JP2015151620A - Steel sheet for can and production method of steel sheet for can - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high strength and high workability steel sheet for a can, excellent in isotropy of mechanical properties and suitable as a material for a 3-piece can body, an EOE (Easy Open End) or the like, and a production method of the steel sheet for a can.SOLUTION: The steel sheet for a can is provided which contains, by mass%, C:0.001% or more and less than 0.020%, Si:0.003% to 0.100%, Mn:0.10% to 0.60%, P:0.001% to 0.100%, S:0.001% to 0.020%, Al:0.005% to 0.100%, N:over 0.0120% and 0.0200% or less and the balance Fe with inevitable impurities, N existing as AIN being contained in an amount of 0.0050% or less, and which has a tensile strength of 500 MPa to 600 MPa and a [EL-L] of 8 to 25, a [EL-C] of 8 to 25 and an absolute value of [EL-L]-[EL-C] of 5 or less where [EL-L]% is an elongation at break in a rolling direction and [EL-C]% is an elongation at break in a width direction.

Description

  TECHNICAL FIELD The present invention relates to a steel plate for cans used as a container material for beverages and foods, and a method for producing a steel plate for cans. It relates to the manufacturing method.

  A steel plate called a DR (Double Reduced) material is a steel plate that is cold-rolled again after annealing, and has a thickness that is smaller than that of an SR (Single Reduced) material that only undergoes temper rolling with a small rolling rate after annealing. It is easy to make it thinner. Because it is possible to reduce can manufacturing costs by using thin steel plates, DR materials are used for lids, bottoms, 3 piece can bodies, drawn cans, etc. among steel plates used for beverage cans and food cans. May be.

  In the DR method for manufacturing the DR material, work hardening occurs by performing cold rolling again after annealing, and thus a thin and hard steel plate can be manufactured. However, on the other hand, the DR material manufactured by the DR method is poor in workability compared to the SR material because it is poor in ductility. Further, the DR material exhibits anisotropy of mechanical properties that the strength in the width direction is large and the elongation is small compared to the rolling direction due to cold rolling after annealing.

  The body of food cans and beverage cans composed of three pieces is molded into a cylindrical shape, and then flanged at both ends in order to tighten the lid and the bottom. Therefore, good workability is required at the end of the can body. The body of food cans and beverage cans composed of two pieces is formed by drawing or ironing. It is impossible to make such cans using steel plates with poor workability.

  Here, the forming method of the body of the three-piece can includes a forming method in which welding is performed along the rolling direction of the steel sheet and a forming method in which welding is performed along the width direction. In a can maker, these forming methods may be used properly depending on the can shape, so the steel sheet used has a small difference in mechanical properties between the rolling direction and the width direction, that is, a good isotropic property. Preferably there is. Further, when forming EOE (Easy Open End), rivets are formed by overhanging. When the anisotropy of the steel sheet is large, cracks and wrinkles are generated during the overhanging process, and rivet forming becomes difficult. Therefore, a steel sheet with good isotropic mechanical properties is required.

  However, since it is difficult to achieve the above processability and isotropic mechanical properties with DR material, SR material has mainly been used for the body of food cans and beverage cans. However, at present, in order to reduce the thickness by reducing the plate thickness, there is an increasing demand for applying the DR material to the body of food cans and beverage cans. In addition, as exemplified below, many techniques for manufacturing a steel plate (DR material) excellent in plate take-up property (width direction ductility) are disclosed.

In Patent Document 1, a steel slab containing C: more than 0.0060% to 0.0290% is reheated to 1050 ° C. or higher, and the finishing temperature is set to Ar ₃ transformation point or higher and the coiling temperature is set to 680 ° C. or lower. A technique is disclosed in which hot rolling is performed, and cold rolling and annealing are followed by secondary cold rolling with a rolling reduction of less than 2 to 10%.

In Patent Document 2, a steel slab containing C: more than 0.0060% to less than 0.0300% is reheated to 1050 ° C. or higher, and hot rolling is performed so that the finishing temperature is higher than the Ar ₃ transformation point. A technique for performing secondary cold rolling with a rolling reduction of less than 10 to 25% after hot rolling and annealing is disclosed.

