JP2015116596A - Method for production of hot-rolled steel strip - Google Patents
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Abstract
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本発明は、熱延鋼帯（特に、高強度熱延鋼帯）の製造方法に関するものである。 The present invention relates to a method for producing a hot-rolled steel strip (in particular, a high-strength hot-rolled steel strip).
一般熱延鋼帯では、熱間圧延され、所定の巻取り温度まで冷却され、コイルに巻き取られるまでの間には、フェライト＋パーライトへの変態はほぼ完了している。 In the general hot-rolled steel strip, the transformation to ferrite + pearlite is almost completed between hot rolling, cooling to a predetermined winding temperature, and winding on a coil.
一方、近年、高強度・高伸び、高ヤング率など、様々な機械的特性に優れた鋼板が開発されており、ＣやＳｉ、Ｍｎなどの強化元素を多量に含んでいる高強度鋼板素材の熱延鋼帯（高強度熱延鋼帯）の場合には、これらの添加成分によってフェライト変態が遅延するため、巻き取った時点では変態が完了しないか、ほとんど変態が進行していない。こうした強化元素を含有した高強度熱延鋼帯の場合、熱間圧延され、巻き取られた後、次工程への搬送途中および／またはコイルヤードにおいても変態を起こすことになる。 On the other hand, in recent years, steel plates with various mechanical properties such as high strength, high elongation, and high Young's modulus have been developed, and high strength steel plate materials containing a large amount of reinforcing elements such as C, Si, and Mn. In the case of a hot-rolled steel strip (high-strength hot-rolled steel strip), since the ferrite transformation is delayed by these additive components, the transformation is not completed at the time of winding or the transformation has hardly progressed. In the case of a high-strength hot-rolled steel strip containing such a strengthening element, it is hot-rolled and wound, and then undergoes transformation even during conveyance to the next process and / or in the coil yard.
これによって、特に、熱延後の冷却速度が大きい熱延鋼帯先端・尾端（熱延コイルの内周・外周に相当する箇所）は硬質になる。その結果、冷延時の荷重が大きくなる、あるいは巻き周期に応じた硬さの変動が生じるなど、圧延速度を低下させたり、寸法精度や伸びなどの機械的特性において要求特性を満たさない箇所が生じ、歩留まりの低下を招いたりする。 Thereby, in particular, the hot-rolled steel strip tip and tail ends (locations corresponding to the inner and outer circumferences of the hot-rolled coil) having a high cooling rate after hot-rolling become hard. As a result, there are places where the load during cold rolling increases or the hardness varies according to the winding cycle, which reduces the rolling speed and does not satisfy the required characteristics in mechanical characteristics such as dimensional accuracy and elongation. , Leading to a decrease in yield.
従来、こうした課題を解決するため、熱延鋼帯の機械的特性や品質を全長にわたり均一化させる技術が開発されている。 Conventionally, in order to solve these problems, a technique for making the mechanical properties and quality of a hot-rolled steel strip uniform over the entire length has been developed.
例えば、特許文献１には、熱延鋼帯を巻取った直後の熱延コイルを、搬送装置および／またはコイル置き場において冷却するに当たり、コイル外周面のコイル置台または地面に接する部分と接していない部分の冷却速度を等しくするよう、接している部分を加熱する、あるいは、接していない部分を強制冷却する方法が開示されている。 For example, in Patent Document 1, when a hot-rolled coil immediately after winding a hot-rolled steel strip is cooled in a transfer device and / or a coil storage site, the coil outer peripheral surface is not in contact with a portion that contacts a coil mount or the ground. A method is disclosed in which the contacting part is heated or the non-contacting part is forcibly cooled so as to equalize the cooling rate of the part.
また、特許文献２には、８３０〜９５０℃の条件で熱間圧延し、６５０℃までの温度域を平均２０〜９０℃／ｓで冷却し、その後、４７０〜６４０℃の温度域にて巻取る際の該巻取り温度までの平均冷却速度を５〜３０℃／ｓで冷却する方法が開示されている。 In Patent Document 2, hot rolling is performed at a temperature of 830 to 950 ° C., a temperature range up to 650 ° C. is cooled at an average of 20 to 90 ° C./s, and then wound at a temperature range of 470 to 640 ° C. A method of cooling at an average cooling rate up to the coiling temperature at the time of taking at 5 to 30 ° C./s is disclosed.
さらに、特許文献３には、鋼板先端部と巻取り機のマンドレルが接触して冷却されることによる機械的性質の変動を抑え、「すりかき疵」を防止するために、鋼板先端部を巻取り機のマンドレルに到達する以前に残部より４０〜８０℃低い温度に冷却する技術が開示されている。 Further, Patent Document 3 discloses that a steel plate tip is wound in order to suppress fluctuations in mechanical properties due to contact between the steel plate tip and the mandrel of the winder and being cooled and to prevent “scratching”. A technique is disclosed for cooling to a temperature 40-80 ° C. below the remainder before reaching the mandrel of the take-off machine.
なお、［発明を実施するための形態］の欄において、下記の非特許文献１を引用するので、ここに併せて記載しておく。 In the [Mode for Carrying Out the Invention] column, the following Non-Patent Document 1 is cited, which is also described here.
しかしながら、上記の特許文献１〜３には以下のような問題点がある。 However, the above Patent Documents 1 to 3 have the following problems.
