TWI593811B - Can steel plate and its manufacturing method - Google Patents

Description

Steel plate for can and manufacturing method thereof

The present invention relates to a steel sheet for cans which is used as a material for a three-piece can formed by processing a can body having a high degree of processing, a two-piece can having a pressure resistance, and the like. More specifically, the present invention relates to a steel sheet for a can having a large total elongation and an excellent upper and lower strength, and a method for producing the same.

In recent years, in order to expand the demand for steel cans, strategies to reduce the cost of cans have been adopted, and strategies for investing in steel cans in novel cans such as bottles or cans have been adopted.

As a strategy for reducing the cost of the can, the cost of the material can be reduced. Needless to say, even in the case of a three-piece can in which a simple cylinder is formed as a main body, the steel plate to be used is thinned.

However, if the steel sheet is simply thinned, the strength of the can body is lowered. Therefore, in a portion where a high-strength material is used like a can body portion of a drawing and redrawing (DRD) can or a welded can, a steel plate which is simply thinned can not be used. Therefore, a steel sheet for cans having high strength and extremely thinness is desired.

At present, an extremely thin and rigid steel sheet for cans is produced by a double-rolling method (hereinafter referred to as DR method) of secondary cold rolling having a reduction ratio of 20% or more after annealing. The steel sheet produced by the DR method has high strength but has a characteristic of low total elongation.

On the other hand, it is difficult to use a DR material lacking ductility from the viewpoint of workability as a material of a can formed by a can processing such as a can-shaped can, which has been put into the market recently. Further, since the DR material is increased in comparison with a steel sheet which is usually subjected to quenching and tempering after annealing, the manufacturing cost is high.

In the following patent documents, a single reduction method (SR method) for controlling characteristics in a single cold rolling and annealing step in order to avoid the disadvantage of such a DR material is omitted, secondary cold rolling is omitted, and various strengthening methods are used. Or a method of producing a high-strength steel sheet by a secondary reduction of a secondary cold rolling reduction of about 5% or less.

Patent Document 1 discloses an ultra-thin cold-rolled steel sheet for a high-strength can having a thickness of 0.3 mm or less, which is characterized by having a composition containing C: 0.02% or less and Si: 0.10% or less in mass%. Mn: 1.5% or less, P: 0.20% or less, S: 0.01% or less, Al: 0.01% or less, N: 0.0050% to 0.0250%, and 0.0050% or more (solid solution C + solid solution N), and the rest includes Fe and inevitable impurities, and having a recrystallization ratio of 90% or more, and having a calcination hardening amount (BH amount): 100 MPa or more, an increase in tensile strength by coating baking treatment ΔTS : 30 MPa or more, the lodging stress after coating and firing treatment: 550 MPa or more. Further, Patent Document 1 proposes a technique of adjusting hot rolling conditions and cooling conditions, rapidly cooling to a low temperature region after continuous annealing, effectively utilizing the effect of solid solution C amount + solid solution N amount, and utilizing age hardening phenomenon. Thereby, a steel sheet for high strength cans which is usually used for DR materials is obtained. The steel sheet for cans described in Patent Document 1 has a drop stress after the coating and firing treatment of up to 550 MPa or more.

Patent Document 2 discloses a steel sheet for can making which is excellent in deep extensibility and flange workability at the time of canning, and which is excellent in surface properties after canning and has sufficient can strength, and is characterized in that the steel sheet for can making is characterized in that C: 0.020% to 0.150%, Si: 0.05% or less, Mn: 1.00% or less, P: 0.050% or less, S: 0.010% or less, N: 0.0100% or less, and Al: 0.100% or less, by weight ratio. Nb: 0.005% to 0.025%, the rest contains unavoidable impurities and iron, which is a substantial single-phase structure of ferrite and iron, with a drop strength of 40 kgf/mm ² or more, an average crystal grain size of 10 μm or less, and a plate thickness. It is 0.300 mm or less. Further, Patent Document 2 proposes a steel sheet obtained by precipitation strengthening of Nb carbide or by refining and strengthening of carbonitrides of Nb, Ti, and B, thereby achieving a balance between strength and ductility.

Patent Document 3 discloses a steel sheet for a thin-walled deep-extension extrusion can, which is characterized by comprising a low carbon steel sheet containing C: 0.001% by weight to 0.010% by weight, Si: ≦ 0.05% by weight, Mn : ≦ 0.9% by weight, P: 0.131% by weight to 0.200% by weight, S: ≦ 0.04% by weight, Al: 0.006% by weight to 0.08% by weight, N: 0.0010% by weight to 0.015% by weight, the balance being Fe and inevitable A method of increasing the strength by solid solution strengthening using Mn, P, N or the like has been proposed. Prior art literature

Japanese Patent Laid-Open Publication No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei.

