JPH11222647A - Original sheet for surface treated steel sheet excellent in aging resistance and small in generating rate of earing and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an extremely thin steel sheet excellent in deep drawability and aging resistance, free from the generation of surface roughness and stretcher strains after can-making, low in the generating rate of earing after can-making and suitable as the original sheet of a surface treated steel sheet for a deep drawn can. SOLUTION: A steel stock contg., by weight, <0.02% C, 0.4 to 1.0% Mn, 0.01 to 0.1% Al, <=0.0050% N and 0.0010 to 0.0050% B is subjected to hot rolling at the Ar3 transformation point or above and is coiled at 700 to 650 deg.C. Then, it is subjected to primary cold rolling at 80 to 88% draft, is thereafter subjected to continuous annealing of holding in a short time at the recrystallization temp. to 720 deg.C and is subjected to secondary cold rolling at 1.0 to 8% draft to regulate the average grain size to <=6 μm, the index of aging property, i.e., AI value to <=40 MPa, the (r) value to >1.0, and Δr showing the face anisotropy of the (r) value to ±0.1.

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 deep-drawing cans suitable for use in two-piece cans such as food cans and beverage cans, and more particularly, as a base plate for cans that is coated with a polyester resin and can be processed. It relates to a suitable ultra-thin steel sheet.

[0002]

2. Description of the Related Art In a two-piece can, a DRD (Draw & Redra) is used.
w) As in cans and DWI (Draw & Wall Ironing) cans, an organic paint is applied after molding to protect the contents of the can. However, recently, a can-making method of forming a film using a film-laminated steel sheet having a resin film coated on its surface in advance has attracted attention. As an example of a film-laminated steel sheet, for example, JP-A-2-269647 discloses a steel sheet in which a tin-free steel sheet is used as an original sheet and the original sheet is coated with biaxially stretched polyethylene terephthalate.

[0003] This canning method in which an original plate is coated with a film in advance to make a can eliminates the need for lubricating oil, which has conventionally been required for deep drawing or deep drawing / ironing.
The subsequent step of cleaning the lubricating oil can be omitted, and the omission of the cleaning step eliminates the discharge of cleaning wastewater. Conventionally, the inside of the can and the baking treatment, which have been conventionally performed to protect the contents of the can, are not required, and therefore, the emission of carbon dioxide gas generated during the baking treatment is eliminated. Such contributions can be expected in terms of global environmental protection.

However, the manufacturing cost of cans using a film-laminated steel sheet is generally higher than that of conventional DRD cans and DWI cans. Therefore, there is a demand for a thinner material for cost reduction. Properties required for thinner two-piece cans are: (i) High r-value and excellent deep drawability.

(Ii) Δr is close to 0, and the ear incidence after molding is low. (iii) The crystal grains are fine and no roughening occurs after molding. (iv) It has excellent aging resistance and does not generate stretcher strain after molding. Is mentioned.

It is well known that the ear incidence is correlated with Δr (= (r _L + r _C -2 r _D ) / 2) which indicates the in-plane anisotropy of the r value of the original plate. Is closer to 0, ears are less generated and the material yield is improved. In addition, the coarser the crystal grains are, the more easily the surface becomes rough after molding.
No. 35 discloses a method of adjusting the crystal grain size of an original plate to 5 μm or less and the surface roughness Ra to 0.5 μm or less as a method for preventing roughening after molding. However,
According to the technique described in Japanese Patent Application Laid-Open No. 4-314535, the C content is increased to 0.1 to 0.2% in order to achieve the refinement of crystal grains, and since Mn and P are added, the steel sheet becomes harder. ,
When the r value is about 1.1, there is a problem that the deep drawability is deteriorated and the formability is inferior.

[0007]

If the amount of carbon is extremely reduced and softened, the formability such as r value is improved, but in ultra-low carbon steel sheets with extremely reduced amount of C, the crystal grains are refined. Is difficult to do. In order to achieve both softening and crystal grain refinement, it is conceivable to use low-carbon steel with a slightly increased C content as a material. However, even in low-carbon steel, annealing is performed to suppress the coarsening of crystal grains. As a method, it is required to adopt continuous annealing that can shorten the annealing time instead of box annealing.

