JP2017214619A - Steel sheet for container - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel sheet for container hard, excellent in processability and having age-hardening property.SOLUTION: There is provided a steel sheet for container having a component composition containing C:0.010 to 0.050 mass%, Si:0.05 mass% or less, Mn:0.10 to 0.40 mass%, P:0.020 mass% or less, S:0.020 mass% or less, N:0.0060 to 0.020 mass%, Al:0.040 to 0.200 mass% and the balance Fe with inevitable impurities, and having a solid solution N amount of 0.0050 mass% or more, an average r value of 1.2 to 1.4 and an aging index of 10 MPa or more.SELECTED DRAWING: None

Description

  The present invention relates to a steel plate for containers. The present invention particularly relates to a steel plate for containers that is hard, excellent in workability, and has age-hardening properties.

  Steel plates (steel plates for containers and steel plates for cans) specified in JIS G3303 “plates and tinplates” and JIS G3315 “tin-free steels” have a tempering degree according to the hardness required for their use. T-1 to DR-10 (the higher the number, the harder it is). Among these, the steel sheets having a tempering degree of T-1 to T-6 should be annealed (recrystallized annealing) after the cold rolling of the low carbon steel once, that is, the low carbon steel once rolling method. In addition, when the steel sheets having a tempering degree of DR-8 to DR-10 are manufactured by the “low carbon steel twice rolling” method, that is, by performing the second cold rolling on the steel sheet after the annealing treatment. It is prescribed.

  Among the steel plates for containers produced by the above-mentioned “low rolling carbon steel” method, the annealing treatment of the steel sheets having a tempering degree of T-1 to T-3 is carried out by using a “batch annealing method ( In general, the annealing treatment of steel sheets having a tempering degree of T-4 to T-6 is generally performed by a “continuous annealing method” using a continuous annealing line CAL.

  By the way, in recent years, the manufacturing process of steel sheets for containers has been proceeding with continuation of equipment from the viewpoint of increasing productivity, and as part of this, processing can be performed at high temperature and in a short time from batch annealing with a long processing time. Switching to continuous annealing is underway. Also, in the field of steel plates for containers, from the viewpoint of reducing material costs for users, plate thickness reduction (plate thickness) by hardening (switching from T-1 to T-3 to T-4 to T-6) (Less than 0.20 mm) is being actively promoted. As a result, the ratio of steel plates for containers manufactured by a continuous annealing method has increased greatly in recent years.

  However, the hardening, thinning, and continuous annealing accompanying it cause a decrease in the workability of the steel sheet. Furthermore, manufacturing a thin steel plate by continuous annealing not only causes a decrease in productivity due to the extension of the plate length, but also operations such as heat buckle due to rapid heating and rapid cooling, and plate breakage due to meandering. Since trouble is likely to occur and stable production becomes difficult, advanced threading technology is required. On the other hand, with the switch from batch annealing to continuous annealing, the production capacity of the batch annealing furnace continues to have a margin. Then, development of the technique which manufactures the steel plate for containers which is harder and excellent in workability by batch annealing is desired.

  As a technique for achieving both high strength and thinning, there is the above-mentioned “low carbon steel twice rolling” method. For example, Patent Document 1 proposes a technique for manufacturing a steel sheet having a tempering degree from T-1 to DR-10 by using a low carbon steel as a raw material and performing batch annealing. However, in this method, in order to obtain a refining degree equal to or higher than T-4, it is necessary to set the reduction ratio of the second cold rolling to 15% or more, and because the ductility of the steel sheet is greatly reduced, workability is reduced. It cannot be used for required applications.

  Further, in Patent Document 2, in mass%, C: 0.018 to 0.060%, Mn: 0.20 to 0.30%, Al: 0.020 to 0.080%, N: 0.003 The steel sheet after primary cold rolling containing ~ 0.013% is subjected to annealing in a batch annealing furnace (BAF annealing) held at a temperature range of 600 to 700 ° C for 2 to 8 hours, There has been proposed a technique for producing a steel plate for a three-piece can having high strength, a high r value, and excellent expandability by performing the next cold rolling.

JP2013-119649A JP 2009-97045 A

  However, any of the techniques proposed in Patent Document 1 and Patent Document 2 has a problem that it cannot be easily adopted because it causes a decrease in productivity and an increase in cost due to secondary cold rolling.

  Moreover, in the said technique, since the steel plate is manufactured by batch annealing, the steel plate obtained does not have bake hardenability fundamentally. Therefore, from the viewpoint of securing strength as a container, there is a problem that a steel sheet with a higher tempering degree is required or reduction of the plate thickness is limited.

  The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to provide a container steel plate that is hard and excellent in workability and has age-hardening properties.

