TWI668313B - Steel plate and manufacturing method thereof, crown and DRD tank - Google Patents

Abstract

The present invention provides a steel sheet, including: C: more than 0.0060% and 0.0100% or less, Si: 0.05% or less, Mn: 0.05% or more and 0.60% or less, P: 0.050% or less, and S: 0.050% or less. , Al: more than 0.020% and less than 0.050%, N: more than 0.0140% and less than 0.0180%, and Cr: less than 0.040%, the remaining component composition is Fe and unavoidable impurities, and has an aging index in the rolling direction With mechanical properties of 25 MPa to 55 MPa and drop strength of 620 MPa to 700 MPa, even if the steel sheet is thinned, it has sufficient strength and excellent formability.

Description

Steel plate and manufacturing method thereof, crown and DRD tank

The present invention relates to a steel sheet, and more particularly, to a high-strength thin steel sheet excellent in formability and a method for manufacturing the same. Typical examples of such a steel sheet include a thin steel sheet supplied as a drawing and redrawing (DRD) can formed by combining drawing and redrawing, and a raw material used as a raw material for crowns such as glass bottles. The present invention further relates to a crown and a DRD can obtained by forming the steel sheet.

In addition, in the past, containers for beverages such as soft drinks and alcoholic beverages have mostly used glass bottles. Particularly, a metal stopper called a crown is widely used in a narrow-mouth glass bottle. Generally, a crown is manufactured by press forming a thin steel plate as a raw material. The crown includes a disc-shaped portion that blocks the mouth of the bottle, and a pleated portion provided around the disc-shaped portion, and the pleated portion is fastened. Seal the bottle at the mouth.

Most crown-filled bottles are filled with beer or carbonated beverages, which produce high internal pressure. Therefore, the crown must have a high compressive strength so that even when the internal pressure becomes high due to a change in temperature, etc., the crown will not deform and the seal of the bottle will not be broken. In addition, even if the strength of the raw material is sufficient, when the material uniformity of the steel plate used in the crown is low, the shape of the crown may become inconsistent and include crowns that do not meet the product specifications. Even if you tighten this badly shaped crown If it is fixed to the mouth of the bottle, sufficient sealability may not be obtained. Therefore, the steel plate as the raw material of the crown must also have excellent material uniformity.

As the thin steel sheet to be supplied to the crown, a single reduced (SR) steel sheet is mainly used. This SR steel sheet is obtained by thinning a steel sheet by cold rolling, annealing it, and performing temper rolling. The thickness of the conventional steel sheet for crowns is usually 0.22 mm or more, and sufficient compressive strength and formability can be ensured by applying an SR material using mild steel used in food or beverage cans as a raw material.

In recent years, similar to steel plates for cans, thinning requirements for cost reduction of steel plates for crowns have been increasing. If the thickness of the steel sheet for the crown is less than 0.22 mm, and particularly if it is 0.20 mm or less, the crown made of the conventional SR material will have insufficient compressive strength. As a steel sheet for crowns, in order to ensure the compressive strength, it is necessary to compensate for the reduction in strength associated with thinning. Therefore, a double-reduced (DR) steel sheet that has been subjected to cold rolling after annealing to work hardening is applied.

In addition, in the initial stage of the crown, the central portion was drawn to some extent, and thereafter, the outer edge portion was formed into a pleated shape. Here, if the raw material of the crown is a steel plate having low material uniformity, the outer diameter and height of the crown made of the steel plate may be inconsistent and may not meet product specifications. If the outer diameters and heights of the crowns become inconsistent and there are crowns that do not meet the product specifications, there is a problem that the yield is reduced when the crowns are manufactured in large quantities. Furthermore, crowns with outside diameters and heights that do not meet the specifications also have the following problems: leakage of the contents is prone to occur during transportation after being tied to the bottle, and cannot function as a cap. In addition, even if the outer diameter and height of the crown are within the product specifications, if the strength of the steel plate is low, the crown may fall off due to insufficient compressive strength. Sex. In particular, when the plate thickness is thin and is, for example, 0.17 mm or less, according to the previous compressive strength standards, crowns often fall off, and thus require higher compressive strength than before.

In addition, if a steel sheet with low material uniformity is used as a raw material of the DRD can, a shape failure such as wrinkles generated at the flange portion of the can may be caused during forming of the DRD can. Regarding this DRD can, if it has a DRD can that does not conform to the product specifications due to its poor shape, it will also cause a reduction in the yield when a large number of DRD cans are manufactured. This is the same problem as in the case of the crown.

Based on the above, regarding the high-strength thin steel sheet for a crown, for example, Patent Document 1 discloses a steel sheet for a crown and a method for manufacturing the same, that is, the steel sheet for a crown contains C: 0.0010% or more by mass% and 0.0060% or less, Si: 0.005% or more and 0.050% or less, Mn: 0.10% or more and 0.50% or less, P: 0.040% or less, S: 0.040% or less, Al: 0.1000% or less, N: 0.0100% or less, and The minimum value of the r value in the direction of 25 ° to 65 ° with respect to the rolling direction, the average value of the r values in all directions, and the yield strength are appropriately controlled, thereby satisfying a sufficient crown even if the thickness is thin. Withstand pressure.

Patent Document 1: Japanese Patent No. 6057023

The steel sheet described in Patent Document 1 uses steel containing 0.0060% or less of C, and sets a predetermined relationship between the stand tension and the annealing temperature in the secondary cold rolling, thereby obtaining r suitable for crown processing. Value (direction, size). This method is not correct Since the hot rolling step which affects the formation of the metal structure is controlled, the variation in the material of the obtained steel sheet becomes large, and it is difficult to put it into practical use.

