JP2001089828A - Steel sheet for can, good in surface property and suitable for three piece can - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a steel sheet for a three piece can small in rust, almost free from deterioration in deformability caused by inclusions and precipitates, also free from surface defects caused by clusterlike inclusions, good in surface properties and excellent in formability in the weld zone. SOLUTION: This steel sheet for a three piece can good in surface properties is composed of extra low carbon steel and has a composition containing, by weight, 0.015 to 0.10% Ti, 0.001 to 0.01% Al, <=0.02% N and one or two kinds of Ca and REM by 0.0005 to 0.01% in total, in which the contents of S and one or two kinds of Ca and REM satisfy the relation in the following inequality of S-5×((32/40) Ca+(32/140) REM)<=0.0014 wt.%, and the balance Fe with inevitable impurities, in which, also, oxide inclusions with the grain size of 1 to 50 μm contain Ti oxide and one or two kinds of CaO oxide and REM oxide, tensile strength is controlled to <540 MPa, and the (r) value of the stock is controlled to <=1.0 in the L or C direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel plate for a can (having a surface coating such as plating) which is particularly suitable for use in a three-piece can having good surface properties and which is not easily rusted.

[0002]

2. Description of the Related Art A steel plate for a three-piece can is required to be soft and easy to make at the time of can-making, while a sufficient strength of the can after the can-making is required for various external loads. Is done. Further, it is important that the three-piece can has good flange formability at the welded portion, and if the components and the manufacturing method are inappropriate, insufficient tightening may occur due to a failure in the flange formation. Improving the stretch flangeability of such welds is important as a property of a steel plate used for a three-piece can.

Regarding the improvement of formability of a steel sheet including a weld,
As disclosed in JP-A-63-192849.
A method for lowering the melting point of inclusions by controlling the composition of the inclusion
In steel as disclosed in Japanese Unexamined Patent Publication No. Hei.
A method to control the precipitation of TiN and MnS by adjusting the dissolved oxygen
Which have been proposed. However, long rolling in the rolling process
Due to the presence of MnS and oxides in steel
It is still difficult to obtain sufficient deformability
Met. Also disclosed in JP-A-5-9549.
In the method, the inclusion is CaO-Al _TwoO_ThreeBecome a system, rust
There is a problem that it becomes a starting point and the corrosion resistance is deteriorated.

[0004]

SUMMARY OF THE INVENTION The present invention has been developed as a result of experiments, investigations, and studies in order to solve the above-mentioned problems of the prior art, and has low rust, inclusions and precipitates. It is an object of the present invention to propose a steel sheet for cans which is hardly deteriorated in deformability due to deformation and has no surface defects due to cluster-like inclusions, and has excellent expressiveness and is suitable for three-pieces having excellent formability of a welded portion.

[0005]

Means for Solving the Problems The inventors of the present invention have made intensive studies to achieve the above object, and as a result, controlling the composition of oxides and sulfides remaining in steel has solved these problems. I came to realize that this is an important factor to solve.
That is, by controlling the composition of these inclusions in an appropriate range, and more preferably, by optimizing the production process of these steel sheets, it is difficult to rust as a final product, the surface properties are good, and welding is performed. It has been found that a steel plate for a can suitable for a three-piece can having a good formability of a part can be obtained.

That is, the oxide-based inclusions in the steel are controlled, the formation of giant cluster-like inclusions is suppressed, and fine dispersion into inclusions having a size of 50 μm or less is achieved.
By reducing the amount of MnS and making all oxides and sulfides in steel finer and non-ductile, the required can-making properties as a three-piece can and the workability of the weld as a weld can It has been found that an extremely thin (thickness of 0.3 mm or less) steel sheet having excellent resistance can be obtained. The present invention is based on the above findings.

That is, the present invention relates to: C: more than 0.005 wt% and 0.10 wt% or less, Si: 0.2 wt% or less, Mn: 0.05 to 1.0 wt%, P: 0.04 wt% or less, Ti: 0.015 to 0.10 wt% , Al: 0.001 to 0.01 wt%, N: 0.02 wt% or less and one or two of Ca and REM in total
0.0005 to 0.01 wt%, and the content of one or two of S and Ca, REM is expressed by the following formula: S−5 × ((32/40) Ca + (32/140) REM) ≦ 0.0014 wt% The balance satisfies the relationship and the remainder has the composition of Fe and unavoidable impurities, and the oxide-based inclusions having a particle size of 1 to 50 μm are composed of Ti oxide and
Contains one or two CaO and REM oxides, and has a tensile strength
Good surface texture, with a recrystallization texture of less than 540 MPa and an r value in at least one of the rolling direction and the direction perpendicular to the rolling direction (a direction at 90 ° to the rolling direction on the sheet surface) of 0.1 or less. A steel plate for cans suitable for piece cans. Further, the present invention provides: C: more than 0.005 wt% and 0.10 wt% or less, Si: 0.2 wt% or less, Mn: 0.05 to 1.0 wt%, P: 0.04 wt% or less, Ti: 0.015 to 0.10 wt%, Al: 0.001 to 0.01 wt%, N: 0.02 wt% or less and one or two of Ca and REM in total
0.0005 to 0.01 wt%, Ni: 0.005 to 1.0 wt%, Cr: 0.005 to 1.0 wt%, Nb: 0.002 to 0.04 wt%, B: 0.0002 to 0.005 wt% And S, Ca, REM
When the content of one or two types satisfies the relationship of S-5 × ((32/40) Ca + (32/140) REM) ≤ 0.0014 wt%, the balance is Fe and inevitable impurities, Oxide-based inclusions with a particle size of 1 to 50 μm
Contains one or two CaO and REM oxides, and has a tensile strength
A can steel sheet suitable for a three-piece can having good surface properties, having a recrystallization texture of less than 540 MPa and an r value of at least one of a rolling direction and a direction perpendicular to the rolling corresponding to 1.0 or less. In the present invention, the oxide-based inclusion having a particle size of 1 to 50 μm is composed of Ti oxide: 20 wt% to 90 wt%, CaO, REM
Total of one or two oxides: 10 wt% or more and 40 wt% or less,
Al ₂ O ₃ : preferably 40% or less (one or two of Ti oxide, CaO and REM oxide, and the total of Al ₂ O ₃ is 100% or less), and the particle size is 15 μm or less It is more preferable that the fine particles have uniform and fine crystal grains.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described more specifically. In the present invention, Al is 0.001 wt% or more and 0.01 wt% or less, Ti is 0.015 wt% or more, and Ca and / or REM is
By satisfying the condition of 0.0005 wt% or more and 0.01 wt% or less, a steel sheet with less rust is obtained. At this time, the inclusions are Ti ₂ O ₃ -CaO
(And / or REN oxide system) When it is an oxide of —Al ₂ O ₃ —SiO ₂ and the Ca concentration in the inclusions is 40 wt% or less, it does not become a starting point of rust. If the amount of Al exceeds 0.01 wt%, the inclusions become Al ₂ O ₃ —CaO-based (and / or REN oxide-based), so the Ca concentration in the inclusions becomes about 50% and becomes the starting point of rust. Degrades corrosion resistance. In order to improve the plastic deformability of the steel sheet including the welded parts, 1) do not coarsen oxides in the steel, 2) do not coarsen sulfides in the steel, and 3) refine the crystal structure This is very important.

