JP6210177B2 - Steel plate for can and manufacturing method thereof - Google Patents

Description

  The present invention relates to a steel plate for cans and a method for producing the same, and more particularly to a steel plate for cans having excellent workability, excellent surface roughness in surface appearance, and striped defects and a method for producing the same.

  Several properties are required for cold-rolled steel sheets used in two-piece cans such as deep-drawn cans, DRD (Drawn and Redrawn) cans, and DI (Drawn and Ironed) cans. Specifically, (1) no defects such as cracks occur during processing, excellent press workability (hereinafter also referred to simply as workability), and (2) rough surface of the steel sheet after press processing. There is a demand for a small, stretcher strain (hereinafter also referred to as a stripe defect) and a good finished appearance.

  Among these, regarding the workability of (1), it is effective to decrease the yield strength (YP), increase the elongation (El) and the r value of the steel sheet. As for (2), it is well known that the surface roughness of the steel sheet after processing is improved by reducing the crystal grain size of the steel sheet structure. In response to such a demand, for example, Patent Document 1 and Patent Document 2 propose a steel sheet in which Ti or Nb is added to an ultra-low carbon steel, yield strength (YP) is lowered, and workability is improved. Moreover, in patent document 3, the steel plate which made small the surface roughness after a process is proposed by using the low carbon steel whose crystal grain is a fine grain.

Japanese Patent No. 3548314 JP 2009-1555692 A Japanese Patent Laid-Open No. 10-30152

  However, like the techniques described in Patent Document 1 and Patent Document 2, the ultra-low carbon steel in which Ti or Nb is added and solid solution C is completely precipitated and fixed has coarse crystal grains and is excellent. However, there is a problem that rough skin occurs after press working and the rough skin resistance is poor. Moreover, the low carbon steel obtained by patent document 3 has a problem that a crystal grain is fine and yield strength (YP) is high, and it is inferior to workability by the crack at the time of can molding. Thus, coarsening of the crystal grain size is effective for workability, and fine grain size is effective for rough skin resistance. Conventionally, it has been difficult to satisfy both. It was. Moreover, in the prior art, the suppression of stripe defects was not sufficient as the surface appearance.

  The object of the present invention is to solve the above-mentioned problems, and to provide a steel plate for cans which has excellent workability, excellent surface roughness in surface appearance and suppresses striped defects, and a method for producing the same.

  The inventors of the present invention have made extensive studies to solve the above-described problems and to develop a steel plate for a can that can achieve all of improvement of workability, improvement of rough skin resistance, and suppression of striped defects. As described above, a reduction in yield strength (YP) due to coarsening of the crystal grain size is effective for improving workability. Further, it is effective to reduce the crystal grain size in order to improve the rough skin resistance. Although this feature is contradictory at first glance, the crystal grain size that affects the yield strength (YP) is the crystal grain size in the entire region of the steel sheet, whereas the crystal grain size that affects the rough skin resistance is a crystal near the surface layer of the steel sheet. We focused on the particle size. Therefore, the present inventors have found that it is possible to control the distribution of crystal grain size in the plate thickness direction by controlling the equivalent dislocation density of the surface layer of the original steel plate before annealing (steel plate before annealing). It was.

  FIG. 1 shows the relationship between the equivalent dislocation density of the steel sheet surface layer before recrystallization by annealing, the surface layer average crystal grain size and the total thickness average crystal grain size of the steel sheet after annealing. The measurement of the equivalent dislocation density of the steel sheet surface layer was performed according to the method described later. As shown in FIG. 1, as the equivalent dislocation density of the steel sheet surface layer increases, the surface average grain size of the steel sheet after annealing (in the figure, simply referred to as the surface average grain size) significantly decreases. On the other hand, the total thickness average grain size of the steel sheet after annealing (in the figure, simply referred to as the total thickness average grain size) hardly changes. Furthermore, the high equivalent dislocation density on the surface layer of the steel plate promotes recrystallization during annealing, suppresses the remaining non-recrystallized grains that are problematic in the ultra-low carbon steel plate added with Ti and Nb described above, and the steel plate surface after annealing. Suppresses striped defects. Therefore, by increasing the equivalent dislocation density of the steel sheet surface layer, it is possible to obtain a steel sheet having low yield strength (YP), excellent workability, excellent surface roughness in the surface appearance, and having suppressed stripe defects. .