In Patent Document 3, a steel slab containing Cr: 0.005 to 0.100% is reheated to 1100 ° C. or higher, hot-rolled with a finishing temperature of Ar ₃ transformation point or higher, cold rolled, A technique of performing secondary cold rolling with a rolling reduction of less than 10 to 25% after annealing is disclosed.

In Patent Document 4, a steel slab containing Cr: 0.005 to 0.100% is reheated to 1100 ° C. or higher, and the finishing temperature is higher than the Ar ₃ transformation point and the coiling temperature is 680 ° C. or lower. A technique for performing secondary cold rolling with a rolling reduction of less than 2 to 10% after rolling and cold rolling and annealing is disclosed.

In Patent Literature 5, a steel slab containing C: 0.0060% or less and N: more than 0.0060% is reheated to 1050 ° C. or more, and hot rolling is performed with the finishing temperature being the Ar ₃ transformation point or more. A technique for performing secondary cold rolling with a reduction rate of less than 10 to 25% after cold rolling and annealing is disclosed.

Japanese Patent No. 2714994 JP-A-3-257123 JP-A-4-333525 JP-A-4-350125 JP-A-3-294432

  However, since the steel plate (DR material) manufactured by the techniques described in Patent Documents 1 to 4 has an inappropriate component composition, the balance between strength and elongation is poor, and it cannot be said that it is highly workable. Not applicable to beverage can body. Moreover, the steel plate manufactured by the technique described in Patent Document 5 has an excessive residual amount of AlN deposited during slab cooling, and lacks strength against elongation. Not applicable.

  The present invention has been made in view of such circumstances, and is suitable for materials such as a three-piece can body and EOE, and has a high strength and high workability steel plate for cans and excellent for isotropic mechanical properties. It aims at providing the manufacturing method of a steel plate.

  In order to solve the above-described problems and achieve the object, the present inventors have conducted intensive research and obtained the following knowledge. That is, in order to achieve both workability and tensile strength, a large amount of N is added to ensure strength, and in order to ensure workability, the content of C is lowered to reduce carbide. It is effective to suppress the occurrence of fine cracks. Further, keeping the C content low is also effective in improving the isotropy of mechanical properties.

  The steel plate for cans according to the present invention made based on the above findings is mass%, C: 0.001% or more and less than 0.020%, Si: 0.003% or more and 0.100% or less, Mn: 0 10% to 0.60%, P: 0.001% to 0.100%, S: 0.001% to 0.020%, Al: 0.005% to 0.100%, N : More than 0.0120% and 0.0200% or less, the balance is made of Fe and inevitable impurities, the amount of N present as AlN is 0.0050% or less, and the tensile strength is 500 MPa or more and 600 MPa or less, [EL-L] is 8 or more and 25 or less, and [EL-C] is 8 or more and 25 or less, when the rolling direction breaking elongation is [EL-L]% and the width direction breaking elongation is [EL-C]%. The absolute value of [EL-L]-[EL-C] is 5 or less And wherein the Rukoto.

Moreover, the manufacturing method of the steel plate for cans concerning this invention is a manufacturing method of the steel plate for cans of the said invention, Comprising: By mass%, C: 0.001% or more and less than 0.020%, Si: 0.003% Or more, 0.100% or less, Mn: 0.10% or more and 0.60% 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: 0.0120% or more and 0.0200% or less, and the balance is made of steel consisting of Fe and inevitable impurities into a slab by continuous casting, and the slab reheating temperature exceeds 1240 ° C as after hot rolling, 530 ° C. or higher 740 ° C. or less of the coiling temperature, subjected to primary cold rolling at a rolling reduction of 95% or less than 85%, subsequently annealed at a temperature lower than the a ₁ transformation point Secondary cold rolling at a rolling rate of 7% to 20% It is characterized by performing. In addition, in this specification,% which shows the component of steel is mass% altogether.

  ADVANTAGE OF THE INVENTION According to this invention, the steel plate for cans of the high intensity | strength and high workability excellent in the isotropy of a mechanical property suitable as materials, such as a 3 piece can barrel and EOE, can be obtained.

