TW201837202A - Steel sheet, method for producing same, crown cap, and drawn and redrawn (drd) can - Google Patents

Abstract

Provided is a steel sheet which has a component composition including, in mass%, over 0.0060% but not more than 0.0100% of C, not more than 0.05% of Si, at least 0.05% but not more than 0.60% of Mn, not more than 0.050% of P, not more than 0.050% of S, at least 0.020% but not more than 0.050% of Al, and at least 0.0070% but not more than 0.0140% of N, the remainder being Fe and unavoidable impurities. Furthermore, the steel sheet has, in a region up to a sheet-thickness centre portion from a depth of 1/4 of the sheet thickness, a structure having a ferrite phase in which the standard deviation of the ferrite particle diameter is 7.0 [mu]m or lower. The steel sheet has a yield strength of 560 MPa or higher. Accordingly, the steel sheet exhibits sufficient strength and excellent moulding properties, despite being thin.

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 for a crown of a plug such as a glass bottle. 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 a crown with such a bad shape is fastened to the bottle mouth, sufficient sealing properties may not be obtained. Therefore, a steel plate as a 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. By using an SR material using mild steel used in food or beverage cans, etc. as a raw material, sufficient compressive strength and formability can be ensured.

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, when the strength of the steel sheet is low, the crown may fall off due to insufficient compressive strength.

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.

Regarding the high-strength thin steel sheet for a crown based on the above aspect, 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% by mass or more 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 value in all directions, and the yield strength are appropriately controlled, thereby satisfying a sufficient crown even with a thin thickness Withstand pressure. [Prior Art Literature] [Patent Literature]

Patent Document 1: Japanese Patent No. 6057023

[Problems to be Solved by the Invention] The steel sheet described in Patent Document 1 uses steel containing 0.0060% or less of C, and sets the tension between stands and the annealing temperature in the secondary cold rolling to a predetermined relationship. This gives the r value (direction, size) suitable for crown processing. This method does not control the hot-rolling step that affects the formation of the metal structure, so the variation in the material quality of the obtained steel sheet becomes large, and it is difficult to put it to 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. [Means for solving problems]

The inventors have intensively studied a method for solving the above problems, and as a result, they have found that by restricting the structure under a predetermined 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 having the following component composition, including C in mass%: 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, S: 0.050% or less, Al: 0.020% or more and 0.050% or less, and N: 0.0070% or more and 0.0140% or less. The remainder is Fe and unavoidable impurities, and the depth ranges from 1/4 of the plate thickness to the plate thickness. The region of the central part has a ferrite phase, and the standard deviation of the ferrite particle size in the ferrite phase is 7.0 μm or less, and the yield strength is 560 MPa or more.

(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 as described in (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 the 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 is performed: a cold rolling of 88% or more; the annealing step is performed on the cold-rolled sheet after the first cold-rolling at 660 After holding for 60 seconds or less in a temperature range of ℃ to 760 ℃, it is cooled to a temperature range of 450 ° C or less at an average cooling rate of 10 ° C / s or more, and then cooled to 140 ° C or less 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%. [Effect of the invention]

According to the present invention, it is possible to provide a steel sheet having sufficient strength and excellent material uniformity 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, crowns or DRD cans that are not deformed in shape can be formed.

The steel sheet of the present invention has a component composition that contains C in mass%: more than 0.0060% and 0.0100% or less, Si: 0.05% or less, Mn: 0.05% or more and 0.60% or less, and P: 0.050% or less , S: 0.050% or less, Al: 0.020% or more and 0.050% or less, N: 0.0070% or more and 0.0140% or less, the remainder contains Fe and unavoidable impurities, and the depth ranges from 1/4 of the plate thickness to the plate thickness The region of the central portion has a ferrous iron phase, and the standard deviation of the ferrous iron particle diameter in the ferrous iron phase is 7.0 μm or less. 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, "%" with respect to a component means "mass%" unless there is particular notice.