This invention is made | formed based on such knowledge, The summary is as follows.
[1] By mass%, C: 0.0010% to 0.0050%, Si: 0.03% or less, Mn: 0.3% or less, P: 0.02% or less, S: 0.02% In the following, Al: 0.01% or more and 0.10% or less, N: 0.004% or less, Ti: 0.01% or more and 0.06% or less and / or Nb: 0.01% or more and 0.0. Containing no more than 04%, with the balance being composed of Fe and inevitable impurities,
The area ratio of the non-recrystallized grains on the steel sheet surface is 0.10% or less, and the average crystal grain diameter d1 and the average crystal grain diameter d2 of the total thickness in the structure from the steel sheet surface to a depth of 50 μm are d1 ≦ 0.8 ×. A steel plate for cans satisfying the relationship of d2 and d2 of 11.0 μm or more.
[2] The steel plate for cans according to [1], further containing B: 0.0003% or more and 0.0030% or less in terms of mass% as the component composition.
[3] The steel plate for cans according to [1] or [2], wherein a plating film is formed on the surface of the steel plate.
[4] The steel plate for cans according to any one of [1] to [3], wherein the plate thickness is 0.1 mm or more and 0.6 mm or less.
[5] A method for producing a steel plate for cans according to any one of [1] to [4],
The steel slab is heated at a heating temperature of 1000 ° C. to 1300 ° C., hot-rolled at a finish rolling temperature of 800 ° C. to 1000 ° C., wound at a temperature of 600 ° C. to 700 ° C., pickled, and cold-rolled. Thereafter, the steel sheet for cans that is annealed at 550 ° C. or more and 700 ° C. or less with respect to a steel sheet having an equivalent dislocation density ρ of 1.0 × 10 ¹⁵ m ⁻² or more in the depth direction from the surface of the steel sheet before annealing. Manufacturing method.

Here, the equivalent transition density ρ is calculated from 14.4ε ² / b ² (ε represents a non-uniform strain of the steel sheet, and b is 2.5 × 10 ⁻¹⁰ m).

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the steel plate for cans which has low yield strength (YP), is excellent in workability, is excellent in surface roughness, and has excellent anti-skin roughness and suppresses stripe defects.

It is a graph which shows the relationship between the equivalent transition density of the steel plate surface layer before recrystallization by annealing and the average crystal grain size of the steel plate after annealing (total thickness average crystal grain size and surface layer average crystal grain size of the steel plate after annealing) .

  The steel plate for cans according to the present invention is in mass%, C: 0.0010% or more and 0.0050% or less, Si: 0.03% or less, Mn: 0.3% or less, P: 0.02% or less, S: 0.02% or less, Al: 0.01% or more and 0.10% or less, N: 0.004% or less, Ti: 0.01% or more and 0.06% or less and / or Nb: 0 0.01% or more and 0.04% or less, and the balance is composed of Fe and inevitable impurities, the area ratio of unrecrystallized grains on the steel sheet surface is 0.10% or less, The average crystal grain size d1 and the average crystal grain size d2 of the entire thickness satisfy the relationship of d1 ≦ 0.8 × d2, and d2 is 11.0 μm or more. Hereinafter, the steel plate for cans of the present invention will be described.

[Ingredient composition]
First, the component composition of the steel plate for cans which concerns on this invention is demonstrated. In the following, “%” of the component amount means “% by mass” unless otherwise specified.

