WO2008102899A1

WO2008102899A1 - Processes for production of steel sheets for cans

Info

Publication number: WO2008102899A1
Application number: PCT/JP2008/053125
Authority: WO
Inventors: Yuka Nishihara; Katsumi Kojima; Hiroki Iwasa
Original assignee: Jfe Steel Corporation
Priority date: 2007-02-21
Filing date: 2008-02-19
Publication date: 2008-08-28
Also published as: EP2123780A1; CN101578381A; JP5076544B2; KR101128315B1; JP2008202113A; EP2123780B1; CN101578381B; KR20090084885A; EP2123780A4

Abstract

A high-strength steel sheet for cans which has a tensile strength of 550 to 650MPa and a total elongation of 5% or above is obtained by conducting hot rolling with a finishing temperature of the Ar3 transformation temperature or above, cold rolling, and then recovery annealing at a temperature of the recrystallization initiation temperature minus 200°C to the recrystallization initiation temperature minus 20°C. Further, the addition of Nb: 0.001 to 0.05% and/or B: 0.0001 to 0.005% brings about a steel sheet for cans which has a tensile strength of 550 to 700MPa and a total elongation of 4% or above while enabling the annealing in the same temperature range as that of conventional steel sheets for cans.

Description

Description Manufacturing method of steel sheet for cans Technical field

The present invention is a beverage canning (canned beverage) and food container of canned (caniied food) and {can or container) "I 2-piece DR Di ± r used, two- piece drawn and redrawn can) and 3 arsenide ¹ The present invention relates to a method of manufacturing a tin steel plate for use in a three-piece welded can.

In recent years, in order to increase the demand for steel cans as steel plates for cans, reduction of can manufacturing costs has been promoted. One way to reduce can manufacturing costs is to reduce the cost of materials. In other words, extremely thin high-strength steel plates can be used for both 2-piece cans that are drawn and 3-piece cans that are mainly made of simple cylinders.

For example, when a steel plate with a thickness of 0.16 mm is used, at least the body of weld cans has a mouth cwell hardness (HR30T) of about 73 to 77 (at least 73 to 76, preferably 74-77), it is necessary to use a high-strength material with a bow I tensile strength (TS: tensile strength) of about 550 MPa to 620 MPa. Currently, ultra-thin and hard steel plates for cans are manufactured by the Double Reduce method (hereinafter referred to as DR method) in which secondary cold rolling is performed after annealing. However, in the DR method, the steel sheet is manufactured through a process of hot rolling, cold rolling and annealing, and secondary cold rolling. In other words, since there is one more process than the normal process that is completed by annealing, the manufacturing cost increases accordingly. Therefore, in this type of steel sheet for cans, cost reduction is desired, and various strengthening elements (alloy elements that increase the strength) are added for annealing (here, recrystallization annealing). In other words, a manufacturing method has been proposed (ie, without secondary cold rolling). ' For example, JP-A-2001-107186 (Patent Document 1) and JP-A-2005-336610 (Patent Document 2) disclose high-strength steel sheets for cans that have been subjected to recrystallization annealing. . The steel sheet obtained by recrystallization annealing has low anisotropy and is suitable for drawn cans where earing should be suppressed as much as possible. 'However, steel sheets that do not require a small amount of anisotropy do not necessarily require recrystallization annealing after cold rolling. After increasing the strength by cold rolling, heat treatment at a low temperature is performed to relieve strain introduced in the cold rolling process and restore the ductility of the material to the minimum necessary range. A method (called recovery annealing) can be applied instead of recrystallization annealing. In this method, recrystallization annealing is not performed, and there is no significant decrease in hardness due to recrystallization, so there is the ability for precipitation hardening and the ability for solid solution hardening. The necessary power to add elements. Therefore, there is no need to worry about the effect of these elements on the corrosion resistance. Thus, recovery annealing is effective for steel sheets that do not require small anisotropy, and the following techniques have been proposed.

In Japanese Patent Publication No. 53-20445 (Patent Document 3), the finishing temperature in hot rolling is set to the Ar3 transformation point or less, and the crystal grain size after hot rolling is reduced to 50 / X. The technology described above is disclosed. In this technology, after the above hot rolling, after cold rolling at a reduction rate of 85 to 90%, continuous annealing of 450 to 580 is performed. Steel plates for cans with E 1 (total elongation) force of 6-8% at 57kgf / mm ² are obtained. The material used is Capped 0.05% to 06% Capped steel.

