JP2021155849A - Steel plate for can and method for manufacturing the same - Google Patents

Abstract

To provide a steel plate for a can, which has high intensity and excellent workability, and to provide a method for manufacturing the same.SOLUTION: A steel plate for a can comprises, by mass: 0.020% or more and 0.130% or less of C; 0.04% or less of Si; 0.10% or more and 0.60% or less of Mn; 0.020% or less of P; 0.005% or more and 0.020% or less of S; 0.01% or more and 0.10% or less of Al; 0.0050% or more and 0.0180% or less of N; 0.007% or more and 0.030% or less of Nb; and 0.010% or more and 0.050% or less of Mo, with the balance comprising Fe and inevitable impurities, wherein the steel plate has tensile strength of 500 MPa or more and elongation of 10% or more.SELECTED DRAWING: None

Description

The present invention relates to a steel sheet for cans and a method for producing the same. The present invention particularly relates to a steel sheet for cans suitable for application to a material for can containers used for food cans, beverage cans and the like, and a method for producing the same.

From the viewpoint of reducing the environmental load and cost, it is required to reduce the amount of steel sheet used for food cans and beverage cans, and the thickness of steel sheet is being thinned regardless of whether it is a 2-piece can or a 3-piece can.
Since the strength of the can body decreases when the steel plate is thinned, it is necessary to use a high-strength steel plate. As a high-strength steel sheet for cans, a steel sheet called a DR (Double Reduced) material may be conventionally used. The DR material is a steel sheet manufactured by cold rolling (secondary rolling) again after annealing. Although the DR material has high strength, it has low elongation and is inferior in workability, so that it has not always been applicable to can body processing cans that require high workability.

In order to meet such problems, a steel sheet for cans having high strength and excellent workability is required. For example, high-strength steel sheets for cans have been proposed in Patent Documents 1 and 2.

Patent Document 1 describes in terms of mass%, C: 0.020% or more and 0.130% or less, Si: 0.04% or less, Mn: 0.10% or more and 1.2% or less, P: 0.007%. More than 0.100% or less, S: 0.03% or less, Al: 0.0010% or more and 0.10% or less, N: 0.0120% or more and 0.020% or less, and Nb: 0.010 % Or more and 0.050% or less, Ti: 0.010% or more and 0.050% or less, B: 0.0010% or more and 0.010% or less. It has a component composition composed of impurities, the structure has a ferrite phase, the area ratio of the ferrite phase is 50% or more, the top yield strength is 480 to 700 MPa, and the total elongation is after heat treatment at 210 ° C. for 20 minutes. Is 12% or more, and the amount of solid solution N in the region from the surface to the 1/8 depth position in the plate thickness direction and the solid solution in the region from the surface to the 3/8 depth position to the 4/8 depth position. A steel plate for cans has been proposed in which the ratio of the amount of N satisfies the following formula 1.

In Patent Document 2, the component composition is, in mass%, C: 0.020% or more and 0.130% or less, Si: 0.04% or less, Mn: 0.10% or more and 1.20% or less, P: 0.007% or more and 0.100% or less, S: 0.030% or less, Al: 0.001% or more and 0.100% or less, N: 0.0120% or more and 0.0200% or less, Nb: 0.0060 % Or more and 0.0300% or less, the balance is composed of iron and unavoidable impurities, the top yield strength is 460 to 680 MPa, the total elongation is 12% or more, and in the region from the surface to the 1/8 depth position. A steel plate for cans characterized in that the absolute value of the difference between the amount of solid-dissolved Nb and the amount of solid-dissolved Nb in the region from the 3/8 depth position to the 4/8 depth position is 0.0010% by mass or more. Has been proposed.

WO2016 / 157878 WO2017 / 150066

The steel sheets for cans disclosed in Patent Documents 1 and 2 can obtain high yield strength and high total elongation, but cannot always obtain sufficient tensile strength, or even when tensile strength is obtained, the can body. There was a problem that the strength (axial buckling strength) was insufficient.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a steel sheet for cans having high strength and excellent workability and a method for producing the same.