[0009] Regarding the prevention of the oxide coarsening of 1), the Al content is 0.001 wt% or more and 0.01 wt% or less, and the Ti content is 0.015 wt% or less.
It can be achieved by satisfying the condition that the content of Ca and / or REM is 0.0005 wt% or more and 0.01 wt% or less.
In order to prevent the sulfide from coarsening in 2), it is important to suppress MnS precipitated during solidification. This is because the presence of MnS extends during hot rolling and promotes cracking of the final product during can making. For this solution, it is necessary to fix (detoxify) S in the steel with Ca and / or REM which forms more stable sulfide. Specifically, S and
Regarding the content of one or two types of Ca and REM, the following formula: S-5 x ((32/40) Ca + (32/140) REM) ≤ 0.0014 wt% (where S is the S content (wt%) , Ca is the amount of Ca (wt%), RE
M indicates the amount of REM (wt%). ). That is, in order to fix S by forming CaS or REM sulfide, the larger the amount of Ca or REM added, the better. However, the lower limit is 0.0014 wt% or less as the amount of unfixed S as shown by the above inequality. It was obtained from the experimental result that it was necessary to be.

Regarding the refinement of the crystal structure of the above 3), 15
By using fine crystal grains of μm or less, a remarkable effect of improving stretch flangeability was confirmed in both the welded portion and the non-welded portion. It is also important not to increase the crystal grain size of the welded part. For this purpose, the inclusions must be fine, that is, to prevent the inclusions from coarsening as described in 1) and 2) above. is important. As a result of various studies based on the above experimental results, the inventors have arrived at the present invention.

Next, the reason why the composition range of the steel sheet for cans of the present invention is limited will be described. C: more than 0.005 wt% and 0.10 wt% or less; C is one of the important additive components in the present invention. By increasing the amount of C, the strength of the steel sheet as-annealed can be determined. When the C content is 0.005 wt% or less, the crystal grains become too coarse, and the risk of causing a skin roughening phenomenon when applied for cans increases. However, when the amount of C is increased and the amount of addition exceeds 0.10 wt%, the amount of pearlite in the ferrite / pearlite structure is increased, and in addition to deterioration of both hot rolling property and cold rolling property, The corrosion resistance is significantly reduced, which is not preferable for use as a steel sheet for cans. Therefore, the C content exceeds 0.005 wt% and 0.10 wt%
The following is assumed. The C content has a direct effect on the increase in the hardness of the welded portion, and the higher the C content, the higher the hardness of the welded portion and, as a result, the lower the formability of the welded portion.
In order to ensure better weld formability, the content is more preferably not more than 0.07 wt%. Also, regarding the lower limit,
From the viewpoint of ensuring the stability of the product material, it is desirable that the content be 0.010 wt% or more.

Si: 0.2 wt% or less (excluding 0); Si
Is a component necessary for deoxidation at the time of smelting, but as the amount of addition increases, the steel is solid-solution strengthened, and any of hot deformation resistance, cold deformation resistance, and deformation resistance in secondary cold rolling after annealing Is also undesirably increased. Although the detailed mechanism is unknown, when used as a steel sheet for cans, the corrosion resistance is significantly reduced. From the above, the upper limit of the added amount of Si was set to 0.2 wt%. The preferred lower limit is not particularly limited, but the
0.002wt% in view of the increase in cost required for

Mn: 0.05 to 1.0 wt%; Mn is effective for deoxidation during melting, like Si. It also has the effect of suppressing hot brittleness of steel. In order to exhibit these desirable effects, it is desirable to add approximately 0.05 wt% or more. on the other hand,
The present invention relates to a steel sheet which is subjected to cylindrical forming, flange forming, and the like for a three-piece can, and in particular, improvement in stretch flangeability is desired. Here, if the Mn content is 1.0 wt% or less, the decrease in stretch flangeability due to its content is small. Therefore, the upper limit of Mn was 1.0 wt%.
0.7 wt% or less is more desirable.

