JP3757633B2 - Steel plate for cans with excellent workability - Google Patents

Description

【００４５】
一方、比較のために、転炉出鋼後、300 ton の溶鋼をRH真空脱ガス装置にて脱炭処理し、Ｃ＝0.003 wt％、Si＝0.02〜0.05wt％、Mn＝0.2 〜0.5 wt％、Ｐ＝0.010 〜0.020 wt％、Ｓ＝0.001 〜0.008 wt％に調整するとともに、溶鋼温度を1590℃に調整した。この溶鋼中に、Alを1.2 〜1.6kg/ton 添加し脱酸処理を行った。脱酸処理後の溶鋼中のAl濃度は0.035 wt％であった（Alキルド鋼）。その後、FeTiを添加するとともに、成分調整を行った。この処理の後のTi濃度は0.040 wt％であった。
【００４６】
次に、この溶鋼を２ストランドスラブ連続鋳造装置にて鋳造し連鋳スラブを製造した。なお、このときの、タンディッシュ内溶鋼の介在物の平均的な組成は、95〜98wt％Al₂O₃, 5％以下のTi₂O₃ のクラスター状の介在物が主体であった。
【００４７】
鋳造時にタンディッシュならびに浸漬ノズル内にArガスを吹き込まなかった場合には、著しくノズルにAl₂O₃ が付着し、３チャージ目にスライディングノズルの開度が著しく増加し、ノズル詰まりにより鋳込みを中止した。また、Arガスを吹いた場合にも、ノズル内にはAl₂O₃ が大量に付着しており、８チャージ目にはモールド内の湯面の変動が大きくなり鋳込みを中止した。
【００４８】
次に、上記連鋳スラブはスラブ加熱温度：1150℃、仕上圧延温度：890 ℃、巻取り温度：680 ℃で1.8 mmまで熱間圧延したのち、酸洗・冷延して板厚0.25mmの冷延板とした。その後、750 ℃で20 s均熱の連続焼鈍型の短時間焼鈍を行い、介在物の調査、成形性調査試験（穴拡げ加工性試験）及び錆発生の調査を行った。この冷延鋼板にはヘゲ、スリーバー、スケールなどの非金属介在物性の欠陥は0.45個/1000m−コイル認められた。
得られた冷延板の穴拡げ加工性試験の結果を、Ｓ− 5×（(32/40) Ca＋(32/140) REM) との関係で表１及び図１に示す。ここで、比較例１〜６は、Ｓ、Ca、REM の関係以外はこの発明に従う方法で製造した鋼であり、比較例７は比較用に溶製したAlキルド鋼である。なお、この穴拡げ試験は、10mmφの打ち抜き孔を頂角60℃の円錐台ポンチで押拡げる加工を行うものであり、割れが板厚を貫通するまでに拡がった穴の径と元の打ち抜き径との比で穴拡げ率が定義される。この発明が対象とする極薄の缶用鋼板では加工の限界を決定する要因の一つであり、より高い値が要求される。
表１及び図１より、この発明の方法で溶製し、Ｓ− 5×（(32/40) Ca＋(32/140) REM) が0.0014wt％以下の鋼板は、優れた穴拡げ性を示した。なお、鋼板の錆発生率（50℃、湿度95％中に10時間放置後）については、発明鋼、比較鋼とも問題のない値であった。
【００４９】
（実施例２）
表２に示す鋼組成のスラブをこの発明の鋼板の好適な溶製方法に従い作製した。ただし、比較材（No.7及び8 ）は、この発明の成分組成範囲を満足しないアルミキルド鋼である。これらのスラブを用いて表３に示す製造条件で最終的に0.28mm厚みの極薄冷延鋼板とした。なお、製造条件Ａ−２においては、４％の調質圧延を、他の条件については１％未満の調質圧延をそれぞれ施した。これにクロムめっき、いわゆるティンフリーめっきを行い、更に塗装・焼き付け処理を行った後に引張試験と穴拡げ試験を行い成形性を調査した。この鋼板の介在物の分析結果を表３に、機械的性質、穴拡げ率の評価を表４に示す。なお、表３中の酸化物系介在物組成は粒径1 〜50μm の介在物を調査し、平均値（介在物サイズによる重み付けはせず）をとった。本発明の成分組成範囲になる試料は、介在物の個数の50％以上がTi酸化物：20wt％以上90wt％以下、CaO ，REM 酸化物の1 種又は2 種の合計：10wt％以上40wt％以下、Al₂O₃ ：40％以下の範囲内になることを確認している。また、この発明の鋼板は、良加工性を示すことが分かる。また、成分のみならず適正な製造条件を組み合わせることにより、優れた特性が得られること明らかである。
また、本発明鋼の範囲内のものでは、製造工程の各段階で表面に錆を生ずるというような不具合もなく、最終的にも極めて美麗な表面性状が得られた。また、より硬質な特性が要求される場合は、必要に応じて１〜５％の範囲で焼鈍後に調質圧延（二次圧延）を行うことも有効であり、本発明鋼においても有効に適用できた。特にウェットスキンパスを行っても、錆などを生ずることはなかった。
【００５０】
【表２】

【００５１】
【表３】

【００５２】
【表４】

【００５３】
【発明の効果】
以上説明したように、この発明に係る極薄板厚の極低炭素冷延鋼板は、その製造にあたり、連続鋳造時に浸漬ノズルの閉塞を引き起こすことがなく、極めて安定した連続鋳造が可能であり、圧延鋼板の表面は非金属介在物に起因する表面欠陥がほとんど皆無で極めて清浄である。更に、板厚が薄いにも関わらず極めて厳しいプレス成形を行った際の広範囲な成形可能範囲と耐食性に優れた性質を有する鋼板として缶用などとしての広範な用途に用いることができる。
【図面の簡単な説明】
【図１】穴拡げ成形性をＳ、Ca、REM の含有量の関係式との関係で示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a steel plate for cans that is extremely excellent in workability.
