JPWO2018061787A1 - Crown steel plate, method for producing the same, and crown - Google Patents

Abstract

To provide a crown steel plate having sufficient pressure strength and formability even when it is thinned, a manufacturing method thereof, and a crown. N total- (N as AlN) is 0.0090% or more and 0.0170% or less in the rolling direction cross section, and the maximum grain size of the carbide is 2.0 μm or less in the rolling direction. A steel plate for a crown having a yield strength of 420 MPa or more and 600 MPa or less. A hot rolling process in which a steel material having a predetermined component composition is wound at a predetermined temperature after finish rolling, a primary cold rolling process, and a temperature range A of 500 to 600 ° C. in the heating process is 10 ° C./s or more and 30 or more. Heated at an average heating rate of ℃ / s or less, annealed at an annealing temperature B in a temperature range of 620 to 740 ° C, and a temperature of 400 ° C or more and 580 ° C or less from the annealing temperature B at an average cooling rate of 20 ° C / s or more. A continuous annealing step of cooling to a cooling stop temperature C of the region and stopping the cooling at the average cooling rate, and then retaining the residence time in the temperature range of 400 ° C. to 580 ° C. for 30 seconds to 90 seconds. And a secondary cold rolling step of cold rolling at a rolling reduction of 1.0 to 12%.

Description

  The present invention relates to a crown steel plate having excellent shape uniformity and pressure resistance against internal pressure, a manufacturing method thereof, and a crown made using the crown steel plate, which are used for beer bottles and the like.

  A metal stopper called a crown is widely used in containers for beverages such as soft drinks and alcoholic beverages. In general, 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.

  In a bottle filled with beer or carbonated drink, an internal pressure is generated by the contents. The crown needs to have high pressure strength so that when the internal pressure increases due to temperature changes or the like, the crown will not deform and the bottle will not be sealed and the contents will not leak. In addition, even if the strength of the material is sufficient, if the moldability is poor, the shape of the jar will be non-uniform, and even if it is caulked to the mouth of the bottle, sufficient sealing performance may not be obtained, so moldability is improved. It must also be excellent.

  SR (Single Reduced) steel plates are mainly used as thin steel plates 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 the purpose of reducing costs. When the thickness of the steel plate for the crown is 0.20 mm or less, the crown manufactured with the conventional SR material has insufficient pressure resistance. In order to ensure the compressive strength, it is conceivable to apply a DR (Double Reduced) steel sheet that can be subjected to secondary cold rolling after annealing to make use of work hardening that compensates for the decrease in strength accompanying thinning. If the rolling reduction during the next cold rolling is increased, the steel sheet becomes hard and the formability is lowered. In crown molding, the central part is squeezed to some extent at the initial stage of molding, and then the outer edge part is molded into a bowl shape. In the case of a steel sheet with low formability, there may be a shape defect in which the shape of the ridge is not uniform. A crown with a non-uniform shape of the heel has a problem that even if it is plugged into a bottle, pressure resistance cannot be obtained, the contents leak, and it does not serve as a lid. Even if the shape of the ridge is uniform, if the steel plate strength is low, the crown may be removed due to insufficient pressure resistance. Furthermore, the method of evaluating the pressure strength is becoming stricter as the crown steel sheet is made thinner. The conventional pressure-resistant strength evaluation was a method of measuring the pressure at which the crown comes off by increasing the internal pressure of the bottle at a constant speed by caulking the crown into the bottle and injecting air from the top of the crown. Then, the pressure is maintained at a predetermined pressure for a certain time, and the internal pressure is further increased.

  In the past, the following techniques have been proposed in order to obtain a steel sheet that is excellent in both strength and formability during thinning.

Patent Document 1 contains, in mass%, N: 0.0040 to 0.0300%, Al: 0.005 to 0.080%, 0.2% proof stress in a tensile test using a JIS No. 5 test piece: 430 MPa. Hereinafter, an ultrathin soft steel plate for containers excellent in can strength and can moldability of 0.4 mm or less, characterized by total elongation of 15 to 40% and Q ⁻¹ due to internal friction of 0.0010 or more. It is disclosed.

  In Patent Document 2, in mass%, C: 0.001 to 0.080%, Si: 0.003 to 0.100%, Mn: 0.10 to 0.80%, P: 0.001 to 0 100%, S: 0.001 to 0.020%, Al: 0.005 to 0.100%, N: 0.0050 to 0.0150%, B: 0.0002 to 0.0050% Further disclosed is a steel plate for a high-strength and high-workability can characterized by containing 0.01 to 1.00% in terms of area ratio of crystal grains having a degree of elongation of crystal grains of 5.0 or more in the cross section in the rolling direction. ing.

  In Patent Document 3, in mass%, C: 0.001 to 0.040%, Si: 0.003 to 0.100%, Mn: 0.10 to 0.80%, P: 0.001 to 0 100%, S: 0.001 to 0.020%, Al: 0.005 to 0.100%, N: more than 0.015% and 0.020% or less, B: 0.0002 to 0.0050% The content of N contained as AlN is 0.0060% or less, and in the cross section in the rolling direction, the average crystal grain size is 5.00 μm or more, the elongation of crystal grains is 2.50 or less, and the tensile strength A steel sheet for a high-strength, high-workability can that has a breaking elongation of 7% or more and 550 MPa or more is disclosed.