<C: 0.0010% or more and 0.0050% or less>
If C is less than 0.0010%, the ferrite crystal grains are excessively coarsened, so the lower limit of the C content is 0.0010%. On the other hand, when the C content exceeds 0.0050%, the yield strength increases and the workability at the time of draw forming decreases, so the upper limit of the C content is set to 0.0050%. Therefore, the C content is set to 0.0010% or more and 0.0050% or less. Preferably, the C content is 0.0015% or more. Preferably, the C content is 0.0040% or less.

<Si: 0.03% or less>
Even if Si is not intentionally contained, it is an element that remains in the steel as an impurity component and degrades the corrosion resistance and plating adhesion of the steel sheet. In order to ensure good corrosion resistance, the Si content is 0. 0.03% or less. Preferably, the Si content is 0.02% or less.

<Mn: 0.3% or less>
Mn prevents hot cracking of the slab by precipitating S in the steel as MnS. In order to precipitate and fix S, it is desirable to contain 0.1% or more of Mn. Further, Mn is a solid solution strengthening element, and the workability at the time of drawing is reduced by increasing the yield strength, so the upper limit of the Mn content is 0.3%.

<P: 0.02% or less>
P is a solid solution strengthening element, and decreases the workability at the time of drawing by increasing the yield strength. Moreover, it is an element which reduces the adhesiveness of Ni plating, P content shall be 0.02% or less.

<S: 0.02% or less>
S is preferably as small as possible from the viewpoint of preventing hot cracking of the slab, and the S content is 0.02% or less.

<Al: 0.01% or more and 0.10% or less>
When Al is contained in an amount of 0.01% or more, it combines with N in the steel to form AlN, and by reducing the solid solution N, an increase in yield strength (YP) due to aging of the steel sheet is suppressed. On the other hand, when the Al content exceeds 0.10%, inclusions such as alumina are likely to occur, and the defect occurrence rate after processing increases. Therefore, it is 0.10% or less. Therefore, the Al content is set to 0.01% or more and 0.10% or less. The Al content is preferably 0.02% or more. Moreover, as Al content, 0.08% or less is preferable and 0.07% or less is more preferable.

<N: 0.004% or less>
N forms a nitride with Al or B and tends to be harmless, but the N content is preferably as low as possible, and is 0.004% or less. Preferably, the N content is 0.003% or less.

<Ti: 0.01% to 0.06% and / or Nb: 0.01% to 0.04%>
Ti precipitates and fixes C and N in the steel and improves the aging resistance of the steel sheet. If the content is less than 0.01%, the effect is not sufficient, and aging deterioration is caused. If the content exceeds 0.06%, the recrystallization temperature is remarkably increased, so that unrecrystallized grains tend to remain. Therefore, when Ti is contained, the Ti content is 0.01% or more and 0.06% or less. When Ti is contained, the Ti content is preferably 0.01% or more and 0.05% or less, and more preferably 0.01% or more and 0.04% or less.

  Nb precipitates and fixes C in the steel and improves the aging resistance of the steel sheet. If it is less than 0.01%, the effect is not sufficient, and aging deterioration is caused. If it exceeds 0.04%, the recrystallization temperature is remarkably increased, so that unrecrystallized grains tend to remain. Therefore, when Nb is contained, the Nb content is set to 0.01% or more and 0.04% or less. When Nb is contained, the Nb content is preferably 0.01% or more and 0.03% or less, and more preferably 0.01% or more and 0.02% or less.

  The balance other than the above components is Fe and inevitable impurities. In the present invention, B is not an essential component, but can be contained in the following range as required.

