JP6819838B1 - Steel sheet for cans and its manufacturing method - Google Patents

Abstract

In terms of component composition, in mass%, C: 0.100% or more and less than 0.130%, Si: 0.04% or less, Mn: 0.10% or more and 0.60% or less, P: 0.020% or less, S: 0.020% or less, Al: 0.01% or more and 0.10% or less, N: 0.0005% or more and 0.0040% or less, Nb: 0.005% or more and 0.030% or less, B: 0 It contains more than 0005% and 0.0050% or less, the balance is composed of Fe and unavoidable impurities, has a ferrite structure containing pearlite in an area fraction of 1.0% or more, and is heat-treated at 210 ° C. for 20 minutes. A steel plate for cans having a tensile strength of 630 MPa or more and 750 MPa or less, a yield elongation of 3.0% or less, and an elongation of 3.0% or more and less than 10.0%.

Description

The present invention relates to a can steel plate suitable for application to a material for a can container used for food cans, beverage cans, etc. and a method for producing the same, and can be particularly preferably applied to the production of an easy open end (EOE). The present invention relates to a steel plate for cans and a method for manufacturing the same.

In recent years, from the viewpoint of reducing the environmental load and cost, it has been required to reduce the amount of steel sheets used for food cans and beverage cans, and the thickness of steel sheets is being reduced regardless of whether they are 2-piece cans or 3-piece cans. In addition, there is an increasing demand for thinning not only in the can body but also in the can lid such as EOE.

If the steel plate for the can lid is thinned, the pressure resistance will decrease, so it is necessary to use a high-strength steel plate. As a high-strength steel sheet for cans, consideration is being given to increasing the strength of SR (Single Redduced) materials, which have traditionally been good in workability, and improving workability with DR (Double Redduced) materials, which generally have low workability. Has been done. Here, the SR material is a material manufactured by temper rolling after annealing, and the DR material is a steel sheet manufactured by cold rolling (secondary cold rolling) again after annealing. ..

Patent Document 1 states that as a high-strength SR steel plate, C: 0.03 to 0.13%, Si: 0.03% or less, Mn: 0.3 to 0.6%, P: 0. 02% or less, Al: 0.1% or less, N: 0.012% or less, and further, Nb: 0.005-0.05%, Ti: 0.005-0.05%, b: 0.0005 It contains 1 or more of ~ 0.005%, has a composition of iron and unavoidable impurities as the balance, and has a ferrite structure with a cementite ratio of 0.5% or more, and has a ferrite average grain size of 7 μm or less. There have been proposed steel plates for cans having a tensile strength of 450 to 550 MPa after a coating baking process, a total elongation of 20% or more, and a yield elongation of 5% or less.

Patent Document 2 states that as a DR steel plate having good workability, C: 0.010 to 0.080%, Si: 0.05% or less, Mn: 0.10% or more and 0.70% or less in mass%. P: 0.03% or less, S: 0.020% or less, N: 0.0120% or more and 0.0180% or less, Al: 0.005% or more and 0.070% or less, and the balance is an unavoidable impurity The content of N as a solid solution N is 0.0100% or more, the ferrite particle size is 7.0 μm or less, and the depth is 1/4 of the plate thickness from the surface layer. The displacement density at the position is 4.0 × 10 ¹⁴ m- ² or more and 2.0 × 10 ¹⁵ m- ² or less, the tensile strength in the direction perpendicular to rolling after aging treatment is 530 MPa or more, and the elongation is 7% or more. A high-strength steel plate characterized by this has been proposed.

Japanese Unexamined Patent Publication No. 2008-274332 International Publication No. 2015/1664646

However, the above-mentioned prior art has the following problems.
The technique described in Patent Document 1 can be applied only to steel sheets having a tensile strength of up to 550 MPa, and cannot cope with further thinning. In the technique described in Patent Document 2, since the N content is high, there is a problem that the yield elongation is large and a stretcher strain is generated at the time of lid processing and the appearance is deteriorated. Further, there is a problem that the can-opening force required to open the EOE increases simply by increasing the strength.

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 excellent processability and openability, and a method for producing the same.

