TWI565812B - Steel plate for cap and method for manufacturing the same - Google Patents

Description

Steel plate for bottle cap and manufacturing method thereof

The present invention relates to a steel sheet for a bottle cap used as a cap material for a cover of a glass bottle and a method for producing the same.

Glass bottles have been used in containers for beverages such as cold drinks or alcoholic beverages. Moreover, the glass bottle of the fine mouth is made of a metal cover called a crown cap. In general, the cap is made of a thin steel plate and is formed by press forming. The cap includes a disc-shaped portion that blocks the mouth of the bottle, and a pleated portion disposed around the bottle mouth, and the bottle is sealed by engaging the pleated portion with the bottle mouth.

The properties required for the steel sheet to be the material of the bottle cap include strength and formability. There is a tendency to fill a bottle using a bottle cap to increase the internal pressure of the bottle after filling, such as beer or carbonated beverage. The cap needs sufficient strength so that the cap does not deform and breaks the seal of the bottle even when the internal pressure rises due to a change in temperature or the like, or the impact caused by the conveyance or the like. Further, even if the strength of the steel sheet is sufficient, the shape of the crease is not uniform when the formability is insufficient, and sufficient sealing property cannot be obtained even if the bottle mouth is caught.

As a thin steel plate for the material of the cap, a primary reduction (SR, Single Reduced) steel plate is mainly used. The SR steel sheet is obtained by thinning a steel sheet by cold rolling, annealing it, and further performing temper rolling. The conventional cap material has a plate thickness of 0.22 to 0.24 mm and is used as a material for soft steel such as food or beverage cans.

In recent years, similarly to the steel sheet for cans, the steel sheet for bottle caps is required to be thinned for the purpose of cost reduction. However, when the thickness of the steel sheet for the cap material which is the material of the cap is less than 0.20 mm, the conventional SR steel sheet has the same moldability and insufficient strength, so that the airtightness cannot be ensured. Further, in the case where the sheet thickness is less than 0.20 mm, in order to secure the strength, it is easy to consider the secondary rolling (DR, Double Reduced) steel sheet after the secondary annealing is applied, but the application to the bottle cap is low. The carbon steel DR steel plate also has a poor sealing condition due to the low formability.

Further, in order to obtain a steel sheet excellent in both strength and formability, the following techniques are disclosed.

Patent Document 1 discloses an ultra-thin soft steel sheet for containers having excellent pot strength and pot formability, and is characterized by having N: 0.0040 to 0.0300%, Al: 0.005 to 0.080%, and 0.2% by mass. % endurance: below 430MPa, total elongation: 15~40%, Q ^-1 due to internal friction: 0.0010 or more.

Patent Document 2 discloses a steel sheet for high strength and high workability, which comprises C: 0.001 to 0.080%, Si: 0.003 to 0.100%, Mn: 0.10 to 0.80%, and P: 0.001 to 0.100. %, S: 0.001 to 0.020%, Al: 0.005 to 0.100%, N: 0.0050 to 0.0150%, B: 0.0002 to 0.0050%, and in the rolling direction cross section, including crystals having an area ratio of 0.01 to 1.00% The crystal grains having a degree of extension of 5.0 or more.

[Previous Technical Literature] [Patent Literature]

Patent Document 1: Japanese Patent Laid-Open No. 2001-49383

Patent Document 2: Japanese Patent Laid-Open Publication No. 2013-28842

The techniques described in Patent Document 1 and Patent Document 2 are used to manufacture a can as a container, not to manufacture a bottle cap. Further, as described below, the steel sheets described in the above patent documents are not suitable for forming the bottle cap.

Since the steel sheet described in Patent Document 1 is soft, if the secondary cold rolling ratio is increased in order to obtain the required strength, the anisotropy is also increased, and the formability is impaired.

It is also difficult for the steel sheet described in Patent Document 2 to have both the strength and the formability required for the cap. Thus, the technique of forming moldability and strength which is conventionally carried out cannot be applied to a steel sheet for a bottle cap.

The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a steel sheet for a cap and a method for producing the same, which are suitable for molding a bottle cap even if the thickness is reduced, and which have sufficient strength and formability.

