KR101871735B1 - Steel sheet for crown cap, method for manufacturing same, and crown cap - Google Patents

Abstract

It is an object of the present invention to provide a steel sheet for a crown cap excellent in workability, which solves the problem of defective shape of a crown cap and insufficient strength of a pressure resistance, a method of producing the same, and a crown cap formed by molding a steel sheet for a crown cap .
The steel sheet for a crown cap according to claim 1, wherein the steel sheet for a crown cap comprises 0.0005 to 0.0050% of C, 0.020% or less of Si, 0.10 to 0.60% of Mn, 0.020% or less of P, 0.0050% or less, Nb: 0.010 to 0.050%, the balance being Fe and inevitable impurities, and having an average r value of 1.30 or more and YP of 450 to 650 MPa. The steel slabs were hot rolled at a slab reheating temperature of 1150 DEG C or higher and a finishing temperature of 870 DEG C or higher, rolled at a coiling temperature of 600 DEG C or higher, washed with acid, subjected to primary cold rolling, Annealing at an annealing temperature of not higher than 50 占 폚, and then performing secondary cold rolling at a reduction ratio of 10% or higher and 50% or lower.

Description

STEEL SHEET FOR CROWN CAP, METHOD FOR MANUFACTURING SAME, AND CROWN CAP}

The present invention relates to a steel sheet for a crown cap, which is excellent in shape uniformity at the time of forming a crown cap, used for beer bottles and the like, a method for producing the same, and a crown cap.

From the viewpoint of recent environmental load reduction and cost reduction, a steel sheet for a crown cap used for a beer bottle lid is becoming thinner. Generally, there are the following two kinds of thinned steel sheets. That is, SR (Single Reduce) material subjected to temper rolling followed by hot rolling, cold rolling and annealing, and DR (Double Reduce) material subjected to secondary cold rolling. In the case of a steel sheet for a crown cap, the plate thickness is in a demand of 0.20 mm or less, and it is preferable to use a DR material that performs secondary cold rolling which can utilize work hardening to compensate for the decrease in strength of pressure resistance accompanying thinning. However, since the DR material is generally harder than the SR material, there is a problem that the workability is low.

In the crown cap molding, the center portion is tightened to some extent at the initial stage of molding, and then the outer edge portion is formed into a fluted shape. In the case of a steel sheet having a low workability, there may be a case where a shape defect in which the shape of a fold is uneven may occur. The crown cap having a non-uniformly folded shape has a problem in that when the bottle is put on, the pressure resistance is not obtained and leakage of the contents occurs and the cap does not function as a lid. Further, even if the shape of the folded portion is uniform, when the strength of the steel sheet is low, there is a risk that the crown cap is displaced due to insufficient strength of the internal pressure.

Extremely low carbon IF (Interstitial Free) steel sheet is well known as a steel sheet having good workability. In the DR material using ultra-low carbon steel, there are a number of studies aiming at compatibility between workability improvement and thinning (for example, Patent Documents 1 to 3).

Japanese Patent Application Laid-Open No. 7-11333 Japanese Patent Application Laid-Open No. 5-287445 Japanese Laid-Open Patent Publication No. 2010-255021

However, when the above-described conventional technique is applied to a crown cap, the performance as a crown cap can not be secured.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a steel sheet for a crown cap excellent in workability, a method of manufacturing the same, and a crown cap.

In order to solve the above-described problems, the inventors have conducted extensive research. By studying the chemical composition, the hot rolling condition, the cold rolling condition (primary and secondary) and the continuous annealing conditions on the basis of the extremely low carbon steel, the average r value is improved and the YP is controlled to an appropriate value, And it is possible to secure the withstand pressure strength.

The present invention has been made on the basis of the above-described recognition, and its main points are as follows.

