CN113748220A

CN113748220A - Steel sheet for can and method for producing same

Info

Publication number: CN113748220A
Application number: CN202080025702.9A
Authority: CN
Inventors: 斋藤勇人; 假屋房亮; 小岛克己
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2019-03-29
Filing date: 2020-03-24
Publication date: 2021-12-03
Anticipated expiration: 2040-03-24
Also published as: KR20210131407A; JP6819838B1; TW202104616A; TWI730689B; KR102549938B1; WO2020203470A1; JPWO2020203470A1; CN113748220B; MY196420A

Abstract

The invention provides a steel sheet for cans, which comprises the following components in percentage by mass: 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: more than 0.0005% and not more than 0.0050%, with the balance consisting of Fe and unavoidable impurities, wherein the steel sheet for can has a ferrite structure containing pearlite in an amount of 1.0% or more by area percentage, and has a tensile strength after heat treatment at 210 ℃ for 20 minutes of 630MPa or more and not more than 750MPa, a yield elongation of 3.0% or less, and an elongation of 3.0% or more and less than 10.0%.

Description

Steel sheet for can and method for producing same

Technical Field

The present invention relates to a steel sheet for cans suitable for use as a material for cans used for food cans, beverage cans, and the like, and a method for producing the same, and more particularly, to a steel sheet for cans which can be suitably used for producing Easy Open End (EOE) and a method for producing the same.

Background

In recent years, from the viewpoint of reducing environmental load and cost, it is required to reduce the amount of steel sheet used for food cans and beverage cans, and the steel sheet is thinned for both two-piece cans and three-piece cans. In addition, there is a strong demand for thinning of not only the can body but also the can lid portion such as EOE.

When the steel sheet for can lids is thinned, the compressive strength is lowered, and therefore, it is necessary to use a high-strength steel sheet. As high-strength steel sheets for cans, the enhancement of the strength of sr (single reduced) materials having good workability and the improvement of the workability of dr (double reduced) materials having low workability have been studied. Here, the SR material is a material produced by temper rolling after annealing, and the DR material is a steel sheet produced by cold rolling again (secondary cold rolling) after annealing.

Patent document 1 proposes a steel sheet for can having the following composition and ferrite structure as a high-strength SR steel sheet: the composition contains, in mass%, C: 0.03 to 0.13%, Si: 0.03% or less, Mn: 0.3-0.6%, P: 0.02% or less, Al: 0.1% or less, N: 0.012% or less, and Nb: 0.005-0.05%, Ti: 0.005-0.05%, B: 0.0005-0.005% of 1 or more, the balance consisting of iron and unavoidable impurities, and the ferrite structure having a cementite ratio of 0.5% or more; the ferrite has an average crystal grain diameter of 7 μm or less, a tensile strength of 450 to 550MPa after the coating and baking treatment, a total elongation of 20% or more, and a yield elongation of 5% or less.

Patent document 2 proposes a high-strength steel sheet characterized by being added as an additiveA DR steel sheet having excellent workability, which contains, in mass%, C: 0.010-0.080%, Si: 0.05% or less, Mn: 0.10% or more and 0.70% or less, P: 0.03% or less, S: 0.020% or less, N: 0.0120% or more and 0.0180% or less, Al: 0.005% to 0.070%, the balance being iron and unavoidable impurities, wherein the content of N as solid solution N in the N is 0.0100% or more, the ferrite grain diameter is 7.0 μm or less, and the dislocation density at the 1/4 depth position of the sheet thickness from the surface layer is 4.0X 10¹⁴m^-2Above and 2.0X 10¹⁵m^-2The tensile strength in the direction perpendicular to rolling after aging treatment is 530MPa or more, and the elongation is 7% or more.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2008-274332

Patent document 2: international publication No. 2015/166646

Disclosure of Invention

However, the above-described conventional techniques have problems as described below.

The technique described in patent document 1 can be applied only to steel sheets having a tensile strength of up to 550MPa, and cannot cope with further thinning. The technique described in patent document 2 has a problem that the yield elongation is large because of a large N content, and the appearance is poor because tensile deformation occurs during the capping process. Further, only strengthening increases the can opening force required for opening the EOE.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a steel sheet for a can having excellent workability and can openability, and a method for manufacturing the same.

In order to achieve the above object, the gist of the present invention is as follows.