  In order to solve the above-mentioned problems, the inventors have made extensive studies by paying attention to the component composition and production conditions of the low-carbon steel as a raw material. As a result, by increasing the Al content of the steel material, nitriding during annealing (batch annealing) is promoted to increase the precipitation amount of AlN and ensure a solid solution N amount (solid solution nitrogen amount) of a predetermined amount or more. Thus, the present inventors have found that a steel plate for containers that is hard and excellent in workability and has age-hardening properties can be obtained, leading to the development of the present invention.

The present invention based on the above findings
[1] C: 0.010 to 0.050 mass%, Si: 0.05 mass% or less, Mn: 0.10 to 0.40 mass%, P: 0.020 mass% or less, S: 0.020 mass% or less, N : 0.0060 to 0.020 mass%, Al: 0.040 to 0.200 mass%, with the balance being composed of Fe and unavoidable impurities, and the amount of solid solution N is 0.0050 mass% or more Yes, a steel plate for containers having an average r value of 1.2 to 1.4 and an aging index of 10 MPa or more.
[2] There are 30 or more carbides having a particle size of 3.1 μm or more per area of 0.1375 mm × 0.1375 mm, and the number of carbides having a particle size of 3.1 μm or more with respect to the total number of carbides per area. The steel plate for containers according to [1], wherein the ratio is 60% or more.
[3] In addition to the above component composition, Cr: 0.01-0.10 mass%, Ti: 0.005-0.05 mass%, Nb: 0.005-0.05 mass%, V: 0.005 Steel plate for containers as described in [1] or [2] containing 1 type (s) or 2 or more types chosen from -0.05 mass% and Zr: 0.005-0.05 mass%.
[4] At least one surface of the steel plate for containers according to any one of [1] to [3] has a plating layer made of one or more selected from Sn, Cr, and Ni, and one side of the plating layer A steel plate for containers having a per unit adhesion amount of 1 mg / m ² or more.
[5] A container having an oil coating layer on at least one surface of the steel plate for containers according to any one of [1] to [4], and an adhesion amount per one surface of the oil coating layer is 1 mg / dm ² or more. Steel plate.

  ADVANTAGE OF THE INVENTION According to this invention, it is excellent in workability, Furthermore, the steel plate for containers which is hard and has age-hardening property can be provided. ADVANTAGE OF THE INVENTION According to this invention, even if it manufactures by batch annealing, the steel plate for containers which has age-hardening property can be provided. According to the present invention, it is possible to provide a container steel plate that is not limited in reduction of plate thickness, can suppress a decrease in productivity and an increase in cost, and can be stably manufactured.

  First, the basic technical idea of the present invention will be described.

  About steel used when manufacturing a steel sheet for containers having a tempering degree of T-4 or more by batch annealing, conventionally, an MC type steel in which P is added to an MR type steel used for general food containers as defined in ASTM. N type steels in which N is added to the above MR type steel and MC type steel are known (“Bukiki and Tin Free Steel” by Toyo Kohan Co., Ltd., published by Agne, May 10, 1974, p. 21. -22).

  However, P is an element that has a large effect of increasing the strength and hardness of steel, but is easily segregated, and is also an element that lowers corrosion resistance, which is the most important characteristic required for a steel plate for containers. For this reason, steel sheets to which P is added are not currently used.

  Further, N is a useful element that can increase the hardness of the steel sheet with a slight addition when the steel sheet is produced by continuous annealing. Further, N, when rapidly cooled from a high temperature like continuous annealing, is present in a supersaturated solid solution state in ferrite, and therefore has an effect of increasing age-hardening (bake hardenability) after temper rolling. However, it is difficult to contain more than 0.015 mass% of nitrogen in steel with ordinary steelmaking facilities.

  By the way, since the steel plate for containers used for food cans etc. is required to have excellent corrosion resistance, there are few components allowed to be contained in steel, and the steel is strengthened (hardened) in addition to the above P and N. Only Si and Mn are listed as components. However, the addition of Si or Mn is not preferable because it concentrates on the surface of the steel sheet by batch annealing and forms an oxide film, thereby causing an appearance defect called temper color and a corresponding decrease in corrosion resistance.

  Then, the present inventors repeated examination about the method of raising the hardness of a steel plate paying attention also to manufacturing conditions in addition to the component composition of the raw material (slab) of the steel plate for containers. As a result, Al is added as a steel component higher than before, nitriding in annealing (batch annealing) is promoted, and the N content in the steel sheet is increased to increase the precipitation amount of AlN, thereby increasing the hardness. In addition, the solid solution N (free N) that has penetrated into the steel plate during the annealing (batch annealing) and remained without being bonded to Al has age-hardening properties, and it can be hardened after painting and baking. As a result, the present invention was developed.

