JPH08311613A - Steel sheet excellent in side wall breaking resistance and suitable for dtr can - Google Patents

Abstract

PURPOSE: To produce a steel sheet excellent in side wall breaking resistance and suitable for a DTR can by specifying the compsn. composed of C, Si, Mn, P, S, Al, N, O, Nb and Fe and forming its structure of ferritic phases and finely dispersed carbides. CONSTITUTION: This steel sheet has a componental compsn. contg., by weight, >0.02 to 0.1% C, >0.03% Si, 0.4 to 1.2% Mn, <=0.03% P, <=0.02%, preferably 0.015% S, 0.02 to 0.1% Sol. Al, <=0.007% N, <=0.005%, preferably 0.0025% Total- O, (3.0×10<-4> )/C<=Nb<=0.03%, 10C+Mn>=0.8%, S×O<=4.0×10<-5> , preferably 2.5×10<-5> , and the balance Fe with inevitable impurities and has a structure formed of ferritic phases and finely dispersed carbides, and in which microcracking is hardly generated even if being applied with thinning of about >=30%.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a DTR (Draw and Thin Red)
The present invention relates to a steel sheet for cans which is suitable for use in can manufacturing, and provides a steel sheet which is less likely to cause a side wall rupture phenomenon which becomes apparent during tension-added deep drawing of a can body performed in the can manufacturing process.

[0002]

2. Description of the Related Art Focusing on beverage cans and the like, from the viewpoints of weight reduction, process omission, material and manufacturing cost reduction, the shift from 3 piece cans to 2 piece cans and further reduction of the thickness of the can body are being promoted. . The mainstream of two-piece cans for beverages today is the deep drawing of circular blanks into cups (Draw).
After that, the can body is ironed by ironing 2-3 times to obtain a thin wall and obtain a predetermined can height DI (Draw an
d Ironing) molding method, but is generally limited to positive pressure can applications and is not used for negative pressure cans such as retort cans (coffee cans, tea cans) that hot-pack contents.

On the other hand, as a forming method which does not involve ironing, a DRD (Draw and ReDraw) forming method in which drawing is performed twice and a flange with a high wrinkle holding force applied to the flange portion during the second and subsequent drawing DTR (Draw and Draw and thin) to reduce the thickness of the can body by suppressing the flow from the wall to the side wall and applying tension deep drawing to positively apply tension to the side wall.
Thin Redraw) molding method has been put to practical use. The greatest advantage of these methods is that they do not undergo ironing, so the use of pre-coated steel sheets and laminated steel sheets enables the production of beverage cans not only with a simplified process but also with good design and design. That is the point.

In recent years, a technique for developing the above-mentioned DTR molding for use in beverage cans has been developed and is in the stage of practical application. For this application, tin-free steel (TFS), which generally has a temper degree from T5-CA to DR-9, is used.
After forming a cup from a steel sheet laminated with a polyester film (PET) as a raw material, two-stage tension-added deep drawing is performed. As a result, the thickness of the can side wall has been reduced by 20% or more, and the weight of the can has been reduced.In addition, by changing the steel plate thickness, the temper of the steel plate and the dome shape of the can bottom, positive pressure can, It is possible to fit both negative pressure cans. However, in the molding method, it is necessary to solve the following problems in designing the material. 1. Peeling of the laminated film by sliding with the shoulder of the die during tension drawing. 2. During tension drawing, the can wall portion is not constrained between the punch and the die and is subjected to tensile deformation in a free surface state, so that rough skin is likely to occur. 3. Since tension drawing is performed at a high speed, side wall rupture is likely to occur at the point of contact with the punch shoulder (shock line) at the time of forming each cup.

Regarding the problems 2 and 3 related to the design of the base steel plate among the above technical problems, some patented techniques have been disclosed in the past. For example, in Japanese Patent Laid-Open No. 4-314535, A technique is disclosed in which the crystal grain size is reduced to a predetermined size or less to suppress rough skin.

Particularly, regarding the side wall rupture resistance, JP-A-7-
No. 34192, JP-A-7-34193, and JP-A-7-34194 disclose techniques for improving workability, surface roughness, and corrosion resistance by defining the crystal grain size under a certain manufacturing method. . These technologies disclose that the solid solution C and N are reduced including the steel plate added with Nb, the occurrence of necking and the connection of voids are suppressed, and thereby the side wall fracture resistance is enhanced. The part that systematically becomes the starting point of the side wall fracture is not mentioned, and the side wall fracture cannot be fundamentally avoided.