The present invention has been made in view of the problems described above, and an object thereof is to provide a steel sheet having sufficient strength and excellent formability even when thinned, and a method for manufacturing the same. Furthermore, an object of the present invention is to provide a crown and a DRD can having a predetermined size and shape, and excellent shape stability.

The inventors have intensively studied a method for solving the above problems, and as a result, they have found that by specifying the mechanical properties under a predetermined component composition, high strength and excellent moldability can be imparted. This invention is derived from the said knowledge, and the summary is as follows.

(1) A steel sheet containing, in mass%, C: more than 0.0060% and 0.0100% or less, Si: 0.05% or less, Mn: 0.05% and 0.60% or less, P: 0.050% or less, and S: 0.050% Below, Al: 0.020% or more and 0.050% or less, N: Over 0.0140% or more and 0.0180% or less, and Cr: 0.040% or less, the remainder has a composition of Fe and unavoidable impurities, and the aging index in the rolling direction 25MPa ~ 55MPa, The yielding strength is 620MPa ~ 700MPa.

(2) The steel plate according to the above (1), wherein the plate thickness is 0.20 mm or less.

(3) A crown comprising the steel plate according to (1) or (2) above.

(4) A DRD can comprising the steel plate according to (1) or (2).

(5) A method for manufacturing a steel sheet, as described in (1) or (2), wherein the method for manufacturing a steel sheet includes a hot rolling step of heating steel raw materials at a temperature of 1200 ° C or higher and finishing rolling. Temperature: 870 ° C or higher and rolling reduction of the final stand: 10% or more, and rolling in a temperature range of 550 ° C to 750 ° C; pickling step, the hot-rolled The hot-rolled sheet is pickled; a cold rolling step is performed on the hot-rolled sheet after the pickling: a cold rolling of more than 88%; the annealing step is performed at a temperature of 660. After holding for 60 seconds or less in the temperature range from ℃ to 760 ℃, it is cooled to a temperature range below 450 ° C at an average cooling rate of 10 ° C / s or more, and then cooled to 140 ° C or below at an average cooling rate of 5 ° C / s or more. A temperature region; and a secondary cold rolling step of cold rolling the annealed sheet at a reduction ratio of 10% to 40%.

According to the present invention, it is possible to provide a steel sheet having sufficient strength and excellent formability even if thinned, and an advantageous manufacturing method thereof. Furthermore, when the steel sheet of the present invention is used for, for example, crown applications or DRD can applications, a crown having stable high compressive strength or a DRD can excellent in shape stability can be formed.

The steel sheet of the present invention contains C: more than 0.0060% and not more than 0.0100%, Si: 0.05% or less, Mn: 0.05% or more and 0.60% or less, P: 0.050% or less, S: 0.050% or less, Al : 0.020% or more and 0.050% or less, N: more than 0.0140% and 0.0180% or less, and Cr: 0.040% or less, the remainder has a composition of Fe and inevitable impurities, and the aging index in the rolling direction is 25MPa ~ 55MPa.

First, the reasons for limiting the amount of each component in the component composition of the steel sheet will be described in order. In addition, "%" for ingredients means "mass%" ° C unless otherwise specified.

C: more than 0.0060% and less than 0.0100%

When the content of C is 0.0060% or less, the aging index in the rolling direction of the steel sheet after the secondary cold rolling described below becomes less than 25 MPa, and for example, when used for crown applications, the compressive strength is reduced. Similarly, when it is used for a DRD can, for example, wrinkles are generated at the flange portion when the DRD can is formed, and the can becomes a bad shape can. On the other hand, if the C content exceeds 0.0100%, the Ferrite becomes too fine, the strength of the steel sheet is excessively increased, and the formability is deteriorated. For example, when it is used for a crown, the shape of the formed crown is deteriorated, so the compressive strength is reduced. Similarly, when it is used for a DRD can, for example, wrinkles are generated at the flange portion when the DRD can is formed, and the can becomes a bad shape can. Therefore, the content of C is set to be more than 0.0060% and 0.0100% or less. The content of C is preferably 0.0065% or more and 0.0090% or less.

Si: 0.05% or less

When Si is contained in a large amount, the strength of the steel sheet is excessively increased and the formability is deteriorated. For example, when it is used in a DRD can, the shape of the wrinkles at the flange portion may be defective when the DRD can is formed. Therefore, the content of Si is set to 0.05% or less. In addition, excessively reducing Si causes an increase in the cost of steelmaking. Therefore, the Si content is preferably set to 0.004% or more. More preferably, it is 0.01% or more and 0.03% or less.

Mn: 0.05% or more and 0.60% or less

If the content of Mn is less than 0.05%, it is difficult to avoid thermal embrittlement even if the content of S is reduced, and problems such as surface cracking may occur during continuous casting. Therefore, the content of Mn is set to 0.05% or more. On the other hand, if Mn is contained in a large amount, for the same reason as C, for example, when it is used for a crown, the shape of the formed crown deteriorates and the compressive strength decreases. Similarly, when it is used for a DRD can, for example, when a DRD can is formed, the shape of a wrinkle in a flange part becomes bad. Therefore, the content of Mn is set to 0.60% or less. The content of Mn is preferably from 0.10% to 0.50%.

P: 0.050% or less

When the content of P exceeds 0.050%, the steel sheet is excessively hardened, and the aging index of the rolling direction of the steel sheet after the second cold rolling becomes less than 25 MPa. For example, when used for a crown, the shape of the formed crown deteriorates. , And the compressive strength is reduced. Similarly, when it is used for a DRD can, for example, when a DRD can is formed, the shape of a wrinkle in a flange part becomes bad. Therefore, the upper limit of the content of P is set to 0.050%. In addition, when P is set to less than 0.001%, the cost of removing P becomes excessively large. Therefore, the content of P is preferably set to 0.001% or more.

