JP2013133483A - High-strength high-processability steel sheet for can, and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-strength high-processability steel sheet for a can, which has a tensile strength of 550 MPa or more and a total elongation of 10% or more, and to provide a method for producing the steel sheet.SOLUTION: A high-strength high-processability steel sheet for a can includes, by mass, 0.020-0.100% of C, 0.100% or less of Si, 0.10-0.80% of Mn, more than 0.10% and 0.30% or less of P, 0.001-0.020% of S, 0.005-0.100% of Al, more than 0.0250% and 0.0350% or less of N, and the remainder comprising Fe and inevitable impurities, and has the elongation rate of crystal grains of 2.00 or less, the tensile strength of 550 MPa or more, and the total elongation of 10% or more.

Description

  The present invention relates to a steel plate for cans having high strength and high workability, and a method for producing the same.

  Among steel plates used for beverage cans and food cans, steel plates called DR (Double-Reduce) materials may be used for lids, bottoms, three-piece can bodies, drawn cans, and the like. The DR material that is cold-rolled again after annealing is easier to reduce the plate thickness than the SR (Single-Reduce) material that performs only temper rolling with a small rolling rate. By using a thin steel plate The can manufacturing cost can be reduced.

  In the DR method for producing the DR material, work hardening occurs by performing cold rolling after annealing, so that a thin and hard steel plate can be produced. However, on the other hand, the DR material manufactured by the DR method is poor in ductility and therefore has poor workability compared to the SR material.

  In addition, as a lid for beverage cans and food cans, an EOE (Easy Open End) system is widely used. When manufacturing a lid by the EOE method, it is necessary to form a rivet for attaching a tab by an extension process and a drawing process, and the ductility of the material required for this process corresponds to an elongation of about 10% in a tensile test. To do.

  In addition, the body of the three-piece beverage can is formed into a cylindrical shape, and then flanged at both ends in order to tighten the lid and the bottom. Therefore, the end of the can body at this time is required to have an elongation of about 10%.

  On the other hand, a steel plate as a can-making material is required to have a strength corresponding to the plate thickness, and in the case of a DR material, a tensile strength of about 550 MPa or more is required to ensure the strength of the can by reducing the thickness.

  Conventionally used DR materials are difficult to achieve both the above-described ductility and strength, and SR materials have been used for EOE lids and beverage can body materials. However, at present, from the viewpoint of cost reduction, there is an increasing demand for applying DR materials to EOE-type lids and beverage can body materials. Furthermore, the request | requirement which uses DR material for a 2 piece can body has also come out.

  In view of these, in Patent Document 1, in mass%, C: more than 0.02% and 0.10% or less, Si: 0.10% or less, Mn: 1.5% or less, P: 0.20% Hereinafter, S: 0.20% or less, Al: 0.10% or less, N: 0.0120-0.0250% is contained, and 0.0100% or more is included as the solid solution N in the N, and the balance By using a low carbon material consisting of Fe and inevitable impurities, decomposing AlN generated during slab casting at a slab extraction temperature of 1200 ° C. or higher, and winding a hot rolled coil at 650 ° C. or lower to suppress precipitation of AlN The absolute amount of the solute N of the cold-rolled steel sheet is ensured to a certain level or more, and the secondary cold rolling is performed at the low pressure rate without secondary cold rolling by age hardening after the coating baking process. Steel plate for high-strength can with high productivity and manufacturing The law has been disclosed.

  In Patent Document 2, it is possible to lower the rolling reduction in the second cold rolling by hardening using P component, the tensile strength TS is 500 MPa or more, and the sheet width direction and the rolling direction are A steel plate for containers having a proof stress difference of 40 MPa or less and excellent workability and a method for producing the same are disclosed.

JP 2009-263788 A JP 2009-263789 A

  However, each of the above conventional techniques has the following problems.