P: not more than 0.04 wt%; P has the effect of strengthening the steel, and is a component that is desirable to be added when obtaining a high-strength steel sheet. However, P has a strong tendency to segregate, and the corrosion resistance of the surface is low. There are specific problems such as a tendency to decrease and a decrease in the strength of the joint interface of the welded portion. The amount of P added
If it is 0.04 wt% or less, such a problem does not occur. Although the lower limit is not particularly defined, about 0.005 wt% is considered to be a level that can be reduced without significantly increasing the production cost.

Ti: 0.015 to 0.10 wt%; Ti is an important component in the present invention, and fine oxide inclusions having a size of 50 μm or less are formed by Ti deoxidation, and grain growth during cold rolling and annealing. By controlling the properties, the crystal grains can be refined and the strength-elongation balance can be improved. Furthermore, the fine oxide of Ti can suppress the coarsening of the structure of the welded part (particularly, the heat-affected zone), thereby improving the formability of the welded part.
If the amount of Ti is less than 0.015 wt%, the desired effect cannot be obtained because the effect of addition, that is, the amount of the fine oxide is too small. However, if the added amount of Ti exceeds 0.10 wt%, the hot rolling property, the cold rolling property, and the secondary cold rolling property after annealing are significantly reduced, and the properties of the product surface are also significantly reduced. Therefore, Ti is set in the range of 0.015 to 0.10 wt%. In order to secure more excellent surface properties, it is more preferable that the content be 0.05 wt% or less. The addition of Ti is also an important element in controlling the r value of the steel sheet described later.

Al: 0.001 to 0.01% by weight; Al is an important component in the present invention. If the amount exceeds 0.01% by weight, deoxidation becomes Al deoxidization and a large amount of Al ₂ O ₃ clusters are formed. In addition, since the amount of fine oxides of 50 μm or less that can control the grain growth during cold rolling and annealing is reduced while deteriorating the surface properties, the risk of problems such as rough skin during can making increases. In addition, the effect of improving the surface properties is not exhibited. Therefore, the content is limited to 0.01 wt% or less. More importantly, since the composition of inclusions and Al amount is large is Al ₂ O ₃ -CaO and / or Al ₂ O _3-REM oxide, such inclusions become a starting point of rust, degrade the corrosion resistance In steel plates for cans, the important corrosion resistance tends to decrease. From this point, the upper limit of Al is set to 0.01 wt%. On the other hand, the lower limit of Al is 0.00% from the viewpoint of degassing and stabilizing the operation of continuous casting.
1 wt%.

N: 0.02 wt% or less (excluding 0); N
Contributes as a solid solution strengthening component, and when applied to extremely severe plastic working as in the present invention, it leads to a decrease in ductility. Therefore, it is desirable to reduce as much as possible. Considering the amount of ductility degradation accompanying an increase in the N content, the upper limit was made 0.02 wt%. The preferred lower limit is not particularly limited, but is 0.001 wt% in consideration of an increase in manufacturing cost for preventing nitrification and a change in mechanical properties. The preferred upper limit is 0.005 wt%, more preferably 0.003 wt% or less.

One or two types of Ca and REM are added in a total amount of 0.0005 to
0.01 wt%; Ca and metal REM (refer to rare earth elements such as La and Ce) are important components in the present invention.
It is necessary to add at least 0.0005 wt% of one or two types of REM. That is, after Ti deoxidation, 0.0005wt
% Or more of Ca and REM are added so that the oxide composition in the molten steel is changed to Ti oxide: 20 wt%.
90 wt% or less, preferably 85 wt% or less, CaO and / or REM oxide: 5 wt% to 40 wt%, Al ₂ O ₃ 40 wt%
The following low melting point oxide-based inclusions are used. Then, at the time of continuous casting, it is possible to effectively prevent the Ti oxide containing the metal from adhering to the nozzle, and to prevent the nozzle from being blocked. Further, CaO and / or REM oxide can contribute to suppressing grain growth after cold rolling and annealing and preventing the welded portion (particularly the heat affected zone) from becoming coarse. For these reasons, one or two of Ca and REM should be contained in a total of 0.0005 wt% or more. On the other hand, if the total amount of Ca and REM exceeds 0.01 wt%, the risk of surface defects increases, and the disadvantage of reduced corrosion resistance, which is important for steel sheets for cans, becomes apparent. The upper limit is 0.
Limited to 01 wt%.

(S−5 × ((32/40) Ca + (32/140) REM)
≦ 0.0014 wt%) S is a harmful component to the workability of steel, so it is desirable to reduce it as much as possible. However, excessive desulfurization treatment causes an increase in cost. Therefore, the upper limit is set to 0.01 wt% in consideration of the cost required for desulfurization treatment and the effect of improving mechanical properties by desulfurization. A more preferred upper limit is 0.005 wt%. In addition, S can exist as various sulfides in steel, but when present as MnS-based inclusions, it remarkably expands in the rolling direction during hot rolling, so that it can be used during can forming of a final product. Promote cracking. In this regard, by adding Ca and REM, the form and non-ductility of the sulfide are improved, and the formability of the processed portion including the welded portion, which is the main focus of the present invention, is significantly improved. According to the inventors' research, the addition of Ca and REM
For unknown reasons, the atomic ratio of S is about 5 times that of these elements.
Is considered to be harmless sulfide. Therefore,
Harmful S content, ie S-5 × ((32/40) Ca + (32/140)
If the value of (REM) is sufficiently small, the workability does not decrease due to sulfide. From the investigation, it was found that there was no problem if the amount of harmful S was 0.0014 wt% or less.

