WO2018181450A1

WO2018181450A1 - Steel sheet, method for producing same, crown cap, and drawn and redrawn (drd) can

Info

Publication number: WO2018181450A1
Application number: PCT/JP2018/012698
Authority: WO
Inventors: 房亮假屋; 卓嗣植野; 嘉秀山本; 克己小島; 文吾舘野
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2017-03-31
Filing date: 2018-03-28
Publication date: 2018-10-04
Also published as: PH12019501998A1; KR20190129986A; CN110506135A; TWI675112B; KR102259719B1; CN110506135B; TW201837202A; JP6468404B1; JPWO2018181450A1

Abstract

Provided is a steel sheet which has a component composition including, in mass%, over 0.0060% but not more than 0.0100% of C, not more than 0.05% of Si, at least 0.05% but not more than 0.60% of Mn, not more than 0.050% of P, not more than 0.050% of S, at least 0.020% but not more than 0.050% of Al, and at least 0.0070% but not more than 0.0140% of N, the remainder being Fe and unavoidable impurities. Furthermore, the steel sheet has, in a region up to a sheet-thickness centre portion from a depth of 1/4 of the sheet thickness, a structure having a ferrite phase in which the standard deviation of the ferrite particle diameter is 7.0 µm or lower. The steel sheet has a yield strength of 560 MPa or higher. Accordingly, the steel sheet exhibits sufficient strength and excellent moulding properties, despite being thin.

Description

Steel plate and manufacturing method thereof, crown and DRD can

The present invention relates to a steel sheet, particularly a high-strength thin steel sheet having excellent formability and a method for producing the same. Typical examples of such steel plates include DRD (Drawing and Redrawing) cans formed by combining drawing and redrawing, as well as thin steel plates that serve as crown materials used as stoppers for glass bottles and the like. . Furthermore, the present invention relates to a crown and a DRD can obtained by forming the steel plate.

Well, many glass bottles are conventionally used for containers for beverages such as soft drinks and alcoholic beverages. In particular, metal caps called crowns are widely used for narrow-mouthed glass bottles. Generally, a crown is manufactured by press-molding a thin steel plate, and consists of a disk-shaped part that closes the mouth of the bottle and a bowl-shaped part around it. Seal the jar by caulking.

Bottles that use crowns are often filled with high internal pressure contents such as beer and carbonated drinks. For this reason, even when the internal pressure increases due to a change in temperature or the like, the crown needs to have high pressure strength so that the crown is not deformed and the sealing of the bottle is not broken. Moreover, even if the strength of the material is sufficient, if the material uniformity of the steel plate used for the crown is low, the shape of the crown is not uniform, and those that are out of product specifications are included. Even if such a poorly shaped crown is caulked to the mouth of the bottle, sufficient sealing performance may not be obtained. Therefore, the steel plate used as the crown material must also be excellent in material uniformity.

SR (Single Reduced) steel sheet is mainly used for the thin steel sheet used for the crown material. In this method, after thinning a steel sheet by cold rolling, annealing is performed and temper rolling is performed. The sheet thickness of conventional steel plates for crowns is generally 0.22 mm or more, and sufficient compressive strength and formability are ensured by applying SR material made of mild steel used for food and beverage cans and the like. It was possible.

In recent years, as with steel plates for cans, there is an increasing demand for thinning the crown steel plate for cost reduction purposes. When the plate thickness of the steel plate for the crown is less than 0.22 mm, particularly 0.20 mm or less, the pressure strength is insufficient in the crown manufactured with the conventional SR material. In order to ensure the compressive strength as a steel plate for crowns, it is necessary to compensate for the decrease in strength due to thinning, and DR (Double Reduced) steel plates that are cold-rolled and annealed after annealing are applied. .

By the way, the center of the crown is squeezed to some extent in the initial stage of molding, and then the outer edge is molded into a bowl shape. Here, if the material of the crown is a steel plate with low material uniformity, the crown manufactured from the steel plate may have irregular outer diameters and heights, which may be out of product specifications. If the outer diameter and height of the crown become uneven, and there are things that deviate from the product specification, there is a problem that the yield when a large number of crowns are manufactured decreases. Furthermore, a crown whose outer diameter and height are out of specification is liable to cause leakage of contents during transportation after being plugged into a bottle, and has a problem that it does not serve as a lid. Even if the outer diameter and height of the crown are within the product specification, if the steel plate strength is low, the crown may be removed due to insufficient pressure strength.

In addition, if a steel plate with low material uniformity is used as the material for the DRD can, there is a possibility that it may lead to a shape defect typified by wrinkles generated at the flange portion of the can when the DRD can is formed. Even if this DRD can deviates from the product standard due to a defective shape, it causes the same problem as in the case of the above-mentioned crown that the yield when a large number of DRD cans are manufactured decreases.