The inventors of the present invention have repeatedly conducted intensive studies in order to solve the above problems. As a result, it has been found that the above problems can be solved by optimizing the components and adjusting the lodging strength in the rolling direction and the average Rankford value to a specific range, thereby completing the present invention. More specifically, the present invention provides the following.

[1] A steel sheet for a bottle cap comprising C: 0.002% or more and 0.010% or less, Si: 0.05% or less, Mn: 0.05% or more and 0.30% or less, and P: 0.030% or less in mass%. , S: 0.020% or less, Al: less than 0.0100%, N: 0.0050% or less, and when the Al content is 0.005% or more, the C content exceeds 0.003%, and the remaining portion contains a component containing Fe and unavoidable impurities. Composition, the rolling strength in the rolling direction is 500 MPa or more, the following average Rankford value is 1.3 or more, and the average Rankford value = (r _L + 2 × r _D + r _C ) / 4

Wherein r _L is the Rankford value in the direction parallel to the rolling direction, r _D is the Rankford value in the direction of 45° with respect to the rolling direction, and r _C is 90° with respect to the rolling direction. The direction of the Rankford value.

[2] The steel sheet for caps according to [1], wherein the absolute value of Δr below is 0.40 or less, and Δr = (r _L - 2 × r _D + r _C ) /2

Wherein r _L is the Rankford value in the direction parallel to the rolling direction, r _D is the Rankford value in the direction of 45° with respect to the rolling direction, and r _C is 90° with respect to the rolling direction. The direction of the Rankford value.

[3] A method for producing a steel sheet for a bottle cap, characterized in that it has the following step: a hot rolling step of rough rolling a slab having the composition of the composition described in [1], and a finishing rolling temperature of 850 Finishing rolling is performed at a temperature above °C; the coiling step is performed by winding the hot-rolled sheet obtained in the hot rolling step above 450 ° C and below 750 ° C; the pickling step is performed after the heat of the coiling step The rolled sheet is subjected to pickling; a cold rolling step is performed by cold rolling the hot rolled sheet after the pickling step; and an annealing step is performed on the cold rolled sheet obtained in the first cold rolling step at 650 ° C or higher and The annealing is performed at 790 ° C or lower; the second cold rolling step is performed on the annealed sheet obtained in the annealing step at a rolling ratio of 10% or more and 50% or less at an Al content of 0.003% or less, and in Al. When the content exceeds 0.003%, the rolling reduction is performed under the conditions of a rolling reduction ratio of 20% or more and 50% or less.

According to the present invention, it is possible to obtain a suitable bottle cap even if it is thinned. Steel plate for caps of strength and formability.

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

<Steel plate for caps>

C: 0.002% or more and 0.010% or less, Si: 0.05% or less, Mn: 0.05% or more and 0.30% or less, P: 0.030% or less, S: 0.020% or less, and Al: less than 0.0100% by mass% N: 0.0050% or less, and when Al is 0.005 or more, C is made to be more than 0.003%, and the remainder has a composition including Fe and unavoidable impurities, and the rolling strength in the rolling direction is 500 MPa or more, and the average Rank is The Ford value is 1.3 or more. Preferably, the absolute value of Δr is 0.40 or less. Hereinafter, the steel sheet for caps of the present invention will be described in the order of component composition and physical properties.

In the following description of the component composition, the "%" of the content of each component contained in the steel sheet for caps of the present invention means "% by mass".

C: 0.002% or more and 0.010% or less

When the C content exceeds 0.010%, the average Rankford value after the secondary cold rolling is lowered, and the formability is impaired as described below, and the steel sheet which is not suitable for the formation of the bottle cap is obtained. Moreover, when the C content exceeds 0.010%, the shape of the pleats of the formed bottle cap becomes uneven and the shape is poor. On the other hand, if the C content is less than 0.002%, it is difficult to obtain the required strength even by secondary cold rolling. Therefore, the content of C is set to be 0.002% or more and 0.010%. the following. The content of C is preferably 0.002% or more and 0.006% or less, more preferably 0.003% or more and 0.005% or less.

Si: 0.05% or less

Si also affects formability for the same reason as C, and it is less desirable to contain more than 0.05%. Therefore, the content of Si is set to 0.05% or less. More preferably, the content of Si is 0.03% or less. Further, it is preferably 0.01% or less.