特許文献１の方法は、加熱あるいは冷却設備を新設して、強制的に冷却履歴を等しくする方法であるが、新たな設備投資を必要し、エネルギー面もコストアップする他、局所的な加熱・冷却のため特に外気と接触する熱延コイルの最内周、最外周において表面品質が他の部分より劣化しやすい。 The method of Patent Document 1 is a method of newly establishing a heating or cooling facility and forcibly equalizing the cooling history. However, it requires new facility investment and increases the cost of energy. In particular, the surface quality of the hot-rolled coil in contact with the outside air for cooling is more likely to deteriorate than the other parts on the innermost and outermost circumferences.
特許文献２の方法は、巻取り前に十分な時間的余地を設けることによって、フェライトへ変態させる方法であるが、熱間圧延ラインは粗圧延から巻取りまでの連続ラインであるため、仕上げ圧延の出側から巻取りまでの間にそれだけの時間的あるいは距離的な余地を設けることは現実的には不可能である。 The method of Patent Document 2 is a method of transforming into ferrite by providing sufficient time before winding, but since the hot rolling line is a continuous line from rough rolling to winding, finish rolling It is practically impossible to provide such a time or distance room between the exit side and the take-up side.
特許文献３の方法は、巻取り時の冷却を制御することによって、全長で均一な機械的特性を得ようとする技術であるが、一般熱延鋼帯を対象としており、高強度熱延鋼帯のような変態が巻取り後の冷却中に生じる場合には効果がない。 The method of Patent Document 3 is a technique for obtaining uniform mechanical properties over the entire length by controlling the cooling during winding, but is intended for general hot-rolled steel strips, and is a high-strength hot-rolled steel. If a belt-like transformation occurs during cooling after winding, it is ineffective.
本発明では、上記のような事情に鑑みてなされたものであり、熱延鋼帯（特に、高強度熱延鋼帯）を製造するに際して、その全長にわたって機械的特性や品質を適切に均一化させることができる熱延鋼帯の製造方法を提供することを目的とするものである。 The present invention has been made in view of the above circumstances, and when manufacturing a hot-rolled steel strip (especially a high-strength hot-rolled steel strip), mechanical characteristics and quality are appropriately uniformized over the entire length. It is an object of the present invention to provide a method for producing a hot-rolled steel strip that can be made to occur.
上記課題を解決するために、本発明は以下の特徴を有する。 In order to solve the above problems, the present invention has the following features.
［１］Ｍｎ：２．０〜３．０質量％を含有する鋼を熱間圧延して鋼帯となし、該鋼帯をコイル状に巻取った後、常温まで冷却する際に、前記巻取りを終了してから常温まで冷却する過程で、金属組織がオーステナイト相から他の相に変態する熱延鋼帯の製造方法であって、鋼帯の先端部または／および尾端部の巻取り温度を鋼帯の中央部の巻取り温度に対して５０〜３００℃高温にすることを特徴とする熱延鋼帯の製造方法。 [1] When steel containing Mn: 2.0 to 3.0 mass% is hot-rolled to form a steel strip, the steel strip is wound into a coil shape, and then cooled to room temperature, the winding A method of manufacturing a hot-rolled steel strip in which the metallographic structure is transformed from an austenite phase to another phase in the process of cooling to room temperature after finishing, and winding the tip or / and tail end of the steel strip A method for producing a hot-rolled steel strip, characterized in that the temperature is 50 to 300 ° C higher than the winding temperature at the center of the steel strip.
［２］鋼がＣ：０．０３〜０．２質量％を含有することを特徴とする前記［１］に記載の熱延鋼帯の製造方法。 [2] The method for producing a hot-rolled steel strip according to [1], wherein the steel contains C: 0.03 to 0.2% by mass.
［３］熱間圧延を終了してから巻取りを開始するまでの間の鋼帯の冷却条件を鋼帯の長手方向で制御することを特徴とする前記［１］または［２］に記載の熱延鋼帯の製造方法。 [3] The cooling condition of the steel strip between the end of hot rolling and the start of winding is controlled in the longitudinal direction of the steel strip, as described in [1] or [2] Manufacturing method of hot-rolled steel strip.
本発明においては、熱延鋼帯（特に、高強度熱延鋼帯）を製造するに際して、その全長にわたって機械的特性や品質を適切に均一化させることができる。その結果、製品歩留まりを向上させることが可能になる。 In the present invention, when producing a hot-rolled steel strip (particularly, a high-strength hot-rolled steel strip), mechanical properties and quality can be appropriately uniformed over the entire length. As a result, the product yield can be improved.
以下に本発明の詳細について説明する。 Details of the present invention will be described below.
鋼の冷却中の変態や、冷却後の組織を予測するために、連続冷却変態線図（以下、ＣＣＴ線図；Ｃｏｎｔｉｎｕｏｕｓ Ｃｏｏｌｉｎｇ Ｔｒａｎｓｆｏｒｍａｔｉｏｎ ｃｕｒｖｅ）が広く用いられている。ＣＣＴ線図は、ある組成の鋼をオーステナイト状態から色々な冷却速度で常温まで連続冷却した際、途中で起こる変態の温度と時刻を記録したものであり、連続冷却過程で得られる組織や機械的性質を推測できるものである（非特許文献１）。このため、鋼の冷却履歴をＣＣＴ線図内に描いた際に、冷却曲線がどの連続冷却変態曲線（以下、ＣＣＴ曲線）を横断するかにより、冷却時の金属組織を推定することができる。そのため、冷却開始温度が同じでも異なるＣＣＴ曲線を横断すれば異なる組織となり、冷却履歴が異なっていても同一のＣＣＴ曲線を横断すれば、同じ金属組織を示すと言える。 In order to predict the transformation of steel during cooling and the structure after cooling, a continuous cooling transformation diagram (hereinafter referred to as a CCT diagram; Continuous Cooling Transformation curve) is widely used. The CCT diagram records the temperature and time of the transformation that occurs during the continuous cooling of a composition steel from the austenite state to room temperature at various cooling rates. The structure and mechanical properties obtained during the continuous cooling process are recorded. The property can be estimated (Non-patent Document 1). For this reason, when the cooling history of steel is drawn in the CCT diagram, the metal structure at the time of cooling can be estimated depending on which continuous cooling transformation curve (hereinafter referred to as CCT curve) the cooling curve crosses. Therefore, even if the cooling start temperature is the same, a different structure is obtained if the different CCT curves are crossed, and if the same CCT curve is crossed even if the cooling history is different, the same metal structure is indicated.