Further, in Japanese Patent Laid-Open No. 5-247669, a steel sheet added with B for improving hardenability is rapidly cooled from a ferrite-austenite two-phase region during continuous annealing to transform a microstructure into a ferrite phase and a low temperature transformation. A technique is disclosed in which a two-phase structure of phases is obtained and a sufficiently high strength is obtained by cold pressure once. Further, Japanese Patent Application Laid-Open No. 4-337049 discloses a technique in which a steel sheet to which Nb is added has a microstructure having a two-phase structure including a ferrite phase and a low temperature transformation phase.

However, in such a two-phase structure, voids are apt to occur at the interface between the ferrite phase and the hard low temperature transformation phase due to the DTR processing, so that sufficient side wall fracture resistance cannot be obtained. .

[0009] Common to these techniques is to reduce the inclusions in the steel, which are the origins of the refinement of the structure and cracks, based on the metallographic principle.

However, a detailed study of the individual technologies shows that the absolute strength level required for the material, the essential mechanism of the sidewall breakage phenomenon, and the optimum mechanism against the problem of the can sidewall breakage during DTR molding. The ideal microstructure,
The optimum technique has not been disclosed for specific process conditions for obtaining the optimum microstructure. Therefore, 2
It is considered impossible to stably achieve a wall thickness reduction of more than 5% within the range of the conventional material design technology, and it is thought that ironing will have to be added after all.

[0011]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art with respect to steel sheets laminated with various resins and the like applied to DTR molding and steel sheets precoated with various paints. The purpose is to significantly improve breakability.

FIG. 8 and FIG. 9 are the results of scanning electron microscope (SEM) observation of the microstructure of the side wall of the beverage can DTR-molded by the conventional technique. The beverage can has the performance required as a beverage can such as film adhesion, corrosion resistance, surface properties such as rough skin, pressure resistance, side paneling strength and the like.

However, in terms of microstructure, many fine cracks are observed at the interface between MnS and the matrix or between the carbide and the matrix. When such a material is subjected to further intense deep drawing, it is expected that these minute cracks will cause the side walls to fracture.

The present invention provides a steel sheet which has no side wall breakage when the wall thickness is reduced to 20% or more and hardly causes such minute cracks even when the wall thickness is reduced to 30% or more.

[0015]

Means for Solving the Problems The subject matter of the present invention in order to achieve the above object is as follows.

(1) 0.02 <C ≦ 0.1%, Si <
0.03%, 0.4 ≦ Mn ≦ 1.2%, P ≦ 0.03%, S ≦ 0.02%,
0.02 ≦ Sol.Al ≦ 0.1%, N ≦ 0.007%, Total-O ≦ 0.005
%, (3.0 × 10 ^-4 ) /C≦Nb≦0.03%, 10C + Mn ≧ 0.8
%, S × O ≦ 4.0 × 10 ^−5, and the composition of the balance Fe and unavoidable impurities, and is composed of a structure consisting of a ferrite phase and finely dispersed carbides. Excellent DTR can compatible steel plate, (2) wt%, 0.02 <C ≦ 0.1%, Si <0.03%, 0.4 ≦
Mn ≦ 1.2%, P ≦ 0.03%, S ≦ 0.015%, 0.02 ≦ sol.Al ≦
0.1%, N ≦ 0.007%, (3.0 × 10 ^-4 ) /C≦Nb≦0.03%
, Total-O ≦ 0.0025%, 10C + Mn ≧ 0.8%, S × O ≦ 2.5
DT with excellent side wall rupture resistance, which has a composition of × 10 ^-5 and the balance Fe and unavoidable impurities, and is composed of a structure composed of a ferrite phase and finely dispersed carbide.
In the R-can-compatible steel plate and further the present invention, in addition to the above basic structural requirements, the following structural requirements are added in order to further improve the side wall fracture resistance during DTR molding. (3) In (1) and (2), the side wall rupture resistance is excellent, in which the length Lc of the cementite in the form of canopy, which forms the ferrite crystal grains, which constitutes the finely dispersed carbide, is 10 μm or less. It is a DTR can compatible steel plate.

[0017]

The basic concept that led to the present invention, the present invention constructed on the basis of the basic idea, and the reasons for limitation thereof will be described below.

First, the inventors of the present invention focused on the microstructure of the current DTR molded product shown in FIGS. 8 and 9, and the main causes of side wall rupture were steelmaking oxide nonmetallic inclusions and steel plates. The presence of MnS, AlN, and cementite (Fe ₃ C), which are precipitated by solid-state reaction during the manufacturing process, and the amount, size, and
It was clarified that it is a precipitation morphology such as distribution density.

