KR20170063744A - Steel sheet for two-piece can and manufacturing method therefor - Google Patents

Abstract

There is provided a two-piece can steel sheet which can be suitably used for shaping a bead or a can body portion of a geometrical shape into a can body portion in addition to drawing processing or ironing processing. At least 0.020% of Si, at most 0.04% of Si, at least 0.10% of Si, at most 0.60% of P, at most 0.02% of P, at most 0.015% of S, at most 0.010% : 0.0005% or more and 0.0030% or less, the balance being Fe and inevitable impurities, having a tensile strength of 480 MPa or more, an elongation of 7% or more, a yield elongation of 3% or less, a ferrite grain size of 6 탆 Of the steel sheet for a two-piece can.

Description

TECHNICAL FIELD [0001] The present invention relates to a steel sheet for a two-piece can,

The present invention relates to a steel sheet for a can which is suitable for a material for a can container used in a food or beverage can, and a method for producing the same. Particularly, the present invention relates to a two-piece high strength steel sheet excellent in moldability and a method for producing the same. The high strength steel sheet for two-piece can according to the present invention is preferably applied to a two- .

From the viewpoint of recent environmental load reduction and cost reduction, it is required to reduce the amount of steel plates used for food cans and beverage cans. For this reason, the thinning of the steel sheet as the material regardless of the two-piece can and the three-piece can is progressing.

In recent years, in order to compensate for the decrease in the strength of the can body due to the thinning of the steel sheet, it is often the case that the can body is formed as a can with a bead or a geometric shape. In the case of manufacturing a two-piece can of a mold (sometimes referred to as a two-piece mold), the can body is processed after drawing with a relatively high degree of processing by drawing or ironing. For this reason, a steel sheet to be used in the production of mold release can of two-piece can requires higher moldability. On the other hand, the bottom of the can having a low degree of processing has a small increase in strength due to work hardening. For this reason, when the steel sheet is made thin, the strength of the steel sheet tends to be insufficient at the bottom of the can. In particular, in the case of a negative pressure can having a flat can bottom shape, a strength higher than that of a conventional SR (Single Reduce) steel plate is required. For this reason, it is effective to use a DR (Double Reduce) steel plate which is likely to have a high strength even if it is made thinner at the bottom of the can.

Since the DR steel sheet is hardened mainly by work hardening, the moldability is generally lowered. If the moldability is lowered, it is not preferable in the can body portion as described above. Therefore, a technique for increasing the formability of the DR steel sheet has been studied.

For example, Patent Document 1 discloses a steel sheet comprising, by mass%, 0.001 to 0.10% of C, 0.05 to 0.50% of Mn, 0.015 to 0.13% of Al, 0.05% And the balance of Fe and inevitable impurities and having a thickness of 10 to 20 mm on both sides of an electrolytic chromate-treated steel sheet having a grain size of 6 to 30 탆, a center line average roughness of 0.05 to 0.6 탆 and a plate thickness of 0.15 to 0.30 mm, Coated steel sheet for a dry drawn ironing can which is coated with a thermoplastic resin having a thickness of from 50 to 50 mu m and a surface of which is coated with a high-temperature volatile lubricant.

Patent Document 2 discloses a ferritic stainless steel comprising 0.001 to 0.06% of C, 0.05 to 0.50% of Mn, 0.015 to 0.13% of Al, 0.05% or less of Si, 0.03% or less of P and 0.03% or less of S, Rolled at a rolling rate of 5 to 25% after pickling, cold rolling and continuous annealing to obtain a center line average roughness of 0.05 to 0.6 탆 and a plate thickness of 0.15 to 0.30 mm, Coated steel sheet for electrolytic chromic acid treatment, followed by coating a thermoplastic resin having a thickness of 10 to 50 占 퐉 on both surfaces thereof and applying a high-temperature volatile lubricant to the surface of the resin coated steel sheet for a dry drawing ironing can. .