  In the production method described in Patent Document 1, since N is as low as 0.0120 to 0.0250%, a sufficient strength of 550 MPa or more is obtained at a low pressure reduction rate of secondary cold rolling of less than 5 to 10%. Therefore, it is difficult to cope with higher strength. In addition, in order to secure a solid solution N amount of 0.0100% or more, it is necessary to decompose AlN generated during slab casting at a slab extraction temperature of 1200 ° C. or more, and an extra heating time for heating to a high temperature is required. Therefore, scale defects etc. occur and it cannot be manufactured stably.

  In the production method described in Patent Document 2, since P is as low as 0.1% or less, sufficient strength cannot be obtained at a low-pressure reduction rate of secondary cold rolling of less than 5 to 10%, and high strength is achieved. It is difficult to respond.

  The present invention has been made in view of such circumstances. A steel plate for cans having a tensile strength of 550 MPa or more, a total elongation of 10% or more, and excellent strength and workability, and a method for producing the same. The purpose is to provide.

  The inventors of the present invention have intensively studied to solve the above problems. As a result, the following knowledge was obtained.

  To ensure workability with a high-strength material, an appropriate amount of C is added to impart strength, while an appropriate amount of N and P is added to control the secondary cold rolling rate within an appropriate range. Thus, it is possible to achieve both strength and workability by work hardening.

  Moreover, when the coiling temperature after hot rolling is high, the cementite that precipitates becomes coarse, and the local elongation decreases. Therefore, the coiling temperature needs to be controlled within an appropriate temperature range.

The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] By mass%, C: 0.020% to 0.100%, Si: 0.100% or less, Mn: 0.10% to 0.80%, P: more than 0.10% 30% or less, S: 0.001% or more and 0.020% or less, Al: 0.005% or more and 0.100% or less, N: 0.0250% to 0.0350% or less, with the balance being Fe and A steel plate for a high-strength, high-workability can, comprising unavoidable impurities, having a crystal grain extension of 2.00 or less, a tensile strength of 550 MPa or more, and a total elongation of 10% or more.
[2] By mass%, C: 0.020% to 0.100%, Si: 0.100% or less, Mn: 0.10% to 0.80%, P: more than 0.10% 30% or less, S: 0.001% or more and 0.020% or less, Al: 0.005% or more and 0.100% or less, N: 0.0250% to 0.0350% or less, with the balance being Fe and Steel consisting of inevitable impurities is made into a slab by continuous casting, hot rolled at a finishing temperature not lower than the Ar3 transformation point, wound up at a temperature of 650 ° C or lower, and then primary cold rolled at a rolling rate of 80% or higher. And, further, secondary cold rolling is performed at a rolling rate of 5% or more and less than 10%.
In addition, in this specification,% which shows the component of steel is mass% altogether. In the steel sheet for high strength and high workability cans of the present invention, high strength means a tensile strength (TS) of 550 MPa or more, and high workability means a total elongation of 10% or more.

  According to the present invention, it is possible to obtain a high-strength and highly workable steel plate for cans having a tensile strength of 550 MPa or more and a total elongation of 10% or more. As a result, by improving the workability of the steel plate, cracks do not occur during rivet processing when manufacturing a lid by the EOE method or flange processing of a three-piece can, and cans can be made with a thin DR material. A significant reduction in the thickness of the steel sheet is achieved. In addition, since the production conditions are controlled to be within an appropriate range and cured, the production stability is also excellent.

  Hereinafter, the present invention will be described in detail.

  The steel plate for cans of the present invention is a high-strength, high-workability steel plate for cans having a tensile strength of 550 MPa or more and a total elongation of 10% or more. And such a steel plate contains 0.020% or more and 0.100% or less of C, contains 0.0250% or more and 0.0350% or less of N, and exceeds 0.10% or more and 0.30% or less. Other components can be made within the scope of claims of the present invention using steel containing P. Moreover, it becomes possible to manufacture by setting the coiling temperature after the hot rolling and the secondary cold rolling rate to appropriate conditions.

