JPWO2013151085A1 - High-strength, high-workability steel sheet and manufacturing method - Google Patents

Abstract

The high-strength, high-workability steel sheet is steel sheet mass%, C: more than 0.020% and less than 0.040%, Si: 0.003% to 0.100%, Mn: 0.10% to 0.60% P: 0.001% or more and 0.100% or less, S: 0.001% or more and 0.020% or less, Al: 0.005% or more and 0.100% or less, N: more than 0.0130% 0170% or less, the balance is made of Fe and inevitable impurities, the tensile strength in the rolling direction is 520 MPa or more, the Erichsen value is 5.0 mm or more, and has a resin film layer at least on the side that becomes the inner surface of the can .

Description

  The present invention relates to a high-strength, high-workability steel sheet suitable for application to an easy open end steel sheet and a method for producing the same.

  Among steel plates used for beverage cans and food cans, steel plates called DR (Double Reduce) materials are sometimes used for lids, bottoms, three-piece can bodies, drawn cans, and the like. The DR material manufactured by the DR method in which cold rolling is performed again after annealing is easier to reduce the plate thickness than the SR (Single Reduce) material manufactured only by temper rolling with a small rolling rate. . For this reason, can-making cost can be reduced by using DR material. On the other hand, according to the DR method, work hardening occurs by performing cold rolling again after annealing, so that a thin and hard steel plate can be manufactured, but on the other hand, it is inferior in workability as compared with the R material.

  As a lid for beverage cans and food cans, EOE (Easy Open End), which can be easily opened, is widely used. When manufacturing the EOE, it is necessary to form a rivet for attaching a tab to hang a finger by an overhanging process. On the other hand, a steel plate as a can-making material is required to have a strength corresponding to the plate thickness. In the case of a DR material, a tensile strength of about 520 MPa or more is required in order to ensure an economic effect by making it thin. Since it is difficult for the conventional DR material to achieve both the workability and strength as described above, the SR material has been used for EOE. However, at present, there is an increasing demand for applying DR material to EOE from the viewpoint of cost reduction.

  Against this background, Patent Document 1 discloses a rivet formability characterized in that the carbon content is 0.02% or less and the boron content is in the range of 0.010 to 0.020%. An excellent easy open can lid steel sheet and a method for producing the steel sheet characterized by performing secondary cold rolling at a rolling reduction of 30% or less are disclosed. Patent Document 2 discloses a DR material characterized in that the average rankford value after aging treatment is 1.0 or less, and this DR material is excellent in rivet formability of EOE. Is stated.

Japanese Patent No. 3740779 International Publication No. 2008/018531

  However, all of the above conventional techniques have problems. That is, the greater the diameter of the can lid to be applied, the greater the strength required for the steel sheet. However, since the steel sheet described in Patent Document 1 has a low carbon content, the nitrogen content is intended to obtain a large strength. Need to be larger. However, since this steel sheet contains a certain amount or more of boron, when the nitrogen content increases, the high temperature ductility decreases and slab cracking occurs during continuous casting. For this reason, the steel sheet described in Patent Document 1 cannot be applied to a large-diameter EOE.

  On the other hand, the steel sheet described in Patent Document 2 achieves good rivet formability by reducing the average Rankford value. However, this method is effective only when a rivet is formed by a nearly cylindrical projecting process, and when the rivet is formed by a nearly spherical projecting process, the rivet formability becomes insufficient. . Therefore, it has been expected to provide a high-strength and high-workability steel sheet having a tensile strength of 520 MPa or more and an Erichsen value of 5.0 mm or more.

  The present invention has been made in view of the above problems, and its purpose is to provide a high strength and high workability steel sheet having a tensile strength of 520 MPa or more and an Erichsen value of 5.0 mm or more. It is providing the high workability steel plate and its manufacturing method.

  Inventors of the present invention, as a result of earnest research, in order to achieve both the workability and strength of the steel sheet, while limiting the carbon content to an appropriate range, while preventing deterioration of workability, It has been found that it is effective to secure the strength by increasing the nitrogen content and to limit the secondary cold rolling rate after annealing to an appropriate range. In addition, the inventors of the present invention need to limit the coiling temperature to an appropriate temperature range because the cementite deposited becomes coarse and the local elongation decreases when the coiling temperature after hot rolling is high. I found out. Furthermore, the inventors of the present invention have found that providing a resin film layer having an appropriate thickness on the side that becomes the inner surface of the can significantly improves the rivet formability by overhanging.