That is, it has been found that it is extremely important to control the precipitation morphology of precipitates and optimize the microstructure itself of the steel sheet in order to achieve a higher level of wall thickness reduction than ever before. It was

That is, it was found that minute cracks are generated at the interface between those precipitates and the mother phase, and the generated minute cracks are easily propagated depending on the form of precipitation, which easily leads to sidewall fracture during DTR processing. It was

As an evaluation method, the inventors of the present invention accurately and quantitatively evaluate the significant difference between the materials with respect to the sidewall breakage resistance, which has been extremely vague and qualitatively evaluated by the conventional techniques. As a possible index, the critical thinning rate (еth) obtained by the high speed draw bead pull-out test method shown in FIG. 7 was used.

Eth = 100 (e ₀ −e) / e ₀ where e ₀ is the initial plate thickness and e is the plate thickness in the vicinity of the fracture surface.

A simulation test of DTR molding was also conducted in the laboratory. A circular blank is punched out, a cup is formed by ordinary drawing using a crank press, and a double-action high-speed hydraulic deep drawing tester is used to control the tool condition, wrinkle suppressing force, and forming temperature of this cup. 350cc
DTR molded into a 211 diameter size equivalent to a can.

FIG. 6 shows the relationship between the limit thinning rate eth obtained by the high speed draw bead test and the limit thinning rate Rth obtained by the DTR molding simulation test. As shown in the figure, it can be confirmed that the larger the eth is, the higher the critical thinning rate of the side wall of the can body and the excellent resistance to side wall rupture are. Еth is the side wall of the can body that can be DTR-molded without side wall rupture. It was confirmed that there was a positive correlation with the critical thinning rate of, and that the value of approximately (еth + 5%) and the critical thinning rate were in agreement.

Using this high-speed draw bead pull-out test method, specific constitutional requirements and limiting ranges were determined.

The steel sheet of the present invention has a microstructure of a substantially ferrite single-phase structure composed of a ferrite phase and finely dispersed carbide. This is because when a phase (martensite, bainite, etc.) other than carbides (pearlite or cementite) inevitably present in low carbon steel is intentionally generated, the interface between such hard second phase and ferrite matrix phase is This is because it becomes a starting point of minute cracks during DTR molding and further deteriorates side wall fracture resistance.

FIG. 1 shows the effect of Nb addition on the eth of TFS containing 0.07% C and adjusted to a temper degree equivalent to DR9, total.
This shows the effect of the amount of O. By reducing the total O amount, eth increases, and it can be seen that a decrease in the O amount is effective for increasing the thinning rate, but a decrease in the O amount alone results in 0.0025%.
Even if it is reduced to below, eth is about 20%.

On the other hand, the steel sheet added with 0.01% Nb has a larger eth than the conventional steel without Nb regardless of the O content, and the O content is 0.005% or less.
Is over 30%. Further, when the amount of O is reduced to 0.0025% or less, eth becomes 35% or more.

This is due to the fact that the ferrite crystal grain size of the TFS original plate was made finer by the addition of Nb, and the precipitation morphology of the carbide was changed, and the carbide was finely dispersed relatively uniformly. By adding Nb, the austenite grain size during hot rolling becomes finer, and the ferrite grain size after transformation, the cold pressure, and the ferrite grain size after annealing also become finer.

In the Nb-added steel sheet, a part of C precipitates as Nb carbide (NbC) of about 10 to 20 nm, which is extremely fine compared to iron carbide. Therefore, due to the synergistic effect with the ferrite grain refinement effect, iron carbide The size is reduced, the distribution density is increased, and the average precipitation interval is made uniform. It is considered that these effects improve the side wall fracture resistance.

On the other hand, in the conventional steel sheet containing no Nb, C precipitates as cementite and a part of pearlite in grain boundaries and grains. Since such iron carbide is relatively large and has a size of the submicron or micron order, the interface between the carbide and the matrix phase is likely to be a starting point of cracking, which causes many microcracks during DTR forming, causing side wall rupture. Becomes

Al ₂ O ₃ is mainly used, and MnO
Oxide inclusions including CaO, CaO, and SiO ₂ are the starting points of cracking, so the smaller the number, the better the workability. totalO
The dramatic increase in eth due to the addition of Nb accompanying the reduction in the amount is
This is because the oxide inclusions decreased and the influence of the carbide on eth became relatively large, and the effect of refining the carbide by the addition of Nb became remarkable. That is, in order to maximize the Nb addition effect, O
Reducing the amount is extremely important.

Next, the influence of the total O amount and S amount on eth was examined. DR9 containing 0.06 to 0.09% C, 0.008 to 0.015% Nb and different total O and S contents
The result of measuring the eth of TFS adjusted to a corresponding degree of temper is shown in FIG. By reducing the total O amount and S amount, et
Although h is improved, when the O content is relatively high and exceeds 0.005%, sufficient eth is not obtained even if S is reduced to about 0.005%.