In order to achieve the above object, the present invention has the following gist.
(1) As the component composition, in terms of mass%, C: 0.100% or more and less than 0.130%, Si: 0.04% or less, Mn: 0.10% or more and 0.60% or less, P: 0.020 % Or less, S: 0.020% or less, Al: 0.01% or more and 0.10% or less, N: 0.0005% or more and 0.0040% or less, Nb: 0.005% or more and 0.030% or less, B: Containing more than 0.0005% and 0.0050% or less, the balance is composed of Fe and unavoidable impurities, has a ferrite structure containing pearlite in an area fraction of 1.0% or more, and has a ferrite structure at 210 ° C. for 20 minutes. A steel plate for cans having a tensile strength of 630 MPa or more and 750 MPa or less, a yield elongation of 3.0% or less, and an elongation of 3.0% or more and less than 10.0% after being heat-treated.
(2) As the component composition, in terms of mass%, Ti: 0.005% or more and 0.030% or less, Mo: 0.01% or more and 0.05% or less, Cr: 0.05% or more and 0.20% or less. The steel sheet for cans according to (1), which contains one or more of them.
(3) The method for producing a steel plate for a can according to (1) or (2), wherein a step of heating a steel slab, a step of hot rolling the heated steel slab, and a hot-rolled sheet obtained. A step of pickling the wound hot-rolled sheet, a step of primary cold-rolling the pickled hot-rolled sheet, and a step of quenching the primary cold-rolled cold-rolled sheet. In the annealing step, the cold-rolled sheet obtained in the primary cold rolling step is annealed at an annealing temperature of 720 ° C. or higher and 780 ° C. or lower. Then, in the secondary cold rolling, a method for producing a steel plate for cans, in which the annealed plate obtained in the annealing step is cold rolled at a rolling ratio of 6.0% or more and 30.0% or less.

The steel sheet for cans of the present invention has excellent workability and openability. 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. In the present invention, the processability means the lid-making property, and the excellent lid-making property means that there is no stretcher strain and there is no rivet cracking.

Hereinafter, the component composition, the steel sheet structure, 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. Further, the following "opening of a can" means opening an EOE to which the steel plate for a can of the present invention is applied.
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%.

C: 0.100% or more and less than 0.130% C is an important element that contributes to the reduction of yield elongation and the reduction of can opening force by forming pearlite in addition to the improvement of tensile strength. By setting the C content to 0.100% or more, the pearlite can be set to 1.0% or more and the tensile strength can be set to 630 MPa or more. It is preferably 0.105% or more. More preferably, it is 0.110% or more. On the other hand, when the C content is 0.130% or more, the yield elongation increases due to the increase in the solid solution C. Therefore, the C content needs to be less than 0.130%. It is preferably 0.125% or less.

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

Mn: 0.10% or more and 0.60% or less Mn not only contributes to the improvement of tensile strength by solid solution strengthening, but also promotes the formation of pearlite. As a result, work hardening is promoted, and in addition to a tensile strength of 630 MPa or more, a yield elongation of 3.0% or less and a decrease in can opening force can be contributed. In order to obtain such an effect, the Mn content needs to be 0.10% or more. It is preferably 0.20% or more. More preferably, it is 0.40% or more. On the other hand, when the Mn content exceeds 0.60%, not only the contribution to pearlite formation is saturated, but also the can opening force is increased due to excessive solid solution strengthening. Therefore, the Mn content needs to be 0.60% or less. Preferably, it is 0.50% or less.

P: 0.020% or less When a large amount of P is added, workability is lowered due to excessive hardening and central segregation, and corrosion resistance is also lowered. Therefore, the P content is set to 0.020% or less. Preferably, it is 0.018% or less. On the other hand, since P contributes to the improvement of tensile strength, it is preferable to add 0.005% or more. More preferably, it is 0.008% or more.

S: 0.020% or less S forms sulfide in steel and lowers hot rollability. Therefore, the S content is set to 0.020% or less. It is preferably 0.015% or less. More preferably, it is 0.012% or less. When the S content is 0.005% or more, pitting corrosion can be prevented regardless of the contents of the can, so it is preferable to add 0.005% or more of S. More preferably, it is 0.008% or more.

Al: 0.01% or more and 0.10% or less Al is useful as a deoxidizing element and contributes to reduction of yield elongation by forming a nitride. Therefore, it is necessary to contain 0.01% or more. It is preferably 0.03% or more. If it is excessively contained, a large amount of alumina is generated and remains in the steel sheet to reduce workability. Therefore, the Al content needs to be 0.10% or less. It is preferably 0.09% or less. More preferably, it is 0.08% or less.

N: 0.0005% or more and 0.0040% or less When N exists as a solid solution N, the yield elongation increases and the workability decreases. Therefore, the N content needs to be 0.0040% or less. It is preferably 0.0030% or less. More preferably, it is 0.0025% or less. On the other hand, it is difficult to stably set N to less than 0.0005%, and the manufacturing cost also increases. Therefore, the N content is set to 0.0005% or more.