In Japanese Patent Laid-Open No. 8-269568 (Patent Document 4), after using copper containing REM as an essential component, the finishing temperature in hot rolling is below the Ar3 transformation point, and cold rolling is performed at a reduction rate of 85% or less. The technology for obtaining steel plates for cans with a YS (yield strength) of 640 MPa or more by heat treatment for 10 minutes or more in the range of 200 to 500: is disclosed. Japanese Patent Application Laid-Open No. 6-248338 (Patent Document 5) discloses a stretchy yarn having a tempered grade of T 4 to T 6 by annealing at a recrystallization temperature of 400 or more after cold rolling. A technique for making a steel plate for containers without a stretcher strain is disclosed. A maximum of 72.9 is disclosed as the mouth-kwell hardness (HR30T) obtained with this technology.

In JP-A-6-248339 (Patent Document 6), copper having the same composition as that of Patent Document 5 (C: 0.03% by weight or less, N: 0.005% by weight or less, etc.) is used at a temperature below the Ar3 transformation point. High-rigidity is achieved by performing hot rolling at least 50% and cold rolling at a reduction rate of 50% or more and then annealing at a recrystallization temperature of 400 or more. The technology to obtain steel plates for containers of the same level as the above is disclosed. In Patent Documents 5 and 6, the recrystallization temperature is defined as the temperature at which the recrystallization rate becomes a structure of less than 10%.

In JP-A-8-41549 (Patent Document 7), finish rolling is performed by setting the total reduction ratio below the Ar3 transformation point to 40% or more during hot rolling, and cold rolling is performed at a reduction ratio of 50% or more. A technique for obtaining a steel having a YS of 54 to 70 kgf / mm ² by performing low-temperature annealing at 350 to 650¾ for a short time after rolling is disclosed. Disclosure of the invention

[Problems to be solved by the invention]

However, the above-mentioned conventional techniques have the following problems.

For example, in Patent Document 3, Patent Document 4, Patent Document 6, and Patent Document 7, it is necessary to perform finish rolling below the Ar3 transformation point during hot rolling. When the finish rolling is performed below the Ar3 transformation point, the ferrite grain size of the hot rolled steel sheet increases, and after hot rolling as shown in Fig. 3 of Patent Document 3. The strength of the steel decreases. Therefore, it is effective as a method of reducing the strength of copper itself to the extent that sufficient workability is ensured. However, when finish rolling is performed below the Ar3 transformation point, the temperature in the finish rolling tends to be lower in the widthwise edge portion where the cooling rate is faster than the central portion in the width direction. For this reason, at the edge part, the strain introduced during finish rolling is not sufficiently released by recrystallization or recovery immediately after hot rolling, and the strength tends to increase. The result As a result, the strength difference between the central part and the edge part becomes large, and it is difficult to obtain a uniform hot-rolled sheet in the width direction, so it is difficult to obtain a uniform one in the current operation. Although the expression “below the Ar3 transformation point” is used here, the above conventional technology is intended to perform hot rolling (at least a part of) at a temperature that does not initiate the Ar3 transformation. Therefore, strictly speaking, it is accurate to express “below the Ar3 transformation point”.

According to Patent Document 4, the strain is recovered by annealing at 200 to 500 after cold rolling for 10 minutes or more to recover the strain. However, if annealing is performed for 10 minutes or more in a continuous annealing furnace, the line speed is lowered. It must significantly reduce productivity. Although Patent Document 5 and Patent Document 6 are characterized by annealing at 400 mm or more and below the recrystallization temperature, the Rockwell hardness of the obtained steel is less than 73.0, and the intended strength level in the present invention In order to obtain this copper, it is necessary to further lower the annealing temperature. As a result, the annealing temperature employed in the production of normal can materials will be removed, and a dedicated annealing cycle will need to be provided separately, reducing productivity.

The present invention has been made in view of such circumstances, and an object of the present invention is to solve the above-described problems of the prior art and to propose a method for manufacturing a steel plate for cans with high strength. That is, the present invention is applied to a steel sheet for a can which is applied to a use where a small anisotropy is not required, such as a welded can, and which requires workability in addition to strength. An object of the present invention is to propose a method for producing a steel sheet for cans with high strength while ensuring the ductility, for example, the minimum ductility necessary for the flange workability of a welded can.

[Means for solving the problems]

In order to solve the above problems, the present inventors have conducted extensive research. As a result, the following knowledge was obtained.