ところで、本発明で対象とするＭｎを多量に含んでいる高強度熱延鋼帯の場合には、一般的な熱延鋼帯とは異なり、ＣＣＴ曲線のフェライトノーズがＣＣＴ線図中の比較的長時間側（１０２〜１０４秒）に存在しているため、組織を決定付けるのはコイル状に巻取った後の冷却過程であり、これを鋼帯全長で等しくすることによって、冷却後の金属組織は鋼帯の長手方向の位置によらず均質になると考えられる。 By the way, in the case of a high-strength hot-rolled steel strip containing a large amount of Mn, which is the subject of the present invention, unlike a general hot-rolled steel strip, the ferrite nose of the CCT curve is relatively because present in long side (10 2 to 10 4 sec), the determines the tissue is a cooling process after the wound in a coil shape, which by equally strip full length, cooled It is considered that the metallographic structure is uniform regardless of the position in the longitudinal direction of the steel strip.
しかし、熱延鋼帯はある一定の温度で巻取るのが通例であり、この場合、常温まで冷却される際、空気や水など抜熱媒体に接触しているコイルの内周部および外周部は早急に冷却され、一方で、コイルの中央部は、内周部および外周部からの熱伝達により、ある程度の時間保熱されるという冷却履歴の差異が生じる。このような冷却履歴の差異から、本発明の対象鋼種のように、特にＣＣＴ曲線のノーズが長時間側（１０２〜１０４秒）に存在する鋼種では、冷却後にコイルの内外周部と中央部では異なる金属組織を形成してしまう。この金属組織のコイル長手方向（鋼帯長手方向）の差異によって、鋼帯の機械的性質（硬さ、伸びなど）や寸法、表面性状がコイル長手方向（鋼帯長手方向）で変動するため、冷却履歴の差異は最終製品の歩留まりを悪化させる一因となっていた。 However, the hot-rolled steel strip is usually wound at a certain temperature, and in this case, when cooled to room temperature, the inner and outer peripheral portions of the coil that are in contact with the heat removal medium such as air or water On the other hand, the central portion of the coil is cooled rapidly, and the difference in cooling history is generated in that the heat is transmitted from the inner peripheral portion and the outer peripheral portion for a certain period of time. From the difference of such cooling history, as the subject grades of the present invention, especially in steels nose of CCT curve exists in long side (10 2 to 10 4 sec), the inner peripheral portion of the coil after cooling and the central Different metal structures are formed at the part. Because of the difference in the coil longitudinal direction (steel strip longitudinal direction) of this metal structure, the mechanical properties (hardness, elongation, etc.), dimensions, and surface properties of the steel strip vary in the coil longitudinal direction (steel strip longitudinal direction). The difference in cooling history contributed to the deterioration of the final product yield.
これらの改善方法を検討した結果、鋼帯のいずれの位置においてもＣＣＴ曲線を横断する箇所のみが一致するように、その地点までの冷却履歴を鋼帯の長手方向の位置によって変化させることで、全長で均質な金属組織（フェライト分率のばらつきが小さい金属組織）の造り込みが可能であることを見出した。図１にその考え方を模式図で示す。すなわち、図１（ａ）が従来パターンであり、図１（ｂ）が本発明パターンである。 As a result of examining these improvement methods, by changing the cooling history up to that point depending on the position in the longitudinal direction of the steel strip so that only the location that crosses the CCT curve matches at any location of the steel strip, It has been found that it is possible to build a metal structure that is homogeneous over its entire length (a metal structure with a small variation in ferrite fraction). FIG. 1 schematically shows the concept. That is, FIG. 1 (a) is a conventional pattern, and FIG. 1 (b) is a pattern of the present invention.
さらに、熱延鋼帯の全長で同一のＣＣＴ曲線を横断するような冷却履歴を実現するための具体的な方法について検討した結果、鋼帯の冷却開始温度に相当する「巻取り温度」を熱延鋼帯の長手位置によって変更することが最も工業的に有効であった。以下にその詳細を述べる。 Furthermore, as a result of examining a specific method for realizing a cooling history that crosses the same CCT curve over the entire length of the hot-rolled steel strip, the “coiling temperature” corresponding to the cooling start temperature of the steel strip is heated. It was most industrially effective to change the length of the steel strip. Details are described below.
まず、対象とする鋼素材について述べる。 First, the target steel material will be described.
一般冷延鋼帯の母材となる熱延鋼帯の巻取り後の組織は、フェライト＋パーライト組織であることが普通であるが、高強度鋼帯の場合、焼入れ性を高める元素を添加しているために、巻取り後の組織はベイナイト組織であることが多い。焼入れ性を高める強化元素の中でも、ＣｒやＭｏは安定かつ安価に入手することが困難であるため、Ｃ、Ｓｉ、Ｍｎを主体として添加した成分系での高強度鋼帯の製造が望まれている。本発明においては、特に、フェライト変態を遅延させる効果が著しいＭｎ量を規定する。 The structure after coiling of a hot-rolled steel strip, which is the base material of a general cold-rolled steel strip, is usually a ferrite + pearlite structure, but in the case of a high-strength steel strip, an element that enhances hardenability is added. Therefore, the structure after winding is often a bainite structure. Among the strengthening elements that enhance the hardenability, it is difficult to obtain Cr and Mo stably and inexpensively. Therefore, it is desired to produce a high-strength steel strip with a component system mainly containing C, Si, and Mn. Yes. In the present invention, the amount of Mn having a remarkable effect of delaying the ferrite transformation is specified.