S: 0.050% or less

S combines with Mn in the steel sheet to form MnS and precipitates in a large amount. Therefore, the hot ductility of the steel sheet is reduced. If the content of S exceeds 0.050%, this effect becomes significant. Therefore, the upper limit value of the content of S is set to 0.050%. In addition, when S is set to less than 0.005%, the cost of removing S becomes excessively large. Therefore, the content of S is preferably set to 0.004% or more.

Al: 0.020% or more and 0.050% or less

Al is an element contained as a deoxidizing agent, and forms AlN with N in the steel to reduce solid solution N in the steel. If the Al content is less than 0.020%, the effect as a deoxidizer becomes insufficient, which causes the occurrence of solidification defects and increases the cost of steel making. Furthermore, the aging index in the rolling direction of the steel sheet after the secondary cold rolling becomes less than 25 MPa, and when it is used for a crown, for example, the compressive strength decreases. Similarly, when it is used for a DRD can, for example, when a DRD can is formed, the shape of a wrinkle in a flange part becomes bad. On the other hand, if the content of Al exceeds 0.050%, the formation of AlN increases, and the amount of N that contributes to the strength of the steel sheet as solid solution N described later is increased. As the steel sheet strength decreases, the Al content is reduced to 0.050% or less. The Al content is preferably 0.030% or more and 0.045% or less.

N: more than 0.0140% and less than 0.0180%

When the content of N is 0.0140% or less, the aging index in the rolling direction of the steel sheet after the second cold rolling becomes less than 25 MPa. For example, when it is used for crown applications, the compressive strength is reduced, and it will be described later. The amount of solid solution N that contributes to the strength of the steel sheet decreases, and the strength of the steel sheet decreases. Or, when it is used for DRD cans, for example, wrinkles are generated in the flange portion when the DRD can is formed, and the can becomes a bad shape can. On the other hand, if the N content exceeds 0.0180%, the aging index exceeds 55 MPa, and the steel sheet after the second cold rolling is excessively hardened. For example, when it is used for a crown, the shape of the formed crown is deteriorated to withstand the pressure. Reduced strength. Alternatively, for example, when it is used for a DRD can, the shape of the wrinkles at the flange portion may be defective when the DRD can is formed. The N content is preferably more than 0.0150% and 0.0170% or less.

Cr: 0.040% or less

When the content of Cr exceeds 0.040%, the aging index in the rolling direction of the steel sheet after the second cold rolling becomes less than 25 MPa. For example, when it is used for crown applications, the compressive strength is reduced, and the solid solution C is reduced. The amount of C that contributes to the strength of the steel sheet decreases, and the strength of the steel sheet decreases. Alternatively, for example, when it is used for a DRD can, the shape of the wrinkles at the flange portion may be defective when the DRD can is formed. Therefore, the upper limit of the Cr content is set to 0.040%. In addition, the cost of steel making the Cr content to less than 0.001% will be excessively high. Therefore, the Cr content is preferably set to 0.001% or more.

The balance other than the above components is Fe and unavoidable impurities.

Next, as the mechanical properties of the steel sheet of the present invention, it is important that the aging index in the rolling direction is 25 MPa to 55 MPa.

That is, if the aging index of the steel sheet in the rolling direction is less than 25 MPa, when the steel sheet is used for a crown, for example, a large number of crowns are formed and subjected to a pressure test, a crown with low compressive strength is scattered and manufactured. Yields were reduced in the crown. Alternatively, for example, when it is used for a DRD can, the shape of the wrinkles at the flange portion may be defective when the DRD can is formed. On the other hand, if the aging index exceeds 55 MPa, the strength of the steel sheet is excessively increased. Therefore, for example, when used for crown applications, the shape of the crown becomes uneven. When a large number of crowns are formed and subjected to a pressure test, they are scattered. For crowns with low compressive strength, the yield during crown production decreases. Alternatively, for example, when it is used for a DRD can, the shape of the wrinkles at the flange portion may be defective when the DRD can is formed.

Here, the aging index of the rolling direction of the steel sheet is a tensile test piece of size 5 of the Japanese Industrial Standards (Japanese Industrial Standards) in parallel with the rolling direction of the steel sheet, and the test is performed with reference to "JIS G3135" And get. That is, a pre-strain of 8% is applied to the test piece, the load at this time (8% pre-strain load; P1) is read, and the load is removed thereafter. Then, the test piece to which the pre-strain was given was heat-processed at 100 degreeC for 1 hour. The tensile test was performed after the heat treatment, and the undulating load (load after heat treatment; P2) was read, and the aging index was obtained by the following formula.

Aging index = (P2-P1) / A (A: cross-sectional area of the parallel portion of the test piece before pre-straining)

By adjusting the composition of the composition; adjusting the heating temperature, finishing rolling temperature, final rolling reduction, and rolling temperature in the hot rolling step; adjusting the rolling reduction in a cold rolling step; adjusting the cooling in the continuous annealing step Speed; adjusting the reduction ratio in the secondary cold rolling step to obtain the aging index satisfying the above. The details of the manufacturing conditions will be described later.

In a steel sheet having the above composition and mechanical properties, even if the thickness is, for example, 0.20 mm or less, a high strength can be secured, and specifically, a drop strength of 620 MPa or more.