(O: 0.010 wt% or less) O is a necessary component from the viewpoint of forming a fine oxide,
%, A large amount of coarse Al ₂ O ₃ is generated, and the ductility during processing and the deep drawability are reduced.
The upper limit was 0 wt%. Further, a preferable upper limit is 0.007 wt.
%, More preferably 0.005 wt% or less.

Ni: 0.005 to 1.0 wt%: Cr: 0.005 to 1.0
wt%; Ni and Cr are used during the can-making process, which is the target of the present invention, by making the structure finer without solid solution strengthening the steel sheet or by facilitating deformation in low temperature and high strain rate environments. Of the stretch flange characteristics can be improved. In addition, since each component has an effect of reducing the transformation point of steel, it is also effective in relaxing the regulation condition of the hot finishing temperature. Therefore, in the present invention, if necessary, one or more of Ni and Cu
Two types can be added. 0.00 for both Ni and Cr
A remarkable effect is exhibited by addition of 5 wt% or more, and this effect is not offset even when added in combination. However, the effect tends to be saturated even if added in excess of 1.0 wt%, so the upper limit was set to 1.0 wt% in each case. From the viewpoint of stabilizing the material, the range of 0.01 to 0.5 wt% is more preferable.

Nb: 0.002 to 0.04 wt%; Nb is extremely effective in refining the crystal grains of the steel sheet. Therefore, in the present invention, Nb can be added as needed. By refining the crystal grains, the present invention particularly exerts a remarkable effect on the prevention of surface roughness after forming and the improvement of ductility in relation to the three-piece steel plate for the present invention. Nb exerts a remarkable effect when added at about 0.002 wt% or more. However, even if Nb is added in excess of 0.04 wt%, the effect tends to be saturated, and conversely, there is a possibility that a problem of significantly increasing the hot and cold deformation resistance of the steel may occur. -0.04 wt%. From the viewpoint of stabilizing the material, 0.01 to 0.025 wt% is more preferable.

B: 0.0002 to 0.005 wt%; The addition of B effectively contributes to the refinement of the structure of the steel sheet, like Nb. To achieve this desired effect, it is almost 0.
It is necessary to add 0002 wt% or more. However, 0.005 wt%
If the addition exceeds the above range, the effect is saturated and the hot deformation resistance of the steel is significantly increased. From the above, 0.00
The range was from 02 to 0.005 wt%.

In a steel satisfying the above composition ranges, oxide inclusions having a particle size of 1 to 50 μm contain Ti oxide and Ca
It is particularly important in the present invention that the inclusions contain one or two of O 2 and REM oxides. Inclusions as such deoxidation products include Ti oxide and CaO, REM oxide.
One containing one or two, more specifically, Ti oxide-CaO and / or REM oxide-Al ₂ O _3- SiO ₂ oxide-based inclusions, less rust, Cans expected in this invention, with little deterioration of deformability due to inclusions and precipitates, no surface defects due to cluster-like inclusions, and no adhesion of Ti oxide containing metal to the nozzle Steel sheet.

The reason why the oxide inclusions specified in the present invention are limited to those having a particle diameter of 1 to 50 μm is that inclusions in such a range can be regarded as inclusions formed by deoxidation. Inclusions having a particle size of more than 50 μm are generally caused mainly by exogenous inclusions such as slag or mold powder. Some Al ₂ O ₃ clusters are larger than this, but if the oxide composition of inclusions with a particle size of 50 μm or less satisfies the above requirements, a large Al ₂ O ₃ cluster can be sufficient. It can be considered that it is decreasing. The content of such inclusions is set to 80% by weight or more. The reason is that if the content is less than 80 wt%, the control of inclusions is insufficient, which may cause a surface defect of the coil or a nozzle clogging.

The above-mentioned oxide-based inclusions having a particle size of 1 to 50 μm
Composition: Ti oxide: 20 wt% or more and 90 wt% or less, CaO, REM
Total of one or two oxides: 10 wt% or more and 40 wt% or less,
Al_TwoO _Three: 40% or less (one of Ti oxide, CaO, REM oxide
Or 2 types, Al_TwoO_ThreeIs less than 100%)
More preferred.

If the content of Ti oxides in the inclusions is less than 20% by weight, Ti deoxidized steel is used instead of Ti deoxidized steel, and nozzle clogging occurs because the Al ₂ O ₃ concentration increases. Also, CaO, R
As the EM oxide concentration increases, the rusting property becomes remarkable.
The oxide concentration is set to 20% wt% or less. On the other hand, if the Ti oxide concentration exceeds 90 wt%, the proportion of CaO and REM oxides decreases, and nozzle clogging rather occurs. Therefore, the Ti oxide concentration is set to 20 wt% or more and 90 wt% or less. More preferably, the content is 30 wt% or more and 80 wt% or less.

The CaO and REM oxides in the inclusions
If the total of one or two kinds is less than 10% by weight, the inclusion does not have a low melting point and causes the nozzle to be blocked as described above. On the other hand, if it exceeds 40% by weight, the inclusions subsequently absorb S and change to water-soluble, and become the starting point of rust, so that the corrosion resistance decreases. In addition, a more preferable range is 20 to 40 wt%.

Further, regarding Al ₂ O ₃ in the above inclusions,
If it exceeds 40% by weight, the composition will have a high melting point and not only will the nozzle be clogged, but also the inclusions will be clustered and defects of non-metallic inclusions on the product plate will increase. When Al is hardly contained in steel, the concentration of Al ₂ O _{3 in} inclusions is almost negligible.

