JP6123735B2 - Crown steel sheet, method for producing the same, and crown - Google Patents

Description

  The present invention relates to a steel plate for a crown that is used in a beer bottle or the like and has excellent shape uniformity during crown molding, a method for producing the same, and a crown formed by molding the steel plate for a crown.

  From the viewpoint of reducing environmental burden and reducing costs in recent years, thinning of steel plates for crowns used for beer bottle lids is progressing. Generally, there are the following two methods for manufacturing a steel sheet used for a crown. The first is a method of performing temper rolling with a stretch rate of up to several percent following hot rolling, cold rolling, and annealing, and a steel plate manufactured by this method is called an SR (Single Reduce) material. The second is a method of further performing secondary cold rolling with a rolling reduction exceeding about 10% after the annealing, and a steel plate manufactured by this method is called a DR (Double Reduce) material.

  The plate thickness of the conventional crown steel plate is generally 0.22 mm or more. However, recently, thinning has progressed, and it is required to make the plate thickness 0.18 mm or less. From the viewpoint of such thinning, it is preferable to use DR material rather than SR material because thinning is easily performed by secondary cold rolling. Also, it is desirable to use a DR material from the viewpoint that high strength can be easily obtained by using work hardening in order to compensate for a decrease in pressure strength accompanying the thinning. However, since DR material is generally harder and has higher deformation resistance than SR material, there is a problem that workability is inferior.

  In the formation of the crown, the central portion is squeezed at the initial stage of molding, and then the outer edge portion is formed into a pleated shape. In the case of a steel plate having low workability, a shape defect that causes uneven pleat shapes may occur. A crown with a non-uniform pleat shape will cause the contents to leak out of the non-uniform shape even if it is plugged into a bottle. When the internal pressure of the bottle is increased by carbon dioxide gas such as beer and carbonated beverages, it is necessary to maintain the sealing performance without causing the crown to leak in a state where the internal pressure is applied. If the workability of the crown steel plate is low, the pressure resistance, which is a characteristic representing this sealing property, may be insufficient. In this case, the crown does not play a role as a crown, which is a problem. Even if the pleat shape is uniform, the pressure strength is insufficient when the strength of the steel sheet is low.

  An extremely low carbon IF steel is well known as a steel sheet having good workability. For DR materials using ultra-low carbon steel, there are many studies aimed at achieving both workability improvement and thinning.

  For example, in Patent Document 1, components and manufacturing conditions that affect earring properties are examined in detail, and the texture can be effectively controlled by adding Sn without extremely thinning the hot-rolled sheet. A technique capable of significantly reducing the above is disclosed.

  In Patent Document 2, in the ultra-low carbon steel in which Nb and Ti which are carbide forming elements are added in combination, the content of Ti and Nb is reduced to a predetermined value or less, and the non-aging excellent in necked-in workability. A technique for providing a steel sheet is disclosed.

  Patent Document 3 discloses a steel plate for cans that can be manufactured by continuous annealing using ultra-low carbon steel as a raw material by effectively using Sn mixed as an inevitable impurity, and a technology for manufacturing them. ing.

JP 7-11333 A Japanese Patent Laid-Open No. 5-287445 JP 2010-255021 A

  However, none of the above prior arts relates to crown steel plates. When the techniques of Patent Documents 1 to 3 are applied to the crown, problems arise as follows.

  In the technique described in Patent Document 1, Sn is added in order to improve the earring property. However, when the Sn content increases, the average r value decreases, so that the drawing property decreases. This adversely affects the drawing at the early stage of crown molding.

  The technique described in Patent Document 2 aims to improve necked-in workability performed on the opening after forming the can body of the drawn can. In patent document 2, in order to suppress YP rise which deteriorates necked-in workability, the steel plate which does not raise YP by coating baking is provided. However, in crown applications, if the YP of the steel plate for the crown is low, there is a problem because the pressure strength is insufficient.

  In patent document 3, in order to improve the can-expanding moldability of the can body part of the three-piece can, a steel sheet having an average r value as low as 1.0 ± 0.2 is provided by utilizing the r value reducing action of Sn. However, for crown applications, extremely good moldability is required to make the pleat shape uniform. If the average r value is low, the moldability is insufficient for crown use.

  The present invention has been made in view of the above circumstances, and solves the problems of the prior art described above, and provides a crown steel plate excellent in pressure strength and workability, a method for producing the steel plate, and a crown formed by molding the steel plate. The purpose is to do.