  The high-strength, high-workability steel sheet according to the present invention is, in mass%, C: more than 0.020% and less than 0.040%, Si: 0.003% to 0.100%, Mn: 0.10% to 0 .60% or less, P: 0.001% to 0.100%, S: 0.001% to 0.020%, Al: 0.005% to 0.100%, N: 0.0130% More than 0.0170% is contained, the remainder is made of Fe and inevitable impurities, has a resin film layer on at least the inner surface of the can, has a tensile strength in the rolling direction of 520 MPa or more, and an Erichsen value of 5. It is 0 mm or more.

  The thickness of the resin film layer is desirably in the range of 5 to 100 μm.

  The manufacturing method of the high-strength, high-workability steel sheet according to the present invention is, in mass%, C: more than 0.020% and less than 0.040%, Si: 0.003% to 0.100%, Mn: 0.10 %: 0.61% or less, P: 0.001% or more and 0.100% or less, S: 0.001% or more and 0.020% or less, Al: 0.005% or more and 0.100% or less, N: 0 .0130% and 0.0170% or less, the balance being Fe and inevitable impurities made into steel as a slab by continuous casting, slab reheating temperature is 1150 ° C or higher and hot rolling is performed at a temperature of 600 ° C or lower , Followed by primary cold rolling, followed by continuous annealing at a soaking temperature of 600 to 700 ° C. and a soaking time of 10 to 50 seconds, and then secondary cooling at a rolling rate of 8.0 to 15.0%. Hot-rolled and surface-treated film by electrolytic method Paste the resin film on the side where the at least can inner After forming, the tensile strength in the rolling direction is not less than 520 MPa, characterized in that to produce a steel sheet Erichsen value is 5.0mm or more.

  According to the high-strength and highly workable steel sheet and the manufacturing method thereof according to the present invention, a high-strength and highly workable steel sheet having a tensile strength of 520 MPa or more and an Erichsen value of 5.0 mm or more can be obtained. As a result, cracks do not occur during rivet molding of EOE, and it is possible to make a lid made of a DR material having a thin plate thickness, thereby realizing a significant reduction in the thickness of the EOE steel plate.

  Hereinafter, the present invention will be described in detail.

  The high-strength, high-workability steel sheet according to the present invention can be applied to an easy open-end steel sheet having a tensile strength of 520 MPa or more and an Erichsen value of 5.0 mm or more. Such a steel sheet uses steel containing less than 0.040% carbon, sets the coiling temperature after hot rolling and the secondary cold rolling rate to appropriate conditions, and further becomes the inner surface of the can It becomes possible to manufacture by sticking a resin film on the substrate. Hereinafter, the component composition of the high-strength, high-workability steel sheet according to the present invention will be described.

[Component composition of high-strength, high-workability steel sheet]
(1) C: More than 0.020% and less than 0.040% In the high-strength, high-workability steel sheet according to the present invention, high workability is exhibited by keeping the C (carbon) content low. If the C content is 0.040% or more, the steel sheet becomes excessively hard, and it becomes impossible to produce a thin steel sheet by secondary cold rolling while ensuring workability. For this reason, the upper limit of the C content is less than 0.040%. On the other hand, if the C content is 0.020% or less, the tensile strength 520 MPa necessary for obtaining a remarkable economic effect due to the thinning of the steel sheet cannot be obtained. For this reason, the lower limit of the C content is over 0.020%.

(2) Si: 0.003% or more and 0.100% or less When the content of Si (silicon) exceeds 0.100%, problems such as deterioration of surface treatment property and deterioration of corrosion resistance are caused. For this reason, the upper limit of the Si content is set to 0.100%. On the other hand, the refining cost becomes excessive to make the Si content less than 0.003%. For this reason, the lower limit of the Si content is set to 0.003%. A preferable Si content is in the range of 0.003% to 0.035%.