That is, when the steel sheet of the present invention is supplied to a crown, for example, a pressure resistance strength is required so that the crown fastened to the bottle mouth does not fall off due to internal pressure. The thickness of the steel sheet for a crown used conventionally is 0.22 mm or more. However, when the thickness is reduced to 0.20 mm or less, particularly 0.18 mm or less, higher strength is required than before. If the undulated strength of the steel sheet is less than 620 MPa, sufficient compressive strength cannot be imparted to the thinned crown as described above. Therefore, the drop strength must be above 620MPa. If the yield strength is too high, the crown height will be lowered during crown formation, and the crown shape will become uneven. Therefore, the yield strength in the rolling direction must be 700 MPa or less.

The drop strength can be measured by the tensile test method for metal materials shown in "JIS Z 2241".

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

The steel sheet of the present invention is manufactured by the following steps: a hot rolling step, which heats a steel raw material (slab) containing the above-mentioned component composition at a temperature of 1200 ° C or higher, the finishing rolling temperature is set to 870 ° C or higher, and the final reduction of the stand The rate is set above 10% and at 550 ° C Winding in a temperature range of ~ 750 ° C; pickling step, pickling after the hot rolling; one cold rolling step, after the pickling step, cold rolling with a reduction ratio of 88% or more; In the continuous annealing step, after the first cold rolling, the holding time in a temperature range with a soaking temperature of 660 ° C to 760 ° C is set to 60 seconds or less, and the average cooling rate of 10 ° C / s or more is cooled to 450 ° C or less. And a secondary cold rolling at a reduction ratio of 10% to 40% at an average cooling rate of 5 ° C / s or more and a temperature range of 140 ° C or less.

In the following description, the temperature is specified based on the surface temperature of the steel sheet. The average cooling rate is a value obtained by calculation based on the surface temperature. For example, the average cooling rate in the temperature range from the soaking temperature to 450 ° C or lower is from ((soaking temperature) to (450 ° C or lower temperature region)) / (from the soaking temperature to (450 ° C or lower temperature region)). Cooling time) display. In addition, the "temperature region below 450 ° C" in the above formula refers to a cooling stop temperature in the temperature region.

When the steel sheet of the present invention is manufactured, the molten steel is adjusted to the above-mentioned chemical composition by a known method using a converter or the like, and thereafter, a slab is prepared as a steel raw material by, for example, a continuous casting method.

(Steel raw material heating temperature: above 1200 ℃)

The heating temperature of the steel material in the hot rolling step is set to 1200 ° C or higher. If the heating temperature is less than 1200 ° C, the amount of solid solution N necessary for securing the strength in the present invention decreases and the strength decreases. Therefore, the heating temperature is set to 1200 ° C or higher. Furthermore, in the steel composition of the present invention, it is considered that N in the steel mainly exists in the form of AlN. Therefore, the total amount (Ntotal) of N is subtracted from the amount of N (NasAlN) in the form of AlN (Ntotal - (NasAlN)) was regarded as the amount of solid solution N. In order to set the rolling strength of the steel sheet in the rolling direction to 600 MPa or more, the amount of solid solution N is preferably 0.0141% or more, which can be ensured by setting the heating temperature of the steel material to 1200 ° C or more. A more preferable solid solution N content is 0.0150% or more. To this end, the heating temperature of the steel raw material can be set to 1220 ° C or more. Even if the heating temperature of the steel material exceeds 1300 ° C, the effect is saturated, so it is preferably 1300 ° C or lower.

(Finishing temperature: above 870 ℃)

If the finish rolling temperature in the hot rolling step is less than 870 ° C, the aging index in the rolling direction of the steel sheet will be less than 25 MPa, and the compressive strength will be reduced when it is used for crown applications, for example. Furthermore, when a steel plate is used for, for example, a DRD can, the shape of the wrinkles at the flange portion is defective during the DRD can forming. Therefore, when it is used for a DRD tank, for example, a finishing rolling temperature of less than 870 ° C. may cause a defective shape of a wrinkle at a flange portion when the DRD tank is formed. Therefore, the finishing rolling temperature is set to 870 ° C or higher. On the other hand, when the finishing rolling temperature is increased above a necessary level, the production of a thin steel sheet may be difficult. Specifically, the finishing rolling temperature is preferably set in a temperature range of 870 ° C to 950 ° C.

(Reduction rate of final rack: more than 10%)

The reduction ratio of the final stand in the hot rolling step is set to 10% or more. If the reduction ratio of the final stand is less than 10%, the aging index in the rolling direction of the steel sheet will be less than 25 MPa, and the compressive strength will be reduced when it is used for a crown, for example. Furthermore, when a steel plate is used for, for example, a DRD can, the shape of the wrinkles at the flange portion is defective during the DRD can forming. Therefore, set the final frame reduction rate to 10% the above. In order to reduce the standard deviation of the iron particle diameter of the fertilizer, the reduction ratio of the final frame is preferably set to more than 12%. From the viewpoint of rolling load, the upper limit of the reduction ratio of the final stand is preferably 15% or less.

(Rolling temperature: 550 ℃ ~ 750 ℃)

The reason is that if the coiling temperature in the hot rolling step is less than 550 ° C, the aging index in the rolling direction of the steel sheet becomes less than 25 MPa, and the compressive strength decreases when it is used for a crown, for example, or In the case of a DRD can, the shape of the wrinkles at the flange portion is bad when the DRD can is formed. Therefore, the winding temperature is set to 550 ° C or higher. On the other hand, when the winding temperature is higher than 750 ° C., a part of the ferrous iron in the steel sheet becomes coarse, and the strength of the steel sheet decreases, and the compressive strength decreases when it is used for a crown, for example. Furthermore, when a steel plate is used for, for example, a DRD can, the shape of the wrinkles at the flange portion is defective during the DRD can forming. Therefore, the winding temperature is preferably 750 ° C or lower. More preferably, it is 600 ° C or more and 700 ° C or less.