In order to achieve the above object, the present invention has the following gist.
[1] By mass%,
C: 0.020% or more, 0.130% or less,
Si: 0.04% or less,
Mn: 0.10% or more, 0.60% or less,
P: 0.020% or less,
S: 0.005% or more, 0.020% or less,
Al: 0.01% or more, 0.10% or less,
N: 0.0050% or more, 0.0180% or less,
Nb: 0.007% or more, 0.030% or less,
Mo: 0.010% or more, 0.050% or less,
The balance has a component composition of Fe and unavoidable impurities,
The tensile strength is 500 MPa or more,
Growth is 10% or more,
Steel plate for cans.
[2] As a component composition, further in mass%,
B: 0.0005% or more, 0.0040% or less,
Cr: Contains one or more of 0.04% or more and 0.20% or less.
The steel plate for cans according to [1].
[3] The metal structure has ferrite and is composed of one or more of pearlite and granular cementite.
The steel plate for cans according to [1] or [2].
[4] The method for manufacturing a steel sheet for cans according to any one of [1] to [3].
A heating step of heating a steel slab having the above component composition at a heating temperature of 1100 ° C. or higher,
A hot rolling step of hot rolling the steel slab after the heating step under the condition of a hot rolling finishing temperature of 830 ° C. or higher and 950 ° C. or lower, and a hot rolling step.
A winding step of winding the hot-rolled plate obtained in the hot rolling step at a winding temperature of 450 ° C. or higher and 650 ° C. or lower, and a winding step.
A cold rolling step of cold rolling the hot rolled sheet after the winding step under the condition of a rolling ratio of 85% or more, and a cold rolling step.
An annealing step of annealing the cold rolled sheet obtained in the cold rolling step under the conditions of an annealing temperature of 700 ° C. or higher and 780 ° C. or lower.
A temper rolling step in which the annealed plate obtained in the annealing step is rolled under conditions of an elongation rate of 0.5% or more and 5.0% or less, and a temper rolling step.
A method for manufacturing a steel sheet for a can.

The steel sheet for cans of the present invention has high strength and excellent workability. According to the present invention, the steel plate used for food cans, beverage cans and the like can be further thinned, and resource saving and cost reduction can be achieved.

Hereinafter, the component composition, the steel sheet characteristics, and the manufacturing method of the steel sheet for cans of the present invention will be described in order. The present invention is not limited to the following embodiments.

First, the component composition of the steel sheet for cans of the present invention will be described. In the description of the component composition,% indicating the content of each component means mass%. The steel sheet for cans of the present invention is also simply referred to as a steel sheet.

C: 0.020% or more, 0.130% or less C is an important element for improving tensile strength. By setting the C content to 0.020% or more, the tensile strength can be set to 500 MPa or more. The C content is preferably 0.030% or more. More preferably, it is 0.085% or more. On the other hand, when the C content exceeds 0.130%, the elongation decreases. Therefore, the C content needs to be 0.130% or less.

Si: 0.04% or less When a large amount of Si is added, the surface treatment property deteriorates due to surface thickening and the corrosion resistance deteriorates. Therefore, the content of Si needs to be 0.04% or less. The Si content is preferably 0.03% or less. On the other hand, since Si contributes to the improvement of tensile strength, it is preferable to add 0.01% or more.

Mn: 0.10% or more, 0.60% or less Mn contributes to the improvement of tensile strength by solid solution strengthening, and a tensile strength of 500 MPa or more can be obtained. In order to obtain such an effect, the Mn content needs to be 0.10% or more. The Mn content is preferably 0.30% or more. On the other hand, when the Mn content exceeds 0.60%, the elongation decreases. Therefore, the upper limit of the Mn content needs to be 0.60%. The Mn content is preferably 0.55% or less.