  Inventors conducted earnest research in order to solve the said subject. As a result, the shape of the crown is controlled by controlling the average TS (tensile strength) and average YP (yield strength) of the steel sheet to an appropriate relationship based on ultra-low carbon steel, which generally has a high r value and excellent formability. The present inventors have found that a crown steel plate excellent in workability and pressure strength that enables reduction of the defect rate and securing of pressure strength can be obtained.

  Moreover, the chemical composition, the hot rolling conditions, the cold rolling conditions, the continuous annealing conditions, and the secondary cold rolling conditions were studied, and the production conditions for obtaining the above steel sheet were found.

  The present invention has been made based on the above findings, and the gist thereof is as follows.

(1) By mass%, C: 0.0005 to 0.0050%, Si: 0.02% or less, Mn: 0.10 to 0.60%, P: 0.02% or less, S: 0.02 %: Al: 0.01 to 0.10 %, N: 0.0050% or less, Nb: 0.010 to 0.050%, the balance having a component composition consisting of Fe and inevitable impurities The average value of TS (tensile strength) in the rolling direction of the steel sheet and the TS in the direction perpendicular to the rolling is 500 MPa or more, and the average value of YP (yield strength) in the rolling direction and YP in the direction perpendicular to the rolling A steel plate for a crown excellent in workability, characterized in that a certain average YP and the average TS satisfy a relationship of average YP (MPa) ≦ 130 + 0.746 × average TS (MPa).

  (2) Further, by mass%, it contains at least one selected from Cu: 0.2% or less, Ni: 0.15% or less, Cr: 0.10% or less, and Mo: 0.05% or less. A steel plate for a crown having excellent workability as described in (1).

  (3) The steel plate for a crown having excellent workability as described in (1) or (2), further comprising Sn: less than 0.0050% by mass.

(4) A method for manufacturing a steel plate for a crown excellent in workability according to any one of (1) to (3),
A hot rolling process in which hot rolling is performed on a steel slab under conditions where the slab reheating temperature is 1150 ° C. or higher and 1350 ° C. or lower, the finishing temperature is 870 ° C. or higher and 950 ° C. or lower, and the winding temperature is 590 ° C. or higher and 730 ° C. or lower. And after the hot rolling step, pickling and primary cold rolling in which the rolling reduction is primary cold rolling under conditions of 80% or more and 95% or less, and after the primary cold rolling step, 710 ° C. or higher and 790 ° C. A recrystallization annealing step for recrystallization annealing under the following conditions, and a secondary cold rolling step for secondary cold rolling at a reduction rate of 25% to 50% after the recrystallization annealing step. A method for producing a steel plate for a crown having excellent processability.

  (5) A crown formed by forming the crown steel plate according to any one of (1) to (3).

  The crown steel plate of the present invention has a specific component composition, the average TS of the steel plate in the rolling direction TS and the average TS in the rolling perpendicular direction is 500 MPa or more, YP in the rolling direction and the rolling perpendicular direction Since average YP (yield strength), which is an average value of YP, and average TS satisfy the relationship of average YP (MPa) ≦ 130 + 0.746 × average TS (MPa), it has extremely excellent formability and pressure strength. For this reason, according to this invention, even if it reduces the plate | board thickness of the steel plate for crowns conventionally, it becomes possible to obtain a crown provided with sufficient proof strength. Thereby, resource saving, environmental load reduction and cost reduction can be achieved.

It is a figure which shows the pleat shape of a crown.

  Hereinafter, modes for carrying out the present invention will be described. In addition, this invention is not limited to the following embodiment.

  The inventors obtained the following new knowledge about the mechanical characteristics that the steel plate for a crown should have by examining the forming process of the crown in detail in completing the present invention.

  In forming the crown, the central portion is squeezed in the initial stage of molding, and then the outer edge portion is formed into a pleated shape. The mold used in this molding is as follows. The punch and wrinkle presser are solid cylindrical punches and hollow cylindrical wrinkle pressers that are the same as in general drawing. A drawing die is a flat die used for general drawing, which is provided with a circular hole. However, the difference from drawing is that a pleated shape is formed. It is having the groove | channel along the radial direction. The structure of the drawing die with such a groove is indispensable to form a unique pleat shape in the crown. However, wrinkle pressing pressure does not act on the groove portion, so wrinkles are likely to occur, and the pleat shape tends to be uneven. In a thinned steel plate, wrinkles are more likely to occur, and the pleat shape tends to be uneven. Here, the non-uniform shape means that the shape of each pleat extending from the outer periphery of the crown upper surface 1 which is usually 21 places is not substantially constant, specifically, the height L of the fold portion 2 shown in FIG. The standard deviation is greater than 0.1 mm. The inventors examined the mechanical properties of a steel sheet that obtains a uniform pleat shape in such forming. As a result, the inventors have found that it is necessary to avoid an excessively high YP (yield strength) of the steel sheet in order to suppress the generation of wrinkles. Further, when TS (tensile strength) was low, there was a problem that the steel sheet was broken at the groove portion of the die during the formation of the pleats. From the above, it was concluded that the steel sheet for crowns must have an appropriate relationship between the average YP (yield strength) and the average TS (tensile strength) while having an appropriate TS (tensile strength). . Hereinafter, the crown steel plate of the present invention will be described in the order of component composition, material, and manufacturing method, and finally, the crown formed by using the crown steel plate of the present invention will be described.