C: more than 0.0060% and 0.0100% or less When the content of C is 0.0060% or less, the ferrite grains of the steel sheet after the secondary cold rolling described later become coarse and the formability is deteriorated. For example, it is used for crown applications In the case of the crown, the outer diameter and crown height of the formed crown become uneven. 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 ferrous iron of the steel sheet after the second cold rolling becomes too fine, the strength of the steel sheet excessively increases, and the formability is deteriorated. For example, when used for crown applications, The outer diameter and height of the crown became uneven. 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 If Si is contained in a large amount, for the same reason as C, for example, when used for a crown, the uniformity of the outer diameter and height of the crown is impaired, and for example, when used for a DRD tank When the DRD can is formed, the shape of the wrinkles at the flange portion is not good. 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 Mn content is less than 0.05%, it is difficult to avoid thermal embrittlement even if the S content 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, the outer diameter and the uniformity of the crown are impaired when, for example, the crown is used for the same reason as for C, and when it is used for the DRD tank, for example, When forming a DRD can, wrinkle formation in a flange part is 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 If the content of P exceeds 0.050%, hardening of the steel sheet or decrease in corrosion resistance will be caused. In addition, the standard deviation of the iron particle diameter of the fertilized grains after the annealing exceeds 7.0 μm and the formability deteriorates. For example, when used for crown applications, the uniformity of the outer diameter and height of the crown is impaired. For example, when supplied to a DRD tank In the case of use, the shape of the wrinkles at the flange portion is poor during the DRD can forming. 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. In addition, if the Al content is less than 0.020%, an appropriate amount of AlN cannot be ensured when recrystallizing the ferrous iron by annealing, so the standard deviation of the iron particle diameter of the ferrous iron after annealing becomes large. The grain iron of the steel sheet after the sub-cold rolling becomes coarse and the formability is deteriorated. In this way, for example, when used for a crown, the uniformity of the outer diameter and height of the crown is impaired. For example, when used for a DRD tank, wrinkles are generated at the flange portion when the DRD tank is formed. Bad shape. 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 to be described later decreases and the strength of the steel sheet decreases. Therefore, the Al content is set to 0.050% or less. . The Al content is preferably 0.030% or less and 0.045% or less.

N: 0.0070% or more and 0.0140% or less When the content of N is less than 0.0070%, the ferrous iron of the steel sheet after the second cold rolling becomes coarse and the formability is deteriorated. For example, when it is used for crown applications Next, the outer diameter and height of the formed crown become non-uniform, and the amount of N that contributes to the strength of the steel sheet, which is solid solution N to be described later, is reduced, and the strength of the steel sheet 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 N content exceeds 0.0140%, the ferrous iron of the steel sheet after the second cold rolling becomes too fine, the strength of the steel sheet excessively increases, and the formability is deteriorated. When the uniformity of diameter and height is impaired, 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 set to be 0.0085% or more and 0.0125% or less. A more preferable setting is more than 0.0100%. The balance other than the above components is Fe and unavoidable impurities.

Next, regarding the metal structure of the steel sheet of the present invention, it is important to have a ferrous iron phase in a region from a depth of 1/4 of the plate thickness to the center of the plate thickness, and the ferrous iron in the ferrous iron phase The standard deviation of the particle diameter is 7.0 μm or less. First, the metal structure of the steel sheet of the present invention is mainly composed of a ferrite phase, and the remainder is cementite, and the ferrite phase is preferably 85% by volume or more. More preferably, it is 90% or more. That is, if the iron phase of the fat particles is less than 85% by volume, it is easy to break at the starting point of hard cis-carbon iron during processing, and the formability is deteriorated.

In the above-mentioned metal structure, the standard deviation of the ferrous grain iron particle size in the ferrous grain iron phase in a region from the depth of 1/4 of the plate thickness to the center of the plate thickness is set to 7.0 μm or less. That is, if the standard deviation of the iron particle diameter of the fertilized grains exceeds 7.0 μm, the formability is deteriorated. For example, when used for crown applications, the outer diameter and height of the crown after molding become uneven, and the compressive strength decreases. And the yield when making the crown 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. The standard deviation of the iron particle size of the fertilizer particles is preferably 6.5 μm or less.