The oxide-based inclusions may contain oxides other than those listed above. In such a case, the amount of the oxides other than those listed above is particularly limited. but not, for SiO ₂ is less than 30wt%, MnO
Is preferably controlled to 15 wt% or less. The reason for this is that if they exceed the respective amounts, they cannot be said to be the titanium-killed steels targeted in the present invention.Under such a composition, there is no nozzle clogging without Ca addition, and there is no problem of rusting. It is because it disappears. Moreover, in order to include SiO ₂ and MnO in the inclusions, the Si and Mn concentrations of the molten steel are set to Mn / Ti> 100 and Si /
It is preferable to set Ti> 50, but in this case, hardening of the steel and deterioration of the surface properties are caused.

The steel sheet of the present invention has a tensile strength of less than 540 MPa. When the tensile strength (TS) is 540 MPa or more, the difference in strength between the base metal and the welded portion (heat affected zone) increases, and work deformation concentrates on the welded portion, leading to defects during processing. This is because the shape freezing property also deteriorates due to an increase in yield strength accompanying an increase in strength. 400M in terms of can body strength
It is desirable to set it to Pa or more. Note that TS is controlled to a target value mainly by controlling the content of the strengthening element (Mn, Si, P, etc.) and the rolling reduction of skin pass rolling or secondary cold rolling performed after annealing.

Control of the texture of the steel sheet is also important as a material for a three-piece can. When a can is made, the material corresponding to the circumferential direction of the can body (without secondary rolling after recrystallization annealing) has a texture with an r value of 1.0 or less. It is important to prevent the occurrence of defects such as wrinkles during molding. Therefore, in a normal so-called normal grain can (a can body circumferential direction corresponding to the L direction of a steel sheet), the L direction (rolling direction) of the steel sheet is the reverse grain can (the circumferential direction of the can body is the C direction of the steel sheet). ), The r value in the C direction (direction perpendicular to the rolling direction) of the steel sheet is important. As a result of conducting various can-making experiments, it is clear that when the r-value of the material in the direction corresponding to the circumferential direction of the can body exceeds 1.0, wrinkle defects and shape defects are likely to occur during neck-in molding. Based on that. Like this, L
Alternatively, it has become clear that the Ti-Ca-added steel of the present invention is suitable for producing a steel sheet having a reduced r value in the C direction. The r value is measured by a so-called tensile method, but in the case of secondary cold rolling after annealing in the production stage of a product, necking easily occurs due to reduced ductility. 20% strain cannot be applied within the range of uniform elongation. As a result of various investigations, if the r-value measured in the as-annealed state or in the state in which a few percent of the skin pass is applied does not exceed 1.0, the secondary cold-rolled material similarly causes a problem during neck-in forming. I knew it wasn't. In other words, it is important that the r value not exceed 1.0 in a state where the recrystallized texture is sufficiently maintained (as annealed or in a light skin pass state) in order to prevent the occurrence of problems during neck-in molding. In addition, in order to obtain a texture equivalent to an r value of 1.0% or less in the material, in addition to the addition of Ti-Ca, the primary cold rolling is performed under a high pressure and annealing is performed at a low temperature in the L and C directions. In both cases, it is preferable to decrease the r value (although Δr slightly increases to the negative side). The thickness of the steel sheet of the present invention is desirably 0.3 mm or less, at which the advantage of thinning can be obtained.

When the steel sheet of the present invention has a structure composed of uniform and fine crystal grains having a crystal grain size of 15 μm or less, even in an ultra-thin steel sheet, poor appearance due to surface roughness after forming and elongation due to the poor appearance are caused. Problems such as reduction can be avoided. Therefore, it is preferable to have a structure composed of uniform and fine crystal grains having a crystal grain size of 15 μm or less, and it is more preferable that the grain size be 12 μm or less. In addition,
Uniform means that it is not a so-called mixed grain structure including coarse grains, and such a uniform and fine structure is obtained by adjusting the steel composition and hot rolling conditions (slab heating temperature, finishing temperature, etc. described later). Obtainable.

Next, the method for producing steel according to the present invention will be described. In the present invention, Ti as an adjusting component is
The reason for setting i: 0.015 wt% or more is that if Ti is less than 0.015 wt%, the deoxidizing ability is weak, the total oxygen concentration in the molten steel increases, and the material properties such as elongation and drawing are deteriorated.
In this case, it is conceivable to increase the deoxidizing power by increasing the concentrations of Si and Mn. However, if Ti is less than 0.015 wt%, SiO ₂ or MnO
Inclusion inclusions are generated in large quantities, causing hardening of the steel material and deterioration of the plating property. To prevent this, (wt% Mn) / (wt% Ti) <10
It is necessary to contain Ti so as to be 0. In that case, the Ti oxide concentration in the inclusion becomes 20% or more.

In manufacturing the titanium-killed steel sheet according to the present invention, first, molten steel is deoxidized with a Ti-containing alloy such as FeTi to generate an oxide-based inclusion mainly composed of Ti oxide in the steel. The inclusions are not in the form of giant clusters as in the case of deoxidation with Al, but are mostly in the form of grains or fractures having a size of about 1 to 50 μm. However, at this time, Al
If the concentration exceeds 0.010 wt%, huge Al ₂ O ₃ clusters are formed. Such Al ₂ O ₃ clusters cannot be reduced even if the Ti concentration is increased by adding a Ti alloy, and remain as cluster-like inclusions in the steel. Therefore, regarding the steel sheet according to the present invention, during the manufacturing stage,
Preferably, a Ti oxide is formed.

Under the present invention, the yield of Ti alloy is lower than that of the conventional method of deoxidizing with Al, and
Alloys for adjusting the composition of inclusions are expensive because they contain Ca and REM. From this, the addition of such alloys to molten steel
It is economically preferable that the amount of inclusions be controlled so as to be as small as possible within the controllable range. In this sense, prior to the addition of a deoxidizing agent such as a Ti-containing alloy, it is desirable to carry out preliminary deoxidation in order to reduce dissolved oxygen in the molten steel and FeO and MnO in the slab. This preliminary deoxidation is preferably carried out by deoxidation with a small amount of Al such that the content of Al in the molten steel after deoxidation becomes 0.010 wt% or less, and addition of Si, FeSi, Mn, or FeMn.

