JP2017025352A - Steel sheet for can and production method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel sheet for a can, providing excellent can shape after being spinned, and a production method therefor.SOLUTION: The steel sheet for a can is provided that has: a component composition containing, by mass%, C:0.0015% to less than 0.010%, Si:0.01 to 0.10%, Mn:0.10 to 1.00%, P:0.03% or less, N:0.005% or less, S:0.03% or less, Al:0.020 to 0.100% and the balance Fe with inevitable impurities; a structure in which a ferrite phase accounts for 95% or more by an area ratio, average crystal particle diameter of the ferrite phase is 15.0 μm or less, amount of solid solution carbon in the steel is over 15 mass.ppm and 60 mass.ppm or less; and a yield strength (YP) of 300 MPa or more and an elongation (El) of 15% or more.SELECTED DRAWING: None

Description

  The present invention relates to a steel plate for cans suitable as a can container material used as a container material for beverages and foods, and a method for producing the same. In particular, the present invention relates to a steel plate for cans having a good can shape after spinning and a method for producing the same.

  The 3-piece can is a can made up of 3 parts, which is formed by bending a surface-treated steel plate into a cylindrical shape, joining the ends and forming a can body, and then attaching a canopy and a bottom cover through neck-in processing and flange processing, Widely used as a negative pressure can with negative pressure inside.

  In recent years, since the use of aluminum cans has been expanded, the steel plate for steel cans is being made thinner from the viewpoint of reducing the cost of steel cans. From the viewpoint of constricting the can body in order to suppress a decrease in can strength due to the thinning of the material and compensating the can strength by the effect of the shape, the can body may be subjected to spinning processing. Specifically, the can body portion is rotated, the rotating indenter is pressed against the can body, and compressive strain is applied in the circumferential direction for processing. However, in this processing method, shear deformation occurs in the plate thickness direction of the steel sheet, and the processed portion is cracked or wrinkled.

  Many studies have been conducted to solve the above problems. For example, in Patent Document 1, in order to prevent cracking at the time of spinning neck processing, the solute carbon in the steel is reduced, and the local ductility is increased to increase local ductility. A method for mitigating stress concentration is disclosed.

  Further, Patent Document 2 controls the rankford value of the steel sheet in the can height direction, the ratio of the yield strength before and after the processing, and reduces the number of inclusions to prevent wrinkling in the constricted portion, A method for suppressing the decrease in thickness is disclosed.

JP 7-207406 A JP2003-183776

  However, all of the above conventional techniques have problems.

  Since the steel sheet obtained by the technique of Patent Document 1 has a small amount of dissolved carbon in the steel, the strength of the can is lowered, and the can is deformed and broken during transportation.

  Further, the steel sheet obtained by the technique of Patent Document 2 does not take into consideration any particle size. When the particle size increases, the can body portion is likely to break at the grain boundary during spinning. In addition, there is a problem that rough skin generated on the surface of the processed part becomes remarkable.

  Thus, all of the conventional techniques have problems. Spinning is a process in which a rotating indenter is pressed against a can body to impart compressive strain in the circumferential direction. In this process, deformation of the steel sheet occurs both in the height direction and in the circumferential direction. When the amount of deformation in the height direction of the can increases, the processed portion is recessed in the radial direction of the can, the shape of the can collapses, the roundness deteriorates, and the strength of the can decreases. Further, when the amount of deformation in the circumferential direction becomes large, the plate thickness becomes non-uniform, the buckling deformation is likely to occur, and there is a possibility of being broken. In any case, it is important to keep the can shape by minimizing the thickness variation of the steel sheet when spinning.

  This invention is made | formed in view of this situation, and it aims at solving the problem of the prior art mentioned above, and providing the steel plate for cans which can shape is excellent after a spinning process, and its manufacturing method.

  The present inventors have intensively studied to solve the above problems. As a result, in order to reduce plate thickness fluctuation and can shape change during spinning, the increase in crystal grain size is suppressed, sufficient elongation and strength are secured, and the amount of solute carbon in the steel is reduced. We have found that proper control is extremely effective.

