JP4858126B2 - Steel sheet for high strength and high ductility can and method for producing the same - Google Patents

Description

  The present invention relates to a steel plate for cans used as a raw material for a three-piece can with a high degree of can body processing, a two-piece can whose bottom portion is processed by several percent, and a manufacturing method thereof. The present invention relates to a steel plate for cans having a small elongation and a small anisotropy (Δr) and a method for producing the same.

In recent years, in order to increase the demand for steel cans as steel plates for cans, measures have been taken such as reducing can manufacturing costs and introducing new can types such as bottle cans and deformed cans to the market.
As a measure to reduce can manufacturing costs, the cost of materials can be reduced, and not only two-piece cans that are drawn, but also three-piece cans mainly made of simple cylindrical molding, the use of thinner steel sheets can be achieved. It is being advanced.
However, simply reducing the thickness of the steel sheet reduces the strength of the can body, so it is not possible to use a thinned steel sheet in places where high-strength materials such as DRD cans and can bodies of welded cans are used, A high strength and extremely thin steel plate for cans has been desired.
Currently, ultra-thin and hard steel plates for cans are manufactured by the Duble Reduce method (hereinafter referred to as DR method) in which secondary cold rolling is performed after annealing. Steel sheets manufactured using the DR method are characterized by high strength and low yield elongation. In a DRD can application involving bottom processing, it is desirable that the yield elongation is as small as possible in order to prevent the occurrence of a threshold strain, and the DR method is effective in that respect. However, DRD cans are required to have small ear cracks, but the DR method tends to increase anisotropy, so ear cracks occur, and anisotropy (Δr) is reduced to prevent ear cracks. There is a problem of doing.
On the other hand, DR materials having poor ductility are difficult to apply to cans with cans having a high degree of processing, such as deformed cans that have recently been put on the market, because of poor workability. In addition, the DR material is expensive because the number of manufacturing steps is increased as compared with a steel plate that is pressure-regulated after normal annealing.

  In order to avoid the disadvantages of DR materials, secondary cold rolling is omitted, and high strength steel sheets are manufactured by the Single Reduce method (SR method), which controls the properties in the primary cold pressure and annealing processes using various strengthening methods. The following patents propose a method for producing a high-strength steel plate having a small yield elongation, or a method for producing a steel plate having a low ear generation rate.

Patent Document 1 proposes that a steel plate for high strength can similar to DR can be obtained by adding a large amount of C and N and bake hardening. The yield stress after paint baking is as high as 550 MPa, and the amount of N added and the hardness obtained by heat treatment can be adjusted.
In Patent Document 2, as in Patent Document 1, the strength is increased by about +50 MPa by post-coating baking treatment.
Patent Document 3 proposes a steel sheet having a balance between strength and ductility by combining precipitation strengthening with Nb carbide and solid solution strengthening with P in a composite manner.
Patent Document 4 proposes a manufacturing method in which the yield elongation is 1.0% or less to prevent the occurrence of stretcher strain and to obtain a steel having a strength level equivalent to T6.
Patent Document 5 proposes a method using box annealing in order to improve the flange processability of the DI can and prevent the occurrence of ears.
Patent Document 6 is an invention for obtaining a high-strength steel sheet using transformation strengthening, and hot rolling low carbon steel in an α + γ region, cooling at a high speed, and defining a heating rate for annealing, thereby providing a tensile strength of 600 MPa. A steel sheet having a total elongation of 30% or more has been proposed.
JP 2001-107186 Japanese Patent Laid-Open No. 11-199991 JP 2005-336610 A JP 59-129733 A JP 53-48913 JP 2003-34825 A