<Ingredient composition>
The crown steel plate of the present invention is in mass%, C: 0.0005 to 0.0050%, Si: 0.02% or less, Mn: 0.10 to 0.60%, P: 0.02% or less, S: 0.02% or less, Al: 0.01 to 0.10 %, N: 0.0050% or less, Nb: 0.010 to 0.050%, with the balance being Fe and inevitable impurities It has an ingredient composition. Hereinafter, each component will be described. In the description of each component, “%” means “mass%”.

C: 0.0005 to 0.0050%
In the present invention, it is necessary that the average YP (yield strength) and the average TS (tensile strength) have an appropriate relationship. Although the specific relationship between the two will be described later, YP needs to be moderately low with respect to TS. In order to obtain the characteristics, it is necessary to eliminate the factor that makes YP a value close to TS. Specifically, it is necessary to suppress an increase in YP that occurs when a steel sheet is painted, that is, age hardening. Since age hardening is mainly expressed by solute C, it is necessary to suppress solute C as much as possible in the steel sheet of the present invention. For that purpose, it is necessary to reduce the C content, specifically 0.0050% or less. Accordingly, the C content is set to 0.0050% or less. In consideration of ensuring better shape uniformity, the C content is preferably 0.0035% or less, more preferably 0.0023% or less.

  On the other hand, in the present invention, it is necessary to provide a moderately high TS (tensile strength). When C is small, the TS required in the present invention cannot be obtained. For this reason, C content makes 0.0005% a minimum. Furthermore, the C content desirable for securing TS is 0.0015% or more.

Si: 0.02% or less Si is an element effective for improving TS by solid solution strengthening. However, when Si is contained excessively, Si is concentrated on the surface of the steel sheet, leading to a decrease in corrosion resistance of the steel sheet. The decrease in corrosion resistance is a fatal defect for crown steel sheets containing beverages. Therefore, in the present invention, the Si content is not more than 0.02% in order to prevent deterioration of corrosion resistance without using the effect of Si for improving TS.

Mn: 0.10 to 0.60%
In the present invention, since the crown steel plate needs to have a reasonably high TS, it is necessary to add Mn which is effective for improving TS by solid solution strengthening. However, in the ladle analysis value of the American Society for Testing and Materials (ASTM A623M-10), the upper limit of the Mn content of the tin plate used for ordinary food containers is defined as 0.60%. From the above, the Mn content of the present invention is set to 0.60% or less. From the relationship between the average YP and the average TS, the upper limit of the Mn content is desirably 0.30%. Further, Mn forms S and MnS contained in the steel, and has an effect of preventing a decrease in hot ductility due to S. In order to obtain these effects, the Mn content needs to be 0.10% or more.

P: 0.02% or less P is an element effective for improving TS by solid solution strengthening. However, if the steel plate for crowns contains P excessively, P will concentrate on the surface of the steel plate, leading to a decrease in corrosion resistance of the steel plate. The decrease in corrosion resistance is a fatal defect for crown steel sheets containing beverages. For this reason, in this invention, the effect of P is not used for improvement of TS, but P content is made into 0.02% or less in the meaning which prevents deterioration of corrosion resistance.

S: 0.02% or less S combines with Fe in steel to form FeS, and reduces the hot ductility of the steel. When the hot ductility is reduced, the steel is cracked during the casting and hot rolling of the steel, and the iron oxide generated in the cracked portion is pressed into the steel during the hot rolling process to cause surface defects. The surface defect hinders the appearance of the crown steel plate and can also be a starting point of cracking or corrosion in forming. Thus, the surface defect may be a fatal problem. In order to prevent this, a technique of depositing S as MnS is effective. From the relationship with the Mn content, the S content in the present invention is 0.02% or less. On the other hand, if the S content is too low, the risk of pitting corrosion may increase. In order to prevent this, an S content of 0.008% or more is desirable.