P: 0.020% or less When a large amount of P is contained, workability is lowered due to excessive hardening and central segregation, and corrosion resistance is also lowered. Therefore, the upper limit of the P content is 0.020%. On the other hand, since P contributes to the improvement of tensile strength, the P content is preferably 0.005% or more. The P content is more preferably 0.010% or more.

S: 0.005% or more and 0.020% or less S forms sulfide in steel and lowers castability. Therefore, the S content is set to 0.020% or less. If the S content is less than 0.005%, there is a possibility of pitting corrosion depending on the contents of the can, so the S content needs to be 0.005% or more. It is preferably over 0.010%. More preferably, it is 0.011% or more.

Al: 0.01% or more, 0.10% or less Al is useful as a deoxidizing element and contributes to improvement of steel cleanliness. Therefore, Al needs to be contained in an amount of 0.01% or more. On the other hand, if Al is excessively contained, AlN is excessively generated, the solid solution N is reduced, and the tensile strength is lowered. Therefore, the Al content needs to be 0.10% or less. The Al content is preferably 0.08% or less. More preferably, it is 0.04% or less.

N: 0.0050% or more and 0.0180% or less N contributes to the improvement of tensile strength by existing as a solid solution N. Further, when Mo is added, the strength of the can body can be improved by increasing the N content. Therefore, the content of N needs to be 0.0050% or more. On the other hand, if it is excessively contained, the elongation is lowered due to the formation of coarse nitrides and the like, so the N content needs to be 0.0180% or less.

Nb: 0.007% or more, 0.030% or less Nb is an important element for improving tensile strength by refining ferrite crystal grains and forming carbides, and in order to obtain such an effect, Nb The content should be 0.007% or more. The Nb content is preferably 0.010% or more. On the other hand, when the Nb content exceeds 0.030%, the recrystallization temperature becomes excessively high, and it becomes difficult to achieve both tensile strength and elongation. Therefore, the Nb content is set to 0.030% or less.

Mo: 0.010% or more and 0.050% or less Mo is an important element in the present invention and contributes to the improvement of tensile strength by refining ferrite crystal grains and forming carbonitride. Further, it contributes not only to the improvement of the tensile strength but also to the improvement of the axial buckling strength of the can body. Therefore, Mo needs to be contained in an amount of 0.010% or more. The Mo content is preferably 0.020% or more. On the other hand, when Mo is contained in an amount of more than 0.050%, such an effect is saturated, and grain boundary segregation becomes excessive, resulting in a decrease in elongation. Therefore, the upper limit of the Mo content needs to be 0.050%. It is preferably 0.045% or less.

The steel sheet for cans of the present invention may contain the above-mentioned components, and the balance may be composed of Fe and unavoidable impurities.

Further, the steel sheet for cans of the present invention further contains one or more of B: 0.0005% or more and 0.0040% or less and Cr: 0.04% or more and 0.20% or less in addition to the above component composition. Is preferable.

B: 0.0005% or more, 0.0040% or less B has the effect of refining ferrite crystal grains and increasing the tensile strength. Therefore, the B content is preferably 0.0005% or more. Further, from the viewpoint of improving the strength and elongation by finely dispersing pearlite and granular cementite, it is more preferably more than 0.0020%. If B is added in excess, the amount of solid solution N decreases due to the formation of BN, and the tensile strength decreases. Therefore, the content is preferably 0.0040% or less.

Cr: 0.04% or more, 0.20% or less Cr has the effect of increasing the tensile strength by forming carbides and refining ferrite crystal grains. Therefore, the Cr content is preferably 0.04% or more. Since the effect is saturated even if it is contained in an excessive amount, it is preferably 0.20% or less.

Next, the steel plate characteristics of the steel plate for cans of the present invention will be described.