JP 2001-49383 A JP 2013-28842 A JP 2012-72439 A

  However, when the above-mentioned conventional techniques are applied to the thinning of the steel plate for crowns, any of them has a problem that the performance as a crown cannot be secured. Since the steel sheet described in Patent Document 1 is soft and contains a large amount of N, increasing the secondary cold rolling reduction to obtain the required strength increases the anisotropy and impairs formability. In addition, Patent Document 1 evaluates flange formability and can strength after making cans into a two-piece can, but nothing is said about crown molding and crown pressure strength after the crown is plugged into a bottle. Not. Similarly, the steel sheet described in Patent Document 2 is also strengthened by N, but it is difficult to achieve both the pressure strength required for the crown and formability. In the steel sheet described in Patent Document 3, although the solid solution N amount, the average crystal grain diameter, and the elongation of the crystal grains are controlled to achieve both high strength and workability of the steel sheet, crown molding is a process. Since the can body is mainly molded by different bending methods, it is not suitable for forming crowns, which are mainly drawn.

  This invention is made | formed in view of the said subject, The objective is to provide the steel plate for crowns provided with sufficient pressure strength and a formability even if it thins, its manufacturing method, and a crown.

[1] By mass%, C: 0.02% to 0.08%, Si: 0.02% or less, Mn: 0.10% to 0.60%, P: 0.020% or less, S : 0.020% or less, Al: 0.01% or more and 0.06% or less, N: 0.0100% or more and 0.0180% or less, with the remainder having a component composition consisting of Fe and inevitable impurities N total- (N as AlN) is 0.0090% or more and 0.0170% or less, the maximum grain size of carbide is 2.0 μm or less in the cross section in the rolling direction, and the yield strength in the rolling direction is 420 MPa or more and 600 MPa or less. A steel plate for a crown characterized by being. However, the N total is a total amount of N, and the N as AlN is an N amount existing as AlN.
[2] A hot rolling process in which the steel material having the component composition described in [1] is wound at a temperature of 670 ° C. or less after finish rolling in hot rolling, and cold rolling is performed after the hot rolling process. After the primary cold rolling step and the cold rolling step, the temperature range A of 500 to 600 ° C. in the heating process is heated at an average heating rate of 10 ° C./s to 30 ° C./s, and the temperature is 620 to 740 ° C. Annealing is performed at an annealing temperature B in the temperature range, and the cooling is performed from the annealing temperature B to a cooling stop temperature C in a temperature range of 400 ° C. to 580 ° C. at an average cooling rate of 20 ° C./s or more, and cooling at the average cooling rate A continuous annealing step in which the residence time for retaining in the temperature range from 400 ° C. to 580 ° C. is 30 seconds to 90 seconds and after the continuous annealing step, a rolling reduction of 1.0 to 12% Having a secondary cold rolling process for cold rolling Method of manufacturing a crown for steel sheet and butterflies.
[3] A crown produced by using the crown steel plate according to [1].
[4] The crown according to [3], wherein the cross-sectional hardness of the side surface portion of the crown is 180 Hv or more and 220 Hv or less.

  ADVANTAGE OF THE INVENTION According to this invention, even if it thins, the steel plate for crowns provided with sufficient pressure strength and a moldability, its manufacturing method, and a crown can be provided.

It is a figure explaining the measuring method of the cross-sectional hardness of a crown side part. It is a figure which shows the shape of the collar of a crown.

  The crown steel plate according to the present invention is, in mass%, C: 0.02% to 0.08%, Si: 0.02% or less, Mn: 0.10% to 0.60%, P: 0 0.020% or less, S: 0.020% or less, Al: 0.01% or more and 0.06% or less, N: 0.0100% or more and 0.0180% or less, and the balance from Fe and inevitable impurities N total- (N as AlN) is 0.0090% or more and 0.0170% or less, and the maximum grain size of carbide is 2.0 μm or less in the cross section in the rolling direction, yielding in the rolling direction. The strength is 420 MPa or more and 600 MPa or less. Hereinafter, the steel plate for crowns of the present invention will be described.

  First, the component composition of the steel plate for crowns according to the present invention will be described. The unit of content “%” is all “mass%”.

[C content: 0.02% to 0.08%]
When the C content is less than 0.02%, the steel sheet strength decreases, the cross-sectional hardness of the crown side surface after crown forming decreases, and the pressure resistance decreases. On the other hand, if the content of C exceeds 0.08%, the strength of the steel sheet becomes remarkably high, so that the shape of the crown of the formed crown becomes non-uniform and the shape becomes defective. In addition, since the maximum grain size of the carbide in the cross section in the rolling direction is increased, the shape of the crown of the molded crown becomes non-uniform, resulting in a defective shape and a decrease in pressure strength. Therefore, the C content is 0.02% or more and 0.08% or less. The C content is preferably 0.03% or more. Further, the content of C is preferably 0.06% or less.

[Si content: 0.02% or less]
If a large amount of Si is contained, the moldability of the crown is impaired for the same reason as C. In addition, the Si content is set to 0.02% or less in order to cause deterioration of the surface treatment property and corrosion resistance of the steel plate. Further, the lower limit of the Si content is not particularly limited, but excessively lowering Si causes an increase in steelmaking costs, so the Si content is preferably 0.004% or more.

[Mn content: 0.10% or more and 0.60% or less]
When the Mn content is less than 0.10%, it becomes difficult to avoid hot brittleness even when the S content is reduced, and problems such as surface cracks occur during continuous casting. Therefore, the Mn content is 0.10% or more. On the other hand, if Mn is also contained in a large amount, the moldability of the crown is impaired for the same reason as C and Si. Therefore, the Mn content is set to 0.60% or less. When more excellent pressure strength is required, the Mn content is preferably 0.20% or more.

[P content: 0.020% or less]
If the P content exceeds 0.020%, the steel sheet becomes hard and the formability of the crown decreases, and in addition, the corrosion resistance decreases. Therefore, the upper limit of the P content is 0.020%.

[S content: 0.020% or less]
S is a harmful element that forms inclusions in the steel sheet and causes a decrease in hot ductility and corrosion resistance of the steel sheet. Therefore, the upper limit of the S content is 0.020%.