<B: 0.0003% or more and 0.0030% or less>
B, like Al, binds to N in steel to form BN, and reduces the amount of solid solution N, thereby suppressing an increase in yield strength (YP) due to aging. Moreover, it has the effect | action which improves the uniformity of the structure | tissue of the width direction of a hot-rolled steel plate after winding, and a longitudinal direction by precipitating N in steel as BN before becoming AlN. Therefore, B is contained if necessary. However, if the B content is less than 0.0003%, it may be difficult to exert the above effect. On the other hand, if the B content exceeds 0.0030%, the above action may be saturated, or the solid solution B may increase, resulting in deterioration of deep drawability. Therefore, the B content is preferably 0.0003% or more and 0.0030% or less. The B content is more preferably 0.0005% or more. Further, the B content is more preferably 0.0020% or less.
[Organization]
Although the structure of the steel plate for cans of this invention is not specifically limited, It is preferable that a ferrite is included as a main phase. The main phase means that ferrite is contained in an area ratio of 90% or more, preferably 95% or more in area ratio, more preferably 98% or more in area ratio, and 100% in area ratio. There may be. The balance other than ferrite includes bainite.

<The area ratio occupied by non-recrystallized grains on the steel sheet surface is 0.10% or less>
Non-recrystallized grains are harder than recrystallized grains, and due to their different deformability, striped surface defects (hereinafter also referred to as stripe defects) are generated after press working. Since the presence of non-recrystallized grains on the steel sheet surface becomes a problem for striped defects, the area ratio of the non-recrystallized grains on the steel sheet surface after recrystallization annealing is reduced to 0.10% or less, A steel plate for cans having an excellent appearance after processing can be obtained. In order to obtain the area ratio of the non-recrystallized grains on the surface of the steel sheet after recrystallization annealing, the surface of the steel sheet is observed and the ratio (area ratio) of the non-recrystallized structure to the entire structure is obtained. The area ratio occupied by crystal grains may be used. The non-recrystallized grains present inside the steel sheet do not specifically define because they do not affect the surface appearance. It is preferable that the amount is as small as possible. Moreover, the area ratio which the non-recrystallized grain accounts on the steel plate surface after recrystallization annealing can be adjusted by controlling the equivalent dislocation density from the steel plate surface before recrystallization by annealing to a depth of 50 μm.

<The average crystal grain size (d1) and the total thickness average crystal grain size (d2) in the structure from the steel sheet surface to a depth of 50 μm satisfy the relationship of d1 ≦ 0.8 × d2 and d2 is 11.0 μm or more>
The larger the crystal grain size of the steel sheet surface layer, the more likely it is that the surface becomes rough after press working, and the poor surface roughness resistance is obtained. In the present invention, the average crystal grain size (d1) in the structure from the steel sheet surface to the depth of 50 μm representing the crystal grain size of the steel sheet surface layer, and the average crystal grain size of the total thickness of the steel sheet (d2, hereinafter referred to as total thickness average crystal grain) In the case of d1 ≦ 0.8 × d2, the crystal grain size in the vicinity of the steel plate surface layer is made fine, and the crystal grain size in the region other than the steel plate surface layer is made coarse so that the workability is improved. And excellent resistance to rough skin.

  When the total thickness average crystal grain size (d2) of the steel sheet is less than 11.0 μm, the yield strength (YP) is high and the workability is inferior, so d2 is set to 11.0 μm or more.

  Moreover, although the upper limit of the average crystal grain size of the steel sheet surface layer, that is, the average crystal grain size (d1) in the structure from the steel sheet surface to the depth of 50 μm is not particularly specified, when the crystal grains are coarse, D1 is preferably 10 μm or less because it is difficult to satisfy the definition of the surface roughness Ra. The lower limit of d1 / d2 is not particularly limited, but is preferably 0.3 or more from the viewpoint of surface peeling due to a difference in hardness.

  Here, the average crystal grain size is obtained by measuring the average crystal grain size by a cutting method based on JIS G0551. When the structure of the steel sheet for cans of the present invention has ferrite as the main phase, the above average crystal grain size is obtained by measuring the ferrite average crystal grain size by a cutting method based on JIS G0551. . The average crystal grain size (d1) in the structure from the steel sheet surface to a depth of 50 μm can be adjusted by controlling the equivalent dislocation density from the steel sheet surface before the recrystallization by annealing to a depth of 50 μm. The total thickness average crystal grain size (d2) can be adjusted by changing the annealing temperature and the steel plate components.