Regarding the high-strength thin steel sheet for crowns based on the above points, 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 %: 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 A steel plate for a crown that satisfies a sufficient crown pressure even with a thin thickness by appropriately controlling the minimum value of r value in the direction of 25 to 65 ° relative to the rolling direction, the average value of the r value in all directions, and the yield strength. And a method of manufacturing the same.

Japanese Patent No. 6057023

The steel sheet described in Patent Document 1 uses steel containing 0.0060% or less of C, and has a predetermined relationship between the tension between the stands and the annealing temperature in secondary cold rolling. Value (direction / size) is obtained. Since this method does not control the hot rolling process that affects the formation of the metal structure, the obtained steel sheet has a large variation in material, and is difficult to put into practical use.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a steel plate having sufficient strength and excellent formability even when it is thinned, and a method for manufacturing the steel plate. Furthermore, an object of the present invention is to provide a crown and a DRD can which are adjusted to a predetermined size and shape and have excellent shape stability.

The inventors diligently studied how to solve the above-mentioned problems, and found that high strength and excellent formability can be imparted by regulating the structure under a predetermined component composition. The present invention is derived from this finding, and the gist of the present invention 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, with the balance having a component composition of Fe and inevitable impurities,
Having a ferrite phase in the region from the 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 plate according to (1), wherein the plate thickness is 0.20 mm or less.

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

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

(5) The method for producing a steel sheet according to (1) or (2),
A hot rolling process in which a steel material is heated at 1200 ° C. or higher, rolled at a finish rolling temperature of 870 ° C. or higher and a reduction ratio of the final stand of 10% or higher, and wound in a temperature range of 550 to 750 ° C. When,
Pickling step of pickling the hot-rolled sheet after hot rolling;
A primary cold rolling step of performing cold rolling with a reduction ratio of 88% or more on the hot-rolled sheet after pickling,
The cold-rolled sheet after the primary cold rolling is held in a temperature range of 660 to 760 ° C. for 60 seconds or less, and then cooled to a temperature range of 450 ° C. or less at an average cooling rate of 10 ° C./s or more. An annealing step of cooling to a temperature range of 140 ° C. or lower at an average cooling rate of at least C / s;
A secondary cold rolling step of performing cold rolling on the annealed plate at a rolling reduction of 10% to 40%.

According to the present invention, it is possible to provide a steel sheet having sufficient strength even when thinned and having excellent material uniformity together with its advantageous manufacturing method. Furthermore, when the steel plate of the present invention is used for, for example, a crown or a DRD can, a crown or a DRD can having no shape distortion can be formed.

The steel sheet according to the present invention is 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. %: 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, with the balance being Fe and inevitable impurities It has a composition and has a ferrite phase in a region from a depth of ¼ 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.
First, it demonstrates in order from the reason for limitation of each component amount in the component composition of a steel plate. In addition, unless otherwise indicated, the "%" display regarding a component shows "mass%".

C: more than 0.0060% and 0.0100% or less When the C content is 0.0060% or less, the ferrite of the steel sheet after the secondary cold rolling described later becomes coarse and the formability deteriorates. When it is used for the purpose, the outer diameter and the height of the formed crown are not uniform. Similarly, when it is used for a DRD can, for example, wrinkles are generated in the flange portion when the DRD can is formed, resulting in a poorly shaped can. On the other hand, when the C content exceeds 0.0100%, the ferrite of the steel sheet after the secondary cold rolling becomes too fine, the steel sheet strength is excessively increased, and the formability deteriorates, for example, when used for a crown Further, the outer diameter and height of the molded crown are not uniform. Similarly, when it is used for a DRD can, for example, wrinkles are generated in the flange portion when the DRD can is formed, resulting in a poorly shaped can. Therefore, the C content is 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 containing a large amount of Si, for the same reason as C, for example, when used for the crown, the outer diameter and the uniformity of the height of the crown are impaired. For example, when used for a DRD can In addition, it causes a shape defect in which wrinkles are generated in the flange portion during DRD can molding. Therefore, the Si content is 0.05% or less. Moreover, since excessively reducing Si causes an increase in steelmaking cost, the Si content is preferably 0.004% or more. More preferably, it is 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. Problems such as surface cracks occur. Therefore, the Mn content is 0.05% or more. On the other hand, when Mn is contained in a large amount, the uniformity of the outer diameter and height of the crown is impaired when used for a crown, for example, for the same reason as C. For example, when used for a DRD can, a DRD can This leads to shape defects that cause wrinkles in the flange during molding. Therefore, the Mn content is set to 0.60% or less. Preferably, the Mn content is 0.10% or more and 0.50% or less.