Al: 0.01-0.10 %
Al is an element originally added as a deoxidizer. Further, when Al forms N and AlN, solid solution N in the steel decreases. In the present invention, it is necessary that the average YP (yield strength) and the average TS (tensile strength) have an appropriate relationship. That is, as described in the explanation of C, the average YP needs to be moderately lower than the average TS, and for this purpose, it is necessary to suppress age hardening. Since age hardening is manifested by solute N in addition to solute C, it is necessary to suppress solute N as much as possible in the steel sheet of the present invention. Therefore, it is necessary to set the Al content necessary for forming AlN. If the Al content is less than 0.01%, a sufficient deoxidizing effect or a solid solution N reducing effect cannot be obtained. For this reason, the lower limit of the Al content is set to 0.01%. On the other hand, if the Al content exceeds 0.10%, not only is the above effect saturated, but also inclusions such as alumina increase, such being undesirable. Inclusions can also be the starting point of surface defects, cracks in molding, or starting points of corrosion, leading to the occurrence of fatal defects. In order to prevent this, the upper limit of the Al content is 0.10%.

N: 0.0050% or less In the present invention, it is necessary that the average YP (yield strength) and the average TS (tensile strength) have an appropriate relationship. Therefore, the average YP needs to be moderately lower than the average TS, and for this purpose, it is necessary to suppress age hardening. Since age hardening is manifested by solute N in addition to solute C, it is necessary to suppress solute N as much as possible in the steel sheet of the present invention. Therefore, the upper limit of the N content is set to 0.0050% or less from the relationship with the Al content. On the other hand, inclusion of inclusions may occur if the molten steel treatment is excessively performed in order to excessively reduce the N content. Therefore, the lower limit of the N content is preferably 0.0010% or more.

Nb: 0.010 to 0.050%
Nb has the effect of forming C and NbC in the steel sheet and reducing solute C necessary for obtaining the characteristics of the present invention. Moreover, Nb has the effect of refining which suppresses the grain growth in hot rolling, and contributes to obtaining a moderately high TS. The lower limit of the Nb content for obtaining these effects is set to 0.010%. On the other hand, when the Nb content increases, the recrystallization temperature rises, so that non-recrystallization occurs after annealing. As a result, YP increases, and the relationship between average YP and average TS defined in the present invention cannot be obtained. Therefore, the upper limit of Nb content is 0.050%.

  The balance other than the above components is Fe and inevitable impurities. However, according to ASTM (A623M-10), the impurity element is 0.02% or less. Examples of the impurity element include V, B, Ca, Zn, Co, As, and the like.

  Cu, Ni, Cr, and Mo may be contained within a range that does not impair the effects of the present invention. However, according to ASTM (A623M-10), Cu is 0.2% or less, Ni is 0.15% or less, Cr is 0.10% or less, and Mo is 0.05% or less.

  Moreover, you may contain Sn in the range which does not impair the effect of this invention. However, when Sn is contained in a large amount, the average r value of the steel sheet decreases. Since the molding of the crown involves drawing, it is desirable that the r value is high. From this viewpoint, the upper limit of the Sn content when Sn is contained is desirably 0.0050%.

<Material>
The crown steel plate of the present invention has an average TS (tensile strength) of 500 MPa or more, which is an average value of TS (tensile strength) in the rolling direction and TS in the direction perpendicular to the rolling direction, and YP (yield strength) in the rolling direction. The average YP which is an average value of YP in the direction perpendicular to the rolling and the average TS satisfies the relationship of average YP (MPa) ≦ 130 + 0.746 × average TS (MPa).

  As a result of studying the mechanical properties necessary for obtaining a uniform pleat shape in the formation of the crown, the inventors have found that it is necessary to avoid that the YP (yield strength) of the steel sheet is excessively high. Further, when TS (tensile strength) was low, there was a problem that the steel sheet was broken at the groove portion of the die during the formation of the pleats. From the above, the inventors have come to the knowledge that YP and TS can be taken into consideration, and further, in order to take into account, it has come to the finding that the average YP and the average TS in the rolling direction and the direction perpendicular to the rolling may be used. And it came to the conclusion that the steel plate for crowns had moderate average TS (tensile strength), and average YP (yield strength) and average TS (tensile strength) needed to have an appropriate relationship. Here, YP and TS of the steel plate are obtained by a tensile test according to JIS Z 2241.

  From the above examination, the average TS (tensile strength) of the steel sheet is set to 500 MPa or more. That is, if the average TS (tensile strength) is less than 500 MPa, the steel sheet breaks at the groove portion of the die during the formation of the pleats.

  Further, the relationship between the average YP and the average TS is defined as average YP (MPa) ≦ 130 + 0.746 × average TS (MPa). That is, the relationship between the above average YP and average TS is that the steel sheet avoids excessively high average YP and the condition that the steel sheet avoids breakage in the groove portion of the die during the formation of pleats when the average TS is low. It is. In addition, since the steel plate for crowns is formed into a crown after being coated, the above mechanical characteristics are values measured after heat treatment at 210 ° C. for 20 minutes as a coating baking process.