As is clear from the figure, total O ≦ 0.005
%, S ≦ 0.02%, S × O ≦ 4.0 × 10 ^-5 % eth
≧ 30%, total O ≦ 0.0025%, S ≦ 0.01
In the case of 5% and S × O ≦ 2.5 × 10 ⁻⁵ %, eth ≧ 35% is obtained, and the side wall fracture resistance is remarkably improved. That is, by simultaneously reducing O and S, it is possible to obtain excellent side wall fracture resistance.

This is because the amount of MnS, which is the starting point for the generation of minute cracks, was decreased as described above. However, when the oxide-based inclusions are relatively large, the oxide can be the starting point for cracking. Even if S is reduced, the effect is not fully exerted. However, when the amount of oxide inclusions is small and the total amount of O is low, the effect of MnS becomes relatively large, so that the effect of reducing MnS, which can be the starting point of microcracking due to S reduction, becomes remarkable. That is, it is important to reduce the amount of O in order to maximize the effect of improving the side wall fracture resistance by reducing S.

Next, the reasons for limiting the scope of the claims of the present invention will be described. Nb: Nb is an extremely important element in the present invention, and is added in order to reduce the grain size of the ferrite structure, reduce the iron carbide that is the starting point of cracking, and increase the strength of the steel sheet. Fine Nb
In order to precipitate carbides and fully exert these effects, it is important to add more than the necessary minimum amount of Nb determined according to the amount of C. FIG. 3 shows the relationship between the C amount, the Nb amount and eth.

The relationship between Nb and C content is 3.0 × 10 ^-4 /
By adding C or more, the above effects are exhibited and a high eth can be obtained. Therefore, the lower limit of the addition amount is set.
Set to 3.0 × 10 ^-4 / C (%). On the other hand, even if the addition exceeds 0.03%, the above effect is saturated and no remarkable improvement in properties can be expected, so the upper limit is specified as 0.03%.

O: As described above, the oxide-based inclusions in the steel are the starting points for cracking during DTR forming, and thus significantly impair the side wall rupture resistance. In the present invention, in order to improve the side wall rupture resistance, Nb is added to finely disperse the carbide and the S amount is also reduced, but as shown in FIGS. 1 and 2, the total O amount is 50 ppm or less. By doing so, these effects can be sufficiently exerted.

Therefore, in the present invention, the total O amount in steel is 50 p
Limited to pm or less. Further, in the relationship with the S amount described above, as an upper limit at which eth ≧ 30% can be stably obtained, S × O
It is limited to ^≤4.0 × 10 ^-5 %. Also, total O ≦ 0.0025
% And S × O ≦ 2.5 × 10 ⁻⁵ %, the effects of the present invention can be maximized and even better side wall rupture resistance can be obtained.

S: S is an extremely important element in the present invention. S exists in steel as MnS, and expanded MnS is DTR.
It tends to be the starting point of cracks that lead to side wall fracture during molding. Therefore, it is desirable that S is as small as possible, and it is limited to 0.02% or less. Furthermore, by limiting the relationship between the S content and the O content in steel within a specific range, it becomes possible to obtain good side wall rupture resistance.

In the present invention, as shown in FIG.
With the above-mentioned O amount, eth ≧ 30% is stably obtained as the upper limit, total O ≦ 0.005%, S ≦ 0.02%, S × O ≦
Limited to 4.0 x 10 ^-5 %. Furthermore, total O ≦ 0.0025
%, S ≦ 0.015%, and S × O ≦ 2.5 × 10 ⁻⁵ %, it is possible to obtain even better resistance to fast wall breakage.

C: C is an extremely important element for ensuring the strength level required for a DTR can-compatible steel sheet. In the present invention, the steel plate is reinforced with C, Mn and fine Nb carbide in order to secure the can strength required for the DTR can. When C is 0.02% or less, it becomes difficult to obtain the required strength even if Mn and Nb are added. Therefore, in the present invention, it is essential that the content of C exceeds 0.02%.

However, part of C precipitates as pearlite or cementite in the ferrite grain boundaries or in the grains during annealing, so that the interface between these iron carbides and the matrix is likely to be the origin of cracking, and is shown in FIG. As described above, it causes many microcracks during DTR molding. In the present invention, in order to mitigate these adverse effects of iron carbide, Nb addition is essential, and part of C is precipitated as fine Nb carbide at higher temperature before the iron carbide is formed.

Further, the sidewall rupture resistance can be further improved by controlling the precipitation morphology of carbides other than fine Nb carbides, that is, cementite. On the other hand, if the C content exceeds 0.1%, sidewall breakage starting from pearlite will become apparent even if Nb is added, so the C content is limited to 0.1% or less.