The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] Component composition is mass%, C: 0.0015% to less than 0.010%, Si: 0.01 to 0.10%, Mn: 0.10 to 1.00%, P: 0.03% or less, N: 0.005% or less, S: 0.03% In the following, Al: 0.020 to 0.100% is contained, the balance is made of Fe and inevitable impurities, and the structure has a ferrite phase area ratio of 95% or more, and the ferrite crystal has an average grain size of 15.0 μm or less, steel A steel sheet for cans characterized in that the amount of solid solution carbon exceeds 15 mass ppm and is 60 mass ppm or less, the yield strength (YP) is 300 MPa or more, and the elongation (El) is 15% or more.
[2] The steel plate for cans according to [1], further containing at least one of Nb: 0.01 to 0.10% and Ti: 0.01 to 0.20% by mass%.
[3] Component composition is mass%, C: 0.010-0.10%, Si: 0.01-0.10%, Mn: 0.10-1.00%, P: 0.03% or less, N: 0.005% or less, S: 0.03% or less, Al: 0.020 to 0.100%, Nb: 0.01 to 0.10% and / or Ti: 0.01 to 0.20%, the balance consists of Fe and inevitable impurities, the structure is ferrite phase is 95% or more in area ratio, The ferrite phase has an average grain size of 15.0 μm or less, the amount of solid solution carbon in the steel is more than 15 ppm and 60 ppm or less, the yield strength (YP) is 300 MPa or more, and the elongation (El) is 15% or more. Steel sheet for cans.
[4] A steel having the composition described in any one of [1] to [3] above is hot-rolled at a finishing temperature of 840 ° C. or higher and wound at a winding temperature of 500 to 700 ° C., 80% A method for producing a steel plate for cans, comprising cold rolling at the above rolling reduction, annealing at an annealing temperature of 790 ° C. or less, and temper rolling at a rolling reduction of 0.6 to 5.0%.
[5] Manufacture of steel plate for can according to [4], wherein the steel plate stays for 30 seconds to 10 minutes in a temperature range of more than 250 ° C. and 500 ° C. or less before the temper rolling after annealing. Method.
In addition, in this specification,% which shows the component of steel is mass% altogether.

According to the present invention, a steel plate for cans having an excellent can shape is obtained after spinning.
In the steel plate of the present invention, by appropriately controlling the amount of solute carbon in the steel and increasing the strength of the steel plate when spinning, the dent in the can radial direction is small, the roundness is good, and the can height The variation in thickness is reduced. In addition, by providing high strength and high elongation, it is possible to increase the can strength by minimizing the plate thickness fluctuation in the circumferential direction.
Therefore, by using the steel plate for cans of the present invention as a container material for beverages and foods, it is possible to further reduce the thickness of the steel plate and achieve cost reduction.

It is a figure which shows the external appearance of the deformation | transformation 3 piece can which provided the constriction part.

Hereinafter, the present invention will be described in detail.
The steel plate for cans of the present invention has a component composition of mass%, C: 0.0015% to less than 0.010%, Si: 0.01 to 0.10%, Mn: 0.10 to 1.00%, P: 0.03% or less, N: 0.005% or less, S: not more than 0.03%, Al: 0.020-0.100%, the balance is composed of Fe and inevitable impurities, the structure has a ferrite phase area ratio of 95% or more, the average grain size of the ferrite phase is 15.0 μm or less, the amount of solute carbon in steel is more than 15 ppm by mass and 60 ppm by mass or less, the yield strength (YP) is 300 MPa or more, and the elongation (El) is 15% or more. Alternatively, the component composition is mass%, C: 0.010 to 0.10%, Si: 0.01 to 0.10%, Mn: 0.10 to 1.00%, P: 0.03% or less, N: 0.005% or less, S: 0.03% or less, Al: 0.020 to 0.100%, Nb: 0.01 to 0.10% and / or Ti: 0.01 to 0.20%, the balance is composed of Fe and inevitable impurities, and the structure has a ferrite phase area ratio of 95% or more, and the ferrite The average crystal grain size of the phase is 15.0 μm or less, the amount of solute carbon in the steel is more than 15 ppm by mass and 60 ppm by mass or less, the yield strength (YP) is 300 MPa or more, and the elongation (El) is 15% or more. Such a steel sheet for cans is obtained by hot rolling steel having the above composition at a finishing temperature of 840 ° C. or higher, winding at a winding temperature of 500 to 700 ° C., and cooling at a rolling reduction of 80% or higher. It becomes possible to manufacture by performing hot rolling, annealing at an annealing temperature of 790 ° C. or less, and temper rolling at a rolling reduction of 0.6 to 5.0%. These are important requirements of the present invention.