Ｍｎ：２．０〜３．０質量％
Ｍｎは固溶強化により、鋼のＴＳを向上させる元素である。Ｍｎ量は所望の強度を確保させるために含有させる必要があるが、２．０質量％未満であると、熱延鋼帯の巻取り前、つまり、ランナウトテーブル上でフェライト変態が進行してしまう。そのため、本発明のような巻取り温度の制御によって冷却履歴を制御する効果を得ることができない。一方、３．０質量％より多く含有させた場合、１０５秒オーダーまで高温で保持しないとフェライト変態が生じない。この場合、熱延鋼帯巻取り後のコイルを保熱する必要が生じるため、本発明のような巻取り温度の制御のみでは、フェライト分率を制御できない。以上の理由から、Ｍｎ含有量は２．０〜３．０質量％の範囲に限定した。
Mn: 2.0 to 3.0% by mass
Mn is an element that improves the TS of steel by solid solution strengthening. The amount of Mn needs to be contained in order to ensure a desired strength, but if it is less than 2.0% by mass, ferrite transformation proceeds before winding of the hot-rolled steel strip, that is, on the runout table. . Therefore, the effect of controlling the cooling history by controlling the winding temperature as in the present invention cannot be obtained. On the other hand, when is contained more than 3.0 wt%, ferrite transformation does not occur unless held at elevated temperatures up to 10 5 seconds the order. In this case, since it is necessary to heat the coil after winding the hot-rolled steel strip, the ferrite fraction cannot be controlled only by controlling the winding temperature as in the present invention. For the above reasons, the Mn content is limited to the range of 2.0 to 3.0% by mass.
また、本発明では主として高強度鋼帯を対象としており、所定量のＣやＳｉを含有することが望ましい。 In the present invention, high strength steel strip is mainly targeted, and it is desirable to contain a predetermined amount of C or Si.
Ｃは、鋼板の強度増加や炭化物生成の観点から重要な元素であり、所望の強度と炭化物量を確保するために０．０３質量％以上含有させるものとした。一方、０．２質量％を超える含有は溶接性を著しく劣化させるため、０．０３〜０．２質量％の範囲が望ましい。 C is an important element from the viewpoint of increasing the strength of the steel sheet and generating carbides, and is contained in an amount of 0.03% by mass or more in order to ensure the desired strength and carbide content. On the other hand, the content exceeding 0.2% by mass remarkably deteriorates the weldability, so the range of 0.03 to 0.2% by mass is desirable.
ＳｉはＣと同様に、鋼の強度を増加させ、さらに加工性の向上にも寄与する。安価な元素であり、強度を得るためにはある程度の添加量が必要であるが、必ずしも含有させる必要はない。ただし、２．５質量％を超えて含有させると、脆化を引き起こす上、赤スケールなどの発生による表面性状の劣化を引き起こす。そのため、Ｓｉは２．５質量％以下が望ましい。 Si, like C, increases the strength of steel and contributes to the improvement of workability. It is an inexpensive element, and a certain amount of addition is necessary to obtain strength, but it is not always necessary to contain it. However, if the content exceeds 2.5% by mass, embrittlement occurs and surface properties are deteriorated due to the occurrence of red scale and the like. Therefore, Si is desirably 2.5% by mass or less.
さらに、所望の強度を得るために、Ｎｂ、Ｔｉ、Ｖを含有することも許容する。 Furthermore, it is allowed to contain Nb, Ti, and V in order to obtain a desired strength.
Ｎｂ、Ｔｉ、Ｖはいずれも、炭窒化物を形成し、析出強化により、鋼帯の強度増加に寄与する元素であり、必要に応じて選択して、１種または２種以上含有できる。このような効果を得るには、いずれも０．００５質量％以上の含有を必要とするが、いずれも０．１５質量％を超えて含有しても効果が飽和し、含有量に見合う効果が期待できなくなる。そのため、いずれの元素も０．００５〜０．１５質量％の範囲に限定することが望ましい。 Each of Nb, Ti, and V is an element that forms carbonitrides and contributes to an increase in the strength of the steel strip by precipitation strengthening. It can be selected as necessary and can be contained singly or in combination. In order to obtain such an effect, it is necessary to contain 0.005% by mass or more in any case, but even if the content exceeds 0.15% by mass, the effect is saturated and an effect corresponding to the content is achieved. You can't expect. Therefore, it is desirable that any element is limited to the range of 0.005 to 0.15% by mass.
上記組成の鋼素材では、Ｍｎの添加により一般鋼帯に比べてフェライト変態が遅延し、ノーズは長時間側（１０２〜１０４秒）になるため、保熱されやすいコイル中央部（熱延鋼帯の中央部）ではフェライト＋パーライト組織を形成しやすく、一方、コイル内周部・外周部（熱延鋼帯の先端部・尾端部）は比較的早く冷却されることによりベイナイト組織を形成するため、１コイル内の長手方向によって異なる金属組織を形成しやすくなる。本発明は、このような鋼素材において有効な方法である。 The steel material having the above composition, ferrite transformation is delayed as compared with general steel strip by the addition of Mn, for nose becomes long side (10 2 to 10 4 sec), the heat keeping is susceptible coil central portion (hot rolled Ferrite + pearlite structure is easy to form at the center of the steel strip, while the inner and outer peripheries of the coil (the tip and tail ends of the hot-rolled steel strip) are cooled relatively quickly, resulting in a bainite structure. Since it forms, it becomes easy to form a metal structure which changes with longitudinal directions in one coil. The present invention is an effective method for such a steel material.