[0002]
[Prior art]
In a thin steel plate, deformation may localize and cause cracking during press working. Such a tendency to cause plastic instability becomes particularly remarkable in an ultrathin steel plate (thickness 0.2 to 0.5 mm) used for a can because its uniform elongation is relatively small. The state of occurrence of cracks (destruction) due to such local deformation is limited by the ease of deformation of the part to be processed, in other words, the degree of local deformability. Therefore, in order to prevent cracking during processing in the steel plate for cans, it is important to improve the local deformability of the steel plate.
[0003]
In steels for processing, it is known that coarse inclusions reduce local deformability, and in particular, Al accumulated in clusters.₂O_ThreeSystem inclusions are considered to have significant adverse effects. In order to avoid such adverse effects of inclusions and improve local deformability, a method for lowering the melting point of inclusions by controlling the composition of inclusions as disclosed in JP-A-63-192846, A method of controlling the precipitation of TiN and MnS by adjusting dissolved oxygen in steel as disclosed in JP-A-2-220735 has been proposed. However, since the local deformability deteriorates due to the presence of MnS and the oxide in the steel that extend long in the rolling stage, it was still difficult to obtain sufficient deformability.
Moreover, in steel containing Ti, a streak-like pattern is produced on the surface after plating, and an appearance defect may be caused. In this regard, Japanese Patent Application Laid-Open No. 5-9549 discloses a method of further adding Ca to change sulfide inclusions in steel to other complex inclusions. However, in this method, inclusions are CaO-Al₂O_ThreeThere was a problem that the system became a starting point of rust and the corrosion resistance deteriorated.
[0004]
[Problems to be solved by the invention]
This invention has been developed as a result of adding experiments, investigations, and studies to solve the above-mentioned problems of the prior art, has little rust, and there is almost no deterioration of deformability due to inclusions and precipitates. And it aims at proposing the ultra-thin steel plate for cans (a plated steel plate is included) which is very excellent in workability with almost no fall of the surface property by inclusions.
[0005]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above object, the inventors have controlled the composition of oxide inclusions remaining in the steel, thereby controlling the oxides and sulfides present in the steel. It was concluded that this is effective in improving the surface texture and workability of ultra-thin steel sheets, especially the local deformability. In other words, the formation of large cluster inclusions is suppressed to achieve fine dispersion into inclusions with a size of 50 μm or less, and the amount of MnS in the steel is reduced to reduce all oxides and sulfides in the steel. By making the material finer and making it non-ductile that does not easily deform as it extends for a long time by rolling, it is possible to obtain extremely excellent characteristics in workability, particularly local deformability, and clogging of casting nozzles when manufacturing steel sheets It has been found that various problems such as rusting and deterioration of surface properties can be solved.
[0006]
  The present invention is based on the above findings.
  That is, this invention
  C: 0.0005 to 0.005 wt%,
  Si: 0.05 wt% or less,
  Mn: 0.05 to 1.0 wt%,
  P: 0.02 wt% or less,
  Ti:0.021~ 0.10wt%,
  Al: 0.01 wt% or less,
  N: 0.02 wt% or less and
  0.0005 to 0.1 wt% of one or two of Ca and REM in total
In addition,
The content of one or two of S, Ca and REM is
S-5 × ((32/40) Ca + (32/140) REM) ≦ 0.0014wt%
The balance is the composition of Fe and inevitable impurities, and the oxide inclusions with a particle size (maximum diameter; the same applies below) of 1 to 50 μm are one or two of Ti oxide, CaO and REM oxide. A steel plate for cans which is excellent in workability, characterized by containing seeds and having a plate thickness of more than 0.2 mm to 0.5 mm; and
  C: 0.0005 to 0.005 wt%,
  Si: 0.05 wt% or less,
  Mn: 0.05 to 1.0 wt%,
  P: 0.02 wt% or less,
  Ti:0.021~ 0.10wt%,
  Al: 0.01 wt% or less,
  N: 0.02 wt% or less and
  0.0005 to 0.1 wt% of one or two of Ca and REM in total
Including, and
  Ni: 0.005 to 1.0 wt%,
  Cu: 0.005 to 1.0 wt%,
  Cr: 0.005 to 1.0 wt%,
  Mo: 0.005 to 1.0 wt%,
  Nb: 0.002 to 0.04 wt%,
  B: 0.0002 to 0.005 wt%
1 type or 2 types or more, and
The content of one or two of S, Ca and REM is
S-5 × ((32/40) Ca + (32/140) REM) ≦ 0.0014wt%
And the balance is composed of Fe and inevitable impurities, and oxide inclusions having a particle size of 1 to 50 μm contain one or two of Ti oxide, CaO and REM oxide, It is a steel plate for cans that is extremely excellent in workability, characterized by having a plate thickness of more than 0.2 mm to 0.5 mm.
[0007]
  In the present invention, oxide inclusions having a particle size of 1 to 50 μm are Ti oxide: 20 wt% or more and 90 wt% or less, total of one or two kinds of CaO and REM oxide: 10 wt% or more and 40 wt% or less, Al₂O_Three : 40wt %(Ti oxide, CaO, REM oxide 1 or 2 types, Al₂O_Three The total is 100wt %It is more preferable that the base structure is composed of fine crystal grains having a grain size of 15 μm or less.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the results of research on which the present invention was based will be described.
As described above, in order to improve the workability, particularly local deformability, 1) the oxide in the steel is not coarsened, 2) the sulfide in the steel is not coarsened, and 3) It is important to refine the crystal grains.
[0009]
  For the oxide of 1) above, Al is 0.01 wt% or less, Ti is0.021By satisfying the condition that wt% or more and Ca or REM is 0.0005 wt% or more, the oxide becomes Al.₂O_Three It changes from the main to Ti-based oxide, and since this Ti-based oxide has good wettability with molten steel and it is difficult to form clusters, Al₂O_Three It does not become coarse like the inclusions of the main body.