Mn: 0.05% or more and 0.30% or less

When the Mn content is less than 0.05%, even when the S content is lowered, it is difficult to avoid hot brittleness, and problems such as surface cracking during continuous casting occur. On the other hand, Mn is also less than ideally contained for more than 0.30% for the same reason as C. Therefore, the content of Mn is set to be 0.05% or more and 0.30% or less. More preferably, the content of Mn is 0.10% or more and 0.30% or less. Further, it is preferably 0.15% or more and 0.25% or less.

P: 0.030% or less

If the P content exceeds 0.030%, the steel is hardened or the corrosion resistance is lowered. Therefore, the upper limit of the P content is set to 0.030%. More preferably, the upper limit of the P content is 0.020%.

S: 0.020% or less

S is formed by the formation of MnS in the steel by bonding with Mn, and precipitates in a large amount to reduce the thermal ductility of the steel. This effect becomes more pronounced if the S content exceeds 0.020%. Therefore, the upper limit of the content of S is set to 0.020%. More preferably, the upper limit of the content of S is 0.011%. Further, it is preferably 0.007% or less.

Al: less than 0.0100%

Al is an element added as a deoxidizer. By reducing the oxygen (O) in the molten steel, the effect of suppressing the occurrence of solidification defects in the steel block is obtained, and in order to obtain this effect, the Al content is preferably 0.0005% or more. However, a large amount of Al is a factor that reduces formability. Specifically, when the Al content is 0.0100% or more, the shape of the creases becomes uneven during the molding of the cap due to the decrease in the average Rankford value, resulting in a shape defect. Therefore, the Al content is set to be less than 0.0100%.

Further, when the Al content is 0.003% or less, since the solid solution strengthening ability due to C or N can be improved, the rolling reduction ratio of the secondary cold rolling can be prevented. Specifically, even in the case of producing a steel sheet for a bottle cap having a thickness of less than 0.20 mm, the rolling reduction ratio of the secondary cold rolling can be set to 10 to 40% to achieve desired characteristics. Therefore, it is preferred to make the Al content 0.003% or less. Further, it is preferably 0.002% or less. In the case where the Al content is 0.003% or less and the strength is increased as described above, by setting the C content to 0.002 to 0.006%, the decrease in moldability due to C can be prevented.

N: 0.0050% or less

If the N content exceeds 0.0050%, the average Rankford value after the secondary cold rolling is lowered, and the formability is deteriorated. Therefore, the content of N is made 0.0050% or less. Further, it is preferred that the N content is less than 0.0040%.

When the Al content is 0.005% or more, the C content exceeds 0.003%.

When Al is 0.005% or more, N in the steel is bonded to Al to cause lodging. The strength is reduced. Therefore, when Al is 0.005% or more, C is set to exceed 0.003% to ensure the fall strength.

The remainder other than the above components is defined as Fe and unavoidable impurities. Inevitable impurities are included in components which are inevitably mixed in the manufacturing process, and are included in components which are inevitably added in order not to impair the effects of the present invention in order to impart desired properties. As an unavoidable impurity, at least one of V, B, Ca, Zn, Co, and As is 0.02% or less, Cu: 0.10% or less, Ni: 0.10% or less, Cr: 0.09% or less, and O: 0.0150% or less.

Next, the mechanical properties of the steel sheet for caps of the present invention will be described.

Falling strength: 500MPa or more

The steel plate for the cap requires that the cap does not depress the strength of the bottle. In general, the thickness of the steel sheet for caps is about 0.22 to 0.24 mm, and when the thickness is less than this, it is necessary to further increase the strength of the steel sheets for caps. If the strength of the rolling direction of the steel sheet for the cap is less than 500 MPa, the above-mentioned thinned cap may not be sufficiently strong, and the compressive strength may be insufficient. Therefore, the fall strength in the rolling direction is set to 500 MPa or more. Further, it is preferably 550 MPa or more. On the other hand, when the lodging strength in the rolling direction exceeds 650 MPa, it is difficult to adjust the pressing conditions at the time of forming the cap, and therefore, the lodging strength in the rolling direction is preferably 650 MPa or less. Further, the lodging strength can be measured by a tensile test method for a metal material as shown in "JIS Z 2241".