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

C: 0.020% or more and 0.100% or less This is an important requirement in the present invention. C suppresses the secondary cold rolling rate and ensures elongation, while increasing the content contributes to high strength. If the amount of C exceeds 0.100%, it becomes excessively hard, and it becomes impossible to produce a thin steel plate by secondary cold rolling while ensuring workability. Therefore, the upper limit of the C amount is 0.100%. On the other hand, if the C content is less than 0.020%, a tensile strength of 550 MPa or more necessary for obtaining a remarkable economic effect due to the thinning of the steel sheet cannot be obtained. Therefore, the lower limit of the C amount is 0.020%.

Si: 0.100% or less If the amount of Si exceeds 0.100%, problems such as deterioration of surface treatment properties and deterioration of corrosion resistance are caused, so the upper limit is made 0.100%.

Mn: 0.10% or more and 0.80% or less Mn is an element necessary to prevent red heat embrittlement during hot rolling due to S and to refine crystal grains and to secure a desirable material. is there. Furthermore, it is an element necessary for obtaining the strength required for securing the strength of the can with the thinned material. In order to obtain such an effect, the lower limit of the amount of Mn is 0.10%. On the other hand, if Mn is added in a large amount, the corrosion resistance deteriorates and the steel sheet becomes excessively hardened, so the upper limit is made 0.80%.

P: More than 0.10% and 0.30% 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 is made 0.30%. On the other hand, if the P content is 0.10% or less, a tensile strength of 550 MPa or more cannot be obtained. Therefore, the lower limit is made 0.10%.

S: 0.001% or more and 0.020% or less S exists as an inclusion in steel, and is a harmful element that causes reduction in ductility and deterioration in corrosion resistance. Therefore, the upper limit is made 0.020%. On the other hand, desulfurization cost becomes excessive to make the S amount less than 0.001%. Therefore, the lower limit is made 0.001%.

Al: 0.005% or more and 0.100% or less Al is an element necessary as a deoxidizer during steelmaking. When there is little Al, deoxidation will become inadequate, an inclusion will increase and workability will deteriorate. If the amount of Al is 0.005% or more, deoxidation is sufficiently performed. Therefore, the lower limit is made 0.005%. On the other hand, when the Al content exceeds 0.100%, the occurrence frequency of surface defects due to alumina clusters and the like increases. Therefore, the upper limit is made 0.100%.

N: 0.0250% to 0.0350% or less When N is added in a large amount, the hot ductility deteriorates and cracking of the slab occurs in continuous casting. Therefore, the upper limit is 0.0350%. Note that when the N content is 0.0250% or less, a tensile strength of 550 MPa or more cannot be obtained. Therefore, the lower limit is 0.0250%.

  The balance is Fe and inevitable impurities.

  Next, the mechanical properties of the steel plate for cans of the present invention will be described.

  The tensile strength is 550 MPa or more. If the tensile strength is less than 550 MPa, the steel plate cannot be thinned so that a remarkable economic effect is obtained in order to secure the strength of the steel plate as a can-making material. Therefore, the tensile strength is set to 550 MPa or more.

  The total elongation (breaking elongation) is 10% or more. If the total elongation is less than 10%, for example, cracking occurs during rivet processing when applied to the EOE method. For example, cracking occurs during flange processing when applied to a three-piece can body. Therefore, the total elongation is 10% or more.

  The tensile strength and the total elongation can be measured by a metallic material tensile test method described in “JIS Z 2241”.

  Next, the crystal grain of the steel plate for cans of this invention is demonstrated.

  The elongation of the crystal grains in the cross section in the rolling direction is 2.00 or less. The degree of extension is a value that represents the degree to which the ferrite crystal grains have been extended by processing, as shown in “JIS G 0202”. When the elongation of the crystal grains in the cross section in the rolling direction exceeds 2.00, elongation in the direction perpendicular to the rolling, which is important for flange workability and neck workability, is insufficient.