Si: Si is a substitutional solid solution element and has a strengthening ability, but in the present invention, Si is used for the following reasons.
Is not added aggressively. Si is an element that remains in the steel as an impurity component and embrittles the steel sheet even when intentional addition is not carried out, and when used as a TFS base steel sheet, it is against the electrodeposition of metallic Cr. However, since it has a bad effect, it is desirable that the content is small. Further, when added in a large amount, SiO ₂ inclusions may remain in the steel, degrading the side wall fracture resistance.

Therefore, in the present invention, in order to avoid these adverse effects, the content thereof is limited to less than 0.03%. Furthermore, in order to improve the local ductility of the steel sheet and to obtain even more excellent side wall fracture resistance, the Si content of the impurity component
It is preferable to regulate the content of the above to 0.01% or less.

Mn: Mn prevents hot cracking of cast slabs and cast plates (slabs, etc.) by precipitating S in steel as MnS, and at the time of overaging after continuous annealing, MnS
It plays a role of promoting the precipitation of fine cementite in the grains centered on. In the present invention, since the addition of Nb is essential, part of C is precipitated as Nb carbide, but the remaining C becomes iron carbide, so the above-mentioned action of MnS is important. Furthermore, Mn
As a solid solution strengthening element, plays a role of supplementing the strengthening by C and the strengthening by Nb carbide.

In the present invention, the lower limit for precipitating and fixing S and obtaining the strength of the can body required for a DTR can is 0.4%.
It is essential to add Mn so that 10C + Mn is 0.8% or more in relation to the C content.

On the other hand, addition of a large amount of Mn is effective for increasing the strength of the material, but on the other hand, the solubility product of MnS increases, so that not only a relatively large MnS is formed in the slab stage, but also hot rolling is performed. Sometimes it promotes the formation of a band structure and C in steel
Promote microscopic non-uniform distribution of. These are all DTR
Mn is a factor that deteriorates the side wall fracture resistance during molding.
The upper limit of 1.2%.

P: P is also a substitutional solid solution element like Si and is an element which has a greater strengthening ability than Si and is effective for increasing the strength of the steel sheet. Since it is also an element that segregates and embrittles the grain boundaries, it is preferable that the content thereof be as small as possible from the viewpoint of side wall fracture resistance.

Therefore, the upper limit at which the adverse effect on the practical side wall fracture resistance can be avoided is limited to 0.03% or less.
Further, in order to obtain even more excellent side wall rupture resistance, it is effective to reduce the content thereof to less than 0.01%.

Sol.Al: sol.Al precipitates N in the steel as AlN to reduce the adverse effect of solid solution N, which lowers the local ductility of the steel sheet by dynamic strain aging. In addition, fine AlN is effective for refining ferrite grains, and M
Similar to nS, it acts as a nucleus for intragrain precipitation of fine cementite during the overaging process of continuous annealing, and therefore also effectively acts on the fine dispersion of carbides.

However, a large amount of Al is added to increase the amount of sol.Al.
When Al is added, fine Al ₂ O ₃ inclusions are likely to remain, which causes sidewall breakage. Therefore, in the present invention, the lower limit is 0.02% in order to exert the above effect.
In addition, the upper limit is set to 0.1% as a limit for practically adding more to deteriorate the sidewall rupture resistance.

N: N has a function of making ferrite grains finer and becoming a precipitation site of fine cementite by finely dispersing it as AlN. However, in order to exert such an action, it is not necessary to particularly positively add it, and the range contained in ordinary steel is sufficient. Excessive addition of N makes it easier for solid solution N to remain even if Al is added, causing a decrease in local ductility and a deterioration in side wall fracture resistance. Therefore, N is limited to 70 ppm or less.

However, in the present invention, since the addition of Nb is indispensable, the ferrite grains can be made finer by Nb carbide and the carbide can be made finer, so that the above-mentioned action by AlN is not positively utilized. However, the object of the present invention can be achieved. Therefore, in order to completely avoid the adverse effect caused by the residual solid solution N and to further improve the sidewall rupture resistance, it is effective to set N to 30 ppm or less.

In the present invention, the steel having the above composition is used, and its microstructure is made to be a substantially ferrite single-phase structure composed of a ferrite phase and finely dispersed carbide. This intentionally includes low-temperature transformation-generated phases (martensite, bainite, etc.) other than Nb carbide (NbC), which is inevitably present in low carbon steel and is precipitated by positive addition of iron carbide (pearlite or cementite) and Nb. This is because, in the case of being generated, the interface between the hard second phase and the ferrite mother phase becomes a starting point of minute cracks during DTR forming, and deteriorates the side wall rupture resistance.

