JP4069591B2 - Manufacturing method of cold-rolled steel sheet with excellent workability and low anisotropy - Google Patents

Description

【００７２】
【表２】

【００７３】
表２に示すように、急速冷却を行う本発明のプロセス条件により製造されたＮｏ．２，４，６，８，１０，１２，１４，１６，１８の鋼板は、いずれも伸びおよび平均ｒ値が極めて高く、かつ、Δｒまたはｒ値の最大値−最小値が極めて低く抑えられており、加工性および異方性が極めて優れていた。これに対して、最終パス後のランナウトテーブルにて鋼板の上下からラミナー冷却を行ったＮｏ．１，３，５，７，９，１１，１３，１５，１７の鋼板は、いずれかの特性が劣っていた。
【００７４】
以上のように、本発明で規定された範囲の組成を有する鋼を用いて、本発明で規定されたプロセス条件により冷延鋼板を製造すれば、形状性や搬送性に優れ、かつ、従来よりも格段に優れた加工性および異方性を有する冷延鋼板を製造することができることが確認された。
【００７５】
［実施例２］
表３に示す成分を有する鋼を連続鋳造により２２０ｍｍ厚さのスラブとし、このスラブに手入れを行った後、１２００℃に加熱し、表４に示した条件で熱間圧延し、冷間圧延した後に、昇温速度１０℃／ｓｅｃ以上２０℃／ｓｅｃ以下で、８４０℃の焼鈍温度で９０秒間連続焼鈍してＮｏ．１９〜４４の冷延鋼板を得た。熱間圧延に際しては、熱延鋼帯の搬送性、形状性を問題のないレベルに確保するために、粗バー（粗圧延を完了した熱延鋼帯）を、仕上圧延装置へ導入する直前に誘導加熱装置により加熱して、鋼帯の板幅方向の温度分布を一定にした。この際、Ｎｏ．３０については熱延板の板厚を１．５ｍｍ、冷延焼鈍板の板厚を０．７５ｍｍとしたが、その他のＮｏ．１９〜２９，３１〜４４については、いずれの場合も熱延板板厚を２．８±０．２ｍｍ、冷延焼鈍板の板厚を０．８ｍｍとした。また、表４に示したＮｏ．３０の冷却速度は熱延板の板厚が１．５ｍｍの場合の値であり、２．８〜３．５ｍｍの板厚材で冷却速度を確認したところ２７０±７０℃／ｓｅｃであった。以上のようにして得られた冷延鋼板の特性を、実施例１と同様に評価した結果を表４に示す。なお、表４中、Ｎｏ．３０の全伸びについては、厚さ０．７５ｍｍの冷延鋼板で測定された値を、Ｏｌｉｖｅｒ則によって０．８ｍｍ材の伸びに変換した値を示す。
【００７６】
【表３】

【００７７】
【表４】

【００７８】
表４に示すように、本発明のプロセス条件により製造されたＮｏ．２０，２５〜３０，３３〜３６，３８〜４０，４４の鋼板は、いずれも鋼板の形状性、搬送性が問題のないレベルに確保されており、しかも、伸びおよび平均ｒ値が極めて高く、かつ、Δｒが極めて低く抑えられており、加工性および異方性が極めて優れていた。これに対して、いずれかの条件が本発明の範囲外であるＮｏ．１９，２１〜２４，３１，３２，３７，４１〜４３の鋼板では、いずれかの特性が劣っていた。
【００７９】
具体的には、Ｎｏ．１９では最終パス前２パスの合計圧下率が本発明の範囲を超えたため、Ｎｏ．２１では最終パスの圧下率が本発明の範囲を超えたため、どちらの場合も製造時に蛇行したり、鋼板の形状および搬送性が劣っており、安定的に製造することが困難であった。表４には、製造することができた熱延コイルの一部分より得られた冷延焼鈍板のサンプルの示した材質特性の中で、最も良好なデータを示した。表４に示すように、Ｎｏ．１９，２１では優れた材質特性を示す場合もあったが、製造自体が困難で、材質特性のバラツキも大きかった。
【００８０】
また、Ｎｏ．２２では仕上温度が本発明範囲よりも低くα域圧延になってしまったため、特に全伸びの劣化が顕著であった。一方、Ｎｏ．２３では仕上温度が本発明範囲を超えたため、特性が劣化しているが、これは急冷を行うまでにγ粒の成長が進行したためと考えられる。Ｎｏ．２４では、冷却速度が本発明範囲よりも低かったため、急冷が十分でなく、熱延板の細粒化ができず、γ値の向上効果が十分に得られなかった。Ｎｏ．３１およびＮｏ．３２では、冷却開始時間が本発明範囲を超えたために、粒成長してしまったものと考えられ、熱延板の微細化が十分でなく、加工性および異方性の向上効果が十分に得られなかった。Ｎｏ．３７では、急冷の温度降下量が本発明範囲よりも小さく、急冷停止温度が本発明範囲よりも高かったため、熱延板の細粒化が十分でなく、ｒ値の向上効果が十分に得られなかった。Ｎｏ．４１では、急冷の温度降下量が本発明範囲を超えて大きく、また、急冷停止温度が本発明範囲よりも低かく、かつ、巻取温度も本発明の好ましい範囲よりも低かったため、熱延板の組織が焼き入れ組織状の粒になってしまい、特性値の劣化が顕著であった。Ｎｏ．４２では、急冷停止温度が本発明範囲よりも低かったため、熱延板の組織がポリゴナルな細粒とならず、特性値が劣化してしまった。Ｎｏ．４３では、急冷後の冷却速度が本発明範囲を超えて高かったため、熱延板の段階でポリゴナルな微細粒が得られず、いずれの特性値も劣っていた。
【００８１】
以上のように、本発明で規定された条件を全て満たした製造方法によってはじめて、従来よりも格段に優れた加工性および異方性を有する冷延鋼板を、形状性や搬送性に問題を生じることなく製造することができることが確認された。
【００８２】
［実施例３］
冷却開始時間の効果を調べるため、表５に示した成分を有する鋼を連続鋳造により２００〜３００ｍｍ厚さのスラブとし、１１８０℃〜１２５０℃に加熱して、表６に示した範囲の最終パス前２パスの合計圧下率、最終パス圧下率、仕上温度、冷却条件および巻取温度にて熱間圧延を行い、板厚２．８ｍｍの熱延板とし、板厚０．８ｍｍに冷間圧延した後、昇温速度６℃／ｓｅｃ以上２０℃／ｓｅｃ以下で昇温し、焼鈍温度８５０℃で９０秒間連続焼鈍して種々の冷延鋼板を得た。この際、表６に「従来のラミナー冷却」と示したものでは、仕上圧延の最終パスを通過した熱延鋼帯に、水蒸気を上げながら冷却するラミナー冷却を行った。一方、仕上圧延後に２００℃／ｓｅｃ以上の急冷を行ったものにおいては、膜沸騰モードの冷却では冷却の際に蒸気が発生して、蒸気膜が鋼板を包み込んでしまい急冷を行うことができないので、多孔噴流方式の冷却装置を用いて、蒸気膜を破壊しながら冷却を行うためにフレッシュな水が常に鋼板にあたり、急速冷却を行うことが可能な核沸騰モードの冷却を実現した。
【００８３】
これらの鋼板について、実施例１と同様に、冷延鋼板の０．８ｍｍ材にて全伸びを測定し、また、各方向のｒ値であるｒ０、ｒ４５、ｒ９０をそれぞれ測定した。測定された全伸びの値と冷却開始時間との関係を図１に示し、測定されたｒ値から得られた平均ｒ値と冷却開始時間との関係を図２に示す。また、異方性を評価するための指標としてΔｒを用い、図２には一部の鋼板についてΔｒの値を併記する。
【００８４】
図１および図２に示すように、冷却開始時間を０．５秒以下とした場合には、全伸びの挙動が一様でなく大きく変動し、かつ、平均ｒ値は冷却開始時間が短くなるほど高い増加率で上昇している。このため、冷却開始時間が０．５秒以下では冷却開始時間がわずかにずれるだけで材質が大きく変化してしまい、長手方向の材質が均一な鋼板を工業的に製造することは難しい。
【００８５】
これに対して、冷却開始時間が０．５秒超１秒以下の範囲とした場合には、全伸び、ｒ値ともにほぼ一定である。このため、冷却開始時間が多少ずれても長手方向の材質が均一な鋼板を製造することができる。また、膜沸騰モードのラミナー冷却を行った場合と比較して全伸び、平均ｒ値はともに向上している。
【００８６】
一方、逆に冷却開始時間が１秒を超えると、全伸び、ｒ値ともに単調減少して材質レベルが膜沸騰モードのラミナー冷却を行った場合と大差なくなる。
【００８７】
なお、Δｒは全ての冷却開始時間については示さないが、図２に示すように、冷却によりｒ値が向上した鋼板ではΔｒが小さくなっている。このことからｒ値が同レベルの条件ならばΔｒもほぼ同じレベルと考えてよい。したがって、冷却開始時間を０．５秒超１秒以下の範囲とした場合には、従来のラミナー冷却を行った場合と比較してΔｒの値も安定的に向上するものと考えられる。
【００８８】
以上より、冷却開始時間を０．５秒超１秒以下の範囲とした場合に、加工性に優れ、異方性が小さく、長手方向の材質が均一な冷延鋼板が製造できることが確認された。
【００８９】
【表５】

【００９０】
【表６】

【００９１】
［実施例４］
表７に示した成分を有する鋼を連続鋳造により２００〜３００ｍｍ厚さのスラブとし、１１８０〜１２５０℃に加熱して、表８に示した冷却条件をはじめとする熱延条件の熱間圧延により板厚２．８ｍｍの熱延板とし、板厚０．８ｍｍに冷間圧延した後、昇温速度６℃／ｓｅｃ以上２０℃／ｓｅｃ以下で昇温し、表８に示す焼鈍温度で９０秒間連続焼鈍してＮｏ．４５〜６４の冷延鋼板を得た。熱間圧延に際しては、熱延鋼帯の搬送性、形状性を問題のないレベルに確保するために、粗バー（祖圧延を終了した熱延鋼帯）を、仕上圧延装置に導入する直前に誘導加熱装置により加熱して、鋼帯の板幅方向の温度分布を均一にした。また、表８に「従来のラミナー冷却」と示したものでは、仕上圧延の最終パスを通過した熱延鋼帯に、水蒸気を上げながら冷却するラミナー冷却を行った。一方、仕上圧延後に２００℃／ｓｅｃ以上の急冷を行ったものにおいては、膜沸騰モードの冷却では冷却の際に蒸気が発生し、蒸気膜が鋼板を包み込んでしまい急冷を行うことができないので、多孔噴流方式の冷却装置を用いて、蒸気膜を破壊しながら冷却を行うためにフレッシュな水が常に鋼板にあたり、急速冷却を行うことが可能な核沸騰モードの冷却を実現し、その水量や水圧を変化させて表８に示した種々の冷却速度により冷却を行った。以上のようにして得られた冷延鋼板の特性を、実施例１と同様に評価した。その結果を表８に示す。
【００９２】
【表７】

