or more is provided.

Description

Steel sheet, its manufacturing method, crown, and DRD can {STEEL SHEET, METHOD OF MANUFACTURING SAME, CROWN CAP, AND DRAWING AND REDRAWING (DRD) CAN}

The present invention relates to a steel sheet, particularly a high-strength thin steel sheet excellent in formability, and a method for manufacturing the same. Typical examples of such a steel sheet include a thin steel sheet provided as a material for a crown cap used as a stopper for glass bottles and the like, in addition to a DRD (Drawing and Redrawing) can formed by combining drawing and redrawing processing. Moreover, this invention relates to the crown and DRD can obtained by shape|molding the said steel plate.

By the way, many glass bottles are used conventionally for containers for drinks, such as a soft drink and alcoholic beverage. In particular, a metal stopper called a crown is widely used for a glass bottle with a narrow mouth. In general, a crown is manufactured by press molding using a thin steel plate as a material, and consists of a disk-shaped portion for blocking the mouth of a bottle, and a corrugated portion formed around it, and the corrugated portion Seal the bottle by fixing it to the mouth of the bottle.

A bottle in which a crown is used is often filled with a content that generates a high internal pressure, such as beer or carbonated beverage. For this reason, even when the internal pressure is increased due to a change in temperature or the like, the crown needs high pressure resistance so that the crown is not deformed and the seal of the bottle is not broken. In addition, even if the strength of the material is sufficient, when the material uniformity of the steel sheet used for the crown is low, the shape of the crown becomes uneven and deviates from the product standard. Since sufficient sealing performance may not be obtained even if such a defective-shaped crown is fixed to the mouth of a bottle, the steel plate used as the raw material of a crown also needs to be excellent in material uniformity.

For the thin steel sheet provided for the material of the crown, SR (Single Reduced) steel sheet is mainly used. This is to perform annealing and temper rolling after thinning a steel sheet by cold rolling. The plate thickness of the conventional steel plate for crown is generally 0.22 mm or more, and by applying the SR material made of mild steel used for food and beverage cans, it was possible to secure sufficient pressure resistance and formability. .

In recent years, like the steel plate for cans, the request|requirement of thickness reduction for the purpose of cost reduction also increases with respect to the steel plate for crowns. When the sheet thickness of the steel sheet for a crown is less than 0.22 mm, especially 0.20 mm or less, the pressure resistance strength is insufficient in the crown made of the conventional SR material. In order to secure the pressure-resistant strength as a steel sheet for a crown, it is necessary to compensate for the decrease in strength accompanying thickness reduction, and a DR (Double Reduced) steel sheet is applied, which is subjected to work hardening by cold rolling again after annealing.

By the way, as for the crown, the central part is drawn to some extent at the beginning of shaping|molding, and after that, the outer edge part is shape|molded in a wavy shape. Here, if the material of the crown is a steel sheet having low material uniformity, the crown manufactured from the steel sheet may have uneven outer diameter and height, which may deviate from product specifications. If the outer diameter and height of the crown are uneven and there is something out of the product specification, there is a problem that the yield when the crown is manufactured in large quantities is reduced. In addition, a crown having an outer diameter and height outside the standard has a problem in that the contents are easily leaked during transportation after the bottle is capped, and thus cannot fulfill its role as a lid. In addition, even if the outer diameter and height of the crown are within the product specifications, when the steel sheet strength is low, the crown may come off due to insufficient pressure strength.

In addition, when a steel sheet with low material uniformity is used as a material for a DRD can, there is a possibility that a shape defect, typified by wrinkle generated in the flange portion of the can during the forming of the DRD can, may result. Regarding this DRD can, if there is a deviation from the product standard due to a shape defect, there is a problem similar to the case of the crown described above, in that the yield when a large amount of the DRD can is produced is reduced.

Considering the above points, regarding high-strength steel sheet for crown, for example, in Patent Document 1, in mass%, C: 0.0010% or more and 0.0060% or less, Si: 0.005% or more and 0.050% or less, Mn: 0.10% or more and 0.50 % or less, P: 0.040% or less, S: 0.040% or less, Al: 0.1000% or less, N: 0.0100% or less; Disclosed are a steel sheet for a crown that satisfies a sufficient internal pressure for a crown even with a thin thickness by appropriately controlling the average value of the r-values in the direction and the yield strength, and a method for manufacturing the same.

Japanese Patent Publication No. 6057023

The steel sheet described in Patent Document 1 uses a steel containing 0.0060% or less of C, and sets the inter-stand tension and annealing temperature in the secondary cold rolling into a predetermined relationship, so that the r value (direction/ size) is obtained. Since this method does not control the hot rolling process which affects metal structure formation, the dispersion|variation in the material of the steel plate obtained becomes large, and it is difficult to provide practically.

The present invention has been made in view of the above problems, and an object thereof is to provide a steel sheet having sufficient strength and excellent formability even if the thickness is reduced, and a method for manufacturing the same. Another object of the present invention is to provide a crown and a DRD can which are arranged in a predetermined size and shape and are excellent in shape stability.

As a result of earnestly clarified about the method for solving the said subject, the inventors discovered that high strength and excellent moldability could be provided by regulating a structure|tissue under a predetermined|prescribed component composition. The present invention originates from this recognition, and the summary structure is as follows.