Since the steel sheet of the present invention contains Nb,
Compared with the conventional steel sheet without additives, precipitation strengthening is achieved by fine dispersion of Nb carbide, and ferrite grain is made finer,
The refinement of carbides and the reduction of iron carbides are achieved, and the side wall fracture resistance is improved.

However, not all of C is precipitated as Nb carbide, but a part thereof is precipitated as iron carbide.
As described above, Nb carbide is extremely fine and does not become the starting point of cracking during DTR processing, but iron carbide can be the starting point of cracking. Therefore, the sidewall rupture resistance can be further improved by controlling the precipitation form of the iron carbide.

No precipitation of Nb carbide in the hot rolling stage
After the coiling, C aggregates at the crystal grain boundaries of the hot rolled steel sheet and partially precipitates as pearlite. These carbides are crushed by cold rolling and, after recrystallization annealing, temper rolling or DR rolling, form a dense cluster of fine cementite that crosses the ferrite grain boundaries and continues into the grains of adjacent crystal grains. Existing. Further, a part of 0.02% or less of C dissolves in the ferrite during the recrystallization annealing, and precipitates as cementite in the ferrite grain boundaries and in the grains during the cooling process after the annealing.
The precipitation morphology of these cementites is schematically shown in FIG.

Of these, a dense cluster of fine cementite which crosses the ferrite crystal grain boundaries and continues into the grains of the adjacent crystal grains is most likely to be the starting point of cracking, and therefore the length Lc in the rolling direction thereof is (The definition of Lc is not limited to the rolling direction, but the length in the rolling direction is usually the largest.) It is effective to further improve the side wall fracture resistance.

FIG. 4 is a graph showing the relationship between Lc and eth of a steel sheet containing 0.012% Nb and adjusted to a temper degree equivalent to DR9. From the figure, it is understood that by setting Lc to 10 μm or less, eth is further improved and stable and good side wall rupture resistance can be obtained.

Therefore, the effect of the present invention is maximized,
As a condition for obtaining extremely good sidewall rupture resistance, the length Lc in the rolling direction of a dense cluster of fine cementite that crosses the ferrite grain boundaries and continues into the grains of adjacent crystal grains is specified to be 10 μm or less. To do. It is preferable that the average inter-particle distance MFP of the fine cementite precipitated in the ferrite crystal grains is 2 μm or less.

Next, a general method for manufacturing the steel sheet of the present invention will be described. After melting in a converter, it is continuously cast into a slab with a normal thickness of about 200 to 280 mm or a thin slab with a thickness of about 30 mm, and then hot rolled. For continuous casting, slab light pressure casting is preferred because it reduces the semi-macro and macro segregation of P and S in steel.

The slab heating temperature, finishing temperature and winding temperature are
The temperature ranges of 1100 to 1250 ° C, 800 to 890 ° C, and 500 to 700 ° C can be set, respectively, but from the viewpoint of uniform MnS miniaturization, high temperature heating of the slab at 1150 ° C or higher causes a reduction in the structure of the hot rolled sheet. From the viewpoint of granulation, low-temperature finishing at 870 ° C or lower is desirable, and from the viewpoint of fine dispersion of pearlite, medium / low-temperature winding at 640 ° C or lower is desirable.

After the hot rolled steel sheet was pickled and cold rolled,
Perform recrystallization annealing. Recrystallization annealing can be either continuous annealing or box annealing, and in the case of continuous annealing, it can be manufactured without overaging treatment, but from the viewpoint of precipitation morphology control of iron carbide, It is desirable to add.
As the overaging treatment, any method of in-line overaging treatment in a continuous annealing furnace (CAL-OA) and batch overaging treatment by box annealing after continuous annealing (CAL-BAF) may be used.

The overaging treatment reduces the residual solid solution C which deteriorates the local ductility of the steel sheet by dynamic strain aging, and finely disperses the cementite in the crystal grains.
In the case of A, the holding time is 300 to 400 ° C for 20 seconds or more, CAL-B
Also in the case of AF, it is effective to carry out in the temperature range of 400 ° C or lower.

The annealed steel plate is finished to a predetermined plate thickness by temper rolling or DR rolling, and then subjected to various surface treatments such as tin plating, ultra-thin tin plating, tin-nickel plating, nickel plating, and chromium plating. It

In particular, when these surface-treated steel sheets are used as base steel sheets for film-laminated steel sheets and pre-coated steel sheets, electrolytic chromic acid-treated steel sheet having a two-layer structure of metallic chromium in the lower layer and hydrated chromium oxide in the upper layer, that is, TFS.
However, it is most desirable from the viewpoint of processing adhesion. These surface-treated steel sheets are applied to DTR can applications as steel sheets alone, as film-laminated steel sheets laminated with a resin film such as polyester, or as pre-coated steel sheets coated with a paint such as epoxy.