P: 0.050% or less When the P content exceeds 0.050%, the steel sheet is hardened and the corrosion resistance is lowered. Further, the standard deviation of the ferrite grain size after annealing exceeds 7.0 μm and the formability deteriorates. For example, when used for a crown, the uniformity of the outer diameter and height of the crown is impaired. When used for cans, it leads to shape defects that cause wrinkles in the flanges during DRD can molding. Therefore, the upper limit of the P content is 0.050%. Further, in order to make P less than 0.001%, the removal P cost becomes excessive, so the content of P is preferably made 0.001% or more.

S: 0.050% or less S combines with Mn in a steel plate to form MnS, and precipitates in a large amount to lower the hot ductility of the steel plate. This effect becomes significant when the S content exceeds 0.050%. Therefore, the upper limit of the S content is 0.050%. Further, in order to make S less than 0.005%, the removal S cost becomes excessive, so the S content is preferably made 0.004% or more.

Al: 0.020% or more and 0.050% or less Al is an element to be contained as a deoxidizing agent, and forms N and AlN in the steel to reduce the solid solution N in the steel. If the Al content is less than 0.020%, the effect as a deoxidizer becomes insufficient, causing solidification defects and increasing the steelmaking cost. Also, if the amount of Al is less than 0.020%, an appropriate amount of AlN cannot be ensured during recrystallization of ferrite during annealing, so the standard deviation of the ferrite grain size after annealing increases, and after secondary cold rolling The ferrite of the steel sheet becomes coarse and the formability deteriorates. Then, for example, when used for a crown, the uniformity of the outer diameter and height of the crown is impaired, and when used for a DRD can, for example, it leads to a shape defect that causes wrinkles in the flange portion during DRD can molding. On the other hand, when the Al content exceeds 0.050%, the formation of AlN increases, the amount of N contributing to the steel sheet strength as solute N described later decreases, and the steel sheet strength decreases. Is 0.050% or less. Preferably, the Al content is 0.030% or less and 0.045% or less.

N: 0.0070% or more and 0.0140% or less When the N content is less than 0.0070%, the ferrite of the steel sheet after the secondary cold rolling becomes coarse and the formability deteriorates. For example, for the crown When provided, the outer diameter and height of the molded crown are not uniform, and the amount of N that contributes to the steel sheet strength as solute N described later is reduced, and the steel sheet strength is reduced. Similarly, when it is used for a DRD can, for example, wrinkles are generated in the flange portion when the DRD can is formed, resulting in a poorly shaped can. On the other hand, when the N content exceeds 0.0140%, the ferrite of the steel sheet after the secondary cold rolling becomes too fine, the steel sheet strength is excessively increased and the formability deteriorates, for example, when used for a crown. The uniformity of the outer diameter and height of the crown is impaired. For example, when it is used for a DRD can, it causes a shape defect in which a wrinkle is generated in the flange portion when the DRD can is formed. Preferably, the N content is 0.0085 or more and 0.0125% or less. More preferably, it is over 0.0100%.
The balance other than the above components is Fe and inevitable impurities.

Next, the metal structure of the steel sheet according to the present invention has a ferrite phase at least in a region from a depth of ¼ 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 It is important that the thickness is 0.0 μm or less.
First, the metal structure of the steel sheet of the present invention is preferably composed mainly of a ferrite phase, the balance being cementite, and the ferrite phase being 85% by volume or more. More preferably, it is 90% or more. That is, when the ferrite phase is less than 85% by volume, breakage tends to occur starting from hard cementite during processing, and formability deteriorates.

In the metal structure described above, the standard deviation of the ferrite grain size in the ferrite phase in the region from at least a quarter of the plate thickness to the center of the plate thickness is set to 7.0 μm or less.
That is, when the standard deviation of the ferrite grain size exceeds 7.0 μm, the formability deteriorates. For example, when used for a crown, the outer diameter and height of the crown after molding become non-uniform, and the pressure strength decreases. At the same time, the yield when manufacturing the crown decreases. Similarly, when it is used for a DRD can, for example, wrinkles are generated in the flange portion when the DRD can is formed, resulting in a poorly shaped can. Preferably, the standard deviation of the ferrite grain size is not more than 6.5 μm.