 Patent Document 3 discloses a steel sheet which comprises 0.02 to 0.07% of C, 0.005 to 0.05% of Si, 0.1 to 1.5% of Mn, 0.04% or less of P, 0.02% or less of S, 0.005 to 0.1% of Al, : 0.003 to 0.007%, B: 0.001 to 0.01%, B / N: 0.3 to 1.5, and the balance being Fe and inevitable impurities, And a rank pod value (r value) of at least one of them is 0.8 or less.

Japanese Patent Publication No. 3140929 Japanese Patent Publication No. 2937788 Japanese Patent Publication No. 4630268

However, the above-mentioned prior arts have the following problems.

According to the technique described in Patent Document 1, the moldability required when molding a straight can is secured. However, in the technique described in Patent Document 1, the moldability required for molding a mold releasing can in which processing of a processing bead or the like is performed on the can body portion can not be ensured.

In the technique described in Patent Document 2, similarly to the technique described in Patent Document 1, the moldability required for forming a straight can is secured. However, similarly to the technique described in Patent Document 2, the moldability required for molding a mold release can not be ensured.

The technique described in Patent Document 3 is for a three-piece can. In the steel sheet described in Patent Document 3, since the r value of at least one of the rolling direction and the plate width direction is 0.8 or less, the anisotropy becomes large. This anisotropic steel sheet has no formability required for forming a two-piece can including drawing.

SUMMARY OF THE INVENTION The present invention has been made in view of the circumstances, and it is an object of the present invention to provide a high strength steel sheet for two-piece can which can be suitably used for forming a two- .

The inventors of the present invention conducted intensive studies in order to solve the above problems. Specifically, in order to find a method of achieving both the excellent strength required for the can bottom and the excellent moldability required for the can body, there have been intensive researches. As a result, the composition, tensile strength, elongation, yield elongation , And that the above-mentioned problems can be solved by adjusting the ferrite particle size to a specific range. The present invention has been accomplished on the basis of this finding.

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

C: not more than 0.080%, Si: not more than 0.04%, Mn: not less than 0.10% and not more than 0.60%, P: not more than 0.02%, S: not more than 0.015%, Al: not less than 0.010% Or less, N: not less than 0.0005% and not more than 0.0030%, the balance being Fe and inevitable impurities, having a tensile strength of not less than 480 MPa, an elongation of not less than 7%, a yield elongation of not more than 3% Is less than 6 占 퐉.

(2) The high strength steel sheet for a two-piece can according to (1), further comprising 0.0001% or more and 0.0030% or less of B by mass%.

(3) A method for producing a high-strength steel sheet for a two-piece can as set forth in (1) or (2), comprising the steps of: heating a slab at a heating temperature of 1130 DEG C or higher; and heating the slab at a hot rolling temperature of 820 to 930 DEG C A rolling step of winding the hot rolled sheet obtained in the hot rolling step at a coiling temperature of 640 DEG C or lower; a pickling step of pickling the hot rolled sheet after the winding step; A primary cold rolling step of primary cold rolling under the conditions of a rolling rate of 85% or more, and a continuous annealing step of continuously annealing the cold-rolled sheet obtained in the primary cold rolling step at an annealing temperature of 620 캜 or higher and 690 캜 or lower , And the annealing plate obtained in the continuous annealing step is subjected to a second cold rolling step under a condition of a rolling rate of 6 to 20% The method of two-piece cans with a high-strength steel sheet which.

 The high strength steel sheet for two-piece can according to the present invention is adjusted to have a specific component composition and has a tensile strength of 480 MPa or more, an elongation of 7% or more, a yield elongation of 3% or less and a ferrite grain size of less than 6.0 탆. As a result, the high-strength steel sheet for a two-piece can of the present invention has excellent moldability required for the can body and has excellent strength required for the can bottom. Therefore, by using the high-strength steel sheet for a two-piece can according to the present invention, a two-piece release can can be easily manufactured.

INDUSTRIAL APPLICABILITY As described above, according to the present invention, it is possible to reduce the thickness of a steel sheet used in the production of food cans and beverage cans, to achieve resource savings and cost reduction, and to exert special effects in industry.