  Next, the component composition of the steel material of the steel plate for containers according to the present invention will be described.

C: 0.010-0.050 mass%
C is an element that has the greatest influence on the strength of the steel, and in order to obtain sufficient hardness (50 or more with HR30T) by batch annealing, it is necessary to contain 0.010 mass% or more. On the other hand, if the C content exceeds 0.050 mass%, graphite may precipitate on the surface of the steel plate during batch annealing, which may cause abnormal gloss during temper rolling. Therefore, the C content is in the range of 0.010 to 0.050 mass%. The C content is preferably in the range of 0.020 to 0.050 mass%. When the C content is 0.020 mass% or more, the hardness (tempering degree) is further increased, and a hardness of 54 or more can be obtained with HR30T. The C content is more preferably in the range of 0.030 to 0.050 mass%.

Si: 0.05 mass% or less Si is an element added as a deoxidizer, but is also an element that increases the hardness by solid solution strengthening of steel. However, if it is added in a large amount, it causes a scale-like surface defect, concentrates on the surface of the steel sheet during batch annealing, generates a temper color, impairs the appearance, or inhibits the plating property and lowers the corrosion resistance. Therefore, in this invention, Si shall be 0.05 mass% or less. Preferably it is 0.02 mass% or less.

Mn: 0.10 to 0.40 mass%
Mn is an element that prevents hot brittleness due to S and improves hot workability. Further, Mn has a solid solution strengthening ability, and has an effect of refining crystal grains and increasing hardness. Therefore, in the present invention, 0.10 mass% or more of Mn is added. On the other hand, if Mn exceeds 0.40 mass% and is added excessively, it concentrates on the surface of the steel sheet during batch annealing and generates a temper color or lowers the corrosion resistance. Therefore, in this invention, it is set as the range of 0.10-0.40 mass%. Preferably it is the range of 0.24-0.35 mass%.

P: 0.020 mass% or less P is an impurity element that inevitably penetrates into the steel, and is also an element that lowers the corrosion resistance. Therefore, in the present invention, P is 0.020 mass% or less. Preferably it is 0.016 mass% or less.

S: 0.020 mass% or less S, like P, is an impurity element that inevitably enters the steel, and is also a harmful element that impairs the hot workability of the steel and reduces the corrosion resistance. Therefore, in the present invention, S is 0.020 mass% or less. Preferably it is 0.010 mass% or less, More preferably, it is 0.009 mass%, More preferably, it is 0.005 mass% or less.

Al: 0.040-0.200 mass%
Al has the effect of increasing the hardness of the steel sheet after annealing by forming N in the steel and nitriding N and AlN in batch annealing, through precipitation effects and fine graining effects. Furthermore, according to the inventors' new knowledge, Al promotes the penetration (nitrogenation) of nitrogen in the atmospheric gas into the steel sheet to increase the amount of solute N, and has the effect of improving age hardening. Have. In order to acquire these effects, it is necessary to contain 0.040 mass% or more of Al. However, excessive addition exceeding 0.200 mass% saturates the above effect, raises the recrystallization temperature, and excessively inhibits the grain growth. Therefore, in the present invention, Al is in the range of 0.040 to 0.200 mass%. Preferably it is 0.050-0.200 mass%, More preferably, it is the range of 0.060-0.100 mass%.

N: 0.0020 to 0.0150 mass%
N combines with the Al to form fine AlN, and has the effect of increasing the hardness of the steel sheet due to the precipitation effect and the fine grain effect. Moreover, in order to acquire said effect, it is necessary to make N contain 0.0020 mass% or more in a steel raw material. However, it is difficult to stably contain N exceeding 0.0150 mass% in the steel material under normal melting conditions of the steel plate for containers. Therefore, N is set to a range of 0.0020 to 0.0150 mass%. Preferably it is the range of 0.0030-0.010 mass%.

  In addition to the essential components described above, the steel material of the steel plate for containers of the present invention is Cr: 0.01 to 0.10 mass%, Ti for the purpose of suppressing the precipitation of graphite on the steel plate surface during batch annealing. : 0.005 to 0.05 mass%, Nb: 0.005 to 0.05 mass%, V: 0.005 to 0.05 mass%, and Zr: 0.005 to 0.05 mass%, or one kind selected from Two or more kinds can be contained. In particular, Cr has the effect of suppressing the precipitation of graphite on the steel sheet surface during batch annealing and improving the corrosion resistance after plating, in addition to the above effects, so it is preferable to add Cr.