[Al content: 0.01% or more and 0.06% or less]
Al is an element necessary as a deoxidizer during steelmaking. When the Al content is less than 0.01%, deoxidation is insufficient, inclusions increase, and the moldability of the crown deteriorates. On the other hand, Al forms N and AlN in the steel and reduces the solute N in the steel. When the Al content exceeds 0.06%, the amount of N total- (N as AlN) described later cannot be sufficiently obtained, and the steel sheet strength is lowered. Therefore, the Al content is 0.01% or more and 0.06% or less. Preferably, the Al content is 0.01% or more and 0.04% or less.

[N content: 0.0100% or more and 0.0180% or less]
If the N content is less than 0.0100%, the amount of N total- (N as AlN) described later cannot be sufficiently obtained, the steel plate strength is lowered, and the pressure strength is lowered. On the other hand, if the N content exceeds 0.0180%, the steel sheet strength increases excessively, leading to deterioration of the crown formability, and the pressure resistance decreases. Therefore, the N content is set to 0.0100% or more and 0.0180% or less. In the case where a higher pressure resistance is required, the N content is preferably 0.0135% or more.

[N total- (N as AlN): 0.0090% or more and 0.0170% or less]
In order to ensure strength in the present invention, a desired amount of dissolved N is required. In the steel composition of the present invention, it is considered that N in steel is mainly present as AlN. Therefore, the N amount (N as AlN) present as AlN is subtracted from the total amount of N (N total) (N total- (N as AlN). )) Was regarded as the amount of dissolved N. When the content of N total- (N as AlN) is less than 0.0090%, the strength of the steel sheet is lowered and the pressure resistance is lowered. On the other hand, when the content of N total- (N as AlN) exceeds 0.0170%, the steel sheet strength increases excessively, the crown formability decreases, and the pressure resistance decreases. Therefore, the content of N total- (N as AlN) is set to 0.0090% or more and 0.0170% or less. Preferably, the content is 0.0110% or more and 0.0170% or less. The amount of N present as AlN can be confirmed by, for example, dissolving and extracting AlN using a 10% Br-methanol solution and performing quantitative analysis of N present as AlN by absorptiometry. it can.

  The balance is Fe and inevitable impurities.

Next, the structure of the crown steel plate according to the present invention will be described.
The crown steel plate according to the present invention has a structure containing carbides, and the maximum particle size of carbides in the cross section in the rolling direction is 2.0 μm or less. In the steel composition of the present invention, carbides in the steel exist mainly as cementite. If the maximum grain size of the carbide in the cross section in the rolling direction exceeds 2.0 μm, the shape of the crown of the molded crown becomes non-uniform, resulting in a defective shape and a decrease in pressure strength. The reason for this is not clear, but is presumed as follows. Since the crown of the crown is a part that undergoes tension and compression, or tension and compression superimposed in the rolling direction of the steel sheet, the direction perpendicular to the rolling direction and the thickness direction, there is coarse carbide Then, it is thought that distortion concentrates locally during molding, resulting in a shape defect. Note that when the maximum particle size of carbide (cementite) is less than 0.3 μm, the steel sheet becomes excessively strong and the formability of the crown may be impaired. Therefore, the maximum particle size of cementite is preferably 0.3 μm or more. The cementite metallographic structure was corroded with a corrosive solution (3% by volume nital) after polishing a plate thickness cross-section parallel to the rolling direction of the steel plate, and with a scanning electron microscope (SEM) plate thickness of 1 at a magnification of 2000 × 10. / 4 position (in the above cross section, 1/4 position from the surface in the plate thickness direction), cementite was identified by visual judgment using a structural photograph taken with SEM, and each cementite particle size was analyzed for image analysis. Thus, the area of each cementite was obtained and converted to an equivalent circle diameter to obtain each cementite particle diameter. The largest cementite particle size in 10 fields of view was defined as the maximum particle size of the carbide.

Next, the mechanical properties of the crown steel plate according to the present invention will be described.
The crown steel plate of the present invention is required to have a pressure strength that prevents the crown from coming off against the internal pressure of the bottle. The steel plate for crowns that has been used conventionally has a thickness of 0.22 mm or more, but a higher strength than before is required in order to reduce the thickness to 0.20 mm or less. When the yield strength in the rolling direction of the steel sheet is less than 420 MPa, it is difficult to give sufficient pressure resistance to the thinned crown as described above. On the other hand, if the yield strength exceeds 600 MPa, the compressive stress in the circumferential direction of the crown of the crown increases, and the yield strength exceeds the critical buckling strength at the early stage of the crown molding. Become. Therefore, the yield strength in the rolling direction is set to 420 MPa or more and 600 MPa or less. In order to achieve both a good crown shape and pressure strength, the yield strength is preferably 450 MPa or more and 600 MPa or less. The yield strength can be measured by a metal material tensile test method shown in “JIS Z 2241”. The desired yield strength is adjusted by adjusting the component composition, adjusting the coiling temperature of hot rolling, the average heating rate after cold rolling, the annealing temperature, the average cooling rate after annealing, and the cooling stop temperature, after cooling stop. It can be obtained by adjusting the holding time. The yield strength of 420 MPa or more and 600 MPa or less is the above component composition, the coiling temperature in the hot rolling process is 670 ° C. or less, and the continuous annealing process after the cold rolling process is 500 to 600 ° C. in the heating process. The average heating rate in the temperature range A is 10 ° C./s or more and 30 ° C./s or less, annealing is performed at the annealing temperature B in the temperature range of 620 to 740 ° C., and the average cooling rate is 20 ° C./s or more from the annealing temperature B. Cooling to a cooling stop temperature C in a temperature range of 400 ° C. or more and 580 ° C. or less, stopping the cooling at the average cooling rate, and then retaining the residence time in the temperature range of 400 ° C. or more and 580 ° C. or less for 30 seconds or more 90 It can be obtained by performing the second cold rolling at a rolling reduction of 1.0 to 12%. Note that the yield strength in the direction perpendicular to the rolling direction of the steel sheet (sheet width direction) is preferably 450 MPa or more and 600 MPa or less.