[Surface roughness Ra after press working is 0.7 μm or less]
The smaller the surface roughness Ra of the steel sheet after press working, the better the skin resistance. In particular, in the steel sheet for cans of the present invention, when the surface roughness Ra after press working is 0.7 μm or less, the rough skin resistance can be improved. Therefore, in the steel plate for cans of this invention, it is preferable that surface roughness Ra after press work shall be 0.7 micrometer or less. Here, the surface roughness Ra is an arithmetic average roughness Ra, and can be measured using a stylus type roughness measuring instrument based on JIS B0601: '01. Further, the surface roughness Ra after the press working can be adjusted by changing the equivalent dislocation density up to 50 μm in the depth direction from the steel plate surface of the steel plate before annealing.

[Plating film]
When a plating film is applied to the steel plate for cans of the present invention, Sn plating, Ni plating, Cr plating, or the like may be applied as the surface treatment of the steel plate. Furthermore, chemical conversion treatment may be performed, or an organic film such as a laminate may be formed.

<Plate thickness is 0.1mm to 0.6mm>
When the steel plate for cans of the present invention has a thickness of 0.1 mm or more and 0.6 mm or less, the effect of improving both the workability and the rough skin resistance can be remarkably obtained. Therefore, the plate thickness is preferably set to 0.1 mm or more and 0.6 mm or less. More preferably, the plate thickness is 0.1 mm or more and 0.4 mm or less. In the present invention, the desired plate thickness can be adjusted by changing the cold rolling rate.

[Production method]
Then, the manufacturing method of the steel plate for cans of this invention is demonstrated. In the method for producing a steel plate for cans of the present invention, a slab having the above-described component composition is heated at a heating temperature of 1000 ° C. to 1300 ° C. and hot-rolled at a finish rolling temperature of 800 ° C. to 1000 ° C., 600 The equivalent dislocation density ρ is 1.0 × 10 ¹⁵ m ⁻² or more up to 50 μm in the depth direction from the steel sheet surface of the steel sheet before annealing after pickling, cold rolling, and cold rolling at a temperature of ≧ 700 ° C. A certain steel plate is annealed at 550 ° C. or more and 700 ° C. or less.

<Slab heating at a temperature of 1000 ° C to 1300 ° C>
In the present invention, the method for melting the steel material is not particularly limited, and a known melting method such as a converter or an electric furnace can be employed. In addition, after melting, it is preferable to use a slab (steel material) by a continuous casting method because of problems such as segregation, but it may also be used as a slab by a known casting method such as an ingot-bundling rolling method or a thin slab continuous casting method. good. The obtained slab is subjected to hot rolling after rough rolling or directly into a hot finish rolling mill. Slab heating temperature shall be 1000 degreeC or more from a viewpoint of ensuring the finishing rolling temperature mentioned later. When the slab heating temperature exceeds 1300 ° C., a large amount of nitride is generated, causing unrecrystallized grains to remain after annealing, and yield strength is increased. Therefore, slab heating temperature shall be 1300 degrees C or less.

<Hot rolling at a finish rolling temperature of 800 ° C to 1000 ° C>
In hot rolling, after rough rolling is performed as necessary, finish rolling is performed at a finish rolling temperature of 800 ° C. or higher and 1000 ° C. or lower. When the finish rolling temperature is lower than 800 ° C., the structure of the steel sheet original plate becomes non-uniform, and the workability and surface appearance deteriorate. Therefore, the finish rolling temperature is 800 ° C. or higher. Moreover, if it rolls over 1000 degreeC, it will cause a scale flaw and the surface appearance will be impaired. Therefore, finish rolling temperature shall be 1000 degrees C or less.