(Pickling)

Thereafter, it is preferable to perform pickling. As long as the surface scale can be removed by pickling, the conditions are not particularly limited.

Next, cold rolling was performed twice by annealing.

(One-time cold rolling reduction rate: 88% or more)

First, the reduction ratio in the primary cold rolling step is set to 88% or more. If the reduction ratio in a single cold rolling step is less than 88%, the strain applied to the steel sheet by cold rolling is reduced, and therefore, the recrystallization in the continuous annealing step becomes uneven, and the ferrous iron after recrystallization is not uniform. The dimensional unevenness of the particle size becomes large, and the aging index in the rolling direction of the steel sheet after the secondary cold rolling becomes less than 25 MPa, and the compressive strength decreases. Furthermore, when a steel plate is used for, for example, a DRD can, the shape of the wrinkles at the flange portion is defective during the DRD can forming. Therefore, the reduction ratio in the primary cold rolling step is set to 88% or more. A more preferable setting is 89% to 94%.

In the annealing step after one cold rolling, after maintaining in a temperature range of 660 ° C to 760 ° C for 60 seconds or less, the first stage cooling is performed at a temperature range of 10 ° C / s or more to a temperature range of 450 ° C or less, and then The latter stage cooling is performed at a temperature range of 5 ° C./s or higher to a temperature range of 140 ° C. or lower.

(Soaking temperature: 660 ℃ ~ 760 ℃)

That is, the soaking temperature in the continuous annealing step is performed at a temperature of 660 ° C to 760 ° C. When the soaking temperature is set to exceed 760 ° C, it is not preferable to cause a plate failure such as heat buckling during continuous annealing. In addition, a part of the grain size of the iron particles of the steel sheet is coarsened, the strength of the steel sheet is reduced, and the aging index in the rolling direction of the steel sheet is less than 25 MPa. For example, when it is used for crown applications, the compressive strength is reduced. Furthermore, when a steel plate is used for, for example, a DRD can, the shape of the wrinkles at the flange portion is defective during the DRD can forming. On the other hand, if the annealing temperature is less than 660 ° C, recrystallization becomes incomplete, a part of the grain size of the iron particles of the steel sheet becomes fine, and the aging index in the rolling direction of the steel sheet after secondary cold rolling becomes less than 25 MPa. The compressive strength decreases. Furthermore, when a steel plate is used for, for example, a DRD can, the shape of the wrinkles at the flange portion is defective during the DRD can forming. Therefore, it is performed at the temperature which the soaking temperature is 660 degreeC-760 degreeC. Preferably at 680 ℃ ~ 730 ℃.

The holding time in a temperature range where the soaking temperature is 660 ° C to 760 ° C is set to 60 seconds or less. If the holding time exceeds 60 seconds, the C contained in the steel plate segregates to the fat and iron grain boundaries and precipitates in the form of carbides during the cooling process in the continuous annealing step, thereby reducing the amount of solid solution C that contributes to the strength of the steel plate. , The drop strength is reduced, and the aging index in the rolling direction of the steel sheet after the secondary cold rolling becomes less than 25 MPa, and the compressive strength is reduced. Furthermore, when a steel plate is used for, for example, a DRD can, the shape of the wrinkles at the flange portion is defective during the DRD can forming. Therefore, the holding time in a temperature range where the soaking temperature is 660 ° C to 760 ° C is set to 60 seconds or less. In addition, if the holding time is less than 5 seconds, the stability of the steel sheet when it passes on a uniformly heated roll is impaired. Therefore, the holding time is preferably 5 seconds or more.

(Front stage cooling: Cool to 450 ° C or less at an average cooling rate of 10 ° C / s or more)

After the soaking, the temperature is cooled to a temperature range of 450 ° C or lower at an average cooling rate of 10 ° C / s or higher. If the average cooling rate is less than 10 ° C / s, carbide precipitation will be accelerated during the cooling process, so that the amount of solid solution C that contributes to the strength of the steel plate will be reduced, the yield strength will be reduced, and the steel plate after the second cold rolling will be rolled. The aging index in the direction becomes less than 25 MPa, and the compressive strength decreases. Furthermore, when a steel plate is used for, for example, a DRD can, the shape of the wrinkles at the flange portion is defective during the DRD can forming. In addition, if the average cooling rate exceeds 50 ° C / s, the effect is saturated, so the average cooling rate is preferably set to 50 ° C / s or less.

In addition, if the cooling stop temperature during the first-stage cooling after soaking exceeds 450 ° C, After the first-stage cooling, carbide precipitation will be accelerated, so that the amount of solid solution C that contributes to the strength of the steel sheet will be reduced, and the yield strength will be reduced. Also, the aging index of the rolling direction of the steel sheet after the second cold rolling will be less than 25 MPa and pressure resistance. Reduced strength. Furthermore, when a steel plate is used for, for example, a DRD can, the shape of the wrinkles at the flange portion is defective during the DRD can forming. Furthermore, if the cooling stop temperature during the first-stage cooling after soaking is less than 300 ° C, not only the carbide precipitation suppression effect is saturated, but also the aging index in the rolling direction of the steel sheet after the second cold rolling becomes more than 55 MPa, and the steel sheet The strength is excessively increased, so that, for example, when used for crowns, the shape of the crown becomes uneven. When a large number of crowns are formed and used in a pressure test, the crowns with low compressive strength will be scattered. Rate decreases. Furthermore, when a steel plate is used for, for example, a DRD can, the shape of the wrinkles at the flange portion is defective during the DRD can forming. In addition, there is a possibility that the shape of the steel sheet may deteriorate due to failure at the time of passing through the plate. Therefore, the cooling stop temperature after soaking is preferably 300 ° C. or higher.