  The crown steel plate is punched into a circular blank and then formed into a crown by press molding. After molding, the crown is caulked to the bottle mouth by a stopper, so that the sealing performance after the stopper is maintained. If the strength of the side surface after the crown molding is low, the crown may come off from the bottle mouth when held in a state where the internal pressure of the bottle is increased, leading to leakage of the contents of the bottle. The strength of the side surface after crown molding is closely related to the Vickers hardness value of the cross section. If the cross sectional hardness of the crown side surface is less than 180 Hv, the strength of the side surface of the crown is reduced and the sealing performance is reduced. The pressure strength at is reduced. On the other hand, when the cross-sectional hardness of the crown side surface portion is more than 220 Hv, the strength of the crown side surface portion becomes excessively high, so that the side surface portion is cracked. In order to achieve both a good crown shape and pressure resistance, the cross-sectional hardness of the crown side surface is set to 180 Hv or more and 220 Hv or less. The cross-sectional hardness of the crown side portion is preferably 190 Hv or higher and 220 Hv or lower.

  The cross-sectional hardness of the crown side surface can be evaluated by the method shown in “JIS Z 2244”. In the present invention, the cross-sectional hardness evaluation position of the crown side surface portion is the crown side surface cross section between the crown and the heel of the crown, and the measuring method is Vickers hardness. In the present invention, as shown in FIG. 1, the evaluation position is centered on a position (H / 2) that is 1/2 of the crown height H, one point at the center, two points in the direction of the crown upper surface, and the direction below the crown. The total score was 2 points. The Vickers indentation load was 100 gf, and the interval between the points was 3d (d: diagonal length of the indentation). The average value of the five Vickers hardness values was taken as the cross-sectional hardness of the crown side surface. The desired cross-sectional hardness is adjusted by adjusting the composition of components, adjusting the coiling temperature of hot rolling, the average heating rate after cold rolling, the annealing temperature, the average cooling rate after annealing, and adjusting the secondary cold rolling rate. It can be obtained by forming a crown from the crown steel plate obtained by doing so. The cross-sectional hardness of the crown side surface portion of 180 Hv or more and 220 Hv or less is the above component composition, the coiling temperature in the hot rolling process is 670 ° C. or less, and in the continuous annealing process after the primary cold rolling process, An average heating rate in a temperature range A of 500 to 600 ° C. is set to 10 ° C./s or more and 30 ° C./s or less, and annealing is performed at an annealing temperature B in a temperature range of 620 to 740 ° C., and 20 ° C./s or more from the annealing temperature B. The cooling time is cooled to the cooling stop temperature C in the temperature range of 400 ° C. or more and 580 ° C. or less at an average cooling rate of, and the residence time is retained in the temperature range of 400 ° C. or more and 580 ° C. or less after stopping cooling at the average cooling rate Can be obtained by forming a crown from a steel plate for a crown obtained by secondary cold rolling at a rolling reduction of 1.0 to 12%.

  Next, an example of a method for manufacturing a crown steel plate according to the present invention will be described. The steel plate for crowns of the present invention is a steel material (steel slab) having the above component composition, after a hot rolling step of finishing rolling in hot rolling at a temperature of 670 ° C. or lower, and after the hot rolling step, A pickling step for pickling as necessary, a primary cold rolling step for cold rolling after the pickling step, and a temperature range A of 500 to 600 ° C. in the heating process after the primary cold rolling step. Heat at an average heating rate of 10 ° C./s or more and 30 ° C./s or less, anneal at an annealing temperature B in a temperature range of 620 to 740 ° C., and 400 ° C. at an average cooling rate of 20 ° C./s or more from the annealing temperature B. Cooling to the cooling stop temperature C in the temperature range of 580 ° C. or lower and stopping the cooling at the average cooling rate, the residence time for staying in the temperature range of 400 ° C. or higher and 580 ° C. or lower is 30 seconds or longer and 90 seconds or shorter. After the continuous annealing step and the continuous annealing step, At a reduction ratio of .0～12% is prepared by carrying out the secondary cold rolling step of cold rolling. In the following description, the temperature is the surface temperature of a steel plate or the like. The average heating rate and average cooling rate are values obtained by calculation based on the surface temperature. The average heating rate in the temperature range A of 500 to 600 ° C. in the heating process is represented by ((600 ° C.-500 ° C.) / Heating time from 500 ° C. to 600 ° C.). The average cooling rate from the annealing temperature B to the cooling stop temperature C is represented by ((annealing temperature B−cooling stop temperature C) / cooling time from the annealing temperature B to the cooling stop temperature C).

  When the crown steel plate according to the present invention is manufactured, the molten steel is adjusted to the above chemical components by a known method using a converter or the like, for example, to form a slab by a continuous casting method. Subsequently, it is preferable that the slab is roughly rolled hot. The method of rough rolling is not limited, but in order to secure N total- (N as AlN) of 0.0090% or more, the heating temperature of the slab is preferably 1200 ° C. or more. In order to further increase N total- (N as AlN), the slab heating temperature is more preferably 1230 ° C. or higher.

  The finish rolling temperature in the hot rolling step is preferably 850 ° C. or higher from the viewpoint of rolling load stability. 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 850 to 960 ° C.