(1) in mass %,

C: more than 0.0060% and 0.0100% or less;

Si: 0.05% or less;

Mn: 0.05% or more and 0.60% or less;

P: 0.050% or less;

S: 0.050% or less;

Al: 0.020% or more and 0.050% or less, and

N: 0.0070% or more and 0.0140% or less

contains, and the remainder has a component composition of Fe and unavoidable impurities,

It has a ferrite phase in the region from a depth of 1/4 of the plate thickness to the center of the plate thickness, and the standard deviation of the ferrite grain size in the ferrite phase is 7.0 µm or less,

A steel sheet having a yield strength of 560 MPa or more.

(2) The steel sheet according to (1), wherein the sheet thickness is 0.20 mm or less.

(3) A crown made of the steel sheet according to (1) or (2) above.

(4) A DRD can comprising the steel sheet according to (1) or (2) above.

(5) A method for producing a steel sheet according to (1) or (2), the method comprising:

A hot rolling process in which the steel material is heated at 1200 ° C. or higher, the finish rolling temperature: 870 ° C. or higher, and the final stand rolling reduction: 10% or higher, and wound within a temperature range of 550 to 750 ° C.;

a pickling step of performing pickling on the hot-rolled sheet after the hot rolling;

a primary cold-rolling step of cold-rolling the hot-rolled sheet after pickling with a reduction ratio of 88% or more;

The cold-rolled sheet after the primary cold rolling is stored and maintained for 60 seconds or less in a temperature range of 660 to 760° C., then cooled to a temperature range of 450° C. or less at an average cooling rate of 10° C./s or more, and then 5° C./ An annealing process of cooling to a temperature range of 140 ° C. or less at an average cooling rate of s or more;

The manufacturing method of the steel plate which has a secondary cold-rolling process which cold-rolls to the said annealing plate at the rolling-reduction|draft ratio of 10% or more and 40% or less.

ADVANTAGE OF THE INVENTION According to this invention, the steel plate which has sufficient intensity|strength even if it reduces thickness and is excellent in material uniformity can be provided with the advantageous manufacturing method. Further, when the steel sheet of the present invention is provided for, for example, a crown or a DRD can, a crown or DRD can without deformation in shape can be formed.

(Form for carrying out the invention)

The steel sheet according to the present invention, in mass%, C: more than 0.0060% and 0.0100% or less, Si: 0.05% or less, Mn: 0.05% or more and 0.60% or less, P: 0.050% or less, S: 0.050% or less, Al: 0.020 % or more and 0.050% or less, N: 0.0070% or more and 0.0140% or less, the balance has a component composition consisting of Fe and unavoidable impurities, and a ferrite phase is formed in the region from a depth of 1/4 of the plate thickness to the center of the plate thickness. and the standard deviation of the ferrite particle size in the ferrite phase is 7.0 µm or less.

First, the reason for limitation of each component amount in the component composition of a steel plate is demonstrated in order. In addition, unless otherwise indicated, "%" indication regarding a component shows "mass %".

C: more than 0.0060% and less than or equal to 0.0100%

When the content of C is 0.0060% or less, the ferrite of the steel sheet after secondary cold rolling, which will be described later, becomes coarse and the formability deteriorates, for example, when used for a crown, the formed crown outer diameter and crown height become non-uniform. . Similarly, in the case of supplying for DRD cans, for example, wrinkles are generated in the flange portion during DRD can molding, resulting in poorly shaped cans. On the other hand, when the C content is more than 0.0100%, the ferrite of the steel sheet after secondary cold rolling becomes too fine, the strength of the steel sheet excessively increases, and the formability deteriorates. The outer diameter and height of the crown become non-uniform. Similarly, in the case of supplying for DRD cans, for example, wrinkles are generated in the flange portion during DRD can molding, resulting in poorly shaped cans. Therefore, the content of C is made more than 0.0060% and 0.0100% or less. Preferably, the C content is 0.0065% or more and 0.0090% or less.

Si: 0.05% or less

When Si is included in a large amount, for the same reason as C, for example, when provided for a crown, the uniformity of the outer diameter and height of the crown is impaired, for example, when providing for a DRD can, DRD can molding It causes a shape defect in which wrinkles are generated in the flange part during operation. Therefore, the content of Si is made 0.05% or less. Moreover, since reducing Si excessively causes increase in steelmaking cost, it is preferable to make content of Si into 0.004 % or more. More preferably, they are 0.01 % or more and 0.03 % or less.

Mn: 0.05% or more and 0.60% or less

When the content of Mn is less than 0.05%, it becomes difficult to avoid hot embrittlement even if the content of S is reduced, and problems such as surface cracking occur during continuous casting. Therefore, the content of Mn is made 0.05% or more. On the other hand, when Mn is included in a large amount, the uniformity of the outer diameter and height of the crown is impaired for the same reason as C, for example, when it is provided for a crown, for example, when it is provided for a DRD can, When forming DRD cans, wrinkles occur in the flange, resulting in shape defects. Therefore, the content of Mn is made 0.60% or less. Preferably, the content of Mn is 0.10% or more and 0.50% or less.