Tensile strength: 500 MPa or more In order to secure sufficient can body strength in a thinned can body, it is necessary to set the tensile strength of the steel sheet to 500 MPa or more. It is preferably 550 MPa or more.

Elongation: 10% or more Elongation must be 10% or more in order to ensure good moldability without cracking due to neck processing, flange processing, bead processing, etc. of the can body. It is preferably 12% or more. In the present invention, the tensile strength and elongation are evaluated according to JIS Z 2241 after collecting a JIS No. 5 tensile test piece from the rolling direction and subjecting it to aging heat treatment at 210 ° C. for 20 minutes.

The thickness of the steel sheet for cans of the present invention is not particularly limited, but is preferably 0.50 mm or less. Since the steel sheet for cans of the present invention can be thinned, the thickness is more preferably 0.30 mm or less from the viewpoint of resource saving and cost reduction.

Steel plate structure (favorable conditions): The metal structure has ferrite and is either pearlite (P) or granular cementite (θ) in addition to the ferrite (α) structure consisting of at least one of pearlite and granular cementite. High strength and high elongation can be achieved by dispersing one or more of them. If martensite (M) or bainite (B) is contained, the strength may become excessive and the elongation may decrease. Therefore, it is preferable not to include these tissues. Therefore, the metal structure is preferably composed of any one or more of pearlite (P) and granular cementite (θ) in addition to the ferrite (α) structure. The steel sheet structure is cut out from the steel sheet so that the vertical cross section parallel to the rolling direction of the steel sheet can be observed, the observation surface of the sample is polished, and then corroded with nital to reveal the structure, and the magnification is 3000 with a scanning electron microscope. The steel plate structure is photographed and discriminated at the position of 1/2 of the plate thickness at double.

Next, the method for manufacturing the steel sheet for cans of the present invention will be described. The method for producing a steel plate for cans of the present invention includes a heating step of heating a steel slab having the above component composition at a heating temperature of 1100 ° C. or higher, and a hot rolling finish temperature of the steel slab after the heating step of 830 ° C. or higher and 950 ° C. or lower. A hot rolling process in which hot rolling is performed under conditions, a winding step in which the hot rolled plate obtained in the hot rolling process is wound at a winding temperature of 450 ° C. or higher and 650 ° C. or lower, and a hot rolled plate after the winding process. A cold rolling step in which cold rolling is performed under a condition of a rolling ratio of 85% or more, an ablation step in which a cold rolled sheet obtained in the cold rolling step is annealed under a condition of an ablation temperature of 700 ° C. or higher and 780 ° C. or lower, and an ablation step. It is characterized by having a temper rolling step in which the annealed sheet obtained in 1 is rolled under the condition of an elongation rate of 0.5% or more and 5.0% or less. The steel sheet for cans manufactured by the following manufacturing method may be appropriately subjected to steps such as a plating step of applying Sn plating, Ni plating, Cr plating and the like, a chemical conversion treatment step, and a resin film coating step such as laminating.

Heating temperature: 1100 ° C. or higher A steel slab having the above component composition is heated at a heating temperature of 1100 ° C. or higher (heating step). If the heating temperature of the steel slab before hot rolling is too low, coarse nitrides may be generated and the elongation may decrease. Therefore, the heating temperature of the steel slab is set to 1100 ° C. or higher. The heating temperature of the steel slab is preferably 1150 ° C. or higher.

Hot-rolled finishing temperature: 830 ° C. or higher and 950 ° C. or lower Hot-rolling is performed on the steel slab after the heating step under the conditions of hot-rolled finishing temperature of 830 ° C. or higher and 950 ° C. or lower (hot rolling step). When the hot-rolled finishing temperature (finishing temperature of hot rolling) exceeds 950 ° C., the ferrite crystal grains on the hot-rolled plate become coarse, and the ferrite crystal grains after cold rolling, annealing, and temper rolling become coarse, and the tension is increased. Strength is reduced. Therefore, the upper limit of the hot-rolled finishing temperature is set to 950 ° C. On the other hand, if the finishing temperature of hot rolling is less than 830 ° C., coarse Nb carbides are formed during hot rolling, and the tensile strength is lowered. Therefore, the lower limit of the hot rolling finishing temperature is set to 830 ° C. The preferred lower limit of the hot rolling finish temperature is 850 ° C.