Based on the premise that the target strength and ductility were obtained by reducing the strength by recovery annealing, we investigated the optimization of the component composition and manufacturing conditions. And above all,

• Obtaining a hot-rolled steel sheet that is uniform in the width direction with no difference in strength between the central part and the edge part by finishing rolling above the A r3 transformation point, and -After cold rolling, anneal at “recrystallization start temperature—200” or more and “recrystallization start temperature—at 20” or less, and reduce to the target strength level at the recovery stage.

'We have found that these two are the features of the present invention and that the desired characteristics can be obtained by making them the main requirements.

^{_{Furthermore, Nb: 0.001~0.05 ο / ο,}} Β: 0.0001~0.005 ο / at least the _o By adding Rere Zureka, above production conditions, the same as the annealing temperature is employed in the manufacture of current steel sheet for cans It was also found that recovery annealing in the temperature range (00 to 700) is possible, and a tensile strength of 550 MPa to 650 MPa, or 550 MPa to 700 MPa force S can be obtained. The present invention has been made based on the above findings, and the gist thereof is as follows. ,

[1] At mass ⁰ / o, C: 0.003% or less, N: 0.004% or less, Mn: 0.05% to 0.5%, P: 0.02% or less, Si: 0.02% or less, S: 0.03% or less, A1: 0.1 % Steel, the remainder of which is iron and inevitable impurities are hot-rolled at a finishing temperature above the Ar 3 transformation point and coiled at a coiling temperature of 600 to 750¾. Next, after performing cold rolling at a rolling reduction of 60 to 95%, annealing is performed at a temperature of (at a recrystallization start temperature of _200) to (a recrystallization start temperature of 20 :). A method for producing steel plates for cans of 0.18 mm or less.

[2] The steel plate for cans according to [1], wherein the steel further contains at least one of Nb: 0.001% to 0.05% and B: 0.0001% to 0.005% by mass%. Production method. In the present specification, the percentages indicating the components of steel are all mass%. For example, the expression “Mn: 0.05% to 0.5%” means “Μη: 0.05% or more, 0.5% or less”, that is, “0.05% ≤Μη≤0.5%”.

In the present invention, the recrystallization start temperature is a temperature at which the rate of change in strength greatly changes with temperature, as shown in Fig. 1 (Example: conditions will be described later). It is defined as the temperature at which a structure in which the recrystallized structure occupies 5% is obtained. Brief Description of Drawings

FIG. 1 is a graph showing the relationship between annealing temperature (horizontal axis:), Ding S (vertical axis: MPa), and recrystallization start temperature in steel having the composition of the present invention.

FIG. 2 is a graph showing the relationship between annealing temperature (horizontal axis: in), T S (vertical axis: MPa), and recrystallization start temperature in steels of another composition of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail.

The steel plate for cans obtained by the method of the present invention can achieve a tensile strength of 550 to 650 MPa (see FIG. 1) and a total elongation of 5% or more. Alternatively, when Nb and B are added, a tensile strength of 550 to 700 MPa (see FIG. 2 in the example: conditions are described later) and a total elongation of 4% or more can be achieved. In manufacturing the steel plate for cans of the present invention, hot rolling is performed at a finishing temperature equal to or higher than the A _Γ 3 transformation point, and a temperature of (recrystallization start temperature 1 200 t) to (recrystallization start temperature 1 20). It is characterized by annealing within the range. Next, the component composition of the steel plate for cans of this invention is demonstrated.

C: 0.003% or less

The steel plate for cans proposed in the present invention is intended to increase the strength by strain introduced by cold rolling (primary cold rolling). Therefore, strengthening elements are unnecessary, and they are reduced as much as possible from the viewpoint of ensuring ductility. If C is contained in an amount exceeding 0.003%, the local ductility necessary for molding into a can cannot be obtained sufficiently. Also, the amount of residual solute carbon increases, and there is a risk of cracking during stretch-flange forming of the seeding part, which is the final process of can making. An increase in the amount of solute carbon further increases the amount of work hardening, which may cause wrinkles during neck forming and flange processing. Based on the above, the C content is 0.003% or less. On the other hand, if the C content is less than 0.0010%, the operability is lowered, for example, the annealing temperature for obtaining the target strength of the present invention is lowered, and the improvement in ductility is also reduced. The content is preferably 0.0010% or more. N: 0.004% or less

N is an impurity element inevitably mixed in copper. When the N content increases, slab cracking tends to occur in the unbending zone during continuous casting. N forms precipitates and lowers the elongation, while if it remains in a solid solution, it hardens the steel. As a condition for preventing the above action, the N content is 0.004% or less. When steel sheets are used for applications that require further workability, the N content is preferably 0.002% or less.