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

<High strength steel plate for 2-piece can>

A high strength steel sheet for a two-piece can according to the present invention is characterized in that it comprises 0.020% to 0.080% of C, 0.04% or less of Si, 0.10% or more and 0.60% or less of Mn, 0.02% or less of P, Al: not less than 0.010% and not more than 0.100%, N: not less than 0.0005% and not more than 0.0030%, and the remainder has a composition of Fe and inevitable impurities.

The high strength steel sheet for two-piece can according to the present invention has a tensile strength of 480 MPa or more, an elongation of 7% or more, and a yield elongation of 3% or less.

The structure of the high strength steel sheet for a two-piece can according to the present invention is a structure having a ferrite grain size of less than 6 탆.

Hereinafter, the high strength steel sheet for a two-piece can according to the present invention will be described in the order of composition, physical properties, and organization.

As described above, the high strength steel sheet for a two-piece can according to the present invention contains 0.020 to 0.080% of C, 0.04% or less of Si, 0.10 to 0.60% of Mn, 0.015% or less, Al: 0.010% or more and 0.100% or less, N: 0.0005% or more and 0.0030% or less, the balance being Fe and inevitable impurities. The reason why the composition of this component is adopted is as follows. In the following description, "%" representing the content of each component means "% by mass".

C: 0.020% or more and 0.080% or less

C is an important element for strength improvement. When the C content is 0.020% or more, the tensile strength can be 480 MPa or more. If the C content exceeds 0.080%, the elongation is lowered to less than 7% and the can composition is lowered. Therefore, it is necessary to set the upper limit of the C content to 0.080%. In addition, the larger the C content, the finer the ferrite grain size and the higher the strength. Therefore, the C content is preferably 0.030% or more. From the viewpoint of ensuring can-making, the C content is preferably 0.060% or less.

Si: not more than 0.04%

When Si is contained in a large amount, surface treatment is deteriorated by surface concentration, and corrosion resistance is lowered. Therefore, the Si content needs to be 0.04% or less. And preferably 0.03% or less.

Mn: not less than 0.10% and not more than 0.60%

Mn has an effect of improving the hardness of the steel sheet by solid solution strengthening. Further, by forming MnS in Mn, it is possible to prevent deterioration of hot ductility due to S contained in the steel. In order to obtain these effects, it is necessary to set the Mn content to 0.10% or more. In particular, it is preferable to set the Mn content to 0.30% or more in order to secure the tensile strength even if the rolling rate in the DR rolling is reduced by strengthening the solid solution by Mn. When the Mn content exceeds 0.60%, the elongation is remarkably lowered and the can composition is lowered. Therefore, it is necessary to set the Mn content to 0.60% or less.

P: not more than 0.02%

When P is contained in a large amount, moldability is deteriorated from excessive hardening or center segregation. Also, when P is contained in a large amount, the corrosion resistance is deteriorated. Therefore, the upper limit of the P content is set to 0.02%.

S: not more than 0.015%

S forms sulfides in the steel and lowers hot ductility. Therefore, the upper limit of the S content is 0.015% or less.

Al: 0.010% or more and 0.100% or less

Al forms N and AlN to reduce the solid solution N in the steel, lowering the yield elongation, and suppressing the strain strain. Therefore, the Al content needs to be 0.010% or more. From the viewpoint of decreasing the yield elongation and improving can fabrication, the Al content is preferably 0.050% or more, more preferably 0.060% or more. In addition, when the Al content is excessive, a large amount of alumina is generated, and alumina remains in the steel sheet, resulting in deterioration of the can forming composition. Therefore, it is necessary to set the Al content to 0.100% or less. And preferably 0.080% or less.

N: 0.0005% or more and 0.0030% or less

When N is present as solute N, the yield elongation increases, strainer strain occurs, the surface appearance becomes poor, and the can composition becomes poor. Therefore, the N content needs to be 0.0030% or less. It is preferably not more than 0.0025%. On the other hand, it is difficult to stably reduce the N content to less than 0.0005%, and if the N content is less than 0.0005%, the manufacturing cost also increases. Therefore, the lower limit of the N content is 0.0005%.