【００９３】
【表８】

【００９４】
表８に示すように、急速冷却を行う本発明のプロセス条件により製造されたＮｏ．４６，４８，５０，５２，５４，５６，５８，６２，６４の鋼板は、いずれも伸びおよびｒ値が極めて高く、かつ、Δｒまたはｒ値の最大値−最小値が極めて低く抑えられており、加工性および異方性が極めて優れていた。これに対して、最終パス後のランナウトテーブルにて鋼板の上下からラミナー冷却を行ったＮｏ．４５，４７，４９，５１，５３，５５，５７，５９，６１，６３の鋼板は、いずれかの特性が劣っていた。
【００９５】
以上のように、本発明で規定された範囲の組成を有する鋼を用いて、本発明で規定されたプロセス条件により冷延鋼板を製造すれば、形状性や搬送性に優れ、かつ、従来よりも格段に優れた加工性および異方性を有する冷延鋼板を製造することができることが確認された。
【００９６】
［実施例５］
表９に示す成分を有する鋼を連続鋳造により２２０ｍｍ厚さのスラブとし、このスラブに手入れを行った後、１２００℃に加熱し、表１０に示した条件で熱間圧延し、冷間圧延した後に、昇温速度１０℃／ｓｅｃ以上２０℃／ｓｅｃ以下で、８４０℃の焼鈍温度で９０秒間連続焼鈍してＮｏ．６５〜８２の冷延鋼板を得た。熱間圧延に際しては、熱延鋼帯の搬送性、形状性を問題のないレベルに確保するために、粗バー（祖圧延を終了した熱延鋼帯）を、仕上圧延装置へ導入する直前に誘導加熱装置により加熱して、鋼板の板幅方向の温度分布を均一にした。この際、Ｎｏ．７４については熱延板の板厚を１．５ｍｍ、冷延焼鈍板の板厚を０．７５ｍｍとしたが、その他のＮｏ．６５〜７３，７５〜８２については、いずれの場合も熱延板の板厚を２．８±０．２ｍｍ、冷延焼鈍板の板厚を０．８ｍｍとした。また、表１０に示したＮｏ．７４の冷却速度は熱延板の板厚が１．５ｍｍの場合の値であり、２．８〜３．５ｍｍの板厚材で冷却速度を確認したところ２７０±７０℃／ｓｅｃであった。以上のようにして得られた冷延鋼板の特性を、実施例１と同様に評価した結果を表１０に示す。なお、表１０中、Ｎｏ．７４の全伸びについては、厚さ０．７５ｍｍの冷延鋼板で測定された値を、Ｏｌｉｖｅｒ則によって０．８ｍｍ材の伸びに変換した値を示す。
【００９７】
【表９】