<Winding at a temperature of 600 ° C to 700 ° C>
When the coiling temperature is lower than 600 ° C., precipitates are not sufficiently precipitated, so that solid solution C and solid solution N increase and yield strength increases. Furthermore, a further increase in yield strength occurs due to aging deterioration. For this reason, the coiling temperature is set to 600 ° C. or higher. On the other hand, when the coiling temperature exceeds 700 ° C., the scale of the surface layer grows and tends to cause surface defects. For this reason, winding temperature shall be 700 degrees C or less.

<Controlling the equivalent dislocation density from the surface of the steel sheet before annealing to 50 μm in the depth direction to 1.0 × 10 ¹⁵ m ⁻² or more>
After winding, pickling, cold rolling, and cleaning, and then annealing, the equivalent dislocation density from the surface of the steel plate before annealing to 50 μm in the depth direction is 1.0 × 10 ¹⁵ m ⁻² or more. By making it into, the crystal grain of the steel plate surface layer after annealing can be made fine. More preferably, it is 1.0 × 10 ¹⁶ m ⁻² or more. The upper limit of the equivalent dislocation density is not particularly limited, but is preferably 1.0 × 10 ¹⁸ m ⁻² or less from the viewpoint of preventing surface peeling.

The method for setting the equivalent dislocation density from the surface of the steel sheet before annealing to 50 μm in the depth direction to 1.0 × 10 ¹⁵ m ⁻² or more is not particularly specified. However, it is difficult to obtain an equivalent dislocation density of 1.0 × 10 ¹⁵ m ⁻² or more in the steel sheet surface layer in the range of the cold rolling reduction ratio of about 50 to 95% that is normally performed when manufacturing a cold rolled steel sheet. . As a method of setting the equivalent dislocation density from the surface of the steel sheet before annealing to 50 μm in the depth direction to 1.0 × 10 ¹⁵ m ⁻² or more, for example, shot blasting or high strength is applied to the cold-rolled steel sheet after cold rolling. A method of applying a strain imparting process with a brush can be mentioned. Further, as another method of setting the equivalent dislocation density to 1.0 × 10 ¹⁵ m ⁻² or more, the cold rolling steel sheet after the cold rolling final stage or after cold rolling is applied at a low pressure reduction rate by a high roughness roll. The method of performing additional rolling is mentioned. As the high roughness roll, for example, a roll having a roll roughness Ra of 2.0 to 10.0 μm can be used. Further, the additional rolling at the low pressure reduction rate can be performed at a reduction rate of 0.1 to 10%, for example.

[Equivalent dislocation density]
The equivalent dislocation density can be measured by the following method. A 10 mm × 10 mm test piece is sampled from each steel plate before annealing, polished from the back surface of the test piece to a plate thickness of 50 μm, and then the polishing strain layer on the back surface layer is removed with hydrofluoric acid. An X-ray diffraction experiment is performed using this test piece, and the half width of the peak of the (110), (211), (220) crystal plane of the steel sheet is obtained. Using this half width, the non-uniform strain ε of the test piece is obtained by the Williamson-Hall method. This inhomogeneous strain ε is expressed by the formula described in Non-Patent Document 1 (Nakashima et al. “Method of evaluating dislocation density using X-ray diffraction”, CAMP-ISIJ, Vol. 17, 2004, p. 396): ρ = Substituting for 14.4ε ² / b ² , the equivalent dislocation density ρ is obtained. Note that b is the size (m) of the Burgers vector, and the value of b is 2.5 × 10 ⁻¹⁰ m.

<Annealing at a temperature of 550 ° C to 700 ° C>
The annealing may be performed by a method using either a continuous annealing furnace or a box annealing furnace. When the annealing temperature is less than 550 ° C., unrecrystallized grains may remain even if a high equivalent dislocation density is introduced into the steel sheet surface layer. On the other hand, if annealing is performed in a high temperature range exceeding 700 ° C., the crystal grains become very coarse, causing the occurrence of rough skin after pressing, resulting in poor skin resistance. Therefore, annealing temperature shall be 550 degreeC or more and 700 degrees C or less. The annealing temperature is more preferably 570 ° C. or higher and 680 ° C. or lower.