  When the coiling temperature in the hot rolling process exceeds 670 ° C., the amount of AlN precipitated in the steel after winding increases, and the amount of N total- (N as AlN) is less than 0.0090%. The yield strength in the rolling direction is less than 420 MPa, and the cross-sectional hardness of the crown side surface after crown molding may be less than 180 Hv. Also, if the coiling temperature in the hot rolling process exceeds 670 ° C., the maximum particle size of carbide in the cross section in the rolling direction exceeds 2.0 μm, and the shape of the crown collar becomes uneven during crown molding, resulting in poor shape. It may cause, which is not preferable. Therefore, the coiling temperature in the hot rolling process is 670 ° C. or less. In order to ensure a sufficient amount of N total- (N as AlN), the coiling temperature in the hot rolling step is preferably 640 ° C. or lower. On the other hand, when the winding temperature is excessively lowered, the yield strength in the rolling direction of the steel sheet exceeds 600 MPa, and the cross-sectional hardness of the crown side surface after crown forming may exceed 220 Hv. Is preferred.

  Continue pickling if necessary. The pickling is not particularly limited as long as the surface scale can be removed. Further, instead of pickling, a method such as mechanical removal may be used.

  The rolling reduction in the primary cold rolling step is not particularly limited, but is preferably 85 to 94% in order to make the thickness of the steel sheet after the secondary cold rolling 0.20 mm or less.

  In the continuous annealing step, the temperature range A of 500 to 600 ° C. is heated at an average heating rate of 10 ° C./s to 30 ° C./s. When the temperature range A is heated at an average heating rate of less than 10 ° C./s, precipitation of AlN occurs during the heating, and the amount of N total- (N as AlN) is less than 0.0090%, which is in the rolling direction of the steel sheet. The yield strength is less than 420 MPa, and the cross-sectional hardness of the crown side surface after crown molding is less than 180 Hv, which is not preferable because the pressure strength decreases. Therefore, the average heating rate in the temperature range A is 10 ° C./s or more. Preferably it shall be 12 degrees C / s or more. Moreover, when the temperature range A is heated at an average heating rate exceeding 30 ° C./s, the steel sheet is excessively hardened, the shape becomes non-uniform by crown molding, and the pressure strength decreases. Therefore, the average heating rate in the temperature range A is 30 ° C./s or less. On the other hand, when the average heating rate in the temperature range A exceeds 30 ° C./s, the annealing temperature becomes difficult to control, and there is a possibility that overheating may occur and the energy cost increases.

  The annealing temperature B is set to a temperature range of 620 to 740 ° C. When the annealing temperature B is less than 620 ° C., the steel sheet becomes hard due to an incomplete recrystallized structure, so the yield strength in the rolling direction of the steel sheet exceeds 600 MPa, and the cross-sectional hardness of the crown side surface after crown forming Over 220 Hv, the crown moldability is inferior, and the pressure strength is reduced. On the other hand, when the annealing temperature B exceeds 740 ° C., C due to the carbide dissolved during annealing segregates and aggregates at the grain boundary, and the maximum particle size of the carbide in the rolling direction cross section after cooling becomes more than 2.0 μm, In the formation of the crown, the shape of the heel becomes non-uniform and the pressure strength decreases. Further, in continuous annealing, troubles such as a heat buckle are likely to occur, which is not preferable. Therefore, the annealing temperature B is set to a temperature range of 620 to 740 ° C. The annealing temperature B is preferably 640 ° C. or higher in order to achieve a good balance between the moldability of the crown and the pressure strength. The annealing temperature B is preferably 720 ° C. or lower.

  In the cooling in the annealing step, cooling is performed from the annealing temperature B to a cooling stop temperature C in a temperature range of 400 ° C. or more and 580 ° C. or less at an average cooling rate of 20 ° C./s or more. When the average cooling rate is less than 20 ° C./s, AlN is excessively precipitated during cooling, the amount of N total- (N as AlN) is less than 0.0090%, and the yield strength in the rolling direction of the steel sheet is less than 420 MPa. Thus, the cross-sectional hardness of the side surface portion of the crown after crown molding becomes less than 180 Hv, and the pressure resistance may be reduced. Therefore, an average cooling rate shall be 20 degrees C / s or more. Preferably, it is 40 ° C./s or more. The upper limit of the average cooling rate is not particularly limited, but when the average cooling rate exceeds 150 ° C./s, not only the increase in steel sheet strength due to N total- (N as AlN) is saturated, but also into the ferrite grains. The average cooling rate is preferably 150 ° C./s or less because ductility may be reduced due to excessive carbide precipitation and cracking may occur in crown molding. More preferably, the average cooling rate is 120 ° C./s or less.

  The cooling stop temperature C is a temperature range of 400 ° C. or higher and 580 ° C. or lower. When the cooling stop temperature is higher than 580 ° C., AlN is excessively precipitated, the amount of N total- (N as AlN) is less than 0.0090%, and the yield strength in the rolling direction of the steel sheet is less than 420 MPa. In some cases, the cross-sectional hardness of the side surface portion of the crown becomes less than 180 Hv, and the compressive strength decreases. Preferably, the cooling stop temperature is 550 ° C. or lower. The lower limit of the cooling stop temperature is 400 ° C. If the cooling stop temperature is excessively low, the steel sheet is excessively hardened, the shape becomes non-uniform by crown molding, and the pressure resistance may be reduced. Preferably, the cooling stop temperature is 450 ° C. or higher.

  In the step after the cooling at the average cooling rate is stopped, the residence time in the temperature range of 400 ° C. or more and 580 ° C. or less is set to 30 seconds or more and 90 seconds or less. When the residence time in the temperature range of 400 ° C. or higher and 580 ° C. or lower exceeds 90 seconds, the carbide grows as C diffuses into the carbide in the steel, and the maximum particle size of the carbide in the cross section in the rolling direction exceeds 2.0 μm. When forming a crown, the shape of the heel becomes non-uniform, and the pressure resistance decreases. In order to ensure a good shape, the residence time in the temperature range from 400 ° C. to 580 ° C. is preferably 75 seconds or less. Moreover, the minimum of the residence time in the temperature range of 400 degreeC or more and 580 degrees C or less shall be 30 second or more. When the residence time is less than 30 seconds, the steel sheet is excessively hardened, the shape becomes non-uniform by crown molding, and the pressure strength decreases.