Here, regarding the metal structure of the ferrous iron, the cross section in the plate thickness direction parallel to the rolling direction of the steel plate was polished, and then the solution was etched with an etching solution (3 vol% nitric acid-ethanol etching solution (Nital)), and the optical A microscope at 400 times magnification over 10 fields of view from a position of 1/4 depth of the plate thickness (a position of 1/4 of the thickness of the plate in the thickness direction from the surface in the section) to a position of 1/2 of the thickness of the plate Observe the area, and use a tissue photo taken with an optical microscope to determine the ferrous iron by visual judgment and determine the particle size of the ferrous iron by image analysis. The particle size distribution of the ferrous iron particle diameter was calculated in each field of view, and the standard deviation was calculated. The value obtained by averaging the standard deviations of the ten fields of vision was defined as the standard deviation of the ferrous iron particle diameter. For image analysis, Olympus Corporation's image analysis software "Stream Essentials" was used.

By adjusting the composition of the composition; adjusting the heating temperature, the finishing rolling temperature, the rolling reduction of the final stand and the winding temperature in the hot rolling step; adjusting the rolling reduction of a cold rolling; adjusting the cooling rate in the continuous annealing step; The reduction ratio in the secondary cold rolling step is adjusted to obtain a desired metal structure. The details of the manufacturing conditions will be described later.

In a steel sheet having the above-mentioned composition and structure, high strength can be secured even if the thickness is, for example, 0.20 mm or less, and specifically, a drop strength of 560 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, in order to reduce the thickness of the steel sheet to 0.20 mm or less, particularly 0.18 mm or less, higher strength is required than before. If the undulation strength of the steel sheet is less than 560 MPa, sufficient compressive strength cannot be imparted to the thinned crown as described above. Therefore, the yield strength must be above 560 MPa. In order to further ensure sufficient compressive strength, the drop-down strength is preferably 600 MPa or more. 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 is preferably 700 MPa or less. More preferably, it is 600 MPa or more and 680 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 to 10% or more, and the winding is performed in a temperature range of 550 ° C to 750 ° C; the pickling step is performed after the hot rolling; the single cold rolling step is performed after the pickling step; Cold rolling with a reduction ratio of 88% or more; continuous annealing step, after the first cold rolling, the holding time in a temperature range of a soaking temperature of 660 ° C to 760 ° C is set to 60 seconds or less, and 10 ° C / The average cooling rate above s is cooled to a temperature range below 450 ° C, and the average cooling rate above 5 ° C / s is cooled to a temperature range below 140 ° C; and a reduction ratio of 10% to 40% is performed. Secondary cold rolling.

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 below 450 ° C is from ((soaking temperature)-(temperature range below 450 ° C)) / cooling from the soaking temperature to (temperature range below 450 ° C) Time). 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: 1200 ° C or higher) The heating temperature of the steel raw 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 of N (Ntotal) is subtracted from the amount of N (NasAlN) in the form of AlN (Ntotal -(NasAlN)) is regarded as the amount of solid solution N. In order to set the yield strength in the rolling direction of the steel sheet to 560 MPa or more, the amount of solid solution N is preferably 0.0071% or more, and it 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 0.0090% 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.