(1) A steel sheet for cans, which comprises, as component compositions, 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: more than 0.0005% and not more than 0.0050%, with the balance consisting of Fe and unavoidable impurities, wherein the steel sheet for can has a ferrite structure containing pearlite in an amount of 1.0% or more by area percentage, and has a tensile strength after heat treatment at 210 ℃ for 20 minutes of 630MPa or more and not more than 750MPa, a yield elongation of 3.0% or less, and an elongation of 3.0% or more and less than 10.0%.

(2) The steel sheet for can according to (1), further comprising, as a component composition, in mass%: 0.005% to 0.030% of Mo: 0.01% to 0.05%, Cr: 0.05% to 0.20% inclusive.

(3) A method for producing a steel sheet for cans, which is the method for producing a steel sheet for cans described in (1) or (2), comprising: a step of heating a steel slab, a step of hot-rolling the heated steel slab, a step of coiling the obtained hot-rolled steel sheet, a step of pickling the coiled hot-rolled steel sheet, a step of primary cold-rolling the pickled hot-rolled steel sheet, an annealing step of annealing the cold-rolled steel sheet after the primary cold-rolling, and a step of secondary cold-rolling the annealed steel sheet after the annealing; in the annealing step, the cold-rolled steel sheet obtained in the primary cold-rolling step is annealed at an annealing temperature of 720 ℃ to 780 ℃ inclusive, and in the secondary cold-rolling step, the annealed steel sheet obtained in the annealing step is cold-rolled at a reduction ratio of 6.0% to 30.0%.

The steel sheet for can of the present invention has excellent workability and can openability. According to the present invention, the steel sheet 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 workability means the lid-making property, and the excellent lid-making property means that there is no tensile deformation and no caulking crack.

Detailed Description

The composition of the steel sheet for can, the steel sheet structure, the steel sheet characteristics, and the production method of the present invention will be described in order below. The present invention is not limited to the following embodiments. Hereinafter, "can opening" refers to opening of the EOE of the steel sheet for can to which the present invention is applied.

First, the composition of the steel sheet for can of the present invention will be explained. In the description of the component composition, the% representing the content of each component means mass%.

C: more than 0.100 percent and less than 0.130 percent

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

Si: less than 0.04%

If Si is added in a large amount, the surface treatment property deteriorates due to surface thickening, and the corrosion resistance is lowered, so that 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 improvement of tensile strength, and therefore, it is preferable to add 0.01% or more.

Mn: 0.10% or more and 0.60% or less

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

P: 0.020% or less

If a large amount of P is added, the workability is lowered by excessive hardening and center segregation, and the corrosion resistance is lowered. Therefore, the P content is 0.020% or less. Preferably 0.018% or less. On the other hand, P is preferably added in an amount of 0.005% or more because it contributes to improvement of tensile strength. Preferably 0.008% or more.

S: 0.020% or less

S forms sulfides in steel and deteriorates hot rolling properties. Therefore, the S content is 0.020% or less. Preferably 0.015% or less. More preferably 0.012% or less. If the S content is 0.005% or more, pitting corrosion can be prevented regardless of the content of the can, and therefore, it is preferable to add 0.005% or more of S. More preferably 0.008% or more.

Al: 0.01% to 0.10% inclusive

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

N: 0.0005% or more and 0.0040% or less

Since the yield elongation increases and the workability decreases if N is present as solid-solution N, the N content needs to be 0.0040% or less. Preferably 0.0030% or less. More preferably 0.0025% or less. On the other hand, the N content is 0.0005% or more because it is difficult to stably reduce N to less than 0.0005% and the production cost is also increased.

Nb: 0.005% or more and 0.030% or less

Nb is an important element for improving the tensile strength by making ferrite grains fine and forming carbides, and in order to obtain such an effect, Nb needs to be 0.005% or more. Preferably 0.010% or more. More preferably 0.012% or more. On the other hand, if the content exceeds 0.030%, the recrystallization temperature becomes too 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. Preferably 0.023% or less.