  In addition, as described above, it is possible to represent the characteristics of the steel plate for the crown by the average YP and the average TS. The values of YP in the rolling direction, YP in the direction perpendicular to the rolling, TS in the rolling direction, and TS in the direction perpendicular to the rolling are particularly Although not limited, YP in the rolling direction is in the range of 450 to 640 MPa, YP in the direction perpendicular to the rolling is in the range of 510 to 740 MPa, TS in the rolling direction is in the range of 470 to 650 MPa, and TS in the direction perpendicular to the rolling is It is preferably in the range of 530 to 750 MPa.

  In addition, the moldability of the crown is affected by the plate thickness. In crown molding, a die having grooves along the radial direction of a circle is used from the periphery of a circular hole to the flat plate portion. The structure of this die is indispensable for forming a unique pleat shape on the crown, but wrinkles are not easily applied to the groove portion, so that wrinkles are likely to occur, and the pleat shape tends to be uneven. In a thinned steel plate, wrinkles are more likely to occur, and the pleat shape tends to be uneven. In addition, the pressure resistance of the crown is naturally affected by the plate thickness, and if the plate thickness is too thin, the pressure strength is lowered and the function as the crown cannot be achieved. From the above viewpoint, the plate thickness is desirably 0.14 mm or more. On the other hand, from the viewpoint of saving resources by reducing the thickness of the steel plate for crowns, reducing environmental burdens, and reducing material costs, the thickness of the steel plates is aimed to be thinner than 0.22 mm, which is the current plate thickness of crown steel plates. The desirable plate thickness for obtaining the above effect is 0.18 mm or less. In the present invention, even a steel plate having a thickness of 0.18 mm or less, which has heretofore been very difficult to form a crown, can be preferably used for forming a crown.

<Manufacturing method>
Next, an example of a method for producing a crown steel plate excellent in workability of the present invention will be described.

  The crown steel plate of the present invention can be manufactured by a method having the following hot rolling step, primary cold rolling step, recrystallization annealing step, and secondary cold rolling step. Hereinafter, each step will be described.

Hot rolling process Hot rolling is performed on the steel slab having the above component composition. The slab reheating temperature is 1150 ° C. or higher and 1350 ° C. or lower, the finishing temperature is 870 ° C. or higher and 950 ° C. or lower, and the winding temperature is 590 ° C. or higher and 730 ° C. or lower.

  The mechanical properties defined in the present invention can be obtained by controlling the formation of precipitates such as NbC, AlN, MnS, etc. by the steel components and the production method. If the slab reheating temperature is too low, the precipitation state of the precipitate affected by fluctuations in the casting and cooling processes of the steel slab cannot be made uniform. Therefore, the slab heating temperature is 1150 ° C. or higher. On the other hand, if the slab heating temperature is too high, precipitates grow excessively and the mechanical properties cannot be controlled within the scope of the present invention. Therefore, slab heating temperature shall be 1350 degrees C or less. On the other hand, if the slab heating temperature is too low, it will be difficult to ensure the finish rolling temperature of the hot rolling, and if the heating temperature is too high, the steel surface will be excessively oxidized and surface defects will easily occur. For this reason, the slab heating temperature is desirably 1180 ° C. or higher and 1300 ° C. or lower.

  In order to obtain the mechanical characteristics defined in the present invention, it is necessary to adjust the hot rolling conditions. As for the finishing temperature, if the temperature is too low, a partial ferrite structure is formed in the steel, and the strength is lowered by coarsening the part in the process after the finish rolling, and the mechanical characteristics defined in the present invention are obtained. Absent. Therefore, finishing temperature shall be 870 degreeC or more. On the other hand, if the finishing temperature is too high, crystal grains are coarsened throughout the steel and the strength is lowered, and the mechanical properties defined by the present invention cannot be obtained. Therefore, finishing temperature shall be 950 degrees C or less. Desirably, finishing temperature is 890 degreeC or more and 930 degrees C or less.

  Regarding the coiling temperature, if the coiling temperature is too low, NbC and AlN are not sufficiently precipitated, and solid solution C and solid solution N remain. As a result, the provisions of the present invention, particularly the provisions relating to YP, are not satisfied. Therefore, the winding temperature is set to 590 ° C. or higher. On the other hand, if the coiling temperature is too high, the crystal grains are coarsened and the strength is lowered, and the mechanical characteristics defined in the present invention cannot be obtained. Therefore, the winding temperature is set to 730 ° C. or lower. Desirably, the coiling temperature is 620 ° C. or higher and 710 ° C. or lower.