[Problems to be solved by the invention]

First, it is necessary to ensure strength in order to reduce the thickness (thinness). On the other hand, in the case of using a steel sheet formed by a can body processing such as canning processing or a can body formed by flange processing, it is necessary to apply high ductility steel.

For example, in the case of the bottom processing in the production of a two-piece can, and the processing of the can body and the flange processing in the production of a three-piece can represented by the expansion of the can, it is necessary to use a steel plate having a large total elongation as a material in order to prevent the steel sheet from being broken. .

Further, in consideration of resistance to a highly corrosive content, it is necessary to provide a steel sheet having good corrosion resistance. Therefore, excessive element addition which hinders corrosion resistance cannot be performed.

With respect to the above characteristics, in the above-described prior art, although a steel sheet satisfying any of strength, ductility (total elongation), and corrosion resistance can be manufactured, it is impossible to manufacture a steel sheet which is all satisfied.

For example, the method described in Patent Document 1 is a method effective for increasing the strength. However, since the amount of solid solution C and solid solution N in the steel is large, the elongation at break becomes large. The elongation at break is produced by solid solution C or solid solution N fixation dislocations and reduced movable dislocations. In the strain region where the elongation at break is large, uneven deformation occurs due to a local drop phenomenon, so that a wrinkle called Stretcher-Strain is generated to impair the appearance.

Patent Document 2 proposes a steel that achieves high strength by precipitation strengthening and balances strength and ductility. However, the elongation at break is not considered. In the production method described in Patent Document 2, the present invention cannot be obtained. The value of the elongation at break as the target.

Patent Document 3 proposes high strength by solid solution strengthening. In the technique described in the above-mentioned document, P and Mn which are generally known as elements which impede corrosion resistance are excessively added, and thus there is a concern that corrosion resistance is hindered.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a characteristic having an upper falling strength of 450 MPa to 600 MPa and a total elongation of 13% or more after coating and firing, and corrosion resistance of a highly corrosive content. It is also a good high-strength high-strength steel sheet for cans and a method for producing the same. [Means for solving the problem]

The inventors of the present invention have conducted intensive studies in order to solve the above problems. As a result, the following findings were obtained.

By focusing on the combination of precipitation strengthening, solid solution strengthening, and processing strengthening, it is possible to achieve high strength without impairing elongation by achieving a balance between precipitation strengthening and solid solution strengthening.

Further, the reduction ratio of the secondary cold rolling is set to 1% to 19%, and the total elongation can be prevented from being lowered by the processing strengthening of the reduction ratio which is lower than the reduction ratio of the previous secondary cold rolling. In the case of achieving high strength.

Further, by designing the composition of the original plate in an element addition amount in a range not impeding the corrosion resistance, the corrosion-resistant content also exhibits good corrosion resistance.

According to the above findings, the present invention has completed the management of the high-strength high-strength can steel sheet and the method for producing the same by performing overall management of the components and the production method.

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

[1] A steel sheet for high-strength high-strength cans, which has a composition of C: more than 0.020% and 0.130% or less, Si: 0.04% or less, and Mn: 0.10% to 1.20. %, P: 0.100% or less, S: 0.030% or less, Al: 0.10% or less, N: more than 0.0120% and 0.020% or less, Nb: 0.004% to 0.040%, and the balance containing iron and unavoidable impurities, and precipitation of Nb The ratio of the amount to the total amount of Nb is the amount of precipitated Nb/the total amount of Nb ≧0.30, the average particle size of the Nb precipitate is 20 nm or less, and the average grain size of the ferrite iron is 7.0 μm or less, and the upper and lower of the coating after the firing treatment The strength is 450 MPa to 630 MPa, and the total elongation is 13% or more.

[2] The steel sheet for high-workability high-strength cans according to [1], wherein the volume fraction of Nb precipitates in the region from the surface to the depth of 1/8 in the thickness direction, and from the surface to 3/8 The ratio of the volume ratio of the Nb precipitates in the region from the depth position to the 4/8 depth position satisfies the following Expression 1. (Nb precipitate volume ratio of 3/8 to 4/8) / (Nb precipitate volume ratio from surface to 1/8) ≧ 1.10 (Formula 1) [3] Manufacture of high-strength high-strength steel sheet for cans A method for producing a steel sheet for high-process high-strength cans according to [1] or [2], wherein the manufacturing method is characterized by comprising: a hot rolling step for the steel at a finishing temperature of an Ar3 transformation point Calendering is carried out under the conditions of 990 ° C or lower, and coiling is carried out under the conditions of a coiling temperature of 400 ° C or more and less than 600 ° C; a cold rolling step, after the hot rolling step, pickling is performed at a pressure The rolling is performed under the condition that the lowering rate is 80% or more; and the annealing step is performed under the conditions of the soaking temperature of 650 ° C to 780 ° C and the soaking time of 10 s or more and 55 s or less after the primary cold rolling step. Continuous annealing; a secondary cold rolling step, after the annealing step, rolling at a rolling reduction of 1% to 19%. (Effect of the invention)