【００９８】
【表１０】

【００９９】
表１０に示すように、本発明のプロセス条件により製造されたＮｏ．６６，６９〜７４，７６〜７８，８２の鋼板は、いずれも鋼板の形状性、搬送性が問題ないレベルに確保されており、しかも、伸びおよび平均ｒ値が極めて高く、かつ、Δｒが極めて低く抑えられており、加工性および異方性が極めて優れていた。これに対して、いずれかの条件が本発明の範囲外であるＮｏ．６５，６７，６８，７５，７９〜８１の鋼板では、いずれかの特性が劣っていた。
【０１００】
具体的には、Ｎｏ．６５では最終パス前２パスの合計圧下率が本発明範囲を超えて高かったため、Ｎｏ．６７では最終パスの圧下率が本発明の範囲を超えて高かったため、どちらの場合も製造時に蛇行したり、鋼板の形状および搬送性が劣っており、安定的に製造することが困難であった。表１０には、製造することができた熱延コイルの一部分より得られた冷延焼鈍板のサンプルに示した材質の中で、もっとも良好なデータを示した。表１０に示すように、Ｎｏ，６５，６７では優れた材質特性を示す場合もあったが、製造自体が困難で、材質特性のバラツキも大きかった。
【０１０１】
Ｎｏ．６８では、冷却速度が本発明範囲よりも低かったため、急冷が十分でなく、熱延板の細粒化ができず、γ値の向上効果が十分に得られなかった。Ｎｏ．７５では、急冷の温度降下量が本発明範囲よりも小さく、急冷停止温度が本発明範囲よりも高かったため、熱延板の細粒化が十分でなく、ｒ値の向上効果が十分に得られなかった。Ｎｏ．７９では、急冷の温度降下量が本発明範囲を超えて大きく、急冷停止温度が本発明範囲よりも低く、かつ、巻取温度も本発明の好ましい範囲よりも低かったため、熱延板組織が焼き入れ組織状の粒になってしまい、特性値の劣化が顕著であった。Ｎｏ．８０では、急冷停止温度が本発明範囲よりも低かったため、熱延板の組織がポリゴナルな細粒とならず、特性値が劣化してしまった。Ｎｏ．８１では、急冷後の冷却速度が本発明範囲を超えて高かったため、熱延板の段階でポリゴナルな微細粒が得られず、いずれの特性値も劣っていた。
【０１０２】
以上のように、本発明で規定された条件を全て満たした製造方法によってはじめて、従来よりも格段に優れた加工性および異方性を有する冷延鋼板を、形状性や搬送性に問題を生じることなく製造することができることが確認された。
【０１０３】
【発明の効果】
本発明によれば、従来の方法で作られた同じ成分系のものと比較して、格段に優れた加工性および異方性を有する冷延鋼板を、鋼板の形状性や搬送性に問題を生じることなく製造することが可能となる。
【図面の簡単な説明】
【図１】実施例３における全伸びの値と冷却開始時間との関係を示すグラフ。
【図２】実施例３における平均ｒ値と冷却開始時間との関係を示すグラフ。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a cold-rolled steel sheet having excellent workability suitable for uses such as automobiles, electrical products, cans, and building materials and having small anisotropy.
[0002]
[Prior art]
Cold-rolled steel sheets and surface-treated steel sheets that require workability are required to have mechanical properties with excellent elongation and deep drawability and low anisotropy. In addition, the shape of the steel plate and the transportability of the hot-rolled steel strip during production are also important factors in making such a steel plate.
[0003]
Conventionally, it has been aimed at soft high ductility by adding carbide forming elements such as Ti and Nb and nitride forming elements in an extremely low carbon / nitrogen component system. The basic idea is to remove the interstitial elements such as carbon and nitrogen as much as possible at the steelmaking stage, and at that time, it is economical to remove the interstitial elements that remain or cannot be removed. The intrusive element at an unsuitable level is fixed as a precipitate so that the interstitial element does not exist in the steel.
[0004]
However, as the requirements for workability become stricter, it is not possible to obtain a steel sheet that satisfies such requirements only by adjusting the components, and it is necessary to further improve the material from the process aspect. Already, it is conceptually known to make the grain size of a hot-rolled sheet finer and improve the mechanical properties after cold-rolling and annealing by effectively utilizing a cooling technique. The method includes (1) shortening the time from the end of hot rolling to starting cooling (hereinafter referred to as cooling start time), and (2) increasing the cooling rate as much as possible. By simultaneously carrying out the steps, the hot-rolled sheet is miniaturized.
[0005]
The basis of this technique is that for the above (1), after hot rolling is completed, strain introduced during finish rolling is recovered and recrystallized, and γ (austenite) grains grow rapidly. Cooling is started while it is fine, and α (ferrite) grains are formed from fine γ grain boundaries, or (2) cooling is further started in a short time and hot. In the state where the processing strain at the time of rolling has not yet been sufficiently released, the formation of α grains is attempted by forming the α grains with the deformation band in the γ grains as a nucleus.
[0006]
Regarding the above (2), when the cooling rate is slow, recovery and recrystallization of γ grains and grain growth occur during cooling, and α grain growth occurs after transformation. It is to plan. Furthermore, by increasing the cooling rate, there is an advantage that the γ-α transformation point is lowered, and the post-transformation grain growth tends to be suppressed as the temperature after transformation becomes lower.
[0007]
Experimentally, for example, in materials and processes (vol. 3, (1990), p. 785: Kino et al.), The finishing temperature is set to Ar.₃Securing above the transformation point, (1) cooling is started 0.1 seconds after the end of hot rolling, and (2) the cooling rate is about 180 ° C./sec. It is disclosed that the mechanical properties after cold rolling / annealing, particularly the r value, can be improved by performing.
[0008]
In addition, various manufacturing methods have already been disclosed for improving the material quality by performing hot-rolled plate refinement by cooling. For example, Japanese Patent Laid-Open No. 7-70650 discloses Ar as a manufacturing method for achieving a material having an r value of 2.50 or more in an ultra-low carbon steel sheet having a C content of 15 ppm or less in steel.₃After finishing rolling at the transformation point or higher, set the cooling start time within 0.5 seconds after the end of rolling, from the cooling start temperature (Ar₃A technique for cooling a temperature range up to a transformation point of −60 ° C. at 50 to 400 ° C./sec is disclosed. However, in this method, the cumulative rolling reduction of the hot rolling finish rolling 3 passes is regulated to 50% or more. This method is intended to realize r value: 2.50 or more and deep drawability by refining hot-rolled sheet by cooling technology and accumulating a large amount of processing strain in hot rolling.
[0009]
[Problems to be solved by the invention]
However, the technique disclosed by Kino et al. Described above and the technique disclosed in the above publication cannot improve all the mechanical properties including the r value under any condition. In some cases, the workability is not improved and deteriorates. In addition, when a large amount of processing strain is accumulated by hot rolling, the shape of the steel plate is disturbed, which may cause a problem in the transportability of the steel plate. That is, the process conditions that can stably manufacture a steel sheet having a workability such as r value and elongation that is remarkably superior to conventional ones have not yet been obtained without causing problems in the shape and transportability of the steel sheet. . Further, in this type of steel sheet, uniformity in the longitudinal direction of the steel sheet is also important, but in the above-described prior art, no consideration is given to the uniformity in the longitudinal direction of the steel sheet.
[0010]
The present invention has been made in view of such circumstances, has an extremely low carbon / nitrogen component system, and does not cause problems in the formability and transportability of the steel sheet, and has workability and anisotropy. An object of the present invention is to provide a production method capable of stably producing a cold-rolled steel sheet excellent in thickness. Moreover, it aims at providing the manufacturing method which can manufacture stably the cold-rolled steel plate with the uniform material of a longitudinal direction in addition to these characteristics.
[0011]
[Means for Solving the Problems]
As a result of the study by the present inventors, in the technique proposed by Kino et al. Described above and the technique described in the above publication, the amount of rapid cooling and the cooling stop temperature are not controlled within a favorable range. It was found that the mechanical properties (r value and elongation) cannot be improved. That is, when the inventors conducted experiments based on these techniques, when the amount of rapid cooling temperature drop or the cooling stop temperature is out of a favorable range, the elongation is improved even if the average r value is high. On the contrary, it has been found that the elongation may decrease and the average r value may also deteriorate. In other words, too much cooling due to rapid cooling adversely affects the mechanical properties, and improving the material by simply cooling a wide range of temperatures including a specified temperature range (temperature range expanded to the low temperature side) by rapid cooling. I can't see it. Furthermore, in the case of increasing the total rolling reduction of the 3 passes of the finish rolling and accumulating a large amount of processing strain and performing fine graining, if the rolling in these 3 passes is not properly distributed, the transportability of the steel sheet, It was found that the shape was adversely affected.
[0012]
Therefore, the present inventors conducted research to solve such problems, and as a result, in the component system based on ultra-low carbon steel, the hot rolling reduction conditions were controlled, It has been found that by controlling the rolled runout cooling conditions, a cold-rolled steel sheet having significantly superior workability and anisotropy than before can be obtained without causing problems in formability and transportability. That is, in addition to adjusting the steel composition to a very low carbon-based specific composition, the following knowledge was obtained.
[0013]
(1) Regarding the rolling conditions during hot rolling, by appropriately setting the rolling reduction ratio of the final pass of finish rolling and the rolling reduction ratio of the two passes before the final pass, the shape of the steel sheet, the hot rolled steel plate during production Therefore, it is possible to increase the processing distortion in the hot range as long as there is no problem.
[0014]
(2) It is effective to start predetermined rapid cooling within as short a time as possible after finish rolling in order to refine hot rolled sheet and improve mechanical properties. However, if the time is too short, the degree of fine graining is often different due to a slight deviation in the cooling start time. Therefore, there is an appropriate range for the cooling start time in order to make the material uniform in the longitudinal direction of the plate.
[0015]
(3) By appropriately setting the range of the temperature drop due to the rapid cooling, it is possible to suppress excessive cooling due to rapid cooling and improve workability such as elongation and deep drawability and anisotropy.
[0016]
(4) A desired fine structure can be obtained by appropriately setting the cooling stop temperature of the rapid cooling.
[0017]
(5) By making the cooling after rapid cooling appropriate slow cooling, it becomes possible to form appropriate polygonal ferrite grains.
[0018]
  The present invention has been made on the basis of the above findings, and the first invention is in wt%,
C: 0.0003% to 0.01%,
Si: 0.05% or less,
Mn: 0.05% or more and 2.5% or less,
P: 0.003% to 0.1%,
S: 0.0003% to 0.02%,
Sol. Al: 0.005% or more and 0.1% or less,
N: 0.0003% or more and 0.004% or less
IncludingFurthermore, by weight%, one or more of Ti, Nb, V, Zr is contained in a total of 0.005% to 0.1%,In manufacturing a cold-rolled steel sheet by heating a steel slab composed of the remaining Fe and inevitable impurities, hot rolling, cold rolling, and annealing,
  The hot rolling
  In finish rolling, the total rolling reduction of the two passes before the final pass is over 45% and 70% or less, the rolling reduction of the final pass is 5% to 35%, and the finishing temperature is Ar.₃Above the transformation point (Ar₃Finish rolling at a transformation point + 50 ° C. or lower,
  Next, rapid cooling is started at a cooling rate of 200 ° C./sec or more and 2000 ° C./sec or less within 1 second after finishing rolling, and the temperature drop from the finishing temperature of the finishing rolling in this rapid cooling is 50 ° C. The cooling stop temperature for this rapid cooling is 650 ° C. or more and 850 ° C. or less.
  Subsequently, a method for producing a cold-rolled steel sheet having excellent workability and low anisotropy, characterized by winding the obtained hot-rolled steel strip after slow cooling or air cooling at 100 ° C./sec or less. provide.
[0019]
  The second invention is weight percent,
C: 0.0003% to 0.01%,
Si: 0.05% or less,
Mn: 0.05% or more and 2.5% or less,
P: 0.003% to 0.1%,
S: 0.0003% to 0.02%,
Sol. Al: 0.005% or more and 0.1% or less,
N: 0.0003% or more and 0.004% or less
IncludingFurthermore, by weight%, one or more of Ti, Nb, V, Zr is contained in a total of 0.005% to 0.1%,In manufacturing a cold-rolled steel sheet by heating a steel slab composed of the remaining Fe and inevitable impurities, hot rolling, cold rolling, and annealing,
  The hot rolling
  In finish rolling, the total rolling reduction of the two passes before the final pass is over 45% and 70% or less, the rolling reduction of the final pass is 5% to 35%, and the finishing temperature is Ar.₃Above the transformation point (Ar₃Finish rolling at a transformation point + 50 ° C. or lower,
  Next, within 0.5 seconds to 1 second after finishing the finish rolling, rapid cooling is started at a cooling rate of 200 ° C./sec or more and 2000 ° C./sec or less, and the temperature from the finish rolling finish temperature in the rapid cooling is The descending amount is 50 ° C. or more and 250 ° C. or less, and the cooling stop temperature of this rapid cooling is 650 ° C. or more and 850 ° C. or less,
  Subsequently, a method for producing a cold-rolled steel sheet having excellent workability and low anisotropy, characterized by winding the obtained hot-rolled steel strip after slow cooling or air cooling at 100 ° C./sec or less. provide.
[0020]
  3rd invention is weight%,
C: 0.0003% to 0.01%,
Si: 0.05% or less,
Mn: 0.05% or more and 2.5% or less,
P: 0.003% to 0.1%,
S: 0.0003% to 0.02%,
Sol. Al: 0.005% or more and 0.1% or less,
N: 0.0003% or more and 0.004% or less
In addition, the steel slab containing 0.0001% or more and 0.001% or less of B, and the balance Fe and unavoidable impurities, is heated, hot-rolled, cold-rolled, annealed, and cooled. In producing rolled steel sheets,
The hot rolling
In finish rolling, the total rolling reduction of the two passes before the final pass is over 45% and 70% or less, the rolling reduction of the final pass is 5% to 35%, and the finishing temperature is Ar. ₃ Above the transformation point (Ar ₃ Finishing rolling as a transformation point + 50 ° C or less)
Next, rapid cooling is started at a cooling rate of 200 ° C./sec or more and 2000 ° C./sec or less within 1 second after finishing rolling, and the temperature drop from the finishing temperature of the finishing rolling in this rapid cooling is 50 ° C. The cooling stop temperature for this rapid cooling is 650 ° C. or more and 850 ° C. or less.
Subsequently, a method for producing a cold-rolled steel sheet having excellent workability and low anisotropy, characterized by winding the obtained hot-rolled steel strip after slow cooling or air cooling at 100 ° C./sec or less. provide.
[0021]
  4th invention is weight%,
C: 0.0003% to 0.01%,
Si: 0.05% or less,
Mn: 0.05% or more and 2.5% or less,
P: 0.003% to 0.1%,
S: 0.0003% to 0.02%,
Sol. Al: 0.005% or more and 0.1% or less,
N: 0.0003% or more and 0.004% or less
In addition, the steel slab containing 0.0001% or more and 0.001% or less of B, and the balance Fe and unavoidable impurities, is heated, hot-rolled, cold-rolled, annealed, and cooled. In producing rolled steel sheets,
The hot rolling
In finish rolling, the total rolling reduction of the two passes before the final pass is over 45% and 70% or less, the rolling reduction of the final pass is 5% to 35%, and the finishing temperature is Ar. ₃ Above the transformation point (Ar ₃ Finishing rolling as a transformation point + 50 ° C or less)
Next, within 0.5 seconds to 1 second after finishing the finish rolling, rapid cooling is started at a cooling rate of 200 ° C./sec or more and 2000 ° C./sec or less, and the temperature from the finish rolling finish temperature in the rapid cooling is The descending amount is 50 ° C. or more and 250 ° C. or less, and the cooling stop temperature of this rapid cooling is 650 ° C. or more and 850 ° C. or less,
Subsequently, a method for producing a cold-rolled steel sheet having excellent workability and low anisotropy, characterized by winding the obtained hot-rolled steel strip after slow cooling or air cooling at 100 ° C./sec or less. provide.
[0022]
  According to a fifth invention, in the method for producing a cold-rolled steel sheet according to the first invention or the second invention, the steel further contains 0.0001% or more and 0.001% or less of B by weight%. .
According to a sixth invention, in the method for producing a cold-rolled steel sheet according to any one of the first to fifth inventions, the steel further contains 0.015% or more and 0.08% or less of Cu by weight%. Features.
[0023]
In the prior art, for example, JP-A-7-70650, JP-A-6-212354, and JP-A-6-17141 disclose Ar.₃As a rule using the transformation point, “finishing temperature: Ar₃In the case of expressing the temperature itself, such as “above the temperature” or “From (Ar₃-50 ° C) is rapidly cooled ... "and there are both cases where it is used for temperature regulation at the time of cooling.₃Since the transformation point drops, Ar in the latter₃The transformation point is Ar in the former₃The transformation point is not the same temperature, it is always Ar in the former₃The transformation point indicates a low temperature. However, in many conventional techniques, the transformation point in the latter context and the transformation point in the former context are interpreted as the same temperature, which is not academically correct. Furthermore, the faster the cooling rate, the more Ar₃Since the transformation point goes down, Ar in the latter context₃Even if it is said to be a transformation point, it is often difficult to understand what value is actually shown. Therefore, in the present invention, when the temperature is specified for rapid cooling, Ar₃It is defined by numerical values, not an ambiguous expression called a transformation point.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the method for producing a cold-rolled steel sheet according to the present invention will be specifically described by dividing it into a steel composition and process conditions.
1. Steel composition