First, it is essential to secure strength in order to reduce the gauge, and in order to obtain the current can strength with a plate thickness of 0.18 mm or less, the tensile strength must be 500 MPa or more. Moreover, when using a steel plate for a can body that performs high can body processing such as can expansion processing or a can body that performs high flange processing, it is necessary to apply high ductility steel. Furthermore, if a material that yields yield is applied to a DRD can with bottom processing corresponding to several percent of the degree of tensile work, a stretcher strain is generated, which is not preferable in appearance. Therefore, a steel plate that does not yield yield is desirable. When steel with a high ear occurrence rate is applied to the DRD can, the trim margin increases and the yield decreases. Therefore, a steel plate with small ear generation, that is, low anisotropy is desirable.
In view of the above characteristics, in the above-described conventional technology, it is possible to manufacture a steel plate that satisfies any of strength, ductility, yield elongation, and anisotropy, but it is not possible to manufacture a steel plate that satisfies all of the requirements.
For example, the method of increasing the strength by bake hardenability by adding a large amount of C, N described in Patent Document 1 is an effective method for increasing the strength, but there is a concern of strain aging after pressure adjustment, Stretcher strain may occur and damage the can's appearance.
Patent Document 2 mentions age hardening by baking and reducing yield elongation by overaging, but the steel plate obtained by the overaging shown here cannot completely suppress stretcher strain.
Although Patent Document 3 does not describe the yield elongation, it is expected that yield elongation of several percent occurs because low carbon steel is manufactured by continuous annealing and is not over-aged.
Although Patent Document 4 describes a T6 level steel with a yield elongation of almost 0, it is necessary to perform temper rolling at a rolling rate of 10% or more, and the manufacturing method is substantially the same as that of DR material. is there. In addition, there is no description of producing steel exceeding T6. Further, although it is not described in the specification regarding ductility, it is expected that the ductility is inferior when rolling is performed at a rolling reduction of 10% or more.
Patent Document 5 discloses a method of manufacturing a steel sheet that has high flange workability and suppresses the generation of ears by using box annealing. However, the strength of 500 MPa or more targeted by the present invention has not been reached.
The increase in strength by high-speed cooling proposed in Patent Document 6 is costly in operation.

  The present invention has been made in view of such circumstances, and has a tensile strength of 500 MPa or more, an elongation of 20% or more, and a high strength at which the yield elongation is less than 1% and the anisotropy is -0.5 to 0. It aims at providing the steel plate for high ductility cans, and its manufacturing method.

The inventors of the present invention have intensively studied to solve the above problems. As a result, the following knowledge was obtained.
Focusing on the combined combination of solid solution strengthening, precipitation strengthening and refinement strengthening, solid solution strengthening using solid solution strengthening elements, and strengthening by precipitation strengthening with Nb and fine grain strengthening, high strength without impairing elongation Furthermore, by making the structure a substantially single ferrite phase and defining the average grain size of ferrite, the strength-ductility balance can be maintained, and a tensile strength of 500 MPa or more and an elongation of 20% or more can be obtained.
Furthermore, it is possible to reduce the yield elongation to less than 1% by performing box annealing with a specified cooling rate.
And it becomes possible to make anisotropy -0.5-0 by controlling hot rolling conditions.
In this invention, it came to complete the steel plate for high strength and high ductility cans, and its manufacturing method by managing a component and a manufacturing method in total based on the said knowledge.

The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] By mass%, C: 0.01 to 0.12%, Si: 0.01 to 0.5%, Mn: 0.3 to 1.5%, P: 0.01 to 0.2%, Al: 0.1% or less, Nb: 0.005 to 0.1% Contained, the balance is composed of iron and inevitable impurities, and has a ferrite single phase structure substantially, ferrite average crystal grain size is 7μm or less, plate thickness is 0.18mm or less, tensile strength is 500MPa or more, all A steel sheet for high strength and high ductility cans having an elongation of 20% or more, a yield elongation of less than 1%, and an anisotropy (Δr) of −0.5 to 0.
[2] By mass%, C: 0.01 to 0.12%, Si: 0.01 to 0.5%, Mn: 0.3 to 1.5%, P: 0.01 to 0.2%, Al: 0.1% or less, Nb: 0.005 to 0.1% Containing steel, the balance being iron and inevitable impurities,
Hot-rolled at a finishing temperature of 870 ° C or higher, cooled at a rate of 40 ° C / s or lower until winding, wound at a winding temperature of 620 ° C or higher, pickled, and then at a reduction rate of 80% or higher. After cold rolling, box annealing is performed under conditions of a soaking temperature of 600 to 690 ° C. and a cooling rate of 20 ° C./h or less, and temper rolling is performed at a pressure regulation rate of 1.5% or less. The manufacturing method of the steel plate for high strength and high ductility cans which is 0.18 mm or less in thickness.

