JP4378840B2 - Manufacturing method of steel plate for cans - Google Patents

Description

【００３３】
【表２】

【００３４】
表２中、水準a 〜ｇは、鋼記号Ａの鋼種を用い、主に熱延時の摩擦係数を変化させた時の特性を調査したものであるが、水準ｄ，ｅのように熱延時の摩擦係数が0.20を超えた場合には、平均ｒ値が 1.0以下と低いか、あるいはΔｒが−0.30を超える負で大きな値となった。 また、水準ｆは、フェライト域での圧延であったため、熱延板の結晶粒が大きくなり、肌荒れの発生が見られた。さらに、水準ｇは、Ａ値の絶対値が0.30を超え、Δｒが−0.30を超える負で大きな値となった。
水準ｈ〜ｏは、同じく鋼記号Ａの鋼種を用い、主に二次圧延率を変化させた場合であるが、水準ｌ〜ｏのように摩擦係数が0.20を超えた場合は、摩擦係数の小さい水準ｈ〜ｊに比べて、全体的に平均ｒ値が低く、またΔｒも負で大きな値となった。
水準ｐ〜ｔは、鋼記号Ａ〜Ｅの鋼種を用い、主にＣ量の影響を見たものであるが、水準ｓに示したように使用鋼スラブの炭素量が高い場合には、潤滑性がよくてもｒ値が低く、またΔｒも負で大きくなっている。 一方、水準ｔのように使用鋼スラブの炭素量が低すぎる場合には、平均ｒ値が低く、またΔｒも負で大きな値となっている。
【００３５】
【発明の効果】
かくして、この発明によれば、平均ｒ値が 1.0以上と高く、しかもその面内異方性すなわちΔｒの絶対値が0.30と小さく、従って特性のバラツキが小さく、さらに絞り加工後に肌荒れが生じることなく、美麗な外観を呈する缶用鋼板を安定して得ることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a steel plate for a can having a small in-plane anisotropy having an r value suitable for use in a beverage can, particularly a two-piece can subjected to drawing.
[0002]
[Prior art]
Conventionally, various manufacturing methods have been proposed for steel plates for cans used for drawing.
For example, Japanese Patent Laid-Open No. Sho 62-161919 discloses an in-plane anisotropy of r value by adjusting a coiling temperature, a cold rolling reduction ratio, and a recrystallization annealing temperature during the production process of a low carbon aluminum killed steel. The manufacturing method of the steel plate for cans which is excellent in the small drawability of this is disclosed.
[0003]
In the steel sheet for cans for drawing as described above, if the in-plane anisotropy of r value is large, that is, the absolute value of Δr is large, non-uniform cup height called an earring occurs after drawing and the yield decreases. Not only that, but depending on the application, printing may be distorted and defects may be induced in the subsequent flange processing. Therefore, it is particularly important to reduce the in-plane anisotropy of the r value in this type of steel sheet. It is said.
[0004]
Here, Δr is a value defined by the following equation and takes a positive value, 0, or a negative value. The fact that the in-plane anisotropy of the r value is small means that Δr is close to 0, that is, the absolute value of Δr is small.
Δr = (r ₀ + r ₉₀ −2r ₄₅ ) / 2
Here, r ₀ : r value in the rolling direction r ₉₀ : r value in the direction making an inclination of 90 ° with the rolling direction r ₄₅ : r value in the direction making an inclination of 45 ° with the rolling direction
There are various factors that affect the in-plane anisotropy, but among them, the effects of cold rolling reduction and secondary rolling reduction are considered to be significant. "Iron and Steel Vol.86 (2000) No.1P .32-37) and JP-A-9-184018, it was necessary to adjust the hot rolled finish thickness according to the product plate thickness.
[0006]
Moreover, the steel plate for cans is required to have stable mechanical properties over the longitudinal direction and the width direction of the coil.
For this reason, in JP-A-9-104919, although the thickness of the hot-rolled sheet is not described, in an ultra-low carbon steel sheet of 0.0050 mass% or less, the sheet bar is once wound around a coil and then rewound. It is recommended to heat the edges of the steel and to perform lubrication rolling with a friction coefficient of 0.15 or less.
However, the ultra-low carbon steel sheet as described above has a disadvantage that roughening occurs after drawing because crystal grains are likely to be coarsened and a fine crystal structure cannot be finally obtained.