However, there is a problem that the r value of the continuously annealed low carbon steel sheet is low, and excellent deep drawability cannot be secured. Furthermore, short-time annealing causes insufficient precipitation of cementite, and deteriorates aging resistance. When a low-carbon steel sheet that has been subjected to such continuous annealing treatment and has poor aging resistance is used as a base sheet of a film-laminated steel sheet that covers a resin film on the base sheet,
Heat treatment at 0 ° C. for 10 seconds to several seconds causes a problem that strain aging occurs and stress strain is likely to occur during molding.

The present invention advantageously solves the above-mentioned problems,
Excellent in deep drawability and aging resistance, no appearance defects such as rough skin and stretcher strain after can making, and low ear incidence after can making, surface of polyester resin coated steel sheet for deep drawn cans It is an object of the present invention to provide an ultra-thin steel sheet suitable as an original sheet for a treated steel sheet.

[0010]

Means for Solving the Problems The inventors of the present invention have made intensive studies to achieve the above-mentioned object, and as a result, have improved aging resistance, improved r-value, and improved in-plane anisotropy of r-value. In
It was found that the addition of B was effective. B has the effect of fixing solid solution N as BN in the hot rolling process to reduce the aging property of the steel sheet, and further has a deep drawability (r) in the annealing process after cold rolling mainly by reducing the amount of solid solution N. Value) and the formation of a (111) texture advantageous to the in-plane anisotropy of the r value.

Further, the present inventors added B and Mn, and further controlled the amount of C to perform short-time annealing by continuous annealing, thereby improving aging resistance and reducing the size of crystal grains to make cans. It has been found that roughening after processing can be prevented. The present inventors have further studied based on the above-mentioned technical idea. As a result, the average crystal grain size is 6 μm or less, and the aging index A
By setting the I value to 40 MPa or less, exceeding the r value to 1.0, and setting the in-plane anisotropy Δr of the r value to within ± 0.1, even when formed into a deep drawn can, rough surface after forming and occurrence of stretcher strain can be prevented. It has been found that the occurrence of ears after molding can be reduced.

The characteristics of the steel plate described above are obtained from the following experiments. After heating a steel material with various amounts of C, Mn, B, Al, and N, it is subjected to hot rolling with various changes in hot rolling conditions such as a finish rolling temperature, and wound into a coil.
After pickling and primary cold rolling, continuous annealing with various annealing conditions was performed, and then secondary cold rolling was performed to obtain a 0.18 mm thick steel sheet. Next, these steel sheets were subjected to a surface treatment for adhering a surface treatment layer composed of a chromium metal layer and a chromium oxide layer to obtain surface treatment steel sheets.

The average grain size of these surface-treated steel sheets, AI
The values, average r values and Δr were investigated. The average r value and Δr were determined using the following equations. Average r value = (r _L + r _C + 2r _D ) / 4 Δr = (r _L + r _C −2r _D ) / 2 where r _L , r _C , and r _D are 0 degree, 90 degrees, respectively with respect to the rolling direction. The r value in the direction of 45 degrees. The average crystal grain size was obtained by measuring the average value of the thickness cross section (excluding the surface of 0.005 mm) at the center of the width of the sheet in accordance with the provisions of JIS G0552. The AI value was measured at 100 ° C x 7.5% after applying a 7.5% tensile prestrain in a tensile test.
Heat treatment was performed for 30 minutes, and the increase in yield stress before and after the heat treatment was measured.

On both sides of these surface-treated steel sheets, a thickness of 20 μm
A polyester resin film (melting point 230 ° C.) was thermally bonded to form a film-laminated steel sheet (polyester resin-coated steel sheet) coated with a resin film. Next, a 17 mm diameter polyester resin-coated steel
A 9 mm disk was punched out and formed into a shallow draw cup with a draw ratio of 1.56 by a conventional method. Next, this cup has a draw ratio of 1.37
Through the first redrawing step and the second redrawing step with a drawing ratio of 1.27, the cup was formed into a deep drawn cup having a cup diameter of 63 mm and a cup height of 127 mm. Further, the above-described deep drawing cup was subjected to bottom forming by a conventional method to form a dome portion on the bottom of the can.