  In the present specification, “%” indicating the component of steel is “% by mass”.

According to the present invention, a high strength and high ductility steel plate for cans having a tensile strength of 500 MPa or more, an elongation of 20% or more, a yield elongation of less than 1%, and an anisotropy of −0.5 to 0 is obtained. It is done.
More specifically, the present invention uses a solid solution strengthening element to solid solution strengthen, and further performs precipitation strengthening and fine grain strengthening with Nb, thereby strengthening the composite strength without adversely affecting other properties. Therefore, in spite of the box annealing, the temper rolling after the annealing process can reliably produce a steel sheet having a reduction rate of 1.5% or less and a tensile strength of 500 MPa or more.
In addition, by using box annealing to reduce the cooling rate after soaking to 20 ° C / h or less, the yield elongation is less than 1% to reduce the amount of solute C in the steel, drawing and bottom processing. Stretcher strain that was sometimes a concern can be prevented.
Also, in DRD can applications, it is necessary to prevent the occurrence of ears in order to reduce the trim cost of the can and increase the yield. In the present invention, by setting the finishing temperature to 870 ° C or higher, the cooling rate until winding to 40 ° C / s or lower, and the winding temperature to 620 ° C or higher, the anisotropy is suppressed to a range of -0.5 to 0, and ears are generated. Can be prevented.
Also, regarding the productivity during annealing, conventionally, with regard to ultra-thin materials such as 0.18 mm or less, continuous annealing may damage the shape of the plate and break, and there is a risk that high yield cannot be ensured. With box annealing, there is no such fear, and a high yield can be secured.

Hereinafter, the present invention will be described in detail.
The steel plate for cans of the present invention has a tensile strength (hereinafter sometimes referred to as TS) of 500 MPa or more, an elongation of 20% or more, a yield elongation of less than 1%, and an anisotropy (hereinafter also referred to as Δr) -0.5 to It is a 0 steel plate for high strength and high ductility cans. Normally, a steel sheet that has been strengthened by using the DR method has an elongation of only a few percent. On the other hand, a steel sheet produced by continuous annealing and pressure regulation has an elongation of 10% or more, but because the amount of dissolved C in the steel is high, yield elongation occurs several percent. On the other hand, the present invention is characterized by increasing the strength while maintaining high elongation by manufacturing a steel plate strengthened by solid solution strengthening, precipitation strengthening, refinement strengthening by Nb, P, Mn by box annealing. To do. Moreover, yield elongation is made less than 1% by reducing the cooling rate after box annealing. Furthermore, by setting the finishing temperature during hot rolling to 870 ° C. or higher, the subsequent cooling rate to 40 ° C./s or lower, and the coiling temperature to 620 ° C. or higher, Δr can be in the range of −0.5 to 0. These are features of the present invention and are the most important requirements. In this way, by optimizing the components, structure, and manufacturing conditions centering on solid solution strengthening elements, precipitation strengthening elements, and refinement strengthening elements, yielding is achieved despite the addition of C and N. A high-strength steel sheet having an elongation of less than 1%, Δr of −0.5 to 0, and a high elongation of 20% or more can be obtained.