  These effects are obtained when Cr is 0.01 mass% or more, and Ti, Nb, V, and Zr are each contained 0.005 mass% or more. On the other hand, if the Cr content exceeds 0.10 mass% and the Ti, Nb, V, and Zr contents exceed 0.05 mass%, temper color is generated during batch annealing, and the surface quality and corrosion resistance are impaired. There is a fear. Therefore, when adding Cr, Ti, Nb, V, and Zr, it is preferable to add in the said range. More preferably, the contents of Cr, Ti, Nb, V, and Zr are Cr: 0.01 to 0.05 mass%, Ti: 0.005 to 0.01 mass%, and Nb: 0.005 to 0.01 mass, respectively. %, V: 0.005 to 0.01 mass% and Zr: 0.005 to 0.01 mass%.

  The remainder other than the said component in the steel raw material of the steel plate for containers of this invention is Fe and an unavoidable impurity.

  Next, the component composition of the steel plate for containers (product plate) of the present invention will be described.

  If C, Si, Mn, P, S, and Al in the steel material explained above are the manufacturing method and manufacturing conditions of a normal steel plate for containers, it becomes a product plate with the composition of the steel material. However, in the present invention, N is not necessarily the content of N in the steel material and the content of N in the product plate because nitrogen in the atmosphere gas penetrates into the steel (nitriding) during batch annealing. It does not match.

  In the steel plate for containers of the present invention, N is 0.0060 to 0.020 mass%. In the present invention, nitrogen that has penetrated (nitrogenated) into steel in batch annealing forms an AlN by combining with free Al in the steel, and has the effect of increasing the hardness of the steel sheet by the precipitation effect and the fine graining effect. . In addition, free N (solid solution N) that penetrates into the steel sheet during the batch annealing and does not bond with Al is precipitated by forming carbonitrides in the coating baking process at the time of container manufacture, and after coating baking. It has the effect of increasing the steel sheet hardness, so-called age-hardening ability (bake hardenability). In order to obtain such an effect, the N content in the steel plate for containers (product plate) is set to 0.0060 mass% or more. The N content is preferably 0.0080 mass% or more, more preferably 0.010 mass% or more. On the other hand, if the N content exceeds 0.020 mass%, slab cracking may occur during hot rolling, and surface defects may occur, so the N content is set to 0.020 mass% or less. Preferably it is 0.018 mass% or less, More preferably, it is 0.016 mass% or less.

In the present invention, the age-hardening ability is defined as an increase in HR30T hardness before and after the temper-rolled steel sheet is subjected to an aging treatment of 210 ° C. × 20 min.
According to the research conducted by the present inventors, in order to make the age-hardening ability 4 or more in terms of HR30T hardness, 0.0050 mass% (50 massppm) or more of solid solution N exists in the steel sheet after batch annealing. It is clear that this is necessary. Therefore, in this invention, the amount of solute N after batch annealing shall be 0.0050 mass% or more. Preferably it is 0.0055 mass% (55 massppm) or more, More preferably, it is 0.0059 mass% (59 massppm) or more, More preferably, it is 0.0060 mass% (60 massppm) or more. Here, increasing the hardness after temper rolling by 4 is the same as increasing the degree of tempering by one. That is, the steel sheet having a tempering degree of T-3 after temper rolling means that the tempering degree becomes T-4 by age hardening in the subsequent baking coating.

Presence density of carbide having a particle size of 3.1 μm or more The steel plate for containers of the present invention preferably has a structure in which 30 or more carbides having a particle size of 3.1 μm or more exist in an area of 0.1375 mm × 0.1375 mm. Further, the ratio of the number of carbides having a particle size of 3.1 μm or more to the total number of carbides per area [(number of carbides having a particle size of 3.1 μm / number of total carbides) × 100] is 60% or more. Preferably there is. Thereby, it becomes easy to obtain the steel plate for containers which is higher in strength and more excellent in workability. More preferably, 40 or more carbides having a particle size of 3.1 μm or more are present per area.

  In the present invention, the number of carbides having a particle size of 3.1 μm or more and the ratio of the number of carbides having a particle size of 3.1 μm or more to the total number of carbides are determined as follows. A corrosive solution (5 mass% picric acid alcohol solution, “Picral”) is applied to a steel plate for containers (cross section in the rolling direction at a plate thickness of 1/2) and etched sufficiently (80 ° C., 60 seconds). Is washed off with ethanol, and carbides existing in a field of view of 0.1375 mm × 0.1375 mm are observed and photographed with a 400 × optical microscope. Then, the number of carbides having a particle size of 3.1 μm or more is counted from the photographed image. In addition, the number of all carbides is counted from the image, and the particle size is 3.1 μm or more with respect to the number of all carbides according to the formula [(number of carbides having a particle size of 3.1 μm or more) / (number of total carbides) × 100]. The ratio of the number of carbides is determined. Here, the total number of carbides is the total number of carbides visible from the captured image (the total number of carbides having a particle size of 3.1 μm or more and the number of carbides having a particle size of less than 3.1 μm). . The particle size of the carbide is the minimum diameter of the carbide. For example, when the shape of the carbide is an ellipse or the like and the minor axis and the major axis exist, the minor axis value is used.