After molding, the height of the ears was measured, and the average value of the ear heights was defined as the amount of ear generation. In addition, the presence or absence of the stretcher strain was evaluated by visual observation of the appearance of the dome portion of the can bottom. In addition, the case where the stretcher strain pattern was discernible with the naked eye was regarded as the occurrence of the stretcher strain. Thereafter, the deep drawing cup was trimmed, and then neck-in processing was performed. The surface of the can after neck-in processing was visually observed to evaluate the occurrence of rough skin. In addition,
When it was difficult to visually evaluate the resin coating, the resin coating was peeled off and the surface roughness was measured. When Ra ≧ 1.0 μm, the surface was determined to be rough.

The occurrence of rough skin, the occurrence of stretcher strain, and the occurrence of ears are shown in FIGS. From FIG. 1, it can be seen that roughening after forming can be prevented by setting the average crystal grain size of the steel sheet to 6 μm or less. From FIG. 2, the AI value of the steel sheet was set to 40
It can be seen that by setting the pressure to MPa or less, the occurrence of stretcher strain after molding can be prevented. From FIG.
It can be seen that the degree of ear generation is reduced by setting Δr in the range of −0.1 to +0.1.

The present invention has been made based on the above findings. That is, the present invention provides a method for preparing C:
0.02% or more and less than 0.10%, Si: 0.10% or less, Mn: 0.4% or more and 1.0% or less, P: 0.04% or less, S: 0.02% or less, Al:
0.01% or more and 0.1% or less, N: 0.0050% or less, B: 0.0010
% Or more and 0.0050% or less, the balance being Fe and unavoidable impurities, the average crystal grain size is 6 μm or less, the aging index AI value is 40 MPa or less, the r value exceeds 1.0, and the in-plane anisotropy of the r value. An original sheet for a surface-treated steel sheet which is excellent in aging resistance and has a low ear occurrence rate, characterized in that Δr indicating the properties is within ± 0.1.

In the present invention, C: 0.02% to less than 0.10%, Si: 0.10% or less, Mn: 0.4% to 1.0% by weight.
Below, P: 0.04% or less, S: 0.02% or less, Al: 0.01% or more and 0.1% or less, N: 0.0050% or less, B: 0.0010% or more.
0050% or less, the balance being Fe and unavoidable impurities, the average crystal grain size is 6 μm or less, and the aging index AI value is
Surface treatment with excellent aging resistance and low ear incidence, characterized by having at least a resin coating with an r value exceeding 40 MPa, an r value exceeding 1.0, and a Δr representing in-plane anisotropy of the r value within ± 0.1. It is a steel plate.

Further, according to the present invention, C: 0.02% by weight
Not less than 0.10%, Mn: 0.4% to 1.0%, Al: 0.01
% To 0.1% or less, B: 0.0010% to 0.0050%,
N: 0.0050% or less, or further Si: 0.10%
Below, P: 0.04% or less, S: 0.02% or less, with the balance Fe
And a steel material consisting of unavoidable impurities, heated, Ar ₃
After hot rolling at which the finish rolling is completed at the transformation point or higher, the coil is wound at a coiling temperature of 650 to 700 ° C, and then subjected to primary cold rolling at a rolling reduction of 80 to 88%, followed by recrystallization. Perform continuous annealing at a temperature of not less than 720 ° C and not more than 60s, and after annealing, cool to a temperature range of 350 to 500 ° C at a cooling rate of 50 ° C / s or more, apply overaging treatment for 30s or more, and then reduce Rate: 1.0 to 8%, subjected to secondary cold rolling, characterized by an average crystal grain size of 6 μm or less and an aging index AI value of 40 MPa.
The following is a method for producing an original sheet for a surface-treated steel sheet in which the r value exceeds 1.0 and Δr indicating the in-plane anisotropy of the r value is within ± 0.1.