Next, the component composition of the steel plate for cans of this invention is demonstrated.
C: 0.01-0.12%
In the steel sheet for cans of the present invention, it is essential to achieve a strength of not less than a predetermined value (500 MPa or more) after annealing, and at the same time to have an elongation of 20% or more. For this purpose, the crystal grain size must be 7 μm or less. It is. In the production of a steel sheet that satisfies these characteristics, the amount of C added becomes important. In particular, since the amount and density of carbides are greatly related to strength and particle size, it is necessary to secure the amount of carbon used for precipitation. Therefore, the C content is 0.01% or more. On the other hand, if the amount of C added exceeds 0.12%, subperitectic cracks occur during the cooling process during steel melting, so the content is made 0.12% or less. Desirably, it is 0.04% or more and 0.1% or less.

Si: 0.01-0.5%
Si is an element that enhances the strength of steel by solid solution strengthening, but if added in a large amount, corrosion resistance is significantly impaired. Therefore, the Si addition amount is set to 0.01% or more and 0.5% or less.

Mn: 0.3-1.5%
Mn increases the strength of the steel by solid solution strengthening and reduces the crystal grain size. In addition, it is an element that increases the strength even as it is refined. The effect of reducing the crystal grain size is remarkably produced when the Mn addition amount is 0.3% or more, and at least 0.3% Mn addition amount is required to secure the target strength. Therefore, the lower limit of the Mn addition amount is limited to 0.3%. On the other hand, when manufacturing using box annealing, if a large amount of Mn is contained, a large amount of temper color is generated, resulting in poor corrosion resistance. Therefore, the upper limit is limited to 1.5%.

P: 0.01% ~ 0.2%
P is an element having a large solid solution strengthening ability, and the effect is noticeably caused by 0.01% or more. Therefore, the lower limit of the P addition amount is limited to 0.01%. On the other hand, since the corrosion resistance deteriorates when added in a large amount, the upper limit is limited to 0.2%.

Al: 0.1% or less
As the Al content increases, the recrystallization temperature rises, so the annealing temperature needs to be increased. In the present invention, other elements added to increase the strength increase the recrystallization temperature and increase the annealing temperature. Therefore, it is best to avoid the increase of the recrystallization temperature due to Al as much as possible. . Therefore, the Al content is 0.1% or less.

Nb: 0.005% to 0.1%
Nb is an important additive element in the present invention. Nb is an element having a high ability to generate carbides, and precipitates fine carbides to increase the strength. Moreover, strength is raised by making it fine. The grain size and grain shape affect not only the strength but also the surface properties during drawing. The strength and surface properties can be adjusted by the amount of Nb added, and this effect occurs when the amount exceeds 0.005%. Therefore, the lower limit is limited to 0.005%. Further, since the rate of increase in strength tends to increase when 0.015% or more is added, it is desirable to add 0.015% or more when a significant increase in strength is required. On the other hand, Nb brings about an increase in the recrystallization temperature. Therefore, when it is contained in an amount of 0.1% or more, it becomes difficult to anneal, for example, a part of unrecrystallized remains at the annealing temperature of 600 to 690 ° C. described in the present invention. By increasing the annealing temperature, a recrystallized structure can be obtained, but the surface properties are inferior because the elements in the steel are concentrated on the surface layer. Therefore, the upper limit of the Nb addition amount is limited to 0.1%.

N: 0.001% to 0.012% (preferred range)
There is no particular restriction on the amount of N added. However, during continuous casting, slab cracking tends to occur in the lower straightening zone where the temperature decreases. In the case of manufacturing by the box annealing method, most of N is precipitated as ALN during annealing, so there is no solid solution N in the steel and age hardening cannot be obtained. Therefore, when manufacturing by a box annealing method, it is preferable to add only the N amount necessary for controlling the texture. Therefore, it is preferable to add N in a range of 0.001% or more and 0.012% or less as a N addition amount at a level at which ALN affecting the texture is obtained. In order to prevent slab cracking as much as possible, the content is preferably 0.005% or less.