B: more than 0.0005% and not more than 0.0050%

B forms BN with N to reduce the amount of dissolved N, and has the effect of reducing the yield elongation. In addition, since the ferrite grains are refined by the presence of B as a solid solution, which contributes to the improvement of tensile strength, the B content needs to exceed 0.0005%. Preferably 0.0020%. More preferably 0.0025% or more. Even if B is contained excessively, the above-described effects are saturated, and C precipitated as granular cementite increases, pearlite decreases, and the can opening property deteriorates, and the B content needs to be 0.0050% or less. Preferably 0.0035% or less. More preferably 0.0030% or less.

The steel sheet for can of the present invention preferably contains, in addition to the above components, Ti: 0.005% to 0.030% of Mo: 0.01% to 0.05%, Cr: 0.05% to 0.20% inclusive.

Ti: 0.005% or more and 0.030% or less

Ti fixes N as TiN, and has an effect of reducing the yield elongation. Further, generation of TiN is preferentially generated to suppress generation of BN and to secure solid solution B, thereby refining ferrite grains and contributing to improvement of yield stress and tensile strength. Further, the formation of fine carbides also contributes to an improvement in tensile strength. Therefore, it is preferable to contain 0.005% or more of Ti. The Ti content is more preferably 0.010% or more. If Ti is contained in an amount exceeding 0.030%, the recrystallization temperature becomes too high, unrecrystallized grains remain, and the tensile strength becomes excessive. Therefore, the Ti content is preferably 0.030% or less. More preferably 0.025% or less.

Mo: 0.01% or more and 0.05% or less

Mo contributes to improvement of tensile strength and increase of pearlite amount by making ferrite grains fine and forming carbides, and therefore is preferably contained in an amount of 0.01% or more. More preferably 0.02% or more. If Mo is contained in an amount exceeding 0.05%, such effects are saturated, and therefore, the Mo content is preferably 0.05% or less.

Cr: 0.05% to 0.20% inclusive

Cr contributes to increase of the pearlite amount, and therefore, it is preferably contained in an amount of 0.05% or more. More preferably 0.08% or more. Since such an effect is saturated when Cr is contained in an amount increased by more than 0.20%, the Cr content is preferably 0.20% or less. More preferably 0.16% or less.

The remainder of the above-described composition of the steel sheet for can of the present invention is Fe and inevitable impurities.

Next, the steel sheet structure of the steel sheet for can of the present invention will be described.

Area fraction of pearlite: 1.0% or more

When pearlite is dispersed and contained in the steel sheet structure, the fracture of the edge score line can be promoted at the time of can opening, and the can opening force can be reduced. In order to obtain such an effect, the area fraction of pearlite needs to be 1.0% or more. The area fraction of pearlite is preferably 1.5% or more. More preferably 1.8% or more. Since a more satisfactory can-opening property can be obtained if pearlite is 10% or less, the area fraction of pearlite is preferably 10% or less. More preferably 5.0% or less.

The balance is a ferrite phase, and may contain granular cementite. Although it is not necessary to contain a hard phase such as martensite, bainite, or retained austenite, the total of the area fraction may be 1% or less in the steel sheet structure.

In the present invention, a sample is taken out and embedded in a resin so that a vertical cross section of a steel sheet parallel to a rolling direction can be observed, the sample is etched with a nital etching solution after polishing to develop a structure, and then the structure of the steel sheet is photographed with a Scanning Electron Microscope (SEM). The area fraction of pearlite was measured by image processing using the captured image.

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

Tensile strength: 630MPa or more and 750MPa or less, yield elongation: 3.0% or less, elongation: more than 3.0 percent and less than 10.0 percent

In order to ensure sufficient pressure resistance in a thin can lid portion, the tensile strength of the steel sheet used in the can lid portion needs to be 630MPa or more. Preferably 650MPa or more. If the tensile strength is excessive, the can opening force increases, and therefore the tensile strength needs to be 750MPa or less. Preferably 710MPa or less. In order to suppress the occurrence of cracks during caulking, the elongation needs to be 3.0% or more. Preferably 4.0% or more. If the elongation is too large, the EOE notch (edge-drawn line) is not easily broken at the time of can opening, and the can opening force is excessive, so that the elongation needs to be less than 10.0%. Preferably less than 7.0%. In order to prevent tensile deformation during the lid processing, the yield elongation needs to be 3.0% or less. Preferably 2.0% or less. More preferably 1.2% or less.