The surface treatment in the present invention includes various plating, resin coating and the like. In the present invention, a resin coating may be applied after attaching a surface treatment layer composed of a metal chromium and a chromium oxide layer to an original sheet for surface treatment steel sheet.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The steel sheet of the present invention has a thickness of 0.20
It is suitable as an ultra-thin steel plate of not more than mm. First, the reasons for limiting the chemical composition of the steel sheet of the present invention will be described. C: 0.02% or more and less than 0.10% C is one of the important elements in the present invention from the viewpoint of grain refinement and aging of the steel sheet. In order to reduce the aging property, it is necessary to sufficiently precipitate cementite and reduce the amount of solid solution C in steel. However, for this purpose, the distance between cementite is shortened and the diffusion distance of solid solution C is reduced. Shortening is effective. In addition, by reducing the distance between cementite, the growth of crystal grains during annealing is suppressed, and the crystal grains can be refined. In order to shorten the distance between cementite and facilitate the precipitation of cementite, it is preferable to increase the amount of C appropriately and increase the precipitation nuclei of cementite. In the present invention, the amount of C is set to 0.02% or more. If the C content is less than 0.02%, the average crystal grain size cannot be reduced to 6 μm or less even if continuous annealing is performed for a short time. When the C content is 0.10% or more,
It becomes excessively hard and deteriorates moldability. For these reasons, the C content is limited to 0.02% or more and less than 0.10%.

Si: 0.10% or less When Si is added in a large amount, the surface treatment property and the corrosion resistance deteriorate, so the upper limit thereof is limited to 0.10%. In particular, when excellent corrosion resistance is required, the content of Si is preferably set to 0.02% or less. Mn: 0.4 to 1.0% Mn is an element effective for suppressing hot brittleness due to S. Further, Mn is concentrated in cementite, has the effect of reducing the moving speed of the cementite / ferrite interface, suppressing the aggregation and coarsening of cementite, and reducing the crystal grains. Further, Mn also has the effect of preventing cementite precipitated during the hot rolling step from re-solidifying during annealing and suppressing a decrease in aging resistance. These effects are recognized at a content of 0.4% or more. On the other hand, when the content exceeds 1.0%, corrosion resistance tends to deteriorate, and in addition, the steel sheet is hardened and the workability of the can is deteriorated. . Preferably, Mn is 0.5 to 1.0% from the viewpoint of reducing aging.

P: 0.04% or less P hardens steel and deteriorates workability.
It is an element that degrades corrosion resistance. If it exceeds 0.04%, its effect becomes remarkable, so the upper limit was made 0.04%. Note that when corrosion resistance and workability are particularly important, the content is preferably 0.01% or less.

S: 0.02% or less S is an element that exists as an inclusion in steel, reduces the ductility of the steel sheet, and further deteriorates the corrosion resistance. The upper limit is 0.02%. In particular, in applications where workability is required, the content is desirably 0.010% or less. Al: 0.01 to 0.1% Al is an effective element for obtaining low aging because it fixes solid solution N in steel as AlN.
Requires a content of 01% or more. In the case of applications that are severe against aging, the content is preferably 0.04% or more. On the other hand, if the content is too large, the frequency of occurrence of surface defects due to alumina clusters and the like increases rapidly, so the upper limit was set to 0.1%.

N: 0.0050% or less N is an element that enhances aging, and it is desirable to reduce as much as possible in order to increase the frequency of occurrence of stretcher strain. In the present invention, the solid solution N becomes
It is fixed as BN, but if it is limited to 0.0050% or less, the above-mentioned adverse effects can be suppressed and practical problems can be prevented. The lower limit is not particularly limited, but if it is about 0.0010%, it can be said that it is economically and industrially achievable. In addition,
From the viewpoint of ensuring the stability of the material, the content is desirably 0.0030% or less.

B: 0.0010 to 0.0050% B is an important element in the present invention. B has the effect of improving the r-value by controlling the texture, further reducing Δr to close to 0, the effect of reducing aging by fixing N, which cannot be fixed as AlN, as BN, and the effect of refining crystal grains. I have. The desirable effect of B is 0.0010
% Is recognized, but if it exceeds 0.0050%, problems such as generation of surface defects occur. For this reason, B is limited to the range of 0.0010 to 0.0050%. In consideration of the stability of the material, B is in the range of 0.0010 to 0.0030%.