[0010]
In addition, with respect to the sulfide 2), it is important to suppress MnS precipitated during solidification, and if MnS is present, it extends during rolling and promotes cracking during processing. For this solution, S in the steel is fixed by Ca and / or REM which produces a more stable sulfide. For this purpose, the S content, the Ca content, and the REM content are
S-5 x ((32/40) Ca + (32/140) REM)) ≤ 0.0014wt%
(In the formula, S represents the amount of S (wt%), Ca represents the amount of Ca (wt%), and REM represents the amount of REM (wt%).)
It came to the thought that it was necessary to satisfy the relationship. That is, in order to fix S by the formation of CaS and REM sulfide, the larger the amount of Ca and REM added, the better, and the lower limit is shown by the above inequality. That is, an experimental result was obtained that S in a harmful state needs to be 0.0014% or less.
[0011]
Furthermore, with regard to the above-mentioned 3) grain refinement, by reducing the grain size of the steel sheet to 15 μm or less, the skin roughness particularly problematic in an ultra-thin steel sheet having a thickness of 0.2 to 0.5 mm and the like. It is possible to improve the decrease in the elongation due to a practically no problem level.
[0012]
  However, when trying to fix S in steel with Ca or REM in this way, Ca oxide or REM oxide absorbs S and changes to water-soluble, which causes rust to occur and the surface properties to be changed. There is a concern of deterioration. Therefore, in this invention, Al is 0.01 wt% or less and Ti is contained in the steel content.0.021A steel plate with less rust is prepared by melting under suitable conditions a steel that satisfies wt% or more and Ca and / or REM 0.0005 wt% or more. That is, the inclusion is Ti oxide-CaO and / or REM oxide-Al.₂O_Three -SiO₂System oxide (Ti oxide-CaO and / or REM oxide-SiO if not containing Al)₂Rust generation starting from inclusions is suppressed by using a Ti oxide as a considerable amount of oxide. In particular, when the concentration of Ca and REM in the inclusions is 40 wt% or less in total, the origin of rust does not occur and the surface properties are good. On the other hand, when the amount of Al exceeds 0.01 wt%, inclusions are Al.₂O_Three Since it is a CaO system, the CaO concentration in inclusions is about 50%, which becomes a starting point of rust and deteriorates the corrosion resistance.
[0013]
Furthermore, since the above-described oxide inclusions have a low melting point, they hardly adhere to and grow on the immersion nozzle during casting, so that the nozzle is not clogged. Ar gas or N inside₂It was confirmed that there was almost no need to blow gas.
[0014]
As a result of various studies based on the above experimental results, the inventors limited the present invention as follows.
Hereafter, the reason for limitation is shown about each component.
(C: 0.0005-0.005 wt%)
The present invention relates to an ultra-thin steel sheet for cans that can be formed over a wide range including deep drawing, and it is desirable that the ductility, r value, etc. of the steel sheet be as high as possible. By reducing the amount of C, these characteristics are remarkably improved, so it is desirable to reduce as much as possible. A preferable upper limit is 0.005 wt%, and more preferably 0.004 wt% or less. However, when C is extremely small, the crystal grain size becomes coarse, and a rough skin phenomenon occurs at the time of molding, thereby reducing the moldability. Further, when the crystal grain size becomes coarse in this way, the deep drawability tends to deteriorate. From the above, the preferable lower limit is 0.0005 wt%, and more preferably 0.001 wt% or more.
[0015]
(Si: 0.05wt% or less (excluding 0))
Si is a component effective for deoxidation during melting. However, if the amount is too large, work hardening becomes remarkable, corrosion resistance is significantly lowered, and mechanical properties, particularly high ductility, are harmful components, so 0.05 wt% was made the upper limit. Moreover, a preferable upper limit is 0.02 wt%, and it is more preferable if it is 0.01 wt% or less.
[0016]
(Mn: 0.05-1.0 wt%)
  Mn, like Si, is effective for deoxidation during melting. Addition of 0.05 wt% or more is generally desirable from the viewpoint of performing the step acid treatment and preventing hot brittleness. On the other hand, the present invention relates to a steel sheet for various press forming, and it is desirable that the steel sheet has lower strength and excellent ductility. From this point, Mn is a solution strengthening of steel and r valueThe lowSince it is a component to be lowered, it is desirable to reduce it as much as possible. If it is 1.0 wt% or less, the amount of reduction in ductility due to the strengthening is small. Therefore, the upper limit of Mn is 1.0 wt%. If it is 0.7 wt% or less, it is more desirable.
[0017]
(P: 0.02 wt% or less)
P is a component for solid solution strengthening of steel, and it is desirable to reduce it as much as possible as an ultra-thin steel plate applied to various difficult press forming which is the object of the present invention. Moreover, it is desirable to reduce also from a viewpoint of corrosion resistance. If the addition amount is 0.02 wt% or less, it is possible to achieve a level of corrosion resistance and workability with almost no problems. If it is 0.01 wt% or less, it is more suitable. The lower limit is not particularly defined, and is determined by a balance between an increase in production cost necessary for dephosphorization and a characteristic improvement effect.
[0018]
(Ti:0.021~ 0.10wt%)
  Ti is an important component in the present invention, and Ti deoxidation forms fine oxide inclusions with a size of 50 μm or less, controls grain growth during cold rolling and annealing, and balances strength and elongation. In addition to improving the effect, these inclusions have little adverse effect on reducing workability. Furthermore, since this fine oxide is also effective for miniaturization of a hot-rolled sheet, a {111} recrystallization texture develops after cold rolling-annealing and the r value is improved. The amount added0.021If less than wt%, the effect of addition, that is, the amount of fine oxide is too small to obtain the desired effect.0.021It was limited to wt% or more. However, TiWhen the content of Ni exceeds 0.1 wt%, the deformation resistance during hot rolling is remarkably increased, so that hot rolling becomes difficult.