  The balance is Fe and inevitable impurities.

Next, the structure of the steel plate for cans of the present invention will be described.
Ferrite single-phase structure, average crystal grain size: 7 μm or less First, in the present invention, a ferrite single-phase structure is substantially formed. Even when containing about 1% of cementite or the like, it is determined that the ferrite single phase structure is substantially obtained as long as the effects of the present invention are exhibited.
On the other hand, when the average ferrite grain size exceeds 7 μm, the beauty of the surface appearance after canning is lost. This is considered to correspond to an extreme change in surface roughness such as a rough skin phenomenon. This phenomenon is confirmed particularly in a two-piece can, although the site and degree of occurrence are different. From the above, the ferrite average crystal grain size is set to 7 μm or less. The ferrite crystal grain size is measured, for example, according to the ferrite average crystal grain size by the ASTM cutting method. Further, the ferrite average crystal grain size is controlled to a target value by the component, the cold rolling rate, and the annealing temperature. Specifically, C: 0.01 to 0.12%, Si: 0.01 to 0.5%, Mn: 0.3 to 1.5%, P: 0.01 to 0.2%, Al: 0.1% or less, N: 0.005% or less, Nb: 0.005 Add ~ 0.1%, hot-roll at a finishing temperature of 870 ° C or higher, cool at a rate of 40 ° C / s or lower until winding, wind up on a coil in a temperature range of 620 ° C or higher, and then acid After performing cold rolling of 80% or more after washing, crystal grain size of 7 μm or less is obtained by performing box annealing under conditions of soaking temperature of 600 to 690 ° C. and cooling rate of 20 ° C./h or less. It is done.

Steel plate thickness: 0.18 mm or less In the present invention, the plate thickness is an important factor. If the steel sheet has a thickness of more than 0.18 mm, continuous annealing can be easily performed. However, if the steel sheet has a thickness of 0.18 mm or less, there is a possibility that the fracture or the shape of the plate may be deteriorated during continuous annealing, resulting in a decrease in productivity. Therefore, in this invention, in order to express the productivity improvement effect by box annealing notably, board thickness is limited to 0.18 mm or less.

Tensile strength: 500 MPa or more If the tensile strength (TS) is less than 500 MPa, the steel sheet of 0.18 mm or less, which is the subject of the present invention, is insufficient in strength of the can body and causes problems when used. Therefore, the tensile strength (TS) is 500 Mpa or more. TS is controlled to the target value by the component, the cold rolling rate, and the annealing temperature. Specifically, C: 0.01 to 0.12%, Si: 0.01 to 0.5%, Mn: 0.3 to 1.5%, P: 0.01 to 0.2%, Nb: 0.005 to 0.1% are added, and the cold rolling rate Is controlled to a target value by performing box annealing under conditions of a soaking temperature of 600 to 690 ° C. and a cooling rate of 20 ° C./h or less.

Total elongation: When the total elongation is 20% or more and less than 20%, for example, it becomes difficult to apply to a can with high can body processing such as can expansion processing. Therefore, the total elongation is 20% or more.

Yield elongation: Less than 1% Stretcher strain occurs when the bottom part of a DRD can is processed on a steel sheet with a yield elongation of 1% or more. For this reason, a pattern such as a rough surface or a Rueders band is generated on the bottom portion, and the appearance is not excellent. In order not to generate stretcher strain during processing, it is necessary to make the yield elongation less than 1%.