次に、巻取り温度の設定にあたり必要な情報について述べる。 Next, information necessary for setting the coiling temperature will be described.
本発明で対象とする鋼素材は、特にＭｎの含有量によって、フェライト変態の開始時間が異なってくるため、あらかじめ変態曲線を算出しておく必要がある。これら変態曲線は、実験的に求めることも可能であり、どちらを用いても良い。 In the steel material to be used in the present invention, since the start time of the ferrite transformation varies depending on the Mn content, it is necessary to calculate a transformation curve in advance. These transformation curves can be obtained experimentally, and either of them may be used.
また、熱延鋼帯の長手方向の各位置について、冷却開始温度である巻取り温度を様々に変更してあらかじめ冷却曲線を算出する。計算にあたっては、コイル状に巻取った後の最外周および最内周に該当する箇所、熱延鋼帯の中央部に該当する箇所の少なくとも３箇所の位置について計算しておく必要がある。さらに、コイルの寸法（内径、外径）、冷却ヤード内の配置、素材によって冷却曲線は変化するため、コイル温度を実測して、計算冷却履歴との誤差を補正することが望ましい。 Further, for each position in the longitudinal direction of the hot-rolled steel strip, a cooling curve is calculated in advance by variously changing the coiling temperature that is the cooling start temperature. In the calculation, it is necessary to calculate at least three positions of a portion corresponding to the outermost and innermost periphery after winding in a coil shape and a portion corresponding to the central portion of the hot-rolled steel strip. Furthermore, since the cooling curve changes depending on the coil dimensions (inner diameter, outer diameter), the arrangement in the cooling yard, and the material, it is desirable to actually measure the coil temperature and correct the error from the calculated cooling history.
以上の計算結果を用い、フェライト変態曲線と、熱延鋼帯の長手方向の各位置の冷却曲線が交差する箇所が一致するように、鋼帯長手方向の各位置について巻取り温度を設定する。巻取り温度が異なっていても、フェライト変態曲線と各位置の冷却曲線が交差する箇所が同じであれば、フェライト分率は同等となる。 Using the above calculation results, the coiling temperature is set for each position in the longitudinal direction of the steel strip so that the locations where the ferrite transformation curve and the cooling curve at each position in the longitudinal direction of the hot-rolled steel strip intersect each other coincide. Even if the coiling temperatures are different, the ferrite fraction is equivalent if the location where the ferrite transformation curve and the cooling curve at each position intersect is the same.
ところで、熱延鋼帯の製造にあたり、仕上げ圧延機の出側温度は従来どおりオーステナイト域で、全長等温で終了するものとする。本発明では、その後、巻き取った後の冷却が顕著である鋼帯先端部（コイル内周部）・鋼帯尾端部（コイル外周部）においては、フェライト変態ノーズに到達するための時間的余地を確保するために、極力高温を維持したまま巻取る。一方、鋼帯中央部（コイル中央部）は巻取った後に周囲からの熱移動により、巻取り温度のままある程度の時間保熱されるため、フェライト変態ノーズ付近の温度にあらかじめ設定することも可能である。適正な温度を選択すれば、鋼帯先端部・鋼帯尾端部と比較して、５０〜３００以上℃低い巻取り温度でも十分に保熱され、フェライト変態ノーズに到達する。 By the way, in the production of the hot-rolled steel strip, the exit temperature of the finish rolling mill is an austenite region as in the conventional case, and ends with a full-length isothermal temperature. In the present invention, the time required to reach the ferrite transformation nose at the steel strip tip (coil inner periphery) and steel strip tail (coil outer periphery) where cooling after winding is significant thereafter. In order to secure room, it is wound while maintaining as high a temperature as possible. On the other hand, the steel strip center part (coil center part) is kept at the coiling temperature for a certain period of time due to heat transfer from the surroundings after winding, so it can be preset to a temperature near the ferrite transformation nose. is there. If an appropriate temperature is selected, heat is sufficiently retained even at a coiling temperature that is 50 to 300 ° C. lower than that of the steel strip tip and steel strip tail, and reaches the ferrite transformation nose.
巻取り温度を鋼帯の長手方向位置に応じて短時間で変動させるためには、ランナウトテーブル上での冷却条件（注水条件）を熱延鋼帯の長手方向の各位置について変更する方法が有効である。つまり、巻取り温度を高くする鋼帯先端部や鋼帯尾端部では、注水を止め、あるいは注水密度（単位面積当たりの注水量）を小さくし、巻取り温度を低くする鋼帯中央部では、注水密度（単位面積当たりの注水量）を大きくするものである。 In order to change the coiling temperature in a short time according to the longitudinal position of the steel strip, it is effective to change the cooling conditions (water injection conditions) on the runout table for each position in the longitudinal direction of the hot-rolled steel strip. It is. In other words, at the steel strip tip or steel strip tail that raises the coiling temperature, water injection is stopped, or the water injection density (water injection amount per unit area) is reduced, and the steel strip center that lowers the coiling temperature. The water injection density (water injection amount per unit area) is increased.