(3) Mn: 0.10% or more and 0.60% or less Mn (manganese) has a function of preventing red heat embrittlement during hot rolling due to S (sulfur) and refining crystal grains. It is an element necessary for securing. In order to exert these effects, it is necessary to add at least 0.10% of Mn. On the other hand, when Mn is added in a large amount, the corrosion resistance is deteriorated and the steel sheet is excessively hardened. For this reason, the upper limit of the Mn content is set to 0.60%. The preferred Mn content is in the range of 0.19% to 0.60%.

(4) P: 0.001% or more and 0.100% or less P (phosphorus) is a harmful element that hardens steel and deteriorates workability and at the same time deteriorates corrosion resistance. For this reason, the upper limit of the content of P is set to 0.100%. On the other hand, dephosphorization cost becomes excessive to make the P content less than 0.001%. For this reason, the lower limit of the P content is 0.001%. A preferable P content is in the range of 0.001% to 0.015%.

(5) S: 0.001% or more and 0.020% or less S is a harmful element that exists as an inclusion in steel and causes deterioration of workability and corrosion resistance. For this reason, the upper limit of the S content is 0.020%. On the other hand, desulfurization cost becomes excessive to make the S content less than 0.001%. For this reason, the lower limit of the S content is 0.001%. A preferable P content is in the range of 0.007% to 0.014%.

(6) Al: 0.005% or more and 0.100% or less Al (aluminum) is an element necessary as a deoxidizer during steelmaking. When the content of Al is small, deoxidation becomes insufficient, inclusions increase, and workability deteriorates. If the Al content is 0.005% or more, it can be considered that deoxidation is sufficiently performed. On the other hand, when the Al content exceeds 0.100%, the frequency of occurrence of surface defects due to alumina clusters or the like increases. For this reason, content of Al shall be 0.005% or more and 0.100% or less.

(7) N: 0.0130% to 0.0170% or less In the high-strength and high-workability steel sheet according to the present invention, instead of lowering the C content, the N (nitrogen) content is increased and the strength is increased. Secure. Since strengthening with N has little influence on the stretchability, the strength of the steel sheet can be increased without impairing the Erichsen value. If the N content is 0.0130% or less, the strength required for the can lid cannot be obtained. On the other hand, when N is added in a large amount, the hot ductility deteriorates, and slab cracking occurs in continuous casting. For this reason, the upper limit of the content of N is set to 0.0170%.

(8) Other components The balance other than the above components is Fe (iron) and inevitable impurities, but may contain component elements generally contained in known steel sheets for welding cans. For example, Cr (chromium): 0.10% or less, Cu (copper): 0.20% or less, Ni (nickel): 0.15% or less, Mo (molybdenum): 0.05% or less, Ti (titanium) : 0.3% or less, Nb (niobium): 0.3% or less, Zr (zirconium): 0.3% or less, V (vanadium): 0.3% or less, Ca (calcium): 0.01% or less Etc. can be contained according to the purpose.

[Characteristics of high strength and high workability steel sheet]
Next, the mechanical properties of the high strength and high workability steel sheet according to the present invention will be described.

  The tensile strength of the high strength and high workability steel sheet according to the present invention is set to 520 MPa or more. If the tensile strength is less than 520 MPa, the steel plate cannot be made thin enough to obtain a remarkable economic effect in order to secure the strength of the steel plate as the lid-making material. Therefore, the tensile strength is set to 520 MPa or more. The tensile strength can be measured by a metal material tensile test method described in the document “JIS Z 2241”.

  The Erichsen value of the high strength and high workability steel sheet according to the present invention is 5.0 mm or more. If the Eriksen value is less than 5.0 mm, cracking occurs during rivet forming. Therefore, the Erichsen value is 5.0 mm or more. The Erichsen value can be measured by the Eriksen test method shown in the document “JIS Z 2247”. During rivet forming, the processing mode applied to the steel sheet is an overhanging process, which can be considered as tensile deformation in all directions parallel to the plate surface. In order to evaluate the deformability of the steel sheet with respect to such processing, a test by the same overhanging process is necessary, and it cannot be evaluated by the total elongation value or the Rankford value by a simple uniaxial tensile test.

[Surface coating of high-strength, high-workability steel sheet]
Next, the surface coating of the high strength and high workability steel sheet according to the present invention will be described.