The balance consists of Fe and inevitable impurities.
Even if Trump elements such as Sn, Cu, and Cr are mixed as impurities, if each is about 0.10% or less, the effect on use characteristics as a can can be neglected. Average grain size: 6 μm or less The average grain size of the steel sheet is 6 μm or less. If the average crystal grain size exceeds 6 μm, as shown in FIG. 1, the surface becomes rough after molding. Fine graining with an average crystal grain size of 6 μm or less is achieved by adding an appropriate amount of B, adding an appropriate amount of C and Mn, and controlling the winding temperature to tightly control the cementite distribution. This can be achieved by employing annealing conditions of low temperature and short time. It is also important to limit the finish rolling temperature.

Aging index AI value: 40 MPa or less The aging index AI value of the steel sheet is 40 MPa or less. If the aging index AI value exceeds 40 MPa, stretcher strain is generated after molding as shown in FIG. AI value 40MPa
The following aging resistance can be achieved by reducing the amount of solid solution N and solid solution C. The reduction of solid solution N is achieved by adding appropriate amounts of B and Al and controlling the winding temperature to sufficiently precipitate nitrides. The reduction of solid solution C is achieved by containing an appropriate amount of Mn to stabilize cementite. On the other hand, it is necessary to control the winding temperature so that cementite is sufficiently precipitated within the range that does not coarsen, and to perform annealing at low temperature for a short period of time to avoid re-solidification of cementite, followed by sufficient quenching and overaging treatment. Can be achieved.

R value: more than 1.0 In order to be used for deep drawing cans, the r value must be more than 1.0. If the r-value is 1.0 or less, deep drawing becomes difficult, and it becomes impossible to work into a desired can shape. Δr: Within ± 0.1 When Δr showing anisotropy of r value exceeds the range of ± 0.1, the degree of ear generation becomes large after can making. When the r value exceeds 1.0 and Δr is within ± 0.1, the solid solution N is changed to B,
It can be achieved by reducing the amount by adding an appropriate amount of Al and controlling the winding temperature, by performing the finish rolling temperature at the Ar ₃ transformation point or higher, and by limiting the rolling reduction of the cold rolling to a range of 80 to 88%.

Next, the manufacturing conditions of the steel sheet of the present invention will be described. The molten steel having the above composition is melted by a generally known melting method and solidified by a continuous casting method or an ingot forming method to obtain a steel material. The steel material is subjected to hot rolling to form a hot rolled sheet. The steel material may be cooled once to room temperature and then reheated, or may be charged into a heating furnace and heated without cooling.

In the present invention, the heating temperature of the steel material is not particularly limited, but is preferably 1100-1300 ° C. for 10-240 min.
It is desirable to keep it heated. If the heating temperature is lower than 1100 ° C., the target rolling temperature cannot be achieved, and there is a risk that flaws will occur during the subsequent rolling. On the other hand, the heating temperature is 1300 ℃
If it exceeds 300, abnormal grain growth occurs, the structure becomes uneven, and the energy cost increases. For this reason, the heating temperature of the steel material is preferably set in the range of 1100 to 1300 ° C.

If the holding time at the heating temperature is less than 10 minutes, the temperature in the steel material is not uniform, and rolling troubles such as warpage and bending of the sheet bar occur frequently. Also 240
If the value is maintained beyond min, the scale loss becomes significant.
Therefore, it is desirable that the holding time at the heating temperature be 10 to 240 min. The steel material is subjected to hot rolling after heating. In the present invention, it is desirable that the finish rolling temperature (rolling end temperature) of hot rolling be equal to or higher than the Ar ₃ transformation point.

When the finish rolling temperature is lower than the Ar ₃ transformation point, it is difficult to refine the crystal grains of the final product, and the surface aesthetics after can making is impaired. It is to be noted that, if the finish rolling exceeds the Ar ₃ transformation point + 50 ℃, since the scale loss increases, preferably Ar ₃ transformation point + 50 ℃ or less. It is desirable to perform forced cooling after finish rolling. By the forced cooling, the in-plane anisotropy of the material is suppressed, and the descaling property is further improved.