In the present invention, the steel composition is, by weight, C: 0.0003% to 0.01%, Si: 0.05% or less, Mn: 0.05% to 2.5%, P: 0.003. % To 0.1%, S: 0.0003% to 0.02%, Sol. Al: 0.005% or more and 0.1% or less, N: 0.0003% or more and 0.004% or less. Further, from the viewpoint of improving stretch flangeability, in addition to the steel composition, one or more of Ti, Nb, V, and Zr may be added in a range of 0.005% or more and 0.1% or less in total if necessary. Add in. Furthermore, from the viewpoint of reducing the adverse effect of the solute S, Cu is added in a range of 0.015% or more and 0.08% or less as needed in addition to any of the steel compositions described above. Furthermore, from the viewpoint of improving the longitudinal crack resistance of the steel, B is added in the range of 0.0001% to 0.001% as necessary in addition to any of the steel compositions described above.
[0025]
C: 0.0003% to 0.01%
C is set to a level at which ultra-low carbon steel or steel based on IF steel (Interstitial-Free steel) in which a solid solution interstitial element does not exist in the steel can be realized. IF steel here includes BH steel (Bake-Hard steel) based on IF steel. Although the ductility and deep drawability improve as the C content decreases, the lower limit of the C content is set to 0.0003% in consideration of the level of the current steelmaking conditions. On the other hand, if the C content is 0.01% or less, it is possible to improve ductility and deep drawability as IF steel by fixing with a carbide-forming element (Ti, Nb, etc.). The amount was 0.01% or less. If the C content is 0.002% or less, the elongation and deep drawability can be increased to a higher level, and the amount of added carbide-forming elements can be reduced, so the C content is 0.002%. The following is preferable. On the other hand, even when the C content is 0.002% or more and 0.01% or less, by increasing the coiling temperature or adding Ti, Nb or the like as a carbide forming element, elongation, depth The drawability can be set to a higher level, and the anisotropy can be kept low.
[0026]
Si: 0.05% or less
Si is an element that adversely affects the properties of soft and high ductility, and is an element that adversely affects surface treatment such as Zn plating, but is also used as a deoxidizing element. If the amount of Si exceeds 0.05%, the adverse effect on the material and surface treatment becomes significant, so 0.05% or less.
[0027]
Mn: 0.05% to 2.5%
Mn is an element that improves the toughness of steel, and is an element that can be used effectively for solid solution strengthening. However, if added too much, workability is adversely affected. On the other hand, Mn can also be used effectively for depositing S as MnS. In the present invention, priority is given to the development of elongation and deep drawability, and at the same time, the Mn content is set to 2.5% or less because it is used for strengthening steel. On the other hand, the lower limit of the Mn content is set to 0.05% in consideration of the cost of removing S in steelmaking.
[0028]
P: 0.003% to 0.1%
P is a solid solution strengthening element, and ductility deteriorates as the content increases. Therefore, the P content is 0.1% or less. On the other hand, the more the P is removed, the more the ductility is improved. However, the lower limit of the P content is set to 0.003% in view of the balance between the removal cost in steelmaking and workability. In order to obtain better workability, it is preferable to make it 0.015% or less. However, in this case, grain growth becomes vigorous and it becomes difficult to reduce the grain size of the hot-rolled sheet. It is better to set the temperature lower.
[0029]
S: 0.0003% to 0.02%
Since S is an element that causes red heat brittleness, the upper limit is generally defined according to the amount of Mn added that has the function of fixing S, but if the S content is large, the precipitation of sulfides increases. Since elongation and deep drawability deteriorate, in the present invention, considering this point, the S content is set to 0.02% or less. On the other hand, the lower the S content, the better for the workability, but the lower limit of the S content is set to 0.0003% in consideration of the removal cost in steelmaking. If the S content is 0.012% or less, the elongation and deep drawability can be increased to a higher level, and the addition amount of sulfide-forming elements can be reduced. % Or less is preferable. However, in this case, grain growth becomes vigorous and it is difficult to reduce the grain size of the hot-rolled sheet, so the coiling temperature after hot rolling should be set lower. On the other hand, even when S is 0.012% or more and 0.02% or less, by setting the coiling temperature after hot rolling higher, the elongation and deep drawability can be made higher. Further, the anisotropy can also be kept low.
[0030]
Sol. Al: 0.005% to 0.1%
Al effectively acts as a deoxidizing element for molten steel, but if excessive addition of Al adversely affects workability, Sol. The Al content was set to 0.1% or less. On the other hand, even when the amount of Al added is the minimum amount necessary for deoxidation, 0.005% or more of Sol. Since Al remains, the Sol. The lower limit of Al was 0.005%.
[0031]
N: 0.0003% to 0.004%
The smaller the amount of N, the better the ductility and deep drawability, but the lower limit was made 0.0003% considering the level of the current steelmaking conditions. On the other hand, if the N content is 0.004% or less, by fixing with a nitride-forming element (Ti, Nb, etc.), ductility and deep drawing as IF steel in which a solid solution interstitial element does not exist in the steel Therefore, the N content is set to 0.004% or less. If the N content is 0.002% or less, the elongation and deep drawability can be increased to a higher level, and the addition amount of the nitride-forming element can be reduced. Therefore, the N content is 0.002%. % Or less is preferable. However, in this case, grain growth becomes vigorous and it is difficult to make the hot-rolled plate grain size finer, so the coiling temperature should be set lower. On the other hand, even when N is 0.002% or more and 0.004% or less, by setting the coiling temperature higher, the elongation and deep drawability can be made higher, and the anisotropy Can be kept low.
[0032]
Ti, Nb, V, Zr: 0.005% or more and 0.1% or less in total of 1 or more types
Ti, Nb, V, and Zr are elements that improve the elongation and deep drawability by fixing carbide, C, N, and S as precipitates by forming carbides, nitrides, and sulfides. In particular, when these properties are required, it is preferable to add one or more of these. If the total amount of Ti, Nb, V, and Zr is less than 0.005%, the elongation and the effect of improving the deep drawability cannot be obtained. Conversely, if it exceeds 0.1%, the workability deteriorates. Therefore, the total amount of Ti, Nb, V, and Zr is set to 0.005% or more and 0.1% or less.
[0033]
Cu: 0.015% or more and 0.08% or less
Cu is an element that works effectively as a sulfide-forming element and reduces the adverse effect of the solid solution S on the material, and is particularly preferably added when such an action is required. Such an effect can be obtained when 0.005% or more of Cu is added. However, since Cu is contained in steel in an amount of less than 0.01% as an impurity level, the amount of Cu is set to 0.015% or more. On the other hand, if the amount of Cu exceeds 0.08%, the steel becomes hard, so the content is made 0.08% or less.
[0034]
B: 0.0001% to 0.001%
B is an element that improves the longitudinal cracking resistance of steel, and it is preferably added particularly when such an action is required. If B is less than 0.0001%, the effect of improving the vertical crack resistance cannot be obtained, and if it exceeds 0.001%, the effect is saturated. Therefore, when B is added, the amount added is 0.0001% or more and 0.001%. % Or less.
[0035]
2. Process conditions
In the present invention, a slab made of steel having the above composition is heated, hot-rolled, cold-rolled, and annealed to produce a cold-rolled steel sheet. The total rolling reduction of the previous two passes is over 45% and 70% or less, the rolling reduction of the final pass is 5% or more and 35% or less, and the finishing temperature is Ar₃Above the transformation point (Ar₃The finish rolling is finished at the transformation point + 50 ° C. or less, and then rapidly at a cooling rate of 200 ° C./sec or more and 2000 ° C./sec or less within 1 second after the finish rolling is finished or within 0.5 second to 1 second. Starting cooling, the amount of temperature drop from the finishing temperature of the finish rolling in this rapid cooling is 50 ° C. or more and 250 ° C. or less, and the cooling stop temperature of this rapid cooling is 650 ° C. or more and 850 ° C. or less, After slow cooling or air cooling at 100 ° C./sec or less, the obtained hot-rolled steel strip is wound up. Hereinafter, these conditions will be described.
[0036]
(1) Total reduction ratio of two passes before the final pass of finish rolling: More than 45% and 70% or less, Reduction rate of final pass of finish rolling: 5% or more and 35% or less
In this way, a sufficient amount of strain is accumulated to refine the hot-rolled sheet while ensuring the shape of the hot-rolled steel strip and the transportability of the hot-rolled steel strip during production. Because. Note that the reduction ratio in the two passes before the final pass here refers to the plate thickness (L2) before the steel strip enters the two passes before the final pass of the finish rolling device, and the one pass before the final pass. It is assumed that (L2−L1) / L2 × 100 is defined from the plate thickness (L1) after passing through the path.
[0037]
In order to refine the hot-rolled sheet, it is desirable to accumulate strain by hot working in the vicinity immediately above the transformation point. However, in the hot rolling process, the plate temperature decreases as it proceeds from the entry side to the exit side, and the steel strip gradually hardens and the processing resistance increases, so there is a limit to performing large reduction in the final pass. . That is, when large pressure reduction is performed in the final pass, the shape of the steel plate is disturbed, or a problem occurs in the transportability of the steel strip. For this reason, in order to accumulate the processing strain and perform fine graining while ensuring the shape and transportability of the steel sheet, the rolling reduction in the final pass of finish rolling and the two passes before the final pass is as described above. It is necessary to introduce an appropriate amount of distortion at an appropriate timing. In other words, a large amount of distortion is accumulated by increasing the total reduction ratio in the two passes before the final pass, and distortion is also accumulated in the final pass, but in the final pass, the reduction ratio is adjusted to correct shape and transportability. Lower.
[0038]
Specifically, the total rolling reduction ratio in the two passes before the final pass in finish rolling is set to 70% or less because the workability and shape of the steel sheet in these passes are accumulated after processing strain is accumulated. This is to ensure. On the other hand, the reason why the total rolling reduction exceeds 45% is to sufficiently accumulate strain during hot working and to ensure the soft high ductility and high workability of the steel sheet. In addition, the final pass reduction ratio is not a problem from the viewpoint of introducing processing strain, but it is 35% or less in order to ensure the transportability and formability of the steel sheet at a level where there is no problem. The minimum level is 5% or more, which is necessary for correction. If the conditions for hot rolling as described above are satisfied, the rolling reduction of the hot rolling rough rolling process and the pass of three passes before the final pass at the time of finish rolling are not particularly problematic and are conventionally performed. Is sufficient.
[0039]
In order to obtain better elongation, deep drawability, and anisotropy with cold-rolled annealed sheets, the total rolling reduction in 2 passes before the final pass in finish rolling is set to 55% to 70%. Accumulation of large amounts of strain to refine the hot-rolled sheet and / or refine the hot-rolled sheet by reducing the final pass reduction ratio to 15% to 35%. It is preferable to satisfy. When emphasizing the shape of the steel sheet and the transportability of the hot-rolled steel strip at the time of manufacture, the final pass rolling reduction is corrected to 5% to 15% to ensure the transportability, and It is preferable to introduce processing strain.
[0040]
When the rolling reduction in finish rolling is large as in the present invention, generally, shape abnormality occurs, the transportability cannot be ensured (meandering), and as a result, it is not wound neatly when wound on a coiler. May protrude outwards or dent inward. Also, an abnormality may occur in the material characteristics in the width direction. These phenomena occur because a slight temperature unevenness occurs in the hot-rolled steel strip during hot rolling, and the elongation changes at the center and edge portions of the sheet width during rolling.
[0041]
In the present invention, the rolling reduction ratio between the final pass and the two passes before the final pass is defined separately to ensure the shape and transportability of the hot-rolled steel strip, but the shapeability and transportability are even better. In order to achieve this, it is preferable to further heat the hot-rolled steel strip offline or online so that the temperature distribution in the plate width direction is uniform. The method is as follows: (1) an apparatus for heating a rough bar (hot-rolled steel strip after completion of rough rolling) online with an induction heating device, (2) an apparatus for winding the rough bar and then heating it with a coil box, 3) Uniform temperature distribution in the plate width direction using an induction heating device or the like installed in the finish rolling device.
[0042]
The thickness at the coarse bar stage before finish rolling is desirably 20 mm or more. This is because the absolute amount of reduction can be increased by making the coarse bar thickness in this way, and the material can be easily formed by rolling. However, it is not essential to have such a rough bar thickness. For example, even with a hot rolling apparatus in which a continuous casting machine for thin slabs and a hot rolling apparatus are directly connected, a predetermined pass of finish rolling is as described above. If the conditions are satisfied, a material superior to the material (material after cold rolling annealing) made by the conventional method can be realized on condition that the process is controlled to satisfy the following conditions. .
[0043]
(2) Finishing temperature: Ar₃Above the transformation point (Ar₃Transformation point + 50 ° C) or less
The reason for defining the finishing temperature in this way is that finishing rolling is finished in the γ region, and accumulated hot strain in the γ region and the fine γ grains are used to sufficiently refine the hot rolled sheet. It is. Finish temperature at Ar₃If it is less than the transformation point, it becomes α-region rolling, and the coarsening of crystal grains occurs. On the other hand, the finishing temperature is (Ar₃If the temperature exceeds the transformation point + 50 ° C., γ grain growth occurs after the end of rolling, which is disadvantageous for making the hot rolled sheet finer.₃(Transformation point + 50 ° C.) or less.
[0044]
(3) Cooling rate: 200 ° C / sec or more and 2000 ° C / sec or less
The reason for setting the cooling rate after finishing rolling to 200 ° C./sec or more is to refine the hot rolled sheet and to improve the mechanical properties of the obtained cold rolled sheet. In the present invention, the cooling is mainly performed by destroying the vapor film formed on the surface of the steel sheet during cooling, rather than the method of cooling while raising the water vapor as seen in laminar cooling (cooling in the film boiling mode). Cooling mainly intended for the method (cooling in the nucleate boiling mode) is intended, and in such a cooling method, the cooling rate is necessarily 200 ° C./sec or more. Further, the upper limit of the cooling rate is set to 2000 ° C./sec from the approximate theoretical limit value in cooling in the nucleate boiling mode. As a device capable of realizing such a cooling rate, any method can be used as long as it can perform cooling in the nucleate boiling mode, such as a multi-hole jet method, a super close nozzle + high pressure + a large amount of water method. May be used.
[0045]
Since the cooling rate varies depending on the plate thickness, for example, in order to define the cooling rate more accurately, for example, “a steel plate having a plate thickness of 2.5 mm or more and 3.5 mm or less is a rate of 200 ° C./sec or more and 2000 ° C./sec or less However, in the present invention, it is only necessary to have such a cooling rate regardless of the plate thickness. Regardless, it is preferable to use an apparatus having a cooling capacity capable of cooling at such a cooling rate. A more preferable range of the cooling rate is 400 ° C./sec or more and 2000 ° C./sec or less. By cooling in this range, the elongation and deep drawability of the cold-rolled annealed plate can be further improved and the anisotropy can be further suppressed.
[0046]
In the present invention, the cooling rate after finish rolling is defined as 200 / Δt using the time (Δt) required for cooling 200 ° C. from 900 ° C. to 700 ° C. The rapid cooling in the present invention is "Ar.₃Above the transformation point (Ar₃(Transformation point + 50 ° C) or less and within 1 second after completion of finish rolling "Depending on the steel composition of the slab, the actual cooling start temperature may be less than 900 ° C. The cooling rate shall follow this definition. That is, the cooling rate is a value determined when the steel strip is temporarily cooled from 900 ° C to 700 ° C. The temperature at which cooling is actually started may be 900 ° C. or lower, and the temperature at which the rapid cooling is stopped may be 700 ° C. or lower.