[1] A steel according to [1], wherein C is 0.0005 to 0.0050%, Si is more than 0 to 0.020%, Mn is 0.10 to 0.60%, P is more than 0 and less than 0.020%, S is more than 0 and less than 0.020% , Al: 0.01 to 0.10% or less, N: more than 0 to 0.0050%, Nb: 0.010 to 0.050%, the balance being Fe and inevitable impurities and having an average r value of 1.30 or more, YP of 450 ㎫ to 650 MPa.

[2] The steel sheet for a crown cap according to the above [1], wherein the ferrite elongation rate is 4.2 or less.

[3] A steel slab having the chemical composition described in the above [1] is subjected to hot rolling at a slab reheating temperature of 1150 ° C or higher and a finishing temperature of 870 ° C or higher, followed by winding at a coiling temperature of 600 ° C or higher , Followed by primary cold rolling, annealing at an annealing temperature of not lower than 790 占 폚 and recrystallization temperature not higher than 10% and not higher than 50%, followed by secondary cold rolling.

[4] A crown cap formed by molding the steel sheet for a crown cap according to the above [1] or [2].

Further, in the present invention, the percentages indicating the proportions of the component compositions are all% by mass.

According to the present invention, a steel sheet for a crown cap excellent in workability having an average r value of 1.30 or more and YP of 450 MPa to 650 MPa is obtained. By using the steel sheet for a crown cap of the present invention, it is possible to enhance the uniformity of shape of a crown cap used for beer bottles and to obtain a sufficient pressure resistance strength.

1 is a view showing a corrugated shape of a crown cap.

(Mode for carrying out the invention)

Hereinafter, the present invention will be described in detail. First, the composition of the components will be described.

[C: 0.0005 to 0.0050%]

C is an element that increases the strength of steel, but deteriorates workability. If the amount of solid solution C in the steel sheet is large, yield elongation becomes large, and it tends to cause age hardening and stretcher strain at the time of processing. Therefore, in the present invention using the continuous annealing method, it is necessary to control the content of C to be as low as possible in the steelmaking step. In addition, if the amount of the remaining solid solution C is increased, the steel sheet becomes hard and wrinkles are easily generated in the initial stage of forming the crown cap, and the shape defect rate is increased. Also, C is an element that influences the structure of the recrystallized set. As the amount of C is smaller, the texture of the annealing plate increases in the crystal orientation group in which the <111> direction is parallel to the plane normal direction, and the average r value is improved. The improvement of the average r value improves the drawability and improves the shape defects of the crown cap. From the above, the C content is set to 0.0050% or less. In order to enhance the shape uniformity, it is preferably 0.0035% or less, more preferably 0.0023% or less. On the other hand, excessive decarburization causes a rise in the cost of steelmaking, so 0.0005% is the lower limit.

[Si: 0.020% or less],

When a large amount of Si is added, the surface treatment property of the steel sheet is deteriorated and the corrosion resistance is lowered. Therefore, the content of Si is 0.020% or less.

[Mn: 0.10 to 0.60%],

Mn is added for the purpose of preventing hot brittleness. There is also an effect of preventing deterioration of hot ductility due to S contained in the steel. In order to obtain these effects, it is necessary to add 0.10% or more. On the other hand, in terms of the ladle analysis value defined in JIS G 3303 or the ladle analysis value defined in the United States of America Material Test Association Standard (ASTM A623M-11), a tin mill black plates) has an upper limit of Mn of 0.60% or less. From the above, the upper limit of Mn of the present invention is set to 0.60% or less. From the viewpoint of workability, Mn is preferably 0.45% or less.

[P: 0.020% or less]

When P is added in a large amount, the steel is hardened and the workability is lowered, and the corrosion resistance is lowered. Therefore, the upper limit of P is 0.020%.

[S: 0.020% or less]

S combines with Fe in the steel to form FeS, which lowers the hot ductility of the steel. To prevent this, S should be 0.020% or less. On the other hand, if S is too low, the risk of occurrence of pitting corrosion increases, so that it is preferably 0.008% or more.