Here, the ferrite microstructure is corroded with a corrosive liquid (3% by volume nital) after polishing a cross section in the plate thickness direction parallel to the rolling direction of the steel plate, and the plate thickness is 1 with an optical microscope over 10 fields of view at 400 × magnification. / 4 Observe the region from the depth position (in the cross section, 1/4 position of the plate thickness in the thickness direction from the surface) to 1/2 position of the plate thickness, and use the microstructure photograph taken with an optical microscope Is determined by visual judgment, and the particle size of the ferrite is determined by image analysis. The particle size distribution of the ferrite grain size is obtained for each field of view, the standard deviation is calculated, and the value obtained by averaging the standard deviations of the 10 fields of view is taken as the standard deviation of the ferrite grain size. For the image analysis, Olympus Corporation's image analysis software “Stream Essentials” was used.

The desired metallographic structure is adjusted by adjusting the component composition, adjusting the heating temperature in the hot rolling process, the finishing rolling temperature, the rolling reduction and winding temperature of the final stand, adjusting the rolling reduction of the primary cold rolling, and continuously. It can be obtained by adjusting the cooling rate in the annealing process and adjusting the rolling reduction in the secondary cold rolling process. Details of the manufacturing conditions will be described later.

With a steel sheet having the above component composition and structure, for example, a high strength, specifically a yield strength of 560 MPa or more, can be ensured even with a thickness of 0.20 mm or less.
In other words, the steel plate of the present invention is required to have a pressure strength that prevents the crown crimped on the mouth of the bottle from being removed by the internal pressure when the steel plate is used, for example. The steel plate for crowns that has been used conventionally has a thickness of 0.22 mm or more, but in order to reduce the thickness to 0.20 mm or less, particularly 0.18 mm or less, higher strength is required than before. . When the yield strength of the steel sheet is less than 560 MPa, it is impossible to give sufficient pressure resistance to the thin crown as described above. For that purpose, the yield strength needs to be 560 MPa or more. Furthermore, in order to ensure sufficient pressure resistance, the yield strength is preferably 600 MPa or more. If the yield strength is too high, the crown height becomes low at the time of crown molding and the crown shape becomes non-uniform, so the yield strength in the rolling direction is preferably 700 MPa or less. More preferably, it is 600 MPa or more and 680 MPa or less.

Note that the yield strength can be measured by a metal material tensile test method shown in “JIS Z 2241”.

Next, the manufacturing method of the steel plate which concerns on this invention is demonstrated.
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, and the rolling reduction of the final stand is 10% or higher. A hot rolling step of winding within the temperature range, a pickling step of pickling after the hot rolling, a primary cold rolling step of cold rolling at a rolling reduction of 88% or more after the pickling step, After the primary cold rolling, the soaking temperature is in the temperature range of 660 to 760 ° C. The holding time is 60 seconds or less, and the temperature is cooled to 450 ° C. or less at an average cooling rate of 10 ° C./s or more. It is manufactured by carrying out secondary cold rolling at a continuous annealing step of cooling to a temperature range of 140 ° C. or less at an average cooling rate of at least / s and at a reduction rate of 10% or more and 40% or less.

In the following description, the temperature specification is based on the surface temperature of the steel sheet. The average cooling rate is a value obtained by calculation based on the surface temperature. For example, the average cooling rate from the soaking temperature to a temperature range of 450 ° C. or less is ((soaking temperature− (temperature range of 450 ° C. or less)) / cooling time from the soaking temperature to (temperature range of 450 ° C. or less) ). The “temperature range of 450 ° C. or lower” in the above equation means a cooling stop temperature in the temperature range.

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

(Steel material heating temperature: 1200 ° C or higher)
The heating temperature of the steel material in the hot rolling process is set to 1200 ° C. or higher. When the heating temperature is less than 1200 ° C., the amount of solute N necessary for securing strength in the present invention is reduced and the strength is lowered, so that the heating temperature is 1200 ° C. or higher. In the steel composition of the present invention, it is considered that N in the steel is mainly present as AlN. Therefore, the total amount of N (Ntotal) minus the amount of N present as AlN (NasAlN) is subtracted (Ntotal− (NasAlN)). The amount of dissolved N was considered. In order to set the yield strength in the rolling direction of the steel sheet to 560 MPa or more, the solute N amount is preferably 0.0071% or more, and can be ensured by setting the steel material heating temperature to 1200 ° C. or more. A more preferable amount of solute N is 0.0090% or more. For this purpose, the heating temperature of the steel material is preferably 1220 ° C. or more. Even if the steel material heating temperature exceeds 1300 ° C., the effect is saturated, so 1300 ° C. or less is preferable.