[0047]
(4) Cooling start time: within 1 second after finishing rolling or over 0.5 second within 1 second
The reason why the cooling start time is defined in this way is that the grain size of the hot rolled sheet is sufficiently refined by increasing the cooling rate as described above and shortening the cooling start time. As a result, it is possible to obtain the effects of improving elongation and deep drawability and reducing anisotropy. When the cooling start time exceeds 1 second, the particle diameter of the hot-rolled sheet cannot be sufficiently refined, almost the same as the diameter of the hot-rolled sheet in ordinary laminar cooling or air cooling in a laboratory experiment.
[0048]
In the present invention, the lower limit of the cooling start time is not particularly specified, but even if the rolling speed is increased and the cooling is started immediately near the exit side of the finish rolling, the housing of the cooling device, the protrusion for the radius of the rolling roll, etc. In consideration of the above, 0.01 second is substantially the lower limit of the cooling start time.
[0049]
Even if the cooling start time is within 1 second, the characteristics that appear depends on the cooling start time. When the cooling start time is within 0.5 seconds, deep drawability and anisotropy are preferentially improved. However, when the cooling start time is 0.5 seconds or more and 1 second or less, the elongation is preferentially improved. The reason why there is a difference in the characteristics developed in this way is thought to be because the slight ferrite grain size at the cold-rolled annealing plate stage is different, but the mechanism is not clear.
[0050]
In order to make the material uniform in the longitudinal direction of the steel plate, the cooling start time is preferably more than 0.5 seconds and within 1 second. Even when the cooling start time is set to 0.5 seconds or less, improvement of the material can be expected by making the hot rolled sheet finer, but the material changes greatly due to slight deviation of the cooling start time. Inhomogeneity may occur.
[0051]
In order to set the cooling start time within 1 second, for example, when the rolling speed (conveying speed of the hot-rolled steel strip during rolling) is 1300 m / min or less, the cooling device (for example, the nucleate boiling mode described above) A cooling device capable of cooling is installed in the vicinity of within 15 m from the nearest side of the final pass exit side of the finish rolling device according to the rolling speed. That is, when the rolling speed is high, it may be installed at the rear side of this range, and when the rolling speed is low, it is installed at the front side of this range to realize a cooling start time within one second. In addition, when high-speed rolling at a rolling speed exceeding 1300 m / min is possible, it can be predicted that the installation position of the cooling device is further away from the final pass exit side.
[0052]
In addition, from the viewpoint of uniformizing the material in the longitudinal direction of the steel sheet, it is more desirable that the cooling start time is a constant value in the longitudinal direction of the coil, but a cooling device that performs rapid cooling in the current hot rolling mill is a control unit. Then, the cooling start time may change in the coil longitudinal direction. The reason is that hot rolling is not always performed at a constant speed. That is, rolling is performed at a low rolling speed until the leading portion of the steel strip is wound around the coiler, and then the steel strip is wound around the coiler and tension is applied to the steel strip, and then the rolling speed is gradually increased to a constant speed. In this state, rolling is performed up to the rear end of the coil, and the cooling start time changes due to the fluctuation of the rolling speed.
[0053]
In order to avoid such fine graining and variation in material, it is preferable to divide the cooling device into small units and perform ON / OFF control in conjunction with the rolling speed of each unit. In this case, at the coil tip where the rolling speed is slow, cooling is performed using the unit on the final pass side, and then the cooling unit is installed on the coiler side according to the rolling speed that is gradually accelerated. By shifting to the unit, the cooling start time in the coil longitudinal direction can be made uniform, and the fine particles and the material can be made uniform.
[0054]
(5) Rapid cooling temperature drop: 50 ° C to 250 ° C
The reason why rapid cooling is performed in this way is to optimize the fineness of the hot-rolled sheet, improve the elongation and deep drawability of the cold-rolled annealed sheet, and keep the anisotropy low. As described above, when the two conditions “the cooling rate is 200 ° C./sec to 2000 ° C./sec” and “the cooling start time is within 1 second” are satisfied, the temperature drop after the final pass is Since the cooling start temperature and the finishing temperature can be regarded as almost the same temperature, the “temperature drop from the finishing temperature” is defined in this way.
[0055]
In order to optimize hot-rolled sheet refinement, it is not necessary to rapidly cool the specified temperature range as described above. In particular, the temperature drop due to rapid cooling should be within an appropriate range. is required. If the amount of temperature drop due to this rapid cooling exceeds the appropriate range, polygonal ferrite grains cannot be realized, resulting in grains extending in the rolling direction and grains with a hardened structure, and excellent workability and anisotropy. Cannot be obtained. For this reason, in the present invention, the amount of temperature drop due to rapid cooling is defined as described above.
[0056]
The reason why the temperature drop due to rapid cooling is set to 50 ° C. or more is that at least a temperature drop of 50 ° C. is necessary for cooling across the γ-α transformation point at the aforementioned cooling rate. Further, the reason why the temperature drop amount is set to 250 ° C. or less is that when the temperature drop amount exceeds 250 ° C., an adverse effect due to excessive cooling becomes remarkable. In particular, when it is desired to improve the elongation of the cold-rolled annealed plate, it is preferable to set the temperature drop amount to 150 ° C. or less.
[0057]
In order to control the temperature drop due to rapid cooling to the above range, the cooling device that performs rapid cooling in the nucleate boiling mode is divided into small units in the rolling direction, and cooling in each unit is performed in conjunction with the rolling speed. It is effective to perform ON / OFF control. The amount of temperature drop due to rapid cooling is determined by the cooling rate of the cooling device that performs rapid cooling, the length of the portion that performs rapid cooling of the cooling device, and the rolling speed (steel strip conveyance speed). It is difficult to keep the temperature drop due to rapid cooling within the above range, and the temperature drop cannot be made constant over the entire length in the longitudinal direction of the coil, resulting in variations in the characteristics of the cold-rolled annealed plate.
[0058]
More specifically, the cooling rate of the rapid cooling in the nucleate boiling mode varies depending on the plate thickness, and is slow for a thick plate and fast for a thin plate. In addition, the rolling speed is rarely constant over the entire length of the coil, and the speed until the steel strip is wound around the coiler is slowed, and then the steel strip is accelerated in a state where tension is applied to become a constant speed. In many cases, the rolling speed is taken. Therefore, the cooling device is divided into small units, and the number of units to be cooled and the positions of the units are determined according to the rolling speed that varies as described above, and ON / OFF control of each unit is performed. Thus, the amount of temperature drop due to rapid cooling can be controlled appropriately.
[0059]
In addition, it is important to quickly remove the water used for rapid cooling. For example, when water flows out after the exit side of the cooling device, cooling of the steel sheet is continued according to the amount of remaining water. When more water than necessary remains on the steel sheet at the exit of the cooling device, the cooling mode in that area varies depending on the water pressure and rolling speed applied to the steel sheet, but a mode in which the nucleate boiling mode and the film boiling mode are mixed. Or it becomes the mode of the process which transfers to cooling of a film | membrane boiling mode. Regardless of the mode, cooling with a higher cooling rate than the mere film boiling mode is continued. This directly leads to variations in the effect of improving the characteristics of the steel sheet, which is manifested by rapid cooling, and if the steel is cooled too much, polygonal ferrite grains cannot be realized, leading to deterioration of the material. In order to prevent this, a draining device, a draining roll, an air curtain or the like may be installed on the outlet side of the cooling device.
[0060]
(6) Cooling stop temperature for rapid cooling: 650 ° C or higher and 850 ° C or lower
The cooling stop temperature for rapid cooling is defined in this way in combination with the above-mentioned conditions of “cooling rate”, “cooling start time”, and “temperature drop due to rapid cooling”. This is because of appropriate conversion. When the cooling stop temperature exceeds 850 ° C., grain growth after cooling stop may not be negligible, which is not preferable from the viewpoint of making the hot-rolled sheet fine. On the other hand, when the cooling stop temperature is less than 650 ° C., a quenched structure is formed even if the above-described conditions of “cooling rate”, “cooling start time”, and “temperature drop due to rapid cooling” are satisfied. In that case, the characteristics of the cold-rolled annealed sheet cannot be improved. The rapid cooling stop temperature is a plate temperature when it comes out of the rapid cooling device, and is given by (finishing temperature) − (temperature drop due to rapid cooling). In addition, the quenching stop temperature must be set to be equal to or higher than the coiling temperature. The quenching stop temperature is substantially the plate temperature at the time of exiting the rapid cooling device. For example, when the cooling device has a multi-bank configuration, the steel strip is used as the bank used for cooling. You may control the temperature at the time of passing in said appropriate range. In order to control the cooling stop temperature within the above range, it is preferable to install a draining device, a draining roll, an air curtain or the like on the outlet side of the cooling device, and control the cooling stop temperature by these.
[0061]
(7) Cooling after rapid cooling: slow cooling or air cooling at 100 ° C./sec or less
After rapid cooling in the hot-rolled runout performed as described above, slow cooling or air cooling at a coiling temperature of 100 ° C./sec or less is a polygonal and refined ferrite as described above. This is to improve the properties of the cold-rolled annealed plate by making grains. When cooling to the coiling temperature only by rapid cooling, an adverse effect due to excessive cooling is observed and a desired structure cannot be obtained. Therefore, slow cooling or air cooling at 100 ° C./sec or less is essential. If the cooling rate exceeds 100 ° C./sec, it becomes difficult to form polygonal ferrite grains.
[0062]
(8) Winding temperature
The coiling temperature is not particularly limited, but is preferably 550 ° C. or higher and 750 ° C. or lower. If the coiling temperature is less than 550 ° C., the steel hardens. Further, as described above, when rapid cooling is performed, the coiling temperature inevitably has to be 750 ° C. or lower, and even if the coiling temperature exceeds 750 ° C., no improvement in characteristics is observed.
[0063]
Moreover, when there are many amounts of C, S, and N in steel, that is, C: 0.002% or more and 0.01% or less, S: 0.012% or more and 0.02% or less, or N: 0.002% When the content is 0.004% or less, the winding temperature is preferably 630 ° C. or more and 750 ° C. or less. By setting it within this range, it is possible to remove factors (fine precipitates) that promote the formation and growth of precipitates and inhibit the growth of ferrite grains in the cold-rolled annealed sheet.
[0064]
On the other hand, when the amount of C, S, P, and N in the steel is small, that is, C: 0.0003% to 0.002%, S: 0.0003% to 0.012%, P: 0.003 or more In the case of 0.015% or less, or N: 0.0003% or more and 0.002% or less, the winding temperature is preferably 550 ° C. or more and 680 ° C. or less. By setting it as this range, since these elements are few, very vigorous grain growth can be suppressed and the hot-rolled sheet grain size can be effectively reduced.
[0065]
(9) Cold rolling
The conditions for cold rolling are not particularly limited, but the reduction ratio (cold pressure ratio) at that time is preferably 50% or more and 90% or less. By setting the cold pressure ratio within this range, the effect of improving the characteristics from the finely grained hot-rolled sheet obtained as described above is great.
[0066]
(10) Annealing
Conditions for annealing the cold-rolled sheet are not particularly limited, but it is preferable to anneal at a temperature of 700 ° C. or higher and 850 ° C. or lower from the viewpoint of improving characteristics and preventing rough skin. The annealing may be performed by any method such as continuous annealing or batch annealing.
[0067]
In the present invention, a method of hot-rolling a continuously cast slab without heating it in a heating furnace, and heating to a predetermined temperature in a heating furnace in a state where the temperature of the continuously cast slab does not fall to room temperature. The method of hot rolling from slab, the method of hot rolling after the temperature of the slab is lowered to room temperature and then heating to a predetermined temperature in a heating furnace, the apparatus connected with the thin slab continuous casting device and the hot rolling device Even if any method is used, such as a method for hot rolling, a method for hot rolling after heating a slab produced by an ingot in a heating furnace, the above process conditions are applied to the steel having the above composition. By applying, a preferable material can be made.
[0068]
The cold-rolled steel sheet according to the present invention can be suitably used for applications requiring workability, such as automotive steel sheets, electrical steel sheets, can steel sheets, and building steel sheets, but used for other purposes. Even in this case, the characteristics can be sufficiently exhibited. Moreover, the cold-rolled steel sheet in the present invention includes those subjected to surface treatment such as Zn plating or alloyed Zn plating.
[0069]
【Example】
Examples of the present invention will be described below.
[Example 1]
Steel having the components shown in Table 1 is formed into a slab having a thickness of 200 to 300 mm by continuous casting, heated to 1180 to 1250 ° C., and hot rolled under hot rolling conditions including the cooling conditions shown in Table 2. A hot-rolled sheet having a thickness of 2.8 mm was cold-rolled to a thickness of 0.8 mm, and then heated at a temperature increase rate of 6 ° C./sec to 20 ° C./sec, and the annealing temperature shown in Table 2 for 90 seconds. After continuous annealing, no. 1-18 cold-rolled steel sheets were obtained. In hot rolling, in order to ensure the transportability and shape of the hot-rolled steel strip at a level without problems, immediately before the introduction of a rough bar (hot-rolled steel strip that has undergone rough rolling) into the finishing rolling mill Heating was performed with an induction heating device, and the temperature distribution in the plate width direction of the steel strip was made constant. Moreover, in what was shown as "conventional laminar cooling" in Table 2, the laminar cooling which cools while raising water vapor | steam was performed to the hot-rolled steel strip which passed the final pass of finish rolling. On the other hand, in the case of quenching at 200 ° C./sec or more after finish rolling, in the film boiling mode cooling, steam is generated at the time of cooling, and the steam film wraps the steel sheet and cannot be rapidly cooled. Using a perforated jet cooling device, fresh water always hits the steel plate to cool it while destroying the vapor film, realizing nucleate boiling mode cooling that can be rapidly cooled, and the amount of water Rapid cooling was performed at various cooling rates shown in Table 2 while changing the water pressure and the like.
[0070]
For these steel plates, the total elongation was measured with a 0.8 mm material of a cold-rolled steel plate, and the r values in the L direction (0 ° direction with respect to the rolling direction), r0 and D directions (45 ° with respect to the rolling direction). R45 as the r value in the direction) and r90 as the r value in the C direction (90 ° direction with respect to the rolling direction). Table 2 shows the total elongation and average r value as an index for evaluating the workability of the steel sheet, and r45 is the lowest among r0, r45, and r90 as an index for evaluating anisotropy. A steel sheet exhibiting a tendency exhibits Δr, and a steel sheet in which r45 takes an intermediate value between r0 and r90 indicates a maximum value-minimum value of the r value. Here, the average r value is a value defined by average r value = (r0 + 2 × r45 + r90) / 4. Δr is a value defined by Δr = (r0 + r90−2 × r45) / 2.
[0071]
[Table 1]