  Hereinafter, an embodiment of the present invention will be described in detail. In addition, this invention is not limited by this embodiment.

First, the steel plate for cans of the present invention will be described. The rolling elongation at break of the steel sheet is [EL-L]%, and the elongation at break in the width direction is [EL-C]%. At this time, the steel plate for cans of the present invention has [EL-L] of 8 or more and 25 or less, [EL-C] of 8 or more and 25 or less, and an absolute value of [EL-L]-[EL-C]. It is a steel plate for cans having a strength and workability of 5 or less, which is excellent in isotropic mechanical properties. And such a steel plate is manufactured by performing secondary cold rolling which makes a rolling rate an appropriate range with respect to steel with C content restrained low and containing a lot of N. Specifically, such a steel sheet is hot-rolled with a slab reheating temperature exceeding 1240 ° C., wound at a temperature of 530 ° C. or higher and 740 ° C. or lower, and then primary at a rolling rate of 85% or higher and 95% or lower. perform cold rolling, it is subsequently produced by a ₁ performs annealing at a temperature below the transformation point, and then performing the secondary cold rolling at a rolling ratio of 20% or less than 7% or more. These requirements are the most important requirements of the present invention.

  Next, the component composition of the steel plate for cans of this invention is demonstrated.

C: 0.001% or more and less than 0.020% Good isotropy of mechanical properties, which is a feature of the present invention, can be realized by a low C content, and the C content is 0.020%. If it is too high, the isotropy of the mechanical properties decreases. For this reason, the C content is less than 0.020%. On the other hand, in order to make the amount of C less than 0.001%, the C-free cost becomes excessive. Therefore, the C content is 0.001% or more and less than 0.020%. From the viewpoint of isotropic mechanical properties, the C content is more preferably 0.001% or more and less than 0.010%.

Si: 0.003% or more and 0.100% or less When the amount of Si exceeds 0.100%, problems such as deterioration of surface treatment property and deterioration of corrosion resistance occur. Therefore, the upper limit of Si content is 0.100%. On the other hand, in order to make Si amount less than 0.003%, the refining cost becomes excessive. Therefore, the lower limit of the Si amount is 0.003%.

Mn: 0.10% or more and 0.60% or less Mn has an action of refining crystal grains and is an element necessary for securing a desirable material. In order to exert this effect, it is necessary to add at least 0.10% or more. Therefore, the lower limit of the amount of Mn is 0.10%. On the other hand, when Mn is added in a large amount, the corrosion resistance is lowered. Therefore, the upper limit of the Mn amount is 0.60%.

P: 0.001% or more and 0.100% or less P is a harmful element that hardens steel and deteriorates workability and at the same time deteriorates corrosion resistance. Therefore, the upper limit of the P amount is 0.100%. On the other hand, in order to make the P amount less than 0.001%, the de-P cost is excessive. Therefore, the lower limit of the P content is 0.001%.

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 in ductility and deterioration in corrosion resistance. Therefore, the upper limit of the S amount is 0.020%. On the other hand, in order to make the amount of S less than 0.001%, the removal S cost becomes excessive. Therefore, the lower limit of the S amount is 0.001%.

Al: 0.005% or more and 0.100% or less Al is an element necessary as a deoxidizer during steelmaking. When the Al content is less than 0.005%, deoxidation becomes insufficient, inclusions increase, and workability deteriorates. On the other hand, if the Al content exceeds 0.100%, the occurrence frequency of surface defects due to alumina clusters and the like increases. Therefore, the Al content is 0.005% or more and 0.100% or less.

N: More than 0.0120% and 0.0200% or less The steel sheet of the present invention is ensured in strength by containing a large amount of N. If the N amount is 0.0120% or less, the solid solution N that bears the strength becomes too small, and the strength is insufficient. On the other hand, if the N amount exceeds 0.0200%, the strengthening by the solute N becomes excessive, the ductility is lowered, and sufficient flange workability is not exhibited. Therefore, the N content is more than 0.0120% and 0.0200% or less. Preferably, the N amount is more than 0.0130% and not more than 0.0160%.