After finish rolling, it is wound around a coil. Winding temperature is 650-700 ℃. If the winding temperature is lower than 650 ° C., the shape of the steel sheet and the uniformity of the material in the width direction are reduced, which is not preferable as an ultra-thin steel sheet for cans. In addition, cementite and AlN cannot be sufficiently precipitated, and the aging property cannot be lowered and the target r value cannot be obtained. On the other hand, when the temperature exceeds 700 ° C., agglomeration and coarsening of cementite occur, and the grain size becomes insufficient and the scale thickness increases.

After hot rolling, usually, pickling is performed. The conditions for the pickling need not be particularly limited, and the pickling may be carried out with ordinary hydrochloric acid or sulfuric acid. Following the pickling, cold rolling is performed.
Cold rolling after pickling is called primary cold rolling to distinguish it from cold rolling after annealing. Reduction rate of primary cold rolling is 80 ~
88%.

The cold reduction ratio is related to the r value and Δr. When the reduction ratio is less than 80% or more than 88%, the r value decreases. When the rolling reduction is less than 80%, Δr is 0.1% on the positive side.
When the rolling reduction exceeds 88%, it exceeds 0.1 on the negative side. In addition, it is preferable to set it to 85% or more from the viewpoint of the load of the heat treatment. After the primary cold rolling, annealing is performed.

Annealing is performed at a temperature not lower than the recrystallization temperature and not higher than 720 ° C. for not longer than 60 s. In the present invention, the crystal grains are 6
Annealing is performed by a continuous annealing method, which is a short-time annealing, in order to reduce the size to μm or less. In order to obtain excellent formability, particularly a high r-value, the steel sheet is annealed at a temperature higher than the recrystallization temperature of the steel sheet to obtain a recrystallized structure. However, when annealing is performed at a high temperature exceeding 720 ° C., the crystal grains become coarse due to the growth of recrystallized grains and the reduction of the ability to suppress the grain growth due to the re-solution of cementite, resulting in rough skin. Further, the aging property is deteriorated due to the solid solution of cementite again. For this reason, the annealing temperature is 720 ° C or higher than the recrystallization temperature.
The temperature was limited to the following. Preferably, the recrystallization temperature or higher 7
It is below 00 ° C.

The annealing time (substantial soaking time) is 60
s or less. If the annealing time exceeds 60 s, the crystal grains become coarse and the surface becomes rough due to a decrease in the ability to suppress the growth of grains due to the growth of recrystallized grains and the re-solution of cementite. The annealing time is preferably set to 30 s or less. After annealing 3
Cool at a cooling rate of 50 ° C / s or more to a temperature range of 50 to 500 ° C, and perform an overage treatment of 30s or more at a temperature range of 500 to 350 ° C. If any of these conditions is removed, sufficient aging resistance cannot be obtained.

After overaging, secondary cold rolling (temper rolling)
I do. The rolling reduction of the secondary cold rolling is 1.0 to 8%. 2
The next cold rolling needs to be performed at a reduction rate necessary to secure the strength of the can body. In order to make the material of the annealed plate uniform and to reduce aging by introducing movable dislocations, it is necessary to reduce the rolling reduction to at least 1.0% or more. On the other hand, when the rolling reduction exceeds 8%, the formability is degraded due to a decrease in the r value, and the ear occurrence rate is increased due to an increase in Δr. For this reason, the rolling reduction in the secondary cold rolling was set to 1.0 to 8%.

When manufactured under the above conditions, the crystal grain size is 6 μm or less, the aging index AI value is 40 MPa or less, and r
An original sheet for a surface-treated steel sheet having a value of more than 1.0 and having Δr of ± r within ± 0.1 indicating in-plane anisotropy of r value is obtained. These original sheets for surface-treated steel sheets may be further subjected to surface treatment. As the surface treatment, resin coating, tin plating, chromium plating, or a composite plating thereof is suitable. In the present invention, it is particularly preferable to apply at least resin coating to the original sheet for surface-treated steel sheet. Further, it is more preferable to apply a resin coating after attaching a surface treatment layer composed of a metal chromium and chromium oxide layer to the original plate. Moreover, it is good also as an oiled steel plate without plating.