Anisotropy (Δr): -0.5 to 0
In the present invention, Δr represented by the following formula is used as an anisotropy index.
Δr = (r ₀ + r ₉₀ −2 × r ₄₅ ) / 4
r ₀ is the tensile _value in the rolling direction, r ₄₅ is the tensile _value in the rolling direction and 45 ° direction, r ₉₀ is the r value in the rolling direction and 90 ° direction. Show.
For a steel sheet with Δr of less than −0.5, for example, when it is processed into a DRD can, the generation of ears is large, so the trim margin increases and the yield decreases. In order to suppress the ear generation amount from the viewpoint of yield, Δr needs to be in the range of −0.5 to 0. In order to suppress ear generation as much as possible, it is desirable that Δr be in the range of −0.3 to 0. In addition, (DELTA) r is controlled to a target value with the finishing temperature at the time of hot rolling, the cooling rate after finishing, and coiling temperature. Specifically, Δr is set to the target value by hot rolling at a finishing temperature of 870 ° C or higher, cooling at a rate of 40 ° C / s or lower until winding, and winding the coil in a temperature range of 620 ° C or higher. Control.

Next, the manufacturing method of the steel plate for cans of this invention is demonstrated.
The molten steel adjusted to the above-described chemical composition is melted by a generally known melting method using a converter or the like, and then made into a rolled material by a commonly used casting method such as a continuous casting method.
Next, it is set as a hot-rolled sheet by hot rolling using the rolling raw material obtained by the above. At the start of rolling, the rolled material is preferably 1250 ° C. or higher. The finishing temperature is 870 ° C or higher. Moreover, it cools at a speed | rate of 40 degrees C / s or less until winding, and winds at the winding temperature of 620 degreeC or more. From the viewpoint of anisotropy, the ferrite grain size of the hot rolled material obtained here is desirably 7 μm or more as much as possible. Next, after pickling and cold rolling at a reduction rate of 80% or more, box annealing is performed under conditions of a soaking temperature of 600 to 690 ° C. and a cooling rate of 20 ° C./h or less, and 1.5% or less. Temper rolling is performed at the pressure regulation rate.

Hot rolling finish temperature: 870 ° C. or higher The finish rolling temperature in hot rolling is an important item in controlling anisotropy. In order to ensure anisotropy of −0.5 or more in Nb-added steel, it is necessary to control the texture of the hot rolled material to have a ferrite grain size of 7 μm or more. In order to obtain this, the hot rolling finishing temperature is 870 ° C. or higher.

Cooling rate after finish rolling to winding: 40 ° C./s or less Anisotropy is greatly affected by the ferrite grain size of the hot rolled material. In order to make Δr in the range of −0.5 to 0, the ferrite grain size of the hot rolled material needs to be at least 7 μm or more. In order to increase the ferrite grain size of the hot-rolled material to 7 μm or more, it is necessary to reduce the cooling rate after hot rolling, and the condition is that the cooling rate after finishing is 40 ° C./s or less. Further, in order to obtain a steel having a preferable range of Δr for suppressing ear generation as much as −0.3 to 0, the cooling rate needs to be 20 ° C./s or less.

Winding temperature: 620 ° C. or higher In order to increase the ferrite grain size of the hot rolled material to 7 μm or higher, it is necessary to increase the winding temperature, and the winding temperature is 620 ° C. or higher. In order to ensure that the ferrite grain size of the hot-rolled material is 7 μm or more in the full width, it is desirable that the winding temperature is 640 ° C. or more. Further, in order to obtain a steel having a preferable range of Δr for suppressing generation of ears as much as −0.3 to 0, the coiling temperature needs to be 700 ° C. or higher.

Cold rolling rate (rolling rate): 80% or more The rolling rate in cold rolling is one of the important conditions in the present invention. If the rolling reduction in cold rolling is less than 80%, it is difficult to produce a steel sheet having a TS of 500 MPa or more. Furthermore, in order to obtain the target plate thickness (0.18 mm or less), at a rolling reduction of less than 80%, at least the plate thickness of the hot-rolled plate needs to be 1 mm or less, which is difficult in operation. Therefore, the rolling reduction is 80% or more.