P: 0.050% or less

When content of P exceeds 0.050 %, hardening of a steel plate and the fall of corrosion resistance will occur. In addition, the standard deviation of the ferrite particle size after annealing becomes more than 7.0 μm, and the formability deteriorates. For example, when provided for a crown, the uniformity of the outer diameter and height of the crown is impaired, for example, for a DRD can. When provided, a shape defect in which wrinkles occur in the flange portion during DRD can molding is caused. Therefore, the upper limit of the content of P is set to 0.050%. Moreover, in order to make P less than 0.001 %, since P removal cost becomes excessive, it is preferable to make P content into 0.001 % or more.

S: 0.050% or less

S combines with Mn in the steel sheet to form MnS, and by precipitating in a large amount, the hot ductility of the steel sheet is reduced. When the content of S exceeds 0.050%, this influence becomes remarkable. Therefore, the upper limit of the content of S is set to 0.050%. In addition, in order to make S less than 0.005 %, since S removal cost becomes excessive, it is preferable to make S content into 0.004 % or more.

Al: 0.020% or more and 0.050% or less

Al is an element to be contained as a deoxidizer, and further forms N and AlN in steel to reduce solid solution N in steel. When Al content is less than 0.020 %, the effect as a deoxidizer becomes inadequate, while generation|occurrence|production of a solidification defect is brought about, steelmaking cost increases. In addition, when the amount of Al is less than 0.020%, since an appropriate amount of AlN cannot be ensured at the time of recrystallization of ferrite in annealing, the standard deviation of the ferrite grain size after annealing becomes large, and the ferrite of the steel sheet after secondary cold rolling is coarse. and the moldability deteriorates. Then, for example, when provided for a crown, the uniformity of the outer diameter and height of the crown is impaired. For example, when it is provided for a DRD can, a wrinkle occurs in the flange during molding of the DRD can. causes On the other hand, when the content of Al exceeds 0.050%, the formation of AlN increases, the amount of N contributing to the steel sheet strength as solid solution N, which will be described later, decreases, and the steel sheet strength decreases, so the Al content is made 0.050% or less. Preferably, the Al content is 0.030% or more and 0.045% or less.

N: 0.0070% or more and 0.0140% or less

When the content of N is less than 0.0070%, the ferrite of the steel sheet after secondary cold rolling becomes coarse and the formability deteriorates, for example, when used for a crown, the outer diameter and height of the formed crown become non-uniform. , the amount of N contributing to the steel sheet strength as a solid solution N described later decreases, and the steel sheet strength decreases. Similarly, in the case of supplying for DRD cans, for example, wrinkles are generated in the flange portion during DRD can molding, resulting in poorly shaped cans. On the other hand, when the N content exceeds 0.0140%, the ferrite of the steel sheet after secondary cold rolling becomes too fine, the steel sheet strength increases excessively, and the formability deteriorates, for example, when provided for a crown, the outer diameter of the crown And the uniformity of the height is impaired, for example, in the case of providing for a DRD can, it causes a shape defect in which a wrinkle occurs in the flange portion during DRD can molding. Preferably, the content of N is made 0.0085% or more and 0.0125% or less. More preferably, it is made into more than 0.0100 %.

The remainder other than the above components is Fe and unavoidable impurities.

Next, the metal structure of the steel sheet according to the present invention has a ferrite phase in the region from a depth of at least 1/4 of the sheet thickness to the center of the sheet thickness, and the standard deviation of the ferrite grain size in the ferrite phase is 7.0 µm or less. it's simple

First, it is preferable that the metal structure of the steel sheet of this invention has a ferrite phase as a main body, the balance is cementite, and it is preferable that a ferrite phase is 85 volume% or more. More preferably, it is 90 volume% or more. That is, if the ferrite phase is less than 85% by volume, fracture tends to occur starting from hard cementite during processing, and the formability deteriorates.

In the above metal structure, the standard deviation of the ferrite grain size in the ferrite phase in the region from a depth of at least 1/4 of the plate thickness to the plate thickness center is 7.0 µm or less.

That is, when the standard deviation of the ferrite particle size exceeds 7.0 μm, the formability deteriorates, for example, when provided for a crown, the outer diameter and height of the crown after molding become non-uniform, and the pressure resistance strength decreases, and the crown The yield decreases when producing Similarly, in the case of supplying for DRD cans, for example, wrinkles are generated in the flange portion during DRD can molding, resulting in poorly shaped cans. Preferably, the standard deviation of the ferrite particle size is 6.5 μm or less.

Here, the metal structure of the ferrite is corroded with an etchant (3% by volume nital) after grinding the cross section in the plate thickness direction parallel to the steel plate rolling direction, and the plate thickness is observed with an optical microscope over 10 views at a magnification of 400 times. The area from the 1/4 depth position (the position of 1/4 of the plate thickness in the direction from the surface to the plate thickness in the cross section) to the plate thickness 1/2 position was observed, and a tissue photograph taken with an optical microscope was used. Then, the ferrite is identified by visual determination, and the particle size of the ferrite is determined by image analysis. The particle size distribution of the ferrite particle size is calculated|required in each visual field, the standard deviation is computed, and let the value which averaged the standard deviation of 10 views be the standard deviation of the ferrite particle size. For image analysis, image analysis software "Stream Essentials" of Olympus Corporation was used.