  The average crystal grain size in the cross section in the rolling direction is preferably 5 μm or more. The final mechanical properties of the steel plate for cans of the present invention are affected by the state of crystal grains. When the average crystal grain size in the cross section in the rolling direction is less than 5 μm, the elongation of the steel sheet is insufficient, and the workability may be impaired.

  The elongation of crystal grains in the cross section in the rolling direction and the average crystal grain size in the cross section in the rolling direction can be measured by a crystal grain size microscopic test method described in “JIS G 0551”.

  Further, the elongation of crystal grains in the cross section in the rolling direction and the average crystal grain size in the cross section in the rolling direction can be adjusted by the DR ratio.

  Next, the manufacturing method of the steel plate for cans of this invention is demonstrated.

  The steel sheet for a high-strength, high-workability can of the present invention uses a steel slab having the above composition manufactured by continuous casting, and is rolled at a temperature of 650 ° C. or lower after hot rolling at a finishing temperature not lower than the Ar3 transformation point. Then, primary cold rolling is performed at a rolling rate of 80% or more, and then secondary cold rolling is performed at a rolling rate of 5% or more and less than 10%.

  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 difficult depending on the equipment capacity. For example, when the final thickness is 0.14 mm, the primary cold rolling rate as large as 92.2% is required when the thickness after hot rolling is 1.8 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 a second cold rolling after annealing to obtain an ultrathin steel plate.

Finishing temperature: When the finishing temperature is not lower than the Ar3 transformation point and lower than the Ar3 transformation point, ferrite is produced during hot rolling, the hot rolled sheet is coarsened, and the strength of the product is lowered. Therefore, the finishing temperature is preferably not less than the Ar3 transformation point.

Winding temperature: 650 ° C. or less When the coiling temperature after hot rolling exceeds 650 ° C., the pearlite structure to be formed becomes coarse, and this becomes the starting point of brittle fracture. The total elongation cannot be obtained. Therefore, the coiling temperature after hot rolling is set to 650 ° C. or less.

Primary cold rolling rate: 80% or more When the primary cold rolling rate is small, it is necessary to increase the rolling rate of hot rolling and secondary cold rolling in order to finally obtain a very thin steel plate. Increasing the hot rolling rate is not preferable for the above-described reason, and the secondary cold rolling rate needs to be limited for the reason described later. For the above reasons, if the primary cold rolling rate is less than 80%, it is difficult to produce an ultrathin steel sheet, and therefore the primary cold rolling rate is set to 80% or more.

  The annealing conditions are not particularly limited, but recrystallization needs to be completed by annealing. From the viewpoint of production cost, it is preferable to use a continuous annealing method.

Secondary cold rolling rate: 5% or more and less than 10% The secondary cold rolling rate is less than 10%. If the secondary cold rolling rate is 10% or more, work hardening by secondary cold rolling becomes excessive, and a total elongation of 10% or more cannot be obtained. On the other hand, when the secondary cold rolling rate is less than 5%, rolling defects such as steel sheet slipping during rolling occur. Therefore, it is 5% or more.

  After the secondary cold rolling, steps such as plating are performed as usual, and finished as a steel plate for cans.

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. The obtained steel slab was reheated at 1210 ° C., and then hot-rolled at a finishing temperature not lower than the Ar3 transformation point, and subjected to primary cold rolling under the conditions shown in Table 2. The finish rolling temperature of hot rolling is 890 ° C., and pickling is performed after rolling. Subsequently, the secondary cold rolling was performed under the conditions shown in Table 2 and continuous annealing at a soaking temperature of 680 ° C. and a soaking time of 20 seconds. The obtained steel plate was continuously subjected to Sn plating on both surfaces to obtain a tin plate having a single-side Sn adhesion amount of 2.8 g / m ² .