  The rolling reduction of the secondary cold rolling following the continuous annealing process is 1.0 to 12%. When the rolling reduction of secondary cold rolling is less than 1.0%, the cross-sectional hardness of the crown side surface after crown forming is less than 180 Hv, and the pressure strength is reduced. The reason for this is not clear, but is presumed as follows. In a steel sheet in which solid solution N exists, dislocations introduced by secondary cold rolling are fixed by solid solution during the heat treatment process in paint baking. In the subsequent tension, the fixed dislocation becomes an obstacle at the time of deformation, and the strength increases. On the other hand, in the molding of a crown, since a drawing process is mainly used, a slip system force different from that of tension works, so that the fixed dislocation does not work effectively in the crown molding, and the cross-sectional hardness of the side surface portion of the crown does not easily increase. That is, in order to increase the cross-sectional hardness of the side surface portion of the crown in crown molding, it is necessary to introduce a large amount of dislocations by secondary cold rolling, and a rolling reduction of 1.0% or more is required. When the rolling reduction ratio of the secondary cold rolling exceeds 12%, dislocations are introduced excessively, so that the cross-sectional hardness of the crown side surface exceeds 220 Hv, cracks occur during forming, and the pressure strength decreases. Therefore, the reduction ratio of secondary cold rolling is set to 1.0 to 12%. In order to achieve both the formability of the crown and the pressure strength, the reduction ratio of the secondary cold rolling is preferably 3.0% or more. Further, the rolling reduction of secondary cold rolling is preferably 10% 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. on the surface of the steel sheet, for example, by electroplating, if necessary, to form a plating layer, and crown Steel plate. In addition, since the film thickness of surface treatments, such as plating, is sufficiently small with respect to plate | board thickness, the influence on the mechanical characteristic of the steel plate for crowns is a level which can be disregarded.

  As described above, the crown steel plate of the present invention can have sufficient pressure strength and formability even if it is thinned.

  The crown of the present invention is formed using the above-described crown steel plate. 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 being punched into a circular blank. Since the crown of the present invention is manufactured from a crown steel plate having sufficient yield strength and excellent formability, it is excellent in pressure resistance as a crown even if it is thinned. It also has the effect of reducing emissions.

  In this example, first, a steel slab was 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 reheated to 1220 ° C. and then hot-rolled at a rolling start temperature of 1150 ° C. to obtain the finish rolling temperature shown in Table 2, and wound at the winding temperature. After 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 conditions shown in Table 2, followed by secondary cold rolling at the rolling reduction shown in Table 2. The obtained steel plate was continuously subjected to normal Cr plating to obtain tin-free steel.

  The steel plate obtained as described above was subjected to a heat treatment equivalent to coating baking at 210 ° C. for 15 minutes, and then subjected to a tensile test and a measurement of the cross-sectional hardness of the crown side portion. 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 cross-sectional hardness of the crown side surface portion was formed into a crown using a steel plate, and the Vickers hardness was measured by a method according to “JIS Z 2244”. The crown uses a circular blank with a diameter of 37 mm, and the dimensions of the three crowns described in “JIS S 9017” (obsolete standard) by press working (outer diameter 32.1 mm, height 6.5 mm, number of ridges 21) It was formed by molding. The evaluation position was a total of 5 points, with one point at the center, 2 points in the crown upper surface direction, and 2 points in the crown lower direction, centering on the 1/2 position of the crown height. The Vickers indentation load was 100 gf, and the interval between the points was 3d (d: diagonal length of the indentation). The average value of the five Vickers hardness values was taken as the cross-sectional hardness of the crown side surface.

  The grain size of carbides in the cross section in the rolling direction is determined by polishing a plate thickness cross section parallel to the rolling direction of the steel sheet, then corroding with a corrosive liquid (3% by volume nital), and scanning electron microscope (SEM) over 10 fields of view at 2000 times magnification. The sheet thickness is ¼ position (in the cross section, ¼ position from the surface in the sheet thickness direction), and cementite is identified by visual judgment using a structure photograph taken with SEM. Then, the area of each cementite was obtained by image analysis, and converted to an equivalent circle diameter to obtain each cementite particle diameter. The largest cementite particle size in 10 fields of view was defined as the maximum particle size of carbide in the cross section in the rolling direction.

  The obtained steel plate was formed into a crown, and the crown formability was evaluated. Using a circular blank with a diameter of 37 mm, it was molded into the dimensions of the three crowns described in “JIS S 9017” (obsolete standard) (outer diameter: 32.1 mm, height: 6.5 mm, number of ridges: 21) . As shown in FIG. 2, the crown formability is evaluated by measuring the length L of each ridge 2 of the crown, ◯ for a crown whose standard deviation of L value is 0.1 or less, and 0 for standard deviation of L value. ..> 1 crown was rated as x. And the said evaluation was implemented with five crowns, and the standard deviation of L value was 0.1 or less by all (5), and it was set as x (pass) other than that.

  The pressure resistance test was carried out using a molded crown. Place a vinyl chloride liner on the inside of the top of the crown, plug it into a commercial beer bottle, drill a small hole in the top of the crown, and install a device that sends air into the bottle. Inside the bottle at a speed of 5 psi / second The internal pressure in the bottle was increased by injecting air into the bottle. As the pressure increase condition in the bottle, the pressure in the bottle was increased to 100 psi (pressure increase operation), held at 100 psi for 1 minute (hold operation), and increased again at 5 psi / second (repressurization operation). In each of the pressurizing operation, holding operation, and repressurizing operation, the internal pressure value in the bottle when the air leaks from the gap between the crown and the bottle mouth or when the crown is removed from the bottle mouth (unplugging). The pressure resistance value of the crown was evaluated as ○ when the pressure resistance value was equal to or higher than that of the conventional crown, and × when the pressure resistance value of the conventional crown was not reached. Since it was difficult to evaluate further after x, it was indicated as-in the table. In addition, as a conventional crown, a SR (Single Reduced) steel plate having a thickness of 0.22 mm was used. In the above boosting operation, during the holding operation and during the repressurization, a case where ◯ was obtained was evaluated as an overall evaluation ○ (passed) as excellent withstand pressure strength, and other than that as × (failed) as inferior withstand pressure strength. . The obtained results are shown in Table 2.