(Finish rolling temperature: 870 ° C or higher) If the finish rolling temperature in the hot rolling step is less than 870 ° C, part of the ferrous iron in the steel sheet becomes thinner, and the standard deviation of the ferrous iron particle diameter exceeds 7.0 μm, resulting in poor formability. In this way, for example, when the crown is used for a crown, the crown shape becomes non-uniform. For example, when the crown is used for a DRD can, the shape of the wrinkles at the flange portion is defective when the DRD can 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 ratio of the final stand: 10% or more) The reduction ratio of the final stand in the hot rolling step is set to 10% or more. When the reduction ratio of the final stand is less than 10%, a part of the ferrous iron of the steel plate becomes coarse, and the standard deviation of the ferrous iron exceeds 7.0 μm, and the formability is deteriorated. In this way, for example, when the crown is used for a crown, the crown shape becomes non-uniform. For example, when the crown is used for a DRD can, the shape of the wrinkles at the flange portion is defective when the DRD can is formed. Therefore, the reduction ratio of the final frame is set to 10% or more. 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 ° C to 750 ° C) If the winding temperature in the hot rolling step is less than 550 ° C, part of the ferrous iron in the steel sheet becomes thinner, and the standard deviation of the ferrous iron particle diameter exceeds 7.0 μm, and the formability becomes worse. difference. In this way, for example, when the crown is used for a crown, the crown shape becomes non-uniform. For example, when the crown is used for a DRD can, the shape of the wrinkles at the flange portion is defective when the DRD can is formed. Therefore, the winding temperature is set to 550 ° C or higher. On the other hand, if the winding temperature is higher than 750 ° C, a part of the ferrous iron in the steel sheet becomes coarse, and the standard deviation of the ferrous iron exceeds 7.0 μm. For example, when used for crown applications, the crown shape becomes uneven. For example, when it is used for 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 750 ° C or lower. It is preferably 600 ° C or higher and 700 ° C or lower.

(Pickling) Thereafter, pickling is preferably performed. 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. (Reduction ratio of primary cold rolling: 88% or more) First, the reduction ratio of 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, so recrystallization in the continuous annealing step becomes uneven, and the standard deviation of the ferrous iron exceeds 7.0 μm. Formability is deteriorated. In this way, for example, when the crown is used for a crown, the crown shape becomes non-uniform. For example, when the crown is used for a DRD can, the shape of the wrinkles at the flange portion is defective when the DRD can is formed. Therefore, the reduction ratio in the primary cold rolling step is set to 88% or more. It is preferably set to 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 ° C to 760 ° C) That is, the soaking temperature is performed at a temperature of 660 ° C to 760 ° C in the continuous annealing step. If the soaking temperature is set to exceed 760 ° C., continuous plate failures such as heat buckling are likely to occur during continuous annealing, which is not preferable. In addition, a part of the grain size of the ferrous iron of the steel sheet is coarsened, and the standard deviation of the ferrous iron exceeds 7.0 μm. For example, when used for crown applications, the crown shape becomes non-uniform. For example, when used for DRD tank applications. In addition, when forming a DRD can, wrinkle formation in a flange part is bad. On the other hand, if the annealing temperature is less than 660 ° C, recrystallization becomes incomplete, a part of the ferrous iron particle size of the steel sheet becomes fine, and the standard deviation of the ferrous iron particle size exceeds 7.0 μm. In the case of a crown, the shape of the crown becomes uneven, and when it is used for a DRD can, for example, the shape of the wrinkles at the flange portion is defective when the DRD can is formed. Therefore, it is performed at the temperature with a soaking temperature of 660 degreeC-760 degreeC. It is preferably performed at a temperature of 680 ° C to 730 ° C.

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 intensity 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: cooling to 450 ° C or lower at an average cooling rate of 10 ° C / s or higher) After the soaking, the cooling is performed 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, the precipitation of carbides will be accelerated during the cooling process, so that the amount of solid solution C that contributes to the strength of the steel sheet will be reduced, and the drop strength will be 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. 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, carbide precipitation will be accelerated after the first-stage cooling, so that the amount of solid solution C that contributes to the strength of the steel sheet will be reduced, and the drop strength will be 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. In addition, 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 shape of the steel sheet at the time of passing the plate is deteriorated, and the steel sheet cannot be cooled uniformly. In the case of use, the crown shape becomes non-uniform, and further, for example, when used in a DRD tank, the shape of the wrinkles at the flange portion becomes poor during the formation of the DRD tank. Therefore, cooling after soaking is stopped. The temperature is preferably set to 300 ° C or higher.

(Post-stage cooling: Cool to 140 ° C or less at an average cooling rate of 5 ° C / s or more) In the post-stage cooling after front-stage cooling, the average cooling rate of 5 ° C / s or more is used to cool from the cooling stop temperature during the front-stage cooling to 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 is reduced, and the drop 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. In addition, if the average cooling rate exceeds 30 ° C / s, not only the effect is saturated, but also excessive cost of the cooling equipment. Therefore, the average cooling rate in the subsequent cooling is preferably 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. If it exceeds 140 ° C, the amount of solid solution C that contributes to the strength of the steel sheet is reduced, and the drop 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.