N as AlN: 0.0050% or less N contributing to the strength is mainly N in a solid solution state, and a certain amount of solid solution N is required to ensure the strength in the steel sheet of the present invention. In the composition of the steel sheet of the present invention, AlN is mainly considered as a compound that N forms in the steel. Therefore, if the amount of N (N as AlN) present as AlN is more than 0.0050%, the amount of solid solution N decreases and the strength becomes insufficient. Therefore, the amount of N as AlN is 0.0050% or less. More preferably, the amount of N as AlN is 0.0010% or less.

  The balance of the steel sheet of the present invention contains Fe and inevitable impurities. The steel plate of this invention may contain the component element generally contained in the well-known steel plate for welding cans. For example, the following amounts of component elements can be contained in the steel sheet depending on the purpose. Specifically, Cr: 0.10% or less, Cu: 0.20% or less, Ni: 0.15% or less, Mo: 0.05% or less, Ti: 0.3% or less, Nb: 0.3% Hereinafter, component elements such as Zr: 0.3% or less, V: 0.3% or less, and Ca: 0.01% or less may be contained.

  Next, the mechanical properties of the steel plate for cans of the present invention will be described. Flange workability is important as workability required in forming a three-piece can body. Since the flange process is a process of stretching the end of the steel plate, the flange processability can be evaluated by breaking elongation in a tensile test. A rivet is formed by overhanging at the time of forming the EOE. However, since the overhanging portion is subjected to biaxial tensile deformation, the rivet formability can also be evaluated by breaking elongation in a tensile test.

[EL-L]: 8 to 25 [EL-C]: 8 to 25 [EL-L]-[EL-C] absolute value: 5 or less [EL-L] %, And the elongation at break in the width direction is [EL-C]%. At this time, if [EL-L] and [EL-C] are less than 8, the ductility is poor and it is not possible to cope with flange processing or rivet molding. On the other hand, even if [EL-L] and [EL-C] exceed 25, there is no further advantage, and production becomes difficult. If the absolute value of [EL-L]-[EL-C] exceeds 5, the anisotropy of mechanical properties is excessive, and the conditions for forming the three-piece can body must be changed depending on the direction of the steel sheet. Further, when the absolute value of [EL-L]-[EL-C] exceeds 5, cracks and wrinkles occur in rivet molding of EOE. Therefore, the absolute value of [EL-L]-[EL-C] is 5 or less. More preferably, the absolute value of [EL-L]-[EL-C] is 3 or less.

Tensile strength: 500 MPa or more and 600 MPa or less When the tensile strength of the steel sheet is less than 500 MPa, the steel sheet cannot be made thin enough to obtain a remarkable economic effect in order to secure the strength as a can-making material. On the other hand, when the tensile strength of the steel sheet exceeds 600 MPa, the workability of a roll foam or the like deteriorates. Therefore, the tensile strength is 500 MPa or more and 600 MPa or less. The elongation at break and the tensile strength can be measured by a metallic material tensile test method shown in “JIS Z 2241”.

Next, the manufacturing method of the steel plate for cans of this invention is demonstrated. The steel plate for cans of the present invention is made by continuously casting steel having the above composition into a slab by continuous casting, performing hot rolling with a slab reheating temperature exceeding 1240 ° C., and then winding the steel at a temperature of 530 ° C. or higher and 740 ° C. or lower. perform rolling primary cold at% to 95% or less rolling ratio, subsequently, subjected to annealing at a temperature lower than the a ₁ transformation point, prepared by performing secondary cold rolling at a rolling ratio of 20% or less than 7% or more Is done.

  Steel is melted by a generally known melting method using a converter or the like, and is made into a slab (rolled material) by a continuous casting method.

Slab reheating temperature: over 1240 ° C. The slab reheating temperature before hot rolling affects the remelting amount of AlN deposited during slab cooling after casting. When the slab reheating temperature is 1240 ° C. or lower, the remelting of AlN becomes insufficient, and the amount of AlN becomes excessive. Therefore, the slab reheating temperature is over 1240 ° C. More preferably, the slab reheating temperature is 1250 ° C. or higher.