[0019]
(Al: 0.01wt% or less)
Al is a component whose content has a significant effect on the characteristics in the present invention, and when the Al content exceeds 0.01 wt%, Al deoxidation occurs preferentially, so huge Al₂O_ThreeA large amount of clusters are formed, the surface properties are deteriorated, and the fine oxides of 50 μm or less which are considered to be relatively harmless at the time of various press formings are reduced, so that the workability of the steel sheet is deteriorated. Therefore, it was limited to 0.01 wt% or less. More importantly, if the Al content is higher than this, the inclusion composition is Al.₂O_Three-CaO or Al₂O_Three-REM It becomes an oxide system, becomes a starting point of rust, and deteriorates corrosion resistance. From this viewpoint, the upper limit of Al is 0.01 wt%. Al does not necessarily need to be added, and Al is not essential as a deoxidizer by performing Ti deoxidation or the like.
[0020]
(N: 0.02 wt% or less (excluding 0))
Since N contributes as a solid solution strengthening component, when applied to extremely severe plastic working as in the present invention, it leads to a decrease in ductility, so it is desirable to reduce it as much as possible. In consideration of the amount of ductility deterioration accompanying the increase in N content, the upper limit was set to 0.02 wt%. A preferable lower limit value is not particularly limited, but is 0.001 wt% in consideration of an increase in manufacturing cost for preventing nitriding and a change in mechanical characteristics. Moreover, a preferable upper limit is 0.005 wt%, and if it is 0.003 wt% or less, it is more preferable.
[0021]
(Ca and / or metal REM: 0.0005 to 0.1 wt%)
Ca and metal REM (referring to rare earth elements such as La and Ce) are important components in the present invention, and one or two of Ca and REM must be added in an amount of 0.0005 wt% or more. That is, after deoxidizing Ti, one or two of Ca and REM are added so that the content becomes 0.0005 wt% or more, and the oxide composition in the molten steel is changed to Ti oxide: 20 wt% or more and 90 wt%. Or less, preferably 85 wt% or less, CaO and / or REM oxide: 5 wt% to 40 wt%, Al₂O_ThreeIs a low-melting oxide oxide inclusion with a content of 40 wt% or less. If it does so, the adhesion to the nozzle of the Ti oxide containing a base metal can be prevented effectively at the time of continuous casting, and clogging of a nozzle can be prevented. Furthermore, CaO and / or REM oxide is present in the steel as fine particles, and can contribute to the refinement of the hot rolled sheet. Moreover, this inclusion also contributes effectively to improving the mechanical properties of the steel sheet after cold rolling and annealing. For these reasons, one or two of Ca and REM are added in a total amount of 0.0005 wt% or more. However, if the total amount exceeds 0.1 wt%, in addition to difficulty in melting, a decrease in corrosion resistance is a problem. Therefore, the upper limit was limited to 0.1 wt%.
[0022]
(S-5 x ((32/40) Ca + (32/140) REM) ≤ 0.0014 wt%)
The smaller the S, the better the ductility and deep drawability, and at the same time the corrosion resistance is improved. Therefore, it is necessary to make it 0.01% by weight or less. When further excellent characteristics are required, the content is preferably 0.005 wt% or less.
Further, S can exist as various sulfides in the steel, but when it exists as MnS inclusions, it significantly extends in the rolling direction during hot rolling, particularly in the direction perpendicular to the rolling direction. Deteriorates mechanical properties. In other words, this leads to a decrease in workability targeted by the present invention, particularly local deformability.
In this respect, the addition of Ca and REM improves the morphology and non-ductility of the sulfide, and the improvement in local ductility, which is the main focus of the present invention, becomes significant. According to the investigation by the inventors, the addition of Ca and REM is not clear for reasons, but it is considered that harmless sulfides up to about 5 times S of these elements by atomic ratio become harmless sulfides. Therefore, if the harmful amount of S, that is, the value of S-5 × ((32/40) Ca + (32/140) REM) is sufficiently small, the secondary work brittleness resistance is not lowered by sulfide. According to the investigation, it was found that there is no problem if the harmful amount of S is 0.0014 wt% or less.
[0023]
(O: 0.010 wt% or less)
O is an unavoidable component and is not particularly limited. However, O is a component necessary to some extent to produce a fine oxide. However, if it exceeds 0.010 wt%, coarse Al₂O_ThreeAs a result, the ductility during processing and the deep drawability deteriorate, so 0.010 wt% was made the upper limit. In addition, a preferable upper limit is 0.007 wt%, and if it is 0.005 wt% or less, it is more desirable.
[0024]
(Ni: 0.005 to 1.0 wt%)
(Cu: 0.005 to 1.0 wt%)
(Cr: 0.005 to 1.0 wt%)
(Mo: 0.005 to 1.0 wt%)
  Ni, Cu, Cr, and Mo are ultra-thin steel plates targeted by the present invention by refining the structure without solid solution strengthening, or by facilitating deformation in a low temperature / high strain rate environment. It is possible to improve the workability. Moreover, since any component has the effect of reducing the transformation point of steel, it is also effective in relaxing the conditions for regulating the hot finishing temperature. Therefore, in the present invention, one or more of Ni, Cu, Cr, and Mo can be added as necessary. All of Ni, Cu, Cr and Mo exhibit a remarkable effect when added in an amount of 0.005 wt% or more, and this effect is not offset even when they are added in combination. However, even if added over 1.0 wt%, the effect tends to saturate, so the upper limit was set to 1.0 wt% in all cases. From the viewpoint of stabilizing the material, the range of 0.01 to 0.5 wt% is more preferable.
[0025]
(Nb: 0.002 to 0.04 wt%)
Nb is extremely effective for refining the crystal grains of the steel sheet. Therefore, in this invention, Nb can be added as needed. By refining the crystal grains, especially in the ultra-thin steel plate applied to the severe press forming that is the subject of the present invention, the remarkable effect on the prevention of surface roughness after forming and the improvement of ductility is exhibited in this regard. To do. Nb exhibits a remarkable effect when added in an amount of approximately 0.002 wt% or more. However, even if Nb is added in excess of 0.04 wt%, the effect tends to saturate, and conversely, there is a possibility that the hot and cold deformation resistance of the steel is remarkably increased. The range was -0.04 wt%. From the viewpoint of stabilizing the material, 0.01 to 0.5 wt% is more preferable.