As described above, Ti produced by Ti deoxidation
A steel sheet in which ₂ O ₃ contains 70% or more of Ti oxide-based inclusions means that such inclusions are dispersed in the steel in a size of about 2 to 20 μm, and thus, surface defects due to cluster-like inclusions are generated. Is gone. However, Ti oxide is in a solid phase state in molten steel, and ultra-low carbon steel has a high solidification temperature. May trigger.

Therefore, in the steel sheet according to the present invention, the Ti alloy
After deoxidation, so that it becomes more than 0.0005wt%
Add one or two of Ca and REM and add
Oxide inclusions with a particle size of 1 to 50 μm
% To 90% by weight, preferably 85% by weight or less, CaO and / or
Or REM oxide: 5 wt% or more and 40 wt% or less, Al_TwoO_ThreeIs 40wt
% Or less of low melting point oxide-based inclusions. Do so
Effectively prevents Ti oxides containing ingots from adhering to the nozzle.
It becomes possible to stop. More preferred inclusion composition
Is Ti oxide: 30 wt% or more and 80 wt% or less, CaO, REM oxidation
Things (La_TwoO_Three, Ce_TwoO _ThreeEtc.): 10 wt% or more and 40 wt% or less, Al
_TwoO_Three : 20 wt% or less, others (SiO_Two, MnO, etc.): 10 wt% or less
Below. The measurement of the composition of such oxide-based inclusions is based on EPMA
Or using a scanning electron microscope with EDX function
By performing quantitative analysis on each inclusion
You. All of the inclusions in the steel analyzed in this way are
It is most desirable to satisfy the above composition
However, in practice, the number of inclusions with a size of 1 to 50 μm
If 50% or more is within the above composition range, this
The various properties of the hot-rolled steel sheet aimed at in the light are achieved. In addition,
As the particle diameter, the maximum diameter of each particle is used.

In the present invention, when the composition of the formed inclusions is controlled as described above, it is possible to completely prevent oxides and the like from adhering to the inner surfaces of the tundish nozzle and the immersion nozzle of the mold during continuous casting. . Therefore, it is not necessary to blow a gas such as Ar or N ₂ into the tundish or the immersion nozzle for preventing adhesion of oxides or the like. As a result, it is possible to obtain an effect that it is possible to prevent powdery defects of the cast slab due to powder entrainment during continuous casting and bubble-like defects due to the blown gas from being generated in the cast slab.

In the hot rolling step after continuous casting, the slab heating temperature is preferably 900 to 1300 ° C. 900
If the slab heating temperature is lower than 0 ° C., the load applied during rolling becomes excessively high, causing operational problems. On the other hand, at a high temperature exceeding 1300 ° C., the crystal grain size before rolling becomes too large, so that the hot-rolled mother plate does not become fine. Therefore, the slab heating temperature is preferably 900 to 1300 ° C. Above all, a slab heating temperature of 1200 ° C. or less is preferable from the viewpoint of deep drawability. Also, continuous casting-direct rolling (CC-DR) or DHCR (direct hot charge rolling) in which a continuously cast slab is inserted into a heating furnace with a hot piece is preferable from the viewpoint of energy saving.

The hot rolling end temperature is preferably 650 to 960 ° C. At temperatures lower than 650 ° C, the load during rolling of the steel sheet increases remarkably, and the
It becomes uneven in both the width direction and the longitudinal direction,
As a result, the variation of the material at each of these positions becomes remarkable. At a temperature higher than 960 ° C., the risk of scale flaws on the steel sheet surface becomes extremely large, and the crystal grain size increases. The hot rolling end temperature is also important in controlling the texture of the steel sheet, and is preferably within the above temperature range. Further, the coil winding temperature after hot rolling, the higher the temperature, the more advantageous for the coarsening of precipitates, but if too high, the scale becomes too thick, and problems such as an increase in the crystal grain size occur. 400-750 ° C is preferred.

After hot rolling, pickling is performed, cold rolling is performed, and then annealing is performed. In the pickling, the scale layer on the surface is removed with ordinary hydrochloric acid or sulfuric acid. Particularly in the case of a steel sheet having a thin scale phase, the pickling step can be omitted. In the cold rolling, it is preferable that the reduction ratio of the (primary) cold rolling of the ultra-thin steel sheet targeted for the steel sheet of the present invention be 80% or more in order to obtain a uniform material. In order to obtain a texture equivalent to an r value of 1.0 or less, the preferable rolling reduction is 90%.
That is all.

As the annealing, any of continuous annealing and batch annealing can be applied, however, continuous annealing is recommended from the viewpoint of the efficiency of the annealing operation and the uniformity of the material. Annealing must be performed at a temperature higher than the recrystallization temperature. At a temperature lower than the recrystallization temperature, partial recrystallization occurs, and it is extremely difficult to obtain a steel sheet shape that satisfies the specifications after secondary cold rolling after annealing. In order to obtain desired fine grains and recrystallized texture, it is particularly preferable that the annealing temperature is in the range of 680 to 780 ° C.

In the secondary cold rolling after annealing, the rolling reduction is adjusted to obtain a target hardness. About 40% or less is recommended from the viewpoint of material stability. When the secondary cold rolling is added in excess of 40%, particularly the heat-affected zone of the welded portion is significantly softened, and the risk of cracking when the welded portion is flanged is significantly increased. Absent. A preferred secondary cold rolling reduction is about 1% to 15%.