[0007]
Furthermore, in steel sheets for cans, the material has recently been made thinner in order to reduce costs, and as a result, unprecedented high cold rolling reduction and secondary rolling reduction have been required. It is desired that the in-plane anisotropy is small even below.
As a response to the above request, Japanese Patent Application Laid-Open No. 10-223792 discloses a hot rolled sheet having a thickness of 1.8 mm or less for a steel type having a carbon content of 0.02 mass% or less, and a cold reduction ratio of 75%. A technique of performing primary rolling below and performing secondary rolling at a rolling reduction of 20% or less after annealing is disclosed.
However, even with this technique, in the region where the carbon content is extremely low, there is a problem that the crystal grains are coarsened and the skin is likely to be rough, as described above. In the low carbon region of 0.01 to 0.02 mass%, Since it is extremely difficult to control the melt C, there is a problem that the precipitation state of the carbide is changed by a slight variation in the manufacturing conditions, and the strength is likely to vary accordingly.
[0008]
[Problems to be solved by the invention]
The present invention advantageously solves the above-described problem, and does not cause roughening after drawing, and does not cause variations in characteristics even when the material is thinned. It aims at proposing the advantageous manufacturing method of the steel plate for cans with small anisotropy.
[0009]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above object, the inventors have made it advantageous to contain carbon to some extent in order to refine crystal grains and prevent roughening after drawing. In addition, in order to prevent the deterioration of the in-plane anisotropy even when the thickness is reduced, it was found that the hot rolled finish thickness must be 1.5 mm or less.
[0010]
In addition, as a result of further research, in rolling such thin objects, if lubrication rolling is not used not only in the ferrite region but also in the austenite region, an abnormal texture develops in the surface layer, and the r value and its surface The knowledge that internal anisotropy deteriorates was obtained.
The lubrication rolling is also disclosed in the above-mentioned Japanese Patent Laid-Open No. 9-104919. However, in this publication, the steel type is limited to an ultra-low carbon steel sheet having C ≦ 0.005 mass%, and the purpose thereof is as follows. The variation in the longitudinal direction and the width direction of the coil, such as the r value, was reduced.
Further, although lubrication rolling is also disclosed in Japanese Patent Application Laid-Open No. 10-223792, this technique is also a technique related to a steel type having a relatively low carbon content of 0.02 mass% or less.
[0011]
However, when the above-described lubrication rolling is performed, in addition to the variation in the coil, the r value and the in-plane anisotropy of the r value and its in-plane anisotropy are obtained particularly in the material that is made fine by containing carbon to some extent as in the present invention. It was found that the absolute value fluctuated more than expected from when carbon was low.
In such a case, in order to control Δr, it has been determined that various manufacturing conditions including the thickness of the hot-rolled sheet and the friction coefficient need to be controlled within a predetermined range.
The present invention is based on the above findings.
[0012]
That is, the present invention is a mass percentage,
C: 0.020 to 0.050%,
Si: 0.04% or less,
Mn: 0.6% or less,
Al: 0.005 to 0.1%,
P: 0.02% or less,
S: 0.02% or less,
N: 0.0005 to 0.010%
Steel slab with a composition of Fe and unavoidable impurities in the balance, finish rolling temperature: Ar ₃ to (Ar ₃ + 100 ° C.), and at least the final 3 stands of the friction coefficient between the rolling roll and the steel plate: 0.20 or less After hot rolling at 0.8 to 1.5 mm thickness, it is wound into a coil at a temperature of 500 to 750 ° C, pickled, cold rolled at a reduction ratio of 80 to 88.3 %, and then re-rolled. After annealing at the crystal temperature or higher, the steel sheet for cans is manufactured by secondary rolling at a reduction rate of 9.8 % or less. At that time, the carbon content is C (mass%), and the sheet of hot-rolled sheet Thickness is t (mm), maximum value of friction coefficient in the last 3 stands of hot finish rolling is μ, winding temperature is CT (° C), cold rolling reduction ratio is CR (%), secondary rolling reduction ratio is DR ( %)), The following formula (1)
A = 7.882 −3.5 C−0.088 CR−0.014 DR
+0.005 (CT-700) -4μ (1.6-t) ² --- (1)
Each of the above production conditions is adjusted so that the absolute value of A represented by the formula is 0.30 or less. This is a method for producing a steel plate for cans with small in-plane anisotropy.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be specifically described below.
First, the reason why the component composition of the material is limited to the above range in the present invention will be described. In addition, "%" used for display of content of each element shall represent mass percentage (mass%) unless there is particular notice.