しかしながら、鋼帯中央部の巻取り温度を下げるために急冷をした結果、巻取機に到達する前に焼入れ状態となって硬質化が起こると、鋼帯を巻取る時点で破断する危険性がある。これを防ぐため、鋼帯先端部および鋼帯尾端部の巻取り温度と、鋼帯中央部の巻取り温度の差は最大でも３００℃以内に設定する。尚、ランナウトテーブルの冷却能力、熱延圧下率や熱延速度の観点から望ましくは２００℃以内の範囲とする。また、５０℃未満の温度差は、巻取り直後に解消してしまい、鋼帯中央部は必要以上に高温で長時間保熱され、冷却に長時間を要してしまう、あるいは、鋼帯先端部および鋼帯尾端部がフェライト変態を開始する前に冷却されてしまうなど、巻取り温度を変化させる効果を得られない。 However, as a result of rapid cooling to lower the coiling temperature at the center of the steel strip, there is a risk of breaking when the steel strip is wound if it becomes hardened and hardened before reaching the winder. is there. In order to prevent this, the difference between the winding temperature of the steel strip tip and the steel strip tail end and the winding temperature of the steel strip center is set to within 300 ° C. at the maximum. In addition, from the viewpoint of the cooling capacity, the hot rolling reduction rate, and the hot rolling speed of the run-out table, the range is preferably within 200 ° C. Moreover, the temperature difference of less than 50 ° C is eliminated immediately after winding, and the steel strip center is kept at a higher temperature than necessary for a long time, and it takes a long time for cooling, or the tip of the steel strip. The effect of changing the coiling temperature cannot be obtained, for example, the steel plate and the tail end of the steel strip are cooled before starting the ferrite transformation.
さらに、鋼帯の圧延方向（長手方向）の位置によって急激に巻取り温度を変化させることは、ランナウトテーブル上で水圧や水の自重変動による急激な張力変動や材質の変動を併発し、巻取り時の操業トラブルにつながる可能性が高い。これは、巻取り温度を変動させる際に十分な距離あるいは時間的勾配をつけ、張力変動を緩やかにすることで制御系統を追従させることにより解決できる。特に、鋼帯尾端側は張力変動の影響で操業トラブルを発生しやすいため、巻取り温度を低温から高温に推移する際に、十分に緩やかな温度勾配をつけることがより望ましい。 Furthermore, abruptly changing the winding temperature depending on the rolling direction (longitudinal direction) of the steel strip is accompanied by sudden tension fluctuations and material fluctuations due to fluctuations in water pressure and water weight on the run-out table. It is likely to lead to operational troubles at times. This can be solved by making the control system follow by providing a sufficient distance or time gradient when changing the coiling temperature and making the tension fluctuation gentle. In particular, it is more desirable to provide a sufficiently gentle temperature gradient when the coiling temperature is changed from a low temperature to a high temperature because the steel belt tail end side is likely to cause an operation trouble due to the influence of tension fluctuation.
図２に上述の巻取り温度の設定条件の一例を模式図で示す。すなわち、図２（ａ）が従来パターンであり、図２（ｂ）が本発明パターンである。また、図３にコイルの温度分布の変化の一例を模式図で示す。すなわち、図３（ａ）が従来パターンであり、図３（ｂ）が本発明パターンである。 FIG. 2 is a schematic diagram showing an example of the above-described winding temperature setting conditions. That is, FIG. 2 (a) is a conventional pattern, and FIG. 2 (b) is a pattern of the present invention. FIG. 3 is a schematic diagram showing an example of changes in the coil temperature distribution. That is, FIG. 3A is a conventional pattern, and FIG. 3B is a pattern of the present invention.
なお、図２（ｂ）においては、鋼帯先端部（高温部）および鋼帯尾端部（高温部）の巻取り温度を鋼帯中央部（低温部）に対して５０〜３００℃高温にするものであるが、鋼帯先端部（高温部）と鋼帯中央部（低温部）の間および鋼帯中央部（低温部）と鋼帯尾端部（高温部）の間にそれぞれ遷移領域を設けている。 In FIG. 2B, the winding temperature of the steel strip tip (high temperature part) and steel strip tail end (high temperature part) is 50 to 300 ° C. higher than the steel strip center part (low temperature part). The transition region between the steel strip tip (high temperature part) and the steel strip center part (low temperature part) and between the steel strip center part (low temperature part) and the steel strip tail end part (high temperature part), respectively. Is provided.
ここで、例えば、全長６００ｍの熱延鋼帯を対象とするとき、鋼帯先端部（高温部）は、鋼帯最先端を起点にして長手方向に３０ｍ程度の部分であり、鋼帯尾端部（高温部）は、鋼帯最尾端を起点にして長手方向に８０ｍ程度の部分である。また、鋼帯先端部（高温部）の遷移領域の長さは３０ｍ程度、鋼帯尾端部（高温部）の遷移領域の長さは１００ｍ程度とすればよい。 Here, for example, when a hot-rolled steel strip having a total length of 600 m is targeted, the tip of the steel strip (high temperature portion) is a portion of about 30 m in the longitudinal direction starting from the forefront of the steel strip, and the tail end of the steel strip. The part (high temperature part) is a part of about 80 m in the longitudinal direction starting from the tail end of the steel strip. In addition, the length of the transition region of the steel strip tip (high temperature portion) may be about 30 m, and the length of the transition region of the steel strip tail end (high temperature portion) may be about 100 m.
場合によっては、その効果が減少するが、鋼帯先端部と鋼帯尾端部のいずれか一方を高温部になるようにしてもよい。その場合、より抜熱が大きい鋼帯尾端部を高温部にすることが望ましい。 In some cases, the effect is reduced, but either the steel strip tip or the steel strip tail end may be a high temperature portion. In that case, it is desirable that the tail end of the steel strip, which has a higher heat removal, be a high temperature part.