Si: 0.02% or less

Si is a strengthening element that increases the strength of steel by solid solution strengthening. If it is contained in a large amount, corrosion resistance is significantly impaired. Therefore, the Si content is 0.02% or less.

Mn: 0.05% —0.5%

Mn is a strengthening element that increases the strength of copper by solid solution strengthening. Mn is also an element that reduces the crystal grain size and increases the strength as it is further refined. In order not to cause the above effect, the upper limit of the Mn content is 0.5%. Preferably it is 0.3% or less.

On the other hand, if the Mn content is less than 0.05%, it is difficult to avoid hot shortness even when the S content is lowered, and problems such as surface cracks occur during hot rolling. Therefore, the lower limit of Mn is 0.05%. Preferably it is 0.10% or more.

P: 0.02% or less

When the P content is large, the strength of the steel is remarkably increased by solid solution strengthening, and the corrosion resistance is also deteriorated. Therefore, the P content is 0.02% or less.

S: 0.03% or less

S 'exists as an inclusion in steel and is an element that is disadvantageous to the ductility and corrosion resistance of the steel sheet. Preferably it is 0.01% or less.

A1: 0.1% or less

A1 improves the cleanliness in steel as a deoxidizer. Also, it combines with solute N to form A1N, and has the effect of reducing the amount of solute N. Therefore, it is preferable to make it contain to some extent in copper. Add about 0.005% or more as the condition It is desirable to do. On the other hand, when the A1 content exceeds 0.1%, the effect of improving the cleanliness is saturated. In addition, problems such as an increase in manufacturing costs and an increased tendency to generate surface defects also arise. Therefore, the A1 content is 0.1% or less.

In addition to the above, one or more selected from the group consisting of Nb: 0.001 to 0.05% and B: 0.001% to 0.005% force may be further contained.

Nb: 0.001 ~ 0.05%

Nb is an element with high carbide-forming ability, and raises the recrystallization temperature of steel by pinning the grain boundary caused by the generated carbide. Therefore, the recrystallization temperature of steel can be changed by adding Nb or changing the amount of Nb added. In other words, the appropriate annealing temperature can be raised and lowered, and the target temperature can be adjusted as needed. As a result, it can be combined with other steel sheets for annealing, which is very efficient in terms of productivity. However, if Nb is contained in excess of 0.05%, the recrystallization temperature becomes too high and the processing capability in CAL (continuous annealing line) decreases. Also, it becomes higher than the target strength due to precipitation strengthening of carbides. Therefore, the Nb content is 0.05% or less.

Basically, no strengthening element is added in the present invention, but Nb is preferably added from the viewpoint of annealing temperature, and if it is 0.05% or less, the Nb precipitation strengthening can be used by adjusting the addition amount. Thus, the desired strength can be obtained. Further, Nb addition is effective in preventing a decrease in weld strength by suppressing recrystallization during welding. A more preferable upper limit is 0.04%. On the other hand, when the Nb addition amount is less than 0.001%, the above effect cannot be exhibited. Therefore, when Nb is added for the purpose, 0.001% is set as the lower limit. More preferably, 0.005% or more is added. More preferably, it is 0.01% or more.

B: 0.0001-0.005%

B is an element that raises the recrystallization temperature. Therefore, B can be added for the same purpose as Nb. However, excessive addition inhibits recrystallization in the austenite region during hot rolling and increases the rolling load. Therefore, the B addition amount should be 0.005% or less. Preferably it is 0.002% or less. Also, since the effect of increasing the recrystallization temperature cannot be obtained at 0.0001% or less, when adding B for the purpose, 0.0001% is the lower limit. Preferably it is 0.0005% or more. More preferably, it is 0.0008% or more.

B, like Nb, can be made to have the desired strength by precipitation strengthening of B within the above range. It is also effective in preventing the welding strength from decreasing by suppressing recrystallization during welding.

Only one of Nb and B may be added, or both may be added within the above ranges.