C: 0.020 to 0.050%
C is an effective element for refining the structure and strengthening the steel. However, if the content is less than 0.020%, it is difficult to control the solute carbon, and the precipitation state of carbide is easily affected by hot rolling conditions. Material variations are likely to occur. Further, in order to refine crystal grains, suppress roughening after drawing, and improve the surface appearance, the C content needs to be 0.020% or more.
Further, in the ultra-thin hot rolling in the austenite region, which is the main point of the present invention, 0.020% or more, more preferably 0.025%, more preferably from the viewpoint of the effect of improving the in-plane anisotropy and the r value by lubrication rolling. It is important to perform lubrication rolling under the above C content.
However, if the amount of C exceeds 0.050%, the amount of carbide is excessive and the moldability is lowered, so the amount of C is limited to the range of 0.020 to 0.050%.
[0014]
Si: 0.04% or less
If Si is contained in a large amount, it induces scale defects and the like, and the material becomes extremely hard and cold rolling performance is impaired. Therefore, the Si content is limited to 0.04% or less, more preferably 0.02% or less.
[0015]
Mn: 0.6% or less
Mn has a function of fixing S as MnS, so it is preferable to contain 0.05% or more. However, if it exceeds 0.6%, the material is hardened, the cold rolling property deteriorates, and the elongation and the r value decrease. Therefore, the Mn content is limited to 0.6% or less.
[0016]
Al: 0.005 to 0.1%
Al not only contributes effectively as a deoxidizer in the melting stage, but is also an element useful for fixing solid solution N as AlN. For this purpose, it is necessary to contain at least 0.005%. However, if it exceeds 0.1%, the effect not only reaches saturation, but also causes a decrease in elongation. Therefore, Al is contained in the range of 0.005 to 0.1%. It was.
[0017]
P: 0.02% or less P causes hardening of the steel and a decrease in workability. Therefore, its mixing is preferably reduced as much as possible, but 0.02% or less is acceptable.
[0018]
S: 0.02% or less When the S amount exceeds 0.02%, not only hot cracking is induced, but also elongation and the like are reduced. Therefore, the S amount is limited to 0.02% or less.
[0019]
N: 0.0005 to 0.010%
In order to ensure moldability, the N content needs to be reduced to 0.010% or less. However, since it is extremely difficult to reduce it to a value lower than 0.0005% with the current melting technology, the amount of N is limited to a range of 0.0005 to 0.010%.
[0020]
Next, the manufacturing conditions of the present invention will be described.
First, as a method for producing a slab, a continuous casting method is advantageously adapted, but it is needless to say that an ingot-splitting method may be used.
Similarly, the slab heating temperature is not particularly limited, but is preferably about 1000 to 1250 ° C.
[0021]
After the above slab heating, hot rolling is performed. In this hot rolling, the finish thickness, the finish rolling temperature, and the friction coefficient between the rolling roll and the steel plate in the final three stands are important.
1) Finishing thickness of hot rolling: 0.8 to 1.5 mm
Steel sheets for cans need to be hot-rolled sheets with a thickness of 1.5 mm or less in order to control the Δr of the final product as the material becomes thinner. In addition, in lubrication rolling in the austenite region, which is a control item in the present invention, the in-plane anisotropy of the r value greatly changes due to poor lubrication, which is 1.5 mm or less. The reason why the more expected control of Δr is sufficient is the reason why the finished thickness is 1.5 mm or less.
However, finishing to a thickness of less than 0.8 mm is extremely difficult with current equipment, so the finishing thickness in hot rolling is limited to the range of 0.8 to 1.5 mm.
In order to homogenize the material in the coil longitudinal direction and width direction, the sheet bar after rough rolling is temporarily wound around the coil, and when the sheet bar is rewound, the preceding sheet bar and the succeeding sheet bar are joined. It goes without saying that the method, the method of heating the sheet bar including the edge, and the like can be combined as necessary.
[0022]
2) Finishing rolling temperature: Ar ₃ to (Ar ₃ + 100 ° C)
If the finish rolling temperature is lower than the Ar ₃ transformation point, coarse grains are formed on the surface layer, which causes rough skin and increased in-plane anisotropy of the r value. On the other hand, if it exceeds (Ar ₃ + 100 ° C), scale defects occur frequently. Therefore, the finish rolling temperature is limited to a range of Ar ₃ to (Ar ₃ + 100 ° C.).