Annealing conditions: soaking temperature of 600 ° C. to 690 ° C., cooling rate of 20 ° C./h or less. Box annealing is used for annealing. The soaking temperature needs to be equal to or higher than the recrystallization temperature of the steel sheet in order to ensure good workability, and soaking is necessary at a temperature of 600 ° C. or more to make the structure more uniform. . On the other hand, when the annealing temperature becomes high, a temper color is generated by the oxide film formed by the concentration of additive elements in the steel on the surface layer. Therefore, the soaking temperature is 600 ° C. or higher and 690 ° C. or lower. In order to further suppress the surface layer concentration of the additive element in the steel, it is more desirable to set the annealing temperature to 670 ° C. or lower.
Further, in order to make the yield elongation less than 1%, it is necessary to precipitate the solid solution C in the steel as carbide. Solid solution C in steel is determined by the cooling rate from the annealing. Therefore, the cooling rate is 20 ° C./h or less.

Pressure regulation rate: 1.5% or less When the pressure regulation rate is increased, the ductility is lowered because the strain introduced at the time of processing increases as in the case of the DR material. In the present invention, since it is necessary to ensure a total elongation of 20% or more with an ultra-thin material, the pressure regulation rate is 1.5% or less.

Steel containing the composition shown in Table 1 and the balance being Fe and inevitable impurities was melted in an actual converter to obtain a steel slab. The obtained steel slab was reheated at 1250 ° C, then hot-rolled at a finish rolling temperature range of 880 ° C to 900 ° C, cooled at a cooling rate of 30 ° C / s until winding, and a winding temperature of 620-700 ° C. It was wound in the range. Next, after pickling, the steel sheet was cold-rolled at a rolling reduction of 90% or more to produce a thin steel sheet having a thickness of 0.15 to 0.18 mm. The obtained thin steel sheet was allowed to reach 630 to 660 ° C. at a heating rate of 50 ° C./h in a box annealing furnace, and soaked for 3 hours. Next, it was cooled at a cooling rate of about 10 ° C./h, subjected to temper rolling so that the reduction rate was 1.5% or less, and continuously subjected to normal chrome plating to obtain tin-free steel.
Steels 1 to 7 shown in Table 1 are examples of the present invention whose component composition is within the scope of the present invention. On the other hand, Steel 8 is a comparative example whose component composition is outside the scope of the present invention.

  A tensile test was performed on the plated steel plate (tin-free steel) obtained as described above, and the crystal structure and the average crystal grain size were investigated. The survey method is as follows.

The tensile test was performed using a JIS5 size tensile test piece, and the yield elongation (YP-El), tensile strength (TS), and elongation (El) were measured, and the strength, ductility, and aging were evaluated.
The crystal structure was observed with an optical microscope after the sample was polished, the grain boundaries were corroded with nital.
The average crystal grain size was measured using the ASTM cutting method for the crystal structure observed as described above.
The results obtained are shown in Table 2.

In Invention Examples 1 to 7, the steel structure has an average crystal grain size of 7 μm or less, is a uniform and fine ferrite single layer structure that does not include a mixed grain structure, yield elongation does not occur, aging, strength, and ductility It is recognized that all are excellent.
On the other hand, in Comparative Example 8, the ductility is superior to the inventive steel, but the strength is insufficient.

Steel containing the composition shown in Table 3 and the balance being Fe and inevitable impurities was melted in an actual converter to obtain a steel slab. The obtained steel slab was reheated at 1250 ° C and then hot-rolled at a finish rolling temperature of 830 to 900 ° C. The cooling rate until winding was cooled at 18 to 50 ° C / s, and the winding temperature was 580. It wound up in the range of -700 degreeC. Subsequently, it cold-rolled with the rolling reduction of 90% or more, and manufactured the 0.15-0.18 mm thin steel plate. The obtained thin steel sheet was allowed to reach 630 ° C. (partly 700 ° C.) at a heating rate of 50 ° C./h in a box annealing furnace, and subjected to soaking at 630 ° C. (partly 700 ° C.) for 3 hours. . Next, the steel was cooled at a cooling rate of about 10 to 100 ° C./h, subjected to temper rolling so that the reduction rate was 1.5% or less, and continuously subjected to ordinary chromium plating to obtain tin-free steel. Detailed manufacturing conditions are shown in Table 4.
The examples of the present invention are conditions 1 to 3, and the conditions 4 to 10 are comparative examples in which the production conditions are outside the scope of the present invention.