The balance is Fe and inevitable impurities. Thickness: 0.18mm or less

In the present invention, the plate thickness is an important factor. It is particularly meaningful to reduce the thickness to a tensile strength of 550 MPa or more in the range where the plate thickness is 0 · 18 mm or less. In addition, if the steel sheet has a thickness exceeding 0.18 mm, continuous annealing can be performed easily even in a high temperature range exceeding 750 t. Productivity decreases. In the method of the present invention, the annealing temperature is set to a recrystallization start temperature of −20 ^ or less (usually 700 ^: less than or equal to: refer to the examples described later), so even a sheet thickness of 0.18 mm or less can be easily produced. .

Therefore, in the present invention, the plate thickness is limited to 0.18 mm or less because the effect is large in the range of tensile strength of 550 MPa or more and the productivity improvement effect is remarkably exhibited by annealing in the low temperature region. Hereinafter, the reason for the steel plate characteristics targeted in the present invention will be described. Tensile strength: 550 ~ 700MPa

The steel plate for cans produced according to the present invention is one of the purposes that is currently applied to fields that use high-strength and ultra-thin steel plates such as DR materials, such as DRD cans and welded cans. It is said. In such a field, if the plate thickness of the steel sheet is 0.18 mm or less and the tensile strength is 550 MPa or less, the can body strength is insufficient, and there is a concern about the buckling of the can. To avoid this, the target tensile strength is 550 MPa or more. The On the other hand, when trying to obtain strength exceeding 700MPa (exceeding 650MPa when Nb and B are not used), it is necessary to add a large amount of strengthening elements, which may impair corrosion resistance.

The tensile strength is controlled to the target value mainly by adjusting the steel plate composition, cold rolling rate, and annealing temperature.

Specifically, C: 0.003% or less, N: 0.004% or less, Mn: 0.05% to 0.5%, P: 0.02% or less, Si: 0.02% or less, S: 0.03% or less, A1: 0.1% or less As a result, the cold rolling rate is set to 60% or more, and the tensile strength is controlled to 550 to 650 MPa by annealing at a soaking temperature: (at a recrystallization start temperature of 200 :) to (at a recrystallization start temperature of 20). (Figure 1 ).

On the other hand, C: 0.003% or less, N: 0.004% or less, Mn: 0.05% to 0.5%, P: 0.02% or less, Si: 0.02% or less, S: 0.03% or less, A1: 0.1% or less. In addition, Nb: 0.001% to 0.05%, B: Add at least one of 0.0001% to 0.005% to make the cold rolling rate 60% or more, and soaking temperature: (Recrystallization start temperature 1 200) The tensile strength is controlled to 550-700MPa by annealing at a recrystallization start temperature of 20 (Fig. 2).

The Rockwell hardness (HR30T) is about 74 to 77 when Nb and B are not added, and about 74 to 80 when at least one of Nb and B is added. Total elongation: 4% or more

If the total elongation is less than 4%, the flangeability of the weld can deteriorates, and the cracking rate increases, which affects the workability. In order to avoid this, the target for total growth is 4% or more. In order to improve the workability as much as possible, it is desirable to secure a total stretch of 5% or more.

The total elongation is controlled to the target value mainly by adjusting the copper plate composition and the cooling rate after finishing during hot rolling. Next, the manufacturing method of the steel plate for cans of this invention is demonstrated.

Molten steel adjusted to the above-mentioned chemical composition is produced by a generally known steel making method using a converter or the like, and then used for ordinary purposes such as continuous forging. Rolled material (steel ingots, especially slabs) is made by the forging method.

Next, a hot-rolled sheet is obtained by hot rolling using the rolled material obtained as described above. Prior to hot rolling, the rolled material should be heated to 1250 or more. This is because the precipitates in the steel are completely dissolved to eliminate segregation and make the material homogeneous. The finishing temperature should be higher than the A r3 transformation point. Next, scraping is performed at a scraping temperature of 600 to 750. Next, the scale covering the surface of the steel plate is usually removed by pickling. Then, after performing cold rolling at a rolling reduction of 60 to 95%, annealing is performed at a temperature of (recrystallization start temperature—ZOOt) to (recrystallization start temperature—20T:).

(1) Hot rolling conditions

Finishing temperature: A r3 transformation point or higher

The hot rolling finishing temperature should be above the A r3 transformation point. As already mentioned, finish rolling below the A r3 transformation point has the advantage of reducing the strength of the steel during recovery annealing, but finishes so that the center in the width direction of the slab is below the A r3 transformation point. When rolling is performed, the strain introduced in the finish rolling is less likely to be released by recrystallization or recovery in the widthwise wedge part, which has a faster cooling rate than the center part. For this reason, the edge portion becomes hard, the difference in strength between the central portion and the edge portion becomes large, and a hot-rolled sheet having a non-uniform structure is easily obtained. Therefore, in order to obtain a hot-rolled sheet having a uniform structure, the finishing temperature should be higher than the Ar3 transformation point.