[0023]
3) Coefficient of friction between rolling roll and steel plate in at least 3 final finishing stands: 0.20 or less Friction coefficient between rolling roll and steel plate even in the γ region when the finishing thickness in hot rolling becomes thin as shown in 1) above. In particular, at least for the final three stands of finish rolling where the plate thickness is reduced, the coefficient of friction in each stand needs to be 0.20 or less.
This is because when the friction coefficient of at least the final three stands exceeds 0.20, an abnormal texture is formed on the surface of the hot-rolled sheet, and this texture becomes the main texture of the steel sheet because the sheet thickness is thin. is there. This texture remains even after cold rolling-recrystallization annealing, and it is preferable not only to change the in-plane anisotropy of the r value and make the Δr value negative, but also to lower the average r value. Absent.
[0024]
Further, this effect is remarkable in the low carbon steel sheet having the C content of 0.02% or more as described above.
That is, an extremely low carbon region having a C content of 0.020% or less, particularly 0.0050% or less originally has a high r value, and such a component system has sufficient drawability of a steel plate for cans even without lubrication rolling. r value can be obtained, and Δr value after annealing is a positive value, and Δr changes in the negative value direction by secondary rolling. Therefore, Δr can be set to zero, primary rolling rate and secondary It was not so difficult to adjust the rolling rate. On the other hand, when the C content is 0.02% or more, the average r value is inherently low and Δr tends to be a negative value. Therefore, it has been found that lubricating rolling in a γ region of a thin material is very effective.
In this case, as a result of various studies on the contribution of the thickness t of the hot-rolled sheet and the friction coefficient μ to Δr, a function 4 μ (1.6−t) ² expressed by the following equation is obtained.
Where μ is the maximum friction coefficient of the last three stands t is the thickness of the hot-rolled sheet (mm)
Was found to be expressed as:
[0025]
4) Winding temperature: 500-750 ° C
If the coiling temperature is less than 500 ° C, solute carbon tends to remain after winding, so that the in-plane anisotropy may be significantly reduced. Since the formation of coarse particles is a concern, the winding temperature is limited to a range of 500 to 750 ° C.
[0026]
Then, after pickling, cold rolling is performed.
5) Cold rolling reduction: 80 ~ 88.3 %
In the case of steel plates for cans, it is necessary to reduce the product plate thickness, and a cold rolling rate of at least 80% is required in consideration of the hot-rolled finish thickness. However, if the cold rolling reduction ratio exceeds 88.3 %, the Δr value becomes a negative value and a large value, and the earring becomes large, resulting in a decrease in yield. Therefore, the cold rolling reduction ratio is limited to a range of 80 to 88.3 %.
[0027]
6) Annealing temperature: above the recrystallization temperature The annealing temperature needs to be above the recrystallization temperature of the steel sheet. However, if the temperature exceeds 800 ° C., the crystal grains become coarse and cause rough skin when the product is molded. Therefore, the upper limit of the annealing temperature is preferably about 800 ° C. The annealing is preferably continuous annealing.
[0028]
7) Secondary rolling reduction ratio: 9.8 % or less This secondary rolling (also referred to as temper rolling) is performed for the purpose of adjusting to a predetermined hardness. However, when the rolling reduction ratio of the secondary rolling exceeds 9.8 %, not only the workability deteriorates and the press forming becomes unbearable, but also the in-plane anisotropy of the r value becomes large, the earrings become large and the yield decreases. Therefore, the secondary rolling reduction is limited to 9.8 % or less.
[0029]
As mentioned above, although the appropriate range was demonstrated about various manufacturing conditions which influence (DELTA) r, considering the contribution to these (DELTA) r, the result of repeating earnest examination in order to find the parameter | index which can judge (DELTA) r comprehensively The carbon content is C (mass%), the thickness of the hot-rolled sheet is t (mm), the maximum friction coefficient of the final three stands in hot rolling is μ, and the coiling temperature is CT (° C) ), When the cold rolling reduction ratio is CR (%) and the secondary rolling reduction ratio is DR (%), the following formula (1)
A = 7.882 −3.5 C−0.088 CR−0.014 DR
+0.005 (CT-700) -4μ (1.6-t) ² --- (1)
Each production condition is adjusted so that the absolute value of A is 0.30 or less, with A as an index, μ being 0.20 or less, and the finishing rolling temperature being Ar ₃ to (Ar ₃ + 100 ° C.). For example, it has been found that the absolute value of Δr is 0.30 or less and a good in-plane anisotropy can be secured.