According to the present invention, a high-workability high-strength steel sheet having an upper-lowering strength of 450 MPa to 630 MPa and a total elongation of 13% or more can be obtained. Specifically, in the present invention, precipitation strengthening by Nb, solid solution strengthening by N, and processing by secondary cold rolling at a low pressure rate of 1% to 19% after annealing after annealing Strengthen and strengthen the composite and increase the strength without causing damage to other characteristics. As a result, the total elongation was 13% or more, and the upper and lower strength of the final product was 450 MPa to 630 MPa.

Moreover, according to the present invention, even if the fusion can is thin gauged (thinned) by the high strength of the original plate, high tank strength can be ensured. Even when the high-process high-strength steel sheet of the present invention is applied to a two-piece can of a pressure-resistant strength at a required bottom, a high compressive strength as in the current specification can be obtained. Further, by improving the ductility, it is possible to perform strong can processing or flange processing as in the canning process used in the welding can.

Moreover, according to the present invention, the composition of the components is set so as not to impede the corrosion resistance. As a result, the steel sheet for high workability high strength cans of the present invention is excellent in strength, workability, and corrosion resistance.

Hereinafter, embodiments of the present invention will be described. Further, the present invention is not limited to the following embodiments.

The steel sheet for high-workability high-strength cans of the present invention has an upper fall strength (hereinafter sometimes referred to as U-YP) of 450 MPa to 630 MPa, a total elongation of 13% or more, and excellent corrosion resistance. Further, in the steel sheet for high-workability high-strength cans of the present invention, the aging property can be reduced.

In the present invention, Nb is added as a precipitation strengthening element, and N is added as a solid solution strengthening element, and is subjected to processing strengthening by secondary cold rolling at a rolling reduction ratio of 1% to 19% after annealing. The intensity becomes the range. Further, when the upper and lower repulsive strengths are increased by the above-described method by a specific component system, the total elongation is also high. It is a feature of the present invention to have excellent upper and lower elongation strengths and a high total elongation is the most important requirement. By adding a precipitation strengthening element, a solid solution strengthening element, and a state in which the total elongation can be increased, the component composition, the structure, and the production conditions can be appropriately adjusted to obtain an upper degrading strength of 450 MPa. Steel sheet for high-workability high-strength cans with a total elongation of 630 MPa and a total elongation of 13% or more.

Then, the component composition of the steel sheet for high-strength high-strength cans of the present invention (in the present specification, the steel sheet for high-workability high-strength cans may be referred to as a steel sheet for cans) will be described. The steel sheet for high-workability high-strength cans of the present invention has a composition of C: more than 0.020% and 0.130% or less, Si: 0.04% or less, Mn: 0.10% to 1.20%, and P: 0.100% by mass%. Hereinafter, S: 0.030% or less, Al: 0.10% or less, N: more than 0.0120% and 0.020% or less, and Nb: 0.004% to 0.040%, and the balance contains iron and unavoidable impurities. Hereinafter, each component will be described. In addition, in the present specification, "%" in the description of the component composition means "% by mass".

C: more than 0.020% and 0.130% or less In the steel sheet for cans of the present invention, it is necessary to achieve a specific upper or lower relief strength (450 MPa to 630 MPa) after continuous annealing, and a total elongation of 13% or more. Therefore, it is important to set the average grain size of the ferrite iron to 7.0 μm or less, and to use precipitation strengthening by NbC produced by adding Nb. In order to adjust the average grain size of the ferrite iron to the above range, and to use the precipitation strengthening by NbC, it is important that the C content of the steel sheet for cans is used. Specifically, it is necessary to make the C content exceed 0.020%. When the C content exceeds 0.040%, the strength of the hot-rolled sheet increases, and the deformation resistance at the time of cold rolling increases. Therefore, surface defects may easily occur after rolling. In addition, in order to reduce the defects, it is necessary to reduce the rolling speed. However, when the upper drop strength is 600 MPa or more, the C content is preferably set to 0.070% or more. On the other hand, if the C content exceeds 0.130%, sub-peritecracking is caused during cooling in the melting of steel. Therefore, the upper limit of the C content is set to 0.130%. In addition, as described above, when the C content is more than 0.040%, the strength of the hot-rolled sheet increases, and the deformation resistance during cold rolling tends to increase, and in order to avoid surface defects after rolling, it is necessary to reduce the calendering speed. Therefore, from the viewpoint of easiness of production, the C content is preferably more than 0.020% to 0.040%.