<Plating treatment>
After annealing, a plating process may be performed. When performing a plating process, you may give Sn plating, Ni plating, Cr plating etc. as surface treatment of a steel plate. Furthermore, chemical conversion treatment may be performed, or an organic film such as a laminate may be formed. After the plating treatment, it is preferable to perform temper rolling for adjusting the surface roughness. At this time, the rolling rate (elongation rate) of the temper rolling is preferably about 0.5% to 1.5%.

  As mentioned above, the steel plate for cans of the present invention described above has low yield strength, excellent workability, excellent surface roughness resistance in the surface appearance, and striped defects are suppressed. The steel plate for cans of the present invention can be applied, for example, for a two-piece can.

  Examples of the present invention will be described below.

  First, the molten steel having the composition shown in Table 1 was made into a slab by continuous casting after vacuum degassing treatment. Next, the slab was heated at 1250 ° C., scale-removed, and then roughly rolled to a plate thickness of 40 mm. Next, the steel sheet surface layer was cooled with a scale removing device, and then finish-rolled to a thickness of 3.2 mm and wound around a coil at a predetermined temperature.

  Next, the steel sheet after winding was pickled and cold-rolled. After the cold rolling, some samples were subjected to additional rolling using a roll having a roll roughness Ra = 2.1 to 7.4 μm in order to adjust the equivalent transition density, and the thickness was 0.4 mm (cold). Rolling rate: 87%). Additional rolling was performed at a rolling rate of 5%. Further, after the cold rolling, another part of the sample was subjected to shot blasting (shot condition: steel shot (average particle size 0.5 mm) was sprayed at a pressure of 0.5 MPa for 300 seconds). In addition, all the samples adjusted the cold rolling rate in a front | former stage so that final board thickness might be set to 0.4 mm. The cold-rolled sheet was degreased and pickled as a pretreatment, and then annealed in a continuous annealing line, and temper rolled with an elongation rate of 1.0%.

  The equivalent transition density was measured according to the method described above. The obtained steel sheet was subjected to mechanical property evaluation and crystal grain size measurement. Table 2 also shows the surface roughness Ra (μm) of the steel sheet obtained.

  In the mechanical property evaluation, yield strength (YP), tensile strength (TS), and elongation (El) were evaluated by a tensile test. Tensile properties were measured according to the test method described in JIS Z2241, after being processed into a No. 5 test piece described in JIS Z2201. As for the crystal grain size, the ferrite average crystal grain size was measured by a cutting method based on JIS G0551.

  Further, a 100 mm diameter circular blank is sampled from the steel sheet, formed into a 14 mm diameter cylindrical shape by five-stage multistage drawing, and then the surface roughness of the can body using a stylus type roughness measuring instrument. Ra was measured, and the evaluation of workability (formability) and the evaluation of surface appearance were evaluated for the rough skin resistance and the suppression of stripe defects. The evaluation of workability was performed by drawing 200 pieces, and the case where no defects such as cracks and wrinkles occurred was evaluated as ◯, and the case where the defects were generated was evaluated as ×. The evaluation of the rough skin resistance was evaluated as ◎ when the surface roughness Ra of the can body portion was less than 0.5 μm, ◯ when 0.5 μm or more and 0.7 μm or less, and × when 0.7 μm or more. In the evaluation of the suppression of striped defects, those in which defects such as stripes occurred on the processed surface were evaluated as x, and the others were evaluated as ◯.

  The production conditions and evaluation results are shown in Table 2.

  The examples of the present invention were excellent in workability, were excellent in surface roughness, were able to suppress striped defects, and had performance suitable as steel plates for cans. On the other hand, in the comparative example, at least one of workability and surface appearance was inferior. Specifically, in Samples A4 and B3, the area ratio of unrecrystallized grains on the steel sheet surface exceeds 0.10%, and the average crystal grain size (d1) in the structure from the steel sheet surface to a depth of 50 μm Since d1 / d2 exceeded 0.8 with respect to the total thickness average crystal grain size (d2), the surface appearance was inferior in skin roughness resistance, and striped defects were generated.