The high strength steel sheet for two-piece can of the present invention preferably contains B in an amount of 0.0030% or less as an optional component in addition to the above essential components.

B: 0.0001 to 0.0030%

B forms N and BN to reduce the solid solution N and decrease the yield elongation. Therefore, it is preferable to contain B, and in order to obtain the effect of adding B, the B content is preferably 0.0001% or more, more preferably 0.0003% or more. In addition, even if B is excessively contained, not only the effect is saturated but also the elongation rate is lowered, the anisotropy is deteriorated, and the can composition is lowered. Therefore, it is preferable to set the upper limit of the B content to 0.0030%.

In addition, the balance other than the above essential components and optional components is Fe and inevitable impurities. As the inevitable impurities, 0.08% or less of Cr, 0.02% or less of Cu, 0.02% or less of Ni and 0.006% or less of O can be given.

Next, properties of the high strength steel sheet for two-piece can of the present invention will be described. As described above, the high strength steel sheet for a two-piece can according to the present invention has a tensile strength of 480 MPa or more, an elongation of 7% or more, and a yield elongation of 3% or less. The technical significance of each physical property is as follows, but in the present invention, the combination of these physical properties, the composition of the constituents and the structure described below has a viscosity capable of satisfying both the excellent strength required for the can bottom and the excellent moldability required for the can body It is one of the important technical significance.

Tensile strength: 480 ㎫ or more

In order to secure the strength of the bottom of the can, it is necessary to set the tensile strength of the steel sheet to 480 MPa or more. Preferably at least 490 MPa. The tensile strength of the steel sheet is a value obtained by measurement by the method described in the embodiment. In the present invention, the tensile strength is usually 580 MPa or less.

Elongation: 7% or more

In addition to drawing and ironing, it is necessary to set the elongation to 7% or more in order to secure the can body workability of beads and the like. And preferably at least 9%. By incorporating the steel component in a predetermined range and making the ferrite grain size finer under the manufacturing conditions described later, it is possible to obtain a high strength of 480 MPa or more, an elongation of 7% or more, and to ensure can manufacture. The elongation percentage of the steel sheet is a value obtained by measuring by the method described in the embodiment. In the present invention, the elongation is usually 25% or less.

Yield elongation: 3% or less

It is necessary to set the yield elongation to 3% or less in order to prevent stretch strain during can production. And preferably 2% or less. The yield elongation of the steel sheet is a value measured by the method described in the embodiment.

Next, the structure of the high strength steel sheet for two-piece can of the present invention will be described. The ferrite grain size in the structure of the high strength steel sheet for two-piece can of the present invention is less than 6 占 퐉.

Ferrite grain size: less than 6 탆

In addition to adjusting the composition of the steel sheet as described above, the grain size of the ferrite is made finer to improve the balance between high strength and elongation. For this reason, it is necessary to set the ferrite grain size to less than 6.0 mu m. Also, by reducing the ferrite grain size to less than 6.0 μm and decreasing the yield elongation to 3% or less, the adhesion between the resin coated on the steel sheet and the surface of the steel sheet is improved. From this viewpoint, it is preferable that the ferrite grain size be 5.5 m or less. Further, as described in the examples, the particle diameter means the average crystal grain size.

In the present invention, it is preferable that the content of the ferrite phase in the structure is 95 vol% or more because of the improvement of the elongation. More preferably, it is 98 vol% or more. Other phases other than the ferrite phase include cementite, pearlite, martensite, bainite and the like.

&Lt; Process for producing high strength steel sheet for two-piece can &

An example of a method of manufacturing a high strength steel sheet for a two-piece can according to the present invention includes a heating step, a hot rolling step, a winding step, a pickling step, a primary cold rolling step, a continuous annealing step, And the like. Each step will be described below.