[Al: 0.01 to 0.10%]

Al is an element added as a deoxidizer. Further, by forming N and AlN, the effect of reducing the solid solution N in the steel is obtained. However, when the content of Al is less than 0.01%, sufficient deoxidizing effect and solid solution N reducing effect can not be obtained. On the other hand, if it exceeds 0.10%, this effect is not only saturated but also inclusions such as alumina are increased. Therefore, the content of Al is set in the range of 0.01% or more and 0.10% or less.

[N: 0.0050% or less]

When N is increased, strain hardening causes strain hardening and deteriorates workability. In addition, since the element to be added is fixed in order to fix the solid solution N, the cost is increased. Therefore, the upper limit of N is 0.0050% or less. On the other hand, it is difficult to stably reduce N to less than 0.0010%, and the manufacturing cost also increases, so that 0.0010% or more is preferable.

[Nb: 0.010 to 0.050%]

Nb is an element capable of improving the average r value by fixing the solid solution C in the steel sheet as NbC and decreasing the solid solution C. As the average r value increases, the drawability improves, which is effective in suppressing the defective shape. When the amount of Nb is small, the effect of raising the average r value becomes faint, so the lower limit is set to 0.010%. On the other hand, if the amount of Nb added increases, the recrystallization temperature rises, and there is a possibility that unrecrystallization occurs after annealing. Since this causes material unevenness, it should be 0.050% or less.

The remainder is Fe and inevitable impurities.

Further, Cu, Ni, Cr, and Mo may be contained in a range that does not impair the effect of the present invention.

From ASTM A623M-11, Cu is 0.2% or less, Ni is 0.15% or less, Cr is 0.10% or less, and Mo is 0.05% or less. Other elements should be 0.02% or less.

In addition, Sn may be contained within a range that does not impair the effect of the present invention.

[Sn: less than 0.0050%]

When Sn exists in a large amount, the average r value is lowered, so that it is preferably less than 0.0050%.

[Structure of steel sheet]

The structure of the steel sheet for a crown cap of the present invention is a recrystallized structure. If there is non-recrystallization after annealing, the material becomes uneven and unevenness occurs in the mechanical characteristics. However, if the non-recrystallized area ratio is 5% or less, it can be accepted because it hardly affects the material unevenness. The recrystallized structure is preferably a ferrite phase, and the phase other than the ferrite phase is preferably less than 1.0%. From the viewpoint of suppressing the anisotropy during the secondary cold rolling, the ferrite system is preferably 4.2 or less. When the whole body of the ferrite grains of the steel sheet exceeds 4.2, it may be difficult to obtain a uniformly shaped fold in the circumferential direction. The ferrite system can be set to 4.2 or less by setting the rolling rate of the secondary cold rolling to 50% or less in the manufacturing method described later. Further, the ferrite system can be measured by the method described in the following example.

Next, an example of a production method for obtaining a steel sheet for a crown cap excellent in workability of the present invention will be described.

The slab having the above composition was subjected to hot rolling at a slab reheating temperature of 1150 DEG C or higher and a finishing temperature of 870 DEG C or higher, followed by winding at a coiling temperature of 600 DEG C or higher, acid washing, primary cold rolling, , And then subjected to secondary cold rolling at a reduction ratio of 10% or more and 50% or less to obtain a steel sheet for a crown cap excellent in workability.

[Reheating temperature of slab: 1150 DEG C or more],

If the reheating temperature of the slab before the hot rolling is too low, it becomes difficult to secure the final finish rolling temperature, and therefore, it is set to 1150 占 폚 or higher. On the other hand, if the heating temperature is excessively high, problems such as defects on the surface of the product, energy cost increase, and the like arise.