  Rivet forming is performed by an overhanging process, and an overhanging process is performed on the outer surface of the can. For this reason, at the time of a process, a tool contacts the side used as a can inner surface, and deforms a steel plate. The lubricity between the tool and the steel sheet is improved by sandwiching and contacting the resin film between the tool and the steel sheet. Thereby, the uniformity of the overhang process is improved and the occurrence of cracks can be effectively suppressed. In addition, it is more preferable that the resin film is not only sandwiched between the tool and the steel plate but also covered with the resin film, which contributes to corrosion resistance.

  The resin film is not particularly limited, and various thermoplastic resins and thermosetting resins can be used. For example, polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic ester copolymer, olefin resin film such as ionomer, or polyester film such as polybutylene terephthalate, or nylon 6, a non-stretched or biaxially stretched thermoplastic resin film such as a polyamide film such as nylon 66, nylon 11 or nylon 12, a polyvinyl chloride film or a polyvinylidene chloride film.

  When an adhesive is used when a resin film is attached to a steel sheet, a urethane adhesive, an epoxy adhesive, an acid-modified olefin resin adhesive, a copolyamide adhesive, a copolyester adhesive (thickness: 0. 1 to 5.0 μm) is preferably used. Further, a thermosetting paint may be applied to the steel plate side or the resin film side in a thickness range of 0.05 to 2.0 μm, and this may be used as an adhesive. Furthermore, modified epoxy paints such as phenol epoxy and amino-epoxy, vinyl chloride-vinyl acetate copolymer, saponified vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, epoxy-modified- Epoxyamino-modified, epoxyphenol-modified-vinyl paint or modified vinyl paint, acrylic paint, thermoplastic rubber or other thermosetting paint such as styrene-butadiene copolymer, or a combination of two or more of them It may be.

  The thickness of the resin film is preferably in the range of 5 to 100 μm. When the thickness of the resin film is less than 5 μm, the resin film breaks during the overhanging process, and there is a high possibility that the effect is not sufficiently exhibited. On the other hand, when the thickness of the resin film exceeds 100 μm, the effect of increasing the deformation amount of the steel sheet is increased, and the steel sheet is easily cracked.

[Method for producing high-strength, high-workability steel sheet]
Next, the manufacturing method of the high intensity | strength high workability steel plate which concerns on this invention is demonstrated.

  The high-strength, high-workability steel sheet according to the present invention uses a steel slab having the above composition produced by continuous casting, and after hot rolling with a slab reheating temperature of 1150 ° C. or higher, winding at a temperature of 600 ° C. or lower. And then primary cold rolling, followed by continuous annealing at a soaking temperature of 600 to 700 ° C. and a soaking time of 10 to 50 seconds, and then secondary cold at a rolling rate of 8.0 to 15.0%. After rolling and forming a surface treatment film by an electrolytic method, it is manufactured by sticking a resin film on at least the side that becomes the inner surface of the can.

  Normally, it is difficult to achieve a thin plate thickness that provides a remarkable economic effect by only one cold rolling. That is, in order to obtain a thin plate thickness by one cold rolling, the load on the rolling mill is excessive, and it is impossible depending on the equipment capacity. For example, when the final plate thickness is 0.15 mm, the primary cold rolling rate as large as 92.5% is required when the plate thickness after hot rolling is 2.0 mm. In order to reduce the sheet thickness after cold rolling, it is conceivable that rolling is performed thinner than usual in the hot rolling stage, but if the rolling rate of hot rolling is increased, the temperature of the steel sheet during rolling is decreased. A predetermined finish rolling temperature cannot be obtained. Furthermore, if the plate thickness before annealing is reduced, when continuous annealing is performed, the possibility of troubles such as breakage and deformation of the steel plate during annealing increases. For these reasons, in the present invention, it is preferable to perform the second cold rolling (secondary cold rolling) after annealing to obtain an ultrathin steel plate.

  When the coiling temperature after hot rolling is over 600 ° C., the formed pearlite structure becomes coarse, and this becomes the starting point of brittle fracture, so the local elongation is reduced and an Erichsen value of 5.0 mm or more is obtained. Hateful. Therefore, the coiling temperature after hot rolling is preferably 600 ° C. or lower, more preferably 550 to 600 ° C.