Heating process

The heating step is a step of heating the slab at a heating temperature of 1130 DEG C or higher. If the heating temperature before the hot rolling is too low, a part of the AlN is undissolved. This undissolved solution is a cause of occurrence of coarse AlN which deteriorates the can forming composition. Therefore, the heating temperature in the heating step is set to 1130 DEG C or higher. Preferably 1150 DEG C or more. The upper limit of the heating temperature is not specifically defined, but if the heating temperature is excessively high, the scale is excessively generated, resulting in a defect on the surface of the product. Therefore, the upper limit of the heating temperature is preferably 1260 占 폚.

Further, since the composition of the slab becomes the composition of the high strength steel sheet for two-piece can, the composition of the slab needs to be adjusted so as to satisfy the composition of the high strength steel sheet for two-piece according to the present invention.

Hot rolling process

The hot rolling step is a step of hot-rolling the slab after the heating step under the conditions of the hot rolling finishing temperature of 820 to 930 占 폚. When the hot rolling finish rolling temperature is higher than 930 占 폚, the grain size of the ferrite in the hot-rolled sheet becomes large, the ferrite grain size of the annealing plate becomes large, the tensile strength is lowered, and the balance between the tensile strength and the elongation becomes worse. For this reason, the upper limit of the hot rolling finishing temperature is set at 930 캜. When the hot rolling finishing temperature is less than 820 占 폚, the anisotropy of the tensile properties becomes large, and the can composition becomes low. Therefore, the lower limit of the hot rolling finishing temperature is 820 占 폚. The preferred lower limit is 860 ° C.

Winding process

The winding step is a step of winding the hot rolled sheet obtained in the hot rolling step at a winding temperature of 640 DEG C or lower. If the coiling temperature exceeds 640 DEG C, the ferrite grain size in the hot-rolled steel sheet becomes large, the ferrite grain size of the annealing plate becomes large, the tensile strength is lowered, and the balance between the tensile strength and the elongation is also poor. Therefore, the upper limit of the coiling temperature is set to 640 캜. Although the lower limit of the coiling temperature is not particularly defined, it is preferable that the coiling temperature is 570 캜 or higher from the viewpoint of decreasing the yield elongation by decreasing the amount of dissolved N by generating AlN during coiling.

Pickling process

The pickling process is a process of pickling a hot rolled sheet after the winding process. The pickling conditions are not limited as long as the surface scale can be removed. And can be pickled by a conventional method.

Primary cold rolling process

The primary cold rolling step is a step of primary cold rolling the hot rolled sheet after the pickling at a rolling rate of 85% or more. The rolling rate of the primary cold rolling needs to be 85% or more in order to miniaturize the ferrite grain size after annealing and to improve balance between tensile strength and formability. If the rolling rate in the primary cold rolling becomes too large, the anisotropy of the tensile properties becomes large, and the can composition is sometimes lowered. For this reason, the rolling rate of the primary cold rolling is preferably 90% or less.

Continuous annealing process

The continuous annealing step is a step of continuously annealing the cold-rolled sheet obtained in the primary cold rolling step under conditions of an annealing temperature of 620 DEG C or higher and 690 DEG C or lower. In order to ensure moldability, it is necessary to sufficiently recrystallize during annealing, and therefore, it is necessary to set the annealing temperature to 620 DEG C or more. If the annealing temperature is too high, the ferrite grain size becomes coarse, so the annealing temperature needs to be 690 캜 or lower. The annealing method is not limited, but continuous annealing is preferable from the viewpoint of material uniformity.

Secondary cold rolling process

The secondary cold rolling step is a step of secondary cold rolling the annealing sheet obtained in the continuous annealing step under the condition of a rolling rate of 6 to 20%. The annealing plate is strengthened and thinned by secondary cold rolling. In order to sufficiently increase the strength, it is necessary to set the rolling rate to 6% or more. In addition, the yield elongation is reduced by secondary cold rolling. If the rolling rate in the secondary cold rolling is too high, the formability is deteriorated. Therefore, the rolling rate should be 20% or less. When the formability is particularly required, the rolling rate is preferably 15% or less.