(Post-stage cooling: Cool to 140 ° C or lower at an average cooling rate of 5 ° C / s or higher)

In the latter-stage cooling after the first-stage cooling, the average cooling rate of 5 ° C / s or more is used to cool from the cooling stop temperature during the first-stage cooling to a temperature range below 140 ° C. If the average cooling rate is less than 5 ° C / s, the amount of solid solution C that contributes to the strength of the steel sheet will be reduced, and the yield strength will be reduced. Furthermore, the aging index in the rolling direction of the steel sheet after the secondary cold rolling will be less than 25 MPa and will withstand Reduced compressive strength. Furthermore, when a steel plate is used for, for example, a DRD can, the shape of the wrinkles at the flange portion is defective during the DRD can forming. Furthermore, if the average cooling rate exceeds 30 ° C / s, not only the effect is saturated, but In addition, the cooling equipment generates excessive costs. Therefore, the average cooling rate in the subsequent cooling is preferably set to 30 ° C./s or less. It is more preferably 25 ° C / s or less.

It is cooled to below 140 ° C during the subsequent cooling. When it exceeds 140 ° C., the amount of solid solution C contributing to the strength of the steel sheet is reduced, the drop strength is reduced, and the aging index in the rolling direction of the steel sheet after the secondary cold rolling becomes less than 25 MPa, and the compressive strength is reduced. Furthermore, when a steel plate is used for, for example, a DRD can, the shape of the wrinkles at the flange portion is defective during the DRD can forming. Furthermore, if the cooling stop temperature is less than 100 ° C, not only the effect is saturated, but also an excessive cost of cooling equipment is generated. Therefore, it is preferably 100 ° C or higher. It is more preferably 120 ° C or higher.

(Second cold rolling reduction: 10% to 40%)

The steel sheet of the present invention can obtain high dropout strength by the second cold rolling after annealing. That is, if the reduction ratio of the secondary cold rolling is less than 10%, a sufficient drop-out strength cannot be obtained, and for example, the compressive strength when used for a crown is reduced. In addition, when the reduction ratio of the secondary cold rolling exceeds 40%, the anisotropy becomes too large, and for example, the compressive strength in the case of being used for a crown is reduced. Furthermore, when a steel plate is used for, for example, a DRD can, the shape of the wrinkles at the flange portion is defective during the DRD can forming. Therefore, the reduction ratio of the secondary cold rolling is preferably set to 10% or more and 40% or less. It is more preferable that the reduction ratio of the secondary cold rolling exceeds 15% and is 35% or less.

Regarding the cold-rolled steel sheet obtained as described above, if necessary, the surface of the steel sheet may be subjected to a plating treatment such as tin plating, chrome plating, or nickel plating to form a plated layer, and the plate may be used as a plated steel sheet. . In addition, since the film thickness of the surface treatment such as plating is very small compared to the plate thickness, the influence on the mechanical characteristics of the steel sheet is not necessary. Level of view.

As described above, the steel sheet of the present invention can have sufficient strength and excellent material uniformity even if it is thinned. Therefore, the steel sheet of the present invention is most suitable as a raw material for a crown or a DRD tank in particular.

The crown of the present invention is obtained by forming using the steel sheet. The crown mainly includes a disc-shaped portion that blocks the mouth of the bottle, and a pleated portion provided around the disc-shaped portion. The crown of the present invention can be formed by pressing the steel sheet of the present invention into a round blank and then press forming. The crown of the present invention is made of a steel plate having sufficient buckling strength and excellent material uniformity. Therefore, even if thinned, the compressive strength as a crown is excellent, and the outer diameter and height uniformity of the crown are excellent. Therefore, the crown The yield in the manufacturing process is improved, and there is an effect of reducing the discharge amount of waste accompanying the crown manufacturing.

Similarly, the DRD can of the present invention is obtained by forming using the steel sheet. The DRD tank can be formed by stamping the steel sheet of the present invention into a circular blank by performing a deep drawing process and a deep drawing process. The DRD can using the steel sheet of the present invention as a raw material has a uniform shape and does not meet the product specifications. Therefore, the yield in the DRD can manufacturing step is improved, and there is also an effect of reducing the discharge amount of waste accompanying the DRD can manufacturing.

[Example 1]

The steel containing the component composition shown in Table 1 and the remainder containing Fe and unavoidable impurities was melted in a converter, and a steel slab was obtained by continuous casting. The slab obtained here was subjected to the slab heating temperature shown in Table 2 and finishing rolling. Hot rolling at temperature and coiling temperature. After this hot rolling, pickling is performed. Then, cold rolling was performed once at the reduction rates shown in Table 2, and continuous annealing was performed under the continuous annealing conditions shown in Table 2, and then secondary cold rolling was performed at the reduction rates shown in Table 2. The obtained steel sheet was continuously subjected to electrolytic chromic acid treatment to obtain Tin Free Steel.

[Table 1]

The steel sheet obtained as described above was subjected to a heat treatment corresponding to painting and baking at 210 ° C. and 15 minutes, and then subjected to a tensile test. The tensile test was performed using a JIS No. 5 tensile test piece in accordance with "JIS Z 2241" to measure the drop strength in the rolling direction. Moreover, the aging index of the rolling direction of a steel plate was calculated | required according to the said measuring method.

In addition, the heat treatment equivalent to the coating firing does not affect the material of the steel sheet before the heat treatment.