(Finishing rolling temperature: 870 ° C or higher)
When the finishing temperature in the hot rolling process is less than 870 ° C., a part of the ferrite of the steel sheet becomes fine, and the standard deviation of the ferrite grain size exceeds 7.0 μm and the formability deteriorates. Then, for example, when it is used for a crown, the crown shape becomes non-uniform, and when it is used for a DRD can, for example, it leads to a shape defect in which a wrinkle is generated in the flange portion at the time of DRD can molding. Accordingly, the finishing temperature is 870 ° C. or higher. On the other hand, raising the finish rolling temperature more than necessary may make it difficult to produce a thin steel sheet. Specifically, the finish rolling temperature is preferably in the temperature range of 870 ° C. or more and 950 ° C. or less.

(Rolling ratio of final stand: 10% or more)
The rolling reduction of the final stand in the hot rolling process is 10% or more. When the rolling reduction of the final stand is less than 10%, a part of the ferrite of the steel sheet becomes coarse, and the standard deviation of the ferrite exceeds 7.0 μm, and the formability deteriorates. Then, for example, when it is used for a crown, the crown shape becomes non-uniform, and when it is used for a DRD can, for example, it leads to a shape defect in which a wrinkle is generated in the flange portion at the time of DRD can molding. Therefore, the rolling reduction of the final stand is 10% or more. In order to reduce the standard deviation of the ferrite grain size, the rolling reduction of the final stand is preferably 12% or more. The upper limit of the rolling reduction of the final stand is preferably 15% or less from the viewpoint of rolling load.

(Winding temperature: 550-750 ° C)
When the coiling temperature in the hot rolling process is less than 550 ° C., a part of the ferrite of 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 it is used for a crown, the crown shape becomes non-uniform, and when it is used for a DRD can, for example, it leads to a shape defect in which a wrinkle is generated in the flange portion at the time of DRD can molding. Accordingly, the winding temperature is set to 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 becomes coarse, and the standard deviation of the ferrite exceeds 7.0 μm. For example, when used for a crown, the crown shape becomes non-uniform. For example, when it is used for a DRD can, it causes a shape defect in which a wrinkle is generated in the flange portion when the DRD can is formed. Therefore, the coiling temperature is 750 ° C. or lower. Preferably they are 600 degreeC or more and 700 degrees C or less.

. (Pickling)
Thereafter, pickling is preferably performed. The pickling is not particularly limited as long as the surface scale can be removed.

Next, the cold rolling is performed in two steps with the annealing interposed therebetween.
(Primary cold rolling reduction: 88% or more)
First, the rolling reduction in the primary cold rolling process is 88% or more. When the rolling reduction in the primary cold rolling process is less than 88%, the strain imparted to the steel sheet by cold rolling decreases, so recrystallization in the continuous annealing process becomes non-uniform and the standard deviation of ferrite is over 7.0 μm. As a result, the moldability deteriorates. Then, for example, when it is used for a crown, the crown shape becomes non-uniform, and when it is used for a DRD can, for example, it leads to a shape defect in which a wrinkle is generated in the flange portion at the time of DRD can molding. Therefore, the rolling reduction in the primary cold rolling process is set to 88% or more. More preferably, the content is 89 to 94%.

In the annealing process after the primary cold rolling, after maintaining in the temperature range of 660 to 760 ° C. for 60 seconds or less, cooling to the temperature range of 450 ° C. or less at an average cooling rate of 10 ° C./s or more, The latter stage cooling which cools to the temperature range of 140 degrees C or less with an average cooling rate of 5 degrees C / s or more is performed.
(Soaking temperature: 660-760 ° C)
That is, the soaking temperature in the continuous annealing step is 660 to 760 ° C. When the soaking temperature is higher than 760 ° C., it is easy to cause troubles such as a heat buckle during continuous annealing, which is not preferable. In addition, the ferrite grain size of the steel sheet is partially coarsened, the standard deviation of the ferrite is over 7.0 μm, for example, when used for a crown, the crown shape becomes non-uniform, for example, when used for a DRD can, This leads to a shape defect in which wrinkles are generated in the flange part during DRD can molding. On the other hand, if the annealing temperature is less than 660 ° C., the recrystallization becomes incomplete, the ferrite grain size of the steel sheet becomes partly fine, and the standard deviation of the ferrite grain size exceeds 7.0 μm. In addition, the crown shape becomes non-uniform, and when used for a DRD can, for example, it leads to a shape defect that causes wrinkles in the flange portion when the DRD can is formed. Therefore, the soaking temperature is 660 to 760 ° C. Preferably, the temperature is 680 to 730 ° C.