  From Table 2, steel plate No. which is an example of the present invention. The steel plates 1 to 15 are components within the range specified in the present invention, the yield strength in the rolling direction is 420 MPa or more and 600 MPa or less, and the maximum grain size of carbides in the rolling direction cross section is 2.0 μm or less. Steel plate No. The crown molded from 1 to 15 had a cross-sectional hardness of the crown side surface after the crown molding of 180 Hv or more and 220 Hv or less. Steel plate No. The steel plates for crowns 1 to 15 were good in both crown formability and pressure strength.

  On the other hand, steel plate No. which is a comparative example. Since the steel plate No. 16 has a C content of less than 0.02%, the yield strength in the rolling direction of the steel plate is less than 420 MPa, the cross-sectional hardness of the crown side surface after crown forming is less than 180 Hv, and the crown formability is good However, it was found that the pressure strength is insufficient.

  Steel plate No. Steel plate No. 17 has a C content exceeding 0.08%, so the yield strength in the rolling direction exceeds 600 MPa, the maximum grain size of carbide in the cross section in the rolling direction exceeds 2.0 μm, and the crown side surface after crown molding Since the cross-sectional hardness of the part exceeds 220 Hv, it was found that the crown moldability was inferior and the pressure resistance was insufficient.

  Steel plate No. Since the steel plate No. 18 has a Mn content exceeding 0.60%, the yield strength in the rolling direction exceeds 600 MPa, and the cross-sectional hardness of the crown side surface after crown forming exceeds 220 Hv. It was found that the shape became non-uniform, the shape became defective, and the pressure strength was reduced.

  Steel plate No. Since 19 steel plate has an Al content exceeding 0.06%, N total- (N as AlN) is less than 0.0090%, the yield strength in the rolling direction of the steel plate is less than 420 MPa, and the crown after crown forming Since the cross-sectional hardness of the side portion is less than 180 Hv, it was found that the pressure strength is insufficient.

  Steel plate No. The 20 steel plate has an N content of less than 0.0100%, so N total- (N as AlN) is less than 0.0090%, and the yield strength in the rolling direction of the steel plate is less than 420 MPa. Since the cross-sectional hardness of the crown side surface portion was less than 180 Hv, it was found that the pressure strength was insufficient.

  Steel plate No. Steel plate No. 21 has an N content exceeding 0.0180%, so N total- (N as AlN) exceeds 0.0170%, the yield strength in the rolling direction of the steel plate exceeds 600 MPa, and the crown after crown forming Since the cross-sectional hardness of the side surface portion exceeds 220 Hv, it was found that the molded crown had a defective shape and the pressure resistance was insufficient.

  Steel plate No. The steel plate No. 22 has a Si content of more than 0.02%. Steel plate No. 23 has a P content exceeding 0.020%, so the yield strength in the rolling direction exceeds 600 MPa, and the cross-sectional hardness of the crown side surface after crown forming exceeds 220 Hv. I found out that it was insufficient.

  Next, steel No. 1 shown in Table 1 was used. Steel slabs were obtained by containing B, G, K, and S component compositions, with the balance being made of Fe and unavoidable impurities in a converter and continuous casting. The manufacturing conditions shown in Table 3 were applied to the steel slab obtained here. The obtained steel plate was continuously subjected to normal Cr plating to obtain tin-free steel. Steel plate No. obtained by the above. 24 to 56, after performing heat treatment equivalent to baking at 210 ° C. for 15 minutes, the yield strength in the rolling direction, the maximum grain size of carbides in the cross section in the rolling direction, and the crown side surface after crown molding by the above-described methods The cross-sectional hardness was determined. In addition, crown formability and pressure strength were evaluated by the methods described above.

  From Table 3, steel plate No. which is an example of the present invention. 27 to 28, 30, 32 to 33, 35, 37 to 39, 41 to 42, 45 to 48, 50 to 52 have a maximum carbide grain size of 2.0 μm or less in the rolling direction cross section, and the rolling direction. Yield strength of 420 MPa or more and 600 MPa or less, and the cross-sectional hardness of the crown side surface after crown molding is 180 Hv or more and 220 Hv or less, both crown formability and pressure strength were good.

  On the other hand, steel plate No. which is a comparative example. The steel plate No. 24 has a coiling temperature of over 670 ° C., so the amount of N total- (N as AlN) is less than 0.0090%, and the yield strength in the rolling direction of the steel plate is less than 420 MPa. The cross section hardness of the part is less than 180 Hv, the maximum grain size of carbide in the cross section in the rolling direction is over 2.0 μm, the shape of the crown of the crown becomes non-uniform at the time of crown molding, the shape is poor, and the crown moldability is inferior It was also found that the pressure strength was inferior.

  Steel plate No. In the steel plate of 25, the average heating rate is less than 10 ° C./s in the temperature range A of 500 to 600 ° C., so the amount of N total- (N as AlN) is less than 0.0090%, It was found that the yield strength was less than 420 MPa, the cross-sectional hardness of the crown side surface after crown molding was less than 180 Hv, and the pressure strength was inferior.