The desired metal structure is obtained by adjusting the component composition, adjusting the heating temperature in the hot rolling process, the finish rolling temperature, the rolling reduction ratio and the winding temperature of the final stand, adjusting the rolling reduction ratio in the primary cold rolling process, and in the continuous annealing process. It can obtain by adjusting the cooling rate of and adjusting the rolling-reduction|draft ratio in a secondary cold rolling process. In addition, the detail of manufacturing conditions is mentioned later.

In the steel sheet having the above component composition and structure, for example, even with a sheet thickness of 0.20 mm or less, high strength, specifically, yield strength of 560 MPa or more can be secured.

That is, the steel sheet of the present invention is required to have a pressure-resistant strength so that the crown fixed to the mouth of the bottle does not fall off due to the internal pressure, for example, when provided to a crown. Although the plate thickness of the steel plate for crowns used conventionally was 0.22 mm or more, in thickness reduction which makes the plate thickness 0.20 mm or less, especially 0.18 mm or less, the intensity|strength higher than conventional is required. If the yield strength of the steel sheet is less than 560 MPa, it is impossible to impart sufficient pressure strength to the thinned crown as described above. For that purpose, the yield strength needs to be 560 MPa or more. Moreover, in order to ensure sufficient pressure-resistant strength, 600 MPa or more of yield strength is preferable. When the yield strength is too high, the crown height becomes low at the time of crown molding and the crown shape becomes non-uniform. Therefore, the yield strength in the rolling direction is preferably 700 MPa or less. More preferably, they are 600 MPa or more and 680 MPa or less.

In addition, yield strength can be measured by the metal material tensile test method shown in "JIS Z 2241".

Next, a method for manufacturing a steel sheet according to the present invention will be described.

In the steel sheet of the present invention, a steel material (steel slab) having the above composition is heated at 1200° C. or higher, the finish rolling temperature is 870° C. or higher, the final stand rolling reduction is 10% or more, and 550 to 750 A hot rolling step of winding within a temperature range of ° C., a pickling step of pickling after the hot rolling, and a primary cold rolling step of cold rolling with a reduction ratio of 88% or more after the pickling step; After secondary cold rolling, the soaking temperature is set to 60 seconds or less in a temperature range of 660 to 760 ° C, and cooled to a temperature range of 450 ° C or less at an average cooling rate of 10 ° C / s or more, It manufactures by performing the continuous annealing process of cooling to the temperature range of 140 degrees C or less at an average cooling rate of 5 degreeC/s or more, and performing secondary cold rolling at the rolling-reduction|draft ratio of 10% or more and 40% or less.

In addition, in the following description, the regulation of temperature is based on the surface temperature of a steel plate. In addition, let the average cooling rate be the value obtained by calculating based on surface temperature. For example, the average cooling rate from the cracking temperature to the temperature range below 450°C is ((cracking temperature - (temperature range below 450°C))/cooling time from the cracking temperature to (temperature range below 450°C)) appears as In addition, the "temperature range of 450 degrees C or less" in the said formula means the cooling stop temperature in the said temperature range.

When manufacturing the steel sheet according to the present invention, molten steel is adjusted to the above chemical composition by a known method using a converter or the like, and then, for example, as a slab by a continuous casting method, made of steel.

(Steel material heating temperature: 1200℃ or higher)

The heating temperature of the steel raw material of a hot rolling process shall be 1200 degreeC or more. If the heating temperature is less than 1200°C, the amount of solid solution N required to ensure strength in the present invention is reduced and the strength is lowered, so it is set to 1200°C or higher. In addition, in the steel composition of the present invention, since it is considered that N in steel mainly exists as AlN, the amount of N present as AlN (N as AlN) is subtracted from the total amount of N (N total) (N total - (N as AlN) )) was regarded as the employment N amount. In order to make the yield strength in the rolling direction of a steel plate into 560 MPa or more, it is preferable that solid solution N content is 0.0071 % or more, and it can ensure by making steel raw material heating temperature 1200 degreeC or more. A more preferable solid solution N content is 0.0090% or more, and for that purpose, the steel material heating temperature may be 1220°C or more. As for the steel material heating temperature, even if it exceeds 1300 degreeC, since an effect is saturated, 1300 degreeC or less is preferable.

(Finishing rolling temperature: 870℃ or higher)

When the finishing temperature of the hot rolling step is lower than 870°C, a part of the ferrite in the steel sheet becomes fine, the standard deviation of the ferrite grain size exceeds 7.0 µm, and the formability deteriorates. Then, for example, when provided for a crown, the shape of the crown becomes non-uniform, and, for example, when it is provided for a DRD can, a shape defect in which a wrinkle occurs in the flange portion during DRD can molding is caused. Therefore, the finishing temperature is set to 870°C or higher. On the other hand, making the finish rolling temperature higher than necessary may make it difficult to manufacture the thin steel sheet. Specifically, the finish rolling temperature is preferably within a temperature range of 870°C or higher and 950°C or lower.

(Reduction ratio of final stand: 10% or more)

The reduction ratio of the final stand in the hot rolling step is set to 10% or more. When the reduction ratio of the final stand is less than 10%, a part of the ferrite of the steel sheet coarsens, the standard deviation of the ferrite becomes more than 7.0 µm, and the formability deteriorates. Then, for example, when provided for a crown, the shape of the crown becomes non-uniform, and, for example, when it is provided for a DRD can, a shape defect in which a wrinkle occurs in the flange portion during DRD can molding is caused. Therefore, the reduction ratio of the final stand is set to 10% or more. In order to reduce the standard deviation of the ferrite grain size, the reduction ratio of the final stand is preferably 12% or more. The upper limit of the reduction ratio of the final stand is preferably 15% or less from the viewpoint of the rolling load.