A crown was formed using the obtained steel sheet, and the crown formability was evaluated. That is, a round blank having a diameter of 37 mm was used to form 50 crowns (N = 50) for each steel plate by press working. Then, the crown height (distance from the crown top surface to the lower end of the side) was measured using a micrometer. In addition, it is determined that the standard deviation of the crown height of N = 20 is 0.09 mm or less, and the crown shape is excellent, and the standard deviation of the crown height of N = 20 is more than 0.09 mm, which is judged to be a crown shape difference. The obtained measurement results are shown in Table 2.

In addition, a pressure test was also performed on the obtained crown.

Here, the pressure resistance test is performed by forming a liner made of vinyl chloride on the inside of the crown and attaching it to a commercially available beer bottle, and it is measured using a Secure Seal Tester manufactured by Secure Pak. The internal pressure when the crown is disengaged, and the internal pressure when the crown is disengaged is taken as the compressive strength. A pressure test was performed on each of the 50 crowns. A case where the number of crowns having a compressive strength of 165 psi or more was 47 or more was evaluated as ◎, and the number of crowns having a compressive strength of 165 psi or more was 45 or 46. Each case was evaluated as ○, and the case where the number of crowns having a compressive strength of 165 psi or more was less than 45 was evaluated as ×. The obtained results are shown in Table 2.

The obtained steel sheet was heat-treated at 210 ° C. for 15 minutes, which was equivalent to a coating burn-in, and formed into a DRD can, and the DRD can formability was evaluated. That is, using a circular blank having a diameter of 158 mm, drawing and redrawing were performed to form a DRD can with an inner diameter of 82.8 mm and a flange diameter of 102 mm, and the DRD can formability was evaluated. Regarding the evaluation, a sample in which fine wrinkles were observed at three or more places in the flange portion was set to ×, a sample in which fine wrinkles in the flange portion were set to two, and a sample in which fine wrinkles were set to one in the flange portion. The following samples are set as?. The evaluation results are shown in Table 2.

Underlined part: outside the scope of the present invention

According to Table 2, the rolling strength of the steel plates No. 1 to No. 22 as examples of the present invention is 600 MPa or more, and the number of crowns with a compressive strength of 165 psi or more is 45 or more, which has a stable pressure resistance. strength. In addition, the undulation strength in the rolling direction is 560 MPa or more, and the standard deviation of the crown height is 0.09 mm or less. The crown formability is good and the DRD tank formability is good.

On the other hand, the steel plates No. 23 to No. 25 as comparative examples have too much C content, so the grain size of the ferrite grains of the steel plate after the second cold rolling becomes fine, and the aging index exceeds 55 MPa, and the steel plate is too hard. As a result, the shape of the crowns formed is not uniform, so that the number of crowns with a compressive strength of 165 psi or more is less than 45, and the compressive strengths of the crowns are uneven, and high compressive strength cannot be obtained stably. Furthermore, it can be seen that the standard deviation of the crown height exceeds 0.09 mm, the crown formability is deteriorated, and the DRD tank formability is also deteriorated.

It can be seen that the steel plate of No.26 ~ No.28 has too little C content, so the aging index of the rolling direction of the steel plate after the second cold rolling is less than 25MPa, and the number of crowns with a compressive strength above 165psi is less than 45. The compressive strength is not uniform among each other. It was also found that the moldability of the DRD tank was also deteriorated.

The steel plate of No. 29 has too much Mn content, so the steel plate is excessively hardened, so the shape of the crown is deteriorated, so that the number of crowns with a compressive strength of 165 psi or more is less than 45, and high compressive strength cannot be obtained stably. It was also found that the moldability of the DRD tank was also deteriorated.

The steel plate of No. 30 has too much Al content, so the formation of AlN increases, so that the amount of N that contributes to the steel plate strength as a solid solution N decreases, and the steel plate strength decreases, and The aging index in the rolling direction of the steel sheet after the secondary cold rolling is less than 25 MPa, so the number of crowns having a compressive strength of 165 psi or more is less than 45, and high compressive strength cannot be obtained stably. It was also found that the moldability of the DRD tank was also deteriorated.

The steel sheet of No. 31 has too little Al content, so the effect as a deoxidizer is insufficient, which causes the occurrence of solidification defects and increases the steel making cost. In addition, the aging index exceeds 55 MPa, the steel sheet after secondary cold rolling is excessively hardened, and the shape of the crowns formed is not uniform. Therefore, the number of crowns with a compressive strength of 165 psi or more is less than 45, and high compressive strength cannot be obtained stably. . It was also found that the moldability of the DRD tank was also deteriorated.

The steel plates No.32 to No.34 have too much N content, so the aging index exceeds 55 MPa. The steel plate after the second cold rolling is excessively hardened, and the shape of the crown formed is not uniform, so the crown with a compressive strength of 165psi or more The number is less than 45, and high compressive strength cannot be obtained stably. It was also found that the moldability of the DRD tank was also deteriorated.

It can be seen that the steel plates of No. 35 to No. 37 have too little N content, so the aging index of the rolling direction of the steel plate after the second cold rolling is less than 25 MPa, and the number of crowns with a compressive strength of 165 psi or less is less than 45. It has stable compressive strength and reduces the amount of N that contributes to the strength of the steel sheet as a solid solution N, thereby reducing the strength of the steel sheet. It was also found that the moldability of the DRD tank was also deteriorated.

The steel plate of No. 38 has too much P content, so the aging index of the rolling direction of the steel plate after the second cold rolling is less than 25 MPa, and the shape of the formed crown is not uniform, so the number of crowns with a compressive strength of 165 psi or more Below 45, high compressive strength cannot be obtained stably. It was also found that the moldability of the DRD tank was also deteriorated.

It can be seen that the steel plate of No. 39 has too much Cr content. The aging index of the steel sheet in the rolling direction is less than 25 MPa, the number of crowns with a compressive strength of 165 psi or more is less than 45, does not have stable compressive strength, and reduces the amount of C that is a solid solution C that contributes to the strength of the steel sheet. , The strength of the steel plate is reduced. It was also found that the moldability of the DRD tank was also deteriorated.