  The container steel plate of the present invention having the above has the following characteristics.

Average r value: 1.2 to 1.4
The average r value (average plastic strain ratio) of the steel plate for containers is 1.2 to 1.4. When the average r value is 1.2 or more, workability, particularly deep drawing workability, is improved. Further, when the r value is 1.4 or less, the uniformity of the height of the can when the expanded can is applied to the welded can after the cylindrical processing by the deep drawing processing is improved.

  The average r value in the present invention is a steel plate for containers of JIS No. 5 tensile test specimens having a tensile direction of 0 ° direction (L direction), 45 ° direction (D direction), and 90 ° direction (C direction) with respect to the rolling direction. The specimen was measured for the width direction true strain and the sheet thickness direction true strain when 10% of uniaxial tensile strain was applied to these specimens. From these measured values, JIS Z 2254 (2008) Calculated in accordance with the year). In addition, the average r value of the steel plate for containers can be adjusted by adjusting batch annealing conditions (soaking temperature, soaking time).

Aging index: 10 MPa or more The aging index (AI) of the steel sheet for containers of the present invention is 10 MPa or more. That is, the steel plate for containers of the present invention has age hardenability. When the aging index is 10 MPa or more, the hardness (tempering degree) after painting and baking is sufficiently increased. The aging index is preferably 15 MPa or more. On the other hand, the upper limit of the aging index is not particularly limited, but if the aging index is too large, the room temperature aging resistance may deteriorate and the workability may deteriorate, so the aging index of the steel plate for containers of the present invention is preferably 45 MPa or less. 30 MPa or less is more preferable.

  The aging index in the present invention is obtained by applying 7.5% pre-strain to a JIS No. 5 tensile test piece taken with the rolling direction of the steel plate for containers as the tensile direction, and then subjecting it to a heat treatment at 100 ° C. for 30 minutes, and again a tensile test. Is obtained from the difference between the stress before heat treatment (stress after 7.5% pre-strain) and the yield stress after heat treatment. In addition, the aging index of the steel plate for containers can be adjusted by adjusting batch annealing conditions (soaking temperature, soaking time, atmospheric conditions).

Hardness The hardness (hardness before aging treatment) of the steel plate for containers of the present invention is HR30T, preferably 50 or more, and more preferably 54 or more. The tempering degree is preferably T-1 or more, and more preferably T-2 or more.

Age-hardening ability The hardness of the steel plate for containers of the present invention is preferably increased by 4 or more, more preferably increased by 5 or more before and after the aging treatment (aging treatment at 210 ° C for 20 minutes).
Further, the hardness after the aging treatment is preferably 57 or more and more preferably 60 or more in HR30T from the viewpoint of maintaining strength.

Plate Thickness The plate thickness of the steel plate for containers of the present invention is not particularly limited, but is preferably 0.10 mm or more, more preferably 0.15 mm or more from the viewpoint of ensuring the strength as a container. Moreover, from the point of aiming at cost reduction, 0.25 mm or less is preferable and 0.22 mm or less is more preferable.

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

  As a manufacturing method of the steel plate for containers of the present invention, a method of hot rolling, cold rolling, batch annealing with nitriding treatment, and temper rolling the steel material (slab) having the above component composition is preferable. .

(Steel material)
There are no particular restrictions on the method of manufacturing the steel material. For example, after the steel is melted in a converter or an electric furnace, the steel composition is prepared to satisfy the above composition by ladle processing, vacuum degassing processing, etc. A method of forming a steel material (slab) by a continuous casting method or an ingot-bundling rolling method is preferable. In addition, it is more preferable to use the continuous casting method from the viewpoint of the uniformity of the component composition and the uniformity of the material.

(Hot rolling)
Thereafter, the steel material (slab) is hot-rolled to form a hot-rolled sheet. In the hot-rolling, after the slab is reheated to a temperature of 1050 to 1300 ° C., the finish rolling finish temperature is set to Ar _3. It is desirable to carry out at or above the transformation point.
When the reheating temperature of the slab is less than 1050 ° C., deformation resistance (rolling load) increases and it becomes difficult to perform hot rolling, or it becomes difficult to ensure the finish rolling finishing temperature. On the other hand, if the reheating temperature of the slab exceeds 1300 ° C., the scale loss becomes large or surface flaws occur, which is not preferable.

In addition, when the finish rolling finish temperature in hot rolling is less than the Ar ₃ transformation point, the crystal grains after hot rolling are coarsened, which may cause a material defect or a shape defect. However, if the finish rolling finish temperature is too high, surface defects due to scale will occur, so the upper limit is preferably about 1000 ° C.
In addition, as long as the said finish rolling completion temperature can be ensured, the said hot rolling may be continuously performed as it is, without reheating the high temperature slab after continuous casting.