Primary cold rolling step After the hot rolling step, pickling is performed, and primary cold rolling is performed under a condition where the rolling reduction is 80% or more and 95% or less.

  Pickling is not particularly limited as long as the surface scale can be removed. Pickling can be performed by a commonly performed method.

  If the rolling reduction of primary cold rolling is too low, the crystal grains formed by hot rolling cannot be sufficiently deformed. As a result, the recrystallized grains formed during the recrystallization annealing become coarse, and the mechanical characteristics defined by the present invention cannot be obtained. Therefore, the reduction ratio of primary cold rolling is 80% or more. On the other hand, if the rolling reduction is too high, the crystal grains become too fine, and the mechanical properties defined by the present invention, particularly the average YP, become excessively high. Therefore, the reduction ratio of primary cold rolling is set to 95%. Desirably, it is 86% or more and 92% or less.

Recrystallization annealing process After a primary cold rolling process, recrystallization annealing is performed on conditions of 710 degreeC or more and 790 degrees C or less.

  The annealing method is preferably a continuous annealing method from the viewpoint of material uniformity and productivity. If the annealing temperature in continuous annealing is too low, complete recrystallization cannot be obtained, and it becomes excessively hard and mechanical properties, particularly average YP, defined in the present invention are excessive. Therefore, annealing temperature shall be 710 degreeC or more. On the other hand, if the annealing temperature is too high, the crystal grains become coarse and the average TS defined in the present invention cannot be obtained. Therefore, annealing temperature shall be 790 degrees C or less. Desirably, it is 730 degreeC or more and 780 degrees C or less. The soaking time at the annealing temperature is preferably 10 seconds or more and 90 seconds or less.

Secondary cold rolling process After the recrystallization annealing process, secondary cold rolling is performed under conditions of a rolling reduction of 25% or more and 50% or less.

  After annealing, secondary cold rolling is performed for thinning of the steel sheet and final adjustment of mechanical properties. Secondary cold rolling is a particularly important production condition in the present invention. If the rolling reduction here is too low, the mechanical characteristics of the present invention, particularly the average TS, will not be an appropriate value. Therefore, the rolling reduction of secondary cold rolling is 25% or more. On the other hand, if the rolling reduction is too high, the steel sheet becomes excessively hard, and YP defined by the present invention cannot be obtained. Therefore, the reduction ratio of secondary cold rolling is set to 50% or less. Desirably, it is 30% or more and 48% or less.

  As described above, the crown steel plate of the present invention is obtained. In addition, before shape | molding in a crown, it is preferable to perform the following surface treatment with respect to the steel plate after secondary cold rolling. The steel plate subjected to the following surface treatment is also a crown steel plate of the present invention.

Surface Treatment Various surface treatments may be applied to the steel sheet surface of the steel sheet after the secondary cold rolling. For example, a method of forming at least one of tin plating, chromium plating, and nickel plating by a general plating method such as electroplating can be given.

  Steels containing the component compositions A to N shown in Table 1 with the balance being Fe and inevitable impurities were melted to obtain steel slabs. Here, it is confirmed that the Sn content in any of the steel slabs from A to N is less than 0.0050%.

  Using the obtained steel slab, a thin steel plate having a thickness of 0.14 to 0.18 mm was manufactured under the manufacturing conditions shown in Table 2.

  The steel plate obtained by the above manufacturing method was subjected to chromium (tin-free) plating as a surface treatment. Next, heat treatment was performed at 210 ° C. for 20 minutes as a simulation of paint baking treatment, and the mechanical characteristics were investigated under the following test conditions.

  The tensile test is performed in accordance with JIS Z 2241 using a JIS No. 5 size tensile test piece, and after measuring YP and TS in the rolling direction and the direction perpendicular to the rolling direction of the steel sheet, the average YP and average TS are obtained from the results. Calculated. Moreover, the calculated value of the upper limit of average YP was computed from 130 + 0.746x average TS (MPa).

  In each of the invention examples, YP in the rolling direction is in the range of 450 to 640 MPa, YP in the direction perpendicular to the rolling is in the range of 510 to 740 MPa, TS in the rolling direction is in the range of 470 to 650 MPa, and rolling right angle The direction TS is in the range of 530-750 MPa.

  Furthermore, the crown was shape | molded using the obtained steel plate. Depending on the presence or absence of breakage at the time of crown molding, no breakage was judged as pass (◯), and breakage was judged as failure (x). Further, the length of each pleat of the crown (L in FIG. 1) was measured for the obtained crown, and the one with a standard deviation σ of L value of 0.1 mm or less passed (◯), 0.1 mm A product exceeding 1 was regarded as rejected (x). This was evaluated as shape uniformity.