  When the soaking temperature of continuous annealing is less than 600 ° C. or the soaking time is less than 10 seconds, recrystallization becomes insufficient and it is difficult to obtain an Erichsen value of 5.0 mm or more. On the other hand, if the soaking temperature exceeds 700 ° C. or the soaking time exceeds 50 seconds, grain growth due to recrystallization becomes excessive, and it is difficult to obtain a tensile strength of 520 MPa. Therefore, it is desirable to perform the continuous annealing under conditions of a soaking temperature of 600 to 700 ° C. and a soaking time of 10 to 50 seconds.

  When the secondary cold rolling rate exceeds 15.0%, work hardening by secondary cold rolling becomes excessive, and it becomes difficult to obtain an Erichsen value of 5.0 mm or more. Therefore, the secondary cold rolling rate is preferably 15.0% or less. On the other hand, if the secondary cold rolling rate is less than 8.0%, it is difficult to obtain the strength required for the can lid. Therefore, the lower limit of the secondary cold rolling rate is preferably 8.0%.

  After the secondary cold rolling, a surface treatment film is formed by an electrolytic method. As the film, Sn electroplating film widely used for tin cans and tin-free steel, and electrolytic Cr acid-treated film can be applied. By providing these films, it becomes possible to improve the adhesion between the resin film and the steel sheet.

  After forming the surface treatment film, a resin film is pasted on at least the side that becomes the inner surface of the can. As a method of attaching, a method of heating a steel plate and thermally fusing a resin film, a method of attaching using an adhesive, and the like are possible.

〔Example〕
Steel containing the component composition shown in Table 1 and the balance being Fe and inevitable impurities was melted in an actual converter, and a steel slab was obtained by a continuous casting method. After the obtained steel slab was reheated, it was hot-rolled under the conditions shown in Table 2. The finish rolling temperature of hot rolling was 880 ° C., and pickling was performed after rolling. Next, after performing primary cold rolling at a rolling rate of 90%, continuous annealing and secondary cold rolling were performed under the conditions shown in Table 2. The steel plate obtained as described above was subjected to electrolytic Cr acid treatment continuously on both sides to obtain tin-free steel with a single-sided Cr deposit of 100 mg / m ² . Further, an isophthalic acid copolymerized polyethylene terephthalate film having a copolymerization ratio of 12 mol% was laminated on both sides to obtain a resin-coated steel sheet. Lamination was performed by sandwiching a steel plate and a film heated to 245 ° C. between a pair of rubber rolls, fusing the film to a metal plate, and cooling with water within 1 second after passing through the rubber roll. At this time, the feeding speed of the steel plate was 40 m / min, and the nip length of the rubber roll was 17 mm. The nip length is the length in the conveyance direction of the portion where the rubber roll and the steel plate are in contact. Table 1 shows the thickness of the film layer.

  A tensile test was performed on the resin-coated steel sheet obtained as described above. In the tensile test, tensile strength (tensile strength) was measured using a tensile test piece of JIS No. 5 size in accordance with a metal material tensile test method shown in the document “JIS Z 2241”. Moreover, the Erichsen test was done with respect to the obtained resin-coated steel plate. In the Erichsen test, the Erichsen value (the overhang height at which a through crack occurs) was measured using a 90 mm × 90 mm test piece in accordance with the Eriksen test method shown in the document “JIS Z 2247”. Moreover, the rivet for EOE tab attachment was shape | molded using the obtained resin-coated steel plate, and rivet moldability was evaluated. Rivet forming was performed by three-stage press work, and after the overhanging process, a diameter reduction process was performed to form a spherical head rivet having a diameter of 4.0 mm and a height of 2.5 mm. The case where cracks occurred at the rivet part was evaluated as x, the case where necking in the thickness direction before cracking occurred was evaluated as ◯, and the case where cracking or necking in the thickness direction did not occur was evaluated as ◎. The obtained results are shown in Table 3.

  As shown in Table 3, No. of the invention example. The steel plates 1 to 6 are excellent in strength, and have achieved a tensile strength of 520 MPa or more necessary as an ultrathin steel plate for cans. Moreover, it is excellent in workability and has an Erichsen value of 5.0 mm or more necessary for EOE processing. Further, even when rivet forming is performed, neither cracking nor thickness constriction occurs. In contrast, No. of the comparative example. Each of the steel sheets Nos. 7 and 9 has insufficient tensile strength because the contents of C and N are too small. Since the steel sheet of Comparative Example 8 has too much C, the workability is impaired by secondary cold rolling, the Erichsen value is insufficient, and cracking occurs in rivet forming.