From the viewpoint of improving product properties (such as ductility), the finishing temperature is more preferably set to Ar 3 transformation point + 5 or more. The finishing temperature is preferably 950¾ or less from the viewpoint of avoiding scale defects.

In addition, in the steel sheet composition and hot rolling conditions of the present invention, the Ar 3 transformation point is generally in the range of 840 to 910. In the present invention, unlike the conventional technique using recovery annealing, the total elongation of the steel can be ensured only by hot rolling above the Ar3 transformation point, for the following reason. The ferrite grain size of the hot-rolled sheet is determined by hot rolling (which is a condition of the present invention). It is relatively small when raising temperature is higher than Ar3 transformation point, and is relatively large when hot rolling finish temperature is lower than Ar3 transformation point (which is a condition in the technology using conventional recovery annealing). . When both are cold-rolled, the strain energy accumulated in the cold-rolled sheet becomes higher when the ferrite grain size of the hot-rolled sheet is smaller. This is because there are many grain boundaries that restrain deformation. Since the recovery phenomenon proceeds using the strain energy accumulated in the cold-rolled sheet as a driving force, it can be said that the conditions of the present invention are conditions that promote the progress of the recovery phenomenon. Due to the recovery phenomenon, the cold-rolled steel sheet decreases the strength. However, since the condition of the present invention is a state of high strain energy, the target high strength can be maintained even after recovery. In addition, since the ductility is improved by the recovery phenomenon, the desired appropriate ductility can be ensured. From the above mechanism, it is preferable to avoid hot-rolling high-temperature finishing and high-purity composition in which the particle size tends to grow.

(2) Cutting temperature: 600¾ ～ 750Τ

In the hot rolling process, the cutting temperature must be 600 to 750. If it is less than 600¾, the heat-retaining effect after scraping is not sufficient, and the ferritic grain size of the hot-rolled sheet becomes unnecessarily small, so that the strength tends to become excessively high. 7 This organization is not desirable because it is easy to make.

— On the other hand, if the steel sheet is scraped at a temperature exceeding 750, the scale thickness of the steel sheet will increase significantly, and the descalability in the next pickling may deteriorate. is there. In order to further improve such problems, it is desirable to reduce the scraping temperature to 700 or below.

(3) Cold rolling conditions (rolling ratio): 60-95%

For cold rolling, the rolling reduction is 60-95%. If the rolling reduction is less than 60%, the desired strength is not achieved after cold rolling and heat treatment (recovery annealing). In addition, there is a problem that is considered to be caused by non-uniformity of the material, especially the non-uniformity in the direction of plate grinding. On the other hand, when the rolling reduction exceeds 95%, it becomes difficult to avoid deterioration of local ductility. A preferable rolling reduction is 80% or more.

(4) Heat treatment after cold rolling (annealing) Conditions:

Temperature: Recrystallization start temperature 1 200 or more, Recrystallization start temperature 1 20 or less The heat treatment (annealing) is performed in a temperature range where the recrystallization start temperature is at least 200Ό and the recrystallization start temperature is _20 or less. Since the recrystallization temperature is changed by the composition, for example, addition of Nb, B, etc., the temperature range (soaking temperature range) is based on the recrystallization start temperature of each steel as _200¾ to 120 Yes.

The purpose of annealing (recovery annealing) in the present invention is to reduce the strength to the target strength by performing strain relief annealing from the state where the strength is increased by the strain introduced by cold rolling. If the recrystallization start temperature is less than 200, the strain is not sufficiently released, and the recrystallization start temperature is about 200¾: as the lower limit because it is higher than the target strength and lower in ductility. A more preferable lower limit temperature from the viewpoint of ensuring ductility is a recrystallization start temperature of 150.

On the other hand, if the temperature is too high, recrystallization will start, and the target strength will not be obtained because it is too soft, and a uniform structure will not be obtained due to partial recrystallization. Is the upper limit. Recrystallized grains and recovered grains can be distinguished by observation with an optical or electron microscope. A more preferable upper limit temperature from the viewpoint of securing the strength is the recrystallization start temperature-30.

In the steel sheet composition and cold rolling conditions of the present invention, the recrystallization start temperature is generally in the range of 560 to 650: (Nb and B not added) or 620 to 780 (Nb and B added at least). .