  In addition, the pressure resistance (pressure strength) is determined in accordance with JIS S 9017 by performing a pressure resistance test after plugging into a bottle, with a result of 115 PSI or higher as pass (◯) and a value of less than 115 PSI as reject (x). . The results are shown in Table 3.

  No. For No. 1, the average TS was below the specified value, and fracture occurred during crown molding. This is because the secondary rolling was performed at a low reduction rate that is less than the standard.

  No. For No. 3, the average TS satisfied the rules and no breakage occurred during crown molding, but the relationship between the average TS and the average YP did not satisfy the specified formula, the shape was inferior in uniformity, and the pressure strength was also met. There wasn't. This is because the secondary rolling was performed at a high rolling reduction exceeding the regulation.

  No. For No. 6, the average TS satisfied the rule and no fracture occurred during the crown molding, but the relationship between the average TS and the average YP did not satisfy the prescribed formula, the shape was inferior in uniformity, and the pressure strength was also met. There wasn't. This is because excessive hardening was caused because the Nb amount was added exceeding the specified amount.

  No. For No. 7, the average TS satisfied the rule and no fracture occurred during the crown molding, but the relationship between the average TS and the average YP did not satisfy the prescribed formula, the shape was inferior in uniformity, and the compressive strength was also met. There wasn't. This is because solid solution C could not be reduced as a result of not containing Nb.

  No. No. 8 did not cause breakage during crown molding even though the average TS was less than the standard, and the average YP satisfied the standard and the shape uniformity was excellent, but it did not meet the standard of the pressure strength. This is because the steel sheet was softened because the annealing temperature was excessively high. Although it was soft and had excellent ductility, it did not break during crown molding. However, because the steel plate was soft, the crown itself could not withstand the internal pressure even though the shape was uniform.

  No. No. 10, the average TS satisfies the regulations, and no breakage occurred during crown molding, but the relationship between the average TS and the average YP does not satisfy the prescribed formula, the shape uniformity is inferior, and the pressure strength is also less than the standard It was. This is because the annealing temperature is excessively low, so that sufficient recrystallization cannot be obtained and the steel sheet is excessively hardened.

  No. In No. 14, the average TS was less than the specified value, and fracture occurred during crown molding. This is because the slab heating temperature is excessively high and the precipitates cannot be controlled according to the purpose of the present invention.

  No. No. 15, the average TS satisfies the regulations, and no breakage occurred during crown molding, but the relationship between the average TS and the average YP does not satisfy the prescribed formula, the uniformity of the shape is inferior, and the compressive strength is also met. There wasn't. This is because excessive hardening was caused because the Nb amount was added exceeding the specified amount.

  No. In No. 16, the average TS satisfied the standard, and no fracture occurred during the crown molding, but the relationship between the average TS and the average YP did not satisfy the specified formula and the shape was inferior in uniformity, and the pressure strength was also satisfied There wasn't. This is because Nb was not included and solid solution C could not be reduced.

  No. For No. 17, the average TS satisfied the rule and no fracture occurred during the crown molding, but the relationship between the average TS and the average YP did not satisfy the specified formula, the shape was inferior in uniformity, and the compressive strength was also met. There wasn't. This is because C was added in excess of the standard and solid solution C could not be reduced.

  No. In No. 18, the average TS satisfied the standard, and no fracture occurred during the crown molding, but the relationship between the average TS and the average YP did not satisfy the standard formula, and the shape was inferior in uniformity, and the compressive strength was also the standard. There wasn't. This is because C and Nb were added in excess of the specified amount, so solid solution C could not be reduced, and the recrystallization temperature rose due to the effect of Nb, and recrystallization during annealing did not occur sufficiently. is there.

  No. In No. 19, the average TS satisfied the standard, and no fracture occurred during the crown molding, but the relationship between the average TS and the average YP did not satisfy the standard formula, the shape was inferior in uniformity, and the compressive strength was also satisfied. There wasn't. This is because C was added in excess of the standard, and Nb for fixing the solid solution C was not added, and the solid solution C could not be reduced.

  No. In No. 20, the average TS satisfied the rule, and no fracture occurred during the crown molding, but the relationship between the average TS and the average YP did not satisfy the specified formula, the shape was inferior in uniformity, and the compressive strength was also met. There wasn't. This is because C was added in excess of the standard, and Nb for fixing the solid solution C was not added, and the solid solution C could not be reduced.