The holding time when the soaking temperature is in the temperature range of 660 to 760 ° C is 60 seconds or less. When the holding time exceeds 60 seconds, C contained in the steel sheet segregates to the ferrite grain boundary, precipitates as carbides in the cooling process in the continuous annealing process, reduces the amount of solute C contributing to the steel sheet strength, and yield. Strength decreases. Furthermore, when a steel plate is used for, for example, a DRD can, a shape defect that causes wrinkles in the flange portion at the time of forming the DRD can results. Therefore, the holding time when the soaking temperature is in the temperature range of 660 to 760 ° C. is set to 60 seconds or less. When the holding time is less than 5 seconds, the stability when the steel plate passes through the soaking roll is impaired, and therefore the holding time is preferably 5 seconds or more.

(Pre-cooling: Cooling to 450 ° C or less at an average cooling rate of 10 ° C / s or more)
After the soaking, it is cooled to a temperature range of 450 ° C. or lower at an average cooling rate of 10 ° C./s or higher. When the average cooling rate is less than 10 ° C./s, carbide precipitation is promoted during cooling, the amount of solute C contributing to the steel plate strength is reduced, and the yield strength is reduced. Furthermore, when a steel plate is used for, for example, a DRD can, a shape defect that causes wrinkles in the flange portion at the time of forming the DRD can results. In addition, since said effect will be saturated when an average cooling rate exceeds 50 degrees C / s, it is preferable that an average cooling rate shall be 50 degrees C / s or less.
Moreover, when the cooling stop temperature in the former stage cooling after soaking exceeds 450 ° C., carbide precipitation is promoted after the former stage cooling, the amount of solute C contributing to the steel sheet strength is reduced, and the yield strength is lowered. Furthermore, when a steel plate is used for, for example, a DRD can, a shape defect in which wrinkles are generated in the flange portion when the DRD can is formed is caused. In addition, when the cooling stop temperature in the pre-cooling after soaking is less than 300 ° C., not only the carbide precipitation suppression effect is saturated, but the steel plate shape deteriorates when passing and the steel plate cannot be cooled uniformly, for example, crown For example, when used for DRD cans, the crown stop shape is uneven. It is preferable to set it to 300 degreeC or more.

(Second-stage cooling: up to 140 ° C or less at an average cooling rate of 5 ° C / s or more)
In the latter stage cooling after the former stage cooling, the cooling is performed at an average cooling rate of 5 ° C./s or more from the cooling stop temperature at the former stage cooling to a temperature range of 140 ° C. or less. When the average cooling rate is less than 5 ° C./s, the amount of solute C contributing to the steel plate strength is reduced, and the yield strength is lowered. Furthermore, when a steel plate is used for, for example, a DRD can, a shape defect that causes wrinkles in the flange portion at the time of forming the DRD can results. When the average cooling rate exceeds 30 ° C./s, not only the effect is saturated, but excessive costs are generated in the cooling equipment, so that the average cooling rate in the subsequent cooling is preferably 30 ° C./s or less. More preferably, it is 25 ° C./s or less.
In the latter stage cooling, it is cooled to 140 ° C. or lower. If it exceeds 140 ° C., the amount of solute C that contributes to the strength of the steel sheet decreases, and the yield strength decreases. Furthermore, when a steel plate is used for, for example, a DRD can, a shape defect in which wrinkles are generated in the flange portion when the DRD can is formed is caused. Note that when the cooling stop temperature is less than 100 ° C., the effect is saturated, and an excessive cost is generated in the cooling facility. More preferably, it is 120 ° C. or higher.

(Secondary cold rolling reduction: 10% to 40%)
The steel sheet of the present invention can obtain high yield strength by the second cold rolling after annealing. That is, when the rolling reduction of secondary cold rolling is less than 10%, sufficient yield strength cannot be obtained. On the other hand, when the rolling reduction of secondary cold rolling exceeds 40%, for example, when the steel sheet is used for a crown, the uniformity of the crown shape is impaired. Furthermore, for example, when it is used for a DRD can, it causes a shape defect in which a wrinkle is generated in the flange portion when the DRD can is formed. Therefore, it is preferable that the rolling reduction of secondary cold rolling shall be 10% or more and 40% or less. More preferably, the rolling reduction of secondary cold rolling is more than 15% and 35% or less.

The cold-rolled steel sheet obtained as described above is then subjected to plating treatment such as tin plating, chromium plating, nickel plating, etc., for example, by electroplating on the surface of the steel sheet, if necessary, to form a plating layer. You may use for a steel plate. Since the film thickness of the surface treatment such as plating is sufficiently small with respect to the plate thickness, the influence on the mechanical properties of the steel plate is negligible.