Average Rankford value: 1.3 or more

The cap was punched into a circular blank with a steel plate, and then formed into a cap by press molding. The shape of the cap after forming was mainly evaluated by the uniformity of the shape of the pleats. If the shape of the pleats is not uniform, there is a case where the sealing property after the capping is impaired, and the contents of the bottle are leaked. The formability of the steel sheet for caps is also related to the composition or the strength of the fall, but is more closely related to the average Rankford value. Specifically, if the average Rankford value is less than 1.3, the shape of the crease after forming becomes uneven. Therefore, the average Rankford value is set to 1.3 or more. Preferably, the average Rankford value is 1.4 or more. Furthermore, the greater the average Rankford value, the better. The average Rankford value can be determined by the method shown in Appendix JA of "JIS Z 2254" and evaluated. Further, the average Lankford value was measured by lines r in the above-described method _L: r a direction parallel to the direction of the rolling pressure value, r _D: relative pressure at 45 ° to rolling direction of the r value, r _C: with respect to the rolling The r value in the direction of the 90° direction is obtained by calculating the average Rankford value (r _L + 2 × r _D + r _c ) / 4.

The absolute value of Δr is 0.40 or less

In the present invention, it is preferred that the absolute value of Δr is 0.40 or less. The cap was punched into a circular blank with a steel plate, and then formed into a cap by press molding. The shape of the cap after forming was mainly evaluated by the uniformity of the shape of the pleats. If the shape of the pleats is not uniform, there is a case where the sealing property after the capping is damaged and the contents of the bottle are leaked. The formability of the steel sheet for the cap is also related to the composition or the strength of the fall, and also to the absolute value of Δr (the in-plane anisotropy of the Rankford value (r value)). Specifically, when the absolute value of Δr exceeds 0.40, the shape of the crease after molding becomes uneven. Therefore, the absolute value of Δr is set to 0.40 or less. Further, it is preferable that the absolute value of the Δr value is small. It is preferably 0.20 or less. Further, the absolute value of Δr is measured by the above method. r _L : r value in the direction parallel to the rolling direction, r _D : r value in the direction of 45° with respect to the rolling direction, r _C : relative to rolling The r direction in the direction of the 90° direction is obtained by calculating (r _L -2 × r _D + r _C )/2.

Thickness: less than 0.20mm

The thickness of the steel sheet for caps of the present invention is not particularly limited, and the steel sheet for caps of the present invention can have both formability and strength even if the thickness is reduced. The term "thinner thickness" means less than 0.20 mm, more specifically 0.13 to 0.19 mm.

<Method of Manufacturing Steel Sheet for Bottle Caps>

Hereinafter, an example of a method for producing a steel sheet for a cap according to the present invention will be described.

The steel sheet for caps of the present invention can be produced by a DR method having a hot rolling step, a coiling step, a pickling step, a primary cold rolling step, an annealing step, and a secondary cold rolling step. Hereinafter, each step will be described.

Hot rolling step

The hot rolling step is a step of rough rolling and finish rolling a steel slab having the above composition. In addition, the steel slab is produced by a continuous casting method by adjusting the molten steel to the above chemical composition (component composition) by a known method such as a converter. Since the composition of the steel slab becomes a component of the steel sheet for the cap, the composition of the steel sheet for the cap can be adjusted when the slab is manufactured.

The conditions of the rough rolling are not particularly limited, and in the case of rough rolling, it is preferred to heat the slab to 1200 ° C or higher. The upper limit of the heating temperature is not particularly limited, and if the heating temperature is too high, scale is excessively generated to cause defects on the surface of the product. Therefore, it is preferable to set the heating temperature to 1300 ° C or lower.

Further, from the viewpoint of the stability of the rolling load, the finish rolling temperature is set to 850 ° C or higher. It is preferably 880 ° C or higher, more preferably 900 ° C or higher. On the other hand, by It is difficult to manufacture a thin steel sheet by increasing the finish rolling temperature to a necessary temperature or higher, and therefore it is preferably 960 ° C or lower.