  First, the component composition of the steel plate for cans of this invention is demonstrated.

C: 0.0015-0.10%
C is present as solid solution carbon, thereby improving the strength. Moreover, it forms fine carbides and contributes to increasing the strength of the steel sheet, and improves the work hardening rate. Therefore, the C content needs to be 0.0015% or more. On the other hand, if the C content exceeds 0.10%, the steel sheet becomes excessively hardened, so that it tends to break during spinning. Therefore, the C content is 0.10% or less. Moreover, in the case of C: 0.010-0.10% among the said range, in order to control the amount of solid solution carbon, as a component composition, the effect which fixes a part of solid solution carbon which precipitates as a carbide | carbonized_material and exists in steel Nb: 0.01 to 0.10% and / or Ti: 0.01 to 0.20%. On the other hand, in the case of C: 0.0015 to less than 0.010%, it is not essential to contain Nb: 0.01 to 0.10% and / or Ti: 0.01 to 0.20%. The effect of the present invention can be obtained without containing Nb: 0.01 to 0.10% and / or Ti: 0.01 to 0.20%.

Si: 0.01-0.10%
Si is an element that has the effect of increasing the hardness of a steel sheet by solid solution strengthening. In order to ensure the yield strength stably, Si needs to contain 0.01% or more. On the other hand, since Si is an element harmful to corrosion resistance for cans, the upper limit is made 0.10%.

Mn: 0.10 to 1.00%
Mn is an element having an effect of increasing the hardness of the steel sheet by solid solution strengthening, and is necessary for stably securing the yield strength. Moreover, it is effective in reducing the particle size. In order to acquire these effects, Mn needs to contain 0.10% or more. On the other hand, as the amount of Mn increases, the cost of the raw material increases, so the upper limit of Mn is set to 1.00%. However, since the upper limit of Mn of the tin plate used for food containers is defined as 0.6%, when used as food containers, it is preferably 0.60% or less.

P: 0.03% or less
P is an element having an effect of increasing the hardness of the steel sheet by solid solution strengthening. In order to obtain this effect, 0.01% or more is preferable. On the other hand, it segregates at the grain boundaries and reduces the ductility and toughness of the steel sheet. It is also a harmful element that reduces corrosion resistance. Therefore, the upper limit of P is 0.03%.

N: 0.005% or less
When N is contained in a large amount, excessive nitride is generated, and the ductility and toughness of the steel sheet are lowered. Moreover, workability is deteriorated. For these reasons, the upper limit of N is set to 0.005%.

S: 0.03% or less
S combines with Mn to form coarse MnS, which degrades the surface properties and lowers the ductility in hot rolling, so the upper limit is made 0.03%.

Al: 0.020 to 0.100%
Al is a useful element that acts as a deoxidizer, and in order to obtain the effect, it is necessary to contain 0.020% or more. On the other hand, if it exceeds 0.100%, surface defects of the steel sheet are induced, so the upper limit of Al is 0.10%.

  Furthermore, for the purpose of improving strength and elongation and controlling the amount of dissolved carbon, the following elements (Nb, Ti) are considered as essential elements in the case of C: 0.010 to 0.10%, and C: 0.0015 to If it is less than 0.010%, it can be contained as an optional additive element.

Nb: 0.01-0.10%
Nb combines with C, precipitates as carbide, and is used to fix a part of the solid solution carbon present in the steel and control the amount of the solid solution carbon. Nb is an element contributing to the improvement of hardness by precipitation strengthening. Furthermore, it contributes to the refinement of ferrite grains and improves elongation. In order to obtain these effects, the Nb content is 0.01% or more. On the other hand, if it exceeds 0.10%, not only the alloy cost increases, but also the rolling load is increased, so that stable steel plate production becomes difficult. For this reason, the upper limit of Nb is set to 0.10%.