Thus, the high strength steel sheet for a two-piece can of the present invention is obtained. As the surface treatment of the steel sheet, Sn plating, Ni plating, Cr plating or the like may be performed, or an organic film such as a chemical conversion treatment or a laminate may be further applied.

Example

A steel containing components of steel symbols A to K shown in Table 1, the balance being Fe and inevitable impurities, was dissolved to obtain a steel slab. The obtained steel slab was subjected to hot rolling, hot rolling, winding, removal of scale by pickling, primary cold rolling, and annealing at each annealing temperature for 15 s in the continuous annealing furnace under the conditions shown in Table 2, (Secondary cold rolling) at a secondary rolling rate shown in Table 1 to obtain steel sheets (steel plate symbols Nos. 1 to 18) having a sheet thickness of 0.17 to 0.19 mm. The steel sheet was subjected to chrome plating (tin free) treatment as a surface treatment, and then a laminated steel sheet coated with an organic coating film was produced.

Tensile strength, elongation, yield elongation

After removing the organic coating from the laminated steel sheet with the concentrated sulfuric acid, a tensile test specimen of JIS No. 5 was taken from the rolling direction and the tensile strength, elongation (total elongation) and yield elongation were evaluated according to JIS Z 2241.

Ferrite grain size

The grain size was measured by a cutting method according to JIS G 0551 to evaluate the ferrite grain size.

Can Manufacturing Evaluation

In order to evaluate the can making composition, the laminated steel sheet was formed into a circular shape and then subjected to deep drawing processing, ironing processing and the like to produce a can in a cylindrical shape. Thereafter, a total of three points To be can be processed in the circumferential direction of the can to mold the same can body as the two-piece can used in the beverage can. Quot ;, &quot; good &quot;, &quot; good &quot;, &quot; good &quot;, &quot; excellent &quot;, &quot; Respectively.

The results are shown in Table 3. In the present invention, all have a tensile strength of 480 MPa or more, an elongation of 7% or more, a yield elongation of 3% or less, and a ferrite particle size of less than 6.0 탆. On the other hand, in the comparative example, at least one of the above properties fell off. For example, the steel plate symbols Nos. 9, 11, 13, and 17 indicate that the can manufacture evaluation is &quot;? &Quot;, but the tensile strength of the steel sheet is low and the strength at the bottom of the can is not sufficient.

Claims (3)

At least 0.020% of Si, at most 0.04% of Si, at least 0.10% of Si, at most 0.60% of P, at most 0.02% of P, at most 0.015% of S, at most 0.010% : 0.0005% or more and 0.0030% or less, the balance being Fe and inevitable impurities,
A tensile strength of 480 MPa or more,
An elongation percentage of 7% or more,
A yield elongation of 3% or less,
Wherein a ferrite grain size is less than 6 占 퐉. The method according to claim 1,
The steel sheet for a two-piece can according to any one of claims 1 to 3, further comprising 0.0001% or more and 0.0030% or less of B by mass%. A method for producing a steel sheet for a two-piece can according to any one of claims 1 to 3,
A heating step of heating the slab at a heating temperature of 1130 DEG C or higher,
A hot rolling step of subjecting the slab after the heating step to hot rolling at a hot rolling finishing temperature of 820 to 930 占 폚,
A winding step of winding the hot rolled sheet obtained in the hot rolling step at a winding temperature of 640 DEG C or lower;
A pickling step of pickling the hot rolled sheet after the winding step,
A primary cold rolling step in which the hot rolled sheet after the pickling is subjected to primary cold rolling under a condition of a rolling rate of 85%
A continuous annealing step of continuously annealing the cold-rolled sheet obtained in the primary cold rolling step under conditions of an annealing temperature of 620 DEG C or higher and 690 DEG C or lower;
Wherein the annealing plate obtained in the continuous annealing step has a secondary cold rolling step of secondary cold rolling under the condition of a rolling rate of 6 to 20%.