Rolling step

The winding step is a step of winding up the hot rolled sheet obtained in the hot rolling step. When the coiling temperature is higher than 750 ° C, the crystal grains are coarsened and the strength is lowered, and the mechanical properties specified in the present invention cannot be obtained. Therefore, the coiling temperature of the hot rolling step is set to 750 ° C or lower. It is preferably 740 ° C or lower, more preferably 700 ° C or lower. More preferably, it is 650 ° C or less. Further, in order to operate the coiling temperature below 450 ° C without impairing the yield, it is necessary to lower the finish rolling temperature in accordance with this. If the finish rolling temperature is lowered, it is difficult to control the shape of the plate, so the coiling temperature is set to 450 ° C or higher. More preferably 500 ° C or more. More preferably, it is 550 ° C or more.

Pickling step

The pickling step is a step of pickling the hot rolled sheet after the coiling step. The pickling step removes the surface scale. The condition is not particularly limited as long as the surface scale is removed.

One cold rolling step

The so-called cold rolling step is a step of cold rolling the hot rolled sheet after the pickling step. The rolling rate in the primary cold rolling step is not particularly limited, and in order to produce an extremely thin material, the rolling reduction ratio is preferably set to 85 to 94%.

Annealing step

The annealing step is a step of annealing the cold rolled sheet obtained in one cold rolling step. If the annealing temperature exceeds 790 ° C, a whole plate failure such as heat buckling is likely to occur in continuous annealing. Further, when the annealing temperature is less than 650 ° C, the recrystallization is incomplete and the material becomes uneven. Therefore, the annealing temperature is set to 650 to 790 °C.

Secondary cold rolling step

The secondary cold rolling step is a step of cold rolling the annealed sheet obtained in the above annealing step. The required strength is imparted by the secondary cold rolling. In the production method of the present invention, the conditions of the optional rolling reduction ratio differ depending on the Al content. Specifically, when the Al content is 0.003% or less, the rolling reduction ratio is 10% or more and 50% or less, and when the Al content is more than 0.003%, the rolling reduction ratio is 20% or more and 50% or less. If the Al content is 0.003% or less, the rolling reduction ratio is less than 10%, and when the Al content exceeds 0.003%, the rolling reduction ratio is less than 20%, and the strength sufficient to ensure the pressure resistance of the cap cannot be obtained. . Moreover, when the rolling reduction ratio of the secondary cold rolling exceeds 50%, the anisotropy becomes too large, and the moldability is impaired. Therefore, the rolling reduction ratio of the secondary cold rolling is set to the above range in accordance with the Al content. Further, in the case where the Al content is any one, the upper limit of the rolling reduction ratio is preferably 40%, but one of the characteristics that the rolling reduction ratio can be reduced when the Al content is 0.003% or less. When the Al content is 0.003% or less, the rolling reduction ratio is preferably 40% or less as follows.

In the case of the present invention, when the Al content is 0.003% or less, since the solid solution strengthening ability by C or N can be improved, the rolling reduction ratio of the secondary cold rolling can be prevented. Specifically, even in the case of manufacturing a steel sheet for a cap having a thickness of less than 0.20 mm, the rolling rate of secondary cold rolling can be set to 10~ 40% to achieve the desired characteristics.

Further, after the secondary cold rolling, a step of plating (electroplating, chrome plating) or the like is conventionally performed, whereby a steel sheet for a cap can be finally produced.

As described above, according to the present embodiment, the strength of the steel sheet and the shape of the cap can be combined, and the thickness of the cap can be reduced.

[Examples]

In the present embodiment, first, a steel containing the composition shown in Table 1 and containing the Fe and the unavoidable impurities in the remainder was melted in a physical converter, and a slab was obtained by continuous casting. After the slab obtained here was reheated to 1,250 ° C, hot rolling was carried out under the conditions of a rolling start temperature of 1,150 ° C and a finish rolling temperature as shown in Table 2, and coiling was carried out at the coiling temperature shown in Table 2. After picking up, pickling is carried out. Next, cold rolling was performed once at the primary cold rolling rate shown in Table 2, and continuous annealing was performed at the annealing temperature shown in Table 2, and then secondary cold rolling was performed at the secondary cold rolling ratio shown in Table 2. The obtained steel sheet was continuously subjected to usual chrome plating to obtain a tin-free steel sheet.

The steel sheet obtained by the above method was subjected to a heat treatment corresponding to coating baking at 210 ° C for 15 minutes, and then subjected to a tensile test, an average Rankord value, and a Δr value.

In the tensile test, a tensile test piece of JIS No. 5 size was used, and the fall strength in the rolling direction was measured in accordance with JIS Z 2241.