Nb: 0.005% or more and 0.030% or less Nb is an important element for improving tensile strength by refining ferrite crystal grains and forming carbides, and Nb is contained in order to obtain such an effect. The amount should be 0.005% or more. It is preferably 0.010% or more. More preferably, it is 0.012% or more. On the other hand, when it is contained in excess of 0.030%, the recrystallization temperature becomes excessively high, unrecrystallized grains remain, the tensile strength becomes excessive, and the can opening force increases. Therefore, the Nb content needs to be 0.030% or less. It is preferably 0.023% or less.

B: More than 0.0005% and 0.0050% or less B has the effect of forming N and BN to reduce the solid solution N and lower the yield elongation. In addition, since it exists as a solid solution B, the ferrite crystal grains are refined and contributes to the improvement of the tensile strength, so that the B content needs to exceed 0.0005%. It is preferably over 0.0020%. More preferably, it is 0.0025% or more. Even if B is excessively contained, not only the above effect is saturated, but also C precipitated as granular cementite increases, pearlite decreases, and the can openability deteriorates. Therefore, the B content is 0.0050. Must be less than or equal to%. It is preferably 0.0035% or less. More preferably, it is 0.0030% or less.

In addition to the above, the steel sheet for cans of the present invention has Ti: 0.005% or more and 0.030% or less, Mo: 0.01% or more and 0.05% or less, Cr: 0.05% or more and 0.20% or less. Of these, it is preferable to contain one or more of them.

Ti: 0.005% or more and 0.030% or less Ti has the effect of fixing N as TiN and reducing the yield elongation. Further, by preferentially generating TiN, the formation of BN is suppressed, and by securing the solid solution B, the ferrite crystal grains are refined, which contributes to the improvement of yield stress and tensile strength. Furthermore, it also contributes to the improvement of tensile strength by forming fine carbides. Therefore, it is preferable to contain Ti at 0.005% or more. The Ti content is more preferably 0.010% or more. If Ti is contained in an amount of more than 0.030%, the recrystallization temperature becomes excessively high, unrecrystallized grains remain, and the tensile strength becomes excessive. Therefore, the Ti content is preferably 0.030% or less. More preferably, it is 0.025% or less.

Mo: 0.01% or more and 0.05% or less Mo is preferably contained in an amount of 0.01% or more because it contributes to the improvement of tensile strength and the increase in the amount of pearlite by refining ferrite crystal grains and forming carbides. .. More preferably, it is 0.02% or more. If Mo is contained in an amount of more than 0.05%, such an effect is saturated. Therefore, the Mo content is preferably 0.05% or less.
Cr: 0.05% or more and 0.20% or less Cr is preferably contained in an amount of 0.05% or more because it contributes to an increase in the amount of pearlite. More preferably, it is 0.08% or more. If Cr is contained in an amount of more than 0.20%, such an effect is saturated. Therefore, the Cr content is preferably 0.20% or less. More preferably, it is 0.16% or less.

The rest of the above component composition in the steel sheet for cans according to the present invention is Fe and unavoidable impurities.

Next, the steel plate structure of the steel plate for cans of the present invention will be described.
Area fraction of pearlite: 1.0% or more By dispersing pearlite in the steel sheet structure and containing it, fracture at the score is promoted at the time of opening the can, and the opening force can be reduced. In order to obtain such an effect, it is necessary to set the surface integral of pearlite to 1.0% or more. The surface integral of pearlite is preferably 1.5% or more. More preferably, it is 1.8% or more. The area fraction of pearlite is preferably 10% or less because better can openability can be obtained when pearlite is 10% or less. More preferably, it is 5.0% or less.

The balance is a ferrite phase and may contain granular cementite. It is not necessary to include a hard phase such as martensite, bainite, and retained austenite, but the steel sheet structure may contain 1% or less of the total surface integral.

In the present invention, a sample is cut out, embedded in a resin, polished, corroded with nital to reveal a structure, and then a scanning electron microscope (SEM) is used so that a vertical cross section parallel to the rolling direction of the steel sheet can be observed. The steel plate structure is photographed at. The surface integral of pearlite is measured by image processing using the captured image.