  The coiling temperature of the hot rolling is preferably in the range of 450 to 750 ° C. If the coil winding temperature is less than 450 ° C., the shape of the steel sheet may be deteriorated. On the other hand, when the coil winding temperature exceeds 750 ° C., the scale generated on the steel sheet surface becomes thick, which adversely affects pickling properties and coarsens the crystal grains of the steel sheet surface layer.

(Cold rolling)
The hot-rolled steel sheet is then pickled and cold-rolled to obtain a cold-rolled sheet having a predetermined thickness.
The rolling reduction in the cold rolling may be determined according to a conventional method and is not particularly limited. However, from the viewpoint of improving workability and anisotropy, the rolling reduction is preferably in the range of 70 to 98%.

(Batch annealing)
Thereafter, it is preferable that the steel sheet (cold rolled sheet) after the cold rolling is subjected to batch annealing that is maintained at a temperature of 600 ° C. or higher and 680 ° C. or lower for 3 to 16 hours. By adopting batch annealing, nitrogen in the atmosphere gas can be satisfactorily nitrogenated in the steel sheet during batch annealing. Nitrogen that has been nitrided combines with Al in the steel sheet, and precipitates fine AlN in the steel sheet. Thereby, a hard steel plate for containers can be obtained.

  In addition, the reason for setting the soaking temperature in batch annealing to 600 ° C. or more and 680 ° C. or less is that if it is less than 600 ° C., recrystallization becomes incomplete and the structure becomes non-uniform, and a homogeneous material and excellent workability are obtained. In addition, since the nitriding does not proceed sufficiently, the amount of precipitated AlN is insufficient and hardening becomes insufficient, or the amount of solute N is insufficient and the prescribed age hardening ability is obtained. It is because it becomes impossible. On the other hand, when the soaking temperature exceeds 680 ° C., the cementite is coarsened and the ductility may be lowered. Moreover, concentration, precipitation, etc. of C, Si, Mn, etc. on the steel plate surface become remarkable, and a temper color is generated or corrosion resistance is hindered. Furthermore, there is a risk that the steel sheet will seize during annealing.

  In addition, the reason for setting the soaking time to 3 to 16 hr is that recrystallization does not proceed sufficiently if the duration is less than 3 hr, the structure becomes non-uniform, and it becomes difficult to obtain a homogeneous material and excellent workability. This is because the nitriding becomes insufficient, the above-mentioned hardening is insufficient, and the desired age-hardening ability cannot be obtained. On the other hand, when the soaking time exceeds 16 hours, the crystal grains become coarse and the steel sheet is easily softened, and a steel sheet having a desired hardness cannot be obtained. A more preferable soaking temperature in the batch annealing is in the range of 610 to 650 ° C. A more preferable soaking time in the batch annealing is in the range of 6 to 10 hr.

  Here, as described above, as described above, in this batch annealing, nitrogen in the annealing atmosphere gas is nitrided in the steel plate, and is combined with Al in the steel to precipitate AlN, and the steel plate after annealing. It is to secure the age-hardening ability by setting the solid solution N amount to 0.0050 mass% or more.

In order to cause the above nitriding, it is necessary to make the atmospheric gas in batch annealing nitriding. Examples of the immersion窒性gas, a dew point is -20 ° C. or _{less, H 2: 1~10vol%, N} 2: containing more than 50 vol%, the balance: mixed gas comprising an inert gas (including 0 vol%) Is preferably used.

(Temper rolling)
Temper rolling (skin pass) for the purpose of shape correction, surface roughness, improvement of mechanical properties (disappearance of yield elongation, adjustment of tempering degree, imparting strain aging), etc. to the steel sheet after batch annealing. To make a steel plate for containers.
Here, it is preferable to limit the elongation rate (rolling rate) of the temper rolling to a range of 0.5% or more and 2.0% or less. If the elongation is less than 0.5%, it is difficult to reliably obtain the effect of the temper rolling. On the other hand, when the elongation of temper rolling is more than 2.0%, the ductility of the steel sheet is reduced and the anisotropy is increased, and it becomes difficult to ensure desired workability. Of course, for steel sheets for applications where the hardness (tempering degree) is important and the workability is not so required, the elongation of temper rolling may be made higher than the above range. .