[0072]
[Table 2]

[0073]
As shown in Table 2, No. 1 manufactured under the process conditions of the present invention for rapid cooling. The steel sheets of 2, 4, 6, 8, 10, 12, 14, 16, and 18 all have extremely high elongation and average r value, and the maximum value-minimum value of Δr or r value is extremely low. The processability and anisotropy were extremely excellent. On the other hand, laminar cooling was performed from the top and bottom of the steel plate at the runout table after the final pass. The steel sheets of 1, 3, 5, 7, 9, 11, 13, 15, and 17 were inferior in any of the characteristics.
[0074]
As described above, if a steel sheet having a composition in the range specified in the present invention is used to produce a cold-rolled steel sheet according to the process conditions specified in the present invention, it is excellent in formability and transportability, and conventionally It was also confirmed that a cold-rolled steel sheet having remarkably excellent workability and anisotropy can be produced.
[0075]
[Example 2]
Steel having the components shown in Table 3 was made into a slab having a thickness of 220 mm by continuous casting. After the slab was maintained, it was heated to 1200 ° C., hot-rolled under the conditions shown in Table 4, and cold-rolled. Thereafter, the film was continuously annealed at an annealing temperature of 840 ° C. for 90 seconds at a temperature rising rate of 10 ° C./sec or more and 20 ° C./sec or less, and No. 19-44 cold-rolled steel sheets were obtained. In hot rolling, in order to ensure the transportability and shape of the hot-rolled steel strip at a level without problems, immediately before the introduction of a rough bar (hot-rolled steel strip that has undergone rough rolling) into the finishing rolling mill Heating was performed with an induction heating device, and the temperature distribution in the plate width direction of the steel strip was made constant. At this time, no. For No. 30, the thickness of the hot-rolled sheet was 1.5 mm and the thickness of the cold-rolled annealed sheet was 0.75 mm. As for 19 to 29 and 31 to 44, the thickness of the hot-rolled sheet was 2.8 ± 0.2 mm, and the thickness of the cold-rolled annealed sheet was 0.8 mm. In addition, No. 1 shown in Table 4 was used. The cooling rate of 30 is a value when the thickness of the hot-rolled sheet is 1.5 mm. When the cooling rate is confirmed with a sheet thickness of 2.8 to 3.5 mm, it is 270 ± 70 ° C./sec. Table 4 shows the results of evaluating the properties of the cold-rolled steel sheet obtained as described above in the same manner as in Example 1. In Table 4, “No. About the total elongation of 30, the value measured with the cold rolled steel plate having a thickness of 0.75 mm is converted into the elongation of 0.8 mm material according to the Oliver law.
[0076]
[Table 3]