[0045]

[Example] (Example 1) After tapping the converter, molten steel of 300 ton was used.
Decarburized by RH degassing equipment, C = 0.014 wt%, Si = 0.
01wt%, Mn = 0.25wt%, P = 0.010wt%, S = 0.005 ~
Adjust the molten steel temperature to 1585 ~ 1615
Adjusted to ° C. Al was added to the molten steel in an amount of 0.2 to 0.8 kg / ton, and preliminarily deoxidized for 3 to 4 minutes to lower the dissolved oxygen concentration in the molten steel to 55 to 260 ppm. Al in molten steel at this time
The concentration was between 0.001 and 0.005 wt%. Then, 0.8 to 1.8 kg / ton of 70 wt% Ti-Fe alloy is added to
The Ti was deoxidized for 9 minutes. After adjusting the composition, the molten steel contained 30wt% Ca-60wt% Si alloy and metal
Ca, Fe, additive mixed with 5-15 wt% REM, or 90
The treatment was performed by adding 0.05 to 0.5 kg / ton of Fe-coated wire of Ca alloy such as wt% Ca-5 wt% Ni alloy and REM alloy. After this treatment, the Ti concentration is 0.026 to 0.058 wt%, and the Al concentration is 0.00
1 to 0.005 wt%, Ca concentration is 0.0000 to 0.0036 wt%, REM concentration is 0.0000 to 0.0021 wt%, and the sum of Ca and REM concentrations is 0.00
It was from 0.05 to 0.0043 wt%.

Next, the steel was cast by a two-strand slab continuous casting apparatus to produce a continuously cast slab. During casting, Ar gas was not blown into the tundish and the immersion nozzle. Observation after continuous casting showed that there was almost no deposit in the tundish and in the immersion nozzle.

Next, the continuous cast slab was hot-rolled to a thickness of 1.8 mm. The hot rolling conditions were as follows: slab heating temperature: 1130 ° C, finish rolling temperature: 890 ° C, hot rolling winding temperature: 620 ° C. The hot-rolled steel sheet was pickled and cold-rolled to obtain a cold-rolled sheet having a thickness of 0.18 mm.
Thereafter, short-time annealing was performed in a continuous annealing type at 740 ° C. for 20 s, and an evaluation test for flange cracking and an investigation of rust generation were performed. Table 1 shows the results of investigations on the steel composition and flange cracking properties. Note that the size of the oxide-based inclusions at this time was mostly 50 μm or less in width. The breakdown of oxides is as follows: Ti ₂ O ₃ : 60 to 70%, CaO + REM oxide: 20 to 70%
30%, Al ₂ O ₃ : 15% or less. Non-metallic inclusion defects such as barbs, slivers, scales and the like were found in the cold-rolled sheet only in an amount of 0.00 to 0.02 / 1000 m-coil or less.

[0048]

[Table 1]

On the other hand, for comparison, 300 to
n is decarburized by RH vacuum degasser, and C = 0.01
4 wt%, Si = 0.01 wt%, Mn = 0.25 wt%, P = 0.010 wt
%, S = 0.002wt%, and the molten steel temperature was adjusted to 15%.
The temperature was adjusted to 90 ° C. 1.2-1.6kg / ton of Al in this molten steel
It was added and deoxidized. The Al concentration in the molten steel after the deoxidation treatment was 0.041 wt% (Al killed steel). Thereafter, FeTi was added and the components were adjusted. After this process
The Ti concentration was 0.040 wt%.

Next, the molten steel was cast by a two-strand slab continuous casting apparatus to produce a continuously cast slab. Incidentally, in this case, the average composition of inclusions in the tundish molten steel, a cluster-like inclusions of _{95~98wt% Al 2 O 3, 5} % or less of Ti ₂ O ₃ was mainly.

When Ar gas was not blown into the tundish and the immersion nozzle during casting, Al ₂ O ₃ was remarkably adhered to the nozzle, and the opening of the sliding nozzle was significantly increased at the third charge. Casting was stopped. In addition, even when Ar gas was blown, a large amount of Al ₂ O ₃ adhered to the nozzle, and at the eighth charge, the level of the molten metal in the mold became large, and the casting was stopped.

Next, the continuous casting slab is heated at a slab heating temperature:
1150 ° C, Finish rolling temperature: 890 ° C, Winding temperature: 680 ° C
Hot rolled to 1.8 mm, pickled and cold rolled to a thickness of 0.18
mm cold-rolled sheet. After that, short-time annealing was performed in a continuous annealing mold at 750 ° C for 20 s soaking to investigate inclusions, formability investigation test (stretch flange crack generation test), and rust generation investigation. Non-metallic inclusion defects such as barbs, slivers and scales were found in the cold rolled steel sheet at 0.45 / 1000 m-coil.

The results of the flange crack test of the obtained cold-rolled sheet are shown in Table 1 in relation to S-5 × ((32/40) Ca + (32/140) REM). Here, Comparative Examples 1 to 6 are steels produced by the method according to the present invention except for the relationship between S, Ca and REM, and Comparative Example 7 is an Al-killed steel melted for comparison.

From Table 1, it can be seen that the smelting by the method of the present invention
A steel sheet having 5 × ((32/40) Ca + (32/140) REM) of 0.0014 wt% or less exhibited excellent stretch flange properties. The rust generation rate of the steel sheet (after left at 0 ° C. and a humidity of 95% for 10 hours) was a value that had no problem in both the invention steel and the comparative steel.