[Hot rolling finish temperature: 870 DEG C or more]

If the hot rolling finishing temperature is too low, coarsening of the? -Lip is caused in the surface layer of the steel sheet, which causes material unevenness. Therefore, the hot rolling finishing temperature should be 870 DEG C or higher. If the hot rolling finishing temperature is too high, the hot rolling scale becomes thick and the pickling performance deteriorates. Therefore, the hot rolling finishing temperature is preferably 910 占 폚 or lower. Further, in the present invention, since the solid-dissolved element is reduced by IF-induced Nb, it is not necessary to carry out precipitation treatment of carbide or the like to finish rolling. Therefore, it can be rolled by ordinary finish rolling.

[Coiling temperature after hot rolling: 600 占 폚 or more]

If the coiling temperature after hot rolling is too low, hot rolled shape defects will occur. Therefore, the coiling temperature after hot rolling is set to 600 ° C or higher. In consideration of the uniformity of the steel sheet, the coiling temperature is preferably higher than 700 deg. On the other hand, if the coiling temperature is too high, the hot rolling scale becomes thick and the pickling property deteriorates. Therefore, the coiling temperature after hot rolling is preferably 730 캜 or lower.

Acid cleansing conditions are not particularly limited as long as the surface scale can be removed. It is possible to determine the acidity by a method usually performed. Although acid cleaning is exemplified as a scale removal method, a method other than acid cleaning may be used as long as the scale can be removed. For example, mechanical removal may be used.

[Reduction ratio of primary cold rolling: 86 to 89% (suitable conditions)]

If the reduction rate of the primary cold rolling is too high, an excessive load is applied to the rolling roll at the time of rolling, resulting in a large load on the equipment. On the other hand, if it is too low, it is necessary to manufacture the hot-rolled steel sheet as thin as possible, so that it becomes difficult to control the material. Therefore, the reduction ratio of the primary cold rolling is preferably 86 to 89%.

[Annealing temperature: recrystallization temperature or more and 790 DEG C or less]

The annealing method is preferably a continuous annealing method in terms of uniformity of material and productivity. The annealing temperature in the continuous annealing is required to be not lower than the recrystallization temperature. However, if the annealing temperature is excessively high, the crystal grains become coarse, the strength of the steel sheet lowers, and there is a possibility that the YP within the range specified in the present invention may not be obtained. Further, in a thin material, the risk of breakage or buckling in the furnace is increased. For this reason, the annealing temperature is set to 790 캜 or lower. The soaking time at the time of annealing is preferably 10 seconds or more and 90 seconds or less from the viewpoint of productivity.

[Reduction ratio of secondary cold rolling: 10% or more and 50% or less]

After the annealing, secondary cold rolling is carried out in order to reduce the thickness and strength of the steel sheet. Secondary cold rolling is a particularly important production condition in the present invention. When the reduction rate exceeds 50%, the steel sheet is excessively hardened and the workability is lowered. Further, a decrease in the average r value and an increase in the? R value are caused. Therefore, the reduction rate of the secondary cold rolling is set to 50% or less. On the other hand, in order to secure pressure resistance, secondary rolling is performed at a reduction ratio of 10% or more. In order to further secure the withstand pressure, the reduction rate is preferably more than 30%.

The cold-rolled steel sheet obtained as described above is preferably subjected to the following surface treatment before being molded into a crown cap. The steel sheet subjected to the surface treatment described below is also a steel sheet for a crown cap of the present invention.

[Surface treatment]

The surface of the steel sheet after the secondary cold rolling may be subjected to various surface treatments. Chromium plating, and nickel plating may be formed by a general plating method such as electroplating, for example.

Further, since the film thickness of the surface treatment such as plating is sufficiently small with respect to the plate thickness, the influence on the mechanical characteristics of the steel sheet for crown cap is negligible.

Next, the material properties of the steel sheet for a crown cap of the present invention will be described.