In the present invention, tensile strength, elongation at yield and elongation are evaluated in accordance with JIS Z2241 after applying JIS No. 5 tensile test pieces from the rolling direction to an aging heat treatment at 210 ℃ for 20 minutes.

The plate thickness of the steel sheet for can of the present invention is not particularly limited, but is preferably 0.30mm or less. Since the steel sheet for can of the present invention can be made extremely thin, it is more preferable to make the sheet thickness 0.10 to 0.25mm from the viewpoint of resource saving and cost reduction.

Next, a method for producing a steel sheet for cans of the present invention will be described. The steel sheet for can of the present invention can be produced under the conditions described below. In addition, a plating step of plating Sn, Ni, Cr, or the like, a chemical conversion treatment step, a resin film coating step such as lamination, or the like may be performed as appropriate.

Heating temperature: above 1100 ℃ (preferred range)

When the slab heating temperature before hot rolling is 1100 ℃ or higher, the produced nitride becomes fine and a more favorable tensile strength can be obtained, and therefore, the slab heating temperature is preferably 1100 ℃ or higher. More preferably 1150 ℃ or higher. When Ti is contained, it is more preferably 1200 ℃ or higher. If the slab heating temperature is no more than 1280 ℃, surface defects caused by scale are easily avoided, and therefore, 1280 ℃ or less is preferable. The slab heating temperature is more preferably 1250 ℃.

The finishing temperature is as follows: 830 ℃ or higher and 960 ℃ or lower (preferred range)

When the finish rolling temperature of hot rolling is 960 ℃ or lower, it is preferable that the finish rolling temperature is 960 ℃ or lower because finer ferrite grains can be obtained and the tensile strength after cold rolling, annealing, and secondary cold rolling becomes good. When the finish rolling temperature of hot rolling is 830 ℃ or higher, the Nb carbide formed during hot rolling becomes fine, and a more favorable tensile strength can be obtained, and therefore, it is preferable to set the finish rolling temperature to 830 ℃ or higher. The finishing temperature is more preferably 850 ℃ or higher.

Coiling temperature: more than 450 ℃ and less than 670 ℃ (preferred range)

If the coiling temperature is less than 670 ℃, cementite in the hot-rolled steel sheet becomes fine and is sufficiently melted at the time of annealing to promote pearlite formation. Further, alloy carbides such as Nb carbides are also made fine, and a further good tensile strength can be obtained. Therefore, the coiling temperature is preferably less than 670 ℃. More preferably 620 ℃ or lower. If the coiling temperature is 450 ℃ or higher, the effect of precipitation of alloy carbide such as Nb is reliably obtained, and the tensile strength is improved, so the coiling temperature is preferably 450 ℃ or higher. The coiling temperature is more preferably 550 ℃ or higher.

The hot rolled sheet after coiling was pickled to remove the surface scale. The pickling conditions are not particularly limited as long as the surface scale can be removed. The acid washing may be performed by a conventional method.

Rolling reduction in primary cold rolling step: 85.0% or more (preferred range)

By the primary cold rolling, ferrite grains after annealing are refined, and the tensile strength is improved. In order to obtain this effect, the rolling reduction in the first cold rolling is preferably 85.0% or more. The rolling reduction in the first cold rolling is more preferably 87% or more. When the rolling reduction in the first cold rolling is 93% or less, the anisotropy of the tensile properties is small, and further good workability can be obtained. Therefore, the rolling reduction in the first cold rolling is preferably 93% or less. The rolling reduction in the primary cold rolling is more preferably 90.4% or less.

Annealing temperature: 720 ℃ to 780 ℃ inclusive

In order to obtain high tensile strength and small yield elongation, it is important to generate pearlite in the annealing step. Therefore, the annealing temperature needs to be 720 ℃ or higher. The annealing temperature is preferably 730 ℃ or higher. On the other hand, if the annealing temperature exceeds 780 ℃, alloy carbides such as Nb carbides coarsen, and ferrite grains coarsen, and the tensile strength decreases, so the annealing temperature needs to be 780 ℃ or lower. The annealing temperature is more preferably 770 ℃ or lower. The annealing method is preferably continuous annealing from the viewpoint of uniformity of the material quality.

The annealing time is not particularly limited, but is preferably 15 seconds or more. From the viewpoint of grain refinement of ferrite grains, the annealing time is preferably 60s or less. More preferably 40s or less.