In addition, the steel plate of No. 40 has too much Si content, so the steel plate is excessively hardened, and the shape of the crowns formed is not uniform. Therefore, the number of crowns having a compressive strength of 165 psi or less is less than 45, and high pressure resistance cannot be obtained stably. strength. It was also found that the moldability of the DRD tank was also deteriorated.

[Example 2]

A steel having a chemical composition of steels No. 4, No. 10, and No. 17 shown in Table 1 and containing Fe and unavoidable impurities in the remainder was melted by a converter, and a steel slab was obtained by continuous casting. The slab obtained here was hot-rolled at the slab heating temperature, the finish rolling temperature, and the coiling temperature shown in Table 3. After hot rolling, pickling is performed. Next, cold rolling was performed once at the reduction rates shown in Table 3, and the soaking temperature, soaking time, average cooling rate, cooling rate, cooling rate, cooling rate, cooling rate Continuous annealing was performed at a stop temperature, and then secondary cold rolling was performed at a reduction ratio shown in Table 3. The obtained steel sheet was continuously subjected to electrolytic chromic acid treatment to obtain a tin-free steel.

The steel sheet obtained as described above was subjected to a tensile test by the same method as described above, and the aging index of the rolling direction of the steel sheet was similarly determined. Furthermore, the crown formability, the compressive strength of the crown, and the DRD can formability were evaluated by the same method as described above. The obtained results are shown in Table 3.

According to Table 3, steel plates No. 41, No. 44, No. 46, No. 48, No. 49, No. 53 to No. 56, No. 59, No. 60, and No. 64 as examples of the present invention. The undulating strength in the rolling direction of the steel sheet is 600 MPa or more, and the number of crowns having a compressive strength of 165 psi or more is 45 or more, and has a stable compressive strength. In addition, the undulation strength in the rolling direction is 560 MPa or more, and the standard deviation of the crown height is 0.09 mm or less. The crown formability is good and the DRD tank formability is also good.

On the other hand, it can be seen that the steel plates No.42, No.43, No.45, No.47, No.50, No.51, No.52, No.57, No.58, No.61, No.62, No.65, No.67 steel plate slab heating temperature, finishing rolling temperature, rolling reduction of the final stand in the hot rolling step, winding temperature, primary cold rolling reduction, soaking temperature, Any of the soaking time, the average cooling rate in the first stage, the reduction rate in the secondary cold rolling, and the average rate in the second stage cooling are outside the scope of the present invention. Therefore, the aging index of the rolling direction of the steel sheet after the secondary cold rolling is not. When the number is over 25 MPa, the number of crowns with a compressive strength of 165 psi or more is less than 45, and the compressive strength does not have a stable compressive strength and / or the undulation strength in the rolling direction is reduced. In addition, it can be seen that the DRD can formability is deteriorated.

It can be seen that the steel plate of steel plate No. 63 as a comparative example has an excessively high anisotropy due to the secondary cold rolling reduction rate, which impairs the uniformity of the crown shape. Therefore, the number of crowns having a compressive strength of 165 psi or less is less than 45. , Does not have stable compressive strength. It was also found that the moldability of the DRD can deteriorated.

It can be seen that the steel plate of steel plate No. 66 as a comparative example has a low cooling stop temperature at the front stage, so the aging index of the rolling direction of the steel plate after the second cold rolling exceeds 55 MPa, the strength of the steel plate is excessively increased, and the compressive strength is a crown of 165 psi or more. quantity Below 45, it does not have stable compressive strength. It was also found that the moldability of the DRD can deteriorated.

Claims (5)

A steel sheet includes, in mass%, C: more than 0.0060% and 0.0100% or less, Si: 0.05% or less, Mn: 0.05% or more and 0.60% or less, P: 0.050% or less, S: 0.050% or less, and Al: 0.020% or more and 0.050% or less, N: more than 0.0140% and 0.0180% or less, and Cr: 0.040% or less, the remainder has a composition of Fe and unavoidable impurities, and the aging index in the rolling direction is 25 MPa to 55 MPa , The drop strength is 620MPa ~ 700MPa. The steel sheet described in item 1 of the scope of patent application has a thickness of 0.20 mm or less. A crown comprising a steel plate as described in item 1 or 2 of the scope of patent application. A stamping-type (DRD) tank comprising a steel plate as described in item 1 or 2 of the scope of patent application. A method for manufacturing a steel plate for manufacturing a steel plate as described in item 1 or 2 of the scope of patent application, including: a hot rolling step, heating steel raw materials at a temperature of 1200 ° C or higher, and a finishing rolling temperature of 870 ° C or higher and Rolling reduction of the final stand: rolling is performed under the condition of more than 10%, and coiling is performed in a temperature range of 550 ° C to 750 ° C; the pickling step is performed with acid on the hot-rolled sheet after the hot rolling step Washing; a cold rolling step, the reduction ratio of the hot-rolled sheet after the pickling step: cold rolling above 88%; an annealing step, the cold-rolled sheet after the first cold rolling step is at 660 ° C ~ 760 After holding in a temperature range of 60 ° C or less for 60 seconds, it is cooled at an average cooling rate of 10 ° C / s or more to a temperature range of 450 ° C or less and 300 ° C or more, followed by an average cooling of 5 ° C / s or more and 30 ° C / s or less. The temperature is cooled to a temperature range of 140 ° C. or lower; and a secondary cold rolling step is performed to cold-roll the annealed sheet after the annealing step at a reduction ratio of 10% to 40%.