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

Tensile strength: 630 MPa or more, 750 MPa or less, yield elongation: 3.0% or less, elongation: 3.0% or more and less than 10.0% In order to secure sufficient pressure resistance in a thinned can lid, a can The tensile strength of the steel plate used for the lid needs to be 630 MPa or more. Preferably, it is 650 MPa or more. If the tensile strength becomes excessive, the can opening force increases, so the tensile strength needs to be 750 MPa or less. It is preferably 710 MPa or less. In order to suppress the occurrence of cracks during rivet processing, the elongation needs to be 3.0% or more. It is preferably 4.0% or more. If the elongation is too large, the notch (score) of the EOE is less likely to break when the can is opened, and the can opening force becomes excessive. Therefore, the elongation needs to be less than 10.0%. It is preferably less than 7.0%. In order to prevent stretcher strain during lid processing, the yield elongation needs to be 3.0% or less. Preferably, it is 2.0% or less. More preferably, it is 1.2% or less.

In the present invention, the tensile strength, yield elongation 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 0.30 mm or less. Since the steel sheet for cans of the present invention can be subjected to ultra-thin gauge reduction, it is more preferable to set the plate thickness to 0.10 to 0.25 mm from the viewpoint of resource saving and cost reduction.

Next, the method for manufacturing the steel sheet for cans of the present invention will be described. A steel sheet for cans can be manufactured under the conditions described below. It should be noted that steps such as a plating step of applying Sn plating, Ni plating, Cr plating and the like, a chemical conversion treatment step, a resin film coating step of laminating and the like may be appropriately performed.

Heating temperature: 1100 ° C or higher (suitable range)
When the slab heating temperature before hot rolling is 1100 ° C. or higher, the generated nitride becomes finer and better tensile strength can be obtained. Therefore, the slab heating temperature is preferably 1100 ° C. or higher. More preferably, it is 1150 ° C. or higher. When Ti is contained, 1200 ° C. or higher is even more preferable. If the slab heating temperature is 1280 ° C. or lower, surface defects due to scale can be easily avoided, and therefore it is preferably 1280 ° C. or lower. The slab heating temperature is more preferably 1250 ° C. or lower.

Finishing temperature: 830 ° C or higher and 960 ° C or lower (suitable range)
When the finishing temperature of hot rolling is 960 ° C or lower, finer ferrite crystal grains can be obtained and the tensile strength after cold rolling, annealing, and secondary cold rolling becomes good, so the finishing temperature is set to 960. The temperature is preferably below ° C. When the finishing temperature of hot rolling is 830 ° C. or higher, the Nb carbides formed during hot rolling become finer and better tensile strength can be obtained. Therefore, it is preferable to set the finishing temperature to 830 ° C. or higher. .. The finishing temperature is more preferably 850 ° C. or higher.

Winding temperature: 450 ° C or more and less than 670 ° C (suitable range)
If the winding temperature is less than 670 ° C., the cementite in the hot-rolled plate becomes fine and sufficiently melts during annealing to promote the formation of pearlite. In addition, alloy carbides such as Nb carbides are also made finer, and better tensile strength can be obtained. Therefore, the winding temperature is preferably less than 670 ° C. More preferably, it is 620 ° C. or lower. When the winding temperature is 450 ° C. or higher, the effect of precipitating alloy carbides such as Nb can be surely obtained and the tensile strength becomes good. Therefore, the winding temperature is preferably 450 ° C. or higher. The winding temperature is more preferably 550 ° C. or higher.

The hot-rolled plate after winding is pickled to remove the surface scale. The pickling conditions are not specified as long as the surface scale can be removed. It can be pickled by a conventional method.

Rolling rate in the primary cold rolling process: 85.0% or more (suitable range)
By the primary cold rolling, the ferrite crystal grains after annealing become finer and the tensile strength is improved. In order to obtain this effect, it is preferable that the rolling ratio of the primary cold rolling is 85.0% or more. The rolling ratio of the primary cold rolling is more preferably 87% or more. When the rolling ratio of the primary cold rolling is 93% or less, the anisotropy of the tensile properties is small and better workability can be obtained. Therefore, the rolling ratio of the primary cold rolling is preferably 93% or less. The rolling ratio of the primary cold rolling is more preferably 90.4% or less.

Annealing temperature: 720 ° C. or higher and 780 ° C. or lower It is important to generate pearlite in the annealing step in order to obtain high tensile strength and small yield elongation. Therefore, it is necessary to set the annealing temperature to 720 ° C. or higher. The annealing temperature is preferably 730 ° 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 and the tensile strength decreases. Therefore, the annealing temperature must be 780 ° C. or lower. .. The annealing temperature is more preferably 770 ° 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 15 s or more. The annealing time is preferably 60 s or less from the viewpoint of fine graining of ferrite crystal grains. More preferably, it is 40 s or less.