[0026]
(B: 0.0002 to 0.005 wt%)
By adding B, it is possible to extremely effectively prevent the secondary processing brittleness when performing particularly severe ultra deep drawing. It is also effective in making the steel sheet microstructure finer. In order to exert these desirable effects, it is necessary to add approximately 0.0002 wt% or more. However, even if added over 0.005 wt%, the effect is saturated and the hot deformation resistance of the steel is remarkably increased. Based on the above, the range was 0.0002 to 0.005 wt%.
[0027]
In the steel satisfying the above component composition range, the oxide inclusions having a particle size of 1 to 50 μm are inclusions containing one or two of Ti oxide, CaO and REM oxide. Then it is particularly important. The inclusion as such a deoxidation product contains one or two of Ti oxide and CaO, REM oxide, more specifically, Ti oxide-CaO and / or REM oxide-Al.₂O_Three-SiO₂System oxide (Ti oxide-CaO and / or REM oxide-SiO if not containing Al)₂Oxide-based inclusions have little rust, almost no deterioration of deformability due to inclusions and precipitates, no surface defects due to cluster-like inclusions, and metal This is the steel sheet for cans as expected in the present invention, in which there is no adhesion of Ti oxide to the nozzle.
The reason why the oxide inclusions defined in the present invention are limited to those having a particle diameter of 1 to 50 μm is because inclusions in such a range can be regarded as inclusions generated by deoxidation, Inclusions with particle sizes greater than 50 μm are generally due to extraneous inclusions such as slag or mold powder. Al₂O_ThreeSome clusters are larger than this, but if the oxide composition of inclusions with a particle size of 50 μm or less satisfies the above requirements, a huge Al₂O_ThreeIt can be considered that the system cluster is also sufficiently reduced.
[0028]
  The composition of the oxide inclusions having a particle size of 1 to 50 μm is as follows: Ti oxide: 20 wt% or more and 90 wt% or less, total of one or two kinds of CaO and REM oxide: 10 wt% or more and 40 wt% or less, Al₂O_Three : 40wt %(Ti oxide, CaO, REM oxide 1 or 2 types, Al₂O_Three The total is 100wt %The following is more preferable.
[0029]
  When the inclusion Ti oxide is less than 20wt%, it is not Ti deoxidized steel but Al deoxidized steel.₂O_Three Nozzle clogging occurs due to increased concentration. In addition, as the CaO and REM oxide concentration increases, the rusting property becomes remarkable, so the Ti oxide concentration is 20wt% or less. On the other hand, when the Ti oxide concentration exceeds 90 wt%, the ratio of CaO and REM oxide decreases, and nozzle clogging occurs. Therefore, the Ti oxide concentration is set to 20 wt% or more and 90 wt% or less. More preferably, it is 30 wt% or more and 80 wt% or less.
[0030]
Further, if the total of one or two of CaO and REM oxides in the inclusion is less than 10 wt%, the inclusion does not have a low melting point and causes the nozzle to be blocked as described above. On the other hand, if it exceeds 40 wt%, the inclusions will subsequently absorb S and change to water-solubility, which becomes the starting point of rust, thus reducing the corrosion resistance. A more preferable range is 20 to 40 wt%.
[0031]
In addition, Al in the inclusion₂O_ThreeWhen the content exceeds 40 wt%, not only the nozzle clogging occurs due to the high melting point composition, but also the inclusions are clustered, increasing non-metallic inclusion physical defects in the product plate. In addition, when Al is hardly contained in steel, Al in inclusions₂O_ThreeIs almost negligible.
[0032]
The oxide inclusions may contain oxides other than those listed above, and the amount of oxides other than those listed above is not particularly limited. , SiO₂Is preferably controlled to 30 wt% or less, and MnO is preferably controlled to 15 wt% or less. The reason for this is that if these amounts exceed the respective amounts, it cannot be said that the titanium killed steel is an object of the present invention, and under such a composition, there is no nozzle clogging even without adding Ca, and there is also a problem of rusting. This is because it disappears. Moreover, SiO in the inclusions₂In order to contain MnO, it is preferable to set the Si and Mn concentrations of the molten steel to Mn / Ti> 100 and Si / Ti> 50 in consideration of the oxide formation tendency. Cause deterioration of surface properties.
The steel sheet according to the present invention has a thickness of more than 0.2 mm to 0.5 mm. A thickness exceeding 0.5 mm is not suitable for the purpose of cans. On the other hand, even if the plate thickness is 0.2 mm or less, the effect of the present invention is obtained, but with the change of the processing method and the like, the processing characteristics other than the local ductility become very important, so they are excluded from the present invention.
[0033]
When the steel sheet of the present invention has a structure composed of uniform and fine crystal grains having a crystal grain size of 15 μm or less, even in an ultrathin steel sheet, such as a poor appearance due to surface roughness after forming, a decrease in elongation caused by this, etc. Problems can be avoided. Accordingly, it is preferable to have a structure composed of uniform and fine crystal grains having a crystal grain size of 15 μm or less, and it is more preferable that the grain size be 12 μm or less. Such a structure can be obtained by adjusting the steel composition and hot rolling conditions (slab heating temperature, finishing temperature, etc. described later).
[0034]
  Next, the manufacturing method of the steel of this invention is demonstrated.
  In this invention, Ti as an adjustment component is Ti:0.021The reason why it is over wt% is that Ti0.021If it is less than wt%, the oxygen removal capacity is weak, the total oxygen concentration in the molten steel becomes high, and material properties such as elongation and drawing are deteriorated. In this case, it may be possible to increase the deoxidizing power by increasing the concentration of Si and Mn.0.021Less than wt% SiO₂Or a large amount of inclusions containing MnO causes hardening of the steel material and deterioration of plating properties. In order to prevent this, it is necessary to contain Ti so that (wt% Mn) / (wt% Ti) <100. In that case, the Ti oxide concentration in the inclusions is 20% or more.