(Secondary cold rolling reduction: 10% or more and 40% or less) The steel sheet of the present invention can obtain high drop 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 strength cannot be obtained. In addition, if the reduction ratio of the secondary cold rolling exceeds 40%, the uniformity of the crown shape is impaired when the steel sheet is used for a crown, for example. Furthermore, 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 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 then 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 properties of the steel sheet is at a level that can be ignored.

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 hot-rolled at the slab heating temperature, the finish rolling temperature, and the coiling temperature shown in Table 2. 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] Table 1 (mass%) Note) Underlined part: outside the scope of the present invention

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. 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 20 crowns (N = 20) for each steel plate by pressing. Use a micrometer to measure the crown's height (the distance from the crown's top surface to the lower end of the side). The crown's height with a standard deviation of N = 20 is 0.09 mm or less. The crown is excellent in shape, and the crown's height is N = 20. A crown with a standard deviation of more than 0.09 mm was judged to be a poor crown shape. The obtained results are shown in Table 2.

Furthermore, using the obtained steel sheet, it heat-processed at 210 degreeC for 15 minutes which is equivalent to a coating burn-in, and it was shape | molded into a DRD can, and the DRD can formability was evaluated. That is, a circular blank having a diameter of 158 mm was subjected to drawing and redrawing 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 regarded as ×, and a sample in which fine wrinkles in the flange portion were 2 or less was regarded as ○. The evaluation results are shown in Table 2.

[表 2] Table 2 Note) Underlined part: outside the scope of the present invention

From Table 2, it can be seen that the rolling strength of the steel plates No. 1 to No. 22 as examples of the present invention is 560 MPa or more, and the standard deviation of the crown height is 0.09 mm or less, and crown formability is good. Furthermore, the number of occurrence of wrinkles in the DRD can forming was two or less, and the DRD can forming property was also good.

On the other hand, it can be seen that the steel plates of No. 23 to No. 25 as comparative examples have too much C content, so the standard deviation of the iron particle diameter of the fertilized grains exceeds 7.0 μm, and the standard deviation of the crown height exceeds 0.09 mm, and the crown formability deteriorates. In addition, the DRD tank formability is also deteriorated. It can be seen that the steel plates of No. 26 to No. 28 have too little C content, so the standard deviation of the iron particle diameter of the fertilizer grains exceeds 7.0 μm, the standard deviation of the crown height exceeds 0.09 mm, and the crown formability deteriorates. It can be seen that the steel plate of No. 29 has too much Mn content, so the standard deviation of the particle size of the ferrous grains exceeds 7.0 μm, 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 sheet of No. 30 has an excessively high Al content, so that the formation of AlN is increased, and the amount of N, which contributes to the strength of the steel sheet as a solid solution N, is reduced and the strength of the steel sheet is reduced. In addition, the DRD can formability is also deteriorated. It is found that the steel sheet of No. 31 has an insufficient content of Al, and therefore, the effect as a deoxidizer is insufficient, which causes the occurrence of solidification defects and increases the steelmaking cost. In addition, an appropriate amount of AlN cannot be ensured during recrystallization of the annealed ferrous iron. Therefore, the standard deviation of the ferrous iron particle size after annealing becomes large, and the ferrous iron particle size of the steel sheet after the second cold rolling becomes large. It becomes coarse, the standard deviation of the iron particle diameter of the fertilizer grains exceeds 7.0 μm, the standard deviation of the crown height exceeds 0.09 mm, and the crown formability deteriorates, and the DRD tank formability also deteriorates. It can be seen that the steel sheets No.32 to No.34 have too much N content, so the grain size of the ferrite grains of the steel sheet after the second cold rolling becomes fine, and the standard deviation of the grain size of the ferrite grains exceeds 7.0 μm. When the deviation exceeds 0.09 mm, the crown formability is deteriorated, and the DRD tank formability is also deteriorated. It can be seen that the steel plates of No.35 to No.37 have too little N content, so the ferrous iron particle diameter of the steel plate becomes coarse, the standard deviation of the ferrous iron particle diameter exceeds 7.0 μm, the standard deviation of the crown height exceeds 0.09 mm, and the crown The formability is deteriorated, and the formability of the DRD can is also deteriorated, and the amount of N that contributes to the strength of the steel sheet as a solid solution N decreases, and the strength of the steel sheet decreases. In addition, it can be seen that the steel plate of No. 38 has too much P content, so the standard deviation of the iron particle diameter of the fertilizer grains exceeds 7.0 μm, 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. 39 has too much Si content, so the standard deviation of the grain size of the ferrous grains exceeds 7.0 μm, the standard deviation of the crown height exceeds 0.09 mm, the crown formability is deteriorated, and the DRD tank formability is also deteriorated. [Example 2]