Rolling rate in the secondary cold rolling step: 6.0% or more and 30.0% or less The secondary cold rolling step after the annealing step improves the tensile strength required for the pressure resistance of the can lid. In order to obtain such an effect, the rolling ratio (secondary rolling ratio) in the secondary cold rolling step is set to 6.0% or more. It is preferably 10.0% or more. If the secondary rolling ratio exceeds 30.0%, strain is excessively introduced, the tensile strength becomes excessive, and the can openability deteriorates. Therefore, the secondary rolling ratio is set to 30.0% or less. The secondary rolling ratio is preferably 20.0% or less. The secondary rolling ratio is more preferably 15.0% or less.

Hereinafter, examples of the present invention will be described. The technical scope of the present invention is not limited to the following examples.

Steel No. shown in Table 1. A steel slab containing 1 to 30 components 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 34).

(Evaluation of tensile strength, yield elongation, elongation)
From the above-mentioned 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, yield elongation, and elongation were evaluated according to JIS Z 2241. The evaluation results are shown in Table 3.

(Measurement of surface integral of pearlite)
A sample was cut out, embedded in resin, and polished so that a vertical cross section parallel to the rolling direction of the steel sheet could be observed. After corroding with nital to reveal the structure, a three-field steel sheet structure randomly selected at a magnification of 3000 was photographed by SEM. The surface integral of pearlite was measured from each SEM image taken by image processing, and the average value was obtained. The measurement results are shown in Table 3.

(Evaluation of workability and can openability)
After aging heat treatment of the above-mentioned steel sheet for cans at 210 ° C. for 20 minutes, a fully open type EOE having a diameter of 63 mm was prepared. Those with no cracks in the rivet processing and no wrinkles due to the stretcher strain were evaluated as good in workability, and those in which either of them occurred were evaluated as inferior in workability. Score processing is performed on the EOE with a score remaining thickness of 50 μm, the tab is pulled, the force (pop load) at which the score starts to break is measured, and if it is 25 N or less, the can openability is considered to be good, and if it exceeds 25 N, the can open The sex was inferior and was marked as x.

発明例は、いずれも引張強さが６３０ＭＰａ以上７５０ＭＰａ以下で、降伏伸びが３．０％以下で、パーライトの面積分率が１．０％以上、伸びが３．０％以上１０．０％未満で、加工性および開缶性が良好であった。

In each of the examples of the invention, the tensile strength is 630 MPa or more and 750 MPa or less, the yield elongation is 3.0% or less, the area fraction of pearlite is 1.0% or more, and the elongation is 3.0% or more and less than 10.0%. The workability and can openability were good.

On the other hand, in the comparative example, any one or more of tensile strength, yield elongation, surface integral of pearlite, workability, and can openability were inferior.

Claims (3)

As a component composition, by mass%,
C: 0.100% or more and less than 0.130%,
Si: 0.04% or less,
Mn: 0.10% or more and 0.60% or less,
P: 0.020% or less,
S: 0.020% or less,
Al: 0.01% or more and 0.10% or less,
N: 0.0005% or more and 0.0040% or less,
Nb: 0.005% or more and 0.030% or less,
B: Contains more than 0.0005% and less than 0.0050%,
The rest consists of Fe and unavoidable impurities
It has a ferrite structure containing pearlite in an area fraction of 1.0% or more.
Tensile strength after heat treatment at 210 ° C. for 20 minutes is 630 MPa or more, 750 MPa or less,
Yield growth is less than 3.0%
A steel sheet for cans having an elongation of 3.0% or more and less than 10.0%. As a component composition, in mass%,
Ti: 0.005% or more and 0.030% or less,
Mo: 0.01% or more and 0.05% or less,
Cr: Contains one or more of 0.05% or more and 0.20% or less.
The steel plate for cans according to claim 1. The method for manufacturing a steel sheet for cans according to claim 1 or 2.
A step of heating the steel slab, a step of hot rolling the heated steel slab, a step of winding the obtained hot-rolled plate, a step of pickling the wound hot-rolled plate, and a pickling process. It has a step of primary cold rolling of a hot-rolled sheet, a step of annealing a cold-rolled primary cold-rolled sheet, and a process of secondary cold-rolling an annealed annealed sheet.
In the annealing step, the cold rolled sheet obtained in the primary cold rolling step is annealed at an annealing temperature of 720 ° C. or higher and 780 ° C. or lower.
In the secondary cold rolling step, the annealed sheet obtained in the annealing step is cold rolled at a rolling ratio of 6.0% or more and 30.0% or less.
Manufacturing method of steel plate for cans.