In the present invention, it is preferable to perform annealing in a continuous annealing furnace from the viewpoint of productivity. Therefore, in order not to impede productivity, the soaking time during annealing is preferably set to 10 s or more and 90 s or less.

〔Example〕

(Example 1)

A steel slab was obtained by melting copper containing the composition shown in Table 1 and the balance being inevitable impurities and Fe. After the obtained steel slab was reheated at each temperature shown in Table 2, hot rolling was started. The hot rolling was performed by changing the finish rolling temperature in the range of 800 to 950 and the cutting temperature in the range of 550 to 700¾ (all shown in Table 2). Next, after pickling, cold rolling was performed at each reduction rate shown in Table 2 to produce a 0.15 mm thin steel plate (here, the thickness of the hot-rolled plate was adjusted according to the reduction rate). The obtained thin steel sheet Annealing temperature 350 ~ 620 ^ and annealing time 30 s in a secondary annealing furnace (recovery) Annealing, temper rolling so that the elongation rate is 1.5% or less, normal chrome plating (electric A plated copper sheet (tin-free steel) was obtained by continuous application. Detailed manufacturing conditions are shown in Table 2.

Regarding the effect of annealing temperature, the recrystallization behavior of the steel plate using steel 1 in Table 1 (manufactured under the conditions of steel plate 1 in Table 2 except for the annealing temperature) was confirmed. The results are shown in FIG. 1. Since it was confirmed that recrystallization started at 590, the temperature range of annealing in copper 1 (90% cold rolled) was set to 390 to 570¾. Recrystallization was almost completed after annealing of 600¾.

table 1

Lake copper C Si n P S N AI Nb B Remarks

1 0.001 7 0.01 0.1 5 0.01 0.003 0.0025 0.05 0 0 Compliant

4 0.0031 0.01 0.28 0.01 0.004 0.0025 0.05 0.022 0.002 Compliant

*-Rank: 獮 [Amount%

Table 2

A tensile test and a Γ value measurement were performed on the plated steel sheet obtained as described above. The tensile test was performed using JIS5 size tensile test pieces (rolling direction), and the tensile strength and elongation (total elongation) were measured to evaluate the strength and ductility. The average r value was obtained by the natural vibration method specified in JIS Z2254.

The results obtained are shown in Table 3. Here, the copper plate characteristics were investigated for samples taken from the center of the plate width, and the special steel plate properties at the edge in the plate width direction were obtained for samples at a position 50 mm from the edge of the plate width. Table 3

* The value in () indicates the value of the edge in the plate width direction.

Table 3 shows that the inventive examples (steel plates 1 and 2 etc.) have a tensile strength of 550 to 600 MPa and a total elongation of 5% or more.

On the other hand, in the comparative example (steel plate 3), the annealing temperature is below the range of the present invention, and the ductility is lowered because the recovery of strain in the steel is small. The comparative example (steel plate 4) is annealed. Since the temperature is higher than the range of the present invention and recrystallization starts locally, the strength is insufficient.

The same applies to the results in Fig. 1. That is, TS: 550 to 650 MPa is obtained at an annealing temperature between the recrystallization start temperature -20 and 200. Note that when recrystallization start temperature is reduced to 40¾ or less, TS: 600 to 650MPa force S is obtained. On the other hand, to obtain a steel plate of 550 to 600MPa, recrystallization start temperature is approximately It can be seen that it is preferable to anneal with ~ -40¾ :).

It can also be seen that when the finishing temperature is lower than the Ar3 transformation point, hardening and property deterioration at the edge are large, and the hardness grades of the steel sheets are actually different (steel sheets 21 and 29). Furthermore, from comparison between steel plates 20 and 25, it can be seen that if the rolling reduction is lowered too much, the strength decreases without improving the ductility.

(Example 2)

A steel slab was obtained by melting the steel containing the composition shown in Table 4 and the balance of inevitable impurities and Fe in an actual converter. The obtained steel slab was reheated at 1 150 to 1250, and hot rolling was started. In hot rolling, the finishing rolling temperature was varied in the range of 880 to 900, and the milling temperature was 620 ^. Next, after pickling, the steel sheet was cold-rolled at a rolling reduction of 80 to 90% to produce a thin steel plate having a thickness of 0.15 to 0.18 mm. The obtained thin steel sheet was annealed in a continuous annealing furnace at an annealing temperature of 300 700 and an annealing time of 30 s (recovery), and subjected to temper rolling so that the elongation was 1.5% or less. Tin-free steel was obtained by continuous chrome plating. Detailed manufacturing conditions are shown in Table 5.