(surface treatment)
The container steel plate obtained as described above is then passed through an electroplating line or the like and subjected to an electroplating treatment, for example, an electrotin plating treatment is performed, and `` Grip '' defined in JIS G3303, A steel plate for containers having a plating layer such as “tin-free steel” defined in JIS G3315 comprising two layers of chromium metal and chromium hydrated oxide can be obtained by performing electrolytic chromic acid treatment. The electroplating process is not limited to the electrotin plating process or the electrolytic chromic acid process. As a kind of plating layer, what consists of 1 or more types chosen from Sn, Cr, and Ni is preferable. Moreover, the plating adhesion amount is not particularly limited, but is preferably 1 mg / m ² or more per side, more preferably 10 mg / m ² or more.

Moreover, it is good also as a steel plate for containers which has an oil coating layer by apply | coating oil to the surface of the steel plate for containers obtained as mentioned above, or the steel plate for containers which has a plating layer. By providing the oil coating layer, rust prevention is further improved. The oil is not particularly limited, and a known oil can be used. Examples of the oil include natural oils such as vegetable oils, animal oils, and mineral oils, and synthetic oils such as hydrocarbons, esters, and amides. The oil is preferably a synthetic oil. Of the synthetic oils, esters are preferred. The ester is preferably a dibasic acid diester. Examples of the dibasic acid diester include dihexyl adipate, dioctyl adipate, dinonyl adipate, didecyl adipate, didodecyl adipate, dihexyl azelate, dioctyl azelate, dinonyl azelate, didecyl azelate, didodecyl azelate, Examples include dihexyl sebacate, dioctyl sebacate, dinonyl sebacate, didecyl sebacate, didodecyl sebacate and the like. Moreover, the adhesion amount of the oil coating layer is not particularly limited, but is preferably 1 mg / dm ² or more per one side. The method for applying oil is not particularly limited, and examples thereof include known methods such as electrostatic oil coating, roll coating, bar coating, dipping, and spraying.

  Moreover, the steel plate for containers of the present invention may be used as a coated steel plate without being subjected to the electroplating treatment, or may be used as it is without any treatment, and is not particularly limited.

A steel material (slab) having the composition of A to F shown in Table 1 is manufactured by a continuous casting method, reheated to a temperature of 1150 ° C., finish rolling finish temperature FDT is 880 ° C., and winding temperature CT is A hot-rolled sheet having a thickness of 2.3 mm is formed by hot rolling at 610 ° C., pickled to remove the scale on the surface of the steel sheet, and then the thickness is reduced to 0.202 mm (reduction rate of 91 by one cold rolling). %) Cold-rolled sheet.
Next, the cold-rolled sheet was subjected to recrystallization annealing in a batch annealing furnace under the conditions shown in Table 2, and then subjected to temper rolling with the elongation shown in Table 2 to obtain a steel plate for containers (original plate). Thereafter, the original plate was passed through the electroplating line ETL, and after electroplating with a plating adhesion amount per one side shown in Table 2, oil was applied to both sides under the conditions shown in Table 2, and the steel plate for containers (Product plate). However, in Table 2, No. No. 3 is not plated on the container steel plate (original plate).

  A sample was taken from the product plate thus obtained and subjected to the following test.

<Measurement of solid solution N amount>
Samples for analysis are collected from each of the above samples, the plating layer is removed, the sample is heated and melted in an inert gas, and nitrogen in the sample is extracted and separated as N ₂ , followed by thermal conductivity detection. The total nitrogen amount (total N amount) was quantified with a vessel. Subsequently, the amount of nitrogen (the amount of precipitated nitrogen) forming a precipitate (nitride) was quantified by electrolytic bromine methanol decomposition (wet N analysis). A value obtained by subtracting the amount of precipitated nitrogen from the total amount of nitrogen was defined as a solid solution N amount.

<Measurement of average r value>
From each of the above samples, JIS No. 5 tensile test pieces having a tensile direction of 0 ° direction (L direction), 45 ° direction (D direction), and 90 ° direction (C direction) with respect to the rolling direction were collected. Measure the true strain in the width direction and the true strain in the thickness direction of each test piece when 10% uniaxial tensile strain was applied to the test piece. The average r value was calculated.
Average r value = (r _L + 2r _D + r _C ) / 4
However, r _L , r _D , and r _C are r values in the rolling direction, the 45 ° direction with respect to the rolling direction, and the 90 ° direction with respect to the rolling direction, respectively.

<Measurement of aging index (AI)>
After applying 7.5% pre-strain to the JIS No. 5 tensile test piece taken with the rolling direction of each sample as the tensile direction with a tensile tester, heat treatment was performed at 100 ° C. for 30 minutes, and the tensile test was performed again. The aging index (AI) was determined from the difference between the stress before heat treatment (stress after applying 7.5% pre-strain) and the yield stress after heat treatment.