Ti: 0.01-0.20%
Ti, like Nb, binds with C and precipitates as carbide, and is used to fix a part of the solute carbon present in the steel and control the amount of solute carbon. Further, the fine carbonitride of Ti is effective in increasing the hardness. In order to obtain these effects, the Ti content is 0.01% or more. On the other hand, if it exceeds 0.20%, the recrystallization completion temperature rises and non-recrystallization tends to occur. When it is not recrystallized, the elongation may be low. For this reason, the upper limit of Ti is 0.20%.

  The balance is Fe and inevitable impurities.

Next, the texture and material characteristics of the present invention will be described.
In the present invention, the area ratio of the ferrite phase is set to 95% or more in order to ensure elongation. More preferably, it is 98% or more. Examples of phases other than the ferrite phase include cementite, pearlite, martensite, and bainite.
Here, the area ratio of the ferrite phase can be measured together with the area ratio of the ferrite phase when measuring the average crystal grain size of the ferrite phase, as will be described later.

Average crystal grain size of ferrite phase: 15.0 μm or less When the average crystal grain size of ferrite phase exceeds 15.0 μm, breakage tends to occur due to the grain boundary of the ferrite phase during spinning. In addition, the yield strength is difficult to be obtained. Therefore, the average crystal grain size of the ferrite phase is 15.0 μm or less. Preferably it is 10.0 μm or less.
Here, the average crystal grain size of the ferrite phase can be measured by a cutting method in accordance with a steel-crystal grain size microscopic test method of JIS G 0552 by taking a structure photograph at 400 times.
Further, by controlling the annealing conditions among the manufacturing conditions described later, an average crystal grain size of 15.0 μm or less of the ferrite phase can be obtained.

The amount of solute carbon in steel: 15 mass ppm to 60 mass ppm or less In order to reduce the plate thickness variation and can shape change during spinning, the solute carbon content in steel should be controlled appropriately. is important. If the amount of solute carbon in steel is 15 mass ppm or less, the strength of the can decreases, and the can may be deformed or damaged during transportation. On the other hand, if it exceeds 60 mass ppm, cracks are likely to occur during spinning. Therefore, the amount of solute carbon in the steel is made to exceed 15 ppm by mass and not more than 60 ppm by mass. Preferably they are 20 mass ppm or more and 50 mass ppm or less.
Here, the amount of solid solution carbon in steel can be measured by the method of the Example mentioned later.
Moreover, the amount of solid solution carbon in steel exceeds 15 mass ppm and 60 mass ppm or less is obtained by carrying out the overaging treatment under appropriate conditions that define the component composition centering on C, Nb, and Ti.

Yield strength (YP): 300 MPa or more The steel sheet for cans of the present invention has a yield strength (YP) of 300 MPa or more. By setting YP to 300 MPa or more, fluctuations in the plate thickness can be suppressed during spinning processing. Here, the yield strength (YP) can be measured by cutting a JIS No. 5 tensile test piece from the rolling direction and performing a tensile test in accordance with JIS Z 2241.

Elongation (El): 15% or more In the steel sheet for cans of the present invention, the elongation is 15% or more. By setting the elongation to 15% or more, it is possible to suppress the concentration of strain during the spinning process, and it is possible to suppress variations in the plate thickness.

Next, an example of the manufacturing method of the steel plate for cans of this invention is demonstrated.
The steel plate for cans of the present invention is hot rolled at a finishing temperature of 840 ° C. or higher, wound at a winding temperature of 500 to 700 ° C., and cold rolled at a reduction rate of 80% or higher. , Annealing is performed at an annealing temperature of 790 ° C. or less, and temper rolling is performed at a rolling reduction of 0.6 to 5.0%.

Slab reheating temperature: 1150-1300 ° C (preferred conditions)
If the slab reheating temperature before hot rolling is too high, problems such as product surface defects and increased energy costs occur. On the other hand, if it is too low, it will be difficult to ensure the final finish rolling temperature. Therefore, the slab reheating temperature is preferably 1150 to 1300 ° C.

Finishing rolling temperature: 840 ° C or higher If the rolling temperature is lower than 840 ° C, the surface roughness becomes rough and surface irregularities are likely to occur. When the indenter that rotates during spinning is pressed against the can body, Shear deformation occurs and wrinkles are likely to occur. Moreover, when it uses as a steel plate for cans with thin plate | board thickness, the temperature of the edge side of a coil tends to fall. For these reasons, the finish rolling temperature is set to 840 ° C. or higher.