[0041]

EXAMPLES (Example 1) Steel having the composition shown in Table 1 was melted in a converter and made into a slab by a continuous casting method. Then, these slabs were subjected to hot rolling, primary cold rolling, continuous annealing, and secondary cold rolling under the conditions shown in Table 2 to obtain an ultra-thin steel sheet having a final finished sheet thickness of 0.18 mm. Subsequently, a surface treatment for attaching a metal chromium layer and a chromium oxide layer was performed to obtain a surface-treated steel sheet (tin-free steel sheet).

The average grain size of these surface-treated steel sheets, AI
The values, average r value and Δr value were measured. The average crystal grain size was determined by averaging the thickness cross section at the center of the width of the sheet in accordance with the provisions of JIS G0552. The average r value and Δr are
The r value in each direction of rolling was determined using a JIS No. 13 test piece, and the average r value and Δr were calculated using the following formulas.

Average r value = (r _L + r _C + 2r _D ) / 4 Δr = (r _L + r _C −2r _D ) / 2 where r _L , r _C , and r _D are each 0 degree with respect to the rolling direction. The r values in the directions of 90 degrees and 45 degrees. The AI value was obtained by applying a 7.5% tensile prestrain in a tensile test, then performing a heat treatment at 100 ° C. for 30 minutes, and measuring the increase in yield stress before and after the heat treatment.

On both sides of these surface-treated steel sheets, a thickness of 20 μm
The polyester resin film (melting point 230 ° C.) was thermally bonded to form a film-laminated steel sheet (polyester resin-coated steel sheet). Next, a disk having a diameter of 179 mm was punched from a polyester resin-coated steel sheet and formed into a shallow drawn cup having a drawing ratio of 1.56 by a conventional method. Next, this cup has a draw ratio
Through a first redrawing step of 1.37 and a second redrawing step of a drawing ratio of 1.27, a deep drawn cup having a cup diameter of 63 mm and a cup height of 127 mm was formed. Furthermore, in the above-mentioned deep drawing cup,
The bottom was formed by a conventional method to form a dome on the bottom of the can.

After molding, the height of the ears was measured, and the average value of the ear heights was defined as the amount of ear generation. The deep drawability was evaluated by visually observing the occurrence of cracks and wrinkles. In addition, the presence or absence of the stretcher strain was evaluated by visual observation of the appearance of the dome portion of the can bottom. Thereafter, the deep drawing cup was trimmed, and then neck-in processing was performed. The surface of the can after neck-in processing was visually observed to evaluate the occurrence of rough skin. The evaluation criteria were the same as those in FIGS.

Table 3 shows the results.

[0047]

[Table 1]

[0048]

[Table 2]

[0049]

[Table 3]

As can be seen from Table 3, the average crystal grain of the present invention example is finer than that of the comparative example, the average r value is more than 1.0, the AI value is 40 MPa or less, and the aging resistance is excellent. It is excellent in drawability and resistance to rough skin, has no occurrence of stretcher strain, has a low height of ear generation, and is suitable as a material for a thin-walled deep-drawing can to be subjected to severe processing. On the other hand, the comparative examples out of the range of the present invention are inferior in aging resistance, deep drawability, and / or inferior skin roughness resistance. It is not suitable as a material for drawing cans.

(Example 2) Steel No. 1 and No. 2 shown in Table 1
Was smelted in a converter and made into a slab by a continuous casting method. Next, these slabs were made into ultra-thin steel sheets having a final finish thickness of 0.13 to 0.18 mm under the conditions shown in Table 4. Subsequently, a surface treatment for attaching a metal chromium layer and a chromium oxide layer was performed to obtain a surface-treated steel sheet (tin-free steel sheet). The same investigation as in Example 1 was conducted on these surface-treated steel sheets, and the results are shown in Table 5.