Winding temperature: 450 ° C. or higher and 650 ° C. or lower The hot rolled plate obtained in the hot rolling process is wound up at a winding temperature of 450 ° C. or higher and 650 ° C. or lower (winding step). When the winding temperature exceeds 650 ° C., alloy carbides such as Nb carbides become coarse and the tensile strength decreases. Therefore, the winding temperature needs to be 650 ° C. or lower. The winding temperature is preferably 620 ° C. or lower. On the other hand, if the take-up temperature is less than 450 ° C., precipitation of alloy carbides such as Nb is suppressed and the tensile strength decreases. Therefore, the lower limit of the take-up temperature is set to 450 ° C. The winding temperature is preferably 470 ° C. or higher.

After that, it is preferable to pickle the hot-rolled plate after the winding step (pickling step). Pickling is limited as long as the surface scale can be removed, and the pickling conditions are not particularly limited. Further, the scale may be removed by a method other than pickling.

Cold rolling rate: 85% or more Cold rolling is performed on a hot-rolled plate after a winding process or a pickling process under a condition of a rolling rate of 85% or more (cold rolling process). By cold rolling, the ferrite crystal grains after annealing become finer and the tensile strength is improved. In order to obtain this effect, the rolling ratio of cold rolling is set to 85% or more. The rolling ratio is preferably 87% or more. As the cold rolling ratio increases, the in-plane anisotropy of the steel sheet increases and the can-making property may decrease. Therefore, the cold rolling ratio is preferably 91.2% or less.

Annealing temperature: 700 ° C. or higher and 780 ° C. or lower The cold rolled plate obtained in the cold rolling step is annealed under the conditions of an annealing temperature of 700 ° C. or higher and 780 ° C. or lower (annealing step). In order to obtain high elongation by recrystallization annealing, it is necessary to set the annealing temperature to 700 ° C. or higher. The annealing temperature is preferably 720 ° C. or higher. On the other hand, when the annealing temperature exceeds 780 ° C., alloy carbides such as Nb carbides become coarse, and ferrite crystal grains also become coarse, the tensile strength decreases, and the can body strength also decreases. Therefore, it is necessary to set the upper limit of the annealing temperature to 780 ° C. The annealing temperature is preferably 760 ° C. or lower. As the annealing method, continuous annealing is preferable from the viewpoint of material uniformity. The annealing time is not particularly limited, but is preferably 10 s or more. The annealing time is preferably 60 s or less from the viewpoint of fine graining of ferrite crystal grains. In order to disperse any one or more of pearlite and granular cementite in addition to the ferrite structure, it is preferable that the average cooling rate from 700 ° C. to 500 ° C. is less than 100 ° C./s in the cooling step after annealing. More preferably, it is less than 30 ° C./s.

Elongation rate: 0.5% or more and 5.0% or less The annealed plate obtained in the annealing step is rolled under the conditions of an elongation rate of 0.5% or more and 5.0% or less (preparation rolling process). By temper rolling after annealing, the surface roughness is adjusted and the plate shape is corrected, and the tensile strength is improved by introducing strain into the steel sheet. In order to obtain such an effect, the lower limit of the rolling ratio (elongation ratio) of temper rolling is set to 0.5%. The elongation rate is preferably 1.2% or more. On the other hand, when the elongation rate exceeds 5.0%, strain is excessively introduced and the uniform elongation decreases. Therefore, the upper limit of the elongation rate is set to 5.0%. The elongation rate is preferably 3.0% or less.