The average Rankford value was measured using the natural vibration method described in Appendix JA of "JIS Z 2254". Further, a tensile test was performed in the rolling direction to measure r _L , and a tensile test was performed in a direction of 45° with respect to the rolling direction to measure r _D , and a tensile test was performed in a direction of 90° with respect to the rolling direction. r _C . The absolute value of Δr was obtained by calculating (r _L -2 × r _D + r _C )/2 from the measurement result.

The obtained steel sheet was used to form a bottle cap, and the cap formability was evaluated. The size of the three types of caps (32.1 mm in outer diameter, 6.5 mm in height, and the number of pleats 21) of the "JIS S 9017" (discontinued specifications) were formed by press processing using a circular blank having a diameter of 37 mm. . The evaluation was performed by visual observation, and the case where the size of the pleats were all matched was evaluated as "○", and the case where the size of the pleats did not match was evaluated as "x".

Further, a pressure test was performed using the formed cap. A vinyl chloride liner was formed on the inside of the bottle cap, a commercial beer bottle was capped, and the internal pressure of the cap detachment was measured using a Secure Seal Tester manufactured by Secure Pak. The case where the pressure resistance equal to or higher than the conventional bottle cap was displayed was evaluated as "○", and the case where the pressure resistance of the conventional bottle cap was not completed was evaluated as "x". The results obtained are shown in Table 3.

As seen from Table 3, the rolling strength of the steel sheets of the standards 1 to 5, 13 and 14 as the examples of the present invention is 500 MPa or more, and the average Rankford value is 1.3 or more, and the absolute value of Δr is 0.40. Hereinafter, the cap formability and the pressure resistance are good. On the other hand, in the steel sheet of the level 6 of the comparative example, since the content of Al exceeds 0.005% but the content of C is less than 0.003%, the drop strength in the rolling direction is less than 500 MPa, and the pressure resistance is insufficient. As a comparative example, the steel plate of level 7 has too much content of C, and the steel plate of level 8 has too much content of Mn. The steel plate of level 9 has too much content of Al, and the steel plate of level 10 has too much content of N, and the steel plate of level 11 is hot. After the rolling, the coiling temperature was too high, and the average Rankford value was less than 1.3, and the cap formability was poor. As the steel sheet of the level 12 of the comparative example, since the secondary cold rolling rate is too small, the lodging strength in the rolling direction becomes less than 500 MPa, and the pressure resistance is insufficient.

Claims (2)

A steel sheet for a bottle cap, characterized by containing: C: 0.002% or more and 0.010% or less, Si: 0.05% or less, Mn: 0.05% or more and 0.30% or less, P: 0.030% or less, and S: 0.020% or less, Al: less than 0.0100%, N: 0.0050% or less, and when the Al content is 0.005% or more, the C content exceeds 0.003%, and the remaining portion has a composition including Fe and unavoidable impurities, and is rolled. The direction of the lodging strength is 500 MPa or more, and the following average Rankford value is 1.3 or more. The absolute value of Δr below is 0.40 or less, and the average Rankford value = (r _L + 2 × r _D + r _C ) / 4 Δr=(r _L -2×r _D +r _C )/2 where r _L is the Rankford value in the direction parallel to the rolling direction, and r _D means 45° with respect to the rolling direction The Rankford value, r _C is the Rankford value in the direction of 90° with respect to the rolling direction. A method for producing a steel sheet for a bottle cap, characterized in that it has the following steps: a hot rolling step of rough rolling a slab having the composition of claim 1 and finishing rolling at a finishing temperature of 850 ° C or higher a winding step of winding the hot-rolled sheet obtained in the hot rolling step above 450 ° C and below 750 ° C; a pickling step of pickling the hot-rolled sheet after the coiling step a cold rolling step of cold rolling the hot rolled sheet after the pickling step; and an annealing step of annealing the cold rolled sheet obtained in the first cold rolling step above 650 ° C and below 790 ° C ; a second cold rolling step, wherein the rolled sheet obtained in the annealing step has a rolling ratio of 10% or more and 50% or less when the Al content is 0.003% or less, and the Al content is more than 0.003%. In the case where the rolling reduction ratio is 20% or more and 50% or less, cold rolling is performed.