Si: 0.04% or less Si is an element which increases the strength of steel by solid solution strengthening. However, if the Si content exceeds 0.04%, the corrosion resistance is remarkably impaired. Therefore, the Si content is set to 0.04% or less. Further, in the present invention, since the upper repulsive strength is improved by adjustment of elements other than Si or manufacturing conditions, it is not necessary to use solid solution strengthening by Si. Therefore, Si may not be contained in the present invention.

Mn: 0.10% to 1.20% Mn increases the strength of the steel by solid solution strengthening, and also reduces the average crystal grain size of the ferrite. The effect of reducing the average crystal grain size of the ferrite grains is remarkably produced by requiring a Mn content of 0.10% or more. Further, in order to secure the upper and lower strength of the target, it is necessary to set the Mn content to 0.10% or more. Therefore, the lower limit of the Mn content is set to 0.10%. On the other hand, when the Mn content exceeds 1.20%, corrosion resistance and surface characteristics are inferior. Therefore, the upper limit of the Mn content is set to 1.20%.

P: 0.100% or less P is an element having a large solid solution strengthening ability. However, if the content of P exceeds 0.100%, the corrosion resistance is poor. Therefore, the P content is set to 0.100% or less.

S: 0.030% or less The steel sheet for high-process high-strength cans of the present invention may not contain S. However, in the practice of this patent, S is preferably made 0.030% or less. Since the steel sheet for cans of the present invention has a high content of Nb, C, and N, the edge of the green sheet is easily broken by the correction tape during continuous casting. In terms of preventing the green sheet from being broken, the S content is preferably set to 0.030% or less. The S content is preferably 0.020% or less. The S content is more preferably 0.010% or less.

Al: 0.10% or less If the Al content is increased, the recrystallization temperature is increased. Therefore, it is necessary to set the annealing temperature to a high level only by increasing the Al content. In the present invention, the annealing temperature is set to a high level because of the influence of other elements added to increase the uppering strength and the recrystallization temperature is increased. Therefore, it is necessary to try to avoid an increase in the recrystallization temperature due to Al. Therefore, the Al content is made 0.10% or less. Further, it is preferable to add Al as a deacidifying agent, and in order to obtain the above effect, the Al content is preferably made 0.010% or more.

N: more than 0.0120% and 0.020% or less N is an element necessary for increasing solid solution strengthening. On the other hand, when the N content is too large, the green sheet is easily broken due to the lower correcting belt whose temperature is lowered during continuous casting. Therefore, the N content is set to 0.020% or less. On the other hand, in order to exert the effect of solid solution strengthening, it is necessary to set the N content to more than 0.0120%.

Nb: 0.004% to 0.040% Nb is an important additive element in the present invention. Nb is an element having a high carbide generating ability, and precipitates fine carbides. Thereby, the upper and lower lodging strengths rise. In the present invention, the upper fall strength or the surface property can be adjusted by the Nb content. The effect is produced when the Nb content is 0.004% or more, and therefore the lower limit of the Nb content is limited to 0.004%. On the other hand, since Nb causes an increase in the recrystallization temperature, if the Nb content exceeds 0.040%, the annealing at a temperature of 650 ° C to 780 ° C and a soaking time of 10 s or more and 55 s or less are not repeated. It is difficult to anneal if a part of the crystal remains or the like. Therefore, the upper limit of the Nb content is limited to 0.040%. Further, from the viewpoint of suppressing an increase in deformation resistance during cold rolling, the Nb content is preferably from 0.004% to 0.020%.

The remaining components other than the essential components and optional components are Fe and unavoidable impurities.

Next, the structure of the steel sheet for cans of the present invention will be described.

Average grain size of ferrite iron: 7.0 μm or less The structure of the steel sheet for cans of the present invention is a single-phase structure of ferrite grains. The average grain size of the ferrite iron not only affects the upper and lower undulation strength, but also affects the surface properties during the extension processing. If the average grain size of the ferrite iron of the final product exceeds 7.0 μm, a part of the surface roughening phenomenon occurs after the extension processing, and the appearance of the surface appearance is lost. Therefore, the average grain size of the ferrite iron is set to 7.0 μm or less. In addition, in order to refine the average grain size of the ferrite iron, it is necessary to reduce the soaking temperature during continuous annealing, and to suppress the grain growth of the ferrite iron crystal, or to add a large amount of fine particles to move the grain boundary. The element of the precipitate is preferably 5.0 μm or more in terms of the average crystal grain size of the ferrite iron in terms of the increase in the production cost. Furthermore, the average crystal grain size of the ferrite iron may be within the above range after the coating and firing, and the average crystal grain size of the ferrite iron does not change before and after the coating and firing treatment, so that it can be before the coating and firing treatment. Or after the measurement. In the present invention, the coating baking treatment refers to a treatment corresponding to heating during coating baking and lamination, and specifically refers to a range of from 170 ° C to 265 ° C for 12 seconds to 30 minutes. Heat treatment. Further, in the examples described below, heat treatment was performed at 210 ° C for 20 minutes as a standard condition.