Steel No. shown in Table 1. A steel slab containing components 1 to 11 and having the balance of Fe and unavoidable impurities was melted to obtain a steel slab. The obtained steel slab is heated, hot-rolled, wound, pickled to remove scale, then cold-rolled, annealed in a continuous annealing furnace, and tempered under the conditions shown in Table 2. Rolling was carried out to obtain steel sheets for cans (steel sheets Nos. 1 to 16).

The obtained steel sheet for cans was evaluated for tensile strength and elongation. In addition, the structure of the steel plate was discriminated and the axial buckling strength of the can body was evaluated. The evaluation method is as follows.
(Evaluation of tensile strength and elongation)
From the obtained steel sheet for cans, JIS No. 5 tensile test pieces were collected along the rolling direction, and after aging heat treatment at 210 ° C. for 20 minutes, tensile strength and elongation were evaluated according to JIS Z 2241.
(Evaluation of steel sheet structure)
Cut out from the obtained steel sheet for cans so that the vertical cross section parallel to the rolling direction of the steel sheet can be observed, polish the observation surface of the sample, corrode it with nital to reveal the structure, and magnify it with a scanning electron microscope. The steel sheet structure was photographed and discriminated at a position of 1/2 of the plate thickness at 3000 times.
(Evaluation of axial buckling strength of can body)
From the obtained steel sheet for cans, a blank is taken with the plate width direction as the can circumference direction, welded so that the can height is 104 mm and the outer diameter is 52.3 mm, neck / flange processing, and the can body. The lid was wrapped up and down to prepare a can body. A load was applied in the can height direction of the can body, and the load of buckling deformation was measured.

The evaluation results are shown in Table 3.

In each of the examples of the invention, the tensile strength is 500 MPa or more, the elongation is 10% or more, and the axial buckling of the can body is good. Therefore, it is a steel sheet for cans with high strength and high workability. On the other hand, in the comparative example, any one or more of tensile strength, elongation, and axial buckling strength was inferior.

Claims (4)

By mass%
C: 0.020% or more, 0.130% or less,
Si: 0.04% or less,
Mn: 0.10% or more, 0.60% or less,
P: 0.020% or less,
S: 0.005% or more, 0.020% or less,
Al: 0.01% or more, 0.10% or less,
N: 0.0050% or more, 0.0180% or less,
Nb: 0.007% or more, 0.030% or less,
Mo: 0.010% or more, 0.050% or less,
The balance has a component composition of Fe and unavoidable impurities,
The tensile strength is 500 MPa or more,
Growth is 10% or more,
Steel plate for cans. As a component composition, further by mass%,
B: 0.0005% or more, 0.0040% or less,
Cr: Contains one or more of 0.04% or more and 0.20% or less.
The steel plate for cans according to claim 1. The metallographic structure has ferrite and is composed of one or more of pearlite and granular cementite.
The steel plate for cans according to claim 1 or 2. The method for manufacturing a steel sheet for cans according to any one of claims 1 to 3.
A heating step of heating a steel slab having the above component composition at a heating temperature of 1100 ° C. or higher,
A hot rolling step of hot rolling the steel slab after the heating step under the condition of a hot rolling finishing temperature of 830 ° C. or higher and 950 ° C. or lower, and a hot rolling step.
A winding step of winding the hot-rolled plate obtained in the hot rolling step at a winding temperature of 450 ° C. or higher and 650 ° C. or lower, and a winding step.
A cold rolling step of cold rolling the hot rolled sheet after the winding step under the condition of a rolling ratio of 85% or more, and a cold rolling step.
An annealing step of annealing the cold rolled sheet obtained in the cold rolling step under the conditions of an annealing temperature of 700 ° C. or higher and 780 ° C. or lower.
A temper rolling step in which the annealed plate obtained in the annealing step is rolled under conditions of an elongation rate of 0.5% or more and 5.0% or less, and a temper rolling step.
A method for manufacturing a steel sheet for a can.