<Measurement of the number of carbides having a particle size of 3.1 μm or more and measurement of the ratio of the number of carbides having a particle size of 3.1 μm or more to the total number of carbides>
Each sample (cross section in the rolling direction at a plate thickness of 1/2) is coated with a corrosive solution (5 mass% picric acid alcohol solution, “Picral”) and etched sufficiently (80 ° C., 60 seconds), and then the corrosion. The liquid was washed with ethanol, and the carbides present in the field of view of 0.1375 mm × 0.1375 mm were observed and photographed with a 400 × optical microscope. And the number of carbide | carbonized_materials with a particle size of 3.1 micrometers or more was counted from the image | photographed image. Further, the number of all carbides is counted from the image, and the carbide having a particle size of 3.1 μm or more with respect to all the carbides is calculated from the formula [(number of carbides having a particle size of 3.1 μm or more) / (number of total carbides) × 100]. The ratio of the number of was determined.
The measurement results are shown in Table 2.

<Hardness evaluation after temper rolling>
The hardness HR30T of each of the above samples was measured, and when the hardness was HR30T, 50 or higher was evaluated as good hardness (◯) and less than 50 was evaluated as poor hardness (×).

<Evaluation of age hardening>
About each said sample, hardness HR30T after performing aging treatment of 210 degreeC x 20 min was measured, and age-hardening property was evaluated from the difference with the hardness after temper rolling (before aging treatment). Specifically, an HR30T hardness increase of 5 or more was evaluated as age-hardening excellent (◎), less than 5 to 3 or more as age-hardening good (◯), and less than 3 as age-hardening inferior (×). Excellent (◎) and Good (○) were accepted.

<Evaluation of rust resistance>
A 40 mm x 80 mm corrosion-resistant test piece is taken from each of the above samples, and a dry / wet repeat test that repeats a dry state (temperature 25 ° C., relative humidity 50%) and a wet state (temperature 50 ° C., relative humidity 98%) every 30 minutes. Was conducted for 96 hours, and the rust resistance was evaluated from the number of spot rust generated on the surface of the test piece. Specifically, if the number of spot rust occurrences on one side of the test piece is 50 or less, it is evaluated as good rust resistance (○), and 51 or more is evaluated as poor rust resistance (×), and passes (good). It was.

<Evaluation of workability>
From each of the above samples, 200 blank blanks having a diameter of 100 mmφ were punched 200 times each, and 200 times each of the processes that simulated drawing of the can body of a two-piece can were performed, and the workability was evaluated from the rate of occurrence of breakage. Specifically, after the primary drawing with a drawing ratio of 0.6, the secondary drawing with a drawing ratio of 0.75 is performed, and the fracture occurrence rate (%) in the drawing process ((number of breaks / total number of processes)). When x100] is less than 0.5%, the workability is good (◯), and 0.5% or more is evaluated as poor workability (x).

  The results of these evaluation tests are shown in Table 3.

From this result, it can be seen that the steel plate of the present invention has an HR30T of 50 or more, excellent workability and corrosion resistance, and excellent age-hardening properties. The steel sheet of the present invention has excellent age-hardening properties even when manufactured by batch annealing.

  The steel plate of the present invention is suitable for containers, but is not limited to this, and can be used, for example, for home appliances, electronic devices, and house members.

Claims (5)

C: 0.010 to 0.050 mass%,
Si: 0.05 mass% or less,
Mn: 0.10 to 0.40 mass%,
P: 0.020 mass% or less,
S: 0.020 mass% or less,
N: 0.0060-0.020 mass%,
Al: 0.040-0.200 mass% is contained, and the balance has a component composition consisting of Fe and inevitable impurities,
The amount of solute N is 0.0050 mass% or more,
A steel plate for containers having an average r value of 1.2 to 1.4 and an aging index of 10 MPa or more. There are 30 or more carbides with a particle size of 3.1 μm or more per area 0.1375 mm × 0.1375 mm, and the ratio of the number of carbides with a particle size of 3.1 μm or more to the total number of carbides per area is 60. The steel plate for containers according to claim 1, which is at least%. In addition to the above component composition,
Cr: 0.01-0.10 mass%,
Ti: 0.005-0.05 mass%,
Nb: 0.005 to 0.05 mass%,
The steel plate for containers according to claim 1 or 2, comprising one or more selected from V: 0.005 to 0.05 mass% and Zr: 0.005 to 0.05 mass%. It has the plating layer which consists of 1 or more types chosen from Sn, Cr, Ni on the surface of at least one side of the steel plate for containers as described in any one of Claims 1-3, and the adhesion amount per one side of this plating layer Is a steel plate for containers, wherein 1 mg / m ² or more. The steel plate for containers which has an oil coating layer in the surface of at least one side of the steel plate for containers as described in any one of Claims 1-4, and the adhesion amount per one surface of this oil coating layer is 1 mg / dm < ² > or more.