Rolling reduction in secondary cold rolling step: 6.0% or more and 30.0% or less

The tensile strength required for the compressive strength of the can lid is improved by the secondary cold rolling step after the annealing step. In order to obtain such an effect, the rolling reduction (secondary rolling reduction) in the secondary cold rolling step is 6.0% or more. Preferably 10.0% or more. If the secondary rolling reduction exceeds 30.0%, strain is excessively introduced, the tensile strength becomes excessive, and the can opening property is deteriorated, so that the secondary rolling reduction is 30.0% or less. The secondary rolling reduction is preferably 20.0% or less. The secondary rolling reduction is more preferably 15.0% or less.

Examples

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

Steel comprising the components of steel Nos. 1 to 30 shown in Table 1 and the balance consisting of Fe and unavoidable impurities is melted to produce a steel slab. The obtained steel slabs were heated under the conditions shown in table 2, hot rolled, coiled, pickled to remove oxide scale, cold rolled, annealed in a continuous annealing furnace, and temper rolled to obtain steel sheets for cans (steel sheet nos. 1 to 34).

(evaluation of tensile Strength, elongation at yield, and elongation)

Tensile test pieces of JIS No. 5 were taken from the above-mentioned steel sheets for cans in the rolling direction, subjected to aging heat treatment at 210 ℃ for 20 minutes, and then evaluated for tensile strength, elongation at yield and elongation in accordance with JIS Z2241. The evaluation results are set forth in Table 3.

(measurement of area fraction of pearlite)

The steel sheet was polished by cutting out a sample so that a vertical cross section parallel to the rolling direction of the steel sheet could be observed, and embedding the sample in resin. After the microstructure was developed by etching with a nital etching solution, the randomly selected steel plate microstructure in 2 fields was photographed at 3000 times magnification by SEM. The area fraction of pearlite was measured from each SEM image obtained by image processing, and the average value thereof was obtained. The measurement results are shown in Table 3.

(evaluation of processability and Can-opening Property)

The steel sheet for can was subjected to aging heat treatment at 210 ℃ for 20 minutes to prepare a 63mm diameter fully open EOE. The case where no crack was generated during the caulking process and no wrinkle was generated due to tensile deformation was regarded as "good" and "good", and the case where any crack was generated was regarded as "poor" and "x". The EOE was subjected to a side draw process with a residual thickness of 50 μm and drawn, and the force (can opening load) at the time of starting breaking of the side draw was measured, and if it was 25N or less, the can opening property was good and it was "O", and if it exceeded 25N, the can opening property was poor and it was "X".

The inventive examples all had a tensile strength of 630MPa or more and 750MPa or less, an elongation at yield of 3.0% or less, an area fraction of pearlite of 1.0% or more, an elongation of 3.0% or more and less than 10.0%, and good workability and can openability.

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

Claims

1. A steel sheet for cans, which comprises, as component compositions, 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: more than 0.0005% and not more than 0.0050%, with the remainder comprising Fe and unavoidable impurities,

the steel sheet for cans has a ferrite structure containing pearlite at an area ratio of 1.0% or more,

a tensile strength of 630MPa or more and 750MPa or less after heat treatment at 210 ℃ for 20 minutes,

the yield elongation is 3.0% or less,

the elongation is 3.0% or more and less than 10.0%.

2. The steel sheet for cans according to claim 1, further comprising, as a component composition, in mass%: 0.005% to 0.030% of Mo: 0.01% to 0.05%, Cr: 0.05% to 0.20% inclusive.

3. A method for producing a steel sheet for cans according to claim 1 or 2, comprising the steps of:

a step of heating a steel slab, a step of hot-rolling the heated steel slab, a step of coiling the obtained hot-rolled steel sheet, a step of pickling the coiled hot-rolled steel sheet, a step of primary cold-rolling the pickled hot-rolled steel sheet, an annealing step of annealing the cold-rolled steel sheet after the primary cold-rolling, and a step of secondary cold-rolling the annealed steel sheet after the annealing;

in the annealing step, the cold-rolled steel sheet obtained in the primary cold-rolling step is annealed at an annealing temperature of 720 ℃ to 780 ℃,

in the secondary cold rolling step, the annealed steel sheet obtained in the annealing step is cold-rolled at a reduction ratio of 6.0% to 30.0%.