Further, the control of the average crystal grain size of the ferrite grains is carried out by the composition of the components, the reduction ratio of cold rolling, and the annealing temperature. Specifically, the average crystal grain size of the ferrite grains of 7.0 μm or less is obtained by using the composition of the components and using the production conditions described later. When the soaking temperature at the time of continuous annealing is increased, the average grain size of the ferrite iron becomes large, and if the soaking temperature is lowered, the average grain size of the ferrite iron becomes small.

The amount of precipitated Nb/the total amount of Nb is ≧0.30. By setting the ratio of the amount of precipitated Nb to the amount of all Nb (the amount of precipitated Nb/the total amount of Nb) to 0.30 or more, the total elongation or corrosion resistance can be improved, and the target 450 can be achieved. Upward strength of MPa ~ 630 MPa. In addition, when the amount of precipitated Nb is increased, the amount of precipitated Nb/the total amount of Nb is preferably 0.9 or less for the reason that the particle size of precipitated Nb is coarsened. Further, the amount of precipitated Nb/the total amount of Nb may be within the above range after the coating is fired. Since the amount of Nb deposited and the amount of all Nb do not change before and after the coating baking treatment, the measurement can be performed before or after the coating baking treatment. Since the coating baking process is the same as the above, description is abbreviate|omitted.

As a method of adjusting the amount of precipitated Nb/the total amount of Nb ≧0.30, for example, the amount of precipitation of Nb can be increased by increasing the soaking temperature during continuous annealing.

Nb precipitate average particle diameter: 20 nm or less If the Nb precipitate average particle diameter is larger than 20 nm, the effect of increasing the strength due to the dislocation of the dislocation due to the precipitate cannot be expected. Therefore, in order to improve the total elongation or the corrosion resistance and obtain a specific strength, the average particle diameter of the Nb precipitate is set to 20 nm or less. Further, the average particle diameter of the Nb precipitates was measured by the method described in the examples. Here, the average particle diameter of the Nb precipitates may be within the above range of the average particle diameter of the Nb precipitates after the coating and firing. Since the average particle diameter of the Nb precipitate does not change before and after the coating baking treatment, the measurement can be performed before or after the coating baking treatment. Since the coating baking process is the same as the above, description is abbreviate|omitted.

As a method of adjusting the average particle diameter of the Nb precipitate to 20 nm or less, for example, when the average particle diameter of the Nb precipitate is to be lowered, the soaking time of the continuous annealing may be shortened to suppress the growth of the Nb precipitate.

(Nb precipitate volume ratio of 3/8 to 4/8) / (Nb precipitate volume ratio from surface to 1/8) ≧ 1.10 by region in the thickness direction from the surface to the 1/8 depth position The ratio of the volume fraction of the Nb precipitate to the volume fraction of the Nb precipitate in the region from the surface to the 3/8 depth position to the 4/8 depth position is 1.10 or less, and is increased from the surface to the 3/8 depth position to 4 The density of Nb precipitates in the region of the /8 depth position increases the amount of precipitation strengthening in the center layer to further increase the upper and lower strengths. In addition, the density of the Nb precipitates is reduced in the region from the surface to the 1/8 depth position to obtain a better total elongation. In this way, by imparting a material difference in the thickness direction, high workability and high strength can be achieved in an extremely excellent state. Further, the ratio of the volume ratio means that the ratio of the volume ratio after the coating firing is within the above range. Since the coating baking process is the same as the above, description is abbreviate|omitted.

The volume fraction of Nb precipitates in the region from the surface to the depth of 1/8 in the thickness direction, for example, by lowering the temperature of the final finish rolling of the hot rolling, coarsening the surface layer and promoting the crystal grains in the surface layer When the method of precipitation of Nb is adjusted, it becomes a large value, and when the temperature of the final finish rolling is raised, the surface layer is finely granulated and Nb precipitation in the crystal grain of the surface layer is suppressed, and it becomes small value.

The volume fraction of Nb precipitates in the region from the surface to the depth position of 3/8 to the depth of 4/8, for example, when the coiling temperature of the hot rolling is increased and the Nb precipitate grows, the value becomes a large value. When the coiling temperature of hot rolling suppresses the growth of the Nb precipitate, it becomes a small value.