As described above, the steel sheet of the present invention can have sufficient strength and excellent material uniformity even if it is thinned. Therefore, the steel sheet of the present invention is particularly suitable as a material for crowns or DRD cans.
The crown of the present invention is formed using the steel plate described above. The crown is mainly composed of a disk-shaped part that closes the mouth of the bottle and a bowl-shaped part provided around the disk-shaped part. The crown of the present invention can be formed by press molding after punching the steel plate of the present invention into a circular blank. Since the crown of the present invention is manufactured from a steel sheet having sufficient yield strength and excellent material uniformity, it has excellent pressure resistance as a crown even when it is thinned, and has an outer diameter and high crown. Since the uniformity of the height is excellent, the yield in the crown manufacturing process is improved, and the amount of waste generated by the crown manufacturing is reduced.

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

Steel slabs were obtained by containing the component composition shown in Table 1, with the balance being made of Fe and unavoidable impurities in a converter and continuously cast. The steel slab obtained here was subjected to hot rolling at the slab heating temperature, finish rolling temperature, and winding temperature shown in Table 2. After this hot rolling, pickling was performed. Next, primary cold rolling was performed at the rolling reduction shown in Table 2, and continuous annealing was performed under the continuous annealing conditions shown in Table 2, followed by secondary cold rolling at the rolling reduction shown in Table 2. The obtained steel sheet was continuously subjected to electrolytic chromic acid treatment to obtain tin-free steel.

The steel sheet obtained in accordance with the above was subjected to a heat treatment equivalent to paint baking at 210 ° C. for 15 minutes and then subjected to a tensile test. The tensile test was performed according to “JIS Z 2241” using a JIS No. 5 size tensile test piece, and the yield strength in the rolling direction was measured. The heat treatment equivalent to this paint baking does not affect the steel plate material before the heat treatment.

The resulting steel sheet was molded into a crown and the crown formability was evaluated. That is, using a circular blank having a diameter of 37 mm, 20 crowns (N = 20) were formed for each steel plate by pressing. The height of the crown (distance from the top 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, more than 0.09 mm The crown shape is inferior. The obtained results are shown in Table 2.

Further, the obtained steel sheet was subjected to a heat treatment equivalent to paint baking at 210 ° C. for 15 minutes, and then formed into a DRD can, and the DRD can formability was evaluated. That is, using a circular blank having a diameter of 158 mm, drawing and redrawing were performed, a DRD can having an inner diameter of 82.8 mm and a flange diameter of 102 mm was formed, and DRD can moldability was evaluated. In the evaluation, a sample in which three or more fine wrinkles are visually observed in the flange portion was evaluated as “x”, and a sample in which the fine wrinkles in the flange portion were two or less locations was evaluated as “good”. The evaluation results are shown in Table 2.

From Table 2, the steel sheets of Nos. 1 to 22 which are examples of the present invention have a yield strength in the rolling direction of 560 MPa or more and a standard deviation of the crown height of 0.09 mm or less, and the crown formability is good. I understand. Furthermore, the number of wrinkles generated in DRD can molding was 2 or less, and the DRD can moldability was also good.

On the other hand, the steel plates No. 23 to 25, which are comparative examples, contain too much C, so the standard deviation of ferrite grain size exceeds 7.0 μm, and the standard deviation of crown height exceeds 0.09 mm. It was found that moldability deteriorates and DRD can moldability also deteriorates. Steel plates No. 26 to 28 have too little C content, so the standard deviation of ferrite grain size exceeds 7.0 μm, the standard deviation of crown height exceeds 0.09 mm, and the crown formability deteriorates. I understood. The No. 29 steel plate contains too much Mn, so the standard deviation of ferrite grain size exceeds 7.0 μm, the standard deviation of crown height exceeds 0.09 mm, and the crown formability deteriorates. It was found that can moldability also deteriorated. It was found that the No. 30 steel sheet contained too much Al, so the formation of AlN was increased, the amount of N contributing to the steel sheet strength as solute N was reduced, and the steel sheet strength was reduced. The DRD can moldability also deteriorated. The steel plate of No. 31 has too little Al content, so that the effect as a deoxidizer is insufficient, causing solidification defects and increasing the steelmaking cost. In addition, since an appropriate amount of AlN cannot be secured during recrystallization of ferrite during annealing, the standard deviation of ferrite grain size after annealing becomes large, and the ferrite grain size of the steel sheet after secondary cold rolling becomes coarse. It was found that the standard deviation of the particle size exceeded 7.0 μm, the standard deviation of the crown height exceeded 0.09 mm, the crown moldability deteriorated, and the DRD can moldability deteriorated. Steel plates No. 32 to 34 have too much N content, so the ferrite grain size of the steel sheet after secondary cold rolling becomes fine, and the standard deviation of ferrite grain size is over 7.0 μm, and the crown height It was found that the standard deviation of the above exceeded 0.09 mm, the crown moldability deteriorated, and the DRD can moldability also deteriorated. Steel sheets No. 35 to 37 have too little N content, so the ferrite grain size of the steel sheet becomes coarse, the standard deviation of ferrite grain size exceeds 7.0 μm, and the standard deviation of crown height is 0.09 mm. It has been found that the crown formability deteriorates, the DRD can formability deteriorates, and the amount of N that contributes to the steel sheet strength as solute N decreases and the steel sheet strength decreases. In addition, the No. 38 steel plate has too much P content, so 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. Moreover, it turned out that DRD can moldability also deteriorates. The No. 39 steel sheet contains too much Si, so the standard deviation of ferrite grain size exceeds 7.0 μm, the standard deviation of crown height exceeds 0.09 mm, and the crown formability deteriorates. It was found that can moldability also deteriorated.