このように、本発明では、熱間圧延後に鋼帯をコイル形状に巻取り、常温まで冷却するにあたり、巻取り後のコイルの冷却過程においてオーステナイト相からフェライト相など様々な金属組織に変態する鋼帯を製造する際に、当該熱延鋼帯の連続冷却中の変態曲線および巻取り後の冷却曲線に基づいて、熱延鋼帯の長手方向における巻取り温度の目標値を変更するようにしている。 As described above, in the present invention, when the steel strip is wound into a coil shape after hot rolling and cooled to room temperature, the steel is transformed into various metal structures such as austenite phase and ferrite phase in the cooling process of the coil after winding. When manufacturing the strip, the target value of the coiling temperature in the longitudinal direction of the hot-rolled steel strip is changed based on the transformation curve during continuous cooling of the hot-rolled steel strip and the cooling curve after winding. Yes.
より詳しく言えば、本発明では、熱間圧延後に鋼帯をコイル形状に巻取り、常温まで冷却するにあたり、巻取り後のコイルの冷却過程においてオーステナイト相からフェライト相など様々な金属組織に変態する鋼帯を製造する際に、当該熱延鋼帯の連続冷却中の変態曲線をあらかじめ算出あるいは測定し、さらに、巻取り温度を変化させた場合の巻取り後の冷却曲線を、巻取り後のコイルの外周部、中央部、内周部の各位置について、あらかじめ算出しておくことにより、コイルの外周部、中央部、内周部の各位置について、前記変態曲線と前記冷却曲線から計算されるフェライト分率が一定になるよう、熱延鋼帯の長手方向に応じて巻取り温度を設定し、かつ、設定した巻取り温度を達成するために、ランナウトテーブル上での注水条件を長手方向で制御するようにしている。 More specifically, in the present invention, when the steel strip is wound into a coil shape after hot rolling and cooled to room temperature, it is transformed into various metal structures such as austenite phase and ferrite phase in the cooling process of the coil after winding. When manufacturing a steel strip, the transformation curve during continuous cooling of the hot-rolled steel strip is calculated or measured in advance, and the cooling curve after winding when the winding temperature is changed is calculated after winding. By calculating in advance the positions of the outer periphery, center, and inner periphery of the coil, the positions of the outer periphery, center, and inner periphery of the coil are calculated from the transformation curve and the cooling curve. The coiling temperature is set according to the longitudinal direction of the hot-rolled steel strip so that the ferrite fraction is constant, and the water injection conditions on the run-out table are set to achieve the set coiling temperature. So as to control manually direction.
本発明の実施例を示す。 The Example of this invention is shown.
表１に示す鋼素材を、連続熱間圧延機で幅１１００ｍｍ、板厚２．５〜４ｍｍに圧延し、直径７６０ｍｍのマンドレルに巻き取った。 The steel materials shown in Table 1 were rolled to a width of 1100 mm and a thickness of 2.5 to 4 mm with a continuous hot rolling mill, and wound on a mandrel having a diameter of 760 mm.
表２に、鋼帯先端部の巻取り温度、鋼帯中央部の巻取り温度、鋼帯尾端部の巻取り温度、鋼帯先端部の巻取り温度と鋼帯中央部の巻取り温度の差（鋼帯先端部の巻取り温度差）、鋼帯尾端部の巻取り温度と鋼帯中央部の巻取り温度の差（鋼帯尾端部の巻取り温度差）を示す。なお、巻取り機に設置した表面温度計によって測定した。 Table 2 shows the coiling temperature of the steel strip tip, the coiling temperature of the steel strip center, the coiling temperature of the steel strip tail, the coiling temperature of the steel strip tip and the coiling temperature of the steel strip. The difference (winding temperature difference at the tip of the steel strip), the difference between the winding temperature at the tail end of the steel strip and the winding temperature at the center of the steel strip (winding temperature difference at the tail end of the steel strip) are shown. In addition, it measured with the surface thermometer installed in the winder.
ここで、従来例（Ｎｏ．１）は、鋼帯全長を一定の温度で巻き取った場合である。 Here, the conventional example (No. 1) is a case where the entire length of the steel strip is wound at a constant temperature.
また、本発明例（Ｎｏ．２〜７）は、Ｍｎを２．０〜３．０質量％％含有するとともに、巻取り温度差を５０〜３００℃にするという条件を満足した場合である。 Moreover, this invention example (No. 2-7) is a case where 2.0-3.0 mass% of Mn is contained, and the conditions of making a winding temperature difference into 50-300 degreeC are satisfied.
一方、比較例（Ｎｏ．８〜１１）は、上記の条件を満足していなかった場合である。 On the other hand, Comparative Examples (Nos. 8 to 11) are cases where the above conditions were not satisfied.
それぞれの場合について、常温になった後、熱延鋼帯の長手方向の組織ばらつきを確認するため、長手方向に鋼帯を５分割し（鋼帯先端部×１、鋼帯中央部×３、鋼帯尾端部×１）、フェライト分率と引張強度（ＴＳ）を測定した。 In each case, after the room temperature was reached, in order to confirm the longitudinal variation in the structure of the hot-rolled steel strip, the steel strip was divided into 5 in the longitudinal direction (steel strip tip × 1, steel strip center × 3, Steel strip tail end x 1), ferrite fraction and tensile strength (TS) were measured.