Upper undulation strength: 450 MPa to 630 MPa In order to ensure the panel strength (panelling strength), dent strength (dent strength) and the compressive strength of the two-piece can for the thickness of 0.2 mm, the upper and lower The strength is set to 450 MPa or more. On the other hand, if an upper and lower strength of more than 630 MPa is to be obtained, a large amount of elements must be added. A large amount of elements are added to the risk of impeding the corrosion resistance of the steel sheet for cans of the present invention. Therefore, the upper drop strength is set to 630 MPa or less. The upper fall strength can be controlled to a target value by using the composition described above and using the manufacturing conditions described later. Further, in the present invention, it means that the upper fall strength after the coating is fired is in the above range. Since the coating baking process is the same as the above, description is abbreviate|omitted.

Total elongation: 13% or more If the total elongation is less than 13%, it is difficult to apply the steel sheet for a can of the present invention at the time of production of a can formed by processing of a can body such as a canning process. Further, when the total elongation is less than 13%, cracks are generated during the flange processing of the can, and therefore it is difficult to apply the steel sheet for a can of the present invention at the time of production of the can. Therefore, the lower limit of the total elongation is set to 13%. In addition, the total elongation is controlled to a target value by setting the component composition to a specific range and setting the reduction ratio of the secondary cold rolling after annealing to a specific range. Further, in the present invention, it means that the total elongation after coating baking is in the above range. Since the coating baking process is the same as the above, description is abbreviate|omitted. Further, in the present invention, the total elongation is usually 35% or less.

Next, an example of a method for producing the steel sheet for a can of the present invention can be preferably produced. The steel sheet for cans of the present invention is produced by a method including a hot rolling step, a primary cold rolling step, an annealing step, and a secondary cold rolling step. Hereinafter, each manufacturing step will be described.

The hot rolling step is a hot rolling step in which the steel (for example, a green sheet) is hot-rolled under conditions where the finishing temperature [finishing temperature] is equal to or higher than the Ar3 transformation point and 990 ° C or lower, and the coiling temperature is 400 ° C or higher. The step of coiling is carried out under conditions of less than 600 °C.

The steel to be used as a raw material will be described. The steel is obtained by melting a molten steel adjusted to the composition of the composition by a generally known melting method using a converter or the like, and then forming a rolled material by a usual casting method such as a continuous casting method. Hereinafter, the rolled material refers to the steel of the raw material.

Hot rolling is performed on the rolled material obtained as described above, and a hot rolled sheet is produced. At the start of rolling of hot rolling, it is preferred to set the temperature of the rolled material to 1230 ° C or higher.

Further, the finish rolling temperature in hot rolling is set to be equal to or higher than the Ar3 transformation point. The finish rolling temperature in hot rolling is an important factor in ensuring the strength of the upper fall. When the finish rolling temperature is less than the Ar3 transformation point, the grain growth is carried out by hot rolling in the two-phase domain of γ+α, so that the upper-lowering strength is lowered and the pressure resistance is insufficient. Therefore, the hot rolling finishing temperature is limited to the Ar3 metamorphic point. In addition, when the finish rolling temperature is more than 990 ° C, the total elongation is insufficient and the formability is deteriorated. Further, from the viewpoint of preventing generation of rust at a high temperature, the finish rolling temperature also sets 990 ° C as the upper limit.

The coiling temperature in the hot rolling step is an important factor in controlling the important upper and lower elongation strengths and total elongations in the present invention as target values. When the coiling temperature is set to 600 ° C or higher, N added for solid solution strengthening is precipitated as AlN, and the amount of solid solution N is lowered, and as a result, the upper and lower lodging strength is lowered. Therefore, the coiling temperature is set to be less than 600 °C. In addition, when the coiling temperature is less than 400 ° C, the total elongation is lowered and the moldability is deteriorated, so the coiling temperature is set to 400 ° C or higher. In addition, when the cooling is rapidly cooled in order to lower the coiling temperature, the cooling becomes uneven and the shape of the sheet deteriorates. Therefore, from the viewpoint of production efficiency, the coiling temperature is set to 400 ° C as the lower limit. Further, from the viewpoint of controlling the Nb precipitate, it is preferred that the cooling rate after coiling is slow cooling, preferably cooling at 11.5 ° C / hour or less, more preferably cooling at 6.3 ° C / hour or less. It is cooled below 1.7 ° C / hour. After such cooling, it is preferred to carry out the treatment in the next step after changing to 200 ° C or lower, more preferably 100 ° C or lower, and particularly preferably 50 ° C or lower.

Primary cold rolling step The primary cold rolling step is a step of pickling a steel sheet (hot rolled sheet) after the hot rolling step and rolling it under the conditions of a reduction ratio of 80% or more.