As for the annealing temperature, as a result of confirming the recrystallization behavior of steels 2-18, it was confirmed that recrystallization was completed at 620-720 as shown in Table 5. For example, Fig. 2 shows the results of confirming the recrystallization behavior of steel 5 in Table 4 (manufactured under the conditions of steel plate 13 in Table 5 except for the annealing temperature).

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Table 5

Tensile tests and r-value measurements were performed on the plated steel sheets (tin-free steel) obtained as described above. Each characteristic was measured in the same manner as in Example 1. The results obtained are shown in Table 6. Table 6

From Table 6, in the inventive examples (copper plates 5, 7, 9, 10, 12, 13, etc.), the tensile strength is 550 to 700 MPa and the total elongation is 4% or more.

On the other hand, in the comparative examples (steel plates 6 and 8), the annealing temperature is lower than the range of the present invention and the recovery of strain in the steel is small, so the strength is high and the ductility is low. In the comparative example (copper plate 11), the annealing temperature exceeds the range of the present invention and the recrystallization starts locally, so that the strength is insufficient.

The same applies to the results in FIG. That is, TS: 550 to 700 MPa is obtained at an annealing temperature between the recrystallization start temperature of 20 to 1 200 ^. Recrystallization start temperature When TS is annealed at _40 or less, TS: 650 to 700 MPa is obtained. On the other hand, to obtain a steel plate with 550 to 650 MPa, annealing at a recrystallization start temperature of −20 to 1-50 (preferably to 1 to 40) It can be seen that it is preferable.

Moreover, since the component exceeds the range of the present invention in the comparative example (steel plate 14 etc.), the strength is high and the ductility is lowered. In the copper plate obtained according to the present invention, the recrystallization behavior changes depending on the amount of Nb and B added, so that the applicable annealing temperature can be changed. Also, the strength obtained can be changed by adding Nb and B. Therefore, the production method of the present invention can be annealed in the same cycle as other steel plates for cans, and can obtain a desired strength. . Industrial applicability

According to the present invention, a steel plate for cans having a tensile strength of 550 to 650 MPa and a total elongation of 5% or more is obtained. Even when the DR process and the recrystallization annealing process are omitted, when Nb and B are added, a tensile strength of 550 to 700 MPa and an elongation of 4% or more can be obtained.

As a result, by applying the manufacturing method of the present invention, a copper plate for high-strength cans can be manufactured and provided at a low cost without sacrificing corrosion resistance for cans that do not require small anisotropy. It becomes possible.

Furthermore, since the manufacturing method of the present invention is annealed in a low temperature region as compared with a normal method for manufacturing steel sheets for cans, it is possible to reduce energy costs. Also, by adding Nb and B, it is possible to anneal in the same temperature range as a normal steel plate for cans. In this case, there is no need to provide a separate annealing opportunity. As a result, it is possible to produce a steel sheet of T S 550 to 700 MPa class without hindering productivity. On the other hand, in the present invention, as shown in FIGS. 1 and 2, it is possible to perform annealing in a temperature range where the change in strength is small depending on the annealing temperature. Therefore, even if the annealing temperature varies, it is uniform in the width direction. A steel plate with an appropriate strength level can be obtained.

The steel plate for cans produced by the production method of the present invention is a container for canned beverages and food cans. Most suitable as steel plate for cans, mainly 2-piece DRD cans and 3-piece welded cans.

Claims

The scope of the claims

1. By mass%

C: 0.003% or less, N: 0.004% or less,

Mn: 0.05% to 0.5%, P: 0.02% or less,

Si: 0.02% or less, S: 0.03% or less,

A1: 0.1% or less

Containing the balance of iron and inevitable impurities,

A _Γ is hot-rolled at a finishing temperature above the 3 transformation point,

Cutting at a cutting temperature of 600-750,

Then, after performing cold rolling at a rolling reduction of 60-95%,

Annealing is performed at a temperature of (recrystallization start temperature 1 200) to (recrystallization start temperature 1 20).

A method for producing a steel plate for cans having a thickness of 0.18 mm or less.

2. The method for producing a steel plate for cans according to claim 1, wherein the steel further contains at least one of Nb: 0.001% to 0.05% and B: 0.0001% to 0.005% in mass%.