  The plated steel sheet (cover) obtained as described above was subjected to a heat treatment equivalent to baking at 210 ° C. for 10 minutes, and then subjected to a tensile test. In the tensile test, tensile strength (breaking strength) and total elongation (breaking elongation) were measured at a tensile speed of 10 mm / min using a JIS No. 5 size tensile test piece.

  Moreover, the sample of the plated steel plate was extract | collected and the average crystal grain diameter and the expansion degree of the crystal grain in the cross section of a rolling direction were measured. The average crystal grain size and the elongation of crystal grains in the cross section in the rolling direction are determined by the linear test line described in “JIS G 0551” after polishing the vertical section of the steel sheet and revealing the grain boundary by night etching. It was measured by the cutting method.

  The pressure strength is measured by molding a 0.182mm sample into a 63mmΦ lid, then winding it around a 63mmΦ welded can body, introducing compressed air into the can, and measuring the pressure when the can lid is deformed. did. The case where the can lid did not deform when the internal pressure was 0.2 MPa was marked with ◯, and the case where the can lid was deformed when less than 0.2 MPa was marked with x. The workability was tested by a method specified in JIS Z 2247 using a test machine specified in JIS 7729. The Erichsen value (molding height when through cracks occurred) was 6 mm or more, and less than 6 mm was x.

  The results obtained above are shown in Table 2 together with the production conditions.

  From Tables 1 and 2, No. No. 7 is excellent in pressure resistance, and has achieved a tensile strength of 550 MPa or more required as an extremely thin steel plate for cans. Moreover, it is excellent in workability and has a total elongation of 10% or more necessary for processing of a lid or a three-piece can body.

  On the other hand, no. No. 1 has insufficient tensile strength because the C content is too small. No. Since 2 has too much C content, total elongation is insufficient. No. No. 3 has insufficient tensile strength because the P content is too small. No. No. 4 is insufficient in total elongation because the P content is too large. No. No. 5 has insufficient tensile strength because the N content is too small. No. Since No. 6 has too much N content, total elongation is insufficient. Comparative Example No. In No. 8, since the winding temperature is too high, the average crystal grain size is large, and the solid solution C precipitates as carbide and softens, so that the tensile strength is insufficient. Comparative Example No. No. 9 has a large degree of spread because the secondary cold rolling rate is too large, and the total elongation is insufficient due to hardening by processing.

  The steel plate for cans of the present invention has a tensile strength of 550 MPa or more, a total elongation of 10% or more, and can be obtained with a thin plate thickness. Therefore, it is optimal as a material for can lids, can bottoms, 3-piece can bodies, 2-piece can bodies, and the like.

Claims (2)

  In mass%, C: 0.020% or more and 0.100% or less, Si: 0.100% or less, Mn: 0.10% or more and 0.80% or less, P: more than 0.10% and 0.30% or less , S: 0.001% or more and 0.020% or less, Al: 0.005% or more and 0.100% or less, N: 0.0250% or more and 0.0350% or less, with the balance being Fe and inevitable impurities A high-strength, high-workability steel plate for cans, characterized in that the elongation of crystal grains is 2.00 or less, the tensile strength is 550 MPa or more, and the total elongation is 10% or more.   In mass%, C: 0.020% or more and 0.100% or less, Si: 0.100% or less, Mn: 0.10% or more and 0.80% or less, P: more than 0.10% and 0.30% or less , S: 0.001% or more and 0.020% or less, Al: 0.005% or more and 0.100% or less, N: 0.0250% or more and 0.0350% or less, with the balance being Fe and inevitable impurities The steel consisting of is made into a slab by continuous casting, after hot rolling at a finishing temperature of Ar3 transformation point or higher, after winding at a temperature of 650 ℃ or less, then primary cold rolling at a rolling rate of 80% or more, Furthermore, secondary cold rolling is performed at a rolling rate of 5% or more and less than 10%, and a method for producing a steel plate for a high-strength, high-workability can.