The slab becomes a hot-rolled sheet by hot rolling. The hot finish rolling temperature is preferably not less than the Ar ₃ transformation point from the viewpoint of preventing grain coarsening of the hot-rolled steel sheet and uniformity of precipitate distribution.

Winding temperature: 530 ° C. or higher and 740 ° C. or lower If the winding temperature is higher than 740 ° C., the amount of AlN precipitated after winding becomes excessive. In order to set the coiling temperature to less than 530 ° C., an excessive cooling capacity is required for the hot rolling equipment. Therefore, the coiling temperature after hot rolling is set to 530 ° C. or higher and 740 ° C. or lower. More preferably, the coiling temperature is 560 ° C. or higher and 710 ° C. or lower.

  Next, pickling is performed as necessary. The pickling is not particularly limited as long as the surface scale can be removed.

Rolling ratio of primary cold rolling: 85% or more and 95% or less As described above, it is easy to reduce the plate thickness in the DR method compared with the SR method in which the SR material is manufactured. Since it can be manufactured, the DR method is adopted in the present invention. When the rolling ratio of the primary cold rolling is small, it is necessary to reduce the finishing thickness of the hot rolling or increase the rolling ratio of the secondary cold rolling in order to produce an extremely thin steel sheet. When the finish thickness of hot rolling becomes thin, it becomes difficult to ensure a predetermined finish rolling temperature. Moreover, it is not preferable to increase the rolling ratio of the secondary cold rolling for the reasons described later. If the rolling rate of primary cold rolling is 85% or more, it is not necessary to reduce the hot rolling finish thickness or increase the rolling rate of secondary cold rolling, and produce an extremely thin steel plate. It is possible. On the other hand, the burden on the rolling mill is excessive to increase the rolling ratio of primary cold rolling to over 95%. Therefore, the rolling ratio of primary cold rolling is 85% or more and 95% or less. More preferably, the rolling rate of primary cold rolling is 88% or more and less than 91.5%.

Annealing Temperature: If the A ₁ transformation point lower than the annealing temperature and A ₁ transformation point or higher, the sheet passing troubles such as heat buckle is likely to occur in the continuous annealing, which is not preferable. Therefore, the annealing temperature is less than the A ₁ transformation point. Considering operation efficiency, more preferably, the annealing temperature is set to 630 to 700 ° C.

Rolling ratio of secondary cold rolling: 7% or more and 20% or less If the rolling ratio of secondary cold rolling exceeds 20%, work hardening by secondary cold rolling becomes excessive and good workability cannot be obtained. . On the other hand, if the rolling ratio of secondary cold rolling is less than 7%, the strength is insufficient. Therefore, the rolling rate of secondary cold rolling is 7% or more and 20% or less. More preferably, the rolling ratio of secondary cold rolling is 9% or more and 18% or less.

  In addition, after secondary cold rolling, processes, such as a plating process, can be performed as usual, and it can finish as a steel plate for cans.

  As described above, according to the present embodiment, the workability of the steel sheet and the isotropy of the mechanical properties are improved, so that it is easy to make a can with a thin DR material, and the thinning is possible. Applicable to a wide range of necessary steel plates for cans.

In this example, first, a steel slab was obtained by containing the component composition shown in Table 1, with the remainder being made of Fe and unavoidable impurities in an actual converter and continuously cast. The steel slab obtained here was reheated to the temperature shown in Table 2, then hot rolled at a rolling start temperature of 1150 ° C., and wound at the winding temperature shown in Table 2. The finish rolling temperature of hot rolling was 880 ° C., and pickling was performed after hot rolling. Next, primary cold rolling was performed at the rolling rates shown in Table 2, and continuous annealing was performed at an annealing temperature of 690 ° C., followed by secondary cold rolling at the rolling rates shown in Table 2.
The steel plate obtained as described above was continuously subjected to Sn plating on both surfaces to obtain a plated steel plate (can steel plate) having a single-side Sn adhesion amount of 2.8 g / m ² .