(Coiling temperature: 550~750℃)

When the coiling temperature of the hot rolling step is lower than 550°C, a part of the ferrite of the steel sheet becomes fine, the standard deviation of the ferrite grain size becomes more than 7.0 µm, and the formability deteriorates. Then, for example, when provided for a crown, the shape of the crown becomes non-uniform, and, for example, when it is provided for a DRD can, a shape defect in which a wrinkle occurs in the flange portion during DRD can molding is caused. Therefore, the coiling temperature is 550°C or higher. On the other hand, when the coiling temperature is higher than 750 ° C., a part of the ferrite of the steel sheet coarsens, and the standard deviation of ferrite becomes more than 7.0 μm, for example, when provided for a crown, the crown shape becomes non-uniform, e.g. For example, when it is provided for a DRD can, it causes a shape defect in which wrinkles occur in the flange portion during DRD can molding. Therefore, the coiling temperature is 750°C or less. Preferably it is 600 degreeC or more and 700 degrees C or less.

(acid washing)

After that, it is preferable to perform pickling. Pickling should just be able to remove surface layer scale, and it is not necessary to restrict|limit conditions in particular.

Next, cold rolling is performed by dividing into two times with annealing interposed therebetween.

(1st cold rolling reduction: 88% or more)

First, the rolling-reduction|draft ratio of a primary cold rolling process shall be 88 % or more. When the reduction ratio in the primary cold rolling process is less than 88%, the strain imparted to the steel sheet in cold rolling decreases. Therefore, recrystallization in the continuous annealing process becomes non-uniform, and the standard deviation of ferrite becomes more than 7.0 µm, resulting in formability this gets worse Then, for example, when provided for a crown, the shape of the crown becomes non-uniform, and, for example, when it is provided for a DRD can, a shape defect in which a wrinkle occurs in the flange portion during DRD can molding is caused. Therefore, the rolling-reduction|draft ratio of a primary cold rolling process shall be 88 % or more. More preferably, it is set as 89 to 94%.

In the annealing process after the primary cold rolling, after storage and holding for 60 seconds or less in a temperature range of 660 to 760 ° C., shear cooling is cooled to a temperature range of 450 ° C. or less at an average cooling rate of 10 ° C./s or more, followed by 5 Post-stage cooling is performed to cool to a temperature range of 140°C or lower at an average cooling rate of °C/s or higher.

(Crack temperature: 660~760℃)

That is, the cracking temperature in a continuous annealing process is performed at the temperature of 660-760 degreeC. When the soaking temperature is higher than 760°C, sheet passage troubles such as heat buckling tend to occur during continuous annealing, which is not preferable. In addition, the ferrite grain size of the steel sheet is partially coarsened, and the standard deviation of ferrite becomes more than 7.0 µm, for example, when provided for a crown, the crown shape becomes non-uniform, for example, when provided for a DRD can , resulting in shape defects in which wrinkles occur in the flange portion during DRD can molding. On the other hand, if the annealing temperature is less than 660 ° C, recrystallization becomes incomplete, the ferrite grain size of the steel sheet becomes partially fine, and the standard deviation of the ferrite grain size becomes more than 7.0 µm, for example, when provided for a crown, the crown shape is It becomes non-uniform, for example, when it is provided for a DRD can, it causes the shape defect in which wrinkles generate|occur|produce in the flange part at the time of DRD can shaping|molding. Therefore, a soaking temperature shall be performed at the temperature of 660-760 degreeC. Preferably, it carries out at the temperature of 680-730 degreeC.

The retention time when the cracking temperature is in the temperature range of 660 to 760 °C is 60 seconds or less. When the retention time exceeds 60 seconds, C contained in the steel sheet segregates at the ferrite grain boundary and precipitates as carbides in the cooling process in the continuous annealing process, and the amount of solid solution C contributing to the strength of the steel sheet decreases, and the yield strength decreases do. In addition, when a steel sheet is provided for, for example, a DRD can, a shape defect in which wrinkles occur in the flange portion during the DRD can forming is caused. Therefore, the retention time when the soaking temperature is in the temperature range of 660 to 760°C is set to 60 seconds or less. In addition, if the retention time is less than 5 seconds, stability at the time the steel sheet is passed through the roll of the crack zone is impaired, so the retention time is preferably 5 seconds or more.

(Shear cooling: cooling down to 450°C or lower at an average cooling rate of 10°C/s or more)

After the cracking, it is cooled to a temperature range of 450°C or less at an average cooling rate of 10°C/s or more. When the average cooling rate is less than 10°C/s, carbide precipitation is promoted during cooling, the amount of solid solution C contributing to the strength of the steel sheet decreases, and the yield strength decreases. In addition, when a steel sheet is provided for, for example, a DRD can, a shape defect in which wrinkles occur in the flange portion during the DRD can forming is caused. Moreover, since the said effect will be saturated when an average cooling rate exceeds 50 degreeC/s, it is preferable that an average cooling rate shall be 50 degrees C/s or less.