In the two-piece can used for drawing, the in-plane anisotropy of the r value, that is, Δr is particularly important. If the absolute value of the A value is controlled to 0.30 or less, extremely good results can be obtained. It can be done.
[0030]
【Example】
The steel plate for cans was manufactured by processing the steel slab which becomes a component composition shown in Table 1 on the conditions shown in Table 2. In Table 2, levels a to f are the effects of hot rolling conditions, levels g to n are the effects of secondary rolling, and levels os are the effects of the C amount. In addition, the friction coefficient μ in Table 2 is the maximum friction coefficient among the friction coefficients of the final three stands.
With respect to the steel sheet for cans thus obtained, Table 2 shows the tensile characteristics, average r value, Δr, and the results of investigating the presence or absence (visual observation) of rough skin after cup forming.
[0031]
Here, the average r value is a value defined by the following equation.
Average r value = (r ₀ + r ₉₀ + 2r ₄₅ ) / 4
Further, the average r value and Δr in Table 2 were determined using a Module Drawability tester of Controlol products (USA). In this method, as shown in Steel Met. Ind., 50 (1973), 328, since there is a correlation between the r value and the Young's modulus, the Young's modulus was determined by the “magnetostrictive vibration method” and measured. The average r value and Δr are obtained from the Young's modulus.
Furthermore, the cup type for evaluating the presence or absence of rough skin was as follows: punching diameter: 150 mm, drawing ratio (punching diameter / molded cup diameter): 2.
[0032]
[Table 1]

[0033]
[Table 2]

[0034]
In Table 2, levels a to g are obtained by investigating the characteristics when the friction coefficient during hot rolling is changed mainly using the steel type A steel grade. When the friction coefficient exceeded 0.20, the average r value was as low as 1.0 or less, or Δr exceeded −0.30 and became a large negative value. Moreover, since the level f was rolling in the ferrite region, the crystal grains of the hot-rolled sheet became large, and the occurrence of rough skin was observed. Furthermore, the level g was a large negative value with an absolute value of A exceeding 0.30 and Δr exceeding −0.30.
Levels h to o are the same when steel grade A is used, and the secondary rolling rate is mainly changed. However, when the friction coefficient exceeds 0.20 as in levels l to o, the friction coefficient Compared to the small levels h to j , the average r value was low overall, and Δr was negative and large.
Levels p to t are steel grades A to E, and mainly look at the effect of the C amount. As shown in the level s, when the carbon content of the steel slab used is high, lubrication is required. Even if the property is good, the r value is low, and Δr is negative and large. On the other hand, when the carbon content of the steel slab used is too low as in the level t, the average r value is low, and Δr is negative and large.
[0035]
【The invention's effect】
Thus, according to the present invention, the average r value is as high as 1.0 or more, and the in-plane anisotropy, that is, the absolute value of Δr is as small as 0.30. A steel plate for cans that exhibits a beautiful appearance can be stably obtained.

Claims (1)

In mass percentage,
C: 0.020 to 0.050%,
Si: 0.04% or less,
Mn: 0.6% or less,
Al: 0.005 to 0.1%,
P: 0.02% or less,
S: 0.02% or less,
N: 0.0005 to 0.010%
Steel slab with a composition of Fe and unavoidable impurities in the balance, finish rolling temperature: Ar ₃ to (Ar ₃ + 100 ° C.), and at least the final 3 stands of the friction coefficient between the rolling roll and the steel plate: 0.20 or less After hot rolling at 0.8 to 1.5 mm thickness, it is wound into a coil at a temperature of 500 to 750 ° C, pickled, cold rolled at a reduction ratio of 80 to 88.3 %, and then re-rolled. After annealing at the crystal temperature or higher, the steel sheet for cans is manufactured by secondary rolling at a reduction rate of 9.8 % or less. At that time, the carbon content is C (mass%), and the sheet of hot-rolled sheet Thickness is t (mm), maximum value of friction coefficient in the last 3 stands of hot finish rolling is μ, winding temperature is CT (° C), cold rolling reduction ratio is CR (%), secondary rolling reduction ratio is DR ( %)), The following formula (1)
A = 7.882 −3.5 C−0.088 CR−0.014 DR
+0.005 (CT-700) -4μ (1.6-t) ² --- (1)
A method for producing a steel plate for cans, characterized in that the production conditions described above are adjusted so that the absolute value of A indicated by the formula is 0.30 or less.