[0035]
In producing the titanium killed steel sheet according to the present invention, first, the molten steel is deoxidized with a Ti-containing alloy such as FeTi, and oxide inclusions mainly composed of Ti oxide are generated in the steel. The inclusions are not in the form of large clusters as in the case of deoxidation with Al, but are mostly granular and ruptured with a size of about 1 to 50 μm. However, if the Al concentration exceeds 0.010 wt% at this time, huge Al₂O_ThreeA cluster is generated. Such Al₂O_ThreeEven if the Ti alloy is added to increase the Ti concentration, the cluster cannot be reduced and remains in the steel as cluster-like inclusions. Therefore, with respect to the steel sheet according to the present invention, it is preferable to first produce Ti oxide in the molten steel at the stage of production.
[0036]
Under the present invention, the yield of the Ti alloy is poor compared to the conventional method of deoxidizing with Al, and the inclusion composition adjusting alloy is expensive because it contains Ca and REM. For this reason, it is economically preferable to add such an alloy into the molten steel so that the amount of the alloy is as small as possible within the range in which the composition of inclusions can be controlled. In this sense, prior to the addition of a deoxidizing agent such as a Ti-containing alloy, pre-deoxidization is performed so that the dissolved oxygen concentration becomes 200 ppm or less in order to reduce the dissolved oxygen in the molten steel and FeO and MnO in the slab. It is desirable. This preliminary deoxidation is preferably performed by stirring the molten steel in a vacuum, deoxidizing with a small amount of Al (the Al in the molten steel after deoxidation is 0.010 wt% or less), and adding Si, FeSi, Mn, or FeMn.
If deoxidation with Ti is performed immediately after preliminary deoxidation, a large number of inclusions that are insufficiently modified remain in the molten steel, making it difficult to control the target inclusion composition. Therefore, by stirring for 3 to 4 minutes after the addition of the predeoxidizer and 8 to 9 minutes after the addition of Ti, the inclusions are Ti oxide: 20 wt% or more and 90 wt% or less, one of CaO and REM oxide Or total of 2 types: 10wt% or more and 40wt% or less, Al₂O_Three: The composition is 40% or less and becomes an inclusion governed by Ti deoxidation.
[0037]
As described above, the Ti oxide inclusions produced by Ti deoxidation are dispersed in the steel with a size of about 2 to 20 μm, so that surface defects due to cluster inclusions are eliminated. However, Ti oxide is in a solid state in molten steel, and ultra-low carbon steel has a high solidification temperature, so it grows on the inner surface of the tundish nozzle in the form of taking in the metal, and clogs the nozzle. There is a risk of triggering.
[0038]
Therefore, in the steel sheet according to the present invention, after deoxidizing with a Ti alloy, either one or two of Ca and REM are further added so as to be 0.0005 wt% or more, and the grain size in the molten steel is 1 to 50 μm. Ti oxide: 20 wt% or more and 90 wt% or less, preferably 85 wt% or less, CaO and / or REM oxide: 5 wt% or more and 40 wt% or less, Al₂O_ThreeIs a low-melting oxide oxide inclusion with a content of 40 wt% or less. If it does so, it will become possible to prevent effectively adhesion to the nozzle of Ti oxide containing bullion. More preferable inclusions are Ti oxide: 30 wt% to 80 wt%, CaO 2 REM oxide (La₂O_Three, Ce₂O_ThreeEtc.): 10 wt% or more and 40 wt% or less.
The composition of such oxide inclusions is measured by performing quantitative analysis on each inclusion using EPMA or a scanning electron microscope having an EDX function. Although it is most desirable that all the inclusions in the steel analyzed in this way satisfy the above composition, in practice, the number of inclusions having a size of 1 to 50 μm is 50% or more. Is within the above composition range, the various properties of the hot-rolled steel sheet as the object of the present invention are achieved. In addition, the largest diameter in each grain shall be used for a particle size.
[0039]
In this invention, when the composition of the inclusions to be generated is controlled as described above, it is possible to completely prevent oxides and the like from adhering to the inner surface of the tundish nozzle and the immersion nozzle of the mold during continuous casting. Therefore, Ar and N are used to prevent adhesion of oxides in tundish and immersion nozzles.₂It is no longer necessary to blow in gas. As a result, it is possible to prevent the occurrence of powder defects in the slab due to powder entrainment during continuous casting and bubble defects due to the blown gas in the slab.
[0040]
Regarding the hot rolling process after continuous casting, the slab heating temperature is preferably 1000 ° C. or higher. In other words, the lower limit of the slab heating temperature is limited in terms of equipment, but by setting the slab heating temperature to approximately 1000 ° C. or higher, the lower limit value of the finishing rolling temperature described later can be secured, and finally fine and uniform severe plastic processing Can be manufactured. On the other hand, at a high temperature exceeding 1300 ° C. as the upper limit, the crystal grain size before rolling becomes too large, so that the hot-rolled sheet is not refined. Therefore, the slab heating temperature is preferably 1000 to 1300 ° C. A slab heating temperature of 1150 ° C. or lower is preferable from the viewpoint of further improving the formability of the steel sheet. In addition, DHCR (direct hot charge rolling), in which a continuously cast slab is inserted into a heating furnace with a hot piece, is preferable from the viewpoint of energy saving, but an insertion temperature that exceeds the transformation point by 100 ° C or more cannot sufficiently refine the structure. Therefore, it is not preferable. .
The hot rolling finish temperature is preferably 850 ° C. or higher. If the temperature is lower than this, the structure becomes coarse and non-uniform, so that the secondary work brittleness resistance decreases. Further, the lower limit of the coil winding temperature after hot rolling is determined from the viewpoint of mechanical properties such as r value and prevention of disturbance of the coil shape, but approximately 600 ° C. or higher is recommended.