As long as the surface rust can be removed by pickling, the conditions are not particularly specified. Pickling can be carried out by a usual method.

The reduction ratio at the time of one cold rolling is one of important conditions in the present invention. When the reduction ratio at the time of primary cold rolling is less than 80%, it is difficult to produce a steel sheet having an upper drop strength of 450 MPa or more. Further, when the reduction ratio in this step is less than 80%, in order to obtain a usual thickness (about 0.17 mm) of the DR material, it is necessary to set the thickness of the hot-rolled sheet to at least 1 mm. However, in operation, it is difficult to set the thickness of the hot rolled sheet to 1 mm or less. Therefore, the reduction ratio in this step is set to 80% or more.

The annealing step is an annealing step in which the steel sheet (cold rolled sheet) is continuously annealed after a single cold rolling step at a soaking temperature of 650 ° C to 780 ° C and a soaking time of 10 s or more and 55 s or less. A step of.

Annealing uses continuous annealing. In order to ensure good workability, the soaking temperature must be equal to or higher than the recrystallization temperature of the steel sheet, and the total elongation should be ensured in order to make the structure more uniform, and the soaking temperature is limited to 650 ° C or higher. On the other hand, when the soaking temperature exceeds 780 ° C, the crystal grain size of the ferrite grains becomes large, the upper and lower lodging strengths are lowered, and the compressive strength is insufficient. Further, in order to carry out continuous annealing under conditions exceeding 780 ° C, in order to prevent breakage of the steel sheet, it is necessary to reduce the conveyance speed as much as possible, and the productivity is lowered. Therefore, the soaking temperature is set to a range of 650 ° C to 780 ° C.

When the soaking time exceeds 55 s, the Nb precipitate particle size becomes too large, the upper and lower lodging strength decreases, and the pressure resistance is insufficient, and productivity cannot be ensured. Therefore, the soaking time is set to 55 s or less. When the soaking time is less than 10 s, there is a concern that heating unevenness occurs at a high speed plate, the Nb precipitation form does not become a desired form, the total elongation is deteriorated, and the tension in the furnace becomes unstable. Breaking, so the soaking time is set to 10 s or more.

Secondary Cold Rolling Step The so-called secondary cold rolling step is a step of rolling a steel sheet (annealed sheet) under the conditions of a rolling reduction of 1% to 19% after the annealing step.

When the reduction ratio at the time of secondary cold rolling after annealing is set to be the same as the normal DR material production conditions, the strain introduced during the processing increases, and the total elongation decreases. In the present invention, it is necessary to ensure a total elongation of 13% or more by an extremely thin material, so that the reduction ratio at the time of secondary cold rolling is set to 19% or less. In addition, in order to adjust the surface roughness of the steel sheet, the unevenness of the roll is transferred to the steel sheet, and the reduction ratio of the secondary cold rolling must be 1% or more. Further, from the viewpoint of preventing the sliding of the steel sheet and the roll which are delayed, and ensuring the total elongation, the reduction ratio of the secondary cold rolling is preferably 4% to 12%. Example

The steel slab was obtained by melting a steel containing the composition shown in Table 1 and containing the Fe and the unavoidable impurities in the actual machine converter. The obtained slab is reheated, and then hot rolled and coiled. Then, after pickling, cold rolling is performed once to produce a steel sheet. Further, the temperature of the steel sheet before pickling is in the range of 25 ° C to 60 ° C for the entire steel ring. The obtained steel sheet was heated at a heating rate of 15 ° C/sec. Then continuous annealing is performed. Then, after cooling, secondary cold rolling is performed, and usual tin plating is continuously performed to obtain tin-plated iron sheets. Further, detailed manufacturing conditions are shown in Table 2. Further, the Ar3 transformation point was calculated by measuring the temperature at which the volume change was the largest from γ to α during cooling.

[Table 1]

[Table 2]

The plated steel sheet (tin-plated iron sheet) obtained above was subjected to a heat treatment corresponding to the coating baking treatment at 210 ° C for 20 minutes, and then subjected to a tensile test to measure the upper-inferior strength and the total elongation, and also The crystal structure and the average crystal grain size were investigated. The survey method is as follows.

The tensile test was carried out using a JIS No. 5 tensile test piece, and the upper drop strength (U-YP) and the total elongation (EI) were measured, and the strength, ductility and timeliness were evaluated. The aging property was evaluated by the elongation at break which contributes to the generation of tensile strain marks at the time of forming. When the elongation at break is 4% or less, the occurrence of tensile strain marks during processing can be suppressed. The results obtained are shown in Table 3.

Regarding the crystal structure, the sample was ground, and the crystal grain boundary was etched by a nitric acid etching solution, and observed by an optical microscope.