フェライト分率は圧延方向に切り出した試験片の断面を研磨した後、王水エッチングで組織を現出させ、組織全体に対するフェライト相の面積率を画像処理によって求めた。同一の鋼帯において、この面積率の５点間のばらつき（最大値−最小値）が１０％未満であれば合格とした。 The ferrite fraction was obtained by polishing the cross section of the test piece cut in the rolling direction, revealing the structure by aqua regia etching, and determining the area ratio of the ferrite phase with respect to the entire structure by image processing. In the same steel strip, if the variation (maximum value-minimum value) between five points of this area ratio was less than 10%, it was determined as acceptable.
また、引張強度はＪＩＳＺ２２４１に則り、ＪＩＳ５号試験片を板幅中央部からＬ方向に採取して試験を行った。試験の結果、５点のＴＳの最大差（最大値−最小値）が８０ＭＰａ未満であれば合格とした。 In addition, the tensile strength was tested in accordance with JISZ2241 by taking a JIS No. 5 test piece in the L direction from the center of the plate width. As a result of the test, if the maximum difference (maximum value−minimum value) of five TSs was less than 80 MPa, the test was accepted.
これらの測定の結果を表２中に示す。表２に示すように、比較例では、巻取り温度差が適切でなくて、コイル内外周とコイル中央部の冷却履歴の差異に起因する鋼帯長手方向のばらつきを生じたが、本発明例では、フェライト分率、引張強度ともに鋼帯長手方向において均質であった。その結果、後の冷延工程において、比較例では、鋼帯の尾端が硬質で板厚不良が発生しやすく、冷延時に減速せざるを得なかったが、本発明例では、鋼帯の全長をほぼ同等の圧延荷重で、減速することなく所定板厚まで圧延することが可能だった。 The results of these measurements are shown in Table 2. As shown in Table 2, in the comparative example, the winding temperature difference was not appropriate, and the variation in the longitudinal direction of the steel strip caused by the difference in cooling history between the inner and outer circumferences of the coil and the center of the coil occurred. Then, both the ferrite fraction and the tensile strength were homogeneous in the longitudinal direction of the steel strip. As a result, in the subsequent cold rolling process, in the comparative example, the tail end of the steel strip was hard and a plate thickness defect was likely to occur, and it had to be decelerated during cold rolling. It was possible to roll to the specified plate thickness without reducing the overall length with almost the same rolling load.
このように、本発明においては、巻取り温度を鋼帯の圧延方向（長手方向）に応じて変化させ、最適化することにより、従来は圧延方向（長手方向）の位置によって変動していた機械的特性を均一にすることが可能になった。 As described above, in the present invention, by changing the coiling temperature in accordance with the rolling direction (longitudinal direction) of the steel strip and optimizing it, the machine has conventionally changed depending on the position in the rolling direction (longitudinal direction). It became possible to make the physical characteristics uniform.
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| JP2013262045A JP2015116596A (en) | 2013-12-19 | 2013-12-19 | Method for production of hot-rolled steel strip |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2016130334A (en) * | 2015-01-13 | 2016-07-21 | Ｊｆｅスチール株式会社 | Hot rolled steel strip, cold rolled steel strip, and production method of hot rolled steel strip |
| EP4056724A4 (en) * | 2019-11-04 | 2022-12-07 | Posco | High-strength steel having high yield ratio and excellent durability, and method for producing same |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH11181526A (en) * | 1997-12-19 | 1999-07-06 | Kobe Steel Ltd | Production of hot rolled steel plate excellent in workability and non-aging characteristic |
| JP2003003240A (en) * | 2001-06-20 | 2003-01-08 | Nippon Steel Corp | High strength hot rolled steel sheet having excellent hole expandability and haz fatigue property and production method therefor |
| JP2009214112A (en) * | 2008-03-07 | 2009-09-24 | Kobe Steel Ltd | Method for manufacturing hot rolled steel sheet |
| JP2012021192A (en) * | 2010-07-14 | 2012-02-02 | Nippon Steel Corp | High strength hot rolled steel sheet superior in coating corrosion resistance and punched part fatigue characteristic, and method for manufacturing the same |
-
2013
- 2013-12-19 JP JP2013262045A patent/JP2015116596A/en active Pending
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH11181526A (en) * | 1997-12-19 | 1999-07-06 | Kobe Steel Ltd | Production of hot rolled steel plate excellent in workability and non-aging characteristic |
| JP2003003240A (en) * | 2001-06-20 | 2003-01-08 | Nippon Steel Corp | High strength hot rolled steel sheet having excellent hole expandability and haz fatigue property and production method therefor |
| JP2009214112A (en) * | 2008-03-07 | 2009-09-24 | Kobe Steel Ltd | Method for manufacturing hot rolled steel sheet |
| JP2012021192A (en) * | 2010-07-14 | 2012-02-02 | Nippon Steel Corp | High strength hot rolled steel sheet superior in coating corrosion resistance and punched part fatigue characteristic, and method for manufacturing the same |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2016130334A (en) * | 2015-01-13 | 2016-07-21 | Ｊｆｅスチール株式会社 | Hot rolled steel strip, cold rolled steel strip, and production method of hot rolled steel strip |
| EP4056724A4 (en) * | 2019-11-04 | 2022-12-07 | Posco | High-strength steel having high yield ratio and excellent durability, and method for producing same |
| JP7453364B2 (en) | 2019-11-04 | 2024-03-19 | ポスコホールディングス インコーポレーティッド | High yield ratio thick high strength steel with excellent durability and its manufacturing method |
| US12049687B2 (en) | 2019-11-04 | 2024-07-30 | Posco | High-strength steel having high yield ratio and excellent durability, and method for manufacturing same |
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