Moreover, when the cooling stop temperature in shear cooling after cracking becomes more than 450 degreeC, carbide precipitation is accelerated|stimulated after shear cooling, the amount of solid solution C contributing to steel plate strength decreases, and yield strength falls. In addition, when a steel sheet is provided for, for example, a DRD can, a shape defect in which wrinkles occur in the flange portion during DRD can forming is caused. In addition, when the cooling stop temperature in the shear cooling after cracking is less than 300 ° C, the carbide precipitation suppression effect is not only saturated, but the shape of the steel sheet at the time of sheeting deteriorates, and the steel sheet cannot be cooled uniformly, for example For example, when provided for a crown, the crown shape becomes non-uniform, and, for example, when it is provided for a DRD can, wrinkles occur in the flange portion during DRD can molding, resulting in poor shape, so cooling after cracking It is preferable that the stopping temperature shall be 300 degreeC or more.

(After-end cooling: up to 140°C or lower at an average cooling rate of 5°C/s or more)

In the downstream cooling after the front-end cooling, it cools from the cooling stop temperature at the time of front-end cooling to the temperature range of 140 degrees C or less at an average cooling rate of 5 degreeC/s or more. When the average cooling rate is less than 5°C/s, the amount of solid solution C contributing to the strength of the steel sheet decreases and the yield strength decreases. In addition, when a steel sheet is provided for, for example, a DRD can, a shape defect in which wrinkles occur in the flange portion during the DRD can forming is caused. In addition, when the average cooling rate exceeds 30°C/s, not only the effect is saturated, but also excessive costs are incurred in cooling equipment, so that the average cooling rate in the downstream cooling is preferably 30°C/s or less. More preferably, it is 25 degreeC/s or less.

In the downstream cooling, it is cooled down to 140°C or less. When it exceeds 140 degreeC, the amount of solid solution C which contributes to steel plate intensity|strength will reduce, and yield strength will fall. In addition, when a steel sheet is provided for, for example, a DRD can, a shape defect in which wrinkles occur in the flange portion during DRD can forming is caused. In addition, when the cooling stop temperature is less than 100°C, not only the effect is saturated, but also excessive cost is generated for the cooling equipment, so 100°C or more is preferable. More preferably, it is 120 degreeC or more.

(Secondary cold rolling reduction: 10% or more and 40% or less)

The steel sheet of this invention can obtain high yield strength by the 2nd cold rolling after annealing. That is, sufficient yield strength cannot be obtained as the rolling-reduction|draft ratio of secondary cold rolling is less than 10 %. Further, when the reduction ratio of the secondary cold rolling exceeds 40%, the uniformity of the crown shape is impaired, for example, when a steel sheet is provided for a crown. In addition, for example, when it is provided for a DRD can, it causes a shape defect in which wrinkles occur in the flange portion during DRD can molding. Therefore, it is preferable that the rolling-reduction|draft ratio of secondary cold rolling shall be 10 % or more and 40 % or less. More preferably, the reduction ratio of secondary cold rolling is more than 15% and 35% or less.

The cold-rolled steel sheet obtained as described above is then, if necessary, subjected to plating treatment such as tin plating, chrome plating, nickel plating, etc. by electroplating on the surface of the steel sheet to form a plating layer, and a plated steel sheet may be provided for use as Moreover, since the film thickness of surface treatment, such as plating, is small enough with respect to the plate|board thickness, the influence on the mechanical property of a steel plate is a negligible level.

As described above, the steel sheet of the present invention can have sufficient strength and excellent material uniformity even when the steel sheet is reduced in thickness. Accordingly, the steel sheet of the present invention is particularly suitable as a material for a crown or DRD can.

In addition, the crown of the present invention is formed using the above-described steel sheet. The crown is mainly composed of a disk-shaped portion that closes the mouth of the bottle and a wavy portion formed around it. The crown of the present invention can be formed by press forming after punching the steel sheet of the present invention into a circular blank. Since the crown of the present invention has sufficient yield strength and is manufactured from a steel sheet excellent in material uniformity, it is excellent in pressure resistance as a crown even if it is thinned, and also excellent in uniformity of the outer diameter and height of the crown. It has the effect of improving the yield in a manufacturing process and reducing the discharge amount of waste accompanying the crown manufacturing.

Similarly, the DRD can of the present invention is formed using the above-described steel sheet. The DRD can can be formed by punching the steel sheet of the present invention into a circular blank, and then performing a drawing process and a redrawing process. Since the DRD can made from the steel sheet of the present invention has a uniform shape and does not deviate from product specifications, the yield in the DRD can manufacturing process is improved and the amount of waste associated with the DRD can manufacturing is reduced. .

Example 1

A steel slab was obtained by melting steel containing the component composition shown in Table 1, and the remainder being Fe and unavoidable impurities in a converter, and casting continuously. The steel slab obtained here was subjected to hot rolling at the slab heating temperature, finish rolling temperature, and coiling temperature shown in Table 2. After this hot rolling, pickling was performed. Next, primary cold rolling was performed at the reduction ratio shown in Table 2, continuous annealing was performed under the continuous annealing conditions shown in Table 2, and then, secondary cold rolling was performed at the reduction ratio shown in Table 2. The obtained steel sheet was continuously subjected to electrolytic chromic acid treatment to obtain tin-free steel.