Regarding the average crystal grain size of the ferrite grains, the crystal structure observed as described above was measured by a dicing method of JIS G5503. The results obtained are shown in Table 3.

Further, regarding the amount of precipitated Nb, electrolytic deposition was carried out using 10% acetalacetone-1% tetramethylammonium chloride-methanol solution, and acid dissolution was carried out, and it was measured by Inductively Coupled Plasma (ICP). Quantify Nb. Regarding the total amount of Nb, the sample was directly subjected to acid dissolution and measured by ICP. Further, the average particle diameter of the Nb precipitate was measured by a transmission electron microscope (TEM). The results obtained are shown in Table 3.

[table 3]

The photographs of the 10 fields of view were observed at various depths by TEM at 100,000 times, and the particle size and the number of precipitates were measured, and the film was measured in the thickness direction from the surface to the depth of 1/8 by the method of conversion to the volume ratio. The volume fraction of Nb precipitates in the region of the position, and the volume fraction of Nb precipitates in the region from the surface to the 3/8 depth position to the 4/8 depth position. The measurement results are shown in Table 4.

For the measurement of the compressive strength, a sample having a thickness of 0.26 mm (plated steel sheet) was formed into a 63 mm Φ cover, and then wound up on a 63 mm Φ welded can body, and compressed air was introduced inside the can, and the can was measured. The pressure when the cover is deformed. In the case where the internal pressure is 0.20 MPa, the can lid is not deformed, it is set to "○", and when the internal pressure is less than 0.20 MPa, the can lid is deformed to "x". The results are shown in Table 4.

For the moldability, a sample having a thickness of 0.26 mm was used and evaluated by a method specified in JIS B 2729 using a test machine specified in JIS B 7729. The Erichsen value (formation height at the time of penetration cracking) is 6.5 mm or more and is set to "○", and less than 6.5 mm is set to "X". The results are shown in Table 4.

[Table 4]

According to Table 3, in the example of the present invention, the structure has an average crystal grain size of 7.0 μm or less and is a fine ferrite iron structure, so that the upper and lower lodging strength is large, and both strength and ductility are excellent. Further, in the present invention, since the chemical composition shown in Table 1 is adjusted, the corrosion resistance is also excellent.

Further, in the comparative examples, the desired characteristics of the present application could not be obtained because of any of the conditions of the patent application scope of the present application. [Industrial availability]

According to the present invention, a steel sheet excellent in any of the properties of strength, ductility, and corrosion resistance can be obtained, and therefore, a three-piece can having a high-workability can be processed, and a two-piece can having a bottom portion processed at a bottom portion is centered. Most suitable as a steel plate for cans.

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Claims (3)

A steel sheet for a can, which has a composition of C: more than 0.020% and 0.130% or less, Si: 0.04% or less, Mn: 0.10% to 1.20%, and P: 0.100% or less. S: 0.030% or less, Al: 0.10% or less, N: more than 0.0120% and 0.020% or less, and Nb: 0.004% to 0.040%, and the balance containing iron and unavoidable impurities, and the ratio of the amount of precipitated Nb to the total amount of Nb is The amount of Nb precipitated/the total amount of Nb is ≧0.30, the average particle size of the Nb precipitate is 20 nm or less, the average grain size of the ferrite iron is 7.0 μm or less, and the upper and lower lodging strength after the coating and firing treatment is 450 MPa to 630 MPa. The total elongation is 13% or more. The steel sheet for cans according to claim 1, wherein a volume fraction of Nb precipitates in a region from a surface to a depth of 1/8 in a thickness direction, and a position from a surface to a depth of 3/8 ～4/ The ratio of the volume ratio of the Nb precipitates in the region at the depth of 8 satisfies the following formula 1: (Nb precipitate volume ratio of 3/8 to 4/8) / (Nb precipitate volume from the surface to 1/8) Rate) ≧1.10 (Formula 1). A method for producing a steel sheet for a can, which is used for producing a steel sheet for a can according to claim 1 or 2, wherein the method for producing the steel sheet for a can is characterized by comprising: a hot rolling step, a steel Rolling is performed under the conditions that the finishing rolling temperature is above the Ar3 transformation point and below 990 ° C, and the winding is performed under the conditions of a coiling temperature of 400 ° C or more and less than 600 ° C; a primary cold rolling step in the hot rolling step Thereafter, pickling is performed, and rolling is performed under the condition that the reduction ratio is 80% or more. The annealing step is performed at the soaking temperature of 650 ° C to 780 ° C and the soaking time is 10 s or more after the primary cold rolling step. Continuous annealing is performed under conditions of 55 s or less; and the secondary cold rolling step is carried out under the conditions of a reduction ratio of 1% to 19% after the annealing step.