(Example 2) Including the components shown in Table 2,
The remainder is made of steel substantially made of iron in a converter, and the steel slab is subjected to hot rolling, cold rolling, continuous annealing, and secondary cold rolling under the conditions shown in Table 3 to obtain a final finished plate thickness. Was set to 0.16 mm. And 25 on the halogen type electroplating line
The tin plating equivalent to the number was continuously applied to finish the tinplate.
For comparison, similar tin plating was applied to conventional steel finished to the same plate thickness, and subjected to various evaluations thereafter.

[0056]

[Table 2]

[0057]

[Table 3]

The tin-plated steel sheet thus obtained was examined for hardness HR30T, corrosion resistance test, and occurrence rate of neck wrinkling and flange cracking as evaluations after can-making. Table 4 shows the results. The corrosion resistance test was performed using a 5% NaCl aqueous solution, and salt water was continuously sprayed on the weld repair coating using a salt water spray tester. The rust generation area was measured 20 days later. ○ within, × over 20%
Those having less than -20% were evaluated as ◎, and are shown in Table 4. In addition, the investigation of the neck wrinkle occurrence rate was carried out by using a normal grain method (a method of forming a cylinder to form a cylinder so that the rolling direction is the circumferential direction of the can) and a reverse grain method (a direction perpendicular to the rolling direction was determined by a can making machine). A can body having the same diameter as that of a commercially available 190 g can was formed by a plate cutting method of forming a cylinder so as to be in the circumferential direction of the cylinder, and then a one-stage neck was formed by a (mouth drawing machine) in a laboratory. Evaluate the occurrence of neck wrinkles by visual inspection, and investigate the rate of occurrence of flange cracking.After trimming the open end, insert a truncated cone-shaped punch into the open end, and compare it with the actual can flange processing. A test was performed to increase the diameter of the opening end up to the processing rate, and the cracking rate at that time was evaluated.

As can be seen from Table 4, the inventive steel did not have any flange cracks, regardless of the normal grain method or the reverse grain method, as compared with the conventional steel.
Also, no neck wrinkles occurred. Corrosion resistance was also superior to conventional steel. The composition of the oxide-based inclusions in Table 4 was measured for inclusions having a particle size of 1 to 50 μm, and the average value was obtained (without weighting according to the size of the inclusions). In the sample having the composition range of the present invention, 50% or more of the number of inclusions was Ti
Oxide: 20 wt% or more and 90 wt% or less, one of CaO and REM oxides
Species or the sum of two: 10 wt% or more and 40 wt% or less, Al ₂ O ₃ : 40
%.

[0060]

[Table 4]

[0061]

The steel sheet of the present invention is manufactured by
Extremely stable continuous casting is possible without causing clogging of the immersion nozzle at the time of continuous casting, there is little rust, there is almost no deterioration of deformability due to inclusions and precipitates, and cluster-like inclusions Excellent weldability with no surface defects and good appearance properties.
Excellent as a steel plate for piece cans.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yuji Miki 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Inside the Technical Research Institute of Kawasaki Steel (72) Inventor Makoto Aratani 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki (72) Inventor Hideo Kukuminato 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Chiba Works

Claims (4)

[Claims] 1. C: more than 0.005 wt% to 0.10 wt% or less, Si: 0.2 wt% or less, Mn: 0.05 to 1.0 wt%, P: 0.04 wt% or less, Ti: 0.015 to 0.10 wt%, Al: 0.001 ~ 0.01wt%, N: 0.02wt% or less and one or two of Ca and REM in total
0.0005 to 0.01 wt%, and the content of one or two of S and Ca, REM is expressed by the following formula: S−5 × ((32/40) Ca + (32/140) REM) ≦ 0.0014 wt% The balance satisfies the relationship and the remainder has the composition of Fe and unavoidable impurities, and the oxide-based inclusions having a particle size of 1 to 50 μm are composed of Ti oxide and
Contains one or two CaO and REM oxides, and has a tensile strength
A steel sheet for cans having a good surface texture, which is less than 540 MPa and whose recrystallization texture has an r value of 1.0 or less in at least one of the rolling direction and the direction perpendicular to the rolling direction. 2. C: more than 0.005 wt% and 0.10 wt% or less, Si: 0.2 wt% or less, Mn: 0.05 to 1.0 wt%, P: 0.04 wt% or less, Ti: 0.015 to 0.10 wt%, Al: 0.001 ~ 0.01wt%, N: 0.02wt% or less and one or two of Ca and REM in total
0.0005 to 0.01 wt%, Ni: 0.005 to 1.0 wt%, Cr: 0.005 to 1.0 wt%, Nb: 0.002 to 0.04 wt%, B: 0.0002 to 0.005 wt% And
Further, the content of one or two of S and Ca, REM satisfies the following equation: S−5 × ((32/40) Ca + (32/140) REM) ≦ 0.0014 wt%, and the balance is Fe and The composition of unavoidable impurities causes oxide-based inclusions with a particle size of 1 to 50 μm to contain Ti oxides and
Contains one or two CaO and REM oxides, and has a tensile strength
A steel sheet for cans having a good surface texture, which is less than 540 MPa and whose recrystallization texture has an r value of 1.0 or less in at least one of the rolling direction and the direction perpendicular to the rolling direction. 3. An oxide-based inclusion having a particle size of 1 to 50 μm is made of Ti acid.
Compound: 20wt% or more and 90wt% or less, one of CaO and REM oxides
Or the sum of two types: 10 wt% or more and 40 wt% or less, Al _TwoO_Three： 40%
The following (one or two of Ti oxide, CaO, REM oxide, Al
_TwoO_ThreeIs less than 100%)
Item 3 or 2 suitable for three-piece cans with good surface properties
Steel plate for cans. 4. The steel sheet for cans suitable for a three-piece can having good surface properties according to claim 1, comprising crystal grains having a particle size of 15 μm or less.