About the steel plate obtained according to the above, after performing the heat treatment equivalent to 210 degreeC and painting baking for 15 minutes, the tensile test was done. The tensile test was performed according to "JIS Z 2241" using the tensile test piece of JIS 5 size, and the yield strength of the rolling direction was measured. In addition, this heat treatment equivalent to painting baking does not affect the steel sheet material before the said heat treatment in any way.

The obtained steel sheet was molded into a crown, and crown formability was evaluated. That is, using a circular blank with a diameter of 37 mm, each of 20 crowns (N=20) was formed for each steel sheet by press working. The height of the crown (the distance from the top surface of the crown to the bottom of the skirt) is measured using a micrometer, and the standard deviation of the crown height of N = 20 is 0.09 mm or less, the crown shape is excellent, and the crown shape is more than 0.09 mm. It was said that the shape of the crown was inferior. The obtained results are shown in Table 2.

Further, the obtained steel sheet was subjected to a heat treatment equivalent to coating baking at 210°C for 15 minutes, and then molded into a DRD can to evaluate the DRD can formability. That is, using a circular blank with a diameter of 158 mm, drawing processing and redrawing processing were performed to shape a DRD can having an inner diameter of 82.8 mm and a flange diameter of 102 mm, and the DRD can formability was evaluated. In evaluation, the sample in which 3 or more places of fine wrinkles were visually observed in the flange part was made into (circle), and the sample in which the fine wrinkle of the flange part was 2 or less places was x. This evaluation result is shown in Table 2.

From Table 2, it can be seen that the steel sheets of Nos. 1-22, which are examples of the present invention, have a yield strength of 560 MPa or more in the rolling direction, a standard deviation of the crown height of 0.09 mm or less, and good crown formability. In addition, the number of wrinkles in the DRD can molding was 2 or less, and the DRD can moldability was also good.

On the other hand, in the steel sheets of Comparative Examples No. 23-25, since the content of C is too large, the standard deviation of the ferrite grain size is more than 7.0 µm, and the standard deviation of the crown height is more than 0.09 mm, and the crown formability is deteriorated. , it was also found that the DRD can formability deteriorated. In the steel sheets Nos. 26 to 28, since the C content was too small, the standard deviation of the ferrite grain size was more than 7.0 µm, and the standard deviation of the crown height was more than 0.09 mm, It was found that the crown formability deteriorated. . Since the steel sheet of No. 29 contains too much Mn, the standard deviation of the ferrite grain size exceeds 7.0 µm, the standard deviation of the crown height exceeds 0.09 mm, and the crown formability deteriorates, and the DRD can formability is also could be seen to deteriorate. In the steel sheet of No. 30, since the content of Al was too large, it was found that the formation of AlN increased, the amount of N contributing to the strength of the steel sheet as solid solution N decreased, and the strength of the steel sheet decreased. Also, the DRD can formability deteriorated. Since the steel sheet of No. 31 has too little content of Al, the effect as a deoxidizer is inadequate, while generation|occurrence|production of a solidification defect is caused, steelmaking cost increases. In addition, since an appropriate amount of AlN cannot be secured at the time of recrystallization of ferrite in annealing, the standard deviation of the ferrite grain size after annealing becomes large, the ferrite grain size of the steel sheet after secondary cold rolling becomes coarse, and the standard deviation of the ferrite grain size is It was found that when the thickness was more than 7.0 µm, the standard deviation of the crown height was more than 0.09 mm, which deteriorated the crown formability and also the DRD can formability. Since the steel sheets No. 32 to 34 contain too much N, the ferrite grain size of the steel sheet after secondary cold rolling becomes fine, the standard deviation of the ferrite grain size exceeds 7.0 µm, and the standard deviation of the crown height is 0.09 It was found that when the thickness exceeds mm, the crown moldability deteriorates, and the DRD can moldability also deteriorates. In the steel sheets No. 35 to 37, since the content of N is too small, the ferrite grain size of the steel sheet becomes coarse, the standard deviation of the ferrite grain size exceeds 7.0 µm, and the standard deviation of the crown height exceeds 0.09 mm, forming a crown It was found that the property deteriorated, and the DRD can formability was also deteriorated, and the amount of N contributing to the steel sheet strength as solid solution N decreased, thereby reducing the steel sheet strength. In addition, since the steel sheet of No. 38 has too much P content, the standard deviation of the ferrite grain size becomes more than 7.0 µm, the standard deviation of the crown height becomes more than 0.09 mm, and the crown formability deteriorates, and furthermore, the DRD can It turned out that the moldability also deteriorated. Since the steel sheet of No. 39 contains too much Si, the standard deviation of the ferrite grain size exceeds 7.0 µm, the standard deviation of the crown height exceeds 0.09 mm, and the crown formability deteriorates, and the DRD can formability is also could be seen to deteriorate.

Example 2

Steel slabs were obtained by melting steel containing the component compositions of steel Nos. 5, 9, 18, and 21 shown in Table 1, with the remainder being Fe and unavoidable impurities in a converter and continuous casting. The steel slab obtained here was subjected to hot rolling at the slab heating temperature, finish rolling temperature, and coiling temperature shown in Table 3. After hot rolling, pickling was performed. Next, primary cold rolling is performed at the reduction ratio shown in Table 3, followed by continuous annealing at the cracking temperature, crack retention time, shear cooling average rate, shear cooling stop temperature, downstream cooling average rate, and downstream cooling stop temperature shown in Table 3 Then, secondary cold rolling was performed at the reduction ratio shown in Table 3. The obtained steel sheet was continuously subjected to electrolytic chromic acid treatment to obtain tin-free steel.