The steel sheet of the present invention disclosed above is a so-called DTR for performing deep drawing while applying tension regardless of whether the can forming process is the Wet process or the Dry process.
This is a technology that can be applied to all steel sheets used in the can manufacturing method.

After the DTR processing, further ironing (Ir
It can also be applied when thinning is performed by carrying out oning).

The effects of the present invention will be more specifically described below with reference to examples.

[0072]

【Example】

Example 1 After smelting steel in a converter, slabs were formed by light pressure continuous casting.
After heating these slabs to 1200 ° C, a hot rolled steel sheet having a finishing temperature of 850 ° C and a winding temperature of 620 ° C and a plate thickness of 1.8 mm was prepared. After pickling, 0.
After cold rolling to 235 mm, recrystallization annealing was performed by continuous annealing and box annealing. In continuous annealing, no aging treatment, CAL
Inside CAL-OA and CAL-BAF by continuous annealing after box annealing furnace
These three conditions were carried out.

The annealed steel sheet was DR-rolled at a reduction rate of 23.4% to have a thickness of 0.180 mm, and then subjected to electrolytic chromic acid treatment in a tin-free plating line to obtain TFS.

The chemical compositions of these steel sheets are shown in Table 1. PET films were laminated on both surfaces of these TFSs in a laboratory, and the critical thinning rate eth and Rth were evaluated by a high speed draw bead test and a DTR simulation test. Furthermore, the can bottom pressure resistance of the DTR molded sample was evaluated using a buckling tester.

The evaluation results are shown in Table 2 together with the annealing conditions.
The steel sheet of the present invention has a higher eth and Rth than the comparative steel sheet
It can be seen that it has TR formability and sufficient pressure resistance.

[0076]

[Table 1]

[0077]

[Table 2]

Example 2 After smelting in a converter, a slab was formed by continuous casting under light pressure, and 1200 ° C.
After heating, the finishing temperature is 840 ℃, the winding temperature is 600 ℃, and the plate thickness is 1.8mm.
Of hot rolled steel sheet. 0.235mm after pickling these hot rolled steel sheets
Cold-rolled and continuously annealed at a soaking temperature of 700 ° C. No overaging treatment was applied.

After that, 0.230 mm was finished by temper rolling, a TFS / PET laminated steel plate was prepared under the same conditions as in Example 1, and subjected to a high speed draw bead test. The target steel plates are steel plates A to M in Table 1.

The results obtained are shown in Table 3. Even when the SR material only temper-rolled is finished to a plate thickness suitable for negative pressure can applications,
Excellent DTR conformity of the steel sheet of the present invention is recognized.

[0081]

[Table 3]

Example 3 After smelting in a converter, a slab was formed by continuous casting under light pressure, and the temperature was 1200 ° C.
After heating to 840 ℃, finish temperature 840 ℃, coiling temperature 600 ℃, thickness 1.6mm
Of hot rolled steel sheet. 0.185mm after pickling these hot rolled steel sheets
Cold-rolled to 70 ° C and continuously annealed at a soaking temperature of 700 ° C and an overaging temperature of 350 ° C. Then, it was temper rolled to a finish of 0180 mm, and made into a TFS / PET laminated steel sheet under the same conditions as in Example 1 and subjected to a high speed draw bead test. The target steel plates are steel plates A to M in Table 1.

The obtained results are shown in Table 4. Even if the SR material only temper-rolled is finished to a plate thickness suitable for positive pressure can applications,
Excellent DTR conformity of the steel sheet of the present invention is recognized.

[0084]

[Table 4]

Example 4 After smelting in a converter, continuous casting under light pressure to form a slab at 1200 ° C.
After heating, the finishing temperature was set to 840 ° C, and the sheets were wound at various temperatures from 520 to 600 ° C to obtain hot-rolled steel sheets having a plate thickness of 1.8 mm. After pickling these hot-rolled steel sheets, cold-roll them down to 0.220 mm, soaking temperature 700
℃ and overaging temperature 350 ℃ continuous annealing. afterwards,
Finished to 0180 mm by temper rolling, under the same conditions as in Example 1
TFS and PET laminated steel sheets were used and subjected to a high speed draw bead test. The target steel plates are steel plates A to M in Table 1.

The results obtained are shown in Table 5. Rolling direction length Lc of a dense cluster of fine cementite, which crosses the ferrite grain boundary and is connected to the inside of adjacent crystal grains, is 10 μm
It can be seen that, in the case of the following, even better DTR moldability is exhibited.