The converter has a composition of steel No. 5, No. 9, No. 18, No. 21, No. 28, No. 29, No. 31 shown in Table 1, and the remainder contains Fe and inevitable impurities The steel is melted and a slab is 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. Pickling is performed after hot rolling. 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 crown formability and DRD can formability were evaluated. The obtained results are shown in Table 3.

[表 3] Table 3 Note) Underlined part: outside the scope of the present invention

According to Table 3, steel plates No. 40, No. 43, No. 45, No. 47, No. 48, No. 52 to No. 55, No. 58, No. 59, No. 63, No.64, No.66, No.69, No.70, No.71 steel plates have rolling strength of 560 MPa or more in the rolling direction, and the standard deviation of crown height is 0.09 mm or less, crown formability, DRD tank Good formability. On the other hand, it can be seen that the steel plates No. 41, No. 49, No. 50, No. 56, No. 61, No. 68, No. 72 of the steel plates as comparative examples have slab heating temperature, soaking time, The average cooling speed at the front stage, the secondary cold rolling reduction rate, the average cooling speed at the rear stage, the cooling stop temperature at the front stage, and the cooling stop temperature at the rear stage are all outside the scope of the present invention. Therefore, the rolling down rolling strength is reduced. It can be seen that the steel sheet of steel sheet No. 62 as a comparative example has an excessively high secondary cold reduction rate, which increases the anisotropy of the steel sheet. The standard deviation of the crown height exceeds 0.09 mm and the crown formability is deteriorated. In addition, the DRD tank formability is also high. Degradation. It can be seen that the slabs of the steel plates No.42, No.44, No.46, No.51, No.57, No.60, No.65, No.67, No.73, No.74 as the comparative examples Any of heating temperature, final rolling reduction of hot rolling, coiling temperature, primary cold rolling ratio, soaking temperature, front cooling stop temperature, average cooling speed at the rear, cooling cooling temperature at the rear, and secondary cold reduction All of them are outside the scope of the present invention. Therefore, the rolling strength in the rolling direction is reduced or the standard deviation of the iron particle diameter of the fertilizer grains exceeds 7.0 μm, and the standard deviation of the crown height exceeds 0.09 mm, and the crown formability is deteriorated. In addition, DRD tank forming Sexual deterioration.

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Claims (5)

A steel sheet in mass% includes: 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, Al: 0.020% or more and 0.050% or less, and N: 0.0070% or more and 0.0140% or less, the remainder is Fe and unavoidable impurities, and there are fertilizer particles in the area from the depth of 1/4 of the plate thickness to the center of the plate thickness In the iron phase, the standard deviation of the particle size of the ferrous iron in the ferrous iron phase is 7.0 μm or less, and the yield strength is 560 MPa or more. 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 according to 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 rolling is performed in a temperature range of 550 ° C to 750 ° C; pickling step, the hot-rolled sheet after the hot rolling step is acidified Washing; one cold rolling step, the hot-rolled sheet after the pickling step is subjected to a rolling reduction of 88% or more; the annealing step, the cold-rolled sheet after the one cold rolling step is at 660 ° C to 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 region of 140 ° C. or lower; and a secondary cold rolling step is performed to cold-roll the annealed sheet at a reduction ratio of 10% to 40%.