[0052]

[Table 4]

[0053]

[Table 5]

As can be seen from Table 5, the present invention example has finer average crystal grains and an average r value of 1.0 as compared with the comparative example.
The AI value is also 40MPa or less, excellent in aging resistance, excellent in deep drawability, excellent in rough skin resistance, no stretcher strain is generated, and the ear generation height is low,
It is suitable as a material for a thin-walled deep-drawn can that undergoes severe processing. In contrast, comparative examples that fall outside the scope of the present invention are:
It is inadequate in at least one of aging resistance, deep drawability, and skin roughness resistance, and is unsuitable as a material for a thin-walled deep-drawing can.

[0055]

According to the present invention, an original sheet of a surface-treated steel sheet for deep drawing cans, which is excellent in deep drawability and aging resistance, does not cause appearance defects such as rough skin and stretcher strain after can manufacturing, In particular, an ultra-thin steel sheet suitable as an original sheet of a polyester resin-coated steel sheet can be manufactured. Furthermore, the steel sheet of the present invention can reduce the material cost as an extremely thin steel sheet having a thickness of 0.20 mm or less, and further, the ear incidence rate is low after can processing,
The material yield can be improved, and an industrially significant effect can be achieved. In addition to the polyester resin-coated steel sheet, the steel sheet of the present invention can be used as a steel sheet for DI cans or a steel sheet for three-piece cans by taking advantage of its excellent workability and aging resistance.

[Brief description of the drawings]

FIG. 1 is a graph showing the influence of the average crystal grain size on the surface roughness after molding.

FIG. 2 is a graph showing the effect of the AI value of a product steel sheet on the occurrence of stretcher strain after forming.

FIG. 3 is a graph showing the effect of Δr on the ear generation height.

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

Claims (3)

[Claims] 1. In weight%, C: 0.02% to less than 0.10%, Si: 0.10% or less, Mn: 0.4% to 1.0%, P: 0.04% or less, S: 0.02% or less, Al: 0.01% or more 0.1% or less, N: 0.0050% or less, B: 0.0010% or more and 0.0050% or less, the balance being Fe and inevitable impurities, the average crystal grain size is 6μm or less, the aging index AI value is 40MPa or less, and the r value. Is greater than 1.0, and Δr representing in-plane anisotropy of r value is within ± 0.1, which is excellent in aging resistance and low in ear occurrence rate. 2. In% by weight, C: 0.02% to less than 0.10%, Si: 0.10% or less, Mn: 0.4% to 1.0%, P: 0.04% or less, S: 0.02% or less, Al: 0.01% or more 0.1% or less, N: 0.0050% or less, B: 0.0010% or more and 0.0050% or less, the balance being Fe and inevitable impurities, the average crystal grain size is 6μm or less, the aging index AI value is 40MPa or less, and the r value. A surface-treated steel sheet having excellent aging resistance and low ear incidence, characterized by having a resin coating of at least 1.0 and a value of Δr representing in-plane anisotropy of r value within ± 0.1. (3) C: 0.02% or more and less than 0.10% by weight.
After heating a steel material containing Mn: 0.4% or more and 1.0% or less, Al: 0.01% or more and 0.1% or less, B: 0.0010% or more and 0.0050% or less, and N: 0.0050% or less, finish rolling at a temperature above the Ar ₃ transformation point after heating. Finish hot rolling and winding temperature: 650 ~ 7
After being wound on a coil at 00 ° C, primary cold rolling is performed at a rolling reduction of 80 to 88%, and then continuous annealing is performed at a temperature not lower than the recrystallization temperature and not higher than 720 ° C for not longer than 60 seconds. After annealing, 350 to 500 ° C Average crystal grains characterized by cooling to a temperature range of 50 ° C./s or more at a cooling rate of 50 ° C./s or more, performing an overage treatment of 30 s or more, and then subjecting to secondary cold rolling at a rolling reduction of 1.0 to 8%. A method for producing a base sheet for a surface-treated steel sheet, having a diameter of 6 μm or less, an aging index AI value of 40 MPa or less, an r value of more than 1.0, and an Δr indicating in-plane anisotropy of the r value of ± 0.1 or less.