  Sample C3 had an area ratio of non-recrystallized grains on the steel sheet surface exceeding 0.10%, and the total thickness average crystal grain size (d2) was less than 11.0 μm. Striped defects occurred. In the sample D1, the C content of the steel used exceeds 0.0050 mass%, the area ratio occupied by unrecrystallized grains on the steel sheet surface exceeds 0.10%, and the total thickness average crystal grain size ( Since d2) was less than 11.0 μm, the workability was poor.

Sample E1 had a C content of less than 0.0010 mass% of the steel used, and the area ratio of non-recrystallized grains on the steel sheet surface exceeded 0.10%, so that workability and rough skin resistance were increased. It was inferior to both. In Sample F1, the Mn content of the steel used exceeded 0.3% by mass, and the area ratio of non-recrystallized grains on the steel plate surface exceeded 0.10%, so that the workability was poor.

Claims (8)

In mass%, C: 0.0010% or more and 0.0050% or less, Si: 0.03% or less, Mn: 0.3% or less, P: 0.02% or less, S: 0.02% or less, Al : 0.01% to 0.10%, N: 0.004% or less, Ti: 0.01% to 0.06% and / or Nb: 0.01% to 0.04% And the balance has a component composition consisting of Fe and inevitable impurities,
The area ratio of the non-recrystallized grains on the steel sheet surface is 0.10% or less, and the average crystal grain diameter (d1) and the total thickness average crystal grain diameter (d2) in the structure from the steel sheet surface to a depth of 50 μm are d1 ≦ 0. Steel plate for cans satisfying the relationship of 8 × d2 and d2 being 11.0 μm or more.   The steel plate for cans according to claim 1, further comprising, by mass%, B: 0.0003% or more and 0.0030% or less as the component composition.   The steel plate for cans according to claim 1 or 2, wherein a plating film is formed on the surface of the steel plate.   The steel plate for cans according to any one of claims 1 to 3, wherein the plate thickness is 0.1 mm or more and 0.6 mm or less. In mass%, C: 0.0010% or more and 0.0050% or less, Si: 0.03% or less, Mn: 0.3% or less, P: 0.02% or less, S: 0.02% or less, Al : 0.01% to 0.10%, N: 0.004% or less, Ti: 0.01% to 0.06% and / or Nb: 0.01% to 0.04% A steel slab having a composition comprising Fe and inevitable impurities as a balance , heated at a heating temperature of 1000 ° C. to 1300 ° C., hot-rolled at a finish rolling temperature of 800 ° C. to 1000 ° C., 600 The equivalent dislocation density ρ from the surface of the steel sheet after annealing, pickling, cold rolling, and before annealing to 50 μm in the depth direction is 1.0 × 10 ¹⁵ m ⁻² or more. performs the following annealed 550 ° C. or higher 700 ° C. relative to the steel plate, the steel plate The average crystal grain size (d1) and the total thickness average crystal grain size (d2) in the structure from the surface of the steel sheet to the depth of 50 μm are d1 ≦ 0. The manufacturing method of the steel plate for cans which satisfy | fills the relationship of 8xd2, and d2 is 11.0 micrometers or more .
Here, the equivalent transition density ρ is calculated from 14.4ε ² / b ² (ε represents a non-uniform strain of the steel sheet, and b is 2.5 × 10 ⁻¹⁰ m). The manufacturing method of the steel plate for cans according to claim 5 which contains B: 0.0003% or more and 0.0030% or less by mass% as said ingredient composition. The manufacturing method of the steel plate for cans according to claim 5 or 6 which performs plating processing after performing said annealing. The manufacturing method of the steel plate for cans of any one of Claims 5-7 whose plate | board thickness of the said steel plate for cans is 0.1 mm or more and 0.6 mm or less.

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