[0077]
[Table 4]

[0078]
As shown in Table 4, No. manufactured according to the process conditions of the present invention. Steel plates of 20, 25 to 30, 33 to 36, 38 to 40, 44 are all secured to a level where the shape and transportability of the steel plate are satisfactory, and the elongation and average r value are extremely high. And (DELTA) r was restrained very low, and workability and anisotropy were very excellent. On the other hand, any of the conditions is outside the scope of the present invention. In the steel sheets of 19, 21 to 24, 31, 32, 37, and 41 to 43, any of the characteristics was inferior.
[0079]
Specifically, no. In No. 19, the total reduction ratio of the two passes before the final pass exceeded the scope of the present invention. In No. 21, the rolling reduction of the final pass exceeded the range of the present invention, and in either case, meandering during production, the shape and transportability of the steel plate were inferior, and it was difficult to produce stably. Table 4 shows the best data among the material properties of the cold-rolled annealed sample obtained from a part of the hot-rolled coil that could be manufactured. As shown in Table 4, no. 19 and 21 sometimes showed excellent material characteristics, but the production itself was difficult and the material characteristics varied greatly.
[0080]
No. In No. 22, the finishing temperature was lower than the range of the present invention and the α-region rolling was performed, and therefore, the deterioration of the total elongation was particularly remarkable. On the other hand, no. In No. 23, the finishing temperature exceeded the range of the present invention, so the characteristics were deteriorated. This is considered to be because the growth of γ grains progressed before rapid cooling. No. In No. 24, since the cooling rate was lower than the range of the present invention, the rapid cooling was not sufficient, the hot-rolled sheet could not be made fine, and the effect of improving the γ value could not be obtained sufficiently. No. 31 and no. In No. 32, the cooling start time exceeded the range of the present invention, so it was considered that the grains had grown, and the hot-rolled sheet was not sufficiently refined, and the effects of improving workability and anisotropy were sufficiently obtained. I couldn't. No. 37, the rapid cooling temperature drop was smaller than the range of the present invention, and the quenching stop temperature was higher than the range of the present invention, so that the hot-rolled sheet was not sufficiently refined and the effect of improving the r value was sufficiently obtained. There wasn't. No. 41, the rapid cooling temperature drop amount is larger than the range of the present invention, the quenching stop temperature is lower than the range of the present invention, and the coiling temperature is also lower than the preferred range of the present invention. Thus, the structure became hardened grains, and the deterioration of the characteristic value was remarkable. No. In No. 42, since the quenching stop temperature was lower than the range of the present invention, the structure of the hot-rolled sheet was not polygonal fine grains, and the characteristic value was deteriorated. No. In No. 43, since the cooling rate after the rapid cooling exceeded the range of the present invention, polygonal fine grains were not obtained at the stage of hot rolling, and all the characteristic values were inferior.
[0081]
As described above, a cold-rolled steel sheet having a workability and anisotropy that are remarkably superior to those of the prior art is produced for the first time by a manufacturing method that satisfies all the conditions defined in the present invention. It was confirmed that it can be manufactured without any problems.
[0082]
[Example 3]
In order to investigate the effect of the cooling start time, a steel having the components shown in Table 5 was made into a slab having a thickness of 200 to 300 mm by continuous casting, heated to 1180 ° C. to 1250 ° C., and the final pass in the range shown in Table 6 Hot rolling is performed at the total rolling reduction ratio, final pass reduction ratio, finishing temperature, cooling conditions, and winding temperature of the previous two passes to obtain a hot rolled sheet having a thickness of 2.8 mm, and cold rolling to a thickness of 0.8 mm. Then, the temperature was raised at a temperature rising rate of 6 ° C./sec or more and 20 ° C./sec or less, and continuously annealed at an annealing temperature of 850 ° C. for 90 seconds to obtain various cold-rolled steel sheets. At this time, in the case of “conventional laminar cooling” in Table 6, laminar cooling was performed in which the hot-rolled steel strip that passed through the final pass of finish rolling was cooled while raising steam. On the other hand, in the case of quenching at 200 ° C./sec or higher after finish rolling, in the film boiling mode cooling, steam is generated at the time of cooling, and the steam film wraps the steel sheet and cannot be rapidly cooled. Using a perforated jet cooling system, fresh water always hits the steel sheet in order to perform cooling while destroying the vapor film, realizing nucleate boiling mode cooling that enables rapid cooling.
[0083]
About these steel plates, like Example 1, total elongation was measured with the 0.8 mm material of the cold rolled steel plate, and r0, r45, and r90 which are r values of each direction were measured, respectively. The relationship between the measured total elongation value and the cooling start time is shown in FIG. 1, and the relationship between the average r value obtained from the measured r value and the cooling start time is shown in FIG. Further, Δr is used as an index for evaluating the anisotropy, and FIG. 2 also shows the value of Δr for some of the steel plates.
[0084]
As shown in FIG. 1 and FIG. 2, when the cooling start time is 0.5 seconds or less, the behavior of total elongation is not uniform and varies greatly, and the average r value decreases as the cooling start time decreases. It is rising at a high rate of increase. For this reason, when the cooling start time is 0.5 seconds or less, the material changes greatly only by slightly shifting the cooling start time, and it is difficult to industrially manufacture a steel plate having a uniform material in the longitudinal direction.
[0085]
On the other hand, when the cooling start time is in the range of more than 0.5 seconds and not more than 1 second, the total elongation and the r value are almost constant. For this reason, even if the cooling start time is slightly shifted, it is possible to manufacture a steel plate having a uniform material in the longitudinal direction. Further, both the total elongation and the average r value are improved as compared with the case of laminar cooling in the film boiling mode.
[0086]
On the other hand, when the cooling start time exceeds 1 second, both the total elongation and the r value monotonously decrease, and the material level is not much different from the case where laminar cooling is performed in the film boiling mode.
[0087]
In addition, although Δr does not show all the cooling start times, as shown in FIG. 2, Δr is small in the steel plate whose r value is improved by cooling. Therefore, if the r value is the same level, Δr may be considered to be almost the same level. Therefore, when the cooling start time is in the range of more than 0.5 seconds and not more than 1 second, it is considered that the value of Δr is stably improved as compared with the case where the conventional laminar cooling is performed.
[0088]
From the above, it was confirmed that when the cooling start time is in the range of more than 0.5 seconds and not more than 1 second, a cold-rolled steel sheet having excellent workability, small anisotropy, and uniform longitudinal material can be produced. .
[0089]
[Table 5]

[0090]
[Table 6]

[0091]
[Example 4]
Steel having the components shown in Table 7 is made into a slab having a thickness of 200 to 300 mm by continuous casting, heated to 1180 to 1250 ° C., and hot rolled under hot rolling conditions including the cooling conditions shown in Table 8. A hot-rolled sheet having a thickness of 2.8 mm was cold-rolled to a thickness of 0.8 mm, and then heated at a temperature increase rate of 6 ° C./sec to 20 ° C./sec, and the annealing temperature shown in Table 8 was applied for 90 seconds. After continuous annealing, no. 45-64 cold rolled steel sheets were obtained. In hot rolling, in order to ensure the transportability and shape of the hot-rolled steel strip at a level that does not cause any problems, a rough bar (hot-rolled steel strip that has finished rolling) is immediately introduced into the finishing rolling mill. It heated with the induction heating apparatus, and the temperature distribution of the sheet width direction of the steel strip was made uniform. Moreover, in what was shown as "conventional laminar cooling" in Table 8, the laminar cooling which cools while raising water vapor | steam was performed to the hot-rolled steel strip which passed the final pass of finish rolling. On the other hand, in the case of quenching at 200 ° C./sec or more after finish rolling, steam is generated during cooling in the film boiling mode, and the steam film wraps the steel sheet and cannot be rapidly cooled. Using a perforated jet cooling system, fresh water always hits the steel sheet for cooling while destroying the vapor film, realizing nucleate boiling mode cooling that allows rapid cooling, and the amount and pressure of water The cooling was performed at various cooling rates shown in Table 8. The characteristics of the cold-rolled steel sheet obtained as described above were evaluated in the same manner as in Example 1. The results are shown in Table 8.
[0092]
[Table 7]

[0093]
[Table 8]