Winding temperature: 500 ~ 700 ℃
When the coiling temperature is below 500 ° C., the elongation is reduced and breakage occurs during spinning. Therefore, the coiling temperature is 500 ° C. or higher. On the other hand, when the coiling temperature exceeds 700 ° C., the ferrite grains in the hot-rolled sheet stage become coarse, the hardness is lowered, and the anisotropy is deteriorated. Therefore, it is preferably 700 ° C. or lower.

  It is preferable to remove the surface scale before cold rolling. The method for removing the surface scale is not limited, but various methods such as pickling and mechanical removal can be applied.

Rolling reduction in cold rolling: 80% or more If the rolling reduction in cold rolling is less than 80%, the anisotropy may increase. As a result, the plate thickness becomes non-uniform along with the spinning process, and cracks are likely to occur. Therefore, the rolling reduction in cold rolling is 80% or more.

Annealing temperature: 790 ° C. or less When the annealing temperature exceeds 790 ° C., the crystal grains become coarse and the hardness decreases. Therefore, the annealing temperature is 790 ° C. or less. On the other hand, if the annealing temperature is lower than 630 ° C., ferrite grains stretched in the rolling direction may remain, and cracking may occur in the can body due to the spinning process. Therefore, it is preferably 630 ° C. or higher. The holding time at the annealing temperature is preferably 20 to 200 seconds from the viewpoint of securing the strength.

  Further, after annealing (after holding) at an annealing temperature of 790 ° C. or lower, cooling is performed. At this time, it is preferable to perform an overaging treatment in which a residence time of not less than 250 ° C. and not more than 500 ° C. is maintained for 30 seconds to 10 minutes during cooling. By performing the overaging treatment, it becomes easy to control the amount of dissolved carbon in the present invention.

Temper rolling reduction: 0.6-5.0%
Temper rolling is performed to adjust the plate shape and surface roughness. If the rolling reduction of temper rolling is less than 0.6%, the effect of temper rolling is not sufficient. On the other hand, if it exceeds 5.0%, the elongation decreases due to work hardening, so that the spinning processability decreases. Preferably it is 1.0 to 3.0%.

  Hot rolling was performed under the conditions shown in Table 2 on a steel slab containing the component composition shown in Table 1 and the balance being Fe and inevitable impurities. Next, after pickling, cold rolling, annealing and temper rolling were performed under the conditions shown in Table 2 to produce a steel plate for cans having a plate thickness of 0.180 to 0.225 mm. The annealing was performed in a continuous annealing furnace with a holding time of 30 seconds. In addition, in order to control the amount of dissolved carbon, some samples with a C content of 0.010% or more were subjected to an overaging treatment that was maintained at a temperature of 300 ° C. for 30 seconds during cooling after annealing.

  About the steel plate for cans obtained above, the average crystal grain size and the amount of solute carbon of the ferrite phase were measured. Each performance was measured and investigated. Each test method and measurement method are as follows.

(1) Microstructure observation The plate thickness cross section parallel to the rolling direction of the obtained steel plate for cans was mirror-polished and etched with 3% nital corrosion solution to reveal ferrite grain boundaries.
Regarding the average crystal grain size of the ferrite phase, a microstructure photograph was taken at 400 times using an optical microscope, and in accordance with the steel-grain size microscopic test method of JIS G 0551, the average grain size of the ferrite phase was cut by a cutting method. The diameter was measured. Further, the area ratio of the ferrite phase was measured by image analysis.

(2) Solid solution carbon content NbC, TiC and cementite were extracted from steel by electrolytic extraction, quantitative analysis was performed, and the amount of solid solution carbon was measured by subtracting the value of the quantitative analysis result from the total C content.

(3) Tensile test From the obtained steel plate for cans, a JIS No. 5 tensile test piece (JIS Z 2201) whose tensile direction is parallel to the rolling direction is collected, and a tensile test in accordance with the provisions of JIS Z 2241. And yield strength and elongation were measured.