  Steel plate No. The steel plate No. 26 has an annealing temperature of less than 620 ° C., so the steel plate becomes hard due to an incomplete recrystallization structure, the yield strength in the rolling direction of the steel plate exceeds 600 MPa, and the cross-section of the crown side portion after crown forming It was found that the hardness was over 220 Hv, the crown moldability was inferior, and the pressure strength was inferior.

  Steel plate No. No. 29 steel plate has an annealing temperature exceeding 740 ° C., so the maximum grain size of carbides in the cross section in the rolling direction is over 2.0 μm, and the shape of the heel is non-uniform in the formation of the crown. It was.

  Steel plate No. The steel plate No. 31 has an average heating rate of more than 30 ° C./s in the temperature range A of 500 to 600 ° C., so that the steel plate becomes hard, the yield strength in the rolling direction of the steel plate exceeds 600 MPa, and the crown side surface after crown forming It was found that the cross-sectional hardness was over 220 Hv, the crown moldability was inferior, and the pressure resistance was inferior.

  Steel plate No. In the steel plate No. 34, although the cooling stop temperature C is in the temperature range of 400 ° C. or higher and 580 ° C. or lower, the average cooling rate is less than 20 ° C./s, so the amount of N total- (N as AlN) is 0.0090. It was found that the yield strength in the rolling direction of the steel sheet was less than 420 MPa, the cross-sectional hardness of the crown side surface after crown forming was less than 180 Hv, and the pressure strength was inferior.

  Steel plate No. Since the steel plate No. 36 has a cooling stop temperature exceeding 580 ° C., the amount of N total- (N as AlN) is less than 0.0090%, the yield strength in the rolling direction of the steel plate is less than 420 MPa, and the crown side surface after crown forming It was found that the sectional hardness of the part was less than 180 Hv, and the pressure resistance was inferior.

  Steel plate No. Since the steel plate No. 40 has a cooling stop temperature of less than 400 ° C., the steel plate becomes hard, the yield strength in the rolling direction of the steel plate exceeds 600 MPa, the cross-sectional hardness of the crown side surface after crown forming exceeds 220 Hv, and crown formability It was found that the pressure strength was inferior. In Table 3, steel plate No. The residence times in the temperature range of 400 ° C. or more and 580 ° C. or less in the steel plates 36 and 40 indicate residence times at the respective cooling stop temperatures C.

  Steel plate No. Since the rolling reduction of the secondary cold rolling exceeds 12%, the yield strength in the rolling direction of the steel sheet exceeds 600 MPa, and the cross-sectional hardness of the crown side surface exceeds 220 Hv. It was found that the pressure strength was inferior.

  Steel plate No. The steel plate No. 44 has a rolling reduction of secondary cold rolling of less than 1.0%, so the yield strength in the rolling direction of the steel plate is less than 420 MPa, and the cross-sectional hardness of the crown side surface after crown forming is less than 180 Hv, It was found that the pressure strength decreased.

  Steel plate No. In the steel plate No. 49, although the cooling stop temperature C is in the temperature range of 400 ° C. or higher and 580 ° C. or lower, the residence time in the temperature range of 400 ° C. or higher and 580 ° C. or lower exceeds 90 seconds. It was found that the particle diameter exceeded 2.0 μm, the shape of the ridge was non-uniform during crown molding, and the pressure strength was inferior.

  Steel plate No. In the steel plate No. 54, although the cooling stop temperature C is in the temperature range of 400 ° C. or higher and 580 ° C. or lower, the residence time in the temperature range of 400 ° C. or higher and 580 ° C. or lower is less than 30 seconds. It was found that the yield strength in the rolling direction was over 600 MPa, the cross-sectional hardness of the crown side surface after crown molding was over 220 Hv, the crown formability was poor, and the pressure resistance was poor.

  Steel plate No. In the steel plates 55 and 56, the Al content exceeds 0.06%, so N total- (N as AlN) is less than 0.0090%, the yield strength in the rolling direction of the steel plate is less than 420 MPa, It was found that the cross-sectional hardness of the crown side surface portion was less than 180 Hv, and the pressure strength was inferior.

1 Crown top 2

Claims (4)

% By mass
C: 0.02% to 0.08%,
Si: 0.02% or less,
Mn: 0.10% or more and 0.60% or less,
P: 0.020% or less,
S: 0.020% or less,
Al: 0.01% or more and 0.06% or less,
N: 0.0100% or more and 0.0180% or less are contained, and the balance has a component composition consisting of Fe and inevitable impurities,
N total- (N as AlN) is 0.0090% or more and 0.0170% or less,
In the rolling direction cross section, the maximum particle size of the carbide is 2.0 μm or less,
A steel plate for a crown, wherein the yield strength in the rolling direction is 420 MPa or more and 600 MPa or less.
However, the N total is a total amount of N, and the N as AlN is an N amount existing as AlN. A hot rolling step of winding at a temperature of 670 ° C. or less after finish rolling in hot rolling of a steel material having the component composition according to claim 1;
After the hot rolling step, a primary cold rolling step for cold rolling,
After the primary cold rolling step, a temperature range A of 500 to 600 ° C. in the heating process is heated at an average heating rate of 10 ° C./s to 30 ° C./s, and an annealing temperature B in a temperature range of 620 to 740 ° C. And cooling to the cooling stop temperature C in the temperature range of 400 ° C. or more and 580 ° C. or less from the annealing temperature B at an average cooling rate of 20 ° C./s or more, and after stopping the cooling at the average cooling rate, A continuous annealing step in which a residence time for residence in a temperature range of 400 ° C. or more and 580 ° C. or less is 30 seconds or more and 90 seconds or less;
And a secondary cold rolling step of cold rolling at a rolling reduction of 1.0 to 12% after the continuous annealing step. A crown produced using the crown steel plate according to claim 1. The crown according to claim 3, wherein the crown has a cross-sectional hardness of 180 Hv or more and 220 Hv or less.

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