[0094]
As shown in Table 8, No. 1 manufactured under the process conditions of the present invention for rapid cooling. The 46, 48, 50, 52, 54, 56, 58, 62, and 64 steel sheets all have extremely high elongation and r value, and the maximum value-minimum value of Δr or r value is extremely low. The processability and anisotropy were extremely excellent. On the other hand, laminar cooling was performed from the top and bottom of the steel plate at the runout table after the final pass. The steel sheets of 45, 47, 49, 51, 53, 55, 57, 59, 61 and 63 were inferior in any of the characteristics.
[0095]
As described above, if a steel sheet having a composition in the range specified in the present invention is used to produce a cold-rolled steel sheet according to the process conditions specified in the present invention, it is excellent in formability and transportability, and conventionally It was also confirmed that a cold-rolled steel sheet having remarkably excellent workability and anisotropy can be produced.
[0096]
[Example 5]
Steel having the components shown in Table 9 was made into a slab having a thickness of 220 mm by continuous casting. After the slab was maintained, it was heated to 1200 ° C., hot-rolled under the conditions shown in Table 10, and cold-rolled. Thereafter, the film was continuously annealed at an annealing temperature of 840 ° C. for 90 seconds at a temperature rising rate of 10 ° C./sec or more and 20 ° C./sec or less, and No. 65 to 82 cold-rolled steel sheets were obtained. In hot rolling, in order to ensure the transportability and shape of the hot-rolled steel strip at a level that does not cause any problems, a rough bar (hot-rolled steel strip that has finished rolling) is immediately introduced into the finishing rolling mill. It heated with the induction heating apparatus, and the temperature distribution of the board width direction of the steel plate was made uniform. At this time, no. Regarding No. 74, the thickness of the hot-rolled sheet was 1.5 mm and the thickness of the cold-rolled annealed sheet was 0.75 mm. About 65-73, 75-82, the thickness of the hot-rolled sheet was 2.8 ± 0.2 mm, and the thickness of the cold-rolled annealed sheet was 0.8 mm. In addition, No. 1 shown in Table 10 was used. The cooling rate of 74 is a value when the thickness of the hot-rolled sheet is 1.5 mm. When the cooling rate is confirmed with a sheet thickness of 2.8 to 3.5 mm, it is 270 ± 70 ° C./sec. Table 10 shows the results of evaluating the properties of the cold-rolled steel sheet obtained as described above in the same manner as in Example 1. In Table 10, no. About the total elongation of 74, the value measured by the cold rolled steel plate of thickness 0.75mm is converted into the elongation of 0.8mm material by Oliver's law.
[0097]
[Table 9]

[0098]
[Table 10]

[0099]
As shown in Table 10, No. manufactured according to the process conditions of the present invention. The steel plates 66, 69 to 74, 76 to 78, 82 are all secured to a level where the shape and transportability of the steel plate are not problematic, and the elongation and average r value are extremely high, and Δr is extremely high. It was kept low and the workability and anisotropy were extremely excellent. On the other hand, any of the conditions is outside the scope of the present invention. In the steel sheets of 65, 67, 68, 75, and 79 to 81, any of the characteristics was inferior.
[0100]
Specifically, no. In No. 65, the total reduction ratio of the two passes before the final pass was higher than the range of the present invention. In No. 67, the rolling reduction of the final pass was high beyond the range of the present invention, and in either case, the meandering during production, the shape and transportability of the steel plate were inferior, and it was difficult to produce stably. . Table 10 shows the best data among the materials shown in the sample of the cold-rolled annealed plate obtained from a part of the hot-rolled coil that could be manufactured. As shown in Table 10, although No, 65, and 67 sometimes showed excellent material characteristics, the manufacturing itself was difficult and the material characteristics varied greatly.
[0101]
No. In No. 68, since the cooling rate was lower than the range of the present invention, the rapid cooling was not sufficient, the hot-rolled sheet could not be made fine, and the effect of improving the γ value could not be obtained sufficiently. No. 75, the rapid cooling temperature drop amount was smaller than the range of the present invention, and the quenching stop temperature was higher than the range of the present invention. Therefore, the hot-rolled sheet was not sufficiently refined, and the effect of improving the r value was sufficiently obtained. There wasn't. No. 79, the rapid cooling temperature drop amount was larger than the range of the present invention, the quenching stop temperature was lower than the range of the present invention, and the coiling temperature was also lower than the preferred range of the present invention. Deterioration of the characteristic value was remarkable due to the textured grains. No. In No. 80, since the quenching stop temperature was lower than the range of the present invention, the structure of the hot-rolled sheet was not polygonal fine grains, and the characteristic value was deteriorated. No. In 81, since the cooling rate after the rapid cooling was higher than the range of the present invention, polygonal fine grains were not obtained at the stage of hot rolling, and all the characteristic values were inferior.
[0102]
As described above, a cold-rolled steel sheet having a workability and anisotropy that are remarkably superior to those of the prior art is produced for the first time by a manufacturing method that satisfies all the conditions defined in the present invention. It was confirmed that it can be manufactured without any problems.
[0103]
【The invention's effect】
According to the present invention, a cold-rolled steel sheet having remarkably superior workability and anisotropy compared with the same component system made by a conventional method has a problem in the formability and transportability of the steel sheet. It becomes possible to manufacture without generating.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the value of total elongation and the cooling start time in Example 3.
FIG. 2 is a graph showing the relationship between the average r value and the cooling start time in Example 3.

Claims (6)

% By weight
C: 0.0003% to 0.01%,
Si: 0.05% or less,
Mn: 0.05% or more and 2.5% or less,
P: 0.003% to 0.1%,
S: 0.0003% to 0.02%,
Sol. Al: 0.005% or more and 0.1% or less,
N: 0.0003% or more and 0.004% or less, and further containing 1 or more of Ti, Nb, V, and Zr by weight% in total of 0.005% or more and 0.1% or less, In manufacturing a cold-rolled steel sheet by heating a steel slab composed of the remaining Fe and inevitable impurities, hot rolling, cold rolling, and annealing,
The hot rolling
In finish rolling, the total rolling reduction of the two passes before the final pass is over 45% and 70% or less, the rolling reduction of the final pass is 5% or more and 35% or less, and the finishing temperature is higher than the Ar ₃ transformation point (Ar ₃ Finish rolling as transformation point + 50 ° C or less),
Next, rapid cooling is started at a cooling rate of 200 ° C./sec or more and 2000 ° C./sec or less within 1 second after finishing rolling, and the temperature drop from the finishing temperature of the finishing rolling in this rapid cooling is 50 ° C. The cooling stop temperature for this rapid cooling is 650 ° C. or more and 850 ° C. or less.
A method for producing a cold-rolled steel sheet having excellent workability and low anisotropy, characterized by winding the obtained hot-rolled steel strip after slow cooling or air cooling at 100 ° C./sec or less. % By weight
C: 0.0003% to 0.01%,
Si: 0.05% or less,
Mn: 0.05% or more and 2.5% or less,
P: 0.003% to 0.1%,
S: 0.0003% to 0.02%,
Sol. Al: 0.005% or more and 0.1% or less,
N: 0.0003% or more and 0.004% or less, and further containing 1 or more of Ti, Nb, V, and Zr by weight% in total of 0.005% or more and 0.1% or less, In manufacturing a cold-rolled steel sheet by heating a steel slab composed of the remaining Fe and inevitable impurities, hot rolling, cold rolling, and annealing,
The hot rolling
In finish rolling, the total rolling reduction of the two passes before the final pass is over 45% and 70% or less, the rolling reduction of the final pass is 5% or more and 35% or less, and the finishing temperature is higher than the Ar ₃ transformation point (Ar ₃ Finish rolling as transformation point + 50 ° C or less),
Next, within 0.5 seconds to 1 second after finishing the finish rolling, rapid cooling is started at a cooling rate of 200 ° C./sec or more and 2000 ° C./sec or less, and the temperature from the finish rolling finish temperature in the rapid cooling is The descending amount is 50 ° C. or more and 250 ° C. or less, and the cooling stop temperature of this rapid cooling is 650 ° C. or more and 850 ° C. or less,
A method for producing a cold-rolled steel sheet having excellent workability and low anisotropy, characterized by winding the obtained hot-rolled steel strip after slow cooling or air cooling at 100 ° C./sec or less. % By weight
C: 0.0003% to 0.01%,
Si: 0.05% or less,
Mn: 0.05% or more and 2.5% or less,
P: 0.003% to 0.1%,
S: 0.0003% to 0.02%,
Sol. Al: 0.005% or more and 0.1% or less,
N: 0.0003% or more and 0.004% or less
In addition, the steel slab containing 0.0001% or more and 0.001% or less of B, and the balance Fe and unavoidable impurities, is heated, hot-rolled, cold-rolled, annealed, and cooled. In producing rolled steel sheets,
  The hot rolling
  In finish rolling, the total rolling reduction of the two passes before the final pass is over 45% and 70% or less, the rolling reduction of the final pass is 5% to 35%, and the finishing temperature is Ar. ₃ Above the transformation point (Ar ₃ Finishing rolling as a transformation point + 50 ° C or less)
  Next, rapid cooling is started at a cooling rate of 200 ° C./sec or more and 2000 ° C./sec or less within 1 second after finishing rolling, and the temperature drop from the finishing temperature of the finishing rolling in this rapid cooling is 50 ° C. The cooling stop temperature for this rapid cooling is 650 ° C. or more and 850 ° C. or less.
  A method for producing a cold-rolled steel sheet having excellent workability and low anisotropy, characterized by winding the obtained hot-rolled steel strip after slow cooling or air cooling at 100 ° C./sec or less. % By weight
C: 0.0003% to 0.01%,
Si: 0.05% or less,
Mn: 0.05% or more and 2.5% or less,
P: 0.003% to 0.1%,
S: 0.0003% to 0.02%,
Sol. Al: 0.005% or more and 0.1% or less,
N: 0.0003% or more and 0.004% or less
In addition, the steel slab containing 0.0001% or more and 0.001% or less of B, and the balance Fe and unavoidable impurities, is heated, hot-rolled, cold-rolled, annealed, and cooled. In producing rolled steel sheets,
  The hot rolling
  In finish rolling, the total rolling reduction of the two passes before the final pass is over 45% and 70% or less, the rolling reduction of the final pass is 5% to 35%, and the finishing temperature is Ar. ₃ Above the transformation point (Ar ₃ Finishing rolling as a transformation point + 50 ° C or less)
  Next, within 0.5 seconds to 1 second after finishing the finish rolling, rapid cooling is started at a cooling rate of 200 ° C./sec or more and 2000 ° C./sec or less, and the temperature from the finish rolling finish temperature in the rapid cooling is The descending amount is 50 ° C. or more and 250 ° C. or less, and the cooling stop temperature of this rapid cooling is 650 ° C. or more and 850 ° C. or less,
  A method for producing a cold-rolled steel sheet having excellent workability and low anisotropy, characterized by winding the obtained hot-rolled steel strip after slow cooling or air cooling at 100 ° C./sec or less. The steel is further cold-rolled with excellent workability and low anisotropy according to claim 1 or 2 , characterized in that the steel further contains B in an amount of 0.0001% to 0.001% by weight. A method of manufacturing a steel sheet. The steel is further excellent in workability according to any one of claims 1 to 5, characterized by containing 0.015% or more and 0.08% or less of Cu by weight%. Manufacturing method of cold-rolled steel sheet with low properties.

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