(4) Measurement of can size after spinning processing In order to evaluate the plate thickness variation after the spinning processing, a three-piece can was formed on the steel plate. Specifically, a 3-piece can (diameter: 52.4 mm, can body length: 100 mm) wound in the rolling direction was formed using the obtained steel plate for cans. Thereafter, while rotating the can body, the tip of the curved tool was pressed against the can copper and subjected to spinning processing by applying an elongation strain in the can height direction and the circumferential direction. FIG. 1 shows an example of the appearance of a deformed three-piece can that has been subjected to spinning processing so that a constriction with a diameter of 48 mm and a length of 40 mm is placed in the center of the can, and the constriction is provided.
As evaluation items, the roundness after the spinning process, the height of the can before and after the spinning process, and the change in the thickness of the spinning part were investigated.
Roundness is represented by the difference in radius between two circles when the distance between the two concentric circles is minimum when the circular body is sandwiched between two concentric circles. The smaller the roundness, the closer to the perfect circle and the better the shape. In the present invention, a roundness of 200 μm or less is indicated by “◯”, and a roundness exceeding 200 μm is indicated by “x”.
For the can height determination, the difference in the can height before and after the spinning process was 1 mm or less, and the case where it exceeded 1 mm was rated as x.
The plate thickness was measured at a total of 12 locations using a micrometer at a circumferential pitch of 30 °. The case where the difference in plate thickness before and after spinning processing is 0.005 mm or less at all 12 locations is judged as ◎, the difference in plate thickness before and after spinning processing is 0.005 mm or less on average, and the difference in plate thickness is 0.005 If there are 3 or less locations exceeding mm, it will be judged as ○, and the average thickness difference before and after spinning will be 0.005 mm or less, and 4 locations where the thickness difference will be more than 0.005 mm The above case was determined to be Δ, and the case where the difference in the plate thickness before and after the spinning process exceeded 0.005 mm on average was rated as x.

  The results obtained as described above are shown in Table 3.

  From Table 3, in the example of the present invention, the can was formed without producing the fluctuation of the plate thickness and the change of the can shape in the production of performing the spinning process after forming the three-piece can using the steel plate for can. . That is, a steel plate for cans having an excellent can shape was obtained after spinning.

Claims (5)

Component composition is mass%, C: 0.0015% to less than 0.010%, Si: 0.01 to 0.10%, Mn: 0.10 to 1.00%, P: 0.03% or less, N: 0.005% or less, S: 0.03% or less, Al : Containing 0.020-0.100%, the balance consists of Fe and inevitable impurities,
In the structure, the ferrite phase has an area ratio of 95% or more, the average crystal grain size of the ferrite phase is 15.0 μm or less, the amount of solute carbon in the steel is more than 15 mass ppm and 60 mass ppm or less,
Steel sheet for cans, characterized by yield strength (YP) of 300 MPa or more and elongation (El) of 15% or more.   The steel plate for cans according to claim 1, further comprising at least one of Nb: 0.01 to 0.10% and Ti: 0.01 to 0.20% in mass%. Ingredient composition is mass%, C: 0.010-0.10%, Si: 0.01-0.10%, Mn: 0.10-1.00%, P: 0.03% or less, N: 0.005% or less, S: 0.03% or less, Al: 0.020 -0.100%, Nb: 0.01-0.10% and / or Ti: 0.01-0.20%, the balance consists of Fe and inevitable impurities,
In the structure, the ferrite phase has an area ratio of 95% or more, the average crystal grain size of the ferrite phase is 15.0 μm or less, the amount of solute carbon in the steel is more than 15 ppm and 60 ppm or less,
Steel sheet for cans, characterized by yield strength (YP) of 300 MPa or more and elongation (El) of 15% or more.   The steel having the component composition according to any one of claims 1 to 3 is hot-rolled at a finishing temperature of 840 ° C or higher, wound at a winding temperature of 500 to 700 ° C, and a reduction rate of 80% or higher. A method for producing a steel plate for cans, characterized in that the steel plate is cold-rolled and annealed at an annealing temperature of 790 ° C. or lower, and temper-rolled at a rolling reduction of 0.6 to 5.0%.   The method for producing a steel plate for a can according to claim 4, wherein the steel plate stays for 30 seconds to 10 minutes in a temperature range of more than 250 ° C and 500 ° C or less before performing the temper rolling after the annealing.

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