About the steel plate obtained by the above, while performing a tensile test by the method similar to the above, crown formability and DRD can formability were evaluated. The obtained results are shown in Table 3.

From Table 3, the yield strength in the rolling direction of the steel sheets Nos. 40, 43, 45, 47, 48, 52 to 55, 58, 59, 63, 64, 66, 69, 70, and 71 which is an example of the present invention was 560. MPa or more, and the standard deviation of the crown height was 0.09 mm or less, and the crown formability and DRD can formability were good.

On the other hand, the steel sheets of steel sheets No. 41, 49, 50, 56, 61, 68, and 72 as comparative examples, slab heating temperature, crack retention time, shear cooling average rate, secondary cold reduction rate, rear stage cooling average rate, shear Since the cooling stop temperature and the downstream cooling stop temperature were outside the range of the present invention, it was found that the yield strength in the rolling direction decreased. Since the steel sheet of steel sheet No. 62 as a comparative example has an excessively high secondary cold rolling reduction ratio, the anisotropy of the steel sheet becomes large, and the standard deviation of the crown height becomes more than 0.09 mm, and the crown formability deteriorates, and the DRD can formability also deteriorates. knew what to do The steel sheets of steel sheets No. 42, 44, 46, 51, 57, 60, 65, 67, 73, and 74, which are comparative examples, had finish rolling temperature, hot rolling final stand rolling reduction, coiling temperature, primary cold rolling rate, and cracking. Since any of the temperature, the front cooling stop temperature, the downstream cooling average speed, the downstream cooling stop temperature, and the secondary cold reduction ratio are outside the scope of the present invention, the yield strength in the rolling direction decreases or the standard deviation of the ferrite grain size exceeds 7.0 μm It was found that the standard deviation of the crown height was more than 0.09 mm, which deteriorated the crown formability and also the DRD can formability.

Claims (5)

in mass %,
C: more than 0.0060% and 0.0100% or less;
Si: 0.05% or less;
Mn: 0.05% or more and 0.60% or less;
P: 0.050% or less;
S: 0.050% or less;
Al: 0.020% or more and 0.050% or less, and
N: 0.0070% or more and 0.0140% or less
contains, and the remainder has a component composition of Fe and unavoidable impurities,
It has a ferrite phase in a region from a depth of 1/4 of the plate thickness to the center of the plate thickness, and the standard deviation of the ferrite grain size in the ferrite phase is 7.0 µm or less;
yield strength of 560 MPa or more,
A steel plate having a plate thickness of 0.20 mm or less. in mass %,
C: more than 0.0060% and 0.0100% or less;
Si: 0.05% or less;
Mn: 0.05% or more and 0.60% or less;
P: 0.050% or less;
S: 0.050% or less;
Al: 0.020% or more and 0.050% or less, and
N: 0.0070% or more and 0.0140% or less
contains, and the remainder has a component composition of Fe and unavoidable impurities,
It has a ferrite phase in a region from a depth of 1/4 of the plate thickness to a central part of the plate thickness, and the standard deviation of the ferrite grain size in the ferrite phase is 7.0 µm or less;
A crown made of a steel sheet having a yield strength of 560 MPa or more. in mass %,
C: more than 0.0060% and 0.0100% or less;
Si: 0.05% or less;
Mn: 0.05% or more and 0.60% or less;
P: 0.050% or less;
S: 0.050% or less;
Al: 0.020% or more and 0.050% or less, and
N: 0.0070% or more and 0.0140% or less
contains, and the remainder has a component composition of Fe and unavoidable impurities,
It has a ferrite phase in a region from a depth of 1/4 of the plate thickness to a central part of the plate thickness, and the standard deviation of the ferrite grain size in the ferrite phase is 7.0 µm or less;
A DRD (Drawing and Redrawing) can made of a steel plate with a yield strength of 560 MPa or more. A method for manufacturing the steel sheet according to claim 1, comprising:
A hot rolling process in which a steel material is heated at 1200 ° C. or higher, the finish rolling temperature is 870 ° C. or higher, and the final stand rolling reduction is 10% or higher, and is wound within a temperature range of 550 to 750 ° C.;
a pickling step of performing pickling on the hot-rolled sheet after the hot rolling;
a primary cold-rolling step of cold-rolling the hot-rolled sheet after pickling with a reduction ratio of 88% or more;
The cold-rolled sheet after the primary cold rolling is stored and maintained for 60 seconds or less in a temperature range of 660 to 760° C., then cooled to a temperature range of 450° C. or less and 300° C. or more at an average cooling rate of 10° C./s or more, and then 5 An annealing process of cooling to a temperature range of 140 °C or less at an average cooling rate of °C / s or more and 30 °C / s or less;
The manufacturing method of the steel plate which has a secondary cold-rolling process which cold-rolls to the annealed plate after the said annealing at a rolling-reduction|draft ratio of 10% or more and 40% or less. delete