  No. No. 22 does not break during crown molding even though the average TS is less than the specified value, and the relationship between the average TS and the average YP satisfies the specified formula and has excellent shape uniformity. The standard was not met. This is because the coiling temperature is excessively high and the steel sheet is softened. Although it was soft and had excellent ductility, it did not break during crown molding. However, because the steel plate was soft, the crown itself could not withstand the internal pressure even though the shape was uniform.

  No. No. 23, no fracture occurred during crown molding even though the average TS was less than specified, and the relationship between the average TS and average YP met the specified formula and the shape uniformity was excellent. The standard was not met. This is because the primary cold rolling reduction is less than specified, and the crystal grains are coarsened and softened.

  No. In No. 27, the average TS satisfied the rule, and no fracture occurred during the crown molding, but the relationship between the average TS and the average YP did not satisfy the specified formula, the shape was inferior in uniformity, and the pressure strength was also met. There wasn't. This is because the steel sheet was excessively hardened because the Nb amount was added exceeding the specified amount.

  No. No. 28 did not cause breakage during crown molding even though the average TS was less than the specified value, and the relationship between the average TS and the average YP satisfied the specified formula and had excellent shape uniformity. The standard was not met. This is because the hot-rolling finishing temperature is less than specified, the hot-rolled steel sheet is coarsened, and the steel sheet is excessively softened.

  No. No. 29 did not cause breakage during crown molding even though the average TS was less than the specified value, and the average YP satisfied the specified value and the shape uniformity was excellent, but it did not meet the standard of pressure strength. This is because the hot-rolling finishing temperature exceeded the standard, and the steel sheet was excessively softened.

  No. No. 30 caused breakage during crown molding despite the average TS meeting the requirements. This is because the steel sheet became excessively hard because the primary cold rolling reduction ratio exceeded the specified level, and the crystal grains became non-uniform, resulting in deterioration of material uniformity.

  No. In No. 32, breakage occurred during crown molding even though the average TS satisfied the specification. This is because N was added in excess of the specified amount, so that the solid solution N increased and the steel sheet was excessively hardened.

  No. In No. 33, breakage occurred during crown molding despite the fact that the average TS exceeded the specified value. This is because C was added exceeding the specified amount, so that the solid solution C increased and the steel sheet was excessively hardened.

  No. other than the above. 2, 4, 5, 9, 11, 12, 13, 21, 24, 25, 26, 31 all conform to the components, mechanical properties, and manufacturing conditions defined in the present invention, A crown with excellent pressure strength was obtained.

1 crown top surface 2 fold part L fold height

Claims (5)

In mass%, C: 0.0005 to 0.0050%, Si: 0.02% or less, Mn: 0.17 to 0.30 %, P: 0.02% or less, S: 0.02% or less, Al: 0.01 to 0.10 %, N: 0.0050% or less, Nb: 0.010 to 0.050%, the balance having a component composition consisting of Fe and inevitable impurities,
The average TS, which is the average value of the TS (tensile strength) in the rolling direction of the steel sheet and the TS in the direction perpendicular to the rolling, is 500 MPa or more,
The average YP, which is an average value of YP (yield strength) in the rolling direction and YP in the direction perpendicular to the rolling, and the average TS satisfy the relationship of average YP (MPa) ≦ 130 + 0.746 × average TS (MPa). A steel plate for crowns with excellent processability.   Furthermore, it is characterized by containing at least one selected from Cu: 0.2% or less, Ni: 0.15% or less, Cr: 0.10% or less, and Mo: 0.05% or less in mass%. The steel plate for crowns excellent in workability of Claim 1.   Furthermore, the steel plate for crowns excellent in workability of Claim 1 or 2 characterized by containing Sn: less than 0.0050% by the mass%. It is a manufacturing method of the steel plate for crowns excellent in workability in any one of claims 1-3,
A hot rolling process in which hot rolling is performed on a steel slab under conditions where the slab reheating temperature is 1150 ° C. or higher and 1350 ° C. or lower, the finishing temperature is 870 ° C. or higher and 950 ° C. or lower, and the winding temperature is 590 ° C. or higher and 730 ° C. or lower. When,
After the hot rolling step, pickling, and a primary cold rolling step of primary cold rolling under conditions where the rolling reduction is 80% or more and 95% or less,
After the primary cold rolling step, a recrystallization annealing step of recrystallization annealing under conditions of 710 ° C. or higher and 790 ° C. or lower;
A secondary cold rolling step of performing secondary cold rolling under conditions of a rolling reduction of 25% or more and 50% or less after the recrystallization annealing step, and a method for producing a steel plate for a crown having excellent workability .   The crown formed by shape | molding the steel plate for crowns in any one of Claims 1-3.

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