A tensile test was performed on the plated steel plate (tin-free steel) obtained as described above, and the crystal structure and the average crystal grain size were investigated.
Anisotropy (Δr) is the r value when the tensile test is performed in the rolling direction (r ₀ ), the rolling direction and 45 ° direction (r ₄₅ ), and the rolling direction and 90 ° direction (r ₉₀ ). Δr = (r ₀ + r ₉₀ −2 × r ₄₅ ) / 4 was calculated.
Other than that, investigation was carried out in the same manner as in Example 1.

From Table 5, in the present invention, the anisotropy is small by decreasing the cooling rate after finish rolling and increasing the coiling temperature, and the yield elongation is small by decreasing the cooling rate after annealing, A high-strength steel sheet having high ductility was obtained.
On the other hand, in the comparative examples (Conditions 4, 6, and 7), the strength, ductility, and yield elongation reach the target values, but the cooling rate after finish rolling is large, the winding temperature is low, and the finish rolling temperature is low. It is a steel plate with large anisotropy. In the comparative examples (Conditions 5 and 8), although the strength, ductility, and anisotropy reach the target values, the steel sheet has a high yield elongation because the cooling rate after finish rolling is high or the cooling rate is high. In the comparative example (condition 9), although the strength and ductility reach the target values, the steel sheet has high yield elongation and large anisotropy because the finish rolling temperature is low and the cooling rate is high. In the comparative example (condition 10), although the ductility, yield elongation, and anisotropy reach the target values, the steel sheet has low strength because the soaking temperature is high.
Moreover, when these steel sheets are drawn, in the present invention example, the surface properties of the steel sheets are good, rough skin and stretcher strain are not recognized, and the amount of generated ears is small.
On the other hand, in the comparative example in which the yield elongation exceeded 1%, minute stretcher strain was observed. In the comparative example in which Δr is less than −0.5, the ear generation amount is large.

  According to the present invention, a steel plate having excellent strength, ductility, yield elongation, and anisotropic properties can be obtained. Most suitable as a steel plate for cans, mainly 2-piece cans.

Claims (2)

  In mass%, C: 0.01 to 0.12%, Si: 0.01 to 0.5%, Mn: 0.3 to 1.5%, P: 0.01 to 0.2%, Al: 0.1% or less, Nb: 0.005 to 0.1%, The balance is composed of iron and inevitable impurities, and has a ferrite single-phase structure, the ferrite average crystal grain size is 7 μm or less, the plate thickness is 0.18 mm or less, the tensile strength is 500 MPa or more, and the total elongation is 20 % Steel sheet for high strength and high ductility cans with yield elongation of less than 1% and anisotropy (Δr) of −0.5 to 0. In mass%, C: 0.01 to 0.12%, Si: 0.01 to 0.5%, Mn: 0.3 to 1.5%, P: 0.01 to 0.2%, Al: 0.1% or less, Nb: 0.005 to 0.1%, Steel with the balance of iron and inevitable impurities
Hot rolled at a finishing temperature of 870 ° C or higher,
Cool down to 40 ℃ / s or less until winding
Winding at a winding temperature of 620 ° C or higher, pickling,
Next, after performing cold rolling at a rolling reduction of 80% or more,
Perform box annealing under conditions of soaking temperature of 600-690 ° C and cooling rate of 20 ° C / h or less,
A method for producing a steel sheet for high strength and high ductility cans having a sheet thickness of 0.18 mm or less, characterized by performing temper rolling at a pressure regulation rate of 1.5% or less.