After hot rolling, pickling and cold rolling are performed before annealing.
The pickling may be performed with normal hydrochloric acid or sulfuric acid, but the pickling process may be omitted particularly in the case of a thin scale phase steel sheet.
It is recommended that the rolling reduction of cold rolling is 80% or more from the viewpoint of improving workability, particularly r value.
It is important to perform the annealing at a temperature higher than the recrystallization temperature from the viewpoint of securing formability. The annealing method may be either so-called continuous annealing or batch annealing, but continuous annealing is recommended from the viewpoint of work efficiency and material uniformity. Thus, the industrial merit of this invention which can manufacture a steel plate with good formability by the continuous annealing method is great.
In order to adjust the shape and surface hardness after annealing, temper rolling of 5% or less may be performed. A reduction exceeding 5% is not preferable because the workability deteriorates significantly. This steel plate is suitably used for containers called so-called general cans and miscellaneous cans. The required properties are that it is soft and easy to process, and that appearance defects such as stretcher strain do not occur.
[0041]
【Example】
(Example 1)
After converter steelmaking, 300 ton molten steel was decarburized with RH degassing equipment, C = 0.003 wt%, Si = 0.02-0.05 wt%, Mn = 0.2-0.5 wt%, P = 0.010-0.020 wt %, S = 0.004 to 0.008 wt%, and the molten steel temperature was adjusted to 1585 to 1615 ° C. In this molten steel, Al was added in an amount of 0.2 to 0.8 kg / ton, and preliminary deoxidation was performed for 3 to 4 minutes to reduce the dissolved oxygen concentration in the molten steel to 55 to 260 ppm. The Al concentration in the molten steel at this time was 0.001 to 0.005 wt%. And 70 wt% Ti-Fe alloy was added to this molten steel 0.8-1.8kg / ton, and Ti deoxidation was carried out over 8-9 minutes. Then, after adjusting the components, the molten steel contains 30wt% Ca-60wt% Si alloy, an additive mixed with metal Ca, Fe, 5-15wt% REM, or 90wt% Ca-5wt% Processing was performed by adding 0.05 to 0.5 kg / ton of Fe-coated wire of Ca alloy such as Ni alloy and REM alloy. After this treatment, the Ti concentration is 0.026 to 0.058 wt%, the Al concentration is 0.001 to 0.005 wt%, the Ca concentration is 0.0000 to 0.0020 wt%, the REM concentration is 0.0000 to 0.0020 wt%, and the sum of the Ca and REM concentrations is It was 0.0005-0.0043 wt%.
[0042]
Next, this steel was cast with a two-strand slab continuous casting apparatus to produce a continuous cast slab. Ar gas was not blown into the tundish and immersion nozzle during casting. As observed after continuous casting, there was almost no deposit in the tundish and the immersion nozzle.
[0043]
Next, the continuous cast slab was hot-rolled to a thickness of 1.8 mm. The hot rolling conditions were slab heating temperature: 1150 ° C, finish rolling temperature: 890 ° C, and hot rolling coiling temperature: 680 ° C. The hot-rolled steel sheet was pickled and cold-rolled to obtain a cold-rolled sheet having a thickness of 0.25 mm. After that, short-time annealing was performed in a continuous annealing mold of 20 s soaking at 750 ° C., and a formability investigation test (hole expansion workability test) and rust generation were investigated. Table 1 shows the results of the investigation on the steel composition and formability. At this time, most of the oxide inclusions had a width of 50 μm or less. The breakdown of oxide is Ti₂O_Three: 60-70%, CaO + REM oxide: 20-30%, Al₂O_Three: 15% or less. In this cold-rolled sheet, defects of non-metallic inclusion physical properties such as heges, slivers, and scales were found to be 0.00 to 0.02 pieces / 1000 m-coil or less.
[0044]
[Table 1]

[0045]
On the other hand, for comparison, 300 ton of molten steel was decarburized by RH vacuum degassing equipment after converter steel, C = 0.003 wt%, Si = 0.02-0.05 wt%, Mn = 0.2-0.5 wt %, P = 0.010 to 0.020 wt%, S = 0.001 to 0.008 wt%, and the molten steel temperature was adjusted to 1590 ° C. The molten steel was deoxidized by adding 1.2 to 1.6 kg / ton of Al. The Al concentration in the molten steel after deoxidation treatment was 0.035 wt% (Al killed steel). Thereafter, FeTi was added and the components were adjusted. The Ti concentration after this treatment was 0.040 wt%.
[0046]
Next, this molten steel was cast with a two-strand slab continuous casting apparatus to produce a continuous cast slab. At this time, the average composition of inclusions in the molten steel in the tundish is 95 to 98 wt% Al.₂O_Three, Ti below 5%₂O_ThreeThe cluster-like inclusions were mainly.
[0047]
If Ar gas is not blown into the tundish and immersion nozzle during casting, the nozzle₂O_ThreeAttached, the opening of the sliding nozzle increased significantly at the third charge, and casting was stopped due to nozzle clogging. In addition, even when Ar gas is blown,₂O_ThreeA large amount of was attached, and the fluctuation of the molten metal surface in the mold increased at the 8th charge, and casting was stopped.
[0048]
Next, the continuous cast slab was hot-rolled to 1.8 mm at a slab heating temperature of 1150 ° C, a finish rolling temperature of 890 ° C and a coiling temperature of 680 ° C, and then pickled and cold-rolled to obtain a sheet thickness of 0.25 mm. Cold-rolled sheet was used. After that, short-time annealing was performed in a continuous annealing mold of 20 s soaking at 750 ° C., and the inclusions were investigated, the formability investigation test (hole expansion workability test) and the occurrence of rust. This cold-rolled steel sheet was found to have defects of non-metallic inclusions such as heges, three bars and scales of 0.45 / 1000 m-coil.