[0087]

[Table 5]

Example 5 After smelting in a converter, a thin slab with a thickness of 30 mm was formed, and after light heating, a hot rolled steel sheet with a finishing temperature of 840 ° C. and a winding temperature of 560 ° C. and a thickness of 1.6 mm was obtained. These hot-rolled steel sheets were pickled, cold-rolled to 0.220 mm, and continuously annealed at a soaking temperature of 700 ° C and an overaging temperature of 350 ° C. Then, it was finished by temper rolling to 0175 mm, and made into a TFS / PET laminated steel sheet under the same conditions as in Example 1, and subjected to a high speed draw bead test.

The target steel plates are steel plates A to M in Table 1. The obtained results are shown in Table 6. The excellent DTR conformity of the steel sheet of the present invention is recognized even when manufactured using a thin slab.

[0090]

[Table 6]

Example 6 After smelting in a converter, a thin slab having a thickness of 30 mm was prepared, lightly heated, and then a hot rolled steel sheet having a finishing temperature of 800 ° C. and a winding temperature of 600 ° C. and a plate thickness of 1.0 mm. These hot-rolled steel sheets were pickled, cold-rolled to 0.185 mm, and continuously annealed at a soaking temperature of 720 ° C and an overaging temperature of 350 ° C.

After that, temper rolling is applied to finish to 0180 mm,
Under the same conditions as in Example 1, a TFS / PET laminated steel sheet was used and subjected to a high speed draw bead test.

The target steel plates are steel plates A to M in Table 1. The results obtained are shown in Table 7. The excellent DTR conformity of the steel sheet of the present invention is recognized even when the thin steel slab is used to produce SR material.

[0094]

[Table 7]

[0095]

EFFECTS OF THE INVENTION According to the steel sheet of the present invention, it becomes possible to manufacture a DTR can having a higher side wall thickness reduction rate than before without causing side wall breakage, and it is possible to reduce the weight of the DTR can body. .

[Brief description of drawings]

FIG. 1 Effect of Nb addition in steel sheet on eth, total O
It is a figure which shows the influence of quantity.

FIG. 2 is a diagram showing an influence of total O amount and S amount in a steel sheet on eth.

FIG. 3 is a diagram showing an influence of C amount and Nb amount in a steel sheet on eth.

FIG. 4 is a diagram showing the influence of Lc on eth.

FIG. 5 is a schematic diagram showing a precipitation form of cementite.

FIG. 6 is a diagram showing a relationship between a limit thinning rate eth obtained by a high speed draw bead test and a limit thinning rate Rth obtained by a DTR simulation test.

FIG. 7 is a diagram showing a high speed draw bead test method.

FIG. 8 is a drawing-substituting photograph of a cross-sectional microstructure showing a cross-sectional state of a crack in a side wall of a can after DTR molding. (MnS
It is a figure which also shows correspondence of a crack. )

FIG. 9 is a drawing-substituting photograph of a cross-sectional microstructure showing a state of a cross section of a crack in a side wall of a can after DTR molding. (It is also a diagram showing correspondence between cementite and cracks.)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukio Kawase 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (72) Hideki Nishihara 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Date Main Steel Pipe Co., Ltd.

Claims (3)

[Claims] 1. By weight%, 0.02 <C ≦ 0.1%, Si <0.03
%, 0.4 ≦ Mn ≦ 1.2%, P ≦ 0.03%, S ≦ 0.02%, 0.02
≦ Sol.Al ≦ 0.1%, N ≦ 0.007%, Total-O ≦ 0.005%,
(3.0 × 10 ^-4 ) /C≦Nb≦0.03%, 10C + Mn ≧ 0.8%, S
DTR with excellent side wall rupture resistance characterized by having a composition of a ferrite phase and finely dispersed carbide, with a composition of xO ≤ 4.0 x 10 ^-5 and the balance Fe and unavoidable impurities. Can-compatible steel plate. 2. In% by weight, 0.02 <C ≦ 0.1%, Si <0.03
%, 0.4 ≦ Mn ≦ 1.2%, P ≦ 0.03%, S ≦ 0.015%, 0.02 ≦
sol.Al ≦ 0.1%, N ≦ 0.007%, (3.0 × 10 ^-4 ) / C ≦ N
b ≦ 0.03%, Total-O ≦ 0.0025%, 10C + Mn ≧ 0.8%, S
DTR with excellent sidewall rupture resistance, characterized by having a composition of a ferrite phase and finely dispersed carbide, with a composition of xO ≤ 2.5 x 10 ^-5 and the balance Fe and unavoidable impurities. Can-compatible steel plate. 3. The sidewall rupture resistance according to claim 1 or 2, wherein the length Lc of the canopy-like cementite having the ferrite crystal grains forming the finely dispersed carbide is 10 μm or less. Excellent DTR can compatible steel plate.