[Average r value: 1.30 or more]

The defective shape of the crown cap is caused by the occurrence of wrinkles accompanying the drawing molding at the initial stage of crown cap molding. Therefore, in order to avoid the occurrence of wrinkles, it is necessary to increase the drawability, that is, to aim at a high average r value. When the average r value is low, the drawability is low, and wrinkles are generated in the initial stage of forming the crown cap, resulting in defective shape. Therefore, the average r value is 1.30 or more. In order to improve the drawability at the initial stage of molding, an average r value of 1.40 or more is preferable. Also, an average r value of 2.00 is a practical upper limit.

[|? R |? 0.5 (conformance condition)]

In molding the crown cap, it is preferable that | DELTA r | &amp;le; 0.5 for forming a fold uniformly in the circumferential direction. More preferably, |? R |? 0.4, and more preferably |? R |? 0.3. The measurement of? R (in-plane anisotropy) can be performed using the natural vibration method specified in JIS Z 2254 Annex JA. That is, the resonance frequency of the steel sheet in the directions of 0 deg., 45 deg. And 90 deg. Relative to the rolling direction is measured, and the anisotropy? E of the Young's modulus is calculated to calculate the value? R from the empirical formula showing the correlation between? R and? E.

[YP: 450MPa or more and 650MPa or less]

The pressure-proof strength of the container is proportional to the YP of the lid. If the strength of the steel sheet is insufficient, sufficient strength of pressure resistance can not be obtained, so the lower limit of YP is set to 450 MPa. If the YP is too high, the compressive stress in the circumferential direction of the crown cap folded portion becomes higher and exceeds the critical buckling stress at the initial stage of forming the crown cap, so that wrinkles tend to occur. In order to prevent such a defective shape, the upper limit is set to 650 MPa. The tensile test is conducted using a tensile test piece of JIS No. 5 in accordance with JIS Z 2241. The tensile direction is the rolling direction (L direction).

[Plate thickness: 0.13 mm or more and 0.18 mm or less (preferable conditions)]

The pressure resistance of the container is proportional to the square of the plate thickness of the lid. If the plate thickness is too thin, the pressure resistance strength is lowered and the function as a lid is not fulfilled. Therefore, the plate thickness is preferably 0.13 mm or more, more preferably 0.16 mm or more. On the other hand, from the viewpoints of resource saving due to thinning of the steel sheet for a crown cap, reduction of environmental load, and reduction of material cost, it is preferable that the thickness of the steel sheet is made thinner than the thickness of 0.22 mm which is the thickness of the current steel sheet for crown cap. In order to obtain such an effect, the plate thickness is preferably 0.18 mm or less.

Thus, a steel sheet for a crown cap excellent in workability of the present invention can be obtained.

Further, by forming the steel sheet for a crown cap of the present invention, a crown cap having excellent shape uniformity and sufficient pressure-proof strength can be obtained. The crown cap is a lid member used for a beverage bottle and the like. The crown cap is provided with projections (generally, the number of folds is 21) on the side of the crown cap. Seal it. On the inner surface of the lid of the crown cap, a packing is provided to improve the sealing property. Cork sheets, PVC (polyvinyl chloride), PE (polyethylene) and the like are used as the material of the packing.

Example 1

A steel containing the composition shown in Table 1 and containing the remainder Fe and inevitable impurities was dissolved to obtain a steel slab. Here, the amount of Sn was confirmed to be less than 0.0050% at all levels. After the obtained steel slabs were reheated to the temperatures shown in Table 2, hot rolling was carried out at the finish rolling temperature and the coiling temperature shown in Table 2. Subsequently, the steel sheet was annealed at the annealing temperature (recrystallization temperature) shown in Table 2 in a continuous annealing furnace and subjected to annealing at a reduction ratio shown in Table 2, Followed by secondary cold rolling to produce a thin steel sheet having a final finish thickness shown in Table 2. [

The steel sheet obtained by the above-mentioned production method was subjected to observation of the structure.