The results of the hole expansion workability test of the obtained cold-rolled sheet are shown in Table 1 and FIG. 1 in relation to S-5 × ((32/40) Ca + (32/140) REM). Here, Comparative Examples 1 to 6 are steels manufactured by the method according to the present invention except for the relationship of S, Ca and REM, and Comparative Example 7 is Al killed steel melted for comparison. In this hole expansion test, punching holes with a diameter of 10mmφ are expanded with a truncated cone punch with an apex angle of 60 ° C. The diameter of the hole expanded until the crack penetrates the plate thickness and the original punching diameter. The ratio of hole expansion is defined by the ratio. The ultra-thin steel plate for cans targeted by the present invention is one of the factors that determine the limit of processing, and a higher value is required.
From Table 1 and FIG. 1, the steel sheet melted by the method of the present invention and having S-5 × ((32/40) Ca + (32/140) REM) of 0.0014 wt% or less shows excellent hole expandability. It was. In addition, the rust generation rate of the steel sheet (after standing for 10 hours in a temperature of 50 ° C. and a humidity of 95%) was a value with no problem in both the inventive steel and the comparative steel.
[0049]
(Example 2)
A slab having a steel composition shown in Table 2 was prepared according to a preferred method for melting steel sheets according to the present invention. However, the comparative materials (Nos. 7 and 8) are aluminum killed steels that do not satisfy the component composition range of the present invention. These slabs were finally used to produce ultrathin cold-rolled steel sheets having a thickness of 0.28 mm under the manufacturing conditions shown in Table 3. In addition, in manufacturing condition A-2, temper rolling of 4% was performed, and temper rolling of less than 1% was performed for the other conditions. This was subjected to chrome plating, so-called tin-free plating, and after coating and baking treatment, a tensile test and a hole expansion test were conducted to investigate the formability. Table 3 shows the analysis results of inclusions in this steel sheet, and Table 4 shows the evaluation of mechanical properties and hole expansion rate. The oxide inclusions in Table 3 were investigated for inclusions having a particle size of 1 to 50 μm and averaged (not weighted by inclusion size). In the sample with the component composition range of the present invention, 50% or more of the number of inclusions is Ti oxide: 20 wt% or more and 90 wt% or less, total of one or two kinds of CaO and REM oxide: 10 wt% or more and 40 wt% Hereafter, Al₂O_Three: Confirmed to be within the range of 40% or less. Moreover, it turns out that the steel plate of this invention shows good workability. It is also clear that excellent characteristics can be obtained by combining not only the components but also appropriate production conditions.
Moreover, in the range of the steel of the present invention, there was no problem that the surface was rusted at each stage of the production process, and finally a very beautiful surface texture was obtained. In addition, when harder properties are required, it is also effective to perform temper rolling (secondary rolling) after annealing within the range of 1 to 5% as necessary, and it is also effectively applied to the steel of the present invention. did it. In particular, rust and the like did not occur even when the wet skin pass was performed.
[0050]
[Table 2]

[0051]
[Table 3]

[0052]
[Table 4]

[0053]
【The invention's effect】
As described above, the ultra-thin carbon cold-rolled steel sheet having an ultra-thin thickness according to the present invention does not cause a clogging of the immersion nozzle during continuous casting, and enables extremely stable continuous casting. The surface of the steel sheet is extremely clean with almost no surface defects due to non-metallic inclusions. Furthermore, it can be used for a wide range of applications such as for cans as a steel sheet having a wide range of formability and excellent corrosion resistance when extremely strict press forming is performed despite its thin plate thickness.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram showing hole expansion formability in relation to a relational expression of S, Ca, and REM contents.

Claims (3)

C: 0.0005 to 0.005 wt%,
Si: 0.05 wt% or less,
Mn: 0.05 to 1.0 wt%,
P: 0.02 wt% or less,
Ti: 0.021 to 0.10 wt%,
Al: 0.01 wt% or less,
N: 0.02 wt% or less and
0.0005 to 0.1 wt% of one or two of Ca and REM in total
In addition,
The content of one or two of S, Ca, and REM is expressed by the following formula: S-5 × ((32/40) Ca + (32/140) REM) ≦ 0.0014wt%
And the balance is composed of Fe and inevitable impurities, and the oxide inclusions having a particle size of 1 to 50 μm contain one or two of Ti oxide, CaO and REM oxide, Steel plate for cans with excellent workability, characterized by having a plate thickness of more than 0.2 mm to 0.5 mm. C: 0.0005 to 0.005 wt%,
Si: 0.05 wt% or less,
Mn: 0.05 to 1.0 wt%,
P: 0.02 wt% or less,
Ti: 0.021 to 0.10 wt%,
Al: 0.01 wt% or less,
N: 0.02 wt% or less and
0.0005 to 0.1 wt% of one or two of Ca and REM in total
Including, and
Ni: 0.005 to 1.0 wt%,
Cu: 0.005 to 1.0 wt%,
Cr: 0.005 to 1.0 wt%,
Mo: 0.005 to 1.0 wt%,
Nb: 0.002 to 0.04 wt%,
B: 0.0002 to 0.005 wt%
1 type or 2 types or more, and
The content of one or two of S, Ca, and REM is expressed by the following formula: S-5 × ((32/40) Ca + (32/140) REM) ≦ 0.0014wt%
And the balance is composed of Fe and inevitable impurities, and the oxide inclusions having a particle size of 1 to 50 μm contain one or two of Ti oxide, CaO and REM oxide, Steel plate for cans with excellent workability, characterized by having a plate thickness of more than 0.2 mm to 0.5 mm. Particle size 1 ～50Myuemu oxide inclusions of Ti oxides: 20 wt% or more 90 wt% or less, CaO, 1 or 2 or the sum of REM oxides: more than 10 wt% 40 wt% or less, Al ₂ O _3: 40 less wt% (Ti oxides, CaO, 1 or 2 or of REM oxides, the total of Al ₂ O ₃ is 100 wt% or less) extremely in workability according to claim 1 or 2, wherein it is Excellent steel plate for cans.

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