  Moreover, No. of the comparative example. Since the steel plate No. 10 has too much N content, slab cracking occurs in continuous casting. Moreover, No. of the comparative example. Steel sheet No. 11 has a coiling temperature after hot rolling that is too high, resulting in a decrease in local elongation, resulting in a lack of Erichsen value and cracking in rivet forming. Moreover, No. of the comparative example. The steel plate No. 12 has a low soaking temperature in continuous annealing, so that recrystallization is insufficient, the Eriksen value is insufficient, and cracking occurs in rivet forming. Moreover, No. of the comparative example. In No. 13, the soaking temperature in continuous annealing is too high, resulting in excessive grain growth and insufficient tensile strength. Comparative Example No. No. 14 steel plate has insufficient recrystallization because the soaking time in continuous annealing is too short, the Eriksen value is insufficient, and cracking occurs in rivet forming.

  Moreover, No. of the comparative example. In No. 15, the soaking time in continuous annealing is too long, resulting in excessive grain growth and insufficient tensile strength. Comparative Example No. No. 16 steel plate has insufficient tensile strength because the secondary cold rolling rate is too small. Comparative Example No. Since the steel plate No. 17 has a secondary cold rolling rate that is too large, the work hardening is excessive, the Erichsen value is insufficient, and cracking occurs in rivet forming. In the inventive examples of claims 1 and 3, the comparative example No. In No. 18, the thickness of the resin film coated on the surface of the steel plate is too thin, so that the effect is not sufficiently exhibited in the rivet forming, and a constriction crack in the thickness direction before cracking occurs. In the inventive examples of claims 1 and 3, the comparative example No. In No. 19, the thickness of the resin film coated on the surface of the steel plate is too thick, so that the deformation amount of the steel plate is increased in rivet forming, and a constriction crack in the thickness direction before cracking occurs.

  From the above, according to the steel sheet of the invention example, it was confirmed that a high strength and high workability steel sheet having a tensile strength of 520 MPa or more and an Erichsen value of 5.0 mm or more can be obtained.

  Although the embodiment to which the invention made by the present inventor is applied has been described above, the present invention is not limited by the description and the drawings that form a part of the disclosure of the present invention according to this embodiment. That is, other embodiments, examples, operational techniques, and the like made by those skilled in the art based on the present embodiment are all included in the scope of the present invention.

  According to the present invention, it is possible to provide a high-strength and high-workability steel sheet having a tensile strength of 520 MPa or more and an Erichsen value of 5.0 mm or more.

Claims (3)

  C: 0.020% to less than 0.040%, Si: 0.003% to 0.100%, Mn: 0.10% to 0.60%, P: 0.001% or more 0.100% or less, S: 0.001% or more and 0.020% or less, Al: 0.005% or more and 0.100% or less, N: 0.0130% or more and 0.0170% or less, the balance being Fe and inevitable impurities, having a resin film layer on at least the inner surface of the can, having a tensile strength in the rolling direction of 520 MPa or more, and an Erichsen value of 5.0 mm or more. Workable steel sheet.   The high-strength and high-workability steel sheet according to claim 1, wherein the thickness of the resin film layer is in the range of 5 to 100 µm.   C: 0.020% to less than 0.040%, Si: 0.003% to 0.100%, Mn: 0.10% to 0.60%, P: 0.001% to 0.100% Hereinafter, S: 0.001% or more and 0.020% or less, Al: 0.005% or more and 0.100% or less, N: 0.0130% to 0.0170% or less, the balance being Fe and inevitable Steel made of impurities is made into a slab by continuous casting, slab reheating temperature is set to 1150 ° C. or higher, hot rolling is performed, winding is performed at a temperature of 600 ° C. or lower, primary cold rolling is performed, and soaking temperature is 600 to 700. C. and a soaking time of 10 to 50 seconds, followed by secondary cold rolling at a rolling rate of 8.0 to 15.0%, and after forming a surface treatment film by electrolytic method, at least the inner surface of the can A resin film on the side Ri attached, and a tensile strength in the rolling direction is 520MPa or more, the method of producing a high strength and high formability steel sheet characterized by producing steel sheet Erichsen value is 5.0mm or more.