Steel No. shown in Table 1 Steel slabs were obtained by containing a component composition of 5, 9, 18, 21, 28, 29, and 31 with the balance being made of Fe and unavoidable impurities in a converter and continuously cast. The steel slab obtained here was hot-rolled 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 rolling reduction shown in Table 3, and the soaking temperature, soaking time, precooling average speed, precooling cooling stop temperature, precooling average cooling speed, and postcooling cooling stop temperature shown in Table 3 are used. Continuous annealing was performed, followed by secondary cold rolling at the rolling reduction shown in Table 3. The obtained steel sheet was continuously subjected to electrolytic chromic acid treatment to obtain tin-free steel.

The steel sheet obtained as described above was subjected to a tensile test in the same manner as described above, and the crown formability and DRD can formability were evaluated. The obtained results are shown in Table 3.

From Table 3, steel plate No. which is an example of the present invention. Steel sheets of 40, 43, 45, 47, 48, 52 to 55, 58, 59, 63, 64, 66, 69, 70, 71 have a high yield strength in the rolling direction of 560 MPa or more and a standard crown height. The deviation was 0.09 mm or less, and the crown moldability and DRD can moldability were good.
On the other hand, steel plate No. which is a comparative example. Steel plates Nos. 41, 49, 50, 56, 61, 68, and 72 have a slab heating temperature, a soaking time, a pre-cooling average speed, a secondary cold reduction rate, a post-cooling average speed, a pre-cooling stop temperature, and a post-cooling. It was found that the yield strength in the rolling direction is lowered because the stop temperature is out of the range of the present invention. Steel plate No. which is a comparative example. The steel plate No. 62 has a secondary cold reduction ratio that is too high, so the anisotropy of the steel plate increases, the standard deviation of the crown height exceeds 0.09 mm, and the crown formability deteriorates, and the DRD can moldability also increases. It turns out that it deteriorates. Steel plate No. which is a comparative example. Steel plates of 42, 44, 46, 51, 57, 60, 65, 67, 73, 74 are slab heating temperature, final stand reduction ratio of hot rolling, winding temperature, primary cold rolling rate, soaking temperature. , Any one of the pre-stage cooling stop temperature, the post-stage cooling average speed, the post-stage cooling stop temperature, and the secondary cold rolling reduction is outside the range of the present invention, so that the yield strength in the rolling direction is reduced or the standard deviation of the ferrite grain size is 7 It was found that the standard deviation of the crown height exceeded 0.09 mm and the crown moldability deteriorated, and the DRD can moldability also deteriorated.

Claims

% By 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, with the balance having a component composition of Fe and inevitable impurities,
Having a ferrite phase in the region from the 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.
The steel plate according to claim 1, wherein the plate thickness is 0.20 mm or less.
A crown made of the steel plate according to claim 1 or 2.
A DRD can comprising the steel plate according to claim 1 or 2.
It is a manufacturing method of the steel plate according to claim 1 or 2.
A hot rolling process in which a steel material is heated at 1200 ° C. or higher, rolled at a finish rolling temperature of 870 ° C. or higher and a reduction ratio of the final stand of 10% or higher, and wound in a temperature range of 550 to 750 ° C. When,
Pickling step of pickling the hot-rolled sheet after hot rolling;
A primary cold rolling step of performing cold rolling with a reduction ratio of 88% or more on the hot-rolled sheet after pickling,
The cold-rolled sheet after the primary cold rolling is held in a temperature range of 660 to 760 ° C. for 60 seconds or less, and 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. Then, an annealing step of cooling to a temperature range of 140 ° C. or less at an average cooling rate of 5 ° C./s or more and 30 ° C./s or less,
A secondary cold rolling step of performing cold rolling on the annealed plate at a rolling reduction of 10% to 40%.