According to JIS G 0551, the ferrite grains appeared by nital and were photographed at 400 times using an optical microscope. The presence or absence of non-recrystallization was visually confirmed by an optical microscope, and the crystal grains that did not reach recrystallization were judged to be non-recrystallized. The area ratio of the non-recrystallized grains is calculated by distinguishing the non-recrystallized portion from the recrystallized finished portion by image processing of a photographed image using an optical microscope. ○, and non-recrystallization exceeding 5% was evaluated as x. The whole body of the ferrite lips was calculated by the technique shown in &quot; JIS G 0202 &quot;.

The steel sheet obtained by the above production method was subjected to chrome (tin free) plating as a surface treatment, followed by coating (baking treatment conditions: 210 ° C for 20 minutes) and press processing in the shape of a crown cap. The mechanical properties and formability were examined under the following test conditions.

The average r value (average plastic deformation ratio (ratio)) was determined by the natural vibration method specified in JIS Z 2254 Annex JA. That is, the resonance frequency and the average Young's modulus of the steel sheet in the directions of 0 deg., 45 deg. And 90 deg. Relative to the rolling direction were determined, and the average r value was calculated. ? R (in-plane anisotropy) was determined by the natural vibration method specified in JIS Z 2254 Annex JA. That is, the resonance frequencies of the steel plates in the directions of 0 deg., 45 deg. And 90 deg. Relative to the rolling direction were measured, and the anisotropy? E of the Young's modulus was calculated, and the value? R was calculated from the empirical formula showing the correlation between? R and? E.

The tensile test for the YP measurement was conducted using a tensile test piece of JIS No. 5 in accordance with JIS Z 2241. The tensile direction was the rolling direction (L direction).

Further, the crown cap was molded to evaluate the uniformity of the shape of the crown cap. What was broken at the time of forming the crown cap was rejected (&quot; x &quot; in Table 3), and the length of each crown of the crown cap (L in Fig. 1) (&Quot;? &Quot; in Table 3) and a standard deviation? Of L value exceeding 0.1 were also rejected ("?" In Table 3).

The pressure resistance (withstand pressure strength) was measured in accordance with JIS S 9017 by placing a crown cap on the bottle and measuring the pressure resistance after passing the test piece. The pressure of 115 PSI or higher was judged as " Quot; in Table 3).

The results are shown in Table 3. In addition, since the crown cap having poor shape uniformity can not be wound, the pressure resistance test is not performed.

From Table 3, it can be seen that the present invention has excellent shape uniformity and pressure resistance without an average r value of 1.30 or more, YP of 450 MPa to 650 MPa, no unrecrystallization which may cause material unevenness have.

On the other hand, in the comparative example, there is a non-recrystallization in which at least one of the shape uniformity and the pressure resistance is inferior or the area ratio exceeds 5%, which may cause material unevenness.

1: Crown cap top surface
2:
L: height of fold

Claims (4)

P: not less than 0% to not more than 0.020%, S: not less than 0% to not more than 0.020%, and Al: not less than 0.0005 to 0.0050% 0.01 to 0.10%, N: more than 0 to 0.0050%, Nb: 0.010 to 0.050%, the balance being Fe and inevitable impurities, and having an average r value of 1.30 or more, YP of 450 to 650 MPa Or less. The method according to claim 1,
A steel plate for a crown cap having a ferrite total body strength of 4.2 or less. A steel slab having the chemical composition according to claim 1 is subjected to hot rolling at a slab reheating temperature of not lower than 1150 DEG C and a finishing temperature of not lower than 870 DEG C and then wound up at a coiling temperature of 600 DEG C or higher, Subjecting the steel sheet to cold cold rolling, annealing the steel sheet at an annealing temperature of not lower than 790 占 폚, and then performing a secondary cold rolling at a reduction ratio of 10% to 50%. A crown cap formed by molding the steel sheet for a crown cap according to claim 1 or 2.

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