  A tensile test was performed on the plated steel sheet (blink) obtained as described above after a heat treatment equivalent to a coating baking at 210 ° C. for 15 minutes. In the tensile test, tensile strength and elongation at break in the rolling direction and the width direction were measured according to JIS Z 2241 using a JIS No. 5 size tensile test piece.

  Further, a can body having an outer diameter of 52.8 mm is formed by seam welding using a plated steel sheet that has been subjected to heat treatment equivalent to paint baking, and the end portion is neck-in processed to an outer diameter of 50.4 mm. Flange processing was performed up to 4 mm, and the presence or absence of occurrence of flange cracking was evaluated. The can body was formed into a 190 g beverage can size and welded along the rolling direction of the steel sheet. Neck-in processing was performed by the die neck method, and flange processing was performed by the spin flange method. When flange cracking occurred, it was evaluated as x, when cracking in the thickness direction before cracking occurred, ○, and when cracking or thickness direction constriction did not occur, evaluated as ◎.

  Moreover, the rivet for EOE tab attachment was shape | molded using the obtained plated steel plate, and rivet workability was evaluated. Rivet forming was performed by three stages of press working. After the overhang processing, diameter reduction processing was performed, and a spherical head rivet having a diameter of 4.0 mm and a height of 2.5 mm was formed. The case where cracks occurred on the rivet surface was evaluated as x, the case where the necking in the thickness direction before the cracking occurred was evaluated as ◯, and the case where cracking or thickness direction necking did not occur was evaluated as ◎.

  Table 3 shows the results obtained above.

  From Table 3, the steel plate for cans of the present invention examples (Nos. 1 to 11) is excellent in strength, and has achieved a tensile strength of 500 MPa or more necessary as an ultra-thin steel plate for cans. Moreover, it was confirmed that the absolute value of [EL-L]-[EL-C] was 5 or less and excellent in workability, and that the flange processing of the three-piece can body and the rivet molding of EOE were possible.

  On the other hand, no. No. 12 has too much C content, so isotropic mechanical properties are inferior, and cracking occurs in flange processing and rivet molding. Comparative Example No. No. 13 has insufficient tensile strength because the N content is too small. Comparative Example No. In No. 14, since the N content is too large, ductility is impaired by secondary cold rolling, the elongation at break is insufficient, and cracking occurs in flange processing and rivet forming. Comparative Example No. No. 15, because the slab reheating temperature is too low, the amount of AlN increases, and the tensile strength is insufficient. Comparative Example No. No. 16 has a winding temperature that is too high, so the amount of AlN increases and the tensile strength is insufficient. Comparative Example No. No. 17 has insufficient tensile strength because the rolling ratio of secondary cold rolling is too small. Comparative Example No. In No. 18, since the rolling ratio of the secondary cold rolling is too large, the ductility is impaired, the elongation at break is insufficient, and cracking occurs in flange processing and rivet forming.

  The steel plate for cans according to the present invention is optimal as a material for producing a three-piece can body and the like at a low cost, and can be suitably used as a material such as EOE.

Claims (2)

  C: 0.001% to less than 0.020%, 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: more than 0.0120% and 0.0200% or less, with the balance being Fe and inevitable impurities, the amount of N present as AlN is 0.0050% or less, the tensile strength is 500 MPa or more and 600 MPa or less, the elongation in the rolling direction is [EL-L]%, and the elongation in the width direction is When [EL-C]%, [EL-L] is 8 or more and 25 or less, [EL-C] is 8 or more and 25 or less, and the absolute value of [EL-L]-[EL-C] is 5 or less. A steel plate for cans, characterized in that C: 0.001% to less than 0.020%, 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: more than 0.0120% and 0.0200% or less, with the balance being Steel made of Fe and inevitable impurities is made into a slab by continuous casting, slab reheating temperature is set to over 1240 ° C, hot rolling is performed, and then wound at a temperature of 530 ° C to 740 ° C, 85% to 95% rolling reduction performed rolling primary cold in the subsequently performed annealing at a temperature below the a ₁ transformation point, claim 1, characterized in that the secondary cold rolling at a rolling ratio of 20% or 7% or less or more The manufacturing method of the steel plate for cans as described in any one of.